L23 - Control of Movement

Question 1

Define motor unit?

Answer 1

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

Question 2

How does fatigue- resistance relate to a motor unit?

Answer 2

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

Question 3

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

Answer 3

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)

Question 4

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

Answer 4

Population coding

Question 5

Which ‘coding’ determines the duration of sustained contraction?

Answer 5

Frequency coding

Question 6

Define the 3 types of movement?

Answer 6

1. Reflexes
2. Rhythmic motor patterns
3. Voluntary movements

Question 7

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

Answer 7

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

Controlled, elicited by stimulus

e.g. stretch reflex, flexion withdrawing reflex

Question 8

Function of reflexes?

Answer 8

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

Question 9

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

Answer 9

False

Reflex = Essential for voluntary action

Question 10

Give examples of rythmic motor patterns. Describe the movement.

Answer 10

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

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

Question 11

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

Answer 11

False
the initiation and termination are voluntary;

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

Question 12

Define the 2 feature of voluntary movements.

Answer 12

1. Complex, goal-directed (intentional)

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

Question 13

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

Answer 13

Partially True

Voluntary movement always need conscious control

But more practice and mastery = require less conscious direction

Question 14

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

Answer 14

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

Question 15

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

Answer 15

 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

Question 16

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

Answer 16

 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

Question 17

Which brain area contains both UMN and LMN?

Answer 17

Brainstem

Question 18

Define the 3 levels of motor control and their organization?

Answer 18

spinal cord, brainstem, cerebral cortex

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

Question 19

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

Answer 19

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

Question 20

Describe the arrangement of ventral horn neurons?

Answer 20

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

Function of stereotyped responses?

Answer 23

Adapted for speed of operation;

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

> > protective

Question 24

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

Answer 24

Protective + coordinates voluntary movement

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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)

Question 27

Function of the UMN and LMN in brainstem?

Answer 27

 LMN = motor innervation to head and neck region  UMN modulate activities of spinal motor neurons and interneurons via the descending pathways >> e.g. Controls posture by integrating visual, vestibular with somatosensory information

Question 28

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

Answer 28

1. General somatic motor neurons 2. Special visceral motor neurons 3. General visceral motor neurons

Question 29

Give examples of CN with general somatic motor functions?

Answer 29

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

Question 30

Give examples of CN with special visceral motor functions?

Answer 30

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)

Question 31

Give examples of CN with general visceral motor functions?

Answer 31

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)

Question 32

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

Answer 32

4 descending output pathways to spinal cord: Lateral brainstem > distal muscle: - Rubrospinal tract Medial brainstem > axial muscle: - Reticulospinal tract - Tectospinal tract - Vestibulospinal tract

Question 33

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

Answer 33

Lateral brainstem pathways control distal limb muscles (e.g. fingers) Medial brainstem pathways control axial muscles, posture

Question 34

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

Answer 34

- 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

Question 35

Define the 3 parts of the motor cortex?

Answer 35

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

Question 36

Define the location of the 3 parts of motor cortex?

Answer 36

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)

Question 37

List all the output tracts from the motor cortex?

Answer 37

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

Question 38

Define functions of lateral and ventral CST?

Answer 38

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

Question 39

Define function of the Corticobulbar tract?

Answer 39

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

Question 40

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

Answer 40

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

Question 41

Describe the functional organization of primary motor cortex?

Answer 41

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)

Question 42

Inputs to M1?

Answer 42

* 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

Question 43

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

Answer 43

 Discharge frequency of single neuron >> encodes FORCE of movement  Specific Populations of motor neurons (not single cells) >> encodes DIRECTION of movement

Question 44

Which 2 areas form the premotor area?

Answer 44

premotor cortex + SMA

Question 45

Inputs into premotor cortex? Role of each input?

Answer 45

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

Question 46

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

Answer 46

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

Question 47

Summarize the overall output function of the Premotor cortex?

Answer 47

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)

Question 48

Clinical manifestations of M1 lesions?

Answer 48

* Interferes with motor proficiency & manual dexterity (can't initiate, plan direction and force) * Independent control of fingers may be lost

Question 49

Clinical manifestations of PMA lesions?

Answer 49

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)

Question 50

Clinical manifestations of SMA lesions?

Answer 50

* 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)

Question 51

How is the cerebellum involved in motor control?

Answer 51

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

Question 52

Clinical manifestations of lesions in cerebellum?

Answer 52

 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)

Question 53

List the components of basal ganglia?

Answer 53

- Putamen - External globus pallidus , Internal globus pallidus - Caudate nucelus - Subthalamic nucleus - Substantia nigra Striatum = caudate nucleus + putamen

Question 54

Input of basal ganglia? Output to which structure?

Answer 54

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)

Question 55

Detail pathways in the output of basal ganlgia?

Answer 55

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

Question 56

Sequence of direct pathway in the output of basal ganglion?

Answer 56

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

Question 57

Sequence of indirect pathway in the output of basal ganglion?

Answer 57

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

Question 58

Overall functions of the Basal ganglia?

Answer 58

processing of information needed for:  Planning, triggering self-initiated movements  Organizing associated postural adjustment

Question 59

Clinical manifestations of lesion in Basal ganglia?

Answer 59

Parkinson's disease Huntington's chorea Hemiballismus Unintentional tremor

Question 60

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

Answer 60

S.N. has D1 and D2 neurons to the Striatum - D1 enhances direct pathway >> more inhibition of cortex - D2 suppresses indirect pathway >> 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

Question 61

Symptoms of Parkinson's disease? Treatment?

Answer 61

hypokinetc disorder Bradykinesia, rigidity, tremor, disturbance of posture and gait Treatment: L-DOPA increases dopamine level

Question 62

Relate the basal ganglia circuit to Huntington's disease?

Answer 62

(hyperkinetic disorder): due to degeneration in caudate nucleus, putamen = inhibit indirect pathway = less tonic suppression of thalamus = Promote movement

Question 63

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

Answer 63

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