Epithelial tissue

Connective tissue

Muscle tissue

Neural tissue

Sarcolemma = plasma membrane of muscle fibre

Sarcoplasm = cytoplasm of muscle fibre

Skeletal

Cardiac

Smooth

• Large (long and cylindrical) muscle cells

• Called muscle fibres

• Multinucleated (just inside the plasma membrane)

• Striated

• Cells do not divide (microsatellite cells make new fibres)

• Moves or stabilizes the position of the skeleton

• Guards entrances and exits to the digestive, respiratory and urinary tracts

• Generates heat

• Protects internal organs

• Bundles of protein filaments called myofilaments

• Thin filaments (actin)

• Thick filaments (myosin)

• Myofibrils are attached to the inner surface of sarcolemma

• When it shortens it enables muscle contraction

• Where transverse tubules encircle a myofibril it is tightly bound to the membrane of the scarcoplasmic reticulum

• Scarcoplasmic reticulum is like the smooth endoplasmic reticulum of muscle cells

• Forms a tubular network around each myofibril

Myofibrils are bundles of myofilaments (thick and thin)

Myofilaments are organised into repeating functional units called Sarcomeres

Myofibril has about 10,000 sarcomeres

• Thick filaments (myosin)

• Thin filaments (actin)

• Proteins that stabilise the position of thin and thick filaments

• Proteins that regulate interactions between thin and thick filaments

• Each sarcomere has dark bands (A bands) and light bands (I bands)

Thick filaments (myosin) at the centre of the sarcomere

3 subdivisions

• M Line = proteins that connect neighbouring thick filaments

• H band = region either side of M line, thick but not thin filaments

• Zone of overlap = thin and thick filaments overlap

Thin filaments (actin) but not thick filaments extends from the A band of one sarcomere to the A band of the next sarcomere

• Skeletal muscle - surrounded by Epimysium, contains muscle fascicles

• Muscle fascicles - surrounded by Perimysium, contains muscle fibres

• Muscle fibre - surrounded by Endomysium, contains myofibrils

• Myofibrils - surrounded by sarcoplasmic reticulum, consists of sarcomeres (z line to z line)

• Sarcomere - contains thick filaments and thin filaments

• Only found in heart

• Cardiocyte - cell is smaller than skeletal muscle

• Typically one central nucleus

• Striations - actin and myosin (same as skeletal muscle)

• Branched network of interconnected muscle cells (join at intercalated discs)

Circulates blood

Maintains blood pressure

Found in walls of blood vessels, respiratory, digestive systems

Cells = small, spindle shaped with a single nucleus often referred to as fusiform in shape

Can divide and regenerate

Actin and myosin are present but organised differently (no striations)

Not voluntarily controlled

• Moves food, urine and reproductive tract secretions

• Controls diameter of respiratory passageways

• Regulates diameter of blood vessels

• No myofibrils and sarcomeres (therefore no striations)

• Thick filaments scattered throughout sarcoplasm

• Thin filaments attach to dense bodies

• Dense bodies transmit the contracile forces between

• The H and I bands get smaller

• The zones of overlap get larger

• The Z lines move closer together

• The width of the A band remains constant

• Sliding occurs in all sarcomeres in the myofibril

• Myofibril gets shorter

• Muscle fibre gets shorter

• Muscle gets shorter

• Produces TENSION

1. Action potential arrives at the synaptic terminal

2. Acetylcholine is released. Permeability of the membrane changes and triggers the release of ACh

3. ACh molecules cross synaptic cleft and bind to ACh receptors on sarcolemma

4. The sodium ions rushing into the sarcolemma generate an action potential which spreads across each T tubule

5. Acetylcholine is broken down by Acetylcholinesterase. Now it is ready for next action potential to arrive at the synaptic terminal

• General muscle weakness

• Chronic muscle fatigue from the slightest exertion

• Begins with muscles of the head

• Weakness results from a reduction in the number of ACh receptors

• These are receptors on the motor end plate

• Action potential (reaches triad)

• Calcium ions released from cisternae of SR

• Calcium binds to and changes shape of troponin molecule

• Troponin molecule roles the tropomyosin from the active sites

• Myosin heads bind to active sites of F-actin
• Contraction cycle begins

1. Resting state

2. Active site exposure

3. Cross-bridge formation

1. Exposure of active sites (calcium ions released from cisternae of SR, calcium binds to and changes shape of troponin molecule, troponin molecule roles the tropomyosin from the active sites)

2. Formation of cross bridges (active sites are exposed, energized myosin heads bind with them forming cross-bridges)

3. Pivoting of myosin heads (myosin head pivots towards M line, requires energy, reffered to as power stroke)

4. Detachment of cross-bridges (ATP binds to myosin head and breaks the link to actin, the active site is now exposed again ready to form a new cross bridge)

5. Reaction of myosin (Free myosin head splits ATP into ADP and a phosphate group, energy released 'cocks' the myosin head, cycle can now be repeated)

1. ACh broken down by AChE

2. Sarcoplasmic reticulum recaptures Ca2

3. Active sites covered, no cross-bridge interaction

4. Contraction ends

5. Relaxation occurs, passive return to resting length

1. Latent period
Begins at stimulation
Action potential sweeps across sarcolemma
Causes SR to release calcium
Before contraction

2. Contraction phase

Tension rises to a peak

3. Relaxation phase

Calcium levels are falling, active sites are being covered, active cross-bridges decreasing, tension falls to resting

Peak tension can increase with successive stimulation

(If the stimulation occurs straight after the relaxation phase of the last twitch tension increases)

Most skeletal muscles do not show treppe

If a higher stimulation frequency eliminates the relaxation phase complete tetanus occurs

Stimuli arrive so rapidly the sarcoplasmic reticulum cannot reclaim the calcium

As the calcium concentration in the sarcoplasm increases contraction is prolonged making it continuous

All of the muscle fibres controlled by a single motor neuron is referred to as a motor unit

Motor unit size depends on the precision of movement required