Chapter 13
Keywords
Properties
 Contractibility
 Extensibility/elasticity
 Excitability
Type
 Cardiac muscle
 Striated
 Smooth muscle
 Non-striated
 Skeletal muscle
 Striated
Movement
 Point of origin
 Point of insertion
 Belly
 Agonist (prime mover)
 Antagonist
 Tendon
Anatomy
 Sacromere
 Myofibrils
 Myofilaments
Physiology
 Sliding filament theory
Muscle tissue
 Muscle tissue consists of highly specialised,
elongated cells, which have elastic
properties.
 Muscle cells get shorter (contract) when
stimulated. When the stimulation is
removed the cells return to their original
shape (relax).
 Muscle tissue provides the source of power
for movement and posture, and alters the
shape and size of internal organs.
Muscles
All muscles have 3 properties:
1. Contractability
2. Extensibility
3. Elasticity
4. Excitability
contractility
excitability
extensibility
elasticity
Types of muscle tissue
 Skeletal muscles are
muscles that are under
voluntary control. They are
attached to the bones of
the skeleton
 Smooth muscles, also
called involuntary
muscles, are not under
conscious control
 Cardiac muscle is the
muscle that makes up the
heart
Skeletal muscle
The cells of skeletal muscle are elongated, striated
in appearance and have many nuclei.
L Slomianka, ANHB-UWA
Skeletal muscle - function
 Most skeletal muscles
are attached to, and
move bones of the
skeleton. An
exception are the
facial muscles,
which are responsible
for facial
expression.
 Skeletal muscle cells
are normally under
voluntary control.
Wellcome Library
Cardiac muscle
 Cardiac muscle tissue occurs only in the heart.
 The cells of cardiac muscle are striated in
appearance and form a network of
interconnected cells, joining with one another
at intercalated discs. They are involuntary.
 Cardiac muscle has the special property of
being able to relax and contract rhythmically
throughout life without becoming tired or
stopping.
Cardiac muscle
Intercalated
disc
L Slomianka, ANHB-UWA
Cardiac muscle
Intercalated disc
Prof Giogio Gabella, Wellcome Images
Smooth muscle
Smooth muscle cells:
 are spindle-shaped, contain a single nucleus
and are not striated.
 either occur in small clusters or form sheets.
 are capable of slow, sustained contraction e.g.
vasoconstriction, or rhythmical, wave-like
contractions e.g. peristalsis.
 occur in the walls of many internal organs e.g.
blood vessels, the bladder, uterus, male and female
reproductive tracts, gut, respiratory tract, intrinsic
muscles of the eye .
Smooth muscle
G Meyer, ANHB-UWA
The muscular system
Wellcome Library
Skeletal muscles working together
 Muscles are attached to the
Origin

Belly



Insertion
bones by tendons
Movement of the skeleton is
achieved by pairs of opposite
muscles moving together, one
relaxing the other contracting
The end of the muscle fixed to
the stationary bone is called
the origin
The attachment to the movable
bone is called the insertion
The fleshy portion between the
tendons is called the belly
Skeletal muscles working together
 A muscle that causes a
desired action is called
Flexion
the agonist or prime
Biceps (agonist)
contracts
mover
Triceps (antagonist)
 The muscle that has the
relaxes
opposite action is called
the antagonist. It has the
opposite effect of the
Extension
agonist
 Muscles that help
indirectly in steadying a
joint during a movement
are called synergists
Biceps (antagonist)
relaxes
triceps (agonist)
contracts
The structure of skeletal muscle
 Muscle cells are held together in



(Muscle cell)

bundles that lie parallel to each
other
Each muscle cell is an elongated
cylinder with many nuclei
Around each cell is a thin
membrane called the
sarcolemma which contains
the cytoplasm called the
sarcoplasm
These cylindrical cells are the
muscle fibres
Within the sarcoplasm of each
fibre there are myofibrils
which lie parallel to each other
and run the length of the fibre
Skeletal muscle
Structure of myofibrils
 The myofibrils are
composed of many smaller
myofilaments. These are
the units involved in
contraction of the muscle
 When the muscle is
stimulated, these filaments
slide past each other in a
manner that shortens the
myofibril
 Myofibrils can be divided
into units called
sarcomeres
https://www.lcmrschooldistrict.com/roth/PowerP
oint_Lectures/chapter35/videos_animation
s/myofibril.swf
http://highered.mcgrawhill.com/sites/0072507470/student_view0/
chapter9/animation__action_potentials_a
nd_muscle_contraction.html
Actin and myosin
 There are 2 types of
filaments:
 Thick myofilaments
composed of the
protein myosin
 Thin filaments
composed of actin
A single myosin
molecule
Myosin – thick
filaments (red)
Actin – thin
filaments (blue)
The sarcomere
Light band
gets shorter
during contraction
Dark
A band Light
I band
Z
M line
M
Sarcomere
University of Edinburugh, Wellcome Images
Dark band
Remains same size
during contraction
Myosin filament
Actin filament
Z line
The alternating dark and light bands of
skeletal muscle fibres results from the
overlapping bundles of actin and myosin
filaments.
The structure of skeletal muscle
Muscle fibres
Myofibril
M I Walker, Wellcome Images
University of Edinburugh, Wellcome Images
Sliding filament model
 We use the sliding filament model to explain how




muscles are able to contract
When muscles contract the sarcomeres shorten
As the thin actin filaments slide over the thick
myosin filaments, the Z lines are drawn closer
together and the sarcomere is shortened
The fibril has shortened because the myofilaments
overlap more
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter10/a
nimation__sarcomere_contraction.html
Sliding filament theory
The control of skeletal muscle
 A motor neuron and all of
the muscle fibres
stimulated by it is called a
motor unit
 Where precise movement
is required motor units are
small
 ie. eye 3-6 motor units
 Where the strength of
contraction is important,
motor units are large
 ie. leg 1000 fibres in
each motor unit
The neuromuscular junction
 The point where the message is passed from the motor




neuron to the muscle fibre is called the
neuromuscular junction
Each motor neuron ends in an enlarged area called the
synaptic knob
The synaptic knob fits into a depression in the surface
of the mucle fibre called the motor end plate. There
is a small gap in between, so they don’t touch.
The neuron releases a chemical called a
neurotransmitter (actylcholine)
https://www.youtube.com/watch?v=BMT4PtXRCVA
The neuromuscular junction
Muscles, bones and nerves
working together
Cerebrum(CNS)
 Initiation of muscle
contraction
Cerebellum (CNS)
 What muscles and how
strong a contraction
Inner ear balance receptors (ANS)
 Balance & equilibrium
Muscle contraction (SNS)
Stretch receptors in joint (ANS)
 Give feedback
Muscles, bones and nerves
working together
 Read page 217 in
particular summary
figure 13.11 page 218
www.newmexicoorthopaedics.com
Links
 http://www.childrensuniversity.manchester.ac.uk/me
dia/services/thechildrensuniversityofmanchester/flas
h/exercise_3b_types_of_muscle.swf
 http://id44.com/Types%20of%20Muscle%20(Created
%20By%20id44.com)/engage.swf
 https://www.youtube.com/watch?v=XoP1diaXVCI
Crash Course
 https://www.youtube.com/watch?v=Ktv-CaOt6UQ
 https://www.youtube.com/watch?v=I80Xx7pA9hQ