muscle architecture, arrangement and tissue types / macrostructure and microstructure

What sort of structure does skeletal muscle have?

Nested

Describe nested structure?

Each level is wrapped in a layer of connective tissue, each level is made up of smaller units of level below it

What order do the levels go in from largest to smallest?

Whole muscle - fasicle - muscle fibre (cell) - myofibril - sarcomere

Why are muscles in a nested structure?

Whole muscle needs to generate single combined force despite being made up of many individual units

Epimysium?

Dense connective tissue surrounding entire muscle

Perimysium?

Surrounds each fascicle within the muscle?

What is a fascicle?

Bundle of individual muscle fibres wrapped in perimysium

Endomysium?

Surrounds each individual muscle fibre (cell(

The connective tissue layers merge together to do what?

Form the tendon anchoring muscle to bone

What is the function of the connective tissue layers (3)?

Structural support, transmit force of contraction to tendon, allow blood vessels/nerves to reach muscle fibres

What is a muscle fibre?

Single, long, cylindrical muscle cell

What does each muscle fibres contain?

Myofibrils

Why does a muscle cell have many nuclei long its length?

Structural adaptation to support function and protein synthesis

What is a myofibril?

Rod like structure inside muscle fibre made up of repeating units called sarcomeres

What is a sarcomere?

Basic functional (contractile) unit of skeletal muscle

How are sarcomeres arranged to give skeletal muscle its striated appearance?

End to end along length of myofibril

Protiens filaments that make up the sarcomere are called myofilaments. What are the two myofilaments and their density?

Actin (thin) Myosin (thick)

What does Z-line (z-disk) mark?

Each end of a single sarcomere

What does the A-band region contain?

Myosin (thick filaments)

What des the I-band region contain?

Only actin (thin filaments)

What do I-band do during contraction?

Shorten

What does A-band do during contraction?

Stays a fixed length

The filaments slide past one another during contraction which explains what?

Distance between z-line decreases even though filaments don’t change length

Why does every layer in the hierarchy exist?

So force generated at smallest scale reaches tendon at end of muscle then bone to create movement

The arrangement of muscle fibres affects what two things?

How much force muscle can produce and range of motion

What is the reason for fibre arrangement affecting force and range of motion?

Fibre length - can only shorten by portion of resting length

Parallel fibre arrangement?

Fibres run parallel to muscles line of pull, along long axis

Parallel fibres allow what but restrict what?

Allow greater range of motion and faster contraction but produce less force

Why is the bicep brachii arranged parallel?

Fits role at elbow joint as it moves through a large range of motion

Pennate fibre arrangement?

Run at an angle to muscles line of pull, attaching diagonally onto a central tendon

What does the pennate fibre arrangement allow but at what cost?

More fibres in same space producing greater force but at cost of smaller range of motion

Why is the rectus femoris in a pennate fibre arrangement?

Suited for producing large forces required at knee joing

A muscles internal architecture is not incidental it reflects what?

Mechanical demands of joint and movement joint serves

What is a tendon?

Cord-like band of dense connective tissue that attaches muscle to bone

A tendon achieves what?

A concentrated pull onto small area of bone

What is aponeurosis?

Broad flat sheet of connective tissue with same attaching function as a tendon but wider and flatter

What does the aponeurosis achieve?

Distribution of its pull across wider attachment area

What does the shape difference reflect?

Where each muscle is used?

Describe attachment, appearance, nuclei and control of skeletal muscle?

Attached to bone, striated, multi-nucleated at periphery of cell, voluntary

Describe location, appearance, nucleus and control of cardiac muscle?

Heart, striated - cells are branched and connected by intercalated disks, single central nucleus involuntary

Describe attachment, appearance and control of smooth muscle?

In walls of internal organs and blood vessels, non-striated, involuntary