Lower Motor Neurons and Spinal Reflexes

Question 1

where does voluntary movement begin

Answer 1

anterior part of frontal lobe (primary motor cortex)

Question 2

where does primary motor cortex receive sensory information from to create voluntary movement

Answer 2

posterior parietal cortex and sensory association areas

Question 3

what are the motor planning areas

Answer 3

premotor and supplemental motor cortices

Question 4

control circuits from _____ and _____ compare and provide additional information to regulate the motor plan via input to extrapyramidal tracts

Answer 4

cerebellum and basal ganglia

Question 5

the primary motor cortex initiates the motor plan carried by the corticospinal/corticobulbar tracts to where

Answer 5

• motor cranial nerve nuclei in brainstem
• LMN in ventral horn of spinal cord

Question 6

simultaneously while primary motor cortex is sending motor plan down the corticospinal/bulbar tracts, _______ carry information to the LMN to modify the motor plan

Answer 6

extrapyramidal tracts

Question 7

_______ (spinal efferents) carry the motor plan to the skeletal muscles

Answer 7

ventral rami

Question 8

where does the synapse occur allowing the result in motor unit response (contraction, relaxation, resting tone)

Answer 8

neuromuscular junction

Question 9

where are cell bodies of UMN found

Answer 9

cerebral cortex, basal ganglia, cerebellum

Question 10

axons descend from cerebral cortex or brainstem to the spinal cord

Answer 10

UMN

Question 11

what do UMN affect

Answer 11

• LMN (alpha motor neurons)
• interneurons indirectly through extrapyramidal tracts

Question 12

where do extrapyramidal tracts synapse

Answer 12

lamina 8 (interneurons)

Question 13

where are cell bodies of LMN found

Answer 13

ventral rami of spinal cord

Question 14

axons are nerves that extend to the periphery

Answer 14

LMN

Question 15

excite or inhibit striated skeletal muscles

Answer 15

LMN

Question 16

_____ receives afferent (sensory) input from skin, joints and muscles of trunk and limbs and transmits to brainstem, cerebellum, and thalamus (lamina 1-5)

Answer 16

dorsal horn

Question 17

what is white mater made of

Answer 17

• ascending tracts (sensory tracts)
• descending tracts (pyramidal and extrapyramidal)

Question 18

what contains LMN with axons that exit the spinal cord to skeletal muscles

Answer 18

ventral horn (lamina 8 and 9)

Question 19

what communicates with ventral horn neurons to mediate reflex responses and pass on information from extrapyramidal tracts to influence voluntary motor responses

Answer 19

interneurons (lamina 10)

Question 20

what do lateral descending tracts influence

Answer 20

flexor tone

Question 21

what do anterior descending tracts influence

Answer 21

extensor tone

Question 22

cell bodies in ventral horns are clustered into

Answer 22

motor neuron pools

Question 23

cell bodies in ventral horn that innervate axial and proximal muscles

Answer 23

medial motor pool

Question 24

cell bodies in ventral horn that innervate distal muscles

Answer 24

lateral motor pool

Question 25

cell bodies in ventral horn that innervate extensors

Answer 25

anterior motor pool

Question 26

cell bodies in ventral horn that innervate flexors

Answer 26

posterior motor pool

Question 27

groups of muscles innervated by single spinal nerve

Answer 27

myotomes

Question 28

C5

Answer 28

elbow flexion

Question 29

C6

Answer 29

wrist extension

Question 30

C7

Answer 30

wrist flexion, finger extension

Question 31

C8

Answer 31

finger extension

Question 32

T1

Answer 32

finger abduction

Question 33

L1, 2

Answer 33

hip abduction

Question 34

L3, 4

Answer 34

knee extension

Question 35

L5, S1

Answer 35

knee flexion

Question 36

L5

Answer 36

great toe extension

Question 37

S1

Answer 37

great toe flexion

Question 38

large cell bodies found in lamina VIII and IX

Answer 38

alpha motor neurons

Question 39

have large myelinated axons and project to extrafusal skeletal muscle fibers

Answer 39

alpha motor neurons

Question 40

what is released to activate skeletal muscles

Answer 40

achetycholine

Question 41

small cell bodies in ventral horn

Answer 41

gamma motor neurons

Question 42

medium-sized myelinated axons that project to intrafusal fibers in muscles spindle to maintain stretch sensitivity

Answer 42

gamma motor neurons

Question 43

help to regulate muscle tone and active in reflex arc

Answer 43

gamma motor neurons

Question 44

an alpha motor neurons and all the muscle fibers it innervates

Answer 44

motor units

Question 45

what make up motor neurons

Answer 45

alpha motor neuron, axon, and neuromuscular junction

Question 46

smaller diameter, slower axons; postural and slowly contracting muscles; high resistance to fatigue (aerobic)

Answer 46

slow twitch motor units

Question 47

large diameter, faster axons; speed and power muscles; easily fatigued (anaerobic)

Answer 47

fast twitch motor units

Question 48

order of requirement from smaller to larger alpha motor neurons

Answer 48

henneman's size principle

Question 49

the point where motor axons from alpha motor neurons synapse with muscle fibers

Answer 49

neuromuscular junction

Question 50

depolarization of motor axon results in release of what

Answer 50

acetycholine

Question 51

T/F acetycholine is always excitatory in skeletal muscles

Answer 51

T

Question 52

what are the spinal cord mechanisms that organize and synchronize muscle contractions to allow SC to deliver the effective motor plan that was communicated by UMN

Answer 52

reciprocal inhibition, muscle synergies, stepping pattern generators, spinal reflexes

Question 53

the inhibition of antagonist muscles during agonist contractions

Answer 53

reciprocal inhibition

Question 54

what is reciprocal inhibitions achieved

Answer 54

interneurons in the spinal cord that link LMNs into functional groups

Question 55

during reciprocal inhibition, a muscle contracts and the muscle spindles within the muscle send signals to the spinal cord that activate ______ that inhibit the motor neurons of the antagonist; also prevent activation of antagonist muscle when an agonist is reflexively relaxed

Answer 55

interneurons

Question 56

describes activity of muscles that are often activated by a normal nervous system; multiple spinal segments activated at the same time to produce a synchronous movement

Answer 56

muscle synergies

Question 57

muscle syngeries occur due to coordination by ______ that receive afferent information from II afferents and then project to muscles acting at other joints

Answer 57

interneurons

Question 58

what do muscle synergies result in

Answer 58

fractionated movement

Question 59

pathological synergies occur with what

Answer 59

UMN lesions

Question 60

adaptable networks of spinal interneurons that activate LMN to produce repetitive, rhythmic alternating output

Answer 60

stepping pattern generators

Question 61

activated by descending signals from UMN to interneurons in the anterior commissure (Renshall cells)

Answer 61

stepping pattern generators

Question 62

involuntary responses to an external stimulus

Answer 62

reflexes

Question 63

sensory receptor stimulated, sends signal to primary afferent, synapse occurs between dorsal horn cells and ventral horn cells, efferent response to effector

Answer 63

spinal reflexes

Question 64

do you need input from brain/cortex for spinal reflexes

Answer 64

no

Question 65

muscle contraction in response to a quick stretch (aka DTR); quick stretch activates signals from muscle spindles to alpha motor neurons of the same muscel

Answer 65

muscle spindles (monosynaptic/phasic reflexes)

Question 66

stimulated by cutaneous stimulus by receptors in the skin; spinal segment receiving the afferent input relays information to interneurons; interneurons coordinate a response to multiple spinal segments to produce the reflexive response

Answer 66

polysynpatic reflexes (Cutaneous)

Question 67

withdrawal or crossed-extension reflex

Answer 67

polysynpatic reflexes (Cutaneous)

Question 68

types of involuntary muscle contractions

Answer 68

- muscle cramps - fasciculations - myoclonus - fibrillations

Question 69

severe, painful muscle contractions

Answer 69

muscle cramps

Question 70

eye twitch; get a twitch in muscle that is fatiguing

Answer 70

fasciculations

Question 71

brief, involuntary contractions; hiccups, head jerk as you fall asleep

Answer 71

myoclonus

Question 72

always a sign of LMN; cannot see them

Answer 72

fibrillations

Question 73

random; spontaneous, brief contractions of a single muscle fiber not visible on the surface of skin; always pathological; occurs when a muscle membrane is unstable owing to denervation, trauma, or electrolyte imbalance; detected by EMG

Answer 73

fibrillations

Question 74

occurs when LMN cell bodies, axons and/or neuromuscular junctions are destroyed

Answer 74

LMN lesions

Question 75

signs of LMN lesion

Answer 75

- decrease or loss of reflexes (hypo) - muscle weakness and/or atrophy - decrease or loss of muscle tone (hypotonia or flaccidity) - fibrillations

Question 76

lack of muscle use

Answer 76

disuse atrophy

Question 77

damage to nervous system leading to muscle weakness

Answer 77

neurogenic atrophy

Question 78

differentiates the site of injury; motor neuron, nerve, neuromuscular junction, muscle; records electric potential when nerve is electrically stimulated; measures velocity it takes for electrical signal to travel from site of proximal electrical stimulation to distal point

Answer 78

nerve conductive velocity test (NVC)

Question 79

needle inserted into muscle to measure electrical activity at needle insertion, rest, minimal muscle contraction, maximal muscle contraction; distinguishes between denervation vs myopathy

Answer 79

electromyography (EMG)

Question 80

common LMN disorders

Answer 80

- polio/post polio syndrome - myasthenia gravis - trigeminal neuralgia - guillain barre' syndrome - peripheral nerve injury - peripheral neuropathy

Question 81

disruption of CNS cell bodies and pathways from cortex, brainstem and descending tracts in spinal cord

Answer 81

UMN lesion

Question 82

signs/sx of UMN lesion

Answer 82

- hypertonia (spasticity, rigidity, clonus) - hyperreflexive - paralysis/paresis - neurogenic atrophy - pathological synergies - abnormal postural control

Question 83

injury or disease to ventral horn cells, spinal nerve, neuromuscular junction, muscle

Answer 83

LMN lesion