|
|
| (107 intermediate revisions by 9 users not shown) |
| Line 1: |
Line 1: |
| − | {{OpenPagesTop}}
| + | [[Image:brainstemcranialnervespyramids.jpg|thumb|right|150px|The brainstem, cranial nerves and pyramids. © BioMed Archive.]] |
| − | [[File:Brain human normal inferior view with labels en.svg|thumb|right|400px|Ventral brain showing labelled cranial nerves, WikiCommons]] | |
| | ==Introduction== | | ==Introduction== |
| − | Cranial nerves are those nerves which arise from the brain and [[Hindbrain - Anatomy & Physiology|brain stem]] rather than the spinal cord. Nerves arising from the spinal cord are the [[PNS Structure - Anatomy & Physiology|spinal nerves]]. There are 12 pairs of cranial nerves and these pairs of nerves passage through [[Skull and Facial Muscles - Anatomy & Physiology|foramina in the skull]], either individually or in groups. Cranial nerves are traditionally referred to by Roman numerals and these numerals begin cranially and run caudally. | + | Cranial nerves are those nerves which arise from the brain and brain stem rather than the spinal cord. Nerves arising from the spinal cord are the [[PNS Structure - Anatomy & Physiology|peripheral nerves]]. There are 12 pairs of cranial nerves and these pairs of nerves passage through foramina in the skull, either individually or in groups. Cranial nerves are traditionally referred to by Roman numerals and these numerals begin cranially and run caudally. |
| | <br /> | | <br /> |
| | <br /> | | <br /> |
| − | The most cranial nerve is the '''Olfactory nerve (I)''' which runs from the nasal cavity through to the olfactory bulb. The next most cranial is the '''Optic nerve (II)''' which runs from the eyes to the [[Forebrain - Anatomy & Physiology#Thalamus|thalamus]]. Cranial nerves III to XII all exit from the brain stem and innervate the head, neck and organs in the thorax and abdomen. In order of most cranial to caudal, these include the '''Oculomotor nerve (III)''', the '''Trochlear nerve (IV)''', the '''Trigeminal nerve (V)''', the '''Abducens nerve (VI)''', the '''Facial nerve (VII)''', the '''Vestibulocochlear nerve (VIII)''', the '''Glossopharyngeal nerve (IX)''', the '''Vagus nerve (X)''', the '''Accessory nerve (XI)''' and the '''Hypoglossal nerve (XII)'''. | + | The most cranial nerve is the '''Olfactory nerve (I)''' which runs from the nasal cavity through to the olfactory bulb. The next most cranial is the '''Optic nerve (II)''' which runs from the eyes to the thalamus. Cranial nerves III to XII all exit from the brain stem and innervate the head, neck and organs in the thorax and abdomen. In order of most cranial to caudal, these include the '''Oculomotor nerve (III)''', the '''Trochlear nerve (IV)''', the '''Trigeminal nerve (V)''', the '''Abducens nerve (VI)''', the '''Facial nerve (VII)''', the '''Vestibulocochlear nerve (VIII)''', the '''Glossopharyngeal nerve (IX)''', the '''Vagus nerve (X)''', the '''Accessory nerve (XI)''' and the '''Hypoglossal nerve (XII)'''. |
| | <br /> | | <br /> |
| | <br /> | | <br /> |
| | Many of the cranial nerves with nuclei within the brain stem contain sensory and motor neurone components. The sensory fibre components have their cell bodies located in ganglia outside the central nervous system and the motor fibre element have their cell bodies within the central nervous system. | | Many of the cranial nerves with nuclei within the brain stem contain sensory and motor neurone components. The sensory fibre components have their cell bodies located in ganglia outside the central nervous system and the motor fibre element have their cell bodies within the central nervous system. |
| − |
| |
| − | ==Cranial Nerve Fibre Types==
| |
| − | Prior to a full explanation of each cranial nerve function, physiology, anatomy and particularly composition, the numerous types of nerve fibre found in cranial nerves must be explained to ensure that the following can be better understood.
| |
| − |
| |
| − | Nerve fibres can undertake numerous roles within the body and their function is dictated by what type of fibre the nerve is composed of. A classification scheme is used to describe the type of fibres found within the cranial nerves and therefore provides a better understanding of the function and composition of that particular nerve. Below is a brief outline of this nerve fibre classification.
| |
| − |
| |
| − | ===Afferent Fibres - Sensory===
| |
| − | ====General Somatic Afferent (GSA)====
| |
| − | This type of fibre is used in the majority of basic senses including temperature, touch and [[Pain|pain]]. These fibres mainly supply sensation to various areas of the head including to the skin and face via the trigeminal nerve (cranial nerve V); to the skin of the [[Ear - Anatomy & Physiology#Outer_Ear|external ear]] via the trigeminal nerve (cranial nerve V), the facial nerve (cranial nerve VII), the glossopharyngeal nerve (cranial nerve IX) and via the vagus nerve (cranial nerve X); to the mucosae of the [[Oral Cavity Overview - Anatomy & Physiology|oral cavity]] via the trigeminal nerve (cranial nerve V) and to the [[Meninges - Anatomy & Physiology|meningies]] of the brain via the trigeminal nerve (cranial nerve V) and the vagus nerve (cranial nerve X).
| |
| − |
| |
| − | :'''Skin Sensation Example'''
| |
| − |
| |
| − | :''Sensory cortex —→ Thalamus —→ Trigeminal nuclei —→ Trigeminal ganglion —→ Skin etc.''
| |
| − |
| |
| − | ====Special Somatic Afferent (SSA)====
| |
| − | The special signifies that this fibre type is found in nerves related to the special senses which include [[Eye - Anatomy & Physiology#Vision|vision]] and [[Ear - Anatomy & Physiology#Function_-_Hearing|hearing]]. This therefore relates to the optic nerves (cranial nerve II) and the auditory/vestibular systems which are the vestibulocochlear nerves (cranial nerve VIII).
| |
| − |
| |
| − | :'''Vision Example'''
| |
| − |
| |
| − | :''Occipital cortex —→ Thalamus MGN —→ Rostral colliculus/Retinal ganglion cell —→ Bipolar cell —→ [[Eye - Anatomy & Physiology|Vision]]''
| |
| − |
| |
| − | :'''Hearing Example'''
| |
| − |
| |
| − | :''Temporal cortex —→ Thalamus MGN —→ Caudal colliculus and hindbrain —→ Spiral ganglion —→ [[Ear - Anatomy & Physiology|Hearing]]''
| |
| − |
| |
| − | ====General Visceral Afferent (GVA)====
| |
| − | This fibre type is commonly found in sensory nerves to organs and to sensory tissues related to chemicals. These include fibres found in the glossopharyngeal nerves (cranial nerve IX) and the vagus nerves (cranial nerve X).
| |
| − |
| |
| − | :'''Organ Sensory Example'''
| |
| − |
| |
| − | :''Sensory cortex —→ Thalamus —→ Cranial nerve nuculi —→ Nerve ganglion —→ Organs etc.''
| |
| − |
| |
| − | ====Special Visceral Afferent (SVA)====
| |
| − | This fibre type is found again in special sense organs related to the sensing of chemicals and therefore including [[Gustatory System - Anatomy & Physiology|taste]] and [[olfaction]]. The olfactory sense relates to the olfactory nerve (cranial nerve I) and the taste senses relate to the facial nerve (cranial nerve VII), the glossopharyngeal nerve (cranial nerve IX) and the vagus nerve (cranial nerve X). The sense of taste is performed by the gustatory organ which are cells located in gustatory papillae in the mucous membrane of the dorsal side of the tongue. Taste buds can also be found in the soft palate, pharynx, larynx, lips and cheeks.
| |
| − |
| |
| − | :'''Olfaction Example'''
| |
| − |
| |
| − | :''Piriform cortex —→ Olfactory tubercle —→ Olfactory Bulb —→ [[Nose - Anatomy & Physiology|Smell]]''
| |
| − |
| |
| − | :'''Taste Example'''
| |
| − |
| |
| − | :''Sensory cortex —→ Thalamus —→ Hindbrain (VII, IX, X) —→ Ganglion —→ [[Gustatory System - Anatomy & Physiology|Taste]]''
| |
| − |
| |
| − | ===Efferent Fibres - Motor===
| |
| − | ====General Somatic Efferent (GSE)====
| |
| − | This type of nerve fibre is mainly found in nerves supplying [[Muscles - Anatomy & Physiology#Skeletal_Muscle|skeletal muscles]]. Motor fibres such as these undertake numerous roles within the body such as control over the external ocular muscles via the oculomotor nerve (cranial nerve III), the trochlear nerve (cranial nerve IV) and the abducent nerve (cranial nerve VI); or for example the muscles around the dorsal and ventral neck including the brachiocephalicus, trapezius, omotransversarius and the sternocephalicus which are all supplied by the accessory nerve (cranial nerve XI).
| |
| − |
| |
| − | :'''Motor Nerve Innervation Example'''
| |
| − |
| |
| − | :''Motor cortex —→ Motor nuculi —→ Muscle''
| |
| − |
| |
| − | ====General Visceral Efferent (GVE)====
| |
| − | This type of nerve fibre is found in nerves supplying [[Muscles - Anatomy & Physiology#Smooth_Muscle|smooth muscle]], [[Muscles - Anatomy & Physiology#Cardiac_Muscle|cardiac muscle]] and glands. Sympathetic innervation for this type of nerve fibre comes directly from the cranial cervical ganglion. However, parasympathetic innervation comes from several cranial nerves including the oculomotor nerve (cranial nerve III), the vestibulocochlear nerve (cranial nerve VIII), the glossopharyngeal nerve (cranial nerve IX) and the vagus nerve (cranial nerve X). Examples of where this type of fibre functions include the pupillary sphinter via the oculomotor nerve, glands of the nasal/oral cavity via the vestibulocochlear and glossopharyngeal nerves and thoracic/abdominal viscera via the vagus nerve.
| |
| − |
| |
| − | :'''Gland Innervation Example'''
| |
| − |
| |
| − | :''Brainstem —→ Parasympathetic nuculi —→ Parasympathetic ganglion —→ Gland etc.''
| |
| | | | |
| | ==Cranial Nerves== | | ==Cranial Nerves== |
| − | There are three main groups of cranial nerves; special senses, innervation of the head muscles and innervation of structures originating from branchial arches. The special senses cranial nerves include the olfactory, ocular and vestibulocochlear. Cranial nerves related to the innervation of the head muscles include the oculomotor, trochlear, abducens and the hypoglossal nerves. Cranial nerves related to innervation of structures originating from branchial arches include the trigeminal, facial, glossopharyngeal, vagus and accessory nerves. | + | There are three main groups of cranial nerves; special senses, innervation of the head muscles and innervation of structures originating from brancial arches. The special senses cranial nerves include the olfactory, ocular and vestibulocochlear. Cranial nerves related to the innervation of the head muscles include the oculomotor, trochlear, abducens and the hypoglossal nerves. Cranial nerves related to innervation of structures originating from branchial arches includes the trigeminal, facial, glossopharyngeal, vagus and accessory nerves. |
| − | | |
| | ===Olfactory Nerve (I)=== | | ===Olfactory Nerve (I)=== |
| − | Olfaction is part of the special senses cranial nerve group and represents the chemical senses of olfaction (smell) and gustation (taste). When chemical substances interact with our bodies they stimulate special sensory cells which in turn generate an action potential. The resultant impulse is sent to the brain via sensory afferent fibres and it is these fibres that represent the olfactory cranial nerve. Note: an action potential is only generated where a special sensory cell for that particular chemical substance exists. If no sensory cell exists, that chemical substance will go undetected. The olfactory neurosensory cells are found within the olfactory epithelium. The olfactory epithelium contains cilia on the surface of the cells to increase the surface area for chemical interactions. | + | Olfaction is part of the special senses cranial nerve group and represents the chemical senses of olfaction (smell) and gustation (taste). When chemical substances interact with our bodies they stimulate special sensory cells which in turn generate an action potential. The resultant impulse is sent to the brain via sensory afferent fibres and it is these fibres that represent the olfactory cranial nerve. Note: an action potential is only generated where a special sensory cell for that particular chemical substance exists. The special sensory cells are found within the olfactory mucous membrane in the nasal fundus and the olfactory neurosensory cells are found within the olfactory epithelium. The olfactory epithelium contains cilia on the surface of the cells to increase the surface area for chemical interactions. |
| | <br /> | | <br /> |
| | <br /> | | <br /> |
| − | The olfactory nerve runs to the olfactory bulb which is found within the [[Forebrain - Anatomy & Physiology#Olfactory_Bulb|telencephalon]]. The olfactory nerve is a sensory nerve and is composed of many '''Special Visceral Afferent''' fibres. The fibres are formed into bundles that are referred to as 'Olfactory filaments'. The olfactory nerve passes through the [[Skull and Facial Muscles - Anatomy & Physiology#Ethmoid Bone (os ethmoidale)|'''Cribiform plate''']] and is surrounded by meningeal sheets including the [[Meninges - Anatomy & Physiology#Subarachnoid_Space|sub-arachnoid space]]. Therefore the route of the olfactory nerve represents a potential site for an infection to track towards the brain. Injury of this nerve can lead to 'anosmia', or loss of smell. | + | The olfactory nerve runs to the olfactory bulb which is found within the [[Forebrain_-_Anatomy_%26_Physiology#Olfactory_Bulb|telencephalon]]. The olfactory nerve is a sensory nerve and is composed of many '''Special Visceral Afferent''' fibres. The fibres are formed into bundles that are referred to as 'Olfactory filaments'. The olfactory nerve passes through the '''Cribiform plate''' and is surrounded by meningeal sheets including the sub-arachnoid space. Therefore the route of the olfactory nerve represents a potential site for an infection to track towards the brain. Injury of this nerve can lead to 'anosmia', or loss of smell. |
| | <br /> | | <br /> |
| | <br /> | | <br /> |
| − | The olfactory organ in dogs is extremely well developed and species such as canines use olfaction to orientate themselves in an environment in a way that humans do not. Olfactory cells are continuously replaced and are only viable sensory cells for between 30 - 60 days. This point is of importance as this is the only area in which nerve cells are able to be replaced or regenerated in adult animals and this area is now under research at Cambridge University for the treatment of damaged nerves and/or nerve disorders in nerves other than those involved in olfaction. | + | The olfactory organ in dogs is extremely well developed and species such as dogs use olfaction to orientate themselves in an environment in a way that humans do not. Olfactory cells are continuously replaced and are only viable sensory cells for between 30 - 60 days. This point is of importance as this is the only area in which nerve cells are able to be replaced or regenerated in adult animals and this area is now under research at Cambridge University for the treatment of damaged nerves and/or nerve disorders in nerves other than those involved in olfaction. |
| − | | |
| | ===Optic Nerve (II)=== | | ===Optic Nerve (II)=== |
| − | The optic nerve is part of the special senses cranial nerves and represents the connection between the receptor cells of the [[Eye - Anatomy & Physiology#The Wall (retina, uvea and sclera)|retina]] and the [[Forebrain - Anatomy & Physiology|diencephalon]]. The optic nerve is a sensory nerve and is composed of '''Special Somatic Afferent fibres'''. Optic nerve axons pass from the optic disc of the retina to the brain, entering the skull via the [[Skull and Facial Muscles - Anatomy & Physiology#Sphenoid Bone (os_sphenoidale)|'''optic canal''']]. The majority of axons decussate at the [[Skull and Facial Muscles - Anatomy & Physiology#Sphenoid Bone (os_sphenoidale)|'''optic chiasm''']] before continuing as the optic tracts. | + | The optic nerve is part of the special senses cranial nerves and represents the connection between the receptor cells of the [[Eye_-_Anatomy_%26_Physiology#The_Wall_.28retina.2C_uvea_and_sclera.29|retina]] and the diencephalon. The optic nerve is a sensory nerve and is composed of '''Special Somatic Afferent fibres'''. The optic nerve passes through the '''optic chiasm''' which is an area of the ventral brain where both optic nerves run in a medial direction and eventually decussate. The optic nerve runs through the '''optic canal'''. |
| | <br /> | | <br /> |
| | <br /> | | <br /> |
| − | The optic nerve can be examined clinically via a [[Neurological Eye Examination - Horse#Menace Response|menace response]] and anopsia (loss of vision) can be seen in injury. | + | The optic nerve can be examined clinically via a menace response and anopsia (loss of vision) can be seen in injury. |
| | | | |
| | ===Oculomotor nerve (III)=== | | ===Oculomotor nerve (III)=== |
| − | The oculomotor nerve is part of the group of cranial nerves responsible for innervating the [[Skull and Facial Muscles - Anatomy & Physiology#Facial_Muscles|muscles of the head]]. The nerves originate from the ventral [[Midbrain - Anatomy & Physiology|midbrain]] and is a motor nerve. It is composed of '''general somatic efferent fibres''' and '''general visceral efferent fibres'''. The general somatic efferent fibres of the oculomotor nerve are responsible for the motor function of four of the six [[Eye - Anatomy & Physiology#Around_the_Eye|external muscles of the eyeball]]; the 'dorsal rectus', 'medial rectus', 'ventral rectus', 'ventral oblique' and 'levator of the upper eyelid'. The general visceral efferent fibres of the oculomotor nerve control the 'sphincter pupillae' muscle (alters pupillary diameter) and the 'ciliaris' muscle (alters curvature of the lens). | + | The oculomotor nerve is part of the group of cranial nerves responsible for innervating the muscles of the head. The nerves originate from the ventral [[Midbrain_-_Anatomy_%26_Physiology|midbrain]] and is a motor nerve. It is composed of '''general somatic efferent fibres''' and '''general visceral efferent fibres'''. The general somatic efferent fibres of the oculomotor nerve are responsible for the motor function of four of the six external muscles of the eyeball; the 'dorsal rectus', 'medial rectus', 'ventral rectus', 'ventral oblique' and 'levator of the upper eyelid'. The general visceral efferent fibres of the oculomotor nerve are responsible for the control of pupil diameter and therefore control the 'spincter pupillae' muscle and the 'ciliaris' muscle. |
| | <br /> | | <br /> |
| | <br /> | | <br /> |
| − | The oculomotor nerve has a pre-ganglionic nucleus in the midbrain and the nerve passes through the [[Skull_and_Facial_Muscles_-_Anatomy_%26_Physiology#Major_Foramen_and_Canals|'''orbital fissure''']], along with the trochlear, abducens and opthalmic branch (V1) of the trigeminal nerve. It synapses in the ciliary ganglion of the eye. During a clinical examination, horizontal eye movements (strabismus) or an absent [[Neurological_Eye_Examination_-_Horse#The_pupillary_light_reflex_(PLR)|pupillary light reflex (PLR)]] may indicate a problem. | + | The oculomotor nerve has a pre-ganglionic nucleus in the midbrain and the nerve passes through the '''orbital fissure''', along with the trochlear, abducens and opthalmic branch (V1) of the trigeminal nerve. It synapses in the ciliary ganglion of the eye. During a clinical examination, horizontal eye movements (strabismus) or an abscent pupillary light reflex (PLR) may indicate a problem. |
| − | | |
| | ===Trochlear nerve (IV)=== | | ===Trochlear nerve (IV)=== |
| − | The trochlear nerve is part of the cranial nerve group responsible for innervation of the muscles of the head. The trochlear nerve originates from the dorsal mid-brain and is a motor nerve. It is composed of '''general somatic efferent fibres''' and is the smallest of the cranial nerves. The nerve is specifically responsible for the 'dorsal oblique muscle' muscle of the eye and also passes through the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''orbital fissure''']].
| |
| − | <br />
| |
| − | <br />
| |
| − | During a clinical examination, a dorso-lateral strabismus may indicate a problem with this nerve.
| |
| − |
| |
| − | ===Trigeminal nerve (V)===
| |
| − | The trigeminal nerve is part of the cranial nerve group responsible for innervation of structures originating from branchial arches. The trigeminal nerve nuclei are in the area of the pons and medulla oblongata and it is the nerve of the 1st branchial arch. In general terms the trigeminal represents the sensory nerve of the head but also provides motor fibres to structures also associated with the 1st branchial arch. There are three primary branches of the trigeminal nerve; the '''Opthalmic nerve (V1)''', the ''' Maxillary nerve (V2)''' and the '''Mandibular nerve (V3)'''.
| |
| − |
| |
| − | ====Ophthalmic nerve (V1)====
| |
| − | The ophthalmic nerve is a sensory nerve composed of '''general somatic afferent fibres''' and passes through the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''orbital fissure''']]. As it enters the orbit of the eye it splits further into the '''lacrimal nerve''', the '''frontal nerve''', the '''nasociliary nerve''' and the '''infratrochlear nerve'''. Therefore the nerve supplies sensory fibres to many components of the orbit.
| |
| − |
| |
| − | ====Maxillary nerve (V2)====
| |
| − | The maxillary nerve is a sensory nerve composed of '''general somatic afferent fibres'''. The maxillary nerve passes through the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''round foramen''']] and the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''alar canal''']]. It also runs across the wall of the '''pterygopalatine fossa''' and enters the '''infraorbital canal''' via the '''maxillary foramen'''. Whilst in the infraorbital canal, the maxillary nerve branch then branches further into the '''infraorbital nerve''' which supplies sensory fibres to the teeth. On exiting the infraorbital canal via the infraorbital foramen, the maxillary nerve branches again into the '''zygomatic nerve''' which supplies sensory fibres to the horn and to the '''pterygopalatine nerve''' supplying sensory fibres to the palate.
| |
| − |
| |
| − | ====Mandibular nerve (V3)====
| |
| − | The mandibular nerve is a mixed sensory '''general somatic afferent fibres''' and motor '''general somatic efferent''' nerves. The mandibular nerve passes through the [[Skull_and_Facial_Muscles_-_Anatomy_%26_Physiology#Major_Foramen_and_Canals|'''oval foramen''']]. It provides motor branches to the [[Mastication|masticatory muscles]], the [[Larynx - Anatomy & Physiology#Intrinsic Musculature|ventral throat]] and [[Tongue - Anatomy & Physiology#Muscles|muscles of the palate]]. The mandibular nerve further branches into the '''masticatory nerve''', the '''masseteric nerve''' and the '''temporal nerve'''. The mandibular nerve provides sensory branches called the '''buccal nerve''', the '''auriculotemporal nerve''', and then itself divides into two smaller branches; the '''lingual nerve''' and the '''inferior alveolar nerve'''. The '''lingual nerve''' receives sensory fibres to the rostral 2/3 of the tongue and also connects some sensory taste fibres to parasympathetic salivary glands via the [[Tongue - Anatomy & Physiology#Innervation|'''chorda tympani''']]. The lingual branch of the glossopharyngeal nerve supplies sensory taste fibres to the caudal 1/3 of the tongue, while the facial nerve supplies sensory taste fibres to the rostral 2/3 of the tongue.
| |
| − |
| |
| − | ===Abducent nerve (VI)===
| |
| − | The abducent nerve is part of the cranial nerve group responsible for innervation of the muscles of the head. The abducent nerve originates from the medulla oblongata and is a motor nerve. It is composed of '''general somatic efferent fibres''' which are responsible for controlling the 'lateral rectus' muscle and the 'retractor bulbi' muscle of the eye. The nerve passes through the '''orbital fissure''' and can be found within the same layer of the meninges as the opthalmic branch (V1) of the trigeminal nerve (V).
| |
| − | <br />
| |
| − | <br />
| |
| − | During a clinical examination, medial deviation strabismus may indicate a problem with this nerve.
| |
| − |
| |
| − | ===Facial nerve (VII)===
| |
| − | The facial nerve is part of the cranial nerve group responsible for the innervation of structures originating from the branchial arches. It originates from the medulla oblongata and from the second branchial arch. It has a common dura sheet with the opthalmic (V1) branch of the trigeminal nerve. The facial nerve is of a mixed composite and is made up of a number of different fibre types. It has a '''general somatic efferent fibre''' within the ear canal, a '''general visceral efferent fibre''' acting under parasympathetic control to some salivary glands, lacrimal glands, nasal cavity and palate, a '''special visceral afferent fibre''' providing taste to the rostral 2/3 of the tongue and finally it has a '''general somatic efferent fibre''' supplying motor function to the muscles of facial expression.
| |
| − | <br />
| |
| − | <br />
| |
| − | The facial nerve enters the petrosal bone via the [[Skull and Facial Muscles - Anatomy & Physiology#Temporal Bone (os_temporale)|'''internal acoustic meatus''']] along with the vestibulocochlear nerve. The facial nerve also runs inside the '''facial canal'''. There are a number of intermediate branches which separate from the main facial nerve inside the facial canal including the '''greater petrosal nerve''', the '''stapedial nerve''' (motor) and the '''chorda tympani'''. These then emerges via the [[Skull and Facial Muscles - Anatomy & Physiology#Major Foramen and Canals|'''stylomastoid foramen''']] at the caudoventral aspect of the skull. The chorda tympani of the facial nerve represents the '''special visceral afferent fibre''' supplying taste to the rostral 2/3 of the tongue.
| |
| − | <br />
| |
| − | <br />
| |
| − | There are also numerous external branches of the facial nerve once the facial nerve has left the facial canal. These include the '''internal auricular nerve''', the '''auriculopalpebral nerve''', the '''rostral auricular nerve''', the '''palpebral nerve''', the '''dorsal buccolabial nerve''', the '''ventral buccolabial nerve''', the '''ramus colli''', the '''digastric nerve''', the '''stylohoid nerve''' and the '''caudal auricular nerve'''.
| |
| − | <br />
| |
| − | <br />
| |
| − | The facial nerve supplies motor innervation to the muscles of facial expression. These are superficial flat, thin muscles that originate from bony areas of fascia and then radiate out around the skin. They may also often from sphincters such as around the mouth and eye.
| |
| − | <br />
| |
| − | <br />
| |
| − | During a clinical examination any facial paralysis, drooling or abscence of blinking may indicate a problem with the facial nerve.
| |
| | | | |
| | ===Vestibulocochlear nerve (VIII)=== | | ===Vestibulocochlear nerve (VIII)=== |
| − | The vestibulocochlear nerve is part of the special senses group of cranial nerves and is made up of two components; the vestibular nerve and the cochlear nerve. The vestibular nerve is responsible for balance whilst the cochlear nerve is responsible for hearing. The nerves send impulses from the inner ear which contains the [[Ear - Anatomy & Physiology#Vestibular Receptors and Balance|vestibular apparatus]] and [[Ear - Anatomy & Physiology#The Cochlea|cochlea]]. The vestibulocochlear nerve is a sensory nerve made up of '''special somatic afferent fibres'''. It passes through the '''internal acoustic meatus''' and into the '''petrosal bone'''. The facial nerve also takes this route. | + | The vestibulocochlear nerve is part of the special senses group of cranial nerves and is made up of two components; the vestibular nerve and the cochlear nerve. The vestibular nerve is responsible for balance whilst the cochlear nerve is responsible for hearing. The nerves send impulses from the inner ear which contains the [[Ear_-_Anatomy_%26_Physiology#Vestibular_Receptors_and_Balance|vestibular apparatus]] and [[Ear_-_Anatomy_%26_Physiology#The_Cochlea|cochlear]]. The vestibulocochlear nerve is a sensory nerve made up of '''special somatic afferent fibres'''. It passes through the '''internal acoustic meatus''' and into the '''petrosal bone'''. The facial nerve also takes this route. |
| − | <br />
| |
| − | <br />
| |
| − | Clinical problems with the vestibulocochlear nerve would be indicated on examination by changes in hearing and/or horizontal and vertical eye movements (strabismus and [[Vestibular System Examination|nystagmus]]). A head tilt is also associated with this nerve.
| |
| − | | |
| − | ===Glossopharyngeal nerve (IX)===
| |
| − | The glossopharyngeal nerve is part of the group of cranial nerves responsible for innervation of structures derived from the branchial arches. This nerve innervates structures related to the third branchial arch. It is also part of a group together with the vagus and accessory nerves that passes through the '''jugular foramen''' which is termed the '''vagus group'''. The glossopharyngeal nerve has cell bodies that are referred to as '''nucleus ambiguus'''. The glossopharyngeal nerve originates from the medulla oblongata and has several branches including the '''pharyngeal nerve''', the '''lingual nerve''' and the '''tympanic branches'''.
| |
| − | <br />
| |
| − | <br />
| |
| − | The glossopharyngeal nerve is composed of many fibre types including '''general somatic efferent fibres''' that innervate the stylopharyngeus muscle; the '''general visceral afferent fibres''' that provide sensory information from the carotid body, the pharynx and the middle ear; the '''general visceral efferent fibres''' that provide parasympathetic innervation to the parotid and zygomatic salivary glands; the '''special visceral afferent fibres''' that provide taste caudal to the tongue and finally the '''general somatic afferent fibres''' that provide sensory information from the external ear.
| |
| − | <br />
| |
| | <br /> | | <br /> |
| − | The '''lingual branch''' of the glossopharyngeal nerve provides '''general somatic afferent fibres''' and '''special visceral afferent fibres''' to the caudal 1/3 of the tongue.
| |
| | <br /> | | <br /> |
| − | <br />
| + | Clinical problems with the vestibulocochlear nerve would be indicated on examination by changes in hearing and/or horizontal and verticle eye movements (strabismus and nystagmus). A head tilt is also associated with this nerve. |
| − | On clinical examination, choking or dysphagia as a result of malfunctioning or absent pharyngeal reflexes would indicate a problem with the glossopharyngeal nerve.
| |
| | | | |
| − | ===Vagus nerve (X)===
| + | ==Cranial Nerve Location and Routes== |
| − | The vagus nerve is part of the group of cranial nerves responsible for innervation of structures derived from the branchial arches. It is also part of a group together with the glossopharyngeal and accessory nerves that passes through the '''jugular foramen''' which is termed the '''vagus group'''. The vagus nerve innervates structures related to the fourth branchial arch. The vagus nerve has cell bodies that are referred to as '''nucleus ambiguus'''.
| + | A summary of the cranial nerves is shown below: |
| − | <br />
| |
| − | <br />
| |
| − | The vagus nerve is composed of many different types of nerve fibre including '''general somatic efferent fibres''' supplying motor function to the muscles of the larynx, pharynx, palate and oesophagus; '''general visceral afferent fibres''' to the base of the tongue, pharynx and larynx; '''general visceral efferent fibres''' for parasympathetic supply of the thoracic and abdominal viscera; '''special visceral afferent fibres''' supplying taste to regions of the epiglottis and palate and finally '''general somatic afferent fibres''' to the external ear and the dura mater. The vagus nerve also supplies '''general somatic afferent fibres''' and '''special visceral afferent fibres''' to the root of the tongue.
| |
| − | <br />
| |
| − | <br />
| |
| − | There are many functional components of the vagus nerve including the heart, larynx, pharynx and many other viscera. On clinical examination any changes related to gag reflexes, blood pressure or heart rate, changes in 'voice' or inspiratory dyspnoea may indicate a problem with the vagus nerve.
| |
| − | | |
| − | ===Accessory nerve (XI)===
| |
| − | The accessory nerve is part of the group of cranial nerves responsible for innervation of structures derived from the branchial arches. It is also part of a group together with the glossopharyngeal and vagus nerves that passes through the '''jugular foramen''' which is termed the '''vagus group'''. The accessory nerve supplies structures related to the fourth branchial arch. The accessory nerve has cell bodies that are referred to as '''nucleus ambiguus''' and originate in the medulla oblongata. The cranial root of the accessory nerve actually contributes to the vagus nerve and to the striated muscles of the pharynx, larynx, palate and oesophagus.
| |
| − |
| |
| − | However, the accessory nerve also contributes to the cervical spinal cord and spinal root through the '''foramen magnum''' providing innervation to muscles of the neck. The spinal root of the accessory nerve branches into the '''dorsal branch''' and the '''ventral branch'''. The dorsal branch innervates the brachiocephalicus, trapezius and omotransversarius muscles of the dorsal neck. The ventral branch innervates the sternocephalicus muscle.
| |
| − | <br />
| |
| − | <br />
| |
| − | During clinical examination any difficulties in turning the neck or muscle atrophy around the dorsal and ventral neck may indicate a problem with the accessory nerve.
| |
| − | | |
| − | ===Hypoglossal nerve (XII)===
| |
| − | The hypoglossal nerve is part of the group of cranial nerves responsible for the control of muscles of the head. It is in part a cervical nerve due to its caudal position on the [[Hindbrain - Anatomy & Physiology|brain stem]]. The nerve is composed of '''general somatic efferent fibres''' which control the intrinsic and extrinsic muscles of the tongue (together with other nerves including the lingual nerve, facial nerve, lingual branch of the glossopharyngeal nerve and the vagus nerve). The nucleus of the nerve is located within the medulla oblongata of the brain stem and it passes through the '''hypoglossal canal'''.
| |
| − | <br />
| |
| − | <br />
| |
| − | During a clinical examination any deviation of the tongue may indicate a problem with this nerve. Deviation of the tongue is always to the side of the lesion.
| |
| − | | |
| − | ==Cranial Nerve Summary/Revision Tables==
| |
| − | These tables are designed to be a revision aid and do not contain any specific details. Details regarding each nerve are in the written section above.
| |
| − | ===Cranial Nerve Location and Routes===
| |
| − | A table summarising the cranial nerve location and route information in the section above has been included to summarise the key points for each cranial nerve. For the fibre type please see the Fibre Type section (heading 2 above) using the fibre type link in the table. | |
| | | | |
| | {| style="width:100%; height:200px" border="1" | | {| style="width:100%; height:200px" border="1" |
| Line 189: |
Line 54: |
| | | Olfactory bulb | | | Olfactory bulb |
| | | Cribriform plate | | | Cribriform plate |
| − | | SVA | + | | SVS |
| | | Olfactory epithelium | | | Olfactory epithelium |
| | | Olfactory epithelium | | | Olfactory epithelium |
| Line 195: |
Line 60: |
| | | | |
| | | '''II - Optic''' | | | '''II - Optic''' |
| − | | Diencephalon (via optic chiasm) | + | | Optic chiasma |
| | | Optic canal | | | Optic canal |
| − | | SSA | + | | SSS |
| | | Retina | | | Retina |
| | | Retina | | | Retina |
| | | | |
| | |- | | |- |
| − | | '''III - Oculomotor''' | + | | '''III - Occulomotor''' |
| | | Midbrain | | | Midbrain |
| − | | Orbital fissure | + | | Orbital fissure and Round Foramen |
| − | | GSE + GVE | + | | GSM + GVM |
| − | | Oculomotor motor nucleus | + | | Nuculi III |
| − | Parasympathetic nucleus of oculomotor nerve
| + | parasympathetic nuculi III |
| | | Extraoccular mm. | | | Extraoccular mm. |
| − | Constrictor pupilli | + | Constrictor pupulli |
| | | | |
| | |- | | |- |
| | | '''IV - Trochlear''' | | | '''IV - Trochlear''' |
| | | Midbrain (dorsal) | | | Midbrain (dorsal) |
| − | | Orbital fissure | + | | Round Foramen |
| − | | GSE | + | | GSM |
| − | | Trochlear nucleus | + | | Nuc IV |
| | | Dorsal oblique mm. | | | Dorsal oblique mm. |
| | |- | | |- |
| Line 223: |
Line 88: |
| | | Pons | | | Pons |
| | | V1 - Orbital fissure | | | V1 - Orbital fissure |
| − | V2 - Round Foramen/Rostral alar foramen | + | V2 - Round Foramen and Orbital Fissure |
| | | | |
| | V3 - Oval Foramen | | V3 - Oval Foramen |
| − | | V1 - GSA | + | | V1 - GSS |
| − | V2 - GSA | + | V2 - GSS |
| | | | |
| − | V3 - GSA & GSE | + | V3 - SVM |
| − | | V1 - Trigeminal gangion (GSA) | + | | V1 - Trigeminal gangion |
| − | V2 - Trigeminal ganglion (GSA) | + | V2 - Trigeminal ganglion |
| | | | |
| − | V3 - Trigeminal ganglion (GSA), Geniculate ganglion (SVA), Trigeminal motor nucleus (motor) | + | V3 - Nuculi V |
| | | V1 - Eye region | | | V1 - Eye region |
| | V2 - Upper jaw inc. teeth | | V2 - Upper jaw inc. teeth |
| | | | |
| − | V3 - mm. of arch 1, lower jaw, rostral 2/3 tongue | + | V3 - mm. of arch 1 |
| | | | |
| | |- | | |- |
| Line 243: |
Line 108: |
| | | Medulla oblongata | | | Medulla oblongata |
| | | Orbital fissure | | | Orbital fissure |
| − | | GSE | + | | GSM |
| − | | Abducent nucleus | + | | Nuc IV |
| | | Lateral rectus and retractor bulbi mm. | | | Lateral rectus and retractor bulbi mm. |
| | |- | | |- |
| Line 251: |
Line 116: |
| | | '''VII - Facial''' | | | '''VII - Facial''' |
| | | Medulla oblongata | | | Medulla oblongata |
| − | | Internal acoustic meatus/facial canal/stylomastoid foramen | + | | Stylomastoid foramen |
| − | | SVA + GVE + GSE + GSA | + | | SVM + GVM + SVS |
| − | | Facial motor nucleus | + | | Nuc III |
| − | Geniculate ganglion
| + | (Taste - gleniailate ganglion) |
| | | mm. of arch 2 | | | mm. of arch 2 |
| | Submaxillary and sublingual glands | | Submaxillary and sublingual glands |
| | | | |
| − | Rostral 2/3 tongue | + | Rostral 2/3 taste |
| | |- | | |- |
| | | | |
| Line 264: |
Line 129: |
| | | '''VIII - Vestibulocochlear''' | | | '''VIII - Vestibulocochlear''' |
| | | Medulla oblongata | | | Medulla oblongata |
| − | | Internal acoustic meatus | + | | Inner accoustic meatus |
| − | | SSA | + | | SSS |
| − | | Vestibular ganglion, spiral ganglion | + | | Vestibular ganglion |
| | | Maculae and cristae | | | Maculae and cristae |
| | |- | | |- |
| Line 273: |
Line 138: |
| | | '''IX - Glossopharyngeal''' | | | '''IX - Glossopharyngeal''' |
| | | Medulla oblongata | | | Medulla oblongata |
| − | | Jugular foramen/tympanooccipital fissure | + | | Jugular foramen |
| − | | GSE GVA GVE GSA SVA | + | | G/S V M/S |
| − | | Glossopharyngeal ganglion | + | | Ganglia IX - SVM |
| − | Glossopharyngeal parasympathetic nucleus, nucleus ambiguus - mm. arch 3
| + | Nuculi ambiguous - mm. arch 3 |
| | | Carotid gland | | | Carotid gland |
| − | Caudal 1/3 tongue | + | Caudal 1/3 taste |
| | mm. of arch 3 | | mm. of arch 3 |
| | | | |
| Line 287: |
Line 152: |
| | | '''X - Vagus''' | | | '''X - Vagus''' |
| | | Medulla oblongata | | | Medulla oblongata |
| − | | Jugular foramen/tympanooccipital fissure | + | | Jugular foramen |
| − | | GSE GVA GVE SVA GSA | + | | GVM + SUM + GVS + GSS |
| − | | Vagal ganglion - (amongst others) | + | | Ganglion X - (amongst others) |
| − | Vagal parasympathetic nucleus, nucleus ambiguus
| |
| | | Thoracic and abdominal organs | | | Thoracic and abdominal organs |
| | mm. of arches 4-6 | | mm. of arches 4-6 |
| Line 300: |
Line 164: |
| | | '''XI - Accessory''' | | | '''XI - Accessory''' |
| | | Medulla oblongata | | | Medulla oblongata |
| − | | Jugular foramen/tympanooccipital fissure | + | | Jugular foramen |
| − | | GSE | + | | GSM |
| − | | Nucleus ambiguus, accessory motor nucleus (cervical spinal cord) | + | | Cervical spinal cord |
| | | Trapezius m. etc | | | Trapezius m. etc |
| | |- | | |- |
| Line 310: |
Line 174: |
| | | Medulla oblongata | | | Medulla oblongata |
| | | Hypoglossal canal | | | Hypoglossal canal |
| − | | GSE | + | | GSM |
| − | | Hypoglossal nucleus | + | | Medulla nuculi XII |
| | | Tongue mm. | | | Tongue mm. |
| | |- | | |- |
| | + | | |
| | |} | | |} |
| | | | |
| − | ===Cranial Nerves Functions=== | + | ==Cranial Nerve Fibre Types== |
| − | This table is designed to provide the basic function of each cranial nerve and has also been designed as a summary/revision aid.
| + | |
| | + | Cranial nerves are best explained by function: |
| | + | |
| | + | |
| | + | *'''General Somatic Motor (GSM)''' |
| | + | |
| | + | Motor cortex —→ Motor nuculi —→ Muscle |
| | + | |
| | + | |
| | + | *'''General Visceral Motor (GVM)''' |
| | + | |
| | + | Brainstem —→ Parasympathetic nuculi —→ Parasympathetic ganglion —→ Gland etc |
| | + | |
| | + | |
| | + | *'''"Branchial motor" - Special Visceral Motor (SVM)''' |
| | + | |
| | + | Motor cortex —→ Motor nuculi —→ Muscle |
| | + | |
| | + | |
| | + | *'''General Somatic Sensory (GSS) and General Visceral Sensory (GVS)''' |
| | + | |
| | + | Sensory cortex —→ Thalamus —→ Trigeminal nuculi —→ Trigeminal ganglion —→ Skin etc |
| | + | |
| | + | |
| | + | ===Special sensory fibres (SSS + SVS):=== |
| | + | |
| | + | '''[[Nose - Anatomy & Physiology|Smell]]''' '''SVS''' |
| | + | |
| | + | Priform cortex —→ Olfactory tubercle —→ Olfactory Bulb —→ '''SMELL''' |
| | + | |
| | + | |
| | + | '''[[Eye - Anatomy & Physiology|Vision]]''' '''SSS''' |
| | + | |
| | + | Occipital cortex —→ Thalamus MGN —→ Rostral colliculus/Retinal ganglion cell —→ Bipolar cell —→ '''VISION''' |
| | + | |
| | + | |
| | + | '''[[Ear - Anatomy & Physiology|Hearing/Balance]]''' '''SSS''' |
| | + | |
| | + | Temporal cortex —→ Thalamus MGN —→ Caudal colliculus and hindbrain —→ Spiral ganglion —→ '''HEARING''' |
| | + | |
| | + | |
| | + | '''[[Gustatory System - Anatomy & Physiology|Taste]]''' '''SVS''' |
| | + | |
| | + | Sensory cortex —→ Thalamus —→ Hindbrain (VII, IX, X) —→ Ganglion —→ '''TASTE''' |
| | + | |
| | + | ==Cranial Nerves and their Functions== |
| | {| border="1" cellpadding="7" | | {| border="1" cellpadding="7" |
| | |-style="background:#B0E0E6; color:black" | | |-style="background:#B0E0E6; color:black" |
| Line 371: |
Line 281: |
| | |} | | |} |
| | | | |
| − | ==Learning Mnemonic==
| |
| − | There are various ways to memorise the cranial nerves including both the names of the actual nerves themselves and also their functions/type of nerve fibre. Here are some examples for the nerve names and also some for the type of nerve.
| |
| − | ===Nerve Name Mnemonics===
| |
| − | ====Mnemonic 1====
| |
| − | * '''O'''h (''O''lfactory I)
| |
| − | * '''O'''h (''O''ptic II)
| |
| − | * '''O'''h (''O''culomotor III)
| |
| − | * '''T'''o (''T''rochlear IV)
| |
| − | * '''T'''ouch (''T''rigeminal V)
| |
| − | * '''A'''nd (''A''bducens VI)
| |
| − | * '''F'''eel (''F''acial VII)
| |
| − | * '''A''' (''A''uditory/Vestibulocochlear VIII)
| |
| − | * '''G'''irl's (''G''lossopharyngeal IX)
| |
| − | * '''V'''ery (''V''agus X)
| |
| − | * '''S'''oft (''S''pinal/Accessory XI)
| |
| − | * '''H'''ands (''H''ypoglossal XII)
| |
| − | ====Mnemonic 2====
| |
| − | * '''O'''h (''O''lfactory I)
| |
| − | * '''O'''nce (''O''ptic II)
| |
| − | * '''O'''ne (''O''culomotor III)
| |
| − | * '''T'''akes (''T''rochlear IV)
| |
| − | * '''T'''he (''T''rigeminal V)
| |
| − | * '''A'''natomy (''A''bducens VI)
| |
| − | * '''F'''inal (''F''acial VII)
| |
| − | * '''A''' (''A''uditory/Vestibulocochlear VIII)
| |
| − | * '''G'''ood (''G''lossopharyngeal IX)
| |
| − | * '''V'''acation (''V''agus X)
| |
| − | * '''S'''eems (''S''pinal/Accessory XI)
| |
| − | * '''H'''eavenly (''H''ypoglossal XII)
| |
| − | ====Mnemonic 3====
| |
| − | * '''O'''nly (''O''lfactory I)
| |
| − | * '''O'''ffer (''O''ptic II)
| |
| − | * '''O'''nce (''O''culomotor III)
| |
| − | * '''T'''o (''T''rochlear IV)
| |
| − | * '''T'''ry (''T''rigeminal V)
| |
| − | * '''A'''nd (''A''bducens VI)
| |
| − | * '''F'''ind (''F''acial VII)
| |
| − | * '''V'''erdant (''A''uditory/Vestibulocochlear VIII)
| |
| − | * '''G'''reen (''G''lossopharyngeal IX)
| |
| − | * '''V'''erges (''V''agus X)
| |
| − | * '''A'''nd (''S''pinal/Accessory XI)
| |
| − | * '''H'''edges (''H''ypoglossal XII)
| |
| − |
| |
| − | ===Nerve Type Mnemonics===
| |
| − | For the mnemonic below ''S = sensory'', ''M = motor'' and ''B = both'' (sensory and motor).
| |
| − | * '''S'''ome
| |
| − | * '''S'''ay
| |
| − | * '''M'''arry
| |
| − | * '''M'''oney
| |
| − | * '''B'''ut
| |
| − | * '''M'''y
| |
| − | * '''B'''rother
| |
| − | * '''S'''ays
| |
| − | * '''B'''ig
| |
| − | * '''B'''usiness
| |
| − | * '''M'''akes
| |
| − | * '''M'''oney
| |
| − |
| |
| − | {{Learning
| |
| − | |videos = [[Video: Lateral surface of the head of the dog potcast 2|Lateral surface of the head of the dog potcast 2]]<br>[[Video: Canine orbit and sagittal section of the canine head|Canine orbit and sagittal section of the canine head]]<br>[[Video: Lateral surface of the head of the dog potcast 3|Lateral surface of the head of the dog potcast]]<br>[[Video: Lateral surface of the head of the dog potcast 5|Lateral surface of the head of the dog potcast 5]]<br>
| |
| − | }}
| |
| | | | |
| − | ==Webinars==
| + | {{unfinished}} |
| − | <rss max="10" highlight="neurological seizure neurology">https://www.thewebinarvet.com/neurology/webinars/feed</rss>
| |
| | [[Category:Nervous System - Anatomy & Physiology]] | | [[Category:Nervous System - Anatomy & Physiology]] |
| − | [[Category:A&P Done]] | + | [[Category:To Do - A&P]] |
The brainstem, cranial nerves and pyramids. © BioMed Archive.
Introduction
Cranial nerves are those nerves which arise from the brain and brain stem rather than the spinal cord. Nerves arising from the spinal cord are the peripheral nerves. There are 12 pairs of cranial nerves and these pairs of nerves passage through foramina in the skull, either individually or in groups. Cranial nerves are traditionally referred to by Roman numerals and these numerals begin cranially and run caudally.
The most cranial nerve is the Olfactory nerve (I) which runs from the nasal cavity through to the olfactory bulb. The next most cranial is the Optic nerve (II) which runs from the eyes to the thalamus. Cranial nerves III to XII all exit from the brain stem and innervate the head, neck and organs in the thorax and abdomen. In order of most cranial to caudal, these include the Oculomotor nerve (III), the Trochlear nerve (IV), the Trigeminal nerve (V), the Abducens nerve (VI), the Facial nerve (VII), the Vestibulocochlear nerve (VIII), the Glossopharyngeal nerve (IX), the Vagus nerve (X), the Accessory nerve (XI) and the Hypoglossal nerve (XII).
Many of the cranial nerves with nuclei within the brain stem contain sensory and motor neurone components. The sensory fibre components have their cell bodies located in ganglia outside the central nervous system and the motor fibre element have their cell bodies within the central nervous system.
Cranial Nerves
There are three main groups of cranial nerves; special senses, innervation of the head muscles and innervation of structures originating from brancial arches. The special senses cranial nerves include the olfactory, ocular and vestibulocochlear. Cranial nerves related to the innervation of the head muscles include the oculomotor, trochlear, abducens and the hypoglossal nerves. Cranial nerves related to innervation of structures originating from branchial arches includes the trigeminal, facial, glossopharyngeal, vagus and accessory nerves.
Olfactory Nerve (I)
Olfaction is part of the special senses cranial nerve group and represents the chemical senses of olfaction (smell) and gustation (taste). When chemical substances interact with our bodies they stimulate special sensory cells which in turn generate an action potential. The resultant impulse is sent to the brain via sensory afferent fibres and it is these fibres that represent the olfactory cranial nerve. Note: an action potential is only generated where a special sensory cell for that particular chemical substance exists. The special sensory cells are found within the olfactory mucous membrane in the nasal fundus and the olfactory neurosensory cells are found within the olfactory epithelium. The olfactory epithelium contains cilia on the surface of the cells to increase the surface area for chemical interactions.
The olfactory nerve runs to the olfactory bulb which is found within the telencephalon. The olfactory nerve is a sensory nerve and is composed of many Special Visceral Afferent fibres. The fibres are formed into bundles that are referred to as 'Olfactory filaments'. The olfactory nerve passes through the Cribiform plate and is surrounded by meningeal sheets including the sub-arachnoid space. Therefore the route of the olfactory nerve represents a potential site for an infection to track towards the brain. Injury of this nerve can lead to 'anosmia', or loss of smell.
The olfactory organ in dogs is extremely well developed and species such as dogs use olfaction to orientate themselves in an environment in a way that humans do not. Olfactory cells are continuously replaced and are only viable sensory cells for between 30 - 60 days. This point is of importance as this is the only area in which nerve cells are able to be replaced or regenerated in adult animals and this area is now under research at Cambridge University for the treatment of damaged nerves and/or nerve disorders in nerves other than those involved in olfaction.
Optic Nerve (II)
The optic nerve is part of the special senses cranial nerves and represents the connection between the receptor cells of the retina and the diencephalon. The optic nerve is a sensory nerve and is composed of Special Somatic Afferent fibres. The optic nerve passes through the optic chiasm which is an area of the ventral brain where both optic nerves run in a medial direction and eventually decussate. The optic nerve runs through the optic canal.
The optic nerve can be examined clinically via a menace response and anopsia (loss of vision) can be seen in injury.
Oculomotor nerve (III)
The oculomotor nerve is part of the group of cranial nerves responsible for innervating the muscles of the head. The nerves originate from the ventral midbrain and is a motor nerve. It is composed of general somatic efferent fibres and general visceral efferent fibres. The general somatic efferent fibres of the oculomotor nerve are responsible for the motor function of four of the six external muscles of the eyeball; the 'dorsal rectus', 'medial rectus', 'ventral rectus', 'ventral oblique' and 'levator of the upper eyelid'. The general visceral efferent fibres of the oculomotor nerve are responsible for the control of pupil diameter and therefore control the 'spincter pupillae' muscle and the 'ciliaris' muscle.
The oculomotor nerve has a pre-ganglionic nucleus in the midbrain and the nerve passes through the orbital fissure, along with the trochlear, abducens and opthalmic branch (V1) of the trigeminal nerve. It synapses in the ciliary ganglion of the eye. During a clinical examination, horizontal eye movements (strabismus) or an abscent pupillary light reflex (PLR) may indicate a problem.
Trochlear nerve (IV)
Vestibulocochlear nerve (VIII)
The vestibulocochlear nerve is part of the special senses group of cranial nerves and is made up of two components; the vestibular nerve and the cochlear nerve. The vestibular nerve is responsible for balance whilst the cochlear nerve is responsible for hearing. The nerves send impulses from the inner ear which contains the vestibular apparatus and cochlear. The vestibulocochlear nerve is a sensory nerve made up of special somatic afferent fibres. It passes through the internal acoustic meatus and into the petrosal bone. The facial nerve also takes this route.
Clinical problems with the vestibulocochlear nerve would be indicated on examination by changes in hearing and/or horizontal and verticle eye movements (strabismus and nystagmus). A head tilt is also associated with this nerve.
Cranial Nerve Location and Routes
A summary of the cranial nerves is shown below:
| Nerve
|
Attatchment to brain
|
Exit Foramen
|
Fibre Type
|
Location of cell bodies
|
Distribution
|
| I - Olfactory
|
Olfactory bulb
|
Cribriform plate
|
SVS
|
Olfactory epithelium
|
Olfactory epithelium
|
| II - Optic
|
Optic chiasma
|
Optic canal
|
SSS
|
Retina
|
Retina
|
| III - Occulomotor
|
Midbrain
|
Orbital fissure and Round Foramen
|
GSM + GVM
|
Nuculi III
parasympathetic nuculi III
|
Extraoccular mm.
Constrictor pupulli
|
| IV - Trochlear
|
Midbrain (dorsal)
|
Round Foramen
|
GSM
|
Nuc IV
|
Dorsal oblique mm.
|
| V - Trigeminal
|
Pons
|
V1 - Orbital fissure
V2 - Round Foramen and Orbital Fissure
V3 - Oval Foramen
|
V1 - GSS
V2 - GSS
V3 - SVM
|
V1 - Trigeminal gangion
V2 - Trigeminal ganglion
V3 - Nuculi V
|
V1 - Eye region
V2 - Upper jaw inc. teeth
V3 - mm. of arch 1
|
| VI - Abducens
|
Medulla oblongata
|
Orbital fissure
|
GSM
|
Nuc IV
|
Lateral rectus and retractor bulbi mm.
|
| VII - Facial
|
Medulla oblongata
|
Stylomastoid foramen
|
SVM + GVM + SVS
|
Nuc III
(Taste - gleniailate ganglion)
|
mm. of arch 2
Submaxillary and sublingual glands
Rostral 2/3 taste
|
| VIII - Vestibulocochlear
|
Medulla oblongata
|
Inner accoustic meatus
|
SSS
|
Vestibular ganglion
|
Maculae and cristae
|
| IX - Glossopharyngeal
|
Medulla oblongata
|
Jugular foramen
|
G/S V M/S
|
Ganglia IX - SVM
Nuculi ambiguous - mm. arch 3
|
Carotid gland
Caudal 1/3 taste
mm. of arch 3
Carotid body
|
| X - Vagus
|
Medulla oblongata
|
Jugular foramen
|
GVM + SUM + GVS + GSS
|
Ganglion X - (amongst others)
|
Thoracic and abdominal organs
mm. of arches 4-6
Pharynx and larynx
External ear
|
| XI - Accessory
|
Medulla oblongata
|
Jugular foramen
|
GSM
|
Cervical spinal cord
|
Trapezius m. etc
|
| XII - Hypoglossal
|
Medulla oblongata
|
Hypoglossal canal
|
GSM
|
Medulla nuculi XII
|
Tongue mm.
|
|
|
Cranial Nerve Fibre Types
Cranial nerves are best explained by function:
- General Somatic Motor (GSM)
Motor cortex —→ Motor nuculi —→ Muscle
- General Visceral Motor (GVM)
Brainstem —→ Parasympathetic nuculi —→ Parasympathetic ganglion —→ Gland etc
- "Branchial motor" - Special Visceral Motor (SVM)
Motor cortex —→ Motor nuculi —→ Muscle
- General Somatic Sensory (GSS) and General Visceral Sensory (GVS)
Sensory cortex —→ Thalamus —→ Trigeminal nuculi —→ Trigeminal ganglion —→ Skin etc
Special sensory fibres (SSS + SVS):
Smell SVS
Priform cortex —→ Olfactory tubercle —→ Olfactory Bulb —→ SMELL
Vision SSS
Occipital cortex —→ Thalamus MGN —→ Rostral colliculus/Retinal ganglion cell —→ Bipolar cell —→ VISION
Hearing/Balance SSS
Temporal cortex —→ Thalamus MGN —→ Caudal colliculus and hindbrain —→ Spiral ganglion —→ HEARING
Taste SVS
Sensory cortex —→ Thalamus —→ Hindbrain (VII, IX, X) —→ Ganglion —→ TASTE
Cranial Nerves and their Functions
| #
|
Name
|
Nuclei
|
Function
|
| I
|
Olfactory nerve
|
Anterior olfactory nucleus
|
Transmits the sense of smell
|
| II
|
Optic nerve
|
Lateral geniculate nucleus
|
Transmits visual information to the brain
|
| III |
Oculomotor nerve |
Oculomotor nucleus, Edinger-Westphal nucleus |
Innervates the dorsal rectus, medial rectus, ventral rectus, and ventral oblique, which collectively perform most eye movements
|
| IV
|
Trochlear nerve
|
Trochlear nucleus
|
Innervates the superior oblique muscle, which depresses, pulls laterally, and intorts the eyeball
|
| V |
Trigeminal nerve |
Principal sensory trigeminal nucleus, Spinal trigeminal nucleus, Mesencephalic trigeminal nucleus, Trigeminal motor nucleus |
Receives sensation from the face and innervates the muscles of mastication
|
| VI
|
Abducens nerve
|
Abducens nucleus
|
Innervates the lateral rectus, which abducts the eye and the retractor bulbi which forces the third eyelid across the surface of the cornea as a protective mechanism.
|
| VII |
Facial nerve |
Facial nucleus, Solitary nucleus, Superior salivary nucleus |
Provides motor innervation to the muscles of facial expression and stapedius, receives the special sense of taste from the anterior 2/3 of the tongue, and provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal gland
|
| VIII
|
Vestibulocochlear nerve
|
Vestibular nuclei, Cochlear nuclei
|
Senses sound, rotation and gravity (essential for balance & movement)
|
| IX |
Glossopharyngeal nerve |
Nucleus ambiguus, Inferior salivary nucleus, Solitary nucleus |
Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus
|
| X
|
Vagus nerve
|
Nucleus ambiguus, Dorsal motor vagal nucleus, Solitary nucleus
|
Supplies branchiomotor innervation to most laryngeal and pharyngeal muscles; provides parasympathetic fibers to nearly all thoracic and abdominal viscera down to the splenic flexure; and receives the special sense of taste from the epiglottis
|
| XI |
Accessory nerve |
Nucleus ambiguus, Spinal accessory nucleus |
Controls muscles of the neck and overlaps with functions of the vagus
|
| XII
|
Hypoglossal nerve
|
Hypoglossal nucleus
|
Provides motor innervation to the intrinsic muscles of the tongue and other glossal muscles
|
