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==Introduction==

==Introduction==

Sensory information at our peripheries ascends through the [[Spinal Cord - Anatomy & Physiology|spinal cord]] and enters the higher levels of the brain. There are numerous pathways which allow different types of information to be passed to the brain. Types of general somatic sensation include:

Sensory information from the periphery of the animal ascends through the [[Spinal Cord - Anatomy & Physiology|spinal cord]] and enters the higher levels of the brain. There are numerous pathways which allow different types of information to be passed to the brain. Types of general somatic sensation include pain, touch, temperature and kinaesthesia (conscious proprioception). This sensory information is sent to one of two destinations; the [[Forebrain - Anatomy & Physiology#Cerebral Coretex|cerebral cortex]] or the [[Hindbrain - Anatomy & Physiology#Cerebellum|cerebellum]].

 

#  Kinaesthesia (conscious proprioception)

 

Sensory information is sent to one of two destinations:

*The '''[[Forebrain - Anatomy & Physiology#Cerebral Cortex|cerebral cortex]]'''

When sensory information is relayed to the [[Forebrain - Anatomy & Physiology#Cerebral Cortex|cerebral cortex]], information first passes via the [[Forebrain - Anatomy & Physiology#Thalamus|thalamus]]. The signal may be relayed one or more times by the [[Forebrain - Anatomy & Physiology#Thalamus|thalamus]] en route to the [[Forebrain - Anatomy & Physiology#Cerebral Cortex|cortex]]. This sensory information reaches higher levels within the brain and therefore consciousness. The [[Hindbrain - Anatomy & Physiology#Cerebellum|cerebellum]] is involved in co-ordination and this sensory information does not reach consciousness.

**Information first passes via the [[Forebrain - Anatomy & Physiology#Thalamus|thalamus]].

**The signal may be relayed one or more times by the [[Forebrain - Anatomy & Physiology#Thalamus|thalamus]] en route to the [[Forebrain - Anatomy & Physiology#Cerebral Cortex|cortex]].

**The information reaches consciousness.

**The [[Hindbrain - Anatomy & Physiology#Cerebellum|cerebellum]] is involved in co-ordination.

**The information does not reach consciousness.

==Pathways==

==Pathways==

===Ascending Pathways===

===Ascending Pathways===

[[Image:The Ascending Pathways.jpg|thumb|right|150px|Ascending Pathways, Sarah Hamilton ''RVC'', 2008]]

[[Image:The Ascending Pathways.jpg|thumb|right|150px|Ascending Pathways, Sarah Hamilton ''RVC'', 2008]]

 

Sensory information enters the [[Spinal Cord - Anatomy &  Physiology|spinal cord]] on the same side of the body as the stimulus. Ascending tracts cross over the midline of the body to the contralateral side of the [[Forebrain - Anatomy & Physiology#Thalamus|thalamus]]. The [[Forebrain - Anatomy & Physiology#Thalamus|thalamus]] directs the signal to the [[Forebrain - Anatomy & Physiology#Cerebral Cortex|cerebral cortex]] for conscious perception. The pathway is direct with very few [[PNS Structure - Anatomy & Physiology#Nerve Fibre|neurones]] involved.

*Sensory information enters the [[Spinal Cord - Anatomy &  Physiology|spinal cord]] on the same side of the body as the stimulus.

*Ascending tracts cross over the midline of the body to the contralateral side of the [[Forebrain - Anatomy & Physiology#Thalamus|thalamus]].

*The [[Forebrain - Anatomy & Physiology#Thalamus|thalamus]] directs the signal to the [[Forebrain - Anatomy & Physiology#Cerebral Cortex|cerebral cortex]] for conscious perception.

**The pathway is direct, with very few [[PNS Structure - Anatomy & Physiology#Nerve Fibre|neurones]] involved.

====1. Dorsal Columns====

====1. Dorsal Columns====

*Transmits information from touch and kinaesthesia, i.e low threshold information.

Dorsal columns transmit information from touch and kinaesthesia; these are both classified as low threshold information. There are two major dorsal columns; the ''gracile fasiculus'' situated medially which conveys information from the hindlimbs and caudal trunk and the ''cuneate fasciculus'' which is situated more laterally and conveys information from the forelimbs and cranial trunk.

*There are two major dorsal columns:

** '''The gracile fasiculus'''

*** Situated medially.

*** Conveys information from the hindlimbs and caudal trunk.

** '''The cuneate fasciculus'''

*** Situated more laterally.

*** Conveys information from the forelimbs and cranial trunk.

====2. Spinothalamic Tracts====

====2. Spinothalamic Tracts====

*Transmits information from temperature and "pin prick" pain.

Spinothalamic tracts transmit information from temperature and "pin prick" pain; these senses are classified as fast, initial pain sensations. These tracts compare with the [[Sensory Pathways - Anatomy & Physiology#Ascending Reticular Formation|ascending reticular formation]].

*Fast, intial pain sensation

*Compare with [[Sensory Pathways - Anatomy & Physiology#Ascending Reticular Formation|ascending reticular formation]]

====3. Spinocervicothalamic Tracts====

====3. Spinocervicothalamic Tracts====

*Transmits information from touch and kinaesthesia.

The spinocervicothalamic tracts transmit information from touch and kinaesthesia, although these are absent in man.

*Absent in man

===Spinocerebellar Tracts===

===Spinocerebellar Tracts===

[[Image:TheSpinocerebellarTract.jpg|thumb|right|150px|Spinocerebellar Tract - © Sarah Hamilton 2008]]

[[Image:TheSpinocerebellarTract.jpg|thumb|right|150px|Spinocerebellar Tract - © Sarah Hamilton 2008]]

*Transmits information from proprioception receptors, including information from muscle receptors, joint receptors and golgi tendon organs.

These tracts transmit information from proprioception receptors, including information from muscle receptors, joint receptors and golgi tendon organs. Most sensory information enters the [[Spinal Cord - Anatomy & Physiology|spinal cord]] on the ipsilateral side to the stimulus but some do cross to the contralateral side of the body. Contralateral signals pass back to the ipsilateral side of the body in the brain. Information is processed in the [[Hindbrain - Anatomy & Physiology#Cerebellum|cerebellum]] and is therefore processed unconsciously.

*Most sensory information enters the [[Spinal Cord - Anatomy & Physiology|spinal cord]] on the ipsilateral side to the stimulus, some crosses to the contralateral side of the body.

 

**Contralateral signals pass back to the ipsilateral side of the body in the brain.

*Information is processed in the [[Hindbrain - Anatomy & Physiology#Cerebellum|cerebellum]] and is therefore processed unconsciously.

The dorsal spinocerebellar tract relays muscle spindle and golgi tendon organ information from the hindlimbs to the [[Hindbrain - Anatomy & Physiology#Cerebellum|cerebellum]].

*The '''dorsal spinocerebellar tract''' relays muscle spindle and Golgi tendon organ information from the hindlimbs to the [[Hindbrain - Anatomy & Physiology#Cerebellum|cerebellum]].

 

* The '''cuneo-cerebellar tract''' serves the same purpose for the forelimbs, but is much smaller.

* The '''ventral spinocerebellar tract''' is similar to the dorsal spinocerebellar tract but it takes a less direct route to the [[Hindbrain - Anatomy & Physiology#Cerebellum|cerebellum]].  

The cuneo-cerebellar tract serves the same purpose for the forelimbs as the dorsal spinocerebellar tract does for the hind limbs, but is much smaller.

** The forelimb equivalent is called the '''rostral spinocerebellar tract'''.

 

The ventral spinocerebellar tract is similar to the dorsal spinocerebellar tract but it takes a less direct route to the [[Hindbrain - Anatomy & Physiology#Cerebellum|cerebellum]]. The forelimb equivalent is called the rostral spinocerebellar tract.

===Ascending Reticular Formation (Spinoreticular Tract)===

===Ascending Reticular Formation (Spinoreticular Tract)===

[[Image:AscendingReticularFormation.jpg|thumb|right|150px|Ascending Reticular Formation - © Sarah Hamilton 2008]]

[[Image:AscendingReticularFormation.jpg|thumb|right|150px|Ascending Reticular Formation - © Sarah Hamilton 2008]]

 

The ascending reticular formation is thought of as the true pain sensation as the pain lasts longer. Sensory information enters the [[Spinal Column - Anatomy & Physiology|spinal cord]] on the ipsilateral side of the stimulus. Some signals cross to the contralateral side of the body. The tract consists of several [[PNS Structure - Anatomy & Physiology#Nerve Fibre|short neurones]]. Therefore the ascending reticular formation is ''bilateral'' and ''multineuronal'', although this pain pathway is thought to be more primitive than the [[Sensory Pathways - Anatomy & Physiology#Spinothalamic Tract|spinothalmic tract]]. In humans, the ascending reticular formation is superceded by the [[Sensory Pathways - Anatomy & Physiology#Spinothalamic Tract|spinothalamic tract]]. In animals, the ascending reticular formation is the main pathway for pain to reach the [[Forebrain - Anatomy & Physiology#Cerebral Cortex|cerebral cortex]].

*True pain sensation; pain lasts longer.

*Sensory information enters the [[Spinal Column - Anatomy & Physiology|spinal cord]] on the ipsilateral side of the stimulus. Some signals cross to the contralateral side of the body.

*The tract consists of '''several''' [[PNS Structure - Anatomy & Physiology#Nerve Fibre|short neurones]].

*Therfore the ascending reticular formation is ''bilateral'' and ''multineuronal''.

*This pain pathway is more primitive than the [[Sensory Pathways - Anatomy & Physiology#Spinothalamic Tract|spinothalmic tract]].

**In '''man''', the ascending reticular formation is superceeded by the [[Sensory Pathways - Anatomy & Physiology#Spinothalamic Tract|spinothalamic tract]]. In '''animals''', the ascending reticular formation is the '''main pathway''' for pain to reach the [[Forebrain - Anatomy & Physiology#Cerebral Cortex|cerebral cortex]].

==Pain==

==Pain==

*"Painful stimuli" can range from itches, to nausea, to being in agony.

Pain is not a sensory modality. The sensory modality that is checked in a neurologic exam is Nociception which is the patients response to a noxious stimuli. Pain is a subjective cerebral response. Noxious stimuli can result in responses ranging from itches, to nausea, to simply being in agony. Noxious stimuli may be transmitted to the brain by one of two pathways: the [[Sensory Pathways - Anatomy & Physiology#Spinothalamic Tract|Spinothalamic Tract]] or the [[Sensory Pathways - Anatomy & Physiology#Ascending Reticular Formation|Ascending Reticular Formation]].

*Painful stimuli may be transmitted to the brain by one of two pathways:

::[[Sensory Pathways - Anatomy & Physiology#Spinothalamic Tract|Spinothalamic Tract]]

::[[Sensory Pathways - Anatomy & Physiology#Ascending Reticular Formation|Ascending Reticular Formation]]

'''Spinothalamic Tract'''

===Spinothalamic Tract===

*Fast, initial pinprick is detected by free [[PNS Structure - Anatomy & Physiology#Nerve Fibres|nerve]] endings

This fast, initial pinprick is detected by free [[PNS Structure - Anatomy & Physiology#Nerve Fibres|nerve]] endings and causes an impulse along large, myelinated fibres. The pain sensation is '''localised, and ends quickly'''.

*Causes an impulse along large, myelinated fibres

*Pain sensation is localised, and ends quickly

'''Ascending Reticular Formation'''

===Ascending Reticular Formation===

*A painful sensation is detected by free [[PNS Structure - Anatomy & Physiology#Nerve Fibres|nerve]] endings

This pain sensation is detected by free [[PNS Structure - Anatomy & Physiology#Nerve Fibres|nerve]] endings which causes an impulse along small, unmyelinated fibres. This results in a delayed perception of the sensation of pain, and that pain is often '''less localised but more persistent'''.

*Causes an impulse along small, unmyelinated fibres

*A delayed sensation of pain is percieved, that is less localised, persistent.

'''Clinical Relevance'''

'''Clinical Relevance'''

*In trauma, the small unmyelinated fibres are the last fibres to fail as they are close to the [[Spinal Cord - Anatomy & Physiology|spinal cord]].

During trauma the small unmyelinated fibres are the last fibres to fail as they are close to the [[Spinal Cord - Anatomy & Physiology|spinal cord]]. If deep pain sensation is lost in a case of trauma, then the prognosis is poor.  

**If deep pain sensation is lost in a case of trauma, then the prognosis is poor.

*''Hyperalgesia'' is an increased pain sensation. Occurs when tissue is damaged because chemicals are released which increase the sensitivity of nociceptors, so that even light pressure can cause pain.

''Hyperalgesia'' is an increased pain sensation. This occurs when tissue is damaged because chemicals are released which increase the sensitivity of nociceptors, so that even light pressure can cause pain. Hyperalgesia may have evolved to aid the healing of injuries.

**May have evolved to aid the healing of injuries.

===Visceral Pain===

===Visceral Pain===

*This refers to pain of the internal organs.

Visceral pain refers to pain related to the internal organs. Pain may be extreme, especially with distension, but the body's ability to localise the pain is poor. Skeletal muscle spasms may be observed during visceral pain. Commonly, the pain is referred to a different part of the body that is unharmed. This is because the areas are served by the same part of the [[Spinal Cord - Anatomy & Physiology|spinal cord]] e.g. in angina (pain in the heart), pain can be felt in the inner left arm or jaw. This is called ''referred pain''.

*Pain may be extreme, especially with distension, but the body's ability to localise the pain is poor.

**Skeletal muscle spasms may be observed.

*Commonly, the pain is referred to a different part of the body that is unharmed. This is because the areas are served by the same part of the [[Spinal Cord - Anatomy & Physiology|spinal cord]] e.g. in angina (pain in the heart), pain can be felt in the inner left arm or jaw.

**This is called '''referred pain'''.

 

 

 

==Links==

==Links==

*[[Nervous System - Pathology|Pathology of the Nervous System]]

*[[:Category:Nervous System - Pathology|Pathology of the Nervous System]]

 

[[Category:Nervous System - Anatomy & Physiology]]

[[Category:Nervous System - Anatomy & Physiology]]