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🫀 Science · Human Anatomy and Physiology · Lesson 5 of 12 · 6 min

Nervous system and senses: CNS, PNS, neurons, brain regions, eye and ear

🧠 The nervous system is one of the most heavily tested systems in TEAS anatomy. Sort its divisions, know the parts of a neuron, and match each brain region to its job.

💡 Key idea

Sympathetic speeds the body up for emergencies, parasympathetic restores rest and digestion.

🧠 The idea

The CENTRAL NERVOUS SYSTEM is the brain and spinal cord; the PERIPHERAL NERVOUS SYSTEM is cranial and spinal nerves. Sensory (afferent) neurons carry signals in; motor (efferent) neurons carry them out. Motor output is SOMATIC (voluntary, skeletal muscle) or AUTONOMIC (heart, smooth muscle, glands). Autonomic branches: SYMPATHETIC ("fight or flight": faster heart rate, dilated pupils and bronchioles, slowed digestion) and PARASYMPATHETIC ("rest and digest"). A NEURON receives signals on dendrites, integrates them in the cell body, and sends an action potential down the axon to terminals that release neurotransmitter at the synapse. Myelin (Schwann cells in the PNS, oligodendrocytes in the CNS) speeds conduction. Cerebrum: thought, voluntary movement, senses (frontal, parietal, temporal, occipital lobes). Cerebellum: balance, coordination. Medulla: breathing, heart rate. Hypothalamus: temperature, hunger, pituitary control. Reflex arc: receptor, sensory neuron, interneuron, motor neuron, effector (the knee-jerk stretch reflex skips the interneuron). Eye: cornea and lens focus light on the retina (rods for dim light, cones for color). Ear: cochlea for hearing, semicircular canals for balance.

✏️ Worked example

You touch a hot pan and pull your hand away before you feel pain. Trace the reflex arc: heat receptors in the skin fire; a sensory neuron carries the signal to the spinal cord; an interneuron relays it to a motor neuron; the motor neuron makes the biceps (the effector) contract. The brain is not needed for the withdrawal, which is why it is so fast. A second later, the signal reaching the parietal lobe lets you feel the burn, and your sympathetic system raises your heart rate.

📌 Takeaways

  • CNS = brain and spinal cord; PNS = nerves; afferent in, efferent out.
  • Dendrite to cell body to axon to axon terminal; myelin speeds the impulse.
  • Cerebellum = coordination, medulla = breathing and heart rate, hypothalamus = homeostasis.

✅ Check yourself

Question 1 of 3

Which response is caused by the parasympathetic division?

  1. Increased digestive activity
  2. Release of glucose from the liver
  3. Dilated pupils
  4. Increased heart rate
Show the answer and rationale

Answer: A

The parasympathetic division promotes rest and digest, so it increases digestive activity. Dilated pupils, a faster heart rate and release of glucose from the liver are all sympathetic fight-or-flight responses.

Question 2 of 3

Which part of the neuron carries the impulse away from the cell body?

  1. Axon
  2. Dendrite
  3. Nucleus
  4. Synaptic cleft
Show the answer and rationale

Answer: A

The axon conducts the action potential away from the cell body toward the axon terminals. Dendrites carry signals toward the cell body, the synaptic cleft is the gap between cells, and the nucleus sits in the cell body.

Question 3 of 3

A patient with damage to the cerebellum would most likely have trouble with which function?

  1. Seeing colors
  2. Regulating body temperature
  3. Forming speech sounds
  4. Coordinating balance
Show the answer and rationale

Answer: D

The cerebellum coordinates movement and balance. Color vision depends on cones and the occipital lobe, temperature is regulated by the hypothalamus, and speech production is a frontal lobe function.

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