chapter 14 autonomic nervous system

Autonomic nervous system (ANS)
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Autonomic nervous system (ANS)
-complex system of nerves for involuntary actions
-works constantly with somatic nervous system (SNS) to regulate body organs and maintain normal internal functions
-Homeostasis: adjusts internal water, electrolytes, nutrients & gas concentrations in the body outside of conscious awareness
SNS and ANS
both part of the peripheral nervous system (PNS)
SNS
operates under our conscious control
ANS
functions are involuntary
SNS
uses somatic sensory neurons to conduct stimulus information from a sensory receptor (tactile receptor in skin) and somatic motor neurons to innervate skeletal muscle fibers
ANS
-also utilizes sensory and motor neurons
-visceral sensory neurons and somatosensory receptors provide input to activate ANS
-Autonomic motor neurons innervate smooth & cardiac muscle fibers or glands
Divisions of ANS
-parasympathetic & sympathetic
-they both use preganglionic & ganglionic neuron to innervate muscles or glands, but perform dramatically different functions
-both contain autonomic ganglia that houses ganglionic neurons
-both are involuntary & concerned with bodies internal environment
Parasympathetic (craniosacral) division
-conserve energy and replenish nutrient stores "rest&digest" "rest&repose"
-most active when body is at rest or digesting a meal
-constricts pupils to restrict light, helps with reading, stim. of defection, constriction of respiratory passageways, reduce H.R, stim. of sexual arousal and glands
Sympathetic (thoracolumbar) division
-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
Dual innervation by parasym & symp
-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