The Nervous System
The Nervous System:
The nervous system is the body's main control and communication system. It collects information from inside and outside the body, processes it, and then sends instructions to different parts of the body to respond.
Key Definitions and Components
What It Is..?
The nervous system is a network of special cells called neurons that transmit electrical impulses throughout the body.
It works closely with the endocrine system (hormones) to maintain homeostasis (a stable internal balance).
Parts of a Neuron (The Nerve Cell)
A neuron is the basic functional unit.
- Cell Body (Soma): Contains the nucleus; controls activities.
Dendrites: Receive impulses (signals) from other neurons.
Axon: Transmits impulses away from the cell body.
Myelin Sheath: A fatty layer around the axon that speeds up impulse transmission.
Synapse: The tiny gap between neurons or between a neuron and a muscle/gland, where impulses are transferred.
Organization of the Nervous System
The nervous system is divided into three main parts:
1. Central Nervous System (CNS)
Components: Brain and Spinal Cord.
Function: Controls thinking, memory, emotions, and decision-making. The spinal cord connects the brain to the rest of the body and handles reflex actions.
2. Peripheral Nervous System (PNS)
Components: All nerves outside the CNS (nerves to limbs and organs).
Function: Connects the CNS to the limbs and organs. It transmits sensory information (from sense organs) to the CNS and carries motor commands (instructions) from the CNS.
3. Autonomic Nervous System (ANS)
Function: Controls involuntary actions (actions we don't think about), such as heartbeat, digestion, and breathing.
Divided into:
Sympathetic: Prepares the body for "fight or flight" (e.g., increased heart rate).
Parasympathetic: Calms the body and restores energy.
Functions and Applications
Main Functions
Sensory: Receives information from sense organs.
Integrative: Processes and interprets sensory input in the brain.
Motor: Sends commands to muscles and glands to respond.
Important Role: Enables learning, memory, and intelligence.
Example: The Reflex Action
A reflex action is a quick, automatic response to a stimulus (e.g., quickly withdrawing a hand from a hot surface).
Stimulus: Touching a hot object.
Pathway (Reflex Arc): Sensory Neuron → Spinal Cord → Motor Neuron → Muscle Contraction (move hand).