Download The Muscular System

By:
Kendra Iverson
& Sarah Bender
• Muscle- fibrous tissue with the ability to
contract, producing movement in or maintaining
the position of an animal body
• System- organized arrangement; network
….
• Set of connected fibrous tissue that work
together to produce movement
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Provide muscle tone
Propel body fluids and food
Generate the heartbeat
Distribute heat throughout the body
• Skeletal muscle
• Moves majority of the body
• Smooth muscle
• Helps most with digestive system
• Cardiac muscle
•Controls the heartbeat
• Location: all skeletal muscles- attach to bones
• Function: movement of bones at joints and
maintaining posture
• Voluntary
• Contracts and relaxes quickly
• Transverse tubule system is well-developed
• Composed of:
• skeletal muscle tissue
• nervous tissue
• blood
• connective tissue
• Fascia- layers of fibrous connective tissue
• covers and separates each muscle surface
• Epimysium- lies beneath the fascia
• Perimysium- surrounds individual bundles
of fibers (fascicles)
• Endomysium- connective tissue layer that
separates individual muscle fibers
• Cells that contract in response to stimulation and
then relax after the stimulation ends
• Thin and elongated cylinders with rounded ends
• Can extend full length of a muscle
• Sarcolemma- muscle fiber membrane
↓
• Sarcoplasm- cytoplasm
↓
• Myofibrils- protein filaments which lie parallel and
play great role in contraction
• Types:
Myosin- thicker, called A bands (dark)
Actin- thinner, called I bands (light)
↓
• Sarcomere- space from center of one I band to the
next I band
• Sarcoplasmic Reticulum- network of
membranous channels that surround each
myofibril and run parellel
• Transverse Tubules (T tubules)- network of
membranous channels between sarcoplasm that
open outside
• Both- activate muscle contraction mechanism
when the fiber is stimulated
• Site where the motor neuron and muscle fiber
meet
• Muscle fiber is specialized to form a motor end
plate
• End branches, has many mitochondria and
contains synaptic vesicles that store chemicals
• Neurotransmitter stimulates muscle fibers to
release acetylcholine
• Travels down a motor neuron axon and
stimulates muscle fiber contraction
• Includes one motor neuron and several
muscle fibers
• The motor neuron transmits an impulse, which
allows all the linked muscle fibers to contract
at the same time
• Sarcomeres shorten and the muscle is pulled against its
attachments
• Sliding Filament Model
• Myosin cross-bridge attaches to the binding site on the actin
filament and bends, causing a pull on the actin filament
• Myosin releases and attaches to the next binding site on the
actin, causing a pull
• ATP converts to ADP
• Repeats this cycle as long as the energy source ATP is
available and the muscle fiber is stimulated to contract
• Stimulated by acetylcholine (neurotransmitter)
• Motor neuron releases acetylcholine into the
synaptic cleft to initiate contraction
• Motor end plate has protein receptors which
detect acetylcholine
• Muscle impulse travels over sarcolemma surface
and into T tubules, reaching the sarcoplasmic
reticulum
• Stored calcium ions in the sarcoplasmic reticulum get
released into the sarcoplasm
• Troponin and tropomyosin (proteins associated with
actin) move to expose the myosin binding sites on the
actin filaments due to the concentration of calcium
• Muscle shortens because myosin binds and pulls on
actin
• After received- acetylcholinesterase breaks down
acetylcholine, calcium returns to sarcoplasmic reticulum,
and myosin and actin links break
• ATP molecules provides the energy
• Must be regenerated because it has a limited
supply
• Creatine phosphate
• Energy can be transferred to ADP molecules,
converting them back ATP molecules as ATP is
decomposing
• Cellular respiration makes a few ATP molecules
in early phases
• Muscles require oxygen
• Glucose in broken down completely in
mitochondria
• Blood carries oxygen, bound to the pigment
hemoglobin
• The pigment myoglobin stores the oxygen in
muscle tissue
• The amount of oxygen that liver cells need
to convert lactic acid into glucose, and the
amount muscle cells must have to recreate
the original concentration of ATP and
creatine phosphate
• Develops during strenuous activity
•Pyruvic acid builds up during anaerobic
respiration and diffuses out of muscle cells
into the liver
• May take hours to repay
• When a muscle can no longer contract
• Usually from a build up of lactic acid in the
muscle, which lowers pH and results in muscle
fibers to not respond to stimulation
• Cramps- a muscle has a sustained involuntary
contraction
• More than half of energy released in cellular
respiration becomes heat
• All active cells generate heat, but muscle cells
make up a large majority of a bodies total
mass
• Blood moves heat from muscle to other tissues,
maintaining body temperature
• Location: walls of hollow internal organs, blood
vessels
• Function: to move food through the digestive
system and constrict blood vessels
• Involuntary
• Contracts and relaxes slowly
• Rhythmic
• No transverse tubules
• Major types:
• Multiunit: muscle fibers are separate
• Usually contract in response to stimulation by
certain hormones or motor nerve impulses
• Visceral: organized in sheets
• Are found in walls of hollow organs
• Can stimulate others, displaying rhythmically
• Responsible for involuntary wavelike motion called
peristalsis
• Reactions of actin and myosin
• Triggered by membrane impulses and increased
intracellular calcium ions
• Uses energy from ATP
• Neurotransmitters are acetylcholine and
norepinephrine
• Affected by hormones
• Fibers can change length without changing
tension
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Location: wall of the heart ONLY
Function: pumping action of the heart
Involuntary
Network of cells contract as a unit
Rhythmic
Transverse tubule system is well-developed
Intercalated discs separating adjacent cells
• Intercalated discs communicate a muscle
impulse throughout entire heart
• Allows the hearts muscle fibers to beat as a
single unit
• Network responds in an all-or-none
manner
• Threshold Stimulus- the minimal strength
required to cause a contraction
• Muscle fibers remain unresponsive until
reached
• All-or-None Response- if a muscle fiber
contracts at all, it contracts fully
• There is no partial contraction
• Once threshold stimulus is reached, fiber
responds to fullest contraction
• Recording a Muscle Contraction:
• Myogram- the pattern resulting from a
movement when connected to a device
•Twitch- a single contraction that lasts only a
fraction of a second
• Latent period- the delay between the time of
stimulation and the time the fiber responds
(a) Series of twitches
(b) Summation
(c) Tetanic Contraction
• Summation- when the stimulus of the next series
arrives before the muscle fiber can completely
relax
• Tetanic Contraction- when a forceful, sustained
contraction lacks any relaxation
• Recruitment of Motor Units:
• Recruitment- the number of motor units
activated as a result of a higher intensity of
stimulation
• The addiction of muscle fibers to take part
in a contraction
• Sustained Contractions:
• Produced by summation and recruitment
together
•Increasing strength
• Muscle tone- fibers undergo some sustained
contraction even when muscles appear to be
relaxed
• Keeps posture maintained
• Muscular hypertrophy: muscles enlarging
in size and strength due to forceful
exercise
• Muscular atrophy: muscles decreasing in
size and strength due to lack of exercise
• Size is relative to strength
• Capillary networks, actin and myosin
filaments, and number of mitochondria
• Slow twitch fibers: lower intensity and
able to resist fatigue, but may not increase
muscle size
•Running or swimming
• Fast twitch fibers: higher intensity and
increase muscle size, but are fatigable
• Lifting weights
• Variety of movements
• Movement depends on:
• The kind of joint
• How the muscle attaches
• Origin: the immovable end of a muscle
• Insertion: the movable end of a muscle
• The insertion is pulled towards the origin when
contraction occurs
• Flexion and extension tell about the angle
between bones that meet at a joint
• Almost always function in groups
• Must will movement to occur and nervous system
allows correct muscles to stimulate
• Prime Mover/Agonist: muscle responsible for a
particular movement
• Synergist: muscles that contract and assist the
prime mover
• Antagonists: muscles that resist the action of the
prime mover
• Tendinitis- a tendon (attaches muscle to bone)
becomes inflamed and swollen after injury or
repeated stress during activity
• Muscle strain- connective tissues are
overstretched and the degree of damage and
seriousness varies
• Botulinum toxin- blocks stimulation of
muscle fibers, paralyzing muscles
• “Botox” to temporarily smooth wrinkles by not
allowing to move facial muscles
• Steroids- (+) increase muscular strength
and used for medical purposes, (-) cause
changes of opposite sex and damage
internal organs
• Muscular Dystrophies
• Missing proteins
• Muscles weaken and degenerate
• Charcot-Marie-Tooth Disease
• A duplicate gene
• Weakens hands and feet, and tendon reflexes
• Myotonic Dystrophy
• An extending gene
• Muscle weakness and irregular heartbeats
• Hereditary Idiopathic Dilated Cardiomyopathy
• A glitch
• Rare form of heart failure in actin
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