Ch3 Motor System

Muscle contracts when motor neurons fires AP

Connected via NeuroMuscular Junction

NT is Ach

Opens nAchR that allow Na and K follow through

AP flows outwards and propagate

Skeletal muscle

Voluntary movement

muscle fiber are cells

only contracts with recruited by motor neuron

1 fiber only controlled by 1 motor neuron

a motor neuron and all the motor fibers that it is connected is a motor unit

the myofibrils directly contains the contractable proteins

Z line is where thin filmant (actin) anchor to

the region between two Z line is a sarcomere and connect to the thick filament via titin

I band, only thin filament

A band, with thick filament (myosin)

H zone, only think filament

M line, middle of sarcomere

Thin filament:

contains troponin, actin, and tropomyosin

Thick filament:

contains heavy chain, light chain, ATP binding site and actin binding site

The fiber contains transverve (T) tubules that facilitate AP

Sarcoplasmic reticulum is close to T tubules

Smooth muscle

around hallow spaces

Cardiac muscle

only in the heart

T tubules are connect to the membrane of the cell

NT for motor fiber contraction is Acetylcholine

nAchR that is binded to Ach will allow Na and K to flow and E channel is 0mV

This will that propagate along the motor fiber membrane and propagate via V-gated Na channels

The t-tubules have DHP receptor (does not need have Ca to flow through to cause contraction) and connected to ryanodine receptor, which DHP allow Ca to flow in when activated by voltage, and opens ryanodine receptor which causes more ca to flow into the cell

Ca binds to troponin which causes tropomyosin to shift and uncover myosin binding site on actin

myosin cross bridges bind to actin and contracts

Ca ATPase pumps Ca back to Sarcoplasmic Reticulum and stop contracting

When the muscle is relaxed and with Ca, then the myosin cross bridge connects to actin binding site

ADP releases and cross bridge moves

ATP detached cross bridge from actin

myosin will hydrolyze ATP and be ready to attach to myosin

Fast glycolytic fibers Type 2X

Fast oxidative glycolytic fiber Type 2A

Slow oxidative fiber Type 1

All fibers within a unit are the same

Fiber recruited in the order from slow (thinner) to fast (thicker)

Recruitment order:

Slow oxidative fiber Type 1 (1st) oxidative phosphorylation ATP

Fast oxidative glycolytic fiber Type 2A (2nd) oxidative phosphorylation ATP

Fast glycolytic fibers Type 2X (3rd) glycolysis ATP