Muscle Receptors, Spinal Reflexes, And Central Pattern Generation Flashcards
Do muscle spindles provide negative or positive feedback?
Negative feedback
What 3 things do muscle spindles contribute to?
Locomotion
Kinesthesia
Muscle tone
Group Ia afferent
- Innervate bag and chain
- sensitive to change in length and velocity
- active during phasic or dynamic change of length change
Group II afferents
- innervate chain fibers
- NOT velocity specific, NOT active during phasic length
- most sensitive to absolute length —> steady state phase of length change and static property
Dynamic gamma motor neurons
Sensitive to velocity of length change
Active during dynamic phase
Static gamma motor neuron
- alters spindle sensitivity to length
- active during steady-state phase
Rate- Sensitivity
Bi-directional
Will pause in firing during a fast shortening then resumes steady state firing rate
What do dynamic motor neurons specifically care about?
Velocity of stretch (only bag)
What is the net effect of static motor neurons?
Enhance information on current muscle length (bag and chain)
Take home message of the gamma system
Maintains spindle firing rate within an optimal range for signaling length changes, whatever the optimal length of the muscle
Muscle contraction & GTOs
Muscle contraction —> collagen fibers shorten —> 1b nerve endings are stretched —> increased firing rate
What are GTOs very sensitive to?
Effects of recruitment
What is a myotactic (deep tendon) reflex an excitatory connection between?
Group 1a afferent and alpha motor neurons
Autogenic excitation myotactic (deep tendon) reflex
Monosynaptic excitatory synapse between spindle 1a afferent and alpha motor neurons of the same muscle, resulting in contraction
Synergist activation myotactic (deep tendon) reflex
Group 1a afferents also may have excitatory synapses on motor neurons innervating synergist muscles
Reciprocal Inhibition (deep tendon reflex)
Via Interneuron, activation of group 1a afferents results in inhibition of antagonist
Tonic vibratory reflex
Primary endings respond to vibrations
Contraction of vibrated muscle
Inhibition of antagonist
When is tonic vibratory reflex strongest?
Under isometric conditions
The longer the initial length of the muscle, the stronger the contraction
Recurrent inhibitions
Increase in alpha motor neuron activity increases activity of inhibitory renshaw cell
Excited renshaw cell dampens firing rate of alpha motor neuron
Inverse myotactic reflex
- Golgi tendon organ
- 1b afferents excite inhibitory Interneuron
- inhibits contracting muscle, excites antagonist m
What activates flexion reflexes?
Sensory receptors and afferents
Crossed extension reflex
- concurrent with activation of flexor withdrawal reflex in ipsilateral limb
- occurs in contralateral limb
- inhibits flexors and activates extensors to maintain balance
Key points of central pattern generator
- CPGs or other spinal circuitry encode a basic sequence of rhythmic locomotor activity
- final locomotory pattern will reflect fine-tuning by peripheral sensory input and descending projections from brain
What are abnormal stretch reflexes often associated with?
Abnormal tone
