Download Nerve activates contraction

Chapter 6
The Muscular System
The Muscular System
 Muscles are responsible for all types of
body movement
 Three basic muscle types are found in
the body
 Skeletal muscle
 Cardiac muscle
 Smooth muscle
Characteristics of Muscles
 Muscle cells are elongated
(muscle cell = muscle fiber)
 Contraction of muscles is due to the
movement of microfilaments
 All muscles share some terminology
 Prefix myo refers to muscle
 Prefix mys refers to muscle
 Prefix sarco refers to flesh
Skeletal Muscle Characteristics
 Most are attached by tendons to bones
 Cells are multinucleate
 Striated – have visible banding
 Voluntary – subject to conscious control
 Cells are surrounded and bundled by
connective tissue
Connective Tissue Wrappings of
Skeletal Muscle
 Endomysium –
around single
muscle fiber
 Perimysium –
around a
fascicle
(bundle) of
fibers
Connective Tissue Wrappings of
Skeletal Muscle
 Epimysium –
covers the
entire skeletal
muscle
 Fascia – on the
outside of the
epimysium
Skeletal Muscle Attachments
 Epimysium blends into a connective
tissue attachment
 Tendon – cord-like structure
 Aponeuroses – sheet-like structure
 Sites of muscle attachment
 Bones
 Cartilages
 Connective tissue coverings
Smooth Muscle Characteristics
 Has no striations
 Spindle-shaped
cells
 Single nucleus
 Involuntary – no
conscious control
 Found mainly in
the walls of hollow
organs
Cardiac Muscle Characteristics
 Has striations
 Usually has a
single nucleus
 Joined to another
muscle cell at an
intercalated disc
 Involuntary
 Found only in the
heart
Function of Muscles
 Produce movement
 Maintain posture
 Stabilize joints
 Generate heat
Microscopic Anatomy of Skeletal
Muscle
 Cells are multinucleate
 Nuclei are just beneath the sarcolemma
Figure 6.3a
Microscopic Anatomy of Skeletal
Muscle
 Sarcolemma – specialized plasma
membrane
 Sarcoplasmic reticulum – specialized
smooth endoplasmic reticulum
Microscopic Anatomy of Skeletal
Muscle
 Myofibril
 Bundles of myofilaments
 Myofibrils are aligned to give distinct bands
 I band =
light band
 A band =
dark band
Microscopic Anatomy of Skeletal
Muscle
 Sarcomere
 Contractile unit of a muscle fiber
Microscopic Anatomy of Skeletal
Muscle
 Organization of the sarcomere
 Thick filaments = myosin filaments
 Composed of the protein myosin
 Has ATPase enzymes
Microscopic Anatomy of Skeletal
Muscle
 Organization of the sarcomere
 Thin filaments = actin filaments
 Composed of the protein actin
Microscopic Anatomy of Skeletal
Muscle
 Myosin filaments have heads
(extensions, or cross bridges)
 Myosin and
actin overlap
somewhat
Microscopic Anatomy of Skeletal
Muscle
 At rest, there is a bare zone that lacks
actin filaments
 Sarcoplasmic
reticulum
(SR) – for
storage of
calcium
Properties of Skeletal Muscle
Activity
 Irritability – ability to receive and
respond to a stimulus
 Contractility – ability to shorten when an
adequate stimulus is received
Nerve Stimulus to Muscles
 Skeletal
muscles must
be stimulated
by a nerve to
contract
 Motor unit
 One neuron
 Muscle cells
stimulated by
that neuron
Figure 6.4a
Nerve Stimulus to Muscles
 Neuromuscular
junctions –
association site
of nerve and
muscle
Nerve Stimulus to Muscles
 Synaptic cleft –
gap between
nerve and
muscle
 Nerve and
muscle do not
make contact
 Area between
nerve and muscle
is filled with
interstitial fluid
Transmission of Nerve Impulse to
Muscle
 Neurotransmitter – chemical released
by nerve upon arrival of nerve impulse
 The neurotransmitter for skeletal muscle is
acetylcholine
 Neurotransmitter attaches to receptors
on the sarcolemma
 Sarcolemma becomes permeable to
sodium (Na+)
Transmission of Nerve Impulse to
Muscle
 Sodium rushing into the cell generates
an action potential
 Once started, muscle contraction
cannot be stopped
The Sliding Filament Theory of
Muscle Contraction
 Activation by nerve
causes myosin
heads
(crossbridges) to
attach to binding
sites on the thin
filament
 Myosin heads then
bind to the next site
of the thin filament
The Sliding Filament Theory of
Muscle Contraction
 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
Contraction of a 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
Types of Graded Responses
 Twitch
 Single, brief contraction
 Not a normal muscle function
Types of Graded Responses
 Tetanus (summing of contractions)
 One contraction is immediately followed by
another
 The muscle does
not completely
return to a
resting state
 The effects
are added
Types of Graded Responses
 Unfused (incomplete) tetanus
 Some relaxation occurs between
contractions
 The results are summed
Figure 6.9a, b
Types of Graded Responses
 Fused (complete) tetanus
 No evidence of relaxation before the
following contractions
 The result is a sustained muscle contraction
Figure 6.9a, b
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 used stored ATP for
energy
 Bonds of ATP 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
 Direct phosphorylation
 Muscle cells contain creatine
phosphate (CP)
 CP is a high-energy
molecule
 After ATP is depleted, ADP is
left
 CP transfers energy to ADP,
to regenerate ATP
 CP supplies are exhausted in
about 20 seconds
Energy for Muscle Contraction
 Aerobic Respiration
 Series of metabolic
pathways that occur in
the mitochondria
 Glucose is broken down
to carbon dioxide and
water, releasing energy
 This is a slower reaction
that requires continuous
oxygen
Energy for Muscle Contraction
 Anaerobic glycolysis
 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
Energy for Muscle Contraction
 Anaerobic glycolysis
(continued)
 This reaction is not as
efficient, but is fast
 Huge amounts of
glucose are needed
 Lactic acid produces
muscle fatigue
Muscle Fatigue and Oxygen Debt
 When a muscle is fatigued, it is unable to
contract
 The common reason for muscle fatigue is
oxygen debt
 Oxygen must be “repaid” to tissue to remove
oxygen debt
 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
Types of Muscle Contractions
 Isotonic contractions
 Myofilaments are able to slide past each
other during contractions
 The muscle shortens
 Isometric contractions
 Tension in the muscles increases
 The muscle is unable to shorten
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
Muscles and Body Movements
 Movement is
attained due to
a muscle
moving an
attached bone
Muscles and Body Movements
 Muscles are
attached to at
least two points
 Insertion–
attachment to a
moveable bone
 Origin –
attachment to an
immovable bone
Effects of Exercise on Muscle
 Results of increased muscle use
 Increase in muscle size
 Increase in muscle strength
 Increase in muscle efficiency
 Muscle becomes more fatigue resistant
Types of Ordinary Body
Movements
Flexion- the
angle at a joint
decreased.
Extension- the angle at a
joint is increased.
Rotation- a
bone turns on
its long axis.
Abductionmovement
away from the
midline of the
body.
Adduction- movement toward the midline of
the body.
Circumduction- movement in a circle.
Special Movements
Dorsiflexion - sole of foot elevates
Plantar flexion - extension of the foot
Special Movements
Inversion - sole of foot turns inward
Eversion - sole of foot twists outward
Special Movements
Supination - turns
palm toward
anterior
Pronation - turns
palm toward
posterior
Opposition - move
thumb to touch
fingers
Types of Muscles
Prime mover – muscle with the major
responsibility for a certain movement
Antagonist – muscle that opposes or
reverses a prime mover
Synergist – muscle that aids a prime
mover in a movement and helps prevent
rotation
Fixator – stabilizes the origin of a prime
mover
Naming of Skeletal Muscles
 Direction of muscle fibers
 Example: rectus (straight)
 Relative size of the muscle
 Example: maximus (largest)
Naming of Skeletal Muscles
 Location of the muscle
Example: many muscles are named
for bones (e.g., temporalis)
 Number of origins
Example: triceps (three heads)
Naming of Skeletal Muscles
 Location of the muscles origin and
insertion
 Example: sterno (on the sternum)
 Shape of the muscle
 Example: deltoid (triangular)
 Action of the muscle
 Example: flexor and extensor (flexes or
extends a bone)
Gross Anatomy of Skeletal Muscles
A. Head and Neck Muscles
1. Facial Muscles
• Inserted into soft tissues such as other
muscles and skin.
• Allow us to grin, frown, pout, etc.
a) Frontalis- covers the frontal bone.
• Allows you to raise your eyebrows
and wrinkle your forehead.
frontalis
orbicularis oculi
b) Orbicularis Oculi- circular
muscles around the eyes.
• Allows you to close your
eyes.
c. Orbicularis Oris- circular muscle around
the mouth.
• Closes the mouth and protrudes the
lips.
orbicularis oris
buccinator
d. Buccinator- crosses the
cheek.
•Flattens and compresses the
cheek.
•Also considered a chewing
muscle.
e. Zygomaticus- from the corner of the
mouth to the cheekbone.
•Raises the corner of the mouth up.
zygomaticus
2. Chewing Muscles
•Begin the breakdown of food.
•The buccinator is both a facial muscle
and a chewing muscle.
a. Masseter- covers the lower jaw.
• Closes the jaw by elevating the
mandible.
temporalis
masseter
b. Temporalis- over the temporal bone.
•Synergist for the masseter in closing
the jaw.
3. Neck Muscles - Move the head and
shoulder girdle.
a. Platysma- covers the
anterolateral neck.
• Pulls the corners of
the mouth down.
platysma
sternocleidomastoid
b. Sternocleidomastoid- from the sternum
and clavicle to the temporal bone.
•Both= bowing the head.
•One= turn toward opposite side.
B. Trunk Muscles
1. Anterior Muscles
a. Pectoralis Major- covers the upper part
of the chest.
• Adducts and flexes the arm.
pectoralis major
b. Intercostal Muscles- found between the
ribs.
•Important in breathing.
rectus abdominis
2. Muscles of the Abdominal Girdle
a. Rectus abdominis- from the pubis to
the rib cage.
• Flex the vertebral column.
b. External oblique- lateral walls of the
abdomen.
•Flex the vertebral column
and rotate the trunk.
external oblique
internal oblique
c. Internal oblique- deep and at right angles
to the external obliques.
•Flex the vertebral column and rotate the
trunk.
d. Transversus abdominis- deepest muscle
of the abdomen and runs horizontally.
•Compresses the abdominal contents.
transversus abdominis
3. Posterior Muscles
a.Trapezius- diamond shaped
muscle of the posterior
neck.
• Extend the head
and move the scapula.
trapezius
latissimus dorsi
b. Latissimus Dorsi- covers the lower back.
• Extends and adducts the humerus.
c. Erector Spinae- deep muscles that span
the entire length of the vertebral column.
• Help control bending.
erector spinae
deltoid
d. Deltoid- rounded part of shoulder.
• Responsible for arm abduction.
C. Muscles of the Upper Limb
Muscles that act on the Humerus
Muscles that act on the Forearm
Muscles that act on the Hand
1. Muscles of the Humerus that act on
the Forearm
a. Biceps Brachii- bulges
when the elbow is flexed.
• Prime mover for flexion of
the forearm and supinates
biceps brachii
the forearm.
brachialis
b. Brachialis- deep to the
biceps and important in
brachioradialis
elbow flexion.
c. Brachioradialis- weak
muscle mainly on the
forearm.
d. Triceps Brachii- located on the
posterior humerus.
•Prime mover for elbow extension.
•Antagonist of biceps brachii.
triceps brachii
D. Muscles of the Lower Limbs
1. Muscles Causing Movement at the
Hip Joint
a. Gluteus Maximus- forms
flesh of buttock.
•Powerful hip extensor.
gluteus maximus
gluteus medius
b. Gluteus Medius- muscle
beneath the gluteus maximus.
• Hip abductor.
c. Iliopsoas- two muscles, the
iliacus and psoas major that
run from the iliac bone to the
femur.
• Prime mover for hip flexion.
iliopsoas
adductor muscles
d. Adductor Muscles- muscle
mass on the medial side of
each thigh.
• Adduct the thighs.
2. Muscles Causing Movement
at the Knee Joint
a. Sartorius- thin, straplike,
superficial thigh muscle.
• Weak thigh flexor.
sartorius
quadriceps group
b. Quadriceps Group- four
muscles of the anterior thigh.
• Extends the knee.
c. Hamstring Group- three
muscles of the posterior
thigh.
• Knee flexors.
hamstring group
3. Muscles Causing Movement
at the Ankle and Foot
a. Tibialis Anterior- superficial
muscle of the anterior leg.
• Acts to dorsiflex and invert
the foot.
tibialis anterior
b. Extensor Digitorum Longuslateral to the tibialis anterior.
• Prime mover of toe
extension and a dorsiflexor
of the foot.
extensor digitorum longus
fibularis muscles
c. Fibularis Muscles- three
muscles on the lateral part of
the leg.
•Plantar flexes and inverts
the foot.
d. Gastrocnemius- muscle
that forms the curve of the
calf.
•Prime mover of plantar
flexion of the foot.
gastrocnemius
soleus
e. Soleus- deep to the
gastrocnemius.
•Plantar flexor of the
foot.