Compendiums 6-9 for eTest 2 - Cardiovascular System PDF

Compendiums 6-9 for eTest 2 Compendium 6 – the cardiovascular system Lecture 1 Components of the cardiovascular system - Heart o A pump used to generate pressure in the blood to move it around the body - Blood vessels o In the form of arteries, veins and capillaries o F...

Compendiums 6-9 for eTest 2 Compendium 6 – the cardiovascular system Lecture 1 Components of the cardiovascular system - Heart o A pump used to generate pressure in the blood to move it around the body - Blood vessels o In the form of arteries, veins and capillaries o Form the conduits to carry the blood around the body - Blood o Carries the substances or material either dissolved or suspended in it and takes it from one location to another or distributes throughout the body Functions of the cardiovascular system - Transport o Gases § Oxygen, carbon dioxide, nitrogen o Nutrients § Glucose, amino acids, viamins, proteins and lipids o Metabolic waste § Urea, uric acid, creatine, ammonium ions o Regulatory molecules § Hormones, enzymes o Processed molecules § Proteins, enzymes, carbohydrates, lipids - Protection o Inflammation o Phagocytosis o Antibodies o Platelets for clotting - Regulation o Fluid balance o pH o Body temperature o Blood pressure o Exchange between blood, extracellular fluid and cells Heart - Function o Pump § Generates pressure in the blood which moves blood through the blood vessels § The heart is a vital organ, it is pumping before birth o Routs blood § Separate pulmonary and systemic circulation  § This is caused by its specific design separating the deoxygenated blood from the oxygenated blood o One way flow § Caused by pressure o Regulates blood supply § Effected by cardiac output § The heart matches the needs of the body (homeostasis) - Protection o Rib cage, protective membranes, fluid § Pericardium - Location o Located in the thoracic cavity, obliquely in the mediastinum, medial to the two lungs and superior to the diaphragm o It is the size of a closed fist and weighs about 300g (250-350) § Females generally smaller and proportionate to the size of the person o Blunt cone shaped 2/3rd towards the left side of midline o The rounded end is the apex, anteriorly and interiorly pointed, above the diaphragm o Broader end is the base, directed posteriorly and slightly superiorly o Sits between the second rib and the 5th intercostal space Pericardium - Fibrous pericardium: tough fibrous outer layer which prevents over distension (overfilling) and it acts as an anchor by connecting it to adjoining tissue - Serous pericardium: thin, transparent inner layer, simple squamous epithelium o Parietal: lines the fibrous outer layer o Visceral: covers the hearts surface (similar in nature to cling film) o The two are continuous and have a pericardial cavity between them filled with pericardial fluid (the pericardial fluid reduces friction and distributes pressure on the heart) o They are protective - The pericardium is attached to the large blood vessels too (aorta and pulmonary trunk) - An infection of the pericardia is called pericarditis Morphology - Anterior and posterior side o Major vessels - Sulci (grooves) o Coronary sulcus § Separates the atria and ventricles o Anterior interventricular sulcus § Separates the right and left ventricle on the anterior side o Posterior interventricular sulcus § Separates the right and left ventricle on the posterior side - Pericardial and epicardial fat o Pericardial fat  § Between the visceral and parietal pericardium o Epicardial fat § Between outer layer of myocardium and visceral layer of pericardium (epicardium) - Superior chambers (collecting) – atria o Walls are thinner - Inferior chambers (discharging) – ventricles o Walls are thicker Heart wall - Three layers of tissue o Epicardium – serous membrane, simple squamous epithelium over areolar tissue, smooth outer surface of the heart (visceral pericardium) o Myocardium – middle layer, thickest layer, composed of cardiac muscle cells, contractability, branched cells, uninucleate o Endocardium – smooth inner surface of heart chambers, simple squamous epithelium over areolar tissue, covers valve surface and continuous with endothelium, very smooth Heart anatomy - Interventricular septum: the separation between the two ventricles - Interatrial septum: the wall between the atria, contains a depression, fossa ovalis, a remanent of the foetal opening (foramen ovale) between the atria - The left ventricle wall is much thicker than the right ventricle wall - Pectinate muscles: muscular ridges in auricle and atrial walls which allow for the stretching of the muscle when blood is coming in and helps in contraction - Trabeculae carnae: muscular ridges and columns on the inside of the ventricle wall which create turbulence in the blood Chambers - Right atrium o Thin walled receiving chamber, most part on the posterior side o Auricles are extensions to increase volume o Contain pectinate muscles for large force of contraction o Receives deoxygenated blood returning from the blood through three openings o Superior and inferior vena cava, coronary sinus - Right ventricle o Pumping chamber, mostly on the anterior side o Thicker walled than the atria o Receives deoxygenated blood from the right atrium o Opens to the pulmonary trunk o Contains trabeculae carnae - Left atrium o Thin walled receiving chamber, most part on posterior side, forms the hearts base o Auricles are extensions to increase volume o Contain pectinate muscles for large force of contraction  o Receives deoxygenated blood returning from the lungs through 4 openings o Four pulmonary veins - Left ventricle o Pumping chamber, forms apex and posteroinferior aspect o Thickest walled chamber of the heart o Receives oxygenated blood from the left atrium o Opens to aorta o Contains trabeculae carnae Great blood vessels of the heart - Blood into the heart: o Into the right atrium: by the superior and inferior vena cava from systemic circulation and coronary sinus from coronary circulation (deoxygenated) o Into the left atrium: by left and right pulmonary veins from pulmonary circulation (oxygenated) - Blood out of the heart: o Out of right ventricle: by pulmonary trunk (which splits into 2 pulmonary arteries, one for each lung) to pulmonary circulation (deoxygenated) o Out of left ventricle: by aorta to systemic circulation (oxygenated) Valves of the heart - Atrioventricular valves o Valves between atria and ventricles o Valves have leaf-like cusps o The cusps are attached to papillary muscles by tendons – chordae tendineae o Open valves have a canal – atrioventricular canal o Right side has three cusps (tricuspid, right AV valve) o Left side has 2 cusps (bicuspid, left AV valve) o When the valve is open blood flows from atrium to ventricle o When it is closed blood exits the ventricle and enters the atrium - Semilunar valves o Valves at the base of large blood vessels (exit of ventricles) o Valves are cup shaped o Pulmonary SL valve is at the base of the pulmonary trunk o Aortic pulmonary valve is at the base of the aorta o When the cups are filled the valves close preventing the backflow of blood into the heart o When cups are empty the valve is open and blood can flow freely out of the heart o Very thin membrane however very strong in nature - Function o Valves – prevent backflow of blood (when asked about this be sure to be specific about which spaces the blackflow would occur in and from and the relevant valve) o Chordae tendineae – strings connecting valve cusps to papillary muscles to prevent the atrioventricular valves from bulging into the aorta  o Papillary muscles – pillar like muscles in ventricles which prevent the prolapse of atrioventricular valves Blood flow - Superior and inferior vena cava and coronary sinus -> right atrium -> tricuspid valve - -> right ventricle -> pulmonary semilunar valve -> pulmonary trunk -> pulmonary arteries -> lung tissue -> pulmonary veins -> left atrium -> bicuspid valve -> left ventricle -> aortic semilunar valve -> aorta -> coronary arteries or body tissues Pump - Pulmonary circulation – deoxygenated blood is transported to the lungs for oxygenation then returned to the heart meaning that there is double circulation for one cardiac cycle o Deoxygenated blood enters the right atrium and flows into the right ventricle o Exits through the pulmonary trunk o The pulmonary trunk divides into left and right pulmonary arteries o The blood travels to the left and right lung for gas exchange o Oxygenated blood travels in the pulmonary veins back to the heart and enters the left atrium - Systemic circulation – oxygenated blood is transported to the body tissues and then returned to the heart o Oxygenated blood enters the left atrium and blood flows into the left ventricle o Left ventricle contracts and pushes blood out of the heart through the Aorta o The aorta branches into the ascending aorta, aortic arch and descending aorta o Blood is delivered to all cells in the body for gas/nutrient/fluid exchange o Deoxygenated blood travels back to the heart and re-enters the right atrium through the vena cava - Coronary circulation is a part of systemic circulation which occurs only to the heart Lecture 2 Cardiac cycle - Contraction of the heart produces the pressure o Blood moves through the circulatory system from areas of higher to lower pressure - Cardiac cycle o Repetitive contraction (systole) and relaxation (diastole) of the heart chambers – moves blood through the heart and body o Blood flow is proportional to the metabolic needs of tissues o The brain, kidneys, liver and exercising skeletal muscles have very high metabolic needs - Cardiac output = heart rate x stroke volume o Stroke volume: the amount of blood ejected from the heart o Heart rate: the number of times the heart beats in a minute o Cardiac output is calculated in millilitres per minute, in a normal adult this is 5-6L/minute at rest  - Nervous system control o The autonomic nervous system maintains blood pressure and thus blood flow o Rerouting blood flow e.g. increase in blood pressure with exercise o Rerout blood flow away from viscera and skin and towards the brain and the cardiac muscles in response to blood loss/injury - Hormonal control o Epinephrin (adrenaline) from the adrenal gland, has the ability to increase heart rate and stroke volume by triggering vasoconstriction as a response to stress Conducting systems - Cardiac conducting system o Internal pacemaker and nerve like pathways through the myocardium - Action potential o A rapid change in membrane potential which acts as an electrical signal/impulse o Action potentials spread through the conducting system of the heart to all cardiac muscle cells – as a result the cardiac muscle cells contract ‘pumping’ the blood o The heart can generate its own action potentials - Auto-rhythmicity o Repetitive contractions caused by autorhythmic contractile cells § Sinoatrial nodes – pacemaker: these are located in the atrial wall. Its function is to create action potentials at regular intervals § Atrioventricular nodes: this is located at the junction of the atrium and ventricle § Atrioventricular bundle: nerve tissue in the form of atrioventricular bundle that continues from the node § Right and left bundle branches: once the bundle passes through the atrioventricular septum it splits into two bundle branches which go to the apex of the heart and through the myocardium and move up to the atrioventricular wall § Purkinje fibres in ventricular walls: the branches given off by the right and left bundle branches and re purkinje branches (maybe look these definitions up in the text book) Blood composition - Life sustaining fluid - Blood is the most commonly studied tissue for disease diagnosis - If blood is left to stand or centrifuged it separates into: o Plasma 55% § Extracellular matrix of blood § 91% water § 7% proteins Albumins (58%): very large proteins which help in controlling osmotic balance  Globulins (38%): transport proteins which carry lipid soluble molecules and antibodies Fibrinogen (4%): fibrous proteins which aid clotting § 2% other solutes Ions (Na, K, Ca, Mg) Nutrients (glucose, amino acids, lipids, cholesterol) Waste products Gases Regulatory substances o Buffy Coat § White blood cells (5-10 thousand/cubic mm) § Platelets (250-400 thousand/cubic mm) o Formed elements 45% (Haematocrit) § Red blood cells (4.2-6.2 million/cubic mm) o Blood is a connective tissue meaning it has few cells with lots of extracellular matrix o In the context of blood the cells are the red and white blood cells which form the formed elements and buffy coat - Usually males have 5-6L of blood while females have 4-5L - The pH of blood is 7.35-7.45 Blood cells - Erythrocytes o Red blood cells o Biconcave disc shaped o 7.5um o Non nucleate with no organelles therefore it can not reproduce and has a fixed lifecycle of 120 days § By having no nucleus or organelles it increases the surface area to volume ratio helping it to carry more oxygen o Contains haemoglobin, a pigmented protein, haemoglobin contains iron o Carries oxygen – from lungs to tissues, 1.5% dissolved in plasma and 98.5% attached to haemoglobin o Carries carbon dioxide – from tissues to the lungs, 7% in plasma, 23% is attached to haemoglobin, 70% as HCO3 (bicarbonate ions) - Leukocytes o White blood cells o A high white blood cell count could mean there is an infection in the body o Complete cells with uncle and organelles o Various types e.g. neutrophils, lymphocytes, monocytes, eosinophils, basophils o Mainly help in protection – phagocytosis, immune response (cell mediated and antibody mediated), develop into macrophages and release histamines ect. - Platelets o Platelets are not true cells but cytoplasmic fractions of very large cells o Important for clotting blood  o We can bleed to death from minor cuts if there are no platelets o When a blood vessel is damaged the platelets stick to the fibroin and create a plug/clot stopping blood flow Blood vessels - Arteries o Take blood away from the heart o Contain blood under pressure § Elastic: the large arteries like the aorta and pulmonary trunk, these are elastic so that they can withstand the high pressure caused by their proximity to the heart § Muscular: facilitates vasoconstriction and vasodilation § Arterioles: smaller arteries which feed into capillaries - Precapillary sphincters o reduce blood flow to certain areas when required so that blood can be directed to essential areas - Capillaries o Site of exchange with tissues (interstitial fluid) - Veins o Cary blood towards the heart o Blood is not under pressure o Thinner walls than arteries, contains less elastic tissue and less smooth muscle o The types of vains are venules, small, medium, large, venules are the smallest Histology of blood vessels - Tunica intima (interna): simple squamous endothelium, basement membrane, lamina propria then elastic tissue are the layers of the interna, the interna is closest to the lumen - Tunica media: smooth muscle cells and elastin arranged circularly o Smooth muscle changes the diameter of the lumen o Elastic tissue allows for distension and recoil § Vasoconstriction: smooth muscles contract, there is a decrease in blood flow § Vasodilation: smooth muscles relax, there is an increase in blood flow - Tunica externa (adventitia): connective tissue transitions from dense to loose connective tissue as it merges with surrounding tissue o Nerves and blood vessels pass through the tunica externa as the smooth muscle needs its own blood supply - Lumen: the inside of the blood vessel, where the blood flows - These are the typical features of a blood vessel but depending on the type it may vary to suit the vessels specific needs Blood vessels comparison table Arteries Veins  Carries blood away from the heart to the Carries blood to the heart from the tissues tissues Located deep in the muscle Located closer to the surface of your body Have very thick walls Have thinner walls than arteries Carry mainly oxygenated and some Carry mainly deoxygenated and some deoxygenated blood (pulmonary and umbilical oxygenated blood (pulmonary and umbilical artery) vein) Have no valves due to the high pressure valves Have valves to prevent the backflow of blood as are not required there is little pressure gravity may try and pull the blood backwards Carry blood under very high pressure Carry blood under very low pressure Round lumen (holds its shape) Flat lumen (looks collapsed) Capillaries - Smallest of the 3 blood vessel types - The capillary wall consists of endothelial cells (simple squamous epithelium) basement membrane and a delicate layer of loose connective tissue o Continuous: no gaps between the endothelial cells, less permeable to large molecules as other types of capillaries e.g. muscle and nervous tissue o Fenestrated: have pores in endothelial cells called fenestrae, these are highly permeable e.g. intestinal villi, glomeruli of kidney o Sinusoidal: large diameter, irregular incomplete wall of endothelial cells, less basement membrane e.g. endocrine glands, liver (as large molecules cross their walls) - Capillaries only have tunica intima, no media or externa - Capillaries have a diameter of 7-9 microns compared to a red blood cell which has a diameter of 7.5 microns Capillary exchange - In order for exchange to occur the cells must bath in interstitial fluid (extracellular fluid) o A substance cant just go from capillary to cell, it must pass through the interstitial fluid - Transport by diffusion in and out of cells requires a pressure gradient - Interstitial fluid needs constant turnover - Source and sink o As the cells are metabolising they are using oxygen so the concentration of oxygen is constantly decreasing but as freshly oxygenated blood is constantly flowing there is a consistent supply of oxygenated blood creating a concentration gradient encouraging the flow of oxygen out of blood vessels, into the interstitial fluid and inter the cells o As the cells are metabolising they are producing carbondioxide so the concentration of carbon dioxide is constantly increasing but as freshly oxygenated blood with low levels of CO2 is constantly flowing there is a consistent supply of blood creating a concentration gradient encouraging the flow of carbon dioxide out of cells, into the interstitial fluid and inter the blood - Capillary exchange: the movement of substances into and out of capillaries  - Diffusion: oxygen, hormones and nutrients diffuse from high concentration in the capillary to low concentration in the interstitial fluid - Lipid soluble substances such as O2, CO2, steroid hormones and fatty acids diffuse through the plasma membrane of endothelial cells - Water soluble molecules such as glucose and amino acids diffuse through intercellular spaces or through fenestrations of capillaries - As there are very small spaces between cells, very few molecules can pass for example blood brain barrier (specialised capillaries only allow certain substances into the brain environment) - There are large spaces between endothelial cells so that proteins of whole cells can pass through for example in the liver or spleen Lymphatic system - Lymphoid organs o Spleen, thymus, tonsils - Lymphoid tissues and cells o MALT, Peyer’s patches, lymphocytes, B and T cells o Lymph: the fluid which passes through the vessels of this system - Lymphatic ducts, trunks, vessels and capillaries - Lymph nodes The link between cardiovascular and lymphatic systems - Capillary permeability, blood pressure and osmotic pressure effect the movement of fluid from capillaries - Fluid moves out of capillaries and into interstitial space and most returns to the capillaries (osmotic pressures) - The fluid which remains in the tissues is picked up by the lymphatic capillaries and eventually returned to venous circulation o If the lymphatic system did not pick it up there would be fluid accumulation in the area and swelling o If it was not returned by the lymphatic system the blood could thicken and reduce in volume o The lymphatic system is vital for homeostasis of the blood and circulatory system - Maintains blood volume, pressure and fluid balance - Oedema: swelling caused by excess fluid in body tissues (interstitial space) o This can be caused by problems with capillaries, heart failure, kidney disease, liver problems, pregnancy, problems with the lymphatic system, standing or walking in hot weather and eating too much salt o If capillaries become leaky to blood, proteins can leak into the interstitial fluid. This increases the osmotic pressure (osmolarity) outside of the capillary and draws more fluid out of the capillary and into the interstitial fluid Compendium 7 Notes – the renal system Lecture 1 Gross anatomy of the renal system - 2 kidneys: responsible for the formation of urine - 2 ureters: responsible for the passage of urine - Urinary bladder: responsible for the storage of urine - Urethra: responsible for the passage of urine - Renal capsule: connective tissue surrounding each kidney - Adipose tissue: surrounds the outside of the capsule for protection (fat) - Renal fascia: thin layer of connective tissue surrounds the adipose tissue and anchors the kidneys to the abdominal wall Location of the kidneys - Posterior to the parietal peritoneum, on the posterior abdominal wall, lateral to the spine - Note: the right kidney is always slightly inferior to the left o This is because of the position of the liver, it pushes the right kidney down a little - Partially protected by lumbar vertebrae and ribs - 11cm long, 5cm wide and 130g - Note: the adrenal glands are located on top of the kidneys External kidney anatomy - Hilum: small area where the nerves and renal blood supply enters and exits, this is on the medial/ concave side of the kidney - Renal artery: delivers oxygenated blood to the kidney, enters via the hilum - Renal vein: takes away deoxygenated blood from the kidney, exits via the hilum Internal anatomy of the kidney - Hilum: on the concave (medial) side, renal artery and nerves enter, renal vein, ureter, lymphatics exit - The hilum opens into the renal sinus, which is filled with fat and loose connective tissue, the renal sinus is a cavity - Kidneys are organised into two major regions o Outer cortex o Inner medulla (pyramids) - Renal pyramids o Their bases project into the cortex o They are cone shaped o The base is the boundry between the medulla and the cortex o The apex of a renal pyramid is called a renal papilla § Papillae extend into minor calyces (calyx is singular) - The renal pelvis is a single large funnel shaped chamber o The renal pelvis is embedded in the renal sinus, at the hilum it narrows, forming the ureter - Renal columns are extensions of cortical tissue into the medulla (between pyramids)  - Papilla -> minor calyx -> major calyx -> renal pelvis The nephron - The functional unit of the kidney - 4 separate nephrons of the nephron, the renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule - Blood enters the nephron for filtration - Filtrate/urine is produced - Urine flows: nephron -> papillary ducts -> minor calyces -> major calyces -> renal pelvis -> ureter - The loop of Henle is the only part of the nephron which extends into the renal pyramids - The distal convoluted tubule drains into the collecting duct Types of nephrons - There are approximately 1.3 million nephrons in each kidney - Each is approximately 50-55mm in length - Juxtamedullary nephrons: o The renal corpuscle is deep in the cortex near the medulla o A long loop of Henle extending deep into the medulla o 15% of nephrons - Cortical nephrons o Renal corpuscle is located near the periphery/cortex o Shorter loop of Henle o 85% of Nephrons Renal corpuscle - The filtration portion of the nephron - Consists of the glomerulus and the Bowman capsule - Glomerulus: a network/ball of capillaries - Bowmans capsule: enlarges end of the nephron, a double walled chamber, filters the blood/fluid, which then enters the proximal convoluted tubule - Blood enters the glomerulus through the afferent arteriole and filtered blood exits through the efferent arteriole - The afferent arteriold is much larger than the efferent arteriole because the blood is under higher pressure in the efferent arteriole Bowmans capsule - Parietal layer o Outer layer of simple squamous epithelium which then becomes simple cuboidal in the proximal convoluted tubule - Visceral layer o Inner layer, constructed of specialised cells called podocytes, which wrap around the glomerular capillaries to facilitate filtration of the blood The filtration membrane  - Fenestrae: the glomerular capillaries are very permeable. Fenestrae are little windows, the innermost layer - Basement membrane: the basement membrane is sandwiched between the endothelial cells of the glomerular capillaries and podocytes - Filtration slits: gaps between the cell processes of the podocytes - Thus, the filtration membrane is specialised for filtration The renal tubules - Proximal convoluted tubule: filtrate drains into here from the Bowman capsule, the proximal convoluted tubule is continuous with the bowmans capsule - Loop of Henle: has a descending and an ascending limb which is continuous with the proximal convoluted tubule - Distal convoluted tubule: shorter than the proximal convoluted tubule - Collecting duct: several distal convoluted tubules connect to a single collecting duct, these have a large diameter. It extends through the medulla and towards the renal papilla towards the ureter Nephron histology - Proximal convoluted tubule: simple cuboidal epithelium with many microvilli. These cells have lots of mitochondria and actively reabsorb Na+, K+ and Cl- ions back into the blood, the convolutions mean that there is a higher surface area for reabsorption - Loop of Henle: the thick parts of the loop are made up of simple cuboidal epithelium and the thin parts are simple squamous for osmosis and diffusion - Distal convoluted tubule: simple cuboidal epithelium with very few microvilli, there are many mitochondria and active reabsorption takes place but not nearly as much as in the proximal convoluted tubule - Collecting duct: simple cuboidal epithelium Major renal veins and arteries - Abdominal aorta: oxygenated blood flowing from the heart to the kidneys - Renal artery (R): branch off of the aorta - Renal artery (L): branch off of the aorta - Renal vein (R): drains into the inferior vena cava - Renal vein (L): drains into the inferior vena cava - Inferior vena cava: deoxygenated blood flows from the kidneys back to the heart - The efferent arteriole branches off into a network of peritubular capillaries around the nephron which eventually drains into the renal vein Urine movement - Pressure forces the urine through the nephron - Smooth muscle forces urine through the ureters o Peristalsis moves urine from the renal pelvis in the kidney to the ureters to the urinary bladder - Ureters enter the bladder obliquely through trigone - Pressure in the bladder compresses the ureter preventing backflow Ureters  - Passageway for urine - From renal pelvis to the urinary bladder - Lined with transitional epithelium (can change shape) - Layers of the ureter o Transitional epithelium o Mucosa o Muscularis o Fibrous adventitia - Ureters enter the urinary bladder from the trigone Urinary bladder - The urinary bladder is a hollow muscular container located in the pelvic cavity posterior to the symphysis pubis - The trigone is a histologically unique area on the posterior wall between the entry of the two ureters and the exit of the urethra. This area doesn’t stretch to the same extent as other surfaces of the bladder. - The volume of the bladder increases and decreases during the day depending on how much urine is being produced/stored - Layers of the urinary bladder o Transitional epithelium o Lamina proper o Submucosa o Detrusor muscle Urethra - Transports urine from the urinary bladder to outside of the body - Transitional epithelium at the top of the urethra, the rest id stratified columnar - At the junction of the urinary bladder and the urethra is the urinary sphincter o Elastic onnective tissue and smooth muscle prevents urine leakage - External urinary sphincter: skeletal muscle surrounds the urethra as it extends through the pelvic floor o We can voluntarily stop the flow of urine - Male urethra: extends from the inferior part of the urinary bladder to the tip of the penis - Female urethra: shorter and opens into vestibule which is anterior to vaginal opening Lecture 2 Function of the renal system - Excretion: rid the body of waste products. Urine production occurs in the kidneys via filtration of the blood and reabsorption of nutrients. Metabolic wastes and toxic molecules are excreted in urine. - Regulation of blood volume and blood pressure o We control our extracellular fluid levels by producing large amounts of dilute urine or small amounts of concentrated urine  - Solute concentration in the blood, extracellular pH, regulation of red blood cell synthesis and regulation of vitamin D synthesis The production of urine - Kidneys: regulate body fluid composition. Sorts chemicals in the blood for removal or for return into the blood - Nephrons: the structural component of the kidney which sorts though all the chemicals and substances in the blood - Urine production: o Filtration – this occurs as the movement of fluids goes out of the glomerulus, across the filtration membrane and out into the Bowmans capsule, a lot of fluid is being moved, anything small enough will pass through this membrane o Tubular reabsorption – reabsorption of the good solutes for example water and glucose, back into the interstitial fluid then to the peritubular capillaries so we can use things like water and glucose in other body cells o Tubular secretion – solutes are secreted across the wall out of the peritubular capillaries through the interstitial fluid and into the nephron filtrate so it can be excteted in urine Process 1: filtration - Movement of fluid derived from blood flowing through the glomerulus and across the filtration membrane - Filtrate: water, small molecules and ions that can pass through the membrane o Doesn’t include blood cells, proteins or large molecules - Renal fraction: the proportion of total cardiac output that passes though the kidneys o Varies from about 12-30% in healthy resting humans - Glomerular filtration rate: amount of filtrate produced each minute o 125ml/min or 180L/day - Average urine production per day is 1-2L - Most of the filtrate (99%) must be reabsorbed into the blood - Removes toxins quickly from the blood Filtration membrane - Learn and remember the components of the filtration membrane - Filtrate consists of water, glucose, fructose, amino acids, urea, urate ions, creatine, sodium, potassium, calcium and chlorine o Very little protein is found in filtrate and urine - Filtration is driven by pressure o Blood pressure - Filtration pressure: the force that causes filtration o Pressure gradient responsible for forcing fluid out of the glomerular capillary across the membrane into the lumen of the bowman capsule The juxtaglomerular apparatus - An important regulatory structure located next to the glomerulus - Where the afferent arteriole enters the renal corpuscle, a cuff of smooth muscle cells surrounds it – the juxtaglomerular cells  - A group of specialised cells at a section of the distal convoluted tubule called the macula densa - These secrete an enzyme called renin which is important in the regulation of filtrate formation and blood pressure regulation Process 2: tubular reabsorption - This is the return of water, small molecules (good substances) and ions back into the blood - As filtrate flows through the lumen of the renal tubules - Firstly substances are reabsorbed across the renal tubule into the interstitial fluid, then from here, into the peritubular capillaries then back into circulation - This process takes place in the proximal convoluted tubule, loop of Henle and distal convoluted tubule (under low pressure) - Substances: water, amino acids, glucose, fructose, Na+, K+, Ca+2, Cl-, HCO3 - Proximal convoluted tubule o Majority of reabsorption happens here; the filtrate remaining is about 35% - Active and passive mechanisms of cell membrane transport - Note: the apical surface of the proximal convoluted tubule has simple cuboidal cells lining the nephron and o Boarders with the nephron lumen - Note: the basal surface boarders with the interstitial fluid - Substances in the filtrate that need to be reabsorbed must cross the apical membrane, they are then inside the cell and must cross the basal membrane. Once crossed they are in the interstitial fluid and then back inside the peritubular capillaries - Loop of Henle: some reabsorption of water and ions, remember thick and thin segments o Thin segments – simple squamous epithelium, highly permeable to water and some solutes can move by diffusion too o The filtrate is further reduced by 15% in the loop of Henle o Ions move through active and passive transport in the loop of Henle - Distal convoluted tubule and collecting duct: some reabsorption o Most of this is under the control of ADH, Anti-Diuretic Hormone § ADH makes the tubule wall more permeable to water and therefore more water reabsorption occurs. This creates less urine, and that urine will be very concentrated § A diuretic such as alcohol or coffee causes the body to increase urine production so an anti-diuretic would do the opposite - Proximal convoluted tubule o Active transport of Na+ across the basal surface – associated with the reabsorption of most solutes o With Na+ being pumped out of the cell, the concentration of Na+ is low inside the cell. Therefore Na+ moves into the nephron cell through the apical surface. Other substances can move into the cell by symport e.g. glucose  §Symport is where a substance ‘piggy backs’/harnesses another substance to take it into a cell down the concentration gradient of the second substance o Once the glucose is inside a cell if can diffuse through the basal membrane and then it will end up back in the peritubular capillaries Process 3: Tubular secretion - The movement of non-filtered substances, toxic by-products of metabolism, drugs, or molecules not normally produced by the body, into the nephron for excretion. This occurs mainly in the distal convoluted tubule - Like reabsorption it can be active or passive - Ammonia is a toxic by-product of protein metabolism. It diffuses passively into the lumen of the nephron - H+, K+, and penicillin: actively secreted into the nephron joining the filtrate and becoming urine Urine movement - Pressure forces the urine through the lumen of the nephron - Peristalsis moves urine through ureters to the urinary bladder, every few seconds to every few minutes (fairly constant movement) o Parasympathetic stimulation: increase frequency § Rest and digest o Sympathetic stimulation: decrease frequency § Fight or flight - Prevention of the backflow of urine in the ureters is trigone pressure Composition of urine - 1% of filtrate - 1-2L produced per day - Proportion of water - Depending on the body’s needs it varies in concentration o Urea, uric acid, ammonia, creatine, H+, K+ o Bile pigments o Drugs and toxins e.g. penicillin - Urine: o 0.05% ammonia (by product of amino acid break down) o 0.18% sulphate o 0.12% phosphate o 0.6% chloride o 0.1% magnesium o 0.015% calcium o 0.6% potassium o 0.1% sodium o 0.1% creatine o 0.03% uric acid o 2% urea (biproduct of protein break down) o 95% water The micturition reflex - While the flow of urine from the ureters to bladder is continuous, the flow from bladder to urethra is not - The bladder has a capacity of 1L - Micturition is the elimination of urine from the bladder - Full bladder -> stretch receptors -> Central Nervous system a message - Voluntary control -> central nervous system of the external urethral spincter Relax in conjunction with bladder contraction -> urination Compendium 8 Notes – the nervous system Lecture 1 Nervous system terminology - Neuron (nerve cell): basic structural and functional unit of the nervous system - Neuroglia: major supporting cells of neurons - Axon: nerve fibre - Nerve: bundle of axons (or nerve) fibres and their sheaths (outer coverings) - Sensory receptors: separate specialised cells which detect temperature , pain, touch, light, sound, odour or other stimuli - Action potential: electronic signal, the way information travels in the nervous system - Effector organ or effector cell: the organ, tissue or in which an effect or action takes place - Synapse: junction of a neuron with another cell, this might be a muscle cell or another neuron Functions of the nervous system 1. Receive sensory input o Internal (monitoring homeostasis) o External (the environment outside the body) o The bodies way of making sense of its environment by using specialised cells 2. Integrate information o This occurs in the central nervous system o The body making sense of the sensory input so it can produce an appropriate response o The response may be immediate or it might be delayed, stored in the body ‘for future reference’ or completely ignored § This is depending on the type of stimulus the body reveives 3. Motor output o The body’s response is relayed by the motor output o For example, the contraction of muscles or glands 4. Maintaining homeostasis o All of the above come together to achieve homeostasis, keep the body in equilibrium o The nervous system stimulates or inhibits activities to maintain homeostasis 5. Establish and maintain homeostasis o Thinking, memory and creating different types of emotion, having consciousness and making appropriate decisions Divisions of the nervous system 1. Central nervous system o Brain o Spinal cord o The decision makers of the body o These structures are very well protected by our skeleton 2. Peripheral nervous system o Sensory receptors o Cranial nerves – 12 pairs § Nerves from brain o Spinal nerves – 31 pairs § Nerves from spinal cord o Ganglia – collection of neuron cell bodies outside of the central nervous system o Plexuses – extensive network of usually axons outside of the central nervous system Functional divisions of the nervous system - The nervous system divides into the central and peripheral nervous system - These two systems interact o PNS senses something, sends message to CNS, CNS responds and sends a motor output through the PNS - PNS o Somatic nervous system § Sensory (afferent) § Motor (efferent) o Autonomic nervous system § Sensory (afferent) § Motor (efferent) Sympathetic (Fight or flight) Parasympathetic (Rest and digest) o Enteric nervous system § Sensory (afferent) § Motor (efferent) Somatic vs autonomic nervous system - Somatic o Voluntary and under conscious control o Action potentials in the motor neurons travel from the CNS to skeletal muscles o Single neuron system, one synapse o Cell bodies are located in the CNS o Skeletal muscle contractions are the response o Myelinated axons - Autonomic  o Involuntary and under unconscious control o Action potentials in the motor neurons travel from the CNS to smooth or cardiac muscle, or glands o Two neuron system with two synapses o Cell bodies of the first neuron are located in the CNS and the second are in an autonomic ganglion o The target tissues can be stimulated or inhibited o The preganglionic are myelinated and the postganglionic are unmyelinated Enteric nervous system - Nerve plexus within the walls of the digestive tract o Sensory neurons connect the digestive tract to the central nervous system o Autonomic nervous system motor neurons connect the central nervous system to the digestive tract o Enteric neurons are confined to the enteric plexus o The digestive tract must be under very specific control to ensure muscle contractions and secretions are happening at the right times - Functions o Stimulate/inhibit smooth muscle contraction o Stimulate/inhibit gland secretion o Detect changes in the contents of the lumen § If its acidic it may stimulate the production of different types of enzymes Sensory vs motor division - Sensory o Also called the afferent division o Detects internal and external environmental stimuli o Collects input from specialised sensory receptors (neural cells or specialised cells) o Transmits input as electrical signals to the CNS (nerves) o The cell body of a sensory neuron is outside the CNS (dorsal root ganglion) - Motor o Also called the efferent division o Transmits electronic signals from the CNS to the effector (e.g., muscles and glands) o The cell body of the motor neuron is located in the CNS Autonomic nervous system (motor division) - Sympathetic o Fight or flight response o Thoraco-lumbar region of the spinal cord o Prepares the body for physical activity o Primes the body to act in threatening situations o Shorter neuron pathway leading to a faster response o Complementary to the action of the parasympathetic response  o E.g. increased heart rate, increased respiratory rate, sweating and pupil dialation - Parasympathetic o Rest and digest/feed and breed response o Cranio-sacral region of the spinal cord o Relaxes the body inhibiting high energy functions o Longer neuron pathways meaning there is a slower response o The body feels relaxed o Complementary to the action of the sympathetic response o E.g., stimulates digestion, defaecation, diuresis(increased urine production), pupil contraction Lecture 2 Cells of the nervous system - Neuron o About 100 billion in the body o The structural and functional units of the nervous system o They collect and receive information from the external and internal environment, integrate it and send an appropriate response to the target o Classified based on structure and function - Neuroglia o 10-50 times more neuroglial cells, they make up half of the brains weight o Supporting cells (support the neurons) o Six different types, 4 in the CNS and 2 in the PNS Neuron - Highly modified to perform its function, electrically excitable as information travels through the body via electric impulses - Three main parts o Neuron cell body (soma) § Nucleus, nucleolus § Nissl bodies (rough endoplasmic reticulum) Protein production § Golgi apparatus § Mitochondria § Other cell organelles o Dendrites § Highly branched extensions of the cell body § Cytoplasmic extensions § Generate an electric current when stimulated § Flow of current moves from the dendrites tip to the cell body § Have dendritic spines which are further extensions of the dendrites § The dendrites main function is to collect the stimuli o Axon § Often one arising from axon hillock (the cone shaped area where the cell body meets the azon) § The trigger zone is the axon hillock and the initial segment  § The initial segment is where the axon hillock narrows and this is where action potentials are generated § Can vary in length from a few millimetres long to a few meters long § They can be branched (collateral axon) § Presynaptic terminal/axon terminals are the endings of axons They are highly branched extensions of the axon § Terminal boutons, synaptic knobs The ends of the axon terminals which are swollen, this is where the neurotransmitters are stored § Myelin sheath Not all axons are myelinated but some are The myelin sheath is made up of Schwann cells o A neuroglia cell o These cells surround themselves around the axon o The nucleus of these cells is located peripherally § Node of Ranvier Gaps between the schwann cells where the axon is left unmyelinated - Unidirectional flow of impulse o Collects stimuli through dendrites, passes through axons to axon terminals Neurons – structural classification (add some illustrations) - Multipolar (many) o The cell body has many extensions, lots of dendrites and an axon, it gives rise to many processes and is therefore a multipolar neuron o One cell body o Many dendritic processes and an axon o Motor neurons and interneurons - Bipolar (two) o The cell body has 2 extensions, one gives rise to dendrites and one gives rise to the axon and therefore is a bipolar neuron o One cell body and two processes, a dendrite and an axon o Specialised sensory neurons o Only found in Retina of the eye and nasal cavity - Unipolar/pseudo unipolar (one) o Only gives rise to one cell body extension, the axon and is therefore a unipolar neuron o One cell body and only one process, axon o Dendrites connected to sensory receptors, axon terminals to CNS o Sensory neurons Neurons – functional classification - Sensory neuron o Conduct an action potential from sensory receptors to the central nervous system o Afferent neuron - Moto neuron  o Conduct an action potential away from the central nervous system towards muscles or glands o Efferent neuron - Inter neuron o Conducts an action potential within the central nervous system from one neuron to another Neuroglia – CNS - Astrocytes o Star shaped o Most numerous type of neuroglial cells in the brain o Highly branched cytoplasmic processes with end feet which surround blood vessels o Synaptic support, scaffold CNS cells and capillaries, control the blood brain barrier’s permeability, homeostasis of the central nervous systems ions, form glial scar during injury o Regulates what can leave the blood and come into the brain tissue o Due to the presence of microfilaments in the cytoskeleton the astrocytes are able to support nerve neurons and blood vessels o By forming scar tissue around injury they stimulate healing but limits the regeneration of neurons o Synthesises, absorbs and recycles neurotransmitters (synaptic support) - Ependymal cells o Line the ventricles of the brain and the central canal of the spinal cord o Ciliated simple cuboidal or columnar, cilia to circulate the cerebral spinal fluid o Production, secretion and regulation of cerebral spinal fluid - Microglial cells o 10-15% of cells in the brain are microglial o Smallest of the neuroglial cells o Oval in shape with finger like projections o Resting microglia: patrol the central nervous system o Active microglia: becomes active when it detects injury or pathogens § Become active, mobile and phagocytic in response to inflammation o Phagocytose foreign substances, necrotic tissue and pathogens - Oligodendrocytes o Have cytoplasmic extensions that wrap around the axon forming the myolin sheath o Each cell can enclose multiple axons o Insulation of axons in the central nervous system o One oligodendrocyte can cover many axons Neuroglia – PNS - Schwann cells o Have cytoplasmic extensions that wrap around the axon forming the myelin sheath o Each cell forms a part of the sheath around one axon o Insulates axons in the PNS  o Leaves nodes of Ranvier in between - Satellite cells o Surrounds cell bodies in sensory and autonomic ganglia o Provides support and nutrition to cell bodies o Protects the cell from heavy metal poisons e.g. pb, hg Myelinated vs non-myelinated axons - Myelinated o Schwann cells (PNS) and oligodendrocytes (CNS) wrap repeatedly around the axon o Nodes of Ranvier o Saltatory conduction of electrical impulses o Faster nerve impulses - Unmyelinated axons o Axons rest in invaginations of Schwann cells (PNS) and oligodendrocytes (CNS) electrical impulses travel as a continuous wave o Thinner >1micron, lower speed of nerve impulse conduction Grey matter vs white matter - Grey matter o Consists of neuronal cell bodies, dendrites, axon terminals, ganglia, unmyelinated axons, glial cells and synapses o Located on the periphery (outer cortex), in cerebrum, cerebellum, brainstem, diencephalon, deeper tissues in the brain (nuclei) o In the middle of the spinal cord, ‘H’ shaped grey column - White matter o Very few cell bodies, mainly long-range myelinated axons, deeper tissues (subcortical), nerves o White due to the myelin sheath o Lies on the inner side of the brain but the outer part of the spinal cord Lecture 3 Electrical signals - Electrical impulses: environment (external and internal), emotions, conscious thought, memory, actions of glands and muscles - Terminology o Resting membrane potential o Action potential o Graded potential o After potential o Depolarisation, repolarisation, hyperpolarisation - Membrane potential: measure of electric properties of a cell membrane o The membrane potential is determined by ionic concentration difference across the plasma membrane and permeability of the plasma membrane Cell membrane – ionic concentration - Selectively permeable  - Continuous communication between the intracellular and extracellular environment - Excitability in cells o Ion movement across the cell membrane o Difference in ionic concentration ( particularly for Na+ and K+) across the cell membrane o Na+/K+ pump - Higher concentration of Na+ and Cl- outside of the cell - Higher concentration of K+, proteins and PO4-3 inside the cell - If we compare extracellular with the intracellular environment they are electrically neutral o There is an equivalent total of cations and anions Cell membrane – ion channels - Selectively permeable o This is based on size, solubility, polarity, gradient, cell requirement, ect. - As ions are charged they cent diffuse through the bilayer and must pass through specialised channels - Non-gated ion channels o Also known as ‘leak’ ion channels as they are always open o Ion specific o Movement based on the concentration gradient o The cell membrane has more K+ and Cl- leak ion channels compared to Na+ leak ion channels § There is more movement of potassium then sodium - Gated ion channels o Gates are closed and require signals to open them o Ion specific o Depending on the stimulant the gates can be classed as: § Ligand gated ion channels Opened when a chemical attaches to the channel § Voltage gated ion channels Opened by stimulation from a difference in charge § Other gated ion channels Other stimuli such as temperature or pressure Resting membrane potential - Resting membrane potential is the difference in charge across the cell membrane in a resting cell - Measured in millivolts (mV) - The resting membrane potential of neurons is -70mV (considered a small magnitude) - The intracellular side is more negative compared to the extracellular side and this difference makes the plasma membrane polarised - Resting membrane potential is caused by the leak of ion channels and the Na+/K+ pump - Other cells have a resting membrane potential, it’s not always -70mV Establishing a resting membrane potential (maybe add pictures to make it make sense)  1. In a resting cell there is a higher concentration of K+ inside the cell membrane and a higher concentration of Na+ outside of the cell membrane. Because the membrane is not permeable to negatively charged proteins they are isolated to the inside of the cell membrane 2. There are more K+ leak channels than Na+ leak channels. In the resting cell only the leak channels are opened; the gated channels are closed. Because of the ion concentration differences across the membrane K+ diffuses out of the cell, down its concentration gradient and sodium diffuses into the cell down its concentration gradient. The tendency for K+ to diffuse out of the cell is opposed by the tendency of the positively charged K+ ions to be attracted back into the cell by negatively charged proteins 3. The sodium potassium pump helps maintain the differential levels of Na+ and K+ by pumping three Na+ out of the cell in exchange for two K+ into the cell. The pump is driven by ATP hydrolysis. The resting membrane potential is established when the movement of K+ out of the cell is equal to the movement of K+ into the cell Action potential – 1 - An action potential is how a neuron sends information down an axon, away from the cell body, to the effector - Multiple step process - Resting membrane potential o All gated Na+ and K+ channels are closed o K+ leak channels are open and allow movement of K+ out of the cell which creates negative intracellular change causing membrane potential o The Na+/K+ pump also contributes to membrane potential o Outside the cell is positive and nside the cell in negative Action potential – 2 - Depolarisation o When the cell gets stimulated depolarisation occurs o Na+ voltage gated channels open and Na+ moves into the cell and inside the cell becomes more positive, due to the concentration gradient the Na+ wants to rush into the cell o K+ voltage gated channels are closed o Membrane potential becomes more positive (no longer -70mV, it increases past 0) o Depolarisation starts from a stimulus which must be strong enough to meet threshold and only then can an action potential occur (around -55mV) o Outside the neuron becomes negative and inside the cell becomes positive o Towards the end of depolarisation K+ channels start to open but they are slow to open Action potential – 3 - Repolarisation o Na+ voltage gated channels close  o K+ voltage gated channels open and K+ moves out of the cell and the intercellular side becomes more negative o Membrane potential becomes more negative o Extracellular environment becomes more positive o After repolarisation is established the potassium voltage gated channels close (they are slow to close) Action potential – 4 - End of repolarisation, and the afterpotential - Na+ voltage gated channels close - K+ voltage gated channels close as well but they close slowly so K+ continues to leave the cell resulting in afterpotential - Afterpotential is where the membrane potential becomes very negative (-75/80mV) Action potential – 5 - Na+ gated channels are closed - K+ gated channels are closed - Resting membrane potential is re-established (-70mV) by Na+/K+ pump (an active process against the concentration gradient) which redistributes ions as all Na+ and K+ gated channels are closed Relevant concepts - Depolarisation: where the membrane potential becomes more positive, i.e. the inside of the cell becomes more positive e.g. -70mV -> -30mV - Repolarisation: membrane potential returns to normal, the outside of the cell becomes more positive - Hyperpolarisation: when the membrane potential becomes more negative i.e. the inside of the cell becomes more negative e.g. -70mV -> -75mV - Afterpotential: a short period of hyperpolarisation of an action potential - Graded potential: short lived, localised changes in membrane potential o Can lead to action potentials o Often occur in dendrites or the cell body of a neuron o Ability to summate (multiple small graded potentials will add up) o Decremental -> not able to transfer information over a long distance - All or none principle o If the stimulus is weak there will be no action potential but once threshold has been reached all action potentials will have the same magnitude. They won’t be bigger given a stronger stimulus o A stronger stimulus will only result in increased frequency - Refractory period: from the point of threshold until the membrane potential has returned to -70mV after the afterpotential o Absolute refractory period: depolarisation and repolarisation, there is no chance an action potential can be triggered during this time o Relative refractory period: afterpotential, with extremely strong stimuli, action potentials could be generated in this time o Another action potential cannot be generated during the refractory period  o The cell membrane needs to re-establish its resting membrane potential before it can start another action potential Propagation of axon potentials (visuals could be helpful) - This takes place in unmyelinated axons only - Following depolarisation, each segment of the axon membrane becomes repolarised - The propagation of the action potential occurs in one direction - ‘Mexican wave’ effect Saltatory conduction (visuals could be helpful) - Latin ‘saltare’ – hop, leap - Propagation of action potentials in myelinated axons - Jumps from one node of Ranvier to the next - Increases the speed of transmission of the impulse Synapse - Junction of a neuron with another cell e.g. dendrites of another neuron, a muscle cell or a gland - A pre-synaptic (the cell transferring) and a post-synaptic cell (the cell receiving) - We can tell neurons are highly specific for their role as they have lots of dendrites to pick up any stimulation and they have lots presynaptic terminals to synapse with many other cells - A neuron can have thousands of synapses - Electrical synapse: a less common electrical signal, only in cardiac muscles and some smooth muscles. In these synapses the cells are connected by gap junctions - Chemical synapse: the most common type which uses chemical messengers called neurotransmitters to transmit an action potential across the synapse Chemical synapse (visuals could be helpful) - Components of a synapse o Pre-synaptic terminal o Pre-synaptic membrane o Post-synaptic membrane o Synaptic cleft o Neurotransmitters o Synaptic vesicles - Neurotransmitter release o An action potential arriving at the presynaptic terminal causes voltge gated Ca2+ channels to open o Ca2+ diffuses into the cell and stimulates exocytosis of the synaptic vesicles which release neurotransmitter molecules o Neurotransmitter molecules diffuse from the presynaptic terminal across the synaptic cleft o Neurotransmitter molecules combine with their receptor sites and cause ligand gated Na+ channels to open. Na+ diffuses into the cell and causes depolarisation - Neurotransmitter removal  1. Acetylcholine molecules bind to their receptors 2. Acetylcholine molecules unbind from their receptors 3. Acetylcholinesterase splits acetylcholine into choline and acetic acid which prevents acetylcholine from again binding to its receptors. Choline is taken up by the presynaptic terminal. 4. Choline is used to make new acetylcholine molecules that are packaged into synaptic vesicles 5. Other acetylcholine simply diffuse into the extracellular fluid away from the synaptic cleft Lecture 4 Introduction to spinal cord - The spinal cord is a part of the CNS - It extends from the brain at the level of the foramen magnum to the second lumbar vertebra along the posterior aspect of the body - The spinal cord is protected by the vertebral column which is a bony structure and the meninges which are which are made up of various layers of connective tissue. These surround the brain and spinal cord - The grey matter of the spinal cord is located on the interior part while the white matter is exterior - Each side of the grey matter of the spinal cord is organised into horns o Posterior (dorsal) horn o Lateral horn o Anterior (ventral) horn - The white matter is arranged into columns o Dorsal (posterior) column o Ventral (anterior) column o Lateral column - The anterior median fissure is the depression on the anterior side in the white matter - The posterior median sulcus is also a depression however it is much narrower and is located on the posterior side - The connection between the two sides of grey matter is called the grey commissure - In the centre of the grey commissure there is a hole known as the central canal - On the sides of the spinal cord there are root-like branches called rootlets and these rootlets arise from both the doral and the ventral side. The rootlets form roots, the dorsal and ventral roots. o The swelling on the dorsal side is called the dorsal root ganglion Organisation of neurons in the spinal cord and the spinal nerves - Information enters the CNS via the dorsal side and exits via the ventral side - Spinal nerves are mixed nerves because they have both sensory and motor information traveling through them Reflexes - Automatic response to a stimulus without a higher brain centre involvement - Are homeostatic doesn’t require mental processing o Help to maintain homeostasis in the body - Are somatic or autonomic o Autonomic: blood pressure, carbon levels in the blood o Somatic: touching something hot, stepping on something sharp and posture - Produces the same stereotyped response from the spinal cord - Rapid, predictable and unlearned o No matter how mnay times you touch a hot stove your body will respond the same - The simplest reflex arcs don’t involve interneurons o Monosynaptic vs polysynaptic Reflex arc 1 1. A sensory receptor detects a stimulus 2. A sensory neuron conducts action potentials through the nerve and dorsal root to the spinal cord 3. In the spina cord the neuron synapses with an interneuron (unless it is monosynaptic) 4. The interneuron synapses with a motor neuron 5. A motor neuron axon conducts action potentials through the central root and spinal nerve to the effector organ - Anatomical pathway of a reflex is called a reflex arc o Sensory receptor o Sensory neuron o Interneuron o Motor neuron o Effector organ Reflex arc 2 - After the response is produced by the reflex arc a signal is sent to the brain to inform it of what has just happened - The brain centres can supress and exaggerate the Types of reflexes - Somatic: involves skeletal muscles e.g. the patellar reflex - Autonomic: involves smooth muscles, cardiac muscles or viscera e.g. the pupillary reflex - Monosynaptic: Simple neuronal pathway sensory synapses with motor neuron (there is one synapse) e.g. stretch reflex - Polysynaptic: a complex pathway with multiple synapses with interneurons between sensory ad motor neurons e.g. knee jerk reflex, Golgi tendon reflex, Babinski reflex, pupillary reflex Reaction - Voluntary response to a stimulus - Initiated by a sensory stimulus - Relatively slower than a reflex - Involves the brain and spinal cord  - Reaction time improves through repetition - E.g. catching a ball or dodging an incoming object Compendium 9 Notes – the brain and spinal cord Lecture 1 Spinal Cord 1 - The spinal cord extends inferiorly from the foramen magnum to the first or second lumber vertebrae - The spinal cord can be divided into the cervical, thoracic, lumbar, sacral and coccygeal regions - There are 31 pairs of spinal nerves that emerge from the spinal cord Spinal cord 2 - Cervical nerves 8 - Thoracic nerves 12 - Lumbar nerves 5 - Sacral nerves 5 - Coccygeal nerve 1 - The diameter of the spinal cord changes from top to bottom because o There are enlargements in the cervical region and the lumbar-sacral region o These enlargements correspond with the limbs cervical supplying the arms and lumbar/sacral supplying the legs - The pointed end of the spinal cord is called the conus medullaris - The cauda equina are the roots of the spinal cord Meninges 1 - Meninges: the connective tissue covering the spinal cord and brain - Functions: o Protect the CNS and its blood vessels o Contains the cerebrospinal fluid o Forms partitions in the skull Meninges 2 - Dura mater o Outermost, superficial and thickest meningeal layer o Surrounds the brain and the outer layer if the spinal nerves o Subdural space: the space between the dura mater and the next layer of meninges containing serous fluid - Arachnoid mater o Looks like cobwebs o Deep to the arachnoid mater is the subarachnoid space containing blood vessels and cerebrospinal fluid - Pia mater o A gentle or tender layer that is the last or most deep layer of meninges o Has many blood vessels in it o Sits tightly over the spinal cord and brain Spinal cord 3 (mostly covered last compendium) CNS PNS Brain Spinal cord Grey matter Cortex of brain Ganglion Outer cortex Inner and nuclei White matter Nerve tracts Nerves Deeper Outer - The spinal cord’s white matter can be divided into a dorsal, ventral, anterior and lateral column - The spinal cord’s grey matter can be divided into a posterior, lateral and anterior ventral horns - The spinal cord has commissures - Rootlets merge to form dorsal and ventral roots which merge to form a spinal nerve - The central canal is in the centre of the grey matter Organisation of neurons in the spinal cord 1 (mostly covered last compendium) - Sensory nerves travel through the dorsal roots - Motor (somatic and autonomic) neurons travel through the ventral roots Organisation of neurons in the spinal cord 2 (mostly covered last compendium) - Cell bodies of motor neurons are in the horns of the grey matter o Autonomic neuron cell bodies are found in the lateral horn o The somatic motor neuron cell bodies are found in the lateral horn Nerve - Endoneurium o Surrounds each axon and its associated Schwann cells - Nerve fascicle o A bunch of axons surrounded by endoneurium - Perineurium o Surrounds a group of axons or a nerve fascicle o It is a more coarse connective tissue than the endoneurium - Epineurium o Surrounds a group of fascicles o A nerve or a spinal nerve The organisation of spinal nerves Spinal nerves Vertebral bones Cervical 8 pairs 7 bones Thoracic 12 pairs 12 bones Lumbar 5 pairs 5 bones Sacral 5 pairs 5 bones Coccygeal 1 pair 5 fused bones = 1 bone - 31 spinal nerves but 30 spinal bones - C1 comes out of the top of the first vertebrae causing the difference in nerves to bones (diagram might help) Lecture 2 The brain 1 - Jelly like mass - Weighs 1.5kg - One of the biggest and most complex organs in the body - The brain is made up of approximately 100billion neurons and a trillion neuroglial cells - The brain is made up of: o The forebrain § Cerebrum § Diencephalon o The midbrain o The hindbrain § Pons § Medulla oblongata § Cerebellum o The midbrain, pons and medulla oblongata form what is referred to as the brain stem The brain stem - The brain stem sits under the diencephalon - The brain stem connects the spinal cord to the rest of the brain - The midbrain, pons and medulla oblongata form what is referred to as the brain stem Medulla oblongata - The medulla oblongata connects directly to the spinal cord o It connects at the level of the foramen magnum - It is an autonomic reflex centre maintaining homeostasis in the body - Contains the cardiovascular centre o Regulates heart rate, force of heart contraction and blood vessel diameter - Contains the respiratory centre o Regulates the rate and depth of breathing - Other reflexes o Swallowing, vomiting, hiccupping, coughing and sneezing - All of these functions are automatic and require no thought Pons - A bulging structure of the brain stem - Pons is the Latin word for bridge o The pons bridges different parts of the brain - Contains conduction tracts which run in two directions o The longitudinal tracts run from the spinal cord to higher brain centres  o The transverse tracts run from the cerebrum (motor cortex) to the cerebellum - The pons contains a sleep centre which regulates rapid eye movement which is something that occurs during sleep - The pons has a respiratory centre which works together with the respiratory centre of the medulla oblongata to regulate respiration Midbrain - The smallest and most superior part of the brain stem - Receives visual, auditory and tactile sensory input generating reflex movements of the head, eyes and body o Eye movement relates to dilation and constriction of the pupil or a change in the shape of the lens Cerebellum - A cauliflower like structure - Sits in the inferior, posterior part of the brain - The cerebellum has an outer cortex made up of grey matter and an inner medulla made up of white matter - The cerebellum is much smaller than the cerebrum - The cerebellum controls locomotion in association with the cerebrum o Walking, running, skipping, ect. - Regulates fine motor control o Writing, using a computer or playing a musical instrument - Controls posture and balance Diencephalon - Made up of the: o Thalamus § The largest part of the diencephalon § Sensory relay centre or “gateway” § Anything you har, see or feel by touch but not smell § Regulates mood, memory and strong emotions like fear and rage o Subthalamus § The area underneath the thalamus o Epithalamus § Made up of the habenula and the pineal gland § Posterior to the thalamus o Hypothalamus § Below the Thalamus § Maintains homeostasis via the endocrine system § Regulates heart rate § Regulates digestive activities (food intake, water balance and thirst) § Controls muscles in swallowing § Controls body temperature by promoting sweating and shivering § Regulates sex drive and sexual pleasure § Regulates mood, and emotions  § Regulates the sleep-wake cycle Cerebrum - Takes up most of the mass of the brain - Most superficial and superior part of the brain - Gyri – elevated tissue or folds - Sulci – grooves - Fissures – deep grooves - The brain can be divided into right and left hemispheres which are divided by the longitudinal fissure - The lateral fissure separates the temporal lobe from the rest of the cerebrum - The central sulcus separates the frontal lobe from the parietal lobe - Lobes o Frontal o Parietal o Occipital o Temporal o Insula Cerebrum 2 - Precentral gyrus – primary somatic motor cortex o Controls voluntary movements in the body, particularly fine motor movements of the hand o Uses skeletal muscle for activities requiring hands or fingers such as picking things up with the fingers o Located just in front of the central sulcus and is a part of the frontal lobe - Postcentral gyrus – primary somatic sensory cortex (AKA primary somatosensory cortex) o This part of the brain receives messages from the somatic sensory receptors in skeletal muscle joints and tendons o These sensations are processed in this area e.g. pain, pressure or temperature o The signals first synapse in the thalamus before going to the postcentral gyrus o Part of the parietal lobe - Frontal lobe o Voluntary motor function o Motivation o Planning o Aggression o Sense of smell o Regulation of emotional behaviour and mood - Parietal lobe o Area which receives most of the sensory input o Does not receive smell, hearing, taste or vision Cerebrum 3  - Occipital lobe o Receives and processes visual input - Temporal role o Receives and processes smell and hearing and also has a role in memory - Insula o Receives and processes taste information Cerebrum 4 - The grey matter of the cerebrum makes up the cerebral cortex o Cell bodies, dendrites, unmyelinated axons, axon terminals and neuroglial cells - This is where consciousness is formed, it allows us to communicate, remember, understand things and be aware of ourselves and any sort of sensations - The white matter is deep to the cerebral cortex and is known as the cerebral medulla o This is made up of myelinated axons o This part of the brain is responsible for communication between cerebral areas and lower nervous system centres e.g. cardiovascular centre , sleep centre, respiratory centre - Corpus callosum o A bundle of fibres known as the commissural fibres o Connects the two cerebral hemispheres together o This ensures the brain all works as one Limbic system - The limbic system runs through the medial aspect of the left and right cerebral hemispheres as well as the diencephalon - Runs around the boarder of the corpus callosum and diencephalon - The limbic system has a role in memory and is referred to as the emotional brain - Expresses emotions though gestures - If you smell a particular smell it could trigger an emotional response or a memory - Damage to the limbic system can cause memory impairment Meninges - Dura mater o Fibrous connective tissue o Periosteal dura § The most superficial meningeal layer which attaches to the inner surface of the bony skull o Meningeal dura § A fine membrane sitting inferior to the periosteal layer § This is continuous with the dura mater of the spinal cord o In some parts of the brain there is a space between the periosteal dura and the meningeal dura, the space is referred to as Dural venous sinus § This cavity contains veins which collect blood that has just nourished the brain and will return to the heart (venous blood) § Dural folds are connective tissue partitions that extend deep into the brain which help hold the brain in place and stop excessive movement of the brain  o In some parts the periosteal and meningeal dura fuse together, the Dural venous sinus doesn’t exist in all parts of the brain o The subdural space contains serous fluid - Arachnoid mater o In the spinal cord this layer is thin, flimsy and fine, like cobwebs. It is similar in the brain o Underneath the arachnoid mater is sub arachnoid space containing cerebrospinal fluid and blood vessels - Pia mater o The deepest meningeal layer o A delicate connective tissue layer containing small blood vessels o This layer sits tightly over the brain and is not removable Ventricles - This word normally means a cavity or chamber such as the ventricles of the heart - The brain has for ventricles which are continuous with each other - The ventricles are lines with ependymal cells - The largest ventricles are the lateral ventricles of the brain. They extend into the cerebral hemispheres (these paired lateral ventricles are considered the first and second ventricle) - The lateral ventricles are continuous with the third ventricle which resembles the head of a bird from a lateral view - The third ventricle is continuous with the fourth ventricle which is located in the brain stem and is continuous with the central canal of the spinal cord Cerebrospinal fluid - Most cerebrospinal fluid is produced by the choroid plexus - The choroid plexus in the brain is made up of specialised ependymal cells, support tissue and blood vessels - Cerebrospinal fluid is a fluid that is found around the brain and spinal cord - The role of cerebrospinal fluid is to protect the brain and spinal cord from trauma and it provides buoyancy to the brain (the brain floats rather than sitting directly on the skull) which reduces the weight of the brain reducing the pressure on structures under the brain - The composition of CSF is similar to the blood plasma but contains less proteins and has a different ionic concentration - The CSF circulates the ventricles and the central canal of the spinal cord as well as the subarachnoid space of the meninges - The cilia of the endymal cells of the ventricles help with the circulation flow Cranial nerves - There are 12 pairs of cranial nerves all named after roman numerals - Cranial nerves emerge directly out of the brain and carry information from the brain to the body and back to the brain - Cranial nerves can be either single or mixed neurons meaning that they either have a just a sensory function, a somatic function or a parasympathetic function or a combination of all 3 Lecture 3 Functional divisions of the nervous system - Autonomic nervous system o Motor (efferent) § Sympathetic § Parasympathetic o Sensory (afferent) - Somatic nervous system o Motor (efferent) o Sensory (afferent) Autonomic vs somatic nervous system Somatic nervous system Autonomic nervous system Effector Skeletal muscle Cardiac muscle, smooth muscle and glands Regulation Controls all conscious and Unconscious regulation unconscious movement of although conscious thought skeletal muscle has an influence Response to stimulation Skeletal muscle contracts Target tissues are stimulated or inhibited Neuron arrangement One neuron extends from the There are two neurons in CNS to the skeletal muscle series; a preganglionic neuron runs from the CNS to an autonomic ganglion and the postganglionic neuron runs from the ganglion to the effector (target tissue) Neuron cell body location Located in the ventral horn of Located in the lateral horn of the spinal cord the spinal cord and autonomic ganglion Number of synapses 1 (motor neuron -> skeletal 2 (neuron to neuron then muscle) neuron to target tissue) Sympathetic and parasympathetic - Sympathetic (‘fight or flight’) o Stimulated in a threatening or exciting situation o May cause deeper breathing, increased heart rate, decreased or halted digestion (this is because blood moves away from the digestive system and towards the muscles), relaxation of the urinary bladder o AKA the ‘E’ division as it is stimulated during exercise, excitement, emergency or embarrassment - Parasympathetic (‘rest and digest’) o This is activated in order to keep the bodies energy usage as low as possible (energy preservation)  o This activates digestion, salivation, formation of tears, elimination of faeces and urine o AKA the ‘D’ division as it is stimulated during digestion, defecation and diuresis (urination) - These responses can serve the same organs but in doing so serve them in opposing ways Sympathetic Parasympathetic Heart rate and blood Increased Decreased pressure Airways in the lungs Dilation Constriction Blood vessels Mainly constriction but No effect vasodilation to skeletal muscles Digestive tract Decreased motility and Increased motility and decreased secretion, secretion, sphincters will constricted sphincters relax Liver Increased glucose released into blood Gall bladder Glands (salivary, gastric, lacrimal, pancreatic) Sweat glands Pupil of the eye Cellular metabolism Urinary bladder Anatomy of the automatic nervous system - The autonomic nervous system is a two neuron system - The cell bodies are located in the lateral horn of the spinal cord and the autonomic ganglion - The location of the cell bodies along the length of the spinal cord is different for sympathetic and parasympathetic divisions o Sympathetic: the cell bodies are found between T1 and L2 (the thoracolumbar division) o Parasympathetic: the cell bodies are found between S2 to S4 and cranial nerve nuclei (craniosacral division) Functional generalisations of the sympathetic and parasympathetic nervous systems - Dual innervation of the of the autonomic nervous system - Opposing effects - Responses generated by both afferent nervous system divisions can regulate o Heart rate o Blood pressure o Airways in the lungs o Digestive tract  o Glands (salivary, gastric, lacrimal) o Pupil of the eye Regulation of the autonomic nervous system - Autonomic nervous system regulation occurs mostly via reflexes o Reflexes are an automatic response to a stimulus, and these are normally homeostatic o Autonomic reflex activity is also influenced by the CNS, in particular the cerebrum, hypothalamus, brain stem and a few other parts which control thoughts, actions and emotions o The hypothalamus integrates the information that’s coming into it and communicates it to other parts of the brain to execute a response o Most autonomic reflexes actually involve a part of the Hypothalamus CNS Component Effect on the ANS Spinal cord Autonomic reflex centre which regulates defecation, urination, erection and ejaculation Brainstem Reflex centre controls tear production , salivation, coughing, swallowing, digestive activities, heart rate and force of contraction, blood vessel diameter and respiration Hypothalamus Integrates the incoming information from the brainstem and the spinal cord and relays any info that goes to higher centres of the brain such as the cerebrum and limbic system Cerebrum and Thoughts and emotions can influence ANS functions through the limbic system hypothalamus e.g. if angry your blood pressure might increase, if you think about your favourite food you may salivate