Ch. 10
Anatomy of the muscular
system
The incredible human
machine
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Introduction
• Myology - Study of muscles
• Energy for Muscular contraction ATP
• Three types of muscle - skeletal,
cardiac, smooth
• Number of skeletal muscles - more
than 600
• Weight of muscles - 40-50%
Full muscular
system
Connective Tissue
coverings
• Fascia - surrounds and separates
muscles
• Tendons - connects muscle to bone
• Aponeurosis - broad sheet of
connective tissue
• Epimysium - covers whole muscle
• Perimysium - covers fascicles
• Endomysium - covers myofibrils
Structure
• Size - range from small to large
• Shape -broad, narrow, short, long
• Arrangement
– Parallel, converging, oblique, pennate,
bi- pennate, sphincter
Attachment of muscles
• Origin - attachment to immovable
bone
• Insertion - attachment to movable
bone
Muscle actions
• Prime movers (agonists) - main
action
• Antagonists - opposite action
• Synergists - helper muscle
The power of muscle
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Lever systems
• Bones serve as levers and joints serve as
fulcrums
• Contracting muscles applies pulling force
on bone lever
• Four components of lever system
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–
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Rigid bar - bone
Fulcrum - joint
Load - what is moved
Pull - muscle contraction
How muscles are named
• Latin based or English
• Naming - supply hints as to muscle
action
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–
–
–
–
Location, function, shape
Direction of fibers
Number of heads
Points of attachment
Relative size
Muscles of
facial
expression
• Epicranius - raises eyebrows
• Orbicularis oculi - closes eye
• Orbicularis oris - draws lips together
• Buccinator - smiling
• Zygomaticus - laughing
Muscles of mastication chewing
• *Masseter - closes jaw
• Temporalis - closes jaw
Muscles that move the
head
• *Sternocleidomastoid - flexes head
• *Splenius capitis - extends head
• Semispinalis capitis - extends head
Muscles of the thorax
• *Intercostals - lift ribs
• *Diaphragm - enlarges thorax
Muscles that move the
shoulder girdle
• *Trapezius - raises shoulders
• Rhomboideus major rotates/retracts scapula
• Levator scapulae elevates/retracts scapula
• Serratus anterior - pulls
shoulder down and forward
• *Pectoralis minor - pulls
shoulder down
Muscles that move the
upper arm
• Flexors
– Coracobrachialis - adduction
– *Pectoralis major - flex upper arm
• Extensors
– Teres major - extension, medial rotation
– *Latissimus dorsi - extends upper arm
• Abductors
– Supraspinatus
– *Deltoid
• Rotators - *rotator cuff
– Subscapularis- medial rotation
– Infraspinatus - outward rotation
– Teres minor - outward rotation
Muscles that move the
forearm
• Flexors
– *Biceps brachii
– Brachialis
– Brachioradialis
• Extensor
– *Triceps brachii
Muscles that move the
hand
• Flexors
– Flexor carpi radialis and ulnaris
– Palmaris longus
– *Flexor digitorum profundus
• Extensors
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–
–
–
Extensor carpi radialis longus
Extensor carpi radialis brevis
Extensor carpi ulnaris
*Extensor digitorum
Muscles of the abdominal
wall
• *external and internal obliques compresses abdoment - allows for
side to side motion
• *Rectus abdominis
• Flexes waist
• Transverse abdominus synergist
Compresses abdomen
Muscles of the back
• *Trapezius
– Extends head/neck
• *Rhomboideus
– Retracts scapula
• Infrapinatus
– Extends/rotate arm
• Teres major and minor
– Extends, adduts arm
• *Latissimus dorsi - extends
– arm
Muscles of the pelvic floor
• Levator ani
• Superficial transversus perinei
• Bulbospongiosus
• Ischiocavernoses
Muscles that move the
thigh
• Anterior group
– *Psoas major
– Iliacus
• Posterior group
– *Gluteus maximus, medius, minimus
– Tensor fasciae latae
• Adductors
– Adductor longus
– Adductor magnus
– Gracilis
Muscles that move the leg
• Flexors
– *Biceps femoris
– Semitendinosus
– Sartorius
• Extensor
– *Quadriceps femoris group
• Rectus femoris
• Vastus lateralis/medialis/intermedius
Muscles that move the
ankle foot and toes
• Dorsal flexors
– *Tibialis anterior
– Peroneus tertius
– Exensor digitorum longus
• Plantar flexors
– *Gastrocnemius
– Soleus (synergist)
– Flexor digitorum longus
Ch. 11 The physiology of the
muscular system
Introduction
• Purpose - move framework of body,
produce heat, facilitate posture
• Characteristics
– Excitability - ability to be stimulated
– Contractibility - ability to shorten
producing movement
– Extensibility - ability to stretch and
return to resting length.
Structure of muscle fibers
• Description - each fiber - muscle cell (spans
a joint)
• Sarcolemma - cell membrane
• Sarcoplasm - cytoplasm of muscle cell
– Contains mitochondria, nuclei, myofibrils
• Myofibrils - filaments
– Myosin - thick
– Actin - thin
• Sarcomere - unit within myofibril
– Extends from z line to z line.
– Z lines produce striations
• Sarcoplasmic reticulum (endoplasmic
reticulum)
– Contains transverse tubules (nerve impulse)
Neuromuscular Junction
• Where neuron and muscle fiber
meet.
• Abundant mitochondria present
for ATP production
• Neurotransmitters - chemical
communicators located at the
end of neuron in the Cytoplasm
• Motor Unit
– Mucle fibers contract at once
when triggered by
neurotransmitters
– Recruitment - increase in number of
motor units activated.
Skeletal Muscle Contraction
• Shortening of sarcomeres results in muscle
pulling against attachments
– Myosin - two twisted strands with crossbridges
– Actin contains myosin binding sites
• Sliding filament theory
– Myosin cross-bridge attaches to binding site
on actin filament and bends
– Pulls actin filament, releases and attaches to
next binding site, pulling again.
– Energy from atp used to prepare the crossbridges.
Stimulus for contraction
– Neurotransmitter - Acetylcholine released from synaptic vesicles at
end of axon of neuron.
• Note - botulinus toxin prevents acetylcholine release.
– Receptors detect neurotransmitter
– Impulse spreads over sarcolemma then travels through transverse
to sarcoplasmic reticulum
– Calcium released by sarcoplasmic reticulum
– High calcium moves Troponin and tropomyosin aside, exposing
binding site
– Myosin Crossbridge attaches to binding site
– Crossbridge shortens pulling filaments across each other
– Sarcomere shortens
– Acetylcholinesterase decomposes acetylcholine
– Calcium returns to sarcoplasmic reticulum
– Link between actin and myosin is broken.
Muscle contraction
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Oxygen supply and cellular respiration
• During rest - enough oxygen to support aerobic cellular
respiration.
• Oxygen deficiency during exercise
– Lactic acid end product of anaerobic respiration. - lactic acid
diffuses out of muscle cells and is carried to liver.
• Oxygen debt - amount of oxygen that liver cells require to
convert lactic acid into glucose plus amt. muscle cells
need to make atp to original concentration.
• Muscle fatigue-muscle loses ability to contract during
strenuous exercise.
• Result of lactic acid accumulation (lower ph)
• Muscle cramp - lack of ATP required to return calcium ions
back to sarcoplasmic reticulum so muscle fibers can relax.
• Heat production - energy produced by cellular respiration
is lost as heat.
Muscular responses
• One method of studying muscle function - remove single fiber
and connect to device that records response to electrical stimuli.
• Muscle fibers remain unresponsive till they reach Threshold
stimulus (stimulus of a certain strength)
• All or none response
• Summation - series of stimuli of increasing frequency
• Recruitment of motor units-increase in number of activated
motor units
• Sustained contractions - muscle tone - achieved by continuous
state of sustained contraction.
• Treppe-staircase phenomenon - twitch contractions 1 second
apart
• Tetanus-multiple wave summation/no relaxation
Recording a muscular
contraction
• Myogram - recording of electrically
stimulated muscle contraction
• Myograph - machine that records the
contraction
• Twitch-single short contraction
• Latent period - time delay followed by
period of contraction and relaxation.
Muscle tone
• Tonic contraction-continual partial contraction
of a muscle
• Flaccid - less tone than normal
• Spastic-more tone than normal
• Negative feedback mechanism controls tone
• Graded strength - affected by:
– Metabolic condition of fibers
– Number of fibers contracting
– Number of motor units recruited
Physical training
• Strength training- results in hypertrophy enlargement of fibers
• Endurance training - increases ability to
sustain moderate contractions for longer
time. Increase of mitochondria.
• Atrophy - result of disuse
– Decreased capillary networks, decreased
mitochondria, decreased filaments.
Smooth
muscle
•
•
•
•
•
•
Fibers - elongated with tapered ends
Lack striations
Undeveloped sarcoplasmic reticulum
Located in iris of eye and walls of hollow organs
Display rhythmicity - allow for peristalsis
Contraction uses acetylcholine and
norepinephrine
• Slower to contract and relax but can contract
longer
Cardiac
muscle
• Mechanism - same as smooth and
skeletal
• Difference: transverse tubules supply extra
calcium allowing for contraction for
longer periods.
• Structure
– Intercalated discs - join cells and cause cells
to contract as a unit.
– Rythmic
– Self-exciting