Motor Units And reflexes/Receptors (Fitz) Flashcards
How are the intrafusual and extrafusal fibers innervated?
By gamma and alpha motor neurons respectively
What are the components of a muscle intrafusual spindle?
- non contractile center
- two receptors
1. Ia annulospiral ending
2. II flower spray
What are Golgi tendon organs?
In series with the extrafusal fibers
What do muscle spindles responsible for?
Stretch fibers
Mechanoreceptors
What do muscle spindles do?
Cause reflexes
What is the activity of muscle spindles if the muscle is relaxed?
Almost zero
How do Ia receptors respond?
Detect velocity or dynamic movements
Primary response
What do II muscle spindles respond to?
Amplitude (static)
Secondary response
What is the primary reaction (Ia) to a stretch depolarization?
Phasic stimulation, followed by adaptation
Why is there no gap in activity in the Ia receptors after stretch release (during adaptation)?
Because the alpha motorneurons stops “gap”
What is the stretch reflex?
Mono synaptic reflex where stretch causes contraction. 5 steps
- Muscle stretches
- Depolarization in spindle afferent
- Activation of both alpha and gamma m neurons
- Cause contraction of extrafusal muscle fibers(alpha) and intrafusal
- Contraction of the intrafusal fiber contraction maintains tension in spindle to allow for continued response
Important for muscle tone
What is the Golgi tendon flex?
- Stretch of tendon
- Depolarization
- Increase activity of inhibitory interneuron
- Decrease activity of alpha motor neuron
- Relaxation
What happens normally with the two reflexes?
The spindle fibers and the Golgi tendon organ work together
What happens if you eliminate the alpha motor neuron!
Flaccid paralysis
What happens of you over activate the gamma motor neurons?
Spastic paralysis
What is the final common pathway for spinal reflexes?
Alpha motor neurons
But is it really final?
Really a feedback loop
Muscles are Non linear force generators
What are the components of a reflex arc?
- Sensory receptor
- Primary afferent
- 1-3 CNS synapses
- Motor neuron
- Muscles
What is an example of a complicated or time delayed reflex?
Can have multiple interneurons in series, and also multiple series
What is recurrent inhibition?
Has a motor neuron shut off, either motor neuron itself or an afferent
How can a motor neuron shut of itself?
By sending a collateral that activates an interneuron called a Rensha cell. The Rensha cell shuts off other motor neurons in the area
What is the lengthening reaction?
Light weight –> moderate stretch –> stretch relfex –> contraction (hold weight in place)
Heavy weight –> strong stretch –> inverse stretch –> relaxation
Modulated by gamma-motorneurons –> normal
–> balanced tension
What happens if your gamma motor neurons (descending pathway) cannot modulate the system?
Clasp knife reflex
How does the withdrawal reflex work?
Contraction of flexors
Relaxation of extensors
What is spinal integration?
Motor control builds on underlying circuits
Descending pathways feeding to the first two
Reflexes –> Central pattern generators –> alpha MN
What happens when you remove upper motor layers?
Reveals lower forms of controls.
Dicks hallpike) (VOR
What is spinal shock?
Shock after cutting the spinal cord
Initial period of no reflexes, however then we get reflexes and maybe clonus
