PoH: Reflexes Flashcards
Define stretch reflex/myotatic reflex
The contraction of a muscle in response to its passive stretching
When a muscle is stretched, the stretch reflex regulates the length of the muscle automatically by increasing its ____
Contractility
(as long as the stretch is within physiological limits)
Define muscle spindle, and give the location
Stretch receptor that signal the length and changes in length of a muscle
They’re located in an independent capsule, parallel to the main muscle
Why do we have a stretch reflex?
Protective mechanism to prevent overstretching
What nerve is activated by a stretch reflex? What does it do?
1a afferent sensory nerves
It increases the number of action potentials in other 1a afferents, projecting through the dorsal horn into the spinal cord
Name the 3 types of connections of spindle sensory afferent nerves
- Directly contacting a motoneurons
- Reciprocal inhibition - indirectly connecting with antagonist muscles
- Travelling up dorsal column to thalamus and somatosensory cortex
What reflex is caused by 1b afferent nerves?
Inverse Stretch Reflex/Golgi-Tendon Organ/Clasp-Knife Reflex
What reflex is caused by 1a afferent nerves?
Stretch reflex
Explain the Inverse Stretch Reflex
Muscle contracts and shortens, pulling on tendon
Sensory 1b afferent nerves from the Golgi-Tendon Organ increases firing of action potentials
Activation of inhibitory interneurones to the agonist muscle. They decrease in contraction strength
Activation of excitatory interneurones to antagonist muscles
Information about muscle tension ascends the dorsal column to the somatosensory cortex
What sensory receptor does the flexor-withdrawal reflex use? What 3 places are they found in the body?
Nociceptors in skin, muscles and joints
What does the flexor-withdrawal reflex lead to?
Withdrawal from painful stimulus and towards the body
If the flexor-withdrawal reflex is caused by a flame to the left foot, which foot responds?
Both.
Ipsilateral flexion in response to pain
To stop us falling over, the contralateral limb extends via excitatory interneurons crossing the spinal cord, to excite the contralateral extensors
In a flexor-withdrawal reflex, how does sensory information ascend to the brain?
Contralateral spinothalmic tract
Define interneurone (in the context of reflexes)
A neurone in between a sensory and motor neurone. They coordinate the motor response needed to address a stimulus and communicate with the brain
Are the following reflexes ipsilateral or contralateral: Stretch Reflex, Inverse Stretch Reflex, Flexor-Withdrawal Reflex
SR - ipsilateral
ISR - ipsilateral
FWR - contralateral
Where in the brain does info about muscle tension in reflexes go?
Somatosensory cortex
Explain the role of higher centres in reflexes?
The brain can modify (e.g. intensity and timing) or inhibit reflex actions.
Can the stretch reflex be overridden?
Yes
What method can doctors use to test the stretch reflex if the patient voluntarily prevents the reflex? Why does it work?
The Jendrassik Manoevre - interlock your fingers in front of your chest and pull hard, trying to pull your hands apart. While doing that, doctor performs a knee-jerk reflex
It works because high activity in upper motorneurones spreads to and depolarises lower level motorneurones, overcoming the descending inhibition
In a withdrawal reflex, more pain causes what? And what’s this concept called?
More powerful pain
Greater spinal segmental spread
More muscles are recruited
Larger response
This is called facilitation
