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Neuroanatomy > 6. Pyramidal system > Flashcards

6. Pyramidal system Flashcards

1
Q

Location of the motor cortex

A
  • Postcruciate +/- precruciate gyrus
  • Rostral suprasylvian gyrus
  • Parietal +/- Frontal lobe
  • Overlaps with SI
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2
Q

General somatotopic organization of the motor cortex

A
  • Postcruciate gyrus: limbs (appendicular)
  • Rostral syprasylvian gyrus: head + neck
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3
Q

Which cortical layers contain the UMN cell bodies in the motor cortex

A

V (Betz cells = giant pyramidal cells)

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4
Q

2 periods of motor cortex development in dogs

A
  • Birth - 3 weeks: no spatial representation of the limbs and limited range of movements
  • 3 weeks - 3 months: Progressive somatotopic representation and complexification of movements
  • 3 months: mature motor cortex
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5
Q

When is the motor cortex mature in dogs?

A

3 months

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6
Q

Where are the UMN cell bodies?

A

Motor cortex + brainstem motor nuclei

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7
Q

The motor tracts of UMN travel in which SC funiculi?

A

Lateral and ventral corticospinal tracts run in the LATERAL and VENTRAL funiculi

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8
Q

UMN typically terminate on a short___

A

INTERNEURON in the brainstem or SC (3-neuron pathway)

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9
Q

Understand the terminology of motor tracts (slide 17)
1. first name
2. 2nd name
3. adjunct name

A
  1. origin
  2. termination
  3. funiculus or nucleus of origin
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10
Q

Pyramidal vs extrapyramidal system

A

Slide 22

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11
Q

What are the 3 neurons of the pyramidal system pathway

A
  1. MOTOR CORTEX
  2. SHORT INTERNEURON (corticonuclear: vicinity of CN motor nucleus; lateral corticospinal: base of dorsal horn. May be missing in primates)
  3. MOTOR NUCLEUS of brainstem or LMN in VENTRAL HORN of SC
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12
Q

Describe the pyramidal system pathway rostral to pyramids (corticonuclear tract)

A
  • Motor cortex (Betz cells, layer V)
  • Corona radiata
  • Internal capsule
  • Crus cerebri (midbrain)
  • Longitudinal fibers (pons)
  • CORTICUNUCLEAR TRACT: decussation in the vicinity of a CN motor nuclei, synapse on short interneuron, to CN motor nuclei
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13
Q

Describe the pyramidal system pathway from pyramids downwards (corticospinal tracts)

A
  • Majority of fibers DECUSSATE at the pyramids (medulla) to form the LATERAL corticospinal tract (travels in controlateral lateral funiculus)
  • Minority of fibers DO NOT decussate, forming the VENTRAL corticospinal tract (travel in ipsilateral ventral funiculus). Will eventually decussate in the vicinity of a target ventral horn, at the ventral commissure.
  • Synapse on short interneuron at the base of dorsal horn
  • Innervates γ > α motorneurons
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14
Q

What is the function of the corticonuclear tract

A

Controls voluntary movements of the head (eyes, jaw, face, tongue, pharynx, larynx, neck)

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15
Q

Which CN are under the influence of the corticonuclear tract

A

All except I, II, VIII

Midbrain: III-IV
Pons: V
Medulla : VI-VII, IX-XII

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16
Q

What is the function of the corticospinal tracts

A

Controls striated muscles/voluntary movements of the limbs (+ lateral CS tract), trunk/neck (+ventral CS tract) and tail

17
Q

What is the % pyramidal decussation in dogs vs cats

A
  • Dogs: 100%
  • Cats: 75-85%; small ventral corticospinal tract ends in cervical SC segments
18
Q

Both corticospinal tracts innervate the ___ side of the body

A

Contralateral

19
Q

The corticopontocerebellar pathway contains ___ neurons and involves ___ decussations

A

5 neurons
2 decussations

20
Q

What are the 5 neurons of the corticopontocerebellar pathway

A
  1. Motor cortex
  2. Pontine nucleus
  3. Controlateral cerebellar cortex (via middle c.p.)
  4. Controlateral cerebellar nucleus (dentate)
  5. Thalamus (ventral lateral nucleus) (via rostral c.p.)
  6. Motor cortex
21
Q

Describe the corticopontocerebellar pathway

A
  • MOTOR CORTEX (N1)
  • Corona radiata
  • Internal capsule
  • Crus cerebri (midbrain)
  • Longitudinal fibers (pons)
  • PONTINE NUCLEUS (N2)
  • Transverse fibers decussate, take middle c.p.
  • contra CEREBELLAR CORTEX (N3)
  • contra DENTATE NUCLEUS (N4)
  • axons take rostral c.p.
  • ipsi VENTRAL LATERAL THALAMIC NUCLEUS (N5)
  • Back to ipsi motor cortex
22
Q

The pyramidal system is ABSENT in which species?

A

Fish & amphibians (only mammals)

23
Q

Destruction of motor cortex in humans vs dogs

A

HUMANS
Controlateral flaccid paralysis and loss of spinal reflexes

DOGS
Mild to no controlateral deficits (paresis, hypertonia, hyperreflexia, dysmetria, postural reaction deficits)
Often minimal impact on gait

Neuroanatomy (20 decks)

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