Anatomy Chpt. 6h Study Guide Jenna Kozlowski
Terms in this set (60)
Name the three types of muscles
Skeletal, cardiac, and smooth
What are two other ways skeletal muscles are 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)
Starting with a muscle fiber, describe how skeletal muscles are bundled.
Each muscle fiber is enclosed in a delicate connective tissue sheath called endomysium. Several sheathed muscle fibers are then wrapped by a coarser fibrous membrane called perimysium to form a bundle of fibers called a fascicle. Many fascicles are bound together by an even tougher overcoat of connective tissue called an epimysium, which covers the entire muscle. The epimysium blend either into strong cordlike tendons or into sheetlike aponeuroses which attach muscle indirectly to bones, cartilages, or connective coverings
Describe a 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 visceral organs such as the stomach, urinary bladder, and respiratory passages, smooth muscle propels substances along a definite tract, or pathway within the body. Smooth muscle cells are spindle shaped, have a single nucleus, and are surrounded by scant endomysium
Where are cardiac muscles found?
The heart, where it forms the bulk of the heart walls
Describe a cardiac muscle.
Cardiac muscle is striated, and like smooth muscle in that it is involuntary and cannot be consciously controlled by most of us. The cardiac cells are cushioned by small amounts of soft connective tissue (endomysium) and are arranged in spiral or figure 8-shaped bundles. Cardiac muscle fibers are branching cells joined by special junctions called intercalated discs
What is the main function of all muscles?
Producing movement (contraction, or shortening)
What functions do skeletal muscle perform that the other muscles do not?
Maintains posture, stabilizes joints, and generates heat
What is the cell plasma membrane of a skeletal muscle called?
What are myofibrils?
The nuclei area pushed aside by long ribbon like organelles, the myofibrils which nearly fill the cytoplasm.
What are I and A bands?
Alternating light (I) and dark (A) bands along the length of the perfectly aligned myofibrils give the muscle cell as a whole its striped appearance.
Describe the structure of I and A bands.
The light I band has a midline interruption, a darker area called the Z disc, and the dark A band has a lighter central area called the H zone. The M one in the center of the H zone contains tiny protein rods that hold adjacent thick filaments together.
What are sacromeres?
The myofibrils are actually chains of tiny contractile sacromeres which are aligned end to end like boxcars in a train along the length of the myofibrils
Describe the different myofilaments.
The larger thick filaments, also called myosin filaments, are made mostly of bundled molecules of the protein myosin, but they also contain ATPase enzymes, which split ATP to generate the power for muscle contraction. The thick filaments extend the entire length of the Dark A band. The midparts of the thick filaments are smooth, but their ends are studded with small projections. These projections, or myosin heads, are called cross bridges when they link thick and thin filaments together during contraction. The thin filaments are composed of contractile protein called actin, plus some regulatory proteins that play a role in allowing (or preventing) binding of myosin heads to actin. The thin filaments, also called actin filaments, are anchored to the Z disc (a disclike membrane). The light I ban includes parts of two adjacent sacromeres and contains only the thin filaments. Although they overlap the ends of the thick filaments, the thin filaments do not extend into the middle of a relaxed sacromeres, and thus the central region (H zone) looks a bit lighter. When contraction occurs and the actin-containing filaments slide toward each other into the center of the sacromeres, these light zones disappear becuase the actin and myosin filaments are completely overlapped.
What does the sacroplasmic reticulum do?
It is a specialized smooth endoplasmic reticulum; the interconnecting tubules and sacs of the SR surround each and every myofibril just as the sleeve of a loosely crocheted sweater; the major role is to store calcium and to release it on demand when the muscle fiber is stimulated to contract
What is a motor unit?
One neuron and all the skeletal muscle cels it stimulates
The long nerve extension is called what?
Nerve fiber or Axon
Where is the neuromuscular junction found?
When a long thread like extension of the neuron, called the nerve fiber or axon, reaches the muscle, it branches into a number of axon terminals, each of which forms junctions with the sacrolemma of a different muscle cell. These junctions called neuromuscular junctions, contain vesicles filled with a chemical referred to as a neurotransmitter.
What is a neurotransmitter?
Neuromuscular junctions contain vesicles with a chemical referred to as a neurotransmitter.
What is the neurotransmitter that stimulates the skeletal muscle?
The neurotransmitter that stimulates skeletal muscle cells is acetylcholine or ACh.
Explain the process of a single muscle contraction in a skeletal muscle.
1. Action potential reaches axon terminal of motor neuron.
2. Calcium (Ca2+) channels open, and Ca2+ enters the axon terminal
3. Ca2+ entry causes some synaptic vesicles to release their contents (acetylcholine, a neurotransmitter) by exocytosis.
4. Acetylcholine diffuses across the synaptic cleft and binds to receptors in the sacrolemma
5. ACh binds and channels open that allow simultaneous passage of Na+ into the muscle fiber and K+ out of the muscle fiber. More Na+ ions enter than K+ ions leave, producing a local change in the electrical conditions of the membrane (depolarization). This eventually leads to an action potential.
6. The enzyme acetylcholinesterase breaks down ACh in the synaptic cleft, ending the process.
What is an action potential?
This "upset" generates an electrical current called an action potential. Once begun, the action potential is unstoppable it travels over the entire surface of the sacrolemma, conducting the electrical impulse from one end of the cell to the other. The result is contraction of muscle.
Explain the sliding filament theory.
Ca2+ ions trigger myosin cross bridges to attach to actin, initiating filament sliding where the myofilaments slide past each other.
How does a contraction of a muscle as a whole differ from a contraction of a single skeletal muscle?
Muscle cells respond to the "all or none" law where a muscle cell will contract fully or not at all
Whole muscle react to stimuli with greased responses, or different degree of shortening
Graded muscle contractions can be produced 2 ways
1. By changing the frequency of muscle stimulation
2. By changing the number of muscle cells being stimulated at one time
What are muscle twitches?
Muscle twitches are single, brief, jerky movements
When a muscle contraction is completely smooth and sustained the muscle is said to be what?
Fused or complete, tetanus
How do muscles respond to stronger stimuli?
Depending if only a few cells or all the muscle cells are stimulated determines how forceful a muscle contraction an be
How do muscles get their energy for muscle contractions?
Muscles store very limited supplies of ATP--only a few seconds worth, just enough to get you going. Because ATP is the only energy source that can be used directly to power muscle activity, ATP must be regenerated continuously if contraction is to continue
Working muscles use three pathways for ATP regeneration
1. Direct phosphorylation of ADP by creatine phosphate
2. Aerobic respiration
3. Anaerobic glycolysis and lactic acid formation
What is muscle fatigue?
Muscle fatigue occurs when we exercise our muscles strenuously for a long time; a muscle is fatigue when it is unable to contract even though it is still being stimulated
When does oxygen deficiency happen?
Muscle fatigue is believe to result from the oxygen deficit that occurs during prolonged muscle activity; when a person is not able to take in oxygen fast enough to keep the muscle supplied with all the oxygen they need when they are working vigorously
Describe the two types of muscle contractions.
An event that all muscle have in common is that tension develops in the muscle as actin and myosin myofilaments interact and the myosin cross bridges attempt to slide the thin actin filaments past the thick myosin filaments
In isotonic contractions, the myofilaments are successful in their sliding movements, the muscle shortens, and movement occurs
Isometric contractions are contractions in which the muscle do not shorten
The myosin myofilaments are trying to slide, but the muscle is pitted against some more or less immovable object, causing tension to increase
What is muscle tone?
Their contraction is not visible, but, as a result of it, their muscle remains firm, healthy, and constantly ready for action. This state of continuous partial contractions is called muscle tone. Muscle tone is the result of different motor units, which are scattered through the muscle, being stimulated by the nervous system in a systematic way.
Describe a muscle as flaccid and undergoing atrophy.
If the nerve supply to a muscle is destroyed the muscle is no longer stimulated in this manner, and it loses tone and becomes paralyzed. Soon after, it becomes flaccid or soft and flabby, and begins to atrophy (waste away)
What are the two types of exercises that can affect muscles?
Aerobic (endurance) exercise and resistance (isometric) exercise
If you want bigger muscles what kind of exercise should you do?
Resistance (isometric) exercise results in bulging muscles
If you want to build endurance what kind of exercise should you do?
Aerobic (endurance) exercise results in stronger, more flexible muscles with greater resistance to fatigue
What is the origin of a muscle?
The origin is attached to the immovable or less movable bone
What is the insertion of a muscle?
The insertion is attached to the movable bone, and when the muscle contracts, the insertion moves toward the origin
Explain the 6 different movements of muscles.
1. Flexion: movement of the sagittal plane that decreases the angle of the joint and brings two bones closer together. Flexion is typically a hinge joint
2. Extension: the opposite of flexion, so it increases the angle between two bones or parts of the body. If extension is greater than 180 degrees it is hyperextension
3. Rotation: movement of a bone around its longitudinal axis
4. Abduction: moving a limb away from the midline of the body
5. Adduction: the opposite of abduction, so it si the movement of a limb toward the body midline
6. Circumduction: combination of flexion, extension, abduction, and adduction, the proximal end of the limb is stationary, and its distal end moves in a circle
Explain the special movements of muscles.
1. Dorsiflexion and plantar flexion: dorsiflexion is lifting the foot so that you are standing on your heels. Plantar flexion is pointing your toes
2. Inversion and version: inversion turns the sole medially, while eversion turning the sole laterally
3. Supination and pronation: supination occurs when eh forearm rotates laterally so that the palm faces anteriorly. Pronation occurs when the forearm rotates medially so that the palm faces posteriorly
4. Opposition: when you move your thumb to touch the tips of the other fingers on the same hand
The muscle that is responsible for most of the muscle movement is called the what?
What are muscles called the work with the prime mover?
What muscles work against the prime mover?
What is a fixator?
Fixators are specialized synergists. They have a bone still or stabilize the origin of a prime mover so all the tension can be used to move the insertion bone
How are skeletal muscles named?
-Direction of the muscle fibers
-Relative size of the muscle
-Location of the muscle
-Number of origins
-Location of the muscle's origin and insertion
-Shape of the muscle
-Action of the muscle
Be able to describe muscle based on their names.
-Direction of muscle fibers: named in reference to some imaginary line, usually the midline of the body or the long axis of a limb bone. Rectus means fibers run parallel to that imaginary line, while oblique tells you that the muscle tuns at a slant to the imaginary line
-Relative size of the muscle: maximus (largest), minimus (smallest), and longus (longest are examples
-Location of the muscle: named for the bone with which they are associated
-Number of origins: biceps, triceps, and 1quadriceps all stand for the number of origins the muscle has 2,3, 4
-Locations of the muscle's origin and insertion: named for their attachment sites
-Shape of the muscle: some have distinctive shape to help identify them
-Action of the muscle: flexor, extensor, and adductor all explain what movement that muscle is undergoing
Explain the different arrangements that fascicles can have.
-Circular: fascicles are arranged in concentric rings. A general term for these muscles is sphincters
-Convergent: the fascicles converge toward a single insertion tendon. Such a muscle is triangular or fan-shaped
-Parallel: length of the fascicle run parallel to the long axis of the muscle. A modification of the parallel arrangement, called a fusiform, results in a spindle-shaped muscle with an expanded belly
-Pennate: short fascicles attached obliquely to a central tendon. Unipennate muscles insert on only one side of the tendon. If fascicles insert into opposite sides of the tendon or from several different sides, the muscle is bipennate or multipennate
The fascicle arrangement of muscles determine what?
Its range of motion and power; the longer and more parallel the fascicles are to the muscle's long axis, the mor the muscle can shorten, but are not very powerful
The most powerful muscles have more what on hand? Which muscles of the head and neck are unpaired muscles?
Muscle cells because muscle power depends on the total number of muscle cells in the muscle; all head and neck muscles are paired except for platysma, orbicularis oris, the frontalis, and the occipitalis
What is torticollis?
In some difficult births, one of the sternocleidomastoid muscles may be injured and develop spasms. A baby injured in this way has torticollis or wryneck.
What do trunk muscles include?
The trunk muscles include
(1) those that move the vertebral column (most of which are posterior antigravity muscles
(2) anterior thorax muscles, which move the ribs, head, and arms and,
(3) muscles of the abdominal wall, which help to move the vertebral column and, most important, form muscular "natural girdle" of the abdominal body wall
Which muscles are good injection sites?
Deltoid and gluteus medius
What three groups do muscles of the upper limb fall into?
1. Muscles that arise from the shoulder girdle and cross the shoulder joint to insert into the humerus
2. Causes movement at the elbow joint, these enclose the humerus and insert on the forearm bones
3. Muscles of the forearm, which insert on the hand bones and cause movement
How are forearm muscles named?
They have names that reflect their movement; flexor carpi and extensor digitorum muscles- extends the same structures
All anterior arm muscles cause what action?
All anterior arm muscles cause elbow flexion. In order of decreasing strength these are the brachialis, biceps brachii, and brachioradialis
Muscles of the lower limb cause action on which body parts?
Muscles that act on the lower limb cause movement at the hip, knee, and foot joints. They are among the largest, strongest muscles in the body and are specialized for walking and balancing
Why are origin and insertion interchangeable for lower limb muscles?
Many muscles of the lower limb span two joints and can cause movement at both of them. Therefore, the terms origin and insertion are often interchangeable in referring to these muscles.
What do muscles in the lower limb specialize in?
They are among the largest, strongest muscles in the body and are specialized for walking and balancing; muscles acting on the thigh are massive muscles that help hold the body upright against the pull of gravity and cause various movements at the hip joint
When can embryonic movement be felt?
The expectant mother is often astonished by the first movements (called the quickening) of the fetus, which usually occur by the 16th week of pregnancy.