Neurophysiology Part Iie

Front 1

What are the 4 components of the motor unit that may be affected by disease or injury?

Back 1

Nerve cell body
Peripheral axon
Neuromuscular junction
Muscle fiber

Front 2

What is the difference between neurogenic and myopathic disease of the motor unit?

Back 2

Neurogenic diseases primarily affect the neuronal part of the motor unit rather than the muscle fiber. Myogenic diseases affect the muscle fiber or neuromuscular junction rather than the neuron.

Front 3

How do neuron diseases differ from peripheral neuropathies?

Back 3

Motor neuron diseases affect the motor neuron cell body (within the CNS) while peripheral neuropathies affect the peripheral axon.

Front 4

What is meant by "lower motor neuron"?

Back 4

The primary motor neuron of the spinal cord and brainstem that directly innervates skeletal muscle.

Front 5

What is meant by "upper motor neuron"?

Back 5

Neurons that originate in higher regions of the brain, such as the motor cortex, and synapse on lower motor neurons to convey commands for movement.

Front 6

Why are the terms "upper motor neuron" and "lower motor neuron" out-of-date?

Back 6

Upper motor neurons are not actually motor neurons but rather pre-motor neurons.

Front 7

What results from damage to upper motor neurons?

Back 7

spasticity
overactive tendon reflexes
abnormal plantar extensor reflex (Babinski sign)

Front 8

What results from damage to lower motor neurons?

Back 8

atrophy
fasciculations
decreased muscle tone
loss of tendon reflexes

Front 9

Is ALS a motor neuron disease or a peripheral neuropathy? What about Guillaume-Barre syndrome?

Back 9

ALS: motor neuron disease
G-B: peripheral neuropathy

Front 10

What is the characteristic lesion of ALS?

Back 10

scarring of the lateral columns of the spinal cord (corticospinal tracts)

Front 11

What causes ALS?

Back 11

We don't know.

Front 12

Does ALS affect motor neurons or sensory neurons?

Back 12

Motor neurons, except for those supplying the ocular muscles and bladder sphincter muscles

Front 13

What are the symptoms of ALS?

Back 13

Painless weakening of the arms or legs
Awkwardness of fine movements
Hyperreflexia
ALS is progressive and fatal

Front 14

What is the characteristic lesion of Guillaume-Barre syndrome?

Back 14

Lesion is in the peripheral nerves, including the cranial nerves

Front 15

What causes Guillaume-Barre syndrome?

Back 15

It can follow respiratory infection but is caused by autoimmune attack on peripheral nerves by circulating antibodies

Front 16

In Guillaume-Barre syndrome, are motor neurons or sensory neurons affected?

Back 16

Both

Front 17

What are the symptoms of Guillaume-Barre syndrome?

Back 17

Condition may be mild to severe (requiring mechanical ventilation) and includes paralysis of ocular, facial, and oropharyngeal muscles. It is an acute disease that can be completely recovered from, however many patients are left with some disability. Treatment is plasmapharesis (removal of antibodies).

Front 18

What are the two categories of peripheral neuropathies?

Back 18

Acute/chronic
Demyelinating/axonal

Front 19

Explain the X-linked causes of Charcot-Marie-Tooth disorder.

Back 19

The X-linked form is caused by a single mutation in the connexin gene which disrupts functional gap-junction channels in Schwann cells and prevents normal flow of metabolites in the myelin sheath.

Front 20

What is myalgia?

Back 20

muscle pain

Front 21

What is myotonia?

Back 21

inability to relax the muscle

Front 22

What is atrophy?

Back 22

wasting away of once-normal muscle

Front 23

What is hyperreflexia?

Back 23

An increase in the tendon reflex

Front 24

What is dysarthria?

Back 24

difficulty speaking

Front 25

What is dysphagia?

Back 25

difficulty swallowing

Front 26

What is paresthesia?

Back 26

sensations like numbness, pins-and-needles, or tingling occurring spontaneously

Front 27

What are the two categories of myopathic disease? Give an example of each.

Back 27

1) Inherited myopathic diseases: duchenne muscular dystrophy
2) Acquired myopathic disease: dermatomyositis

Front 28

What happens in the polysynaptic flexion-withdrawal reflex?

Back 28

Divergent pathways both excite flexor muscles of the stimulated limb and inhibit motor neurons that innervate antagonistic extensor muscles of the same limb. This activation of flexors and coincident inhibition of antagonistic extensors is called reciprocal innervation. Along with the response of the stimulated limb, the contralateral limb expresses opposite responses (activation of extensors and inhibition of flexors) - this is called the crossed-extension reflex and it enhances postural support to the withdrawn limb.

Front 29

What stimuli activate the primary afferents of the muscle spindle and the Golgi tendon organ?

Back 29

Muscle spindles monitor changes in length of muscles
Golgi tendon organs monitor changes in muscle tension

Front 30

What are the 3 main components of the muscle spindle?

Back 30

1) Intrafusal fibers
2) large-diameter myelinated sensory endings
3) small diameter myelinated motor endings

Front 31

How are the components of the muscle spindle arranged?

Back 31

The intrafusual muscle fibers extend the length of the muscle spindle; their central regions are noncontractile and innervated by sensory endings. The contractile end regions are innervated by the motor fibers. This unit is wrapped in connective tissue.

Front 32

What is the function of gamma motor neuron innervation of the poles of the intrafusal fibers in the muscle spindle?

Back 32

They cause the intrafusal fibers to contract. This does not contract the muscle, but rather sensitizes the muscle spindle.

Front 33

How does alpha-gamma coactivation work?

Back 33

When a muscle is contracted through alpha motor fibers, the muscle spindle is unloaded and becomes slack. In this state, the receptor is unable to sense muscle length. If gamma fibers are stimulated at the same time as alpha fibers, the intrafusal muscle fibers maintain tension on the muscle spindle and allow it to continue to signal changes in muscle length.

Front 34

What is meant by "proprioceptive sensory signals"?

Back 34

Sensory signals generated by the body's own movements.

Front 35

Use the Hering-Breur reflex to illustrate how proprioceptive signals help to control aspects of normal movement.

Back 35

Based on proprioceptive information from stretch receptors in the lungs, the Hering-Breur reflex regulates the amplitude of inspiration by triggering the transition from inspiration to expiration when the lungs are sufficiently expanded.

Front 36

What is the primary function of proprioceptive reflexes in regulating voluntary movements?

Back 36

They adjust motor output based on the biomechanical state of the body and limbs.

Front 37

What are long-loop reflexes?

Back 37

Responses mediated by the motor cortex or supraspinal structures. They are usually more important for distal structures, while proximal structures are regulated by subcortical structures.

Front 38

What is the significance of absent or weak stretch reflexes?

Back 38

It indicates a disorder of on or more of the components of the reflex arc: sensory or motor axons, cell bodies of motor neurons, or the muscle itself.

Front 39

What is muscle tone?

Back 39

The force with which a muscle resists being lengthened.

Front 40

What is hypotonus?

Back 40

Abnormal decreases in muscle tone

Front 41

What is hypertonus?

Back 41

abnormal increases in muscle tone

Front 42

What is spasticity?

Back 42

hyperactive response to tendon jerks and increased resistance to rapid muscle stretch

Front 43

What two mechanisms have been hypothesized to cause spasticity?

Back 43

1) Hyperactivity of gamma motor neurons
2) Changes in background activity of alpha motor neurons and interneurons

Front 44

What is the rationale for intrathecal administration of baclofen as a treatment for spasticity?

Back 44

Baclofen is a GABA agonist; binding of GABA to GABAB receptors decreases the influx of calcium into the presynaptic terminals and hence reduces the amount of transmitter released.

Front 45

How many spinal cord injuries occur in the US each year?

Back 45

10,000

Front 46

What is the change in reflex responses that occurs during the initial cord injury?

Back 46

"Spinal shock" occurs when the transection is complete and refers to a period immediately after the accident when all spinal reflexes below the level of the transection are reduced or completely suppressed.

Front 47

How long does spinal shock last?

Back 47

Weeks to months

Front 48

In the period after spinal shock, what is the reflex activity like?

Back 48

The reflexes return and are often greatly exaggerated.

Front 49

What are some possible mechanisms that explain spinal shock and the period directly following it?

Back 49

The spinal shock is due to sudden withdrawal of tonic facilitatory influence from the brain.
The exaggerated reflex response may be due to:
1) denervation supersensitivity
2) increased numbers of postsynaptic receptors
3) sprouting of afferent terminals

Front 50

Compare the responses to damage to motor neurons with the responses to general trauma to the spinal cord.

Back 50

Damage to motor neurons results in weakness, wasting, fasciculation, and loss of tendon reflexes.
General trauma to the spinal cord results in weakness, increased tendon reflexes, and spasticity.

Front 51

If the patient has difficulty breathing a quadriplegia, what level of the spinal cord was most likely injured?

Back 51

C3 or above

Front 52

If the patient quadriplegia but no difficulty breathing, what level of the spinal cord was most likely injured?

Back 52

C5

Front 53

If the patient has paraplegia of the lower limbs only, what level of the spinal cord was most likely injured?

Back 53

A level below C5

Front 54

What is meant by a "spinal preparation"?

Back 54

This is a spinal transection at a lower thoracic level, thus isolating the spinal segments that control the hind limb musculature from the rest of the CNS.

Front 55

What 4 conclusions about stepping were obtained from early studies using spinal preparation?

Back 55

1) Supraspinal structures are not necessary for producing the basic motor pattern for stepping
2) The basic rhythmicity of stepping is produced by neuronal circuits contained entirely within the spinal cord
3) The spinal circuits can be activated by tonic descending signals from the brain
4) The spinal pattern-generating networks do not require sensory input but nevertheless are strongly regulated by input from limb proprioceptors

Front 56

What is a "central pattern generator"?

Back 56

A neuronal network capable of generating a rhythmic pattern of motor activity in the absence of sensory input from peripheral receptors.

Front 57

List 5 examples of motor activities mediated by central pattern generators.

Back 57

Walking
Swimming
Feeding
Flying
Respiration

Front 58

What 3 types of sensory input are used to regulate stepping behavior?

Back 58

Somatosensory input from receptors of muscle and skin
Vestibular input for balance
Visual input

Front 59

Compare the roles of proprioceptors and exteroceptors in the regulation of stepping.

Back 59

Proprioceptor input is involved in automatic regulation of stepping.
Exteroceptor input is involved in adjusting the stepping to external stimuli.

Front 60

What descending pathway is believed to initiate stepping behavior?

Back 60

Reticulospinal tract

Front 61

What neurotransmitter is though to be released by the neurons of the reticulospinal tract to trigger activity of central pattern generators in the spinal cord?

Back 61

Glutamate

Front 62

How do lesions to the cerebellum affect stepping behavior?

Back 62

Stepping behavior shows marked abnormalities in locomotor movements, including abnormal variations in speed and range of movements at different joints in single limbs and abnormal coupling between stepping in different limbs. This is called ataxia - it resembles a drunken gait.

Front 63

What two spinal pathways provide information about stepping? What kind of information does each convey?

Back 63

Dorsal spinocerebellar tract: provides proprioceptor information about the biomechanical position and movements of the limb.
Ventral spinocerebellar tract: provides information about the state of the spinal locomotor from the interneuron in the central pattern generator.

Front 64

What three groups in the brainstem nuclei give rise to descending motor pathways?

Back 64

Vestibular nuclei
Red nucleus
Medullary reticular formation nuclei

Front 65

What can we conclude about the existence of central pattern generators in humans using studies of infants?

Back 65

When held erect and moved along a horizontal surface, infants exhibit rhythmic stepping motions.

Front 66

To what degree do descending pathways influence walking in humans as compared to quadrupedal animals?

Back 66

Humans depend much more on supraspinal centers for locomotion than do quadrupedal animals.

Front 67

What is the relevance of the greater influence of supraspinal centers on human locomotion for spinal cord injury?

Back 67

The dependence may explain the relatively few observations of spontaneous stepping movements in humans with a spinal cord injury.

Front 68

What are 3 differences between reflexive and voluntary movements?

Back 68

1) Voluntary movements are organized around the performance of a particular goal
2) Voluntary movements become more effective with practice
3) Voluntary movements are generated internally and are not responses to environmental stimuli

Front 69

What is meant by "dissociation of stimulus"?

Back 69

The higher levels of our motor system can dissociate two aspects of a stimulus - its informational content and its capacity to trigger a movement - and then the brain can choose whether or not to respond to that stimulus.

Front 70

What are the major inputs to the primary motor cortex?

Back 70

4 premotor areas: lateral dorsal premotor area, lateral ventral premotor area, supplementary motor area, cingulate motor area
Sensory inputs are from the primary somatosensory cortex and posterior parietal cortex
Also, input from the basal ganglia and cerebellum via different sets of nuclei in the ventrolateral thalamus

Front 71

What does the lateral dorsal premotor area control?

Back 71

proximal limb muscles

Front 72

What does the supplementary motor area control? What BA is it?

Back 72

BA 6; gives rise to bilateral movements, helps coordinate movements bilaterally, and controls the digit and hand muscles

Front 73

What are the inputs into the premotor cortex?

Back 73

Posterior parietal cortex (BA 5 and 7)
Prefrontal cortex (BA 46)
Input from the basal ganglia and cerebellum via thalamic nuclei

Front 74

What does the prefrontal cortex do?

Back 74

working memory
stores information about the location of objects in the environment to guide movement

Front 75

What are the two principle projections of the premotor cortex?

Back 75

Primary motor cortex and spinal cord

Front 76

What is the principle projection of the primary motor cortex?

Back 76

Spinal cord (corticospinal projections)

Front 77

Compare the kinds of motor behavior elicited by electrical stimulation of the primary motor cortex and the premotor cortex.

Back 77

Stimulation of the primary motor cortex results in simple movements of single joints.
Stimulation of the premotor cortex results in more coordinated, complex movements involving multiple joints and resembling natural coordinated hand shaping or reaching movements.

Front 78

Describe the functional reorganization of the primary motor cortex in rats whose whiskers were denervated.

Back 78

After the whisker motor neurons were denervated, electrical stimulation of the cortical region that had caused whisker movement subsequently produced forelimb movement.

Front 79

Describe the effect of retraining on the manual dexterity of squirrel monkeys subjected to damage of portions of the primary motor cortex that govern hand movement.

Back 79

In squirrel monkeys that practiced use of their hands daily, the undamaged cortex controlling the hand and digit expanded into adjacent undamaged cortex previously occupied by neurons controlling the elbow and shoulder. They regained full function of their hands.

Front 80

What is the clinical significance of plasticity for patients who have suffered focal brain damage?

Back 80

It emphasizes the importance of practice in sensorimotor tasks for rehabilitation following stroke and other focal brain damage.

Front 81

Describe direct contacts between corticospinal neurons and alpha-motor neurons in the spinal cord. What kinds of movement is mediated by this contact?

Back 81

Direct connections between these two neurons are unique because successive cortical stimulation produces progressively larger excitatory postsynaptic potentials in spinal motor neurons, allowing for fine-tuned movements.

Front 82

Describe the indirect connections between corticospinal neurons and alpha-motor neurons in the spinal cord. What kind of movement is mediated by the contact?

Back 82

Corticospinal neurons also make indirect contact with alpha-motor neurons by terminating on interneurons that terminate on alpha-motor neurons. These indirect connections regulate a larger number of muscles and contribute to organization of multi-jointed movements such as reaching or walking.

Front 83

Describe the deficits of individuated movements of the digits that remain in monkeys following bilateral sectioning of the medullary pyramidal tract.

Back 83

Produces contralateral weakness, but recovery occurs over a period of months, leaving only deficits in speed of movement and the rate of force development. Individuated movements are lost permanently and the wrist, elbow, and shoulder become linked in flexor or extensor synergies.

Front 84

What 3 factors influence the firing rate of individual neurons in the primary motor cortex?

Back 84

1) Intent to perform a movement
2) Movement in a particular direction
3) force of movement

Front 85

How far in advance of onset of movement does the firing rate of primary motor cortex neurons change?

Back 85

100 ms or more

Front 86

Which premotor area performs internal initiation of movement?

Back 86

supplementary motor area

Front 87

Which premotor area initiates movement in response to external sensory events?

Back 87

Lateral premotor areas

Front 88

What is the "preparatory potential"?

Back 88

It precedes self-initiated voluntary movement. Nearly a full second before self-initiated movement begins, a characteristic negative shift in cortical potentials is seen in the medial premotor regions, where the supplementary motor area is located. This signals the planning that occurs before movement.