Mammalian Neuronal Pathways

Mammalian Neuronal Pathways - XVI. Ascending Pathways...

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XVI. Ascending Pathways 2-2-2010 -Sensory= PNS term. -Ascending=Once in CNS A. The Dorsal Column System: 3 Neurons -Voluntary -Drawn as one spinal nerve, but it is paired (left and right) and in virtually all spinal nerves -Afferent pathways are in almost all 31 spinal nerves coming in from dermatomes on both sides of the body 1. Functions - Exteroreceptive - receives information from outside organism particularly touch requiring high amount of localization or precision. Ex. Can you distinguish two close but separate pin pricks or just feel as one? Distinguish objects in a bag? - Proprioreceptive - Somatic information but more about relative position of soma in respect to other somas . Doesn't do a lot of different things, but has a lot of discrimination in the things that it does do 2. Anatomy -Pathway originates with some receptor in soma -First neuron synapses in the medulla- either in Nucleus Gracilis (if synapses in more posterior spinal nerves) or Nucleus Cuneatus (if synapses in more anterior spinal nerves) -Goes into medulla and terminates in Sensory Cortex -Pseudounipolar neuron -Afferent enters thru the dorsal horn then runs up thru white matter so is now ascending - Contralateral pathway to sensory cortex- pathway crosses; sensory cortex and left cerebral hemisphere receive information from right side of body and vice versa - Synapses again in thalamus of ventro-basal complex - Thalamus functions- involved in processing afferent information; pathway synapses in the Thalamus -Processing signal is easier if synapse is present -Starts at soma, first synapses in medulla (nucleus gracilis or cuneatus), second synapses in thalamus (ventro-basal complex) and ends in sensory cortex. B. The Spinothalamic System: 3Neurons 1. Functions -Perceive pain, thermal sensations, and crude touch/sensation (can't distinguish 2 headed pin) 2. Anatomy -Pseudounipolar neuron synapses at grey matter first then goes up cord; Also synapses in thalamus but at Ventral Posterolateral Nucleus then to sensory cortex. -Starts at soma, first synapses in grey matter, second synapses in thalamus (ventral posterolateral nucleus), and ends in sensory cortex. C. The Spinocerebellar Pathway: 2 Neurons 1. Functions -Advises the cerebellum of muscle performance; Proprioceptive on muscle movement 2. Anatomy - Contralateral and Ipsilateral fibers. 2 neurons from soma and into cerebellum -Advises Cerebellum on muscle movement -Starts at soma, synapses in grey matter, and ends in cerebellum
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XVII. Descending Pathways (Efferent) A. Pyramidal: 2 Neurons 1. Functions -
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Mammalian Neuronal Pathways - XVI. Ascending Pathways...

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