Human Nervous System & Sensory Organs Explained
The Human Nervous System & Sensory Organs
Peripheral Nervous System (PNS)
The Peripheral Nervous System (PNS) encompasses all parts of the nervous system located outside of the brain and spinal cord. It includes both cranial nerves (originating from the brain) and spinal nerves (originating from the spinal cord).
Functional Divisions of the Nervous System
The nervous system is broadly divided into several functional components:
Somatic Nervous System
The Somatic Nervous System receives information from external stimuli and transmits signals for voluntary muscle contractions.
Autonomic Nervous System
The Autonomic Nervous System is responsible for regulating and controlling involuntary body functions, such as heart rate, digestion, and respiration.
The Body’s Sensory Systems
Our bodies are equipped with sophisticated sensory systems that allow us to perceive and interact with the world around us.
Vision: The Eye and Pupil
The size of the pupils adjusts, opening more or less, through the contraction or relaxation of very small muscles located in the iris. This regulates the amount of light entering the eye.
The eye’s lens modifies its thickness thanks to muscles in the ciliary body. This allows the lens to become flatter for distant vision or more curved for close-up focus, a process known as accommodation.
Hearing & Balance: The Ear
The ear is responsible for detecting sounds and sensing changes in body position (balance).
The ear is divided into three main parts:
- Outer Ear: Made up of the pinna (auricle) and the ear canal, which ends at the eardrum (tympanic membrane).
- Middle Ear: Starts at the eardrum and extends to the oval window and round window, containing the ossicles (malleus, incus, stapes).
- Inner Ear: Composed of two primary parts: the cochlea (for hearing) and the vestibule (for balance).
Taste: Gustation
Taste buds are very small structures located on the tongue and throughout the mouth, which detect flavors in food and drinks.
Smell: Olfaction
The sense of smell, or olfaction, allows us to detect gas molecules that reach the nose.
Touch: Somatosensation
The sense of touch, or somatosensation, allows us to perceive various stimuli through the skin, including:
- The shape and texture of objects and substances
- Pressure from force that contacts the body
- Heat or cold (temperature)
- Pain