Physiology Unit 1 PDF

Physiology Unit 1 (Weeks 1-3) Reading 1: Understanding Mass and Compartments Homeostasis Refers to the maintenance of relatively constant conditions in our bodies o In order to maintain this our physiological systems need to maintain, increase and/o...

Physiology Unit 1 (Weeks 1-3) Reading 1: Understanding Mass and Compartments Homeostasis Refers to the maintenance of relatively constant conditions in our bodies o In order to maintain this our physiological systems need to maintain, increase and/or decrease the amount of a substance in specific compartments The amount of a substance in a specific compartment will be referred to as mass Mass is the first component of the mass balance model Examples of masses o Amount of potassium ions inside a cell (from unit 1) Error! Filename not specified. o Amount of glucose in our blood (from unit 2) Error! Filename not specified. o Amount of oxygen in our alveoli (from unit 3) Important to remember masses exist in compartments o Mass= potassium ions; compartments = inside a cell Reading 2: Same Substances in Different Compartments Mass refers to the amount of a substance in a specific compartment Examples of how the same substance can exist in two different compartments o The temperature inside the house (m1) and the temperature outside the house (m2) o The amount of water in a drain pipe (m1) and the amount of water in a bathtub (m2) o The number of people in the boarding line (m1) and the number and the number of people on an airplane (m2) o Represents different masses because the mass refers to the amount of a substance in a specific compartment Reading 3: Understanding Inflow and Outflow The amount of a mass in a specific compartment is determined by two factors: inflow and outflow Inflow o Is the rate the substance is being added to the compartment Outflow o Is the rate that the substance is being removed Example of the components of mass balance is the amount of water in a bathtub (mass in compartment)  o Opening that tap increases inflow o Opening the drain increases outflow Masses may have multiple inflows and outflows Reading 4: Understanding How Changes in Inflow and Outflow Affect Mass Mass can increase or decrease depending on the rates of inflow and outflow o Mass increases o Mass decreases o Mass does not change Possible changes in inflow and/or outflow that cause an increase in mass o Inflow increases and outflow does not change o Outflow decreases and inflow does not change o Inflow increases and outflow decreases o Outflow increases a little but inflow increases a lot o Inflow decreases a little but outflow decreases a lot Possible changes in inflow and/or outflow that cause a decrease in mass o Outflow increases and inflow does not change o Inflow decreases and outflow does not change o Outflow increases and inflow decreases o Inflow increases a little but outflow increases a lot o Outflow decreases a little but inflow decreases a lot Possible changes in inflow/or outflow that cause mass to not change o Inflow and outflow do not change o Inflow decreases and outflow decreases at the same time (changes in inflow and outflow are equal o Inflow increases and outflow increases at the same time (changes in inflow and outflow are equal) In every physiological system there is always an inflow and outflow for every mass Masses are regulated by the balance between inflow and outflow A change in mass means there is an imbalance between inflow and outflow Maintenance of homeostasis involves o Detecting changes in masses within compartments o Activating responses that alter inflow or outflow for that compartment The concept of homeostasis applies to every physiological system in our bodies/cells of other living things Lecture 2: Deciding to Move Sees open lane to net and drives o Visual stimuli is sensed in the brain and interpreted o Decision to drive is made o Signal travels to muscles and movement to begin o Sees open path to net the visual stimuli activates action potential in optic nerve traveling to brain synapses at back of the brain o Visual stimuli afferent signal travels from the eye to brain o Brain interprets signals o Decision to move is made Control of voluntary movement o Limbic system o Motor cortex o Cerebellum o Basal ganglia o Brain stem and spinal cord Limbic system o Responds to afferent signals and where the decision to move actually originates o Responds to sensory afferent input o Origins of voluntary movement Motor cortex o Neurons control movement of the different areas of body o Primary motor cortex is neurons within the PMC control movement o Premotor cortex generate the complex neural signals that cause complex movement o Excites the PMC o Rarely exert simple contractions Bicep curl o Most of the time doing complex movements Walking hamstring, calf, feet etc. Require specific order of contractions with specific timing relative to Premotor helps with this to perform complex Basal ganglia o Executes patterns of movement activity o Closed movement o Helps organize contractions Closed skills such as writing pitching darts etc. o Controls speed and size of contractions Walking wants large in quad smaller in calf o Organizing not changing based on outside stimuli o Helps motor cortex organize o Needs helps from cerebellum once open Cerebellum o Interprets incoming info o Controls timing, sequence, and intensity of motor patterns  o Cerebellum corrects movements o Reaching out to grab glass, glass starts to fall you can catch the glass because of cerebellum correcting movement o Improves overtime o Gets better at performing open skills Shooting basketball off balance, catching a ball on the run o External info gathered and helps execute what we are trying to do Brain stem and spinal cord o Signal transported via the motor nerves to the muscle and movement occurs Control of voluntary movement o Action potentials generated in the limbic system Spontaneously generated AP? Response to sensory input o Aps excite appropriate areas of the motor cortex o Travel through the basal ganglia where order, and size of movement is sorted (closed) o Back to motor cortex and out the brain via the cerebellum o Cerebellum compares actual movement (open) to desired movement, makes corrections o Aps leaves brain through brainstem, spinal cord and effect motor neurons and excited muscle Sees open late to net and drives o Decision to move is made o Efferent signal travels to muscles and movements begins Switching hands (MJ DUNK) o Sees he isn't going to make the dunk Interprets that sensory info changes to left hand Afferent signals Interpretation Decision Efferent signal and movement o Switches ball to other hand Afferent signals Interpretation Decision Efferent signal and movement o Lays ball in (perfectly) Action potentials travel along afferent and efferent nerves  o Respond to lots of different stimuli Lecture 3: Neural cell physiology Neural cells-neurons Dendrites receive incoming signals and pass them on to other areas of the cell o Come from other cells or stimuli o Multiple per neuron o Contact with others Cell body soma o Resembles a normal cell o Carries out functions required for neuron to survive Axon o Originates at axon hillock Location of trigger zone o Conducts AP o Terminates synapse o Cause contraction of muscle Depolarization starts on dendrite into cell body if big enough hits neuron and activates AP Synapse o Site of communication between neurons and other cells Neural cell communication 1. Depolarization of cell body  2. Initiation of AP at the axon trigger zone 3. Conduction of AP 4. Release of neurotransmitter from axon terminals 5. Neurotransmitter excite/inhibit postsynaptic cell Depolarization of cell body Membrane potential o Concentration gradients o Membrane permeability o Na-K pump Membrane potential Potential for change The potential for change in charge in the inside of a cell Potential for inside to become negative Potential change in charge inside a cell Many small molecules positive or negative o Sodium outside o Potassium inside If ions move they change the charge of the cell o Add +sodium to cell the cell becomes positive The potential to move sodium to move in the membrane potential is high and positive o Potassium to diffuse out the cell becomes negative Loosing positive ions Flow Pressure gradients And conducts deltaP X k= FLOW deltaP is pressure gradient o =P high - P low Calculating membrane potential Diffusion occurs down a concentration gradient Pressure gradient Diffusion will always proceed to equilibrium o Allow flow we go till no pressure gradient left Potential for change in gradient not amount of diffusion Because ions are changed not just charge in concentration gradient but also charge of cell Potential for charge in charge inside cell  Resting is 12 Positive charge +12 Diffuse Charge now 0 Potential change in charge was -12 Potential change in charge inside a cell Cells have a higher intracellular concentration of k+ K creates diffusion gradient + creates electrical charge Membrane potential for k+ = -94mv Cells have a higher extracellular concentration of na+ Na creates diffusion gradient + creates electrical charge Membrane potential for na+ = +61mv Resting membrane potential is not -33mv Because : o Na+/k+ pump Flow = delta p x k K= conductance K= permeability If membrane is no permeable positive ions will not diffuse and will therefore have little effect on membrane potential If membrane is there is potential for diffusion ion and will continue to membrane potential Existence of membrane potential makes depolarization possible Without them we couldn’t initiate action potentials o Sense our environment o Move our bodies o Regulate homeostasis Leak channels Cell membranes have open channels that allow both na and k to cross membrane These channels allow 100x more k cross than na More permeable to k and it contributes more to resting potential Primary active transport Energy for transport is derived directly from ATP Move molecules against the concentration gradient Example sodium-potassium pump Resting membrane potential 1. Concentration gradients of na and k 2. \permeability of membrane for na and k 3. Concentration of na and k pump Lecture 4: Membrane potential Concentration gradients of Na+ and K+ Permeability of membrane for NA+ and K+ Contribution of the Na+ and K+ pump Existence of -70 to -90 resting membrane potential makes depolarization possible Without them we couldn’t initiate action potentials o Sense our environment o Move our bodies o Regulate homeostasis Changes in membrane potential Movement away from the equator= polarization Depolarization of cell body Understand o what is membrane potential? o The factors that contribute to resting membrane potential Concentration gradients Membrane permeability Na-k pump o How does depolarization occur Membrane channels Effects of neurotransmitters on membrane channels and membrane potential Summation Potential change in charge inside a cell How could we depolarize this cell? o Make cells less negative/more positive o Flow= deltaP x K Simple diffusion For membrane permeable substances flow is proportional to deltaP (K is always high) Diffusion through channels o Charged ions are not membrane permeable (K is low)  o Require channels to flow across membranes o Ligand gated channels Reading 5: Defining Flow and the Flow Principle components Flow is the physical movement of substance from one compartment to another Also can be the conversion of a substance from one form to another in a metabolic reaction Examples o Flow of molecules from the GI tract through the epithelium and into the blood stream o The flow of blood through the cardiovascular system o Conversion of ADP + Pi to make ATP The flow principle states that flow is the product of energy gradient and a conductance Conductance is the opposite of resistance o A material with high allows flow to occur through it o Letter k o Dictates the ease with which flow can occur between compartments o Greater conductance between compartments facilitates greater flow The energy gradient is the difference in "energy" between the masses of two different compartments o deltaE o Flow almost always occurs down an energy gradient o Mass flows from an area with high energy to an area with low energy o EHI-ELO o Flow + k x deltaE o Flow = k x (EHI-ELO) Reading 6: Types of Energy gradients Encompasses all types of physiological gradients that exist in our body Three specific types of physiological gradients 1. Pressure gradient deltaP o Pressure is the physical force exerted by a substance on the walls of its compartment o This gradient is created by the differences in pressure between 2 compartments 2. Concentration gradient deltaC o This gradient is created by the difference in the concentration of a substance in one compartment compared to another compartment 3. Electrical gradient deltae o This gradient is created by the difference in the electrical charge, which is determined by the number of charged particles (+/-), of one compartment compared to another compartment Examples o Pressure gradient the difference between blood pressure between the heart and the aorta o Concentration gradient the difference of lactate between the muscle and the blood o Electrical gradient the difference between one side of a membrane and the other side of a membrane Reading 7: Types of Energy gradients Encompasses all types of physiological gradients that exist in our body Three specific types of physiological gradients 1. Pressure gradient deltaP o Pressure is the physical force exerted by a substance on the walls of its compartment o This gradient is created by the differences in pressure between 2 compartments 2. Concentration gradient deltaC o This gradient is created by the difference in the concentration of a substance in one compartment compared to another compartment 3. Electrical gradient deltae o This gradient is created by the difference in the electrical charge, which is determined by the number of charged particles (+/-), of one compartment compared to another compartment Examples o Pressure gradient the difference between blood pressure between the heart and the aorta o Concentration gradient the difference of lactate between the muscle and the blood  o Electrical gradient the difference between one side of a membrane and the other side of a membrane Reading 8: Understanding How Changes in Components of the Flow Principle Affect Flow Flow = K x deltaE or flow = K x (EHI-ELO) Flow will increase if o Conductance (K) increases o The energy gradient increases because the high energy increased o The energy gradient increases because the low energy decreased o The energy gradient increases because the high energy increases and the low energy decreased Flow will decrease o Conductance (K) decreases o The energy gradient decreases because the high energy decreased o The energy gradient decreases because the low energy increased o The energy gradient decreases because the high energy decreased and the low energy increased Flow will not change o Conductance (K) does not change o The energy gradient does not change because neither the high energy or low energy changed Lecture 5: Membrane Transport 1. Simple Diffusion o Passive (no energy needed). o Molecules move from high to low concentration directly across the membrane. o Example: gases (O₂, CO₂). 2. Facilitated Diffusion o Passive but requires transport proteins (channels or carriers). o Moves larger or polar molecules (e.g., glucose, ions). 3. Active Transport o Requires ATP (energy). o Moves molecules against their concentration gradient. o Example: Na⁺/K⁺ pump (pumps 3 Na⁺ out, 2 K⁺ in). Sensory Receptors 1. Thermoreceptors: Detect temperature changes (hot or cold). 2. Chemoreceptors: Detect chemicals (e.g., smell, taste, CO₂ in blood).  3. Mechanoreceptors: Detect physical forces (e.g., pressure, touch, vibration). 4. Nociceptors: Detect pain from tissue damage. 5. Electromagnetic Receptors: Detect light (e.g., photoreceptors in the retina). Action Potentials 1. Subthreshold Depolarization: Small stimulus → no action potential (not enough to reach threshold). 2. All-or-None Principle: Once threshold is reached, an action potential fires completely. 3. Summation: o Spatial Summation: Multiple signals from different neurons combine to reach threshold. o Temporal Summation: Repeated signals from one neuron over time add up to reach threshold. 4. Action Potential Steps: o Resting Potential: ~-70 mV (inside more negative). o Depolarization: Na⁺ channels open, Na⁺ enters, making inside more positive. o Repolarization: K⁺ channels open, K⁺ exits, restoring negativity. o Hyperpolarization: Overshoot of negativity before returning to resting potential. Voltage-Gated Channels 1. At resting potential, channels are closed. 2. During depolarization, Na⁺ channels open (Na⁺ enters). 3. During repolarization, K⁺ channels open (K⁺ exits). 4. Hyperpolarization: Slow K⁺ channel closure causes overshoot of negativity. Disorders Affecting the Nervous System 1. Multiple Sclerosis (MS) o Autoimmune disease attacking myelin in the CNS. o Slows or blocks nerve signal transmission. o Symptoms: muscle weakness, vision loss, coordination issues. 2. Guillain-Barré Syndrome (GBS) o Autoimmune attack on myelin in the PNS. o Rapid onset of muscle weakness and paralysis. o Often temporary but can be life-threatening. Lecture 6: Deciding to move review 1. The nervous system is divided into the Central Nervous System and the Peripheral Nervous System. Each of these components of the nervous system can be subdivided into 2 sub- components, what are these subcomponents and what are their primary functions? Central nervous system o Brain and spinal cord o Understanding and interpreting signals o Transportation for signals Peripheral nervous system o Somatic: functions you manage by thinking about them o Autonomic: brain runs them without thinking o Has afferent signals which input to the cns and efferent signals which output from the cns o Controls senses 2. How do each of the following areas of the brain contribute to movement? i. Limbic System Hypothalamus, amygdala, hippocampus, thalamus Control emotional behavior and motivational drive Responds to sensory afferent input Voluntary movement ii. Motor Cortex Neurons control movement of different areas of the body Primary mc neurons control movement Premotor cortex generate complex neural signals that cause complex movement Excites the primary mc Signals leaving direct muscles via red nucleus and spinal cord Indirect via cerebellum and basal ganglia iii. Cerebellum Controls timing, sequence and intensity of motor patterns Control of voluntary movement Monitors and corrects movement o Open skills shooting ball off balance, catching while running Learns and improves iv. Basal Ganglia Executes patterns of movement activity Accessory motor system to motor cortex Helps organize complex patterns of movement o Closed skills writing, pitching, darts, speaking Controls speed and size of movement v. Brain Stem and Spinal Cord Signal transported via the motor nerves to the muscle and movement occurs 3. What are the 5 Steps involved in neural cell communication? Depolarization of cell body Initiation of action potential at axon trigger zone Conduction of action potential Release of neurotransmitter from axon terminals Neurotransmitters excite/inhibit postsynaptic cell 4. What does opening Na+ channels on a cell membrane do to membrane potential? Why does opening Na+ channels have this effect? It depolarizes Because there is more Na+ so more positive ions move inside the cell Membrane potential for Na+ = +61mv 5. What does opening K+ channels on a cell membrane do to membrane potential? Why does opening K+ channels have this effect? Repolarizes the cell 6. Opening Cl- channels causes a hyperpolarization of cell membranes. Knowing this would the PHI for Cl- be inside or outside of the cell? inside Reading 9: Defining Regulated Mass Regulated mass is a substance in a compartment that needs to stay within a certain range Range that’s a regulated mass needs to stay within is the critical range Negative consequences when a regulates mass is not within its critical range o Amount of fish in a tank and amount of food given 1. Regulated mass: concentration of protein inside a cell 2. Regulated mass: amount of glucose in the blood 3. Regulated mass: pressure of blood in large arteries Reading 10: Integrating Mass Balance and Flow Principle Masses can affect flow and flow can affect masses Masses regulated by the balance of its inflow and outflow Inflow and outflow are separate flows o They each have their own energy gradient and conductance  All high energies and low energies are masses The regulated mass represents the low energy for its inflow The regulated mass also represents the high energy for its outflow Inflow and outflow each contain their own energy gradient Given flow represents an inflow for one mass and an outflow for another Bathtub analogy o Regulated mass= amount of water in tub o Inflow for regulated mass = rate of water being added to the tub o EHI for inflow (mass 1) for regulated mass = amount of water in the tap pipe o Conductance for inflow for regulated mass= width of tap o Outflow for regulated mass= rate of water being removed from the tub o ELO for outflow (mass 2) for regulated mass = amount of water in the drain pipe o Conductance for outflow for regulated mass = width of drain The ELO for inflow and the EHI for outflow for the regulated mass is the regulated mass  Reading 11: Understanding How Disturbances in Mass or Flow Affect a Regulated Mass Flows are the product of conductance and energy gradient with changes in flow occurring when conductance and/or the energy gradient change A change in mass balance is an increase or decrease in the regulated mass due to change in inflow and/or outflow Disturbances in mass balance Mass 1 increases 1. The EHI for inflow for the regulated mass increases a. This is the direct effect of the disturbance 2. The inflow for the regulated mass increases a. Because the EHI for this flow increases 3. The regulated mass increases a. Because inflow for regulated mass increases Decreases the conductance for outflow 1. Conductance for outflow for the regulated mass decreases  a. This is the direct effect of the disturbance 2. Outflow for the regulated mass decreases a. Because the conductance for this flow decreases 3. The regulated mass increases a. Because outflow for regulated mass decreased Reading 4: Understanding How Disturbances Affect a Regulated Mass Using Non-Physiological Examples Disturbances o Increases the width of the drain o 3. The width of the drain increases (i.e. the conductance for outflow for the regulated mass increases) 4. The flow of the water from the bathtub to the drain pipe increases (i.e. the outflow for the regulated mass increases) 5. The amount of water in the bathtub decreases (i.e. the regulated mass decreases) 6. The amount of water in the drain pipe increases (i.e. the PLO for outflow for the regulated mass increases) 7. The flow of water from the bathtub to the drain pipe decreases (i.e. the outflow for the regulated mass decreases) 8. The amount of water in the bathtub increases (i.e. the regulated mass increases) Lecture 7: Deciding to move 5 Depolarization caused by Binding to ligand gated channels o Sodium channels pulled open when responding to sensory G-protein linked receptors Specialized sensory receptors Primarily Na+ channels but sometimes Ca2+ Action potential only generated if depolarization reaches threshold o Voltage gated Na+ channels Optic nerve Action potential releases neurotransmitters Release of neurotransmitters from axon terminals Neuron will interface with another neuron Site of action is the synapse Cell being excited is pre synaptic Cell after excited is post synaptic The synapse Junction between either  Axon and dendrite Axon and effector o Muscle o Heart o Other organ Neurotransmitter is released by the pre-synaptic neuron Then binds to the postsynaptic cell and excites, inhibits, or otherwise alters functions The chemical synapse Within pre has vesicles which contain neurotransmitters When action potential reaches terminal end, action potential causes vesicles to release neurotransmitters Trigger release is through another voltage gated channel o Calcium gated o Respond to changes in membrane potential and open with action potential o Goes down axon, reaches axon terminus, in there have calcium channels that open when depolarized o High concentration ca outside low inside When opened we get flow into the cell Calcium signalling leads to movement of axon vessels Neurotransmitter binding causes response in the postsynaptic cell Amount and length of neurotransmitter release More presynaptic action potentials increase the release of neurotransmitters Neurotransmitter is cleared by degradation in the synaptic cleft Once neurotransmitter is gone post synaptic events end o Acytocholine no longer released, the ones left broken down by acytocholine esterase Post-synaptic actions of neurotransmitters 1. Directly alter ion channels (fast response) a. Depolarization or hyperpolarization 2. Direct coupling to ion channels (slow via g-protein a. Receptor binds neurotransmitter b. G-protein linked to receptor; when light hits receptor causes close 3. Activation of second messenger systems a. Slow via g-protein b. Besides channels c. Have variety of effects i. Open ion channels ii. Lead to longer lasting]g functional changes in the postsynaptic cell via activation of protein synthesis iii. Can include cellular adaptation Molecular mechanisms of memory initially exposed to a new experience a group of neurons is recruited When you recall that experience that same group of neurons is activated Memory is achieved by forming and remodelling c=neuronal circuits  Theis is achieved through stable synaptic change vis the second messenger systems Glutamate binds to the NMDA receptors NMDA allows ca2+ to enter neuron (second messenger) Ca2+ activates protein synthesis Afferent signalling pathway Organization of the nervous system o Spinal chord Reflexes Afferent conduction of signals to the brain Efferent conduction of signals from the brain Peripheral nervous system Afferent neurons input o Sight o Taste o Hearing o Feeling o Smell Efferent neurons output (used to actually move) Afferent signalling pathway Afferent neurons enters the CNS and it synapses in the spinal cord (reflex) or brain stem (conscious sensation) Second order neurons travel through the brainstem where they synapse again Third order neurons terminate in the somatosensory area of the cortex 3 principles of sensory reception 1. All receptors elicit action potential in afferent nerve fibers 2. Each type of receptor is highly sensitive to 1 type of stimuli only 3. Afferent action potentials are interpreted differently based on where they terminate in the CNS How do we sense touch 1. Sensory nerve disturbs and action potential initiated 2. Travels up afferent neuron into spinal cord (through dorsal roots) 3. Afferent signals travels up spinal cord into brainstem (medulla) 4. Afferent nerve synapses at the medulla and the thalamus before reaching the somatosensory area of the cortex Control of voluntary movement Action potentials generated in the limbic system o Spontaneously generated AP? o Response to sensory input AP's excite appropriate areas of the motor cortex AP's travel through the basal ganglia where order, speed, and size of movement is sorted (closed) AP's travel back to motor cortex and out of brain via cerebellum  Cerebellum compares actual movement (open) to desired movement, makes corrections to AP's AP's levels brain through brainstem, spinal cord and efferent motor neurons and excites muscle Lecture 8: Moving Control of voluntary movement Action potentials generated in the limbic system o Spontaneously generated AP? o Response to sensory input AP's excite appropriate areas of the motor cortex AP's travel through the basal ganglia where order, speed, and size of movement is sorted (closed) AP's travel back to motor cortex and out of brain via cerebellum Cerebellum compares actual movement (open) to desired movement, makes corrections to AP's AP's levels brain through brainstem, spinal cord and efferent motor neurons and excites muscle Types of muscle 1. Skeletal muscle 2. Cardiac muscle 3. Smooth muscle CNS where aps are being generated Now focus on efferent o Autonomic ns What we don’t think about (heart rate, digestive, etc.) Spinal cord Through brain stem, down spinal cord, exit through ventral route, travel through to the periphery where they interact with skeletal muscle The muscle fibre A muscle fibre is a muscle cell Muscle fibres run parallel to each other to form skeletal muscle Longest cells in the body can be up to 12 cm long Myofibril contain the contraction units that allow shortening and lengthening Muscle fibre individual is tiny 20 micrometres wide Many of them Sarcolemma where excitation occurs  Myofibrils shorten which causes movement Sarcolemma Membrane surrounding muscle fibre Site of neuromuscular junction and initiation of muscular action potentials Sodium and potassium channels on it Controls substrate entry and exit from the cell o Regulating fuel prevision Site of excitation o Nervous system for our muscles to contract Action potential on, which excites muscle fibre, w=eventually leads to contraction Excitation-contraction coupling Have to excite sarcolemma which is coupled to contraction Motor nerves Contraction initiated by motor nerve One motor nerve innervates a group of muscle fibres called a motor unit o Activates more then one muscle fibre to contract and that group activated is the motor unit They are myelinated The motor unit MUs enervate fibres in a scattered pattern o Demonstrated by glycogen depletion following stimulation of a single motor neuron o Break down glycogen during glycolysis which gives ATP which gives energy for muscle movement o During contraction activated muscles fibres are utilizing glycogen o Any muscle fibre activated will have muscle glycogen and wont have any left Excite the motor unit its an all or nothing response o Gradient reactions mean not smashing your face with a cup o Recruit small or large for force level The number of MUs in a muscle vary widely Number of fibres recruited by each MU can be small or large o Generally muscles preforming fine movement have fewer fibres/units o Motor unit of 1 force of 1 o Motor unit of 100 force of 100 o Bigger muscles have bigger force Don’t need fine movements More body and heavy weight Large motor units in big muscle unit Neuromuscular junction When nerve impulse reaches the end of neuron Ach is released into the neuromuscular junction Ach binds to receptors causing depolarization Excitation-contraction coupling Somatic motor neuron releases Ach at neuromuscular junction Net energy of Na+ through Ach receptor-channel initiates a muscle action potential Fusion The fusion protein SNAP-25 is required for fusion of vesicles to membrane in neuronal cells  Action potential travels through the T-tubules Excitation of them will cause sensors to open on sarcoplasmic reticulum which will release calcium and cause muscle contraction ECC- The Triad 1. T-tubules 2. Sarcoplasmic reticulum 3. Feet Location of the coupling and eventual contraction T-tubules carries action potential into muscle Sarcoplasmic reticulum stores, releases and uptakes Ca+ Feet o Dihydropyridine receptor Located is membrane of t-tubule Voltage sensitive Changes shape and pulls ryanodine receptor open o Ryanodine receptor Located in membrane of SR Controls release of Ca+ Calcium flows out and floods cytosol around contraction site Depolarization of t-tubules change in DHPR, then RYR and Ca+ is released Development and improvement of movement pathways Resistance training Strength improves more quickly than muscle changes Performance of dynamic movements improves more than max strength of single muscles Lecture 9: Study course pack o Questions from there on test Worksheet Where channels are located Study and memorize lecture notes o Questions from slides 30 mc questions o 22 lecture sides o 8 course pack Moving 2 Motor nerves Contraction initiated by a motor nerve One motor nerve innervates a group of muscle fibres called a motor unit o Bigger motor unit bigger force Large muscles o Small motor unit smaller force (eyes) fine tasks Sodium in depolarization by neurotransmitters or cell body's depolarized Ca causes contraction The myofibril Site of force generation Sarcolemma muscle membrane Action potential into cell through t-tubules into sarcoplasmic reticulum Ca released directly onto myofibrils Highly organized bundles of contractile protein Comprise the majority of volume in a muscle fibre Where force generation takes place Made up of a series of sarcomeres joined end to end The sarcomere Joined at the z-disc When contract we shorten sarcomere o Pull two z-disks closer together force generated These joints are what give muscle its striated shape M line and A band made up of myosin thick filament The motor unit Mus enervate fibres in a scattered pattern Demonstrated by glycogen depletion following stim of single motor unit Myosin Single myosin filament end at the myosin head o Head capable of movement and pulling things over o Myosin head pulls actin which causes sarcomere to shorten  o Lots of myosin heads branches off in three dimensions Myosin head is an ATP enzyme o Energy for movement comes from ATP Tail region and two heads Myosin head is an ATPase enzyme o Can break ATP down to ADP which is release of energy which harnesses it to preform work Actin Thin filament Extends from z disk to centre of sarcomeres Comprised of two actin chains o Have sites that myoglobin can bind to o Myosin bind to actin to shorten sarcomere o Called a cross bridge Thin filament also made up of troponin and tropomyosin o Tropomyosin covers active sites which allows for relaxation of muscles o Regulate contraction Myosin bind to actin in presence of calcium Sliding filament theory I band present disappears Myosin and actin slide overtop of each other Causes sarcomere to shorten Cross bridges Binding of myosin head to actin active site This binding allows contraction to occur When bound to actin myosin undergoes a power stroke pulling actin and shortening the sarcomere Troponin and contraction Troponin T attaches to tropomyosin Troponin I inhibits active site on actin Troponin c is the active binding site for ca When calcium binds to troponin c tropomyosin is moved away from actin active site This allows myosin head to bind to actin Forms a cross-bridge Contraction cycle Myosin undergoes to continually pull actin over itself Single contraction is not a single power stroke Myosin heads have multiple power strokes during one contraction 1. Rigor state a. Myosin head is tightly bound to actin active site b. There is no atp bound to the myosin head c. Cross bridge is at 45 degrees relative to the filaments 2. Myosin release  a. ATP binds to myosin head b. Affinity of myosin for actin is decreased c. Cross bridge is broken 3. ATP hydrolysis a. ATP broken down i. ADP and pi remain bound to myosin head b. Energy released allows f=myosin head to move down actin filaments into cocked position 4. Myosin reattaches a. Myosin head binds weakly to the actin active site b. Binding occurs one or two positions away from first c. The myosin head is still in its cocked position 5. Power stroke a. Pi is released from myosin head b. This strengthens the bond between actin and myosin head c. Myosin head swings towards the m line pulling actin with it 6. ADP release a. During power stroke ADP released b. Crossbridge is returned to rigor state awaiting ATP and next cycle Relaxation Smooth movement involve both contraction and relaxation Get rid of ca When depolarization stops RYR closes Ca removed from cytosol back to SR Accomplished by active transport via SERCA or SR ca pump As long as ca is present contraction will continue o Importance of calcium pumps on ER o Brody's disease Cant clear calcium (pump doesn’t work) Contraction cycle As long as ca is present myosin will remain bound Allows a series of contraction cycles to cause large sustained contractions Removal of ca results in recovering of actin active site by tropomyosin