MUSCULAR SYSTEM

REVIEW OF MUSCLE TISSUE Muscle tissue contracts in response to stimulation 3 types of muscle tissue: -Skeletal -Cardiac -Smooth

REVIEW OF MUSCLE TISSUE continued Skeletal Muscle: Characteristics -Cylindrical cells -Striated -Multiple, peripheral nuclei -Voluntary -Attached to skeleton

Cardiac Muscle: Characteristics -Branching cells -Striated -One or two central nuclei -Involuntary -Heart REVIEW OF MUSCLE TISSUE continued

Smooth Muscle: Characteristics -Spindle-shaped cells -Non-striated -Single, central nucleus -Involuntary -Located in the walls of hollow organs REVIEW OF MUSCLE TISSUE continued

FUNCTIONS OF SKELETAL MUSCLE Produces voluntary movement -Locomotion -Manipulation -Assists in breathing, eating, speech, support of organs -With nervous system, generates reflexes -Provides facial expressions Stabilizes joints Maintains posture Produces body heat

Makes up “flesh” of body ( ~ 40% by weight) Most “meat” is skeletal muscle Muscles are organs -Fibers (muscle cells) -Motor neurons -Blood vessels -Connective tissue CHARACTERISTICS OF SKELETAL MUSCLE

Connective tissue coverings provide strength & support -Endomysium: Around each muscle fiber -Perimysium: Around fascicles (bundles of cells) -Epimysium: Around entire muscle (bundles of fascicles) -Fascia: loose connective tissue around muscle groups and between muscles & skin ARRANGEMENT OF SKELETAL MUSCLE

Connective tissue attachments attach muscles to bones (blend w/periosteum), cartilages, or to CT coverings of other muscles -Tendons - cordlike bundles of collagen fibers -Aponeuroses (sing. -sis) - sheetlike arrangements of collagen fibers ATTACHMENTS OF SKELETAL MUSCLE

Fibers (skeletal muscle cells): -Long, cylindrical, multinucleate -Arranged parallel to one another Sarcolemma: cell membrane Sarcoplasm: cytoplasm Numerous mitochondria Sarcoplasmic Reticulum (SR): Smooth E.R., stores Ca 2+ MICROSCOPIC ANATOMY OF A MUSCLE CELL

MICROSCOPIC ANATOMY OF A MUSCLE CELL continued Myofibrils -Contractile organelles -Lie parallel to one another -Run entire length of cell -Composed of Myofilaments (Protein) *Actin – Thin filament *Myosin – Thick filament

MICROSCOPIC ANATOMY: MYOFIBRILS Myofilaments composed of repeating subunits -Sarcomeres: *Contractile subunits *Source of fiber’s striations

A (Dark) bands: correspond to length of myosin filaments I (Light) bands: actin only Z line: anchor for actin; separates sarcomeres H zone: center of A band; no actin M line: Narrow region at center of H zone; anchor for myosin MICROSCOPIC ANATOMY: MYOFIBRILS

MICROSCOPIC ANATOMY: Neuromuscular Junction Neuromuscular Junction (NMJ) -Definition: Point of communication between a motor neuron and a fiber -Fibers contract only when stimulated -Synaptic Knob – terminal end of motor neuron -Synaptic Cleft (Gap) – space between synaptic knob & sarcolemma

MICROSCOPIC ANATOMY: Neuromuscular Junction -Motor End Plate: *Sarcolemma at NMJ *Invaginated *High SA *Ach Receptors

STEPS IN CONTRACTION Sliding Filament Theory Nerve Impulse arrives at synaptic knob Exocytosis of synaptic vesicles Neurotransmitter Acetylcholine (Ach) diffuses across cleft Ach binds to receptors on sarcolemma Prior to contraction, sarcolemma must be polarized (+ outside/- within) Sarcolemma now permeable to Na + and K + (depolarizes)

STEPS IN CONTRACTION Sliding Filament Theory Na + diffuses into fiber SR release Ca 2+ into sarcoplasm Ca 2+ binds to troponin on actin Tropomyosin on actin moves, exposing binding site ATP  ADP + E ; Myosin heads attach to actin, form cross-bridges Myosin heads swivel, release ADP

STEPS IN CONTRACTION Sliding Filament Theory Actin slides towards center of sarcomere ATP binds to Myosin heads; cross- bridges detach Relaxation occurs from: -Cholinesterase breaks down Ach at NMJ -Ca 2+ actively pumped back into SR

ACTIVITY OF SINGLE FIBERS “All-or-None” Law: At threshold, a fiber will contract to its maximum extent -No “partial” contractions -Increasing stimulus strength has no additional effect Single nerve impulse produces one contraction

ACTIVITY OF MOTOR UNITS A muscle is composed of motor units Motor Unit: a motor neuron + all the fibers it controls Number of fibers varies Each motor unit responds independently All muscle cells in a motor unit respond maximally, or they don’t respond at all

ACTIVITY OF MOTOR UNITS Strength of contraction is determined by number of motor units stimulated Recruitment: Process of increasing the number of motor units responding Strength increases as number of motor units increases

ACTIVITY OF WHOLE MUSCLES Skeletal muscles are capable of Graded Responses Different degrees of shortening occur by: -Changing frequency of stimulation -Changing the number of motor units activated

ACTIVITY OF WHOLE MUSCLES: EVENTS IN A TWITCH Threshold Stimulus: Strength of stimulus required to cause contraction Latent period: Delay between stimulus & contraction Twitch: Single, brief contraction following single threshold stimulus -Contraction -Relaxation – caused by transport of Ca 2+ back into SR

ACTIVITY OF WHOLE MUSCLES: FREQENCY OF STIMULATION Refractory Period: Time between initial and subsequent stimuli that is required for sarcolemma to repolarize Summation: Larger contractions with more frequent stimuli Tetanic contraction: Smooth, continuous contraction without relaxation between stimuli Fatigue: loss of response due to insufficient ATP

ACTIVITY OF WHOLE MUSCLES : TYPES OF CONTRACTION Tonus: Partial, sustained contraction Isometric: Contraction in which muscle contracts but stays the same length, but resistance is increased Isotonic: Contraction in which resistance stays the same, muscle contracts, fibers shorten, attachment sites move

EFFECTS OF EXERCISE Skeletal muscle cells do not undergo mitosis Exercise does not increase the number of skeletal muscle cells Hypertrophy: Enlargement of muscle cells due to exercise -The number of actin and myosin myofilaments increases -Mitochondria increase -Blood supply increases

EFFECTS OF LACK OF EXERCISE Atrophy: Decrease in the size of muscle cells due to lack of use -The number of actin and myosin myofilaments decreases -Mitochondria decrease -Blood supply decreases

BODY MOVEMENTS Produced by contraction of skeletal muscle Shortening of a skeletal muscle resulting in movement of attachments Movement depends on joint, attachments Skeletal muscles have at least two attachments -One attachment is relatively immobile -The other attachment is more mobile

BODY MOVEMENTS : MUSCLE ATTACHMENTS Origin: Less movable attachment Insertion: More movable attachment Action: What the muscle “does” -Moves insertion toward origin -The “movement” produced

Types of Ordinary Body Movements Slide 6.32 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Flexion – decreases angle between bones  Extension – increases angle between bones  Rotation – movement around an axis  Abduction – moves appendage away from midline  Circumduction – moves appendage in a circle around joint

Body Movements Slide 6.33 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 6.13

Special Movements Slide 6.34 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings  Dorsiflexion: toes point “up”  Plantar flexion: toes point “down”  Inversion: soles of feet “in”  Eversion: soles of feet “out”  Supination: face or palm “up”  Pronation: face or palm “down”

BODY MOVEMENTS: MUSCLE GROUPS Prime mover: Muscle primarily responsible for an action Synergist: Muscle(s) that assist(s) prime mover Antagonist: Muscle(s) that resist prime mover, or move opposite to it

NAMING SKELETAL MUSCLES: CRITERIA Muscle attachments: Origin and/or insertion Muscle action Direction of muscle fibers Location of muscle Size of muscle Number of origins (heads) Shape of muscle

NAMING SKELETAL MUSCLES: EXAMPLES Muscle attachments -Sternocleidomastoid Muscle action -Flexors and extensors *Flexor carpi radialis *Extensor carpi radialis -Abductors and adductors *Adductor longus *Adductor magnus

NAMING SKELETAL MUSCLES: EXAMPLES Direction of muscle fibers -Rectus abdominis -External oblique Location of muscle -Temporalis -Tibialis anterior

NAMING SKELETAL MUSCLES: EXAMPLES Size of muscle -Gluteus maximus -Teres major -Vastus lateralis Number of origins (heads) -Triceps brachii -Biceps femoris Shape of muscle -Trapezius -Deltoideus -Rhomboideus