Autonomic and Visceral Sensory
sympathetic pathways
- most autonomic innervation of a visceral target is dual (both parasympathetic and sympathetic innervate a particular target to provide antagonistic control of the target, eg. The heart pacemaker -sole sympathetic innervation to the following superficial targets: a) sweat glands b) arrector pili muscles c) peripheral blood vessels
autonomic versus somatic motor system
-ANS: 2 motor neurons (preganglionic and ganglionic) + thinly/unmyelinated axons and motor neuron synapses in ganglion (slower conduction) + cardiac/smooth muscle/glands + stimulate/inhibit -somatic: 1 motor neuron extends from CNS to skeletal muscle + axons myelinated and motor neuron synapses in effector target(fast conduction) + skeletal muscle +stimulate
sympathetic ganglia
-Two Types: 1. Sympathetic Trunk Ganglia: lie along the vertebral column along the dorsal root on each side 2. Sympathetic Collateral Ganglia: Prevertebral (anterior to the vertebral column, not paired) in abdomen and pelvis
sympathetic
-autonomic nervous system -"fight, flight, or fright" -activated during STRESS situations a) exercise b) excitement c) emergencies -mobilizes the body during extreme situations a) increase heart rate and breathing rate b) increases blood and oxygen to skeletal muscles c) dilates pupils and airways d) motility of the digestive tract and urinary tracts are inhibited -location: T1-L2
parasympathetic
-autonomic nervous system -"rest and digest" -concerned with conserving energy -controls routine maintenance functions -active when the body is at rest -concerned with conserving energy -directs "housekeeping" activities a) heart rate and breathing are at low-normal levels b) gastrointestinal tract digests food c) pupils are constricted -locations: cranial and sacral outflow
sympathetic vs parasympathetic ANS
-chains of two motor neurons -innervate mostly the same structures -cause opposite effects
parasympathetic - cranial outflow
-comes from the brain -innervates organs of the head, neck, thorax, and abdomen -includes vagus nerve
central control of ANS
-control by the brain stem and spinal cord -reticular formation exerts most direct influence a) medulla oblongata b) periaqueductal gray matter -control by the hypothalamus and amygdala a) hypothalamus—the main integration center of the ANS b) amygdala—main limbic region for emotions -control by the cerebral cortex
ANS and aging
-efficiency of the ANS declines with advancing age a) constipation due to reduced mobility of gastrointestinal (GI) tract b) dry eyes due to reduced tear formation
vagus nerve (X) outflow
-fibers innervate visceral organs of the thorax and most of the abdomen -stimulates digestion, reduction in heart rate and reduction in blood pressure -preganglionic cell bodies: located in dorsal motor nucleus in the medulla -ganglionic neurons: confined within the walls of organs being innervated
parasympathetic - sacral outflow
-innervation supplies remaining abdominal and pelvic organs -preganglionic cell bodies: located in visceral motor region of gray matter -ganglionic neurons: confined within the walls of organs being innervated
sympathetic region
-issues from T1-L2 -preganglionic fibers form the lateral gray horn -supplies visceral organs and structures of superficial body regions -contains more ganglia than the parasympathetic division
sympathetic trunk ganglia
-joined to ventral rami by white and gray rami communicantes -fusion of ganglia fewer ganglia than spinal nerves -fusion of ganglia most apparent in the cervical region (superior, middle, and inferior cervical ganglia)
adrenal medulla
-major organ of the sympathetic nervous system -constitutes largest sympathetic ganglia -secretes great quantities of norepinephrine and adrenaline -stimulated to secrete by preganglionic sympathetic fibers
visceral sensory neurons
-monitor stretch, temperature, chemical changes, and irritation -cell bodies are located in the dorsal root ganglion at spinal level and equivalent just outside of brain or at the level of the sensory organ (eg, olfactory bulb for smell) -visceral pain: no pain results when visceral organs are cut; instead visceral pain results from chemical irritation or inflammation, cramping smooth muscle -often perceived to be of somatic origin, as if from the skin or outer body because innervated by same spinal segment
general visceral sensory system
-monitors the activities of the visceral organs t ensure the ANS can make adjustments as necessary
autonomic nervous system (ANS)
-system of motor neurons -innervates: a) smooth muscle b) cardia muscle c) glands -regulates visceral functions (heart rate, blood pressure, digestion, urination) -general visceral motor division of the PNS
visceral reflex
-visceral sensory and autonomic neurons: participate in visceral reflex arcs a) defecation reflex b) micturition reflex
ANS disorders
1. Raynaud's disease—characterized by constriction of blood vessels -provoked by exposure to cold or by emotional stress 2. hypertension—high blood pressure -can result from overactive sympathetic vasoconstriction
sympathetic vs parasympathetic: anatomical differences
1. length of preganglionic + postganglionic fibers - sympathetic: short preganglionic, long postganglionic fibers - parasympathetic: long preganglionic, short postganglionic fibers 2. branching of axons - sympathetic axons: highly branched (influences many organs) - parasympathetic axons- few branches (localized effect) 3. neurotransmitter released by postganglionic axons -sympathetic: most release norepinephrine (adrenergic) -parasympathetic: release acetylcholine (cholinergic) 4. ganglia -sympathetic: close to CNA -parasympathetic: in or close to visceral organ
