Download The Muscular System

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. SarcomereSections of myofibrils.
Sarcomeres
The smallest contractile unit of a muscle
The region of a myofibril between two
successive Z discs
Composed 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 Sarcomere
Longitudinal 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 milliseconds after
stimulation
when excitationcontraction
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 slowdeveloping 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
Muscles of the Neck: Head Movements
• 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
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 intraabdominal 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