Lesson 21: Skeletal muscle

Functions of muscular system

PRODUCTION OF BODY MOVEMENTS

STABILIZING BODY POSITIONS

ORGAN VOLUME REGULATION

DISPLACEMENT OF SUBSTANCES WITHIN THE ORGANISM

HEAT GENERATION

What are the types of proteins in each myofibril of muscle fiber

Contractile proteins: Actin, myosin

Regulatory proteins: Troponin, Tropomyosin

Giant Accessory proteins: Titin nebulin

Contractile proteins

The fine filament is formed by the aggregation of actin molecules

Each actin molecule contains a myosin binding site.

The actin aggregates clump together in a helical arrangement

to form two strands of filamentous actin or F actin.

Regulatory proteins

Allow muscle fibers to start or stop contracting

Tropomyosin: fibrillar protein, which in a

resting state covers the binding sites of actin,

preventing their interaction with the myosin heads.

Troponin: consist of 3 subunits: ITC

3 subunits of troponin

- I: affine for actin

- T: affine for tropomyosin

- C: affine for calcium

How does tropomyosin deattach from actin binding site?

Through binding of calcium with tropnin c

Thick myosin filaments

Each thick filament is made up of hundreds of myosin molecules

Each myosin consists of 2 interlocking subunits

Each of subunits has a long tail and a head

What does the head of myosin do

It generates the mechanical force

Has a actin binding site and ATPase site that hydolyzes atp

Titin and nebulin function

Titin:

• Stabilizes the position of the myosin filaments.

• Its elasticity returns the stretched muscles to their resting length

Nebulin:

Nebulin helps align the actin filaments in the

sarcomere.

What controls skeletal muscle movement

CNS

What is a motor unit

A neuron and all the muscle fibers it stimulates make up a motor unit.

What are the 3 basic steps of contraction

Muscle fiber excitation

Excitation contraction coupling

Contraction cycle

Excitation and relaxation cycle

Two conditions that causes mucle fibers to relax after contracting

The breakdown of ACh by the enzyme acetylcholinesterase, which determines the termination of muscle action potentials

The closure of the channels that release calcium to the sarcoplasm, so that the calcium is trapped in the SR membrane

What is most important components

ATP and Calcium

What is wave summation?

When multiple stimuli appear before complete relaxation of the muscle, the following contraction is more intense because it begins when the fiber has a higher tension level.

What is an incomplete tetanus contraction

When a fiber is stimulated faster (20-30 stimuli) per second)

Only partially relax between stimuli

What is a complete tetanus contraction

More tgab 80-100 stimuli per seconds with no relax

What is muscular fatique

inability of a muscle to contract strongly after prolonged activity, due to: Release of calcium, glycogen, oxygen