Muscles

SRJC, BIO 2.2, Swinstorm

What are the functions of muscles?

1. movement

2. generate heat

3. stabilizing body, form, and position

4. pumping and controlling fluids: blood, lymph, digestive

what are the three types of muscle tissue?

1. smooth

2. cardiac

3. skeletal 

Cardiac

Striated, branched uninucleated fibers, its involuntary movements, occurs only in the walls of the heart. It is usually small rhythmic contractions

Skeletal

voluntary movements, striated, multinucleic, strong contractions usually attached to the skeleton

Smooth

spindle shape non-striated involuntary movements uninucleic. usually continuous strong contractions found in wall of hallow organs.

Describe the basic skeletal muscle

the skeletal muscle is comprised of multiple fasciculus and one fasciculus has various myofibers

describe myofiber structure

one myofiber contains various myofibrils and inside the myofibrils are sarcomeres that consist of thin and thick filaments and m-line and z-line. 

Thin filament

are composed of actin, troponin, and tropomysin

Thick filament

contains myosin and myosin head

Describe the sliding filament model

ATP is bound to myosin head which is a low energy state → myosin head hydrolyzes ATP into ADP and Pi which is a high energy configuration → myosin head binds to actin forming a cross-bridge → myosin relates ADP + Pi while in a cross-bridge formation. This brings the thin filament towards the center of the sarcomere using a power stroke restoring it back to a low energy state → ATP binds to myosin head releases if from acting starting the cycle again

What is the process to get the sliding-filament model started?

A motor neuron releases acetylcholine and diffuses across the synaptic cleft and binds to receptor proteins on the muscle fiber, triggering an action potential → The action potential goes down t-tubules which triggers calcium ions to be release from the sarcoplasmic reticulum → calcium ions bind to the troponin complex exposing the myosin binding sites → a cross bridge forms and the sliding filament model comes into play → movement stops and calcium ions return to the sarcoplasmic reticulum → contraction ends and muscle fibers relax 

Motorunit

a single motor neuron and all the muscle fibers that it stimulates. Fibers work together like a unit.

Large motorunit

like legs or arms and the neuron controls more muscle cells

Small motor unit

would be the fingers or eyes and they control less muscle cells

Fast Twitch

brief rapid powerful contractions. People who have fast twitch muscles contain less mitochondria and myoglobin and is anaerobic

Slow Twitch

Sarcoplasmic reticulum pumps calcium ions more slowly which lasts longer. These muscles contain more mitochondria and myoglobin and is aerobic 

What is the main difference between the two twitches?

the rate at which the myosin head hydrolyzes ATP.