Chapter 15 notes PDF

Preview

Summary

Types notes...

Description

CHAPTER 15- The Autonomic Nervous System 1.) Compare the structural and functional characteristics of the somatic and autonomic nervous systems comparison of somatic and autonomic nervous systems Somatic Nervous System: Contains sensory and motor neurons Sensory neurons receive info from receptors for somatic senses -> tactile, thermal, pain, and proprioceptive sensations, and from receptors for special senses: (sight, hearing, taste, smell, equilibrium) These sensations are consciously perceived- and somatic motor neurons stimulate the skeletal muscles that are the effectors of the somatic nervous system- they produce reflex movements, and voluntary movements. When somatic motor neuron is stimulates a muscle it contracts- effect is always excitation. When a somatic motor neuron does not stimulate a muscle , it results in a paralyzed, limp muscle with no tone. Skeletal muscles that are controlled by somatic motor neurons generate respiration movements even though they are not conscious of breathing Autonomic nervous system gets its main input from the autonomic(visceral) sensory neurons. Usually associated with interoceptors and sensory signals are not consciously perceived most of the time. But the exceptions: 2 examples of perceived visceral pain include: pain from damaged viscera and angina pectoris due to inadequate blood flow to the heart interoceptors- sensory receptors located in blood vessels, visceral organs muscles and the nervous system that monitor changes in the internal environment. Example: Chemoreceptors- monitor blood CO2 levels Mechanoreceptors- detect the degree of stretch in the walls of organs or blood vessels. Pain can produce dramatic changes in autonomic activites Input that influences the ANS also include some sensation monitored by somatic sensory special sensory neurons autonomic motor neurons- function to regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities in their effector tissues. Effector tissues: cardiac muscle, smooth muscle, and glands Example of Autonomic responses: changes in diameter of the pupils, dilation and constriction of blood vessels and adjustment of the rate and force of the heartbeat. Will continue to function to some extend even if nerve supply is damaged. autonomic ganglion- a cluster of nerve cell bodies in the autonomic nervous system and consist of 2 types.

CHAPTER 15- The Autonomic Nervous System Autonomic motor pathways consist of two motor neurons, one following the other. 1st Neuron- extends from CNS to the Autonomic ganglion and is myelinated 2nd Neuron – is the same autonomic ganglion, it is unmyelinated axon extends from the ganglion directly to the effector, the effector being smooth muscle cardiac muscle or a gland) Chromaffin cells- located in the adrenal medullae, secrete the neurotransmitter epinephrine and norepinephrine. Somatic motor neurons secrete: ACh only Autonomic motor neurons secrete: ACh & NE sympathetic division- (fight or flight) nerve impulses cause increased activity and excitation (causes increased HR), increased alertness an metabolic activities, preparing for emergency situations. Release of glucose from the liver parasympathetic division( rest and digest)- nerve impulses cause decreased activity and inhibition (decreased HR) conserves energy, replenishes nutrient stores dual innervation- the ability of organs to receive impulses from both sympathetic and parasympathetic neurons.

CHAPTER 15- The Autonomic Nervous System Describe preganglionic and postganglionic neurons of the autonomic nervous system. Each division of the ANS has 2 motor neurons 1st- Any autonomic motor pathway called the preganglionic neuron- its cell body is in the brain or spinal cord. Axon exits the CNS as part of cranial or spinal nerve axon is small in diameter, and synapses with a post ganglionic neuron 2nd – Post ganglionic neuron- located outside the CNS, in the PNS cell body and dendrites located in the autonomic ganglion. Small diameter, C fiber, ends at visceral effector. Preganglionic neuron-> conveys nerve impulses from CNS to autonomic ganglia Postganglionic neuron-> relays impulses from autonomic ganglia to visceral effectors preganglionic neurons: In the sympathetic division preganglionic neurons have cell bodies located in the lateral horns of the gray matter in the 12 thoracic segments, and 2 lumbar segments of the spinal cord. thoracolumbar division- another term used for the sympathetic division. thoracolumbar outflow- axons of sympathetic preganglionic neurons In the parasympathetic division cell bodies of preganglionic neurons are located in the nuclei of four cranial nerves in brain stem (III, VII, IX, X), and in lateral gray matter of the 2nd -4th sacral segments of the spinal cord. craniosacral division- another term used for the parasympathetic division. craniosacral outflow- axons of the parasympathetic preganglionic neurons. autonomic ganglia (no specifics on each individual ganglia) 2 major groups of autonomic ganglia: sympathetic ganglia, and parasympathetic ganglia sympathetic ganglia- components of sympathetic division, sites of synapses between preganglionic and postganglionic neurons. 2 types of sympathetic ganglia: sympathetic trunk ganglia- (or vertebral chain ganglia or paravertebral ganglia) – extend from base of skull to the coccyx and innervate organs above the diaphragm, (head, neck, shoulder, and heart) contain the superior, middle, and inferior cervical ganglia prevertebral ganglia (or collateral ganglia)-anterior or vertebral column and close to large abdominal arteries, innervate organs below the diaphragm contain the celiac, superior mesenteric, inferior mesenteric, aorticorenal, and renal ganglions Parasympathetic ganglia

CHAPTER 15- The Autonomic Nervous System preganglionic axons of the parasympathetic division synapse with postganglionic neurons in the terminal ganglia (or intramural ganglia). Located close or within the walls of a visceral organ.- contain : ciliary, pterygopalatine, submandibular, and otic ganglion Parasympathetic preganglionic axons are long Parasympathetic postganglionic axons are short Postganglionic neurons Preganglionic neurons connect with postganglionic neurons in one of the following ways: 1) axon may synapse with postganglionic neurons in the ganglion it reaches 1st 2) Axon may ascend or descend to a higher or lower ganglion before synapsing with post ganglionic neurons. 3) An axon may continue without synapsing through the sympathetic trunk ganglion to end at a prevertebral ganglion and synapse with the postganglionic neurons 4) An axon may pass without synapsing though the sympathetic trunk ganglion to end at a prevertebral ganglion and then extends to chromaffin cells of the adrenal medullae. autonomic plexuses- located in the thorax, abdomen, and pelvis both sympathetic and parasympathetic neurons form tangled networks. Cardiac plexus- supplies the heart located in the thorax Pulmonary plexus- supplies the bronchial tree, located in the thorax Celiac plexus- the largest autonomic plexus and surrounds the celiac trunk, contains 2 large celiac ganglia, and 2 aorticorenal ganglia and a dense network of autonomic axons , distributes to the stomach, spleen, pancreas, liver, gallbladder, kidneys, adrenal medullae, testes, and ovaries. Superior mesenteric plexus- supplies small and large intestine Inferior mesenteric plexus- innervates the large intestine Hypogastric Plexus- anterior to the firth lumbar vertebra to supply the pelvic vicera Renal Plexus- contrain renal ganglion and supplies renal arteries within the kidneys and ureters Compare the anatomical components of the sympathetic and parasympathetic divisions of the autonomic nervous system. Structure of the sympathetic division White ramus (plural is rami)—white rami communicantes- structures that contain sympathetic preganglionic axons that connect the anterior ramus of the spinal nerve with the ganglia of the sympathetic trunk. ‘White’ refers to the myelinated axons. - Thoracic and 1,2,3 lumbar nerves have white rami communicates

CHAPTER 15- The Autonomic Nervous System Gray ramus (plural is rami)—gray rami communicates- axons of some postganglionic neurons leave the sympathetic trunk by entering the gray ramus. They are structures containing sympathetic postganglionic axons that connect the ganglia of the sympathetic trunk to spinal nerves. “gray” means unmyelinated Horner’s syndrome- oculosympathetic paresis- group of symptoms that arise when nerves known as the sympathetic trunk is damaged, damage to sympathetic nerves of the face. signs and symptoms occur on the same side as the lesion of the sympathetic trunk. Symptoms include decrease in pupil side, drooping eyelid, and decreased sweating on affected side of face, usually a result of another medical problem such a stroke, tumor, or spinal cord injury, currently no specific treatment or cure. structure of the parasympathetic division cell bodies of parasympathetic preganglionic neurons are found in nuclei in brain stem and in lateral gray matter of the second through fourth sacral segments of the spinal cord. Their axons emerge as part of a cranial nerve or as part of the anterior root of a spinal nerve cranial parasympathetic outflow- consists of preganglionic axons that extend from the brain stem in four cranial nerves. Cranial outflow has 4 pairs of ganglia and the ganglia associated with the vagus nerve (X) and carries 80% of the total craniosacraloutflow -Vagus nerve passes through the thorax and it sends axons to the heart, airways of lungs, in abdomen it supplies the liver, gallbladder, stomach, pancreas, small intestine, and part of the large intestine sacral parasympathetic outflow- consists of preganglionic axons in the anterior roots of the second through fourth sacra; spinal nerves. Preganglionic axons of both the cranial and sacral outflows end in the terminal ganglia- where they synapse with post ganglionic neurons. - consist of preganglionic axons from the anterior root of S2-S4 -the sacral spinal nerves branch off to form the pelvicsplanchnic nerves pelvic splachnic nerves- synapse with parasympathetic post ganglionic neurons located in the terminal ganglia in the walls of innervated viscera. They innervate the smooth muscle glands in the walls of the colon, ureters, urinary bladder and reproductive organs Enteric division-the specialized collection of nerves and ganglia forming a complex, integrated neuronal network within the wall of the gastrointestinal tract, pancreas, and gallbladder. - capable of monitoring tension in the intestinal wall and accessing the composition of the intestinal contents Nerve fibers that innervate the digestive system arise from 2 plexuses within the enteric division:

CHAPTER 15- The Autonomic Nervous System myenteric plexus: the largest plexus, positioned between the outer longitudinal and circular muscle layers from the upper esophagus to the anus. Communicates with greatly with the submucosal plexus. submucosal plexus: located gut wall between circular muscle later and muscularis mucosae, runs from stomach to anus (this system of nerves makes it possible that normal motility and secretory functions of the GI tract) Describe the neurotransmitters and receptors involved in autonomic responses. ANS neurotransmitters and receptors - Autonomic neurons are classified on the bases of the neurotransmitter they produce and release as either cholinergic or adrenergic. -receptors for the neurotransmitters are integral membrane proteins they are located in the plasma membrane of the postsynaptic neuron or effector cell. cholinergic neurons- release the neurotransmitter acetylcholine they also include in the ANS- 1) all sympathetic and parasympathetic preganglionic neurons. 2) sympathetic postganglionic neurons that innervate most sweat glands 3) all parasympathetic postganglionic neurons. acetylcholine (ACh)- a neurotransmitter stored in the synaptic vesicles and is released by exocytosis then diffuses across the synaptic cleft and binds with specific cholinergic receptors. cholinergic receptors- are integral membrane proteins located in the post-synaptic plasma membrane. 2 types of cholinergic receptors: nicotinic receptors: present in plasma membrane of dendrites and cell bodies of both sympathetic and parasympathetic postganglionic neurons muscarinic receptors: present in the plasma membranes of all effectors (smooth muscle, cardiac muscle, glands) innervated by parasympathetic postganglionic axons. Most sweat glands receive innervation from cholinergic sympathetic postganglionic neurons and possess muscarinic receptors acetylcholinesterase (AChE)- enzyme that inactivates ACh adrenergic neurons- in ANS these neurons release norepinephrine also called noradrenalin norepinephrine (NE) or noradrenalin- neurotransmitter stored synaptic vesicles and released by exocytosis. adrenergic receptors: bind both norepinephrine and epinephrine. The --norepinephrine can either be released as a neurotransmitter by sympathetic postganglionic neurons OR released as a hormone into the blood by chromaffin cells of the adrenal medulla. Epinephrine- is released as hormone

CHAPTER 15- The Autonomic Nervous System alpha receptors and beta receptors-2 types of adrenergic receptors, found on visceral effectors innervated by most sympathetic post ganglionic axons. (divided further into a1, a2, B1, B2, B3) Activation of B1 & A1-- produce excitation Activation of B2 & A2 - cause inhibition B3  present only in cells of brown adipose tissue, activation causes thermogenesis (heat production) Norepinephrine stimulates – Alpha receptors more strongly then beta receptors Epinephrine is a strong stimulant for both Alpha and Beta receptors. Activity of norepinephrine at a synapse is terminated either when it is taken up by the axon that released it, or when the NE is inactivated by the enzyme COMT or MAO. NE lingers in the synaptic cleft for a longer time so it usually has a longer lasting effect. Adrenergic neurons are longer lasting then those triggered by cholinergic neurons. receptor agonists and receptor antagonists Agonist- substance that binds to and activates a receptor in the process mimicking the effect of a natural neurotransmitter or hormone Example: Phenylephrine is a adrenergic agonist at A1 receptors common ingredient in cough medicine, it constricts blood vessels in nasal mucosa, reduces production of mucus to relieve congestion. Antagonist- substance that binds to abd blocks a receptor to prevent a natural neurotransmitter or hormone from exerting its effects. Example: Atropine, blocks muscarinic ACh receptors, dilates the pupils, reduces glandular secretions and relaxes smooth muscle in the GI tract, Example: Propranolol- a BP medication functions as a non-selective beta blocker meaning it binds to all types of the beta receptors and prevents their activation by Epi and Norepi. Blocked B1 – decreases HR, and Decreases BP Blocked B2- causes low BGL, because of decreased glycogen breakdown and decreased gluconeogenesis, mild bronchoconstriction

Describe the major responses of the body to stimulation by the sympathetic and parasympathetic divisions of the ANS.

physiological effects of the ANS

CHAPTER 15- The Autonomic Nervous System autonomic tone- the balance between sympathetic and parasympathetic activity, regulated by the hypothalamus. Works by when increasing sympathetic tone, decreases parasympathetic tone and vice versa. Structures that receive only sympathetic response- sweat glands, arrector pili muscle, kidneys, spleen and most blood vessels. sympathetic responses- Highly active during emergency, exercise, excitement and embaressment , activation of the medullae set in motion a series of physiological responses. fight-or-flight response: The effects of sympathetic stimulation are longer lasting and more widespread than the effects of parasympathetic stimulation for three reasons: (1) Sympathetic postganglionic axons diverge more extensively; as a result, many tissues are activated simultaneously. (2) Acetylcholinesterase quickly inactivates acetyl- choline, but norepinephrine lingers in the synaptic cleft for a longer period. (3) Epinephrine and norepinephrine secreted into the blood from the adrenal medullae intensify and prolong the responses caused by NE liberated from sympathetic postganglionic axons. parasympathetic responses- support body functions that conserve and restore body energy during times of rest and recovery rest-and-digest- SLUDD – 5 parasympathetic responses- Salvation, lacrimation, urination, digestion, defecation. Describe the components of an autonomic reflex. autonomic reflexes- responses that occur when nerve impulses pass through an autonomic reflex arc. These reflexes play a role in blood pressure, adjusting HR, digestion, defecation, urination receptor- distal end of a sensory neuron responds to a stimulus and produces a change that will trigger nerve impulses sensory neuron- conducts nerve impulses from receptors to the CNS integrating centre- interneurons within CNS relay signals from sensory neurons to motor neurons. (main intergration center in autonomic reflexes located in the Hypothalamus and brain stem) Urination and defecation- have integrating centers located in the spinal cord motor neuron-nerve impulses that are triggered by the integrating center travel outside of the CNS along motor neurons to an effector. In autonomic reflex arc 2 motor neurons connect the CNS to the effector. Preganglionic neuron conducts impulse from CNS-> to an autonomic ganglion Postganglionic neuron conducts motor impulses from an autonomic ganglion to an effector. Effector- autonomic reflex arc, the effectors are smooth muscle, cardiac muscle and glands. autonomic control by higher centers

CHAPTER 15- The Autonomic Nervous System Hypothalamus is the major control and integration center of the ANS. It receives sensory input related to visceral functions (smell) and gustation (taste), changes in temperature osmolarity, and substances in blood. Also receives input relating to emotion from the limbic system. Output from hypothalamus contributes to autonomic center in the brain stem and spinal cord. Anatomically hypothalamus is connected to both the sympathetic and parasympathetic divisions of the ANS. Posterior and lateral parts of hypothalamus control sympathetic responses Anterior and medial parts of hypothalamus control parasympathetic responses...