Motor control lab Flashcards
What is a stretch reflex?
a stretch reflex causes contraction of a skeletal muscle (the effector) in response to stretching of the muscle
Describe the stretch reflex arc
A monosynaptic reflex arc
How does a stretch reflex occur?
by activation of a single sensory neuron that forms one synapse in the CNS with a single motor neuron
How can stretch reflexes be elicited?
by tapping on the tendons attached to muscles at the elbow, wrist, knee and ankle joints
What are muscle spindles?
sensory receptors in the muscle that monitor changes to the length of the muscle
Describe the stretch reflex
- slight stretching of the muscle stimulates muscle spindles
- muscle spindles generate nerve impulses that propagate along a somatic sensory neuron through the dorsal root of the spinal nerve and into the spinal cord
- In the cord (integrating center), the sensory neuron makes an excitatory synapse with and activates a motor neuron in the ventral gray horn
- If impulse is strong enough, impulses will arise in the motor neuron and propagate along its axon to the muscle
- Acetylcholine is released at the neuromusculor junction, triggering APs to contract the muscle
Where does a motor neuron axon extend?
extends from the spinal cord into the anterior root and through peripheral nerves to the stimulated muscle
What is an ipsilateral reflex?
sensory nerve impulses enter the spinal cord on the same side from which motor
nerve impulses leave it.
All monosynaptic reflexes are
ipsilateral.
How does the stretch reflex prevent injury?
Preventing the overstretching of muscles
How is muscle tone maintained?
- large-diameter motro neurons innervate typical skeletal muscle, while smaller diameter motor neurons innervate smaller specialised muscle fibers within the muscle spindles
- This allows regulation from the brain
- By adjusting how vigorously a muscle spindle responds to stretching, the brain sets an overall level of muscle
tone
What is the function of proprioceptors in the joints?
Sensors that provide information about joint angle, muscle length, and muscle tension, (i.e position of the limb in space)
How is information from proprioceptors received in the brain?
APs reach the cerebellum and transmits this into information allowing adjustment and fine tuning of coordination
what are muscle spindles?
found in skeletal muscle and provide information about changes in muscle lengths and participate in stretch reflexes
Where are muscle spindles most predominant?
In the muscles of the limbs
Describe the muscle spindle structure
- Each muscle spindle consists of several slowly adapting sensory nerve endings that wrap around specialized
muscle fibers, called intrafusal muscle fibers (intrafusal = within a spindle). - A connective tissue capsule encloses the sensory nerve endings and intrafusal fibers and anchors the spindle to
the endomysium and perimysium
Describe the arangement of muscle spindles
Interspersed among most skeletal muscle fibers and aligned parallel to them
- more plentiful in muscles that produce fine movements
Which muscles do not contain any muscle spindles?
the muscles of the middle ear
What are gamma motor neurons?
These motor neurons terminate near both ends of the intrafusal fibers and adjust the tension in a muscle
spindle to variations in the length of the muscle.
E.g. when a muscle shortens, gamma motor neurons stimulate the ends of the intrafusal fibers to contract
slightly.
What are golgi tendon organs?
- also called neurotendinous receptors
- located at the junction of a tendon and a muscle
- provide information about changes in muscle tension
What is the importance of golgi tendon organs?
They initiate tendon reflexes and protect tendons and associated muscles from damage due to excessive tension
What happens when a tendon reflex is initiated?
When tension is applied to a muscle, the tendon organs generate nerve impulses that propagate into the CNS,
providing information about changes in muscle tension.
Tendon reflexes decrease muscle tension by causing muscle relaxation
What types of joint kinaesthetic receptors are there?
- free nerve endings
- ruffini corpuscles
- pacinian corpuscles
- articular ligaments
Which joint kinaesthetic receptors respond to pressure?
- free nerve endings
- ruffini corpuscles
What do pacinian corpuscles respond to?
acceleration and deceleration of joints during movement
What do articular ligaments respond to?
contain receptors similar to tendon organs that adjust reflex inhibition of the adjacent muscles when excessive strain is placed on the joint
What are the different groups of axons in the peripheral nerve?
Grouped according to conduction velocity
- A
- B
- C
How are A axons further categorised?
- Aalpha
- Abeta
- Agamma
- Adelta
What are the features of C axons?
unmyelinated
What are the features of B axons?
Thinly myelinated and are preganglion sympathetic and are therefore not found in peripheral nerves
Describe the axons of nociceptors
- small myelinated Adelta
- unmyelinated group c
How can you work out the diameter of an axon?
only if conduction velocity if known (and vice versa)
Using Hursh’s conversion factor
What events make up the monosynaptic circuit for the knee jerk reflex?
o Stimulus (tendon tap) stretches muscle
o activates muscle spindle receptors
o conduction along afferent (sensory) fibres (Ia afferent)
o transmission at synapses between Ia afferent and motoneurone
o conduction along efferent (motor) fibre
o neuromuscular transmission
o excitation contraction coupling
o twitch contraction of skeletal muscle
Explain why vibrating tendons leads to errors in perception of joint angles
- vibration distorts perception of static joint angle and movement and causes errors in the end point of movement
- muscle spindle afferents are activated by vibration which evokes perceptual changes
- bias in perception appears to be related to the difference between vibration and movement evoked activity in the muscle spindle afferents
Describe a non-invasive method of demonstrating descending motor pathways connecting with muscles
- magnetic stimuli (principle of electromagnetic induction) applies over the motor cortex and activates the corticospinal tract
-APs produces in pyramidal neurons, which have long axons descending to the spinal cord - These descending motor fibres connect directly or indirectly with motorneurons and therefore when activated,
twitch contractions are elicited in skeletal muscles
