intro motor system

Question 1

define alpha motoneurons

Answer 1

• also called LMN, can be called anterior or ventral horn cell when in spinal cord

Question 2

define final common path (FCP)

Answer 2

• Lower motor neurons are only link between central nervous system and skeletal muscles
• thus they are COMMON PATH by which all other parts of the nervous system control skeletal muscles

Question 3

define motorneuron pool

Answer 3

• all of the motor units that serve a single muscles are considered a motor unit pool

Question 4

define motor unit

Answer 4

• one alpha motor neuron plus ALL the skeletal muscles fibers its innervates

Question 5

define poliomyelitis

Answer 5

• affects the size of the motor unit
• can result in very large motor units in affected muscles
• due to surviving motor units ADOPTING orphaned muscle fibers
• Post-polio syndrome partially caused by stress on surviving motor neurons b/c nerve-muscles connects undergo repeated remodeling with denervation and reinnervation

Question 6

define fibrillations

Answer 6

• spontaneous activity within single muscle fibers
• not visible clinically since they are too small to be seen as movement through the skin
• can only be recognized by electromyography

Question 7

define fasiculation

Answer 7

• visible twitched of muscle that can be seen as ripples under the skin
• can involve one or more motor units

Question 8

describe graded muscle contractions

Answer 8

• Increase muscle force production via:
• -> recruitment or multiunit summation (increase number of motor units activated)
• -> Increase firing rate of activated motor units

Question 9

What size motor units are expected in extra-ocular eye muscles, muscles controlling fingers, large postural muscles, and limb muscles that have been affected by polio

Answer 9

• Extra-ocular eye muscles/muscles controlling individual fingers HAVE MANY SMALL MOTOR UNITS
• Large postural muscles/limb muscles that have been affected by polio = LARGE MOTOR UNITS

Question 10

affects of LMN damage

Answer 10

• profound muscle atrophy
• decreased muscle tone/flaccid paralysis or weakness
• weak or absent stretch reflexes (HYPOREFLEXIA)
• Fibrillations present
• fasciculations present
• Negative for Babinski

Question 11

affects of UMN damage

Answer 11

• Hypertonic muscles (spasticity, clasp-knife effect, clonus)
• hyperreflexia (deep tendon reflexes)
• positive babinski sign
• fibrillations and fasiculations are ABSENT

Question 12

Immediate effects of spinal cord trasected

Answer 12

• spinal shock = initial flaccid paralysis due to damage to descending motor pathway
• flaccid paralysis
• areflexia (loss of reflexes)
• loss of autonomic function

Question 13

What are permanent effects of spinal cord transection

Answer 13

• loss of voluntary movement for muscles innervated by spinal segments below level of transection
• loss of TURE sensation, anesthesia, for areas innervated by sensory neurons below level of transaction

Question 14

describe the patients changes over time

Answer 14

• recovery from spinal shock usually takes 1 to 6 weeks
• -> patient shows HYPERREFLEXIA, different types of reflexes return at different times.
• After spinal shock, SLOW RETURN of reflex activity in the following order:
• -> Babinski sign > flexor spasms > alternate flexor and extensor spasms > predominant extensor spasms > release phenomena > spastic paralysis

Question 15

babinski sign

Answer 15

• AKA estensor plantar response
• BIG TOE DORSIFLEXES and other toes FAN OUT (Positive sign)
• indicates damage to UMN in the thoracic or lumbar region or brain disease constituting damage to the corticospinal tract
• Normal primitive reflex seen in infants, disappears at around 1 yo