HLTAP301A ANATOMY & PHYSIOLOGY
LECTURE 5 - THE MUSCULAR SYSTEM
Muscle tissue is one of the four primary types of tissue found within the body
and it is comprised mostly of muscle cells that are highly specialized for
contraction. Without these muscle tissues, nothing in the body would move,
and no body movement could occur.
Muscles perform 4 major functions - Movement, maintenance of posture,
stabilization of joints and generation of body heat:
Movement – All movements of the human body are a result of muscle
contraction
Maintenance of posture – skeletal muscles allow us to maintain body posture
despite the never ending downward pull of gravity
Stabilization of joints – as the skeletal muscles pull on bones to cause
movements they also stabilize the joints of the skeleton
Generating heat – muscular activity generated body heat. Skeletal muscle
accounts for at least 40% of body mass so is the muscle type most
responsible for heat generation.
There are three types of muscle tissue: cardiac muscle, smooth muscle and
skeletal muscle.
Cardiac Muscle is found only in one place – the heart. The heart acts as a
pump, propelling blood into the bloody vessels and to all tissues of the body.
Cardiac muscle is striated (striations are the appearance of stripes in the
muscle tissue), involuntary and the cells are uninucleate (having a single
nucleus). They are structured as branching cells that are ‘chained’ together at
junctions called intercalated disks. These disks allow ions to pass freely from
cell to cell, allowing rapid conduction of electrical impulses across the heart.
Smooth Muscle has no striations and is involuntary, meaning that we cannot
consciously control it. Smooth muscle is found in the walls of the hollow
visceral organs, such as the stomach and urinary bladder as well as the small
intestine. The muscle fibers are spindle shaped and have only one nucleus.
They are often arranged in sheets or layers, usually one running circularly and
the other longitudinally – as they contract, they change the size and shape of
the organ. For example, food is moved through the small intestine by the
contraction of these two layers of smooth muscle tissue – this movement is
known as peristalsis.
Skeletal muscles are organs comprised of muscle tissue, connective tissues,
nerves, and blood vessels. Skeletal muscles are directly or indirectly attached
to the bones of the skeleton or in some facial muscles, directly to the skin.
The muscle fibers are cigar-shaped and are striated.
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They are multinucleate cells and are the largest of the muscle fiber types (ie.
look at the quadriceps muscles).
They are the only muscle type subject to conscious control and are known as
voluntary muscle, although skeletal muscles are often activated by reflexes as
well. Skeletal muscles are soft and surprisingly fragile yet can exert
tremendous power, because of their structure - thousands of fibers are
bundled together by connective tissue which provides strength and support to
the muscle as a whole.
Muscles cells have special functional properties
1. Irritability – the ability to receive and respond to a stimulus
2. Contractility – the ability to shorten when an adequate stimulus is received.
Muscles can only pull, they never push and they often work in pairs or teams
to bring about a variety of body movements. Skeletal muscles must be
stimulated by nerve impulses to contract.
Muscles make common types of movements - in this side you can see flexion,
which commonly closes the joint; the opposite movement, extension which
opens the joint and hyperextension where the extension is beyond 180
degrees. Rotation is the movement of a bone around its longitudinal axis, and
this describes the movement of shaking your head 'no' when the atlas (C1)
moves around the dens of the axis (C2).
Abduction is the movement of a limb away from the midline of the body
whereas adduction is the opposite, moving the limb towards the midline.
Circumduction is commonly seen in the ball and socket joint of the shoulder
where the proximal end of the limb remains stationary and the distal end
moves in a circle. The up and down movements of the foot are given special
names - plantar flexion, when you point your toes and dorsiflexion when you
pull your toes towards your knees.
Inversion of the foot turns the sole medially and eversion turns the sole
laterally. Pronation occurs when the forearm is rolled medially so that the
palm of the hand faces posteriorly. The opposing movement, supination, rolls
the forearm laterally so that the palm faces anteriorly.
Opposition is a movement of moving the thumb to touch the tips of the other
fingers on the same hand. This action is unique to the human hand, allowing
fine motor movements.
Skeletal muscles are often named in relation to their location, their shape,
their action, their size or the direction of the muscle fibers. For example, the
rectus abdominus or obliques are so named because of the direction of the
muscle fibers, whereas the gluteus maximus or minimum are named because
of their relative size. The biceps, triceps and quadriceps indicate the number
of points of origin (that is, bi meaning two and ceps meaning heads or
origins).
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The deltoid, meaning triangular is named because of it’s shape and the
adductors, flexors and extensors indicate the action these muscles perform.
You do not need to know the names of all of the muscles on these two slides.
Your facilitator will post the list of muscles you must know on the My.TAFE
platform. If you are unsure of where to find this information, please ask your
facilitator.
Tendons usually attach skeletal muscles to bones. Where they contact the
bone, the collagen fibers extend into the bone matrix, providing a firm
attachment. As a result, any contraction of the muscle will exert a pull on the
attached bone (or bones). Tendons not only anchor muscles, but also cross
rough bony projections that would otherwise tear the more fragile muscle
tissue and because they are relatively small in size, more tendons can pass
over a joint.
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