Chapter 6 – Muscular SystemAnatomy and Physiology

Mrs. Harborth

Muscle Types

ALL muscle cells are elongated – Muscle fibers

Contractility depends on myofilaments

“myo” – muscle; “sarco” – flesh

Three types: Skeletal: striated, voluntary.

Endoysium, perimysium, epimysium, tendons, aponeuroses.

Smooth: no striations, involuntary. Found in hollow visceral organs. Usually two layers.

Cardiac: striated, involuntary. Found in heart. Spiral or figure 8 bundles. Intercalated discs.

Muscle Functions

Movement – skeletal muscle (s.m.) contractions move the body in whole or in part.

Posture – continued partial contraction of s.m. makes it possible to sit, stand, and maintain a stable position while walking, running, etc.

Stabilizing joints – muscle tendons reinforce and stabilize joints that have poorly fitting articulating surfaces.

Heat Production – muscle cells produce heat via catabolism; S.M. contractions are one of the most important parts of maintaining temperature homeostasis

Microscopic Anatomy of Skeletal Muscle

Multinucleate

Sarcolemma – plasma membrane

Myofibrils – long ribbonlike organelles. Push nuclei to the side.

Light (I) and Dark (A) bands – alternate along the myofibrils, giving striped appearance. I band has Z disc (darker), A band has H zone (lighter).

Sarcomere – contractile units lined up end-to-end along myofibrils. Made up of myofilaments.

Myofilaments – thick and thin filaments

Sarcoplasmic reticulum – specialized smooth ER. Stores calcium and releases it on demand for contractions.

Myofilaments

Myosin filaments: “thick filaments”, made of myosin protein and ATPase. Extend entire length of dark A band. Midparts are smooth, but ends are studded with myosin “heads” or cross bridges.

Actin filaments: “thin filaments”, made of actin protein and regulatory proteins that allow/prevent myosin head binding to actin. Anchored to the Z disc. Do not extend to middle of relaxed sarcomere, forms H zone (bare zone).

Neuromuscular Junction

Irritability: the ability to receive and respond to a stimulus

Contractility: ability to shorten when an adequate stimulus is received

Motor unit: one neuron and all the s.m. cells it stimulates

Neuromuscular junctions: axon reaches muscle and branches into axonal terminals, which form junctions with sarcolemma of different muscle cell.

Synaptic cleft: gap between neurons and muscle cells (they never touch). Filled with interstitial fluid.

Neuromuscular junctions

Nerve Stimulus and Action Potential Acetylcholine (ACh) – neurotransmitter that stimulates s.m.

Diffuses across synaptic cleft and attaches to receptors on sarcolemma.

If enough Ach is released, sarcolemma becomes temporarily permeable to sodium ions.

Na+ rushes into muscle cell, making cell positive, upsets electrical conditions, thus setting up an action potential.

Action potential is unstoppable, travels entire surface of sarcolemma, conducting electrical impulse from one end of cell to other, making a contraction.

Sliding Filament Theory

Animations

Action Potential

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html

Myofilament Contraction

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__myofilament_contraction.html

Sarcomere Contraction http://highered.mcgraw-hill.com/sites/0072495855/student

_view0/chapter10/animation__sarcomere_contraction.html

Graded Response

A muscle CELL is “all or nothing”, but whole muscles have graded response.

Graded response can be produced by 1) changing frequency of stimulation or 2) changing # of cells stimulated

1) Increased stimulation Muscles are stimulated back to back, so can’t relax between

stimuations. Contractions get stronger and smoother (complete or fused tetanus)

2) Increased # of cells stimulated Few or hundreds of cells stimulated. Changes strength of contraction

(soothing hand –vs- slap)

Energy for Contractions

Muscles only have 4-6 seconds worth of ATP stored

Three ways to get more Direct phosphorylation of ADP by creatine

phosphate (CP gives phosphate to ADP, making ATP). Only about 20 seconds worth of CP in cells

Aerobic respiration (95% of ATP used comes from this. Glucose is broken down in mitochondria to make 36 ATP. Slow reaction and requires oxygen)

Anaerobic respiration (glycolysis occurs in cytoplasm, glucose broken down into pyruvic acid and 2 ATPs. Pyruvic acid can continue into Aerobic respiration if O2 is present, but if intense muscle work then it’s made into lactic acid. 2.5x as fast as Aerobic but few ATPs. About 30-60 sec of strenuous muscle activity)

Fatigue and Oxygen Debt

Muscle fatigue – when muscles are stimulated but cannot contract anymore. Caused by oxygen debt.

Oxygen debt – when low amounts of O2 are present, lactic acid builds up and ATP levels run low. Oxygen debt is “paid back” after workout (breathing hard) so muscles can get rid of accumulated lactic acid and make more ATP

Types of Muscle Contractions

Isotonic – Myofilaments are successful in sliding movements, the muscle shortens, and movement occurs. Ex: bending knee, rotating arm, smiling

Isometric – myosin myofilaments are “skidding their wheels” and tension keeps increasing. They’re trying to slide, but trying to move an object that is immovable.

Muscle Tone and Exercise

Even when you’re relaxed some of your muscle fibers are stimulated, keeping muscles firm and healthy. This is muscle tone.

Aerobic (endurance) exercise

Resistance (isometric) exercise

Types of Body Movements S.M.’s are all attached at an origin (immovable or less movable bone)

and an insertion (movable bone)

Flexion – brings 2 bones closer together

Extension – increases angle between two bones

Rotation – movement of bone around its longitudinal axis

Abduction – moving a limb away from midline

Adduction – moving a limb toward the midline

Circumduction – in leg or arm; distal end rotates, proximal end stationary (cone)

Dorsiflexion and plantar flexion – standing on heels; pointing toes

Inversion and eversion – turn sole medially; turn sole laterally

Supination and pronation – palm facing anteriorly (radius and ulna parallel); palm faces posteriorly (bones form x)

Opposition – touch thumb to tip of each finger on same hand

Origin –vs- Insertion

Types of Muscles

Prime mover – muscle with major responsibility for movement

Antagonists – muscles that oppose or reverse movements

Synergists – help prime movers by producing same movement or reducing undesirable movements (ex: making fist without moving wrist)

Fixators – specialized synergists. Hold bone still or stabilize origin

Naming Skeletal Muscles

Direction of muscle fibers – rectus (straight), oblique (slanted)

Relative size of muscle – maximus (largest), minimus (smallest), longus (long)

Location of the muscle – name of bone on which muscle is associated

Number of origins – biceps (2), triceps (3), quadriceps (4)

Location of the muscle’s origin and insertion – named for attachment sites

Shape of the muscle – ex: deltoid “triangular”

Action of the muscle – flexor, extensor, adductor

Head and Neck Muscles

Facial Frontalis

Orbicularis Oculi

Zygomaticus

Orbicularis Oris

Buccinator

Chewing Masseter

Temporalis

Neck Platysma

Sternocleidomastoid

Trunk Muscles

Pectoralis major

Intercostal muscles

Abdominal muscles Rectus abdominis

External oblique

Internal oblique

Transverse abdominis

Posterior muscles Trapezius

Latissimus dorsi

Erector spinae

Deltoid

Muscles of Arm/Leg

Upper Limb:

Biceps brachii

Brachialis

Brachioradialis

Triceps Brachii

Lower Limb:

Gluteus maximus

Gluteus medius

Iliopsoas

Adductor muscles

Hamstring group (biceps femoris, semimembranosus, semitendinosus)

Sartorius

Quadriceps group (rectus femoris and 3 vastus muscles)

Leg Continued

Tibialis anterior

Extensor digitorum longus

Fibularis muscles

Gastrocnemius

Soleus