Muscular System
Chapter 6
Functions of the Muscular System
 Produces Movement-skeletal muscles are responsible for all
locomotion and manipulation of the skeleton. Their speed
and power help us stay safe.
 Maintaining Posture- muscle functions almost continuously as
we sit or stand making tiny adjustments to help us overcome
gravity
 Stabilizing Joints-muscle reinforces and stabilizes joints
 Generate Heat- by product of muscle activity is producing
heat. Helps maintain normal body temperature
3 types of muscle
 Skeletal- attached to bones or skin, appear to be long and
cylindrical, multinucleated with obvious striations, voluntary,
speed of contraction varies, no rhythmic contractions,
controlled by nervous system.
 Cardiac- makes up muscle of the heart, uninucleate, has
striated appearance, involuntary, serves as a pacemaker so
also controlled by nervous system, slow rhythmic
contractions
 Smooth- mostly makes up walls of organs, uninucleate, no
striations, involuntary, nervous system controls, contractions
are very slow and some are rhythmic.
Microscopic Anatomy of Skeletal
Muscle
 See notes on page 1. The picture you see will be on the test
and can be found on p. 164 also see p. 167 for diagrams.
 Matching section will expect you to know
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Actin- thin filaments
Myosin- thick filament, studded with myosin heads
A Band- bands where both actin and myosin are found
H Zone- lighter central portion of the A band
I band- contains only actin filaments
Z discs- actin filament anchored to disclike membranes
Sarcomere- tiny contractile unit that shortens during muscle
contraction
Types of Graded Responses
 Twitch: single, brief contraction, not a normal muscle
function.
 Tetanus-summing of contractions, one contraction
immediately followed by another, muscle doesn’t completely
return to resting state, effects are added
 Unfused (incomplete) Tetanus-some relaxation occurs
between contractions
 Fused (Complete) Tetanus- no evidence of relaxation
following contractions.
Energy for muscle contraction (ATP)
 ATP is the only source of energy to power muscle. There is
only enough for 4-6 seconds worth of energy.
 There are 3 pathways to get more ATP
 Direct phosphorylaton- ADP reacts with creatine phosphate
(CP). Energy source is CP. 1 ATP per CP is created and will
give 15 seconds of energy.
 Anaerobic: (glycolysis and lactic acid formation) Energy comes
from glucose, 2 ATP per glucose produces, 30-60 seconds of
energy.
 Aerobic: 95% of ATP created this way. Occurs in mitochondria,
uses oxygen. Glucose is broken down and energy is released,
creates 36 ATP per glucose, gives hours of energy.
Muscle Fatigue
 Unable to contract even though the muscle is being
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stimulated. If no rest, muscle will continue to contract
weakly and finally stops contracting.
Due to Oxygen debt
Oxygen must be repaid to tissue to remove oxygen deficit.
Oxygen is required to get rid of accumulated lactic acid.
Increasing acidity and lack of ATP causes the muscles to
contract less.
Types of Muscle Contractions:
 Isotonic Contractions: myofiliaments are able to slide past
each other during contractions, muscle shortens and
movement occurs.
 Isometric contractions “Tension in muscle increases, the
muscle is unable to shorten or produce movement.
Muscle Tone
 The state of partial contractions. The contraction is not
visible but the muscle remains firm, healthy and constantly
ready for action.
 Different fibers contract at different times
 The process of stimulating various fibers is under invlountary
control.
 People who have had injury can lose muscle tone. If
paralyzed, muscle become flaccid or soft and flabby and
begins to waste away
Exercise and Muscle (use it or lose it)
 Aerobic Exercise: endurance exercise (biking, jogging)
results in stronger more flexible muscles with greater
resistance to fatigue, makes body metabolism more efficient,
improves digestion and coordination
 Resistance Exercise: isometric exercise (weight lifting),
increases muscle size and strength
 Best to include both types of exercise in your routine.
5 Golden Rules for Skeletal Muscle
Activity
 All muscles cross at least one joint
 Typically, the bulk of the muscle lies proximal to the joint
crossed.
 All muscles have at least two attachments: The origin and the
insertion
 Muscles can only pull, they never push
 During contraction, the muscle insertion moves toward the
origin.
Muscles and Body Movements
 Movement is attained due to a muscle moving an attached
bone.
 Muscles are attached to at least two points
 Origin: attachment to a moveable bone
 Insertion: attachment to an immovable bone
Ordinary Body Movements
 Flexion: decreases the angle of the joint, brings 2 bones
closer together, typical of hinge joints like knee and elbow
 Extension: opposite of flexion, increases angle between 2
bones.
 Rotation: movement of a bone around its longitudinal axis,
common in ball and socket joints; ex. Shaking your head no.
Ordinary Body Movements
 Abduction: movement of a limb away from the midline.
 Adduction: opposite of abduction; movement of a limb
toward the midline
 Circumduction: combination of flexion, extension, abduction
and adduction; common in ball and socket joints.
Special Movements
 Dorsiflexion-lifting the foot so that the superior surface
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approaches the shin.
Plantar flexion- depressing the foot(point thetoes)
Inversion-turn the sole of foot medially
Eversion- turn sole of foot laterally
Supination- forearm rotates laterally so palm faces anteriorly
Pronation- forearm rotates medially so palm faces posteriorly
Opposition- move thumb to touch the tips of other fingers
on the same hand
Types of Muscles
 Prime mover- muscles with the major responsibility for a
certain movement
 Antagonist- muscles 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
 By direction of muscle fibers. Ex. Rectus(straight)
 By relative size of the muscle. Ex. Maximus (largest)
 By location of the muscle. Ex. Temporalis (temporal bone)
 By number of origins. Ex. Triceps (three heads)
 By location of the muscle’s origin and insertion. Ex.
Sterno(on the sternum)
 By shape of the muscle. Ex. Deltoid(triangular)
 By action of the muscle. Ex. Flexor and extensor
Muscles of Head and Neck
 Facial muscles
 Frontalis – raises eyebrows
 Orbicularis oculi- closes eyes, squintes, blinks, winks
 Orbicularis oris – closes mouth and protrudes the lips
 Buccinator- flattens the cheeks, chews
 Zygomaticus- raises corners of the mouth
Chewing Muscles:
Masseter- closes the jaw and elevates the mandible
Temporalis- synergist of the masseter, closes jaw
Head and Neck Muscles
 Platysma- pulls the corners of the mouth inferiorly
 Sternocleidomastoid – flexes the neck, rotates the head
Head and Neck Muscles
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
Arm and Shoulder Muscles
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
Posterior Muscles
 Trapezius –elevates, depresses, adducts, and stabilizes the
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scapula
Latissimus dorsi- extends and adducts the humerus
Erector spinae- back extension
Quadratus lumborum- flexes the spine laterally
Deltoid – arm abduction
Muscles of Upper Limb
 Biceps Brachii- supinates forearm, flexes elbow
 Brachialis- elbow flexion
 Brachioradialis- weak muscle
 Triceps Brachii- elbow extension (antagonist to biceps
brachii)
Muscles of 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 lower limb
 Muscles causing movement at the knee joint
 Hamstring group- thigh extension and knee flexion
 Biceps femoris
 Semimembranosus
 semitendinosus
Hamstring group
Muscles of Lower limb
 Muscles causing movement at the knee joint
 Sartorius- flexes the thigh
 Quadriceps group- extends the knee
 Rectus femoris
 Vastus muscles (3)
Muscles of the Lower Limb
 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 Lower Leg
Anterior Muscles of the Body
Posterior Muscles of the Body
Intramuscular Injection Sites