Human Sensory System: Receptors, Organs, and Health
The Role of Relationship in Sensory Processes
The role of relationship involves three groups of processes: the reception of stimuli, processing of information for the development of coordinated responses, and execution of responses. Humans have specialized organs to carry out these processes: receptor organs, systems of coordination, and effector organs.
Reception of Stimuli
A stimulus is a change in our environment or within us that we perceive and provokes a response from our body. Receptor cells are specialized to react when they receive a certain type of information (light waves, sound vibrations, etc.), issuing a nerve impulse. For a receiver to capture the stimulus, it must reach a minimal intensity, called the perception threshold.
Processing of Information and Coordination
The systems responsible for processing the nerve impulses sent by receptor cells and preparing the answers are the nervous system and endocrine system.
Nervous Coordination
The nervous system conducts electrochemical impulses produced by the receptors. It processes, interprets, and develops new answers in the form of electrochemical signals that lead to the effectors and coordinates their response.
Endocrine Coordination
Endocrine glands release substances into the blood when receiving nerve impulses or chemical information from the internal environment. Hormones are chemical messengers that travel slowly through the internal environment to some effector organs and coordinate their response.
Execution of Responses
Although any organ that produces a response is an effector, muscles and glands are highlighted. Coordinated responses by the nervous system and carried out by the muscles are immediate and short-lived. The coordinated responses by the endocrine system are slow and very durable.
Receptors and Sensory Organs
The Receptors and Their Types
The human body has specialized systems to receive information and transform it into nerve impulses. These are the receptors.
There are two types of receptors:
- Internal Receptors: Capture internal environmental changes, such as a rise of CO2 in the blood or any body damage. These receptors are dispersed throughout the body.
- External Receptors: Capture stimuli from the external environment, such as light waves or temperature differences. Some are scattered in the skin, while others are grouped into the sensory organs.
The Skin and Touch
The skin contains a large number of different receptors, each sensitive to a given stimulus. These receptors allow us to recognize shapes and textures, and to perceive temperature changes, giving us the sense of touch. Some receptors are easily saturated, and when they receive a stimulus for a long time, they initially respond with great intensity but then adapt and only respond if the intensity increases. Pressure receptors adapt quickly, but pain receptors do not adapt completely.
The Nose and Smell
The sense of smell is less developed, but it still allows us to recognize 10,000 different smells, remember them, and associate them with something or someone. These odors are sensations that occur when the following sequence of processes happens:
- Volatile molecules enter the nostrils and dissolve in the mucus that coats them.
- They are detected by olfactory cells, chemoreceptors lining the upper nasal cavity.
- The olfactory cells are stimulated to produce a nerve impulse transmitted to the olfactory bulb neurons, leading to the brain via the olfactory nerve.
The Tongue and Taste
When we introduce something into our mouth, we experience a series of sensations through the sense of taste, which we call flavor. This happens because the surface of our tongue has taste cells called chemoreceptors, which are sensitive to chemicals that dissolve in the saliva and reach them.
The Ear, Hearing, and Balance
The ear is the organ that provides us with hearing and balance.
Hearing
This sense allows us to capture vibrations transmitted through the air (sound waves). These are picked up by the external ear pinna, enter through the ear canal, and vibrate the eardrum. This membrane transmits its vibrations to the ossicles of the middle ear, which increases the strength of the movement and, in turn, to a small membrane of the cochlea in the middle ear. The vibration is transmitted through the liquid that fills the cochlea and travels in waves through the coiled ducts, which house the auditory cells of the organ of Corti. Stimulation of cells by auditory nerve impulses originates waves that pass through the cochlear nerve to the brain, where they are interpreted as sound.
Balance
This sense allows us to perceive turns, accelerations, and the positioning of our body. The inner ear has two interconnected chambers called the saccule and utricle, and three semicircular canals oriented in three planes of space. All are filled with a liquid and contain sensory cells for balance. When your body moves, the fluid moves and stimulates the sensory cells that send nerve impulses to the brain via the vestibular nerve. When analyzing the pulse, the brain sends instructions to the muscles to maintain balance.
The Eye and Vision
The eye, whose parts are detailed in the chart below, gives us the sense of vision, which allows us to receive information from the outside in an image. Its process is as follows:
The Eye Receives Light and Focuses on the Retina
The eye functions like a camera with two lenses. The outermost layer, the cornea, directs light into the pupil, which is the center hole of the eye. The pupil is in the middle of the iris, a muscular colored disk. The second lens is the lens that automatically adapts, changing its shape by the action of certain muscles to focus the light on the eye background.
The Retina Converts Light Stimuli into Nerve Impulses
In the retina, there are thousands of photoreceptor cells called rods and cones. These are excited to receive the light focused on it and send a nerve impulse to a network of neurons that processes it and sends it to the brain via the optic nerve. The area of the retina where the optic nerve connects is called the blind spot because it has no receptor cells and does not transmit images.
The Health of the Receptor Organs
Diseases of the Senses
Due to their incidence among the population and the importance of the disability generated, the main diseases of the senses are those that affect hearing and vision.
Diseases of the Hearing and Balance
- Hearing Loss: The decrease or loss of hearing, which may be congenital or caused by infection.
- Vertigo: Strong dizziness due to changes in the sense of balance. Its causes are damage to the inner ear or vestibular nerve, produced, for example, by infection.
Diseases of the Vision
These involve the loss of vision or a decrease in quality and are due to different causes. We highlight the following:
- Eye Injuries: Injury to the eye because of infection or accidents of diverse nature.
- Cataracts: An opaque layer that develops on the lens and prevents the passage of light into the eye. It can cause blindness.
- Refractive Anomalies: The most common are nearsightedness and farsightedness.
- Myopia: People affected see blurred objects at a distance. It is caused by an abnormal elongation of the eyeball. It tends to be genetic or due to common effort of the hearing.
- Hyperopia: People affected see blurred objects located near the eye. It is caused by abnormal shortening of the eyeball. Its causes are the same as those of myopia.
Risk Factors and Prevention
There are certain environmental factors or lifestyle habits that increase the risk of suffering a disease of the organs of the senses. Some measures are:
- Staying in noisy environments
- Intense light exposure
- Long screen use
- Diet low in vitamin A