Reflex Arc Flashcards
What is the receptor?
Site of the stimulus
What are the 5 components of a reflex arc?
- Receptor
- Sensory neuron
- Integration center
- Motor neuron
- Effector
What does the sensory neuron do?
Transmits the afferent impulse
What does the integration center do?
Either monosynaptic or polysynaptic region within the CNS
What does the motor neuron do?
Conducts efferent impulses from the integration center to the effector.
What is the effector?
Muscle fiber or gland that responds to the efferent impulse.
What are the 2 components the nervous system needs in order for skeletal muscle to perform in a normal coordinated fashion?
- Length of muscle.
2. Amount if tension in the muscle
Length if muscle is provided by what?
Muscle Spindles
Amount of tension is provided by what?
Golgi tendon organs.
What are muscle spindles composed of?
Muscle fibers called Intrafusal Muscle Fibers that are wrapped in a connective tissue capsule that serves as a receptive surface.
Where is the contractile portion of a muscle spindle?
What type of fiber is it innervate by?
The ends are contractile.
Innervated by gamma efferent fibers
*note: contractile skeletal fibers are Innervated by alpha efferent fibers.
How does a muscle spindle operate?
Gamma efferent signals from the brain cause the muscle spindles to be more taut (ready for a vertical jump) or less taut, depending on the situation.
How does stretching activate a muscle spindle?
It sends an afferent impulse to the spinal cord.
The greater the stretch, the higher the impulse frequency.
Tapping the patellar tendon quickly causes what?
Stretching of the quadriceps & starts the reflex action.
What are the 2 components of a stretch reflex?
- Monosynaptic Component
2. Polysynaptic Component
What happens during the monosynaptic component?
- There is an afferent impulse sent to the spinal cord.
- it synapses with an alpha motor neuron in the ipsilateral ventral horn.
- causing immediate contraction of the quadriceps = knee extension.
What happens during the polysnaptic component?
- there is an afferent signal sent to the spinal cord.
- it synapses with an Inhibitory Interneuron which subsequently synapses with the ventral horn alpha-motor neuron for the antagonist muscle.
What is the net result of the monosynaptic & polysnaptic components?
Reciprocal Inhibition
Quads contract & hamstrings relax
What is the stretch reflex?
When the brain sends commands to the gamma-motor neurons setting a muscle’s length (or tone).
Ex: knees don’t buckle during a squat.
