muscle system Flashcards
(12 cards)
muscle system
Movement: Muscles contract to move bones and body parts. This includes both voluntary movements like walking and involuntary ones like blinking.
Heat Generation: When muscles contract, they produce heat as a byproduct, helping to maintain body temperature.
Joint Stabilization: Muscles help stabilize joints by maintaining tension and keeping bones properly aligned during movement.
How muscle contraction works:
Muscles are made up of fibers that contain proteins like actin and myosin. During contraction:
These proteins slide past each other, which shortens the muscle.
The more overlap between actin and myosin, the stronger the contraction.
When the muscle relaxes, the overlap decreases and the muscle returns to its original length.
Internal Movement:
Breathing: Muscles like the diaphragm and intercostal muscles help move air in and out of the lungs.
Digesting Food: Smooth muscles in the digestive tract push food along through a process called peristalsis.
Circulating Blood: Cardiac muscle pumps blood through the heart, and skeletal muscle contractions help push blood through veins.
the background of the name of muscle
Because contracting muscles look like mice scurrying beneath the skin, a scientist long ago dubbed them muscles, from the Latin word mus, meaning “little mouse.” Indeed, the rippling muscles of professional athletes often come to mind when we hear the word muscle. But muscle is also the dominant tissue in the heart and in the walls of other hollow organs of the body such as the intestines and blood vessels, and it makes up nearly half the body’s mass.
The essential function of muscle is to contract, or shorten—a unique characteristic that sets it apart from other body tissues. As a result of this ability, muscles are responsible for all body movements and can be viewed as the “machines” of the body.
how many types of mucsles are there
There are three types of muscle tissue—skeletal, smooth, and cardiac (Table 6.1). These differ in their cell structure, body location, and how they are stimulated to contract. But before we explore their differences, let’s look at how they are similar.
the similarieties of the muscles
First, skeletal and smooth muscle cells are elongated. For this reason, these types of muscle cells (but not cardiac muscle cells) are called muscle fibers. Second, the ability of muscle to shorten, or contract, depends on two types of myofilaments, the muscle cell equivalents of the microfilaments of the cytoskeleton (studied in Chapter 3). A third similarity has to do with terminology. Whenever you see the prefixes myo- or mys- (“muscle”) or sarco- (“flesh”), you will know that muscle is being referred to. For example, in muscle cells, the cytoplasm is called sarcoplasm (sar′ko-plaz″um).
Skeletal muscle fibers
Skeletal muscle fibers (the cells that make up skeletal muscles) are grouped together to form organs called skeletal muscles.
➤ These muscles are attached to your bones and help you move.
These muscles cover the skeleton, so they shape your body — giving it smooth curves or contours.
Skeletal muscle fibers (the actual cells) are:
Very large
Shaped like cigars (long and rounded at the ends)
Multinucleate (they have more than one nucleus per cell)
The largest muscle cells in your body
Some are up to 30 cm (about 1 foot) long!
In big, strong muscles like the ones near your hips (called antigravity muscles, because they help you stand up straight), the muscle fibers are so big and thick that you can actually see them without a microscope.
Skeletal muscle is also known as striated muscle (because its fibers have obvious stripes) and as voluntary muscle (because it is the only muscle type subject to conscious control). However, it is important to recognize that skeletal muscles can be activated by reflexes (without our “willed command”) as well. Skeletal muscle tissue can contract rapidly and with great force, but it tires easily and must rest after short periods of activity. When you think of skeletal muscle tissue, the key words to remember are skeletal, striated, and voluntary.
Skeletal muscle fibers are soft and surprisingly fragile. Yet skeletal muscles can exert tremendous power—indeed, the force they generate while lifting a weight is often much greater than that required to lift the weight. The reason they are not ripped apart as they exert force is that connective tissue bundles thousands of their fibers together, which strengthens and supports the muscle as a whole (Figure 6.1).
Endomysium
A thin layer that wraps each individual muscle fiber (cell).
Perimysium
A thicker layer that wraps groups of muscle fibers into bundles called fascicles.
Epimysium
A tough outer layer that wraps around the entire muscle, holding all the fascicles together.
Tendon or Aponeurosis
The ends of the epimysium can extend beyond the muscle and form:
A tendon (strong cord)
Or an aponeurosis (flat sheet)
➤ These structures attach the muscle to bone, cartilage, or other connective tissues.
Endo- = inside
Peri- = middle layer / surrounding
Epi- = outermost
Tendons help anchor muscles to bones. They’re strong and small, which means they can fit around joints without taking up too much space. Because they’re made of tough collagen, they can handle rubbing against bones and won’t tear easily. This allows muscles to move bones smoothly and helps us move better.
smooth muscle
Smooth muscle has no striations and is involuntary, which means that we cannot consciously control it. Found mainly in the walls of hollow (tubelike) organs such as the stomach, urinary bladder, and respiratory passages, smooth muscle propels substances along a pathway. Think of smooth muscle as visceral, nonstriated, and involuntary.
What this paragraph is saying about smooth muscle:
Shape and Structure:
Spindle-shaped = thicker in the middle and tapered at the ends (like a leaf or stretched-out football).
Uninucleate = each cell has one nucleus.
Surrounded by a thin layer of connective tissue called endomysium.
How it’s arranged:
Found in layers — usually two:
One layer wraps around the organ (circular).
The other runs along the length of the organ (longitudinal).
These two layers work together: as one contracts, the other relaxes — this squeezes and moves stuff through the organ.
Function:
This kind of muscle movement helps with “housekeeping” tasks in the body:
Moving food through the digestive system.
Emptying the bladder and bowels.
These are automatic (involuntary) processes.
Speed and Strength:
Smooth muscle contracts slowly, but it can keep going for a long time.
Compared to skeletal muscle:
Skeletal muscle = like a sprinter (fast but tires quickly).
Smooth muscle = like a marathoner (slow but steady and long-lasting).
uninucleate means one nucleous
Cardiac Muscle
Cardiac muscle is found in only one place in the body—the heart, where it forms the bulk of the heart walls. The heart serves as a pump, propelling blood through blood vessels to all body tissues. Like skeletal muscle, cardiac muscle is striated, and like smooth muscle, it is uninucleate and under involuntary control. Important key words for this muscle type are cardiac, striated, and involuntary.
Cardiac Muscle – Key Points:
Endomysium Support:
Each cardiac muscle cell is surrounded by a small amount of endomysium, a thin connective tissue layer (just like in smooth and skeletal muscle).
Arrangement:
The cardiac muscle fibers are arranged in spiral or figure 8-shaped bundles.
This pattern helps the heart squeeze blood efficiently through the chambers and out into the arteries.
Cell Shape & Connection:
Cardiac muscle cells are branching — meaning they split and connect with other cells.
They are joined by intercalated discs, which are special structures that include gap junctions.
These junctions allow electrical signals to pass quickly from cell to cell.
Function:
This setup allows the heart to contract as one unit, in a coordinated and rhythmic way — critical for pumping blood.
Cardiac muscle usually contracts at a fairly steady rate set by the heart’s “in-house” pacemaker. However, the nervous system can also stimulate the heart to shift into “high gear” for short periods, as when you run to catch a bus.
skeletal muscle and movement
Skeletal muscles are responsible for our body’s mobility, including all locomotion (walking, swimming, and cross-country skiing, for instance) and manipulating things with your agile upper limbs. They enable us to respond quickly to changes in the external environment. For example, their speed and power enable us to jump out of the way of a runaway car and then follow its flight with our eyes. They also allow us to express our emotions with the silent language of facial expressions.
They are distinct from the smooth muscle of blood vessel walls and cardiac muscle of the heart, which work together to circulate blood and maintain blood pressure, and the smooth muscle of other hollow organs, which forces fluids (urine, bile) and other substances (food, a baby) through internal body channels.
Maintain Posture and Body Position
We are rarely aware of the workings of the skeletal muscles that maintain body posture. Yet they function almost continuously, making one tiny adjustment after another so that we maintain an erect or seated posture, even when we slouch, despite the never-ending downward pull of gravity.
Stabilize Joints
As skeletal muscles pull on bones to cause movements, they also stabilize the joints of the skeleton. Muscles and tendons are extremely important in reinforcing and stabilizing joints that have poorly articulating surfaces, such as the shoulder and knee joints. In fact, physical therapy for knee injuries includes exercise to strengthen thigh muscles because they support the knee.
Generate Heat
Muscle activity generates body heat as a by-product of contraction. As ATP is used to power muscle contraction, nearly three-quarters of its energy escapes as heat. This heat is vital in maintaining normal body temperature. Skeletal muscle accounts for at least 40 percent of body mass, so it is the muscle type most responsible for generating heat.
Additional Function
Additional Functions
Muscles perform other important functions as well. Smooth muscles form valves that regulate the passage of substances through internal body openings, dilate and constrict the pupils of our eyes, and make up the arrector pili muscles that cause our hairs to stand on end. Skeletal muscles form valves that are under voluntary control, and they enclose and protect fragile internal organs.
