Chapter 16: NS pt 3

Question 1

what are tracts composed of?

Answer 1

bundle of nerve fibres connecting nuclei in CNS

Question 2

how are the spinal cord tracts organized medial to lateral?

Answer 2

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

Question 3

what are the 3 major somatosensory tracts?

Answer 3

1) posterior columns
2) spinothalamic tracts
3) spinocerebellar tracts

Question 4

what is the general organization of sensory tracts? (i.e. of first, second, third order neurons)

Answer 4

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

Question 5

what are the two tracts of the posterior column? where are they located relative to each other?

Answer 5

gracile fasciculus (medial) and cuneate fasciculus (lateral)

Question 6

what do sensory tracts of the posterior column sense?

Answer 6

-proprioception (sensory, awareness), fine touch, pressure, vibration

Question 7

what is the difference between gracile fasciculus and cuneate fasciculus

Answer 7

• gracile - info from anywhere below T6
• consists of medial portion of posterior column

cuneate - info from anywhere above T6
-lateral portion of posterior column

Question 8

in which spinal segments can we see the indentation in the posterior column that differentiates between the gracile fasciculus and the cuneate fasciculus?

Answer 8

anywhere above T6

Question 9

which cranial nerves feed into the sensory tracts of the posterior column?

Answer 9

V, VII, IX, and X

-does NOT make part of the input

Question 10

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

Answer 10

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

Question 11

what do the sponothalamic tracts detect?

Answer 11

info on pain (nociceptors), temperature (thermoreceptors), and “crude” (less precise) touch and pressure

Question 12

what are the two spinothalamic tracts?

Answer 12

• anterior

- lateral

Question 13

where do the spinothalamic tracts cross over?

Answer 13

spinal cord

Question 14

where do the sensory tracts in the posterior column cross over?

Answer 14

medulla (brainstem)

Question 15

describe the pathway of spinothalamic tracts from a sensory receptor to its final destination

Answer 15

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

Question 16

what kind of info do spinocerebellar tracts sense?

Answer 16

proprioception information (not sensory)

Question 17

which spinocerebellar tract crosses over twice?

Answer 17

anterior

Question 18

what is different from the way spinocerebellar tracts process information as opposed to the other two tracts?

Answer 18

information is processed on the ipsilateral side as the stimulus

Question 19

describe the pathway of spinocerebellar tracts from a sensory receptor to its final destination

Answer 19

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

Question 20

what are the two spinocerebellar tracts? where are they found?

Answer 20

anterior and posterior tracts

-both found in lateral white columns

Question 21

what are the two motor tracts?

Answer 21

1) corticospinal tracts

2) subconscious motor pathways

Question 22

where are the cell bodies of upper and lower motor neurons in the motor tracts?

Answer 22

both their cell bodies are found in the CNS

Question 23

where do UMNs from the motor tracts synapse with LMNs?

Answer 23

start in primary motor cortex and travel to SC (synapse with LMNs)

Question 24

where do LMNs go in the motor tracts?

Answer 24

cell bodies still in CNS, axons extend to peripheral NS - can synapse either in brainstem or SC

Question 25

where do the neurons originate in the SNS motor tracts vs the ANS motor tracts?

Answer 25

SNS tracts - UMNs originate in primary motor cortex

ANS tracts -
UMNs originate in visceral motor nuclei in hypothalamus

Question 26

what differs between somatic motor tracts and visceral motor tracts?

Answer 26

visceral motor tracts have 3 different neurons rather than just 2 (so they don’t have UMNs and LMNs)

Question 27

what’s another name for corticospinal tract?

Answer 27

pyramidal tract

Question 28

what are the three corticospinal tracts?

Answer 28

1) corticobulbar
- brainstem (nuclei of CN III< IV< V, VI, VII, IX, XI, XII)
2) anterior corticospinal tract
3) lateral corticospinal tract

Question 29

what type of info goes to the anterior and lateral corticospinal tracts?

Answer 29

all other info given to skeletal muscle not given by cranial nerves

Question 30

where do most of the corticospinal tracts decussate?

Answer 30

in the medulla

• some stay in anterior portion
• those that do cross over go to lateral cortocispinal tract

Question 31

where do the LMNs begin in the anterior/lateral corticospinal tracts?

Answer 31

in the spinal cord, where the UMNs synapse with the LMNs

BOTH CELL BODIES ARE IN THE CNS

Question 32

describe the path for corticobulbar tracts from its origin to its effector

Answer 32

• 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

Question 33

describe the path for anterior and lateral corticospinal tracts from their origin to their effectors

Answer 33

• 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

Question 34

what is the purpose of our subconscious motor pathways?

Answer 34

• unconsciously modify muscle contraction

- stimulate or inhibits LMNs via interneurons