Neuroanatomy

Question 1

What does this show? Describe it

Answer 1

The pyramidal tract (corticospinal).
This begins in the precentral gyrus. It then passes through the internal capsule crossing over at the pyramids (decussation).
A few fibers don’t decussate here, but at the level of the spinal cord.

Question 2

Where is the specific origin of the pyramidal/corticospinal tract?

Answer 2

The origin of the pyramidal tract is in the cerebral cortex (precentral gyrus). More specifically the pyramidal cells in layer 5 of the cortex

Question 3

What is the blood supply for the pyramidal/corticospinal tract?

Answer 3

The blood supply to this region is via the middle cerebral artery laterally and the anterior cerebral medially

Question 4

The pyramidal/corticospinal tract then converges through this structure. Describe and explain what this structure is

Answer 4

The pyramidal tract descends from the cortex and aggregates/converges in the internal capsule.
The internal capsule is divided into the anterior and posterior limb
And all the motor components of the corticospinal tract will descend in the posterior limb

Question 5

The internal capsule has an anterior and posterior limb. Describe the blood supply to each of these

Answer 5

Anterior: Striate branches of anterior cerebral- inc the recurrent artery of Heubner and the middle cerebral artery

Posterior: Striate branches from the middle cerebral artery, inc the charcot artery of cerebral haemorrhage and the anterior choroidal

Question 6

Describe the blood supply for the remainder of the internal capsule, inc the Genu, sublentiform part and retrolentiform part

Answer 6

Genu: anterior and middle cerebral, direct branches from the internal carotid
Sublentiform part: Striate branches from the posterior, cerebral and anterior chorodial
Retrolentiform: Striate branches from posterior cerebral

Question 7

The pyramidal tract begins in the precentral gyrus. It then passes through the internal capsule, then where does it go from here? What is the clinical significance of this?

Answer 7

The corticospinal tract then passes through the midbrain via the crus cerebri.
It descends down the pons, where majority of fibres cross over at the pyramids into the medulla
NOTE: close proximity to the oculomotor nerve nucleus and red nucleus can cause crossed syndrome presentations such as webers.

Question 8

What does this diagram show?

Answer 8

The fibres at the top right come down at the pons and then cross over at the medulla to form the decussation of the pyramids.
This then forms a white matter bundle (2), aka your lateral corticospinal tract, which continues down into the spinal cord

Question 9

Label and explain this

Answer 9

Question 10

What is the Primary somatosensory cortex?

Answer 10

Primary somatosensory cortex is located in the postcentral gyrus
It is posterior to central sulcus, and the target for the ascending tract
Processes somatic sensations, eg touch and temp.
It has a somatotopic arrangement, ie each part receives info from a particular part of the body, esp receptors for more sensitive areas like the face

Question 11

What is the primary motor cortex?

Answer 11

Primary motor cortex (aka motor strip)- located in precentral gyrus of frontal lobe (anterior to central sulcus)
Involved in voluntary movement of contralateral body. NOTE: size of cortical representation for each body part is in proportion to the precision of motor control

Question 12

Label this

Answer 12

Question 13

What is the dorsal column tract and what is it responsible for?

Answer 13

Somatosensory pathway for touch, vibration and proprioception
To test the dorsal columns you can use a cotton wool tip and a tuning fork

Question 14

Describe the pathway for the dorsal column tract

Answer 14

Neurones from large proprioceptive fibres (have high conduction velocity) ascend in the dorsal columns.
At the medulla, they synapse at the dorsal column nuclei. These= in the posterior spinal cord
Neurones then ascend in the medial meniscus, up brainstem and then synapse to the ventral thalamus.
Finally the neurones reach the primary somatosensory cortex

Question 15

Label this

Answer 15

Question 16

What is the spinothalamic tract responsible for?

Answer 16

Nociception- pain. Crude touch. Temperature
Noci and thermoreceptors transmit impulses via thinly-myelinated A-delta fibres and unmyelinated c-fibres (small diameters + slow conduction velocities).

Question 17

Describe the pathway for the spinothalamic tract

Answer 17

Neurones from noci/thermoreceptors go up to the dorsal root ganglia, synapsing w the dorsal horn of the spinal cord.
note: anterior is for motor function, posterior horn is for sensory function.
2nd order neurons decussate in anterior spinal cord to ascend as the spinothalamic tract. This then forms the spinal lemniscus in the brainstem.
2nd order neuron synapses in the thalamus, third order neurone finally reaches pscortex.

Question 18

Label this

Answer 18

Question 19

What is the main difference between the dorsal and spinothalamic tract pathways?

Answer 19

The spinothalamic tract synapses in the spinal cord, but the dorsal column just descends and synapses in the medulla to form the second order neurone
dorsal: fine touch, vibration, proprioception
spino: crude touch, pain, temperature

Question 20

In the spinothalamic tract, first order neurones go up to the dorsal root ganglia, synapsing w the dorsal horn of the spinal cord.
Describe this dorsal/posterior horn

Answer 20

There are different layers of the posterior horn
Different fibres synapse in different aspects of these lamina.
The spinothalamic tract synapses predominantly in lamina II.

Question 21

What is proprioception?

Answer 21

Proprioception- awareness of position and movement of body
Dependent on vision, vestibular system, cerebellum and sensory feedback
Receptors found in muscles, joints and tendon that give a sense of where your body is and how it is moving.

Question 22

Describe the spinocerebellar tracts. What can happen if you get isolated lesion of the spinocerebellar tract?

Answer 22

Involved in proprioception and coordination
They carry fibres in the anterior aspect of spinal cord to the cerebellar nuclei via the inferior cerebellar peduncle
If you have an isolated lesion of your spinocerebellar tract (rare) patients can have ataxia= lack of coordination and balance.

Question 23

65male w T2DM and hypertension presents with sudden onset right sided weakness for last 3 hrs.
He is weaker in his arms than legs and cannot walk properly. Speech difficulty, some altered sensation and numbness of his right side.
Explain the diagnosis and any associated features

Answer 23

Classic stroke presentation.
Upper motor neuron lesion which affects the corticospinal tract up to the anterior horn cell where the corticospinal tract synapses to form the spinal nerve.
Any lesion of the cst=upper motor neuron signs
Weakness right hand side- left side of cst affected
Associated features inc dysphasia, visual disturbances as visual pathways also affected

Question 24

What are upper motor neuron lesion signs?

Answer 24

Increased tone, esp spasticity which is velocity dependent
Exaggeration of reflexes
Weakness
Upper motor neuron signs are caused by defects to the descending pyramidal tract up to the anterior horn cell.

Question 25

72 male: sudden onset weakness of entire left side. Hypertension, T2DM. On examination he has dense hemiparesis and facial asymmetry.
Tone is normal but has weakness in left upper limb. Increased reflexes in his upper and lower limbs. No cerebellar signs and pupils are reactive. Lost his left nasolabial fold. BP is 180/90 other vitals normal
Diagnosis?

Answer 25