Reflex & Voluntary Control of Posture & Movement

Question 1

Define reflex activity

Answer 1

subconscious response brought about by PNS stimulation

Question 2

Reflex arc is

Answer 2

the basic unit of integrated reflex activity/nervous pathway for a reflex action

Question 3

5 components of a reflex arc are?

Answer 3

1. Receptor/Sense/End organ
2. Sensory/Afferent neuron
3. Integration center
4. Motor/Efferent neuron
5. Effector organ

Question 4

Define effector organ

Answer 4

the structure in which response to stimulus occurs

Question 5

Name reflexes classified according to their function

Answer 5

Extensor/anti-gravity reflex

Flexor/protective reflex

Question 6

Give two examples of monosynaptic reflex.

Answer 6

Knee-jerk reflex

Stretch reflex

Question 7

Differentiate monosynaptic from polysynaptic reflexes

Answer 7

Monosynaptic have only one synapse between the sensory neuron and the motor neuron at the integration center
Polysynaptic reflexes involved interneurons inbetween the sensory and motor neuron

Question 8

Classic example of polysynaptic reflex

Answer 8

withdrawal reflex

Question 9

Difference between autonomic and somatic reflexes

Answer 9

Autonomic - made of autonomic fibers, involve smooth and cardiac muscle
Somatic - made of somatic nerve fibers, involve skeletal muscle (for flexion and extension at joints)

Question 10

State the types of reflexes based on clinical significance

Answer 10

Superficial reflexes (mucous membrane reflexes like corneal reflex and conjunctival reflex and skin reflexes) 
Deep reflexes (ellicited from structures deep to skin like tendons) 
Visceral reflexes (include oculocardiac reflex, carotid sinus reflex, & pupillary reflex)

Question 11

What are pathological reflexes?

Answer 11

Those ellicited only in pathologic conditions

Question 12

State the conditions under which individuals show positive Babinski sign.

Answer 12

1. UMN lesions
2. In infancy because pyramidal tracts are unmyelinated
3. During deep sleep

Question 13

Name three types of pathological reflexes

Answer 13

1. Babinski reflex
2. Clonus
3. Pendullar movements

Question 14

What is clonus?

Answer 14

Repeated, jerky involuntary movements when deep reflex is initiated, instead of it being smooth and continuous

Question 15

What stimulus causes ankle clonus and what is the response?

Answer 15

Sudden dorsiflexion of foot initiates repeated plantar flexion as calf muscles repeatedly contract

Question 16

What are the properties of reflexes?

*Hint: there are 7

Answer 16

1. One-way conduction / Bell-Magendie law
2. Reaction time
3. Summation
4. Definite recruitment
5. After discharge
6. Rebound phenomenon
7. Fatigue

Question 17

Define a subliminal stimulus

Answer 17

One that is not enough to initiate a reflex; threshold is below conscious perception

Question 18

What are the two types of summation in a reflex arc?

Answer 18

Spatial summation

Temporal summation

Question 19

Differentiate spatial summation from temporal summation.

Answer 19

Spatial summation involves more than one efferent nerve fiber supplying the same muscle such that when a subliminal stimulus is applied separately to each, there is no response, but when all are stimulated at once, it causes the muscle to contract

Temporal summation refers to one nerve fiber supplying a muscle. When subliminal stimulus is applied, there is no response, but when it is applied continuously, then over time it is summated to cause contraction of the muscle.

Question 20

How is sublimal fringe related to spatial summation?

Answer 20

It’s a phenomenon in which the tension developed when nerve fibers are stimulated all together at once is greater than if they are stimulated separately. Spatial summation requires that nerve fibers must have subliminal stimulus applied so that there can be a response.
Sublimal fringe is an effect of spatial summation.
*NOTE: applies to nerve fibers that DO NOT overlap

Question 21

How is occlusion different from sublimal fringe?

Answer 21

While sublimal fringe the tension developed is greater when both fibers are stimulated at the same time, in occlusion, the tension developed is greater if both fibers are stimulated separately than if they they are stimulated all at once.
Occlusion is a result of overlapping fibers while sublimal fringe is seen in non-overlapping fibers

Question 22

Define recruitment.

Answer 22

successive activation of muscle fibers (motor units) to increase force of contraction

Question 23

Factors affecting reaction time.

Answer 23

1. Velocity of conduction
2. Synaptic delay
3. Length of axon

Question 24

Where is the first place fatigue occurs in a reflex arc?

Answer 24

Integration center

Question 25

Reciprocal innervation is a result of …

Answer 25

reciprocal innervation

Question 26

Describe the crossed extensor reflex.

Answer 26

Seen in UMN lesions, it’s when in one limb extension and flexion of a group of muscles occurs, and in the opposite limb, the opposite group of muscles are extended and flexed

Question 27

Factors that cause increase in gamma motor neuron discharge.

Answer 27

Sudden unexpected movements
Stress and anxiety
Stimulation of skin especially by noxious stimuli
Descending excitatory input from brain

Question 28

What does ‘alpha-gamma coactivation’ imply?

Answer 28

When excitatory signals descend through spinal cord from brain, both alpha and gamma motor neurons are activated

Question 29

What’s the difference in the effects of activation of gamma and alpha motor neurons on muscle contraction?

Answer 29

When gamma motor neurons are activated, they don’t cause a direct contraction. Instead, they cause shortening of intrafusal fibers = stretch of nuclear bags of spindles = impulses initiated in Ia fibers = reflex contraction of muscle

When alpha motor neurons are activated, they directly cause contraction because they innervate the extrafusal fibers which unlike the intrafusal fibers are strong and plenty enough to cause contraction

Question 30

State the two kinds of afferent fibers to muscle spindles

Answer 30

1. only one primary ending (group Ia fibers)

2. up to 8 secondary endings (group II fibers)

Question 31

Give the functions of Ia afferents and group II afferents?

Answer 31

Ia fibers detect velocity of change in muscle length (dynamic response)

Group II afferents detect static response (which does not involve change in length)

Question 32

Hyperactive reflex means what part of the reflex arc is damaged?

Answer 32

The descending fibers in the spinal cord involved in inhibition are no longer inhibiting the alpha motor neurons

Question 33

Differentiate afferent Ia and II sensory endings from group Ib fibers?

*BOTH ARE MYELINATED

Answer 33

Ia and II fibers
-are found in stretch spindles

Ib fibers
-are find in Golgi tendon organs

Question 34

The receptor for the inverse stretch reflex is the…

Answer 34

Gogli tendon organ

Question 35

True or false: Golgi tendon organs have high threshold.

Answer 35

False: Golgi tendon organs have a low threshold

Question 36

3 factors determining discharge of alpha motor neurons.

Answer 36

1. Stretch spindle discharge
2. Golgi tendon organ discharge
3. Reciprocal innervation

Question 37

Describe the mechanism of the withdrawal reflex.

Answer 37

1. Noxious stimulus is applied and nociceptors shoot off signals
2. Signals travel through primary sensory neurons
3. Primary sensory neurons synapse with interneurons
4. Interneurons synapse with alpha motor neurons
5. alpha motor neurons go to supply the ipsilateral flexors’ extrafusal fibers causing flexion
6. at the same time collateral branches cause inhibition of extensors (reciprocal inhibition)

*at the same time the primary sensory neuron synapses with ipsilateral alpha motor neurons, it also synapses with the contralateral alpha motor neurons which sends signal up spinal cord to causes contraction of contralateral antigraviy muscles to prevent person from losing balance.