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22 Cards in this Set
- Front
- Back
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Overall organization of the Nervous System (chart)
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Characteristics of the ANS
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Two divisions: sympathetic and parasympathetic
Each pathway has two neurons: preganglionic and postganglionic SNS and PNS distinguished by anatomy and neurochemistry Generally work in opposition to each other - Regulates involuntary function of the viscera (internal organs) - Consists of sympathetic and parasympathetic nervous systems |
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Vasovagal syncope
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Vasovagal syncope
Loss of balance between the two divisions In anticipation of a stressful event (blood draw, birth), SNS surges A rapid PNS response “overshoots” and causes bradycardia, hypotension, and cerebral hypoperfusion Patient loses consciousness |
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Somatic motor system
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- Regulates skeletal muscles that make up the body wall, which encloses the body cavity where most viscera are harbored
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Each autonomic pathway consists of two neurons in series (Figure 2):
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- Pre-ganglionic neurons, which originate in the central nervous system (brainstem and spinal cord)
- Post-ganglionic neurons, which synapse with the pre-synaptic neurons in the autonomic ganglia outside of the spinal cord *Ganglion = collection of neuronal cell bodies, which is covered by a connective tissue sheath when outside the central nervous system |
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SNS Target Organs
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End-organ effects are “fight or flight” derived
Mydriasis Tachycardia Relaxes bronchiolar smooth muscle Contracts GI sphincters Contracts bladder sphincter Stimulates adrenal gland |
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The Adrenal Glands
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Lie on top of the kidneys
Preganglionic sympathetic neurons connect directly onto secretory cells in the medullae Secretory cells in the medullae release epinephrine and norepinephrine (adrenaline and noradrenaline) 80% of norepinephrine is methylated to make epinephrine Act as hormones rather than neurotransmitters and permit a longer-acting sympathetic effect |
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Parasympathetic Neurons
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Preganglionic fibers of PNS leave the CNS in cranial nerves or from the sacral spinal cord.
Postganglionic cells of PNS reside in ganglia near or in the organ that is innervated. |
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Parasympathetic Target Organs
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End-organ effects are “rest and digest” derived
Miosis Bradycardia Smooth muscle in GI wall contracs GI sphincters relax GI secretion increases Bladder wall contracts Bladder sphincter relaxes |
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Neurotransmitters
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Acetylcholine metabolism
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Majority is broken down by acetylcholinesterase and choline is recycled back into presynaptic cell for new acetylcholine synthesis. No reuptake without breakdown.
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Noepinephrine Metabolism
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Cleared mostly (50-80%) by reuptake. Some cleared by enzymatic breakdown or diffusion away from nerve endings.
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Comparing the SNS & PNS: Neuron Structure and Neurotransmitters
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Cholinergic receptors
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-detect ach
1. Nicotinic – found on skeletal muscles and postganglionic neurons of SNS & PNS 2. Muscarinic – found on target cells of PNS post-ganglionic fibers |
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Adrenergic receptors:
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detect epinephrine & norepinephrine
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alpha receptors
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1. alpha-1 – found on target cells of postganglionic SNS fibers; prefers norepinephrine; associated with constriction of smooth muscle
2. alpha-2 – found on presynaptic postganglionic membranes (negative feedback) |
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beta receptors
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3. beta-1 – found in heart muscle and kidney; equal affinity for norepinephrine & epinephrine
4. beta-2 – found on certain blood vessels and smooth muscles; equal affinity for norepinephrine & epinephrine; associated with dilation of blood vessels and smooth muscle |
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Asthma
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Asthma is a chronic inflammatory disorder characterized by increased responsiveness of the airways to multiple stimuli
Classic clinical triad Episodic dyspnea (shortness of breath) Cough Wheezing As exacerbation progresses, expiration becomes prolonged, accessory muscles are used |
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Asthma Treatment
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Treatment strategies based on these 3 components
Bronchoconstriction Beta adrenergic agonists (albuterol) Delivered in aerosolized form Metered dose inhaler (MDI) or nebulized Secretions Anticholinergic agents (atrovent) MDI or nebulizer Inflammation Steroids MDI or, if severe, pills |
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Autonomic “Tone”
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Refers to the basal rates of each system
The normal resting rate of secretion by the adrenal medulla is about 0.2 mcg/kg/min of E and 0.05 mcg/kg/min of NE Important in that it allows for a single nervous system to increase or decrease the activity of a stimulated organ Sympathetic tone --> blood vessels Parasympathetic tone --> GI tract |
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Therapeutic Use of ANS Drugs
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Heart disease
Beta-1 blockers (metoprolol, atenolol) Cardiac arrest Epinephrine Atropine Asthma Bronchoconstriction --> beta-2 agonist (albuterol) Secretions --> anticholinergic (ipratroprium) Shock Norepinephrine Nasal congestion Ephedrine |
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Toxidromes
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