Spinal Reflexes Flashcards
What is the simplest reflex?
The stretch reflex
What provides information for the stretch reflex?
Muscle spindles (monitor muscle length)
How does a muscle stretch reflex affect muscle spindles?
The muscle stretch causes the spindle to stretch
This activates 1a sensory nerves in the muscle spindle
This increases the number of APs in afferent nerves
How many connections do spindle sensory afferent fibres make?
3
How does a stretch reflex affect the stretched muscle?
The first connection of the afferent fibres activates the alpha-motorneuron fibres to the stretched muscle
This causes rapid contraction of the AGONIST muscle.
This is a monosynaptic reflex
How do afferent sensory fibres connect ot antagonist muscles?
spindle afferent fibres activate inhibitory interneurons
They decrease activation of alpha-motorneurons to antagonist muscles.
Tbis causes the antagonist to relax (reciprocal inhibition)
How do spindle afferent fibres connect to the brain?
They ascend in dorsal columns and connect with somatosensory cortex to tell the brain about the muscle length.
How does the inverse stretch reflex affect the golgi tendon organ?
- Muscles contracts & shortens
- Tendon is pulled and 1b sensory nerves from GTO fire more APs
How does the inverse stretch reflex affect muscles?
The afferent nerve fibres from the GTO affect:
- Activates inhibitory interneurones to the agonist muscle (weakens contraction)
- Activates excitatoy interneurones to antagonist muscles
How does information from the inverse stretch reflex reach the brain?
Info about the muscle tension ascends the 1b sensory afferent fibres in dorsal columns to somatosensory cortex.
What is the purpose of the inverse stretch reflex?
Prevents muscle contracting so hard the tendon tears from the bone (think sudden release of muscle tension when losing at arm wrestling)
Is the inverse stretch reflex poly- or mono- synaptic?
Polysynaptic
What receptors are involed in the Flexor (withrdrawal) reflex?
Nociceptors or pain receptors in the skin, muscles and joints
Whats the purpose of the flexor (withdrawal) reflex?
To withdraw the body part from painful stimulus (and towards the body).
What does increased APs from pain receptors cause in flexor muscles?
Increased activity via excitatory neurons