Physiology Lab: Reflexes Flashcards
What is a reflex?
Involuntary response to a stimulus
What does a reflex consist of?
A receptor, sensory input to an integrative centre in the CNS, output via a somatic or autonomic motor nerve and an effector organ
Receptor pathway may be monosynaptic or multi-synaptic
What is the purpose of testing reflexes?
Valuable when determining the nature and extent of neurological disorders
This is because the integrity of the reflex depends on an intact neural pathway between the point of stimulation and the effector organ
Describe how a stretch reflex occurs.
When a muscle is stretched, muscle spindles are stretched and sensory axons are activated. These run in the spinal cord and make direct synapse onto alpha motor neurons.
These generate AP in their axons which run to the muscle and evoke contraction.
Gamma motor neurons innervate and regulate the sensitivity of the muscle spindle.
= monosynaptic relflex by tapping on a tendon
When are monosynaptic reflexes lost?
In diseases affecting peripheral nerves
When are monosynaptic reflexes increased?
Damage to descending motor pathways
What is a flexor reflex?
Withdrawal of a limb following a painful or potentially painful stimulation.
Widespread contraction of flexors throughout the limb and immediate withdrawal.
Contralateral limb is simulatenously extended.
Why does the contralateral limb extend in a flexor reflex?
Collaterals of interneurons that excite ipsilateral flexors cross to the contralateral side of the spinal cord and excite extensor and inhibit flexor motor units at the same segmental level. This supports the weight of the body when flexion withdrawal prevents another limb from making its weight-bearing contribution.
What is reaction time (RT)?
Reactions to external stimuli (voluntary process) requiring processing and choice - this interval to initiate a movement in response to a sensory signal is the reaction time.
What factors cause RT to vary?
- Simple RT (you know what to do when the stimulus arrives) or Choice RT (several options)
- How complex the required response is
- How much attention is devoted exclusively to the task
- Drugs that affect brain function e.g. alcohol
Which parts of the brain are important in the RT?
Basal ganglia
Motor Cortex
What do differences in RT between a simple RT and choice RT tell us?
Differences in RT between these two conditions reflect the time the brain takes to make a selection. This selection involves selecting specific neurons in the motor cortex required to activate the appropriate muscles.
