Chapter 6
The Muscular
System
Muscle Functions
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Movement
Posture
Muscle Tone
Stabilize Joints
Generate Heat
Skeletal Muscle - 40 % of body
mass
• General Features
– epimysium
• covers entire muscle “belly”
– perimysium
• covers fascile
– endomysium
• covers fibers
– sacrolemma
• covers muscle cells
Skeletal Muscle
• Microscopic Anatomy
– muscle cell
– myofibrils
• long, thin organelles
– sacromere
• contractile unit Z line to Z line
– myosin
• thick A bands
– actin
• thin I bands
Muscle Contraction
• Motor Unit
– one neuron
– all skeletal muscle cells it innervates
• Neuromuscular Junction
– axon joins w/ sacrolemma
– where neurotransmitters are released
– acetylcholine ACH
Muscle Contraction
• Sliding Filament Theory
ACH released
membrane becomes permeable to Na +
Na + flows in K + flows out
Ca + released from sarcoplasmic reticulum
Ca + causes actin filament troponin covers to be
uncovered
– myosin forms cross bridges connecting to actin
filament
– sarcomere shortens
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Muscle Contraction
• Relaxation
– acetylcholinesterase break down ACh
– Na + flows out K + flows in
- Ca + reabsorbed
– cross bridges released
- covers on actin fibers reform- A and I bands relax
• All or None Response
– sarcomere lengthens
– each muscle cell and fiber contracts fully or not at
all
• Muscle Twitch
– quick brief jerky movement
• Tetanus
– smooth substained contraction
Energy for Contraction
• CP
– creatine phosphate ---> ATP (1)
• Anaerobic respiration
– no oxygen
– glycogen ---> ATP (1) glycolysis
– stored glucose ---> lactic acid(citric acid)
• Aerobic respiration
- Krebs cycle- citric acid -- ATP(2)
– glucose ---> ATP (32) electron transport
Cellular respiration net gain of 36 ATP’s
Energy for Contraction
• Muscle fatigue
-Oxygen Debt
-Lactic Acid- “soreness”
- too little Recovery time
Exercise & Muscle Tone
• Isotonic
– muscle shortens
• Isometric
– muscle tension
• Muscle tone
– partial contraction of muscles at all times
maintains posture
• Atrophy
– muscle tissue wastes away
• Hypertrophy
– enlarging muscles
Skeletal Muscle Connections
• Origin
– fixed point
• Insertion
– moveable point
Antagonists: Muscle or a group of muscles that is do the
opposite of the primary mover
- If the agonist is flexing the antagonist is
extending.
Synergist: Muscle or muscles that aid in the movement of
either the agonist or the antagonist muscles.
Muscle Movements & Types
• Body Movements
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Flexion
Extension
Abduction
Adduction
Rotation
Circumduction
Pronation
Supination
Inversion
Eversion
Dorsiflexion
Plantar flexion
How Muscles are Named
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Location ~where at in body frontalis
Origin ~ bone # of origins “biceps”
Insertion ~ bone insert “zygomaticus”
Action ~ flexor, extensor
Shapes ~ trapezius & deltoid
Size ~ longus, maximus
Direction of Muscle Fibers ~ rectus ,
transversus
Major Skeletal Muscles
• Muscles of the Head
– Epicranius
• (occipitofrontalis)
• frontalis
– raises eyebrows
• Occipitalis
– draws scalp back
– Orbicularis Oris
• closes lips
– Orbicularis Oculi
• closes eyes
– Zygomaticus
• smile
Major Skeletal Muscles
• Muscles of the Head
– Buccinator
• suck in cheeks
– Masseter
• chewing
• Synergist w/ temporalis
– Temporalis
• close jaw
• Synergist w/ masseter
– Nasalis
• wrinkles nose
• flare nostrils
Major Skeletal Muscles
• Muscles of the Neck
– Sternocleidomastoid
• ear to shoulder
• chin to chest
– Platysma
• frown
• pulls corner of mouth down
Muscles of the Anterior Thorax
• Pectoralis Major
– pulls arm across chest
• Intercostals
– breathing
• Serratus Anterior
– boxers muscles
– abduction of scapula
Abdominal Muscles
• Rectus Abdominus
– compress abdomen
• External Oblique
– flex and rotate the trunk
• Internal Oblique
– flex and rotate the trunk
• Transversus Abdominus
– compress abdomen
Muscles of the Posterior Thorax
• Trapezius
– adducts scapula
– head erect
– occipital cervical thoracic
– inserts on scapula & clavicle
• Deltoid
– abduction of arm
– injection site
– scapula clavicle ---> humerus
•Latissimus dorsi
–lumbar sacrum and ilium
–Insertion: humerus
–Moves arm down and back
•Erector spinae
–3 muscles
–back extensors
Arm Muscles
• Triceps brachii
– extend lower arm
• Pronator Teres
– palms down
Biceps brachii
flex lower arm- rotates
Brachialis
flex lower arm
Brachioradialis
flex lower arm- rotates
Arm Muscles
• Flexor carpi
– flex wrist
insertion: metacarpals
• Flexor digitorum
– flex fingers
Extensor digitorum
– Extend fingers
• Extensor carpi
-extend wrist
-Insertion: metacarpals
Arm Muscles
• Supinator
– palms up
• Abductor pollicis longus
– move thumb
• Extensor and Flexor pollicis
– move thumb
Lower Limb Muscles
• Gluteal Muscles
– gluteus maximus
• hip extension
– gluteus medius
• walking
• hip abductor
– gluteus minimus
• walking
• hip abductor
• Iliopsoas
– hip flexion
– deep muscle
– keeps upper body erect
Lower Limb Muscles
• Adductors (3)
– adducts thigh
• Gracilis “groin”
– long thin medial thigh adducts
Quadriceps Group - injection sites
extend lower leg (quadriceps tendon)
A. rectus femoris
B. vastus medialis
vastus intermedius
D. vastus lateralis
C. *Sartorius
longest
cross legged
Hamstrings
All flex lower leg
biceps femoris
Semitendinosus
semimembranous
Lower Limb Muscles
• Tibialis Anterior
– dorsiflexion of foot
• Extensor & Flexor Digitorums
• Peroneus Group
– plantar flexion
Lower Limb Muscles
• Gastrocnemius
– plantar flexion
– Attched to achilles tendon
which attaches to calcaneus
• Soleus
– Attched to achilles tendon
which attaches to calcaneus
– plantar flexion
Developmental Aspects
• Congenital problems
– muscular dystrophy
– muscles ---> fat & connective tissues
• Muscular diseases
– trichnosis worms
– polio viral infection of nerves going into
muscles
– myasthenia gravis
• muscle weakness too little ACH
• Aging
– muscles ---> connective tissue
– atrophy