The Nervous System

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Understanding the Central Nervous System: The Brain’s Command Network

The Brain and Spinal Cord: The Processing Powerhouse

At the core of your nervous system is the Central Nervous System (CNS), which includes:

  • Brain: The ultimate control center.

  • Spinal Cord: The highway for signals between your body and brain.

  • Together, they act as the processing center for all bodily functions, from simple reflexes to complex thoughts.

The Peripheral Nervous System: The Body’s Messenger

Branching out from the CNS is the Peripheral Nervous System (PNS), which is like a network of wires carrying signals to and from every part of your body. It’s divided into:

  • Somatic Sensory: Feels the world around you. It receives signals like touch, pain, and temperature.

  • Somatic Motor: Controls voluntary movements, like lifting your hand or walking.

  • Autonomic Motor: Handles involuntary actions, like your heartbeat or digestion, without you even thinking about it.

Sympathetic vs. Parasympathetic: Two Sides of the Autonomic System

The Autonomic Nervous System is further split into two key players:

1. Sympathetic Nervous System – Fight or Flight

  • Kicks in during emergencies or stress.

  • Releases adrenaline, increasing your heart rate.

  • Blood flows to your legs and extremities, preparing your body for action.

  • Blood vessels widen, boosting blood flow.

2. Parasympathetic Nervous System – Rest and Digest

  • Activates when you're relaxed.

  • Slows heart rate, helps digestion.

  • Brings your body back to a calm state after stress.

  • Brings blood to the digestive tract.

Blood Flow and Nerve Signals

Your nervous system doesn’t just control thoughts—it even tells your blood vessels what to do:

  • In a fight or flight situation, blood vessels expand, increasing blood flow to muscles.

  • More blood flow means more oxygen and nutrients where you need them the most in the extremities of your body

Neuron Structure and Function

Neurons are the basic units of the nervous system, sending and receiving signals like microscopic messengers. Here’s a quick guide to the parts:

  • Dendrites: Branch-like structures that receive signals from the environment or other neurons.

  • Cell Body (Soma): Contains the nucleus and is the cell’s processing center.

  • Axon: Long extension that transmits the electrical signal down the neuron.

  • Myelin Sheath: Fatty layer covering the axon, speeding up signal transmission.

  • Nodes of Ranvier: Gaps in the myelin where the signal jumps, boosting speed.

  • Vesicles & Neurotransmitters: Located at the axon terminal; they release chemicals into the synapse to pass the signal to the next neuron.


How Reflex Arcs Work

Imagine touching a hot stove. Here's what happens behind the scenes in a reflex arc:

  • Sensory neurons pick up the stimulus (heat).

  • Signal goes to the interneuron in your spinal cord.

  • Then a motor neuron sends a message to your muscles to pull your hand away.

  • This happens before your brain even realizes what’s going on. Wild, right?



Action Potential

An action potential is the rapid change in electrical charge that travels along a neuron's axon. Think of it like flipping a switch.

  • Resting potential: The neuron is at -70 mV, ready but inactive.

  • Threshold (-55 mV): The tipping point to fire. Prevents false signals.

  • Depolarization: Sodium (Na⁺) floods into the neuron—charge spikes.

  • Repolarization: Potassium (K⁺) exits—charge drops.

  • Hyperpolarization: It dips and Na+ and K+ slowly swap places.

  • Then, it resets for the next signal.






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