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General And Special Somatic Afferent Pathways Notes

Veterinary Medicine Notes > Neuroscience 1 Notes

This is an extract of our General And Special Somatic Afferent Pathways document, which we sell as part of our Neuroscience 1 Notes collection written by the top tier of University Of Nottingham students.

The following is a more accessble plain text extract of the PDF sample above, taken from our Neuroscience 1 Notes. Due to the challenges of extracting text from PDFs, it will have odd formatting:

Somatic Afferent Pathways General somatic afferent pathways Somatic afferent pathways are the fibre tracts and nuclei that convey general sensory information from a wide range of receptors to the CNS. It excludes special somatic afferent pathways from the eye and inner ear, and pathways from visceral receptors. To distinguish this, they may be referred to as general somatic afferent (GSA) pathways. The general somatic afferent system conveys sensory information such as ...

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Pain

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Temperature

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Touch/pressure

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Kinaesthesia (conscious proprioception)

The primary neurons of all these senses are located within the dorsal root ganglia of the spinal nerves (and corresponding ganglion of the trigeminal nerve for structures of the head). Their axons enter the CNS by the dorsal roots of spinal nerves (or afferent root of the trigeminal nerve). Upon entering the CNS, the axons branch. Some branches end on interneurons in the grey matter of the segment they entered, or of an adjacent segment. The interneurons project onto the ventral horn of the same or an adjacent segment. This forms the short neuron chain that allows local reflex responses. The ventral horn neuron whose axon ends directly on the effector is called the lower motor neuron. Other branches of the primary axons connect directly, or through interneurons, to higher centres of the CNS. Ascending tract systems such as these include ...

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The spinothalamic tract - transmits some pain and temperature information.

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Gracile tract - transmits touch and kinaesthesia information from hindlimb.

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Cuneate tract - transmits touch and kinaesthesia information from forelimb.

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Trigeminothalamic tract - equivalent to all above tracts, but serves the head region.

1. The lemniscal system (gracile and cuneate tracts) The gracile and cuneate tracts are part of the lemniscal system. They consist of a three neurone contralateral (crosses midline of the body) relay. The primary axons (running from receptors in the skin or elsewhere) enter the spinal cord and dorsal funiculus without synapsing. Those that enter through the sacral nerves are located medially, while those that enter at more cranial levels are located laterally.

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