Lecture 8

Question 1

What is a reflex (simplified)

Answer 1

involuntary reaction to some type of stimulus

Question 2

A reflex is a stereotyped response to specific stimuli that are generated by simple neural circuits in the ________ and _________

Answer 2

spinal cord and brain stem

Question 3

One central synapse

Answer 3

monosynaptic

Question 4

Where are the monosynaptic synapses located

Answer 4

in the spinal cord

Question 5

A few central synapses; usually 2-3, with interneurons involved

Answer 5

oligosynaptic

Question 6

Many central synapses; pathway cannot be traced

Answer 6

polysynaptic

Question 7

Describing a reflex as slow, steady state, maintained

Answer 7

tonic

Question 8

Describing a reflex as fast, transient, in response to a change in the stimulus

Answer 8

phasic

Question 9

How would you describe a monosynaptic reflex

Answer 9

phasic

Question 10

How would you describe a polysynaptic reflex

Answer 10

tonic

Question 11

A muscle contraction induced by an external stimulus that cannot be changed by pure thinking

Answer 11

reflex

Question 12

Reflexes are highly __________ to changes in behavioral goals, mainly b/c several different circuits exist to connect sensory and motor neurons, but they cannot be directly controlled ________.

Answer 12

adaptable

voluntarily

Question 13

Why should we study reflexes

Answer 13

1. can assist in the diagnosis of certain conditions

2. help localize injury or disease in the CNS

Question 14

Hypoactive reflexes

Answer 14

absent or weak, often indicate disorder in one or more of the components of the reflex arc

Question 15

__________ can cause both hyperactive and hypoactive reflexes

Answer 15

lesions in the CNS (spinal cord)

Question 16

What is the most common form of hyperactive reflexes

Answer 16

spasticity

Question 17

What does spasticity result in

Answer 17

hypertonia or increase muscle tone

Question 18

What is an example of a disease that causes spasticity

Answer 18

cerebral palsy

Question 19

What does a reflex arc consist of

Answer 19

a sensory element (receptor)
an afferent (sensory) nerve
a central processing unit
an efferent (command) nerve
an effector (for example a muscle)

Question 20

Where is the central processing unit located

Answer 20

in the spinal cord

Question 21

What are the components of the reflex latency

Answer 21

afferent conduction delay (get into the spinal cord)
central processing delay (get through the spinal cord)
efferent conduction delay (down motor to muscle)

Question 22

What would affect each reflex delay (latency)

Answer 22

the location of the tendon (achilles vs. patellar)

Question 23

Where do the monosynaptic reflexes originate from in humans and what do they induce

Answer 23

• Ia spindle afferents

- induce responses in the same muscle or in muscles in the same vicinity (share common functions)

Question 24

What is the H-reflex

Answer 24

technique for examining monosynaptic reflexes

Question 25

Who came up with the H-reflex and when

Answer 25

P. Hoffman in the 1950s

Question 26

How does the H-reflex work

Answer 26

electrically stimulate Ia afferents in a peripheral nerve and recording the motor (reflex) response in the same muscle

Question 27

How is the H-reflex commonly assessed

Answer 27

by stimulating the tibial nerve and measuring the response of the soleus

Question 28

Where would you place the electrode when trying to stimulate the tibial nerve

Answer 28

in the popliteal region of the knee (behind the knee)

Question 29

What two pieces of equipment are needed for the H-reflex test

Answer 29

a nerve stimulator | EMG

Question 30

Why is the H-reflex better than the tendon tap method

Answer 30

it allows for better control

Question 31

What are the 5 components of the standard reflex arc

Answer 31

1. receptor(s) 2. sensory (afferent) neuron(s) 3. central processing unit 4. motor (efferent) neuron(s) 5. muscle(s)

Question 32

In a monosynaptic reflex, what type of receptor is activated to begin the reflex group

Answer 32

primary spindle endings (Ia)

Question 33

In a monosynaptic reflex, which muscle is activated/contracts to complete the reflex loop

Answer 33

same one that was lengthening

Question 34

diminished reflex?

Answer 34

hypoactive

Question 35

exaggerated reflex?

Answer 35

hyperactive

Question 36

why is electrical stimulation of a peripheral nerve applied to both afferent and efferent fibers

Answer 36

a peripheral nerve has both fibers running close together and the electrode cannot be selective between the two

Question 37

what fibers are the first to react to a slowly increasing electrical stimulus

Answer 37

afferent

Question 38

what do afferent fibers induce

Answer 38

reflexive muscle contraction (H-reflex)

Question 39

what do efferent fibers induce

Answer 39

direct muscle contraction (M-response)

Question 40

what is the M-response

Answer 40

direct stimulation of the muscle

Question 41

why is the M-response faster than the H-reflex

Answer 41

b/c it does not have to travel to the spinal cord first

Question 42

voltage, strength of a current measured in Volts or millivolts

Answer 42

intensity

Question 43

strength of the muscular response measured in Volts or millivolts

Answer 43

amplitude

Question 44

how often the stimulation is applied measure in Hertz

Answer 44

frequency

Question 45

further increase in the strength of the stimulation leads to an increase in the _________ and a suppression in the __________

Answer 45

M-response | H-reflex

Question 46

what does the peak-to-peak amplitude of the H-reflex and M-response depend on

Answer 46

the strength of the stimulation

Question 47

Why does the H-reflex increase and then decrease, while the M-response gradually continues to increase until in plateaus and remains at that level

Answer 47

it has to do with the response of the motor neurons to the stimulation as the intensity increases

Question 48

The stimulation of the afferent fiber results in the _______

Answer 48

H-reflex

Question 49

once the afferent fiber is stimulated, the signal travels _______ up the sensory neuron, into the spinal cord where it synapses with an _________

Answer 49

antidromically | alpha motoneuron

Question 50

Once the signal synapses with the alpha motoneuron, it travels __________ down the motor neuron to the target muscle, resulting in a ________ muscle contraction

Answer 50

orthodromically | reflexive

Question 51

the stimulation of the _________ fiber results in a signal traveling orthodromically down the motor neuron to the muscle, resulting in a _____- ______ contraction (M-response wave)

Answer 51

efferent | direct muscle

Question 52

time for M-response

Answer 52

8ms

Question 53

time for H-reflex

Answer 53

35ms

Question 54

why can't a motoneuron generate another efferent AP when an afferent fiber delivers a presynaptic AP to an alpha motoneuron whose axon hillock has just responded to and antidromic efferent AP

Answer 54

b/c of the refractory period

Question 55

sensory neurons conduct action potentials _________

Answer 55

antidromically

Question 56

motor neurons conduct action potentials ___________

Answer 56

orthodromically

Question 57

when can motor neurons also start generating APs antidromically

Answer 57

at high levels of electrical stimulation

Question 58

how does the H-reflex disappear

Answer 58

the antidromic AP from the motor neuron cancels out the antidromic AP from the sensory neuron

Question 59

what does successive stimuli at a high frequency induce

Answer 59

similar M-responses but progressively smaller H-reflexes

Question 60

the refractory period for the central synapse is longer than ________

Answer 60

the refractory period for the axon of the motor neuron