NPB: Controlling Skeletal Muscle

T/F: With contraction of skeletal muscle we do not intend the contraction

False, with contraction of skeletal msucle we do intend these contractions, (i.e. using apple pencil on ipad)

The skeletal muscle is ___(uncontrolled/controlled)

controlled → very well

Hierarchy of Control

High - Cerebral Cortex

- Brain Stem Subcortical/ Cerebellar

Low - Spinal Cord

Cerebral Cortex

• Highest level of control

• decided what you want to do with the contraction

  • also for the future (i.e. want to run two miles)

Spinal Cord

• Reflexive

• Myostatic Reflux

  • muscle spindle

  • basic

• Controls the CPU

• Control motor activities

  • specific patterned motor activities

    • chew → central pattern generator

    • swim → central pattern generator

CPU

• located: gray matter of spinal cord

Alpha Motor Neuron

• Comes from: ventral gray matter

  • cell bodies & neuron are there

Crosstalk occurs with

low levels all the way to the top → cortical control

• control really well → coordinated

Upper Motor Neuron

• associated with the brain → spinal cord → lower motor neuron (alpha motor neuron) → skeletal muscle

Muscle Spindle

• stretch when the muscle is stretch → activates the 1-a-afferent neuron → info sent to spinal cord

T/F: The muscle spindle sends stretch information to the spinal cord by activating the 1a afferent neuron.

True

What is the role of the muscle spindle in skeletal muscle?
A) It generates contraction by releasing neurotransmitters
B) It detects stretch and sends signals via 1a afferent neurons
C) It prevents overstretch by relaxing the tendon
D) It stores calcium for muscle activation

B) It detects stretch and sends signals via 1a afferent neurons

When a muscle is stretched, the __________ is also stretched, activating the __________ neuron, which sends information to the spinal cord.

muscle spindle, 1-a-afferent

Monosynaptic Connection

• AP travel all the way down on same muscle

Inhibitory Interneuron

• The neurotransmitter it releases is an inhibitory neurotransmitter (GABA, glycine)

• Causes alpha motor neuron to hyperpolarize → no AP fired → goes to opposite muscle (antagonistic muscle)

Interneuron

• helps makes decisions

• process lots of things

What is this process called?

• Myotatic reflex

• Stretch reflex

• Knee-jerk reflex

What occurs in myotatic reflex/knee-jerk reflex?

1. The muscle spindle will stretch when the muscle is stretched

2. This activate the 1a afferent

3. The information will be sent to the spinal cord

4. The result response will appear

   1. Stretched muscle will contract. This is the extensor.

   2. Flexor will not contract

Activate 1a afferent → info to spinal cord → Result/Response

1. Stretched muscle will contract (Extensor)

   1. Knee-jerk: wack knee → stretched quadriceps → leg kick out → contraction

2. Flexor (antagonistic muscle) will not contract bc we inhibit the motor neuron that goes to it at the level of spinal cord

Spinal Cord: Pain Withdrawal Reflex

1. Step on tack with right leg

2. withdrawal right leg form painful stimulus

3. contract the flexor NOT extensor → this allows you to pull leg away from the painful stimulus

4. opposite leg is extended (extensor muscles) NOT flexor

Nociceptor Afferent Neuron

• pain sensitive neuron

• sent to spinal cord

  • interneurons immediate response

T/F: In a reflex, you have to activate the hamstrings, which allows them to contract.

True, you need to contract it as in flexor to withdrawal from the pain

The foot for posture activates the ___(flexor/extensor)

extensor → quad

T/F: The hamstring on the side of the injured leg contracts to lift the foot during a withdrawal reflex.

True, The hamstring is a flexor that contracts to bend the knee and lift the foot away from pain.

T/F: The quadriceps on the injured leg contract to stabilize posture.

False, that would be the opposite leg quad extensor

Excitatory interneuron (green)

• talks downstream → flexor (hamstring)

Inhibitory interneuron (red)

• inhibit extensor (quad), but activate flexor (hamstring)

T/F: You cannot override the pain withdrawal reflex

False, you actually can override the pain withdrawal reflex bc there are so many synaptic connections (descending pathway)

T/F: You cannot override the knee-jerk reflex

True, you cannot override the knee-jerk reflex because there is a lack of synaptic connections

T/F: The spinal cord mediates reflex responses without input from the brain.

True, Reflexes like the withdrawal or stretch reflex are handled at the level of the spinal cord.