Focus: Human Neural System, Neuron Structure, and Brain Functions.
1. Introduction to the Neural System
The neural system is the network of specialized cells (neurons) that transmit signals between different parts of the body. In humans, this system is highly developed to provide coordination—the process through which two or more organs interact and complement the functions of one another.
Rich Insight: While the Endocrine system uses hormones (slow), the Neural system uses electrical impulses (fast) to maintain homeostasis.
2. The Neuron: Unit of Neural System
A neuron is a microscopic structure composed of three major parts: Cell body, Dendrites, and Axon.
- Dendrites: Short fibers which branch repeatedly and project out of the cell body. They receive impulses.
- Cell Body: Contains cytoplasm with typical cell organelles and specific granular bodies called Nissl’s granules.
- Axon: A long fiber that transmits impulses away from the cell body to a synapse.
Types of Neurons
- Multipolar: One axon and two or more dendrites (found in the Cerebral Cortex).
- Bipolar: One axon and one dendrite (found in the Retina of the eye).
- Unipolar: Cell body with one axon only (found usually in the embryonic stage).
3. Generation and Conduction of Nerve Impulse
This is a favorite topic for NEET examiners. It happens in three stages:
| Stage | State of Membrane | Electrical Charge |
| Resting Potential | Polarized | Inside is Negative (-70mV) |
| Action Potential | Depolarized | Na+ floods in; Inside becomes Positive |
| Repolarization | Recovery | K+ moves out; Returning to Negative |
4. The Human Brain (Central Nervous System)
The brain is the central information processing organ of our body and acts as the ‘command and control system’.
A. Forebrain
- Cerebrum: The largest part; responsible for memory, communication, and intelligence.
- Thalamus: The relay station for sensory and motor signaling.
- Hypothalamus: Controls body temperature, urge for eating and drinking, and secretes hypothalamic hormones.
B. Midbrain
Located between the thalamus/hypothalamus and the pons. It contains four round swellings called Corpora Quadrigemina (responsible for visual and auditory reflexes).
C. Hindbrain
- Pons: Connects different regions of the brain.
- Cerebellum: Has a very convoluted surface to provide extra space for more neurons (controls balance and posture).
- Medulla: Connected to the spinal cord; controls respiration, cardiovascular reflexes, and gastric secretions.
5. Reflex Action and Reflex Arc
A reflex action is an immediate, involuntary response to a stimulus.
- The Pathway: Receptor→Sensory Neuron→Spinal Cord (CNS) → Motor Neuron → Effector (Muscle).
📽️ Recommended Video Masterclass
To visualize how a nerve impulse actually “jumps” across a synapse, watch this curated expert explanation:
NEET Focus Points (High Yield)
- Nissl’s Granules: Present in the cell body and dendrites but absent in the Axon.
- Myelin Sheath: In the CNS, it is formed by Oligodendrocytes; in the PNS, it is formed by Schwann cells.
- Vitreous Humor: The transparent gel between the lens and the retina.
Ask a Doubt / Student Discussion
Found a concept difficult? Or noticed a point we missed? Comment below and our team (or your fellow students) will help you out!