The Muscular System
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
Neuromuscular Junction
Neuromuscular Junction
• 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
Neuromuscular Junction
– 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
Excitation-Contraction Coupling
• 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
Excitation-Contraction Coupling
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
Role of Ionic Calcium (Ca2+) in the Contraction Mechanism
• 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
Role of Ionic Calcium (Ca2+) in the Contraction Mechanism
• Calcium-activated troponin undergoes a conformational change
• This change moves tropomyosin away from actin’s binding sites
Role of Ionic Calcium (Ca2+) in the Contraction Mechanism
• Myosin head can now bind and cycle
• This permits contraction (sliding of the thin filaments by the myosin cross bridges) to begin
Role of Ionic Calcium (Ca2+) in the Contraction Mechanism
• 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 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
Muscles Crossing the Shoulder
Muscles Crossing the Shoulder
• 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 Shoulder
Muscles Crossing the Shoulder
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
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
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