Exam 2 opening questions

What is the definition of a reflex?

Response triggered by a stimulus

What is the term for a diminished reflex? What is the term for an exaggerated reflex?

Hypoactive - diminished

Hyperactive - exaggerated, A-relax - now reflex

What are the five components of the reflex arc?

1. Sensory receptor 

2. Afferent neuron (up to spinal cord)

3. Sensory processing structure unit in spinal cord 

4. Efferent neuron 

5. effector/muscle that contracts

What type of proprioceptor/receptor is involved in a monosynaptic reflex?

• Muscle spindle is stimulated  

• Called monosynaptic because there is only one central synapse

When stimulating/measuring the H-reflex, why is the electrical stimulation applied to both the sensory and motor neurons instead of just the sensory neurons?

• Gives you more control over the experiment 

• Both are in the peripheral

What specifically causes the H-reflex? What is the pathway of the H-reflex through the nervous system?

• Simulation of 1a afferent causes the H-reflex 

• 1a afferent - spinal cord - alpha MNs - muscle (effector) 

• Roughly 35 m/s

What specifically causes the M-response/wave? What is the pathway of the M-response through the nervous system?

• Only the alpha MNs

• Alpha MNs - muscle 

• Roughly 8 m/s

Why does the H-reflex diminish when a high intensity electrical stimulation is applied to a peripheral nerve?

High intensity - Action potential collision

Why does the H-reflex diminish when high frequency stimulation is applied to a peripheral nerve?

High frequency - central synapse refractory period

What happens to the H and T-reflex when the patient voluntarily activates the agonist muscle before the reflex is stimulated? What happens when they voluntarily activate the antagonist muscle?

• If activating the agonist gets bigger, more excitability in the alpha motor neuron.

• Antagonist - gets smaller 

What is an example of an oligosynaptic reflex?

Muscle spindle (1a afferent/interneuron), GTO (1b afferent/interneuron)

What are three differences between monosynaptic and polysynaptic reflexes (think about the H-reflex vs. the flexor reflex)?

• Mono - only one central synapse, 1 sensory neuron, one muscle

• Poly - a lot of central synapse/ interneuron involved, many sensory neuron, many muscles

What happens at the threshold of the tonic stretch reflex?

recruitment/activation of the alpha motoneuron in the muscle group that is being stretched or lengthened 

What happens to muscle spindle activity when a muscle lengthens?

It increases

What happens to the activity of the Ia afferents when a muscle lengthens?

Increases

What happens to the activity of the alpha motoneurons due to the activity of the Ia afferents

Increase

What happens to muscle force due to the activity of the alpha motoneurons?

Increase

What is a pre-programmed reaction/long loop reflex?

 Semiautomatic reaction/intermediate response, in between reflex and voluntary

What is the latency of a pre-programmed reaction?

50-100 m/s

Put the following responses in order from the fastest to the slowest: Reflex, Preprogrammed, Involuntary

1. Reflex (very specific)(weakest)

2. Pre-programmed (broader what can trigger them) 

3. Voluntary

What type of stimulus can trigger a pre-programmed reaction?

Preturbation

What happens to H-reflex when you apply vibration?

Decrease response; presynaptic inhibition