Overview
The central nervous system (CNS) is the brain and spinal cord, protected by bone, three meninges (dura, arachnoid, pia) and cerebrospinal fluid. The peripheral nervous system includes 12 pairs of cranial nerves and 31 pairs of spinal nerves.
The autonomic nervous system controls organs without conscious effort. The sympathetic division prepares for "fight or flight" (faster heart, dilated pupils and bronchi), while the parasympathetic division supports "rest and digest" (slower heart, digestion, urination).
Main functions
- Sensing the internal and external environment
- Integrating information, memory and decision-making
- Controlling voluntary movement
- Regulating organs through the autonomic nervous system
- Coordinating with the endocrine system through the hypothalamus
Key structures
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Cerebrum and cerebral lobes
The largest part of the brain, divided into two hemispheres and four lobes.
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Cerebellum
The "little brain" at the back of the skull that coordinates movement and balance.
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Brainstem
The stalk connecting the brain to the spinal cord, controlling breathing, heart rate and consciousness.
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Spinal cord
The cable of nerve tissue that carries signals between the brain and body and handles reflexes.
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Ventricles of the brain
Four connected cavities in the brain filled with cerebrospinal fluid.
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Hypothalamus
A small control center that links the nervous and endocrine systems.
How a nerve signal travels
At rest, a neuron is negative inside. When stimulated, sodium rushes in (depolarization) and the impulse travels down the axon as an action potential; potassium then flows out to restore the resting state (repolarization). Myelin lets the impulse jump between nodes, making conduction much faster.
At the synapse, the electrical signal becomes chemical: neurotransmitters such as acetylcholine, dopamine, serotonin, norepinephrine and GABA cross the gap and bind receptors on the next cell. Many drugs act at this step.
Nursing assessment
- Level of consciousness is the most sensitive indicator of neurologic change.
- Glasgow Coma Scale: eye opening (1–4), verbal response (1–5), motor response (1–6); total 3–15, and 8 or below usually means the airway must be protected.
- Pupils: size, equality and reaction to light (PERRLA).
- Motor strength and sensation in all four limbs, compared side to side.
- Stroke screening with BE-FAST: balance, eyes, face, arms, speech, time to call.
Common conditions
| Condition | What happens | Key signs | Nursing priorities |
|---|---|---|---|
| Stroke | Interruption of blood flow to the brain: ischemic (clot, about 87%) or hemorrhagic (bleed) | Sudden facial droop, arm weakness, speech difficulty, vision loss, imbalance | Note last known well time, rapid CT, check glucose, swallow screen before any oral intake |
| Increased intracranial pressure | Rising pressure inside the skull from bleeding, swelling or tumor | Decreasing level of consciousness first, headache, vomiting; late: Cushing's triad (hypertension with wide pulse pressure, bradycardia, irregular respirations) | Head of bed 30°, head midline, avoid hip flexion and straining, cluster care |
| Seizure | Abnormal electrical discharge in the brain | Varies: convulsions, staring, altered awareness | Protect from injury, turn to the side, time it, nothing in the mouth, never restrain |
| Spinal cord injury | Damage to the cord causing loss of function below the level | Paralysis, sensory loss; injuries at T6 or above risk autonomic dysreflexia | Immobilize, airway for high injuries; for dysreflexia sit the client up and find the trigger (often a full bladder) |
| Meningitis | Inflammation of the meninges, often infectious | Fever, severe headache, neck stiffness, photophobia, positive Kernig's and Brudzinski's signs | Droplet precautions for bacterial meningitis until 24 hours of antibiotics, quiet dark room, neuro checks |
| Parkinson's disease | Loss of dopamine-producing neurons | Resting tremor, rigidity, bradykinesia, shuffling gait | Fall prevention, give carbidopa-levodopa on schedule, swallowing and nutrition support |
Labs and normal values
| Test | Typical adult range | Why it matters |
|---|---|---|
| Cerebrospinal fluid: appearance | Clear and colorless | Cloudy suggests infection; bloody suggests hemorrhage or traumatic tap |
| CSF glucose | About 50–80 mg/dL (about 60–70% of blood glucose) | Low in bacterial meningitis |
| CSF protein | 15–45 mg/dL | High in meningitis and some neurologic diseases |
| Blood glucose | 70–99 mg/dL fasting | Always check in altered mental status: hypoglycemia can mimic stroke |
| Intracranial pressure | 5–15 mmHg | Sustained values above 20 mmHg need treatment |
Reference ranges differ between laboratories and textbooks. Use the values your program and facility use.
Exam tips
- A change in level of consciousness is the earliest sign of increased intracranial pressure; Cushing's triad is a late sign.
- Autonomic dysreflexia (injury at T6 or above): sit the client up first, then check the bladder, bowel and skin for the trigger.
- For any client with altered mental status, check the blood glucose.
Practice questions
8 NCLEX-style questions on the nervous system. Pick an answer to see the rationale.
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Which is the earliest sign of increased intracranial pressure?
Show the answer and rationale
Answer B: Change in level of consciousness. Level of consciousness changes first. Cushing's triad, pupil changes and posturing are late signs.
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A client's Glasgow Coma Scale score drops to 7. What is the nurse's priority?
Show the answer and rationale
Answer B: Protect the airway. A GCS of 8 or below indicates the client may not protect their own airway; prepare for airway management.
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A client with a T4 spinal cord injury has a pounding headache and BP 210/110. What is the first action?
Show the answer and rationale
Answer B: Sit the client upright. This is autonomic dysreflexia. Raising the head lowers blood pressure; then find and remove the trigger, often a full bladder.
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A client had a left-hemisphere stroke. Which finding does the nurse expect?
Show the answer and rationale
Answer B: Right-sided weakness and aphasia. Motor control is crossed, and language centers are usually in the left hemisphere.
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Which nursing action helps reduce intracranial pressure?
Show the answer and rationale
Answer B: Keep the head midline with the head of the bed at 30°. A midline head and 30° elevation promote venous drainage. Hip flexion, coughing and straining raise ICP.
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Which structure coordinates balance and smooth movement?
Show the answer and rationale
Answer A: Cerebellum. The cerebellum coordinates movement and balance; damage causes ataxia and intention tremor.
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During a tonic-clonic seizure, which action is appropriate?
Show the answer and rationale
Answer C: Turn the client to the side and time the seizure. Side-lying keeps the airway clear. Never put anything in the mouth or restrain the client.
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Lumbar puncture findings of cloudy CSF with low glucose and high protein suggest:
Show the answer and rationale
Answer B: Bacterial meningitis. Bacteria consume glucose and raise protein and white cells, making the fluid cloudy.