Cognitive Connie
Nervous System Organisation
The nervous system is the body's primary rapid-communication network, translating external and internal stimuli into coordinated responses. Understanding its organisation — anatomically into CNS and PNS, and functionally into somatic and autonomic divisions — is foundational to all of biopsychology.
Key figures
Charles Bell & François Magendie
1774–1842 / 1783–1855Independently established the Bell-Magendie law (1811/1822): dorsal spinal nerve roots are sensory (afferent); ventral roots are motor (efferent). This was one of the first demonstrations of functional specialisation within the nervous system and remains a foundational principle of neuroanatomy.
John Newport Langley
1852–1925British physiologist who coined the term "autonomic nervous system" (1898) and established its division into sympathetic and parasympathetic components. He mapped the thoracolumbar and craniosacral origins of these divisions and described the two-neuron (preganglionic/postganglionic) architecture through meticulous pharmacological and anatomical experiments.
Key concepts
Central nervous system (CNS)
The brain and spinal cord. The primary integration and processing centre of the nervous system, enclosed within the skull (brain) and vertebral column (spinal cord) and protected by three meningeal layers (dura mater, arachnoid mater, pia mater) and cerebrospinal fluid (CSF). The CNS receives sensory input, integrates it, and generates motor output; it also mediates all higher cognitive functions.
Peripheral nervous system (PNS)
All neural tissue outside the CNS: the 12 pairs of cranial nerves, 31 pairs of spinal nerves, and their associated ganglia (clusters of neuronal cell bodies outside the CNS). The PNS connects the CNS to the rest of the body via afferent (sensory) and efferent (motor) pathways. The PNS is subdivided into somatic and autonomic divisions.
Somatic nervous system
The division of the PNS that serves voluntary, conscious functions: carries somatic sensory information (touch, pain, temperature, proprioception) from the body surface, muscles, and joints to the CNS, and carries motor commands from the CNS to skeletal muscle. The motor pathway uses a single lower motor neuron running directly from the spinal cord (or brainstem) to skeletal muscle, releasing acetylcholine at the neuromuscular junction.
Autonomic nervous system (ANS)
The division of the PNS that regulates involuntary visceral functions: cardiac muscle (heart rate, contractility), smooth muscle (blood vessels, airways, digestive tract, bladder, pupil), and exocrine glands. Operates largely outside conscious awareness. Uses a two-neuron chain: preganglionic neuron (CNS → autonomic ganglion) and postganglionic neuron (ganglion → effector). Divided into sympathetic and parasympathetic divisions.
Sympathetic division ("thoracolumbar")
Prepares the body for emergency action ("fight or flight"). Preganglionic neurons originate in the thoracic (T1–T12) and upper lumbar (L1–L2) spinal segments. Effects: increases heart rate and cardiac output, dilates bronchioles, constricts blood vessels in skin and viscera (redirecting blood to skeletal muscle), raises blood glucose (glycogenolysis), dilates pupils, reduces digestive activity. Postganglionic neurons release noradrenaline on adrenergic receptors; the adrenal medulla releases adrenaline and noradrenaline into the bloodstream.
Parasympathetic division ("craniosacral")
Promotes rest, digestion, and energy conservation ("rest and digest"). Preganglionic neurons originate from cranial nerves (CN III, VII, IX, X) and the sacral spinal cord (S2–S4). The vagus nerve (CN X) provides the majority of parasympathetic outflow, reaching the heart, lungs, and abdominal viscera. Effects: reduces heart rate, stimulates gastrointestinal motility and secretion, constricts pupils, promotes urination. Postganglionic neurons release acetylcholine on muscarinic receptors.
Afferent and efferent pathways
Direction of signal flow relative to the CNS. Afferent (from Latin ad = toward): sensory information travelling from peripheral receptors toward the CNS — includes pain, temperature, touch, proprioception, and visceral sensory signals. Efferent (from Latin ex = away from): motor commands travelling from the CNS to effectors. In spinal nerves, dorsal roots are afferent (cell bodies in dorsal root ganglia) and ventral roots are efferent — the Bell-Magendie law.
Blood-brain barrier (BBB)
A selective permeability barrier between the systemic bloodstream and the CNS, formed by tight junctions between cerebral endothelial cells, with contributions from astrocyte end-feet and pericytes. Blocks the passage of most pathogens, toxins, large proteins, and hydrophilic molecules; allows glucose (via GLUT1), O2, CO2, and lipid-soluble molecules (including many drugs, alcohol, steroid hormones) to cross. Efflux transporters (P-glycoprotein) actively remove many substances. The BBB is a major challenge in CNS pharmacology.
Autonomic ganglion
A cluster of postganglionic neuronal cell bodies located outside the CNS. In the sympathetic division, ganglia are located in two chains running parallel to the spinal cord (paravertebral sympathetic chain) or in pre-aortic plexuses. Preganglionic neurons synapse here, releasing acetylcholine onto nicotinic receptors on postganglionic neurons. In the parasympathetic division, ganglia are located close to or within the target organ (terminal ganglia).
Enteric nervous system (ENS)
A large, semi-autonomous neural network embedded in the wall of the gastrointestinal tract, containing 200–600 million neurons in two plexuses: myenteric (Auerbach's, controls motility) and submucosal (Meissner's, controls secretion and blood flow). The ENS can regulate gastrointestinal function independently of the brain or spinal cord. It communicates bidirectionally with the CNS via the vagus nerve (gut-brain axis) and produces ~95% of the body's serotonin.
Test your knowledge
Sources
Last reviewed July 2025- 1.
Kandel, E. R., Schwartz, J. H., Jessell, T. M., Siegelbaum, S. A., & Hudspeth, A. J. (2021). Principles of Neural Science (6th ed.). McGraw-Hill.
+About this source
Comprehensive reference for the anatomy and physiology of the CNS and PNS, somatic and autonomic divisions, and the blood-brain barrier.
- 2.
Langley, J. N. (1921). The Autonomic Nervous System, Part 1. Heffer.
+About this source
Langley's foundational monograph defining the autonomic nervous system, its sympathetic and parasympathetic divisions, and the two-neuron preganglionic/postganglionic architecture.
- 3.
Purves, D., Augustine, G. J., Fitzpatrick, D., Hall, W. C., LaMantia, A. S., Mooney, R. D., Bhatt, D. L., & White, L. E. (2018). Neuroscience (6th ed.). Sinauer Associates.
+About this source
Standard undergraduate neuroscience textbook covering nervous system organisation, afferent and efferent pathways, somatic and autonomic divisions.