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Neuroscience > Lecture 22 > Flashcards

Lecture 22 Flashcards

1
Q

What does the spinal cord contain?

A

Central pattern generators that can generate complex behaviors without input from the brain

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2
Q

What are upper motor neurons?

A

Neurons found in the primary motor cortex that control motor function

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3
Q

What does the somatotopy in motor cortex reflect?

A

Topological organiation of spinal motor neurons

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4
Q

What does each lower motor neuron innervate?

A

Fibers of just one muscle

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5
Q

What is a motor pool for a muscle?

A

Grouped in rod-shaped clusters within the spinal cord extending over several vertebral segments
- innervation for each muscle occupies a distinct mediolateral (and rostrocaudal) position within the ventral horn of the spinal cord

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6
Q

How are motor pools organized?

A

somatotopically

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7
Q

How do lower motor neuron circuits project?

A

medially

- may synapse on interneurons which synapse on motor neurons

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8
Q

What forms 90% of the cortex?

A

Six layered structures

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9
Q

Where do the main inputs go to?

A

stellate cells in layer IV

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10
Q

Where do the main outputs leave?

A

From layers III, V and VI

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11
Q

Where do axons of corticospinal tract derive from?

A

Large pyramidal or Betz cells in Layer V

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12
Q

How do upper motor neurons project?

A

contralaterally via the corticospinal tract
- primarily to muscles involved in precise limb movements, particularly those of the hands in humans
Via the corticobulbar tract to the hypoglossal nucleus in the brainstem, which controls movements of the tongue
- important for speech in humans

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13
Q

Where are upper motor neurons located?

A

several nuclei including:
Reticular formation
Vestibular nucleus (vestibular coordination)
Superior colliculus (visual coordination)

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14
Q

How do upper motor neurons project to lower motor neurons?

A

Ipsilaterally controlling axial muscles concerned with maintaining posture

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15
Q

Where do lower motor neurons always synapse on?

A

Directly on muscle fibers

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16
Q

What can someone lift a lever in response to?

A

Auditory stimulus (tone)

17
Q

What does the anticipatory “feedforward” mechanism allow?

A

Pre-adjusts body posture to compensate for the forces that will be generated when the lever is lifted

18
Q

How do the upper motor neurons in the cortex influence spinal cord circuits?

A

Two routes:

  1. Cerebrum (medial and lateral premotor cortex - planning and initiation in primary and premotor cortices)
    - brainstem - reticular formation - cortocoreticulospinal tract - spinal cord
    - - Anticipated by indirect projection via reticular formation to muscles
  2. Cerebrum - brainstem - pyramidal decussation - lateral corticospinal tract - spinal cord
    - - Activation of voluntary movement direct to spinal cord via corticospinal tract
19
Q

What does the motor cortex innervate?

A

Brainstem and spinal cord

20
Q

What does anticipation involve?

A

Circuit from motor cortex to brainstem nuclei
- motor cortex upper motor neurons to brainstem upper motor neurons project to medial motor pools primarily concerned with postural movement

21
Q

What is Motor Neuron Disease?

A

Or Amyotrophic lateral sclerosis (ALS) is a degenerative disease of motor neurons (also called Lou Gerhig’s disease)

22
Q

What can motor neuron disease affect?

A

Either upper or lower motor neurons

23
Q

How is lower motor neuron disease characterized by?

A

Muscle paresis (weakness) or paralysis
Loss of muscle tone due to loss of stretch reflexes
Ultimately leads to severe muscle atrophy
Patients usually die from lung dysfunction (due to atrophy of intercostal muscles)

24
Q

How is upper motor neuron disease characterized by?

A

Muscle weakness
Spasticity due to increased muscle tone (no modulation of stretch reflex)
Hyperactive reflexes
Loss of fine voluntary movement
Patient usually die from bulbar (tongue and pharynx) involvement

25
Q

Is intellect compromised in motor neuron disease?

A

No (PROF STEPHEN HAWKING)

26
Q

How long do motor neuron disease patients live?

A

Die within 5 years of diagnosis (usually)

27
Q

What does the basal ganglia and cerebellum influence?

A

Movement indirectly by regulating the function of upper motor neurons

28
Q

What does the basal ganglia feedback to?

A 
Premotor area (area 6) via the ventrolateral complex of the thalamus (VLo) to control the initiation of movement 
 - known as motor loop
29
Q

How does the basal ganglia initiate movement?

A
  1. With no initiating cortical input, the Globus Pallidus tonically inhibits the VLo due to tonic activation from the caudate/Putamen (=striatum)
  2. Input from many cortical regions converges on the striatum
  3. When activated by this input, the Striatum inhibits the inhibitory activity of the globus pallidus, releasing the VLo to activate Area 6 and initiate movement
30
Q

What can degeneration in the Striatum in Huntington’s Disease result in?

A

Reduced tonic inhibition of the VLo by the globus pallidus and increased initiation of inappropriate, rapid and jerky movements (hyperkinesis)

31
Q

What does Parkinson’s Disease lead to?

A

Hypokinesis

  • the Substantia nigra has a more complex role and acts via the striatum to maintain the balance between:
    • The activation of tonic inhibition of the VLo by the globus pallidus
    • The inhibition of the globus pallidus by the striatum in response to cortical output input
32
Q

What does degeneration in teh substantia nigra lead to in Parkinson’s Disease?

A

Upsets this balance leading to increased tonic inhibition ofthe VLo by the globus pallidus and suppressed initiation of movement by the cortex (hypokinesis)

33
Q

What is the cerebellum required for?

A

Proper execution of planned, voluntary, multijoint movements

Forms a “loop” with the motor cortex

34
Q

Where does the cerebellum receive input from?

A

Many areas of the cortex
Corticopontocerebellar projection
Sensory information from the spinal cord and vestibular system
- projects back to the motor cortex via thalamus (has no direct output to spinal cord)

35
Q

What is the primary function of the cerebellum?

A

Detect and correct differences between the intended movement and the actual movement, the so-called motor error

36
Q

What do lesions in the cerebellum lead to?

A

Cerebellar ataxia

- a condition characterized by poorly integrated movement

37
Q

What is the cerebellum a major target in?

A

Bovine spongiform encephalitis

- caused by neuronal degeneration cased by prions

Neuroscience (28 decks)

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