the muscular system. a. there are three types of muscle tissue: –1. smooth muscle a. found in the...

The Muscular System

• A. There are three types of muscle tissue:– 1. Smooth muscle

• a. Found in the walls of your internal organs and blood vessels.

• b. They are involuntary-there is no conscious control of this muscle.

• 2. Cardiac muscle– a. Involuntary muscle

found only in the heart.

– b. Generate and conduct electrical impulses.

Types of Muscle Tissue

– 3. Skeletal muscle• a. This muscle is attached to and moves your

bones.• b. They are all voluntary-you have control over

their movement.

How Muscles Work

How Muscles Perform Work

• Do muscles push or pull on bones?

• Pull

• How then can bones move in opposite directions?

• Muscles are found in pairs surrounding bones

Muscle Attachments

• The muscle is attached to two bones• At one end it is attached to an anchoring bone• This end is called the origin of the muscle• At the other end it is attached to the bone it is to move• This end is called the insertion.• Which part is moved when a muscle contracts? The

insertion or the origin?• The insertion

• B. Anatomy of a muscle fiber:– 1. Myofibril-Smaller units found in a muscle

fiber.

Skeletal Muscle

• Each muscle is a discrete organ composed of muscle tissue, blood vessels, nerve fibers, and connective tissue

• The three connective tissue sheaths are:

– Endomysium – fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber

– Perimysium – fibrous connective tissue that surrounds groups of muscle fibers called fascicles

– Epimysium – an overcoat of dense regular connective tissue that surrounds the entire muscle

• Myofibrils

• Myofibrils are densely packed, rodlike contractile elements

• They make up most of the muscle volume

• The arrangement of myofibrils within a fiber is such that a perfectly aligned repeating series of dark A bands and light I bands is evident

– 2. Myosin- Thick filaments are made of this protein.

– 3. Actin- thin filaments are made of this protein.

– 4. Sarcomere- Sections of myofibrils.

Sarcomeres

The smallest contractile unit of a muscleThe region of a myofibril between two successive Z discsComposed of myofilaments made up of contractile proteins

Myofilaments are of two types – thick and thin

– 5. The sliding filament theory-When signaled, the actin filaments within each sarcomere slide toward one another, shortening the fiber and causing muscle to contract.

• Muscle fiber = muscle cell• Composed of many myofibrils• Composed of light and dark

bands• Light band due to thin

filaments (actin) alone • Dark bands due to thick

filaments (myosin)• Z lines connect thin filaments• Sarcomere = repeating unit

within myofibrils (from Z line to Z line)

Myofilaments: Banding Pattern

• Thick filaments – extend the entire length of an A band

• Thin filaments – extend across the I band and partway into the A band

• Z-disc – coin-shaped sheet of proteins (connectins) that anchors the thin filaments and connects myofibrils to one another

Ultrastructure of Myofilaments: Thick Filaments

• Thick filaments are composed of the protein myosin

• Each myosin molecule has a rodlike tail and two globular heads– Tails – two interwoven,

heavy polypeptide chains– Heads – two smaller, light

polypeptide chains called cross bridges

Ultrastructure of Myofilaments: Thin Filaments

• Thin filaments are chiefly composed of the protein actin

• Each actin molecule is a helical polymer of globular subunits called G actin

• The subunits contain the active sites to which myosin heads attach during contraction

• Tropomyosin and troponin are regulatory subunits bound to actin

• Arrangement of the Filaments in a SarcomereLongitudinal section within one sarcomere

• Sarcoplasmic Reticulum (SR)

• SR is an elaborate, smooth endoplasmic reticulum that mostly runs longitudinally and surrounds each myofibril

• Paired terminal cisternae form perpendicular cross channels

• Functions in the regulation of intracellular calcium levels

• Elongated tubes called T tubules penetrate into the cell’s interior at each A band–I band junction

• T tubules associate with the paired terminal cisternae to form triads

T Tubules

• T tubules are continuous with the sarcolemma

• They conduct impulses to the deepest regions of the muscle

• These impulses signal for the release of Ca2+ from adjacent terminal cisternae

Review

• What ion opens up binding sites on the actin?• Calcium• What releases the bond between the myosin heads and

actin?• ATP• What causes the myosin head to change its structure

( and thereby pull the thin filaments)?• Release of ADP and Phosphate from the myosin head.• What is the only movement a muscle can perform?• Contraction

• Why Is A Dead Person Called a Stiff?

• When a person is dead there is no more ATP source

• Without ATP the actin and myosin cross bridges cannot detach

• All skeletal muscles in the body remain “stiff”

• How Do Muscles Know When to Contract?

• Nervous control• Nerve cells extend

into muscle fibers and signal muscle contraction

Skeletal Muscle Contraction

• In order to contract, a skeletal muscle must:– Be stimulated by a nerve ending– Propagate an electrical current, or action potential,

along its sarcolemma– Have a rise in intracellular Ca2+ levels, the final trigger

for contraction

• Linking the electrical signal to the contraction is excitation-contraction coupling

Nerve Stimulus of Skeletal Muscle

• Skeletal muscles are stimulated by motor neurons of the somatic nervous system

• Axons of these neurons travel in nerves to muscle cells

• Axons of motor neurons branch profusely as they enter muscles

• Each axonal branch forms a neuromuscular junction with a single muscle fiber

Neuromuscular Junction

• The neuromuscular junction is formed from:– Axonal endings, which have small membranous sacs

(synaptic vesicles) that contain the neurotransmitter acetylcholine (ACh)

– The motor end plate of a muscle, which is a specific part of the sarcolemma that contains ACh receptors and helps form the neuromuscular junction

• Though exceedingly close, axonal ends and muscle fibers are always separated by a space called the synaptic cleft


• When a nerve impulse reaches the end of an axon at the neuromuscular junction:– Voltage-regulated calcium channels open and

allow Ca2+ to enter the axon– Ca2+ inside the axon terminal causes axonal

vesicles to fuse with the axonal membrane


– This fusion releases ACh into the synaptic cleft via exocytosis

– ACh diffuses across the synaptic cleft to ACh receptors on the sarcolemma

– Binding of ACh to its receptors initiates an action potential in the muscle

Destruction of Acetylcholine

• ACh bound to ACh receptors is quickly destroyed by the enzyme acetylcholinesterase

• This destruction prevents continued muscle fiber contraction in the absence of additional stimuli

Action Potential

• A transient depolarization event that includes polarity reversal of a sarcolemma (or nerve cell membrane) and the propagation of an action potential along the membrane

Role of Acetylcholine (Ach)

•

• ACh binds its receptors at the motor end plate

• Binding opens chemically (ligand) gated channels

• Na+ and K+ diffuse out and the interior of the sarcolemma becomes less negative

• This event is called depolarization

Depolarization

• Initially, this is a local electrical event called end plate potential

• Later, it ignites an action potential that spreads in all directions across the sarcolemma

• 6. Muscle strength:– a. Depends on thickness of fibers.– b. Regular exercise increases diameter of

fibers.• 1. aerobic exercise- Uses ATP efficiently• 2. anaerobic exercise- Uses ATP inefficiently

producing lactic acid.

Depolarization

• Initially, this is a local electrical event called end plate potential

• Later, it ignites an action potential that spreads in all directions across the sarcolemma

Action Potential: Electrical Conditions of a Polarized Sarcolemma

• The outside (extracellular) face is positive, while the inside face is negative

• This difference in charge is the resting membrane potential

Action Potential: Electrical Conditions of a Polarized Sarcolemma

• The predominant extracellular ion is Na+

• The predominant intracellular ion is K+

• The sarcolemma is relatively impermeable to both ions

Action Potential: Depolarization and Generation of the Action Potential

• An axonal terminal of a motor neuron releases ACh and causes a patch of the sarcolemma to become permeable to Na+ (sodium channels open)

Action Potential: Depolarization and Generation of the Action Potential

• Na+ enters the cell, and the resting potential is decreased (depolarization occurs)

• If the stimulus is strong enough, an action potential is initiated

Action Potential: Propagation of the Action Potential

• Polarity reversal of the initial patch of sarcolemma changes the permeability of the adjacent patch

• Voltage-regulated Na+ channels now open in the adjacent patch causing it to depolarize

Action Potential: Propagation of the Action Potential

• Thus, the action potential travels rapidly along the sarcolemma

• Once initiated, the action potential is unstoppable, and ultimately results in the contraction of a muscle

Action Potential: Repolarization

• Immediately after the depolarization wave passes, the sarcolemma permeability changes

• Na+ channels close and K+ channels open

• K+ diffuses from the cell, restoring the electrical polarity of the sarcolemma

Action Potential: Repolarization

• Repolarization occurs in the same direction as depolarization, and must occur before the muscle can be stimulated again (refractory period)

• The ionic concentration of the resting state is restored by the Na+-K+ pump

Excitation-Contraction Coupling

• Once generated, the action potential:– Is propagated along the sarcolemma– Travels down the T tubules– Triggers Ca2+ release from terminal cisternae

• Ca2+ binds to troponin and causes: – The blocking action of tropomyosin to cease– Actin active binding sites to be exposed


• Myosin cross bridges alternately attach and detach

• Thin filaments move toward the center of the sarcomere

• Hydrolysis of ATP powers this cycling process

• Ca2+ is removed into the SR, tropomyosin blockage is restored, and the muscle fiber relaxes

Role of Ionic Calcium (Ca2+) in the Contraction Mechanism

• At low intracellular Ca2+ concentration:– Tropomyosin blocks

the binding sites on actin

– Myosin cross bridges cannot attach to binding sites on actin

– The relaxed state of the muscle is enforced


• At higher intracellular Ca2+ concentrations:– Additional calcium

binds to troponin (inactive troponin binds two Ca2+)

– Calcium-activated troponin binds an additional two Ca2+ at a separate regulatory site


• Calcium-activated troponin undergoes a conformational change

• This change moves tropomyosin away from actin’s binding sites


• Myosin head can now bind and cycle

• This permits contraction (sliding of the thin filaments by the myosin cross bridges) to begin

Sequential Events of Contraction

• Cross bridge formation – myosin cross bridge attaches to actin filament

• Working (power) stroke – myosin head pivots and pulls actin filament toward M line

• Cross bridge detachment – ATP attaches to myosin head and the cross bridge detaches

• “Cocking” of the myosin head – energy from hydrolysis of ATP cocks the myosin head into the high-energy state

Sequential Events of Contraction

Contraction of Skeletal Muscle (Organ Level)

• Contraction of muscle fibers (cells) and muscles (organs) is similar

• The two types of muscle contractions are:– Isometric contraction – increasing muscle

tension (muscle does not shorten during contraction)

– Isotonic contraction – decreasing muscle length (muscle shortens during contraction)

Motor Unit: The Nerve-Muscle Functional Unit

• A motor unit is a motor neuron and all the muscle fibers it supplies

• The number of muscle fibers per motor unit can vary from four to several hundred

• Muscles that control fine movements (fingers, eyes) have small motor units

Motor Unit: The Nerve-Muscle Functional Unit

Muscle Twitch

• A muscle twitch is the response of a muscle to a single, brief threshold stimulus

• The three phases of a muscle twitch are:– Latent period –

first few milli-seconds after stimulation when excitation-contraction coupling is taking place

Muscle Twitch

– Period of contraction – cross bridges actively form and the muscle shortens

– Period of relaxation – Ca2+ is reabsorbed into the SR, and muscle tension goes to zero

Muscle Response: Stimulation Strength

• Threshold stimulus – the stimulus strength at which the first observable muscle contraction occurs

• Beyond threshold, muscle contracts more vigorously as stimulus strength is increased

• Force of contraction is precisely controlled by multiple motor unit summation

• This phenomenon, called recruitment, brings more and more muscle fibers into play

Stimulus Intensity and Muscle Tension

Muscle Tone

• Muscle tone:– Is the constant, slightly contracted state of all

muscles, which does not produce active movements– Keeps the muscles firm, healthy, and ready to

respond to stimulus

• Spinal reflexes account for muscle tone by:– Activating one motor unit and then another– Responding to activation of stretch receptors in

muscles and tendons

Isotonic Contractions

• In isotonic contractions, the muscle changes in length (decreasing the angle of the joint) and moves the load

• The two types of isotonic contractions are concentric and eccentric– Concentric contractions –

the muscle shortens and does work

– Eccentric contractions – the muscle contracts as it lengthens

Isometric Contractions

• Tension increases to the muscle’s capacity, but the muscle neither shortens nor lengthens

• Occurs if the load is greater than the tension the muscle is able to develop

Muscle Metabolism: Energy for Contraction

• ATP is the only source used directly for contractile activity

• As soon as available stores of ATP are hydrolyzed (4-6 seconds), they are regenerated by:– The interaction of ADP with creatine

phosphate (CP) – Anaerobic glycolysis – Aerobic respiration

Muscle Fatigue

• Muscle fatigue – the muscle is in a state of physiological inability to contract

• Muscle fatigue occurs when:– ATP production fails to keep pace with ATP use– There is a relative deficit of ATP, causing contractures– Lactic acid accumulates in the muscle– Ionic imbalances are present

Muscle Fatigue

• Intense exercise produces rapid muscle fatigue (with rapid recovery)

• Na+-K+ pumps cannot restore ionic balances quickly enough

• Low-intensity exercise produces slow-developing fatigue

• SR is damaged and Ca2+ regulation is disrupted

Oxygen Debt

• Vigorous exercise causes dramatic changes in muscle chemistry

• For a muscle to return to a resting state:– Oxygen reserves must be replenished– Lactic acid must be converted to pyruvic acid– Glycogen stores must be replaced– ATP and CP reserves must be resynthesized

• Oxygen debt – the extra amount of O2 needed for the above restorative processes

Heat Production During Muscle Activity

• Only 40% of the energy released in muscle activity is useful as work

• The remaining 60% is given off as heat

• Dangerous heat levels are prevented by radiation of heat from the skin and sweating

Smooth Muscle

Peristalsis

• When the longitudinal layer contracts, the organ dilates and contracts

• When the circular layer contracts, the organ elongates

• Peristalsis – alternating contractions and relaxations of smooth muscles that mix and squeeze substances through the lumen of hollow organs

Special Features of Smooth Muscle Contraction

• Unique characteristics of smooth muscle include:– Smooth muscle tone– Slow, prolonged contractile activity– Low energy requirements– Response to stretch

Summary

Interactions of Skeletal Muscles

• Skeletal muscles work together or in opposition

• Muscles only pull (never push)

• As muscles shorten, the insertion generally moves toward the origin

• Whatever a muscle (or group of muscles) does, another muscle (or group) “undoes”

Muscle Classification: Functional Groups

• Prime movers – provide the major force for producing a specific movement

• Antagonists – oppose or reverse a particular movement

• Synergists– Add force to a movement– Reduce undesirable or unnecessary movement

• Fixators – synergists that immobilize a bone or muscle’s origin

Naming Skeletal Muscles

• Location of muscle – bone or body region associated with the muscle

• Shape of muscle – e.g., the deltoid muscle (deltoid = triangle)

• Relative size – e.g., maximus (largest), minimus (smallest), longus (long)

• Direction of fibers – e.g., rectus (fibers run straight), transversus, and oblique (fibers run at angles to an imaginary defined axis)

Naming Skeletal Muscles

• Number of origins – e.g., biceps (two origins) and triceps (three origins)

• Location of attachments – named according to point of origin or insertion

• Action – e.g., flexor or extensor, as in the names of muscles that flex or extend, respectively

Arrangement of Fascicles

• Parallel – fascicles run parallel to the long axis of the muscle (e.g., sartorius)

• Fusiform – spindle-shaped muscles (e.g., biceps brachii)

• Pennate – short fascicles that attach obliquely to a central tendon running the length of the muscle (e.g., rectus femoris)

• Convergent – fascicles converge from a broad origin to a single tendon insertion (e.g., pectoralis major)

• Circular – fascicles are arranged in concentric rings (e.g., orbicularis oris)

Bone-Muscle Relationships: Lever Systems

• Lever – a rigid bar that moves on a fulcrum, or fixed point

• Effort – force applied to a lever

• Load – resistance moved by the effort

Bone-Muscle Relationships: Lever Systems

Lever Systems: Classes

• First class – the fulcrum is between the load and the effort

• Second class – the load is between the fulcrum and the effort

• Third class – the effort is applied between the fulcrum and the load

Lever Systems: First Class

Lever Systems: Second Class

Lever Systems: Third Class

Major Skeletal Muscles: Anterior View

• The 40 superficial muscles here are divided into 10 regional areas of the body

Major Skeletal Muscles: Posterior View

• The 27 superficial muscles here are divided into seven regional areas of the body

Muscles: Name, Action, and Innervation

• Name and description of the muscle – be alert to information given in the name

• Origin and insertion – there is always a joint between the origin and insertion

• Action – best learned by acting out a muscle’s movement on one’s own body

• Nerve supply – name of major nerve that innervates the muscle

Muscles of the Scalp

• Epicranius (occipitofrontalis) – bipartite muscle consisting of the:– Frontalis – Occipitalis – Galea aponeurotica – cranial aponeurosis

connecting above muscles

• These two muscles have alternate actions of pulling the scalp forward and backward

Muscles of the Face

• 11 muscles are involved in lifting the eyebrows, flaring the nostrils, opening and closing the eyes and mouth, and smiling

• All are innervated by cranial nerve VII (facial nerve)

• Usually insert in skin (rather than bone), and adjacent muscles often fuse

Muscles of Mastication

• There are four pairs of muscles involved in mastication– Prime movers – temporalis

and masseter– Grinding movements –

pterygoids and buccinators

• All are innervated by cranial nerve V (trigeminal nerve)

Muscles of Mastication

Extrinsic Tongue Muscles

• Three major muscles that anchor and move the tongue

• All are innervated by cranial nerve XII (hypoglossal nerve)

Muscles of the Anterior Neck and Throat: Suprahyoid

• Four deep throat muscles – Form the floor of the

oral cavity– Anchor the tongue– Elevate the hyoid– Move the larynx

superiorly during swallowing

Muscles of the Anterior Neck and Throat: Infrahyoid

• Straplike muscles that depress the hyoid and larynx during swallowing and speaking

• Major head flexor is the sternocleidomastoid

• Synergists to head flexion are the suprahyoid and infrahyoid

• Lateral head movements are accomplished by the sternocleidomastoid and scalene muscles

• Head extension is accomplished by the deep splenius muscles and aided by the superficial trapezius

Muscles of the Neck: Head Movements

Muscles of the Neck: Head Movements

Trunk Movements: Deep Back Muscles

• The prime mover of back extension is the erector spinae

• Erector spinae, or sacrospinalis, muscles consist of three columns on each side of the vertebrae – iliocostalis, longissimus, and spinalis

• Lateral bending of the back is accomplished by unilateral contraction of these muscles

• Other deep back extensors include the semispinalis muscles and the quadratus lumborum

Trunk Movements: Short Muscles

• Four short muscles extend from one vertebra to another

• These muscles are synergists in extension and rotation of the spine

Muscles of Respiration

• The primary function of deep thoracic muscles is to promote movement for breathing

• External intercostals – more superficial layer that lifts the rib cage and increases thoracic volume to allow inspiration

Muscles of Respiration

• Internal intercostals – deeper layer that aids in forced expiration

• Diaphragm – most important muscle in inspiration

Muscles of Respiration: The Diaphragm

Muscles of the Abdominal Wall

• The abdominal wall is composed of four paired muscles (internal and external obliques, transversus abdominis, and rectus abdominis), their fasciae, and their aponeuroses

• Fascicles of these muscles run at right and oblique angles to one another, giving the abdominal wall added strength

Muscles of the Abdominal Wall

Muscles of the Pelvic Floor (Pelvic Diaphragm)

• The pelvic diaphragm is composed of two paired muscles – levator ani and coccygeus

• These muscles: – Close the inferior outlet of

the pelvis– Support the pelvic floor– Elevate the pelvic floor to

help release feces – Resist increased intra-

abdominal pressure

Muscles Inferior to the Pelvic Floor

• Two sphincter muscles allow voluntary control of urination (sphincter urethrae) and defecation (external anal sphincter)

• The ischiocavernosus and bulbospongiosus assist in erection of the penis and clitoris

Extrinsic Shoulder Muscles

• Muscles of the thorax– Anterior: pectoralis major,

pectoralis minor, serratus anterior, and subclavius

– Posterior: latissimus dorsi, trapezius muscles, levator scapulae, and rhomboids

– These muscles are involved with the movements of the scapula including elevation, depression, rotation, and lateral and medial movements

• Prime movers of shoulder elevation are the trapezius and levator scapulae

Muscles Crossing the Shoulder

• Nine muscles cross the shoulder joint and insert into the humerus

• Prime movers include:– Pectoralis major – arm

flexion– Latissimus dorsi and

posterior fibers of the deltoid – arm extension

– Middle fibers of the deltoid – arm abduction


• Rotator cuff muscles – supraspinatus, infraspinatus, teres minor, and subscapularis – Function mainly to

reinforce the capsule of the shoulder

– Secondarily act as synergists and fixators

• The coracobrachialis and teres major: – Act as synergists – Do not contribute to

reinforcement of the shoulder joint

Muscles Crossing the Elbow

• Forearm extension– The triceps brachii is the prime mover of

forearm extension– The anconeus is a weak synergist

• Forearm flexion– Brachialis and biceps brachii are the chief

forearm flexors– The brachioradialis acts as a synergist and

helps stabilize the elbow

Muscles of the Forearm: Anterior Compartment

• These muscles are primarily flexors of the wrist and fingers

Muscles of the Forearm: Anterior Compartment

Muscles of the Forearm: Posterior Compartment

• These muscles are primarily extensors of the wrist and fingers

Muscle Action of the Arm: Summary

• The posterior extensor and anterior flexor muscles are shown

Muscle Action of the Forearm: Summary

• Posterior extensors of the wrist and fingers, and anterior flexor muscles are shown

Intrinsic Muscles of the Hand

• These small muscles: – Lie in the palm of the hand

(none on the dorsal side)– Move the metacarpals and

fingers– Control precise movements

(e.g., threading a needle)– Are the main abductors

and adductors of the fingers

– Produce opposition – move the thumb toward the little finger

Intrinsic Muscles of the Hand

Finger and Thumb Movements

• Flexion– Thumb – bends medially along the palm– Fingers – bend anteriorly

• Extension– Thumb – points laterally– Fingers – move posteriorly

Intrinsic Muscles of the Hand: Groups

• There are three groups of intrinsic hand muscles

• The thenar eminence (ball of the thumb) and hypothenar eminence (ball of the little finger) – each have a flexor, an abductor, and an opponens muscle

• The midpalm muscles, the lumbricals and interossei, extend the fingers

• The interossei also abduct and adduct the fingers

Muscles Crossing Hip and Knee Joints

• Most anterior compartment muscles of the hip and thigh flex the femur at the hip and extend the leg at the knee

• Posterior compartment muscles of the hip and thigh extend the thigh and flex the leg

• The medial compartment muscles all adduct the thigh

• These three groups are enclosed by the fascia lata

Movements of the Thigh at the Hip: Flexion and Extension

• The ball-and-socket hip joint permits flexion, extension, abduction, adduction, circumduction, and rotation

• The most important thigh flexors are the iliopsoas (prime mover), tensor fasciae latae, and rectus femoris

• The medially located adductor muscles and sartorius assist in thigh flexion

Movements of the Thigh at the Hip: Flexion and Extension

• Thigh extension is primarily effected by the hamstring muscles (biceps femoris, semitendinosus, and semimembranosus)

• Forceful extension is aided by the gluteus maximus

Movements of the Thigh at the Hip: Other Movements

• Abduction and rotation are effected by the gluteus medius and gluteus minimus, and are antagonized by the lateral rotators

• Thigh adduction is the role of five adductor muscles (adductor magnus, adductor longus, and adductor brevis; the pectineus, and the gracilis)

Movements of the Thigh at the Hip: Other Movements

Movements of the Knee Joint

• The sole extensor of the knee is the quadriceps femoris

• The hamstring muscles flex the knee, and are antagonists to the quadriceps femoris

Fascia of the Leg

• A deep fascia of the leg is continuous with the fascia lata

• This fascia segregates the leg into three compartments: anterior, lateral, and posterior

• Distally, the fascia thickens and forms the flexor, extensor, and fibular retinaculae

Muscles of the Leg: Movements

• Various leg muscles produce the following movements at the:– Ankle – dorsiflexion and plantar flexion– Intertarsal joints – inversion and eversion of

the foot– Toes – flexion and extension

Muscles of the Anterior Compartment

• These muscles are the primary toe extensors and ankle dorsiflexors

• They include the tibialis anterior, extensor digitorum longus, extensor hallucis longus, and fibularis tertius

Muscles of the Anterior Compartment

Muscles of the Lateral Compartment

• These muscles plantar flex and evert the foot

• They include the fibularis longus and fibularis brevis muscles

Muscles of the Lateral Compartment

Muscles of the Posterior Compartment

• These muscles primarily flex the foot and the toes

• They include the gastrocnemius, soleus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus

Muscles of the Posterior Compartment

Muscle Actions of the Thigh: Summary

• Thigh muscles: – Flex and extend the thigh (posterior

compartment)– Extend the leg (anterior compartment)– Adduct the thigh (medial compartment)

Muscle Actions of the Thigh: Summary

Muscle Actions of the Leg: Summary

• Leg muscles:– Plantar flex and evert the foot (lateral

compartment)– Plantar flex the foot and flex the toes

(posterior compartment)– Dorsiflex the foot and extend the toes

(anterior compartment)

Muscle Actions of the Leg: Summary

Intrinsic Muscles of the Foot

• These muscles help flex, extend, abduct, and adduct the toes

• In addition, along with some leg tendons, they support the arch of the foot

• There is a single dorsal foot muscle, the extensor digitorum brevis, which extends the toes

• The plantar muscles occur in four layers

Plantar Muscles: First Layer (Superficial)

• Superficial muscles of the plantar aspect of the foot

• These muscles are similar to the corresponding muscles of the hand

Plantar Muscles: Second Layer

Plantar Muscles: Third Layer

Plantar Muscles: Fourth Layer

the muscular system. a. there are three types of muscle tissue: –1. smooth muscle a. found in the...

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