Week 5 -- Muscle function and structure

What are the location, appearance, function, innervation and contractility differences of skeletal, cardiac and smooth muscle?

	Skeletal	Cardiac	Smooth
Location	Attached to skeleton	Heart muscle	Lines hollow intestines/blood vessels/airways
Appearance	Obviously Striated (Long & Cylindrical)	Not obviously Striated (Inter colated disks)	Non-striated
Function	Movement, produce heat, stabilise joints	Makes rhythmic contractions to pump blood throughout the body	regulates blood pressure, sends food through the GI tract, manages bladder, controls airway diameter.
Innervation	Voluntary/Involuntary	Involuntary	Involuntary
Contractility	Powerful and rapid, but fatigue easily	Autorhythmic	Not powerful but sustained

What is muscle made up of (hint: group, cell, organelle)

Skeletal Muscle —> Fascicle —> Muscle Fiber —> Myofibril (organelle made up of overlapping action and myscine)

Muscle connective tissue coverings (hint: mysiums)

Endomysium

• Surrounds each muscle fibre

Perimysium

• Surrounds each fascicle

Epimysium

• Surrounds each skeletal muscle

What happens when the mysiums combine?

They combine to form tendons and attach to periosteum (the layer surrounding bone)

Each muscle is supplied by ….. nerve, …… artery and ……or more veins

Each muscle is supplied by one nerve, one artery and one or more veins

Each one of those nerves and arteries …… to extend to each …. ……..

• A single somatic motor neuron innervates each muscle, which branches many times to extend to each muscle fibre

• An artery runs alongside the somatic motor neuron and branches into capillaries so that each muscle fibre is in close contact with a capillary

Muscle fibre meaning

Long, cylindrical, multinucleated muscle cell

What is the sarcolemma? What makes it special?

the plasma membrane of a muscle cell.

T-tubules (infoldings of sarcolemma towards center of each muscle fibre) quickly spread an AP (Action potential) through muscle fibre — ensures AP stimulates all parts of the muscle fibre at the same time.

What is the sarcoplasm? what makes it special?

the cytoplasm of a muscle cell

Sarcoplasm contains large amounts of glycogen (glucose) and myoglobin (muscle protein that binds to oxygen for quick diffusion)

What is a myofibril?

Contractile organelles of muscle fibres (very narrow in diameter but extend entire length of muscle)

Anatomy of a myofibril?

A sarcoplasmic reticulum wraps around each myofibril

Dilated ends of the sarcoplasmic reticulum (terminal cisterns) lie against T-tubule.

• Myofibrils contain thick and thin filaments arranged into sarcomeres (basic functional unit of myofibrils).

• Thin filaments mostly composed of actin

• Thick filaments mostly composed of myosin

• Z disc separates one sacomere from the next

What is the thick filament

Thick filament = Myosin
Myosin has a tail and two heads

• Myosin contains binding sites for actin and ATP

What is the thin filament

• Composed of actin, troponin and tropomyosin

• Actin contains binding site for myosin

• Tropomyosin blocks myosin binding site

• Tropomyosin strands held in place by troponin molecules

What is tropomyosin

a rod-shaped, two-stranded -helical coiled-coil protein that stabilizes and regulates actin filaments