THE AUTONOMIC NERVOUS SYSTEM
What is a ganglion?
A ganglion is a collection of nerve cell bodies located in a specific site within the body, but outside the CNS.
Comparison of somatic and autonomic nervous systems: AUTONOMIC
AUTONOMIC receptor types? chemoreceptors, baroreceptors, mechanoreceptors conscious? unconscious excitatory or inhibitory? excitatory or inhibitory for cardiac muscle, smooth, and glands number of motor neurons? two motor neurons
Describe the following: Relative length of fibers
Because of the closeness of the spinal cord to the sympathetic chain ganglia and the collateral ganglia, sympathetic preganglionic neurons are fairly short. Because of the distance between the brain or spinal cord and the innervated organs, parasympathetic preganglionic fibers are relatively long.
Describe the postganglionic neurons of the two systems.
Because of the locations of ganglia, sympathetic postganglionic fibers are relatively long while parasympathetic postganglionic fibers are relatively short. Regardless, all postganglionic neurons of either system have their axons pass from their respective ganglia to the effector for innervation.
ANS neurotransmitters: CHOLINERGIC
CHOLINERGIC neurotransmitter? acetylcholine Which neurons use this neurotransmitter? all preganglionic neurons, all postganglionic para- sympathetic neurons, a very few postganglionic sympathetic neurons enzymes used to destroy neurotransmitter? acetylcholinesterase
What is meant by the concept of dual innervation?
In general, if one division starts or increases the activity of an organ, the other division will stop or decrease the activity. This is called dual innervation.
Which ANS division is usually in control of autonomic tone
In general, we are in parasympathetic tone, except during states of emergency when we immediately switch to sympathetic tone.
What is the origin of the parasympathetic system?
Parasympathetic preganglionic neurons arise from the nuclei of cranial nerves III, VII, IX, and X, and the lateral gray horns of spinal cord segments S2-4. For this reason, the parasym-pathetic division is also called the craniosacral division and the preganglionic axons are the craniosacral outflow.
Describe the following: Prevertebral ganglia
Prevertebral (collateral) ganglia lie as three clusters associated with the three unpaired arteries arising from the abdominal aorta (celiac, superior mesenteric, and inferior mesenteric). These ganglia are used by the sympathetic division.
Comparison of somatic and autonomic nervous systems: SOMATIC
SOMATIC receptor types? cutaneous receptors, proprioceptors, special senses conscious? may become conscious excitatory or inhibitory? excitatory for skeletal muscles only number of motor neurons? single motor neuron
Describe the following: Sympathetic chain ganglia
Sympathetic chain (vertebral chain or paravertebral) ganglia are located in a series that lie in a vertical row on either side of the vertebral column, extending from the base of the skull to the coccyx.
What is the origin of the sympathetic division?
Sympathetic preganglionic neurons originate from the lateral gray horns of spinal cord segments T1-L2. Their axons travel in the spinal nerves of these segments. Therefore, the sympathetic division is called the thoracolumbar division and the preganglionic axons are called the thoracolumbar outflow.
How does the ANS operate? What controls it?
The ANS operates without conscious control, relying upon reflex arcs that are dependent upon the hypothalamus and medulla for overriding control.
What is the general function of the autonomic nervous system?
The autonomic nervous system (ANS) regulates the activities of cardiac muscle, smooth muscle, and glands.
Where is the cell body of a postganglionic neuron located?
The cell body is located in a specific ganglion. The location of the ganglion is dependent upon the division of the ANS to which the neuron belongs and which organ it will innervate.
Where is the cell body of a preganglionic neuron located?
The cell body is located in gray matter of the spinal cord or brain.
What is the ultimate controller of autonomic tone?
The hypothalamus regulates the balance of sympathetic versus parasympathetic activity or tone.
Describe the following: Terminal ganglia
The parasympathetic division uses terminal (intramural) ganglia located very close to or within the walls of the organ to be innervated.
In general, describe the activities of the parasympathetic nervous system. What is meant by the name "rest and recovery" system?
The parasympathetic nervous system is an energy conservation-restorative system. It regulates those activities that conserve and restore body energy during times of rest and recovery. The parasympathetic nervous system dominates over sympathetic activity in the glands and smooth muscle of the gut, stimulating glandular secretion and the gut movements necessary for food to be digested and absorbed. The acronym SLUD stands for salivation, lacrimation, urination, and defecation, all controlled by the parasympathetic nervous system.
In general. describe why parasympathetic responses are short-lived and very precise while sympathetic responses are much longer-lived and body wide.
The parasympathetic system has very little divergence in the connections between preganglionic and postganglionic fibers, so that only very small areas of effectors are stimulated at any given time. Also, acetylcholine is rapidly destroyed in the synaptic clefts, so that the response to neurotransmitter is very short-lived. The sympathetic system has a good deal of divergence between preganglionic and postganglionic fibers (1:5-500), so that the sympathetic message is sent body-wide. Secondly, norepinephrine is poorly removed from the synapse, so that it diffuses into the bloodstream for delivery throughout the body. Lastly, activation of the sympathetic nervous system results in secretion of norepine-phrine and epinephrine, hormones that have stronger and body wide effects.
What effect does the postganglionic neuron have on the effector?
The peripheral effector (cardiac muscle, smooth muscle, or gland) is either stimulated or inhibited, depending upon which division of the ANS is being discussed.
Where does the axon of the postganglionic neuron terminate?
The postganglionic axon passes from the ganglion to the effector.
How does the axon of a preganglionic neuron pass from the CNS?
The preganglionic axon passes from the CNS in a spinal or a cranial nerve.
Where does the preganglionic axon terminate?
The preganglionic axon terminates in a ganglion.
In general, describe the activities of the sympathetic nervous system. What is meant by the name "fight or flight" system?
The sympathetic system prepares the body to meet emergency demands and is primarily involved with processes that expend energy. During physical or emotional stress, the sympathetic division dominates the parasympathetic system, initiating a series of activities known as the fight-or-flight response. This includes increased heart rate, force of contraction, and blood pressure; increased blood flow to essential structures (brain, lungs, heart, skeletal muscles) and decreased activity in nonessential ones; increased rate and depth of respiration. In addition, there is activation of the adrenal medulla, causing secretion of norepinephrine and epinephrine as hormones to greatly heighten the response.
Most effectors receive innervation from both divisions of the ANS, one causing excitation and the other causing inhibition. How is this possible?
This is possible because the postganglionic neurons use different neurotransmitters and the effectors bear different receptors.
Structurally, the ANS consists of two types of neurons. Name and give a brief description of each.
Visceral afferent (sensory) neurons - provide a continual flow of information to the CNS from the viscera and blood vessels Visceral efferent (motor) neurons - provide motor innervation to the various effectors (cardiac muscle, smooth muscle, glands)
ANS neurotransmitters: ADRENERGIC
neurotransmitter? norepinephrine Which neurons use this neurotransmitter? most postganglionic sympathetic neurons enzymes used to destroy neurotransmitter? catechol-O-, methyltransferase, monoamine oxidase
Name the two types of visceral motor neurons by the divisions of the ANS?
preganglionic and postganglionic
Name the two separate divisions of the ANS.
sympathetic and parasympathetic nervous systems