Muscle Anatomy

Learning goal I will understand the anatomy of a muscle fibre. I will understand the components involved in muscle contraction.

a single muscle is defined as...a number of muscle fibres: SKELETAL MUSCLE a single muscle is defined as...a number of muscle fibres: bound together by connective tissue and usually linked to bone via … Tendons!!

MUSCLE CELLS (FIBRES)

A single muscle is made up of many cells or fibres diameter of fibres - varies btw. 0.05 mm and 0.1mm (NOTE: hair is about 0.15mm) length of fibres - depends on length of muscle (e.g. bicep fibres = 15 cm) cell organelles - because they are such big cells, they have multiple nuclei & because they use so much NRG, they have many mitochondria

Remember, each fibre is a CELL with it’s own set of organelles.

A muscle: from the outside in connective tissue that covers the outside of a muscle: EPIMYSIUM protects and reduces friction connective tissue inside actual muscle: PERIMYSIUM bounds groups of muscle fibres together the groups of muscle fibres are called FIBRE BUNDLES (fascicle) individual muscle fibres are surrounded by a sheath of connective tissue, called the ENDOMYSIUM muscle fibre is an actual muscle cell: MYOFIBER

Video

Looking inward

Sarcolemma muscle cell membrane beneath the endomysium contains the cell’s cytoplasm – SARCOPLASM sarcoplasm contains large amounts of glycogen, protein myoglobin, high concentrations of Ca and mitochondria MITOCHONDRIA – energy production site

Within a single MUSCLE FIBRE, are many MYOFIBRILS that run the length of the fibre (# per fibre varies greatly)

Each MYOFIBRIL is made up of 1000’s of SARCOMERES that attach end-to-end down the entire length of the MYOFIBRIL (i.e. think bands on a snake)

Inside these SARCOMERES are the actual proteins that are responsible for muscle contraction ACTIN (thin filament) and MYOSIN (thick filament), stacked up on top of each other

there are many myosin & actin filaments stacked in both directions INSIDE MYOFIBRILS... Within 1 sarcomere, there are many myosin & actin filaments stacked in both directions

During muscular contraction…the SARCOMERES are brought closer together (making muscle smaller) due to an overlap between ACTIN and MYOSIN

video

The sarcomere is often divided up into different zones to show how it behaves during muscle action.

Video The Z - line separates each sarcomere. The H - Zone is the center of the sarcomere. distance btw. the actin filaments within the same sarcomere (only myosin)

The M – Line is where adjacent myosin filaments anchor on to each other. It is the midpoint of a sarcomere

The darker A - Bands are where myosin filaments align The lighter I – Bands are where actin filaments align. distance btw. the myosin filaments of 2 neighbouring sarcomeres (only actin)

When muscle contracts the H-zone and I-band both shorten as the z-lines are pulled towards each other. In full contraction the H – zone can disappear.

Learning goal I will understand the anatomy of a muscle fibre. I will understand the components involved in muscle contraction.