Chapter 6 Outline

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 – found only in heart
iii. Smooth – internal systems like tube shaped organs, also hairs
c. Characteristics
i. Muscle cells are elongated (Muscle fiber = muscle cell)
ii. Contraction of muscles is due to the movement of microfilaments
iii. Prefixes
1. Sarcolemma
2. Sarcoplasm
3. Prefixes:
a. Myo and Mys = muscle
b. Sarco = flesh
d. Functional characteristics of muscle tissue
i. Excitability (also called responsiveness or irritability)—ability to receive and respond to a stimulus
ii. Contractility—ability to shorten when an adequate stimulus is recieved
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. Striations—have visible banding (straight lines)
iv. Control—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. When epimysium blends into a connective tissue attachment.
2. Epimysium is a wrapping that extends into a tendon
3. Mostly collagen fibers
4. 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:
i. Bones
ii. Cartilages
iii. Connective Tissue coverings
3. Smooth muscles
a. Characteristics
i. Lacks striations
ii. Spindle-shaped cells
iii. Single Nucleus
iv. Control: involuntary—no conscious control
v. Where: found mainly in the walls of hollow organs
4. Cardiac muscles
a. Characteristics
i. Striations
ii. Usually single Nucleus
iii. Branching Cells
iv. Joined to another muscle cell at an intercalated disc
v. Control: involuntary
vi. Where: only in the heart
5. Physiology of skeletal muscle
a. Muscle functions
i. Produce movement
ii. Maintain posture
iii. Stabilize joints
iv. Generate heat (movement)
b. Microscopic anatomy of skeletal muscle
i. Sarcolemma—specialized plasma membrane
ii. Myofibrils—long organelles inside muscle cell
iii. Sarcoplasmic reticulum—specialized smooth endoplasmic reticulum
c. Myofibrils are aligned to give distinct bands
i. Sarcomere – functional unit of classification
1. Myofilaments
a. Myosin = thick filaments
b. Actin = 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
ii. Ultrastructure and chemical composition of myofilaments (Fig. 6.7)
1. Myosin
a. Two heads
i. Actin binding site
ii. ATP binding site and ATPase
b. One tail
2. Thin filaments = actin + tropomyosin + troponin
a. Two strands of G-actin twisted
b. Two strands of tropomyosin
c. Troponin covers binding sites
iii. Sarcoplasmic reticulum – transmits calcium to myoplasm when stimulated
d. Generation of action potential across sarcolemma
i. Action potential defined -
ii. Resting potential
iii. Depolarization
iv. Repolarization
6. Contraction of skeletal muscle fiber
a. Muscle fiber contraction is “all or none”
b. Within a skeletal muscle, not all fibers may be stimulated during the same interval
c. Different combinations of muscle fiber contractions may give differing responses
d. The neuromuscular junction (Fig. 6.5)
e. The nerve stimulus and action potential
i. The motor unit (Fig. 6.4)
f. From nerve impulse to muscle contraction
i. Neurotransmitters –
ii. Acetylcholine (Ach) -
g. The Sliding Filament Theory of muscle contraction
7. Physiology of skeletal muscle contraction
a. Characteristics
i. “All or none”
ii. Stimulated fibers
iii. Combinations of fibers
iv. Graded responses—different degrees of skeletal muscle shortening
1. Can be produced by changing:
2. The frequency of muscle stimulation
3. The number of muscle cells being stimulated at one time
b. Types of graded responses
i. Twitch – a single, brief contraction
1. Not a normal muscle function
2. Stimulus, latent period, contraction, relaxation
3. 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
iv. Unfused (Incomplete) tetanus
1. Some relaxation occurs between contractions
2. The results are summed
v. Fused (complete) tetanus
1. No evidence of relaxation before the following contractions
2. The result is a sustained muscle contraction
vi. Muscle response to strong stimuli
1. Muscle force depends upon the number of fibers stimulated
2. More fibers contracting results inu greater muscle tension
3. Muscles can continue to contract unless they run out of energy
c. Energy for muscle contraction
i. Initially muscles used stored ATP for energy:
1. ATP bonds are broken to release energy
2. Only 4-6 seconds worth of ATP is stored by muscles
ii. After initial time, other pathways must be utilized to produced ATP
iii. Direct phosphorylation of ADP by creatine phosphate (CP):
1. Muscle cells stored CP
a. CP is a high-energy molecule
2. After ATP (high energy) is depleted, ADP (low energy) is left
3. CP Transfers energy to ADP, to regenerate ATP
4. CP supplies are exhausted in less than 15 seconds
iv. 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
v. Anaerobic respiration/lactic acid formation
1. Reaction that breaks down glucose without oxygen
2. When glucose is broken down only limited ATP is produced
3. This reaction is not as efficient, but is fast
4. Lactic acid produces muscle fatigue
vi. Muscle fatigue/oxygen debt
1. When a muscle is fatigued, it is unable to contract even with a stimulus
2. Common cause for muscle fatigue is oxygen debt:
3. Oxygen must be “repaid” to tissue to remove oxygen deficit (heavy breathing)
4. Oxygen is required to get rid of accumulated lactic acid
5. Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less
vii. Isotonic contractions:
1. Myofilaments are able to slide past each other during contractions
2. The muscle shortens and movement occurs
viii. Isometric contractions:
1. Tension in the muscles increases
2. The muscle is unable to shorten or produce movement
ix. Muscle tone
1. Some fibers are contracted even in a relaxed muscle
2. Different fibers contract at different times to provide muscle tone
3. What is rigor mortis?
a. Muscles 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
x. Effect of exercise on muscles
1. Exercise increases muscle size, strength, and endurance:
2. Low resistance (aerobic)
a. Aerobic (endurance) exercise (biking, jogging):
i. Stronger, more flexible muscles, greater resistance to fatigue:
b. Makes body metabolism more efficent
3. Resistance (isometric) exercise (weight lifting) increases muscle size and strength
4. High resistance (anaerobic)
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 attachments
Muscles are attached to atleast two points:
i. Origin – anchored end of muscle, doesn’t move
1. Attachment to an immovable bone
ii. Insertion – anchored end of muscle that does move
1. Attachment to a movable bone
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
a. Increasing angle beyond 180 degrees
ii. Rotation
1. Movement of a bone around its longitudinal axis
2. Common in ball-and-socket joints
3. Example is when you move atlas around the dens of axis (shake your head ”no”)
iii. Abduction & adduction
1. Abduction
a. Movement of a limb away from the midline
2. Adduction
a. Opposite of abduction
b. Movement of a limb toward the midline
iv. Circumduction
1. Combination of flexion, extension, abduction, and adduction: swing with one end free and one end stable
2. Common in ball-and-socket joints
v. Dorsiflexion & plantar flexion
1. Dorsiflexion
a. Lifting the foot so that the superior surface approaches the shin
2. Plantar flexion
a. Depressing the foot (pointing the toes)
vi. Inversion & eversion
1. Inversion
a. Turn sole of foot medially
2. Eversion
a. Turn sole of foot laterally
vii. Supination & pronation
1. Supination
a. Forearm rotates laterally so palm faces anteriorly
2. Pronation
a. Forearm rotates medially so palm faces posteriorly
viii. Special Movements
1. Opposition
a. Move thumb to touch the tips of other fingers on the same hand
2. Protraction
a. Sticking out head or parts of face
3. Retraction
a. Pulling in head or parts of face
e. Types of muscle movement
1. Prime mover = agonists
a. Muscle with the major responsibility for a certain movement
2. Antagonist
a. Muscle that opposes or reverses a prime mover
3. Synergist
a. Muscle that aids a prime mover in a movement and helps prevent rotation
4. Fixator
a. Stabilizes the origin of a prime mover (hold a bone still), back muscles for posture
f. Naming skeletal muscles
i. Location
1. Example
a. Temporalis (temporal bone)
ii. By number of origins
1. Examples
a. Triceps (three heads)
iii. By location of the muscle’s origin and insertion
1. Example
a. Sterno (on the sternum)
iv. Shape of muscle
1. Deltoid (triangular)
2. Trapezius
3. Serratus
4. Rhomboid
v. Relative size
1. Maximus
2. Minimus
3. Longus
4. Brevis
vi. By action of the muscle
1. Example
a. Flexor and extensor (flexes or extends a bone)
vii. Direction of muscle fibers
1. Rectus
2. Transverses
3. Oblique
g. Number of origins
i. Bi
ii. Tri
iii. Quad
h. Location of attachments
i. Origin – anchored end of muscle, doesn’t move
ii. Insertion – anchored end of muscle that does move
i. 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