Peripheral nerves
The peripheral nervous system (PNS) is all the nerve structures outside the brain and spinal cord. It connects the central nervous system with organs, muscles, skin and blood vessels, providing two-way transmission of signals.
Cranial nerves
12 pairs of cranial nerves arise directly from the brain:
| Number | Title | Function |
|---|---|---|
| I | Olfactory | Smell |
| II | Visual | Vision |
| III | Oculomotor | Eye movements, pupil |
| V | Trigeminal | Facial sensitivity, chewing |
| VII | Facial | Facial expressions, taste |
| VIII | vestibulocochlear | Hearing, balance |
| X | Wandering | Regulation of internal organs |
| XII | Sublingual | Tongue movements |
The vagus nerve (n. vagus) is the longest cranial nerve. It innervates the heart, lungs, esophagus, stomach and intestines, regulating their work through the parasympathetic system.
Spinal nerves and plexuses
31 pairs of spinal nerves form four large plexuses:
- Cervical plexus (C1–C4) - innervation of the skin of the neck, phrenic nerve
- Brachial plexus (C5–Th1) - innervation of the upper limb
- Lumbar plexus (L1–L4) - femoral nerve, anterior thigh
- Sacral plexus (L4–S3) - sciatic nerve - the largest nerve of the body
The sciatic nerve (n. ischiadicus) has a thickness of up to 2 cm and runs from the lower back to the foot. Pinching it (sciatica) is one of the most common causes of leg pain.
Autonomic nervous system
The vegetative (autonomous) NS regulates the functioning of internal organs without the participation of consciousness:
- Sympathetic - activated during stress (fight or flight): increases heart rate, dilates pupils, increases blood pressure
- Parasympathetic - predominates at rest (rest and digest): slows down the pulse, stimulates digestion
Their balance ensures the body’s adaptation to constantly changing conditions.
Nerve structure
A peripheral nerve is not a single fiber, but a cable of thousands of axons surrounded by sheaths:
- Endoneurium - around each fiber
- Perineurium - around the bundle of fibers
- Epineurium - around the entire nerve
The myelin sheath accelerates impulse conduction to 120 m/s - that’s 430 km/h. Demyelinating diseases (multiple sclerosis, Guillain-Barré syndrome) disrupt this insulation by slowing or blocking signal transmission.
All structures of the peripheral nervous system - from cranial nerves to the sacral plexus - can be studied in the free 3D atlas Humio. Rotate, scale and view each nerve.