Key Takeaways
- CNS = brain and spinal cord; PNS = all nerves outside CNS
- Neurons have dendrites (receive), cell body, axon (transmit), and synaptic terminals (release)
- Sensory neurons carry signals to CNS; motor neurons carry signals from CNS
- Sympathetic = "fight or flight"; Parasympathetic = "rest and digest"
- The four cerebral lobes are frontal (reasoning), parietal (sensory), temporal (hearing), occipital (vision)
Last updated: January 2026
The Nervous System
The nervous system controls and coordinates all body functions through electrical and chemical signals. It is divided into the central nervous system (CNS) and peripheral nervous system (PNS).
Nervous System Divisions
| Division | Components | Function |
|---|---|---|
| Central Nervous System (CNS) | Brain, spinal cord | Integration, processing |
| Peripheral Nervous System (PNS) | Nerves, ganglia | Communication with body |
The Brain
| Region | Location | Functions |
|---|---|---|
| Cerebrum | Largest part, top | Thinking, memory, voluntary movement, senses |
| Cerebellum | Back, below cerebrum | Balance, coordination, fine motor skills |
| Brainstem | Base | Vital functions (breathing, heart rate, consciousness) |
| Diencephalon | Between cerebrum and brainstem | Thalamus (relay), hypothalamus (homeostasis) |
Cerebral Lobes
| Lobe | Location | Functions |
|---|---|---|
| Frontal | Front | Reasoning, planning, speech, voluntary movement |
| Parietal | Top-back | Sensory processing, spatial awareness |
| Temporal | Sides | Hearing, memory, language comprehension |
| Occipital | Back | Vision |
Neurons
Neurons are the functional units of the nervous system.
| Part | Function |
|---|---|
| Cell body (soma) | Contains nucleus, metabolic center |
| Dendrites | Receive signals from other neurons |
| Axon | Carries signals away from cell body |
| Myelin sheath | Insulates axon, speeds transmission |
| Synaptic terminals | Release neurotransmitters |
Types of Neurons
| Type | Function | Example |
|---|---|---|
| Sensory (afferent) | Carry signals TO CNS | Touch receptors |
| Motor (efferent) | Carry signals FROM CNS | Muscle activation |
| Interneurons | Connect neurons within CNS | Integration |
Nerve Impulse Transmission
- Resting potential: Neuron at rest (-70 mV)
- Depolarization: Sodium rushes in (becomes positive)
- Action potential: Electrical signal travels down axon
- Repolarization: Potassium rushes out (returns to negative)
- Synaptic transmission: Neurotransmitter released at synapse
Neurotransmitters
| Neurotransmitter | Function |
|---|---|
| Acetylcholine | Muscle activation, memory |
| Dopamine | Reward, movement, mood |
| Serotonin | Mood, sleep, appetite |
| Norepinephrine | Alertness, fight-or-flight |
| GABA | Inhibition, calming |
| Glutamate | Excitation, learning |
Peripheral Nervous System
| Division | Components | Function |
|---|---|---|
| Somatic | Voluntary motor nerves | Conscious control of muscles |
| Autonomic | Involuntary nerves | Controls organs, glands |
Autonomic Nervous System
| Branch | State | Effects |
|---|---|---|
| Sympathetic | "Fight or flight" | ↑ Heart rate, ↑ breathing, dilates pupils |
| Parasympathetic | "Rest and digest" | ↓ Heart rate, ↑ digestion, constricts pupils |
Reflex Arc
The pathway for automatic responses:
- Stimulus → 2. Receptor → 3. Sensory neuron → 4. Integration center (spinal cord) → 5. Motor neuron → 6. Effector (muscle/gland) → 7. Response
Example: Touching a hot stove triggers withdrawal before you consciously feel pain.
Protective Structures
| Structure | Function |
|---|---|
| Skull/vertebrae | Bone protection |
| Meninges | Three membrane layers (dura, arachnoid, pia) |
| Cerebrospinal fluid | Cushions and nourishes CNS |
| Blood-brain barrier | Filters harmful substances from blood |
Test Your Knowledge
Which part of a neuron receives signals from other neurons?
A
B
C
D
Test Your Knowledge
Which division of the autonomic nervous system is active during "fight or flight"?
A
B
C
D
Test Your Knowledge
Which lobe of the brain is primarily responsible for processing vision?
A
B
C
D