Neuron: The Building Block of Your Nervous System 🧠

Neurons are special cells that detect, receive, and send signals in your body. They’re the structural and functional units of your nervous system!

🧩 Parts of a Neuron

  • Cell body: The control center with cytoplasm, nucleus, and Nissl’s granules (special protein-making granules).
  • Dendrites: Branch-like structures carrying signals toward the cell body.
  • Axon: A long cable sending signals away from the cell body. Ends with synaptic knobs (bulb-shaped tips) that store neurotransmitters (chemical messengers).

🔤 Neuron Types (Based on Branches)

  • Multipolar: 1 axon + 2+ dendrites (e.g., brain’s cerebral cortex) 🧠
  • Bipolar: 1 axon + 1 dendrite (e.g., eye’s retina 👁️)
  • Unipolar: Only 1 axon (mostly in embryos 👶)

⚡ Nerve Wires: Axons

  • Myelinated axons: Wrapped in Schwann cells that form a fatty myelin sheath. Gaps between sheaths are Nodes of Ranvier (like speed-boosters!). Found in spinal/cranial nerves.
  • Non-myelinated axons: Covered by Schwann cells without myelin. Common in automatic body functions (e.g., digestion).

🔋 How Nerve Signals Work

Resting State (Charging Up!):

  • Neuron membrane is polarized (inside: negative, outside: positive).
  • Maintained by the sodium-potassium pump (moves 3 Na⁺ out, 2 K⁺ in).
  • This voltage difference is the resting potential.

Signal Trigger (Action Time!):

  1. Stimulus opens sodium (Na⁺) gates → Na⁺ rushes INSIDE.
  2. Membrane flips charge at that spot (depolarization).
  3. This creates an action potential (nerve signal!).
  4. Signal “jumps” along the axon via current flow between nodes.
  5. Potassium (K⁺) leaks out afterward → restores resting charge (repolarization).

💌 Passing Signals: Synapses

Neurons chat at junctions called synapses:

  • Electrical synapse: Super fast! Current zaps directly between cells. (Rare in humans). ⚡
  • Chemical synapse (Most common):
    1. Signal reaches axon tip → releases neurotransmitters into the synaptic cleft (tiny gap).
    2. Chemicals bind to receptors on the next neuron.
    3. This opens ion channels → new signal starts! 🚦
    4. Can be excitatory (GO signal) or inhibitory (STOP signal).

🏛️ Central Nervous System (CNS)

Your brain + spinal cord = Mission Control! 🎮 It:

  • Processes info, controls voluntary moves, balance, organs (heart/lungs), temperature, hunger, sleep cycles, hormones, and emotions.
  • Protected by: skull + 3 meninges layers (dura mater → arachnoid → pia mater).
  • 3 main parts: Forebrain, Midbrain, Hindbrain.

🎯 NEET Super-Important Concepts!

  1. Neuron structure (dendrites vs. axon, synaptic knobs, Nissl’s granules).
  2. Action potential generation (resting potential, depolarization, Na⁺/K⁺ movement).
  3. Synaptic transmission (neurotransmitters, excitatory/inhibitory signals).
  4. Axon types (myelinated vs. non-myelinated; Schwann cells, Nodes of Ranvier).
  5. CNS protection (meninges layers: dura, arachnoid, pia mater).

You’ve got this! Break a leg! 💪✨