Chapter 6 Muscles

Chapter 6: The Muscular System
1. Overview/similarities of muscle tissue
a. Muscles: responsible for all types of body movement
b. Muscle types (Table 6.1)
i. Skeletal
ii. Cardiac
iii. Smooth
c. Characteristics
i. Muscle cells are elongated
ii. Muscle fiber = muscle cell
iii. Contraction of muscles is due to the movement of micrfilaments
iv. All muscles share some terminology
v. Prefixes
1. Sarcolemma
2. Sarcoplasm
3. Prefixes: myo, mys = muscle sarco = flesh
d. Functional characteristics of muscle tissue
i. Excitability (also called responsiveness or irritability)- ability to receive or respond to a stimulus
ii. Contractility- ability to shorten when an adequate stimulus is received
iii. Extensibility- ability of muscle cells to be stretched
iv. Elasticity- ability to recoil and resume resting length after stretching
2. Skeletal muscle
a. Characteristics
i. Most are attached by tendons to bones
ii. Cells are multinucleate
iii. Striated- have visible banding
iv. Voluntary- subject to conscious control
b. Connective tissue wrappings:
i. Endomysium- encloses a single muscle fiber
ii. Epimysium- covers the entire skeletal muscle
iii. Perimysium- wraps around a fascicle (bundle) of muscle fibers
iv. Fascia- on the outside of the epimysium
v. Tendon- cord like structures
1. mostly collagen fibers
2. often cross a joint due to toughness and small size
vi. Aponeurosis- sheet-like structures
1. attach muscles indirectly to bones, cartilages, or connective tissue coverings
c. Where skeletal muscles attach- bones, cartilages, and connective tissue coverings
3. Smooth muscles
a. Characteristics
i. Lacks striations
ii. Shape- spindle-shaped cells
iii. Single nucleus
iv. Involuntary- no conscious control
v. Found mainly in the walls of hollow organs
4. Cardiac muscles
a. Characteristics
i. Striations
ii. Single nucleus
iii. Branching cells
iv. Joined to another muscle cell at an intercalated discs
v. Involuntary
vi. Only in the heart
5. Physiology of skeletal muscle
a. Muscle functions
i. Motion of the organism (produce movement)
ii. Maintaining posture
iii. Stabilizing joints
iv. Generating heat
b. Microscopic anatomy of skeletal muscle
i. Sarcolemma- specialized plasma membrane
ii. Myofibrils- long organelles insude muscle cell
iii. Sarcoplasmic reticulum- specialized smooth endoplasmic reticulum
c. Myofibrils- aligned to give destinct bands
i. Sarcomere – contractile unit of a muscle fiber
ii. Organization of sarcomere:
1. Myofilaments (protein)
a. Myosin filaments = thick filaments
b. Actin filaments = thin filaments
2. Striations = patterns of cross stripes (Fig 6.3)
a. A band = dark band
i. Contains the entire length of the thick filaments
b. I band = light band
i. Contains only thin filaments
c. Z line
d. H zone
e. M line
f. (thin means actin) (thick means myosin)
iii. Ultrastructure and chemical composition of myofilaments (Fig. 6.7)
1. Myosin (thick filaments)
a. Composed of the protein myosin
b. Has ATPase (energy releasing) enzymes
c. Myosin filaments have heads (extensions, or cross bridges)
d. Myosin and actin overlap somewhat
e. Two heads
i. Actin binding site
ii. ATP binding site and ATPase
f. One tail
2. Thin filaments = actin + tropomyosin + troponin
a. Composed of the protein actin
b. Anchored to the Z disc
c. Two strands of G-actin twisted
d. Two strands of tropomyosin
e. Troponin covers binding sites
iv. At rest theres is a bare zone that lacks actin filaments called the H zone
v. Sarcoplasmic reticulum – transmits calcium to myoplasm when stimulated
1. stores and releases calcium
d. Generation of action potential across sarcolemma
i. Action potential- electrical event, when stimulus causes sodium to flow in, reversing polarity
ii. Resting potential
iii. Synaptic cleft:
1. gap between nerve and muscle
2. nerve and muscle do not make contact
3. area between nerve and muscle is filled with interstitial fluid
4. motor unit: one motor neuron and all of its ___
iv. Depolarization
v. Repolarization
6. Contraction of skeletal muscle fiber
a. The neuromuscular junction (Fig. 6.5)
i. Must be stimulated by a motor neuron (nerve cell) to contract
ii. Motor unit- one motor neuron and all the skeletal muscle cells stimulated by that neuron
b. The nerve stimulus and action potential
i. The motor unit (Fig. 6.4)
c. From nerve impulse to muscle contraction
i. Neurotransmitters – for skeletal muscke is acetylocholine
ii. Acetylcholine (Ach) – attaches to receptors on the sarcolemma
iii. Sarcolemma becomes permeable ¬¬¬____
iv. Sodium rushes into the cell generating an action potential
v. Once started, muscle contraction cannot be stopped
d. The Sliding Filament Theory of muscle contraction
i. Activation by never cause myosin heads (cross bridges) to attach to binding on the thin filament
ii. Myosin heads then bing to the next site of the thin filament and pull them toward the center of the sarcomere
iii. This continued action causes a sliding of the myosin along the actin
iv. The result it that the muscle is shortened (contracted)
7. Physiology of skeletal muscle contraction
a. Characteristics
i. “All or none”
ii. Within a skeletal muscle, not all fibers may be stimulated during the same interval
iii. Different combinations of muscle fiber contractions may give differing responses
iv. Graded responses—different degrees of skeletal muscle shortening
v. Graded responses can be produced by changing:
vi. The frequency of muscle stimulation
vii. The number of muscle cells being stimulated at one time
b. Types of graded responses
i. Twitch -
1. Single brief contraction
2. Not a normal muscle function
3. Stimulus, latent period, contraction, relaxation
4. Latent period, contraction, relaxation
5. Incomplete and complete tetanus
ii. Summation –
1. Incomplete (treppe)
2. Fused
iii. Tetanus
1. One contraction immediately followed by another
2. The muscle does not completely
return to resting state
3. The effects are added
4. Incomplete tetanus
a. Some relaxation occurs between contractions
b. The results are summed
5. Fused (complete) tetanus
a. No evidence of relaxation before the following contractions
b. The result is a sustained muscle contraction
iv. Muscle response to strong stimuli
1. Muscle force depends upon the number of fibers stimulated
2. More fibers contracting results in greater muscle tension
3. Muscles can continue to contract unless they run out of energy
c. Energy for muscle contraction
i. Initially, muscles use stored ATP for energy:
ii. ATP bonds are broken to release energy
iii. Only 4–6 seconds worth of ATP is stored by muscles
iv. After this initial time, other pathways must be utilized to produce ATP
v. Direct phosphorylation of ADP by creatine phosphate (CP):
vi. Muscle cells store CP
vii. CP is a high-energy molecule
viii. After ATP is depleted, ADP is left
ix. CP transfers energy to ADP, to regenerate ATP
x. CP supplies are exhausted in less than 15 seconds
xi. Aerobic respiration
1. Glucose is broken down to carbon dioxide and water, releasing energy (ATP)
2. This is a slower reaction that requires continuous oxygen
3. A series of metabolic pathways in the mitochondria
xii. Anaerobic glycolysis and lactic acid formation
xiii. Reaction that breaks down glucose without oxygen
xiv. Glucose is broken down to pyruvic acid to produce limited ATP
xv. Pyruvic acid is converted to lactic acid
xvi. This reaction is not as efficient, but is fast
xvii. Lactic acid produces muscle fatigue
xviii. Muscle fatigue/oxygen debt
xix. When a muscle is fatigued, it is unable to contract even with a stimulus
xx. Common cause for muscle fatigue is oxygen debt:
xxi. Oxygen must be “repaid” to tissue to remove oxygen deficit (heavy breathing)
xxii. Oxygen is required to get rid of accumulated lactic acid
xxiii. Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less
xxiv. Isotonic contractions-
1. Myofilaments are able to slide past each other during contractions
2. The muscle shortens and movement occurs
3. Isometric contractions:
4. Tension in the muscles increases
5. The muscle is unable to shorten or produce movement
xxv. Isometric contractions-
1. Tension in the muscles increases
2. The muscle is unable to shorten or produce movement
xxvi. Muscle tone-
1. Some fibers are contracted even in a relaxed muscle
2. Different fibers contract at different times to provide muscle tone
3. Rigor mortis
a. muscle stiffen 3-4 hours after death, dissipates in 48-72 hours as muscle fibers begin to decompose
b. Due to cross bridge formation but no ATP synthesis to release the bridges
xxvii. Effect of exercise on muscles
1. Increases muscle size, strength, and endurance
2. Low resistance (aerobic)- (biking jogging) stronger, more flexible muscles, greater resistance to fatigue, makes body metabolism more efficient, improves digestion, coordination
3. High resistance (anaerobic)- (weight lifting) increases muscle size and strength
d. Velocity and duration of contraction
i. Muscle fiber type
1. Slow oxidative fibers – dark meat
2. Fast oxidative fibers – white meat
8. Muscles and body movement
a. Movement is attained due to a muscle moving an attached bone
b. Five golden rules of skeletal muscle activity – Table 6.2
c. Muscle attached to at least two points
i. Origin – anchored end of muscle, doesn’t move
ii. Insertion – anchored end of muscle that does move
iii. Action – describes the movement of the muscle (ie. Extensor)
d. Types of body movement
i. Flexion & extension
1. Flexion
a. Decreases the angle of the joint
b. Brings two bones closer together
c. Typical of hinge joints like knee and elbow
2. Extension
a. Increases angle between two bones
3. Hyperextension
ii. Rotation
1. Movement of a bone around its longitudinal axis
2. Common in ball and socket joints
3. Ex: is when you move atlas around the dens of axis (shake your head “no”)
iii. Abduction & adduction
1. Abduction- movement of a limb away from the midline
2. Adduction- opposite of abduction, movement of a limb toward the midline
iv. Circumduction- combination of flexion, extension, abduction, and adduction: swing with one end free and one end stable
1. Common in the ball and socket joints
v. Dorsiflexion & plantar flexion
1. Dorsiflexion- lifting the foot so that the superior surface approaches the shin
2. Plantar flexion- depressing the foot (pointing the toes)
vi. Inversion & eversion
1. Inversion- turn sole of foot medially
2. Eversion- turn sole of foot laterally
vii. Supination & pronation
1. Supination- forearm rotates laterally so palm faces anteriorly
2. Pronation- forearm rotates medially so palms faces posteriorly
viii. Opposition- move thumb to touch the tips of other fingers on the same hand
ix. Protraction- sticking out head or parts of face
x. Retraction- pulling in head of parts of face
e. Types of muscle movement
1. Prime mover- muscle with the major responsibility for a certain movement
2. Antagonist- muscle that opposes or reverses a prime mover
3. Synergist- muscle that aids a prime mover in a movement and helps prevent rotation
4. Fixator- stabilizes the origin of a prime mover (hold a bone still): back muscles for posture
f. Naming skeletal muscles
i. Direction of muscle fibers
1. Rectus (straight)
2. Transverses
3. Oblique
ii. Relative size
1. Maximus (largest)
2. Minimus
3. Longus
4. Brevis
iii. Location
1. Temporalis (temporal bone)
iv. Muscles origin and insertion
1. Sterno (on the sternum)
v. Action
1. Flexor or extensor (flexes or extends a bone)
vi. Shape
1. Deltoid (triangular)
2. Trapezius
3. Serratus
4. Rhomboid
g. Direction of muscle fibers
i. Rectus
ii. Transverses
iii. Oblique
h. Number of origins
i. Bi- two
ii. Tri- three heads (triceps)
iii. Quad- four
i. Location of attachments
i. Origin – anchored end of muscle, doesn’t move
ii. Insertion – anchored end of muscle that does move
j. Action – describes the movement of the muscle (ie. Extensor)
9. Major skeletal muscles of the body & prime action
a. Muscles of the head
i. Muscles of the scalp
1. Frontalis
2. Occipitalis
ii. Muscles of the face
1. Orbicularis oculi
2. Zygomaticus major
3. Levator labii superioris
4. Orbicularis oris
b. Muscles of mastication (chewing)
i. Masseter
ii. Temporalis
c. Muscles of the neck
i. Sternocleidomastoid
d. Muscles of the thorax/breathing
i. External intercostals
ii. Internal intercostals
iii. Diaphragm
e. Muscles of the abdominal wall
i. Rectus abdominis
ii. Transverse abdominis
iii. External oblique
iv. Internal oblique
f. Muscles of anterior thorax/ moving scapulae
i. Serratus anterior
g. Muscles of posterior thorax
i. Trapezius
ii. Levator scapulae
iii. Rhomboid major and minor
h. Muscles crossing the shoulder (arm movement)
i. Pectoralis major
ii. Latissimus dorsi
iii. Deltoid
iv. Rotator cuff = supraspinatus, infraspinatus, teres minor, subscapularis
i. Muscles crossing the elbow (flexion & extension of forearm)
i. Triceps brachii
ii. Biceps brachii
iii. Brachioradialis
j. Muscles moving wrist and hand
i. Flexor carpi radialis
ii. Flexor carpi ulnaris
iii. Extensor carpi radialis longus and brevis
k. Muscles crossing hip & knee joint (movement of thigh & leg)
i. Sartorius
ii. Gracilis
iii. Quadriceps femoris
1. Rectus femoris
2. Vastus medialis
3. Vastus intermedius
4. Vastus lateralis
iv. Gluteus maximus
v. Hamstrings (posterior thigh muscles)
1. Biceps femoris
2. Semimembranosus
3. Semitendinosus
l. Muscles of the leg
i. Tibialis anterior
ii. Gastrocnemius
iii. Soleus