Download Muscle Function and Anatomy

Muscle Function and Anatomy
Characteristics of Muscles
 Muscle cells are elongated
(muscle cell = muscle fiber)
 Contraction of muscles is due to the
movement of microfilaments
 All muscles share some terminology
 Prefix myo refers to muscle
 Prefix mys refers to muscle
 Prefix sarco refers to flesh
2
The Muscular System
 Muscles are responsible for all types of
body movement
 Three basic muscle types are found in
the body
 Skeletal muscle
 Cardiac muscle
 Smooth muscle
Classifications
of
Muscles
Skeletal
Cardiac
Smooth
Cardiac muscle tissue
• Makes up myocardium of heart
• Unconsciously (involuntarily) controlled
• Microscopically appears striated
• Cells are short, branching & have a single nucleus
• Cells connect to each other at intercalated discs
Smooth (visceral) muscle tissue
• Makes up walls of organs & blood vessels
• Tissue is non-striated & involuntary
• Cells are short, spindle-shaped & have a single
nucleus
• Tissue is extremely extensible, while still retaining
ability to contract
Skeletal muscle tissue
• Associated with & attached to the skeleton
• Under our conscious (voluntary) control
• Microscopically the tissue appears striated
• Cells are long, cylindrical & multinucleate
Skeletal muscles
•
Are the prime movers of the human body. They produce
forces under the control of the nervous system. Man has
645 skeletal muscles of many shapes and sizes
•
Muscles are situated across joints and are attached at two
or more points to bony levers.
•
Each muscle is well adapted to provide an appropriate
range, direction and force of contraction to meet the
requirements.
Properties of Skeletal Muscles
•
Irritability: is the ability of the muscle to respond to stimulus.
•
Contracility: is the capacity of the muscle to produce tension between it’s
ends.
•
Relaxation: is the opposite of contraction and is the giving up of tension.
•
Distensibility: is the ability of the muscle to be stretched or lengthened up to
a certain limit by an outside force; e.g. pull of an antagonist muscle, of
gravity or by an opponent. The muscle suffers no harm so long as it is not
stretched beyond its physiological limits.
•
Elasticity: is the ability of the muscle to recoil to its original length when an
outside force is removed unless it has been overstretched.
Function of the skeletal Muscles
•
Create the force responsible for human
movement and positioning of the bony
segments of the body.
•
Give shape to body segments.
•
Form supportive walls.
Classification of Muscles:
1. According to the shape and fascicular architecture:
•
•
•
Parallel: spindle.
Oblique: e.g. pennate.
Spiral: Supinator.
•
The muscles designed for strength are of pennate type & the
ones designed for speed have parallel fibers.
Shape of Muscles and
Fiber Arrangement

Parallel muscles (range
of motion
1.
2.
3.
4.
5.

Strap
Flat (rectus abdominus)
Fusiform (biceps)
Strap (sartorius)
Radiate (trapezius)
Sphincter
Pennate (force)
1. Unipennate (biceps femoris)
2. Bipennate (rectus femoris)
3. Multipennate (deltoid)
Sphinter
Muscle Shapes
Muscle Shapes
2) According to the myoglobin content:
• Red: contain more red fibers and they are responsible for movement,
which require slow action for a long time e.g antigravity muscles.
• White: contain more white fibers and they are responsible for
movement, which require rapid action for a short time.
3) According to the type of contractile activity:
a. Tonic muscles (stabilizers): for continuous low level of contractile
activity which is required to maintain a given posture.
b. Phasic muscle (mobilizers): for rapid (fast twitch) activity which is
required when changing from one position to another.
4) According to general limb appearance:

Contractors: those muscles pull the body into approximation of the fetal
position/ midline e.g. flexor adductors and medial rotators.

Expanders: those muscles which expand or open up the body e.g.
extensors. Abductors and lateral rotators.
5) According to the relative magnitude of their stabilizing
and rotatory components (muscle attachments):

Spurt: mainly rotator muscles which have their origin away from the
joint and their insertion near to the joint e.g. biceps muscle.

Shunt: mainly stabilizer muscles which have origin near the joint and
their insertion away from the joint e.g. brachio-radialis.
6) According to the orientation of the line of pull to the joint
structure:
e.g. flexors, extensors, abductors and adductors
•
The muscle located anterior to a joint may be extensor (knee
joint) or may be flexor (elbow joint).
•
The possible axes of motion are determined by the structure of
the joint itself.
7) According to the number of joints over which the muscle
crosses:
– One joint muscle ( e.g. vastus mediales).
– Two joint muscle( e.g. rectus femoris).
– Multi-joint muscle ( e.g. finger flexors).
8) According to the type of muscle action or
function (their interaction in joint
movement):
•
One action of the joint is not only the
responsibility of one muscle but it is the
responsibility of different groups of muscles,
which can be classified as follows:
Agonists, antagonists, synergists, fixators.
FIBRE TYPES OF SKELETAL
MUSCLE
• 2 types of muscle fibres:
– Fast twitch
– slow twitch
due to speed at which they contract.
Slow twitch fibres
Type 1:
•
•
•
•
•
Red in colour – have good blood supply.
Dense network of blood vessels.
Suited to endurance work.
Slow to fatigue.
Contain many mitochondria
to make them more efficient
at producing energy using
oxygen.
Mitochondria – energy-producing
organelles with in cells.
Fast twitch fibres
Type 2:
• Contract twice as fast and
are thicker in size.
• Poor blood supply.
• Whiter in appearance:
– due to lack of oxygen.
• Fatigue fairly quickly.
• Suitable for: producing fast,
powerful actions such as
sprinting & lifting heavy weights.
Fast twitch fibres:
• Within the group of fast twitch fibres there are 2
types: 2A & 2B.
• Type 2B work when a person is working very
close to their maximum intensity, eg. 100 m
sprint.
• Type 2A work at a slightly lower intensities but
higher intensities than slow twitch, eg. 400 m
sprint.
Training Effect on Muscle Fibres:
• Type 1 & type 2B fibres don’t change.
• Type 2A can take on characteristics of Type 1 & 2B.
• More endurance training = 2A would develop more
endurance.
• More speed training = 2A would develop more speed.
• They don’t change their fibre type.
Training Effect on Muscle Fibres:
• Postural muscles predominantly slow twitch.
• Arms tend to be more fast twitch.
• Legs depends on endurance running or
sprinting.
Muscle Terminology
• Origin
– proximal attachment
– least moveable end
– closest to the midline of the body
• Insertion
– distal attachment
– most moveable end
– furthest from the midline of the body
• Action
– The movement at the joint when the muscle(s) contract
Anatomy of the Muscular System
•Origin Muscle attachment that remains
.
fixed
•Insertion
Muscle attachment that moves
•Action
What joint movement a muscle
produces
i.e. flexion, extension, abduction,
etc.
Attachments and Actions of Skeletal
Muscles
•
Actions depend largely on
what the muscles are
attached to
•
Attachment sites
– Origin – an attachment site
for a less movable bone
– Insertion – an attachment
site for a more moveable
bone
• For muscles to create a movement, they can
only pull, not push
• Muscles in the body rarely work alone, &
are usually arranged in groups surrounding a
joint
• A muscle that contracts to create the desired
action is known as an agonist or prime
mover
• A muscle that helps the prime mover by
stabilizing joints is a synergist
• A muscle that opposes the action of the
agonist, therefore undoing the desired action
is an antagonist
(Relaxes when prime mover contracts)
Types of
muscle
action
•
Antagonists
Agonists
Prime
movers
•
•
•
Synergists
Conjoint
•
Secondary
movers
Stabilizers
Neutralizers
Around •
The target
•
joint
•
•
•
On another
joint
•
•
Fixators
•
Agonist and Antagonist
Agonist
Agonist
Antagonist
Antagonist
•
Antagonists:
Muscles which oppose the prime movers as they relax and lengthen
progressively to allow agonists to move.
For every action, there are agonists and antagonists (e.g. Gluteus
maximus is antagonist for iliopsoas).
•
Synergists:
Synergists are muscles that work together in a close cooperation as
they either contract or relax to modify the action of the agonist.
Their aims are:
1) To make the agonist stronger
2) To eliminate the action of undesired movement.
They may alter the direction of pull and that depends on their
power in relation to the agonist muscle.
Types of Synergists:
a) Conjoint:
•
They are the two muscles acting together to produce a
certain movement which neither of them could produce it
alone. They are considered as prime movers of agonists and
they are parallel to each other.
•
E.g. tibialis anterior and peroneous tertious work together to
produce dorsiflexion.
b) Neutralizer:
They are the muscles that neutralize or cancel the undesired action
of prime movers.
This is more apparent in two- joint muscles which cross more than
one joint and are capable of performing more than one action
which are not needed
therefore, the neutralizers must contract to counteract the
undesired movement.
Neutralizers for undesired motion on another joint in case of
two joint muscles:
•
For example: Contraction of the finger flexors to grasp an
object also tend to flex the wrist. The unwanted wrist flexion
is neutralized by wrist extensors.
• Stabilizers:
Muscles that surround the proximal joint. They contract and
become firm to allow distal joint to move smoothly.
Their contraction is generally isometric (e.g. the rotator cuff muscles all
contribute their opposing tension to support the humeral head against the
glenoid fossa when the arm is moved away from the body and the hand
reaches for an object).
• Fixators:
Muscles which contract in both agonists and antagonists simultaneously
and that occur especially under stress conditions.
The tension will develop inside both groups of muscles to prevent any
degree of freedom. That occurs in normal physiological conditions during
strenuous effort and increased demand (e.g. during standing on one leg).
Types of bodily movements
• Movements can be classified into:
• Passive: Subject is relaxed and movement is
performed by any outside force.
• Active: Is volitionally performed or reflex reaction to
an external stimulus:
a. Slow or rapid tension movement that involve constant
. application of force.
b. Ballistic movement: Movement is initiated by
vigorous muscular contraction and completed by
momentum.
Types of Muscle Contraction
• Concentric contraction
– Length of muscle shortens
– Muscle force is greater than the resistance
• Static or Isometric contraction
– No change in muscle length
– Muscle force is equal to the resistance
• Eccentric contraction
– Muscle lengthens
– Muscle force is less than the resistance
Concentric
Concentric
Lengthens
Eccentric
Lengthens
Eccentric
Eccentric Contraction
• Used to control agonist and
prevent over lengthening of the
antagonist.
• Example: triceps lowers
dumbbell while biceps
’controls’ the triceps activity
(action)
• Causes more damage than other
types
• Also, results in more muscle
soreness.
Determination of Muscle Action
• Muscle location
– Origin and insertion
– What joint(s) it crosses
• Planes and their actions
– Most muscle can not perform opposite actions (e.g.
flexion AND extension)
• Line of pull
– Muscles only pull on bones, they do not push bones!
– Insertion is pulled towards the origin
Nomenclature
• Muscles are named according to:
– Location: pectoralis gluteus, brachial
– Size: maximus, minimus, longus, brevis
– Shape: deltoid, quadratus, teres
– Orientation: rectus
– Origin and insertion: sternocleidomastoid,
brachioradialis
– Number of heads: biceps, triceps
– Function: abductor, adductor, masseter