The Peripheral and Autonomic Nervous Systems Study Pack

Kibin's free study pack on The Peripheral and Autonomic Nervous Systems includes a 3-section study guide, 8 quiz questions, 10 flashcards, and 1 open-ended Explain review question. Sign up free to track your progress toward mastery, plus upload your own notes and recordings to create personalized study packs organized by course.

Last updated May 21, 2026

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The Peripheral and Autonomic Nervous Systems Study Guide

Trace the full architecture of the peripheral and autonomic nervous systems, from somatic motor and sensory pathways to the sympathetic fight-or-flight and parasympathetic rest-and-digest divisions. This pack covers preganglionic and postganglionic fiber arrangements, neurotransmitter release at target organs, dual innervation, and the enteric nervous system's independent control of digestion — everything you need to master ANS function for your A&P exam.

Key Takeaways

  • •The peripheral nervous system (PNS) consists of all neural tissue outside the brain and spinal cord, divided into the somatic nervous system (voluntary motor and sensory control) and the autonomic nervous system (involuntary regulation of internal organs).
  • •The autonomic nervous system is subdivided into the sympathetic, parasympathetic, and enteric divisions, each with distinct anatomical origins, neurotransmitters, and functional roles.
  • •Sympathetic pathways originate from the thoracic and lumbar spinal cord (T1–L2), use short preganglionic and long postganglionic fibers, and release norepinephrine at target organs to prepare the body for 'fight-or-flight' responses.
  • •Parasympathetic pathways originate from cranial nerves (III, VII, IX, X) and sacral spinal cord segments (S2–S4), use long preganglionic and short postganglionic fibers, and release acetylcholine to promote 'rest-and-digest' functions.
  • •Both autonomic divisions use a two-neuron chain — a preganglionic neuron synapsing in an autonomic ganglion onto a postganglionic neuron — unlike somatic motor pathways, which contact effectors directly.
  • •Most organs receive dual innervation from both sympathetic and parasympathetic divisions, and the balance between their opposing effects determines the organ's functional state at any given moment.
  • •The enteric nervous system, embedded in the gastrointestinal wall, contains roughly 100 million neurons and can regulate digestion independently of the brain and spinal cord.

Organization of the Peripheral Nervous System

The peripheral nervous system encompasses every neural structure that lies outside the central nervous system, forming the communication network between the brain and spinal cord and the rest of the body.

Structural Definition of the PNS

  • •The PNS includes cranial nerves, spinal nerves, peripheral ganglia, and sensory receptors — all tissue not enclosed within the skull or vertebral column.
  • •Peripheral nerves are bundles of axons wrapped in connective tissue sheaths (endoneurium around individual fibers, perineurium around fascicles, epineurium around the entire nerve).

Somatic Nervous System

  • •Controls skeletal muscle contraction consciously and relays somatic sensory information (touch, pain, proprioception, temperature) from the body surface and musculoskeletal system to the CNS.
  • •Motor commands travel from the CNS along a single lower motor neuron that synapses directly on skeletal muscle fibers, releasing acetylcholine at the neuromuscular junction.

Autonomic Nervous System

  • •Regulates smooth muscle, cardiac muscle, and glands — organs that are not under direct voluntary control — to maintain homeostasis.
  • •Unlike somatic pathways, every autonomic motor command passes through at least one peripheral ganglion before reaching its effector, creating a two-neuron chain.

The Two-Neuron Autonomic Pathway

A defining structural feature of all autonomic motor output is the relay synapse in a peripheral ganglion, which separates the central and peripheral components of each pathway.

Preganglionic Neurons

  • •The preganglionic neuron originates in the CNS (brainstem or spinal cord) and its myelinated axon (B fiber) travels to an autonomic ganglion located outside the CNS.
  • •Preganglionic neurons in both the sympathetic and parasympathetic divisions release acetylcholine, which binds to nicotinic acetylcholine receptors on the postganglionic cell body.

Postganglionic Neurons

  • •The postganglionic neuron has its cell body in the ganglion and sends an unmyelinated axon (C fiber) to the target organ.
  • •The neurotransmitter released by postganglionic fibers differs between divisions: sympathetic fibers typically release norepinephrine, while parasympathetic fibers release acetylcholine.
  • •The type of receptor on the target organ — adrenergic (for norepinephrine) or muscarinic (for acetylcholine) — determines whether the response is excitatory or inhibitory.

Comparison With Somatic Motor Pathways

  • •Somatic motor neurons have no intermediate relay; one neuron travels continuously from the spinal cord to the skeletal muscle.
  • •The peripheral ganglion relay in autonomic pathways allows local reflex integration independent of the CNS, a capability the somatic motor system lacks.

About this Study Pack

Created by Kibin to help students review key concepts, prepare for exams, and study more effectively. This Study Pack was checked for accuracy and curriculum alignment using authoritative educational sources. See sources below.

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