Chapter 3 Support and locomotion – muscles and movement. Year 13- Biology 2

By the end of this session I should be able to: Describe the histology and ultrastructure of striated muscle. Describe the sliding filament theroy of muscle contraction, including the roles of troponin and tropomyosin. Describe the structure of a neuromuscular junction and explain how a nerve impulse causes muscle to contract.

Discussion pairs –two minutes Give reasons why animals move from place to place: 1. To obtain food 2. To escape from predators 3. To find a mate 4. To distribute offspring 5. To reduce competition 6. To avoid danger 7. To maintain position 8. To avoid waste products

Muscular Movement muscles are attached to bones to form lever systems for movement muscle contraction creates a driving force when obtains energy from respiration; when a muscle relaxes, energy is not necessary There are 3 types of muscle: Skeletal muscle, Smooth muscles, Cardiac muscle.

Three types of Muscle: A. Smooth: involuntary control of internal organs for digestion, & blood vessels B. Cardiac: involuntary control of the heart C. Skeletal: Voluntary control of the skeletal muscles for movement

The Musculature System…….. Structure: Voluntary Muscles Striated-Skeletal Involuntary Muscles Cardiac- Heart Smooth-Stomach Striated Skeletal Several nuclei Box shaped, many mitochondria

Cardiac Muscle: Fewer Striations Fewer Mitochondria Large nuclei Lattice work of spaces between some cells Still square shape One nuclei per cell

Smooth Muscle: Eye shaped One nuclei per cell No lattice work No striations Long & drawn out Fewer Mitochondria

Skeletal muscle structure

Muscle structure

Actin / myosin filaments

Actin / myosin 2

Sarcomere structure Sarcomere Sarcolemma Z line A band I band H band M line

Muscle structure

sarcolemma: membrane of muscle fibre sarcomere: each repeating unit of cross striations sarcoplasm: cytoplasm with a system of membranes called sarcoplasmic reticulum

dark band and light band Z line: central line of each light band; 2 Z lines marks a sarcomere H zone: lighter region in dark band with a central dark line - M line Myosin: thick filaments Actin: thin filaments

actin

troponin actin

tropomyosin troponin actin

tropomyosin troponin actin

myosin binding site tropomyosin troponin actin

Ca2+ Ca2+ Ca2+ Ca2+

Ca2+ Ca2+ Ca2+ Ca2+ Calcium ions are released from the sarcolemma after stimulation from the T system

Ca2+ Ca2+ Ca2+ Ca2+

the calcium ions bind to the troponin and changes its shape

the calcium ions bind to the troponin and changes its shape

Ca2+ Ca2+ Ca2+ Ca2+

Ca2+ Ca2+ Ca2+ Ca2+

Ca2+ Ca2+ Ca2+ Ca2+ the troponin displaces the tropomyosin and exposes the myosin binding sites

Ca2+ Ca2+ Ca2+ Ca2+

Ca2+ Ca2+ Ca2+ Ca2+

Ca2+ Ca2+ Ca2+ Ca2+ the bulbous heads of the myosin attach to the binding sites on the actin filaments

Ca2+ Ca2+ Ca2+ Ca2+

Ca2+ Ca2+ Ca2+ Ca2+

Ca2+ Ca2+ Ca2+ Ca2+ the myosin heads change position to achieve a lower energy state and slide the actin filaments past the stationary myosin

Ca2+ Ca2+ Ca2+ Ca2+ A Pi A Pi A Pi

A Pi Ca2+ A Pi Ca2+ A Pi Ca2+ Ca2+

ATP binds to the bulbous heads and causes it to become detached Pi Ca2+ A Pi Ca2+ A Pi Ca2+ Ca2+ ATP binds to the bulbous heads and causes it to become detached

ATP binds to the bulbous heads and causes it to become detached Pi A Pi A Pi Ca2+ Ca2+ Ca2+ Ca2+ ATP binds to the bulbous heads and causes it to become detached

hydrolysis of ATP provides the energy to “re-cock” the heads Pi Pi Pi A Pi Pi Pi Pi A Pi Pi A Ca2+ Ca2+ Ca2+ Ca2+ hydrolysis of ATP provides the energy to “re-cock” the heads

hydrolysis of ATP provides the energy to “re-cock” the heads Pi Pi Pi A Pi Pi Pi Pi A Pi Pi A Ca2+ Ca2+ Ca2+ Ca2+ hydrolysis of ATP provides the energy to “re-cock” the heads

Pi Pi Pi A Pi Pi Pi Pi A Pi Pi A Ca2+ Ca2+ Ca2+ Ca2+

calcium ions are re-absorbed back into the T system Pi Pi Pi A Pi Pi Pi Pi A Pi Pi A Ca2+ Ca2+ Ca2+ Ca2+ calcium ions are re-absorbed back into the T system

calcium ions are re-absorbed back into the T system Pi Pi Pi A Pi Pi Pi Pi A Pi Pi A Ca2+ calcium ions are re-absorbed back into the T system

Pi Pi Pi A Pi Pi Pi Pi A Pi Pi A Ca2+ the troponin reverts to its normal shape and the tropomyosin move back to block the myosin binding sites

Pi Pi Pi A Pi Pi Pi Pi A Pi Pi A Ca2+ the troponin reverts to its normal shape and the tropomyosin move back to block the myosin binding sites

Pi Pi Pi A Pi Pi Pi Pi A Pi Pi A Ca2+ the troponin reverts to its normal shape and the tropomyosin move back to block the myosin binding sites

phosphocreatine regenerates ATP Pi Pi Pi A Pi Pi Pi Pi A Pi Pi A Ca2+ phosphocreatine regenerates ATP

phosphocreatine regenerates ATP Pi Pi Pi A Pi Pi Pi Pi A Pi Pi A Ca2+ phosphocreatine regenerates ATP

phosphocreatine regenerates ATP Pi Pi Pi A Pi Pi Pi A Pi Pi Pi A Ca2+ phosphocreatine regenerates ATP

Neuromuscular junction: Note Ach = Acetylcholine

Sarcoplasmic Reticulum

Sequence of events 1. An action potential arrives at the end of a motor neurone, at the neuromuscular junction. 2. This causes the release of the neurotransmitter acetylcholine. 3 This initiates an action potential in the muscle cell membrane (Sarcolemma). 4. This action potential is carried quickly into the large muscle cell by invaginations in the cell membrane called T-tubules.

Sequence of events 5. The action potential causes the sarcoplasmic reticulum to release its store of calcium into the myofibrils. 6. Ca2+ causes tropomoysin to be displaced uncovering myosin binding sites on actin. 7. Myosin cross bridges can now attach and the cross bridge cycle can take place. Relaxation is the reverse of these steps