Term
| What are the 3 essential aspects of all reflex arcs? |
|
Definition
1. Sensory receptor
2. Afferent fibers
3. Interneurons and motor neurons |
|
|
Term
| Describe the negative feedback loop that regulates reflex arcs? |
|
Definition
1. Initial stimulus (lowering of arm) causes neurons to fire sensing this displacement
2. In response, muscle contraction occurs to counter this motion (raising of arm)
3. The countering of motion (raising of arm) decreases sensory inputs, leading to a decreased contraction response as you approach your initial position |
|
|
Term
| What are the 5 steps involved in a reflex arc action? |
|
Definition
1. Sensory receptors firing
2. Afferent nerve fibers going to CNS fire
3. Central (localized) synaptic connections with interneurons or motor neurons
4. Efferent motor neurons leading back from the CNS
5. Effectors (muscles, etc.) |
|
|
Term
| How do higher brain centers affect reflex arcs? |
|
Definition
Based on sensory inputs the higher brain functions can:
1. Modulate motor components of the response
2. Modulate sensory components of the response (i.e. sensory sensitivity) |
|
|
Term
| Will a spinal cord injury affect reflex arcs? If so, how? |
|
Definition
1. Yes. The automaticity of the reflex remains due to the control of localized circuits.
2. Without the input of higher brain areas, the reflexes can however be stronger or weaker then they originally were |
|
|
Term
| How do stretch receptors work and what type of motion do they respond to? |
|
Definition
1. Mechanical deformation (stretching, hence the name) causes these receptors to fire, sensing a change in muscle length as well as change in rate of muscle length (dL/dt)
2. Stretch fibers sense elongation |
|
|
Term
| How are stretch receptors arranged in relation to muscle fibers? |
|
Definition
|
|
Term
| How do Golgi tendon organs function and what do they sense? |
|
Definition
1. While elongation of a muscle will not cause stress in GTO's due to elasticity of muscle fibers, contraction will put a compressive force on them, causing them to fire
2. GTO's sense contraction |
|
|
Term
| Name two factors that contribute to the improvement of reflex compensation |
|
Definition
1. Reciprocal inhibition of stretch response in antagonistic muscle (bicep/tricep for example)
2. Voluntary excitatory inputs from higher brain levels (alpha and gamma neurons) |
|
|
Term
| What part of the muscle do gamma fibers excite and what role does this accomplish in muscle contraction? |
|
Definition
1. Gamma fibers excite and cause muscle spindle ends to contract, stretching the stretch receptors during contraction
2. This causes stretch receptors to continuously fire during contraction, and allows the spindle fibers to stay at the same length as the muscle fibers (important for muscle orientation sensing) |
|
|
Term
| What is crossed extension reflex? |
|
Definition
| A more complicated reflex response from which a sensory input from one joint triggers a response in multiple joints |
|
|
Term
| Disturbances in flexor/extensor balance typically manifest how? |
|
Definition
| Abnormal resting limb postures as well as hypo and hyper reflexivity |
|
|
