L26 Spinal Reflexes X Flashcards
(22 cards)
What is a reflex?
A reflex is a rapid, involuntary, yet stereotyped and co-ordinated response to a sensory stimulus
What are pavlovian reflexes?
unlearned reflexes and specifically somatic reflexes, ie those involving the somatic nervous system (visceral reflexes will be considered elsewhere)
What are extensors and flexers?
- Extensors: muscle causing limb to extend
- Flexors: muscle causing limb to flex (bend)
What are spinal reflexes? What are the shared characteristics with muscle reflexes?
Spinal reflexes are reflexes that require stimulation, that are quick, they are involuntary and automatic: you are often aware of them only as they happen and they are difficult to suppress and they are sterotyped ( occur the same way each time).
What is the patellar reflex?
The patellar reflex, also commonly known as the knee-jerk reflex, is a type of stretch reflex. It involves the sudden kicking movement of the lower leg in response to a sharp tap on the patellar tendon, which is located just below the kneecap (patella)
Explain the process of the patellar reflex
- Sensory stimulus is generated
- Motor neurons stimulates extensor muscle contraction.
- Signal is passed to the primary afferent.
- Direct synapse to motor neuron.
What is the Proprioception system?
Sense organs that monitor the position and movement of body parts
Why does the tap on the knee make us want to kick?
The tap on the knee stretches the thigh extensor muscle and associated tendon and sets in motion a process to correct the stretching
What happens to your forearm when the cup you’re holding is filled with liquid?
- Sensory fibres sense muscle stretch and send signals to spinal cord.
- Direct (monosynaptic) connection to motor neuron fires action potential which contracts the biceps muscle
What does the muscle spindle do?
The muscle spindle is a special sensory receptor that detects muscle stretch.
Where are muscle spindles normally found?
Muscle spindles are found in most striated muscle and are adundant in muscles involved in fine motor control.
What is reciprocal inhibition?
a distinct connection to an inhibitory interneuron (black) inhibits the firing of motor neurons connected to the triceps, thus relaxing the antagonistic muscle. This is known as reciprocal inhibition
Why does the muscle spindles have muscles? What is the need?
They stimulate the intrafusal (muscle) fibres to adjust the tension in the spindle as the extrafusal (muscle) fibres of the surrounding muscle contract (so that the muscle spindle is never slack).
What is the Golgi Tendon Organ (GTO)?
GTOs are a another kind of proprioceptors that detect muscle tension due to muscle contraction, not muscle stretch (which is detected by muscle spindles)
How does the activation of GTO sensory (Ib) afferents control the muscle tension?
Activation of GTO sensory (Ib) afferents leads to activation of inhibitory interneurons which, in turn, inhibit motor neurons that innervate the same muscle
Give me an example of negative feedback with relation to the Golgi Tendon organ
the Golgi Tendon Reflex is a negative feedback circuit that regulates muscle tension and protects the muscle (and tendon) from damage when large forces are generated.
What does the flexor (withdrawal) reflex do?
Flexor reflex is a quick contraction of flexor muscles to withdraw a limb from an injurious stimulus (e.g. heat or cut)
It results from the activation of nocieptive sensory receptors or nociceptors
Out of patellar reflex and flexor (withdrawal) reflex, which one is faster?
The patellar reflex (knee-jerk reflex) is generally faster than the flexor (withdrawal) reflex.
Why do we have the activation of multiple excitatory inter neurons in a parallel circuit form?
Activation of multiple excitatory interneurons sustains the response:
’Parallel after-discharge circuit’
What is ‘parallel after-discharge circuit’?
A parallel after-discharge circuit is a neural circuit arrangement in the nervous system where a presynaptic neuron stimulates several neurons in parallel, and these postsynaptic neurons then converge onto a common output neuron.
Explain the crossed extensor reflex
- Stepping on glass stimulates pain receptors in right foot.
- Sensory neurons activated multiple interneurons (Both excitatory and inhibitory).
- Ipsilateral motor neurons (to flexor) excited.
- Ipsilateral flexor contracts.
- Contralateral motor neurons excited.
- Contralateral extensors contracts.
Explain what central pattern generators are
the presence of local circuits that can generate the pattern of alternating flexion and extension are known as central pattern generators
