Lucas part 6 Flashcards
3 components of the CNS
Motor cortex, cellebrum, spinal cord
4 main purposes of skeletal muscle control systems
Voluntary Motion
Coordination of Multiple Muscles
Graded Force Levels (adjust contraction intensity)
Automatic Systems (reflexes)
which part of the CNS controls voluntary motion
motor cortex
what does the cerebellum do
coordinate timing and accuracy of complex movements
what does the spinal cord do in the CNS
Houses central pattern generators for rhythmic activities like walking, and reflex arcs for automatic responses
whats the order that leads to a motor output
stimuli - sensory neuron - interneuorn - motor neuron - muscle
Signals from the ____travel down to motor neurons in the spinal cord.
motor cortex
____ motor neurons directly control muscle contraction.
alpha
____ lets us modulate the level of force produced by a muscle
modulate
____ levels of force are achieved through ____
graded, summation
temporal vs spatial summation
temporal: single presynaptic neuron sends signals to a postsynaptic neuron at a rapid rate, the signals add up.
spatial:** multiple** presynaptic neurons send signals to a postsynaptic neuron at the same time, the signals add up
Small motor units involve =
Large motor units involve =
fine control (e.g., fingers).
strong force (e.g., thighs).
Problem: Too many motor units (thousands) for the brain to control individually.
Solution: ?
Solution: Recruitment based on the size principle
small alpha neurons are used for:
SO fibres, slow endurance tasks
big alpha neurons are for:
FG fibres, powerful, short bursts.
which motor neurons require more or less ESPS to fir
small: require less epsps to fire
large: require more esps to fire
what do you do on alpha motor neurons to recruit faster fibers
Increase stimulation rate of brain
3 type of reflex arcs
Withdrawal (Flexor) Reflex
Crossed-Extensor Reflex
Stretch (Myotactic) Reflex
what is the purpose of the Withdrawal (Flexor) Reflex
Pull a limb back in response to pain.
purpose of the Crossed-Extensor Reflex
Maintain balance when one limb is withdrawn.
purpose of Stretch (Myotactic) Reflex
Maintain Posture: Keeps muscles at a baseline level of tension (muscle tone).
Prevent Overstretching: Protects muscles from being stretched too far, potentially causing damage.
Stabilize Joints: Ensures smooth and coordinated movements by regulating muscle length.
explain the withdrawal reflex steps
sensory receptor detects pain
action potential travels from sensory to spinal cord
interneuron communication
INI is excited, stimulates 1.1 (flexor/hamstring) - pull limb away
1.2 excites 1N2 to stimulate extensor (quadriceps) - smooth movement
what is reciprocal innervation
prevents the muscles from working against each other.
Flexor Muscle: Activated (contracts to pull the limb away).
Extensor Muscle: Inhibited (relaxes to allow smooth withdrawal)
Why Does the Reflex Bypass the Brain?
If you waited for your brain to process the pain, you might not withdraw your foot quickly enough to prevent further injury.
a signal is also sent to the brain so you become aware of the pain (but this happens after the reflex action).
steps of the cross extensor reflex
finish the withdrawal reflex first, then with reciprocal innervation, (pained limb - withdrawal)
branch 1.3 excites 1N3 interneuron
1N3 in standing limb, 3.1 excites extensor (quads), 3.2 excites flexor inhibited (hamstring)
so 1.3 - 1N3 - 3.1 - 3.2 - 1N4
Neural tone refers to the
baseline level of activity in alpha motor neurons.
Increase Tone:
More frequent APs, resulting in stronger muscle contractions.
Decrease Tone
Fewer APs, resulting in less contraction.
Where Would You Find Large Motor Units?
Found in muscles requiring strong force (e.g., quadriceps).
Small Motor Units:
Found in muscles requiring fine control (e.g., eye muscles).
speed of less tone, default, and more tone:
less: slower
more: faster
____ tighten the ends of the muscle spindles, maintaining their sensitivity even when the muscle is contracted.
gamma motor neurons
which reflex involves only Involves only one synapse between the sensory neuron and motor neuron, making it fast.
myotactic reflex
example of myotactic reflex
A tap on the patellar tendon stretches the quadriceps muscle.
Muscle spindles in the quadriceps detect the stretch and send signals via sensory neurons to the spinal cord.
The sensory neurons:
Activate alpha motor neurons, causing the quadriceps to contract (knee extends).
Inhibit the hamstring muscles (antagonists) to ensure smooth movement.
The result is the familiar “knee jerk” motion.
steps of myotactic reflex
Muscle Stretch:
A sudden stretch of a muscle (e.g., due to a tap on a tendon) activates muscle spindles.
Example: The patellar reflex when the patellar tendon is tapped during a knee-jerk test.
Sensory Neuron Activation:
The stretch-sensitive neurons (Ia afferent fibers) wrapped around the muscle spindles detect the stretch.
These neurons fire action potentials and send the signal to the spinal cord.
Integration in the Spinal Cord:
The sensory neurons synapse directly onto alpha motor neurons of the same muscle (a monosynaptic reflex).
This is the simplest reflex arc, involving only one synapse between the sensory and motor neurons.
Motor Neuron Activation:
The alpha motor neurons send signals back to the muscle, causing it to contract.
This contraction resists the initial stretch and restores the muscle to its original length.
Inhibition of Antagonist Muscles:
At the same time, interneurons in the spinal cord inhibit the alpha motor neurons of the antagonist muscle.
This ensures smooth contraction of the stretched muscle without resistance from its opposing muscle (reciprocal inhibition).
in terms of stimulation rate, what is the order from lowest to highest fibres
SO, FOG, FG
