View
339
Download
0
Category
Tags:
Preview:
Citation preview
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
Recommended