Motor Systems

Front 1

What does the NMS do?

Back 1

Generates the neural signals tha activate selected muscles and set the level and timing of muscle activity

Front 2

Lower motoneuron signs include:

Back 2

1. Paresis (weakness)or paralysis (inability to produce muscle contraction)

2. Signs of muscle denervation (fasciculation, fibrillation, atrophy)

3. Flaccidity (low or absent muscle tone)

4. Decreased or absent stretch reflexes

Front 3

When the force of voluntary isometric contraction is increased, motor units are activated how?

Back 3

In increasing numbers and at increasing firing rates

Front 4

Is motor unit recruitment random or nonrandom?

Back 4

Nonrandom- motor units are recruited in the same fixed order, related to functional specializations of the motor units (Size Principle)

Front 5

Muscle weakness in neurological disorders might result from difficulties with what?

Back 5

Recruitment or rate modulation

Front 6

Control over alpha motoneuron recruitment and firing rate is achieved by?

Back 6

1. The strength of synaptic input and 2. alphamotoneuron excitability (response to synaptic input)

Front 7

Serial pathways involve?

Back 7

Cerebral cortex--> brainstem
--> spinal cord

Front 8

Parallel pathways involve?

Back 8

Cerebral cortex--> spinal cord

Front 9

Alpha-motoneurons are found where?

Back 9

Brainstem (cranial skeletal muscles) and spinal cord (somatic skeletal muscles)

Front 10

Alpha-motoneurons are only neurons which can initiate...

Back 10

Skeletal muscle contraction

Front 11

Total muscle force results from what?

Back 11

20% recruitment of motor unit twitch force; 80% temporal summation of individual twitches

Front 12

Maximal temporal twitch summation results in what?

Back 12

Tetanic contraction

Front 13

Interruption of descending motor pathways can result in?

Back 13

1. Loss of voluntary movement (paraplegia, quadriplegia)

2. Temporary absence of reflexes (spinal shock) followed by permanent exaggeration of some reflexes (hyper-reflexia)

Front 14

Reflexes can result in?

Back 14

1. muscle activation 2. muscle inactivation 3. activation of some muscles together with inactivation of others

Front 15

The stretch reflex (myotatic reflex) is a key contributor to what?

Back 15

Spasticity, clonus and muscle tone

Front 16

Tendon jerks or deep tendon reflexes are?

Back 16

Stretch reflexes evoked by quick stretch such as tendon tap

Front 17

Tonic stretch reflexes are?

Back 17

Stretch reflexes produced by slow or maintained stretch

Front 18

The stretch reflex pathway involves?

Back 18

Stretch activates muscle spindle receptors and afferents which conduct action potentials into the spinal cord, where excitatory synapses bring selected alpha motoneurons to firing threshold

Front 19

What is muscle tone?

Back 19

Muscles are always under some degree of stretch, and the stretch reflex therefore maintains a steady level of tension in muscles

Front 20

The effects of stretching one muscle is distributed to other muscles about the joint to cause what two things?

Back 20

1. Reflex contraction of all muscles having the same primary action at a given joint (agonists or synergists)

2. Reflex inhibition of antagonists

Front 21

What is a myotatic unit?

Back 21

A coordinated group of muscles affected by a stretch reflex

Front 22

A myotatic unit assists in what?

Back 22

Opposing stretch and restoring the intended position of the displaced limb

Front 23

Electroneurological examination by EMG can identify?

Back 23

Neuropathies (nerve compression or demyelination) and reflex abnormalities

Front 24

During EMG, the response having the shorter time delay from stimulation which results from direct activation of motor units is called the?

Back 24

M-wave

Front 25

In EMG, the time-delayed synaptic activation of motor units caused by direct electrical stimulation of stretch reflex afferents is called the?

Back 25

H-reflex

Front 26

The first neural protection against falling is the?

Back 26

Stretch reflex; vestibular and visual responses have longer delays from unexpected shifts in posture

Front 27

In which funiculi are descending tracts primarily found?

Back 27

Lateral and anterior

Front 28

In which funiculi are ascending tracts primarily found?

Back 28

All funiculi

Front 29

Spasticity is defined as?

Back 29

Hyperactive stretch reflexes and increased resistance to rapid muscle stretch

Video: lifting upper leg causes lower leg to lift also, instead of bending at knee

Front 30

Clonus is defined as?

Back 30

Uncontrolled oscillating limb movement initiated by muscle stretch

Front 31

A reflex is defined as?

Back 31

A stereotyped motor response that is unlearned and is elicited involuntarily by activation of sensory receptors

Front 32

Spinal reflexes coordinate the activities of muscles acting at?

Back 32

1. Single joints (i.e. stretch reflex)

2. Multiple joints throughout a limb (i.e. flexor reflex)

3. Joints of both sides of the body (i.e. crossed extension reflex)

Front 33

Tonic stretch reflexes contribute to?

Back 33

Muscle tone

Front 34

The stretch reflex involves how many neurons?

Back 34

Only two

Front 35

Do M-wave and H-reflex occur in tendon tap reflexes?

Back 35

M-wave yes, H-reflex no (H-reflex in EMG only)

Front 36

Conduction Velocity is calculated by?

Back 36

CV = CD (m) / CT (sec)

Front 37

What is the range of normal conduction velocity?

Back 37

Arms: 50 m/s
Legs: 40 m/s

Front 38

Demyelinating neuropathies are characterized by conduction velocities that are?

Back 38

25% below normal

Front 39

Central conduction time (intraspinal pathway)contributes how much to total H-reflex delay time?

Back 39

Central conduction time = the difference between sensory + motor conduction time and the measured H-reflex delay time:

Ex: 30 ms/ 31 ms = 1 ms

Normal values = 0-2 ms

Front 40

Stimulation of a Ia fiber from a muscle spindle will elicit what effect?

Back 40

Excitatory (reflex)

Front 41

Stimulation of a Ib fiber from a Golgi tendon organ will elicit what effect?

Back 41

Variable- depends on position and activity of limb at time of stimulation. May be excitatory or inhibitory

Front 42

What is autogenic stimulation?

Back 42

When the alpha-motoneurons connected to a Golgi tendon organ (Ib fiber) that innervate a muscle are inhibited, usually involving an inhibitory interneuron between the afferent and efferent fibers.

Front 43

The clasp-knife response is and example of what?

Back 43

Autogenic inhibition

Front 44

What occurs in the clasp-knife response?

Back 44

During forced flexion of a resistant limb, the resistance suddenly disappears and the limb collapses into flexion

Front 45

Stretch reflexes are initiated by which types of receptors?

Back 45

Muscle spindle or Golgi tendon organ

Front 46

The flexor reflex is initiated by mechanoreceptors located where?

Back 46

Skin (i.e. withdrawal from painful stimuli)

Front 47

What is local sign?

Back 47

Modification of the reflex response so that it reflects the area being stimulated (i.e. activating extensors, not flexors when front of thigh receives painful stimulus)

Front 48

What is reciprocal inhibition?

Back 48

When reflex activity in a given muscle produces similar activity in its ipsilateral synergists and the opposite activity in its ipsilateral antagonists

Front 49

What are crossed effects?

Back 49

When a flexor reflex occurs, the simultaneous and opposite pattern of activity is induced in the contralateral limb (i.e. to prevent falling)

Front 50

What is hemiparesis?

Back 50

Weakness of one side of the body (may be present with spasticity); stroke is most common cause

Front 51

Spastic hemiparesis is characterized by what?

Back 51

The leg is swung in a semi-circle from the hip; knee may be hyperextended; arm may be held flexed and adducted with minimal swing

Front 52

The corticobulbar tract projects to where?

Back 52

Brainstem motoneurons and other supraspinal motor centers, including basal ganglia, red nucleus reticular nuclei and vestibular nuclei

Front 53

The corticospinal tract projects where?

Back 53

Motoneurons (alpha & gamma) and interneurons in the spinal cord

Front 54

Upper motoneurons project where?

Back 54

From cerebral cortex and brainstem to connect with alpha motoneurons, mostly through premotor interneurons

Front 55

Hemiparesis affects what?

Back 55

Large muscle groups contralateral to the site of cortical injury

Front 56

Upper motoneuron signs include?

Back 56

Hemiparesis, spasticity and permanent loss of individuated movement of digits

Front 57

Spasticity result from what?

Back 57

Damage to corticobulbar tracts creates an imbalance in synapic excitation/ihibition from descending brainstem motor systems to lower motoneurons

Front 58

What is one effect of the imbalance in excitation/ihibition of lower motoneurons in spasticity?

Back 58

Over-excitement of gamma motoneurons with the effect of exaggerating muscle stretch reflexes (antagonist muscles reflexively contract during voluntary movement)

Front 59

Lesions located in the primary motor cortex produce paresis or paralysis where?

Back 59

Contralateral face and body

Front 60

The ability to recover some movement after injury/disease is due to what?

Back 60

The distributed nature of cortical organization together with cortical plasticity

Front 61

What is cortical plasticity?

Back 61

The ability of cortical neurons and circuits to transform their responses

Front 62

What is a population code?

Back 62

Because the directional sensitivity of most cortical motoneurons is imprecise (firing rate is high and in several directions), there is the notion that precision in direction, force, etc. is encoded not by single neurons, but by a population of neurons.

Front 63

The supplementary motor area and lateral premotor cortex (premotor cortices) are active when?

Back 63

During preparation for movement

Front 64

Visually-guided movements are encoded by what?

Back 64

Premotor neurons

Front 65

Subjects with lesions to the dorsal premotor area cannot make what type of associations?

Back 65

Visuomotor associations

Front 66

Why does the M-wave have a shorter delay time than the H-reflex?

Back 66

The H-reflex results from a circuit which passes through the CNS, whereas the M-wave bypasses the CNS

Front 67

What is spastic hemiparesis?

Back 67

Weakness of the muscles on one side of the body coupled with hyperactive stretch reflexes

Front 68

Spasticity can result from damage to what?

Back 68

Spinal cord or cerebral motor cortex

Front 69

What is the difference in response of the limbs in spastic hemiparesis following cortical injury?

Back 69

Arms flexed, legs extended

Front 70

The primary motor cortex is located in which Brodmann's Area?

Back 70

Area 4

Front 71

The supplementary motor area is located in which Brodmann's Area?

Back 71

Medial Area 6

Front 72

The lateral premotor cortex is located in which Brodmann's Area?

Back 72

Lateral Area 6

Front 73

How does the corticobulbar tract affect reflexes?

Back 73

Cortical neurons synapse onto neurons in the brainstem that determine the extent, magnitude and type of signal sent to lower motoneurons in the spinal cord

Front 74

What is the regulator of brainstem neurons?

Back 74

The corticobulbar tract

Front 75

How does damage to the corticobulbar tract result in spasticity?

Back 75

It changes the balance of input of descending information from the brainstem into the spinal cord

Front 76

How do individuated finger movements occur?

Back 76

Excitatory signals are sent to multiple fingers and inhibitory signals inhibit those fingers we don't want to move to create specific movements

Front 77

Major inputs to the primary motor cortex come from where? (neural activity begins diffusely throughout cortex and converges on primary motor cortex)

Back 77

The supplemental motor area, premotor areas, primary somatosensory cortex posterior parietal area (Brodmann's Area 5)

Front 78

What is the temporal sequence of cortical activity during simple movements?

Back 78

Premotor cortices--> primary motor cortex--> muscle activity (EMG)--> movement

Front 79

Why is the potential for cortical control of digits only partially eliminated by focal infarcts?

Back 79

Because digit representation is spatially distributed; also, neural representation is plastic (changes within weeks of infarct). These allow for behavioral recovery of skilled hand function

Front 80

Primary motor cortex encodes what aspects of movement?

Back 80

Direction, force and velocity

Front 81

Premotor cortices (supp. & lat.) are involved in what types of functions?

Back 81

Planning of movement:

1. sequencing movements
2. associating sensory cues with motor response
3. delaying task execution
4. conforming hand shape to objects
5. using visual imagery to plan movement

Front 82

Premotor cortices encode what?

Back 82

Memory-guided movement sequences

Front 83

What is the pattern of visually-guided versus memory-guided movements?

Back 83

Primary motor cortex= visually and memory-guided movements

Premotor cortex= visually-guided movements

Supplementary motor areas= memory-guided movements

Front 84

The lateral premotor area is particularly involved in what?

Back 84

Visually-guided movements