Exam 5 Review:  Chapter 14:  ANS Histology & Pharmacology

general visceral motor neurons - Those neurons which transmit instructions to various effectors (smooth and cardiac muscle tissues, endocrine and exocrine glands) which can adjust the conditions of homeostasis of the internal environment in response to integration of sensory information in control centers in the central nervous system, e.g., nuclei of the medulla oblongata or the hypothalamus; these neurons form two cell pathways which often supply dual innervation to effectors, representing the output of both the parasympathetic and sympathetic divisions of the ANS.

preganglionic neuron = preganglionic fiber - A neuron, whose cell body is in the CNS, which receives stimuli from the CNS and transmits resulting nerve impulses along its axon which ends in a ganglion; a term most often used in reference to the first of a pair of general visceral motor neurons in a two neuron pathway in the ANS.

postganglionic neuron = postganglionic fiber - A neuron, whose cell body is in an autonomic ganglion, which receives stimulation by ACh from the preganglionic CNS and transmits resulting nerve impulses along its axon which ends at an effector cell or tissue; a term most often used in reference to the second of a pair of general visceral motor neurons in a two neuron pathway in the ANS.

acetylcholine (ACh) - A neurotransmitter which is a derivative of choline; it is synthesized, stored and released at the ends of nerve fibers at the neuromuscular junction; it is the primary neurotransmitter in parasympathetic ANS pathways, as well as being the neurotransmitter released by sympathetic ANS preganglionic neurons and by the sympathetic ANS postganglionic neurons which innervate sweat glands; in the somatic and parasympathetic nervous systems, and in the brain  it may also act as a neuromodulator.

cholinergic neuron - A term referring to both those neurons which release the neurotransmitter acetyl choline and those neurons which respond to acetyl choline due to their having receptors for ACh.

nicotinic receptors - One of two types of cell surface receptors for the neurotransmitter acetyl choline found on various neurons and visceral effectors; named in recognition of the fact that the chemical nicotine will bind and stimulate these receptors mimicking the activity of ACh; most cells with these receptors respond to the binding of ACh with excitatory effects.

muscarinic receptors - One of two types of cell surface receptors for the neurotransmitter acetyl choline found on various neurons and visceral effectors; named in recognition of the fact that the chemical muscarine, a compound derived from certain mushrooms, will bind and stimulate these receptors mimicking the activity of ACh;  cells with these receptors may respond to the binding of ACh with either excitatory or inhibitory effects, depending on the cell type.

acetylcholinesterase - The enzyme found in the blood stream and at peripheral synapses, e.g., the neuromuscular junction, in autonomic ganglia, in parasympathetic terminal/intramural ganglia which breaks down the neurotransmitter ACh = acetylcholine.

adrenergic neuron - A term referring to both those neurons which release the neurotransmitter norepinephrine and those neurons which respond to norepinephrnie due to their having receptors for NE.

norepinephrine = noradrenaline - A catecholamine neurotransmitter and neurohormone derived from the amino acid tyrosine which is the neurotransmitter released by most sympathetic postganglionic neurons and by the adrenal medulla.

alpha receptors  - One of two general types of cell surface receptors for the neurotransmitter norepinephrine found on various neurons and visceral effectors; most cells with these receptors respond to the binding of NE with excitatory effects; subtypes alpha₁ and alpha₂ are recognized.

beta receptors - One of two general types of cell surface receptors for the neurotransmitter norepinephrine found on various neurons and visceral effectors; cells with these receptors respond to the binding of NE with either excitatory effects or inhibitory effects, depending on the cell type; subtypes beta₁, beta₂, and beta₃ are recognized.

beta blocker - The common name or nickname given to the class of drugs which interferes with, antagonizes, the effect of norepinehrine on cardiac muscle; these drugs tend to slow the heart rate and prevent irregular heartbeats (arrhythmias) without interfering with other sympathetic effects.

Sketch and label :

1. the basic components of an autonomic motor pathway. Describe the functions of each component.

Remember that the ANS is strictly the motor side of control of internal homeostasis.

1.  The autonomic preganglionic neuron receives some sort of command to act; that command may be as simple as the sensory input indicated in the visceral reflex arc illustrated above, or it may be a more complex response which processed a variety of visceral sensory information at higher centers such as the cortex, limbic system, hypothalamus and brain stem. 2.  When stimulated, the autonomic preganglionic neuron which lies in a gray matter nucleus in the hypothalamus or brainstem or in the lateral horn of an appropriate spinal cord segment, sends an impulse outward on a cranial or spinal nerve to an autonomic ganglion. 3.  Within the autonomic ganglion, the autonomic preganglionic neuron synapses with one or more autonomic postganglionic neurons, releasing acetyl choline neurotransmitter. 4.  Depending on the type of synapse (axodendritic, axosomatic, or axoaxonic), the cholinergic communication will excite/stimulate or repress/inhibit the autonomic postganglionic neuron(s) in the pathway. 5.  If the autonomic postganglionic neuron(s) is/are stimulated, they will send an impulse outward on a branch of a cranial or spinal nerve to the visceral effector (smooth or cardiac muscle or exocrine or endocrine gland cells). 6.  The autonomic postganglionic neuron(s) will release either acetyl choline or norepinephrine at the synapse with the visceral effector. 7.  The response of the visceral effector to the arrival of the autonomic motor impulse may be either stimulation/excitation or supression/inhibition, depending on the type of neurotransmitter receptors present on the visceral effector cell.

List  and describe:

2. the ways in which a preganglionic sympathetic neuron may synapse with a postganglionic sympathetic neuron.

3. the neurons of the autonomic nervous system and neurotransmitters they release.

Construct a table:

1. describing the neurotransmitters of the autonomic nervous system. For each neurotransmitter list the type of receptor it binds, and the possible effect (stimulatory versus inhibitory)

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