Download The Skeletal Muscles

The Muscular System
or “Everything you ever
wanted to know about
Muscles, but were afraid to
ask” !!!
Did you know that ?
- more than 50% of body weight
is muscle !
- And muscle is made up of
proteins and water
The Muscular System
• Muscles are responsible for all movement of
the body
• There are three basic types of muscle
– Skeletal
– Cardiac
– Smooth
Info About Muscles
Only body tissue able
to contract
create movement by
flexing and extending
joints
Body energy
converters (many
muscle cells contain
many mitochondria)
3 Types of Muscles
Three types of muscle
Skeletal
Cardiac
Smooth
Classification of Muscle
SkeletalCardiacfound in limbs found in heart
SmoothFound in
viscera
Striated, multi- Striated, 1
nucleated
nucleus
Not striated, 1
nucleus
voluntary
involuntary
involuntary
Characteristics of Muscle
• Skeletal and smooth muscle are elongated
• Muscle cell = muscle fiber
• Contraction of a muscle is due to movement
of microfilaments (protein fibers)
• All muscles share some terminology
– Prefixes myo and mys refer to muscle
– Prefix sarco refers to flesh
Shapes of Muscles
•
•
•
•
Triangular- shoulder, neck
Spindle- arms, legs
Flat- diaphragm, forehead
Circular- mouth, anus
Skeletal Muscle
• Most are attached by tendons to bones
• Cells have more than one nucleus
(multinucleated)
• Striated- have stripes, banding
• Voluntary- subject to conscious control
• Tendons are mostly made of collagen fibers
• Found in the limbs
• Produce movement, maintain posture,
generate heat, stabilize joints
Structure of skeletal muscle
• Each cell (fibre) is long and cylindrical
• Muscle fibres are multi-nucleated
• Typically 50-60mm in diameter, and up to
10cm long
• The contractile elements of
skeletal muscle cells are
myofibrils
Microscopic Anatomy of Skeletal
Muscle
• Myofibrils are aligned to give distinct bands
– I band = light band
• Contains only thin filaments
– A band = dark band
• Contains the entire length of the thick filaments
Microscopic Anatomy of Skeletal
Muscle
Figure 6.3b
Microscopic Anatomy of Skeletal
Muscle
• Sarcomere—contractile unit of a muscle fiber
• Organization of the sarcomere
– Myofilaments
• Thick filaments = myosin filaments
• Thin filaments = actin filaments
Microscopic Anatomy of Skeletal
Muscle
• Thick filaments = myosin filaments
– Composed of the protein myosin
– Has ATPase enzymes
– Myosin filaments have heads (extensions, or cross
bridges)
– Myosin and actin overlap somewhat
• Thin filaments = actin filaments
– Composed of the protein actin
– Anchored to the Z disc
Microscopic Anatomy of Skeletal
Muscle
Figure 6.3c
Microscopic Anatomy of Skeletal
Muscle
• At rest, there is a bare zone that lacks actin
filaments called the H zone
• Sarcoplasmic reticulum (SR)
– Stores and releases calcium
– Surrounds the myofibril
Microscopic Anatomy of Skeletal
Muscle
Figure 6.3d
Skeletal Muscle Attachments
• Epimysium blends into a connective tissue
attachment
– Tendons—cord-like structures
• Mostly collagen fibers
• Often cross a joint due to toughness and small size
– Aponeuroses—sheet-like structures
• Attach muscles indirectly to bones, cartilages, or
connective tissue coverings
Stimulation and Contraction of
Single Skeletal Muscle Cells
• Excitability (also called responsiveness or
irritability)—ability to receive and respond to
a stimulus
• Contractility—ability to shorten when an
adequate stimulus is received
• Extensibility—ability of muscle cells to be
stretched
• Elasticity—ability to recoil and resume resting
length after stretching
The Nerve Stimulus and Action
Potential
• Skeletal muscles must be stimulated by a
motor neuron (nerve cell) to contract
• Motor unit—one motor neuron and all the
skeletal muscle cells stimulated by that
neuron
The Nerve Stimulus and Action
Potential
Figure 6.4a
The Nerve Stimulus and Action
Potential
Figure 6.4b
The Nerve Stimulus and Action
Potential
• Neuromuscular junction
– Association site of axon terminal of the motor
neuron and muscle
The Nerve Stimulus and Action
Potential
Figure 6.5a
The Nerve Stimulus and Action
Potential
• Synaptic cleft
– Gap between nerve and muscle
– Nerve and muscle do not make contact
– Area between nerve and muscle is filled with
interstitial fluid
The Nerve Stimulus and Action
Potential
Figure 6.5b
Transmission of Nerve Impulse to
Muscle
• Neurotransmitter—chemical released by
nerve upon arrival of nerve impulse
– The neurotransmitter for skeletal muscle is
acetylcholine (ACh)
• Acetylcholine attaches to receptors on the
sarcolemma
• Sarcolemma becomes permeable to sodium
(Na+)
Transmission of Nerve Impulse to
Muscle
Figure 6.5c
Transmission of Nerve Impulse to
Muscle
• Sodium rushes into the cell generating an
action potential
• Once started, muscle contraction cannot be
stopped
The Sliding Filament Theory
of Muscle Contraction
• Activation by nerve causes myosin heads (cross
bridges) to attach to binding sites on the thin
filament
• Myosin heads then bind to the next site of the
thin filament and pull them toward the center of
the sarcomere
• This continued action causes a sliding of the
myosin along the actin
• The result is that the muscle is shortened
(contracted)
The Sliding Filament Theory
of Muscle Contraction
Figure 6.7a–b
Skeletal muscle - Summary
• Voluntary movement
of skeletal parts
• Spans joints and
attached to skeleton
• Multi-nucleated,
striated, cylindrical
fibres
Smooth Muscle
•
•
•
•
•
No striations
Spindle shaped
Single nucleus
Involuntary- no conscious control
Found mainly in the walls of hollow organs
Smooth muscle
• Lines walls of viscera
• Found in longitudinal or
circular arrangement
• Alternate contraction of
circular & longitudinal
muscle in the intestine
leads to peristalsis
Structure of smooth muscle
• Spindle shaped uni-nucleated cells
• Striations not observed
• Actin and myosin filaments are present(
protein fibers)
Smooth muscle - Summary
• Found in walls of
hollow internal
organs
• Involuntary
movement of
internal organs
• Elongated, spindle
shaped fibre with
single nucleus
Cardiac Muscle
•
•
•
•
•
Striations
Branching cells
Involuntary
Found only in the heart
Usually has a single nucleus, but can have
more than one
Cardiac muscle
•
•
•
•
Main muscle of heart
Pumping mass of heart
Critical in humans
Heart muscle cells
behave as one unit
• Heart always contracts
to it’s full extent
Structure of cardiac muscle
• Cardiac muscle cells (fibres) are
short, branched and interconnected
• Cells are striated & usually have 1
nucleus
• Adjacent cardiac cells are joined
via electrical synapses (gap
junctions)
• These gap junctions appear as
dark lines and are called
intercalated discs
Cardiac muscle - Summary
• Found in the heart
• Involuntary rhythmic
contraction
• Branched, striated
fibre with single
nucleus and
intercalated discs
Muscle Control
Type of
muscle
Nervous
control
Type of
control
Example
Skeletal
Skeletal
Controlled
by CNS
Voluntary
Lifting a
glass
Cardiac
Regulated
by ANS
Involuntary Heart
beating
Smooth
Controlled
by ANS
Involuntary Peristalsis
Types of Responses
• Twitch– A single brief contraction
– Not a normal muscle function
• Tetanus
– One contraction immediately followed by
another
– Muscle never completely returns to a relaxed
state
– Effects are compounded
Contraction of Skeletal Muscle
• Muscle fiber contraction is “all or none”
• Within a skeletal muscle, not all fibers may be
stimulated during the same interval
• Different combinations of muscle fiber
contractions may give differing responses
• Graded responses—different degrees of
skeletal muscle shortening
Contraction of Skeletal Muscle
• Graded responses can be produced by
changing
– The frequency of muscle stimulation
– The number of muscle cells being stimulated at
one time
Types of Graded Responses
Figure 6.9a
Types of Graded Responses
Figure 6.9b
Types of Graded Responses
• Unfused (incomplete) tetanus
– Some relaxation occurs between contractions
– The results are summed
Types of Graded Responses
Figure 6.9c
Types of Graded Responses
• Fused (complete) tetanus
– No evidence of relaxation before the following
contractions
– The result is a sustained muscle contraction
Types of Graded Responses
Figure 6.9d
Muscle Response to Strong Stimuli
• Muscle force depends upon the number of
fibers stimulated
• More fibers contracting results in greater
muscle tension
• Muscles can continue to contract unless they
run out of energy
Energy for Muscle Contraction
• Initially, muscles use stored ATP for energy
– ATP bonds are broken to release energy
– Only 4–6 seconds worth of ATP is stored by
muscles
• After this initial time, other pathways must be
utilized to produce ATP
Energy for Muscle Contraction
Figure 6.10a
Energy for Muscle Contraction
• Aerobic respiration
– Glucose is broken down to carbon dioxide and
water, releasing energy (ATP)
– This is a slower reaction that requires continuous
oxygen
– A series of metabolic pathways occur in the
mitochondria
Energy for Muscle Contraction
Figure 6.10b
Energy for Muscle Contraction
• Anaerobic glycolysis and lactic acid formation
– Reaction that breaks down glucose without
oxygen
– Glucose is broken down to pyruvic acid to produce
some ATP
– Pyruvic acid is converted to lactic acid
• This reaction is not as efficient, but is fast
• Huge amounts of glucose are needed
• Lactic acid produces muscle fatigue
Energy for Muscle Contraction
Figure 6.10c
Muscle Fatigue and Oxygen Deficit
• When a muscle is fatigued, it is unable to contract
even with a stimulus
• Common cause for muscle fatigue is oxygen debt
– Oxygen must be “repaid” to tissue to remove oxygen
deficit
– Oxygen is required to get rid of accumulated lactic
acid
• Increasing acidity (from lactic acid) and lack of
ATP causes the muscle to contract less
Exercise and Muscles
• Isotonic- muscles shorten and movement
occurs ( most normal exercise)
• Isometric- tension in muscles increases, no
movement occurs (pushing one hand against
the other)
Muscle Tone
• Some fibers are contracted even in a relaxed
muscle
• Different fibers contract at different times to
provide muscle tone
• The process of stimulating various fibers is
under involuntary control
Effect of Exercise on Muscles
• Exercise increases muscle size, strength, and
endurance
– Aerobic (endurance) exercise (biking, jogging)
results in stronger, more flexible muscles with
greater resistance to fatigue
• Makes body metabolism more efficient
• Improves digestion, coordination
– Resistance (isometric) exercise (weight lifting)
increases muscle size and strength
How are Muscles Attached to Bone?
• Origin-attachment to a movable bone
• Insertion- attachment to an immovable
bone
• Muscles are always attached to at least 2
points
• Movement is attained due to a muscle
moving an attached bone
Types of Musculo-Skeletal Movement
Flexion
Extension
Hyperextension
Abduction, Adduction & Circumduction
Rotation
Special Movements
Figure 6.13e
More Types of Movement……
•
•
•
•
•
Inversion- turn sole of foot medially
Eversion- turn sole of foot laterally
Pronation- palm facing down
Supination- palm facing up
Opposition- thumb touches tips of fingers on
the same hand
The Skeletal Muscles
There are about 650 muscles in the
human body. They enable us to
move, maintain posture and
generate heat. In this section we
will only study a sample of the major
muscles.
Naming Skeletal Muscles
• By direction of muscle fibers
– Example: Rectus (straight)
• By relative size of the muscle
– Example: Maximus (largest)
Naming Skeletal Muscles
• By location of the muscle
– Example: Temporalis (temporal bone)
• By number of origins
– Example: Triceps (three heads)
Naming Skeletal Muscles
• By location of the muscle’s origin and
insertion
– Example: Sterno (on the sternum)
• By shape of the muscle
– Example: Deltoid (triangular)
• By action of the muscle
– Example: Flexor and extensor (flexes or extends
a bone)
Arrangement of Fascicles
Figure 6.14
Head and Neck Muscles
• Facial muscles
– Frontalis—raises eyebrows
– Orbicularis oculi—closes eyes, squints, blinks,
winks
– Orbicularis oris—closes mouth and protrudes the
lips
– Buccinator—flattens the cheek, chews
– Zygomaticus—raises corners of the mouth
• Chewing muscles
– Masseter—closes the jaw and elevates mandible
– Temporalis—synergist of the masseter, closes jaw
Head and Neck Muscles
• Neck muscles
– Platysma—pulls the corners of the mouth
inferiorly
– Sternocleidomastoid—flexes the neck, rotates the
head
Head and Neck Muscles
Figure 6.15
Muscles of Trunk, Shoulder, Arm
• Anterior muscles
– Pectoralis major—adducts and flexes the humerus
– Intercostal muscles
• External intercostals—raise rib cage during inhalation
• Internal intercostals—depress the rib cage to move air
out of the lungs when you exhale forcibly
Anterior Muscles of Trunk, Shoulder,
Arm
Figure 6.16a
Muscles of Trunk, Shoulder, Arm
• Muscles of the abdominal girdle
– Rectus abdominis—flexes vertebral column and
compresses abdominal contents (defecation,
childbirth, forced breathing)
– External and internal obliques—flex vertebral
column; rotate trunk and bend it laterally
– Transversus abdominis—compresses abdominal
contents
Anterior Muscles of Trunk, Shoulder,
Arm
Figure 6.16b
Muscles of Trunk, Shoulder, Arm
• Posterior muscles
– Trapezius—elevates, depresses, adducts, and
stabilizes the scapula
– Latissimus dorsi—extends and adducts the
humerus
– Erector spinae—back extension
– Quadratus lumborum—flexes the spine laterally
– Deltoid—arm abduction
Muscles of Posterior Neck, Trunk, Arm
Figure 6.17a
Muscles of Posterior Neck, Trunk, Arm
Figure 6.17b
Muscles of the Upper Limb
• Biceps brachii—supinates forearm, flexes
elbow
• Brachialis—elbow flexion
• Brachioradialis—weak muscle
• Triceps brachii—elbow extension (antagonist
to biceps brachii)
Anterior Muscles of Trunk, Shoulder,
Arm
Figure 6.16a
Muscles of Posterior Neck, Trunk, Arm
Figure 6.17a
Muscles of the Lower Limb
• Gluteus maximus—hip extension
• Gluteus medius—hip abduction, steadies
pelvis when walking
• Iliopsoas—hip flexion, keeps the upper body
from falling backward when standing erect
• Adductor muscles—adduct the thighs
Muscles of the Pelvis, Hip, Thigh
Figure 6.19a
Muscles of the Pelvis, Hip, Thigh
Figure 6.19c
Muscles of the Lower Limb
• Muscles causing movement at the knee joint
– Hamstring group—thigh extension and knee
flexion
• Biceps femoris
• Semimembranosus
• Semitendinosus
Muscles of the Pelvis, Hip, Thigh
Figure 6.19a
Muscles of the Lower Limb
• Muscles causing movement at the knee joint
– Sartorius—flexes the thigh
– Quadriceps group—extends the knee
• Rectus femoris
• Vastus muscles (three)
Muscles of the Pelvis, Hip, Thigh
Figure 6.19c
Muscles of the Lower Limb
• Muscles causing movement at ankle and foot
– Tibialis anterior—dorsiflexion and foot inversion
– Extensor digitorum longus—toe extension and
dorsiflexion of the foot
– Fibularis muscles—plantar flexion, everts the foot
– Soleus—plantar flexion
Muscles of the Lower Leg
Figure 6.20a
Muscles of the Lower Leg
Figure 6.20b
Sternocleidomastoideus
Flexes and Rotates Head
Masseter
Elevate Mandible
Temporalis
Elevate & Retract Mandible
Trapezius
Extend Head, Adduct, Elevate or
Depress Scapula
Latissimus Dorsi
Extend, Adduct & Rotate Arm Medially
Deltoid
Abduct, Flex & Extend Arm
Pectoralis Major
Flexes, adducts & rotates arm medially
Biceps Brachii
Flexes Elbow Joint
Triceps Brachii
Extend Elbow Joint
Rectus Abdominus
Flexes Abdomen
External Oblique
Compress Abdomen
External Intercostals
Elevate ribs
Internal Intercostals
Depress ribs
Diaphragm
Inspiration
Forearm Muscles
•
•
•
•
•
•
Flexor carpi—Flexes wrist
Extensor carpi—Extends wrist
Flexor digitorum—Flexes fingers
Extensor digitorum—Extends fingers
Pronator—Pronates
Supinator—Supinates
Gluteus Maximus
Extends & Rotates
Thigh Laterally
Rectus Femoris
Flexes Thigh,
Extends Lower Leg
Gracilis
Adducts and Flexes Thigh
Sartorius
Flexes Thigh, &
Rotates Thigh
Laterally
Biceps Femoris
Extends Thigh &
Flexes Lower Leg
Gastrocnemius
Plantar Flexes Foot &
Flex Lower Leg
Tibialis Anterior
Dorsiflexes and Inverts Foot
Superficial Muscles: Anterior
Figure 6.21
Superficial Muscles: Posterior
Figure 6.22