Chpt 14 handout/ Homeostatic imbalance, T and F
The autonomic Nervous system
Terms in this set (11)
1. Define autonomic nervous system and explain its relationship to the peripheral nervous system.
Autonomic Nervous system (ANS)- (Motor) Efferent division of the PNS that innervates cardiac and smooth muscles and glands: also called the involuntary or visceral motor system.
2. Compare the somatic and autonomic nervous systems relative to effectors, efferent
1. The somatic nervous system stimulates skeletal muscles, while the ANS innervates cardiac and smooth muscle and glands.
2. In the somatic nervous system, the cell bodies of the neurons are in the spinal cord and their axons extend to the skeletal muscles they innervate. The ANS consists of a two-neuron chain.
3. The neurotransmitter released by the somatic motor neurons is acetylcholine, which always has an excitatory effect; the neurotransmitters released by the ANS are epinephrine and acetylcholine, and both may have either an excitatory or an inhibitory effect.
4. There is overlap between the somatic and autonomic nervous systems, and most body responses to changing internal and external stimuli involve both skeletal muscle activity and visceral organ responses.
3. Compare and contrast the functions of the parasympathetic and sympathetic divisions.
1. The parasympathetic division keeps body energy use as low as possible while directing digestion and elimination activities.
2. The sympathetic division prepares the body to respond to an emergency or threatening situation (or vigorous exercise).
4. For the parasympathetic and sympathetic divisions, describe the site of CNS origin, locations of ganglia, and general fiber pathways.
1. Their origin sites. Parasympathetic (axon) fibers emerge from the brain and sacral spinal cord (are craniosacral). Sympathetic fibers (axons) originate in the thoracolumbar region of the spinal cord.
2. The relative lengths of their fibers. The parasympathetic division has long preganglionic and short postganglionic fibers. The sympathetic division has the opposite condition.
3.The location of their ganglia. Most parasympathetic
ganglia are located in the visceral effector organs. Sympathetic ganglia lie close to the spinal cord.
A. Parasympathetic (Craniosacral) Division (pp. 529-530; Figs. 14.3-14.4; Table 14.1)
1. The preganglionic axons extend from the CNS nearly all the way to the structures to be innervated, where they synapse with ganglionic neurons in the terminal ganglia.
2. The cranial outflow consists of preganglionic fibers that run in the oculomotor, facial, glossopharyngeal, and vagus cranial nerves.
3. The rest of the large intestine and the pelvic organs are served by the sacral outflow, which arises from neurons located in the lateral gray matter of spinal cord segments S2-S4.
B. Sympathetic (Thoracolumbar) Division (pp. 530-534; Figs. 14.3, 14.5-14.6; Table 14.1)
1. The sympathetic division supplies the visceral organs in the internal body cavities but also all visceral structures in the somatic part of the body.
2. When synapses are made in chain ganglia, the postganglionic axons enter the ventral (or dorsal) ramus of the adjoining spinal nerves by way of communicating branches called gray rami communicantes.
3. The preganglionic fibers from T5 down synapse in collateral ganglia; thus these fibers enter and leave the sympathetic chains without synapsing.
4. Some fibers of the thoracic splanchnic nerves terminate by synapsing with the hormone-producing medullary cells of the adrenal cortex. 0p
5. (A.) Define cholinergic and adrenergic fibers
and (B.) list the different types of their receptors.
A. Cholinergic Fibers- Nerve endings that upon stimulation release acetylcholine
Adrenergic Fibers- Nerve fibers that release norepinephrine
B. Cholinergic Receptors :
1. Nicotinic Receptors- respond to nicotine
2. Muscarinic Receptors- can be activated by mushroom poison muscarine
Adrenergic Receptors: (2 major classes then subdivided)
1. Alpha (a1 and a2)
2. Beta (b1,b2,b3)
6. Describe the clinical importance of drugs that mimic or inhibit adrenergic or cholinergic effects.
Knowing the locations of the cholinergic and adrenergic receptor subtypes allows specific drugs to be prescribed to obtain desired inhibitory or stimulatory effects on target organs.
7. State the effects of the parasympathetic and sympathetic divisions on the following organs: heart, blood vessels, gastrointestinal tract, lungs, adrenal medulla, and external genitalia.
1. Most visceral organs receive dual innervation by both ANS divisions, allowing for a dynamic antagonism to exist between the divisions and precise control of visceral activity.
2. The sympathetic division increases heart rate, dilates airways, and inhibits digestion and elimination while the body is under stress.
3. After the stress has passed, the parasympathetic division returns heart rate and airway diameter to normal, and allows digestion and elimination to resume.
4. Sympathetic tone throughout the vascular system allows the firing rate of sympathetic neurons to control the diameter of blood vessels, regulating systemic blood pressure.
5. Parasympathetic tone is usually dominant in the heart, digestive system, and urinary tracts, maintaining normal homeostatic levels of function unless overridden by the sympathetic system during stress.
6. The divisions of the autonomic nervous system may work together, rather than antagonistically, as in sexual arousal.
7. The sympathetic system has a unique role in control of the adrenal medulla, sweat glands, arrector pili muscles of the skin, the kidneys, and most blood vessels.
8. The parasympathetic division exerts short-lived, localized control over its effectors, whereas effects of the sympathetic division are persistent and widespread.
8. Describe autonomic nervous system controls.
1. The brain stem appears to exert the most direct influence over autonomic functions.
2. The hypothalamus is the main integration center for the autonomic nervous system.
3. Cortical or voluntary control of the autonomic nervous system appears to be possible.
Although the ANS is not usually considered to be under voluntary control, its activity is regulated by CNS controls in the spinal cord, brain stem, hypothalamus, and cerebral cortex (Figure 14.9). In general, the "hypothalamus" is the integrative center at the top of the ANS control hierarchy. From there, orders flow to lower and lower CNS centers for execution. Although the "cerebral cortex" may modify the workings of the ANS, it does so at the subconscious level and by acting through limbic system structures on hypothalamic centers.
The hypothalamus is the "boss," but the brain stem reticular formation appears to exert the most direct influence over autonomic functions .
9. Explain the relationship of some types of hypertension, Raynaud's disease, and autonomic dysreflexia to disorders of autonomic function.
A. Hypertension, or high blood pressure, may result from an overactive sympathetic vasoconstrictor response due to continuous high levels of stress
B. Raynaud's disease is characterized by intermittent attacks causing the skin of the fingers and the toes to become pale, then cyanotic and painful.
C. Autonomic dysreflexia is a life-threatening condition involving uncontrolled activation of both somatic and autonomic motor neurons
Autonomic neuropathy (damage to autonomic nerves) is a common complication of diabetes mellitus. One of the earliest and most troubling symptoms is sexual dysfunction, with up to 75% of male diabetics experiencing erectile dysfunction. Women, on the other hand, often experience reduced vaginal lubrica- tion. Other frequent manifestations of autonomic neuropathy include dizziness after standing suddenly (poor blood pressure control), urinary incontinence, sluggish eye pupil reactions, and impaired sweating. Just how the elevated blood glucose levels in diabetics damage nerves is still a mystery.