Human Sensory Systems and Nervous System Functions

Taste and the Tongue

Flavors are perceived by the tongue through chemoreceptors known as taste cells. There are four basic tastes from which others are derived: sour, bitter, sweet, and salty.

The Ear and Hearing

Hearing allows us to perceive sound waves. These waves are collected by the pinna, penetrate the ear canal, and vibrate the eardrum. This membrane transmits vibrations to the ossicles, which move another small membrane located in the cochlea. The vibration is transmitted through the liquid filling the cochlea, traveling in waves to the cochlear nerve, which sends signals to the brain to be interpreted as sound.

Balance and Equilibrium

Balance allows us to perceive turns, accelerations, and the positioning of our body; this process occurs in the semicircular canals.

The Eye and Vision

The eye utilizes two lenses:

• Cornea: The outer lens that directs light toward the pupil.
• Lens: The inner lens that adjusts automatically.

The pupil is the center hole of the eye, situated in the middle of the iris, a colored muscular disc. Light forms an inverted but clear image on the retina. Thousands of retinal photoreceptor cells, called rods and cones, are excited by the light and send nerve impulses to a network of neurons, which processes the information and sends it to the brain via the optic nerve.

Common Sensory Disorders

• Hearing loss: Impairment of auditory function.
• Vertigo: Strong dizziness caused by inner ear damage.
• Myopia: Difficulty seeing distant objects.
• Hyperopia: Difficulty seeing near objects.
• Cataracts: An opaque layer that develops on the lens, preventing the passage of light.

The Nervous System

The Central Nervous System (CNS) is responsible for the coordination and processing of information; it consists of the brain and the spinal cord.

The Brain

The brain is composed of several specialized parts:

• Sensory Cortex: Interprets information from the senses.
• Motor Cortex: Controls voluntary movements.
• Association Cortex: Responsible for thinking, speaking, and remembering.
• Cerebellum: Coordinates voluntary muscle movements.
• Brain Stem: Connects the encephalon to the spinal cord and controls involuntary actions.
• Medulla Oblongata: Controls heart rate and breathing.

The Spinal Cord

The spinal cord is a nerve cord with two primary functions:

1. It serves as a means of communication for stimuli.
2. It produces simple reflex responses (e.g., removing a hand from fire).