White Matter / Descending Pathways

Question 0

What areas do commisural fibres transmit impulses between? What is the largest of the commisural tracts?

Answer 0

• gyri of the opposite hemisphere

- corpus callosum

Question 1

What areas do association fibres transmit impulses between?

Answer 1

gyri in the same hemisphere

Question 2

Where do projection fibres transmit impulses between?

Answer 2

cerebrum and other parts of the CNS via ascending and descending pathways

Question 3

What are the four afferent fibre types?

Answer 3

1a/1b, beta, A-delta, C-fibre

Question 4

What are the two receptor types for 1a/1b fibres?
What is their stimulus?
What is their relative axon diameter?
Are they myelinated?
What is their relative conduction velocity?

Answer 4

• muscle spindle (1a), golgi tendon organ (1b)
• proprioception
• largest
• yes
• fastest

Question 5

What is the receptor for A-delta fibres?
What is their stimulus?
What is their relative axon diameter?
Are they myelinated?
What is their relative conduction velocity?

Answer 5

• A-delta nociceptor
• tissue injury (mechanical, thermal)
• small
• yes
• slower (fast pain)

Question 6

What is the receptor for C-fibres?
What is their stimulus?
What is their relative axon diameter?
Are they myelinated?
What is their relative conduction velocity?

Answer 6

• C-PMN nociceptor (polymodal)
• tissue injury (mechanical, thermal, alogogenic chemical)
• smallest
• no
• slowest (slow pain)

Question 7

What are the 4 events between stimulus and experience? Describe them.

Answer 7

• transduction (stimuli converted to action potentials)
• transmission (signals enter and ascend the CNS)
• modulation (intensity is defined)
• perception (feeling)

Question 8

What information does the dorsal column relay? Give 2 examples.

Answer 8

somatosensory information entering the spinal cord.

• proprioception
• vibratory sensations from the body (except face, mouth, head)

Question 9

List 3 parallel ascending (sensory) tracts.

Answer 9

• dorsal column
• spinocerebellar tract
• spinothalamic tract

Question 10

Where is somatosensory information from the face, mouth and head supplied from?

Answer 10

trigeminal nerve (CN V)

Question 11

What information do the spinocerebellar tracts relay? (2)

Answer 11

• subconcious muscle

- joint position sense (proprioception)

Question 12

What information does the spinothalamic tract relay? (2)

Answer 12

• pain

- temperature

Question 13

What does crude touch imply?

Answer 13

that a person will not be able to localize where they were touched, only that they were touched

Question 14

What are the two sub-divisions of the spinothalamic tract called?

Answer 14

• neospinothalamic

- paleospinothalamic

Question 16

The neospinothalamic tract has ___ major neurons. The 1st order neuron is attached to a _______.

Answer 16

3 / A-delta nociceptor

Question 17

What tract is associated with withdrawl reflexes and escape behaviour?

Answer 17

neospinothalamic tract

Question 18

What information does the paleospinothalamic tract carry?
Via what?
Where to?
How is it interpreted?

Answer 18

• slow pain
• unmyelinated C-fibres
• contralateral side
• dull, ache, chronic pain

Question 19

In the paleospinothalamic tract, the ______ neuron is attached to a _________.

Answer 19

unipolar / C-PMN nociceptor

Question 20

What tract mediates reflexes and integrated responses (fear, memory) related to nociceptive impulses?

Answer 20

paleospinothalamic tract

Question 21

Tracts of myelinated axons (white matter) in the CNS travel in ___ directions. What are they called, and what direction are they?

Answer 21

3

• association (anterior-posterior)
• commisural (lateral)
• projection (superior-inferior)

Question 22

Where are lower motor neuron cell bodies located?

Answer 22

neuraxis

Question 23

Motor (descending) pathways are divided into two main divisions called ______ and ______.

Answer 23

direct / indirect

Question 24

Direct motor pathways travel from ______ directly to ______ via the ______ tract.

Answer 24

motor cortex / lower motor neurons / corticospinal (aka. direct motor)

Question 25

Indirect motor pathways travel from the motor cortex to the lower motor neurons via the ______, ______, and ______ tracts.

Answer 25

rubrospinal / tectospinal / vestibulospinal

Question 26

What does CN VII control?

Answer 26

facial muscle (expression)

Question 27

What is the only direct connection between the motor cortex and the spinal cord?

Answer 27

corticospinal tract (aka. direct motor tract)

Question 28

About ___% of the corticospinal tract axons _______ to the other side of the body in the distal _______.

Answer 28

90 / decussate / medulla

Question 29

What separates the medulla from the spinal cord?

Answer 29

pyramidal decussation

Question 30

What is the internal capsule? | What does is consist of?

Answer 30

- massive layer of white matter (8-10mm thick) | - ascending and descending projection fibres

Question 31

What is the major route by which the cerebral cortex is connected to the brain stem and spinal cord?

Answer 31

internal capsule

Question 32

Where is the most common stroke location?

Answer 32

part of the internal capsule which carries the corticospinal tract

Question 33

What is the rubrospinal tract directed by? | What is it's function?

Answer 33

- red nucleus in the brain stem | - alternative route for voluntary motor commands

Question 34

What is the vestibulospinal tract directed by? | What is it's function? (2)

Answer 34

- brain stem - maintain correct position of head and neck - mainaint upright posture by stimulating extensors (antigravity)

Question 35

What is the tectospinal tract directed by? | What is it's function?

Answer 35

- brain stem | - coordinates head and eye movement

Question 36

What is divergence?

Answer 36

information in the CNS carried by neurons to many different neurons

Question 37

What is convergence?

Answer 37

information in the CNS from many different sources sent to the same neuron/nucleus

Question 47

What information does the neospinothalamic tract carry? Where to? How is the information interperated?

Answer 47

- fast pain (as well as crude touch) - contralateral sensory cortex - sharp, acute, localized pain