muscular system

elongated

skeletal and smooth muscle cells are

_______. For this reason, these types of muscle

cells (but not cardiac muscle cells) are called muscle fibers

myofilaments

the ability of muscle to shorten,

or contract, depends on two types of ______, the muscle cell equivalents of the microfilaments of the cytoskeleton

terminology

A third similarity has to do with _____.

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

are packaged into organs

called skeletal muscles that attach to the skeleton.

are large,

cigar-shaped, multinucleate cells. They are the

largest muscle fibers—some ranging up to 30 cm

(nearly 1 foot) in length.

cover our bone and cartilage framework, they help form the smooth contours of the body.

cover our bone and cartilage framework, they help form the smooth contours of the body.

skeletal muscle

striated

muscle (because its fibers have obvious stripes)

and as voluntary muscle (because it is the only

muscle type subject to conscious control).

can be activated by reflexes

endomysium

skeletal muscle fiber is enclosed in a delicate

connective tissue sheath

perimysium, fascicle

Several sheathed muscle fibers

are then wrapped by a coarser fibrous membrane

called _____ to form a bundle of fibers

called a _______

epimysium

Many fascicles are

bound together by an even tougher “overcoat” of

connective tissue called an ______, which

covers the entire muscle.

tendon, aponeurosis,

The ends of the epimysium that extend beyond the muscle (like the

wrapper on a piece of candy) blend either into a

strong, cordlike ________ or a sheetlike ______ which indirectly attaches the

muscle to bone, cartilage, or another connective

tissue covering.

tendons

perform several other functions. The most important

are providing durability and conserving space

smooth muscle

has no striations and is involuntary, which means that we cannot consciously

control it. Found mainly in the walls of hollow

(tubelike) visceral organs such as the stomach,

urinary bladder, and respiratory passages, _______ propels substances along a pathway.

VISCERAL, INVOLUNTARY, NONSTRIATED VIN

smooth muscle fibers, scant endoysium

spindle-shaped, uninucleate, and surrounded by _______. They are arranged in layers, and

most often there are two such layers, one running circularly and the other longitudinally. As the two layers alternately contract

and relax, they change the size and shape of the

organ.

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,

striated, uninucleate, involuntary, cardiac, striated

endomysium, spiral or figure 8–shaped bundles

The cardiac cells are cushioned by small

amounts of _____ and are arranged in ______

intercalated discs

Cardiac muscle fibers are

branching cells joined by special gap junctions

called ________

PRODUCE MOVEMENT

skeletal muscle 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.

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. 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

sarcolemma

oval nuclei can be seen just beneath the plasma membrane,

which is called the ______ “muscle husk”) in muscle fibers

myofibrils

The nuclei are

pushed aside by long ribbonlike organelles, the

_______, which nearly fill the

cytoplasm.

irritability/responsiveness

contractility

extensibility

elasticity

Muscle fibers speical functional properties

sarcolemma

specialized plasma membrane

sarcoplasmic reticulum

specialized endoplasmic reticulum. the interconnecting tubules

and sacs of the SR surround every myofibril just as

the sleeve of a loosely crocheted sweater surrounds your arm. The major role of this elaborate

system is to store calcium and to release it on

demand when the muscle fiber is stimulated to

contract.

myofibril

bundles of myofilaments

myofibrils are aligned to give distinct bands

I band- lIght band

A band-dArk band

sarcomere

contractile unit of muscle fiber

A bands

Thick filaments-myosin filaments

composed of protein myosin

has ATPase enzymes

Anisotropic

M line

central portion connected to neighbors by proteins that help stailize their position

h zone

ligher region, containing only thick filaments

zone of overlap

with thin filamenrs between thick filamnets

I bands

from a-bands to a-bands: THIN FILAMENTS

thin filaments=actin filaments

composed of protein actin

Isotropic

z line (z disk)

marks the boundary between adjacent sarcomeres

contains ACTININ that interconnect thin filaments of adjacent sarcormers

titin

extend from tips of thick filmaments ti attachment stes at z line; keeps think and thin filaments in alignment

myosin head

midparts of the

thick filaments are smooth, but their ends are

studded with small projections (Figure 6.3c).

These projections, form cross

bridges when they link the thick and thin filaments together during contraction

irritability

also termed responsiveness, which is the ability to receive and respond

to a stimulus.

contractility

the ability to forcibly shorten when adequately stimulated

Extensibility

is the ability of muscle fibers to

stretch

elasticity

is their ability to recoil and

resume their resting length after being stretched

motor unit

consists of one

neuron and all the skeletal muscle fibers it stimulates (

axon, axon

terminals

When a long, threadlike

extension of the neuron, called the _____, reaches

the muscle, it branches into a number of _____, each of which forms junctions with the

sarcolemma of a different muscle cell

neuromuscular junctions

association site of nerve and muscle

neurotransmitter

chemical released by nerve upon arrival of nerve impulse

acetylcholine

the specific neurotransmitter

that stimulates skeletal muscle fibers is

synaptic cleft

gap between nerve and muscle filled with interstitial fluid

nerve and muscle dont make contact

ALS, or amyotrophic lateral sclerosis

motor

neurons degenerate over time, resulting in paralysis

that gradually worsens.

1 calcium channels open, and calcium (Ca2+) enters the terminal'

2 Calcium entry causes some of the synaptic vesicles in the axon

terminal to fuse with the cell membrane and release acetylcholine

3 which then diffuses across the synaptic cleft and attaches to mem

brane receptors in highly folded regions of the sarcolemma

4 If enough acetylcholine is

released, the sarcolemma at that point becomes

temporarily even more permeable to sodium ions

(Na+), which rush into the muscle fiber, and to

potassium ions (K+), which diffuse out of the

muscle fiber. However, more Na

+ enters than K+

leaves. This imbalance gives the cell interior an

excess of positive ions, which reverses the resting

electrical conditions of the sarcolemma. This

event, called depolarization, opens more channels

that only allow Na+ entry

5 This movement of

ions generates an electrical current called an

action potential.

6 For this reason, a single nerve impulse

produces only one contraction. This prevents continued contraction of the muscle fiber in the

absence of additional nerve impulses. The muscle

fiber relaxes until stimulated by the next round of

acetylcholine release

the sliding filament theory

Muscles shorten when thin (actin) and thick (myosin) filaments slide past each other; the filaments themselves do not get shorter. Myosin heads grab actin, pull it toward the center of the sarcomere (power stroke), release, and reset—repeating this “walking” action to produce movement. ATP is needed for myosin to let go and re-cock, while calcium (Ca2+) reveals the binding sites on actin by moving troponin–tropomyosin out of the way. A nerve signal causes Ca2+ to be released from the sarcoplasmic reticulum, starting cross-bridge cycling; when the signal stops, Ca2+ is pumped back into storage, the sites are covered again, and the muscle relaxes.

graded responses

different degrees of skeletal muscle shortnening

contractions can be produced

two ways: (1) by changing the frequency of muscle stimulation and (2) by changing the number of muscle fibers being stimulated at one time

oxygen debt

reasonfor muscle fatigue. oxygen must be repaid to tissue, to get rid of accumulated lactic acid

increasing acidity and lack of atp causes muscle to contract less

isotonic contractions

myofiilamnetss are able to slide past each other during contractions

muscle shortens

isometric contractions

tension in muscle increases

muscle is unable to shorten

origin

attachment to a moveable bone

insertion

attachment to an immovable bone

fused tetanus

When the muscle is stimulated so rapidly that no evidence of

relaxation is seen and the contractions are completely smooth and sustained, the muscle is in

unfused tetanus

nerve impulses are delivered to the muscle at a very rapid rate—so rapid that the muscle

does not get a chance to relax completely between

stimuli. As a result, the effects of the successive

contractions are “summed” (added) together, and

the contractions of the muscle get stronger and

smoother.

Direct phosphorylation of ADP by creatine phosphate

The

unique high-energy molecule creatine phosphate (CP) is found in muscle fibers but not

other cell types. As ATP is depleted, interactions between CP and ADP result in transfers

of a high-energy phosphate group from CP Direct phosphorylation of ADP by creatine phosphate

aerobic pathway

At rest and

during light to moderate exercise, some 95 percent of the ATP used for muscle activity comes

from aerobic respiration. Aerobic respiration

occurs in the mitochondria and involves a series

of metabolic pathways that use oxygen. These

pathways are collectively referred to as oxidative phosphorylation. During aerobic respiration,

glucose is broken down completely to carbon

dioxide and water, and some of the energy released as the bonds are broken is captured in

the bonds of ATP molecules. Although aerobic

respiration provides a rich ATP harvest (about

32 ATP per 1 glucose), it is fairly slow and requires continuous delivery of oxygen and nutrient fuels to the muscle to keep it going

Anaerobic glycolysis and lactic acid formation

The initial steps of glucose breakdown occur via a pathway called

glycolysis, which does not use oxygen and

hence is anaerobic (literally “without oxygen”).

During glycolysis, which occurs in the cytosol, glucose is broken down to pyruvic acid,

and small amounts of energy are captured in

ATP bonds (2 ATP per 1 glucose molecule). As

long as enough oxygen is present, the pyruvic acid then enters the oxygen-requiring aerobic

pathways that occur within the mitochondria

to produce more ATP as described above.

However, when muscle activity is intense,

or oxygen and glucose delivery is temporarily inadequate to meet the needs of working

muscles, the sluggish aerobic pathways cannot keep up with the demands for ATP. Under

these conditions, the pyruvic acid generated

during glycolysis is converted to lactic acid,

and the overall process

muscle tone

state of continuous partial

contractions, result of different motor units, which are

scattered through the muscle, being stimulated by

the nervous system in a systematic way

Aerobic/endurance exercise

such as participating in an aerobics class, jogging,

or biking (Figure 6.11a), results in stronger, more

flexible muscles with greater resistance to fatigue.

These changes come about, at least partly, because

the blood supply to the muscles increases, and the

individual muscle fibers form more mitochondria

and store more oxygen.

resistance/isometric exercise

require very little time and

little or no special equipment. A few minutes every

other day is usually sufficient. You can push against

a wall, and you can strongly contract buttock muscles even while standing in line at the grocery store.

The key is forcing your muscles to contract with as

much force as possible. The increased muscle size

and strength that result are due mainly to enlargement of individual muscle fibers (they make more

contractile myofilaments) rather than to an increase

in their number. The amount of connective tissue

that reinforces the muscle also increases.

flexion

is a movement, generally in

the sagittal plane, that decreases the angle of

the joint and brings two bones closer together. is typical of

hinge joints (bending the knee or elbow), but

it is also common at ball-and-socket joints (for

example, bending forward at the hip)

Extension

is the opposite of flexion, so it is a movement that increases the

angle, or distance, between two bones or parts

of the body (straightening the knee or elbow).

Extension that is greater than 180° (as when

you move your arm posteriorly beyond its

normal anatomical position, or tip your head

so that your chin points toward the ceiling)

is called hyperextension

Rotation

is movement of a bone

around its longitudinal axis (Figure 6.13c).

is a common movement of ball-andsocket joints and describes the movement of

the atlas around the dens of the axis (as in

shaking your head “no”).

Abduction

is moving a limb away

(generally on the frontal plane) from the midline, or median plane, of the body (Figure

6.13d). The terminology also applies to the

fanning movement of your fingers or toes

when they are spread apart.

Adduction

is the opposite of abduction, so it is the movement of a limb toward the body midline (Figure 6.13d). Think of

adduction as “adding” a body part by bringing

it closer to the trunk.

Circumduction

is a combination of flexion, extension, abduction, and adduction commonly seen in ball-and-socket joints,

such as the shoulder. The proximal end of the

limb is stationary, and its distal end moves in

a circle. The limb as a whole outlines a cone

(Figure 6.13d), as when you do big arm circles.

dorsiflexion, plantar flexion

Up-anddown movements of the foot at the ankle

are given special names. Lifting the foot so

that its superior surface approaches the shin

(pointing your toe toward your head) is _______, whereas pointing the toes away from

your head is _______

inversion and eversion

are also special movements of the foot

(Figure 6.13f). To invert the foot, turn the sole

medially, as if you were looking at the bottom

of your foot. To evert the foot, turn the sole

laterally.

Supination, Pronation

rrefer to movements of the radius

around the ulna (Figure 6.13g). ______

occurs when the forearm rotates laterally so

that the palm faces anteriorly (or up) and the

radius and ulna are parallel, as in anatomical

position. ______ occurs when the forearm

rotates medially so that the palm faces posteriorly (or down).

opposition

In the palm of the hand, the saddle joint between metacarpal 1 and the carpals

allows _______ of the thumb (Figure 6.13h).

This is the action by which you move your

thumb to touch the tips of the other fingers on the same hand. This unique action makes the

human hand a fine tool for grasping and manipulating object

antagonist

Muscles that oppose or reverse a

movement are, When

a prime mover is active, its ______ is stretched

and relaxed.

prime mover

muscle that has the major responsibility

for causing a particular movement

synergists

help prime movers by producing the same

movement or by reducing undesirable movements.

When a muscle crosses two or more joints, its contraction will cause movement in all the joints

crossed unless _____ are there to stabilize

them.

fixators

are specialized synergists. They hold

a bone still or stabilize the origin of a prime mover

so all the tension can be used to move the insertion bone

direction of the muscle fibers

Some muscles are named in reference to some imaginary

line, usually the midline of the body or the

long axis of a limb bone. When a muscle’s

name includes the term rectus (straight), its fibers run parallel to that imaginary line. For example, the rectus femoris is the straight muscle

of the thigh. Similarly, the term oblique in a

muscle’s name tells you that the muscle fibers

run obliquely (at a slant) to the imaginary line

Relative size of the muscle

Such terms as

maximus (largest), minimus (smallest), and longus (long) are sometimes used in the names of

muscles—for example, the gluteus maximus is

the largest muscle of the gluteus muscle group.

Location of the muscle

Some muscles are

named for the bone with which they are associated. For example, the temporalis and frontalis muscles overlie the temporal and frontal

bones of the skull, respectively.

Number of origins

When the term biceps,

triceps, or quadriceps forms part of a muscle

name, you can assume that the muscle has two,

three, or four origins, respectively. For example,

the biceps muscle of the arm has two heads, or

origins, and the triceps muscle has three

Location of the muscle’s origin and insertion

Occasionally, muscles are named for their

attachment sites. For example, the sternocleidomastoid muscle has its origin on the sternum (sterno) and clavicle (cleido) and inserts on the mastoid process of the temporal

bone

Shape of the muscle

Some muscles have a

distinctive shape that helps to identify them.

For example, the deltoid muscle is roughly triangular (deltoid means “triangular”)

Action of the muscle

When muscles are

named for their actions, terms such as flexor,

extensor, and adductor appear in their names.

For example, the adductor muscles of the thigh

all bring about its adduction, and the extensor

muscles of the wrist all extend the wrist

circular patttern

the fascicles are arranged

in concentric rings (Figure 6.15a). Circular muscles

are typically found surrounding external body

openings which they close by contracting, creating

a valve. A general term for such muscles is sphincters (“squeezers”). Examples are the orbicularis

muscles surrounding the eyes and mouth

convergent muscle

the fascicles converge toward a single insertion tendon. A convergent muscle is triangular or fan-shaped, such as

the pectoralis major muscle of the anterior thorax

parallel arrangement

the length of the

fascicles run parallel to the long axis of the muscle, as in the sartorius of the anterior thigh. These

muscles are straplike (Figure 6.15d). A modification of the parallel arrangement, called fusiform,

results in a spindle-shaped muscle with an

expanded belly (midsection); an example is the

biceps brachii muscle of the arm (Figure 6.15c).

pennate pattern

short

fascicles attach obliquely to a central tendon. In the

extensor digitorum muscle of the leg, the fascicles

insert into only one side of the tendon, and the

muscle is unipennate (Figure 6.15g). If the fascicles

insert into opposite sides of the tendon, the muscle

is bipennate (Figure 6.15f). If the fascicles insert

from several different sides, the muscle is multipennate (Figure 6.15e).

facial muscles

are unique because they insert

into soft tissues, such as other muscles or skin.

When they pull on the skin of the face, they

permit us to express ourselves by frowning, smiling, and so forth.

chewing muscle

begin

to break down food for the body. All head and

neck muscles we describe are paired except

for the platysma, orbicularis oris, frontalis, and

occipitalis

frontalis

Raises eyebrows
which covers the frontal

bone, runs from the cranial aponeurosis to the

skin of the eyebrows, where it inserts. This muscle

allows you to raise your eyebrows, as in surprise,

and to wrinkle your forehead. At the posterior end

of the cranial aponeurosis is the small occipitalis muscle, which covers the posterior aspect of the

skull and pulls the scalp posteriorly

Orbicularis Oculi

Blinks and closes eye
fibers run in circles around

the eyes. It allows you to close your eyes, squint,

blink, and wink.

Orbicularis Oris

Closes and protrudes lips

is the circular muscle of the lips. Often called the “kissing”

muscle, it closes the mouth and protrudes the lips.

Buccinator

Compresses cheek (as

in sucking); holds food

between teeth during

chewing
muscle runs horizontally across the cheek and

inserts into the orbicularis oris. It flattens the cheek

(as in whistling or blowing a trumpet). It is also

listed as a chewing muscle because it compresses

the cheek to hold food between the teeth during

chewing.

Zygomaticus

Raises corner of mouth
extends from the corner of the mouth to the

cheekbone. It is often referred to as the “smiling”

muscle because it raises the corners of the mouth.

Masseter

Closes jaw
As it runs from the zygomatic process

of the temporal bone to the mandible, the _______ covers the angle of the lower

jaw. This muscle closes the jaw by elevating the

mandible.

Temporalis

Closes jaw

is a fan-shaped muscle overlying the temporal bone. It inserts into the

mandible and acts as a synergist of the masseter in

closing the jaw.

plastysma

Tenses skin of neck (as in

shaving)
a single sheetlike muscle that covers the anterolateral neck (see Figure

6.16). It originates from the connective tissue covering of the chest muscles and inserts into the area

around the mouth. Its action is to pull the corners

of the mouth inferiorly, producing a downward

sag of the mouth (the “sad clown” face).

Sternocleidomastoid

Flexes neck; laterally rotates

head

muscles are twoheaded muscles, one found on each side of the

neck. Of the two heads of each muscle, one arises

from the sternum, and the other arises from the

clavicle (see Figure 6.22, p. 240). The heads fuse

before inserting into the mastoid process of the

temporal bone

Intercostal Muscles

are

deep muscles found between the ribs. (Although

they are not shown in Figure 6.17, which shows

only superficial muscles, they are illustrated in

Figure 6.22, p. 240.) The external intercostals

are important in breathing because they help to

raise the rib cage when you inhale. The internal

intercostals, which lie deep to the external

intercostals, depress the rib cage, helping to

move air out of the lungs when you exhale

forcibly.