Physiology of reflexes Flashcards
What are the two classifications of reflexes?
Somatic
Autonomic
What name is given to the orderly sequence of events in a reflex?
Reflex arc
What is the definition of a reflex?
Involuntary, stereotyped but coordinated response to a stimulus
Name an example of the stretch reflex.
Knee jerk
What is the sensory receptor in stretch reflexes?
Muscle spindle
What is the afferent nerve fiber in stretch reflexes?
IA afferents
Where do stretch reflexes synapse?
Spinal cord
What are the motor fibers in the stretch reflex?
Alpha motor neurons
What is the muscle spindle in essence?
Mechanoreceptor
What does the muscle spindle respond to?
Responds to stretch and therefore responds to length changes in the muscle
What is the muscle spindle composed of?
Intrafusal muscle fibers
What are intrafusal fibres made up of?
Non-contractile centre and contractile tissue at the poles
What are the two types of intrafusal fibers?
Nuclear bag
Nuclear chain
What is the motor innervation of the muscle spindle?
Gamma motor neurons as they innervate intrafusal fibers
What is the sensory innervation of the muscle spindle?
Primary nerve endings
What do type 1a afferents detect?
onset of muscle stretch and the rate of change of stretching
What are secondary flower spray endings?
Type II afferents that maintain stratch
What do primary sensory nerve endings innervate?
Nuclear bag
Nuclear chain fibers (mostly by type II)
What happens when a gamma neuron is stimulated?
Causes contraction and takes slack out of spindle while the muscle is contracting even
Where are golgi tendon organs located?
Junction between tendon and muscle
What are golgi tendon organs sensitive to?
Muscle tension
How do golgi tendon organs receive sensory information?
Ib afferents
How does the GTO work?
When muscle is contracting GTO detects tension in contracting muscle
Sensory information is carried into spinal cord
Synapses with interneuron
If tension is excessive, results in inhibition of contracting muscle and therefore muscle relaxation
Protective reflex
What do the muscle spindles and GTOs allow?
Continuous feedback of information to the brain from contracting muscle about its status as the contraction takes place
What do reflexes allow?
Rapid automatic adjustments in the muscle as required
Where are stretch reflexes especially prominent?
Anti-gravity muscles including the neck
Muscles where fine control is required
What do muscle spindles and stretch reflexes prevent?
Overstretching of a muscle by initiating reflex contraction
What does the GTO prevent?
Excessive force generation in a muscle
What does the pathway for the withdrawal reflex show?
Considerable divergence of 1a afferent
What is another name for lower motor neurons?
Final common pathway
What is the relationship between LMN and UMN?
LMN previously stimulated/inhibited by UMN
What does damage to LMN lead to for stretch reflexes?
Reduced/absent stretch reflexes
Flaccid paralysis
