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BRAIN AND BEHAVIOUR 1 > NEURAL CONTROL OF MOVEMENT > Flashcards

NEURAL CONTROL OF MOVEMENT Flashcards

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1
Q

What are lower Motor Neurons

A

Found in the brainstem and spinal cord

-Each motor neuron supplies skeletal muscle fibres and constitutes a motor unit

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2
Q

What are upper Motor Neurons

A

Found in the cerebral cortex and brainstem

  • Carries voluntary motor commands to lower motor neurons
  • Reflex modulation
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3
Q

What are the three Functionally distinct upper motor neuron pathways?

A

The descending tracts:

  1. Corticospinal and corticobulbar tracts (precise movement)
  2. Rubrospinal tract (gross movement, flexion)
  3. Vestibulospinal and reticulospinal (posture)
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4
Q

a-motor neurons

A

All motor acts depend on neural circuits that eventually impinge on a-motor neurons that form the OUTPUT of the motor system

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5
Q

What is voluntary movement?

A

Many voluntary motor acts are guided by the intrinsic properties of the REFLEX ARCS but are modified by commands from higher centres in the brain and from sensory inputs

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6
Q

What are the two kinds of voluntary movement?

A
  1. Maintenance of position (posture)
  2. Goal-direction movements
    - These two are linked, a goal-directed movement will only be performed successfully if the moving limb is correctly positioned first and posture will only be maintained if compensatory movements are made to counteract any force opposing the posture
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7
Q

What does voluntary movement require?

A
  1. Knowledge of where the body is
  2. Where it intends to go
  3. Plan of how to get there (must be held in memory after selected)
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8
Q

What brain regions are involved in voluntary movement?

A

All of the frontal lobe

-The more anterior the cortical region, the more complex or abstract its role is

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9
Q

What is the primary motor area

A

Generates motor impulses that control the execution of movement , instructions to move and activation of descending pathways

  • Anterior to central sulcus
  • Lowest level of motor “hierarchy
  • Local lesions causes paralysis of specific muscle groups
  • Larger lesions=more muscle group involved
  • Damage depends on which part of the motor homunculus is involved
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10
Q

What other cortical regions are involved in motor function?

A
  1. Posterior parietal cortex (Areas 5 and 7)
    - Decision to move and functional consequence of action
  2. Association motor cortex (Area 6- Premotor cortex)
    - Plans to move are stored until required
    - Pre motor= external cues
    - Supplementary motor= internal cues
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11
Q

What is the posterior parietal cortex?

A

The posterior parietal cortex plays an important role in planned movements (controlling the decision to move) , spatial reasoning, and attention
-Areas 5 and 7

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12
Q

What is the association motor cortex?

A

Plans to move are stored until required

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13
Q

What are the general effects of lesions of the motor cortex?

A
  • Initial paralysis followed by variable degree of recovery
  • Recovery depends on the plasticity of the cortex (eg. after a face lesion, the face area muscles may be driven by cells from different parts of the cortex)
  • Larger lesions lead to slower recovery and permanent loss of movement
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14
Q

What are the effects of lesions to the premotor cortex?

A

Damage leads to motor apraxia

  • Difficulty with motor planning to perform tasks
  • Normal reflexes and no muscle weakness
  • Difficulty performing complex motor tasks (eg. tying shoelace)
  • Damage to one side (in a stroke) produce only minimal symptoms as the CONTRALATERAL area may be able to take over functions of the damaged tissue
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15
Q

What are the specialized motor areas of the premotor areaa?

A

The frontal eye fields and Broca’s area are two specialized parts of the premotor area
-Controls the extraocular eye muscles and the muscles regulating speech

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16
Q

What is the parietal lobe?

A

The parietal lobe is one of the major lobes in the brain, roughly located at the upper back area in the skull. It processes sensory information it receives from the outside world, mainly relating to touch, taste, and temperature.

  • 40% of the corticobulbospinal tract arises from the somatosensory cortex (areas 1,2 and 3)
  • Lies immediately posterior to the central sulcus
  • These axons send commands down to the spinal cord that modulates sensory input to reflexes
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17
Q

What is the corticospinal tract?

A

The Corticospinal tract (CST), also known as the pyramidal tract, is a collection of axons that carry movement-related information from the cerebral cortex to the spinal cord. It forms part of the descending spinal tract system that originate from the cortex or brainstem.
-Has monosynaptic connections only with motor neurons of the thumb and digits

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18
Q

What are the spinal interneurons?

A

A spinal interneuron, found in the spinal cord, relays signals between (afferent) sensory neurons, and (efferent) motor neurons. Different classes of spinal interneurons are involved in the process of sensory-motor integration.

  • Motor actions initiated in other muscles by the corticospinal tract are mediated by the actions of the corticospinal tract on spinal interneurons
  • The CST drives interneurons which modulate spinal reflexes (eg. inhibition of flexion reflexes)
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19
Q

Pathway of the corticospinal tract

A

Goes to the lower medulla where is decussates to form the large LATERAL corticospinal tract and the smaller ANTERIOR corticospinal tract

  • Crossing fibres in the motor decussation at C1-C5
  • If the brain is injured ABOVE the spinal cord, the motor deficit is on the opposite side
  • If the spinal cord is injured, the motor deficit is on the same side
20
Q

Where is the corticospinal tract on the spinal column?

A

Lateral corticospinal tract is in the DORSAL quadrant of the cord, near the motor neurons supplying distal muscles

The anterior corticospinal tract terminates in the cervical cord

21
Q

What is the corticobulbar tract?

A

The corticobulbar tract is a descending pathway responsible for innervating several cranial nerves, and runs in parallel with the corticospinal tract

  • Terminates on various cranial nerve nuclei for cortical control of the head and neck muscles
  • Also terminates on the cells of the pontine nuclei, the reticular formation and the red nucleus
  • Courses through the internal capsule on its way to the brainstem, especially vulnerable to damage by stroke
22
Q

What is the red nucleus?

A

The red nucleus is a structure in the rostral midbrain involved in motor coordination. The red nucleus is pale pink, which is believed to be due to the presence of iron in at least two different forms: hemoglobin and ferritin.

23
Q

What is the clinical significance of the internal capsule?

A

The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the globus pallidus.

  • The corticobulbar and corticospinal tracts descend through the internal capsule, served by the middle cerebral artery
  • This is often affected by stroke
24
Q

What is the extrapyramidal system?

A

The extrapyramidal system is a part of the motor system network causing involuntary actions. The system is called extrapyramidal to distinguish it from the tracts of the motor cortex that reach their targets by traveling through the pyramids of the medulla.

  • Other motor systems that mediate the motor functions of posture and locomotion
  • Originates from groups of cell bodies in the brainstem
25
Q

What are the extrapyramidal tracts?

A
  1. Vestibulospinal tract: Controls posture and balance
    - Originates in vestibular nuclei in upper medulla
    - Nucleus projects ipsilaterally to antigravity muscles
    - Tonically active during upright posture
  2. Reticulospinal tract: Arousal of spinal cord, automatic control
    - Arises in the reticular formation of the pons and the medulla
    - Projects down spinal cord
  3. Rubrospinal tract: Carries cerebellar commands to the spinal cord
    - Originates in the red nucleus in the midbrain
    - Red nucleus receives main input from cerebellum
26
Q

What is the role of the cerebellum in movement?

A

The cerebellum does not initiate movements, its role is to help the motor cortex produce accurate and smooth movements by MODULATING and REFINING the motor cortex commands

  • Uses feedback from proprioceptors and other sensory organs
  • Receives direct input from muscles and compares it with the intended signal for movement from the motor cortex
27
Q

Effects of cerebellar damage

A

Produces overall clumsiness, abnormal fatigue and instability of movement
-The cerebellar cortex exhibits neuronal plasticity so recovery of function is possible

28
Q

Anatomy of the cerebellum

A
  1. Vestibulocerebellum: Balance, posture, eye movements
  2. Spinocerebellum: Locomotion, voluntary arm and leg movement
  3. Cerebrocerebellum: Skilled motor tasks (hand eye coordination, cognitive eye movements)
29
Q

What is the dorsal spinocerebellar tract?

A

The dorsal spinocerebellar tract conveys proprioceptive information from proprioceptors in the skeletal muscles and joints to the cerebellum. It is part of the somatosensory system and runs in parallel with the ventral spinocerebellar tract.
-This tract involves two neurons and ends up on the same side of the body. IPSILATERAL

30
Q

What is the stretch reflex?

A

The stretch reflex can be a monosynaptic reflex which provides automatic regulation of skeletal muscle length, whereby the signal entering the spinal cord arises from a change in muscle length or velocity. It can also include a polysynaptic component, as in the tonic stretch reflex.

31
Q

What is the strength of stretch receptors controlled by?

A

Gamma motor neurons

  • Innervates muscle spindle at each end
  • Receives both excitatory and inhibitory input
  • Increased excitation or decreased inhibition of gamma motor neurons increases tension of intrafusal muscle fibres, becoming hypersensitive to muscle stretch (SPASTICITY(
32
Q

What are basal ganglia?

A

The basal ganglia are a group of structures found deep within the cerebral hemispheres that control the ability to promote or inhibit movement

  • “decision-making” about what to do next
  • In conjunction with the motor association cortex, they scale the strength of the response organize correct sequences of activity
33
Q

What are the nuclei of the basal ganglia?

A

Caudate, putamen, globus pallidus, substantia nigra and subthalamic nuclei

34
Q

What is the brake theory?

A

To keep still, you must put brakes on all movements except those reflexes that maintain upright posture
-To move, you must apply a brake to some postural reflexes and release the brake on voluntary movement

35
Q

How is movement initiated in the basal ganglia?

A

The internal globus pallidus has an inhibitory effect on the thalamus which in turn decreases output from the motor cortex

When the direct pathway is stimulated, neuronal activity in the cerebral cortex is received via the putamen, inhibiting the function of the globus pallidus

This increases thalamic output back to the cortex, which initiates movement

36
Q

What is the indirect pathway of the basal ganglia?

A

Offers opposing system of movement regulation

  • Excitation of the subthalamic nucleus leads to the increase suppression of thalamic activity
  • This in turn reduces the activity in the motor cortex
  • Limits movement
  • Eg. Loss of dopamine neurons in Parkinson’s disease, slowing or unwanted movements HYPOKINESIA
37
Q

What is Spasticity?

A

Upper motor neuron sign

  • Abnormally increased muscle tone due to the loss of inhibition of the gamma motor neurons
  • Increased tendon reflexes HYPERREFLEXIA
  • A Babinski sign will be normally present
38
Q

Describe the babinski sign

A

Stimulation of the sole of the foot inducing big toe dorsiflexion and abduction (fanning out)nand dorsiflexion of the other toes

39
Q

What is clonus?

A

Series of alternating contractions and relaxations of flexors and extensors produced by passive stretch of the limb.

  • Seen with corticospinal tract damage
  • Due to hyperactive stretch reflexes
40
Q

What is flaccidity?

A

Hypotonia

-When the nerve or the LMNs are damaged

41
Q

What are fasciculations?

A

Small localized involuntary muscle contractions and relaxations visible under the skin
-Indicate LMN damage

42
Q

What is decorticate posturing?

A

Arms are adducted and flexed, with the wrist and fingers flexed on the chest

  • Legs may be internally rotated and stiffly extended
  • Plantar Flexion of feet
  • indication of damage to corticospinal tract areas including the cerebral hemispheres, internal capsule and thalamus
  • More favorable than the decerebrate posture
43
Q

What is decerebrate posturing?

A

Arms are adducted and extended with wrist pronated and the fingers flexed

  • Legs may be internally rotated and stiffly extended
  • Plantar flexion of feet
  • Indicates damage to brainstem, specifically below the level of the brainstem
  • If the red nucleus is damaged by severe midbrain injury, decerebrate posturing may develop
44
Q

Characteristics of a UMN lesion

A
  • Location: CNS only
  • Causes: Cerebrovascular accident (stroke), trauma, multiple sclerosis, ALS, infectious disease
  • Structures involved: Motor cortex, the corticospinal tract
  • Distribution: Group of muscles
  • Movements: Paralysis of skilled movements
  • Muscle tone: Increased, particularly in antigravity muscles
  • Myotatic reflexes: Hyperactive
  • Cutaneous reflexes: Positive babinski sign
  • Muscle bulk: Slight atrophy
  • Classical description: SPASTIC PARALYSIS
45
Q

Characteristics of a LMN lesion

A
  • Location: CNS or PNS
  • Causes: Cerebrovascular accident (stroke), trauma, polio, tumor, diabetes, alcoholism
  • Structures involved: Spinal or brainstem motor neurons, or PNS
  • Distribution: Segmental- limited to muscles innervated by damaged motor neurons
  • Movements: Paralysis
  • Muscle tone: Decreased
  • Myotatic reflexes: Decreased/absent
  • Cutaneous reflexes: Decreased/absent
  • Muscle bulk: Pronounce atrophy
  • Classical description: FLACCID PARALYSIS

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