BIOA02 Module 2 Physiology Notes for EXam

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Department
Biological Sciences
Course
BIOA02H3
Professor
Shelley A.Brunt
Semester
Fall

Description
Nervous System Simple Reflex Arc -Afferent neuron carries sensory perception of pain/stimulus to central nervous system - Goes to higher brain centre or spinal cord - Goes to CNS and synapses with efferent neurons; can act as inhibitory or excitory -Stimulus sensed by a particular receptor cells - Sensors can sense internal or environmental stimulus depending on its type Afferent path: Neurons that are directed towards the CNS also called sensory path Efferent path: Neurons that are directed away from CNS Interneurons: Transmit information between neurons in the CNS, acts like a middle man between the afferent pathway and efferent path way Has 4 Major Steps: Reception: The whole cause and effect of the nervous system starts with the sensory system receptors Detecting the stimuli - There are 3 main types of receptors that sense the stimuli either internal or external  Chemoreceptors which sense a variety of chemical stimuli  Mechanical receptors sense a pressure stimuli  Photoreceptors sense a change in light intensity 1. In all three cases there is a membrane protein that is activated by the stimulus 2. Leads to the opening of an ion channel 3. This causes a change in membrane potential which triggers an action potential 4. Signal gets transmitted to integration centre 2 types of reception: 1. Only a single cell is involved, the receptor cell is directly connected with the CNS. The stimulated action potential goes straight to the brain 2. Indirect connection with interneurons- Sensing of stimuli promotes the release of a neurotransmitter, which causes an action potential that travels to the brain ( basically the receptor cells are not directly linked to the brain… 2 step process) Transmission: The transport of the messages along the nerves and neurons to the integration centres. Integration: The area where neural message is sorted and interpreted, which occurs in the brain or ganglia (a bunch of nerves coming together like a simple brain… in this case we are talking about the spine) Response: Neural message from integration centre is sent to the effectors via the efferent neurons, this is the response to the stimuli Nervous Systems: Divided into two Peripheral Nervous system: Afferent and Efferent neurons that deal with information going in and out of the CNS Central nervous system (CNS): Includes the brain and spine (integrative site) Brain(evolutionary standpoint) is divided into forebrain, hindbrain and midbrain - The forebrain evolved to a larger size for increased complexity in thought and perception - The midbrain got smaller; it is the relay station - Hindbrain is responsible for physiological survival (medulla oblongata and pons mainly), and is the most primitive part of the brain. Only the hindbrain is required to live Peripheral Nervous System: Afferent Nervous system: Receives signal from sensory receptors and relays it to the CNS Efferent Nervous system: Sends Nervous system from the CNS to the other parts of the body. Subdivided into Autonomic and Somatic systems 1. Somatic system deals with the signals being transmitted to the skeletal muscles(voluntary muscles that contract with our conscious control) 2. Autonomic system deals with involuntary processes affecting smooth muscles (involuntary muscles that are stimulated by nerve impulses, hormones and metabolic processes… happens on its own) and glands Has two divisions:  Parasympathetic division: Nerves come out of the brain(cranial and vagus) and some that come out of lower spinal cord - Cranial deals with salivary glands - Vagus nerve supplies nerves to the many organs in the body (heart, lungs….)  Sympathetic division: All the sympathetic nerves are coming out of the spinal cord and pass through the sympathetic chain ganglia  The two systems work antagonistically. If the parasympathetic system stimulates the decrease of heart rate, the sympathetic system will increase the heart rate. Whatever one does the other does the opposite The one exception is the bladder, in which they work together to perform the process of urination (on contracts bladder the other will relax it) Neurons and the functional cells of the nervous system  Dendrites: Receive sensory information  Axon Hillock: Electrical signal generation  Axon: Transmission and are covered by myelin sheath  Synaptic Terminal and Synapse: Cell to cell communication  Composition of nerve: A nerve consists of many neurons or nerve cells  Function of the nerve as a whole: a function of the amalgamation of activity in all the neurons within the nerve  Picture: 2 neurons (one on left is connected to the one on the right)  The neuron on the left—the action is making connections on the dendrites (and sometimes on the cell body) with neuron 2  Connection of axon of 1 cell to the dendrite of cell body of the nd 2 cell is referred to as synapses and location is referred to as synapses terminal (thus neuron on the left is synapsing the neuron on the right)  Coming off the cell body are processes called dendrites  One neuron signals to another neuron by causing connection from neuron 1 onto the dendrites of neuron 2  Coming of the cell body is a large process called Axon  Axon: long fibers that is going to carry nerve signals or electrical impulses from 1 neuron to the next neuron  Axon Hillock: the area that moves just into the cell body to the axon  Also called ‗trigger zone‘, ‗spike initiation zone‘, ‗action potential generator zone‘  This is the area which the electrical impulse that is going to be propagates (or move along the axon) is being generated  This is where the action potential is going to be generated then the action potential moves down the axon  In general: some electrical events that result in larger changes in membrane potential that then propagates along the axon  Process: Dendrites have the receptors that cause depolarization which causes the axon hillock to produce action potential-> gets sent along the axon-> stimulates dendrite and synapse occurs Glial Cells (support cells) *Support cells of the nervous systems that are responsible for the structural integrity and normal functioning of neurons(supply nutrients and remove waste) - Microglial cells get rid of waste - Astrocytes anchors neurons in brain and creates a blood brain barrier that prevents from crossing the blood into the brain - Oligodendrocytes (CNS) and Schwann cells (PNS) form the myelin sheath -> Myelin sheath is a plasma membrane that wraps around axon acting as an insulator to allow optimal transmission of action potential… it does not cover everything though there are small gaps called nodes of ranvier that have ion channel -> Schwann cells form myelin around axons in the peripheral nervous system  Myelin consists of concentric layers of plasma membrane  Lipid bilayers have a low permeability to ions good for action potential  Myelin: layers of lipid that wrap around the axon  Myelin sheath  acts as insulation and prevents ions from crossing the axon wherever it is covered with myelin  Important for nerve conduction in vertebrate species allows for them to have fast rates of nerve conduction compared to invertebrates which is slow The Action Potential: The reversible change in the electrical potential of a nerve cell‘s membrane from negative-> less negative and back again - Resting potential is the electrical potential when there is no stimulus - Depolarization is when the membrane becomes less negative(more positive) Refractory periods: - Repolarization is the phase when membrane potential starts to drop (more negative) - Hyperpolarization is when electrical potential is below than the resting value - Threshold potential: the membrane potential when the action potential is produced…. Has to be at a specific range for the action potential to occur… say threshold is -50mv and if you get -60 nothing will happen Resting potential: - The electrical potential of a cell membrane when there is no stimulus around -70mv to -100mv depends on the organism - The negative potential is the due to the distribution of ions on the inside of the membrane and outside. The inside is less positive than the outside… which means there is a larger concentration of positive ions outside in correspondence to the inside of the membrane… - The Na+ concentration is greater outside than the Na+ concentration inside - The K+ concentration is greater inside than the K+ concentration outside Generating an action potential - Generated by the movement of Na+ and K+ ions through, which changes the membrane potential - Sodium channels have to gates:  Activation gate: Is closed at resting potential but quickly opens when threshold potential is reached  Inactivation gate: Open at the resting potential, starts to close very slowly when the threshold potential is reached 1. Stimulus from sensory receptors increase membrane potential slightly  This causes the opening of some of the Na+ activation gates  This increase the membrane potential from resting to threshold  When threshold potential is reached and surpassed slightly all the Na+ activation gates open  Large amounts of Na+ enter from the extracellular fluids  Depolarization of membrane occurs 2. At the peak the Na+ inactivation gates start to close and at the same time the closed K+ gates open to remove K+ from the membrane to bring potential back down  At this point there is no more Na+ ions entering the cell  Now the k+ ions are leaving the membrane 3. Repolarization: Reduction of membrane potential towards rest  The removal of K+ ions makes the membrane more negative  At threshold the Na+ inactivation gates open and the activation gates close 4. Hyperpolarization occurs due to excess K+ ions moving out of cell before the gates close 5. Sodium Potassium channels open to balance potential back to the resting potential Process gets repeated along the length of the axon until synapse is reached Propagating an action potential  In vertebrates the action potential jumps in the axon from one node of ranvier to the next. Saltatory Conduction: 1. Action potential is generated 2. Na+ enters the axon and spreads on to the next node 3. Elevation of Na+ depolarizes the membrane of the next node and opens up more Na+ channels 4. Action potential moves from one node to and next and keeps going *no action potential forms in the area of the myelin because myelin is an insulator and no ions are able to move in and out Myelinated vs. Non-myelinated axon - Myelination allows for rapid conduction of action potential - In Invertebrate species: There is no myelination, and so each portion of the membrane has to be depolarized for the continuous movement of the action potential  Slow and inefficient Refractory period Action potential can only go in one direction because of what is known as a refractory period: - When an area is stimulated it goes into refractory period, which means it cannot be further stimulated - There are two phases of refractory periods: absolute and relative refractory period - Immediately after the beginning of the generation of action potential: we go into an absolute refractory period (cannot generate another action potential if given another stimulus) - Move into a secondary phase called relatively refractory period: where a strong stimulus can generate a second action potential o The strength of that stimulus diminishes as we move forward in time  Absolute Refractory Period + 1) During depolarization phase of AP the opening of Na channels has already been set in motion and cannot be affected by a second stimulus. 2) During repolarization phase of AP, the inactivation gate is closed and cannot be opened by a second stimulus.  Initial state of action refraction period any stimulus given will not result in 2daction potential to be generated  Why?  At point, cannot generate action potential since all of the sodium channels are open (sodium is already coming in)  On the way down in the repolarisation phase the first repolarisation phase cannot generate another action potential via second stimulus because inactivation gaits are closed  Inactivation gaits close as membrane potential goes upwards (close in response to electrical stimulation)  Relative Refractory Period 1) Occurs immediately after absolute refractory period. 2) A second AP can be generated with a strong stimulus (opens closed activation-gates).  Where a second stimulus CAN cause a second action potential nd  Reason this is relative refractoriness is because large stimuli can trigger a 2 action potential (in the beginning phases smaller stimuli can cause action potential as we move along)  In this period, the activation gates of sodium channels are closed (have a lot of sodium channels) nd  2 stimulus can cause action gates to open prematurely (they are going to open on their own as membrane potential begins to rest, but they can be triggered to open by a second stimulus) nd  Thus, can have 2 action potential generated in the relative refractory period because thndstimulus opens the activation gaits  Cannot have second stimulus give an action potential in the absolute period since 2 stimulus cannot reopen the inactivation gait Synaptic Transmission: Communication between neurons 1. Electrical Synapse: 2 cells are connected by gap junctions, ions flow from one cell to another directly carrying current from one cell to another 2. Chemical synapse: Neurochemicals are released in response to the action potential on the first cell, the NT bind to the next cell as a stimuli Chemical Synapse:  Shows the progression of events action potential coming downaction potential causes the opening of calcium channels  increase of calcium into the cell causes membrane bound vesicles with neurotransmitters to come and fuse with the plasma membrane and release the neurotransmitters  neurotransmitters bind to the receptors on the post synaptic cell (receptors are referred to as ligangated ion channels)  Receptor for the neurotransmitters is itself an ion channel Types of chemical synapse: st nd  In both cases, neurotransmitters are released into an area between 1 cell and 2 cell  bind to the receptors on the post synaptic cell  Receptor is an ion channel  1 example: ion channel is a sodium channel so the binding of neurotransmitter to receptor causes binding on sodium channel, so sodium can go into the cell and membrane potential can go up  generator potential or receptor potential  Small polarization caused by the movement of sodium through these liganated ion channels is going to be enough to bring the membrane potential up to threshold for action potential firing nd  2 example: inhibitory neurotransmitter  The receptor is an ion channel, but it is a chloride ion channel  binding of neurotransmitter to receptor causes binding on chloride channel (allows negatively charged chlorine ions into the cell)  As we bring negative ions into the cell, we LOWER the membrane potential (membrane potential is being hyperpolarized) Thus, makes it harder for the signals to come in raise membrane potential up to the threshold and allow action potential to be generated Lecture 3: Endocrine System Physiological Regulatory systems: Nervous system: Neural networks, fast signalling  Command and regulatory system Endocrine System: Endocrine glands secrete hormones that mediate slower but longer lasting responses  More regulatory than command  Releases hormones or other substances that circulate through the blood  Can be rapid or slow and long lasting depending on the type of hormone or response Higher cortisol accelerates aging process Pineal gland in the brain produces melatonin which is needed for sleep Common endocrine structures: Hypothalamus: A structure that releases hormones into the pituitary that stimulates or inhibits other hormones Thyroid Gland produces thyroid hormones T3 and T4 necessary for metabolism Parathyroid maintains calcium levels Adrenal gland produces steroids and aldosterone (corticosteroid hormone that regulates ions in the kidney) Pancreas aids in digestion and maintains blood sugar levels through insulin and glucagon Types of cell signaling: Circulating hormone: The classical hormone that is produced by a gland and circulates to the target cells and bind to the receptor which leads to a series of secondary messenger systems or induces transcription/inhibition of specific genes Neuroendocrine Signalling: Hormones secreted from the nerve are called neurohormones - Instead of glands producing hormones, the nerves produce and secrete hormones-> created in the extracellular fluid-> stored in the synaptic terminal - -> excreted-> diffuses into the blood-> circulates to target cells Paracrine and Autocrine Signalling- Released from endocrine cells Autocrine: hormones that act on cells that produced and released them - Where a cell would release a particular hormone and that hormone feeds back on the cell that released it Paracrine: Hormones that is able to diffuse through extracellular fluid and act on nearby cells - They do not circulate through the blood, but just act on the nearby cells that are within the extracellular fluid ie) cell released acetylcholine and dopamine which can act in both paracrine and autocrine signalling  Acetylcholine acts as paracrine whereas dopamine acts as autocrine  Often you can get an autocrine substance which has an autocrine effect on the cell which either inhibits the release the of paracrine substance or even accelerates the release of paracrine substance Types of Hormones(4 major types): 1. Amines: Amine hormones have an amine group and are derived from tyrosine (hydrophilic)  Thus, start off with phenylalanine then Tyrosine, then 3 substances Dopamine, Norepinephrine, Epinephrine  Norepinephrine: is also known as adrenaline  Epinephrine: ‗Epi‘ means to surround and ‗nephro‘ means kidney  The adrenal gland which synthesizes and releases the hormones is wrapped around the upper portion of kidney (surrounds the kidneys)  These hormones are referred to as catecholamine since they contain both a catechol group (benzene ring with 2 hydroxyl ion) & an amine group  Both dopamine and Norepinephrine can function as neurotransmitters  Epinephrine and Norepinephrine can function as hormones  Dopamine cannot function as hormones  Norepinephrine can either be a neurotransmitter or hormone  Dopamine is just a neurotransmitter (not a hormone)  Epinephrine is just a hormone (not a neurotransmitter) 2. Peptide Hormones(protein) - Proteins can also be hormones(hydrophilic) ie) Angiotensin 1. Liver produces angiotensinogen and releases it all the time 2. Renin released by kidney(sometimes) upon a stimuli (such as low blood pressure) acts on angiotensinogen and converts it to angiotensin I 3. Angiotensin I circulates in the blood and when in the lungs ACE converts it to angiotensin II 4. Angiotensin II acts on blood pressure by narrowing blood vessels and has effects on ion-regulation  Triggers adrenal cortex to release aldosterone 3. Steroid hormones- like cortisol - Derivatives of cholesterol and are hydrophobic - They bind to the receptors within the cell as they are able to pass through plasma membrane of cell - Transported in the blood via carrier proteins 4. Fatty Acids(used only in insects) - Fatty acids can also act as hormones… but only in insects the other three are important for vertebrates Hormone Receptors: Affect the target cell by binding to a cell surface receptor or diffuses directly into the cell and interacts with receptors in the nucleus or cytoplasm Cell Surface Receptors - Usually steroid hormones as they are polar and the membrane is polar allowing them to diffuse over - Hormone secreted by gland-> into blood-> diffuses into extracellular region-> binds to a surface receptor (signal transduction)->can affect many factors ..-> cytoplasmic response-> either a series of intermediate reactions or secondary nuclear response Intracellular Receptors: - Usually peptide hormones are able to do this due their non-polar/hydrophilic capabilities - Same steps as cell surface hormones but they bind to receptors within the cell cytoplasm - Ultimately affects DNA transcription Ie) Example of intracellular receptor: aldosterone  Hormone released by the outer regions of adrenal cortex (# of signals that cause the adrenal cortex to release aldosterone which some of them is angiotensin 2, high plasma potassium)  In general: We see aldosterone moving into the cell binding with the receptor receptor hormone complex moves into nucleus alters gene transcription  Result: increase in transcription increase in protein synthesis Increase synthesis of 3 things: one of which is the Sodium channels (sodium channel can get inserted into a plasma membrane)  occurs in the kidneys  Occurring in the kidney tubule cell (more to the response than a sodium channel)  Bottom line- Aldosterone stimulates K+ secretion and Na+ reabsorption in the kidneys(stimulated by high plasma K+ or low Na+ in blood) Endocrine Glands - The hypothalamus produces two hormones that act on the anterior pituitary a) Releasing hormone(RH) b) Inhibiting Hormone(IH) - RH and IH are released directly from the hypothalamus to the portal vein  Moves into the capillary bed of the anterior pituitary (Hypothalamic pituitary portal system)  In the anterior pituitary it stimulates the release or inhibition of a series of hormones Hypothalamus and posterior pituitary - The hypothalamus produces ADH and oxytocin (they are neurohormones) - Transported down the nerve terminal that joins the posterior pituitary - When stimulated the hormones are secreted from the posterior pituitary and travel in the blood to target areas Ie) ADH stimulates the kidneys to retain water… ADH is inhibited by alcohol (that‘s you pee frequently) Hypothalamus and Anterior Pituitary  The hypothalamus produces: 1) Releasing hormones (RH) 2) Inhibiting Hormones (IH)  RHs and IHs move to the anterior pituitary via a portal vein. There they trigger (or inhibit) the release of hormones synthesised by endocrine cells in the anterior pituitary.  The hypothalamus is also the body‘s thermostat – the centre of temperature regulation. Anterior Pituitary hormones: The anterior pituitary releases a series of hormones when stimulated by the hypothalamus - Thyroid stimulating hormone that stimulates thyroid gland to release thyroid hormone to increase metabolism - Adrenocotropic hormone (ACTH) helps regular fluid balance (adrenal cortex) - Many of which are tropic hormones- that are released into the blood stream to stimulate other hormones The hypothalamic pituitary thyroid axis 1. Hypothalamus produces thyroid releasing hormone (TRH)  Released into the capillary bed  Transported to the portal vein  Moved to the anterior pituitary  Releases thyroid stimulating hormone (TSH)  Goes to thyroid gland and releases thyroid hormones T3 and T4  Both hormones have the same effect of stimulating the rate of metabolism to increase and regulate growth and development 2. T3 and T4 can feedback inhibit the release of TRH and TSH if the levels are too high Thyroid and Parathyroid glands: Calcium regulation - Thyroid gland releases calcitonin when Ca2+ levels are too high - The parathyroid gland releases parathyroid hormone when Ca2+ levels are too low 1. When Ca2+ levels are too high calcitonin is released from the thyroid gland which stimulates the deposition of Ca2+ into the bones and reduces the uptake of Ca2+ in the kidneys to lower the Ca2+ levels to main homeostatic balance 2. When Ca2+ levers too low parathyroid gland releases the PTH into the blood stream which then stimulate the release of Ca2+ from the bones and ensure the uptake of Ca2+ in the kidneys and *only in the presence of vitamin D increases the Ca2+ uptake from the intestines Hypothalamic- Pituitary- Adrenal Axis  Review: Adrenal glands sit on top of the kidney they have 2 parts; inner cortex and outer medulla inner cortex produces steroid hormones, the medulla produced catecholamine  Adrenal Gland is a general stress response gland  Cortisol: initial stimulus is low blood glucose  triggers hypothalamus to release corticotrophin releasing hormone which stimulates the anterior pituitary to release ACTH or adrenal corticotrophin hormone  stimulates the adrenal cortex to release cortisol  Cortisol has a number of effects which causes blood glucose level to increase  Cortisol has negative feedback effects: inhibits the pituitary from releasing ACTH and also inhibits the hypothalamus from releasing the corticotrophin releasing hormone Process: - The hypothalamus produces corticotrophin releasing hormone when stimulated by the decrease in blood sugar levels  Portal vein  Anterior pituitary  Releases adrenocorticotropic releasing hormone (ACTH)  Travels through the blood  Stimulates the anterior region of the adrenal gland cortex to release cortisol (glucocorticoids)  Cortisol causes the breakdown of glycogen to glucose, lipids to fatty acids and protein to amino acids *Cortisol can inhibit CRH and ACTH - Short term hormones are released from the adrenal medulla for short term stress response - Adrenal cortex releases hormones for long term stress response - Adrenal Medulla releases adrenaline and noradrenaline to optimize cardiovascular and respiratory functions The Adrenal Cortex and Aldosterone - High plasma K+ or low plasma Na+  Stimulates adrenal cortex  Releases aldosterone and circulates in the blood  Moves into kidney cells and binds to receptors  It either lowers K+ or raises Na+ in plasma  Opens gates that stimulate Na+ reabsorption and K+ secretion The pancreas and Islets of Langerhans Pancreas is a leaf like structure that sits under the stomach that has endocrine function and exocrine(releases hormones through a duct into an epithelium) - Secretes digestive substances into small intestines (exocrine) - Endocrine cells form islets to control blood glucose level a) Beta Cells- Releases insulin(chaperone or move glucose into cells) when blood glucose levels go up to decrease blood glucose levels in the blood b) Alpha Cells- Release glucagon(breaks down glycogen to produce glucose) when blood glucose levels go down to increase blood glucose levels in the blood Regulation: 1. When plasma glucose levels are too high Blood glucose goes up insulin released Blood glucose goes down a. When blood glucose goes up beta cells and pancreas release insulin the insulin is going to trig in liver and other organs to take glucose up  in the liver, it is also going to stimulate to produce a molecule called glycogen which stores polymers of glucose organs take up glucose, so blood glucose goes down 2. When plasma glucose levels are too low Blood glucose goes down glucagon is released blood glucose goes up a. Alpha cells in pancreas release glucagon  signals liver to start breaking down glycogen and release glucose in blood blood glucose goes back up again Diabetes Mellitus 1. Type 1 is insulin dependent and the cells in pancrease do not produce insulin (this is due to the failure of beta cells to releases insulin. Treated by insulin injections 2. Type II is due to metabolic reasons (obesity) there is a lack of response by target tissues to take up the insulin Long term Effects Atherosclerosis: Also known as heart disease that leads to stroke due to the narrowing of blood vessels Reduced Peripheral circulation deals in slow healing of wounds Blindness (diabetic retropathy) in which blood vessels are damaged due to the narrowing of arteries and lack of blood flow damages the eyes Pineal Gland  located within brain  produces melatonin from amino acid tryptophan  secretes melatonin into blood  primary functions of melatonin  controls biorhythms (based on light/dark cycles)  release stimulated in dark  light inhibits release of hormone  related to biological rhythms associated with reproduction  secretes a substance called melatonin  regulate biorhythm and helps us sleep  Its release is triggered by darkness Skeletal Muscles Neuromuscular junction: - Muscles are innovated by motor nerves - The neurotransmitter is acetylcholine - An action potential comes down the nerve and sets forth a series of events that ultimately release Ach  Ach gets released into the synaptic cleft and then bind to the muscle cells cell membrane (sarcolemma)  Ach receptors are called nicotine-receptors and causes the muscle cell to depolarize  Causes a series of events that allows for Ca2+ release into muscle cell that enables muscle contraction as long as ATP is present Skeletal Muscle Structure - The basic unit of muscle is a cell or a muscle fibre, long fibres that run along the length of the muscle are multinucleated - Muscle fibres are bundled together to form a Fascicle  Made up of repeating units called Myofibril which are composed of two types of contractile filaments a) Actin- Thin filament b) Myosin- Thick filament - The myosin are surrounded by actin - Sarcolemma: plasma membrane of muscle cell - Sarcoplasmic reticulum: Site of intercellular calcium storage - Sacromere: a contractile unit Actin- Thin Filament - Composed of double helix  Each strand is made up of a single monomer g acting and forms a chain  Each monomer has a binding site for myosin molecule  This binding allows the sliding over - Interacts with several proteins - Tropomyosin is a long fibrous protein that covers the binding sites on Actin  Not possible for binding and sliding - Troponin: Is a protein complex that is bound to the tropomyosin  In the presence of Ca2+ troponin changes configuration that causes the tropomyosin to move off the binding sites Myosin- Thick Filament - Consits of a two intertwined components of a tail and head which are made up of thousands of myosin molecules - Myosin molecules bind at their tails such that the heads extend in the opposite direction - Myosin head has 2 binding sites a) One for binding to actin b) ATP binding site: ATP hydrolyzes ADP for contraction and relaxation The myosin head: Energy States The head of the myosin can exist in a low energy state or a high energy state - If the head of the myosin is pointed to the left that it in a low energy state - If the head of the myosin in directed to the right it is a high energy state - Goes from high energy state to low energy state after sliding - The binding of myosin heads to the actin binding site is called a cross bridge Regulation of Muscle Contraction - Action potential comes down motor nerve - Releases Ach->Ach binds to receptor and depolarizes sarcolemma - Generates action potential and causes Ca2+ to be released from sarcoplasmic reticulum - Ca2+ starts the process by binding to the troponin complex - Tropomyosin changes position - Myosin binding site bind to actin binding site - Forms cross bridge cross bridge which causes contraction *Before that happens previous cycle of force generation must end Force generation in muscle cells - Cycle starts at the end of the previous cycle when the myosin head is bound to the actin in low energy state  In order for next contraction termination of current contraction is required  Hydrolyses of ATP will move configuration from low energy state to high 1. Rigour: when the two sites are bound together and myosin is in low energy state  ATP is required to bind to site on myosin head  Cross bridge detaches  Still remains in low energy state 2. ATP hydrolysis  Myosin head needs to go to high energy in order for new contraction  ATP-> ADP+Pi causes the myosin head to go from low to high energy due to the energy released from the hydrolysis  The products are bound to the ATP site 3. Actin Myosin Binding  Myosin head pivots and pushes actin molecules across it  When myosin head binds to actin Pi is released 4. Power Stroke  Actin filament is pushed inward toward the centre  This will cause myosin to go to the lower energy level  ADP is released  Back to rigour and they are still bound together *After contractile process Ca2+ is taken back into sarcoplasmic reticulum because it comes off the troponin complex -> Tropomyosin goes back and blocks binding site when the ATP unbinds the two sites *Waits for new action potential Muscle Twitch - Is defined as the unit of muscle contraction and is an all or none event - Twitches happen many times per second in response to stimulus Latent Period: Events leading to the cross bridge formation Contraction: Tension develops Relaxation: time between peak tension and zero tension - Takes about 100-120ms Isometric Twitch - Tension develops in muscles but does not shorten - Occurs when a muscle attempts to move a load that is greater than the force produced - There is contraction but no shortening of muscle (me trying to deadlift 300) Isotonic Twitch is when there is shorting of the muscles Cause of Muscle Twitch - Action potentials can occur in a muscle fibre for a single muscle twitch - If an action potential arrives before a twitch is completed the twich can super impose -  Summation: The muscle is stimulated repetitively such that additional action potentials arrive before the end of a twitch. The twitches superimpose on one another leading to a force greater than that of a single twitch.  action potential during twitch causes accumulation of tension  Complete (fused) tetanus: Caused by constant, very high frequency stimulation. Individual twitches are indistinguishable; tension rises smoothly and then reaches a plateau.  build up of tension  When summation ceases: tension begins to drop (muscle cannot contract forever)  Each action potential generates a twitch Tetanus Lock jaw Bacteria clastridium tetani  Produces tetanospasm (neurotoxin)  Inhibits motor neurons  Motor neurons become over excited leading to over stimulation of skeletal muscle Neurons keep firing->stimulate muscles -> extreme contractions Regulation of strength of muscle contraction Motor unit= motor neuron + fibres - One motor neuron can innovate multiple fibres - One fibre is only innovated by on motor neuron *Motor units are activated in such way that they either produce small contraction or a large contraction, and they get activated by size (smaller ones are always first) *Size principle: if you need a small amount of muscle tension only motor units consisting the needed amount will be used *Muscle Tension is proportional to the amount of Ca2+ present (because it is the stimulating factor) **The all or none principle states that the signal coming to the muscles either causes depolarization followed by contraction or it does not. The strength of the stimulus is not relevant as long as it passes the threshold. Circulatory Systems Closed Circulatory system: - , the series of vessels are all connected - Blood flows from the heart to arteries to capillaries to veins back to the heart again - Very high pressure system that is maintained to ensure high rate of flow - In humans there are 2 closed circuits a) pulmonary system to the lungs and back (low pressure) b) Systemic system to the tissues (high pressure) Open Circulatory system: - haemolymph is pumped from the heart, ―dumped‖ into the body cavity or sinuses in the tissues, picked up by veins and returned to the heart - Hemolymph is a mixture of blood and extracellular fluid - Low pressure system due to no continuous vessel - Lack of regular to different organs because it is not very directed - Not as effective as closed system Ie) In crayfish the heart-> extraceullar space and bathes the tissues and organs Human/Mammalian(birds) heart - Consists of two atria and two ventricles (one on the left and one on the right) - Right side receives blood and pumps blood to the lungs - Left side receives blood from lungs and pumps it to the body Flow: - Superior and inferior vena cava-> right atrium-> through the atrial-ventricular valve(controls blood flow)-> right ventricle - Semilunar valve-> pulmonary arteries -> lungs -> pulmonary veins -> left atrium ->AV valve -> left ventricle -> semilunar valve-> Aorta -> systemic circulation - Right side pumps to lungs - Left side pumps to systemic circuit Arteries: Vessels that pump blood away from the heart (oxygenated except for pulmonary artery) Veins: Blood flowing back to the heart (deoxygenated except for pulmonary vien) Fetal Mammalian Heart: - The fetus receives blood from the placenta via the umbilical vein which flows into the right atria - In utero, the fetal lungs are breathing amniotic fluid rather than air. As such, the lungs are not involved in obtaining oxygen. As a result of this, there is no point sending blood to the lungs (there is no oxygen there to move into the blood). - Therefore, just like the diving crocodile, blood is shunted away from the lungs and is done in two ways 1) Right atrium can move blood directly to the left atrium via the Formane Ovale avoiding the lungs 2) Some blood that goes to the lungs can go into the second hole ductus arteriosus directly from right ventricle to the aorta  It‘s a hole that is between pulmonary artery and aorta Cephalopods (squids, octopi) circulatory system - They have the most advanced closed system - They have a total of 3 hearts  2 branchial that are connected to the gills equivalent to mammals right side of the heart  1 systemic that pushes blood to the tissues like human‘s left side of the heart - Deoxygenated is pumped through the branchial hearts into the gills where they are oxygenated - Oxygenated blood flows through the systemic heart into the systemic system *cephalopods do not have haemoglobin, so their blood is always blue but the shade gets darker with increase in oxygen concentration Fish Heart - 4 chamebered heart but the most simple vertebrate heart - Blood from venus system flows into the sinus venosus - Than flows through valve into an atrium - Blood then passes through the atrioventricular valve into a muscular ventricle. Finally blood moves through the bulbal valve into the bulbus arteriosus - The bulbous arteriosus expands when the ventricle contracts and relaxes when ventricle relaxes and blood flows into the systemic system Circulation in gill fish - Heart-> ventral aorta -> Gills-> dorsal aorta-> systemic circulation -> heart - Blood is pumped across two capillary beds (ventral and dorsal) and so there needs to be enough pressure - Deoxygenated blood from the systemic system
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