Sensory Receptors and the Human Body Systems
Sensory Receptors
Structures formed by specialized nerve cells to capture and transform stimuli into nerve impulses.
According to Stimuli Captured
- Chemoreceptors: Sensitive to chemicals.
- Mechanoreceptors: Sensitive to mechanical stimuli.
- Photoreceptors: Light-sensitive.
- Thermoreceptors: Sensitive to temperature variations.
- Nociceptors: Responsible for the sensation of pain.
Depending on Their Position
- Internal receptors: Responsible for collecting information inside the body.
- External receptors: Responsible for collecting information from the outside through the sense organs.
Vision
This sense resides in the eyes, organs that capture light stimuli.
Operation
Light enters the eye through the cornea. The pupil controls the amount of light that enters. From the cornea, light is directed to the lens, which focuses the image. The image formed on the retina is captured by photoreceptors and transformed into nerve impulses. These impulses are transmitted by the optic nerve to the cerebral cortex.
Hearing
The ears are the organs responsible for hearing and balance.
Operation
- Audition: Vibrations reach the eardrum, which transmits them to the ossicles (hammer, anvil, and stirrup). These vibrations are then transmitted to the cochlea, and then via nerve impulses through the auditory nerve to the brain.
- Equilibrium: This is located in the semicircular canals. Internal cells transmit information about head position to the brain via nerve impulses.
Touch
- Epidermis: The outer layer of skin, formed by epithelial cells that shed and renew continuously. These cells produce keratin, which waterproofs the skin.
- Dermis: The inner layer of the skin, formed by connective tissue. It contains corpuscles responsible for different sensations, such as Meissner’s corpuscles (touch-sensitive), Vater-Pacini corpuscles (pressure-sensitive), Krause corpuscles (cold-sensitive), and Ruffini corpuscles (heat-sensitive).
Smell
Inside the nose is the pituitary gland. There are two regions:
- Red Pituitary: Lower region. Warms the inspired air.
- Yellow Pituitary: Upper region. Contains many olfactory receptors, from which the olfactory nerve carries information to the brain.
Taste
On the surface of the tongue are numerous projections called papillae.
The tongue detects four basic tastes: sweet, salty, sour, and bitter.
The Locomotive System
Responsible for carrying out motor responses prepared by the nervous system. It is divided into two subsystems:
- Skeletal system: The passive part of the musculoskeletal system.
- Muscular system: The active part of the musculoskeletal system.
Bones
Bones are living organisms that feed and grow. There are three types of bones: short, long, and flat. All bones are surrounded by a thin layer of tissue called the periosteum. Ossification is the process of bone growth with advancing age.
Joints
- Immobile: No movement is allowed between the bones. Example: bones of the skull.
- Semi-mobile: Allow very little movement. Cartilage and ligaments strengthen the joint between the bones. Example: Intervertebral discs.
- Mobile: Allow a wide range of motion. The bones are joined by a joint capsule containing cartilage.
Synovial fluid cushions blows in elbows and knees.
Muscles
Muscles are made up of muscle fibers that can contract or relax. There are three types of muscles:
- Smooth muscle: Involuntary and slow contraction.
- Skeletal muscle: Rapid and voluntary movements. Each fiber is surrounded by a thin layer of connective tissue (endomysium). These muscle fiber bundles are surrounded by another layer of connective tissue (perimysium), and many of these bundles cluster and are surrounded by another layer (epimysium). The union of all these envelopes forms the tendons.
- Cardiac muscle: Rapid and involuntary contraction. Composed of striated muscle fibers.
Skeletal Muscle Types
According to shape: Annular, flat, orbicular, and fusiform (spindle-shaped).
According to function: Flexors and extensors, abductors and adductors, pronators and supinators, elevators and depressors, sphincters and dilators.