the ascending and descending pathways Flashcards
what cells in the motor cortex make the descending tracts in the corticospinal tract
the betz cells in layer 5 of the cerebral grey matter
where do the axons of the neurons in the corticospinal tract move through in the cerebrum and brainstem
they travel through the internal capsule, then through the midbrain and pons, then travelling through the medullary pyramids
where do the corticospinal tract axons cross over
at the pyramidal decussation of the medulla - closed medulla
what happens to the fibres of the corticospinal tract that decussate
these travel contralaterally down the lateral corticospinal tract of the spinal cord before synapsing to the LMN at some point in the ventral horn of spinal cord
what happens to the neurons that do not decussate in the medulla
these travel arteriorly down the spinal cord in the ventral tracts down to LMN
in general terms what do the LMNs that are innervated by decussated and non decussated UMN control
decussated - these are the more distal muscles or the muscles of the appendicular skeleton but also do do axial
non-decussated - these are the more proximal muscles of the trunk of the axial skeleton.
significance of having the non-decussated fibres in the corticospinal tract
the non-decussated ones tend to innervate more proximal axial skeleton muscles. so when we have a stroke we lose the motor function of limbs on the contralateral side but the axial muscles are still all good because they receive innervation from both sides, so less affected by stroke
the somatotopy of the corticospinal tract is maintained throughout the corticospinal tract, describe the arrangement at each place
motor cortex - Medial to lateral LAH
internal capsule in posterior part - anterior to posterior HAL
midbrain - medial to lateral HAL
pons medial to lateral - shoulder/hip - hand/feet
medullary pyramids - medial to lateral LAH
whats our somatic sensation types
discriminative sensation - information about the environment
non-discriminative - affective sensation, things that elicit a response so like pain, temperature, erotic stimuli
what are the names for the dorsal column pathway
medial lemniscal pathway, the discriminative pathway
describe the path through to the point of crossing over for neurons in the dorsal column pathway
enters the spinal cord via the dorsal root, then the neurons ascend ipsilaterally in the dorsal column tract of the spinal cord and then going up through the medulla via the cuneate and gracile nucleus, then crossing over in the arcuate fasciculus
what happens in the dorsal column pathway after crossing over
then it goes up through the medial lemniscus to the thalamus before going to the primary somatosensory cortex.
in the dorsal column pathway what goes through the cuneate nucleus and the gracile nucleus
Gracile is fibres from the legs, cuneate is the arms.
whats the somatotopy of the dorsal column pathway
lateral to medial in the spinal cord HAL
arcuate fasciculus - anterior to posterior HAL
in the medial lemniscus lateral to medial LAH
whats the path of the spinothalamic pathway
the first order neuron synapses to the second order in the dorsal horn. the second order then decussates at that level in the anterior commisure then ascends up the anterolateral tract before going to thalamus and then different areas in the cortex
what pathway does the lower body unconcious proprioception take
lower body and abdomen go to the clarkes nucleus then the neurons go to the cerebellum.
what pathway does unconscious proprioception of the upper limb take
Proprioceptive neurons from
the upper body synapse in
cuneate nucleus then go to the cerebellum
