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Medicine Year 1 - Semester 2 - Part 1 > Descending Neural Pathways > Flashcards

Descending Neural Pathways Flashcards

1
Q

What are descending pathways ?

A

Pathways that are involved in us doing an action/ movement.

Also known as motor pathways

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2
Q

Describe some signs of upper motor neurone lesion

A

Increased muscle tome
Spasticity (painful)
Increased deep tendon reflexes
Clonus

Abnormal reflex (Babinski/ Hoffmann sign)

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3
Q

Describe some signs of lower motor neurone lesion

A

Reduced muscle tone
Flaccid paralysis
Decreased tendon reflexes
Fasciculation
Atrophy

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4
Q

Tests for motor neurone lesions

A

Babinski reflex

Hoffmann sign

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5
Q

Describe movement generation

A
  1. Goal/purpose
  2. Activation of relevant movement
  3. Feedback of movement
  4. Refinement/ correction of movement
  5. Cessation on completion
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6
Q

State the structures in the motor pathway

A

Idea
DLPFC and Parietal cortex

Thalamus
Basal nuclei
Supplementary motor area
Pre-motor cortex
Lateral cerebellum

Motor cortex
Brainstem
Spinal cord

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7
Q

Cerebellum function

A

Involved in spatial awareness

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8
Q

Where is the primary motor cortex (M1) located ?

A

Within the pre central gyrus

Anterior to the central sulcus

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9
Q

State input to the primary motor cortex

A

Somatosensory cortex
Premotor cortex
Supplementary motor cortex
Cerebellum

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10
Q

Function of the primary motor cortex

A

Gives rise to 60-80% of the corticospinal tract.

> 1/2 of the primary motor cortex controls hands and muscles of speech

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11
Q

Pre-motor cortex

A

One of secondary motor cortices

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12
Q

Function of the pre-motor cortex

A

Responds to external stimuli

Involved in bilateral postural fixation, planning and control of movement.

Coordinated muscle movements in more than 1 joint

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13
Q

Input to the pre-motor cortex

A

It receives cognitive inputs from the frontal lobe in the context of motor intentions and a rich sensory input form the parietal lobe incorporating tactile and visuospatial signals.

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14
Q

Function of the supplementary motor cortex

A

Responds to internal stimuli

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15
Q

Describe activation of supplementary motor cortex

A

Activated by the dorsi-lateral prefrontal cortex, when we intend to make a movement.

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16
Q

Difference between premotor and supplementary motor cortex

A

Premotor - responds to external stimuli

Supplementary motor - responds to internal stimuli

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17
Q

Supplementary motor cortex

A

Pre-programming movement sequences - built into motor memory

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18
Q

State other motor areas

A

Brocas area
Frontal eye field

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19
Q

Brocas area

A

Motor speech area
Dominant hemisphere location

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20
Q

Frontal eye field

A

Voluntary eye movement

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21
Q

State a structure involved in voluntary movement

A

Basal nuclei

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22
Q

Basal nuclei

A

A mass of grey matter / a mass of cell bodies found within the white matter of the brain/brainstem

23
Q

State some features of basal nuclei

A

Has connections with the thalamus and cerebellum

24
Q

Function of the basal nuclei

A

Involved in initiation, fine tuning of movement.

(Basal nuclei cannot initiate voluntary movement, it just helps)

25
Q

Describe the circuit for motor, cognitive, limbic and oculomotor

A

Between cortex –> Basal Nuclei –> Cortex

Connections with thalamus and cerebellum

26
Q

State the basal nuclei

A

Caudate nucleus

Putamen (lentiform nucleus)
Globus pallidus (lentiform nucleus)

Subthalamic nucleus
Substantia nigra

27
Q

Where are the cell bodies of upper motor neurones found ?

A

Cell bodies found in the cortex and brainstem nuclei.

Restricted to the CNS and do not contact muscle.

28
Q

Where are the cell bodies of lower motor neurones found ?

A

Cell bodies found in the brainstem and spinal cord.

Leave the CNS and contact muscle to stimulate.

29
Q

State the function of the upper motor neurones

A

Executive function for lower motor neurones and circuits controlling LMNs

30
Q

State the function of the lower motor neurones

A

Motor function to muscles

31
Q

What can be found between upper and lower motor neurones ?

A

Sometimes :
Interneurones (which can have an inhibitory or excitatory effect)

32
Q

Cortico-nuclear Tract

A

Axons of the UMN end up in the motor nuclei of cranial nerves.

Motor nuclei of cranial nerves are only found in the brainstem.

UMN synapse with LMNs found in the motor nuclei of some of the cranial nerves (usually bilateral).

33
Q

What do LMNs in the cortico-nuclear tract supply ?

A

Extraocular muscles (CN III, IV and VI)
Muscles of mastication (CN V)
Muscles of Facial Expression (CN VII)
Pharynx and Larynx muscles (CN IX and X)
Tongue (CN XII)

34
Q

Cotricospinal tract function

A

Concerned with voluntary, discrete, skilled movements, especially distal parts of the limbs.

35
Q

Origins of the corticospinal tract

A

30% from the primary motor cortex
30% from the premotor and supplementary motor areas

40% from the somatosensory areas

36
Q

Describe the corticospinal tract

A

Axons descend through corona radiate and posterior limb of the internal capsule to reach the brainstem

It continues through the crus of the midbrain and then pons to reach the medulla

In lower medulla, it forms the pyramid

About -85% of the fibres cross the midline in the pyramidal decussation.

Axons up to the decussation are referred to as the corticospinal tract.

37
Q

State the structures of the corticospinal tract

A

Corona Radiata
Posterior limb of internal capsule
Cerebral peduncle of the midbrain
Pyramid (of medulla oblongata)
Pyramidal decussation

38
Q

What is the lateral corticospinal tract ?

A

Axons that crossed the midline in the pyramidal decussation become lateral corticospinal tract and descend.

Synapse w LMNs vis interneurones.

39
Q

Function of the lateral corticospinal tract

A

Voluntary movement of the limbs

40
Q

What is the anterior corticospinal tract ?

A

Most of the axons that do not decussate in the pyramid descend ipsilaterally as the anterior corticospinal tract.

41
Q

Function of the anterior cortciospinal tract

A

Controls voluntary movement of the axial and girdle muscles and proximal limb muscles.

42
Q

Key function of anterolateral corticospinal tract

A

Helps control movements of axial muscles

43
Q

What is the extra-pyramidal system ?

A

A system of nuclei and tracts that regulate involuntary motor functions to maintain posture and fine tune voluntary movements.

44
Q

Difference between corticospinal tract and extra-pyramidal system

A

Corticospinal tract passes through the pyramid

Extra-pyramidal passes through the tegmentum rather than the pyramid

45
Q

What happens if the corticospinal tract is severed ?

A

Discrete movements can still occur, except that the movements for fine control of the fingers and hands are considerably impaired.

(DONE WITH THE HELP OF EXTRA-PYRAMIDAL SYSTEM)

46
Q

State the nuclei in the extrapyramidal system

A

Basal nuclei
Cerebellar nuclei
Reticular formation
Vestibular nuclei
Nuclear ruber
Substantia nigra

47
Q

State the tracts in the extrapyramidal system

A

Reticulospinal
Vestibulospinal
Rubrospinal
Tectospial

Don’t originate form the cortex
Not voluntary, they are unconscious

48
Q

Function of the extra-pyramidal system

A

Fine-tuning and adjustments of voluntary movements

Control of AN voluntary movements

Adjusting and Maintaining posture

Planning and preparation of involuntary movements

Control of reflex actions

Inhibition of involuntary movements

49
Q

Vestibulospinal tract

A

Activate extensor muscles
Inhibit flexor muscles

50
Q

Potine Reticulospinal tract

A

Activate extensor muscles
Inhibit flexor muscles

51
Q

What is involved in posture ?

A

Ventromedial pathways of the extrapyramidal system are involved

Controlled and driven by the brainstem

52
Q

Where is posture information integrated from ?

A

Muscle proprioceptors

Gravitational field

Visual Inputs

Sensory information predominantly integrated in the brainstem.

53
Q

Decorticate posturing

A

Corticospinal tract interrupted
Extrapyramidal tracts beomce dominant distally

Flexion of upper limb, extension of lower limb

Lesion above red nucleus

54
Q

Decerebrate posturing

A

Lesion inferior to red nucleus

Extension

Unopposed extension of vestibulospinal and pontine reticulo spinal tracts

Medicine Year 1 - Semester 2 - Part 1 (51 decks)

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