Anatomy: Neuroanatomy Flashcards

1
Q

What does this show? Describe it

A

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.

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2
Q

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

A

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

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3
Q

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

A

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

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4
Q

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

A

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

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5
Q

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

A

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

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6
Q

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

A

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

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7
Q

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?

A

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.

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8
Q

What does this diagram show?

A

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

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9
Q

Label and explain this

A
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10
Q

What is the Primary somatosensory cortex?

A

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

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11
Q

What is the primary motor cortex?

A

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

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12
Q

Label this

A
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13
Q

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

A

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

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14
Q

Describe the pathway for the dorsal column tract

A

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

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15
Q

Label this

A
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16
Q

What is the spinothalamic tract responsible for?

A

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).

17
Q

Describe the pathway for the spinothalamic tract

A

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.

18
Q

Label this

A
19
Q

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

A

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

20
Q

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

A

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.

21
Q

What is proprioception?

A

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.

22
Q

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

A

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.

23
Q

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

A

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

24
Q

What are upper motor neuron lesion signs?

A

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.

25
Q

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?

A