Chapt 12: Peripheral Nervous System (PNS) - Key Vocabulary from Lecture Notes

A set of vocabulary cards covering the key anatomy, physiology, pharmacology, and clinical implications of the Peripheral Nervous System and local anesthetics as described in the notes.

Peripheral Nervous System (PNS)

Nervous system components outside the CNS; connects brain and spinal cord to organs, limbs, and skin.

Central Nervous System (CNS)

Brain and spinal cord; primary site of information processing and coordination.

Autonomic Nervous System (ANS)

PNS subdivision that governs involuntary activities of smooth and cardiac muscle and glandular secretion.

Sensory-Somatic Nervous System

PNS subdivision responsible for relaying sensory inputs to the CNS and controlling voluntary muscle movements.

Cranial Nerves

12 pairs of nerves arising from the brain and brainstem; I and II originate in the brain, others from the brainstem.

Spinal Nerves

31 pairs arising from the spinal cord; exit through the intervertebral foramina.

Cervical Nerves

8 cervical nerves (C1–C8) in the cervical region.

Thoracic Nerves

12 thoracic nerves (T1–T12) in the thoracic region.

Lumbar Nerves

5 lumbar nerves (L1–L5) in the lumbar region.

Sacral Nerves

5 sacral nerves (S1–S5) in the sacral region.

Coccygeal Nerve

1 coccygeal nerve pair at the tail end of the spinal cord.

Ventral Root

Motor (efferent) root, located anteriorly on the spinal nerve.

Dorsal Root

Sensory (afferent) root, located posteriorly on the spinal nerve.

Mixed Nerve

Nerve formed by the union of dorsal and ventral roots; conducts both sensory and motor information.

Myotome

Muscle group innervated by a specific spinal segment.

Dermatome

Skin region innervated by a specific spinal segment.

Afferent Nerves

Nerves that transmit sensory information toward the CNS.

Efferent Nerves

Nerves that transmit motor commands away from the CNS to muscles.

Mixed Peripheral Nerves

Nerves containing both afferent and efferent fibers; enable bidirectional signaling.

Neuron

Basic nerve cell with dendrites, soma, axon, and axon terminals.

Dendrites

Branching structures receiving synaptic input from other neurons.

Soma

Neuron cell body containing the nucleus and metabolic machinery.

Axon

Long projection that conducts nerve impulses away from the soma.

Axon Terminals

Endings of the axon where neurotransmitters are released.

Glial Cells

Support cells in the nervous system; do not conduct electrical signals.

Endoneurium

Connective tissue sheath surrounding a single axon.

Perineurium

Protective sheath surrounding a fascicle of axons.

Epineurium

Outer connective tissue covering the entire nerve.

Vasa Nervorum

Blood vessels that supply nerves.

Resting Membrane Potential

Electrical potential difference across the neuronal membrane at rest.

Sodium-Potassium Pump

Na+/K+ ATPase that maintains ion gradients across the cell membrane.

Depolarization

Sudden influx of Na+ causing the interior of the neuron to become more positive.

Action Potential

Rapid, all-or-none electrical impulse that propagates along the axon.

Synapse

Junction where neurotransmitter release from the presynaptic cell affects the postsynaptic cell.

Neurotransmitter

Chemical messenger released at the synapse to transmit signals.

Nodes of Ranvier

Gaps in the myelin sheath where ion channels are concentrated.

Saltatory Conduction

Rapid nerve impulse transmission as the action potential 'jumps' between nodes of Ranvier.

Myelination

Formation of a myelin sheath around axons to speed up signal transmission.

Schwann Cells

PNS glial cells that form the myelin sheath around peripheral nerves.

Repolarization

Return to the resting membrane potential after depolarization, mainly via K+ efflux.

Ischemia

Insufficient blood flow; neurons are highly vulnerable due to high metabolic demand.

Peripheral Neuropathy

Nerve dysfunction causing sensory and/or motor deficits; may be systemic or focal.

Nerve Injury

Damage to nerve tissue from trauma, ischemia, toxins, or inflammation.

Local Anesthetics

Drugs that block nerve conduction by inhibiting voltage-gated Na+ channels.

pKa

Acid-base property indicating the pH at which 50% of the drug is ionized; influences onset of local anesthetics.

Lipophilicity (Lipid Solubility)

Property that affects drug potency and membrane penetration; higher lipophilicity generally speeds onset and increases potency.

Aromatic Ring

Lipophilic ring structure in local anesthetics facilitating membrane penetration.

Intermediate Chain (Amide vs Ester)

Chemical linker determining class of LA; amides are metabolized hepatically, esters by plasma cholinesterases.

Amine Group

Hydrophilic portion of local anesthetics that contributes to ionization.

Amide Local Anesthetics

Local anesthetics with an amide linkage; typically metabolized in the liver.

Ester Local Anesthetics

Local anesthetics with an ester linkage; rapidly hydrolyzed by plasma cholinesterases.

Hepatic Metabolism

Metabolism of amide LAs primarily in the liver.

Plasma Cholinesterases

Enzymes that hydrolyze ester local anesthetics in the bloodstream.

Bicarbonate Addition

Adding bicarbonate to LA solutions to raise pH and increase nonionized fraction for faster onset.

Toxicity Signs (General)

Early CNS signs (metallic taste, numbness, tinnitus) progressing to seizures and cardiovascular collapse.

Cardiotoxicity

Severe heart toxicity risk, notably with certain LAs like bupivacaine.

Preservative-Free Formulations

LA preparations without preservatives; preferred for nerve/spinal administration to reduce toxicity risk.