Spinal cord and periphery 1

Question 1

In the spinal cord, where do motor neurones have their cell bodies?

Answer 1

Motor neurons have their cell bodies in the ventral horn

Question 2

The white matter of the spinal cord is split into three columns

How are these arranged

Answer 2

yes

Question 3

What is the primary difference between descending and ascending tracts in the spinal cord?

Answer 3

Descending = motor

Ascending = sensory

Question 4

What is the most important descending tract of the spinal cord?

Answer 4

Corticospinal / pyramidal tract

carries motor impulses from motor cortex to skeletal muscles

Question 5

What are the 2 important sensory tracts in the spinal cord?

Answer 5

Posterior/ dorsal column:

• carries touch, tactile localisation, vibration sense, proprioception

Lateral spinothalamic tract:

• pain and temperature

Question 6

Using the diagram, describe the pathway of nerve fibres in the Corticospinal tract

Answer 6

Pathway starts in Area 4 (motor cortex) and projection fibres pass through the posterior limb of the Internal capsule

These fibres then pass through cerebral peduncles and into medulla

Most fibres then cross over in the decussation of pyramids and are now Corticospinal fibres

Question 7

In this diagram of the midbrain, where do the motor fibres run through on their way down

Answer 7

Question 8

At different spinal levels, different nerves from the corticospinal tract (or any motor tract) may leave depending on which nerve it is

How do they leave the tract?

Answer 8

Nerve from tract will enter into the grey matter of the spinal cord where it synapses in the ventral horn

The second-order neuron will leave through the ventral root and so on…

Question 9

What is the fate of corticospinal motor fibres that do not cross at the decussation of the pyramids in the lower medulla?

Answer 9

Very small number of fibres do not cross at the decussation

These travel in the Anterior corticospinal tract - which we dont care about

Question 10

What is the pathway for motor fibres that are in cranial nerves?

Answer 10

10 of the 12 cranial nerves leave in the brainstem

Motor fibres in cranial nerves (eg oculomotor or something) will leave really high up

These fibres that leave early are “Corticobulbar”

Question 11

Complete the schematic showing the route of descending fibres

Answer 11

2 neurons in the pathway. These are called the upper and lower motor neurons respectively

The ventral horn is the site of the lower motor neurones

Question 12

How do ascending spinal tracts differ from descending tracts in terms of the number of neurones?

Answer 12

Ascending tracts (sensory) reaching conscious level will have 3 neurones between the peripheral receptor and the cortex

Question 13

Identify the labels showing the route of ascending tract fibres

Answer 13

Question 14

In the diagram of the Posterior/dorsal column (sensory tract) identify the labels

Use this to describe the route taken by fibres in this tract

Answer 14

1st order neuron enters via dorsal root and enters tract

This then synapses with 2nd order neuron in lower part of medulla and immediately decussates

The tract now is called medial lemniscus and passes through the medulla, pons and midbrain to reach the thalamus where 2nd Order fibres synapse with 3rd order neurons

3rd order neuron starts from the thalamus and axons pass through the Internal Capsule and radiate to the post-central gyrus (Area 2,1,3)