Human Body: Sensory Receptors, Senses, and Musculoskeletal System

Sensory Receptors

The receptors are classified as:

• Chemoreceptors: Sensitive to chemicals.
• Mechanoreceptors: Sensitive to mechanical stimuli.
• Photoreceptors: Light-sensitive.
• Thermoreceptors: Sensitive to temperature variations.
• Nociceptors: Sensitive to internal pressures.

Sensory Receptors:

• Internal receptors: Report the condition of the body, e.g., hunger, thirst, need to urinate.
• External receptors: Collect stimuli from outside, e.g., light, sound, temperature.

The Senses of Touch, Smell, and Taste

Touch

• Epidermis: Epithelial tissue formed by several layers of cells. These cells contain keratin, a protein whose function is to waterproof the skin.
• Dermis: Formed by connective tissue, which provides elasticity to the skin. The dermis contains many blood vessels and touch receptors.

Smell

The inside of the nostrils is lined by a mucosa called the pituitary.

• Red pituitary: Has abundant blood vessels that warm the inspired air.
• Yellow pituitary: Contains numerous olfactory receptors, which form the olfactory bulb.

Taste

On the tongue, there are numerous protrusions called taste buds. Taste buds detect four basic tastes: sweet, salty, sour, and bitter.

The Musculoskeletal System

The musculoskeletal system performs motor responses, serves as internal support to the body, and facilitates its movement and displacement.

• Skeletal system: Consists of the skeleton, composed of a moving inner shell of bones and complementary structures, involved in body movement, shape, and supporting the weight of the body.
• Muscular system: Consists of the muscles and tendons, which produce the movements necessary to maintain posture and allow mimicry.

Joints

There are three types of joints:

• Stationary: Do not allow the movement of the bones. The bones are joined edge to edge. Example: Joints that join the skull bones.
• Semi-movable: Strongly bind the bones but allow a little movement. They are united by cartilage and ligaments that strengthen them. Example: Joints of the vertebrae.
• Mobile: Allow a great variety of movements between the bones that form them. Example: Shoulder, elbow, and knee.

Muscles

There are three types of muscles:

• Smooth muscles: Consist of smooth muscle fibers.
• Cardiac muscles: Consist of striated muscle fibers.
• Skeletal muscles: Consist of striated muscle fibers.

The Action of Muscles on the Skeleton

When a muscle contracts, it shortens the distance between the tendons at both ends and increases in thickness without changing the volume. To shorten, it pulls the bone to which it is anchored and moves it.

Muscles alone are unable to make any movement. To produce movement, bones and joints are necessary. The group acts as a lever.