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The Muscular System
Overview of Muscular System
Types of Muscle Tissue
• Under voluntary control
• Skeletal muscles
• The muscular system
• Under involuntary control
• Cardiac muscle
• Heart wall
• Smooth muscle
• Visceral organs
Overview of Muscular System
• Skeletal muscles attach to bones directly or indirectly
• Perform five functions
• Produce movement of skeleton
• Maintain posture and body position
• Support soft tissues
• Guard entrances and exits
• Maintain body temperature
Anatomy of Skeletal Muscles
Gross Anatomy
• Connective tissue organization
• Epimysium
• Fibrous covering of whole muscle
• Perimysium
• Fibrous covering of fascicle
• Endomysium
• Fibrous covering of a single cell (a muscle fiber)
• Tendons (or aponeurosis)
Anatomy of Skeletal Muscles
The Organization of a Skeletal Muscle
Anatomy of Skeletal Muscles
Microanatomy of a Muscle Fiber
• Sarcolemma
• Muscle cell membrane
• Sarcoplasm
• Muscle cell cytoplasm
• Sarcoplasmic reticulum (SR)
• Like smooth ER
• Transverse tubules (T tubules)
• Myofibrils (contraction organelle)
• Sarcomeres
Anatomy of Skeletal Muscles
Sarcomere—Repeating structural unit of the myofibril
• Components of a sarcomere
• Myofilaments
• Thin filaments (mostly actin)
• Thick filaments (mostly myosin)
• Z lines at each end
• Anchor for thin filaments
Anatomy of Skeletal Muscles
The Organization of a Single Muscle Fiber
Anatomy of Skeletal Muscles
The Organization of a Single Muscle Fiber
Anatomy of Skeletal Muscles
The Organization of a Single Muscle Fiber
Anatomy of Skeletal Muscles
Changes in the Appearance of a Sarcomere During Contraction of a
Skeletal Muscle Fiber
Anatomy of Skeletal Muscles
Changes in the Appearance of a Sarcomere During Contraction of a
Skeletal Muscle Fiber
Control of Muscle Contraction
Steps in Neuromuscular Transmission
• Motor neuron action potential
• Acetylcholine release and binding
• Action potential in sarcolemma
• T tubule action potential
• Calcium release from SR
Control of Muscle Contraction
The Neuromuscular Junction
• Synaptic terminal
• Acetylcholine release
• Synaptic cleft
• Motor end plate
• Acetylcholine receptors
• Acetylcholine binding
• Acetylcholinesterase
• Acetylcholine removal
Control of Muscle Contraction
The Structure and Function of the Neuromuscular Junction
Anatomy of Skeletal Muscles
The Contraction Process
• Actin active sites and myosin cross-bridges interact
• Thin filaments slide past thick filaments
• Cross-bridges undergo a cycle of movement
• Attach, pivot, detach, return
• Troponin-tropomyosin control interaction
• Prevent interaction at rest
Control of Muscle Contraction
Summary of Contraction Process
Control of Muscle Contraction
Key Note
Skeletal muscle fibers shorten as thin filaments interact with thick
filaments and sliding occurs. The trigger for contraction is the calcium
ions released by the SR when the muscle fiber is stimulated by its
motor neuron. Contraction is an active process; relaxation and the
return to resting length is entirely passive.
Muscle Mechanics
Some Basic Muscle Definitions
• Muscle tension—The pulling force on the tendons that muscle cells
generate when contracting
• Muscle twitch—A brief contraction-relaxation response to a single
action potential
Muscle Mechanics
The Twitch and Development of Tension
Muscle Mechanics
The Frequency of Muscle Fiber Stimulation
• Summation—Addition of twitch tension when a stimulus is
applied before tension has completely relaxed
• Incomplete tetanus—Tension peaks and falls repeatedly and
builds up beyond twitch tension
• Complete tetanus—Tension is steady (no relaxation phase) and
largest if stimuli arrive at very high rates
Muscle Mechanics
The Effects of Repeated Stimulations
Muscle Mechanics
Motor Units
• Motor Unit —A motor neuron and all the muscle cells it controls
• Recruitment—To increase muscle tension by activating more
motor units
• Small motor units provide finer control
• Motor units are intermixed in the muscle to pull evenly on the
tendon
Muscle Mechanics
Motor Units
Muscle Mechanics
Key Note
All voluntary (intentional) movements involve the sustained, subtetanic contractions of skeletal muscle fibers organized into distinct
motor units. The force generated can be increased by increasing the
frequency of action potentials or by recruiting additional motor units.
Muscle Mechanics
• Muscle tone—Tension in a “resting” muscle produced by a low
level of spontaneous motor neuron activity. Distinct from resting
tension produced by passive stretching.
• Function of muscle tone
• Stabilizes bones, joints
• Prevents atrophy (muscle wasting )
Muscle Mechanics
Types of Contractions
• Isotonic contraction
The tension (load) on a muscle stays constant (iso = same,
tonic = tension) during a movement. (Example: lifting a baby)
• Isometric contraction
The length of a muscle stays constant (iso = same, metric =
length) during a “contraction” (Example: holding a baby at
arms length)
Muscle Mechanics
Muscle Elongation
• Muscle contracts actively
• Muscles can only pull
• Muscles never push
• Muscle elongates passively
• Elastic forces
• Contraction of opposing muscles
• Effects of gravity
Energetics of Muscle Contraction
ATP and Creatine Phosphate Reserves
• Muscle contraction consumes much ATP
• ATP transfers energy directly to cycling cross-bridges and
calcium pumping
• CP stores energy and regenerates ATP
• CP transfers its energy to ADP
• Creatine phosphokinase (CPK) catalyzes
• ADP (2 “P”s) becomes ATP(3 “P”s)
• CP levels greatly exceed ATP levels
Energetics of Muscle Contraction
ATP Generation
• Light activity
• Aerobic metabolism of fatty acids
• Storage of glucose as glycogen
• Moderate activity
• Breakdown of glycogen to glucose
• Glycolysis of glucose
• Peak activity
• Anerobic breakdown of glucose
• Production of lactic acid
Energetics of Muscle Contraction
Muscle Metabolism
Energetics of Muscle Contraction
Muscle Metabolism
Energetics of Muscle Contraction
Muscle Metabolism
Energetics of Muscle Contraction
Muscle Fatigue—When a muscle loses ability to contract due to a low
pH (lactic acid buildup), low ATP levels, or other problems
Recovery Period—Time after muscle activity that it takes to restore
pre-exertion conditions
Oxygen Debt—Amount of excess oxygen used during the recovery
period
Energetics of Muscle Contraction
Key Note
Skeletal muscles at rest metabolize fatty acids and store glycogen.
During light activity, muscles can generate ATP through the aerobic
breakdown of carbohydrates, lipids, or amino acids. At peak levels of
activity, most of the energy is provided by anaerobic reactions that
generate lactic acid.
Muscle Performance
Two Types of Skeletal Muscle Fibers
• Fast fibers
Large diameter, abundant myofibrils, ample glycogen, scant
mitochondria. Produce powerful, brief contractions
• Slow fibers
Smaller diameter, rich capillary supply, many mitochondria,
much myoglobin. Produce slow, steady contractions
Muscle Performance
Physical Conditioning
• Anaerobic endurance
Time over which a muscle can contract effectively under
anerobic conditions.
• Hypertrophy
Increase in muscle bulk. Can result from anerobic training.
• Aerobic endurance
Time over which a muscle can contract supported by
mitochondria.
Muscle Performance
Key Note
What you don’t use, you lose. When motor units are inactive for days
or weeks, muscle fibers break down their contractile proteins and
grow smaller and weaker. If inactive for long periods, muscle fibers
may be replaced by fibrous tissue.
Cardiac and Smooth Muscle
Cardiac Muscle Tissue
• Small cells
• Single nucleus/cell
• Aerobic metabolism
• Intercalated discs
• Long contraction time
• Self-exciting (automaticity)
• No tetanic contraction
Cardiac and Smooth Muscle
Smooth Muscle Tissue
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•
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Nonstriated cells (no sarcomeres)
Calcium control of contraction different from striated muscle
Wide range of operating lengths
Involuntary muscle
• Under hormonal or local control
• Pacesetter cells
• Motor neurons often unneeded
Cardiac and Smooth Muscle
Cardiac Muscle Tissue
Cardiac and Smooth Muscle
Smooth Muscle Tissue
Cardiac and Smooth Muscle
Anatomy of the Muscular System
An Overview of the Major Skeletal Muscles
Anatomy of the Muscular System
An Overview of the Major Skeletal Muscles
Anatomy of the Muscular System
Origins, Insertions, and Actions
• Origin
Muscle attachment that remains fixed
• Insertion
Muscle attachment that moves
• Action
What joint movement a muscle produces
Anatomy of the Muscular System
Primary Action Categories
• Prime mover (agonist)
• Main muscle in an action
• Synergist
• Helper muscle in an action
• Antagonist
• Opposed muscle to an action
Anatomy of the Muscular System
Muscle Terminology
• Names of muscles provide clues to location, orientation, or
action
• Axial musculature—Muscles with origins on the axial skeleton
that position and move head, spine, rib cage
• Appendicular musculature—Muscles that stabilize or move
appendicular components
Anatomy of the Muscular System
The Axial Muscles
• Four groups of axial muscles
• Head and neck
• Spine
• Trunk
• Pelvic floor
Anatomy of the Muscular System
Selected Muscles of the Head
• Frontalis
• Orbicularis oris
• Buccinator
• Masseter
• Temporalis
• Pterygoids
Anatomy of the Muscular System
Selected Muscles of the Neck
• Platysma
• Digastric
• Mylohyoid
• Stylohyoid
• Sternocleidmastoid
Anatomy of the Muscular System
Muscles of the Head and Neck
Anatomy of the Muscular System
Muscles of the Head and Neck
Anatomy of the Muscular System
Muscles of the Head and Neck
Anatomy of the Muscular System
Muscles of the Anterior Neck
Anatomy of the Muscular System
Selected Muscles of the Spine
• Splenius capitis
• Semispinalis capitis
• Erector spinae groups
• Spinalis
• Longissimus
• Iliocostalis
Anatomy of the Muscular System
Muscles of the Spine
Anatomy of the Muscular System
Axial Muscles of the Trunk
• Thoracic region
• External intercostals
• Internal intercostals
• Diaphragm
• Abdominal region
• Rectus abdominis
• External oblique
• Internal oblique
• Transversus abdominis
Anatomy of the Muscular System
Oblique and Rectus Muscles and the Diaphragm
Anatomy of the Muscular System
Oblique and Rectus Muscles and the Diaphragm
Anatomy of the Muscular System
Oblique and Rectus Muscles and the Diaphragm
Anatomy of the Muscular System
Muscles of the Pelvic Floor (Perineum)
• Sheets of muscle
• From sacrum and coccyx
• To pubis and ischium
• Pelvic organ support
• Control of material passing through urethra and anus
Anatomy of the Muscular System
Muscles of the Perineum—Female
Anatomy of the Muscular System
Muscles of the Perineum—Male
Anatomy of the Muscular System
The Appendicular Muscles
• Two functionally distinct groups
• Muscles of the shoulder and upper limbs
• Muscles of the pelvic girdle and lower limbs
Anatomy of the Muscular System
Selected Shoulder Muscles
• Trapezius
• Rhomboid
• Levator scapulae
• Serratus anterior
• Pectoralis minor
Anatomy of the Muscular System
Muscles of the Shoulder
Anatomy of the Muscular System
Muscles of the Shoulder
Anatomy of the Muscular System
Muscles the Move the Arm
• Deltoid
• Supraspinatus
• Subscapularis
• Teres major
• Infraspinatus
• Teres minor
• Pectoralis major
• Latissiumus dorsi
Anatomy of the Muscular System
Muscles that Move the Arm
Anatomy of the Muscular System
Muscles that Move the Arm
Anatomy of the Muscular System
Muscles That Move the Forearm
• Biceps brachii
• Triceps brachii
• Brachialis
• Brachioradialis
• Pronators
• Supinator
Anatomy of the Muscular System
Muscles That Move the Wrist
• Wrist flexors
• Flexor carpi ulnaris
• Flexor carpi radialis
• Palmaris longus
• Wrist extensors
• Extensor carpi radialis
• Extensor carpi ulnaris
Anatomy of the Muscular System
Muscles That Move the Forearm and Wrist
Anatomy of the Muscular System
Muscle of the Pelvis and Lower Limbs
• Three functional groups
• Thigh movement
• Leg movement
• Ankle, foot, and toe movement
Anatomy of the Muscular System
Muscles That Move the Thigh
• Gluteal muscles
• Thigh adductors
• Adductor magnus
• Adductor brevis
• Adductor longus
• Pectineus
• Gracilis
• Thigh flexors
• Iliopsoas (psoas major + iliacus)
Anatomy of the Muscular System
Muscles That Move the Thigh
Anatomy of the Muscular System
Muscles That Move the Thigh
Anatomy of the Muscular System
Flexors of the Knee
• Biceps femoris
• Semimembranosus
• Semitendinosus
• Sartorius
• Popliteus
• Synergist muscle unlocks knee
Anatomy of the Muscular System
Extensors of the Knee
• Quadriceps femoris group
• Rectus femoris
• Vastus lateralis
• Vastus intermedius
• Vastus medialis
Anatomy of the Muscular System
Muscles That Move the Leg
Anatomy of the Muscular System
Muscles That Move the Foot
• Plantar flexion
• Gastrocnemius
• Soleus
• Eversion and plantar flexion
• Fibularis (peroneus)
• Dorsiflexion
• Tibialis anterior
Anatomy of the Muscular System
Muscles That Move the Foot and Toes
Anatomy of the Muscular System
Muscles That Move the Foot and Toes
Anatomy of the Muscular System
Muscles That Move the Foot and Toes
Anatomy of the Muscular System
Muscles That Move the Foot and Toes
Aging and the Muscular System
Age-Related Reductions
• Muscle size
• Muscle elasticity
• Muscle strength
• Exercise tolerance
• Injury recovery ability
The Integumentary System
• Removes excess body heat; synthesizes vitamin D3 for calcium
and phosphate absorption; protects underlying muscles
• Skeletal muscles pulling on skin of face produce facial expressions
The Skeletal System
• Maintains normal calcium and phosphate levels in body fluids;
supports skeletal muscles; provides sites of attachment
• Provides movement and support; stresses exerted by tendons
maintain bone mass; stabilizes bones and joints
The Nervous System
• Controls skeletal muscle contractions; adjusts activities of
respiratory and cardiovascular systems during periods of muscular
activity
• Muscle spindles monitor body position; facial muscles express
emotion; muscles of the larynx, tongue, lips and cheeks permit
speech
The Endocrine System
• Hormones adjust muscle metabolism and growth; parathyroid
hormone and calcitonin regulate calcium and phosphate ion
concentrations
• Skeletal muscles provide protection for some endocrine organs
The Cardiovascular System
• Delivers oxygen and nutrients; removes carbon dioxide, lactic acid,
and heat
• Skeletal muscle contractions assist in moving blood through veins;
protects deep blood vessels
The Lymphatic System
• Defends skeletal muscles against infection and assists in tissue
repairs after injury
• Protects superficial lymph nodes and the lymphatic vessels in the
abdominopelvic cavity
The Respiratory System
• Provides oxygen and eliminates carbon dioxide
• Muscles generate carbon dioxide; control entrances to respiratory
tract, fill and empty lungs, control airflow through larynx, and
produce sounds
The Digestive System
• Provides nutrients; liver regulates blood glucose and fatty acid
levels and removes lactic acid from circulation
• Protects and supports soft tissues in abdominal cavity; controls
entrances to and exits from digestive tract
The Urinary System
• Removes waste products of protein metabolism; assists in
regulation of calcium and phosphate concentrations
• External sphincter controls urination by constricting urethra
The Reproductive System
• Reproductive hormones accelerate skeletal muscle growth
• Contractions of skeletal muscles eject semen from male
reproductive tract; muscle contractions during sex act produce
• pleasurable sensations