7. The Muscular System

Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.

The Muscular SystemThe Muscular System


Learning ObjectivesLearning Objectives List the 3 types of muscles and describe the characteristics of each.List the 3 types of muscles and describe the characteristics of each. Describe the structure and function of tendons, aponeuroses, and Describe the structure and function of tendons, aponeuroses, and

ligaments.ligaments. Differentiate between prime mover, antagonist, syngergist, and fixator Differentiate between prime mover, antagonist, syngergist, and fixator

muscles.muscles. List the locations and actions of the muscles of the head and neck, List the locations and actions of the muscles of the head and neck,

abdomen, thoracic limb, pelvic limb, and the muscles of respiration.abdomen, thoracic limb, pelvic limb, and the muscles of respiration. Describe the microscopic anatomy of skeletal, smooth, and cardiac muscle Describe the microscopic anatomy of skeletal, smooth, and cardiac muscle

cells.cells. List the components of a neuromuscular junction and describe the function List the components of a neuromuscular junction and describe the function

of each.of each. Describe the events that occur in muscle cells during muscle contraction Describe the events that occur in muscle cells during muscle contraction

and relaxation.and relaxation. Differentiate between visceral smooth muscle and multiunit smooth muscleDifferentiate between visceral smooth muscle and multiunit smooth muscle


MuscleMuscle

One of the four basic tissues of the bodyOne of the four basic tissues of the body Made up of cells that can shorten or Made up of cells that can shorten or

contractcontract Three different types of muscleThree different types of muscle

1.1. skeletal muscle skeletal muscle

2.2. cardiac musclecardiac muscle

3.3. smooth musclesmooth muscle


Skeletal Muscle Gross AnatomySkeletal Muscle Gross Anatomy

Tendons: fibrous connective tissue bandsTendons: fibrous connective tissue bands Aponeuroses: sheets of fibrous connective Aponeuroses: sheets of fibrous connective

tissuetissue Origin: the more stable of a muscle's Origin: the more stable of a muscle's

attachment sites attachment sites Insertion: site that undergoes most of the Insertion: site that undergoes most of the

movement when a muscle contractsmovement when a muscle contracts


Muscle ActionsMuscle Actions

Prime mover (agonist): a muscle or muscle Prime mover (agonist): a muscle or muscle group that directly produces a desired group that directly produces a desired movement movement

Antagonist: a muscle or muscle group that Antagonist: a muscle or muscle group that directly opposes the action of a prime directly opposes the action of a prime movermover


Muscle ActionsMuscle Actions

Synergist: a muscle that contracts at the Synergist: a muscle that contracts at the same time as a prime mover and assists it same time as a prime mover and assists it in carrying out its actionin carrying out its action

Fixator: muscles that stabilize joints to Fixator: muscles that stabilize joints to allow other movements to take placeallow other movements to take place


Muscle-Naming ConventionsMuscle-Naming Conventions

Action: e.g., flexor muscles; extensor Action: e.g., flexor muscles; extensor muscles muscles

Shape: e.g., Shape: e.g., deltoiddeltoid means “triangular means “triangular shaped”shaped”

Location: e.g., biceps brachii muscle is Location: e.g., biceps brachii muscle is located in the brachial regionlocated in the brachial region

Direction of fibers: e.g., Direction of fibers: e.g., rectusrectus means means “straight”“straight”


Muscle-Naming ConventionsMuscle-Naming Conventions

Number of heads or divisions: Number of heads or divisions: -cep-cep means means “head”; biceps brachii muscle has two “head”; biceps brachii muscle has two headsheads

Attachment sites: e.g., origin of the Attachment sites: e.g., origin of the sternocephalicus muscle is the sternum sternocephalicus muscle is the sternum and insertion is the back of the headand insertion is the back of the head


Cutaneous MusclesCutaneous Muscles Thin, broad, Thin, broad,

superficial musclessuperficial muscles Found in the fascia Found in the fascia

just beneath the skin just beneath the skin Little or no Little or no

attachment to bones attachment to bones Serve to twitch the Serve to twitch the

skinskin


Head and Neck MusclesHead and Neck Muscles

FunctionsFunctions Control facial expressionsControl facial expressions Enable masticationEnable mastication Move structures such as eyes and ears Move structures such as eyes and ears Support the head Support the head Allow the head and neck to flex, extend, and Allow the head and neck to flex, extend, and

move laterallymove laterally


Head and Neck MusclesHead and Neck Muscles

Masseter muscle - closes the jaw Masseter muscle - closes the jaw Splenius and trapezius muscles - extend Splenius and trapezius muscles - extend

the head and neck the head and neck Brachiocephalicus muscle - extends the Brachiocephalicus muscle - extends the

head and neck; also pulls the front leg head and neck; also pulls the front leg forward forward

Sternocephalicus muscle - flexes the head Sternocephalicus muscle - flexes the head and neck and neck


Abdominal MusclesAbdominal Muscles

FunctionsFunctions Support the abdominal organsSupport the abdominal organs Help flex the back Help flex the back Participate in various functions that involve Participate in various functions that involve

straining straining Play a role in respirationPlay a role in respiration


Abdominal MusclesAbdominal Muscles

Arranged in layersArranged in layers External abdominal oblique muscle External abdominal oblique muscle Internal abdominal oblique muscle Internal abdominal oblique muscle Rectus abdominis muscleRectus abdominis muscle Transversus abdominis muscleTransversus abdominis muscle

Left and right parts of each muscle come Left and right parts of each muscle come together on the ventral midline at the linea together on the ventral midline at the linea albaalba


Thoracic Limb MusclesThoracic Limb Muscles

Superficial muscles of the shoulder regionSuperficial muscles of the shoulder region Latissimus dorsi muscle - flexes the shoulder Latissimus dorsi muscle - flexes the shoulder Pectoral muscles - one superficial and one Pectoral muscles - one superficial and one

deep; adduct the front legdeep; adduct the front leg Deltoid muscle - abducts and flexes the Deltoid muscle - abducts and flexes the

shoulder jointshoulder joint


Thoracic Limb MusclesThoracic Limb Muscles

Brachial musclesBrachial muscles Biceps brachii muscle - flexes the elbow jointBiceps brachii muscle - flexes the elbow joint Triceps brachii muscle - extends the elbow Triceps brachii muscle - extends the elbow

jointjoint Carpal and digital musclesCarpal and digital muscles

Extensor carpi radialis muscle - extends the Extensor carpi radialis muscle - extends the carpus carpus

Deep digital flexor muscle - flexes the digitDeep digital flexor muscle - flexes the digit


Pelvic Limb MusclesPelvic Limb Muscles

Gluteal muscles - extensor muscles of the Gluteal muscles - extensor muscles of the hip hip

““Hamstring" muscle group - extend the hip Hamstring" muscle group - extend the hip joint; main flexors of the stifle jointjoint; main flexors of the stifle joint Biceps femoris muscleBiceps femoris muscle Semimembranosus muscleSemimembranosus muscle Semitendinosus muscleSemitendinosus muscle


Pelvic Limb MusclesPelvic Limb Muscles

Quadriceps femoris muscle - main Quadriceps femoris muscle - main extensor muscle of the stifle jointextensor muscle of the stifle joint

Gastrocnemius muscle - extensor muscle Gastrocnemius muscle - extensor muscle of the hockof the hock


Muscles of respirationMuscles of respiration

FunctionFunction Increase and decrease the size of the Increase and decrease the size of the

thoracic cavitythoracic cavity Inspiratory musclesInspiratory muscles

• Diaphragm Diaphragm

• External intercostal musclesExternal intercostal muscles Expiratory musclesExpiratory muscles

• Internal intercostal muscles Internal intercostal muscles

• Abdominal musclesAbdominal muscles


Skeletal Muscle CellsSkeletal Muscle Cells

Very largeVery large MultinucleateMultinucleate Numerous myofibrils Numerous myofibrils

composed of actin composed of actin

and myosinand myosin Network of sarcoplasmic Network of sarcoplasmic

reticulum reticulum T tubulesT tubules



A bands:A bands: thick thick

myosin filamentsmyosin filaments I bands: thin I bands: thin

actin filamentsactin filaments Dark line in the center Dark line in the center

of the I band is the Z line of the I band is the Z line Disk that is the attachment Disk that is the attachment

site for the actin filamentssite for the actin filaments



Sarcomere - basic Sarcomere - basic

contracting unit of contracting unit of

skeletal muscle skeletal muscle Area from one Z Area from one Z

line to the next Z line line to the next Z line Each myofibril is Each myofibril is

made up of many made up of many

sarcomeres lined sarcomeres lined

up end to end.up end to end.


Neuromuscular JunctionNeuromuscular Junction Nerves and muscles Nerves and muscles

separated by the separated by the synaptic spacesynaptic space

Synaptic vesicles - Synaptic vesicles - sacs at the end of a sacs at the end of a nerve fiber; contain nerve fiber; contain acetylcholineacetylcholine Acetylcholinesterase - Acetylcholinesterase -

enzyme in the synaptic enzyme in the synaptic space that removes space that removes acetylcholineacetylcholine


Motor UnitMotor Unit

One nerve fiber and all the muscle fibers it One nerve fiber and all the muscle fibers it innervates innervates

Muscles that make small, delicate Muscles that make small, delicate movements have only a few muscle fibers movements have only a few muscle fibers per nerve fiber in each motor unitper nerve fiber in each motor unit

Large, powerful muscles may have a Large, powerful muscles may have a hundred or more muscle fibers per motor hundred or more muscle fibers per motor unitunit


Connective Tissue LayersConnective Tissue Layers

Hold components of the muscle together Hold components of the muscle together Contain the blood vessels and nerve fibers Contain the blood vessels and nerve fibers

that supply the muscle fibersthat supply the muscle fibers Continuous with tendons or aponeuroses Continuous with tendons or aponeuroses

that connect muscle to bones or other that connect muscle to bones or other musclesmuscles


Connective Tissue LayersConnective Tissue Layers

Endomysium - composed of fine, reticular Endomysium - composed of fine, reticular fibers; surrounds each muscle fiberfibers; surrounds each muscle fiber

Fascicles - groups of skeletal muscle Fascicles - groups of skeletal muscle fibersfibers

Perimysium - composed of reticular fibers Perimysium - composed of reticular fibers and thick collagen fibers; surrounds and thick collagen fibers; surrounds fasciclesfascicles

Epimysium - fibrous layer composed of Epimysium - fibrous layer composed of tough collagen fibers; surrounds groups of tough collagen fibers; surrounds groups of muscle fascicles muscle fascicles


Initiation of Muscle Contraction & Initiation of Muscle Contraction & RelaxationRelaxation

Nerve impulse reaches the end bulb of the Nerve impulse reaches the end bulb of the motor nerve fibermotor nerve fiber

Acetylcholine is released into the synaptic Acetylcholine is released into the synaptic spacespace

Acetylcholine molecules bind to receptors Acetylcholine molecules bind to receptors on the surface of the sarcolemma on the surface of the sarcolemma

Impulse travels along the sarcolemma and Impulse travels along the sarcolemma and through the T tubules to the interior of the through the T tubules to the interior of the cellcell



Impulse reaches the sarcoplasmic Impulse reaches the sarcoplasmic reticulumreticulum

Calcium ions (CaCalcium ions (Ca++++) are released into the ) are released into the sarcoplasmsarcoplasm

CaCa++++ diffuses into the myofibrils and starts diffuses into the myofibrils and starts the contraction processthe contraction process



Sarcoplasmic reticulum begins pumping Sarcoplasmic reticulum begins pumping CaCa++++ back in again back in again

CaCa++++ is pulled out of the myofibrils is pulled out of the myofibrils Contraction stops, muscle returns to its Contraction stops, muscle returns to its

original lengthoriginal length


Mechanics of Muscle ContractionMechanics of Muscle Contraction

Relaxed muscle fibers have actin and Relaxed muscle fibers have actin and myosin filaments that slightly overlap myosin filaments that slightly overlap

When stimulated to contract, crossbridges When stimulated to contract, crossbridges on myosin filaments slide back and forthon myosin filaments slide back and forth


Mechanics of Muscle ContractionMechanics of Muscle Contraction

Actin filaments on both sides are pulled Actin filaments on both sides are pulled toward the center of the myosin filaments.toward the center of the myosin filaments.

This shortens the sarcomere.This shortens the sarcomere. Shortening of all the end-to-end Shortening of all the end-to-end

sarcomeres in a muscle fiber results in a sarcomeres in a muscle fiber results in a muscle contraction.muscle contraction.


Characteristics of Muscle Characteristics of Muscle ContractionContraction

All-or-nothing principleAll-or-nothing principle When stimulated, an individual muscle fiber either When stimulated, an individual muscle fiber either

contracts completely or not at all.contracts completely or not at all. Nervous system controls the number of muscle Nervous system controls the number of muscle

fibers it stimulates for a particular movementfibers it stimulates for a particular movement Small, fine movements require only a few muscle fibers Small, fine movements require only a few muscle fibers

to contract. to contract. Larger, more powerful movements require contraction of Larger, more powerful movements require contraction of

many muscle fibers.many muscle fibers.


Muscle ContractionMuscle Contraction

Three phases:Three phases:

1. 1. Latent phase - time between nerve Latent phase - time between nerve stimulus and beginning of contraction stimulus and beginning of contraction (about 10 ms)(about 10 ms)

2. Contracting phase - lasts about 40 ms 2. Contracting phase - lasts about 40 ms

3. Relaxation phase - lasts about 50 ms3. Relaxation phase - lasts about 50 ms


Muscle ContractionMuscle Contraction

Maximum contraction efficiency occurs if Maximum contraction efficiency occurs if nerve impulses arrive about 0.1 second nerve impulses arrive about 0.1 second apart. apart.

Results in a series of complete muscle Results in a series of complete muscle fiber twitches fiber twitches

Careful timing of the nerve impulses to Careful timing of the nerve impulses to motor units of the muscle is needed to motor units of the muscle is needed to make muscle contract smoothly.make muscle contract smoothly.


Chemistry of Muscle ContractionChemistry of Muscle Contraction

ATP provides energy to allow the sliding of ATP provides energy to allow the sliding of the actin and myosin filamentsthe actin and myosin filaments

Creatine phosphate converts ADP back to Creatine phosphate converts ADP back to ATPATP

Glucose and Oxygen - help produce ATP & Glucose and Oxygen - help produce ATP & CPCP Glucose stored in muscle as glycogenGlucose stored in muscle as glycogen Oxygen stored as myoglobinOxygen stored as myoglobin


Chemistry of Muscle ContractionChemistry of Muscle Contraction

Anaerobic metabolism - used if oxygen Anaerobic metabolism - used if oxygen need exceeds oxygen supplyneed exceeds oxygen supply Results in lactic acid formationResults in lactic acid formation Lactic acid accumulation causes discomfortLactic acid accumulation causes discomfort


Heat ProductionHeat Production

Muscle activity generates heatMuscle activity generates heat Panting or sweating - mechanisms to Panting or sweating - mechanisms to

eliminate excess heateliminate excess heat Shivering - spasmodic muscle contractions Shivering - spasmodic muscle contractions

that increase heat productionthat increase heat production


Cardiac MuscleCardiac Muscle

Small cells with single nucleus Small cells with single nucleus Intercalated disks: Intercalated disks:

attachments between cardiac attachments between cardiac muscle cellsmuscle cells Allow transmission of impulses Allow transmission of impulses

from cell to cell for coordinated from cell to cell for coordinated

contraction of large groups of cellscontraction of large groups of cells


Physiology of Cardiac MusclePhysiology of Cardiac Muscle

Cardiac cells contract without any external Cardiac cells contract without any external stimulationstimulation

Groups of cardiac muscle cells contract at Groups of cardiac muscle cells contract at the rate of the most rapid cell in the groupthe rate of the most rapid cell in the group

Contractions are rapid and wavelikeContractions are rapid and wavelike


Physiology of Cardiac MusclePhysiology of Cardiac Muscle

Cardiac Conduction SystemCardiac Conduction System Sinoatrial (SA) nodeSinoatrial (SA) node

Generates the impulse that starts each Generates the impulse that starts each heartbeat heartbeat

Located in the wall of the right atriumLocated in the wall of the right atrium Impulse follows a controlled path through Impulse follows a controlled path through

the conduction system of the heart the conduction system of the heart Structures in the system transmit, delay, Structures in the system transmit, delay,

and redirectand redirect


Nerve SupplyNerve Supply

Heart is innervated by nerves from both Heart is innervated by nerves from both the sympathetic and parasympathetic the sympathetic and parasympathetic systemssystems

Sympathetic fibers stimulate the heart to Sympathetic fibers stimulate the heart to beat harder and faster as part of the "fight beat harder and faster as part of the "fight or flight response”or flight response”

Parasympathetic fibers inhibit cardiac Parasympathetic fibers inhibit cardiac function, causing the heart to beat more function, causing the heart to beat more slowly and with less forceslowly and with less force


Smooth Muscle Gross AnatomySmooth Muscle Gross Anatomy

Two main formsTwo main forms Visceral smooth muscleVisceral smooth muscle

Large sheets of cells in the walls of some Large sheets of cells in the walls of some hollow organs hollow organs

Multiunit smooth muscleMultiunit smooth muscle Small, discrete groups of cellsSmall, discrete groups of cells


Smooth Muscle CellsSmooth Muscle Cells

Small, spindle-shaped; Small, spindle-shaped;

single nucleus single nucleus Actin and myosin Actin and myosin

filaments arranged filaments arranged

as small contractile as small contractile

units that crisscross units that crisscross

the cellthe cell Attached at both ends to Attached at both ends to

"dense bodies" that correspond "dense bodies" that correspond

to the Z lines of skeletal muscleto the Z lines of skeletal muscle


Visceral MuscleVisceral Muscle

Found in the walls of many internal organs Found in the walls of many internal organs (e.g., stomach, intestines, uterus, urinary (e.g., stomach, intestines, uterus, urinary bladder)bladder)

Contracts in large, rhythmic wavesContracts in large, rhythmic waves Contracts without external stimulationContracts without external stimulation

Reacts to stretching by contracting more Reacts to stretching by contracting more stronglystrongly

Innervated by nerves from both the Innervated by nerves from both the sympathetic and parasympathetic systemssympathetic and parasympathetic systems

Sympathetic stimulation decreases activity; Sympathetic stimulation decreases activity; parasympathetic stimulation increases activityparasympathetic stimulation increases activity


Multi-Unit Smooth MuscleMulti-Unit Smooth Muscle

Individual smooth muscle cells or small Individual smooth muscle cells or small groups of cellsgroups of cells

Found where small, delicate contractions Found where small, delicate contractions are needed (e.g., iris, walls of small blood are needed (e.g., iris, walls of small blood vessels)vessels)

Contraction requires autonomic nervous Contraction requires autonomic nervous system impulsesystem impulse

7. The Muscular System

Health & Medicine

Transcript of 7. The Muscular System