Sensory Systems L3

Question 1

What is the pathway of discriminative sensation through the spinal path?

Answer 1

Called the Dorsal-Column- Medial Lemniscus pathway.

1st order nerve enters through dorsal root into the gracile or cuneate fasciculus.

Ascends fasciculus until it reaches the gracile or cuneate nuclei in the medulla.
Synapse with 2nd order nerve.
Decussates via the internal arcuate fibres.
Ascends out of the dorsal columns up through the medial lemniscus.
Enters the ventral-posterior nucleus of the thalamus.
Synapses with 3rd order nerve.
Crosses the internal capsule to the primary somatosensory cortex. (arm area)

Question 2

What are 1st order nerves?

Answer 2

Convey impulses from the skin to the 2nd order nerves

Question 3

What are 2nd order nerves?

Answer 3

Convey impulses from 1st order nerves to 3rd order nerves

Question 4

What are 3rd order nerves?

Answer 4

Convey impulses from 2nd order nerves to primary somatosensory cortex

Question 5

What is the pathway for non-discriminative sensation to the cerebral cortex?

Answer 5

Called the lateral spinothalamic tract.

1st order nerve enters through the dorsal root, into the dorsolateral tract of lissauer.
Synapses with a 2nd order nerve.
Decussates via the anterior white commissure.
Enters the lateral spinothalamic tract.
Ascends through the medulla where it joins the medial lemniscus pathway in the pons.
Reaches the ventral-posterior nucleus of the thalamus.
Synapses with a 3rd order neuron.
Goes through the internal capsule to the somatosensory cortex.

Question 6

What is dissociative sensory loss?

Answer 6

Loss of discriminative sensation in the same side of the body as the lesion but loss of non-discriminative sensation in the opposite side of the body. This is due to a lesion occurring when the discriminative pathway has not decussated, but the non-discriminative has.

Question 7

What is associative sensory loss?

Answer 7

Loss of discriminative and non-discriminative sensation in the same side of the body due to a lesion occurring after both types of pathway have decussated. (occurs in the opposite side to lesion)

Question 8

What information does gracile fasciculus carry?

Answer 8

lower limb

Question 9

What information does cuneate fasciculus carry?

Answer 9

upper limb

Question 10

Proprioception

Answer 10

Ability to distinguish touch
Spatial feedback

Question 11

Dorsal Funiculi/ Columns

Answer 11

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 12

What area of the spine only has gracile fasciculus?

Answer 12

Thoracic and lumbnar spinal cord levels

Question 13

What area is responsible for proprioception?

Answer 13

Area 3+4. Up to Nucleus proprius

Question 13

Intermediate area function

Answer 13

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

Ventral root

Answer 13

carries motor info to the muscle

Question 14

Myotactic reflex

Answer 14

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 15

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

Answer 15

Anterior white commissure

Question 16

Thalamus

Answer 16

differentiates important information