Key Terms

abduction

when a bone moves away from the midline of the body

acetylcholinesterase

(AChE) enzyme that breaks down ACh into acetyl and choline

actin

globular contractile protein that interacts with myosin for muscle contraction

adduction

movement of the limbs inward after abduction

amphiarthrosis

joint that allows slight movement; includes syndesmoses and symphyses

angular movement

produced when the angle between the bones of a joint changes

appendicular skeleton

composed of the bones of the upper limbs, which function to grasp and manipulate objects, and the lower limbs, which permit locomotion

appositional growth

increase in the diameter of bones by the addition of bone tissue at the surface of bones

articulation

any place where two bones are joined

auditory ossicle

(also, middle ear) transduces sounds from the air into vibrations in the fluid-filled cochlea

axial skeleton

forms the central axis of the body and includes the bones of the skull, the ossicles of the middle ear, the hyoid bone of the throat, the vertebral column, and the thoracic cage (ribcage)

ball-and-socket joint

joint with a rounded, ball-like end of one bone fitting into a cuplike socket of another bone

bone

(also, osseous tissue) connective tissue that constitutes the endoskeleton

bone remodeling

replacement of old bone tissue by new bone tissue

calcification

process of deposition of mineral salts in the collagen fiber matrix that crystallizes and hardens the tissue

cardiac muscle tissue

muscle tissue found only in the heart; cardiac contractions pump blood throughout the body and maintain blood pressure

carpus

eight bones that comprise the wrist

cartilaginous joint

joint in which the bones are connected by cartilage

circumduction

movement of a limb in a circular motion

clavicle

S-shaped bone that positions the arms laterally

compact bone

forms the hard external layer of all bones

condyloid joint

oval-shaped end of one bone fitting into a similarly oval-shaped hollow of another bone

coxal bone

hip bone

cranial bone

one of eight bones that form the cranial cavity that encloses the brain and serves as an attachment site for the muscles of the head and neck

depression

movement downward of a bone, such as after the shoulders are shrugged and the scapulae return to their normal position from an elevated position; opposite of elevation

diaphysis

central shaft of bone, contains bone marrow in a medullary cavity

diarthrosis

joint that allows for free movement of the joint; found in synovial joints

dorsiflexion

bending at the ankle such that the toes are lifted toward the knee

elevation

movement of a bone upward, such as when the shoulders are shrugged, lifting the scapulae

endochondral ossification

process of bone development from hyaline cartilage

endoskeleton

skeleton of living cells that produces a hard, mineralized tissue located within the soft tissue of organisms

epiphyseal plate

region between the diaphysis and epiphysis that is responsible for the lengthwise growth of long bones

epiphysis

rounded end of bone, covered with articular cartilage and filled with red bone marrow, which produces blood cells

eversion

movement of the sole of the foot outward, away from the midline of the body; opposite of inversion

exoskeleton

a secreted cellular product external skeleton that consists of a hard encasement on the surface of an organism

extension

movement in which the angle between the bones of a joint increases; opposite of flexion

facial bone

one of the 14 bones that form the face; provides cavities for the sense organs (eyes, mouth, and nose) and attachment points for facial muscles

femur

(also, thighbone) longest, heaviest, and strongest bone in the body

fibrous joint

joint held together by fibrous connective tissue

fibula

(also, calf bone) parallels and articulates with the tibia

flat bone

thin and relatively broad bone found where extensive protection of organs is required or where broad surfaces of muscle attachment are required

flexion

movement in which the angle between the bones decreases; opposite of extension

forearm

extends from the elbow to the wrist and consists of two bones: the ulna and the radius

gliding movement

when relatively flat bone surfaces move past each other

gomphosis

the joint in which the tooth fits into the socket like a peg

Haversian canal

contains the bone’s blood vessels and nerve fibers

hinge joint

slightly rounded end of one bone fits into the slightly hollow end of the other bone

humerus

only bone of the arm

hydrostatic skeleton

skeleton that consists of aqueous fluid held under pressure in a closed body compartment

hyoid bone

lies below the mandible in the front of the neck

hyperextension

extension past the regular anatomical position

intervertebral disc

composed of fibrous cartilage; lies between adjacent vertebrae from the second cervical vertebra to the sacrum

intramembranous ossification

process of bone development from fibrous membranes

inversion

soles of the feet moving inward, toward the midline of the body

irregular bone

bone with complex shapes; examples include vertebrae and hip bones

joint

point at which two or more bones meet

lamella

layer of compact tissue that surrounds a central canal called the Haversian canal

lateral rotation

rotation away from the midline of the body

long bone

bone that is longer than wide, and has a shaft and two ends

lower limb

consists of the thigh, the leg, and the foot

medial rotation

rotation toward the midline of the body

metacarpus

five bones that comprise the palm

metatarsal

one of the five bones of the foot

motor end plate

sarcolemma of the muscle fiber that interacts with the neuron

myofibril

long cylindrical structures that lie parallel to the muscle fiber

myofilament

small structures that make up myofibrils

myosin

contractile protein that interacts with actin for muscle contraction

opposition

movement of the thumb toward the fingers of the same hand, making it possible to grasp and hold objects

osseous tissue

connective tissue that constitutes the endoskeleton

ossification

(also, osteogenesis) process of bone formation by osteoblasts

osteoblast

bone cell responsible for bone formation

osteoclast

large bone cells with up to 50 nuclei, responsible for bone remodeling

osteocyte

mature bone cells and the main cell in bone tissue

osteon

cylindrical structure aligned parallel to the long axis of the bone

patella

(also, kneecap) triangular bone that lies anterior to the knee joint

pectoral girdle

bones that transmit the force generated by the upper limbs to the axial skeleton

pelvic girdle

bones that transmit the force generated by the lower limbs to the axial skeleton

phalange

one of the bones of the fingers or toes

pivot joint

joint with the rounded end of one bone fitting into a ring formed by the other bone

planar joint

joint with bones whose articulating surfaces are flat

plantar flexion

bending at the ankle such that the heel is lifted, such as when standing on the toes

pronation

movement in which the palm faces backward

protraction

anterior movement of a bone in the horizontal plane

radius

bone located along the lateral (thumb) side of the forearm; articulates with the humerus at the elbow

resorption

process by which osteoclasts release minerals stored in bones

retraction

movement in which a joint moves back into position after protraction

rib

one of 12 pairs of long, curved bones that attach to the thoracic vertebrae and curve toward the front of the body to form the ribcage

rotational movement

movement of a bone as it rotates around its own longitudinal axis

saddle joint

joint with concave and convex portions that fit together; named because the ends of each bone resemble a saddle

sarcolemma

plasma membrane of a skeletal muscle fiber

sarcomere

functional unit of skeletal muscle

scapula

flat, triangular bone located at the posterior pectoral girdle

sesamoid bone

small, flat bone shaped like a sesame seed; develops inside tendons

short bone

bone that has the same width and length, giving it a cube-like shape

skeletal muscle tissue

forms skeletal muscles, which attach to bones and control locomotion and any movement that can be consciously controlled

skull

bone that supports the structures of the face and protects the brain

smooth muscle tissue

occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels

spongy bone tissue

forms the inner layer of all bones

sternum

(also, breastbone) long, flat bone located at the front of the chest

supination

movement of the radius and ulna bones of the forearm so that the palm faces forward

sutural bone

small, flat, irregularly shaped bone that forms between the flat bones of the cranium

suture

short fiber of connective tissue that holds the skull bones tightly in place; found only in the skull

symphysis

hyaline cartilage covers the end of the bone, but the connection between bones occurs through fibrocartilage; symphyses are found at the joints between vertebrae

synarthrosis

joint that is immovable

synchondrosis

bones joined by hyaline cartilage; synchondroses are found in the epiphyseal plates of growing bones in children

syndesmosis

joint in which the bones are connected by a band of connective tissue, allowing for more movement than in a suture

synovial joint

only joint that has a space between the adjoining bones

tarsal

one of the seven bones of the ankle

thick filament

a group of myosin molecules

thin filament

two polymers of actin wound together along with tropomyosin and troponin

thoracic cage

(also, ribcage) skeleton of the chest, which consists of the ribs, thoracic vertebrae, sternum, and costal cartilages

tibia

(also, shinbone) large bone of the leg that is located directly below the knee

trabeculae

lamellae that are arranged as rods or plates

tropomyosin

acts to block myosin binding sites on actin molecules, preventing cross-bridge formation and preventing contraction until a muscle receives a neuron signal

troponin

binds to tropomyosin and helps to position it on the actin molecule, and also binds calcium ions

ulna

bone located on the medial aspect (pinky-finger side) of the forearm

vertebral column

(also, spine) surrounds and protects the spinal cord, supports the head, and acts as an attachment point for ribs and muscles of the back and neck