Muscles Section 9.4

Muscles

3 Types of Muscle Tissue  1. Cardiac: muscles of the heart. (Involuntary Control)  2. Smooth: muscle Stomach, esophagus, uterus, blood vessels. (Involuntary Control)  3. Skeletal: muscle that are under conscious (voluntary) control.

Cardiac Muscle

Smooth Muscle

Tendons  Tendon is the tissue that attaches skeletal muscle to the bone.  Tendonitis: inflammation of one of these structures.  Torn Tendon

Basics of Muscles  Contraction: when a muscle shortens  Relaxation: when a muscle lengthens

Antagonistic Muscles  Pairs of muscles that work against each other  Best example: bicep and triceps (also quadriceps and hamstring)

Antagonistic Muscles

Flexor vs. Extensor  Flexor: Contracts to bend a joint (biceps)  Extensor: Contracts to straighten a joint (triceps)

Skeletal Muscle  Muscle cells are unique in their function as well as their construction  Unlike nearly every other cell in the body, muscle cells contain multiple nuclei.  Muscles are composed of bundles called fibres that work together to accomplish specific tasks.  Muscle fibres are surrounded by a sheath called the sarcolemma.

Skeletal Muscle

Myofilaments  A thread of contractile protein located in the muscles.  2 kinds of myofilaments: 1) actin 2) myosin  The 2 myofilaments overlap to appear striated

Sliding Filament Theory

 Actin filaments slide over myosin filaments.  Projections on the thicker myosin filaments form cross- bridges on receptor sites of actin filaments.  Cross bridges detach as actin filaments are drawn inward

Sliding Filament Theory  Calcium binds to sites on actin to initiate formation of cross- bridges with the myosin fibres.  ATP begins to breakdown in presence of calcium ions.  ATP is necessary for muscle contraction

Muscle Fatigue

 Lack of energy and build up of lactic acid will cause muscle fatigue and soreness.  Muscle tissue can store very little ATP.

Muscle Fatigue  Creatine Phosphate in the muscle cells release ADP and help to regenerate ATP supplies in the muscles.  High creatine Phosphate levels = ATP levels can be maintained.  If energy demand exceeds ATP supply, lactic acid builds up leading to soreness.

Muscle Contraction  Muscle action is broken down into a contraction and relaxation cycle.  If contraction occurs before relaxation has fully begun, the overlap of myofilaments is increased  This leads to a greater shortening of the muscle.  Net Effect: greater force of contraction

Tetanus  Constant muscle contraction.

Fast and Slow Twitch Muscle:  Muscle fibres are broken down into 2 categories  1.) Fast twitch: sprinters, explosive movements  2.) Slow twitch: distance athletes

Myosin types  The thick myosin determines the speed of muscle contraction.  3 forms of myosin exist.

Type 1  Slower muscle twitch.  Abundant in distance runners  Breakdown ATP slowly, but more efficiently  Relies predominantly on aerobic respiration

Type II a and Type II x  Faster twitch muscle  Abundant in sprinters/football/basketball players  Breakdown ATP faster, but less efficiently  Rely predominantly on anaerobic respiration

Fast and Slow Twitch Muscle:  All people have both types of muscle fiber, but in differing amounts

Fast and Slow Twitch Muscle:

Motor System Injuries  Muscles require a balanced diet and regular exercise to remain healthy.  Injuries are common when muscles are under-exercised, or when over-exercised  Common injuries: torn muscles, stretched tendons, torn ligaments, joint sprains, and joint dislocations.

Arthroscopic Surgery  Small incision(s) are made near the point of injury.  A light source and camera as well as surgical instruments are inserted through the incisions.  Allows for the precise removal/repair of damaged tissue  Advantage?  Spares the healthy tissue, minimizing surgical damage, and shortening recovery times.