Skeletal Muscles

4 Main functions of Skeletal Muscles

1. Causes movement of the skeleton

2. Maintains posture

3. Stabilises bones & joints

4. Generate heat in the body

Unique Characteristics of Muscle Tissue:

Excitability

Excitability - Able to receive and respond to a stimulus (can be electrically stimulated)

Contractility - Able to contract/shorten when stimulated

Extensibility - Able to be stretched a little

Elasticity - Able to return to original shape/recoil after being stretched, resuming resting length

Unique Characteristics of Muscle Tissue:

Contractility

Contractility - Able to contract/shorten when stimulated

Unique Characteristics of Muscle Tissue:

Extensibility

Extensibility - Able to be stretched a little

Unique Characteristics of Muscle Tissue:

Elasticity

Elasticity - Able to return to original shape/recoil after being stretched, resuming resting length

Skeletal Muscle Tissue Structure:

Epimysium

A covering of connective tissue around the entire muscle.

Epi- meaning upon

Outermost covering of muscle.

• Not muscle tissue, but a dense fibrous connective tissue

• Provide the muscle structural integrity

Skeletal Muscle Tissue Structure:

Muscle Fascicles

Bunched together muscle fibres

Skeletal Muscle Tissue Structure:

Perimysium

A covering of connective tissue around the muscle fascicles.

Peri- meaning around

Wraps around each muscle fascicle

• Not muscle tissue, but a dense fibrous connective tissue

Skeletal Muscle Tissue Structure:

Muscle Fibre/Muscle cell

A single muscle cell running the entire length of the muscle, from one end to the other

• Multinucleated

• Abundance of mitochondria

Skeletal Muscle Tissue Structure:

Endomysium

A covering of connective tissue around a muscle fibre.

Endo- meaning within

Wraps around each muscle fibre

• Not muscle tissue, but a dense fibrous connective tissue

Epimysium, perimysium & endomysium

All three layers of connective tissue combine at the end of the muscle body with the tendon’s connective tissue.

• Contribute to the elasticity and flexibility of the muscle

Origin (muscle attachment site)

Proximal attachment site

Located closer to the attachment to the body’s trunk

Insertion (muscle attachment site)

Distal attachment site

Located further from the attachment to the body’s trunk

Skeletal Muscle Tissue Structure:

Blood vessels & Nerves

Run through the connective tissues of muscles

• Good blood supply, good ability to repair

Skeletal Muscle Tissue Structure:

Sarcolemma

The cell membrane of the muscle cell/fibre. Located directly under the endomysium

• Part of the muscle cell, unlike the endomysium

Skeletal Muscle Tissue Structure:

Myofibril

The functional unit of the muscle cell. Packed within the muscle fibre.

Skeletal Muscle Tissue Structure:

Sarcomere

Repeating units from end to ends of a myofibril. There are many sarcomeres inside a single myofibril.

Skeletal Muscle Tissue Structure:

Z-discs

Regions flanking each end of the sarcomere. Used to isolate each sarcomere.

• z-discs are proteins

• From one z-disc to another, is a sarcomere, the functional unit of a myofibril

• Located in the I-band

Skeletal Muscle Tissue Structure:

Myofilament: Myosin

Thick filaments.

Myosin is a protein

Skeletal Muscle Tissue Structure:

Myofilament: Actin

Thin filaments.

Actin is a protein twisted upon itself.

Skeletal Muscle Tissue Structure:

Striated Pattern

Unique banding pattern of skeletal muscles

• The arrangement of myofilaments (actin & myosin) is what differs between smooth, cardiac & skeletal muscle

Skeletal Muscle Tissue Structure:

I-band

Region of the sarcomere sans thick filaments (myosin), where the z-discs are found.

• Only actin (thin filaments) are in the I-band

• ‘Lighter‘ areas when looking at sarcomeres under the microscope

Skeletal Muscle Tissue Structure:

A-band

Region of the sarcomere with myosin present as well as actin, region between the z-discs.

• Both actin and myosin filaments are in the A-band

• ‘Darker‘ areas when looking at sarcomeres under the microscope

  • Due to myosin, the thicker filament being present, giving a striped, striated banding pattern