chapter 14 autonomic nervous system

Autonomic nervous system (ANS)
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-prepare body for emergency, "fight or flight"
-increases activity results in increased alertness & metabolic activity necessary in times of fear, stress, increased exertion, or emergency
-increases feelings of euphoria, increased activity of cardiovascular & respiratory centers, elevated B.P, H.R, depth and rate of breathing, muscle tone (look tense, shiver, mobilize E reserves.
-preganglionic neurons from T1-L2; postganglionic neuron near spinal cord
-usually happens in most organs
-actions of divisions usually oppose each other
-opposing affects are often from increase or decrease of activity in one division
-autonomic plexuses: innervate organs through specific axon bundles
-communication by neurotransmitters, specific in each division
-maintains homeostasis through autonomic reflexes that occur in innervated organs
Neurotransmitters-two used by ANS are acetylcholine (ACh) & norepinephrine (NE) -released by presynaptic cell -bind to specific receptors in post synaptic cell membrane -binding has either excitatory or inhibitory effect depending on receptorPre and postganglionic axons-both release acetylcholine in parasymp division & are thus called cholinergic -pre and some post are also cholinergic in symp division -most of the post in the symp division release norepinephrine & are called adrenergicAutonomic reflexes-or visceral reflexes help maintain homeostasis similar to spinal reflexes -reflex arcs consist of smooth & cardiac muscle contractions or secretions by glands in response to a specific stimulus (micturition reflex which partly controls release of urine) -other reflexes: alteration of heart rate, changes in respiratory rate & depth, regulation of digestive system activities, alteration of pupil diameterCNS Control of Autonomic Function-Autonomic function is influenced by the: Cerebrum, Hypothalamus , Brainstem, Spinal Cord -Hypothalamus: central brain structure involved in emotions and drives that act through ANS -Sensory processing in the thalamus & emotional states controlled in limbic system directly affect hypothalamus -brainstem nuclei in the mesencephalon, pons, and medulla oblongata mediate visceral reflexesCNS Control of Autonomic Function-reflex centers control accomodation of the lens, blood pressure changes, blood vessel diameter changes, digestive activities, heart rate changes & pupil size -centers for cardiac, digestive, & vasometer functions are housed within the brainstem -Some responses (defacation & urination) are processed and controlled at the level of the spinal cord without the involvement of the brain. Higher centers in the brain may consciously inhibit these reflex activities