Railway Science (Biology – Skeleton System)

In humans, the vertebral column (spinal column or backbone) usually consists of 33 vertebrae, but it may vary between 32-35. There are 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4 caudal (coccygeal) vertebrae.

The skull is composed of two sets of bones – cranial (8 bones, form the hard protective outer covering, cranium for the brain) and facial (14 skeletal elements). A single U-shaped bone called hyoid is present at the base of the buccal cavity and it is also included in the skull. Each middle ear contains – Ear Ossicles {Malleus, Incus and Stapes (smallest bone)}.

Spinal nerve is a mixed nerve, which carries sensory, and autonomic signals between the spinal cord and the body. These are grouped into five regions - 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. These are a part of the peripheral nervous system.

Knee Joint - It is a hinge joint that connects the thigh bone (femur) to the shin bone (tibia). It is a complex joint that also involves patella (kneecap) and fibula (the other bone in the lower leg).
Neck - The primary joint in the neck is the atlanto-occipital joint, which connects the base of the skull (occipital bone) to the top of the spine (atlas vertebra).
Pelvis - Consists of several joints, including the sacroiliac joint, pubic symphysis, and hip joints. Shoulder Joint - It is a ball-and-socket joint between the scapula and the humerus.

The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. There are a total of 206 bones in the adult human body.

Neck: The content of the neck is grouped into 4 neck spaces called compartments. Vertebral compartment: Contains cervical vertebrae and postural muscles, Visceral compartment: Contains glands (thyroid, parathyroid, and thymus), the larynx, pharynx and trachea, Two vascular compartments: Contain the common carotid artery, internal jugular vein and the vagus nerve, on each side of the neck. Joint: Areas where two or more bones meet. Types of freely movable joints: Ball and socket (shoulder and hip joints), hinge (fingers, knees, elbows, and toes), condyloid, pivot, and gliding, saddle.

These filaments, usually in association with myosin, are responsible for many types of cell movements. During muscle contraction, the myosin heads or cross bridges come in close contact with the thin filaments.
Myosin is the prototype of a molecular motor - a protein that converts chemical energy in the form of ATP to mechanical energy, thus generating force and movement. Each muscle is surrounded by a connective tissue sheath called the epimysium.
Portions of the epimysium project inward to divide the muscle into compartments. Each compartment contains a bundle of muscle fibers. Each muscle fiber is called a fasciculus.

Three main types of muscle - Skeletal Muscle: Attached to bones, responsible for skeletal movements. The peripheral portion of the central nervous system (CNS) controls the skeletal muscles.
They act voluntarily. Smooth Muscle: Found in the walls of the hollow internal organs such as blood vessels, the gastrointestinal tract, bladder, and uterus, is under control of the autonomic nervous system.
Smooth muscle cannot be controlled consciously and thus acts involuntarily. Cardiac Muscle: Found in the walls of the heart, is also under control of the autonomic nervous system.
Gracilis muscle (thigh), Soleus muscle (Calf muscle) (superficial posterior compartment of the leg), Trapezius muscle (upper back of the shoulders and neck) are all examples of skeletal muscles.

Ear allows us to convert pressure variations in air with audible frequencies into electric signals that travel to the brain via the auditory nerve. The middle ear transmits the amplified pressure variations received from the sound wave to the inner ear.

Freely movable joint - These joints, also called synovial joints, are characterized by the presence of a joint capsule and are found in many parts of the body, including the shoulders, hips, knees, and elbows.
Cartilaginous joints are a type of joint where the bones are entirely joined by cartilage, either hyaline cartilage or fibrocartilage. Fibrous joints are a type of joint where the bones are joined by strong fibrous tissue rich in collagen.