chapter 6 notes

Chapter 6: The Muscular System

1.     Overview/similarities of muscle tissue

a.    Muscles: Are responsible for all types of body movement.

b.    Muscle types (Table 6.1)

                                          i.    Skeletal

                                        ii.    Cardiac

                                       iii.    Smooth

c.    Characteristics

                                          i.    Muscle fiber = muscle cell- Are elongated.

                                        ii.    Contraction- Is due to the movement of microfibers.

                                       iii.    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 and 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.    Attachment- Are attached by tendons to bones.

                                        ii.    Cells- Multinucleate.

                                       iii.    Striations-Have visible banding.

                                       iv.    Control – Voluntary, subject to conscious control.

b.    Connective tissue wrappings: Cells are surrounded and bundled by connective tissue.

                                          i.    Endomysium – Encloses a single muscle fiber.

                                        ii.    Epimysium- Covers the entire skeletal muscle.

                                       iii.    Perimysium- Warps around a fascicle(bundle) of muscle fibers.

                                       iv.    Fascia – On the outside of the epimysium.

                                         v.    Tendon- Cord-like structures, mostly collagen fibers, often cross a joint due to toughness and small size.

                                       vi.    Aponeurosis-Sheet-like structure, attach muscles indirectly to bones, cartilages, or connective tissue.

c.    Where skeletal muscles attach- bones, cartilages, connective tissue coverings.

3.    Smooth muscles

a.    Characteristics

                                          i.    Striations- lacks.

                                        ii.    Shape-Spindle shaped cells.

                                       iii.    Nucleus -Single nucleus.

                                       iv.    Control –No conscious control.

                                         v.    Where- Found mainly in the walls of hollow organs.

4.    Cardiac muscles

a.    Characteristics

                                          i.    Striations

                                        ii.    Nucleus-Single.

                                       iii.    Cells- branching.

                                       iv.    Intercalated discs-Joined to another muscle cells at an intercalated disc.

                                         v.    Control-Involuntary.

                                       vi.    Where –Heart.

5.    Physiology of skeletal muscle

a.    Muscle functions

                                          i.    Motion of the organism

                                        ii.    Maintaining posture

                                       iii.    Stabilizing joints

                                       iv.    Generating heat

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- Contractile unit of muscle fiber.

1.     Myofilaments(protein)

a.    Myosin = thick filaments

b.    Actin = thin filaments

2.    Striations = patterns of cross stripes (Fig 6.3)

a.    A band=Dark band, contains the entire length of the thick filaments.

b.    I band= Light band, 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- Energy releasing enzymes.

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 –Electrical event, when stimulus causes sodium to flow, reversing polarity.

                                        ii.    Resting potential-At rest, there is a bare zone that lacks actin filaments called the H zone.

                                       iii.    Depolarization

                                       iv.    Repolarization

6.    Contraction of skeletal muscle fiber

a.    The neuromuscular junction (Fig. 6.5)

b.    The nerve stimulus and action potential-skeletal muscles must be stimulated by a motor neuron(nerve cell) to contract.

                                          i.    The motor unit (Fig. 6.4)- One motor neuron and all the skeletal muscle cells stimulated by that neuron.

c.    From nerve impulse to muscle contraction

                                          i.    Neurotransmitters – -Chemical released by nerve upon arrival of nerve impulse.

                                        ii.    Acetylcholine (Ach) – The neurotransmitter for skeletal muscles, attaches to receptors on the sarcolemma, sarcolemma becomes permeable to sodium.

d.    The Sliding Filament Theory of muscle contraction-Actibvation by nerve causes myosin heads(dross bridges) to attach to binding site on the thin filament. Myosin heads then bind to the next site of the thin filament and pull them toward the center of the sarcomere. This continued action causes a sliding of the myosin along the actin. Muscle contracts.

7.    Physiology of skeletal muscle contraction

a.    Characteristics

                                          i.    “All or none”

                                        ii.    Stimulated fibers-Not all fibers may be stimulated during the same interval.

                                       iii.    Combinations of fibers-Different combinations of muscle fiber contractions may give differing responses.

                                       iv.    Graded responses- Different degrees of skeletal muscle shortening. Can be produced by changing the frequency of muscle stimulation, the number of muscle cells being stimulated at one time.

b.    Types of graded responses

                                          i.    Twitch – Single, brief contraction, not a normal muscle function

1.     Latent period, contraction, relaxation.

2.    Incomplete and complete tetanus…Tetanus- summing of contraction, one contraction immediately followed by another, the muscle does not completely return to resting state, the effects are added.

                                        ii.    Summation –

1.     Incomplete (treppe)

2.    Fused

                                       iii.    Incomplete tetanus- Unfused,  some relaxation occurs between contractions, the results are summed.

                                       iv.    Fused (complete) tetanus- No evidence of relaxation before the following contractions, the result is sustained muscle contraction

                                         v.    Muscle response to strong stimuli- Muscle force depends upon the number of fibers stimulated, more fibers contracting results in greater muscle tension, muscles can continue to contract unless they run out of energy.

c.    Energy for muscle contraction

                                          i.    Initially-Muscles use stored ATP for energy, ATP bonds are broken to release energy, only 4-6 seconds worth of ATP is stored by muscles.

                                        ii.    After a while-After this initial time, other pathways must be utilized to produce ATP.

                                       iii.    Direct phosphorylation of ADP by creatine phosphate (CP)- Muscle cells store CP, CP is a high-energy molecule, after ATP is depleted, ADP is left, CP transfers energy to ADP, to regenerate ATP, CP supplies are exhausted in less than 15 seconds.

                                       iv.    Aerobic respiration-Sugar is broken down to carbon dioxide and water, releasing energy(ATP), this is a slower reaction that requires continuous oxygen, a series of metabolic pathways in the mitochondria.

                                         v.    Anaerobic respiration/lactic acid formation- Anaerobic glycolysis and lactic acid formation, reaction that breaks down glucose without oxygen, sugar is broken down to pyruvic acid to produce limited ATP. This reaction is not as efficient, but it fast.

                                       vi.    Muscle fatigue/oxygen debt-Lactic acid produces muscle fatigue. When a muscle is fatigued, it is unable to contract even with a stimulus. Common cause for muscle fatigue is oxygen debt. Oxygen must be “repaid” to tissue to remove oxygen deficit(heavy breathing). Oxygen is required to get rid of accumulated lactic acid, increasing acidity(from lactic acid) and lack of ATP causes the muscle to contract less.

                                      vii.    Isotonic contractions- Myofilaments are able to slide past each other during contractions, the muscle shortens and movement occurs.

                                     viii.    Isometric contractions- Tension in the muscles increases, the muscle in unable to shorten or produce movement.

                                       ix.    Muscle tone- Some fibers are contracted even in a relaxed muscle, different fibers contract at different times to provide muscle tone.

                                        x.    Effect of exercise on muscles- Exercise increases muscle size, strength, and endurance.

1.     Low resistance (aerobic)(Endurance, biking, jogging): Stronger, more flexible muscles, greater resistance to fatigue, makes body metabolism more efficient, improves digestion, coordination.

2.    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 – Movement is attained due to a muscle moving an attached bone, muscle are attached to at least two points.

a.    Five golden rules of skeletal muscle activity – Table 6.2

b.    Muscle attachments

                                          i.    Origin – anchored end of muscle, doesn’t move, attachment to an immovable bone.

                                        ii.    Insertion – anchored end of muscle that does move-Attachment to a moveable bone.

                                       iii.    Action – describes the movement of the muscle (ie. Extensor)

c.    Types of body movement

                                          i.    Flexion & extension

1.     Flexion- Decreases the angle of the joint, brings two bones closer together, typical of hinge joints like knee and elbow.

2.    Extension-Increases angel between two bones.

3.    Hyperextension- Increasing angel beyond 180 degrees.

                                        ii.    Rotation-Movement of a bone around its longitudinal axis, common in ball-and-socket joints(ex: when you move atlas around the dens of axis…saying “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 flexsion, extension, abduction, and adduction: swing with one end free and one end stable. Common in 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(inward).

2.    Eversion – Turn sole of foot laterally(outward).

                                      vii.    Supination & pronation

1.     Supination- Forearm rotates laterally so palm faces anteriorly(up)….Face up.

2.    Pronation –Forearm rotates medially so palm faces posteriorly(down)….Face down.

                                     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 or parts of face.

d.    Types of muscle movement

1.     Prime mover = agonists- 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.

e.    Naming skeletal muscles

                                          i.    Direction of muscle fibers

1.     Rectus-Straight…crunches.

2.    Transverses

3.    Oblique

                                        ii.    Relative size

1.     Maximus-Largest…butt

2.    Minimus

3.    Longus

4.    Brevis

                                       iii.    Location

                                       iv.    Shape

1.     Deltoid-Triangular.

2.    Trapezius

3.    Serratus

4.    Rhomboid

Number of origins

                                         v.    Bi -2

                                       vi.    Tri-3

                                      vii.    Quad-4

f.    Location of attachments

                                          i.    Origin – anchored end of muscle, doesn’t move

                                        ii.    Insertion – anchored end of muscle that does move

g.    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-Temporal bone

c.    Muscles of the neck

                                          i.    Sternocleidomastoid-Sternum

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