Sliding Filament Theory

Ca+ causes

Troponin to move tropomyosin aside

What happens when troponin moves tropomyosin aside?

Active sites on action are exposed

What happens when active sites are exposed on actin?

Myosin attaches to tropomyosin

What happens after the myosin heads attach to tropomyosin?

ADP and Pi are released and the protein changes conformation and pivots

What happens after the myosin protein pivots?

ATP binds to myosin reducing its affinity for actin and causing release of actin

What happens after the myosin detaches from the actin?

ATP is hydrolyzed into ADP + Pi and the myosin is primed for another cycle

SERCA Calcium Pumps are found

Embedded in the membrane of the sarcophagi can reticulum

What do SERCA pumps do?

They pump calcium back into the SR

SERCA pumps are an antagonist to the release of

saturating amounts of Ca+

Latent Period

Time when Ca+ is released by diffusion

Contraction time

Tension of the Muscle twitch increases

What happens at the top of the muscle twitch curve?

Myosin begins sliding because it loses Ca+

Relaxation time

The tension of the muscle twitch decreases

Rigor mortis starts at

3-4 hours after death

Rigor mortis peaks at

12 hours after death

Rigor mortis ends at

About 24 hours due to enzymatic breakdown

Why does Rigor Mortis occur??

Ca+ leakage into the cell because Ca+ pumps stop working as they run out of ATP

In what step does Rigor Mortis stop the sliding filament theory?

The pivot phase because ATP cannot bind to cause Myosin to detach from actin

Muscle tension is dependent on

Frequency of neural stimulation and recruitment of motor units

Frequency of neural stimulation is also known as

Twitch summation/temporal summation

Continuous firing is antagonized by

SERCA’s winning by moving Ca+ out of the cell

Incomplete tetanus looks like

Oscillation even up to the maximum tension

Can the nervous system induce complete tetanus?

Yes, but it doesn’t because allows the muscle to contract in a controlled manner and resists rapid fatigue

Complete tetanus

Happens by keeping troponin Ca+ saturated

Recruitment is also known as

Motor unit summation

Recruitment

Motor unit neurons are accumulated to increase contraction strength

Motor neuron units vary in

The amount of fibers per unit (Motor homonculus)

Asynchronous recruitment

Certain # of motor units fire, then relax while other ones fire to maintain consistent force (take turns)

Optimal Length can’t be too long or else

Myosin wont be able to attach and pull

Optimal length can’t be too short or else

Myosin has nowhere to attach further

Isotonic contraction

Tension remains constant but muscle length changes (shorter or longer)

Isometric contraction

No change in muscle length but muscle gets tone

2 types of isotonic contraction

Concentric contraction and eccentric contraction

Eccentric contraction

Muscle lengths and contraction resistance controls lengthening

Concentric contraction

Actively shortening the muscle

Afferent information comes from

Muscle spindles and golgi tendon organs

Muscle spindles

Are inside of special infrafusal muscle fibers and sense stretching of the muscle fiber (length) and increase firing rate of motor neuron→ reflexes

Golgi tendon organs

Inside of the tendons of the muscle and respond to changes in tension of the muscle

Important differentiation between muscle spindles and golgi tendon organs

Golgi tendon organs reach the level of consciousness→ the brain is aware of tension only, not length of muscles from the muscle spindles

3 classes of motor control

1. Reflexes

2. Rhythmic activities

3. Voluntary

Reflexes

Skeletal muscle reflexes that occur without conscious thought

Reflexes receive input from

Proprioceptors in the muscles and joints, vestibular apparatus in the inner ear, though receptors, and the eyes

Voluntary movements

Goal-directed movements that are initiated and terminated at will

Voluntary movements are integrated at the

Cerebral cortex

Reflexes are integrated by the

Brain stem or spinal cord

Rhythmic activities

Stereotypical movements repeated in a general pattern

Rhythmic activities are integrated by

Cerebral cortex to start and stop but carried out by brain stem and spinal cord

3 sources of motor control

1. Afferent neurons

2. Primary motor cortex

3. Brain stem nuclei

Afferent neurons

Input at the spinal cord level and often proprioceptive or protective in function

Primary motor cortex

Pyramidal cells in the primary motor cortex terminate on motor neurons

Brain stem nuclei

Include reticular formation and vestibular formation and multi neural system in the brain stem but influenced by other parts of the brain

Brainstem and primary motor unit control of motor neurons must go through

The thalamus

Flaccid Paralysis

Loss of excitatory input

Flaccid paralysis leads to

No muscle tone and no voluntary control

Spastic paralysis

Loss of inhibitory input

Spastic paralysis leads to

Increased muscle rigidity and increased reflexes

Examples of flaccid paralysis

Alpha neurotoxin (snake venom), curare, botulism

Alpha neurotoxin

Arch. Antagonist but the mongoose has anti venom, and antibody that prevents binding

Curare

Ach. Antagonist

Botulism

Causes local paralysis of the muscle by disrupting exocytosis of Ach at the neuromuscular junction

Examples of spastic paralysis

Latrotoxin, black mamba toxin, tetanus

Latrotoxin (black widow venom)

Explosive Ca+ release releases Ach. Causing muscle contraction but also flaccid paralysis because the cells cannot respond

Tetanus “clostridium tetani”

Obligate anaerobe that grows in deep puncture wounds and dirty conditions

Tetanus causes

Massive muscular spasms that can break bones by blocking inhibitors in the nervous system

Tetanus does not cause anything to happen in the

Neuromuscular junction