Human Sensory and Nervous Systems: Functions and Processes

Posted on Nov 26, 2024 in Biology

Processes Related to Sensory Function: There are three main groups of processes: the reception of stimuli, the development of coordinated responses, and the implementation of responses. To carry these out, the human being has receptors or sensory organs, systems of coordination, and effector organs.

Stimulus: A change in our environment or within us that we perceive and that provokes a response from our body.

Reception of Stimuli: Our body can capture stimuli because we have receptors that react when they receive certain types of information, emitting an electromagnetic signal or nerve impulse.

Information Processing and Coordination:

Nervous Coordination

The nervous system conducts electrochemical impulses. It receives information from receptors, processes it, interprets it, and develops new answers in the form of electrochemical signals.

Endocrine Coordination

Endocrine organs are glands that discharge substances into the blood when receiving nerve impulses or chemical information from the internal environment.

Receptors and Their Types:

Internal Receptors

Capture changes in the internal environment; they are located throughout the body.

External Receptors

Capture stimuli from the outside environment.

The Skin and Touch: The skin contains a large number of different receptors, each sensitive to a specific stimulus. These sensitive skin receptors allow us to recognize shapes and textures of objects without seeing them.

Receptors of the Skin:

  • Thermoreceptors: Detect temperature differences between the outside and the body, generating the sensations of cold and heat.
  • Nociceptors: Respond to attacks on the skin, generating the sensation of pain.
  • Mechanoreceptors: Detect changes in pressure on the skin or hair movement, allowing us to notice contact with objects.

The Nose and Smell: Although less developed in humans, we can still distinguish over 10,000 different smells. This process occurs as follows:

  1. Volatile molecules enter the nostrils and dissolve in the mucus of the nasal cavity.
  2. They are detected by olfactory cells, chemoreceptors lining the upper inside of the nasal cavity.
  3. Stimulated olfactory cells produce a nerve impulse transmitted to the olfactory bulb neurons, which lead 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 taste cells, known as chemoreceptors, are located on the surface of our tongue. These cells are sensitive to chemicals that dissolve in saliva and reach them.

Taste Receptors: Taste cells are located inside bulb-shaped structures called taste buds. Most taste buds are housed in small prominences on the tongue called papillae.

Main Diseases


The Ear, Hearing, and Balance:

Hearing

The ear is the receptor organ for hearing and balance. We can hear and pick up vibrations transmitted through the air.

Balance

The ear allows us to perceive turns, accelerations, and the positioning of our body.

Parts of the Ear:

  • Outer Ear: Consists of the pinna and external auditory canal.
  • Middle Ear: Consists of the eustachian tube and a chain of three tiny bones: the malleus (hammer), incus (anvil), and stapes (stirrup).
  • Inner Ear: Composed of the cochlea and the semicircular canals.

The Eye and Vision: The eye provides us with the sense of vision, allowing us to perceive information from the outside world such as light, colors, and images.

  • The eye receives light and focuses it onto the retina. The eye has two lenses: the cornea, which directs light into the pupil and is situated in the middle of the iris, and the lens, which changes shape through the action of muscles to focus light on the back of the eye, forming an inverted but sharp image on the retina.
  • The retina converts light stimuli into nerve impulses. Thousands of photoreceptor cells, called rods and cones, send nerve impulses to a network of neurons that processes them and sends them to the brain via the optic nerve. The area of the retina where the optic nerve connects is called the blind spot.

Parts of the Eye: The eye is surrounded by three layers:

  • Sclera: The outermost layer, white in color, but clear in front, forming the cornea.
  • Choroid: The middle layer, with many blood vessels and a dark color.
  • Retina: The inner layer, containing the photoreceptors.

Diseases of the Senses:

Diseases of Hearing and Balance
  • Hearing Loss: The reduction or loss of hearing.
  • Dizziness: Severe dizziness due to an altered sense of balance.
Diseases of Vision
  • Eye Injury: Damage to the eye due to infections or accidents.
  • Cataract: An opaque layer that develops on the lens, preventing the passage of light.
  • Refractive Abnormalities: Most commonly, myopia (nearsightedness) and hyperopia (farsightedness).

Nervous Coordination: The nervous system is responsible for receiving information from receptor organs, processing it, coordinating responses, and sending answers to effector organs. It consists of the central nervous system (CNS) and the peripheral nervous system (PNS).

The Central Nervous System: The part of the nervous system responsible for processing and coordinating information. It consists of the brain and spinal cord.

Parts of the Central Nervous System:

  • Brain: Located inside the head, it has three parts:
    • Cerebrum: A body divided into two hemispheres by a deep central cleft.
    • Cerebellum: Divided into two hemispheres and has convolutions.
    • Brainstem: Connects the brain to the spinal cord.
  • Spinal Cord: A large nerve cord connected to the brainstem and extending through the interior of the spine. It has two functions: channel of communication and development of responses.

The Skeleton: The brain is enclosed inside the skull, and the spinal cord runs through the inside of the spine.

Meninges: Three membranes surround the nerve organs.

The Peripheral Nervous System: Consists of nerves, which are cords that connect the central nervous system to all parts of the body. These nerves can be cranial or spinal.

  • Somatic Nervous System: Connects the central nervous system to the skeletal muscles of our body and skin receptors.
  • Autonomic Nervous System: Connects to many internal organs and is composed of two opposing components: the sympathetic and parasympathetic systems.

Cells of the Nervous System: Composed of nerve tissue formed by neurons and glial cells.

  • Neurons: The basic units of the nervous system, responsible for receiving sensory information. A neuron has a cell body and dendrites. The axons of many neurons are grouped in bundles that make up nerve fibers.
  • Glial Cells: Principal cells include astrocytes, microglia cells, and Schwann cells.

How the Nervous System Works:

  • Sensory Neurons: Transmit impulses from the sense organs to the spinal cord and brain; these are sensory nerves.
  • Motor Neurons: Transmit nerve impulses from the brain and spinal cord to effectors; these are motor nerves.
  • Interneurons: Responsible for connecting with other neurons in the central nervous system.

Depending on the needs of the body, we distinguish between:

  • Voluntary Acts
  • Reflex Actions

Major Diseases of the Nervous System:

  • Disturbances Due to Organ Damage: Degenerative diseases, abnormal development of the nervous system, and trauma.
  • Psychological Disorders: Mood swings and behavioral disorders.

Some Psychological Disorders: The effects of stress, depression, and eating disorders.