THE MUSCULAR SYSTEM

Human Physiology Chapter 6 DOERFLER

Overview

Movement would be impossible without muscle tissue

Contractile cell – allows muscles to do job Have specialized cell membrane and cytoskeleton that

permit them to change their shape Can shorten along one or more planes

Muscle cells are laid out as sheets of muscle tissue that produce coordinated contractions

Over ½ of body’s mass is composed of muscle tissue Over 90% of muscle tissue is involved in skeletal

movement.

Overview, cont.

Contractile cells have HIGH energy needs

Associated with ample blood supply (lots)

Blood provides glucose and oxygen while removing metabolic wastes

Electrolytes – transported by blood – essential components of muscle cell contractions

Along with nervous tissue, muscle consumes almost 70% of food energy

Body Mass Index

BMI – indirect measure of body density

Muscle makes up large component of BMI

People with a lean body have higher amounts of muscle mass compared with body fat composition

Leanness is known to reduce heart disease and metabolic disorders

Muscle Categorization

Categorized several ways

1st - Evaluates microscopic appearance

Nonstriated – have random pattern of contractile proteins

Provide weaker contractions than striated

Contractile protein – cytoskeleton proteins involved in contraction

Striated – striped appearance – results from uniform arrangement of cytoskeleton

Cardiac & skeletal

Muscle Categorization, cont. 2nd – Control

Voluntary – people have large degree of control Some function involuntary – muscles needed for

breathing, but you can control when needed

Involuntary – contract without conscious control Carry out jobs that must be done automatically

3rd – Location Cardiac - The muscle of the heart

involuntary

Skeletal - Muscle attached to bone; produces body movement Voluntary

Smooth - Found in the linings of blood vessels and tubular organs Involuntary provide the body with weak contractions that can last for

long periods of time

Types of Muscle Tissue

End 6.1

6.2 Types of Muscle Tissue

All muscle tissue develops from mesoderm in process called myogenesis

Begins when stem cells in mesoderm form into myoblasts

Myoblasts (stem cells) help develop the 3 muscle types

Cardiac Muscle

Heart

Involuntary, striated

Provides strong contractions

Cells have 2 nuclei

Communicate at special junctions called intercalated disks

Intrinsic beat – a natural contraction cycle

Smooth Muscle

Found in many organ systems

Nonstriated

Produce weak involuntary contractions

Peristalsis – weak, pulsating contractions that move food and wastes through the digestive system

Skeletal Muscle

Focus of this chapter…..

Provides movement of the bones and joints

Voluntary, striated

Powerful contractile capabilities

Muscle fiber – several myoblasts fused together, a muscle tissue cell

Motor nerve cells – contract skeletal muscle fibers

Muscle Cell Structure

Skeletal muscles are long, cylindrical cells covered by excitable membrane filled with specialized cytoskeleton Respond to signals from others cells + environment

Sarcolemma = membrane (covering) of muscle cells

Cytoskeleton – composed of band of proteins called myofilaments Thick – composed of protein called myosin

Thin – 3 proteins – actin, tropomyosis, and troponin

Titin - elastic

Muscle Cell Structure, cont.

Sarcomere – contractile unit of muscle cell Many thousands run length of muscle cell

Chains of sarcomeres form myofibrils Each muscle fiber is made of many bundled myofibrils

Thick and thin myofilaments arrange to form overlapping pattern Overlapping is what carries out the muscle cell’s contraction,

and what gives it a striated pattern

Z line – marks the boundaries between each sarcomere Movement of Z line changes length of muscle

Sarcoplasmic reticulum – surrounds each sarcomere System of tubes that stores and transports calcium

needed for muscle contraction

Muscle Cell Structure

Its important to remember the heirarchy muscles

Composed of

Muscle fibers

bundles

Composed of

Light and Thin Dark & thicker

filaments

fibers

Composed of

fasicles

myofilaments

Individual types Myosin Actin

Actin

Fasicles Muscles

Myofilaments Myosin

Myofibrils Muscle fibers

Myofibrils

Threads

Muscle Cell Function

Contraction is achieved by simultaneous shortenings of all sarcomeres in a cell

Process of contraction

*Each on individual slide……

Neural stimulation (1st)

Muscle cell contraction (2nd)

Muscle cell relaxation (3rd)

Neural Stimulation (1st) Takes place at neuromuscular junction

Where nerve cells communicate with muscles

Contraction initiated when end of nerve cell releases neurotransmitter Chemicals used for cell-to-cell communication

Acetylcholine – neurotransmitter that communicates with muscle cells Binds to acetylcholine receptors, located on sarcolemma

Sodium-potassium pump – controls the ionic distribution of Na and K inside and outside of cell In resting cell, Na+ is higher outside cell, K+ higher

inside Pumps maintains this unequal ion concentrations

When stimulated, it loses its ability to maintain the imbalance Imbalance opens ions channel’s causing free flow of ions,

initiating the muscle contraction phase……….

http://www.youtube.com/watch?v=uJTdx1GbEqU

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Muscle Cell Contraction (2nd)

Begins when calcium released by sarcoplasmic reticulum binds to troponin on thin myofibrils

Results in temporary rigid tension that keeps filaments in place

ATP provides energy

Swivel motion brings the two Z-lines together, shortening sarcomere

Takes another neural stimulation to continue another cycle

1 muscle contraction requires several cycles of neural stimulation

Sliding Filament Model

Muscle Cell Relaxation (3rd)

When no more neural stimulations are exciting the sarcolemma

Calcium leakage out of the sarcoplasmic reticulum into the sarcomere is common after death Rigor mortis – muscle stiffness

Eventually, this stops

Creatine phosphate – stores energy in cells Collects ATP from cells, can store for long periods of

time

Glycogen – stored form of glucose Myoglobin – stores oxygen for muscle cells

6.3 Musculature

Muscle morphology – shape of muscle

Determined by arrangement of muscle fibers

Most muscles attach to two or more bones

Origin – stable, immovable attachment point

Insertion – connects a muscle to the body part it moves

Muscle Terminology

Muscle PATTERNS

Parallel – Sheets of muscle cells that run in the same direction

Provide contractions for moving light loads over a long distance

Latissimus dorsi (back)

Pinnate – feather-patterned

Provide great strengths for moving heavy loads over a short distance

Laid out in various directions to provide greater strength

Arms and legs

Muscle Terminology, cont.

Pinnate and parallel form different gross muscle SHAPES

Deltoid (triangular) – broad origin, narrow insertion

Deltoid, latissimus dorsi

Provide pulling power

Trapezius (trapezoid) – broad origin, narrow insertion

Rhomboideus – diamond-shaped

Provide holding power (levator scapulae)

Serratus – saw-toothed

Involved in short movements of arm, rib cage, and shoulders

Deep, not visible under skin

Serratus anterior

Muscle Terminology, cont.

ORIGINS

Biceps – muscle with 2 origins

Biceps brachii – 2 points on the scapula

Triceps – muscle with 3 origins

Triceps brachii – 2 points on humerus, 1 on scapula

Quadriceps – muscle with 4 origins

Quads of upper leg includes rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis

1 origin on the ilium, 3 on the femur

Muscle Terminology, cont.

SIZE

Maximus – largest of muscle group

Provides great pulling power

Minimus – smaller muscle of group

Gluteus maximus v gluteus minimus

Longus – longest muscle of group

Brevis – shorted muscle of group

Extensors of forearms and legs have longus and brevis groups

6.4 Skeletal Muscle Structure

Skeletal muscle = complex organ composed of striated muscle tissue and connective tissues

Nerve cells and blood vessels are integral parts of muscle structure

Skeletal Muscle Structure, cont. Basic structure = muscle fiber, or cell

Endomysium = CT, covers muscle fiber Maintains chemical environment of contracting cells

Fascicles = bundles of muscle tissue Perimysium = CT, surrounds each fascicle

Epimysium = CT, covers gross muscle Holds fascicles in place, provides lubricating

surfaces for muscles

Covers tendons that attach muscle to bone and skin

Skeletal Muscle responds…

Regular disuse of muscles will call muscle atrophy When not in regular use, cells lose sarcomere

proteins, will cause muscle shrinkage

Also trophy when there is lack of neural stimulation

Regular use will produce muscle hypertrophy Increased blood flow during regular use enlarges

muscle cells Produces more muscle strength

Skeletal Muscle Action

Tendon fixes the muscle origin to a firm foundation of bone Origin – point of attachment that remains fixed during

contraction Muscles insert onto surface of moveable component

Shortening brings origin closer to insertion

Threshold – level of stimulation needed to induce muscle cell to contract

Anatagonistic – one muscle opposes or resists the action of another muscle Weakens muscle strength Gravity also can have antagonist effect on muscle Essential for pulling relaxed muscles back to their original

length

Categories of Muscle Action

Abductor – move a bone away from body’s midline

Adductor – move a bone closer to the body’s midline

Depressor – produce a downward movement

Extensor – increase the angle of a joint

Flexor – decrease the angle of a joint

Levator – produce an upward movement

Categories of Muscle Action, cont.

Pronator – turn the palm downward

Rotator – move a bone around its longitudinal axis in a circular direction

Sphincter – decrease the size of an opening

Supinator – turn the palms upward

Tensor – make a body part more rigid or tense

Isotonic vs. Isometric

Isotonic – occurs when a muscle is actively shortening or lengthening

Lifting a weight with the arm, shortens the muscle involved, and returning the weight to its original position

Isometric – does NOT lengthen muscle

Muscle remains at steady length

Has indistinguishable pulses of shortening and lengthening

Pushing against something that is too heavy to move

6.5 Pathology of Musculature

Many disorders of the musculature are due to interactions with the skeletal and nervous system

Strains – overworking the muscle’s force on the joints Most common muscle ailment

Sprains – resulting from sudden stress on a joint or muscle Injury

More severe than strains

Require time for muscle tissue to repair muscle cell proteins

Muscle pathology, cont.

Contusions – caused by direct hit or battering of muscle Common in falls and impacts

Spasms – involuntary, abnormal muscle contraction Not always painful

Cramps – painful contraction of a muscle Caused by extreme muscle exertion & working in cold

conditions

Muscle sensitivity – continuous muscle pain due to muscle tissue damage or inflammatory disease

Muscle pathology, cont.

Paralysis – complete failure of muscle function

Rigid paralysis - caused by muscle stiffness

Flaccid paralysis– lack of muscle contraction

Tetanus – caused by soil bacteria that produce toxic secretions from a food-poisoning bacterium

Can cause death

Neuromuscular disorders

Myopathy, or neuromuscular disorders are characterized by the nervous system’s inability to communicate with the muscular system

Neuromuscular disorders, cont.

Dermatomyositis – inflammation of muscle and skin

Familial periodic paralysis – periodic weakness in the arms and legs; genetic

Glycogen storage diseases – cause muscle weakness due to a diminished ability to use glucose

Mitochondrial myopathies – genetic mitochondrial abnormalities that prevent muscle for producing energy

Muscular dystrophy – progressive weakness of voluntary muscles

Neuromuscular disorders, cont.

Myoglobinurias – affect how my0globin provides oxygen to muscles

Myositis ossificans – bone growing within muscle tissue

Myotonia – slow relaxation of muscles after contraction

Neuromyotonia – nerve disorder; bouts of muscle twitching and stiffness

Stiff-man syndrome – rigidity, and spasms of the spine and lower-extremity muscles

Tetany – periods of arm and leg muscle spasms caused by calcium imbalances

Muscle System Aging

Cachexia – muscle loss Associated with diseases such as AIDS and Cancer Common consequence of anorexia and bulimia

Protein turnover – rate at which a cell replaces damaged proteins Worsens with malnutrition and undernutrition

Insulin-Like Growth Factor-1 or IGF-1 Chemical needed for muscle cell growth, maintenance and

repair Levels lower with maturity

Aromatase – enzyme that reduces the level of sex hormones needed for muscle mass and strength BMI increases as you age, stimulates production or

aromatase