ROLES OF HUMAN MUSCLES
If a muscle is the primary agent in the production of a desired movement, it is called “a
prime mover” muscle.
If the same muscle serves to counteract or slow the action of another prime mover it is
called an “antagonistic” muscle
If it serves to steady a movement it is called a “synergist” muscle
When muscles come to rest in the body, it is considered “fixed” in motion (still).
Muscles that maintain the body at rest are called “fixators”.
So, when the body is at rest these fixed muscles are holding the body at a state of “tetnae,
or fix”.
Example:
The biceps brachii is a flexor of the elbow joint and in this movement would be
considered a “prime mover” muscle.
But, when the biceps brachii relaxes, gravity tends to cause the elbow to extend, but this
movement is slowed by a slight contraction or holding by the biceps brachii. In this
situation it would be then fall into the role of being an “antagonist” to the triceps brachii.
In general, muscles are arranged in opposing positions on various parts of the body,,,
flexors/extensors,, abductors/addactors.
Example:
When you clench your fist (fingers) flexors of the fingers and thumb contract---if this
action were unopposed, the wrist would bend over too, and then it would interfere with
the fist clenching..
This could happen as an example:
To involve your fist in a threatening gesture: it is feasible to have the shoulder “fixed” in
a position where the muscles contributing to cause this position would be “fixators”.
All of these movements would fall under the category of “coordination”, which comes
from the cerebellum of the brain.
Classes of levers:
Tendons act as operating pulleys for muscles
First class levers:
lifted.
The fulcrum lies between the power point and the weight to be
Second class levers: The weight is between the fulcrum and the point at which pull is
exerted. A wheelbarrow. Used a lot in the human body.
Calcaneus/gastrocnemius/soleus muscle/Achilles tendon.
Third class levers:
The power is exerted between the fulcrum and the weight. The use
of golf clubs or tennis rackets are examples.
Muscle power at an optimum
The angle of the pull of a muscle on any lever is the factor that considers how strong it is.
The optimum angle is 90 degrees for full strength. At greater or lesser angles than 90
degrees some of the strength is dissipated.
Fiber direction and muscle action
Some muscles have their fiber bundles(bellies) all running parallel to each other, along
the long axis of the muscle.
These muscles can be shortened by about 30% when the muscle is contracted(
biceps/Popey muscle)
Fiber bundles or bellies are called “fasciluli”.
TENDON ATTACHMENTS
Most tendons attach muscle to bones.
When tendons attach to bones, they spread out their ends so they can attach at any
number of places to be stronger in their site of attachment.
This spreading out is called a “pinnate” or feathering of the tissue on the bone.
If the fasciculi all come in from one side of the tendon the muscle is “unipennate.
(Semimembranosus muscle)
If the fasciculi come in from two sides to the central tendon it is “bipennate”
(rectus femoris)
If the fasciculi come in from many tendons they are called “multipennate”
(deltoids)
“radiating” tendon attachments are those types where they spread out over a large surface
area.
Gravity on muscles
The force of gravity has a great influence upon the actions of muscles.
We see it when we try to move from a crawl to an upright walking position.
Fasciae
Defined as the dissectable fibrous connective tissues of the body other than the
specifically organized structures, tendons and ligaments.
Fasciae differ in length and thickness and relative amounts of fat
They are a structural and functional system of the body
3 Categories of Fasciae
1.
2.
3.
Superficial
Deep
Subserous
1.
Superficial:
Found between the skin and deep fascia over the entire body
It has two layers:
Outer layer—usually contains fat cells
Inner layer (deep)---very elastic
The two layers can be separated during dissection and have arteries, veins, lymph, nerves,
and muscles
Superficial Fasciae is found on the external section of the human body
2.
Deep Fascia
Is the most extensive amount of fascia
It holds muscles together
Forms a continuous system of membranes throughout all of the bodies membranes
Found in such tissue that we’ve studied as the periosteum of bones
The membranes vary in thickness and strength
3.
Subserous Fascia
Found between layers of deep fascia and serous membranes lining body cavities
Very thin in most areas
Considered a “visceral” or very thin transparent layer of tissue
Bursae Sacs and Tendon Sheaths
Tendons are attached to bones and muscles usually through fibrous sheaths of tissue
This sheath is lined by a synovial membrane or Bursae sac with fluid in it
The fluid is snyovial fluid
The synovial membrane secretes a small amount of fluid that lubricates the membranes
and allows them to move without friction on bones
Are usually found at the distal ends of limbs
Located under tendons and muscles,,, and between some muscles
Some lie between the skin and a boney structure/knee cap, elbow joint
Classification of
Muscles
This is how areas of muscles are broken down into:
A.
Muscles of the Axial Skeleton
i.
ii.
iii.
iv.
v.
vi.
B.
Muscles of the Upper Extremity
i.
ii.
iii.
iv.
v.
vi.
C.
muscles of the head and neck
muscles of the vertebral column
muscles of the thorax
muscles of the abdomen
muscles of the pelvis
muscles of the perineum
Muscles connecting the axial skeleton and shoulder
Muscles connecting the axial skeleton and arm
Muscles connecting the shoulder and arm
Muscles and facia of the arm
Muscles and fascia of the forearm
Intrinsic muscles of the hands
Muscles of the Lower Extremity
i.
ii.
iii.
iv.
Muscles of the hip
Muscles of the thigh
Muscles of the lower leg
Intrinsic muscles of the foot
Muscles of the Face
These muscles mostly have their origins on bone surfaces and insert on the skin. There
are no tendons of attachment for most all of these muscles.
They are cutaneous muscles and are supplied by the facial nerve for movement
Many of these muscles merge one into another
Muscles of the face
Palpebral
used in gently closing the eyes or blink them
Strong contractions over time cause “crows feet”
Corrugator
frowning or sorrow facial movements
Orbicularis oris
encircles the mouth—kissing motion, smiling, lowering the
Lips in a frown
Procerus
the “pinching” of the nose causing wrinkles between the
Eyes on the bridge of the nose
Buccinator
principal muscle of the cheek, used principally in the mastication
Of food, or holding food in the mouth, compressing air
In the mouth to blow it out (playing an instrument in band)
Frontalis
the expression of surprise on a face
Muscles of the neck/throat area
Temporalis
closes the jaws for chewing or talking
Masseter
clenches the jaw/teeth you can feel it when you clench your
teeth try it
pterygoideus medialis
suspends the angle of the mandible so you don’t get
temporomandibular joint (TMJ)
grinding food between the teeth
side to side movement of the jaw
pterygoideus lateris
moves the jaw during grinding back to the anatomical
position/opposing the medialis muscle group
Tongue
primarilary a muscular organ with mucous membranes
Sternocleidomatoideus (lateral cervical muscle)
Turns the head from side to side
Trapezius
Muscles of the vertebral
Area/Neck to Shoulders