Muscular System
Ch 8 Notes
Three types of muscles
• Skeletal muscle
• Smooth muscle
• Cardiac muscle
Functions
• Movement – pull on the structures to which they
are attached.
• Provides muscle tone
• Propels body fluids and food
• Generates the heartbeat
• Distributes heat
Structure
Skeletal Muscle Activity
• Neuromuscular junction –
where a neuron meets a
muscle.
• Where the axon endings of the
neuron meet up with the
sarcolemma of the muscle is
called a motor end plate.
Skeletal Fiber Contraction
• A neurotransmitter called
acetylcholine is released from
the synaptic vesicles into the
synaptic cleft and into the
sarcolemma.
• This starts an impulse that
travels through the transverse
tubules and reaches the
sarcoplasmic reticulum.
• This opens the Calcium
channels.
Skeletal Fiber Contraction
• The calcium ions bond to the troponin molecules.
• Tropomyosin move and expose sites on the actin.
• Actin and myosin link up to form cross-bridges. Actin are pulled to
the center, shortening the muscle fiber.
Skeletal Fiber Relaxation
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•
•
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Acetylcholinesterase – an enzyme – breaks down acetylcholine.
Calcium ions are pushed back into the sarcoplasmic reticulum.
Troponin and tropomyosin go back to their original position.
Muscle remains relaxed until stimulated again.
Video
• Muscular System Video
Energy for Contraction
• Four sources of ATP for contraction
▫ Stored ATP – only available for a few seconds
▫ Creatine phosphate – can replenish ATP for a few
more seconds
▫ Cellular respiration – glucose -> ATP for a few
minutes while oxygen is available
 Requires oxygen to move from blood (hemoglobin)
to muscles (myoglobin)
Energy for Contraction
• Four sources of ATP for contraction
▫ Fermentation – glucose->pyruvic acid->lactic acid
and ATP
 Lactic acid goes to liver cells and turns back into
glucose.
 Builds an oxygen debt = amount the liver needs to
turn lactic acid back to glucose + replenish store +
replenish creatine phosphate
Fatigue and Cramps
• Fatigue - occurs when muscles are exercised
strenuously for long periods of time and lose
their ability to contract.
▫ Can occur because of lactic acid buildup.
• Cramp – sustained involuntary contraction.
▫ Changes in extracellular fluid trigger uncontrolled
stimulation.
Heat
• Less than 50% of the energy available is used in
muscles.
• What’s not used is released as heat and carried
throughout the body to maintain stable
temperature.
Journal 3/6
• Read the Clinical Application 8.1 on pg 188.
▫ Write a paragraph summary of the article.
▫ Write a paragraph response to the article.
Muscle Response
• Muscles are “activated” by nerve impulses that
release Calcium into the muscle fiber.
• If an impulse is not strong enough, it will not
release the Calcium.
• Threshold stimulus = the strength of stimulation
required to contract a muscle fiber.
▫ Threshold is reached by releasing enough
acetylcholine.
Single Fiber - Twitch
• A twitch is any contraction cycle of a single
muscle fiber.
▫ Stimulation
▫ Contraction
▫ Relaxation
• It is NOT just when a fiber contracts
involuntarily.
• All-or-nothing response.
▫ Each twitch generates the same force.
Whole Muscle - Summation and
Recruitment
• How do you pick up a balloon without
popping it?
• Mucle tension is determined by two
things
▫ The frequency with which the fibers are
stimulated. (Summation)
▫ How many fibers take part. (Recruitment)
Whole Muscle - Summation
• Each twitch can “encourage” the next
twitch within the muscle which causes
increasing twitch strength.
• Summation – when the force of
individual twitches combine so that a
muscle doesn’t completely relax
between twitches.
• Tetanic contraction (tetanus) is when
the muscle doesn’t relax at all
between contractions.
▫ Also called sustained contraction.
Whole Muscle - Recruitment
• Motor Unit – One neuron and all of
the muscle fibers it contracts.
• The more motor units that are
activated, the stronger the response.
• Recruitment - increase in the number
of motor units being activated during
contraction
• Different motor units respond to
different intensities.
Whole Muscle – Summation and
Recruitment
• Summation – when the force of
individual twitches combine so that a
muscle doesn’t completely relax
between twitches.
• Recruitment - increase in the number
of motor units being activated during
contraction
• Put the two together and you can
produce a sustained contraction.
• Muscle tone – sustained contraction
when muscle appears to be at rest.
▫ Used every day to hold up your head, your
body – to maintain posture.
To do...
• Practice Q’s - Pg 191 #14-18
• Actions of Muscles Table
• Read the rest of the chapter and finish outline
• Test Wednesday
Skeletal Muscle Actions
• Origin – Attached to the
immovable bone
• Insertion – Attached to the
movable bone
• Example: biceps brachii
▫ Flexes forearm at the elbow
• Origin:
• Insertion:
Skeletal Muscle Actions
• Prime mover – muscle that
does most of the contraction.
▫ AKA – agonist
• Synergist – muscle that assists
in the action of the prime
mover
• Antagonist – muscle that
opposes the action of the
prime mover
Skeletal Muscle
Actions
• Example
• Prime mover – biceps brachii
• Synergists – brachialis and
brachioradialis
• Antagonist – triceps brachii
Smooth Muscle
• Stilll use actin and myosin, but they are more
randomly distributed, which removes the
striations.
Smooth Muscle – Two Types
• Multi-unit – muscle fibers are separate (iris of
the eye, walls of blood vessels)
• Visceral – sheets of muscle fibers (stomach,
intestines, bladder)
▫ Demonstrate peristalsis – wavelike motion of
contraction caused by cell to cell stimulation and
rhythmicity (repeated contractions)
Cardiac Muscle
• Found only in the __________.
• Still use actin and myosin in a similar layout as
that of skeletal muscle.
• Stores less calcium than skeletal, so T tubules
are bigger in order to deliver more calcium from
extracellular fluid causing longer twitches.
• Intercalated discs between fibers relay impulses
from one cell to another so it contracts as a unit.
Lab Ex 19b
• For each of the following actions, identify the
prime mover, synergist(s), and antagonists.
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Flexing your wrist
Standing on your tippy-toes
Rotating forearm laterally
Chewing
Extending the leg at the knee