Download Muscles and Muscle Tissue

Skeletal Muscle
Skeletal Muscle Anatomy
Figure 12-3a-2: ANATOMY SUMMARY: Skeletal Muscle
Figure 12-4: T-tubules and the sarcoplasmic reticulum
Myofibrils: Site of Contraction
Figure 12-3c-f: ANATOMY SUMMARY: Skeletal Muscle
Smooth muscle fascicles!
Smooth Muscle
• The smooth muscle
looks smooth and
works
automatically. It can
be found in the
intestines, lungs, and
bladder.
Cardiac Muscle
Cardiac muscle is located only in the heart. It has a
striated appearance and is involuntarily
controlled. Cardiac muscle also has a feature that
is foreign to the other muscle types: intercalated
discs.
• This muscle is striped
and branched (like a
tree!) It keeps your
heart beating
automatically. Wher
e is it found?
Intercalated Disc
Skeletal Muscles:
Muscular Machines
VII. Interactions of Skeletal Muscles in
the Body
A. Attachment Points (could be one or multiple):
1. Origin- point of attachment on bone; does not move
during contraction
2. Insertion- point of attachment; does move during
contraction
Muscles work in groups- some contract
and some relax and some assist.
• Four functional classifications
–
–
–
–
Prime Movers
Antagonist
Synergist
Fixators
Prime Mover
• Agonist
• Provides the major force for producing
a specific movement
• For elbow flexion: biceps brachii
Antagonists
• Muscles that oppose, or reverse, a particular movement
• When the prime mover is active, the antagonist muscles are
often stretched and may be relaxed
– Ex. Triceps brachii- rest during flex
• Prime movers and its antagonist are located on opposite sides
of the joints
• Flexion of the arm by the biceps brachii muscle of the arm is
antagonized by the triceps brachii, the prime mover for
extending the forearm
Synergists
• Help the prime movers by
– Adding a little extra force
– Reducing undesirable or unnecessary movements that
might occur
– Ex. Brachioradialis- assists in flex
They act as stabilizers:
When muscles cross two or more joints it’s contraction causes
movement of all the spanned joints so these muscles act to
stabilize the joints
Fixators
•
Synergist that immobilize a bone
–
–
Fixator- joint stabilizers; maintain posture/balance
Ex. Deltoid- maintains shoulder joint stability
–
Scapula is held to the axial skeleton only by muscles
and the scapula is freely moveable. The fixator
muscles can immobilize the scapula so only desired
movements occur at the shoulder joint
Most skeletal muscles have names
that describe some feature of the
muscle.
Often several criteria are combined
into one name.
Associating the muscle's
characteristics with its name will help
you learn and remember them. The
following are some terms relating to
muscle features that are used in
naming muscles.
1. Location:
“brachii” means arm
Ex. Brachialis
in upper arm
1. Location:
–pectoralis (chest)
–gluteus (buttock or rump)
–brachii (arm)
–supra- (above)
–infra- (below)
–sub- (under or beneath)
–lateralis (lateral).
2. Function- direction of movement
Ex. Adductor longus in thigh moves leg
towards median
3. Shape- “delta” means triangle
Ex. Deltoid on shoulder is triangular.
• deltoid (triangular)
• rhomboid (like a rhombus with equal and
parallel sides)
• latissimus (wide)
• teres (round)
• trapezius (like a trapezoid, a four-sided
figure with two sides parallel).
4. Direction of fibers- “rectus” means straight
Ex. Rectus abdominis muscle runs straight up and
down on abdomen
•
•
•
•
rectus (straight)
transverse (across)
oblique (diagonally)
orbicularis (circular)
5. Number of origins- “cep” means head
Ex. Biceps brachii has two heads or attachments to
the shoulder
• biceps (two heads)
• triceps (three heads)
• quadriceps (four heads)
6. Size:
• vastus (huge)
• maximus (large)
• longus (long)
• minimus (small)
• brevis (short)
Muscle Mechanics
For anatomical purposes muscles are classified
by their structure rather than their composition.
Muscle types can be grouped into one of four classes based
on the orientation of the fasciculi:
Circular
Convergent
Parallel
Pennate
Arrangement of Fascicles-determine range of motion & power
1. Circular- concentric rings
Ex. Orbicularis oris
2. Convergent- broad origin  single insertion
Ex. Pectoralis Major
3. Parallel- strap-like
Ex. Sartorius
4. Unipennate- insert into 1 side of tendon
Ex. Extensor digitorum longus
5. Bipennate- insert into tendon from 2 sides
Ex. Rectus femoris
6. Fusiform- spindle-shaped Ex. Biceps brachii
7. Multipennate- many feathers situated side by side
Ex. Deltoid
Circular Muscles
• In a circular muscle, or sphincter, the
fibers are concentrically arranged around
an opening or a recess. When the
muscle contracts, the diameter of the
opening decreases. Circular muscles
guard entrances and exits of internal
passageways such as the digestive and
urinary tracts. An example is the
orbicularis oris muscle of the mouth
Convergent Muscle
• In a convergent muscle, the muscle fibers
are spread over a broad area, but all the fibers
converge at one common attachment site.
They may pull on a tendon, an aponeurosis
(tendinous sheet), or a slender band of
collagen fibers known as a raphe.
Parallel Muscles
• In a parallel muscle, the fascicles are parallel to the long axis of
the muscle. Most of the skeletal muscles in the body are parallel
muscles. Some are flat bands with broad attachments (aponeuroses) at
each end; others are plump and cylindrical with tendons at one or
both ends. In the latter case, the muscle is spindle-shaped , with a
central body, also known as the belly, or gaster. The biceps brachii
muscle of the arm is a parallel muscle with a central body. When a
parallel muscle contracts, it gets shorter and larger in diameter. You
can see the bulge of the contracting biceps brachii on the anterior
surface of your arm when you flex your elbow.
Pennate
• In a pennate muscle, the fascicles form a common angle with the
tendon. They are short and attach obliquely. Because the muscle
cells pull at an angle, contracting pennate muscles do not move their
tendons as far as parallel muscles do. But a pennate muscle contains
more muscle fibers--and, as a result, produces more tension--than
does a parallel muscle of the same size.
• If all the muscle fibers are on the same side of the tendon, the
pennate muscle is unipennate. The extensor digitorum muscle, a forearm
muscle that extends the finger joints, is unipennate
Bipennate Muscle
• More commonly, a
pennate muscle has fibers
on both sides of the
tendon. Such a muscle is
called bipennate. The rectus
femoris muscle, a prominent
muscle that extends the
knee, is bipennate
Multipennate
• If the tendon branches
within a pennate muscle,
the muscle is said to be
multipennate. The
triangular deltoid muscle of
the shoulder is
multipennate
Range of Power and Motion
• A skeletal muscle cell can contract until it has shortened by
roughly 30 percent.
• Because the fibers in a parallel muscle are parallel to the long
axis of the muscle, when the fibers contract together, the
entire muscle shortens by the same amount.
• If the muscle is 10 cm long, the end of the tendon will move
3 cm when the muscle contracts.
• The tension developed during this contraction depends on
the total number of myofibrils the muscle contains.