Spinal Reflexes Flashcards
What is the simplest reflex, found in all muscles?
The stretch reflex.
Describe the stretch reflex.
Muscle spindles are stimulated.
Contraction occurs.
Give an example of a stretch reflex.
Knee jerk reflex.
A sharp tap to a tendon - force is transmitted to muscle fibres, which stretch.
What nerves are activated in the stretch reflex?
What occurs as a result?
Ia afferent nerves (in the muscle spindle).
AP frequency increases in Ia afferents (in the dorsal horn).
Describe how spindle sensory afferents make connections to alpha motoneurons.
One synapse with no interneurons (monosynaptic reflex).
Agonist rapidly contracts.
Describe how spindle sensory afferents make connections to antagonists.
Indirect.
Activates inhibitory interneurons.
Alpha motoneurons are inhibited.
Antagonist relaxes (reciprocal inhibition).
Describe how spindle sensory afferents make connections to the brain.
Travels up dorsal columns.
Thalamus –> somatosensory cortex.
The brain is told information about muscle length.
Describe the inverse stretch reflex.
When the muscle contracts, it pulls on the tendon and Ib afferent nerves from GTOs.
This increases the number of APs.
What does the increase of APs in the inverse stretch reflex cause?
Activation of inhibitory interneurons in the agonist.
Activation of excitatory interneurons in the antagonist.
Information about muscle tension goes to the somatosensory cortex.
What is the result of the inverse stretch reflex?
A large increase in tendon tension causes a collapse in resistance.
This is protective to prevent muscle damage.
Describe the flexor reflex.
- Nociceptive fibres enter the spinal cord.
- They branch and activate interneurons in several spinal segments above the entry point.
- Alpha motoneurons are activated and control the flexor muscles of the affected limb.
What kind of response does the flexor reflex cause?
Ipsilateral flexion.
An increase in APs in nociceptor nerves.
What does an increase in APs of nociceptor nerves in the flexor reflex cause?
Increases activity in flexors (excitatory INs).
Inhibits extensors (excitatory and inhibitory INs).
Excitatory INs excite contralateral extensors.
Other INs synapse with inhibitory neurons and inhibit contralateral flexors.
What effect does the diameter of nociceptive fibres have?
Smaller diameter than muscle spindle afferents.
Conducts more slowly.
Where does sensory information of the flexor reflex go?
The contralateral spinothalamic tract.
