Chapter 16: NS pt 3 Flashcards
what are tracts composed of?
bundle of nerve fibres connecting nuclei in CNS
how are the spinal cord tracts organized medial to lateral?
sensory nerves entering the spinal cord at more inferior levels travel more medially with a sensory tract
- aka nerves entering at T11 will sit more medial in sensory tract than nerve entering at T1
what are the 3 major somatosensory tracts?
1) posterior columns
2) spinothalamic tracts
3) spinocerebellar tracts
what is the general organization of sensory tracts? (i.e. of first, second, third order neurons)
1) first order axons travel up into dorsal root, (cell bodies found in dorsal root ganglion) - travel up through SC
2) second order neurons synapse with first order neurons in SC or brainstem (cell bodies found here)
3) third order neurons synapse with second order neurons in thalamus - send info to primary somatosensory cortex (cell bodies in thalamus)
-WE ARE CONSCIOUSLY AWARE IF INFO GOES TO THALAMUS
what are the two tracts of the posterior column? where are they located relative to each other?
gracile fasciculus (medial) and cuneate fasciculus (lateral)
what do sensory tracts of the posterior column sense?
-proprioception (sensory, awareness), fine touch, pressure, vibration
what is the difference between gracile fasciculus and cuneate fasciculus
- gracile - info from anywhere below T6
- consists of medial portion of posterior column
cuneate - info from anywhere above T6
-lateral portion of posterior column
in which spinal segments can we see the indentation in the posterior column that differentiates between the gracile fasciculus and the cuneate fasciculus?
anywhere above T6
which cranial nerves feed into the sensory tracts of the posterior column?
V, VII, IX, and X
-does NOT make part of the input
what is the organization of sensory tracts in the posterior column? (i.e. first order, second, third) from a sensory receptor to its final destination
First order - synapse in dorsal root ganglia (cell body found here), travels up spinal cord until it meets cell body of second order neuron
Second order - synapse in brain stem (cell body found here) - medulla oblongata - this is where neurons cross over
Third order - synapse in thalamus (cell bodies here) - project to primary somatosensory cortex; conscious perception
what do the sponothalamic tracts detect?
info on pain (nociceptors), temperature (thermoreceptors), and “crude” (less precise) touch and pressure
what are the two spinothalamic tracts?
- anterior
- lateral
where do the spinothalamic tracts cross over?
spinal cord
where do the sensory tracts in the posterior column cross over?
medulla (brainstem)
describe the pathway of spinothalamic tracts from a sensory receptor to its final destination
1) First order - cell body in dorsal root ganglia - crosses over in spinal cord
2) Second order - synapse in dorsal horn (cell body found here) ascends through lateral or anterior spinothalamic tract on opposite side of stim
- Length of neuron is longer than previous - has to travel through spinal cord
3) Third order - synapse in thalamus - travels to primary somatosensory cortex
what kind of info do spinocerebellar tracts sense?
proprioception information (not sensory)
which spinocerebellar tract crosses over twice?
anterior
what is different from the way spinocerebellar tracts process information as opposed to the other two tracts?
information is processed on the ipsilateral side as the stimulus
describe the pathway of spinocerebellar tracts from a sensory receptor to its final destination
1) First order - sensory neuron comes up and synapses in dorsal root ganglion
2) Second order - synapses in posterior horn - enters posterior or anterior spinocerebellar tract - makes its way to cerebellum - no conscious perception
- Anterior tract neurons cross over again in cerebellum - both end up in cerebellum on same side of stimulus
what are the two spinocerebellar tracts? where are they found?
anterior and posterior tracts
-both found in lateral white columns
what are the two motor tracts?
1) corticospinal tracts
2) subconscious motor pathways
where are the cell bodies of upper and lower motor neurons in the motor tracts?
both their cell bodies are found in the CNS
where do UMNs from the motor tracts synapse with LMNs?
start in primary motor cortex and travel to SC (synapse with LMNs)
where do LMNs go in the motor tracts?
cell bodies still in CNS, axons extend to peripheral NS - can synapse either in brainstem or SC
where do the neurons originate in the SNS motor tracts vs the ANS motor tracts?
SNS tracts - UMNs originate in primary motor cortex
ANS tracts -
UMNs originate in visceral motor nuclei in hypothalamus
what differs between somatic motor tracts and visceral motor tracts?
visceral motor tracts have 3 different neurons rather than just 2 (so they don’t have UMNs and LMNs)
what’s another name for corticospinal tract?
pyramidal tract
what are the three corticospinal tracts?
1) corticobulbar
- brainstem (nuclei of CN III< IV< V, VI, VII, IX, XI, XII)
2) anterior corticospinal tract
3) lateral corticospinal tract
what type of info goes to the anterior and lateral corticospinal tracts?
all other info given to skeletal muscle not given by cranial nerves
where do most of the corticospinal tracts decussate?
in the medulla
- some stay in anterior portion
- those that do cross over go to lateral cortocispinal tract
where do the LMNs begin in the anterior/lateral corticospinal tracts?
in the spinal cord, where the UMNs synapse with the LMNs
BOTH CELL BODIES ARE IN THE CNS
describe the path for corticobulbar tracts from its origin to its effector
- start in primary motor cortex
- descend through brainstem (medulla) where they decussate
- synapse with CN III, IV, V, VI, VII, IX, XI
- go to effectors
describe the path for anterior and lateral corticospinal tracts from their origin to their effectors
- start in primary motor cortex
- descend through brainstem, where 85% of the tracts decussate (medulla) then enter either lateral (most of them) or anterior (ipsilateral; not a lot) corticospinal tracts, descending into spinal cord
- synapse in spinal cord (anterior horn) then exit to innervate effector
what is the purpose of our subconscious motor pathways?
- unconsciously modify muscle contraction
- stimulate or inhibits LMNs via interneurons
