Human Sensory Receptors, Senses, and Musculoskeletal System

Sensory Receptors

Sensory receptors are structures formed by nerve cells specialized to capture and transform stimuli into nerve impulses. The receptors are classified as:

• Chemoreceptors: Sensitive to chemicals.
• Mechanoreceptors: Sensitive to mechanical stimuli such as touch, pressure, sound, or gravity.
• Photoreceptors: Sensitive to light.
• Thermoreceptors: Sensitive to changes in temperature.
• Nociceptors: Sensitive to heavy pressure and responsible for pain.

Receptors can also be classified according to their location:

• Internal receptors: Located inside the body, particularly in the viscera. Responsible for collecting information from internal organs.
• External receptors: Located on the surface of the body. Responsible for collecting external stimuli like light, sound, and temperature.

Humans have five senses to inform us about the world: sight, hearing, touch, smell, and taste.

Touch, Smell, and Taste

Touch receptors are found on the skin, smell receptors in the nasal cavity, and taste receptors in the taste buds of the tongue.

Touch

The skin is the largest organ in our body. It consists of two layers:

• Epidermis: The outer layer, consisting of epithelial tissues with several layers of cells.
• Dermis: The inner layer, formed by connective tissue, which provides elasticity to the skin.

Smell

The interior of the nasal cavity is lined by a mucous membrane called the pituitary. Here are two regions:

• Red pituitary: Occupies the bottom. Has abundant blood vessels that heat the inspired air.
• Yellow pituitary: Occupies the upper part. Contains the olfactory bulb, which carries information to the brain.

Taste

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

Diseases of the Sensory Organs

• Hyperopia: The eye is shorter than normal.
• Myopia: The eye is longer than normal.
• Astigmatism: Defects in the curvature of the cornea.
• Eyestrain: The lens does not focus on close objects.

The Musculoskeletal System

The musculoskeletal system is responsible for carrying out the motor responses produced by the nervous system.

Skeletal System

The skeletal system is the passive part of the musculoskeletal system. It consists of the skeleton (bones, joints, ligaments). The skeleton is divided into three parts: head, trunk, and extremities.

Muscular System

The muscular system is the active part of the musculoskeletal system. It consists of the muscles and tendons.

Joints

Joints are structures that connect bones together, preventing their separation. Ligaments connect bones to each other, while tendons attach muscles to bones.

Muscles

Muscles consist of elongated cells called muscle fibers. These organs can contract and relax.