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MBBS II HNNS > L23 - Control of Movement > Flashcards

L23 - Control of Movement Flashcards

1
Q

Define motor unit?

A

Consists of the motor neuron + all of the muscle fibers that it innervates

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2
Q

How does fatigue- resistance relate to a motor unit?

A

Fatigue depends on Number of muscle fibers innervated by a single motor neuron and size of motor units:

 Slow, fatigue-resistant muscles (e.g. eye muscle): fewer muscle fibers per motor neuron

 Fast fatigable muscles: more muscle fibers per motor neuron

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3
Q

Compare the 2 ways the Nervous system controls the force generated by muscle contractions? (coding)

A
  1. Frequency coding: controls frequency of action potential firing in the motor neuron (e.g. forces of successive muscle twitches can summate into tetanic contraction)
  2. Population coding: recruits increasing number of motor units in a fixed order (size principle) from weakest (slow fatigue-resistant) to strongest (fast fatigable)
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4
Q

Which ‘coding’ determines max force generated by a muslce?

A

Population coding

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5
Q

Which ‘coding’ determines the duration of sustained contraction?

A

Frequency coding

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6
Q

Define the 3 types of movement?

A
  1. Reflexes
  2. Rhythmic motor patterns
  3. Voluntary movements
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7
Q

Describe the movement in reflexes. Can it be modulated? Give examples of reflexes.

A

Simple, rapid, stereotyped (= not modulated), involuntary movements with predicatable outcome

Controlled, elicited by stimulus

e.g. stretch reflex, flexion withdrawing reflex

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8
Q

Function of reflexes?

A

Protective, e.g.:
 Withdraw limb from a painful stimulus
 Sneezing, coughing to get rid of germs

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9
Q

Reflexes cannot be part of a voluntary action. T or F?

A

False

Reflex = Essential for voluntary action

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10
Q

Give examples of rythmic motor patterns. Describe the movement.

A

repetitive movements (e.g. walking, running, swallowing)

Combining features of voluntary and reflex acts
&raquo_space; stereotyped, repetitive, may be automatic

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11
Q

Rhythmic motor patterns occur with automatic initiation and termination. T or F?

A

False
the initiation and termination are voluntary;

once initiated, sequence of movement is stereotyped, repetitive and may be automatic

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12
Q

Define the 2 feature of voluntary movements.

A
  1. Complex, goal-directed (intentional)

2. Learned (performance improves with practice); e.g. playing the piano

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13
Q

Voluntary movements always require full conscious control. True or False?

A

Partially True

Voluntary movement always need conscious control

But more practice and mastery = require less conscious direction

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14
Q

List the 5 processes that occur in the control of movements?

A
  1. Accurate time control of contractions of different muscles (sequential)
  2. Associated postural adjustment (balance)
  3. Adjusting mechanical properties of joints & muscles
  4. Sensorimotor integration (posterior parietal cortex)
  5. Error detection, feedforward (anticipation) & feedback control
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15
Q

Define the brain areas with upper motor neurons and their input?

A

 Motor regions of cerebral cortex (input from basal ganglia, cerebellum through thalamus)

 Brainstem (input from motor regions of cerebral cortex, cerebellum, spinal cord)

> > Do not directly innervate muscles, only modulate motor output

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16
Q

Define the CNS areas with lower motor neurons and their input?

A

 Brainstem (motor nuclei of cranial nerves, e.g. facial muscle)

 Spinal cord (receives descending signal from only motor cortex + brainstem; NOT basal ganglia, thalamus, cerebellum)

> > Directly innervates muscle

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17
Q

Which brain area contains both UMN and LMN?

A

Brainstem

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18
Q

Define the 3 levels of motor control and their organization?

A

spinal cord, brainstem, cerebral cortex

Hierarchical organization of the three levels; parallel organization (each level can operate independently or together)

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19
Q

What brain structures modulate the 3 levels of motor control in the brain?

A

All 3 level:

Influenced by 2 independent subcortical structures: basal ganglion, cerebellum

Input of sensory information from environment, vestibular system, joint afferents, and muscle spindles

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20
Q

Describe the arrangement of ventral horn neurons?

A

Somatotopically arranged:
 Medial neurons innervate axial musculature (e.g. back, shoulder, proximal muscle)

 Lateral neurons innervate distal musculature (e.g. limb muscles): further divide:

  • Ventral = extensors
  • Dorsal = flexors
  • Lateral = Distal limb
  • Medial = Proximal limb
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21
Q

What types of movements can be carried out by the spinal cord without input from brain? Give examples of each

A

Reflexes:
• Stereotyped responses e.g. stretch reflex
• Stereotyped motor coordination e.g. flexion reflexes, flexion withdrawal crossed extension

Rhythmic movement:
• locomotor pattern e.g. walking

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22
Q

Define the stimulus, coordination and output of Stretch reflex (stereotyped responses)?

A

MONOSYNAPTIC

Stim: muscle stretch (proprioceptor)

Coordination = Interneurons in the spinal circuitry inhibit the motor neuron innervating the antagonistic muscle

Output: i.e. Flexor contract + Ia inhibitory interneuron cause antagonist to relax

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23
Q

Function of stereotyped responses?

A

Adapted for speed of operation;

allows muscle tone to be regulated quickly and efficiently without intervention from higher centers

> > protective

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24
Q

Define the function of stereotyped motor coordination e.g. flexion reflexes?

A

Protective + coordinates voluntary movement

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25
Q

Define the stimulus, coordination, and output of flexion reflex e.g. flexion withdrawal crossed extension?

A

Stim: e.g. pain

Coordination: POLYSYNAPTIC:

  • Descending control from the brain adjust the strength of the spinal reflexes
  • Multiple interneurons in spinal cord

Output:

  • Opposite leg’s extensor contract for support, flexor relax
  • Withdrawal of stimulated leg by flexor muscle contraction, extensor relax
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26
Q

Stimulus, Coordination and output of rhythmic locomotor pattern (e.g. walking)?

A

Stim = mesencephalic locomotor region (MLR) in the brainstem initiates walking

Coordination = Central pattern generator (neural circuit within spinal cord) can produce rhythmic stepping without brain input

Output: Walking (voluntary action without conscious direction)

27
Q

Function of the UMN and LMN in brainstem?

A

 LMN = motor innervation to head and neck region

 UMN modulate activities of spinal motor neurons and interneurons via the descending pathways&raquo_space; e.g. Controls posture by integrating visual, vestibular with somatosensory information

28
Q

Define the subtypes of motor functions of lower motor neurons in the brainstem?

A
  1. General somatic motor neurons
  2. Special visceral motor neurons
  3. General visceral motor neurons
29
Q

Give examples of CN with general somatic motor functions?

A

 Extraocular muscles (CN III: oculomotor nucleus)

 Intrinsic muscles of tongue (CN XII: hypoglossal nucleus)

30
Q

Give examples of CN with special visceral motor functions?

A

CN5,7,9,10,11

 Chewing (CN V: trigeminal (masticator) motor nucleus)

 Facial expression (CN VII: facial nucleus)

 Larynx (CN X, XI: nucleus ambiguus)

 Pharynx (CN IX, XI: nucleus ambiguus)

31
Q

Give examples of CN with general visceral motor functions?

A

CN 3,7,9,10

 Glands: salivation (CN VII: superior salivatory nucleus, CN IX: inferior salivatory nucleus)

 Smooth muscles: pupillary light reflex (CN III: Edinger-Wesphal nucleus, CN X: dorsal motor vagal nucleus)

32
Q

List the tracts that the brainstem use to modulate activities of spinal motor neurons and interneurons?

A

4 descending output pathways to spinal cord:

Lateral brainstem > distal muscle:
- Rubrospinal tract

Medial brainstem > axial muscle:

  • Reticulospinal tract
  • Tectospinal tract
  • Vestibulospinal tract
33
Q

What is the overall motor control exerted by the medial and lateral brainstem pathways?

A

Lateral brainstem pathways control distal limb muscles (e.g. fingers)

Medial brainstem pathways control axial muscles, posture

34
Q

List the origins and inidividual function of the 4 descending motor pathways from the brainstem?

A
  • Rubrospinal (from magnocellular part of red nucleus): manipulating object, goal-directed movement
  • Tectospinal (from tectum): coordinate eye, head orientation
  • Vestibulospinal (from lateral, medial vestibular nuclei): control posture
  • Reticulospinal (from medial reticular formation): control posture
35
Q

Define the 3 parts of the motor cortex?

A
  1. Primary Motor Cortex (M1)
  2. Premotor Area (PMA)
  3. Supplementary Motor Area (SMA)
36
Q

Define the location of the 3 parts of motor cortex?

A
  1. Primary Motor Cortex (M1)
    = Covers precentral gyrus of frontal lobe, from mid-saggital sulcus to lateral sulcus (Brodmann area 4)
  2. Premotor Area (PMA) = Located immediately anterior to M1 cortex (Brodmann area 8)
  3. Supplementary Motor Area (SMA)
    = Forms the medial part of Brodmann area 6 (buried within the longitudinal fissure)
37
Q

List all the output tracts from the motor cortex?

A
  1. Lateral and ventral corticospinal tract (direct to spinal cord)
  2. Corticobulbar tract (cortex > brainstem)
  3. Modulation circuit (striatum, thalamus, pons, basal ganglia, cerebellum)
38
Q

Define functions of lateral and ventral CST?

A
  1. Lateral corticospinal tract&raquo_space; acts on lateral spinal motor neurons directly&raquo_space; control of contralateral distal muscle after decussation (e.g. fingers)
  2. Ventral corticospinal tract &raquo_space; acts on spinal motor neurons indirectly via brainstem&raquo_space; medial spinal motor neurons&raquo_space; control of ipsilateral axial and proximal muscles for posture
39
Q

Define function of the Corticobulbar tract?

A

acts on lower motor neurons in the brainstem to control head and neck muscle

Control non-ocular CN motor function: innervate brainstem nuclei: Motor trigeminal, Facial, Nucleus Ambiguus, Hypoglossal nuclei

40
Q

Which of the motor cortex areas has the lowest stimulaton threshold? What does this imply?

A

Primary motor cortex

Lowest stimulation threshold to induce movement compared to PMA and SMA, implying that M1 has strong connections with spinal motor and interneurons

> > INITIATE MOVEMENT

41
Q

Describe the functional organization of primary motor cortex?

A

Motor homunculus (like S1):

 Somatotopical organization related to degree of motor control

 Body parts involved in tasks requiring precision, fine motor control have larger representation (e.g. face, hands)

42
Q

Inputs to M1?

A
  • Premotor area and supplementary motor area
  • Sensory areas within the parietal lobe and the thalamus
  • Cerebellum and basal ganglion

> > Collectively provide the M1 the set of instructions required for execution of skilled movements

43
Q

Explain how M1 neurons fire in ways that dictate the motor output? **

A

 Discharge frequency of single neuron&raquo_space; encodes FORCE of movement

 Specific Populations of motor neurons (not single cells)&raquo_space; encodes DIRECTION of movement

44
Q

Which 2 areas form the premotor area?

A

premotor cortex + SMA

45
Q

Inputs into premotor cortex? Role of each input?

A
  1. Posterior parietal cortex (imply premotor areas participate in motor control through visual and somatosensory cues)
  2. Prefrontal cortex (motivation and intention)
46
Q

Compare the stimulation threshold and mapping of Premotor cortex vs Primary motor cortex?

A

Premotor cortex:

• Stronger stimulation threshold (compared to M1) • Motor homunculus not as well defined as the map in M1

47
Q

Summarize the overall output function of the Premotor cortex?

A

SMA + PMA = Produce complex movements

  • PMA = intention and planning of goal-directed movement (not initiation)
  • SMA = programming complex sequence and coordinate bilateral movement (self-initiated planning, not execution)
48
Q

Clinical manifestations of M1 lesions?

A
  • Interferes with motor proficiency & manual dexterity (can’t initiate, plan direction and force)
  • Independent control of fingers may be lost
49
Q

Clinical manifestations of PMA lesions?

A

PMA = intention and planning of goal-directed movement (not initiation)

  • Weakness of axial and proximal muscles
  • Slow execution of complex motor sequences
  • Visually guided movements are severely affected (posterior parietal cortex input)
50
Q

Clinical manifestations of SMA lesions?

A
  • Interferes with goal-directed behaviors that require planning and execution of complex motor sequences
  • Produces deficit in bimanual coordination
  • Deficiency in the initiation and suppression of movements (utilization behavior: compulsively grab objects)
51
Q

How is the cerebellum involved in motor control?

A

1) Feedback control: correct ongoing movements when they deviate from intended movements
2) Feedforward control: modify central programs subsequent movements can fulfill their goal with fewer errors

52
Q

Clinical manifestations of lesions in cerebellum?

A

 Unsteady gait, ataxia

 Delay in initiating responses

 Errors in range, force of movement (dysmetria, past-pointing, intention tremor)

 Errors in the rate, regularity of movements (dysdiadochokinesia, dyssynergia)

53
Q

List the components of basal ganglia?

A
  • Putamen
  • External globus pallidus , Internal globus pallidus
  • Caudate nucelus
  • Subthalamic nucleus
  • Substantia nigra

Striatum = caudate nucleus + putamen

54
Q

Input of basal ganglia? Output to which structure?

A

Input:
 Cortical areas (prefrontal, premotor, supplemental, primary motor, somatosensory)
 Intrinsic nuclei

Output:
Project via thalamus (ventroanterior, ventrolateral nuclei) back to frontal cortex (concerned with motor planning, coordinating movement of body parts)

55
Q

Detail pathways in the output of basal ganlgia?

A

Overall output is balance between:

  • Direct pathway: promote movement: reduce G.P. internal stimulation, remove tonic inhibition on thalamus
  • Indirect pathway: suppress movement: enhance G.P internal stimulation = more tonic inhibition on thalamus
56
Q

Sequence of direct pathway in the output of basal ganglion?

A

Cerebral cortex > Striatum and nucleus accumbens > Globus pallidus internal, Substantia nigra p.r. > VA/VL thalamus > Frontal cortex

57
Q

Sequence of indirect pathway in the output of basal ganglion?

A

Cerebral cortex > Striatum > Globus pallidus external, Substantia nigra p.c. > subthalamic nucleus > globus pallidus internal, Substantia nigra p.r. > VA/VL thalamus > prefrontal cortex

58
Q

Overall functions of the Basal ganglia?

A

processing of information needed for:

 Planning, triggering self-initiated movements

 Organizing associated postural adjustment

59
Q

Clinical manifestations of lesion in Basal ganglia?

A

Parkinson’s disease

Huntington’s chorea

Hemiballismus

Unintentional tremor

60
Q

Relate the role of Substantia nigra in basal ganglia circuit to Parkinson’s disease?

A

S.N. has D1 and D2 neurons to the Striatum

  • D1 enhances direct pathway&raquo_space; more inhibition of cortex
  • D2 suppresses indirect pathway&raquo_space; more inhibition of cortex

Degeneration in substantia nigra = loss of dopaminergic neurons = cannot promote direct pathway, cannot inhibit indirect pathway = more inhibition of motor output

61
Q

Symptoms of Parkinson’s disease? Treatment?

A

hypokinetc disorder

Bradykinesia, rigidity, tremor, disturbance of posture and gait

Treatment: L-DOPA increases dopamine level

62
Q

Relate the basal ganglia circuit to Huntington’s disease?

A

(hyperkinetic disorder): due to degeneration in caudate nucleus, putamen

= inhibit indirect pathway
= less tonic suppression of thalamus
= Promote movement

63
Q

Cause of Hemiballismus? Relate the basal ganglia circuit to Hemiballismus?

A

resulting from stroke involving subthalamic nucleus

Subthalamic nucleus excites internal globus pallidus to inhibit thalamus (indirect pathway)

Loss in subthalamic nucleus = less indirect pathway = increase activity in thalamus

MBBS II HNNS (57 decks)

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