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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.

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 is therefore reaches consciousness. The [[Hindbrain - Anatomy & Physiology#Cerebellum|cerebellum]] is involved in co-ordination and in the main this sensory information does not reach consciousness.

==Pathways==

==Pathways==

===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 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]].

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]].

==Pain==

==Pain==

Painful stimuli can result in responses ranging from itches, to nausea, to simply being in agony. Painful stimuli may be transmitted to the brain by one of two pathways: the [[Sensory Pathways - Anatomy & Physiology#Spinothalamic Tract|Spinothalamic Tract]] or the the [[Sensory Pathways - Anatomy & Physiology#Ascending Reticular Formation|Ascending Reticular Formation]].

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]].  

===Spinothalamic Tract===

===Spinothalamic Tract===

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.

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'''.

===Ascending Reticular Formation===

===Ascending Reticular Formation===

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.

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'''.

'''Clinical Relevance'''

'''Clinical Relevance'''

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. ''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.

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.  

''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.

===Visceral Pain===

===Visceral Pain===

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''.

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''.

==Links==

==Links==

*[[:Category: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]]

[[Category:To Do - Review]]

[[Category:A&P Done]]