Muscular System
Three types of Muscles Found in the Body
Muscle Structure
Functions
•Movement (constriction of organs & vessels, heat beating,
respiration)
•Support (posture)
•Heat production
Communication
Properties of Skeletal (striated) muscle (40% of body weight)
•Contractibility - ability of cells to shorten in length
•Excitability - ability to receive & respond to stimuli
•Extensibility - ability to increase (stretch) in length
•Elasticity - ability of a cell to return (recoil) to its resting
position after it has contracted or stretched.
All muscle is made of the same two proteins (Actin {troponin & tropomyosin} &
Myosin) & require ATP (Adenosine Triphosphate) as energy.
3 Types Appearance
Skeletal Striated/Fibers
Control
Voluntary/
Nervous
Nuclei
Multi
Work
Pairs
(Flexors - Entensors)
Smooth Non-striated/Single Cells Involuntary/
Uni
Nervous & Endocrine
Single
Cardiac Striated/ Single cells
Single
Involuntary/
Uni
Nervous & Endocrine
Anatomy of a skeletal muscle.
PART OF THE MUSCLE
Muscle(fascia)
Bundle (Muscle fasiculi)
Fiber(muscle cells)
Myofibrils
Filaments
COVERING or COMPONENT
Epimysium
Perimysium
Endomysium or Sarcolemma
(cell membrane)
Sarcoplasmic reticulum, T-tubules
Myofilaments (Actin & Myosin)
Microscopic Structure
Sarcomere
Contractile unit of the muscle
Z disk – protein fiber for attaching actin
I Band – light band
A Band – darker band
H zone – center of each sarcomere
M line – place of attachment for myosin
Myofibril
Motor Neurons
carries action potential to the muscle for a
contraction.

Motor unit – a group of fibers (muscle) that are
responding to a motor neuron,


Very percise movements – only a few
Larger muscle (leg) – several thousand
Neuromuscular Junction
Nerve impulse reaches the end of the neuron.
Allows calcium to enter the neuron
Calcium causes the release of a synaptic vesicle that contains
acetylcholine (neurotransmitter)
Floods the synaptic cleft to carry the signal to receptors on the
muscle.
Sliding
Filament
theory
All Muscle work in the same way - Sliding Filament Theory
1. Motor neuron transmits an impulse from the brain/spinal cord to the
muscle.
2. The electrical impulse is changed into a chemical
messenger/neurotransmitter (acetylcholine) at the terminal bud to cross
the synaptic cleft.
3. Signal binds to the motor end plate & travels throughout the muscle.
4. Calcium is released from the sarcoplasmic reticulum & binds to troponin
& causes it to change.
5. The binding sites are exposed to form a cross bridge with the myosin
head & ATP.
6. ATP is broken down to ADP & P & releases energy.
7. Energy that is released causes the myosin head to change shape &
resulting in the actin sliding past myosin.
8. New ATP binds to the myosin heads causing the bridge to break from
the binding site & return to its original shape.
9. Once returned to its original shape it re-forms a cross bridge.
10. Process repeats.
Stopping the signal
1. All the Acetylcholine must be inactivated at the motor
end plate by acetylocholinesterase or AchE from the
sarcolemma.
2. Calcium returns back to the sarcoplasmic reticulum by
active transport (ATP).
3. Troponin is restored to its original shape.
Sliding Filament Theory
Sliding
Filament
Theory
Muscle Twitch – Muscle
contraction in response to a
stimuli
1. Threshold stimuli - weakest
stimuli that can initiate a
contraction.
2. Subthreshold stimuli - stimuli
that will not cause a
contraction.
3. All or none response - stimuli
that is stronger than the
threshold stimuli & will
cause a muscle to contract
completely.
4. Recruitment - activating
more muscle fibers in
corresponding to a stimuli.
Types of Muscle Contractions
1. Twitch - basic unit of muscle
contraction.
•Rapid response to a single
stimuli that is slightly over
threshold.
•Lasts on 1/10 of a second.
Phases of a twitch
•Lag phase - delay contraction
from the time the signal is
sent.
•Contraction phase- muscle
contracts (shortens).
•Relaxation phase- muscle
returns to its original shape.
2. Wave contraction
Muscle to contract & lasts for a definite period of time.
Wave summation - second signal is sent before the first is
completed causing the second contraction to be stronger than the
first.
3. Tetanus
Sustained contraction that occurs when the frequency of
stimulation is so rapid that there is no relaxation.
Incomplete tetanus - partial relaxation occurs between each
stimuli (20 - 30/second).
Complete tetanus - fusion of twitches & provides a forceful
contraction (35-50/sec).
Energy for Contraction
1. ATP (muscles can not store ATP)
2. Creatine Phosphate
3. Glycogen
Uses for energy
1. Mechanical movement of cross bridges.
2. Breakage of cross bridges from actin.
3. Return of calcium to the sarcoplasmic reticulum.
Types of respiration
Aerobic – with oxygen 18x’s more efficient, but slower.
Anaerobic – without oxygen, but faster with a price.
Muscle Exercise


Psychological fatigue – more of the nervous system
Muscle fatigue
Muscles require food, oxygen & waste removal to function
properly.
During sustained exercise blood can not always deliver
enough oxygen to the muscle - oxygen debt.
To get energy, the muscle performs lactic acid fermentation
(anaerobic) to get energy.
ATP is produced, & a waste - lactic acid.
Increase in lactic acid causes the pH to lower, therefore
reducing the muscles ability to contract - muscle fatigue.
Cramp -muscle contracts spasmodically without relaxing & is
caused by an insufficient amount of ATP to properly return
the calcium back to the sarcoplasmic reticulum.
Muscle use can increase in size.
Lack of use can decrease in size -atrophy
Types of muscle contraction
1. Isotonic - Produces movement, the muscle pulls an attach
structure (bone) towards a more stationary structure.
2. Isometric - Produces muscle tension but does not shorten (no
movement).
3. Concentric contraction – isotonic contraction when lifting a
weight.
4. Eccentric contraction – isotonic contraction when lowering a
weight.
Slow & Fast Fibers
Slow type I myosin – contract & fatigue slowly
Darker muscle - myoglobin ability to store oxygen.
Fast type II (a or x) myosin – contract & fatigue quickly
Production of Movement
Origin - muscle attachment to the
more stationary bone.
Insertion - muscle attachment to
the more movable bone.
Group Actions
Group action - coordinated
response of a group of muscles
in order to bring a body
movement.
Prime movers - desired action.
Antagonist - relaxes during the
contraction.
Synergists - steady the
movement.
Fixators - stabilize the origin
of the prime mover
Major Muscles of the Body
Anterior
Major Muscles of the Body
Posterior
Muscles of
the Head
& Neck
Muscles of the Upper Back
Muscles of the Upper Chest
Muscles
of the
Upper
Arm
Muscles of the Lower Arm
Muscles of the Abdominal Pelvic
Muscles of
the Upper
Leg
Muscles of
the Lower
Leg