Muscular System

Three types of Muscles Found in the Body

Muscle Structure Functions •Movement (constriction of organs & vessels, heat beating, respiration) •Support (posture) •Heat production Communication Properties of Skeletal (striated) muscle (40% of body weight) •Contractibility - ability of cells to shorten in length •Excitability - ability to receive & respond to stimuli •Extensibility - ability to increase (stretch) in length •Elasticity - ability of a cell to return (recoil) to its resting position after it has contracted or stretched.

All muscle is made of the same two proteins (Actin {troponin & tropomyosin} & Myosin) & require ATP (Adenosine Triphosphate) as energy. 3 Types Appearance Control Nuclei Work Skeletal Striated/Fibers Voluntary/ Multi Pairs Nervous (Flexors - Entensors) Smooth Non-striated/Single Cells Involuntary/ Uni Single Nervous & Endocrine Cardiac Striated/ Single cells Involuntary/ Uni Single Nervous & Endocrine

Review Questions How is extensibility different from contractibility? How are skeletal, cardiac, & smooth muscles different?

Anatomy of a skeletal muscle. PART OF THE MUSCLE COVERING or COMPONENT Muscle(fascia) Epimysium Bundle (Muscle fasiculi) Perimysium Fiber(muscle cells) Endomysium or Sarcolemma (cell membrane) Myofibrils Sarcoplasmic reticulum, T-tubules Filaments Myofilaments (Actin & Myosin)

Microscopic Structure

Review What is the largest layer of the muscle? What wraps around a myofibril? What are the functioning proteins of the muscle?

Sarcomere Contractile unit of the muscle Z disk – protein fiber for attaching actin I Band – light band A Band – darker band H zone – center of each sarcomere M line – place of attachment for myosin

Myofibril

Motor Neurons carries action potential to the muscle for a contraction. Motor unit – a group of fibers (muscle) that are responding to a motor neuron, Very percise movements – only a few Larger muscle (leg) – several thousand

Neuromuscular Junction Nerve impulse reaches the end of the neuron. Allows calcium to enter the neuron Calcium causes the release of a synaptic vesicle that contains acetylcholine (neurotransmitter) Floods the synaptic cleft to carry the signal to receptors on the muscle.

Review What is the contractile unit of the muscle? Describe the motor unit. How is the synaptic gap different from the synaptic cleft? How the does signal cross the synaptic gap?

Sliding Filament theory

All Muscle work in the same way - Sliding Filament Theory 1. Motor neuron transmits an impulse from the brain/spinal cord to the muscle. 2. The electrical impulse is changed into a chemical messenger/neurotransmitter (acetylcholine) at the terminal bud to cross the synaptic cleft. 3. Signal binds to the motor end plate & travels throughout the muscle. 4. Calcium is released from the sarcoplasmic reticulum & binds to troponin & causes it to change. 5. The binding sites are exposed to form a cross bridge with the myosin head & ATP. 6. ATP is broken down to ADP & P & releases energy. 7. Energy that is released causes the myosin head to change shape & resulting in the actin sliding past myosin. 8. New ATP binds to the myosin heads causing the bridge to break from the binding site & return to its original shape. 9. Once returned to its original shape it re-forms a cross bridge. 10. Process repeats.

Stopping the signal 1. All the Acetylcholine must be inactivated at the motor end plate by acetylocholinesterase or AchE from the sarcolemma. 2. Calcium returns back to the sarcoplasmic reticulum by active transport (ATP). 3. Troponin is restored to its original shape.

Sliding Filament Theory

Sliding Filament Theory

Muscle Twitch – Muscle contraction in response to a stimuli 1. Threshold stimuli - weakest stimuli that can initiate a contraction. 2. Subthreshold stimuli - stimuli that will not cause a contraction. 3. All or none response - stimuli that is stronger than the threshold stimuli & will cause a muscle to contract completely. 4. Recruitment - activating more muscle fibers in corresponding to a stimuli.

Types of Muscle Contractions 1. Twitch - basic unit of muscle contraction. •Rapid response to a single stimuli that is slightly over threshold. •Lasts on 1/10 of a second. Phases of a twitch •Lag phase - delay contraction from the time the signal is sent. •Contraction phase- muscle contracts (shortens). •Relaxation phase- muscle returns to its original shape.

2. Wave contraction Muscle to contract & lasts for a definite period of time. Wave summation - second signal is sent before the first is completed causing the second contraction to be stronger than the first.

3. Tetanus Sustained contraction that occurs when the frequency of stimulation is so rapid that there is no relaxation. Incomplete tetanus - partial relaxation occurs between each stimuli (20 - 30/second). Complete tetanus - fusion of twitches & provides a forceful contraction (35-50/sec).

Energy for Contraction 1. ATP (muscles can not store ATP) 2. Creatine Phosphate 3. Glycogen Uses for energy 1. Mechanical movement of cross bridges. 2. Breakage of cross bridges from actin. 3. Return of calcium to the sarcoplasmic reticulum. Types of respiration Aerobic – with oxygen 18x’s more efficient, but slower. Anaerobic – without oxygen, but faster with a price.

Muscle Exercise Psychological fatigue – more of the nervous system Muscle fatigue Muscles require food, oxygen & waste removal to function properly. During sustained exercise blood can not always deliver enough oxygen to the muscle - oxygen debt. To get energy, the muscle performs lactic acid fermentation (anaerobic) to get energy. ATP is produced, & a waste - lactic acid. Increase in lactic acid causes the pH to lower, therefore reducing the muscles ability to contract - muscle fatigue. Cramp -muscle contracts spasmodically without relaxing & is caused by an insufficient amount of ATP to properly return the calcium back to the sarcoplasmic reticulum. Muscle use can increase in size. Lack of use can decrease in size -atrophy

Types of muscle contraction 1. Isotonic - Produces movement, the muscle pulls an attach structure (bone) towards a more stationary structure. 2. Isometric - Produces muscle tension but does not shorten (no movement). 3. Concentric contraction – isotonic contraction when lifting a weight. 4. Eccentric contraction – isotonic contraction when lowering a weight. Slow & Fast Fibers Slow type I myosin – contract & fatigue slowly Darker muscle - myoglobin ability to store oxygen. Fast type II (a or x) myosin – contract & fatigue quickly

Production of Movement Origin - muscle attachment to the more stationary bone. Insertion - muscle attachment to the more movable bone. Group Actions Group action - coordinated response of a group of muscles in order to bring a body movement. Prime movers - desired action. Antagonist - relaxes during the contraction. Synergists - steady the movement. Fixators - stabilize the origin of the prime mover

Major Muscles of the Body Anterior

Major Muscles of the Body Posterior

Muscles of the Head & Neck

Muscles of the Upper Back

Muscles of the Upper Chest

Muscles of the Upper Arm

Muscles of the Lower Arm

Muscles of the Abdominal Pelvic

Muscles of the Upper Leg

Muscles of the Lower Leg