Understanding Sensory Receptors and Human Senses

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Sensory Receptors: Gateways to Perception

Sensory receptors are specialized nerve cells that capture and transform stimuli into nerve impulses. These vital structures allow the body to perceive and react to its environment.

Classification of Receptors by Stimulus

According to the stimulus to which they are sensitive, receptors are classified as:

  • Chemoreceptors: Sensitive to chemical substances.
  • Mechanoreceptors: Sensitive to mechanical stimuli such as sound, pressure, friction, or gravity.
  • Thermoreceptors: Sensitive to temperature variations.
  • Nociceptors: Sensitive to intense pressure, pain, and potentially damaging stimuli.

Location of Sensory Receptors

Sensory receptors are found throughout the body and can be broadly categorized by their location:

  • Internal (Interoceptors): Located inside the body, primarily within the viscera. They are responsible for collecting information from internal organs, informing us about the organism's general state, including position, hunger, thirst, and urination.
  • External (Exteroceptors): Located on the surface of the body. They gather external stimuli such as light, sound, and temperature. These sensory organs (exteroceptors) are grouped at specific points on the body and surrounded by specialized sensory structures.

Specific Sensory Receptors and Their Functions

Phonoreceptors (Sense of Hearing)

Phonoreceptors are responsible for the sense of hearing and the pickup of sounds. Vibrations of the air move the eardrum, which is transmitted by the ossicles to the oval window membrane. This membrane contacts the chambers and inner ear canals, which are filled with a liquid called endolymph.

Equilibrium Mechanoreceptors

These are sensitive cells within the utricle and saccule that act in response to changes in the internal pressure of the endolymph. They are crucial for detecting body movements, as the internal channels are also filled with endolymph.

Mechanoreceptors in the Skin (Sense of Touch)

These receptors are responsible for the sense of touch, detecting pressures on the skin. Meissner's corpuscles and Pacinian (Vater-Pacini) corpuscles are formed by nerve endings surrounded by a capsule of connective tissue.

Thermoreceptors in the Skin

These receptors are responsible for the detection of body temperature. Krause corpuscles are sensitive to cold, and Ruffini corpuscles are sensitive to heat. They are formed by nerve endings and connective tissue.

Chemoreceptors in the Nostrils (Sense of Smell)

These receptors are responsible for the uptake of substances dispersed in the air. Neurons are interspersed throughout the olfactory mucosa, also known as the yellow pituitary membrane, located in the nostrils.

Chemoreceptors on the Tongue (Sense of Taste)

These receptors are responsible for the uptake of dissolved substances in liquids. These sensitive cells are found in taste buds, which are located in protrusions on the tongue.

Photoreceptors (Sense of Sight)

Photoreceptors are responsible for the sense of sight, specifically the capture of light. In the eyes, light passes through the cornea, which is the transparent front part of the sclera. It then enters the pupil, passes through the lens, and is projected onto the retina. The retina has a layer of light-sensitive cells (rods and cones) that transmit received stimuli via the optic nerve to the brain. The area of the retina where the optic nerve exits is called the blind spot because it lacks visual sensitivity. There is also a depression near the center of the retina called the fovea (often referred to as the yellow spot), where there is a high concentration of cones, making it the area of most efficient and sharpest vision.

The Musculoskeletal System

The musculoskeletal system's primary function is to enable body movements. Besides this,

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