KIN 480 Nervous System

How do interneurons work?

Can be excitatory or inhibitory, postsynaptic neuron only fire if both E and I combine to meet threshold

Temporal & Summation with Excitatory

Both will increase the chance of an action potential

Temporal & Summation with Inhibitory

Both will decrease the chance of an action potential

Autogenic facilitation

excites the muscle that contains the sensor

Autogenic inhibition

inhibits the muscle that contains the sensor

Antagonistic facilitation

excites the antagonist muscle

Antagonistic inhibition

inhibits the antagonist muscle

Muscle spindles location

interspersed among muscle fibers (inside muscle)

What do muscle spindles respond to?

- Muscle velocity

- Muscle length

What can muscle spindles cause?

- Autogenic facilitation (excite same muscle)

- Antagonistic inhibition (inhibit antagonist)

What reflex is associated with muscle spindles?

Stretch reflex (excites quad, inhibits hamstrings)

Golgi tendon organ location

near the muscle-tendon junction

What do golgi tendon organs respond to?

muscle tension

What do golgi tendon organs cause?

-autogenic inhibition (inhibit same)

- antagonistic facilitation (excite antagonist)

GTOs and coordination

GTOs may be a factor in uncoordinated responses in untrained individuals

Ruffini endings

Sensory receptor in joint capsule that responds to change in joint position

Pacinian corpuscles

Sensory receptor in skin stimulated by pressure

Free nerve endings

Pain receptors widely dispersed in body

What do joint sensory receptors do (Ruffini, pacinian, free nerve endings)?

Help kinesthetic sense and proprioception

kinesthetic sense

where your segments are in space

Arthrogenic Muscle Inhibition

diminished ability to produce muscle forces due to inhibition of muscle that occurs after injury

will Arthrogenic Muscle Inhibition occur if there is no pain?

yes. this is independent from pain

Consequences of Arthrogenic Muscle Inhibition

after injury, muscles may become weaker, and may not be able to produce as much force.

May need to rehabilitate muscles even if it is not a muscle injury.

Restrictions to ROM at a joint

- bony structures

- soft tissues surrounding joint

- ligaments

- muscle length of antagonist

- neurological mechanisms during dynamic movements (stretch reflex, arthrogenic muscle inhibition)

What is stretched to increase ROM?

- Fascia, epimysium, perimysium, endomysium and tendons

- NOT muscles fibers

What is best practice for stretching a muscle?

- after a workout (warm)

- long period of time (30-60seconds)

- under a low load

static stretching

hold the stretch to elicit response from GTO ( causing autogenic inhibition)

ballistic stretching

bouncing can activate stretch reflex (autogenic facilitation) which may reduce ROM or damage to muscle fibers

is static or ballistic stretching safer?

static

dynamic stretching

functional movements that mimic the movement of the activity you're about to perform, taking advantage of fun ROM

PNF Stretching meaning

Proprioceptive Neuromuscular Facilitation

PNF Stretching

- stimulates relaxation of the muscle fibers to allow greater stretch of connective tissue

- both antagonist inhibition and autogenic inhibition can be used

Proprioceptive Training

training specifically designed to activate the nervous system

Examples of Proprioceptive Training

- passive movement training

- sensorimotor stimulation

- vibrotactile stimulation

- somatosensory discrimination training

- balance training

- agility training

Motor unit

A motor neuron and all of the muscle fibers it innervates

Action potential definition

localized depolarization. voltage switches (becoming more positive on the inside, more negative on the outside)

What happens when a nerve action potential (AP) arrives at the axon terminal?

Calcium channels open and calcium is released.

What does calcium cause in the axon terminal?

Calcium causes synaptic vesicles to fuse with the axon terminal membrane.

What is released into the synaptic cleft after synaptic vesicles fuse?

Acetylcholine is released into the cleft.

What happens to calcium after acetylcholine is released?

Calcium is pumped out of the terminal.

What occurs when acetylcholine binds to the motor end plate?

It allows sodium in and potassium out, leading to depolarization. (pump K in)

What does depolarization initiate in muscle cells?

It initiates a muscle action potential (AP) that causes muscle contraction.

Nerve to Muscle AP step 1

nerve action potential at axon terminal opens calcium channels and allows calcium ions to enter axon terminals

step 2

calcium ions cause synaptic vesicles to fuse with the axon terminal membrane

step 3

ACh is released into the synaptic cleft. Calcum ions are pumped out of axon terminal

step 4

ACh binds to motor end plate and opens the channels that pump Na in and K out. Causes local depolarization of the motor end plate

step 5

depolarization causes action potential that propagates along the sarcolemma and results in muscle contraction

What affects muscle precision?

number of fibers per motor unit

less fibers/MU = more precision

What determines fiber type

the motor unit neuron

Type I fiber

-maintain posture, stabilize joints, typing

-slowest contraction time

-lowest threshold

Type IIa fiber

swimming, biking

Type IIb fiber

-sprinting, jumping, weight lifting

-fastest contraction time

-highest threshold

Motor Unit Excitation

All-or-nothing event, either all or none of fibers of the MU are activated

Increased tension can be accomplished by

- increasing number of stimulated motor units (recruitment)

- increasing the stimulation rate of the active motor units (rate coding)

Recruitment

increasing the number of stimulated motor units

Rate coding

Increasing the stimulation rate of the active motor units

Temporal summation

summation from a single synapse firing repeatedly

Spatial summation

summation from multiple synapses firing at once

Henneman Size Principle

motor units are recruited from smallest (type I) to largest (type IIb)

When using electrical stimulation, does recruitment follow Henneman Size principle?

No- electrical stimulation will recruit largest motor units first.

Decruitment

motor units decruit large to small (inverse from Henneman Recruitment)

Size and Threshold

smaller motor units have a lower threshold than large ones

Twitch

the response to a single action potential

Summation

the increase tension (increase in force) due to multiple stimuli

Tetanus

sustained maximal tension (contraction) due to high frequency stimulation (no more increase force when increase in stimulus)

Graded maximal contraction

each MU is recruited at its threshold force level AND THEN its stimulation frequency is increased.

only way for smooth contraction.

Graded Contraction Firing Patterns

Graded contractions graph

recruitment and rate coding doesn't happen without the other

Recruitment Exceptions

motor units decrease their threshold as the movement gets more ballistic, and the motor units can fire synchronously

Electromyography

- refers to the electric activity in the muscle

- NOT related to force, just stimulation

What is responsible for improvement in the first 8-12 weeks of training?

Neural Factors

Examples of neural factors responsible for initial improvement

-improved innervation

-learning to control all MUs

-eliminating antagonistic activity (overriding GTO feedback)

-increased synchronization of MUs.

When does hypertrophy occur after training from an untrained state?

after 12 weeks

understand strength gains graph

Factors affecting torque

1. level of stimulation (recruitment, rate coding)

2. muscle fiber type

3. muscle architecture (PCSA, tendon-to-tendon length)

4. muscle velocity

5. muscle length

6. neural mechanisms (SS cycle, GTO)

7. moment arms and angle

Level of stimulation

-percent of activation

-recruitment

-rate coding

-most important to affecting torque

muscle architecture

-PCSA

-tendon-to-tendon length

Neural Mechanisms

-stretch-shortening cycle

-muscle spindles

-GTO

moment arms (d)

angle of pull

larger moment arm = larger torque

the sequence of muscular contraction (technique)

important for maximal performance of dynamic movements

-nervous system is responsible for the "when" of muscle activation.

-shotput

-start with larger muscles that are further away, last thing active is the wrist