Spinal reflexes Flashcards
What is a reflex?
A rapid, involuntary yet stereotyped and coordinated response to a sensory stimulus
What does it mean to be a stereotyped spinal reflex?
The reflex happens in the same way each time
Describe the patellar reflex
Sensory stimulus (tap on the knee) ->
Primary afferent neuron (in dorsal root ganglion of dorsal horn) to directly synapse to a motor neuron (in ventral horn) ->
Results in motor neuron projecting onto the muscle, firing an action potential ->
Causes extensor muscle contraction
Describe the stretch (myotatic) reflex
Counteracting changes in the muscles to correct the stretching
Describe the process of the stretch reflex (myotatic)
- Sensory fibres sense muscle stretch and send signals to the spinal cord.
- Muscle spindle detects the stretch - Direct connection to motor neuron fires ap which contracts the flexor muscles
- Simultaneously, a distinct connection to an inhibitory interneuron, inhibits the firing of motor neurons connected to the extensor, relaxing antagonistic muscle. (Reciprocal inhibition)
What fibres innervate the muscle spindles ?
Ia sensory fibres
Where are muscle spindles particularly abundant?
In muscles involved in fine motor control
Function of a muscle spindle
Proprioceptor
What motor neurons innervate muscle spindles and surrounding muscles?
Alpha and gamma motor neurons
What do gamma motor neurons stimulate and what is their effect?
Intrafusal fibres
- Adjust tension in the spindle
- Spindle cannot become slack
What is kinesthesia?
Being aware of your body moving through space
What is the golgi tendon organ?
Proprioceptor
Function of the golgi tendon organ
Detect muscle tension due to muscle contraction
What does activation of GTO sensory afferents lead to?
Activation of inhibitory interneurons which inhibit neurons that innervate the same muscle (negative feedback)
How is a GTO formed?
Afferent terminals are interlaced with collagen fibrils of tendon
What is the flexor (withdrawal) reflex?
Quick contraction of flexor muscles to withdraw a limb from an injurious stimulus
- Often includes a contralateral element
What receptors are activated during the flexor reflex?
Nociceptive sensory receptors
(noxious)
What type of reflex is the flexor reflex?
Postsynaptic
Describe the parallel after discharge circuit
Activation of multiple excitatory interneurons that converge on a single output cell
- Initial signal is sustained over an extended period of time
Describe the crossed extensor reflex
- Stimulation of pain receptors in the right foot
- Sensory neuron activates multiple interneurons (excitatory and inhibitory)
- Ipsilateral motor neurons to flexor become excited
- Ipsilateral flexor contracts
- Contralateral motor neurons to extensor becomes excited
- Contralateral extensor contracts (motor neurons to flexor is inhibited)
What are central pattern generators?
Local circuits that regulate the pattern of alternating flexion and extension when walking
