What is the Nervous System?
The nervous system is the body's communication network, using electrical and chemical signals to coordinate movement, sensation, and thought. It is organized into the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves connecting the CNS to the rest of the body). Specialized cells called neurons transmit these signals at speeds ranging from under 1 m/s to over 120 m/s.
The nervous system controls the body by sending electrical impulses through neurons, coordinating everything from reflexes to conscious thought via the brain, spinal cord, and peripheral nerves.
- •Brain
- •Spinal cord
- •Processes and integrates information
- •Protected by skull and vertebrae
- •Cranial and spinal nerves
- •Somatic and autonomic divisions
- •Carries signals to/from the CNS
- •Connects the CNS to muscles and organs
Try it: interactive calculator
Step-by-step worked examples
A nerve impulse travels 1.2 meters along a myelinated motor neuron at 120 m/s. How long does it take to reach the muscle?
time = distance / speed = 1.2 m / 120 m/s = 0.01 s = 10 milliseconds
Compare that to an unmyelinated pain fiber conducting at 1 m/s over the same 1.2 m — how long does the signal take?
time = 1.2 m / 1 m/s = 1.2 seconds That is 120× slower than the myelinated motor neuron
A reflex arc (touching a hot object) involves the withdrawal reflex, bypassing the brain. If the spinal reflex path is 0.8 m and conducts at 80 m/s, find the reaction time.
time = 0.8 m / 80 m/s = 0.01 s = 10 milliseconds — much faster than the ~200 ms it takes to consciously perceive pain
Flashcards
Quick quiz
Q1.Which structures make up the CNS?
Q2.A myelinated neuron conducts a signal 1 m in 0.01 s. What's its conduction velocity?
Q3.Which division of the PNS controls involuntary functions like heart rate?
Q4.What role does myelin play?
The full card deck, worked steps and AI-tutor support for “What is the Nervous System?” are in Notek — study by hand before your exam.
Common mistakes
All nerve signals travel at the same speed. — Correct: Speed varies widely — myelinated fibers can conduct over 100 m/s, unmyelinated fibers under 2 m/s.
Reflexes are processed by the brain first. — Correct: Many reflexes route through the spinal cord only, which is why they're faster than conscious reactions.
The PNS includes the brain and spinal cord. — Correct: The PNS is everything OUTSIDE the brain and spinal cord — the CNS is brain + spinal cord only.
The autonomic nervous system is fully voluntary. — Correct: It controls involuntary functions like heart rate and digestion, mostly outside conscious control.
FAQ
What is the nervous system?
It's the body's control network — brain, spinal cord, and nerves — that sends electrical signals to coordinate movement, senses, and thought.
What is the formula for nerve conduction velocity?
Velocity = distance ÷ time (v = d/t), typically measured in meters per second.
What are examples of the nervous system in action?
A knee-jerk reflex, a myelinated motor neuron firing a muscle, and slow unmyelinated pain-fiber signaling are classic examples.
How do you calculate nerve conduction velocity?
Divide the distance a signal travels by the time it takes — try it with your own numbers in the calculator above.