Motor Control Reflexes

Question 1

Cortical Reflexes

Answer 1

placing reaction and hopping reaction

Question 2

Brainstem/midbrain reflexes

Answer 2

vestibular, righting reflex, suckle, yawn, eye/head movement

Question 3

Spinal Reflexes

Answer 3

stretch (myotatic), golgi tendon, crosses extensor

Question 4

Why do reflexes look like volitional movement ?

Answer 4

in order for reflexes to be effective, they must be very precise, and the precision makes the reflexes look volitional

Question 5

Major difference between reflex and voluntary motion

Answer 5

a reflex movement occurs faster than the fastest voluntary motion

Question 6

Reflex Activity

Answer 6

precise motion, mediated by CNS, rapid initiation, can be elicited during unconsciousness

Question 7

Volitional Activity

Answer 7

originates in cortical areas, longer onset and latency, requires conscious awareness

Question 8

Myotatic Reflex Appearance

Answer 8

shortening of a stretched muscle

Question 9

Myotatic Reflex Purpose

Answer 9

protect muscle from tearing due to stretch

Question 10

Myotatic Reflex Characteristics

Answer 10

initiated by muscle spindle
monosynaptic
passive stretch of muscle
contraction of stretched muscle back to normal length

Question 11

Extrafusal fibers characteristics

Answer 11

what you see when you grossly look at a muscle

fxn- do the work

Question 12

Intrafusal fibers characteristics

Answer 12

have both motor and sensory components

in muscle spindle

Question 13

Where is the sensory portion of the muscle spindle located

Answer 13

in the center

Question 14

Where is the motor portion of the muscle spindle located

Answer 14

at both ends

Question 15

Sensory Portion of muscle spindle characteristics

Answer 15

not contractile, sensitive to length, 2 sensors with different afferents

Question 16

2 sensors

Answer 16

nuclear bag fiber, nuclear chain fiber

Question 17

Nuclear bag fiber

Answer 17

nuclei don’t line up and they are in a swelling

Question 18

Nuclear chain fiber

Answer 18

all the nuclei line up together

Question 19

Primary Afferent Characteristics

Answer 19

innervates both nuclear bag and nuclear chain
large, myelinated Ia fiber
sensitive to length of muscle and how fast the length is changing

Question 20

Ia fiber characteristics

Answer 20

high conduction, low threshold

Question 21

Stretch and force relationship

Answer 21

Further it stretches, the more force it has

Faster is stretches, the more action potentials

Question 22

Secondary Afferent Characteristics

Answer 22

only innervates nuclear chain
smaller, myelinated group II fibers
only tells me how long the muscle

Question 23

Group II fibers

Answer 23

smaller diameter, less myelin, still fast

Question 24

Motor portion of intrafusal contractile elements characteristics

Answer 24

innervated by gamma motor neurons
releases Ach
controls length of sensory portion
innervates nuclear bag and chain

Question 25

What happens to sensory portion when we contract the intrafusal muscles

Answer 25

stretch the sensory portion | stretch both the nuclear bag and nuclear chain

Question 26

How to control sensitivity of myotatic reflex

Answer 26

gamma motoneuron

Question 27

Alpha motoneuron characteristics (efferent)

Answer 27

large, heavily myelinated innervates skeletal m gives direct motion responsible for activating muscle

Question 28

Gamme motoneuron characteristics (efferent)

Answer 28

``` smaller and slower than alpha innervates contractile potion of muscle spindle causes contraction controls sensitivity of muscle does NOT give motion ```

Question 29

Reciprocal inhibition

Answer 29

decrease in activity of the alpha motoneuron innervating antagonist m allowing it to relax and lengthen

Question 30

Golgi tendon reflex characteristics

Answer 30

initiated by golgi tendon active contraction of muscle polysynaptic reflex abrupt relaxation of contracted muscle to prevent damage

Question 31

Golgi tendon appearance

Answer 31

sudden relaxation of contracted muscle

Question 32

Golgi Tendon Organs

Answer 32

innervate tendon, action potentials increase with tension use Ib to spinal cord

Question 33

Ib afferent from golgi tendon

Answer 33

releases inhibitory glycine to inhibit alpha motoneuron

Question 34

Reflexes and Spinal shock

Answer 34

Initally - period of aflexia | After - reflex always occurs even below transection

Question 35

How is spinal shock reversible

Answer 35

axonal sprouting below transection

Question 36

Axonal sprouting

Answer 36

neurons are looking for input if they aren't being excited enough randomly branch out and cause random hyperexcitablity to open sodium channels

Question 37

Cause of decerebrate posturing

Answer 37

loss of all structures above to pons

Question 38

Apperance of decerebrate posturing

Answer 38

extension of all anti-gravity muscles | happens instantly

Question 39

Rigidity

Answer 39

Results from - maintained muscle contraction Resists motion in all directions Continual activation of alpha motoneurons Loss of cortical influence

Question 40

Spasticity

Answer 40

Results from - hyperactive myotatic reflex Resists motion in a given direction Continual activation of gamma motoneurons Contracts intrafusal m Lengthens nuclear bag/chain fibers

Question 41

What does brainstem facilitatory region activate?

Answer 41

spasticity spontaneously active gamma-motoneurons, make muscle spindle more sensitive

Question 42

What does brainstem inhibitory region inhibit?

Answer 42

spasticity -- causes decerebrate posturing gamma motoneurons, making muscle spindle less sensitive requires cortical regions

Question 43

What happens in the loss of the cortex?

Answer 43

brainstem inhibitory region is not activated and the facilitatory region is dominate

Question 44

End result of uncontrolled brainstem facilitatory

Answer 44

stretch reflexes that fight any passive motion | causes spasticity

Question 45

Decorticate posturing appearance

Answer 45

rigidity usually not bilaterally flexion of upper limb joints** different than decerebrate extension of lower limbs dependent on head position**

Question 46

Main differences in appearance between decerebrate and decorticate posturing

Answer 46

decorticate is dependent on head positioning and will change with head movement

Question 47

What is a likely cause of decorticate postuing

Answer 47

strokes in the vicinity of the internal capsule

Question 48

Spinal shock characteristics

Answer 48

transection of spinal cord all reflexes abolished cause by hyperpolarization of spinal nerves

Question 49

Decorticate Posture characteristics

Answer 49

``` internal rotation of legs in extended positon flexion of arms dependent on head position may be bilateral or unilateral loss of cortical inputs ```

Question 50

Decerebrate posture

Answer 50

contraction of all anti-gravity muscles (arm extension) Loss of input from all structures above pons usually bilateral and indicative of severe brain injury