October 2026 - Nervous System Study Guide

The divisions, in order

Almost every question on this topic is asking where in this hierarchy something sits.

Sympathetic against parasympathetic

Expect at least one question distinguishing these. They oppose each other organ by organ.

The neuron

Signals travel one way through a neuron, and the parts are named by their role in that journey.

• Dendrites receive incoming signals.
• The cell body integrates them.
• The axon carries the impulse away.
• The myelin sheath insulates the axon and speeds conduction.
• The synapse is the gap between neurons, crossed by chemical neurotransmitters rather than by the electrical signal itself.

Reflex arcs

A reflex bypasses the brain. A sensory neuron carries the signal to the spinal cord, where it connects — sometimes through a single interneuron — straight to a motor neuron that produces the response. The brain is informed afterwards, which is why you have already pulled your hand back before you feel the pain.

That short route is the point: fewer synapses mean less delay, and the protective response happens faster than conscious decision could manage.

Brain regions worth knowing

• Cerebrum — thought, voluntary movement, sensation, language. The largest part.
• Cerebellum — balance, coordination and fine motor control.
• Brainstem — breathing, heart rate and blood pressure. Damage here is life-threatening because these functions are automatic.
• Hypothalamus — temperature, hunger, thirst, and the link between the nervous and endocrine systems.

Terms to know

CNS

Central nervous system: the brain and spinal cord.

PNS

Peripheral nervous system: all nerves outside the CNS.

Somatic

The voluntary division of the PNS, controlling skeletal muscle.

Autonomic

The involuntary division, controlling organs and glands.

Sympathetic

The fight-or-flight branch of the autonomic system.

Parasympathetic

The rest-and-digest branch.

Neuron

A nerve cell: dendrites, cell body, axon.

Synapse

The junction between two neurons, crossed by neurotransmitters.

Myelin

The insulating sheath that speeds signal conduction along an axon.

Reflex arc

A rapid response routed through the spinal cord rather than the brain.

What the TEAS asks most

The same core ideas appear in different wording. If you can answer these without stopping to think, you have what this section requires.

Key points

• CNS is brain and spinal cord; PNS is everything else.
• PNS splits into somatic (voluntary) and autonomic (involuntary).
• Sympathetic is fight or flight; parasympathetic is rest and digest.
• Signals run dendrites → cell body → axon → synapse.
• Reflexes are processed in the spinal cord, which is what makes them fast.