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Function of the Nervous System

Sensory input, integration, and motor output.

CNS (Central Nervous System)

Brain and spinal cord; control center.

PNS (Peripheral Nervous System)

Cranial and spinal nerves; connects CNS to body.

Sensory (Afferent) Division

Carries information to the CNS.

Motor (Efferent) Division

Carries commands from CNS to effectors.

Somatic Nervous System (SNS)

Voluntary control of skeletal muscles.

Autonomic Nervous System (ANS)

Involuntary control of smooth muscle, cardiac muscle, glands.

Sympathetic Division

Fight or flight response.

Parasympathetic Division

Rest and digest response.

Neuron

Basic functional cell of the nervous system.

Dendrites

Receive signals from other neurons.

Axon

Sends impulses away from the cell body.

Axon Hillock

Trigger zone for action potential.

Myelin Sheath

Insulates axon and speeds conduction.

Nodes of Ranvier

Gaps between myelin for saltatory conduction.

Multipolar Neuron

Many dendrites, one axon; motor neurons, CNS.

Bipolar Neuron

One dendrite, one axon; found in eye and ear.

Unipolar (Pseudounipolar) Neuron

One process; sensory neurons.

Astrocytes

Support neurons, regulate environment (CNS).

Microglia

Immune defense cells in CNS.

Ependymal Cells

Line ventricles, produce and circulate CSF.

Oligodendrocytes

Form myelin in CNS.

Schwann Cells

Form myelin in PNS.

Satellite Cells

Support neuron cell bodies in PNS.

⚡ Action Potentials & Conduction

Resting Membrane Potential

–70 mV, maintained by Na⁺/K⁺ pump.

Depolarization

Na⁺ channels open; inside becomes positive.

Repolarization

K⁺ channels open; inside becomes negative again.

Hyperpolarization

Membrane potential more negative than resting.

Absolute Refractory Period

No new AP can occur.

Relative Refractory Period

Stronger stimulus may trigger AP.

Saltatory Conduction

AP jumps node to node in myelinated axons.

Continuous Conduction

Slower; AP travels entire unmyelinated axon.

Step 1: AP reaches axon terminal

Voltage-gated Ca²⁺ channels open.

Step 2: Ca²⁺ influx

Triggers vesicles to release neurotransmitters.

Step 3: Neurotransmitters cross cleft

Bind to receptors on postsynaptic cell.

EPSP (Excitatory Postsynaptic Potential)

Depolarization increases chance of AP.

IPSP (Inhibitory Postsynaptic Potential)

Hyperpolarization decreases chance of AP.

Neurotransmitter removal

By reuptake, enzymatic breakdown, or diffusion.

Acetylcholine (ACh)

Muscle contraction, parasympathetic activity.

Glutamate

Main excitatory neurotransmitter.

GABA

Main inhibitory neurotransmitter in brain.

Glycine

Inhibitory neurotransmitter in spinal cord.

Dopamine

Mood, movement, reward.

Serotonin

Mood and sleep regulation.

Norepinephrine (NE)

Arousal and alertness; sympathetic system.

Endorphins

Natural painkillers, pleasure.

Substance P

Transmits pain signals.

Cerebrum

Thinking, memory, voluntary control.

Diencephalon

Contains thalamus, hypothalamus, epithalamus.