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ANS 1

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imissyou419's version from 2017-01-31 03:07

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Question Answer
Define ANSPortion of the NS that controls the visceral functions of the body
Name the 3 divisions of ANSsympathetic, parasympathetic, enteric (gut)
What is the overall function of ANS?essential for control of individual organ function and homeostasis, operates in the background (housekeeping) e.g. stand up, blood pool in legs, 40% decrease in CO, decrease in blood to brain, faint. Prevented by feedforward arteriole constriction
What are the specific functions of ANS? KNOW ALL THESEHelps to control heart rate, blood pressure and blood flow, body temp, airway resistance, GI motility, secretion by glands, bladder motility, sexual function
ANS exerts it action by controllingsmooth muscle (arterioles, gut muscle, etc), cardiac muscle, glands (saliva, sweat, adrenal medulla, digestive, prostate, etc), NEVER SKELETAL (voluntary activity controlled by alpha motor neuron)
Compare somatic NS vs. ANSANS controls internal (rather than external) environment,
largely involuntary (rather than voluntary),
regulate intrinsically active organs (gut, heart),
dual innervation (SNS/PNS - one excitatory; other inhibitory),
denervation of an organ - no atrophy (vs somatic where muscle will atrophy)
Is SNS always excitatory?No, it can be inhibitory (i.e. inhibit gut motility)
Autonomic Reflex Arc Pathway (4)1. Impulses are initiated in a variety of visceral (sensory) receptors: pressure/stretch receptors (GI tract, bladder, heart), oxygen receptors (carotid bodies), nociceptors.
2. They are relayed via afferent sympathetic and parasympathetic nerves to the CNS.
3. The sensory info is processed at various levels within the CNS (spinal cord, brain stem, hypothalamus, portions of cerebral cortex i.e. cerebral limbic cortex) - synapse with efferent neuron + collateral goes up to cerebral cortex, hypothalamus, brainstem,etc.
4. Information is then transmitted via efferent pathways to visceral effectors (smooth muscle, cardiac muscle, and glands)
What is the efferent pathway made up of?a preganglionic axon and a postganglionic axon
Where does the preganglionic neurons have their cell bodies at?within the CNS
What type of axons are preganglionic axons?myelinated B fibers (slowly conducting)
Where does the postganglionic neurons have their cell bodies at?in ganglia outside the CNS
What type of axons are postganglionic axons?unmyelinated C fibers (very slow conducting)
What are the 6 functional features of the ANS?1. adrenal medulla.
2. distribution to limbs.
3. antagonist effects.
4. only sympathetic innervation.
5. enteric nervous system.
6. neurons in enteric nervous system
Function features of the ANS: adrenal medullasympathetic preganglionic axons end directly on cells of the adrenal medulla which secretes epinephrine (80%) and norepinephrine (20%) into circulating blood (increase HR). Adrenal medulla can be considered to be a collection of postganglionic neurons which has evolved into an endocrine gland
Function features of the ANS: distribution to limbsmany postganglionic axons from the sympathetic ganglion chain re-enter the spinal nerves (via gray ramus) and are then distributed to effector organs: sweat glands, blood vessels, piloerector muscles of hairs
Function features of the ANS: antagonistic effectsmost organs that are influenced by ANS are innervated by both sympathetic and parasympathetic divisions which are usually antagonist e.g. heart rate: sympathetic increases, paraysmpathetic decreases. gut contraction: sympathetic decreases, parasympathetic increases
Function features of the ANS: only sympathetic innervationsome organs are only innervated by sympathetic division: most arterial blood vessels, adrenal medulla, sweat glands, piloerector muscles (only sympathetic axons go out to periphery)
Function features of the ANS: enteric nervous systemcontrols GI movement, GI secretion, local blood flow. Can function independently from ANS input, however this input normally modulates enteric NS activity
Function features of the ANS: # neurons in enteric NSThere are more neurons in enteric nervous system than there are in spinal cord (>100 million)
All preganglionic neurons in ANS arecholinergic (release Ach)
All postganglionic PNS neurons release Ach, therefore PNS is totally cholinergic
Usually postganglionic neurons in SNS releaseNorephinephrine
Postganglionic neurons in SNS release Ach instead of NE when: KNOW THISsweat glands, vasodilator nerves to blood vessels of skeletal muscles, piloerector muscles
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Question Answer
SomaticAch/Nicotinic to skeletal muscle (excitatory only)
Sympathetic normallypreganglionic releases Ach/Nicotinic, postganglionic releases NE/alpha/beta adrenergic (excitatory and inhibitory) to smooth muscle, cardiac muscle, gland
Sympathetic onto adrenal medullapreganglionic releases Ach/Nicotinic, adrenal medulla releases E (80%), NE (20%) into circulating blood
Parasympatheticpreganglionic releases Ach/Nicotinic, postganglionic releases Ach/Muscarinic (excitatory and inhibitory) to smooth muscle, cardiac muscle, gland
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