Chapter 12

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Chapter 12

Muscular System

• Who is this?

• Chelsey Thomas.

• What is her problem?

• Moebius syndrome?

• A rare disorder which causes paralysis of facial muscles!!!

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Outline• Overview of Muscular System• Types and Functions of Muscles• Skeletal Muscle Fiber Contraction• Whole Muscle Contraction

– Muscles Have Motor Units– Energy for Muscle Contraction– Fast-Twitch and Slow-Twitch Fibers

• Muscle Disorders• Homeostasis

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Types and Functions of Muscles

• Smooth muscle is located in the walls of hollow internal organs and contracts involuntarily. (non-striated / involuntary, visceral muscle)

• Cardiac muscle forms the heart wall and contracts involuntarily. (striated, involuntary)

• Skeletal muscle runs the entire length of the muscle and contracts voluntarily. (striated, voluntary)

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Types of Muscle

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Functions of Skeletal Muscles

• Support body.• Movement of bones.• Maintenance of constant body temperature.• Assist movement in cardiovascular and

lymphatic vessels.• Protect internal organs.• Stabilize joints.

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SKELETAL MUSCLES

Macroscopic View

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Skeletal Muscles of the Body• A whole muscle contains bundles of skeletal

muscle fibers (= muscle cells), fascicles.• Muscles are covered with fascia (dense

connective tissue) that becomes tendons.• Muscles originate on the stationary bone

(origin), and insert on the bone that moves (insertion).

• Cooperating muscle pairs have prime movers, synergists, and antagonists.

• Muscles usually work in antagonistic pairs which work opposite one another to move in opposite directions.

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Skeletal Muscles of the Body

• Muscles only contract, never push.• Muscle spindles are modified muscle fibers

that have a sensory nerve fiber wrapped around the middle of the muscle’s length so as to inform the CNS as to the state of that muscle for coordination with other muscles and for posture and muscle tone.

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Names and Actions of Skeletal Muscles• Names based on characteristics.

– Size (ie. gluteus maximus).– Also: vastus (huge), longus (long),

brevis (short).– Shape (ie. deltoid).– Also: trapezius (trapezoid), latissimus

(wide), terres (round).– Location (ie. external obliques)– Also: pectoralis (chest), gluteus (buttock),

brachii (arm), sub (beneath).

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Names and Actions of Skeletal Muscles– Direction of muscle fibers

(ie. rectus, meaning straight, abdominis).– Also: transverse (across), oblique

(diagonal).– Attachment (ie. sternocleidomastoid).– Also: brachioradialis (arm, radius).– Number of attachments (ie. Biceps brachii

or “two origins, arm”)– Also: quadriceps femoris (“four origins,

located on femur”).

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Names and Actions of Skeletal Muscles– Action (ie. extensor digitorum).– Also: flexor (to flex or bend), masseter (to

chew), levator (to lift).

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Science Focus

Rigor Mortis

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SKELETAL MUSCLES

Microscopic View

(Skeletal Muscle Fiber Contraction)

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Skeletal Muscle Fiber Contraction“Sliding Filament Model”When muscle fibers are stimulated to

contract, myofilaments (actin – anchored on Z line, myosin – in the middle) slide past one another.

This causes sarcomeres (muscle units) to shorten and the whole muscle fiber shortens.

Thus, when you see the prefixes myo- or sarco-, you will know these refer to muscles.

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Skeletal Muscle Fiber Contraction• Myosin filament heads break down ATP and

attach to an actin filament, forming cross-bridges that pull the actin filament to the center of the sarcomere.– Contraction continues until nerve impulses

cease.

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“Sliding Filament Model” Video Clips

• Concept 29 - Levels of Muscle Structure• Concept 30 - Sliding Filament Model• Concept 31 - Regulation of Muscle

Contraction

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Control of Muscle Fiber Contraction

– Nerve impulses originate in the brain, travel down motor neurons, and stimulate muscle fibers at neuromuscular junctions and muscle fibers are innervated. . . . .

– Stimulated to contract by motor nerve fibers.

Signaled when nerve impulses bring about release of neurotransmitter molecules at a neuromuscular junction.

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Whole Muscle Contraction

• Method of study: when a muscle (frog’s calf muscle) is attached to a physiograph (machine), a myogram (a recording) will result when muscle is stimulated to contract.

• Characteristics of muscle contraction: a muscle fiber, in contrast to a whole muscle, will behave in an all-or-none manner when a threshold stimulus is applied.

• The force of contraction of a whole muscle depends upon the number of fibers contracting.

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Whole Muscle Contraction (In the Lab)• Muscle Twitch - Single muscle contraction.

– Divided into three stages.Stimulation.Contraction.Relaxation.

• If a muscle is given a rapid series of threshold stimuli, muscle contraction summates in a sustained contraction, tetanus. . . .

• which continues until the muscle fatigues due to depletion of energy reserves.

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Physiology of Whole Muscle Contraction

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Whole Muscle Contraction (In the Body)• A motor neuron, together with all of the muscle

fibers that it innervates, is a motor unit.– As the intensity of nervous stimulation

increases, more motor units are activated (recruitment) resulting in stronger and stronger contractions.

• Also important are the number of muscle fibers within a motor unit. . . . for example:– innervation ratio of 1 motor neuron / 23

muscle fibers (eye muscles). . . . – 1 motor neuron / 1,000 muscle fibers (calf

muscle).

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The Effect of Exercise.• A regular exercise program will bring about 1.

Increased endurance 2. Increased strength of muscles.

• Muscle enlarges, not due to increase in number of muscle fibers, but increased amounts of actin and myosin myofibrils inside each muscle fiber making them bigger and stronger.

• “Use it or lose it !”• Benefits include: lower risk of heart attack,

increased capacity of heart and lungs, decreased body fat and cholesterol levels.

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HEALTH FOCUS

Exercise, Exercise, Exercise.

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Energy for Muscle Contraction

• ATP produced previous to strenuous exercise lasts a few seconds.

• Then muscles acquire new ATP in three ways.– Creatine phosphate (phosphocreatine)

breakdown. (anaerobic)– Fermentation. (anaerobic)– Cellular respiration. (aerobic)

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Oxygen Deficit

• When a muscle uses the anaerobic means of supplying energy, it incurs an oxygen deficit.– Repaying an oxygen deficit requires

replenishing creatine phosphate supplies and disposing of lactic acid.

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Athletics and Muscle Contraction

• Muscles that are not used, or are used in only weak contractions can atrophy.– Can cause muscle fibers to progressively

shorten, leaving body parts contracted in contorted positions.

Hypertrophy occurs if the muscle contracts to at least 75% of its maximum tension.

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*Fast-Twitch and Slow-Twitch Muscle Fibers*• Although all muscle fibers metabolize both

aerobically and anaerobically, some muscle fibers utilize one method more than the other.

• Slow-twitch fibers produce most of their energy aerobically and tire only when their fuel supply is gone.

• Fast-twitch fibers tend to be anaerobic and seem to be designed for strength as their motor units contain many fibers.– Can develop greater, and more rapid,

maximum tension than slow-twitch fibers.

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59Ben Johnson, 1988, Olympic gold medal 100-m sprint.

Delayed Onset Muscle Soreness

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• also known as DOMS.• Generally appears 24-48 hours after strenuous exercise.• Thought to be due to tissue injury that takes several days to heal.• Associated with any activity you are not used to, especially actvities that causes muscles to contract while they are lengthening , ie. Walking down stairs, running down hill, lowering weights.• To avoid: stretch, cool down, start slow.

HISTORICAL FOCUS

Iron Horse: Lou Gehrig (1903-1941)

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Muscle Disorders – Common Muscular Conditions

• Spasms are sudden, involuntary muscular contractions most often accompanied by pain.– Multiple spasms of skeletal muscles are called

a seizure (or convulsion).– Cramps are strong, painful spasms……

• A strain is an overstretching of a muscle near a joint, while a sprain is a twisting of a joint leading to swelling and injury.

• Tendinitis is inflammation of a tendon due to the strain of repeated athletic activity (shoulder, elbow, hip, and knee).

• Bursitis – an inflammation of the bursa.

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Muscular Disorders - Diseases• Myalgia refers to inflammation (pain) of

muscle tissue, achy muscles.• Fibromyalgia is a chronic condition whose

symptoms include achy pain, tenderness, and stiffness of muscles whose cause is not known.

• Infection known as tetanus or lockjaw?• Muscular dystrophy is a broad term applied

to a group of disorders characterized by progressive muscle degeneration and weakening (ie. Duchenne MD).

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Muscular Disorders - Diseases• Myasthenia gravis is an autoimmune disease

characterized by weakness that especially affects the muscles of the eyelids, face, neck, and extremities.

• Amyotrophic lateral sclerosis (ALS) • Also known as Lou Gehrig’s disease.• Sufferers experience gradual loss of the

ability to walk, talk, chew, and swallow while mental abilities and sensations are not affected.

• Drugs slow the disease, but can’t be cured !

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Homeostasis

• Cardiac muscle contraction accounts for the heartbeat, delivering blood to the tissues.

• Smooth muscle contraction accounts for peristalsis and urination.

• Skeletal muscle contraction returns blood to the heart and moves bones, allowing for body movement.

• SEE Homeostasis in the text.

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BIOETHICAL FOCUSAnabolic Steroid Use

• Anabolic steroids to promote muscle growth.• Testosterone or related chemicals.• Danger ! ?• Cardiovascular disease, liver and kidney

dysfunction, impotency and sterility, increase in rash behavior called “roid mania”.

• What is a misconception that some have of these drugs?

• Is becoming a problem with young people!

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Outline• Overview of Muscular System• Types and Functions of Muscles• Skeletal Muscle Fiber Contraction• Whole Muscle Contraction

– Muscles Have Motor Units– Energy for Muscle Contraction– Fast-Twitch and Slow-Twitch Fibers

• Muscle Disorders• Homeostasis

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REVIEW•Remember:•Use the “Study Questions” before each chapter to guide your reading of the text material before coming to class.•Use the “Powerpoint handouts” to review what you read before class and what we covered in class.•After studying the material and when you believe you know and understand it – use the End-of-Chapter material to check your understanding.•Also check your understanding by working in groups.

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