What is the basic structure of a peripheral nerve?

A peripheral nerve consists of bundles of axons (nerve fibers) wrapped in three connective tissue sheaths: Endoneurium around individual fibers, Perineurium around each fasciculus, and Epineurium as the outer sheath, containing blood vessels. These sheaths provide structural support and make up nearly half the nerve's volume.

How are nerves classified based on their function?

Nerves are classified into three main types: Motor nerves transmit signals from the CNS to muscles, sensory nerves transmit signals from receptors to the CNS, and mixed nerves contain both sensory and motor fibers.

What are the key components of a reflex arc?

A reflex arc involves five components: sensory receptor, afferent (sensory) neuron, association (interneuron), efferent (motor) neuron, and effector organ. This allows for automatic, protective responses like the withdrawal reflex to a pinprick.

What happens during nerve degeneration and regeneration after injury?

After injury, the distal axon undergoes Wallerian degeneration, while the cell body shows chromatolysis. Regrowth occurs at about 1 mm/day through a tube formed by Schwann cells, depending on factors like intact endoneurium and no infection.

What are the main types of peripheral nerves?

Peripheral nerves include cranial nerves (12 pairs from the brain) and spinal nerves (31 pairs from the spinal cord). Cranial nerves, such as the olfactory and optic nerves, have specific functions, while spinal nerves supply the body and limbs.

What is a dermatome and why is it important?

A dermatome is a skin area innervated by sensory fibers from a single spinal nerve. It's important for diagnosing nerve lesions because adjacent dermatomes overlap, so loss of sensation typically requires damage to at least two spinal nerves.

What are nerve plexuses and which ones are major?

Nerve plexuses are networks formed by anterior rami of spinal nerves, except T2–T12. Major plexuses include the cervical plexus (C1–C4 for head/neck), brachial plexus (C5–T1 for upper limb), and lumbosacral plexus (L1–S3 for lower limb).

Peripheral Nerves & Plexuses – Spinal Nerves Explained

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