Download Major Concepts of Anatomy and Physiology

Muscular Tissue
Part 2: Support & Movement
Common Traits
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Proteins Needed:
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Four Essential Ions Needed:
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Actin
Myosin
Calcium
Sodium
Chloride
Potassium
Common Characteristics:
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Excitability
Conductivity
Contractility
Extensibility
Elasticity
Skeletal Muscle Tissue

Striations: Alternating light and dark bands
seen on skeletal muscle tissue under the
microscope.
A
Bands: The dark bands
 I Bands: The light bands
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
Multinucleated: Skeletal muscles to have
multiple nuclei in each cell.
Somatic Motor Neurons: Neurons that
stimulate/excite the muscle
 Neuromuscular
Junction (NMJ): The point at which
the neuron and muscle communicate
Skeletal Muscle Structures

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Muscle Fibers: Composed of individual muscle
cells with multiple nuclei.
Sarcolemma: The plasma membrane of each
muscle fiber.
Transverse “T” Tubules: Tunnel from the
surface to the center of the fibers.
 Allows
for action potentials to spread throughout the
muscle fiber

Sarcoplasm: Located within the sarcolemma.
 Glycogen:
Contained within the sarcoplasm;
necessary for ATP production.
 Myoglonin: Contained within the sarcoplasm; helps
release oxygen during ATP production.
Skeletal Muscle Structures

Sarcoplasmic Reticulum: Surrounds each
myofibril and creates a network that acts as a
reservoir for Calcium ions.
 Terminal
Cisternae: Sacs of sarcoplasmic reticulum;
store calcium ions in relaxed muscle fibers and
release calcium ions during contraction.

Myofibrils: Long protein threads; two types;.
 Thick
Filaments: Made up of myosin and somewhat
L shaped.
 Thin Filaments: Made up of actin and have an active
site that binds to myosin.
 Myofilaments: Smaller elements responsible for
muscle contraction; make up the myofibrils.
Nerve-Muscle Interaction
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Motor Neuron: Specific neuron with the cell
body located in the brainstem and spinal cord;
supplies muscles with electrical signals.
Paralysis: Loss of nerve input resulting in a lack
of muscular control.
Atrophy: Degeneration of the muscle tissue due
to a lack of use.
Motor Units: Consists of one nerve fiber and all
of the muscle fibers it innervates.
 Contracts as one unit; varies in
 Examples: Eyes have 23 fibers
size.
per motor unit to
move the eyes, the thigh has over 1,000 fibers per
unit.
Neuro-Muscluar Junction


Similar to the neural synapse - This is the
junction where innervation happens!
Resting Membrane Potential: The state of a
neuron becoming polarized, or having an
electrical charge potential. Maintained by
Sodium-Potassium Pump.
 Sodium-potassium
pump: When the cell is
stimulated, the ion gates open within the membrane
and sodium ions rush in while potassium ions exit,
resulting in a depolarized change in electrical
potential.
 This causes an action potential to be reached.
Neuro-Muscluar Junction

Action Potential (AP): The nerve signal transmitted
from the axon of the nerve to the muscle tissue.
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Acetycholine (Ach): The neurotransmitter responsible for action
potentials being released into the muscle fiber. Triggered by the
resting potential being reached.
Synaptic Knob: The set of vesicles responsible for releasing
ACh.
Threshold: The minimum voltage necessary to trigger an action
potential to produce a contraction.
Twitch: A single action potential one motor neuron resulting in a
brief contraction of the muscle fibers,.
Motor End Plate: The point on the muscle where the
neural impulse is received.
Contraction & Relaxation of
Skeletal Muscle Fibers

Sliding Filament Mechanism: The
model that describes the methods of
skeletal muscle contraction.

Occurs in 4 steps
Contraction & Relaxation of
Skeletal Muscle Fibers
1.
Excitation:
Action potentials transmit from the nerve to
muscle fibers
2. Motor end plate releases ACh
3. Depolarization occurs through the sodiumpotassium pump.
1.
Contraction & Relaxation of
Skeletal Muscle Fibers
2.
Excitation-Contraction Coupling: Action
potentials in the muscle fibers lead to
activation of the microfilaments.
1.
2.
3.
4.
5.
When the action potential reaches the sarcoplasmic
reticulum, Calcium ions are released.
Calcium ions bond to troponin in the thin
myofilaments.
Toponin exposes the active sites on the actin
filaments.
Myosin filament heads can now bind to the actin
filaments.
This initiates contraction.
REMEMBER: Actin & Myosin are contractile proteins!
Contraction & Relaxation of
Skeletal Muscle Fibers
3.
Contraction: The thin myofilaments slide
toward the thick myofilaments, causing the
muscle fiber to shorten.
1.
2.
3.
4.
Myosin molecules release ATP.
Myosin heads contact active actin sites, releasing
the Power Stroke.
Recovery Stroke follows the power stroke, causing
the myosin to release the actin and bind to a new
ATP molecule.
Power Stroke/Recovery Stroke sequence repeated
multiple times per muscle contraction.
Contraction & Relaxation of
Skeletal Muscle Fibers
4.
Relaxation: The muscle relaxes when
the nervous stimulation ends.
Occurs when acetylcholinesterase breaks
down the Ach to cease generation of action
potentials.
2. Calcium is carried back to the sarcoplasmic
reticulum to be stored for future
contractions.
1.
Length-Tension Relationship
Length-Tension Relationship: The force
of the muscle contraction depends on the
length of the sarcomeres before the
contraction occurs.
 Muscle fibers have the most tension when
optimal overlap between thick and thin
filaments occurs.
 If the muscle becomes overly stretched,
there is little to no overlap and the muscle
cannot contract.
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Rigor Mortis
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Rigor Mortis: The rigidity of muscle tissue
beginning 3-4 hours after death.
 The
result of leaky cellular membranes
causing Calcium ions to flow into the cytosol
and myosin heads to bind to actin.
 Muscles are then in a perpetual state of
contraction, causing them to be rigid.
Muscle Tension
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Muscle Tension: The small amount of taughtness or
tension in the muscle due to weak & involuntary
contractions of the motor units.
Contraction Strength: The strength of the contraction
of the whole muscle is increased by the number of motor
units activated.
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Higher-frequency stimulation results in more units
participating and a stronger contraction.
Treppe: AKA the staircase effect… The graduated series
of increasingly stronger contractions as a result of the
muscle being exposed to a series of signals of the same
strength.

Probably due to the buildup of calciun and the inability of the muscle
cells to return to homeostasis.
Refractory Period
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Refractory Period: A period after each muscle
twitch where the muscle cannot respond to
another impulse.
 Wave
Stimulation: Stimuli arriving at different times
result in stronger contractions - any further stimulation
just causes the muscle to become more tense.
 Incomplete or Unfused Tetanus: If stimulation
continues without the muscle being given enough
time to completely relax the muscle maintains a
sustained but wavering contraction.

Can occur at 20-30 stimuli per second.
 Complete
or Fused Tetanus: If the muscle is not
given any period to rest between stimulations, the
muscle becomes completely rigid.

Can occur at 80-100 stimuli per second.
Types of Contractions
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Isometric Contractions: Contraction results in
muscle tension, but produces no change in
length & no movement.
 E.g.

holding a book steady with an outstretched arm.
Isotonic Contractions: Contraction results in a
change of muscle length (movement) but no
change in tension. 2 forms:
 Concentric
Contractions: The muscle shortens as it
contracts.
 Eccentric Contractions: The muscle lengthens as it
contracts.
Muscle Metabolism
Aerobic Respiration: Oxygen exchange
typically supplies the energy for muscle
contraction.
 Anaerobic Fermentation: If aerobic
respiration is insufficient, the muscle
catalyzes stored creatine phosphate to
create ADP, which in turn yields ATP to
fuel the muscle cells.

 Results
in lactic acid buildup on the muscle
cell which prevents oxygen exchange.
Muscle Metabolism
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Muscle Fatigue: A muscle’s inability to contract
after a period of prolonged exercise. Due to….
 Increased
Calcium ion levels
 Buildup of lactic acid
 Insufficient oxygen
 Depletion of glycogen
 Inadequate release of acetylcholine

Oxygen Debt: The amount of oxygen that must
be replenished after periods of exercise.
 Occurs
when the body is still recovering and the heart
and lungs are still working harder.
 AKA Recovering Oxygen Uptake.
Types of Muscle Fibers
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Fast Twitch Fibers (Glycolytic Fibers):
Produce quick energy necessary for stopand-go activities.
 Larger
sized, produce short & powerful
contractions.
 Low in myoglobin, causing them to appear
white.
 Few mitochondria.
 Used for intense anaerobic movements, such
as weight lifting, sprinting, or throwing an
object.
Types of Muscle Fibers
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Slow Twitch Fibers (Oxidative Fibers):
Produce smaller, longer contractions used for
sustained activity.
 Have
a richer blood supply
 Increased mitochondria
 Increased myoglobin (used to store oxygen) giving a
reddish appearance

Called red fibers because of this
 Use
aerobic metabolism to function
 Resist fatigue
 Produced sustained contractions
 Used in activities such as long-distance running.
Muscle Conditioning & Exercise
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Resistance Exercise or Conditioning:
Involves contracting muscles against a
load that resists movement.
 Stimulates
muscle growth by enlarging
existing muscle cells.

Endurance or Aerobic Exercise:
Improves muscle resistance to fatigue.
 Increases
the density of slow-twitch fibers.
 Increases blood and oxygen supply.
Cardiac Muscle

Cardiac Muscle: Similar to skeletal muscles,
with a few differences…
 Fibers
are branched and interconnected
 Intercalated Discs: Gap junctions passing electrical
impulses from cell to cell
 Autorhythmicity: Beats continuously and
rhythmically without stimulation from the nervous
system… But is still affected by the nervous system.
 Involuntary: We cannot control this muscle type!
 25% of the muscle fibers composed of mitochondria
to meet energy needs.
Smooth Muscle
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Smooth Muscle: Composed of both thick
& thin filaments, but are not aligned with
each other to produce striations.
 Single
nucleus per cell
 Involuntary
 Visceral Muscle: Does not attach to bone
 No Z-discs or T-tubules
 Very little sarcoplasmic reticulum
 Calcium for contractions comes mostly from
the extracellular fluid
Smooth Muscle
 Can
be found in blood vessels, the digestive,
respiratory, urinary, & reproductive tracts.
 Can remain partly contracted for long periods
without stimulation – can maintain muscle
tone easily.
 Contracts more slowly and for longer overall
periods.
 Can stretch more than the other muscle types
and still maintain its function.

E.g. the uterus & bladder muscles.