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Questions and Answers
What neurotransmitter is secreted by the adrenal medulla?
The parasympathetic system has long postganglionic fibers.
False
Name the major cranial nerve that supplies parasympathetic fibers to the body.
Vagus nerve
The receptors associated with acetylcholine in target organs of the parasympathetic system are called ______ receptors.
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Match the following effects with the appropriate division of the autonomic nervous system:
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Which of the following is a β-adrenergic blocker?
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Nicotinic receptors are found in target organs of the autonomic nervous system.
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Identify one effect of the sympathetic division on blood vessels.
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Which division of the autonomic nervous system is primarily activated during stress?
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The autonomic nervous system operates under conscious control.
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What is the primary role of the hypothalamus in the autonomic nervous system?
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The __________ division of the autonomic nervous system is most active during rest.
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Match the division of the autonomic nervous system with its primary characteristics:
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What neurotransmitters are primarily involved in the autonomic nervous system?
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The autonomic nervous system includes both sensory and motor pathways.
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What kind of neurons originate in the thoracic or lumbar spinal area for the sympathetic nervous system?
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The consequences of stress are primarily managed by the __________ system.
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Which structure serves as a control center for respiration in the autonomic nervous system?
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Study Notes
Autonomic Nervous System
- Controls body functions unconsciously and involuntarily.
- Key in maintaining homeostasis through autonomic reflexes.
- Controls smooth muscle, cardiac muscle, and glands.
- Involved in respiration, heart rate, blood pressure, digestion, rumination, sleep, arousal, and body temperature.
- Autonomic reflexes involve sensory cells, sensory nerve fibers, integration centers, motor nerve fibers, and effectors.
Control Center
- Primarily controlled by negative feedback.
- Sensory cells vary based on the system (baroreceptors, cold and warm receptors).
- Sensory nerve fibers are similar to those in somatic arc reflexes.
- Control centers include the hypothalamus (master command), brainstem (special control function), and spinal cord (local integration).
- Receive continuous sensory information (frequency of impulses).
- Compare information to a set reference and alter frequency on the motor fiber if there's a difference.
Motor Nerve Fibers
- Differ from somatic motor fibers with two peripheral nerves (versus one in somatic arc reflexes).
- Target organs include smooth muscle, cardiac muscle, and glands.
- Preganglionic neuron with a cell body in the CNS and an axon that innervates a second neuron, the postganglionic neuron.
- Postganglionic neuron cell body is located in a ganglion.
Sympathetic Nervous System
- Also known as the thoracolumbar system.
- Activated during stress or demanding activity.
- Preganglionic neurons originate in the thoracic or lumbar spinal area and send axons to sympathetic ganglia forming a chain parallel to the spinal cord.
- Postganglionic fibers are long and innervate hollow organs, blood vessels, and other structures.
- Some preganglionic fibers extend to the adrenal medulla, stimulating the secretion of epinephrine and norepinephrine into the bloodstream.
Parasympathetic Nervous System
- Also known as the craniosacral system.
- Mostly active during rest.
- Preganglionic neurons originate in the brain or sacral part of the spinal cord and send axons to ganglia near or within effector organs.
- Long preganglionic fibers, especially the vagus nerve (cranial nerve X), are major suppliers to the body.
- Ganglia are located in the wall or adjacent to target organs with no interconnection between ganglia (no chain).
- Short postganglionic fibers connect directly with specific organs without branching or hormonal enhancement for selective action.
Neurotransmitters of the ANS
-
Acetylcholine (ACh):
- Nicotinic receptors: Found at preganglionic synapses and are ionotropic (part of an ion channel, primarily sodium).
- Muscarinic receptors: Found in target organs of the parasympathetic nervous system, separate from ion channels, and require intracellular second messengers for activation. These receptors can be either stimulatory or inhibitory, and their effects are slower and more prolonged than nicotinic receptors.
-
Norepinephrine (NE) and Epinephrine (E):
-
Adrenergic receptors: Associated with G proteins and activate intracellular second messengers.
-
Alpha (α) adrenergic:
- α1: Increases calcium levels
- α2: Decreases cAMP levels
- Effects: Primarily smooth muscle constriction (especially vascular), leading to vasoconstriction.
-
Beta (β) adrenergic:
- β1 and β2: Increases cAMP levels
- β1: Primarily in the heart, increasing contraction strength and rate.
- β2: Relaxation of smooth muscle in the gastrointestinal tract, uterus, and bronchioles.
-
Alpha (α) adrenergic:
-
Adrenergic receptors: Associated with G proteins and activate intracellular second messengers.
Pharmacological Significance
- Agonists and antagonists can selectively activate or block ANS receptors.
- Hypertension treatment's: Beta-adrenergic blockers (e.g., propranolol) decrease heart rate by acting on β1 receptors.
- Asthma treatment: Beta-2 adrenergic agonists (e.g., salbutamol) induce bronchodilation.
- Atropine: Muscarinic receptor blocker used for eye dilation (drop in the eye), inhibition of lower GI tract contraction, and reduction of mucus production in the respiratory tract.
Effects of Sympathetic and Parasympathetic Systems
| Effector | Sympathetic | Parasympathetic |
|---|---|---|
| Eye | Pupil dilation | Pupil constriction |
| Salivary gland | Stimulation | Inhibition |
| Heart rate | Increased | Decreased |
| Blood vessels | Constriction (most) | Dilation (few) |
| Lungs (bronchiole) | Dilation | Constriction |
| Intestinal mobility | Inhibition | Stimulation |
| Sphincters | Stimulate closing | Inhibit closing |
| Urinary bladder | Muscle tone relaxed | Contraction |
| Penis | Ejaculation | Erection |
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Description
Explore the functions and control mechanisms of the autonomic nervous system. This quiz covers its role in maintaining homeostasis, the types of control centers involved, and the pathway of autonomic reflexes. Test your knowledge on sensory and motor nerve fibers within this vital system.
