Sensory And Motor Pathways In The CNS

Question 1

Describe the 3 neurone chain

Answer 1

Primary sensory neurone:
from receptor to SC

Second order (or thalamic projection neurones):
from SC to thalamus

Third order neurones:
from thalamus to cortex

Question 2

What are the different sensory and ascending (afferent) pathways in the spinal cord

Question 3

What is the dorsal column system used for

Answer 3

Fine touch and proprioception sensations from right side of the body

Question 4

What is the spinothalamic tract used for

Answer 4

Pain and temperature sensations from right side of the body

Question 5

Describe the dorsal column pathway

Answer 5

Question 6

Describe the spinothalamic pathway

Answer 6

Question 7

Describe the pathway of the primary sensory nucleus

Answer 7

1st neurone
– primary afferent fibres terminate in either main sensory nucleus or spinal nucleus.
Main sensory nucleus:

-Primary sensory neurone from receptor to main sensory nucleus
-Low threshold afferents – Aβ,
mediating fine touch stimuli (two point discrimination) and vibration

Question 8

Describe the pathway of the 2nd order neurone

Answer 8

2nd neurone
– Axons of second order neurons decussate (cross the midline) to form the trigeminothalamic tract
-The neurones of this tract synapse in VPM (ventroposteromedial) nucleus of the thalamus.

Question 9

Describe the pathway of the 3rd order neurone

Answer 9

Project from VPM in the thalamus to the post central gyrus (primary secondary cortex) where they make the 3rd synapse

-axons course through the internal capsule

Question 10

Describe upper motor neurons

Answer 10

any neurones carrying information within the CNS making up (descending) motor pathways

Question 11

Describe lower motor neurons

Answer 11

neurones conveying motor information from brainstem (cranial nerves) or spinal cord (spinal nerves) to voluntary muscle – essentially the motor component of peripheral nerves

Question 12

What must Each lower motor neuron lying in the ventral horn of the spinal cord may receive information from several descending motor pathways:

Answer 12

Direct corticospinal pathways (fine movement)

Indirect corticospinal pathways (postural movement – receive input from cerebellum)

Tectospinal pathways - from eyes via midbrain – (position in relation to the environment)

Vestibulospinal pathways - from the semicircular canals in the inner ear –for balance

Question 13

Which upper motor neurons do NOT run together

Answer 13

Note that many upper motor neurons run together:
Direct corticospinal
Indirect corticospinal
Tectospinal pathways

Question 14

Injury to which motor pathway causes problems with movement of the contralateral side of the trunk and limbs

Answer 14

Pyramidal decussation