Summarizing Types of Skeletal Systems

Summary

The three types of skeleton designs are hydrostatic skeletons, exoskeletons, and endoskeletons. A hydrostatic skeleton is formed by a fluid-filled compartment held under hydrostatic pressure; movement is created by the muscles producing pressure on the fluid. An exoskeleton is a hard external skeleton that protects the outer surface of an organism and enables movement through muscles attached on the inside. An endoskeleton is an internal skeleton composed of hard, mineralized tissue that also enables movement by attachment to muscles.

The human skeleton is an endoskeleton that is composed of the axial and appendicular skeleton. The axial skeleton is composed of the bones of the skull, ossicles of the ear, hyoid bone, vertebral column, and ribcage. The skull consists of eight cranial bones and 14 facial bones. Six bones make up the ossicles of the middle ear, while the hyoid bone is located in the neck under the mandible. The vertebral column contains 26 bones, and it surrounds and protects the spinal cord.

The thoracic cage consists of the sternum, ribs, thoracic vertebrae, and costal cartilages. The appendicular skeleton is made up of the limbs of the upper and lower limbs. The pectoral girdle is composed of the clavicles and the scapulae. The upper limb contains 30 bones in the arm, the forearm, and the hand. The pelvic girdle attaches the lower limbs to the axial skeleton. The lower limb includes the bones of the thigh, the leg, and the foot.

Glossary

appendicular skeleton

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

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)

carpus

eight bones that comprise the wrist

clavicle

S-shaped bone that positions the arms laterally

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

endoskeleton

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

exoskeleton

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

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

fibula

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

forearm

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

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

intervertebral disc

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

lower limb

consists of the thigh, the leg, and the foot

metacarpus

five bones that comprise the palm

metatarsal

one of the five bones of the foot

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

phalange

one of the bones of the fingers or toes

pelvic girdle

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

radius

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

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

scapula

flat, triangular bone located at the posterior pectoral girdle

skull

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

sternum

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

tarsal

one of the seven bones of the ankle

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

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