Sensory Receptors and Organs: Structure and Function

Sensory Receptors

Sensory receptors are specialized nerve cells that capture stimuli and transform them into nerve impulses. They include chemoreceptors, mechanoreceptors, photoreceptors, thermoreceptors, and nociceptors.

Interoreceptors

Interoreceptors, also called internal receptors, are located inside the body. They detect information from the internal organs and viscera.

Exteroreceptors

Exteroreceptors, also called external receptors, are located on the body surface. They recognize external stimuli such as light, sound, and temperature.

Vision

Vision resides in the eyes, which are complex organs specialized in receiving light stimuli.

Eyeball

The eyeball is spherical, and its walls are made of three layers: the sclera, the choroid, and the retina.

Accessory Organs

The accessory organs protect the eye and allow its movement. They include the eyelids, eyelashes, the tear apparatus, and the eye muscles.

Parts of the Eye

The main parts of the eye are the lens, cornea, pupil, aqueous humor, iris, vitreous humor, sclera, choroid, retina, optic nerve, and blind spot.

Hearing and Balance

The ear is the organ of hearing and balance. It captures sounds and converts them into nerve impulses.

Hearing

The outer ear captures sounds and transmits them through the auditory canal to the eardrum, which vibrates. These vibrations are transmitted by the ossicles (hammer, anvil, and stirrup) to the cochlea, where hair cells transmit them to the auditory nerve.

Balance

Balance depends on fluid in the semicircular canals. When the head moves, the fluid moves and transfers information about position.

Parts of the Ear

The parts of the ear include the auditory pinna (outer ear), auditory canal, eardrum, hammer, anvil, stirrup, Eustachian tube, auditory nerve, cochlea, and semicircular canals.

Touch

The sense of touch is located in the skin, which has two main layers:

• Epidermis: the outer layer, made of epithelial tissue formed by several layers of cells.
• Dermis: the inner layer, made of connective tissue containing elastic fibers and receptors such as Meissner corpuscles (light touch), Vater-Pacini corpuscles (pressure and vibration), Ruffini endings (heat), and cold receptors.

Smell

The olfactory organ is the nasal cavity, which has two regions:

• Inferior region: the lower part, which has blood vessels that warm the inspired air.
• Superior region: the upper part, which contains the olfactory receptors that form the olfactory bulb.

Taste

On the surface of the tongue there are numerous papillae called taste buds, which detect the four basic flavors: sweet, salty, bitter, and sour.

Locomotor System

The locomotor system is responsible for body movement and motor responses, in coordination with the nervous system. It provides internal support for the body and facilitates its movements and displacements.

Skeletal System

The skeletal system is the passive part of the locomotor system. It is formed by the skeleton, made up of bones and joints.

Muscular System

The muscular system is the active part of the locomotor system. It is formed by muscles and their tendons.

Bones

Bones are living organs that grow and renew themselves. They are composed of calcium, phosphorus, and collagen.

Joints

Joints are the points where two or more bones connect.