Cranial Nerves & Autonomic Functions
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Cranial Nerves & Autonomic Functions

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Questions and Answers

Which cranial nerve is primarily responsible for the secretion of tears and saliva?

  • CN 10
  • CN 3
  • CN 9
  • CN 7 (correct)

    • Which neurotransmitter is secreted by the postganglionic fibers of the sympathetic nervous system?

  • Noradrenaline (correct)
  • Serotonin
  • Acetylcholine
  • Dopamine

    • What is the main role of the carotid sinus in regulating blood pressure?

  • Enhancing sympathetic output to increase heart rate
  • Secreting hormones that stabilize heart rate
  • Reacting to changes in blood pressure or arterial stretch (correct)
  • Providing sensory information about oxygen levels

    • Which area of the brain receives afferent input from receptors in major blood vessels and organs for autonomic regulation?

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

    How does the baroreceptor located in the carotid sinus respond to an increase in blood pressure?

    <p>It stimulates parasympathetic activity to lower heart rate</p> Signup and view all the answers

    What characterizes autonomic dysreflexia in individuals with spinal cord lesions?

    <p>Loss of supraspinal control leading to exaggerated reflexive responses</p> Signup and view all the answers

    Which nerves are responsible for the autonomic regulation of the distal half of the abdominal viscera?

    <p>Sacral segments S2, S3, and S4</p> Signup and view all the answers

    What type of reflex is indicated by the carotid sinus reflex?

    <p>Local reflex that regulates blood pressure</p> Signup and view all the answers

    What is the primary function of the sympathetic nervous system?

    <p>Preparation of the body for 'fight or flight' responses</p> Signup and view all the answers

    Which of the following best describes the pathway of the greater splanchnic nerve?

    <p>It conveys autonomic fibers to the viscera of the abdominopelvic cavity.</p> Signup and view all the answers

    Which cranial nerve is NOT part of the parasympathetic outflow?

    <p>Cranial Nerve V</p> Signup and view all the answers

    The ganglion impar is significant for which reason?

    <p>It is the point where paired sympathetic ganglia unite.</p> Signup and view all the answers

    The parasympathetic system primarily acts through which mechanism on the heart?

    <p>Opposes the sympathetic effects by reducing heart rate</p> Signup and view all the answers

    Which of the following statements about the structure of the sympathetic chain ganglia is correct?

    <p>They contain 22-23 pairs of ganglia across the entire length.</p> Signup and view all the answers

    What role does the vagus nerve play in the autonomic nervous system?

    <p>It conveys parasympathetic signals to various organs including the heart and lungs.</p> Signup and view all the answers

    The main difference between the white ramus and gray ramus in the sympathetic nervous system is that:

    <p>White ramus is lateral and contains myelinated fibers, while gray ramus is medial and contains unmyelinated fibers.</p> Signup and view all the answers

    Which statement accurately describes the autonomic nervous system (ANS)?

    <p>The ANS is responsible for involuntary control of homeostatic functions.</p> Signup and view all the answers

    What is the primary function of the parasympathetic nervous system?

    <p>Facilitate 'rest and digest' activities.</p> Signup and view all the answers

    What characterizes the sympathetic nervous system's response to stress?

    <p>It mobilizes resources for quick action and is involved in 'fight or flight.'</p> Signup and view all the answers

    Which of the following accurately reflects the anatomy of the preganglionic and postganglionic fibers in the ANS?

    <p>Preganglionic fibers are usually long and postganglionic fibers are short.</p> Signup and view all the answers

    Which of the following is NOT a responsibility of the autonomic nervous system?

    <p>Controlling skeletal muscle movement.</p> Signup and view all the answers

    Where do preganglionic sympathetic neurons arise from?

    <p>Thoracic and upper lumbar spinal segments.</p> Signup and view all the answers

    What distinguishes the sites of origin for the parasympathetic and sympathetic nervous system?

    <p>Parasympathetic fibers originate from cranial nerves and sacral regions, while sympathetic fibers arise from the thoracic region.</p> Signup and view all the answers

    How does the motor pathway differ in the ANS compared to the peripheral voluntary system?

    <p>The ANS employs two neurons to relay impulses to target organs.</p> Signup and view all the answers

    Which of the following activities would most likely activate the sympathetic nervous system?

    <p>Increased heart rate due to a stressful event.</p> Signup and view all the answers

    What is a common effect of the parasympathetic nervous system on the cardiovascular system?

    <p>Decreased cardiac output.</p> Signup and view all the answers

    Which statement accurately describes the primary function of the sympathetic nervous system?

    <p>It prepares the body for emergencies and physical activity.</p> Signup and view all the answers

    What is a key anatomical difference between the sympathetic and parasympathetic nervous systems?

    <p>Parasympathetic fibers have long preganglionic and short postganglionic fibers.</p> Signup and view all the answers

    Which of the following is NOT a typical effect associated with the activation of the parasympathetic nervous system?

    <p>Inhibition of energy storage.</p> Signup and view all the answers

    How do the effects of the sympathetic and parasympathetic nervous systems generally differ?

    <p>They often have opposing effects to maintain homeostasis.</p> Signup and view all the answers

    Which physiological response is directly triggered by the sympathetic nervous system during stress?

    <p>Dilated pupils to enhance vision.</p> Signup and view all the answers

    Study Notes

    Cranial Nerves & Autonomic Function

    • CN III (Oculomotor): controls smooth muscles that constrict the pupil and adjust lens accommodation
    • CN VII (Facial): controls tear and saliva secretion
    • CN IX (Glossopharyngeal): controls saliva secretion
    • CN X (Vagus): controls cardiac function, bronchi, esophagus, smooth muscle and glands of the trachea, and movements and glandular secretion of the thoracic and proximal half of abdominal viscera
      • Important to note that CN X has branches to the larynx (may be seen in lab/often mistaken for CN XII)
    • S2, S3, S4 (Pelvic Splanchnic Nerves): control the distal half of abdominal viscera through the pelvic splanchnic nerves. They also play a role in digestion.

    Sympathetic vs Parasympathetic Nervous System

    • Location of Preganglionic Cell Bodies: Sympathetic - Thoracic & Lumbar spinal cord; Parasympathetic - Brainstem & Sacral spinal cord
    • Location of Peripheral Ganglia: Sympathetic - Paravertebral (sympathetic chain) & prevertebral (near target organs); Parasympathetic - Near or within target organs
    • Neurotransmitters:
      • Acetylcholine (Ach) - Secreted by preganglionic neurons in both systems (cholinergic)
      • Noradrenaline - Secreted by most sympathetic postganglionic fibers (adrenergic)
      • Acetylcholine (Ach) - Secreted by most parasympathetic postganglionic fibers (cholinergic)
    • Opposing Actions: Sympathetic - primarily responsible for "fight or flight" responses; Parasympathetic - responsible for "rest and digest" functions

    Control of Autonomic Nervous System

    • Hypothalamus & Solitary Nucleus - receive afferent input from receptors in the heart, major blood vessels, lungs, viscera, etc.
    • Local Reflexes - provide regulation of most homeostatic function

    Carotid Sinus Reflex

    • Carotid Sinus - a dilation of the proximal portion of the internal carotid artery (innervated by CN IX & X) containing a baroreceptor that responds to changes in blood pressure or stretch
    • Increase in BP - Sensed by baroreceptors, afferent (sensory) fibers carry information to the solitary nucleus through the vagus nerve and glossopharyngeal nerve (CN IX)
    • Response - Stimulates increased parasympathetic output to the heart, decreasing heart rate and decreasing sympathetic output to the heart and blood vessels (vasodilation), further reducing blood pressure.

    Autonomic Dysreflexia

    • Loss of supraspinal control (hypothalamus & solitary nucleus) of the sympathetic nervous system and sacral segments (parasympathetic) of the spinal cord found in individuals with cervical and high thoracic spinal cord lesions (usually above T5-T6)
    • Dysregulation of the autonomic nervous system - leads to an uncoordinated sympathetic response resulting in potentially life-threatening hypertensive episodes, which can lead to seizures, stroke, or even death.
    • Characterized by - Sudden, exaggerated reflexive increase in blood pressure in response to a stimulus, usually bladder or bowel distension, originating below the level of the neurological injury.

    Autonomic Nervous System Overview

    • Central Nervous System (CNS) - Brain & Spinal Cord
    • Peripheral Nervous System (PNS) - Cranial Nerves & Spinal Nerves
    • Autonomic Nervous System (ANS) - Anatomically part of CNS & PNS; responsible for involuntary and unconscious control of homeostatic function
      • Can be excitatory or inhibitory in nature
      • Controls: cardiac muscle, lungs, smooth muscle, glands, viscera (involuntary structures)

    ANS - Sensory & Motor Responsibilities

    • Sensory Responsibility - Returns sensory information to the brain: visceral (gut) sensation, baroreceptor/chemoreceptor information
    • Motor System - Requires two neurons (preganglionic nerve & postganglionic nerve) to transmit a nerve impulse from the CNS to an end organ (versus a single neuron in the peripheral voluntary system to skeletal muscle)
      • Preganglionic cell bodies arise in the CNS
      • Postganglionic cell bodies arise in ganglia outside the CNS

    ANS - Sympathetic & Parasympathetic Systems

    • Both are two neuron systems
    • Preganglionic (myelinated) fiber synapses with postganglionic (unmyelinated) fibers near the end organ
    • Anatomical distinction between the sympathetic and parasympathetic divisions of the ANS is based primarily on:
      • Location of the presynaptic cell bodies
      • Which nerves conduct the presynaptic fibers from the CNS

    ANS - Parasympathetic System

    • Innervates:
      • Glands in the head & neck (secrete saliva/tears)
      • Sphincter pupillae (constricts pupil)
      • Blood vessels (vasodilation/erection, decrease BP)
      • Heart (decrease HR, decrease force of contraction)
      • Lungs (bronchoconstriction)
      • Digestive tract
      • Bladder
      • Bowel
    • Responsible for maintaining resting function: "rest & digest"
    • Usually a long preganglionic fiber and a short postganglionic fiber

    ANS - Sympathetic Nervous System

    • Responsible for rapid reactions to emergency situations: "fight or flight"
    • Role in mediating response to stress, mobilizing the body's resources for action in an emergency
      • Increased heart rate
      • Increased blood pressure
      • Increased contractility of the heart
      • Vasoconstriction
      • Bronchodilation
      • Sweating
      • Ejaculation
      • Dilates pupil

    Sympathetic Nervous System - Anatomy

    • Each sympathetic pathway from the spinal cord to the stimulated tissue is composed of:
      • A preganglionic neuron
      • A postganglionic neuron
    • Axons of presynaptic neurons - leave the spinal cord through ventral roots and enter the ventral rami of spinal nerves T1–L2 or L3
    • Presynaptic sympathetic fibers - almost immediately after entering, exit the ventral rami of these spinal nerves and pass to the sympathetic trunks (chain) through white rami communicantes (communicating branches)

    Pathway - IMLG >ventral root>spinal nerve>ventral rami of spinal nerve>white rami communicante >sympathetic chain

    • Within the sympathetic trunks, presynaptic fibers can follow one of three paths:
      • 1. Synapse at that level - in a sympathetic chain ganglion & leave via gray rami
      • 2. Synapse in a nearby level - in a sympathetic chain ganglion & leave via gray rami
      • 3. Pass through sympathetic chain - without synapsing as splanchnic nerves & synapse near the target organ

    Sympathetic Chain (Trunk)

    • A series of paired ganglia (paravertebral)
    • Runs from C1-S4; paired ganglia unite to form ganglion impar at the sacral level
    • Lies lateral to the vertebral column, on heads of ribs
    • 22-23 pairs of sympathetic ganglia
    • T1 ganglion blends with lower C ganglion=“stellate ganglion”

    Splanchnic Nerves

    • Convey visceral efferent (autonomic) and afferent fibers to and from the viscera of the body cavities
    • Postsynaptic sympathetic fibers destined for the viscera of the thoracic cavity - (heart, lungs, and esophagus) pass through cardiopulmonary splanchnic nerves to enter the cardiac, pulmonary, and esophageal plexuses
    • Presynaptic sympathetic fibers innervate viscera of the abdominopelvic cavity - (stomach and intestines) pass to the prevertebral ganglia through abdominopelvic splanchnic nerves
      • Greater Splanchnic Ns.-T5-9 or 10
      • Lesser Splanchnic Ns.-T10, T11
      • Least Splanchnic Ns.-T12
      • Lumbar splanchnic Ns – L1, L2 (L3)

    Parasympathetic System

    • Function - Homeostasis; ↓HR, ↓bp, ↓contractility of the heart, vasodilatation, bronchoconstriction, promotes digestion, empty bladder & bowel, constricts pupil
    • Acts - To conserve resources
    • Cranio-sacral outflow - Cell bodies originate in cranial nerves and sacral portion of the spinal cord:
      • CN III, VII, IX, X
      • Sacral segments of the spinal cord S2, 3, 4
      • Usually long preganglionic and short postganglionic fibers

    Parasympathetic System - Innervation

    • CN III (Oculomotor): Pupillary constriction
    • CN VII (Facial): Tears/saliva
    • CN IX (Glossopharyngeal): Saliva
    • CN X (Vags): Heart, lungs, viscera/bowel/bladder
    • S2, S3, S4: bowel/bladder, erection (vasodilation)

    Autonomic Nervous System (ANS)

    • Regulates involuntary bodily functions, including heart rate, digestion, breathing, and blood pressure.
    • Controls smooth muscle, cardiac muscle, and glands.
    • Maintains homeostasis by responding to internal and external stimuli.

    Sympathetic Nervous System (SNS)

    • Prepares the body for "fight-or-flight" responses.
    • Nerves originate from thoracic and lumbar spinal cord segments.
    • Effects:
      • Increases heart rate
      • Dilates airways
      • Dilates pupils
      • Inhibits digestion
      • Mobilizes energy stores

    Parasympathetic Nervous System (PNS)

    • Responsible for "rest-and-digest" activities.
    • Fibers originate from the brainstem and sacral spinal cord.
    • Effects:
      • Decreases heart rate
      • Constricts airways
      • Stimulates digestion
      • Promotes energy storage and conservation

    SNS vs. PNS

    • Anatomical Differences: SNS has short preganglionic fibers and long postganglionic fibers. PNS has long preganglionic fibers and short postganglionic fibers.
    • Functional Differences: SNS prepares for emergencies, PNS conserves energy and facilitates recovery.
    • The SNS and PNS often have opposing effects on target organs to maintain balance.

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    Description

    Explore the intricate roles of cranial nerves and their connections to the autonomic nervous system. This quiz covers important functions of various cranial nerves, including oculomotor and vagus, alongside a comparison of sympathetic and parasympathetic systems. Enhance your understanding of how these systems regulate bodily functions.

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