Motor Reflexes Flashcards
How do you tell the difference between a reflex and a volitional movement?
Speed
Reflex will be faster
What is the level of organization for a reflex?
Any CNS level
Does not require cortex for most
What is the level of organization needed for volitional motion?
Requires cortical and subcortical involvement
What is the purpose of a reflex?
Direct and rapid response to sensory stimuli. Often protective
What s the purpose of volitional movements
Response to stimuli; need; desire
What initiates a reflex?
Sensory input
What initiates volitional motion?
Higher cognition
Sensory input
What describe the circuitry of a reflex?
Versus volitional motion circuitry?
Fixed
Variable depending on motion
What is the specificity of reflexes and volitional motion?
Both have high specificity
What is an example of a monosynaptic reflex?
Myotatic reflex
What is the pathway of a monosynaptic reflex?
Afferent —> alpha motor neuron —> excitatory contraction of m.
What is a polysynaptic reflex?
Pathway?
Example?
More than one synpase
Afferent —> interneuron —> another interneon —> alpha MN.
Golgi tendon relfex
What are the reflexes produced at the level of the spinal cord ?
Myotatic
Golgi tendon
Crossed extensor reflex
What are the reflexes produced at the brainstem/midbrian?
Vestibular reflex
Suckling
Pushing food out of move Sucking on fibers Yawning Stretching Cry Following objects w/ head and eye movements Turn head and eyes to sound
What are cortical reflexes?
Placing response
Hopping response
What innervates the intrafusal muscle fibers of a muscle spindle?
Efferent innervation By gamma MNs
What do intrafusal muscle fibers contain?
Contractile components (actin, myosin etc.)
Similar to sk. M.
What does the sensory portion of the muscle spindle consist of?
Nuclear bag fiber
Nuclear chain fiber
Is the sensory portion of a muscle spindle contractile?
No
What innervates the sensory portion of a muscle spindle?
2 afferent neurons
What is the primary afferent of the muscle spindle?
1a fiber to both nuclear bag and chain fibers
What characterizes the 1a primary afferent fiber?
Large
Myelinated
Fast
What is the primary afferent sensitive to?
Length of muscle
Rate of muscle length change
When is the primary afferent fiber discharged?
Discharged even at normal resting muscle length
And sensitive to length and rate of length change
What is the secondary afferent fiber to muscle spindle?
What characterizes this fiber?
Group 2 fiber
Myelinated, smaller, slower
What does the secondary afferent to the sensory portion of the muscle spindle innervate?
Only the nuclear chain fiber
What doe the secondary afferent fiber respond to?
Responds only to changes in length
What is the purpose of having 2 types of afferent fibers?
Allows the cns to get 2 kind of info
Static and dynamic
What is the efferent innervation of Extrafsusal fiber?
alpha MN via NMJ
Where do Gamma MNs work on the muscle spindle? Using what?
What does this initiate?
On intrafusal fibers on the neds of m. Spindles using NMF
Contraction of intrafusal and stretching of muscle spindle
What does the contraction of the intrafusal fibers by gamma MNs do?
Stretches muscle spindles thus sensitizes nuclear bag and chain fibers to further stretches
Does the activity of Gamma MN lead to motion?
No
Where do Alpha MNs work on the muscle spindle? Using what?
What does this initiate?
Extrafusal fibers via NMJ
Releases EAA to non-NMDA receptors
Excited skeletal muscles and contracts it
What does the contraction of skeletal muscle by alpha MNs cause?
Shortening of intrafusal fibers and stops their increased signaling
Will activation of alpha MNs lead to motion?
Yes
What do gamma MNs controL?
Length of sensory portion and thus sensitivity of muscle spindle
What is the myotatic reflex initiated by?
What is the result of this?
Initiated by muscle spindle in response to passive stretch of muscle
Contracts stretched muscle back to normal length
What is the golgi tendon reflex caused by?
Result of the reflex?
Initiated by active contraction muscle felt by golgi tendon organ
Leads to abrupt relaxation of contracted muscle to prevent damage
What is the muscle spindle enclosed by? Embedded where?
Enclosed in capsule in sk. Muscle
Embedded in fusiform capsule
How is the muscle spindle orientation in comparison to skeletal muscle?
Parallel to sk. M. Proper
What makes up the bulk of msucle, extrafusal or intrafusal?
Extrafusal
What is the stimulus for muscle spindle?
Stretching/lengthening of muscle
What does the full myotatic reflex contain?
Seance efferent limb for reciprocal inhibition of antagonist m.
How does the second efferent limb of the myotatic reflex work?
The 1a afferent goes to alpha MNs —> contract agonist
ALSO goes to interneuron in SC that releases GABA —> Alpha MN of antagonist —> relax m.
What is the golgi tendon organ?
Bare nerve ending w/ lots of branches
Where do you find the golgi tendon organ?
What innervates it?
In tendon
Innervated by 1b fiber
What is the golgi tendon reflex pathway? (Does abrupt relaxation of contracted msucle)
1b —> release EAA to non NMDA to interneuron in SC
Interneuron active —> releases GABA to alpha MN
Allows Cl in, hyperpolarizes alpha MNs —> muscle relaxes abruptly
What is the difference between 1a and 1b fibers?
1a afferents are involved in msucle spindle reflex; myelinated, faster
1b afferents are afferents for golgi tendon reflex; less myelinated; slower
What is the presentation of spasticity?
Why does this happen?
Patient RESIST IN A GIVEN DIRECTION a passive stretch of their muscles c their antagonists don’t relax
Hyperactive myotatic reflex increases gamma motor neuron firing(efferent to intrafusal m. Fiber)
What is the cause of spasticity?
Damage to cortex that abolishes activation of the brainstem inhibition region (can’t inhibit antagonist)
What is rigidity?
Contraction of muscles in absence of other stimuli causing resistance of motion in ALL DIRECTIONS
What is the mechanism of rigidity?
Continual activation of alpha-MNs that causes contraction of Ms. w/o stimuli
What causes rigidity?
Loss of cortical influence that inhibits a medullary input to alpha motor neurons
What is altered in spasticity?
Alter stretch reflexes by changing gamma motor neuron firing rate
What is continual active during spasticity?
What does this cause?
Gamma MNs
Contracts intrafusal and lengthens nuclear bag/chain fibers making spindle more sensitive and spontaneously active
What is spinal shock?
Symptoms?
Transection of the SC that causes LMNs to lose input
LMNs signs, no reflexes
What is the recovery of reflexes after spinal shock thought to be due to?
Axonal sprouting below level of transection
Expression of receptor phenotypes that are self-activating (5HTC Rs.)
What are 5HTC receptors?
Self-exciting
Opens sodium channels
What is Decerebrate posturing a result of?
Loss of all strucutre below and including red nucleus
How is the myotatic reflex in spasticity?
Hyperactive
What is continually active in
Rigidity vs. spasticity?
Rigidity: alpha MNs
Spasticity: gamma MNs
What is decorticate posturing from?
Loss of structure above red nucleus resulting in flexion of upper limb and extension of lower limbs
What can Decorticate posturing result from/
Strokes in vicinity of internal capsule
What is clonus?
Beats of alternating agonist and antagonist contraction
What happens when a muscle is stretched?
Increased AP in 1a fiber
EAA released to Alpha MN via NMJ
increased Muscle contraction
Decreases stretch
Stops 1a from firing
