Human Sensory System and Nervous System Overview
Human Sensory and Nervous Systems
Sensory System
Our senses allow us to gather information from both inside and outside our bodies, analyze it, and generate appropriate responses. This process involves:
- Perception: Sensory organs (eyes, ears, nose, tongue, skin) capture stimuli such as light, sound, taste, and pressure.
- Analysis: Stimuli are transmitted to the nervous system, where the central nervous system analyzes the information and decides on a reaction.
- Response: The body responds through the locomotor (movement) and endocrine (hormone regulation) systems.
Organs of the Senses
Sight
The sense of sight allows us to perceive color, shape, size, and distance. Light enters the eye through the cornea and pupil (regulated by the iris). The lens focuses the light onto the retina. The retina converts light stimuli into nerve impulses, which are sent to the brain via the optic nerve.
Hearing
The ears perceive sound intensity, duration, and timbre. The outer ear (pinna) collects sound vibrations and transmits them through the ear canal to the eardrum. The eardrum vibrates, transmitting the vibrations to the ossicles (hammer, anvil, and stirrup). The stirrup presses on the oval window, sending vibrations into the fluid-filled cochlea. Hair cells in the cochlea convert these vibrations into nerve impulses, which are transmitted to the brain via the auditory nerve.
Balance
The vestibular system, located in the inner ear, helps us maintain balance and body posture. It consists of semicircular canals filled with fluid and tiny sacs containing otolith crystals. Movement of the fluid or otoliths stimulates hair cells, which send nerve impulses to the brain via the auditory nerve.
Smell
The sense of smell detects chemicals in the air. Airborne particles enter the nasal cavity and come into contact with receptors in the olfactory mucosa. This contact triggers nerve impulses, which are sent to the brain.
Taste
The tongue detects sweet, salty, sour, and bitter tastes. Substances dissolve in saliva and stimulate taste buds, which send nerve impulses to the brain.
Touch
The sense of touch allows us to perceive temperature, pressure, and pain. The skin has two main layers: the epidermis (pain) and the dermis (temperature and pressure). Specialized receptors in these layers send nerve impulses to the brain.
Nervous System
The nervous system analyzes sensory information and formulates responses. This communication is facilitated by neurons.
A neuron consists of:
- Cell body: Contains the nucleus.
- Dendrites: Short branches that receive information from other neurons.
- Axon: A long extension that transmits information to other neurons.
Neurons communicate at synapses. A presynaptic neuron releases neurotransmitters into the synaptic cleft (space between neurons). These neurotransmitters bind to receptors on the postsynaptic neuron, triggering a new nerve impulse.
Central Nervous System (CNS)
The CNS consists of the brain and spinal cord.
- Brain: Divided into two hemispheres and various regions (motor cortex, sensory cortex, visual cortex, auditory cortex, association cortex). It controls complex functions.
- Cerebellum: Coordinates movement and balance. It receives information from the inner ear.
- Brain Stem: Controls vital functions like breathing and heart rate.
- Spinal Cord: Connects the brain to the rest of the body. It also controls reflexes.
Peripheral Nervous System (PNS)
The PNS connects the CNS to the rest of the body. It consists of sensory and motor nerves.
Nervous System and Health
Conditions like anxiety and Alzheimer’s disease affect the nervous system.