muscular system total muscles in human body: 650 muscles required to smile:17 muscles required to...
TRANSCRIPT
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MUSCULAR SYSTEM
• Total muscles in human body: 650• Muscles required to smile: 17• Muscles required to frown: 33• Muscles required to walk: at least 200• Longest muscle: Gluteus maximus ( butt muscle)• Shortest muscle: ear muscle
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Characteristics of Muscles
• Muscle cells are elongated (muscle cell = muscle fiber)
• Contraction of muscles is due to the movement of microfilaments (actin and myosin)
• All muscles share some terminology– Prefix myo refers to muscle– Prefix mys refers to muscle– Prefix sarco refers to flesh
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Functions of Muscular system• Contract:• Skeletal Muscles: body movement• Smooth muscles: movement of contents through blood
vessels, digestive organs• Cardiac Muscles: Pumping of heart
• Generate heat : generate heat, by product of ATP needed for muscle contraction
• Stabilize joints: Skeleton muscles pull on bones for movement, also stabilize joints
• Maintaining Posture: Keeps the body straight against gravity
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• Muscles are responsible for all types of body movement
• Three basic muscle types are found in the body– Skeletal muscle– Cardiac muscle– Smooth muscle
The Muscular System
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Smooth Muscle
• Smooth muscles are non striated, uni-nucleated and spindle shaped
• Involuntary
• Found in the walls of visceral organs, eg. Stomach, urinary bladder, respiratory passages
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Smooth Muscles• Arranged in two layers:• circular layer• longitudinal layer
• These two layers alternately contract and relax
• And move food through digestive tract, emptying the bowels & bladder
• Maintain housekeeping activities
• Slow and steady
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Cardiac Muscle
• Responsible for heart pumping
• Cardiac muscles are striated, cylindrical, uninucleated & branched
• The muscle is under involuntary control and contract at regular intervals
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Cardiac Muscle• Cardiac muscle cells are joined to another cell by intercalated discs
• Discs are important in transport of impulses
• Present in heart only
• Cardiac fibers are arranged in spiral or eight-shaped bundles
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Skeletal Muscle
• Under voluntary or CNS control
• Respond to impulses
• Muscles are striated (actin and myosin are alternatively arranged)
• Muscle cells are cylindrical or cigar shaped
• multinucleated
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Skeletal Muscle
• Attached to bones with the help of tendons
• A person has same number of muscle fiber from his birth to adult hood
• However, their size increases or decreases depending on the usage
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Structure of Skeletal Muscle
• Each muscle fiber is enclosed in a connective tissue called endomysium
• Each muscle fiber is supplied with capillary and nerve cell extensions
• Several muscle fibers (cells) called fascicle are enclosed in a connective tissue called perimysium
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Structure of Skeletal Muscle
• Several fascicles are surrounded by third or heavy layer of connective tissue layer called epimysium
• Thus each skeletal muscle is surrounded by epimysium
• In order to form a long muscle, muscle fibers are arranged end to end
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• Epimysium blends into a connective tissue attachment– Tendons — cord-like
structures • Mostly collagen fibers
– Aponeuroses — sheet-like structures
• Attach muscles indirectly to bones, cartilages, or connective tissue coverings
Skeletal Muscle Attachments
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Microscopic Anatomy of Skeletal Muscle
• Skeletal cells are multinucleate
• Outer boundary of the cell is made of plasma membrane – sarcolemma
• Cytoplasm of muscle cell - sarcoplasm
• Endoplasmic reticulum – Sarcoplasmic reticulum
• Sarcoplasm is packed with myofibrils
• Other organelles, such as mitochondria, glycogen granules are found between myofibrils
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• Myofibrils: are thread like organelles
– Composed of protein threads called myofilaments:
– thin (actin) – thick (myosin)
– Sarcomeres: repeating units of myofilaments
• Interaction between actin and myosin filaments leads muscle to shorten or contract
• The tropomyosin/troponin complex regulates the interaction between actin and myosin
Microscopic Anatomy of Skeletal Muscle
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• Repeating units of myofibrils - Sarcomere
• The distance between two Z discs is the sarcomere
• The point where actin originates is called Z disk
• Each sarcomere has alternating actin and myosin filaments
Structure of Sarcomere
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• The arrangement of myosin (dark in color and is called anisotropic band or A band)
• And actin (light in color and is called isotropic or I band) alternatively
• gives the muscle a striated appearance
• H zone (bare zone) - lacks actin filament
Structure of Sarcomere
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Microscopic Anatomy of Skeletal Muscle
• Myosin filaments have heads (extensions, or cross bridges)
• When contraction occurs, actin and myosin overlap
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Properties of Skeletal Muscle Activity
• Irritability – ability to receive and respond to a stimulus
• Contractility – ability to shorten when an adequate stimulus is received
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Nerve Stimulus and Action Potential
• Skeletal muscles must be stimulated by a nerve to contract
• One motor neuron can stimulate many muscle cells – Motor unit
• Axon of the neuron branches into many axon terminals at Neuromuscular junctions
• Neuromuscular junctions – association site of nerve and muscle
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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
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Nerve Stimulus and Action Potential
• When nerve impulse reaches the axon terminal, it releases the chemical known as
Neurotransmitter
• The neurotransmitter for skeletal muscle is acetylcholine
• Neurotransmitter attaches to receptors on the sarcolemma
• Sarcolemma becomes permeable to sodium (Na+)
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• Sodium rushing into the cell generates an action potential
– Once started, muscle contraction cannot be stopped
• Stimulates release of Ca+2 from the sarcoplasmic reticulum
• • Ca +2 binds to the troponin, troponin
changes shape and removes the blocking action of tropomyosin
• Actin active sites exposed
• Actin is now ready to bind to the head of the myosin
Nerve Stimulus and Action Potential
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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
• This continued action causes a sliding of the myosin along the actin
• The result is that the muscle is shortened (contracted)
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The Sliding Filament Theory
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The Sliding Filament Theory
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The Sliding Filament Theory
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Contraction of a Skeletal Muscle as a whole
• Muscle cell contraction is “all or none”
• But in whole 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
• They are of 4 types:– Twitch– Tetanus– Unfused– fused
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• Twitch– Single, brief contraction– Not a normal muscle
function• Following stages
– Stimulus : receives information from nerve
– Lag phase: muscle cell gets ready physiologically
– Contraction phase: actin and myosin slide one over the other
– Relaxation phase: back to non contracted stage
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• 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
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• Unfused (incomplete) tetanus– Some relaxation occurs between contractions– The results are summed
• Fused (complete) tetanus– No evidence of relaxation before the following contractions– The result is a smooth and sustained muscle contraction
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Muscle Response to Stronger 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
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Energy for Muscle Contraction• Initially, muscles use 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
• Working muscles use 3 pathways for ATP production
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• Direct phosphorylation of ADP by creatine phosphate
– Muscle cells contain creatine phosphate (CP)
• CP is a high-energy molecule
– ADP is left, after ATP is depleted,
– CP transfers energy to ADP, to regenerate ATP
– CP supplies are exhausted in about 15 seconds
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• Aerobic Respiration
– Series of metabolic pathways occur in the mitochondria, require oxygen
– Known as oxidative phosphorylation
– Glucose is broken down to carbon dioxide and water, & release energy in the form of ATP
– This is a slower reaction that requires continuous oxygen and nutrient fuel
– 36 ATP/ glucose
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• 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
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• Anaerobic glycolysis
• This reaction is not as efficient, but is fast
• 2ATP/glucose
• Huge amounts of glucose are needed
• Lactic acid produces muscle fatigue
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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 get tired (contract less)
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Muscle Tone
• Some fibers are contracted even in a relaxed muscle
• Contraction is not visible but muscles remain firm, healthy
• This state of continuous partial contraction is Muscle tone
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Effects of Exercise on Muscle• 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
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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 an immovable bone
– Insertion –• attachment to a moveable
bone
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Flexion: movement of a body part anterior to the coronal plane
Extension: movement of a body part posterior to the coronal plane
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Abduction: movement away from the median plane
Adduction: movement toward the median plane
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Pronation/Supination:
Unique rotation of the forearm
Pronation: palm faces posteriorly
Supination: palm faces anteriorly
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Circumduction The circular or conical
movement of a body part
Consists of a combination of flexion, extension, adduction, and abduction
Occurs at freely movable joints
Eg. Windmilling the arms or rotating the hand from the wrist
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– Plantar flexion: standing on the toes
– Dorsiflexion: foot lifted toward the shin,
such as walking on the heels
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• Elevation: moves a structure superior• Depression: moves a structure inferior• Examples: shrugging the shoulders, opening and
closing the mouth
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• Protraction: • Movement of a bone
anteriorly• Eg. Thrusting the jaw
forward, shoulder forward
• Retraction: • Moves structure back to
anatomic position or even further posteriorly
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• Lateral: moving mandible to the right or left of midline• Such as in grinding the teeth or chewing the food• Medial: return the mandible to the midline
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• Opposition: movement of thumb and little finger toward each other
• Reposition: return to anatomical position
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• Inversion: • Inversion is a
movement in which the soles are turned medially
• Eversion: • Eversion is a turning
of the soles to face laterally
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Interaction of Skeletal Muscles in the Body
• Prime mover – muscle with the major responsibility for a certain movement– Biceps is the prime mover for
flexion– Triceps is the prime mover of
extension
• Antagonist – muscle that opposes or reverses a prime mover– Biceps and triceps work against
one another
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• Synergist – muscle that aids a prime mover in a movement and reduce undesirable movement– Cross one or more
joints that connect two or more bones
– Brachialis and brachioradialis help bicep brachii
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Naming of Skeletal Muscles
• Direction of muscle fibers– Example: rectus (straight)
– Rectus abdomonius
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Naming of Skeletal Muscles
• Relative size of the muscle– Example: maximus
(largest)– Gluteus muscles– Maximus– Medius– Minimus
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Naming of Skeletal Muscles
• Location of the muscle– Example:
many muscles are named for bones (e.g., temporalis)
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Naming of Skeletal Muscles
• Location of the muscle’s origin and insertion– Example: sterno (on
the sternum)
• Number of origins– Example: triceps
(three heads)
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Naming of Skeletal Muscles
• Shape of the muscle– Example: deltoid
(triangular)
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Naming of Skeletal Muscles
• Action of the muscle– Example: flexor and extensor (flexes or extends a bone)
– Hamstring( flexor)– Extensor( quadriceps)
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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
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Head and Neck Muscles
• Neck muscles
– Platysma—pulls the corners of the mouth inferiorly
– Sternocleidomastoid—flexes the neck, rotates the head
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• 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
Muscles of Trunk
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Muscles of Trunk
• 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
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Muscles of Trunk• Posterior muscles
– Trapezius— elevates, depresses, adducts, and stabilizes the scapula
– Latissimus dorsi— extends and adducts the humerus
– Deltoid— arm abduction
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• Biceps brachii— supinates forearm, flexes elbow
• Brachialis— elbow flexion
• Brachioradialis— weak muscle
• Triceps brachii— elbow extension (antagonist to biceps brachii)
Muscles of the Upper Limb
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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
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Muscles of the Lower Limb
• Muscles causing movement at the knee joint– Hamstring group—
thigh extension and knee flexion
• Biceps femoris• Semimembranosus• Semitendinosus
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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)
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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