Sensory Receptors and the Nervous System: Functions and Disorders

**Sensory Receptors**

Internal Receptors

Internal receptors capture changes in the internal environment, like the standard of the receptors.

External Receptors

External receptors capture stimuli from outside the body. Some are scattered, and others are grouped into sensory organs.

Receptors in the Skin

• Thermoreceptors: These capture external temperature differences in the body. There are two types: those that react to higher temperatures and those that react to lower temperatures. They generate feelings of cold and heat.
• Nociceptors: These respond to skin aggressions. The nerve impulses they generate are painless.
• Mechanoreceptors: These detect changes in pressure on the skin or movement of the hairs.

Smell

1. The molecules of volatile substances enter the nasal passages and dissolve in the mucus lining.
2. Olfactory cells detect them. They are chemoreceptors.
3. Stimulated olfactory cells produce nerve impulses that are transmitted to the neurons of the olfactory bulb. They are then conducted by the olfactory nerve.

Primary Odors and Flavors: Camphor, musk, flowers, mint, ether, pungent, and putrid. Acid, bitter, sweet, and salty.

Hearing

The pinna captures air vibrations. These enter the ear canal and vibrate the eardrum. The vibration is transmitted to the chain of ossicles, which multiplies the force and movement of the shell membrane. The vibration is transmitted by the liquid that fills the cochlea. Waves reach the auditory cells. Their stimulation causes nerve impulses that exit through the cochlear nerve to the brain, where sounds are interpreted.

Balance

Balance allows us to perceive turns, position, and accelerations of our body. The inner ear has two interconnected chambers, the saccule and the utricle, and three semicircular canals. They are filled with liquid and have balance sensory cells. When we move, the liquid also moves, and this helps us maintain balance.

Eye

The cornea directs light to the pupil. In the middle is the iris, which is colored and adjusts the intensity of light that enters the eye. The lens focuses the amount of light that enters the eye. An inverted image is formed on the retina. There, the rods and cones send nerve impulses to a network of neurons that processes it and sends it to the brain via the optic nerve. The retina, where the optic nerve is reported, has a blind spot. Impulses reach the brain.

**Diseases**

• Hearing Loss: Decrease or loss of hearing, caused by infections in the ear, loud or continuous noises, or accidents.
• Vertigo: Dizziness due to alterations in balance, damage to the vestibular nerve, or the inner ear.
• Ocular Lesions: Damage to the eye due to infections or accidents.
• Cataract: A layer that prevents light from passing is in the lens, and it prevents the passage of light, leaving you blind.
• Refractive Anomalies:
  • Myopia: Blurred vision of things that are far from the eye, caused by a lengthening of the eyeball. It often has a genetic origin or is due to habitual effort of sight.
  • Hyperopia: Blurred vision of things that are close to the eye. It originates from a shortening of the eyeball. It often has a genetic origin or is due to habitual effort of sight.

**Central Nervous System**

Brain

The brain is divided into two parts. The cortex has lobes and circumvolutions. Here, information from the senses is interpreted, movements are controlled, and advanced functions are developed.

Cerebellum

The cerebellum is divided into two parts and has circumvolutions. It controls balance and the movements of the muscles.

Brain Stem

The brain stem connects the brain to the spinal cord. It controls involuntary functions. The medulla oblongata controls expiration and heart rate.

Spinal Cord

• Communication Pathway: It carries stimuli to the brain and responses from the brain.
• Elaboration of Responses: It produces very simple responses.