Spinal Reflexes Flashcards
Where is the stretch reflex found?
in all muscles using information from muscle spindles
When does the stretch reflex occur?
following a sharp tap to the inelastic tendon
Is the stretch reflex by which the alpha motor neurone is activated, monosynaptic or include interneurones?
monosynaptic
Where is the force from the tendon transmitted to?
muscle fibres which are more elastic than tendons and are able to stretch to activate the spindle
What happens after activation of the muscle spindle?
there is an increased number of action potentials that enter the spinal cord in afferent neurones through the dorsal horn
What are the 3 outcomes of activation of the muscle spindle in the stretch reflex?
- alpha motor neurone of the muscle that was stretched is activated (monosynaptic) - is the agonist and causes contraction
- the antagonist muscle relaxes (stretches) by reciprocal inhibition
- spindle afferent information ascends in dorsal columns to brain
What is reciprocal inhibition?
- spindle afferents activate inhibitory interneurones
- interneurones inhibit activation of alpha motor neurones to the antagonist which then relaxes
What is the other name given to the Golgi-tendon organ reflex?
inverse stretch reflex
What do the Golgi Tendon Organs monitor?
muscle tension
What is the purpose of the GTO reflex mechanism?
to prevent the muscle contracting so hard that the tendon insertion is torn from the bone
Does the GTO reflex mechanism work monosynaptically or polysynaptically?
involves lots of interneurones
What effect does the GTO reflex have on the agonist muscle when it contracts?
- muscle contracting pulls on tendons and sensory nerves from GTO, sending APs
- synapses with an inhibitory interneurone
- ultimately leads to decrease in contractile strength
What effect does the GTO reflex have on the antagonist muscle?
- muscle contracting pulls on tendons and sensory nerves from GTO, sending APs
- synapses with excitatory interneurones to antagonist muscles which may contract a little
Where does the information from the GTO ascend to?
once the information from the GTO reaches the spinal column, as well as there being a reflex action, the information also ascends in the dorsal columns to the somatosensory cortex in the brain to provide info about muscle tension
What causes GTO discharge?
muscle contraction
Flexor reflexes (withdrawal reflexes) use information from where?
pain receptors (nocireceptors) in skin, muscle and joints
What do flexor reflexes do?
withdraw part of the body from a painful stimulus by flexing the affected part
How does the flexor reflex result in the withdrawal of the limb?
- increased sensory APs from the pain receptors
- flexor muscles are activated via excitatory interneurones
- extensor muscles are inhibited via excitatory and inhibitory interneurones
In what tract does the information from the flexor reflex ascend?
contralateral spino-thalamic tract
How does the flexor reflex pass information so that contralateral limbs can act with the affected limb?
- several excitatory interneurones cross the spinal cord to excite the contalateral extensors
- at the same time, via a number of interneurones the contralateral limb flexors are inhibited
What will inhibit the GTOs from preventing contraction if it is important that the contraction is maintained?
descending facillitatory and inhibitory inputs to the alpha motor neurones
What can prevent a stretch reflex from being evoked?
strong descending IPSPs to alpha motorneurones
What pathways do the gamma motorneurones depend on for their activity?
descending pathways
What would happen to the muscle if discharge to the muscle from the gamma motroneurone was increased?
muscle become resistant to stretch and said to be ‘spastic’
