Chapter 7Chapter 7The Muscular System

Function of MusclesFunction of Muscles

Produce movement Maintain posture Stabilize joints Generate heat Guards openings

Fun Facts about MusclesFun Facts about Muscles

• There are 656 muscles in the human body.

• It takes 17 muscles to smile and 43 to frown.

• The tongue is the strongest muscle in the body.

• The gluteus maximus (the buttocks) is the largest muscle in the body.

• The sartorius muscle is the longest muscle in the body.

The Muscular SystemThe Muscular SystemThree types of muscle tissue :

Skeletal1) Attach to the bony skeleton2) Have longest fibers, fibers are striated (striped)3) Controlled voluntarily

Smooth1) Linings of organs and cavities2) Fibers are non-striated3) Controlled involuntarily, function constantly

Cardiac1) Found only in the heart2) Fibers are striated3) Controlled involuntarily

Smooth Muscle CharacteristicsSmooth Muscle Characteristics

Has no striations

Single nucleus

Found mainly in the walls of hollow organs

Smooth MuscleSmooth Muscle

Cardiac Muscle CharacteristicsCardiac Muscle Characteristics

Has striations

Usually has a single nucleus

Joined to another muscle cell at an intercalated disc Found only in the heart

Cardiac MuscleCardiac Muscle

Functional Characteristics of Functional Characteristics of MusclesMuscles Four properties of muscle:

1)Excitability: ability to receive and respond to a stimulus

2)Contractility: ability to shorten with force when stimulated

3)Extensibility: ability to be stretched or extended

4)Elasticity: ability of a muscle fiber to return to its original or resting length

SkeletalSkeletal Muscle Organization Muscle Organization

Muscle fascicle (bundle)

Muscle fiber (cell)

Myofibril

Sarcomere (Contractile unit of muscle fiber)

Thick and thin filaments

Skeletal Muscle

Anatomy of a Skeletal Muscle Anatomy of a Skeletal Muscle

• Consists of many bundles, called fascicles, of fibers covered by

connective tissue

• Each muscle contains at least one artery and one or two veins

… why?

• Most attach to bones by tendons (connective tissue extensions)

1) insertion: bone that moves during contraction

2) origin: bone that stays still during contraction

• Some muscles attach directly to bone by their connective

tissue coverings

Connective Tissue Wrappings Connective Tissue Wrappings ofofSkeletal MuscleSkeletal Muscle Epimysium –

covers skeletal muscle

Perimysium – covers fascicle (bundle) of fibers

Endomysium – around single muscle fiber

Microscopic Anatomy of a Microscopic Anatomy of a Skeletal Muscle Skeletal Muscle • Muscle fiber: muscle cell with many nuclei

• Sarcolemma: plasma membrane of a muscle cell

• Sarcoplasm: cytoplasm of muscle cell, contains large amounts of glycogen and oxygen-binding protein

• Each muscle fiber contains large numbers of myofibrils in the sarcoplasm, with mitochondria packed around them

• Myofibrils: contractile portion of the muscle cell, made up of units called sarcomeres

• Sarcomeres contain two types of filaments:

1) thick: contain the protein myosin

2) thin: contain the protein actin

Microscopic Anatomy of the MuscleMicroscopic Anatomy of the Muscle

At rest, there is a bare zone that lacks actin filaments (no filament overlap)

Muscle Contraction: Sliding Filament TheoryMuscle Contraction: Sliding Filament Theory

To start contraction, calcium unlocks active sites on actin

Myosin heads bind to actin active sites – connections are called cross-bridges

Myosin pulls the actin microfilaments toward the bare zone - muscle shortens

Myosin detaches, then reattaches to another active site, shortening the muscle further

Muscle Contraction: Sliding Filament Muscle Contraction: Sliding Filament TheoryTheory

Sliding Filament Animation

Muscle Contraction: Rigor MortisMuscle Contraction: Rigor Mortis• After death, there is an influx of calcium

• Calcium causes myosin to bind with actin (forming cross bridges)

• Breathing stops, no energy is available to detach cross bridges, so they stay attached

• Muscles stiffen after 3 to 4 hours, peaks at 12 hours, and decreases between 48 and 60 hours

Nerve Stimulus for Muscle Nerve Stimulus for Muscle ContractionContraction Skeletal muscles must be stimulated by a motor neuron (nerve) to contract

Motor neuron plus the fibers it supplies is called the “motor unit”

Neuromuscular junctions (NMJ) – site where nerve and muscle meet

Nerve Stimulus for Muscle Nerve Stimulus for Muscle ContractionContraction

Nerve and muscle do not make direct contact

Synaptic cleft – gap between nerve and muscle fiber, filled with fluid

Each muscle fiber has only one neuromuscular junction

Nerve Stimulus for Muscle Contraction:Nerve Stimulus for Muscle Contraction:Neuromuscular JunctionNeuromuscular Junction

Nerve Stimulus for Muscle Nerve Stimulus for Muscle ContractionContraction

Upon arrival of nerve impulse, a chemical called a neurotransmitter is released by nerve The neurotransmitter for skeletal muscle is

acetylcholine Neurotransmitter attaches to receptors on the sarcolemma of the muscle fiber

Brain or spinal cord sends a nerve impulse down the motor neuron in response to a stimulus

Nerve Stimulus for Muscle Nerve Stimulus for Muscle ContractionContraction Sarcolemma becomes permeable to sodium

ions (Na+)

Sodium rushes into the cell and generates an action potential - an explosion of electrical activity

This electrical stimulus starts the muscle contraction

Once the contraction starts, it cannot be stopped - ALL OR NOTHING PRINCIPLE

Neuromuscular Junction Animation

Contraction of a Skeletal MuscleContraction of a Skeletal Muscle Within a skeletal muscle, not all fibers may

be stimulated at the same time

Different combinations of muscle fiber contractions may give differing responses

Graded responses – different degrees of skeletal muscle contraction

Example: finger muscles help you pick up a penny or a textbook

Muscle ToneMuscle Tone Slightly contracted state while

muscle is at rest

Keeps muscles ready to respond to stimulation

Helps maintain posture

Stabilizes your joints

Atrophy – decrease in muscle tone; fibers become small and weak without stimulation

a. Twitch – single, jerky contraction from a single stimulus

Not a normal contraction

b. Tetanus – smooth, sustained contraction from multiple stimuli building upon each other

Cannot go on indefinitely or results in fatigue

c. Treppe effect – increasingly forceful contractions due to increased efficiency of muscle, even with same stimulus

As muscle warms up, more calcium is available, and enzymes are more effective

Muscle Responses to StimuliMuscle Responses to Stimuli

Types of Muscle ContractionsTypes of Muscle Contractions1) Isotonic contractions

Tension remains constant The muscle changes length so

movement can occur

a. Concentric – muscle shortens as it contracts

b. Eccentric – muscle lengthens as it contracts2) Isometric contractions

Tension in the muscles increases The muscle does not change length so positions can be held

**Most body movements are a combination of both types.**

Force of Muscle ContractionForce of Muscle Contraction

Depends on four things:

1) # of muscle fibers contracting – greater the number of motor units contracting, the greater the force

2) Size of the muscle – bigger the muscle, the greater the force

3) Elastic elements (tendons, tissue coverings) – greater the tension on the elastic elements, the greater the force

4) Degree of muscle stretch – slight stretch increases the force of contraction

ATP is the only energy source used for muscle contraction

Only 4-6 seconds worth of ATP is stored by muscles

After this initial time, other pathways must be utilized to produce ATP

a.Anaerobic glycolysis/lactic acid fermentation

b.Aerobic respiration

Energy for Muscle ContractionEnergy for Muscle Contraction

Energy for Muscle ContractionEnergy for Muscle Contraction Anaerobic Glycolysis/Lactic Acid

Fermentation (NO OXYGEN AVAILABLE) Series of chemical reactions that makes ATP from glucose without oxygen

This reaction FAST, but inefficient Huge amounts of glucose are needed to make ATP

Lactic acid is a waste product of the reactions, causes muscle fatigue and soreness

Provides 90 seconds of energy – weightlifting, sprints

Energy for Muscle ContractionEnergy for Muscle Contraction Aerobic Respiration

(OXYGEN IS AVAILABLE) Series of chemical reactions that makes

ATP from glucose in the presence of oxygen This is a slow reaction, but makes huge amounts of ATP

Breaks down glycogen (chains of glucose) stored in muscles and liver

Carbon dioxide and water are waste products of the reactions (breathing out and sweating)

Provides 15-20 minutes of energy – long distance running, endurance exercises

Critical Thinking Question:Critical Thinking Question:

After 20 minutes of exercise, your body has used up all the stored glycogen. What do you use for energy after that? What does

this help with?

Effects of Exercise on MuscleEffects of Exercise on MuscleResults of increased muscle use:

Increase in muscle size (size of fiber, not number of fibers increases)

Increase in muscle strength

Increase in muscle efficiency (more capillaries, more mitochondria)

Muscle becomes more fatigue resistant (more glycogen is stored, more mitochondria)

Muscles and Body MovementsMuscles and Body Movements Movement is

attained due to a muscle moving an attached bone

Insertion – muscle attachment to bone that MOVES during contraction

Review:

Origin – muscle attachment on bone that DOES NOT MOVE during contraction

Types of Body MovementsTypes of Body Movements

Review:

Flexion

Extension

Rotation

Abduction

Circumduction

Types of Body MovementsTypes of Body Movements

Producing Body Movements:Producing Body Movements:Skeletal Muscle InteractionsSkeletal Muscle Interactions

1) Prime Mover or Agonist: muscle(s) that provides the greatest force of a movement

2) Antagonist: muscle(s) that oppose or reverse a particular movement, to regulate or resist the agonist

3) Synergist: muscle that aids the agonist by:

a. Promoting the same movement

b. Reducing unnecessary movement by stabilizing or fixating a joint and/or bone

Naming of Skeletal MusclesNaming of Skeletal Muscles

1) Location of the muscle

Example: temporalis (located on the temporal bone)

2) Number of origins

Example: triceps (three origins)

Naming of Skeletal MusclesNaming of Skeletal Muscles

3) Direction of muscle fibers

Example: rectus abdominis (straight)

4) Relative size of the muscle

Example: gluteus maximus (largest)

Naming of Skeletal MusclesNaming of Skeletal Muscles5) Location of the muscles origin and

insertion

Example: sternocleidomastoid (originates on the sternum and clavicle, inserts on the mastoid)

6) Shape of the muscle

Example: deltoid (triangular)

7) Action of the muscle

Example: extensor digitorum longus (extends the fingers)

Head and Neck MusclesHead and Neck Muscles

Figure 6.14

Superficial Trunk and Arm Superficial Trunk and Arm MusclesMuscles

Deep Trunk and Arm MusclesDeep Trunk and Arm Muscles

Muscles of the Anterior Pelvis, Hip, and Muscles of the Anterior Pelvis, Hip, and ThighThigh

Muscles of the Posterior Pelvis, Hip, and Muscles of the Posterior Pelvis, Hip, and ThighThigh

Superficial Muscles: AnteriorSuperficial Muscles: Anterior

Superficial Muscles: PosteriorSuperficial Muscles: Posterior

Muscular System DisordersMuscular System DisordersChronic Fatigue Syndrome

Fibromyalgia

Duchenne’s Muscular Dystrophy

Rotator Cuff Syndrome

Anterior Compartment Syndrome

Rhabdomyolysis

Cardiomyopathy

Myasthenia Gravis

Rhabdomyosarcoma

Inguinal Hernia

Polio

Carpal Tunnel Syndrome