The Muscular SystemChapter 6

There are three types of muscle tissue (named above)

Muscle tissues differ in their cell structure, body location, and how they are stimulated to contract

Some ways they are the same 1. Skeletal and smooth muscle are both

elongated…these types of muscle cells are called muscle fibers.

2. The ability of muscle to shorten, or contract, depends on the types of myofilaments

3. Terminology: When you see prefixes myo and mys (“muscle”) and sarco (“flesh”), you will know that muscle is being referred to…for example, in muscle cells the cytoplasm is called sarcoplasm.

Comparison of Skeletal, Cardiac, and Smooth Muscles

Body Location: Attached to bone, or for some facial muscles, to skin

Cell shape and appearance: Single, very long, cylindrical, multinucleate cells with

very obvious striations Regulation of contraction:

Voluntary; via nervous system controls Speed of contraction:

Slow to fast Rhythmic contraction:

No

Skeletal(refer to page 179)

Body Location: Walls of the heart

Cell shape and appearance: Branching chains of cells; uninucleate, striations;

intercalated discs Regulation of contraction:

Involuntary; the heart has a pacemaker; also nervous system controls; hormones

Speed of contraction: Slow

Rhythmic contraction: Yes

Cardiac(refer to page 179)

Body Location: Mostly in walls of hollow visceral organs (other than the

heart) like the stomach, bladder, and respiratory passages Cell shape and appearance:

Single, fusiform, uninucleate; no striations Regulation of contraction:

Involuntary; nervous system controls; hormones, chemicals, stretch

Speed of contraction: Very Slow

Rhythmic contraction: Yes, in some

Smooth(refer to page 179 & 181)

Muscle plays four important roles in the body: 1. Produces Movement 2. Maintains posture 3. Stabilizes joints 4. Generates heat

(heat is a by-product of muscle activity)

Muscle Functions

Every one of our 600-odd skeletal muscles is attached to bone, or to other connective tissue structures, at no less than 2 points.

One of these points, the origin, is attached to the immovable or less movable bone.

The insertion is attached to the movable bone, and when the muscle contracts, the insertion moves toward the origin.

Some muscles have interchangeable origins and insertions.

Generally speaking, body movement occurs when muscles contract across joints.

Body Movement

Flexion: Decreases angle of joint and brings bones closer together…typical of hinge joints (bending of knee/elbow or bending forward at hip)

Extension: Opposite of flexion...increases the angle between two bones or parts of body (straightening knee or elbow). If extension is greater than 180 degrees it is hyperextension….

Rotation: Movement of a bone around its longitudinal axis…common of ball and socket joints (shaking your head no)

Abduction: Moving a limb away from the midline, or median plane, of the body…term also applies to the fanning movement of the fingers or toes when they are spread apart.

Adduction: The opposite of abduction…movement of a limb toward the body midline.

Circumduction: Combination of flexion, extension, abduction, and adduction…commonly seen in ball and socket joints such as the shoulder….the limb as a whole outlines a cone.

Common Types of Body Movements(refer to pages 194-195)

Dorsiflexion and Plantar flexion: Up and down movements of the foot at the ankle…lifting the foot so that its superior surface approaches the shin is called dorsiflexion and pointing the toes is called plantar flexion

Inversion and Eversion: Also have to do with the foot…to turn the sole medially is to invert and turning the sole laterally is called eversion.

Supination and Pronation: Supination (“soup”) occurs when the forearm rotates laterally so that your palm faces anteriorly (the radius and ulna are parallel) and Pronation occurs when the forearm rotates medially and the palm faces posteriorly (brings the radius across the ulna so that the 2 bones form an X).

Opposition: In the palm of the hand, the saddle joint between metacarpal 1 and the carpals allows opposition of the thumb. This is the action by which you move your thumb to touch the tips of the other fingers on the same hand…makes the human hand very unique and very good at grasping and manipulating things!

Special MovementsCertain movements do not fit into any of the previous categories and only occur at a few joints.

(refer to pages 194-195)

Muscles can’t push…they can only pull as they contract…so most often body movements are the result of the activity of 2 or more muscles acting together or against each other.

Muscles are arrange in such a way that whatever one muscle (or group of muscles) can do, other muscles can reverse…pretty neat.

Because of this, muscles are able to bring about an immense variety of movements!

Muscles…Based on Functions in the body…

Prime mover: the muscle that has major responsibility for causing a particular movement.

Antagonists: muscles that oppose or reverse a movement. When a prime mover is active, its antagonist is stretched and relaxed. Antagonist

can be prime movers in their own right…example…the biceps of the arm is antagonized by the triceps (but roles reverse in opposite movement!)

Synergists: “syn”=together “erg”=work…help prime movers by producing the same movement or by reducing undesirable movements. When a muscle crosses 2 or more joints, its contraction will cause movement in all

the joints crossed unless synergists are there to stabilize them…the finger-flexor muscles cross both the wrist and the finger joints…you can make a fist w/out bending your wrist because synergist muscles stabilize the wrist joints and allow the prime mover to act on the finger joints.

Fixators: specialized synergists. They hold a bone still or stabilize the origin of a prime mover so that all the tension

can be used to move the insertion bone. The postural muscles that stabilize the vertebral column are fixators.

Muscles…Based on Functions in the body…

Developmental Aspects of the Muscular SystemRead page 214 to yourself (you may skip the Homeostatic Imbalance portions…we will be

discussing these as a class)

A group of inherited muscle-destroying diseases that affect specific muscle groups. The muscles enlarge due to fat and connective tissue deposit, but the muscle fibers degenerate and atrophy (atrophy: decrease in size or wasting away of a body part or tissue)…most common and serious form is

Duchenne’s muscular dystrophy: Expressed almost exclusively in males Usually diagnosed between the ages of 2 & 6 Active, normal appearing children become clumsy and begin to fall frequently as

their muscles weaken The disease progresses from the extremities upward, finally affecting the head and

chest muscles Most victims must use wheelchairs by the age of 12 and generally do not live

beyond young adulthood Although the cause of muscular dystrophy has been pinned down (the diseased

muscle fibers lack a protein: dystrophin that helps maintain the sarcolemma), a cure is still elusive….

Disorders of the Muscular System

Muscular Dystrophy

1. Cramps2. Fibromyalgia3. Fibrositis4. Fibrosis5. Denervation atrophy6. Muscular atrophy 7. Spastic Paralysis8. Flaccid Paralysis9. Myasthenia gravis10. Dermatomyositis11. Compartment Syndrome12. Fibrodysplasia Ossificans Progressiva13. Rhabdomyolysis14. Chronic fatigue syndrome15. Polymyositis16. Myopathy17. Multiple sclerosis18. Muscle strain

Disorders of the Muscular SystemPick 3 topics from the list below to learn more about…

including cause, symptoms, and treatment if any

You will be graded on this

assignment (not for bonus)

Due…