L6 Nervous System and Endocrine System PDF

Nervous System Dr. Pallav Sengupta Assistant Professor, Physiology College of Medicine October 4, 2024 www.gmu.ac.ae COLLEGE OF MEDICINE Learning objectives On completion of...

Nervous System Dr. Pallav Sengupta Assistant Professor, Physiology College of Medicine October 4, 2024 www.gmu.ac.ae COLLEGE OF MEDICINE Learning objectives On completion of this unit, the student will be able to: Discuss the organization of nervous system Explain the structures and functions of neuron and neuroglial cells Describe the various phases of nerve action potential Discuss the role of neurotransmitters Describe the functions of different neural centers Characteristics of nervous system The nervous system receives information from different senses simultaneously. The nervous system integrates information. The nervous system is very fast. It can receive information, integrate it, and produce a response within tenths of a second. The nervous system can initiate specific responses, including muscle contraction, glandular secretion, and even conscious thought and emotions. Divisions of the Nervous System  Neuron Each neuron contains: - Cell body with nucleus, mitochondria , other cell organelles - Dendrites : fibers that receive messages from other neurons - Axons : fibers that send messages to other neurons Neurons do NOT touch; there is a gap between them called a synapse Messages are sent across the synapses by special chemicals called neurotransmitters  Neuroglial cells CNS PNS Microglia Ependymal Astrocytes Oligodenrocytes cells cells Neuroglial cells support and protect neurons. Do not generate or transmit impulse Schwann Satellite Schwann cells (in the PNS) – produce fatty cells cells insulating material – myelin  Membrane Potential Na+-K+ pump maintains resting potential : The Na+-K+ pump actively transports 3 Na+ ions out of the cell in exchange for 2 K+ ions. Most of the K+ leaks out again. However, the inward leak of sodium is so slow that the pump effectively is able to exclude most Na+ from the cell. The exclusion of positive ions (Na+) from the cell creates a voltage difference across the cell membrane – membrane potential a neuron capable of action potentials but not generating one at the moment, the normal membrane potential at rest is its resting (membrane) potential. The resting potential of a neuron is about −70 millivolts (mV).  Action Potential A neuron’s resting potential of about -70mV is maintained by the constant action of the sodium-potassium pump. Impulses arriving from other neurons can cause small local changes in the neuron’s membrane potential called graded potentials. The sum of graded potential is sufficiently strong to reach a certain triggering membrane voltage called the threshold, an action potential results. An action potential is a sudden, temporary reversal of the voltage difference across the cell membrane. An action potential involves 3 events: depolarization, repolarization and reestablishment of the resulting potential. Depolarization Sodium channels open Sodium diffuses into the cytoplasm of axon Membrane depolarizes (meaning membrane potential shifts from negative (-70mV) to positive (+ 30mV) Repolarization Sodium channels close Potassium channels open Potassium diffuses out of axon Loss of positive ions from cell – repolarization (inside of axon again negative) Re-establishment of resting potential Potassium channels close: After a brief hyperpolarization caused by a delay in the full closure of potassium channels, the membrane potential returns to its normal resting value  Neurotransmitter Once an action potential reaches the axon terminals of a neuron, the information inherent in it must be converted to another form for transmitting to its target (muscle cell, gland cell, or another neuron). the action potential causes the release of a chemical that crosses a specialized junction between the two cells called a synapse. This chemical substance is called a neurotransmitter because it transmits a signal from a neuron to its target. The entire process of transmission from a neuron to its target is called synaptic transmission.  Actions of neurotransmitter Neurotransmitters exert excitatory or inhibitory effects  CNS (Central Nervous System) The central nervous system (CNS) is made up of the brain and spinal cord. It is one of 2 parts of the nervous system. The other part is the peripheral nervous system, which consists of nerves that connect the brain and spinal cord to the rest of the body CNS is protected by bone. The brain is encased in the skull, the spinal cord is enclosed in a hollow channel within the vertebrae. CNS is enclosed by three membranes of connective tissue, called meninges, the dura mater, the arachnoid, and the pia mater. These three meninges protect the neurons of the CNS and the blood vessels. CNS is bathed in cerebrospinal fluid, which fills the space between the arachnoid and the pia mater. Act as a liquid shock absorber around the brain and spinal cord and also tends to isolate the central nervous system from infections. Functional barrier between blood and brain is called the blood-brain barrier.  Lobes of the Brain The brain is a complex organ that controls thought, memory, emotion, touch, motor skills, vision, breathing, temperature, hunger and every process that regulates our body. Together, the brain and spinal cord that extends from it make up the central nervous system, or CNS. Frontal Parietal Occipital Temporal * Note: Occasionally, the Insula is considered the fifth lobe. It is located deep to the Temporal Lobe.  Parts of Brain Cerebrum : largest part of human brain Responsible for: - Thought - Language - Senses - Memory - Voluntary movement  Parts of Brain Cerebellum : at base of brain -Responsible for: - Muscle coordination - Balance - Posture  Parts of Brain Brain Stem : connects brain to spinal cord -Responsible for: - Breathing - Swallowing - Heartbeat - Blood pressure  Spinal cord The spinal cord extends downward from the base of your brain. It's made up of nerve cells and groups of nerves that carry messages between your brain and the rest of your body. The spinal cord extends from the base of the skull to the area of about the second lumbar vertebra, or about 17 inches It is protected by the vertebral column. The outer portions of the spinal cord consist primarily of bundles of axons, which in the CNS are called nerve tracts rather than nerves. These axons are generally myelinated, giving them a whitish appearance, the areas of the cord occupied by these ascending (sensory) and descending (motor) nerve tracts are called white matter. Neurons of the PNS enter and leave the spinal cord at regular intervals via the dorsal (sensory) and ventral (motor) horns that fuse to form spinal nerves. Near the center of the spinal cord is a region occupied primarily by the cell bodies, dendrites, and axons of neurons of the CNS, and also neuroglial cells. These structures are not myelinated, so the area they occupy is referred to as gray matter. Within the gray matter, sensory and motor neurons synapse with neurons of the CNS that transmit signals up the spinal cord to the brain.  Spinal cord Responsible for: Conducting impulses between the brain and the rest of the body  Peripheral Nervous System (PNS) PNS comprises of spinal nerves (31 pairs) and cranial nerves (12 pairs)  Disorders of the Nervous System Parkinson’s Disease It is a motor disorder occurring due to neurodegeneration in substantia nigra (part of basal ganglia). Alzheimer’s Disease It is a neurodegenerative disorder that results in memory loss. Epilepsy Epilepsy is a common condition that affects the brain and causes frequent seizures. Seizures are bursts of electrical activity in the brain that temporarily affect how it works. Paralysis Loss of sensation and movement of part of the body due to an injury of the spinal cord or brain References 1. Johnson D Michael.,Human Biology, 8th edition.Pearson education limited 2017.ISBN: 978-1-292-16627-8  Endocrine System – Hormones, Growth and Reproduction Part 1 - 2 Dr Pallav Sengupta Assistant Professor, Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Learning objectives On completion of this unit, the student will be able to: Discuss general functions of the endocrine system in the human body; Classify hormones by their chemical makeup; Describe the endocrine functions of the hypothalamus and pituitary; Discuss the hormone functions of the pancreas and adrenal glands; Describe the hormone functions of the thyroid and parathyroid glands; Discuss the hormones produced by reproductive organs; Describe other hormone sources and other chemical messengers used in control of homeostasis; and Discuss various disorders of the endocrine system.  Endocrine system Collection of specialized cells, tissues, and glands - produce and secrete circulating chemical messenger molecules -- hormones. Hormones are secreted by endocrine glands Endocrine ductless organs that secrete their products into interstitial fluid, lymph, and blood gland Exocrine secrete products such as mucus, sweat, tears, and digestive fluids into ducts that empty into glands the appropriate sites. Overview: Endocrine System Characteristics of Endocrine System Hormones of the endocrine system reach nearly every living cell. Each hormone acts only on certain cells. Endocrine control tends to be slower than nervous system control. The endocrine and nervous systems can interact with each other Classification of Hormones STEROID structurally related to cholesterol - lipid soluble. Hormones NON-STEROID structurally related to proteins - lipid insoluble Mechanism of steroid hormone action on a target cell.  Mechanism of nonsteroid hormone action on a target cell  The Hypothalamus The hypothalamus - homeostatic control center. It is an important link between the nervous system and the endocrine system. It receives neural input about certain internal environmental conditions such as water and solute balance, temperature, and carbohydrate metabolism. Functions: Monitors and controls the hormone secretions of the pituitary gland Synthesizes releasing hormones in cell bodies of neurons Hormones are transported down the axon and stored in the nerve endings Hormones are released in pulses Integrates functions that maintain chemical and temperature homeostasis Functions with the limbic system  The Pituitary Gland Master gland which is located directly beneath it and connected to it by a thin stalk of tissue The anterior pituitary (or adenohypophysis) is a lobe of the gland that regulates several physiological processes including stress, growth, reproduction, and lactation. The intermediate lobe synthesizes and secretes melanocyte-stimulating hormone. The posterior pituitary (or neurohypophysis) is a lobe of the gland that is functionally connected to the hypothalamus by the median eminence via a small tube called the pituitary stalk (also called the infundibular stalk or the infundibulum).  Hypothalamic Releasing Hormones Seven releasing hormones are made in the hypothalamus – Thyrotropin-releasing hormone (TRH) – Corticotropin-releasing hormone (CRH) – Gonadotropin-releasing hormone (GnRH) – Growth hormone-releasing hormone (GHRH) – Growth hormone-release inhibiting hormone (GHIH) – Prolactin-releasing factor (PRF) – Prolactin-inhibiting hormone (PIH) Hypothalamus Releasing Hormones: Secretion Is influenced by emotions Can be influenced by the metabolic state of the individual Delivered to the anterior pituitary via the hypothalamic-hypophyseal portal system Usually initiates a three-hormone sequence A ‘global’ view of Hypothalamic Pituitary Functions Releasing hormones Three Methods of Hypothalamic Control over the Endocrine System  Hypothalamic Control of the Anterior Pituitary Hormonal control mechanism Hypothalamic neurons synthesize releasing and inhibiting peptide hormones. These are transported to axon endings in the median eminence where they are secreted into the hypothalamo-hypophyseal portal system to reach receptors that regulate the secretions of anterior pituitary hormones  How does the neuroendocrine axis work? Hypothalamic parvicellular neurons synthesize release- or release-inhibiting “factors” or “hormones” (peptides) Packaged in secretory granules, transported in axons to nerve terminal storage sites On demand, neurons depolarize, prompting frequency- dependent exocytosis into the median eminence capillaries of the pituitary portal vessels Transported as “hormones” to the anterior pituitary where they exit to the extracellular space Attach to specific G-protein coupled receptors on target cells, triggering exocytosis of appropriate “hormones” that seek their peripheral glandular targets Hypothalamic Releasing Hormones and Respective Anterior Pituitary Trophic Hormones HYPOTHALAMIC HORMONE EFFECTS ON THE ANTERIOR PITUITARY Thyrotropin-releasing hormone (TRH) Stimulates release of TSH (thyrotropin) and Prolactin Corticotropin-releasing hormone Stimulates release of ACTH (CRH) (corticotropin) Gonadrotropin-releasing Stimulates release of FSH and hormone (GnRH) LH (gonadotropins) Growth hormone-releasing hormone Stimulates release of growth (GHRH) hormone Growth hormone-inhibiting hormone Inhibits release of growth (GHIH) hormone Prolactin-inhibiting hormone (PIH) Stimulates release of prolactin Prolactin-inhibiting hormone (PIH) Inhibits release of prolactin Anterior Pituitary Trophic Hormones and Their Actions  Disorders of Pituitory gland GH may be secreted in excess or there can be deficiency of GH with different clinical manifestations GH abnormalities can occur both in children and adults Excess of GH: Giantism in children and Acromegaly in adults Deficiency of GH: Dwarfism in children – Rare in adults  Differences Between Acromegaly and Gigantism Acromegaly Giantism Nature Excess of GH in adults when Excess of GH in children when epiphysis are closed epiphysis are ununited Major action Increase in the size of short Over growth of the long bones of and flat bones especially the limbs especially lower limb extremities Size of skull and lower jaw Prominent skull, fore head Over growth of long bones especially and overgrowth of lower jaw of lower limb Size of the Viscera Enlarged liver and heart No relative increase in size Muscle mass Increase in muscle mass Increase in bone mass Metabolic role Promotion of proteogenesis- Promotion of GIT absorption of Lipolysis and hyperglycemia Ca++ Proteogenesis, Lipolysis and Hyperglycemia Hypogonadism Absent Present usually  Thyroid and Parathyroid Gland Thyroid gland - below the larynx at the front of the trachea, and consists of two lobes The two main hormones produced by the thyroid gland - thyroxine and calcitonin. The four small parathyroid glands are embedded in the back of the thyroid. The parathyroid glands produce parathyroid hormone. Help to regulate calcium balance & role in controlling metabolism.  Thyroid Gland Produces two very similar hormones called thyroxine (T4) and triiodothyronine (T3). Thyroxine concentration increases, the basal metabolic rate (BMR) also increases. Decreasing the blood concentration of thyroxine reduces energy utilization and BMR.  Thyroid Gland Disorders Goitre- A goitre, or goiter, is a swelling in the neck resulting from an enlarged thyroid gland. The main cause is iodine deficiency Hypothroidism- Deficiency of secretion of thyroid hormones In children lack of thyroid hormones leads to stunted growth and mental retardation In adults it leads to lack of energy, dry skin and weight gain Hyperthyroidism- Increased secretion of thyroid hormone. Nervousness, irregular heart rate and weight loss The most common form of hyperthyroidism is Graves’ disease  Parathyroid hormone (PTH) Controls blood calcium levels Parathyroid hormone (PTH) : Removes calcium and phosphate from bone, Increases absorption of calcium by the digestive tract, Causes the kidneys to retain calcium and excrete phosphate.  Pancreas Both an endocrine gland (secreting hormones into the blood) and an exocrine gland (secreting enzymes, fluids, and ions into the digestive tract to aid in digestion). Endocrine cells - located in small clusters scattered throughout the pancreas called the islets of Langerhans Pancreatic islets contain three types of cells and produce 3 hormones secrete glucagon - raises Alpha cells blood sugar. secrete insulin- lowers Beta cells blood sugar. Delta cells secrete somatostatin.  Disorders of Pancreas Diabetes Type 1 diabetes - failure of pancreas to produce enough insulin - insulin-dependent diabetes - an autoimmune disorder in which the person’s own immune system attacks the insulin-producing cells in the pancreas. Type 2 diabetes (non-insulin-dependent diabetes)— cells fail to respond adequately to insulin even when it is present. Type 2 diabetes may have a genetic component, but lifestyle factors are thought to be the major determinants.  Adrenal Glands Two adrenal glands, each weighs about 4 gm lie at the superior poles of the two kidneys. Each gland is composed of two distinct parts: adrenal medulla (20%) and adrenal cortex (80%) Adrenal Cortex is related to corticoids: Glucocorticoids and Mineralocorticoids Adrenal Medulla is related functionally to sympathetic nervous system and secretes epinephrine and norepinephrine in response to sympathetic stimulation  Adrenal Cortex Zones of Adrenal gland 1) Zona glomerulosa  Outer 15% of the adrenal cortex  secrete aldosterone (mineralocorticoid)  (aldosterone synthase) mainly controlled by : a) Renin- Angiotensin system b) Plasma potassium level 2) Zona faciculata Middle 75 % of the adrenal cortex Secretes Cortisol and Corticosterone; (glucocorticoids) small amounts of adrenal androgens and estrogen  controlled by: hypothalamic-pituitary axis via ACTH 3) Zona reticularis Deep layer of the cortex secretes the adrenal androgens: dehydroepiandrosterone and androstenedione small amounts of estrogens and glucocorticoids controlled by : ACTH & cortical androgen-stimulating hormone  Adrenal Medulla Produces the nonsteroid hormones epinephrine (adrenaline) and norepinephrine (noradrenaline) and dopamine Opioid peptides (encephalin) & adrenomedullin Play roles in metabolism and controlling blood pressure and heart activity. Other sources of NE and Dopamine Most of circulating NE come from noradrenergic Nerve ending & about ⅟₂ of circulating dopamine are from sympathetic ganglia.  Disorders of Adrenal Gland Addison’s disease: Too little cortisol and aldosterone Lack of cortisol lowers blood glucose levels, and lack of aldosterone lowers blood sodium. chronic symptoms of fatigue, weakness, abdominal pain, weight loss, and a characteristic “bronzed” skin color. Cushing’s syndrome: Too much cortisol The symptoms of Cushing’s syndrome are due to the exaggerated effects of too much cortisol, including (1) excessive production of glucose from glycogen and protein (2) retention of too much salt and water.  Reproductive Hormones Reproduction is regulated by:  Gonadotrophins (FSH and LH) released by pituitary gland  Sex hormones released by the gonads (ovaries in females and testes in males) Action of gonadotrophins Regulate the function of the gonads Causes the gonads to mature during puberty and release sex hormones FSH stimulates egg and sperm production LH stimulates ovulation  Reproductive Hormones Action of gonadal hormones Androgens are primarily testosterone- the male sex hormone Testosterone regulate the development and function of male reproductive system During puberty they cause the appearance of male secondary sexual characteristics Estrogen and progesterone cause the development of female secondary sexual characteristics, regulate the menstrual cycle, prepare and maintain the uterus during pregnancy  Regulation of Reproductive Hormones In Female In Male Endocrine functions of the heart, the digestive system, and the kidneys  Learning Resources Johnson D Michael.,Human Biology, 8th edition.Pearson education limited 2017.ISBN: 978-1-292-16627-8