Prevention & care

The nervous system: brain, spinal cord, and nerves

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The nervous system includes the brain, spinal cord, nerves, and ganglia. It supports communication, regulation, thought, learning, and memory.[1]

Three overlapping functions

Sensory receptors detect changes inside and outside the body. Neural signals are integrated to produce sensations, thoughts, or decisions. Motor signals direct muscles and glands to respond.[1]

A map of the main divisions

The central nervous system is the brain and spinal cord. Peripheral nerves and ganglia connect it with the rest of the body. Sensory pathways carry information toward the central system; motor pathways carry commands outward. Somatic motor pathways control skeletal muscles. Autonomic pathways influence organs, glands, smooth muscle and heart muscle. Sympathetic and parasympathetic branches are coordinated parts of regulation, not two independent systems with one universally harmful and the other beneficial.[2]

Cells, pathways and supporting tissue are different categories

Sensory neurons carry information toward the central system; motor neurons signal muscles or glands; interneurons connect central pathways. Direction describes function. A nerve contains axons and supporting structures, rather than being one neuron’s cell body.[3]

Glial cells support nervous tissue. Schwann cells make peripheral myelin; oligodendrocytes make central myelin. Myelin disorders can affect conduction separately from neuron-cell-body loss. These anatomical differences help explain distinct disease patterns.[3]

Neural adaptation and making new neurons are separate questions

Rehabilitation after stroke can involve relearning movement, language and thinking skills. Improvement in performance is a meaningful clinical outcome; the word “plasticity” alone does not identify which cells or circuits changed, guarantee full recovery or validate a commercial brain-training product. The chosen task, impairment and support matter when interpreting a recovery claim.[8]

Neurogenesis means producing new neurons. Historical human hippocampal studies reached competing conclusions: Sorrells and colleagues reported very rare or undetectable adult neurogenesis, while Boldrini and colleagues reported persistence into older age. These are tissue studies with different samples and measurements, not trials showing that a wellness intervention improves memory. They illustrate why one biological headline can overstate a broader claim.[9][10]

A 2026 study analyzed gene-expression and chromatin-accessibility profiles from 355,997 nuclei in postmortem hippocampal samples. It identified stem cells, neuroblasts and immature neurons and differences among aging and Alzheimer’s groups. The authors still describe human cognitive relevance and regulatory mechanisms as important gaps. This newer molecular evidence advances the biological question; cross-sectional tissue signatures do not establish that inducing neurogenesis prevents dementia or improves an individual’s memory.[11]

How nervous tissue carries signals

A neuron has a cell body, dendrites that receive signals and an axon that carries signals onward. Myelin insulates many axons and changes how impulses travel. Support cells have roles distinct from neurons, so nervous tissue is more than a collection of electrical wires. These structures help explain why injury to a nerve, its insulation or a central pathway can produce different patterns of difficulty.[3]

Symptoms depend on which pathway is affected

Peripheral nerve disorders can affect movement, sensation or automatic functions. Possible symptoms include weakness, numbness, tingling, pain or organ-control difficulties. Causes include diabetes, injury, infections, medicines, toxic exposures and inherited disorders. A symptom such as tingling does not identify one cause. Assessment combines history and examination with tests selected for the pattern, rather than assuming every unusual sensation requires the same supplement or scan.[4]

Some neurological symptoms need an emergency response

Sudden weakness or numbness on one side, trouble speaking, sudden vision change, difficulty walking or an unexplained severe headache can be stroke symptoms. Symptoms that disappear can still represent a transient ischemic attack and need urgent evaluation. CDC advises immediate emergency services in the US; elsewhere use the local emergency number. Waiting for improvement can delay time-sensitive assessment.[5]

A neurological examination samples several functions

A neurological examination samples several functions
Area	Examples of what is assessed
Mental status	Thinking and recall in the relevant clinical context.[7]
Cranial-nerve functions	Aspects of sight, hearing and other head/face functions.[7]
Movement	Muscle movement, balance and coordination.[7]
Reflexes	Automatic movements responding to a trigger.[7]
Sensation	Responses to temperature, pain or vibration.[7]
Autonomic functions	Processes such as heartbeat, digestion and breathing.[7]

A chemical messenger is different from the cell carrying the signal

NINDS defines neurotransmitters as chemicals conveying messages among neurons and other cells. Dendrites receive neural signals, while a synapse is a communication junction; its chemical signaling involves a neurotransmitter. Naming the messenger does not identify the entire circuit, the cause of a symptom or an effective treatment.[6]

Testing is selected for the question, rather than being one universal brain score

MedlinePlus describes a neurological examination as a combination of questions and tests. The selected functions depend on why the examination is being done. Movement, sensation, reflexes and autonomic activity are separate domains; a memory question alone does not sample all of them. This explains the assessment process without interpreting a reader’s findings.[7]

An electrical signal travels along a neuron

Ions are electrically charged particles. Channels in a neuron’s membrane control their movement, changing the voltage difference across that membrane. When a threshold is reached, successive channels open and an action potential—a brief voltage signal—travels along the axon. Electrical signaling here concerns moving ions, not a miniature wire carrying household electricity.[12]

Many junctions use a chemical handoff

At a chemical synapse, an arriving action potential helps trigger neurotransmitter release. The molecules cross a tiny gap and bind to receptors on the receiving cell, changing its response. Depending on the signaling system, an input can favor or inhibit another signal; every input does not automatically cause another action potential.[13]

Some synapses pass current directly

Electrical synapses also exist. Gap junctions connect cells through channels that allow ionic current to pass directly between them. A chemical-synapse description therefore does not describe every neuronal junction.[14]

Evidence & uncertainty

Knowing how a system works is background knowledge. It does not establish that a marketed brain supplement improves symptoms or function.[1]

Selected-source overview · Independent review pending

Published questions

Is the nervous system only the brain?

Selected-source overview · Independent review pending. Read the evidence context.

No. The spinal cord, nerves, and ganglia also participate.[1]

Evidence behind this answer

Introduction to the Nervous System
agency explanation · Date not stated
Selected page sections · Introduction; sensory, integrative, motor functions