Spinal Reflexes Flashcards
what is a motor unit?
single motor neuron and the muscle fiber it innervates
what is the size principal for motor units?
more units involved means more tension generated
what is a type I muscle fiber?
slow twitch (higher fatigue resistance, many mitochondria, posture maintenance)
what is a type IIb
fast twitch fatigue able (abundant glycogen, larger fiber diameter, fast contraction, high tension but low endurance)
with exercise which muscle fibers can switch?
IIb can switch to IIa
(aging or stopping training with revert the fibers)
which fiber type is darker in appearance?
slow twitch is darker, fast is lighter
how does the primary motor cortex and other brain centers command movement in the body?
No specific muscle motor units in a bundle that can be ordered to contract by the primary motor
cortex. It can only modulate the
contraction in controlling the
execution of the movement.
contraction of whole muscle proceeded by size principal
according to the size principal what fires first?
slow twitch and small motor units first, as more needed bigger/faster become recruited
what are S motor units?
fibers that are small in size and generate ow tension, require little ATP, good for waking or jogging
which fiber type generates lactic acid?
fast twitch
what is the common nerve muscle ratio for motor units?
1:600 (ocular muscles are 1:3)
what determines movement within specific parameters?
feedback
If the motor action is not within the required parameters, what happens?
the number and activation of motor units involved will be adjusted to correct the movement (i.e., learning and memory is involved with this as well)
during sustained activity how do the motor units react?
can rotate through which units are firing to hep resist fatigue it will eventually fatigue (we become less and less precise with time preforming the activity)
what are characteristics of reflexes?
repeatable, directed and purposeful, rapid
by definition reflexes are:
involuntary`
what are Renshaw cells?
inhibitory cells that control surrounding neurons
what are A ang G motor fibers?
a for extrafusal muscle fibers
g for intrafusal
what do extrafusal fibers do?
generate force
does g fibers generate force?
no they are too small to generate force
(they adjust sensitivity in the muscle spindle)
what does the muscle spindle do?
sense muscle length and rate of change (dynamic)
what does co-activation of a and g allow?
muscle spindle remains sensitive to change in length even as the muscle shortens (helps keep spindle from opposing the skeletal muscle and helps smoothen out movement)
what are the two types of length receptors in muscle?
intrafusal (nuclear bag) and nuclear chain fiber
what are intrafusal fibers?
-high compliance and can rapidly
adapt to prolonged stretch.
- Intrafusal fibers mediate the phasic or “dynamic” response. Group Ia afferents detect the velocity of
length change. These are phasic receptors
what happens when the muscle is stretched?
When the muscle is stretched, the mechanoreceptors open on the Ia afferent and open sodium channels (i.e., depolarization).
Nuclear chain fibers are innervated by ______ and are involved in what type of response?
Group II afferents
These fibers are involved in static response
what kind of endings to DYNAMIC gamma motor neurons have? what do they innervate?
flower spray that innervate mainly nuclear bag
what kind of endings to STATIC gamma motor neurons have? what do they innervate?
flower spray also but innervate nuclear chain fibers instead
group II afferents are what kind of receptor?
tonic, give info on where limb is whether it is moving or not
what effect does dampening or smoothing out the movement have?
prevents oscillation or jerky movements
monosynaptic (jerk reflex) reflex responds to change in_____
muscle length
(rapid stretch of muscle triggers the reflex)
reflex establishes _____
tone (in resting muscle to oppose gravity)
what three circuits can modulate the monosynaptic reflex?
reciprocal innervation
Renshaw arc
gamma efferent
what is reciprocal innervation?
afferent Ia can stimulate the interneuron, enhance action of agonist and inhibit antagonist muscles increasing the efficiency of the contraction for the agonist muscle because less energy will be needed to move it (because it will NOT be opposed by antagonist)
renshaw arc do what?
group of interneurons that cause inhibition of a motor neurons preventing too much response or response from unwanted muscle groups (feedback inhibition)
baclofen is used to _______
treat muscle spasticity
what is the primary function of the Golgi tendon organ?
equalize muscle tension between antagonist and agonist to help reduce tension in each muscle preventing damage
what is the seocndary function of the golgi tendon organ?
prevent so much tension that the tendon rips off the bone
what types of responses can be generated from the golgi tendon organ?
dynamic and static responses, meaning it will respond to rate of change in muscle tension and constant tension imposed by the muscle
The _________ will activate an inhibitory interneuron. This will inhibit the anterior motor neuron. This local circuit will not affect adjacent muscles
the above is an example of what?
sensory afferent (Type Ib)
feedforward inhibition
are antagonist muses activated by golgi?
yes they become activated by interneurons during the Golgi tendon reflex
why does the golgi activate the agonist muscles?
helps to relieve stress from the stretched tendon
what is the flexor withdraw reflex?
motor response to protopathic stimuli that cause perception of pain
on the ipsilateral side of the pain, what happens to the muscles?
the flexors are activated to move you away from the pain stimulus
the extensors are inhibited to reduce them resisting the movement
on the contralateral side of the pain what is happening to the muscle groups?
the flexors are inhibited and extensors are activated but ultimate you do not want much movement on this side so that this side can act as a stabilizer
what is another name for the pain reflex?
crossed extensor reflex
what do divergence circuits allow for?
spread reflex to the necessary muscles
what is after discharge?
continued rate of flexor contraction due to recurrent pathways (protects the flexors because it allows the tension to be released more slowly)
what determines the after discharge?
intensity of the sensory stimulus, pain has high AD (reflex will fatigue as it runs out of NT)
what does the after discharge of extensors look like?
even longer latency after discharge
(helping to hold the pained area away from the stimulus)
what are central pattern generators?
makes patterns of repetitive and alternating activity, chewing, doggy paddle
what parts of the brain are involved in the CPG?
-motor cortex for initiation
-BG for maintaining repetitive movement
-CPG control centers
what is a motor unit?
A motor unit is where a single motor neuron innervates the skeletal
muscle. The force of the contraction is graded by recruitment of motor
units
what are some energy differences in sow and fast fibers?
Slow fibers have myoglobin and many mitochondria.
Fast will have abundant glycogen
what does the size principal do?
allows for the recruitment of slow, then fast fatigue resistant, and finally fast fatigable skeletal muscle
when would you have a hyperactivity reflex vs absent?
hyperactive would be in the upper motor neuron
absent would be the result of a compression or lower motor neuron lesion
