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 jointsMaintains postureProduces body heat

Makes up “flesh” of body (~40% by weight)Most “meat” is skeletal muscleMuscles 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 membraneSarcoplasm: cytoplasmNumerous mitochondriaSarcoplasmic Reticulum (SR): Smooth

E.R., stores Ca2+

MICROSCOPIC ANATOMY OF A MUSCLE CELL

MICROSCOPIC ANATOMY OF A MUSCLE CELL continuedMyofibrils

- 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 onlyZ line: anchor for actin; separates

sarcomeresH 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 knobExocytosis of synaptic vesiclesNeurotransmitter Acetylcholine (Ach)

diffuses across cleftAch binds to receptors on sarcolemmaPrior 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 fiberSR release Ca2+ into sarcoplasmCa2+ binds to troponin on actinTropomyosin on actin moves, exposing

binding siteATP ADP + E ; Myosin heads attach to

actin, form cross-bridgesMyosin 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- Ca2+ 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 unitsMotor Unit: a motor neuron + all the

fibers it controlsNumber of fibers variesEach motor unit responds independentlyAll 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

Ca2+ 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 contractionIsometric: 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 EXERCISESkeletal muscle cells do not undergo

mitosisExercise does not increase the number of

skeletal muscle cellsHypertrophy: 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 muscleShortening of a skeletal muscle resulting in

movement of attachmentsMovement depends on joint, attachmentsSkeletal muscles have at least two

attachments- One attachment is relatively immobile- The other attachment is more mobile

BODY MOVEMENTS : MUSCLE ATTACHMENTS

Origin: Less movable attachmentInsertion: More movable attachmentAction: What the muscle “does”

- Moves insertion toward origin

- The “movement” produced

Types of Ordinary Body Types of Ordinary Body MovementsMovements

Slide 6.32Copyright © 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 MovementsBody Movements

Slide 6.33Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 6.13

Special MovementsSpecial Movements

Slide 6.34Copyright © 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 actionDirection of muscle fibersLocation of muscleSize of muscleNumber 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 obliqueLocation 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