Motor Reflexes

Question 1

How do you tell the difference between a reflex and a volitional movement?

Answer 1

Speed

Reflex will be faster

Question 2

What is the level of organization for a reflex?

Answer 2

Any CNS level

Does not require cortex for most

Question 3

What is the level of organization needed for volitional motion?

Answer 3

Requires cortical and subcortical involvement

Question 4

What is the purpose of a reflex?

Answer 4

Direct and rapid response to sensory stimuli. Often protective

Question 5

What s the purpose of volitional movements

Answer 5

Response to stimuli; need; desire

Question 6

What initiates a reflex?

Answer 6

Sensory input

Question 7

What initiates volitional motion?

Answer 7

Higher cognition

Sensory input

Question 8

What describe the circuitry of a reflex?

Versus volitional motion circuitry?

Answer 8

Fixed

Variable depending on motion

Question 9

What is the specificity of reflexes and volitional motion?

Answer 9

Both have high specificity

Question 10

What is an example of a monosynaptic reflex?

Answer 10

Myotatic reflex

Question 11

What is the pathway of a monosynaptic reflex?

Answer 11

Afferent —> alpha motor neuron —> excitatory contraction of m.

Question 12

What is a polysynaptic reflex?

Pathway?

Example?

Answer 12

More than one synpase

Afferent —> interneuron —> another interneon —> alpha MN.

Golgi tendon relfex

Question 13

What are the reflexes produced at the level of the spinal cord ?

Answer 13

Myotatic

Golgi tendon
Crossed extensor reflex

Question 14

What are the reflexes produced at the brainstem/midbrian?

Answer 14

Vestibular reflex

Suckling

Pushing food out of move
Sucking on fibers
Yawning
Stretching
Cry 
Following objects w/ head and eye movements
Turn head and eyes to sound

Question 15

What are cortical reflexes?

Answer 15

Placing response

Hopping response

Question 16

What innervates the intrafusal muscle fibers of a muscle spindle?

Answer 16

Efferent innervation By gamma MNs

Question 17

What do intrafusal muscle fibers contain?

Answer 17

Contractile components (actin, myosin etc.)

Similar to sk. M.

Question 18

What does the sensory portion of the muscle spindle consist of?

Answer 18

Nuclear bag fiber

Nuclear chain fiber

Question 19

Is the sensory portion of a muscle spindle contractile?

Answer 19

No

Question 20

What innervates the sensory portion of a muscle spindle?

Answer 20

2 afferent neurons

Question 21

What is the primary afferent of the muscle spindle?

Answer 21

1a fiber to both nuclear bag and chain fibers

Question 22

What characterizes the 1a primary afferent fiber?

Answer 22

Large
Myelinated
Fast

Question 23

What is the primary afferent sensitive to?

Answer 23

Length of muscle

Rate of muscle length change

Question 24

When is the primary afferent fiber discharged?

Answer 24

Discharged even at normal resting muscle length

And sensitive to length and rate of length change

Question 25

What is the secondary afferent fiber to muscle spindle? What characterizes this fiber?

Answer 25

Group 2 fiber Myelinated, smaller, slower

Question 26

What does the secondary afferent to the sensory portion of the muscle spindle innervate?

Answer 26

Only the nuclear chain fiber

Question 27

What doe the secondary afferent fiber respond to?

Answer 27

Responds only to changes in length

Question 28

What is the purpose of having 2 types of afferent fibers?

Answer 28

Allows the cns to get 2 kind of info Static and dynamic

Question 29

What is the efferent innervation of Extrafsusal fiber?

Answer 29

alpha MN via NMJ

Question 30

Where do Gamma MNs work on the muscle spindle? Using what? What does this initiate?

Answer 30

On intrafusal fibers on the neds of m. Spindles using NMF Contraction of intrafusal and stretching of muscle spindle

Question 31

What does the contraction of the intrafusal fibers by gamma MNs do?

Answer 31

Stretches muscle spindles thus sensitizes nuclear bag and chain fibers to further stretches

Question 32

Does the activity of Gamma MN lead to motion?

Answer 32

No

Question 33

Where do Alpha MNs work on the muscle spindle? Using what? What does this initiate?

Answer 33

Extrafusal fibers via NMJ Releases EAA to non-NMDA receptors Excited skeletal muscles and contracts it

Question 34

What does the contraction of skeletal muscle by alpha MNs cause?

Answer 34

Shortening of intrafusal fibers and stops their increased signaling

Question 35

Will activation of alpha MNs lead to motion?

Answer 35

Yes

Question 36

What do gamma MNs controL?

Answer 36

Length of sensory portion and thus sensitivity of muscle spindle

Question 37

What is the myotatic reflex initiated by? What is the result of this?

Answer 37

Initiated by muscle spindle in response to passive stretch of muscle Contracts stretched muscle back to normal length

Question 38

What is the golgi tendon reflex caused by? Result of the reflex?

Answer 38

Initiated by active contraction muscle felt by golgi tendon organ Leads to abrupt relaxation of contracted muscle to prevent damage

Question 39

What is the muscle spindle enclosed by? Embedded where?

Answer 39

Enclosed in capsule in sk. Muscle | Embedded in fusiform capsule

Question 40

How is the muscle spindle orientation in comparison to skeletal muscle?

Answer 40

Parallel to sk. M. Proper

Question 41

What makes up the bulk of msucle, extrafusal or intrafusal?

Answer 41

Extrafusal

Question 42

What is the stimulus for muscle spindle?

Answer 42

Stretching/lengthening of muscle

Question 43

What does the full myotatic reflex contain?

Answer 43

Seance efferent limb for reciprocal inhibition of antagonist m.

Question 44

How does the second efferent limb of the myotatic reflex work?

Answer 44

The 1a afferent goes to alpha MNs —> contract agonist ALSO goes to interneuron in SC that releases GABA —> Alpha MN of antagonist —> relax m.

Question 45

What is the golgi tendon organ?

Answer 45

Bare nerve ending w/ lots of branches

Question 46

Where do you find the golgi tendon organ? What innervates it?

Answer 46

In tendon Innervated by 1b fiber

Question 47

What is the golgi tendon reflex pathway? (Does abrupt relaxation of contracted msucle)

Answer 47

1b —> release EAA to non NMDA to interneuron in SC Interneuron active —> releases GABA to alpha MN Allows Cl in, hyperpolarizes alpha MNs —> muscle relaxes abruptly

Question 48

What is the difference between 1a and 1b fibers?

Answer 48

1a afferents are involved in msucle spindle reflex; myelinated, faster 1b afferents are afferents for golgi tendon reflex; less myelinated; slower

Question 49

What is the presentation of spasticity? Why does this happen?

Answer 49

Patient RESIST IN A GIVEN DIRECTION a passive stretch of their muscles c their antagonists don’t relax Hyperactive myotatic reflex increases gamma motor neuron firing(efferent to intrafusal m. Fiber)

Question 50

What is the cause of spasticity?

Answer 50

Damage to cortex that abolishes activation of the brainstem inhibition region (can’t inhibit antagonist)

Question 51

What is rigidity?

Answer 51

Contraction of muscles in absence of other stimuli causing resistance of motion in ALL DIRECTIONS

Question 52

What is the mechanism of rigidity?

Answer 52

Continual activation of alpha-MNs that causes contraction of Ms. w/o stimuli

Question 53

What causes rigidity?

Answer 53

Loss of cortical influence that inhibits a medullary input to alpha motor neurons

Question 54

What is altered in spasticity?

Answer 54

Alter stretch reflexes by changing gamma motor neuron firing rate

Question 55

What is continual active during spasticity? | What does this cause?

Answer 55

Gamma MNs Contracts intrafusal and lengthens nuclear bag/chain fibers making spindle more sensitive and spontaneously active

Question 56

What is spinal shock? Symptoms?

Answer 56

Transection of the SC that causes LMNs to lose input LMNs signs, no reflexes

Question 57

What is the recovery of reflexes after spinal shock thought to be due to?

Answer 57

Axonal sprouting below level of transection Expression of receptor phenotypes that are self-activating (5HTC Rs.)

Question 58

What are 5HTC receptors?

Answer 58

Self-exciting | Opens sodium channels

Question 59

What is Decerebrate posturing a result of?

Answer 59

Loss of all strucutre below and including red nucleus

Question 60

How is the myotatic reflex in spasticity?

Answer 60

Hyperactive

Question 61

What is continually active in Rigidity vs. spasticity?

Answer 61

Rigidity: alpha MNs Spasticity: gamma MNs

Question 62

What is decorticate posturing from?

Answer 62

Loss of structure above red nucleus resulting in flexion of upper limb and extension of lower limbs

Question 63

What can Decorticate posturing result from/

Answer 63

Strokes in vicinity of internal capsule

Question 64

What is clonus?

Answer 64

Beats of alternating agonist and antagonist contraction

Question 65

What happens when a muscle is stretched?

Answer 65

Increased AP in 1a fiber EAA released to Alpha MN via NMJ increased Muscle contraction Decreases stretch Stops 1a from firing