Into to Motor System

Question 1

How many layers of the cerebral cortex?

Answer 1

There are 6 layers of the cerebral cortex.
Pyramidal cells which give rise to the pyramidal (corticospinal tract) arise from layer 5

Question 2

Describe how the knowledge of the homunculus can help diagnose lesions of the pyramidal tract

Answer 2

Our knowledge of the homunculus can help with lesions of the pyramidal tract at the cortical level, which can help us further localise vascular territories affected in strokes.

Question 3

How can knowledge of the vascular territiores classsify strokes?

Answer 3

Knowledge of vascular territories classify strokes into the Bamford classification. For example a total anterior circulation stroke leads to dense hemiparesis, hemianopia and dysphasia.

Question 4

Describe fibres of the corticospinal tract with regards to the internal capsule
which fibres are responsible for control of the face and upper limb?

Answer 4

Internal capsule aggregates fibers of the CST from the cortex.
Fibers responsible for control of the face and upper limb are closer to the genu.

Question 5

The corticospinal tract then descends through…

Answer 5

The corticospinal tract then descends through the cerebral peduncles into the midbrain (crus cerebri).

Question 6

Label this

Answer 6

Question 7

As the CST descends through the midbrain, what structure is it anterior to? What can lesions at this level affect and therefore signify?

Answer 7

The CST descends into the midbrain anterior to the substantia nigra.
Lesions at this midbrain level can also affect the 3rd cranial nerve and red nucleus –> hemiparesis and ipsilateral cranial nerve lesions.
Eg Weber syndrome = damage to the oculomotor nucleus –> ipsilateral ptosis and damage to CST

Question 8

The CST descends into the midbrain anterior to the substantia nigra
Where does the CST then decussate? + where does it travel after and where do most of the fibres pass?

Answer 8

The corticospinal tract then decussates at the level of the pyramids of medulla, then travels in the lateral funiculus
Most fibers pass in the lateral corticospinal tract after decussation.

Question 9

Label the 3 layers of the spinal cord in this diagram

Answer 9

Spinal, arachnoid and pia mater

Question 10

Differentiate between the white columns and grey matter in this diagram.

Answer 10

Question 11

Label the spinal nerve, dorsal root, ventral root, and dorsal root ganglion.

Answer 11

Question 12

Label the left hand side (motor pathways)

Answer 12

Question 13

The anterior horn of the spinal cord gives rise to…?

Answer 13

CST fibres terminate at the anterior horn to give rise to the 2nd order efferent neurone.
These neurones will leave via the spinal nerve and make contact w target muscle via the neuromuscular junction.
NMJ relies on the secretion of acetylcholine, due to the influx of calcium into the presynaptic cleft.

Question 14

Describe the nerve plexus

Answer 14

The Nerve plexus intertwines nerve fibers from discrete roots
They then form distinct peripheral nerves.
e.g Brachial and lumbosacral nerve plexuses

Question 15

Describe the bracihial plexus, including the anatomical structure for each element

Answer 15

Question 16

Patient presents w sudden onset weakness in left arm and leg. Difficulty seeing objects in the left of his visual field.
Examination shows left facial weakness sparing the forehead and left sided weakness worse in the left upper arm. The reflexes are pronounced on that side. Visual field test shows deficit in the left (left homonymous hemianopia).
Diagnosis?

Answer 16

The middle cerebral artery supplies the primary motor cortex , particularly along the convexity and therefore can lead to weakness on the opposite side.
Most likely a lesion here