Sensory Receptors and Human Body Functions
Sensory Receptors and Their Functions
Sensory receptors are responsible for capturing information and relaying it to the nervous system. These receptors are activated when there are changes triggered by specific stimuli.
- Photoreceptors: Located in the eyes, they detect light stimuli.
- Mechanoreceptors: Stimulated by mechanical changes, pressure, contact, and sound waves.
- Chemoreceptors: Capture information about chemical changes. Taste and smell belong to this group.
- Thermoreceptors: Stimulated by temperature changes, such as some skin receptors.
The Eye and Vision
The eyeball is a hollow, spherical structure housed in a cavity in the skull called the orbit. It consists of:
- Cornea
- Iris
- Pupil
- Lens
- Retina
- Choroid
- Sclera
- Optic nerve
Lens: A clear, stretchy, convex lens-shaped body that attaches to the inner wall of the eyeball by tiny muscles.
Retina: The innermost layer of the eyeball. It contains photoreceptor cells of two types: rods and cones. Rods are excited by any kind of visible light but do not distinguish colors. Cones, conversely, can distinguish colors but require a higher light intensity.
Choroid: The second layer of the eyeball. It is black, but in the iris, it has a different color for each person. In the center of the iris, there is a hole called the pupil, whose diameter varies.
Sclera: The outermost layer of the globe; it is white, and the front becomes transparent, forming the cornea.
Optic Nerve: A set of extensions of nerve cells that communicate with the rods and cones.
The role of the eyeball is to allow light to excite the rods and cones in the retina.
- Regulate Light Intensity: Excessive light can injure photoreceptor cells, while insufficient light makes visual processing impossible.
- Focus Images: Ensure the light reflected by an object is properly focused on the retina to avoid a blurred image.
The Ear and Hearing/Balance
Sound waves are produced by vibrations of air molecules or any object.
The perception of balance occurs in the utricle and saccule. Within these structures, there are sensory cells, provided with cilia and covered by a gelatinous mass formed by mineral particles. Motion detection is performed in the semicircular canals. When we move, our head and ears also move.
Touch, Taste, and Smell
Touch: Sensory receptors in the skin capture a wide range of stimuli. Touch provides information on the shape, appearance, and texture of objects. Pressure causes intense tactile sensations. Other sensations include:
- Heat (higher temperatures than normal)
- Cold (lower temperatures than normal)
- Pain
Taste: Taste receptor cells are clustered in taste buds, which form papillae. The sensations produced are the flavors: sweet, salty, sour, and bitter.
Smell: The sense of smell is the detection of gas molecules that reach the nose. Within the nasal cavity, in an area called the yellow pituitary, are the olfactory cells.
Muscles and Bones
Muscles are composed of groups of muscle bundles, consisting of a set of muscle cells. The contraction of a muscle is its thickening and shortening. Muscles can be:
- Fusiform or Elongated: Spindle-shaped, usually involved in the execution of a movement.
- Flat: Generally protect organs.
- Circular or Sphincter: Close or open a cavity or duct, depending on whether they contract or relax.
Bones are organs containing calcium salts that provide toughness. They consist of bone tissue, which may be of two types: spongy bone and compact bone tissue. Their functions are:
- They allow the attachment of muscles and, therefore, act as passive organs of the locomotor system.
- They function as skeletal support for the body and serve as a frame.
- They protect delicate organs, such as the brain and spinal cord.