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Muscular System 1
Prof. Abdulameer Al-Nuaimi
E-mail: [email protected]
E. mail: [email protected]
Skeletal muscle tissue
Is so named because the function of most skeletal muscles is
to move bones of the skeleton.
There are a few that attach to structures other than bone,
such as the skin or even other skeletal muscles.
Skeletal muscle tissue is referred to as striated because
alternating light and dark protein bands (striations)
are visible when the tissue is examined under a microscope.
Skeletal muscle tissue works primarily in a voluntary
manner; its activity can be consciously (voluntarily)
controlled.
Functions of Muscular Tissue
1-Producing body movements. Total body movements such
as walking and running, and localized movements such as
grasping a pencil
2-Stabilizing body positions. Skeletal muscle contractions
stabilize joints and help maintain body positions, such as
standing or sitting.
3-Storing and moving substances within the body. Sustained
contractions of ringlike bands of smooth muscles called
sphincters may prevent outflow of the contents of a hollow
organ (like holding urine in the bladder)
4- Producing heat. When muscular tissue contracts, it
produces heat, a process called thermogenesis. Much of that
heat used to maintain normal body temperature. Involuntary
contractions of skeletal muscles, known as shivering, can
dramatically increase the rate of heat production.
Structure of a Skeletal Muscle
Skeletal muscle consists of a muscle belly connected by
tendons attached to the skeleton.
Muscle belly is the reddish or meatlike appearance, it can be
an elongated, thick, rounded mass, a triangular shape, a
thick rectangular mass, or a thin, flat sheet of muscular
tissue.
Tendons: are tough, glistening white dense regular
connective tissue. Tendon attaches the muscle belly to the
bones.
They are minimally vascular, and consist parallel
arrangements of collagen fibres. Their shapes could be
1- long, ropelike structures, 2- flat sheets called aponeuroses
and 3- bands or extensions of connective tissue that are so
short they make the muscle body appear as if it attaches
directly to the bone.
thinner
many
long, ropelike tendons
bands or extensions of
connective tissue that
are so short
flat sheets called aponeuroses
Structure of Skeletal Muscle
If you take one whole muscle and cut through it, you would
find the muscle is covered in a layer of connective muscle
tissue known as the Epimysium.
The Epimysium protects the muscle from friction against other
muscles and bones. It also continues at the end of the muscle
to form (along with other connective tissues) the muscles
tendon.
Looking at the cross section of the muscle you can see bundles
of fibres, known as Fasciculi, which are surrounded by another
connective tissue, called the Perimysium. Each Fascicule
contains anywhere between 10 and 100 muscle fibres
Muscle cell
(
)
Muscle fibre is covered in a fibrous connective tissue, known
as Endomysium which insulates each muscle fibre. Muscle
fibres can range from 10 to 80µ in diameter and may be up to
35cm long.
Beneath the Endomysium and surrounding the muscle fibre is
the Sarcolemma which is the fibres cell membrane and
beneath this is the Sarcoplasm, which is the cells cytoplasm.
This contains Glycogen and Fats for energy and also
Mitochondria which are the cells powerhouses, inside which
the cells energy is produced.
Each muscle fibre itself contains cylindrical organelles known
as Myofibrils. Each muscle fibre contains hundreds to
thousands of Myofibrils.
Myofibril contains bundles of Actin and Myosin proteins
which run the length of the muscle fibre and are important in
muscle contraction.
Surrounding the Myofibril there is a network of tubules and
channels called the Sarcoplasmic Reticulum in which Calcium
is stored which is important in muscle contraction.
Transverse tubules pass inwards from the Sacrolemma
throughout the Myofibril, through which nerve impulses
travel.
Each Myofibril can then be divided into functional repeating
segments called Sarcomeres
Transverse tubule
Sarcoplasmic Reticulum
Myocyte
Skeletal Muscle
The sarcomeric subunits of one myofibril are in nearly
perfect alignment with those of the myofibrils next to it. This
alignment gives rise to certain optical properties which cause
the cell to appear striped or striated.
In smooth muscle cells, this alignment is absent, hence there
are no apparent striations and the cells are called smooth
Myofibril
Myosin
Actin
Myocyte
Striation of skeletal muscle
Muscle action
Lever Systems
A lever is a rigid structure that can move around a fixed point
called a fulcrum, A lever is acted on at two different
points by two different forces: the effort (E), which causes
movement, and the load or resistance, which opposes
movement.
The effort is the force exerted by muscular contraction; the
load is typically the weight of the body part that is moved or
some resistance that the moving body part is trying to
overcome (such as the weight of a book you might be picking
up).
Motion occurs when the effort applied to the bone at the
insertion exceeds the load, an object is lifted.
L = Load
F
F = Fulcrum
E
E = Effort
L
E
L
E
L
F
F
E
E
E
L
L
L
F
F
F
Muscle Function = Lever + Fulcrum + Load
Muscle Attachments And Actions
There are over 600 muscles in the human body
Muscles Attach to Bones At Locations Called Origins and
Insertions They are attached to the membrane covering the
bone called periosteum
Origin: The attachment of a muscle to a bone is called an
origin If that bone remains immobile during contraction of
the muscle.
Insertion: If the muscle attachment is on a bone that moves
during the action, the attachment is called an insertion
Flexion: decreasing the angle between two bones (bending)
Extension: increasing the angle between two bones
(straightening a bend)
Abduction: moving away from the body’s midline.
Adduction: moving toward the body’s midline.
Pronation: rotating the forearm so the palm is facing
backward or down.
Supination: rotating the forearm so the palm is facing forward
or up.
Elevation: moving a body part up.
Depression: moving a body part down.
Protraction: moving a bone forward without changing the
angle.
Retraction: moving a bone backward without changing the
angle.
Inversion: turning the sole of the foot inward.
Eversion: turning the sole of the foot outward.
Dorsiflexion: bringing your foot upward toward your tibia.
Plantar flexion: depressing your foot.
How Skeletal Muscles are Named
Knowing the names of a muscle will give you clues about its
features.
The following features are used in naming the muscles
the pattern of the muscle’s fascicles; the size, shape, action,
number of origins, location of the muscle; the sites of origin
and insertion of the muscle and Orientation of muscle
fascicles relative to the body’s midline
NAME MEANING EXAMPLES
Rectus Parallel to midline: Rectus abdominis
Transverse Perpendicular to midline: Transversus abdominis
Oblique Diagonal to midline :External oblique
SIZE: Relative size of the muscle.
Maximus Largest : Gluteus maximus
Minimus Smallest : Gluteus minimus
Longus Long : Adductor longus
Brevis Short :Adductor brevis
Latissimus Widest : Latissimus dorsi
Longissimus Longest : Longissimus capitis
Magnus Large : Adductor magnus
Major Larger : Pectoralis major
Minor Smaller : Pectoralis minor
Vastus Huge : Vastus lateralis
SHAPE: Relative shape of the muscle.
Deltoid Triangular : Deltoid
Trapezius Trapezoid : Trapezius
Serratus Saw-toothed : Serratus anterior
Rhomboid Diamond-shaped : Rhomboid major
Orbicularis Circular : Orbicularis oculi
Pectinate Comblike : Pectineus
Piriformis Pear-shaped : Piriformis
Platys Flat : Platysma
Quadratus Square, four-sided : Quadratus femoris
Gracilis Slender : Gracilis
ACTION: Principal action of the muscle.
Flexor Decreases a joint angle : Flexor carpi radialis
Extensor Increases a joint angle : Extensor carpi ulnaris
Abductor Moves a bone away from the midline : Abductor
pollicis longus
Adductor Moves a bone closer to the midline : Adductor
longus
Levator Raises or elevates a body part : Levator scapulae
Depressor Lowers or depresses a body part : Depressor labii
inferioris
Supinator Turns palm anteriorly :Supinator
Pronator Turns palm posteriorly : Pronator teres
Sphincter Decreases the size of an opening : External anal
sphincter
Tensor Makes a body part rigid : Tensor fasciae latae
Rotator Rotates a bone around its longitudinal axis :Rotatore
NUMBER OF ORIGINS: Number of tendons of origin.
Biceps Two origins : Biceps brachii
Triceps Three origins : Triceps brachii
Quadriceps Four origins :Quadriceps femoris
LOCATION: Structure near which a muscle is found. Example:
Temporalis, a muscle near the temporal bone.
ORIGIN AND INSERTION: Sites where muscle originates and
inserts. Example:
Sternocleidomastoid, originating on the sternum and
clavicle and Inserting on mastoid process of temporal bone
Thank you