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How the nervous system detects, processes, and responds, what to check during neuro observations, and which signs mean a child needs help urgently.
Quick framework
Core job
Detect - Process - Respond
That is the nervous system in one line.
CNS vs PNS
CNS = brain + spinal cord
PNS = the nerves carrying messages in and out.
Sensory vs motor
Sensory comes in. Motor goes out.
That simple direction rule helps a lot in exams and at the bedside.
Golden rule
A changed child is a neurological sign until proved otherwise.
Reduced interaction, feeding change, floppiness, or odd behaviour all count.
Student translation
CNS means the brain and spinal cord. PNS means the nerves outside them. A synapse is the tiny gap where one nerve cell passes a message to the next. AVPU is a quick consciousness check. GCS is a more structured neurological score. ICP means intracranial pressure, which is the pressure inside the skull.
What the system does
Why this matters in children
| Part | What it means | Simple clinical meaning |
|---|---|---|
| Central nervous system (CNS) | Brain and spinal cord | This is the main control centre where information is processed and responses are organised. |
| Peripheral nervous system (PNS) | All the nerves outside the brain and spinal cord | This is the communication network carrying messages in and instructions out. |
| Sensory pathways | Carry information towards the CNS | They bring in things like pain, touch, temperature, sight, and sound. |
| Motor pathways | Carry instructions away from the CNS | They help produce movement, speech, swallowing, and posture. |
| Somatic system | Controls voluntary movement | This is the part you assess when you ask a child to squeeze, push, lift, or wiggle. |
| Autonomic system | Controls automatic body functions | This influences heart rate, blood pressure, breathing, pupils, and digestion without the child having to think about it. |
Insight
If sensory information cannot get in, or motor instructions cannot get out, the child may look weak, unsteady, floppy, less responsive, or simply not like themselves. That is why a short neurological assessment can tell you a lot very quickly.
Neuron basics
Synapse in plain English
| Neuron part | Main job |
|---|---|
| Dendrites | Receive messages from other cells |
| Cell body | Processes and manages the cell |
| Axon | Carries the electrical signal away from the cell body |
| Myelin | Insulating layer that helps signals travel faster |
| Nerve endings | Pass the message on to the next cell at the synapse |
| Brain part | What it is | Why it matters |
|---|---|---|
| Cerebrum | Largest part of the brain | Thinking, awareness, memory, movement, speech, and interpretation of sensory input |
| Cerebellum | Sits towards the back and below the cerebrum | Balance, posture, coordination, and smooth controlled movement |
| Brainstem | Connects the brain to the spinal cord | Vital control of breathing, heart rate, blood pressure, consciousness, swallowing, and pupil responses |
| Brainstem job | What it controls | Why it matters at the bedside |
|---|---|---|
| Breathing | The brainstem helps control respiratory drive and pattern. | Irregular breathing with neurological change is a major concern, not just a respiratory observation. |
| Heart rate and blood pressure | The brainstem is linked to autonomic cardiovascular control. | This is why severe neurological deterioration can affect both pulse and blood pressure. |
| Consciousness, swallow, and pupils | The brainstem is involved in wakefulness and key protective reflexes. | A reduced conscious level can quickly become an airway risk as well as a neurological one. |
Lobes of the brain
Frontal lobe
Linked with planning, behaviour, personality, speech, and voluntary movement.
Parietal lobe
Helps process touch, position, and other sensory information.
Temporal lobe
Important for hearing, language understanding, and memory.
Occipital lobe
Mainly linked with vision.
Why the brainstem gets special attention
The brainstem is where neuro and vital signs meet. If it is affected, the child's breathing, heart rate, blood pressure, pupils, swallow, and conscious level can all change. That is why neurological deterioration is never just a "head problem".
| Protective feature | What it does | Clinical meaning |
|---|---|---|
| Skull | Hard bony protection around the brain | Helpful, but the skull is a fixed space, so swelling inside it is a problem. |
| Meninges | Protective layers around the brain and spinal cord | Inflammation here is meningitis. |
| Cerebrospinal fluid (CSF) | Fluid cushioning the brain and spinal cord | Helps protect, support, and maintain a stable environment around the CNS. |
Raised ICP basics
Do not wait for the "classic" picture
Late sign
Cushing's triad means bradycardia, hypertension, and irregular respirations. It is a late sign of raised intracranial pressure, not an early screening tool, so never wait for it before escalating concern.
| Raised ICP pattern | What you may notice | How to think about it |
|---|---|---|
| Early concerning clues | Headache, vomiting, irritability, sleepiness, behaviour change, bulging fontanelle | These are enough to escalate concern. Do not wait for a dramatic collapse. |
| Later and more ominous clues | Marked pupil change, worsening reduced consciousness, abnormal posturing, Cushing's triad | By this stage the child may be significantly deteriorating and needs urgent senior input. |
Spinal cord
The spinal cord carries messages between the brain and the rest of the body. If it is affected, movement, sensation, bladder function, and reflexes can all change.
Reflexes
Reflexes are quick automatic responses. They help protect the body and give clues about how well the nervous system pathways are working. Reduced or altered reflexes can matter, especially if they are new or asymmetrical.
Why neuro obs matter
They show trend
One score matters less than whether the child is improving, stable, or slipping.
They catch subtle change
Behaviour, pupils, tone, feeding, and interaction often change before the picture looks dramatic.
They guide escalation
Neuro obs help you recognise when a child needs senior review early, not late.
| Observation | What it tells you | What to keep in mind |
|---|---|---|
| AVPU | Quick screen: Alert, responds to Voice, responds to Pain, Unresponsive | Useful for the first impression. Any drop from fully alert matters. |
| GCS | Structured score using eye, verbal, and motor response | Helpful for trends. A score only matters properly if you compare it with earlier observations. |
| Pupils | Size, equality, and response to light | Unequal pupils or poor reaction to light are worrying neurological signs. |
| Limb strength | Power and symmetry in arms and legs | Ask for squeeze, push, pull, lift, or simple movement. New weakness or one-sided difference matters. |
| Behaviour, interaction, and feeding | Whether the child is behaving like themselves | Irritability, floppiness, poor feeding, difficult waking, or sudden quietness can all be neurological clues. |
| Vital signs | Heart rate, blood pressure, and breathing pattern | Neurological deterioration can affect all three, so neuro obs should always be read alongside full observations. |
| Vital sign link | Neurological meaning | Bedside reminder |
|---|---|---|
| Heart rate | May change if the brainstem is under pressure or the child is deteriorating neurologically | A slowing heart rate with other worrying signs is not reassuring. |
| Blood pressure | Can rise in serious neurological deterioration | A rising blood pressure with altered consciousness or abnormal breathing should make you think bigger. |
| Breathing | Pattern can become irregular if the brainstem is affected | Abnormal respirations are a neurological sign as well as a respiratory one. |
What neurological change may look like in children
Baby
Off feeds, floppy, irritable, difficult to wake, abnormal cry, or a bulging fontanelle may be the clue.
Toddler
Clinginess, sudden quietness, unusual behaviour, poor balance, vomiting, or not using one limb properly can all matter.
Older child
Headache, photophobia, weakness, confusion, altered speech, seizure, or behaviour change may become easier to spot and describe.
| Condition | What's going on | Key signs |
|---|---|---|
| Guillain-Barre syndrome (GBS) | Inflammation of peripheral nerves slows or blocks nerve signals, so weakness can progress upwards. | Progressive weakness, reduced reflexes, pain, floppiness, difficulty walking, possible breathing involvement |
| Encephalitis | Inflammation of the brain itself can affect behaviour, consciousness, and seizures. | Fever, drowsiness, confusion, irritability, seizures, headache, vomiting |
| Meningitis | Inflammation of the protective layers around the brain and spinal cord. | Fever, irritability, poor feeding, vomiting, photophobia, neck stiffness, bulging fontanelle, reduced consciousness |
| Transverse myelitis | Inflammation across part of the spinal cord interrupts messages travelling up and down. | Weakness, sensory change, altered reflexes, back pain, bladder or bowel problems |
Paediatric meaning
Neurological illness in children does not always present in a neat textbook way. A baby may be off feeds, difficult to wake, more irritable, floppy, or have a bulging fontanelle. An older child may show headache, vomiting, behaviour change, limb weakness, or seizure activity. The bedside pattern matters.
Whole-child link
Neuro assessment is never separate from A-E. If conscious level drops, the airway may no longer be protected. If the brainstem is affected, breathing and circulation can change. That is why neurological concern should always lead you back to a full reassessment, not just another GCS score.
Red flags - escalate immediately
Escalation mindset
Do not talk yourself out of neurological concern because the child is still moving or because one number looks acceptable. A changed conscious level, new weakness, pupil change, seizure, or worrying trend in behaviour deserves urgent review.
Quick recap