Peripheral Nervous System – Structure, Function & Repair

Vocabulary flashcards covering key terms from the lecture on PNS structure, receptor types, pain pathways, spinal nerves, plexuses, dermatomes, and nerve regeneration.

Peripheral Nervous System (PNS)

All nerves outside the brain and spinal cord that carry information to and from the CNS.

Sensory Neuron

PNS neuron that conveys information from receptors to the CNS; builds our picture of the outside world.

Motor Neuron

PNS neuron that carries commands from the CNS to muscles or glands.

Nerve

Bundle of axons wrapped in connective tissue in the PNS.

Sensory Nerve

Nerve containing only sensory (afferent) axons that travel toward the CNS.

Motor Nerve

Nerve containing only motor (efferent) axons that travel away from the CNS.

Mixed Nerve

Nerve containing both sensory and motor axons.

Central Nervous System (CNS)

Brain and spinal cord; the body’s central processing center.

Afferent Nerve

Sensory nerve arriving at the CNS.

Efferent Nerve

Motor nerve leaving the CNS toward effectors.

Cranial Nerve

Nerve that enters or exits the CNS at the brain; serves head and neck (plus vagus to viscera).

Spinal Nerve

One of 31 paired mixed nerves that attach to the spinal cord and serve trunk and limbs.

Dorsal Root

Spinal nerve root carrying sensory axons into the spinal cord.

Ventral Root

Spinal nerve root carrying motor axons out of the spinal cord.

Mechanoreceptor

Receptor detecting touch, pressure, vibration, stretch, or itch.

Thermoreceptor

Receptor sensitive to temperature changes.

Photoreceptor

Light-detecting receptor (e.g., in the retina).

Chemoreceptor

Receptor that responds to chemicals such as odorants, tastants, or blood chemistry changes.

Nociceptor

Pain receptor activated by potentially damaging stimuli.

Proprioceptor

Receptor that monitors muscle stretch, joint position, and body posture.

Exteroceptor

Receptor located at the body surface sensing the external environment.

Interoceptor

Receptor inside organs or blood vessels sensing internal conditions.

Phasic Receptor

Rapidly adapting receptor that stops firing to constant, non-threatening stimuli (e.g., smell, touch).

Tonic Receptor

Slow- or non-adapting receptor that continues firing (e.g., nociceptors).

Endorphin

Endogenous neurotransmitter that inhibits pain pathways in the CNS.

Morphine

Drug that acts as an endorphin agonist to block pain.

Sharp Pain

Fast, localized pain carried by thick, myelinated axons.

Dull (Throbbing) Pain

Slower, prolonged pain carried by thin, unmyelinated axons.

Referred Pain

Perception of visceral pain in a superficial body region due to converging neural pathways.

Dermatome

Skin area supplied by a single spinal nerve; used to test sensory function.

Plexus

Network where spinal nerves interweave and redistribute fibers, providing redundancy.

Cervical Plexus

Network from C1–C5 serving the back of head, neck, and diaphragm (phrenic nerve).

Brachial Plexus

Network from C5–T1 serving shoulder and upper limb (axillary, radial, ulnar, etc.).

Lumbar Plexus

Network from L1–L4 serving anterior and medial leg (femoral, obturator, etc.).

Sacral Plexus

Network from L4–S4 serving posterior leg, pelvis, and buttock (sciatic, tibial, etc.).

Schwann Cell

PNS glial cell that forms myelin and guides axon regeneration.

Myelin Sheath

Insulating Schwann-cell wrapping that speeds nerve signal conduction.

Regeneration Tube

Schwann-cell-formed tunnel that guides regrowing PNS axon sprouts.

Macrophage (in nerve repair)

Immune cell that removes debris from the distal segment after axon injury.

Proximal Axon

Portion of a damaged axon still attached to the cell body; can regrow.

Distal Axon

Portion of a damaged axon separated from the cell body; degenerates after injury.

Peripheral Axon Regeneration

Process where a surviving PNS neuron regrows its axon through a Schwann-cell tube to reinnervate targets.