Sensorimotor control Flashcards
What is a reflex?
Rapid, involuntary, stereotyped and coordinated response in response to a sensory stimulus
What are learned reflexes called?
Pavlovian reflexes
What are spinal reflexes?
Reflexes involving the somatic nervous system
What are somatic reflexes?
Same as spinal reflexes
What is the dorsal root ganglion (DRG)?
Collection of cell bodies of afferent sensory neurons
What is an example of a monosynaptic reflex?
Patellar reflex
How does the patellar reflex work?
- Sensory stimulus causes a signal to be sent down the primary afferent sensory neuron, travels through the DRG to the spinal chord
- Sensory neuron synapses directly onto a motor neuron
- Motor neuron stimulates the extensor muscle to contract, causing the knee to jerk
- Inhibitory interneurons inhibit innervation to the flexor muscle to make it relax (reciprocal inhibition)
What is the patellar reflex?
Knee jerk reflex
What are extensor muscles?
Muscles which cause limbs to extend when they contract and increase the angle between the members of a limb e.g. contraction of the triceps causes the arm to straighten
What are flexor muscles?
Muscles which cause limbs to flex (bend)
What is a monosynaptic reflex?
A reflex where only one synapse is involved meaning there is direct communication between the sensory and motor neurons
What is the patellar reflex an example of?
Stretch (myotatic) reflex
What is a myotatic reflex?
Stretch reflex
Why does the patellar reflex happen?
Tapping on the knee stretches the thigh extensor muscle and associated tendon which is corrected by the contraction of the extensor muscle which causes a knee jerk
What is the proprioceptive system?
The system responsible for maintaining posture/balance and awareness of limb positioning
What is reciprocal inhibition?
When an inhibitory interneuron inhibits firing of motor neurons connected to the antagonising muscle involved in the reflex, which forces it to relax so it can’t oppose the movement of the agonist muscle
What is the muscle spindle?
Sensory receptor which detects muscle stretch
How is muscle stretch detected?
By the muscle spindles
What are proprioceptors?
Sense organs that monitor the position and movement of body parts
What kind of receptor is the muscle spindle?
Proprioceptor
Where are muscle spindles found?
In most striated muscle
Where are muscle spindles especially abundant?
Muscles involved in fine motor control e.g. hand
Which class of sensory afferent are muscle spindles innervated by?
Ia
Which class of motor neurons do Ia sensory fibres provide feedback to?
Alpha
Which class of motor neurons are muscle fibres themselves innervated by?
Gamma
How do gamma motor neurons control muscle spindles?
Stimulate the muscle fibres within the muscle spindle to maintain tension so the spindle never slackens
What are the muscles within the muscle spindles called?
Intrafusal
What is the Golgi Tendon Organ (GTO)?
Sensory receptor which detects tension due to muscle contraction
What kind of receptor is the GTO?
Proprioceptor
Where is the GTO found?
In tendons
What is the difference between muscle spindles and GTOs?
GTOs detect tension due to contraction, not stretch which is detected by muscle spindles
Which class of sensory afferent are GTOs innervated by?
Ib
What does innervation of GTO sensory Ib afferents cause?
Activates inhibitory interneurons which inhibit alpha motor neurons which are innervating the same muscle
What is the purpose of the Golgi Tendon Reflex?
Negative feedback circuit which regulates muscle tension in order to protect the muscle/tendon from damage
What are tendons?
Fibrous connective tissue which attaches muscle to bone
What stimulus is the flexor (withdrawal) reflex a response to?
Painful/injurious stimulus
Which receptors are involved in the flexor reflex?
Nociceptors
What is the flexor (withdrawal) reflex?
Quick contraction of flexor muscles to withdraw a limb from an injurious stimulus
What is an example of a polysynaptic reflex?
Flexor (withdrawal) reflex
What do nociceptors detect?
Potentially damaging stimuli
What is a parallel after discharge circuit?
Where a neuron inputs onto several different chains of neurons which all converge onto the same output neuron
What is the purpose of a parallel after discharge circuit?
The result of the initial signal is sustained over an extended period