ParasymPathetic Nervous system Done by : Zaid Al-Ghnaneem
In this lecture we are going to discuss Parasympathetic, in the last lecture we took sympathetic and one of the objectives of last lecture was taking the Plexuses but we will take it in this lecture. Plexuses have both components of BOTH Sympathetic and Parasympathetic. Structure of the Parasympathetic Division Craniosacral division: Preganglionic neurons originate from Brainstem through cranial nerves III, VII, IX and X Sacral spinal nerves S2 S4 Parasympathetic ganglia terminal ganglia. Presynaptic neuron usually synapses with 4 5 postsynaptic neurons all of which supply a single visceral effector. Parasympathetic has pre and post ganglionic, preganglionic cell body in CNS, Postganglionic cell body outside CNS. We will focus on Sacral more than cranial because already we have info about cranial. Parasympathetic ganglia is Terminal which means near the visceral organ, except some cranial which have their own ganglia and also contains cell bodies of Postganglionic fibers, for example oculomotor has ciliary ganglia, and glossopharyngeal has otic ganglia and Facial has submandibular and pterygopalatine ganglia, Vagus will be in Terminal ganglia. Since Parasympathetic ganglia is close to visceral organ, diversion will be less than sympathetic which synapses up to 20 but Parasympathetic up to 4-5 postsynaptic. Autonomic Plexuses in the Thorax, Abdomen and Pelvis
Visceral organs innervation from ANS comes from plexuses, so plexuses is mix of sympathetic and parasympathetic, for example heart will NOT receive separate sympathetic and separate parasympathetic, it WILL receive plexuses contain BOTH. Plexuses components differ in sympathetic and parasympathetic, they contain Preganglionic fibers from Parasympathetic and Postganglionic fibers from sympathetic, so content is different. Autonomic Plexuses A network of sympathetic and parasympathetic axons. Cardiac plexus heart. And sympathetic nerves will be Postganglionic emerge from T6 sympathetic ganglia up to superior cervical ganglia, and Parasympathetic fibers from Vagus nerve, same content to pulmonary. Pulmonary plexus from upper part of thoracic ganglia the bronchial tree. Esophageal Plexus esophagus Celiac plexus largest. Celiac plexus will be formed after celiac ganglia, it contains Postganglionic fibers from sympathetic that will fuse with preganglionic Parasympathetic fibers come from vagus. Now when Parasympathetic reach the organ it will synapse with postganglionic, so this is the reason why we are saying plexuses contain Preganglionic from Parasympathetic! this applies on all plexuses. Supplies the stomach, spleen, pancreas, liver, gallbladder, and adrenal medullae. Superior mesenteric plexus small intestine and proximal colon. Inferior mesenteric plexus remember that vagus nerve innervate 2/3 of the large intestine but here in inferior mesenteric plexus it innervates the distal colon, so the PARASYMPATHETIC fibers in this plexus are coming from sacral segments Not form vagus nerve, same thing to hypogastric plexus the parasympathetic is coming from sacral not vagus. distal colon and rectum. Hypogastric plexus urinary bladder and genital organs. Renal plexus kidneys and ureters. Cranial Parasympathetic Outflow Preganglionc neurons III Edinger Westphal nucleus rostral midbrain VII superior salivatory nucleus caudal pons IX inferior salivatory nucleus rostral medulla X dorsal nucleus of vagus medulla
Vagus nerve carries nearly 80% of the total craniosacral flow. (thoracic and abdominal viscera) Postganglionic neurons: In Head and Neck Reside in four pairs of ganglia Ciliary ganglia (III) ciliary muscles (lens adaptation) & iris (constrictor) Pterygopalatine ganglia (VII) lacrimal gland Submandibular ganglia (VII) submandibular and sublingual glands Otic ganglia (IX) parotid gland In Thorax and Abdomen Terminal ganglia Associated with the vagus nerve Sacral Parasympathetic Outflow Consists of S2 S4. Pelvic splanchnic nerves postganglionic neurons (hypogastric plexus or walls of viscera) Distal GIT (distal colon, sigmoid colon, rectum) because proximal part 2/3 comes from Vagus Urinary bladder (voiding) Penis or clitoris (erection) Only voiding and erection so we are talking about Parasympathetic fibers Again Pelvic splanchnic nerves are Parasympathetic. Pelvic splanchnic nerves Parasympathetic (S2 S4) Inferior hypogastric plexus Inferior mesenteric plexus Parasympathetic fibers exit from sacrum as Pelvic splanchnic nerves within pelvis, they will target inferior hypogastric plexus anterior to sacrum lateral to rectum, or target inferior mesenteric plexus. Hypogastric Plexuses Superior hypogastric plexuses In front of promontory, promontory is anterior superior edge of sacrum, part of inlet of pelvis Forms right & left hypogastric nerves Some neurologists consider it as plexus, or as right and left hypogastric nerves.
Inferior hypogastric plexuses Hypogastric nerves + pelvic splanchnic nerves Lateral to rectum, bladder & vagina Parasympathetic Afferent Fibers,, part of GVA. GVA has both sympathetic and parasympathetic, but in most cases one of them is dominant over another. Follow the efferent pathway Cell bodies Cranial part sensory ganglia of cranial nerves VII geniculate ganglion temporal bone IX inferior (petrosal) ganglion jugular foramen X inferior (nodose) ganglion jugular foramen Sacral part dorsal root ganglia of sacral spinal nerves Sympathetic Responses Stress sympathetic system fight or flight response. production of ATP. Dilation of the pupils. heart rate and blood pressure. Dilation of the airways. Constriction of blood vessels that supply the kidneys and gastrointestinal tract. blood supply to the skeletal muscles, cardiac muscle, liver and adipose tissue glycogenolysis blood glucose. lipolysis. Parasympathetic Responses Rest and digest response. Conserve and restore body energy. digestive and urinary function. body functions that support physical activity. Integration and Control of Autonomic Functions Direct innervation brain stem and spinal cord. Hypothalamus is the major control and integration center of the ANS. It receives input from the limbic system.
Autonomic or Visceral Reflexes Autonomic reflexes occur over autonomic reflex arcs. Components of that reflex arc: sensory receptor sensory neuron integrating center pre & postganglionic motor neurons visceral effectors Unconscious sensations and responses changes in blood pressure, digestive functions etc filling & emptying of bladder or defecation Control of Autonomic NS Not aware of autonomic responses because control center is in lower regions of the brain Hypothalamus is major control center input: emotions and visceral sensory information smell, taste, temperature, osmolarity of blood, etc output: to nuclei in brainstem and spinal cord posterior & lateral portions control sympathetic NS increase heart rate, inhibition GI tract, increase temperature anterior & medial portions control parasympathetic NS decrease in heart rate, lower blood pressure, increased GI tract secretion and mobility Autonomic Dysreflexia if there is spinal injury above T6, there will be cut of descending pathways and impairment of the lower ones below T6, there will be triggering of reflexes because there is no more supraspinal control of reflexes and they will be exaggerated. Now above the level of lesion there will be OPPOSITE as a response to the lower one. But why T6? because the danger of autonomic dysreflexia on vital organs because of any small stimulus it will be so danger and may lead to death. Exaggerated response of sympathetic NS in cases of spinal cord injury above T6 Certain sensory impulses trigger mass stimulation of sympathetic nerves below the injury Result vasoconstriction which elevates blood pressure parasympathetic NS tries to compensate by slowing heart rate & dilating blood vessels above the injury pounding headaches, sweating warm skin above the injury and cool dry skin below
can cause seizures, strokes & heart attacks Example of Spinal and Supraspinal Control of AN: Urinary Bladder Function Urinary bladder has 2 functions Urinary bladder function Storage phase,, walls are relaxed and constriction of internal sphincter which is autonomic external sphincter is somatic. Walls are innervated by parasympathetic, and there is coordination between sympathetic and parasympathetic, in storage phase there is activity of sympathetic and inactivity of parasympathetic, opposite in voiding phase. Example of spinal reflex control on the AN Voiding phase Example of supraspinal control on the AN Effect of SCI on the Urinary Bladder Function The storage and voiding phase will be triggered by spinal reflexes, There is LOSS of coordination. In another words we will not lose reflexes, they are present, but there is No coordination. Spinal cord injury (SCI) eliminates the supraspinal control Urinary bladder dysfunction Visceral Pain Vague and poorly localized Referral pain depend on the spinal segment receiving the afferent every organ has referral pain to specific part but some organs make referral to midline, most of organs innervated bilaterally " such as right and left vagus " the referral pain will be in midline. Why referral pain of liver or gallbladder for example reach neck? because the phrenic nerve innervated the diaphragm and it is sensory of Parietal peritoneum, so then the infection is severe that reaches the parietal peritoneum lining this organs, there will be referral pain via phrenic nerve to cervical region