Case 1: Big Tension PDF

Case 1: Big tension 1. What is the structure and function of the nervous system (conscious and unconscious) Short anatomy of the brain The lobes The nervous system can be divided into central and peripheral nervous systems The central nervous system (CNS) CNS: the brain + spinal cord. Spinal co...

Case 1: Big tension 1. What is the structure and function of the nervous system (conscious and unconscious) Short anatomy of the brain The lobes The nervous system can be divided into central and peripheral nervous systems The central nervous system (CNS) CNS: the brain + spinal cord. Spinal cord covered by three “membranes”—the meninges. - Dura mater: the outer membrane - Arachnoid: the middle - Pia mater: the delicate inner membrane Within the CNS, some neurons that share similar functions are grouped into aggregations called nuclei. The CNS can also be divided into gray matter, which contains neuron cell bodies, and white matter, which is rich in myelin. Major Levels of Central Nervous System Function: The human nervous system has inherited special functional capabilities from each stage of human evolutionary development. From this heritage, three major levels of the central nervous system have specific functional characteristics: (1) the spinal cord level; (2) the lower brain or subcortical level; and (3) the higher brain or cortical level. - Spinal Cord Level: The spinal cord independently controls reflexes and basic bodily functions like movement, pain withdrawal, posture, and regulation of blood vessels, digestion, and urination. - Lower Brain or Subcortical Level: The lower brain regions control essential subconscious functions, including blood pressure, respiration, balance, feeding reflexes, and basic emotional responses. - Higher Brain or Cortical Level: The cerebral cortex stores vast memories, refines lower brain functions, and supports complex thought processes, relying on lower brain centers to activate its stored information. The peripheral nervous system (PNS) Consists of those parts of the nervous system that lie outside the dura mater. These elements include sensory receptors for various kinds of stimuli, the peripheral portions of spinal and cranial nerves, and all the peripheral portions of the autonomic nervous system. - The sensory nerves that carry messages from the periphery to the CNS are termed afferent nerves. - The peripheral motor nerves that carry messages from the CNS to peripheral tissues are called efferent nerves. - Peripheral ganglia are groups of nerve cells concentrated into small knots or clumps that are located outside the CNS. The autonomic nervous system (ANS) is that portion of the nervous system that regulates and controls visceral functions including: - Heart rate - Blood pressure - Digestion - Temperature regulation - Reproductive function Although the ANS is a functionally distinct system, it is anatomically composed of parts of the CNS and PNS. Visceral control is achieved by reflex arcs that consist of visceral afferent (i.e., sensory) neurons that send messages from the periphery to the CNS, control centers in the CNS that receive this input, and visceral motor output. Moreover, visceral afferent fibers typically travel together with visceral efferent fibers. The somatic nervous system (SNS) regulates voluntary activities such as muscular movement. It also controls reflexes, such as pulling your hand away from the hot surface of a stove. 2. What is the function of the autonomic system and its role of homeostasis in the body? Organization of the Visceral Control System General Organization of the Autonomic Nervous System The autonomic nervous system is activated mainly by centers located in the spinal cord, brain stem, and hypothalamus. In addition, portions of the cerebral cortex, especially of the limbic cortex, can transmit signals to the lower centers and in this way can influence autonomic control. The autonomic nervous system also often operates through visceral reflexes. That is, subconscious sensory signals from visceral organs can enter the autonomic ganglia, the brain stem, or the hypothalamus and then return subconscious reflex responses directly back to the visceral organs to control their activities. The efferent autonomic signals are transmitted to the various organs of the body through two major subdivisions called the sympathetic nervous system and the parasympathetic nervous system. The ANS has sympathetic, parasympathetic, and enteric divisions (short) Output from the central nervous system (CNS) travels along two anatomically and functionally distinct pathways: the somatic motor neurons, which innervate striated skeletal muscle; and the autonomic motor neurons, which innervate smooth muscle, cardiac muscle, secretory epithelia, and glands. All viscera are richly supplied by efferent axons from the ANS that constantly adjust organ function. The ANS has three divisions: sympathetic, parasympathetic, and enteric. - The sympathetic and parasympathetic → two major efferent pathways controlling targets other than skeletal muscle. Each innervates target tissue by a two-synapse pathway. Cell bodies of first neuron in CNS (preganglionic neurons) → send axons to make synapses with postganglionic neurons in peripheral ganglia → axons project to target cell. - These preganglionic neurons are found in columns of cells in the brainstem and spinal cord The sympathetic and parasympathetic divisions can act independently of each other. However, in general, they work synergistically to control visceral activity and often act in opposite ways, like an accelerator and brake to regulate visceral function. - An increase in output of the sympathetic division occurs under conditions such as stress, anxiety, physical activity, fear, or excitement, - Parasympathetic output increases during sedentary activity, eating, or other “vegetative” behavior. The enteric division of the ANS is a collection of afferent neurons, interneurons, and motor neurons that form networks of neurons called plexuses that surround the gastrointestinal (GI) tract. It can function as a separate and independent nervous system, but it is normally controlled by the CNS through sympathetic and parasympathetic fibers. Physiologic Anatomy of the Sympathetic Nervous System Shown specifically in the figure are (1) one of the two paravertebral sympathetic chains of ganglia that are interconnected with the spinal nerves on the side of the vertebral column, (2) prevertebral ganglia (the celiac, superior mesenteric, aorticorenal, inferior mesenteric, and hypogastric ), and (3) nerves extending from the ganglia to the different internal organs. The sympathetic nerve fibers originate in the spinal cord along with spinal nerves between cord segments T1 and L2 → pass first into the sympathetic chain → then to the tissues and organs that are stimulated by the sympathetic nerves. Sympathetic pathways consist of two neurons: a preganglionic neuron from the spinal cord and a postganglionic neuron in either a sympathetic chain ganglion or a peripheral ganglion. After leaving the spinal canal, preganglionic fibers pass through the sympathetic chain, where they may (1) synapse immediately, (2) travel up or down the chain to synapse, or (3) pass through the chain to synapse in a peripheral ganglion. Postganglionic fibers then carry signals to target organs. Physiological Anatomy of the Parasympathetic Nervous The parasympathetic nervous system includes fibers that exit the central nervous system through cranial nerves III, VII, IX, and X, as well as sacral spinal nerves (mainly S2 and S3). The vagus nerve (cranial nerve X) carries about 75% of parasympathetic fibers, supplying the heart, lungs, digestive organs, and kidneys. Other cranial nerves serve the eye, salivary, and nasal glands, while sacral parasympathetic fibers reach the lower colon, bladder, and reproductive organs for functions like erection. In the parasympathetic system, preganglionic fibers usually travel directly to the target organ, where they synapse with postganglionic neurons located within the organ walls. These postganglionic fibers are very short, directly innervating the organ tissues. This contrasts with the sympathetic system, where postganglionic neurons are typically located in ganglia outside the target organ. Function para/sym Parasympathetic → anabolic - rest - digest - uses acetylcholine as transmitter in postganglionic neurons Sympathetic → catabolic - action - FFF - uses noradrenaline (activating) as transmitter in postganglionic neurons Eyes Parasympathetic → constricts pupils → atropine can block muscarinic receptors → pupils dilate - Neg chronotropic → heart frequency down 3. What is the function of neurotransmitters and receptors? Nerve cells Neurons are specialized for sending and receiving signals, a purpose reflected in their unique shapes and physiological adaptations. The structure of a typical neuron can generally be divided into four distinct domains: - (1) the cell body, also called the soma or perikaryon - (2) the dendrites - (3) the axon - (4) the presynaptic terminals The shape and organelle composition of these domains depends strongly on their cytoskeleton, which consists of three fibrillary structures: neurofilaments (i.e., intermediate filaments), microtubules, and thin filaments. The cytoskeleton—especially the microtubules and thin filaments, is dynamic and imbues axons and dendrites with the capacity to change shape, a plasticity believed to participate in the synaptic alterations associated with learning and memory. Cell Body: The perikaryon, or cell body, surrounds the nucleus and manages neuronal housekeeping, including protein synthesis and processing. Dendrites: Dendrites are branching extensions from the cell body that receive information via neurotransmitter receptors, translating chemical messages into electrical or biochemical signals that affect neuron excitability, and they contain networks of microtubules and endoplasmic reticulum. Axon: The axon is a long, non-tapering projection from the neuron’s cell body that generates and transmits action potentials to other cells; it relies on cytoskeletal support for material transport, uses glucose and oxygen for energy, and may be myelinated to speed signal conduction. Presynaptic Terminals: At its target, the axon ends in presynaptic terminals that convert electrical signals to chemical ones via synaptic transmission, forming a chemical synapse with the postsynaptic membrane across a synaptic cleft; these target areas often have expanded surfaces to increase receptor availability. Function of Neurotransmitters and Receptors 1. Neurotransmitters are chemical messengers released by neurons to transmit signals across a synapse to another neuron, muscle, or gland. 2. Receptors are proteins on the surface of target cells that bind to neurotransmitters, triggering specific cellular responses. Acetylcholine (ACh) cholinergic system Can bind to nicotinic and muscarinic receptors: Nm → If you want move muscle → want to do it fast → ion channels (nicotinic) is very fast - Nicotine is an Ach agonist → mimics its effects M1 → stimulating Gq-protein → activated → cascade → leads to activation IP3 M2 → inhibitory Gi-protein → decrease activation cAMP → relaxation of your heart M3 → stimulating Gq-protein → activated → cascade → leads to activation IP3 → activation smooth muscle + glands - Muscarine is an Ach agonist → mimics its effects Excitatory in the neuromuscular junction (activates muscles) and involved in autonomic nervous system responses. - Slows the heart rate and reduces contractility - Constricts the airways - Stimulates digestion by increasing peristalsis and secretion in the stomach and intestines - Constricts the pupils (miosis) - Stimulates bladder contraction and promotes urination - Increases saliva production - Stimulates sweat secretion - In certain regions, ACh can cause vasodilation, such as in the coronary arteries, through muscarinic receptors. Adrenergic system Affinity NA → big for alpha; A → big for beta a1 → activation → blood vessels constrict → block → relaxation blood vessels a2 → activation → increase the release of neurotransmitters into synaptic cleft → may stimulate communication between two neurons and thus activation sympathetic nervous system b1 → Gs-protein stimulatory → increased release cAMP → stimulation target tissue (in heart: higher heart rate) b2 → Gs-protein stimulatory → lower activation of MLCK → relaxation (in lungs: airways dilate → facilitate breathing) (in arteries: dilation → lower blood pressure) b3 → Gs-protein → increase cAMP (in fat cells: stimulate fat breakdown) Here is the English translation of the table: Catecholamines and Their Effects on Various Organs Source: Adrenal Medulla Organ/Receptor Reaction Effect Bronchi (β) Dilation Improved ventilation Heart (β) Increase in heart rate and contraction Increased cardiac output force Veins (α) Constriction Increased venous return Arteries (α) Constriction in skin and visceral organs Redistribution of blood flow Dilation in skeletal muscle and coronary to muscles, heart, and brain arteries Skeletal Muscle Glycogenolysis Increased lactate in blood (β) Liver (β) Glycogenolysis Increased blood glucose levels  Fat Tissue (β) Lipolysis Increased free fatty acids in blood Norepinephrine (Noradrenaline) Involved in arousal, attention, and the fight-or-flight response. - Increases heart rate and contractility - Dilates the airways to improve airflow - Constricts most blood vessels to raise blood pressure - Inhibits digestion by reducing peristalsis and secretion - Stimulates glucose release (glycogenolysis) to provide energy during stress - Dilates pupils (mydriasis) for improved vision in low-light conditions - Stimulates sweating for thermoregulation Epinephrine (adrenaline) Adrenaline is involved with the body's fight-or-flight response, increasing heart rate, energy, and alertness in stressful situations. - Increases heart rate and contractility, boost cardiac output - Dilates the bronchial tubes, Enhances oxygen intake for energy - Stimulates glycogen breakdown to release glucose into the bloodstream - Increases blood flow to skeletal muscles by dilating blood vessels - Dilates the pupils, Improves vision in low-light or stressful situations - Constricts blood vessels in certain areas while dilating vessels leading to muscles - Stimulates the release of additional adrenaline and other hormones like cortisol - Inhibits digestion by reducing blood flow and activity in the digestive tract - Causes sweating through sweat glands Types of Receptors Receptors are often named based on the neurotransmitter they bind to and are grouped as ionotropic (ligand-gated ion channels) and metabotropic (G-protein-coupled receptors). Ionotropic Receptors: Open ion channels directly, allowing rapid responses. - Nicotinic Acetylcholine Receptors (nAChR): Involved in neuromuscular activation and autonomic signaling. Metabotropic Receptors: Trigger a signaling cascade via G-proteins, allowing slower but more prolonged responses. - Adrenergic Receptors (α1, α2, β1, β2): Mediate responses to norepinephrine, such as fight-or-flight effects. - Muscarinic Acetylcholine Receptors (mAChR): Involved in parasympathetic nervous system actions. All preganglionic neurons release acetylcholine and stimulate N2 nicotinic receptors on postganglionic neurons In the autonomic nervous system (ANS), both sympathetic and parasympathetic divisions use acetylcholine (ACh) on nicotinic receptors for ganglionic transmission between preganglionic and postganglionic neurons. These nicotinic receptors are ionotropic, ligand-gated channels with a pentameric structure. The nicotinic receptors on postganglionic autonomic neurons are of a molecular subtype (N2) different from that found at the neuromuscular junction (N1). - Both are ligand-gated ion channels activated by ACh or nicotine. - When activated, N1 and N2 receptors are both permeable to Na+ and K+. Thus, nicotinic transmission triggered by stimulation of preganglionic neurons leads to rapid depolarization of postganglionic neurons. Nicotinic receptors are found in: - Skeletal muscles – at the neuromuscular junction, facilitating voluntary muscle contraction. - Autonomic ganglia – in both sympathetic and parasympathetic ganglia, where they mediate transmission from preganglionic to postganglionic neurons. - Adrenal medulla – on chromaffin cells, which release epinephrine and norepinephrine into the bloodstream. - Central nervous system (CNS) – in certain areas of the brain, contributing to cognitive functions and modulation of neurotransmitter release. Postganglionic parasympathetic neurons release ACh and stimulate muscarinic receptors on visceral targets Muscarinic ACh receptors, used by all postganglionic parasympathetic neurons, can either stimulate or inhibit target cell function, generating diverse responses through G protein–coupled receptor pathways. These receptors (subtypes M1 to M5) increase intracellular calcium, decrease cAMP, or modulate potassium channels, leading to slower, prolonged effects compared to nicotinic receptors. Stimulated by acetylcholine and muscarine, muscarinic receptors are blocked by atropine. The five subtypes vary in tissue distribution, and cells often express multiple subtypes, though selective agonists for specific subtypes are unavailable. Most postganglionic sympathetic neurons release norepinephrine onto visceral targets Most postganglionic sympathetic neurons release norepinephrine, which acts on target cells through adrenergic receptors. The sympathetic innervation of sweat glands is an exception to this rule. - Sweat glands are innervated by sympathetic neurons that release ACh and act via muscarinic receptors. The adrenergic receptors are all GPCRs and are highly homologous to the muscarinic receptors. Two major types of adrenergic receptors are recognized, α and β, each of which exists in multiple subtypes (e.g., α 1 , α 2 , β 1 , β 2 , and β 3 ). In addition, there are heterogeneous α 1 and α 2 receptors, with three cloned subtypes of each. Adrenergic receptor subtypes have a tissue-specific distribution. - α 1 receptors predominate on blood vessels - α 2 on presynaptic terminals - β 1 in the heart - β 2 in high concentration in the bronchial muscle of the lungs  - β 3 in fat cells The adrenal medulla, a specialized part of the sympathetic division, acts like a postganglionic neuron but releases epinephrine into the bloodstream from chromaffin cells instead of through axons, enhancing the body's sympathetic response. This neuroendocrine function allows widespread effects, as both norepinephrine and epinephrine activate all five adrenergic receptor subtypes. In general, the α receptors have a greater affinity for norepinephrine, whereas the β receptors have a greater affinity for epinephrine. Rough scheme of parasympathetic and sympathetic: Parasympathetic → ganglion quite closely to target organ Sympathetic → ganglion close to spinal cord - Exception → sweat glands and adrenal medulla Adrenal medulla The enzyme PNMT converts NA to A by adding methyl group, 80% has this enzyme so production 80% A 4. How can a stimulus transfer in the autonomic system? Sympathetic Nervous System "Fight or Flight" Heart: Increases heart rate and contractility. - Neurotransmitter: Norepinephrine (released by postganglionic neurons) acts on beta-1 adrenergic receptors. Lungs: Dilates airways to increase oxygen intake. - Neurotransmitter: Norepinephrine (released by postganglionic neurons) acts on beta-2 adrenergic receptors. Digestive system: Inhibits digestion, slowing peristalsis and secretion. - Neurotransmitter: Norepinephrine (acts on alpha-1 adrenergic receptors) reduces gastrointestinal motility and secretion. Pupils: Dilates pupils for improved vision.  - Neurotransmitter: Norepinephrine (released by postganglionic neurons) acts on alpha-1 adrenergic receptors in the iris to dilate pupils. Blood vessels: Constricts most vessels (increasing blood pressure) but dilates those leading to muscles for better blood flow during stress. - Neurotransmitter: Norepinephrine (acts on alpha-1 adrenergic receptors for vasoconstriction) and Epinephrine (acts on beta-2 adrenergic receptors for vasodilation in muscles). Sweat glands: Stimulates sweating for cooling. - Neurotransmitter: Acetylcholine (ACh) (released by sympathetic cholinergic fibers acting on muscarinic receptors in sweat glands). Liver: Stimulates glucose release for energy. - Neurotransmitter: Norepinephrine (acts on alpha-1 adrenergic receptors) stimulates glucose release by promoting glycogen breakdown. Parasympathetic Nervous System "Rest and Digest" Heart: Slows heart rate and reduces contractility. - Neurotransmitter: Acetylcholine (ACh) (released by postganglionic neurons) acts on muscarinic receptors (primarily M2) to decrease heart rate. Lungs: Constricts airways. - Neurotransmitter: Acetylcholine (ACh) (released by postganglionic neurons) acts on muscarinic receptors (primarily M3) to constrict bronchial smooth muscle. Digestive system: Stimulates digestion, enhancing peristalsis and secretion. - Neurotransmitter: Acetylcholine (ACh) (acts on muscarinic receptors) increases motility and secretions in the gastrointestinal tract. Pupils: Constricts pupils. - Neurotransmitter: Acetylcholine (ACh) (acts on muscarinic receptors in the eye, specifically M3) to constrict the pupils (miosis). Blood vessels: Generally causes dilation, lowering blood pressure. - Neurotransmitter: Acetylcholine (ACh) (acts on muscarinic receptors) causes vasodilation in some blood vessels, such as in the coronary arteries. Liver: Promotes storage of glucose as glycogen. - Neurotransmitter: Acetylcholine (ACh) (activates muscarinic receptors) enhances glycogen synthesis. 5. Link back to the case These symptoms are linked to the autonomic nervous system (ANS), specifically its sympathetic division, which activates the body's "fight-or-flight" response in stressful situations. Here’s how each symptom connects to parts of the nervous system: 1. Dry Mouth: The sympathetic nervous system suppresses saliva production during stress, causing dry mouth. 2. Increased Heart Rate: The sympathetic division stimulates the heart to beat faster, preparing the body for action. 3. Clammy, Sweaty Hands: This is a response from sweat glands, which the sympathetic nervous system activates to help cool the body. 4. Loss of Appetite: The sympathetic system reduces digestive activity during stress, which can result in a lack of appetite. norepinephrine and epinephrine are released and reduces the blood flow → less appetite 5. Dilated Pupils: The sympathetic nervous system dilates the pupils to let in more light, improving vision in potentially dangerous situations. 6. Little urine: Sympathetic effect, restricts the blood … 7. Tension: sympathetic effect, increases muscle tension, need to prepare, have to get in action. Together, these symptoms suggest activation of the sympathetic nervous system, often in response to stress, excitement, or anxiety. Keywords: centra peripheral NS somatic autonomic NS symp para NS neurotransmitters cholinergic, adrenergic, muscarinic, nicotinic