PCB3703 chapter 21
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Questions and Answers

Which of the following correctly describes a feature of the autonomic nervous system?

  • It functions without sensory input.
  • It only utilizes acetylcholine as a neurotransmitter.
  • It can either excite or inhibit effector organs. (correct)
  • It operates exclusively through voluntary control.

    • What characterizes the somatic nervous system's motor pathway?

  • It includes two motor neurons.
  • It terminates at skeletal muscle with distinct receptors. (correct)
  • It utilizes norepinephrine as the primary neurotransmitter.
  • It has ganglia present in the pathway.

    • What physiological role is primarily served by the sympathetic division of the autonomic nervous system?

  • Regulating blood pressure during sleep.
  • Facilitating emergency and stress responses. (correct)
  • Promoting rest and digestion.
  • Controlling fluid levels in the body.

    • How do adrenergic receptors function in the autonomic nervous system?

    <p>They can be activated by norepinephrine as well as epinephrine.</p> Signup and view all the answers

    Which statement accurately reflects a difference between cholinergic and adrenergic receptors?

    <p>Cholinergic receptors can be of nicotinic or muscarinic types.</p> Signup and view all the answers

    Which structures are primarily involved in the segregation of the autonomic pathways?

    <p>Autonomic ganglia and specific nerve pathways.</p> Signup and view all the answers

    What is the primary physiological result of denervation in the autonomic nervous system?

    <p>Disruption of involuntary functions and homeostasis.</p> Signup and view all the answers

    Which factor distinguishes the enteric division of the autonomic nervous system?

    <p>It operates independently within the gastrointestinal system.</p> Signup and view all the answers

    Which division of the autonomic nervous system is responsible for the 'fight or flight' response?

    <p>Sympathetic division</p> Signup and view all the answers

    What is the primary neurotransmitter released by postganglionic neurons in the sympathetic division?

    <p>Norepinephrine</p> Signup and view all the answers

    Which of the following accurately describes the location of terminal ganglia in the parasympathetic division?

    <p>Inside the visceral organs</p> Signup and view all the answers

    How many postganglionic neurons might a single preganglionic neuron synapse with in the sympathetic division?

    <p>200</p> Signup and view all the answers

    Which cranial nerve is NOT involved in distributing parasympathetic preganglionic fibers?

    <p>Optic - II</p> Signup and view all the answers

    What effect does the parasympathetic nervous system typically have on heart rate?

    <p>Decreases heart rate</p> Signup and view all the answers

    Which type of adrenergic receptor is primarily responsible for causes vasoconstriction in blood vessels?

    <p>Alpha-1 receptors</p> Signup and view all the answers

    In the autonomic nervous system, which neurotransmitter is typically associated with the stimulation of intestinal peristalsis?

    <p>Acetylcholine</p> Signup and view all the answers

    What is the primary neurotransmitter released by adrenergic neurons?

    <p>Norepinephrine</p> Signup and view all the answers

    Which receptor type is predominantly affected by the agonist nicotine?

    <p>Nicotinic receptor</p> Signup and view all the answers

    Which effect is primarily associated with the sympathetic nervous system?

    <p>Increased heart rate</p> Signup and view all the answers

    Which statement accurately describes muscarinic receptors?

    <p>They can have both inhibitory and stimulatory effects.</p> Signup and view all the answers

    What physiological response is associated with the activation of the parasympathetic nervous system?

    <p>Decreased heart rate</p> Signup and view all the answers

    How does acetylcholine (ACh) exert its effects on nicotinic receptors?

    <p>By directly opening ion channels</p> Signup and view all the answers

    Which adrenergic receptor subtype is primarily responsible for increasing cardiac output?

    <p>β1</p> Signup and view all the answers

    What role does acetylcholine esterase play in neurotransmission?

    <p>It inactivates acetylcholine to terminate its action.</p> Signup and view all the answers

    Study Notes

    Autonomic Nervous System Overview

    • Regulates gland activity, smooth and cardiac muscle.
    • It's a motor system requiring sensory input.
    • This system is involuntary (Gk = self-governing).
    • It maintains homeostasis including blood pressure, fluid volume, and temperature.
    • Coordinates responses to external stimuli.

    Comparison of Somatic and Autonomic Systems

    • Somatic Motor System:
      • Sensation is consciously perceived.
      • Effector is skeletal muscle.
      • Effector is excited by single motor axon.
      • No ganglia.
      • Neurotransmitter is acetylcholine.
      • Has a distinct neuromuscular junction with receptors on the motor endplate.
      • Damage leads to flaccid paralysis and atrophy.
    • Autonomic System:
      • Visceral sensation is generally unconscious.
      • Effector organs are glands, smooth, and cardiac muscle.
      • Effectors may be excited or inhibited.
      • Consists of two motor neurons in a pathway.
      • Ganglia are paravertebral, peripheral, or terminal.
      • Neurotransmitters are acetylcholine or norepinephrine.
      • Receptors are scattered on the smooth muscle membrane.
      • Damage principally affects autonomic function control.

    Three Divisions of the Autonomic System

    • Sympathetic: Stress, emergency behavior
    • Parasympathetic: Vegetative, restful functions
    • Enteric: Neuron network within the gastrointestinal system.

    Somatic vs Autonomic Reflexes

    • Share common components like afferent and efferent pathways.
    • Autonomic reflexes have two-neuron efferent pathways.

    Anatomy of Autonomic Motor Pathways

    • Preganglionic Neuron: First autonomic motor neuron, cell body in CNS, myelinated axon exiting CNS.
    • Postganglionic Neuron: Second autonomic motor neuron, cell body and dendrites within autonomic ganglion, unmyelinated axon terminates at visceral effector.
    • Autonomic Ganglia: Clusters of cell bodies outside the CNS, may be paravertebral (sympathetic chain), peripheral (prevertebral/collateral), or terminal.

    Sympathetic Chain Ganglia

    • Chain of ganglia parallels the spinal cord (22 pairs).
    • Innervates visceral effectors via spinal nerves.

    Collateral Ganglia

    • Isolated clusters of cell bodies.
    • Examples include superior/inferior mesenteric and celiac ganglia.
    • Innervate visceral organs in the abdominopelvic cavity.

    Terminal Ganglia

    • Located on the surface of effector tissue within parasympathetic branches of the ANS.

    Sympathetic Division

    • Preganglionic neurons originate in the thoracic and first two lumbar segments (thoracolumbar division).
    • Axon exits via anterior (ventral) root with somatic motor neurons.
    • Preganglionic neurons synapse in the paravertebral chain at the level of anterior root or traverse up or down before synapsing in peripheral ganglion.
    • Peripheral sympathetic ganglia are positioned near visceral organs.
    • Each preganglionic axon may synapse with numerous postganglionic neurons (200+).
    • Postganglionic axon is longer than the preganglionic axon.
    • Preganglionic axons also supply adrenal medulla.

    Parasympathetic Division

    • Cell bodies originate in brain stem nuclei or lateral horns of sacral spinal cord (craniosacral division).
    • Cranial preganglionics distribute via four cranial nerves: oculomotor (III), facial (VII), glossopharyngeal (IX), and vagus (X).
    • Sacral preganglionics originate from S2, S3, and S4.
    • Preganglionic fibers synapse with terminal ganglia, often within the walls of peripheral organs.
    • Postganglionic fibers are short.
    • Vagus nerve carries 80% of parasympathetic fibers.

    Physiological Effects of the Autonomic Nervous System

    • Sympathetic (SNS): Excitatory in organs activated during physical activity; increases heart rate.
    • Parasympathetic (PNS): Inhibitory in organs activated during rest; decrease in heart rate, stimulates intestinal peristalsis.
    • SNS and PNS responses are often antagonistic (eg. heart rate).
    • SNS mediates “fight or flight” responses
    • PNS mediates "vegetative" responses

    ANS Synapses

    • Synapses specialized for function within target organs.
    • Many have varicosities along axons within target organs.
    • Increased number of target sites for neurotransmitters.
    • Wider distribution of autonomic output

    Autonomic Neurotransmitters

    • Cholinergic Neurons:
      • Release acetylcholine (ACh).
      • Inactivated by acetylcholine esterase.
      • Pre-ganglionic neurotransmitter for both divisions and neuromuscular junctions (nicotinic receptors).
      • Post-ganglionic neurotransmitter in parasympathetic system (muscarinic receptors).
    • Adrenergic Neurons:
      • Release norepinephrine.
      • Deactivated by monoamine oxidase.
      • Primary neurotransmitter for postganglionic sympathetic neurons (α and β receptors, G-protein coupled).

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