Autonomic Nervous System
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Questions and Answers

How does the autonomic nervous system (ANS) differ from the somatic nervous system?

  • The ANS controls voluntary movements, while the somatic nervous system regulates involuntary functions.
  • The ANS is responsible for sensory perception, while the somatic nervous system is responsible for motor functions.
  • The ANS modulates the activity of glands, cardiac muscle, and smooth muscle, while the somatic nervous system controls skeletal muscles. (correct)
  • The ANS operates consciously, while the somatic nervous system operates unconsciously.

During an emergency situation that triggers the 'fight-or-flight' response, which division of the autonomic nervous system (ANS) is primarily activated, and what are the expected physiological changes?

  • Enteric; increased digestive activity, decreased heart rate, and pupil dilation.
  • Parasympathetic; decreased heart rate, increased digestion, and pupil constriction.
  • Sympathetic; increased heart rate, increased alertness, and elevated blood pressure. (correct)
  • Somatic; increased muscle tone, decreased reaction time, and heightened sensory perception.

Which of the following accurately describes the concept of autonomic tone?

  • The suppression of the parasympathetic division by the sympathetic division during periods of high stress.
  • The exclusive control of an organ by either the sympathetic or parasympathetic division, but not both.
  • The ability of the somatic nervous system to override autonomic functions during voluntary movements.
  • The normal background rate of activity in both the sympathetic and parasympathetic divisions, maintaining baseline functions. (correct)

How does the integration center in a visceral reflex arc differ from that in a somatic reflex arc?

<p>Visceral reflexes have slower responses due to interneurons in the integration center, while somatic reflexes are typically faster. (C)</p> Signup and view all the answers

In the parasympathetic division, what is the effect on heart rate, and how is this maintained under normal conditions?

<p>Decreases heart rate; maintained by the ongoing parasympathetic tone, which keeps the heart rate lower than it would be without autonomic input. (D)</p> Signup and view all the answers

Which of the following accurately describes the path of a sympathetic signal using the spinal nerve route?

<p>Gray ramus -&gt; spinal nerve -&gt; target organ (B)</p> Signup and view all the answers

What is the primary neurotransmitter released by preganglionic fibers in the sympathetic nervous system?

<p>Acetylcholine (ACh) (B)</p> Signup and view all the answers

How does the location of ganglia differ between the sympathetic and parasympathetic nervous systems?

<p>Sympathetic ganglia are in ganglion chains, while parasympathetic ganglia are near the target organs. (B)</p> Signup and view all the answers

What is the functional significance of varicosities in the context of autonomic nerve fibers?

<p>They facilitate the release of neurotransmitters over a broad area of effector tissue. (C)</p> Signup and view all the answers

What is the primary function of intrinsic primary afferent neurons (IPANs) in the context of the peristaltic reflex?

<p>To detect local stimulation and initiate both ascending excitatory and descending inhibitory reflexes. (B)</p> Signup and view all the answers

What is the primary anatomical distinction of the sympathetic division?

<p>Arises from the thoracic and lumbar regions of the spinal cord (T1 to L2). (A)</p> Signup and view all the answers

In Hirschsprung's disease, the absence of the enteric plexus in the sigmoid colon and rectum leads to which of the following?

<p>Permanent constriction, preventing the passage of feces. (C)</p> Signup and view all the answers

What is the significance of collateral ganglia in the sympathetic nervous system?

<p>They are the site of synapse for splanchnic nerves that innervate abdominal organs. (D)</p> Signup and view all the answers

What are the two primary mechanisms by which the autonomic nervous system (ANS) achieves contrasting effects between and within its divisions?

<p>Release of different neurotransmitters and the presence of different receptor types. (A)</p> Signup and view all the answers

How does the adrenal medulla function as part of the sympathoadrenal system?

<p>It acts as a modified sympathetic ganglion, releasing hormones into the bloodstream. (A)</p> Signup and view all the answers

Which of the following is a key characteristic of muscarinic receptors that distinguishes them from nicotinic receptors?

<p>Muscarinic receptors use second messenger systems, while nicotinic receptors are ligand-gated ion channels. (D)</p> Signup and view all the answers

What is a key feature of the Enteric Nervous System (ENS) that allows it to function independently?

<p>It has its own intrinsic sensory neurons, interneurons, and motor neurons. (D)</p> Signup and view all the answers

Norepinephrine (NE) typically elicits excitatory effects through α-adrenergic receptors by what mechanism?

<p>Increasing intracellular Ca2+ concentrations. (C)</p> Signup and view all the answers

In which of the following locations would nicotinic receptors NOT be found?

<p>Cardiac muscle (D)</p> Signup and view all the answers

What is the primary physiological consequence of the descending inhibitory reflex in the intestines?

<p>Relaxation of smooth muscle in front of the bolus to facilitate movement. (C)</p> Signup and view all the answers

How does norepinephrine (NE) inhibit intestinal motility via α-adrenergic receptors?

<p>By preventing cAMP production (B)</p> Signup and view all the answers

Flashcards

Autonomic Nervous System (ANS)

Involuntary motor system that modulates the activity of glands, cardiac muscle, and smooth muscle.

Visceral Reflexes

ANS reflexes involving receptors, afferent neurons, interneurons, efferent neurons, and effectors; slower than somatic reflexes.

Sympathetic Nervous System

Division of the ANS associated with alertness, exercise, stress; triggers the 'fight-or-flight' response.

Parasympathetic Nervous System

Division of the ANS focused on energy conservation, body maintenance, digestion, and waste removal; the 'resting and digesting' state.

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Autonomic Tone

The background rate of activity in the ANS, where both sympathetic and parasympathetic divisions are active.

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Ganglion

Clusters of neuron cell bodies in the peripheral nervous system.

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Preganglionic Fiber

Short, myelinated fibers that transmit signals from the CNS to ganglia; release Acetylcholine (ACh).

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Postganglionic Fiber

Long, unmyelinated fibers extending from the ganglia to effector organs; release Acetylcholine (ACh) or Norepinephrine (NE).

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Varicosities

Enlargements along the terminal axon of postganglionic fibers that release neurotransmitters.

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White Rami

Carry sympathetic signals from the spinal nerve to the sympathetic chain ganglia (myelinated).

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Gray Rami

Carry sympathetic signals from the sympathetic chain ganglia back to the spinal nerve (unmyelinated).

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Parasympathetic Nervous System (PSNS)

Part of the autonomic nervous system, promotes 'rest and digest' functions.

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Peristalsis

Wave-like muscle contractions that move food through the digestive tract.

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Peristaltic reflex

Local stimulation that triggers secretomotor and vasodilator reflexes in the submucosal plexus.

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Intrinsic Primary Afferent Neurons (IPANs)

Neurons in the enteric nervous system that sense stimuli and initiate reflexes.

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Ascending Excitatory Reflex

Reflex that involves excitatory signals that travel upwards in the digestive tract.

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Descending Inhibitory Reflex

Reflex that involves inhibitory signals that travel downwards in the digestive tract.

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Hirschsprung Disease

Hereditary disease characterized by the absence of enteric plexus, leading to constriction and impaction.

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Muscarinic receptors

Acetylcholine receptors that use second messenger systems; found in cardiac muscle, smooth muscle, and glands.

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Nicotinic receptors

Ligand-gated ion channels that are activated by acetylcholine.

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Study Notes

Autonomic Nervous System (ANS)

  • It is involuntary
  • It modulates activity (adjust) within glands, cardiac and smooth muscle
  • It motor visceral functions
  • It regulates homeostasis related to heart rate, blood pressure, respiration rate, digestion, pupil diameter, and metabolism

Visceral Reflexes

  • These reflexes are similar to somatic reflexes, however, they are slower responses
  • The pathway it takes:
  • Receptor
  • Afferent sensory neurons
  • Integration center (interneurons)
  • Efferent motor neurons
  • Effector

Divisions

  • The sympathetic division
  • Its responsible for alertness, heart rate, blood pressure, etc
  • It prepares for exercise, competition, stress, anger, and fear
  • The effects are known as the "flight-or-flight" reaction
  • The parasympathetic division
  • It reduces energy usage and maintains body maintenance (digestion, waste removal)
  • Effects manifest most during resting and digesting state
  • Neither division has universally excitatory nor inhibitory effects

Autonomic Tone

  • It is a normal background rate of activity in both divisions (sympathetic and parasympathetic)
  • Parasympathetic
  • Smooth muscles in intestines and slow heart rate
  • Maintains muscle tone and heartrate ~70-80 bpm
  • Sympathetic
  • Maintains blood pressure in blood vessels being partially constricted

Components

  • CNS
  • Control nuclei - hypothallus and other brainstem regions
  • Motor neurons – spinal cord
  • Peripheral nervous system
  • Ganglion
  • Two fibers to target organ
  • Preganglionic fiber
  • It is myelinated, and has soma in CNS
  • Releases ACh
  • Postganglionic fiber
  • It is unmyelinated and extends to effector
  • Ach or NE

Varicosities

  • Terminal portion
  • NT released along a significant length of the axon
  • The effects are “looser” for easier diffusion
  • NT covers a large surface area of the effector tissue

Sympathetic Division (SNS)

  • Thoracic and lumbar regions (T1 to L2)
  • Fibers extend to every level of the body
  • Ganglion chains (paravertebral)
  • Longitudinal ganglia
  • Cervical to coccygeal levels
  • Input
  • Short preganglionic fibers
  • Myelinated via White Rami
  • Output
  • Long postganglionic fibers
  • Unmyelinated via Gray Rami

White and Grey Rami

  • White rami communicantes
  • Grey rami communicantes

Leaving Sympathetic Ganglia

  • Spinal nerve route
  • Gray ramus returns to spinal nerve or target organ
  • Sympathetic nerve route
  • Sympathetic nerves target carotid or cardiac plexus
  • Splanchnic nerve route
  • No ganglia synapse
  • Continue as splanchnic nerves towards collateral

Collateral Ganglia

  • Splanchnic nerve route
  • Celiac ganglia
  • Superior mesenteric ganglia
  • Inferior mesenteric ganglia
  • Located at points where arteries with the same names branch off aorta
  • Postganglionic fibers accompany these arteries and their branches to the target organs

Adrenal Gland

  • Medulla
  • It is essentially a sympathetic ganglion with a sympathoadrenal system
  • Contains postganglionic neuroendocrine neurons
  • Stimulated by preganglionic sympathetic fibers to secrete epinephrine

Parasympathetic DIV (PSNS)

  • Fibers originate from the brain and sacral region
  • Ganglia are located near target organs
  • It's characterized with long preganglionic fibers
  • Divergence of neurons occurs closer to the target organ
  • It has fewer postganglionic fibers, resulting in more specific stimulation control

Enteric Nervous System

  • Part of digestive tract
  • Has ~500 million neurons
  • Communicates to coordinate smooth muscle and glands
  • Independent from CNS
  • It doesn't arise from the CNS instead making its own ganglia and reflex arcs
  • It's regulated by the PSNS & SNS
  • Functions in:
  • Movement
  • Esophagus
  • Stomach
  • Intestines

Peristaltic Reflex

  • Local stimulation occurs from mouth towards anus
  • The following mechanisms trigger relaxation:
  • Secretomotor and vasodilator reflexes are mediated by neurons located in the submucosal plexus
  • The following mechanisms trigger contraction:
  • intrinsic primary afferent neurons (IPANS)
  • Ascending excitatory reflexes triggered by Myenteric plexus

Hirschsprung Di-

  • Hereditary loss of enteric plexus
  • No innervation in sigmoid colon and rectum
  • This causes permanent constriction and no movement of digested material
  • Stool becomes difficult to pass through
  • Causes Shrunken rectum & Megacolon – massive colon dilation

Neurotransmitters & Receptors

  • Divisions & Contrasting effects
  • Occurs between & within SNS & PSNS
  • Different neurotransmitter (NTs)
  • Acetylcholine
  • Norepinephrine
  • Different receptor types
  • Two classes for each NT

Acetylcholine (ACh)

  • Preganglionic in both ANS divisions
  • Postganglionic parasympathetic
  • Few sympathetic (blood vessels, some glands)
  • Has muscarine receptors:
  • Use second messenger systems
  • Act on cardiac muscle, smooth muscle, glands
  • Example: excites intestinal muscle and inhibits cardiac muscle
  • Has Nicotinic receptors:
    • Ligand-gated channels
    • In Ganglia synapses, Adrenal medulla, Skeletal muscle

Norepinephrine (NE)

  • Released by sympathetic postganglionic neurons
  • Acts on α-adrenergic receptors
  • Uses second messenger system
  • Usually has excitatory effects (e.g., labor contractions)
  • Ca2+ messengers
  • Can be inhibitory (e.g., lowers intestinal motility) with prevention of cAMP production
  • Acts on β-adrenergic receptors
  • Usually inhibitory (e.g., dilates bronchioles, relaxes)
  • Can be excitatory (e.g., excites cardiac

Dual Innervation

  • Nerve fibers from both divisions
  • Antagonistic
  • Same effector cells - e.g., heart muscle cells
  • Different cells - e.g., eye muscles
  • Cooperative
  • Different effectors with unified response
  • E.g., saliva production

Single Innervation

  • Nerve fibers from one division
  • Also produce opposite effects when needed
  • During an emergency/stress situation
  • Sympathetic fibers decrease firing rate
  • Smooth muscles relax (blood vessels)
  • Blood pressure pushes on walls which dilates
  • Can dilate vessels leading to vital organs (brain, heart)

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Autonomic Nervous System Lecture Notes

Description

Explore the autonomic nervous system, contrasting it with the somatic nervous system. Learn about the 'fight-or-flight' response and autonomic tone. Discover neurotransmitters, ganglia locations, and visceral reflex arcs.

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