Nerves: Structure/Classification/Regeneration of nerve axons

What is the structure of nerves?

bundles of axons in the PNS encases within connective tissue wrappings

Structure: Epineurium

encloses fascicles that form the nerve

Structure: Perineurium

binds group of axons into bundles called fascicles

Structure: Endoneurium

encloses fibers associated with Schwann cells

Classification based on origin: Cranial nerves

originate from the brain

Classification based on origin: Spinal nerves

originate from the spinal cord

(C) Direction of impulse conduction: Sensory (afferent) nerves

conduct impulses toward the CNS

(C) Direction of impulse conduction: Motor (efferent) nerves

conduct impulses away from the CNS

(C) Direction of impulse conduction: Mixed nerves contain both ____ and ____ fibers

afferent and efferent

Most/All cranial nerves are mixed

MOST cranial nerves are mixed

Most/All spinal nerves are mixed

ALL spinal nerves are mixed

Regeneration of nerve axons: CNS

Damaged CNS axons CANNOT regenerate (oligodendrocytes suppress axon regeneration)

What suppresses axon regeneration in the CNS?

oligodendrocytes

Regeneration of nerve axons: PNS

Damaged PNS axons can regenerate, but ONLY if body remains intact

When is the only case the PNS axons can regenerate?

IF the body remains intact

Regeneration of nerve axons: Step 1

The axon fragments

Regeneration of nerve axons: Step 2

Schwann cells and macrophages clean out the dead axon distal to the injury

Regeneration of nerve axons: Step 3

Axon filaments grow through a regeneration tube

Regeneration of nerve axons: Step 4

The axon regenerates, and a new myelin sheath forms