S2 Neuro Exam 4: Motor System 1

Front 1

____________ are used for motor planning

Back 1

cortical regions

Front 2

The __________ code the plan into muscle movements (tension) that are processed through the __________ and finally executed through the ______________ (and cortical influences over other descending pathways).

Back 2

basal ganglia

thalamus

corticospinal tract

Front 3

The _____________ provides feedback for correcting & anticipating movements

Back 3

cerebellum

Front 4

Obj.
Explain neurosmuscular synapse

Back 4

a cholinergic synapse is initiated at the neuromuscular junction/motor endplate-->
muscle fibers have nicotinic ACh receptors-->
reception initiates muscle contraction, mediated through calcium dependent mechanism

Front 5

Obj.
Explain motor unit function

Back 5

a single alpha-motor neuron innervates multiple muscle fibers= motor unit

entire motor unit contracts when neuron is activated

more muscle fibers/per unit --> stronger force of contraction

motor units in motor neuron pool are recruited smallest to largest (Size principle)

Front 6

What motor unit type?
-innervated by small diameter,
slow conducting axons
-postural muscles

Back 6

Type 1 (slow twitch, fatigue resistant, oxidative)

Front 7

What motor unit type?
-innervated by large diameter,
rapidly conducting axons
-relatively fast contractile time
-generates large tension
-intermediate to slow fatigue rate
-metabolic pathways are oxidative
& anaerobic glycolytic

Back 7

FOG (FR, Type IIa)

Front 8

What motor unit type?
-innervated by large diameter axons,
large fibers
-rapid contracting fibers
-high contraction force
-rapid fatigue (white muscle)
-metabolic pathways are glycolytic anaerobic.
large glycogen stores

Back 8

Type FG (fast glycolytic, FF, type IIB)

Front 9

What determines the muscle fiber type?

Back 9

the nerve supplying the muscle

*most muscles have mixed fiber types

Front 10

What is a motor neuron pool?

What does it control?

Back 10

all the motor units (motorneurons) that innervate a muscle

controls contraction for that muscle, receives inputs from various sources via interneurons

Front 11

Obj.
Describe the Influence of muscle spindle activity on movement

Back 11

*monitors muscle contraction via feedback
Intrafusal fibers stretch--> stretching Ia annulospiral endings--> AP frequency varies w/ speed of stretch
(Ia sensitive to small stretch, silenced when stretch sustained)

Nuclear chain stretch--> contact II flower spray endings--> Output varies w/ magnitude of stretch
(II reduce output, but does not stop when stretch is released)

Front 12

What do muscle spindles consist of?

Back 12

1. specializes muscle fibers (intrafusal)
A. nuclear bag fibers
(detect dyamic stretch(speed, rate of length change))
A1. dynamic bag fibers (elastic & sensitive to stretch)
A2. static bag fibers (more sensitive to length)
B. nuclear chain fibers
(produce increased AP w/ changes in muscle length)

2. muscle fibers (extrafusal)
(intrafusal fibers are attached in parallel to extrafusal)

Front 13

Describe the 2 types of sensory innervation of muscle spindles

Back 13

Type Ia afferents/ Annulospiral endings:
contact primarily nuclear bag fibers
heavily myelinated
large diameter sensory axons wrap around equatorial region
conduct AP at high velocities (80-120)

Type II/ Flower spray endings:
contact primarily nuclear chain fibers,
near polar regions w/ thin branching axons
axons heavily myelinated
conduct at high velocities
detect magnitude of stretch

Front 14

During muscle movement/stretch, spindle length changes. ____________ compensates for these changes.

Back 14

contractile elements innervated by gamma motor neurons in the spinal cord ventral horn

Front 15

What is alpha-gamma coactivation?

Back 15

contraction of muscle through activation of alpha motor neurons is accompanied by gamma motor neuron activation
(*may be a result of beta motor neurons, which innervate both intrafusal & extrafusal motor fibers)

gamma motor neurons increase sensitivity of annulospiral & flower spray endings by activation contractile polar regions of spindle fibers --> controls amount of tension in spindle

Front 16

Describe the 2 types of gamma motor neurons

Back 16

Dynamic gamma motor neurons:
-primarily influence nuclear bag fibers

Static gamma motor neurons:
-innervate nuclear chain fibers

Front 17

Obj.
Describe gamma loop functions

Back 17

*circuit for contraction of extrafusal muscle that combines reflex sensitivity for stretch w/ the ability for active adjustment through gamma motor neuron contraction

-used by descending central tracts to control postural muscles w/ high density of muscle spindles

Front 18

Obj,
Explain the influence of golgi tendon organs

Back 18

*nerve endings btwn collagen bundles aligned to muscle fascicles-->
inhibitory influence upon passive muscle stretch w/ crossed excitation of antagonist muscle

Front 19

Obj
Describe the contribution of sensory systems to spinal reflexes

Back 19

Skin & Joint capsule receptors--> direct muscle activation (pain influences) & indirect through central mechanism= flexor reflex afferents

Ex: Babinski reflex--> under central inhibition, allows plantar flexion response to predominate (normal)

Front 20

Myotactic reflexes (monosynaptic reflex arc, direct activation for homologous muscle = contraction of same muscle)
are usually under tonic _____________ of central tracts

Back 20

INHIBITION

Front 21

Describe the common mechanism for inhibition of myotactic reflexes

Back 21

presynaptic inhibition*
via GABA

Front 22

Stretch reflexes (IaN connections, second order connections of muscle spindle afferents)
are ______________ influences over antagonists muscles

Back 22

INHIBITORY

Front 23

Inhibitory interneurons involved in the stretch reflex use what neurotransmitter?

Back 23

glycine

Front 24

Balance of muscle tone (flexors & extensors) is via what?

Back 24

cross extensor reflex

(both inhibitory & excitatory)

Front 25

Muscle spindles, Golgi tendon organs, and sensory afferents from joints & skin are carried centrally to the cerebellum through the _______________.

Back 25

spinocerebellar tracts
(ascending)

Front 26

Descending influence (from brainstem to spinal cord) on volitional motor activity is modulated primarily through what 3 tracts?

Back 26

vestibulospinal
reticulospinal
rubrospinal

Front 27

Which of these 3 tracts are extensor biased?

Back 27

vestibulospinal & reticulospinal


(rubrospinal is flexor biased)

Front 28

The medial & lateral vestibulospinal tracts receive input from the vestibular apparatus & cerebellum.
They are primarily (inhibitory/excitatory) to extensor musculature

Back 28

EXCITATORY

*maintain body posture & orientation in space

Front 29

The cerebellum has 2 primary inputs to the vestibular nuclei, what are they & which one goes to the vestibular apparatus?

What does this allow?

Back 29

excitatory & inhibitory, excitatory to vestibular apparatus

allows fine extracortical control over postural extensor musculature

Front 30

The _____________ vestibulospinal tract descend ipsilaterally & terminates in lamina VII & VIII

It is excitatory to motor neurons of what muscles?

Back 30

lateral


paravertebral & proximal limb extensors (antigravity muscles)

Front 31

The _____________ vestibulospinal tract descends bilaterally in the medial ventral funiculus / MLF & terminated in the cervical/uper thoracic regions

What muscles does it influence?

Back 31

medial



neck musculature, controls orientation of head

Front 32

The lateral & medial reticulospinal tracts originate in the brainstem reticular formation & influence primarily paravertebral & limb extensors.

There effects are modulated through what?
What are the reticulospinal tracts involved in?

Back 32

*gamma motor neurons,
corticoreticular fibers,
& ARAS (nociceptive input)

subconscious posture & muscle tone

Front 33

The __________ reticulospinal tract extends bilaterally w/ ipsilateral PREDOMINANCE & has a largely INHIBITORY action on extensor musclulature
-->muscular atonia during REM sleep

Back 33

medullary/lateral reticulospinal tract

Front 34

The ______________ reticulospinal tract travels ipsilaterally in the ventral funiculus & is primarily EXCITATORY to extensors

Back 34

pontine/medial reticulospinal tract

Front 35

The rubrospinal tract is the 2nd major _______ biased tract.
It originates in the ___________ & terminates in lamina V, VI, & VII of spinal grey interneurons

Back 35

FLEXOR biased

red nucleus of rostral midbrain

Front 36

What is the primary function of the rubrospinal tract?

Back 36

facilitation of flexor activity in arm & forearm w/ some inhibition of extensors