Muscular
System:
Chapter 8
Chapter 8
Functions of Muscles

1) Movement
◦ Move the skeleton
◦ Move food and body fluids
◦ Create heartbeat

2) Heat Production
◦ Used to regulate body temperature
Types of Muscle Tissue

1) Skeletal
◦ Striated,Voluntary
◦ Multiple nuclei/cell
◦ Ex: Quadriceps, triceps

2) Cardiac
◦ Striated, Involuntary
◦ 1 nucleus/cell
◦ Ex: heart

3) Smooth
◦ Unstriated, Involuntary
◦ 1 nucleus/cell
◦ Ex: stomach wall, espophagus
Structure of a Muscle

Fascia
◦ Outer layer of fibrous connective tissue
◦ Continuous with tendon and/or bone

Epimysium
◦ Layer under the fascia

Perimysium
◦ Layer under epimysium
◦ Wraps around bundles called fascicles
Structure of a Muscle (cont)

Endomysium
◦ Layer under perimysium
◦ Wraps around muscle fiber

Sarcolemma
◦ Layer under endomysium
◦ Cell membrane of a muscle cell (fiber)
◦ Surrounds bundles of myofibrils
Structure of a Muscle Fiber
Sarcolemma- cell membrane
 Sarcoplasm- cytoplasm
 Sarcoplasmic reticulum- endoplasmic
reticulum
 Multiple nuclei/cell
 Many mitochondria
 Transverse tubules- membrane-bound
canals through the fiber;

 surrounded by cisternae of sarcoplasmic
reticulum

Filled with bundles of myofibrils
Structure of the Myofibril
Composed of myosin (thick) filaments and
actin (thin) filaments
 Filaments overlap creating striations
 Z-line- attachment for actin filaments
 M-line- attachment for myosin filaments
 I-band- zone containing only actin filaments
 A-band- zone containing myosin filaments
 H-zone- zone containing only myosin
filaments
 Sarcomere- unit stretching from one Zline to the next

Neuromuscular Junction
Motor neuron - nerve that connects to
muscle fiber
 Neuromuscular junction - connection
between nerve and muscle fiber
 Motor end plate - specialized area of
the sarcolemma modified to connect with
the nerve
 Neurotransmitters - messengers that
are stored in synaptic vesicles in the
neuron and released across synaptic cleft

Motor Units
A fiber usually has 1 neuromuscular
junction
 A motor neuron can be connected to
many fibers
 Motor unit - a motor neuron and all of
its connected fibers

◦ Fibers will contract as a unit
Quick Review

If your muscle cells were not producing
enough ATP, which part of the cell is
dysfunctional?
◦
◦
◦
◦
A) Sarcoplasmic reticulum
B) Sarcolemma
C) Mitochondria
D) Nucleus
Quick Review

If you were diagnosed with a disease that
affected your ability for your muscles to
communicate (connect) to your nervous
tissue, which part of your muscle would
this affect?
◦
◦
◦
◦
A) Motor unit
B) Motor neuron
C) Neuromuscular junction
D) All of the above
Sliding Filament Model
Structure
animation
 Muscle shortens
as filaments slide
past each other
 This means that
the I-band will
get smaller
during a
contraction

Timeline of a Contraction

Step 1- Release of Acetylcholine
◦ Acetylcholine is a neurotransmitter made and
stored in the neuron
◦ Release with nerve impulse into synaptic cleft
◦ Crosses cleft and binds with receptors on
motor plate

Step 2- Muscle Impulse
◦ Binding of acetylcholine at motor plate
stimulates muscle impulse
◦ Impulse spreads across sarcolemma and down
into T-tubules
Timeline of a Contraction (cont)

Step 3- Movement of Calcium
◦ Cisternae of sarcoplasmic reticulum become
more permeable to Ca+ ions
◦ Ca moves out of reticulum into sarcoplasm

Step 4- Exposing Binding Sites of
Actin
◦ High Ca+ in sarcoplasm cause a change in the
actin filaments
◦ Troponin and tropomyosin
◦ Thin filaments attached to actin; act together to
expose the binding site
Timeline of a Contraction (cont)

Step 5- Contraction
◦ Readied myosin heads attach to exposed actin
binding sites and pull
◦ A new ATP must bind with the myosin ATPase
before myosin will release binding site
◦ Readied myosin head then binds with a new
actin binding site
◦ I-band gets smaller
◦ This will continue as long as acetylcholine is
present
Timeline of a Contraction (cont)

Step 6- Relaxation
◦ Two steps lead to relaxation:
 1) Acetylcholinesterase breaks down acetylcholine
 2) Once acetylcholine is low, Ca+ is actively
pumped back into sarcoplasmic reticulum
◦ Low Ca+ levels in sarcoplasm stop linkage of
actin and myosin and muscle fiber relaxes to it
normal length
Muscle Contraction Animation: Myofibril
Muscle Contraction Animation: Sarcomere
Quick Review

Which protein filaments are involved in
muscle contraction?
◦
◦
◦
◦
A. Actin
B. Myosin
C. ATPase
D. More than one answer is correct
Quick Review

Which muscle fiber structures are
involved in contraction?
◦
◦
◦
◦
A. I-band
B. Sarcomere
C. Active site
D. More than one answer is correct
Quick Review

Acetycholine is a neurotransmitter whose
amount will increase during contraction
(to a point); the amount then decreases
to stimulate relaxation.
◦ True
◦ False
Energy Sources for
Contraction
1st source- available ATP’s (very small
amount)
 2nd source- Creatine phosphate breaks
down to produce more ATP
 3rd source- Cellular respiration to create
new ATP’s

◦ Extra oxygen stored in myoglobin in muscles

4th source- Anarobic respiration
◦ Creates a build-up of lactic acid
Oxygen Debt
Lactic Acid is moved to the liver to be
converted back to glucose
 Oxygen debt

◦ Amount of oxygen needed for liver to
convert the lactic acid
◦ How much is needed by the muscle to reset
the other sources

Debt may take hours to repay after
strenuous activity
Muscle Fatigue

Occurs because:
◦ Blood supply interrupted
◦ Acetylcholine used up
◦ Build-up of lactic acid which lower pH of
muscle which lowers muscles response to
stimulation
Muscle Fiber Responses

Threshold stimulus - intensity of
stimulation needed to make a contraction
occur

All-or-none response - muscle fiber
responds fully or not at all
Recording Muscle Fiber
Contractions
Recording is a myogram
 Latent period- period of time between
stimulus and response
 Period of Contraction
 Period of Relaxation
 Making a muscle fiber go through a single
contraction is called a twitch

Quick Review

Muscles could take hours to recover from
oxygen debt.
◦ True
◦ False
Quick Review

Which of the following is a reason why a
muscle could become fatigued?
◦ A. Blood supply increases
◦ B. Acetylcholine is present
◦ C. Build-up of lactic acid which lowers pH of
muscle
◦ D. None of the above
Summation and Tetany
Summation - strength of muscle fiber
response increases if another stimulus is
applied before relaxation is finished
 Tetany - a sustained maximum muscle
fiber response produced by a high
frequency of stimuli that don’t allow the
muscle to relax

Recruitment
Muscles do NOT have all-or-none
contractions
 Muscles are made of many motor units

◦ Respond to a variety of stimulus strengths
◦ Muscle used for strength normally have more
bigger motor units
◦ Muscles used for fine movements have more
smaller motor units
Muscle Tone
A few motor units go through sustained
contractions
 Help keep posture and support

Skeletal Muscle Action
Origin - muscle attachment on bone that
is immobile during movement
 Insertion- muscle attachment on bone
that will move
 For any body movement:

◦ Prime mover (agonist)- major muscle creating
movement
◦ Synergist- help with movement
◦ Antagonist – create movement in the
opposite direction
Smooth Muscle
Contains myosin and actin filaments but
more randomly arranged (no striations)
 Multiunit- stimulus is through nerves or
hormones (iris or walls of blood vessels)
 Visceral- cells can stimulate each other
(walls of intestine, uterus, urinary tract)

◦ Peristalsis- wave-like contraction
Cardiac Muscle
Cells form interconnecting network
 Cells are connected at intercalated disks
 Impulses can rapidly transmit from cell to
cell
 Network response is all-or-none

Inherited Diseases of Muscle
Disease name
Description
Muscular
Dystrophy
Missing proteins (specifically dystrophin –
which attaches skeletal muscles together),
weakened muscles, degenerate over time,
specific type: Duchenne’s – only affects
boys, die by early adulthood
CharcotMarie-Tooth
Disease
Caused by duplicate gene (impairs
insulating sheath around nerve cells – so
nerves can’t stimulate muscles), causes
slowly progressing weakness in muscles of
hand and feed, symptoms can resemble
AIDS, diabetes, vitamin deficiency
Inherited Diseases of Muscle
Disease name
Description
Myotonic
Dystrophy
Delays muscle relaxation following
contraction, causes facial/limb weakness and
irregular heartbeat, caused by “expanding
gene” – gets worse with subsequent
generations
Hereditary
Idiopathic
Dilated
Cardiomyopathy
Very rare, heart failure – doesn’t begin until
person’s 40s, lethal in 50% of cases within 5
yrs of diagnosis, caused by tiny genetic
error in form of protein actin –cannot
anchor to Z lines in heart muscles, causes
heart chambers to enlarge and not function
Animation and Quiz!

Animation with Quiz:
http://bcs.whfreeman.com/thelifewire/cont
ent/chp47/4702001.html