Medsci L3: Sensory systems of the brain

Question 1

What is discriminative and non-discriminative touch?

Answer 1

There are two kinds of sensory modalities when it comes to touch sensation. These are fine or discriminative touch, and crude or non-discriminative touch(pain & temperature). Fine touch enables a person to not only sense touch, but also localize it.

Question 2

Spinal segmental level

Answer 2

location where 2 spinal nerves( right and left) exit the spinal cord
(looking at 1 cross-section of the spinal cord)

Question 3

Dorsal Funiculi/ Columns

Answer 3

The biggest bundle of white matter
Within: Gracile fasciculus and cuneate fasciculus

Homuncular representation of the body( starting from toes up to the neck).

Question 4

What information does gracile fasciculus carry?

Answer 4

lower limb

Question 5

What information does cuneate fasciculus carry?

Answer 5

upper limb

Question 6

What area of the spine only has gracile fasciculus?

Answer 6

Thoracic and lumbnar spinal cord levels

Question 7

Lateral/Motor columns/ funiculi

Answer 7

responsible for carrying motor info from the brain down the spinal cord

Question 8

Ventral Funiculi

Answer 8

Carry info about pain & temp

Question 9

Where are pain & temp fibers found in the spinal cord?

Answer 9

area 1+ 2 in the grey matter

Question 10

Proprioception

Answer 10

Ability to distinguish touch

Spatial feedback

Question 11

What area is responsible for proprioception?

Answer 11

Area 3+4. Up to Nucleus proprius

Question 12

Intermediate area function

Answer 12

Nervous supply to and from visceral organs( autonomic functions)

Heart, bladder etc

Helps maintain balance and posture. Returns the body to the midline after gesticulation.( swing arms during walking)

Question 13

Motor neuron pool (8+9 area)

Answer 13

Lower motor neurons( drive muscle activity) localized within the spinal cord

Question 14

2 step system for activating muscle:

Answer 14

upper motor neuron( starts in the primary motor cortex) which goes down to the spinal cord lvl where it can synapse with a lower motor neuron(localized in the motor neuron pool), which projects out to the muscle & activates it.

Question 15

Ventral root

Answer 15

carries motor info to the muscle

Question 16

Myotactic reflex

Answer 16

The brain is not aware of the activity

A sensory signal is carried through a sensory nerve, which then goes to the motor neuron pool and synapses with a motor neuron, which goes out the ventral root to the muscle

Question 17

tract of lissaer

Answer 17

transparent

Area of the white matter that pain& temp neurons pass

Question 18

What is the crossing(decussation) point of the pain& temp pathway?

Answer 18

anterior white commissure

Question 19

thalamus

Answer 19

differentiates important information

Question 20

associative sensory loss

Answer 20

the lesion on the right side of the brainstem causes loss of touch & pressure and pain& temp sensation on the left side

Question 21

dissociative sensory loss

Answer 21

lesion in the lower part of spinal cord on the right side- no loss of touch & pain( discriminative) sensation on the left side, BUT loss on the right side and loss of pain& temp information on the left side and not on the right side.

Question 22

The pathway of discriminative sensation( Dorsal column- medial lemniscal system)

Answer 22

The stimulus comes in from sensory nerve ending( e.g. C8-R.Arm)-> cuneate fasciculus( gracile for lower limbs)-> 1st neuron ascends up to lower medulla, where it connects to cuneate nucleus( gracile nucleus for lower limbs) synapses with a 2nd neuron, new cell body arises & crosses over to the other side in the Internal Arcuate fibers -> 2nd neuron fibers go to the pons through the midbrain and synapses with the 3rd neuron in the thalamus( differentiates information)-> 3rd neuron goes through the internal capsule up and is received in the arm area of the sensory homunculus.

Question 23

Spinothalamic system( pain& temp pathway):

Answer 23

-Free nerve ending comes-> synapse in area 1+2 with a 2nd neuron after the tract of Lissauer to come into the dorsal area of the grey matter-> 2nd fiber crosses over the anterior white commissure-> goes up in the ventral funiculus through the medulla, pons, midbrain and synapses in the thalamus-> 3rd order neuron goes into the arm region of the sensory homunculus.

Question 24

What part of the thalamus do the 2nd order neuron in the dorsal column-medial lemniscus pathway and the spinothalamic tract terminate?

Answer 24

VPL( ventral posterolateral nucleus of the thalamus)