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Key Concepts. Function Vs. Process Function why does a system exist, its purpose, what is does for the organism (teleological approach) Process How does a system perform its function, (mechanistic approach)
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Key Concepts Function Vs. Process • Function why does a system exist, its purpose, what is does for the organism (teleological approach) • Process How does a system perform its function, (mechanistic approach) PHYSIOLOGY integrates both approaches to understand “How” physiological systems work, and “Why” they are there
Key Concepts • Homeostasis Maintaining the internal environment of an organism relatively stable by maintaining certain properties within a normal range • E.g. Temperature, blood glucose, blood pressure, salt concentrations, pH
Homeostasis • Keeping these parameters around a set point requires constant monitoring, compensation, and energy input. E.g. Like driving a car straight requires many corrections with the steering wheel • Additionally set points may change, either due to biological rhythms or in response to environmental change
Cell to Cell Communication Add Red Dye to left cell Connexon
Cell to Cell Communication Paracrine Target Cell Cell Autocrine Endocrine Blood
Receptors • Signalling specificity depends on Receptor Proteins • Signalling molecule binds onto a specific receptor found only on target cells transmembrane, cytosolic, or nuclear location • Receptor protein is what brings about the response to signal • Agonists Binds receptor and activates response • Antagonists Binds receptor and produces no response (inhibitory activity)
Receptors Biological Signalling Molecule Foreign “drug” molecule Foreign “drug” molecule Antagonist Pathway Without Response Normal Signal Pathway With Response Agonist Pathway With Response
Nervous System • 1) Receives information Sensory neurons from external environment (light, sound, pressure etc) • 2)Integrates Information Organizes new information, combines with stored information • 3) Transmits Information Sends signals to muscles/glands to carry out action
Neurons Dendrites Axon Terminal Node of Ranvier Soma Myelin Sheath/ Schwann Cell Axon Nucleus Ref: Wikipedia http://en.wikipedia.org/wiki/File:Neuron_Hand-tuned.svg
Glial Cells Neurons Neurons are the VIP’s of the nervous systems! They need other people to help do their laundry, cook food, act as bodyguards, etc etc so they can focus on their jobs
PNS Glial Cells Schwann Cells form myelin sheath which acts as electrical insulator. Only wrap around 1 cell • Structure has many layers of cell membrane with gap junctions connecting layers -Gap Junctions Neuron
PNS Glial Cells • Satellite Cells non-myelinating, support nerve cells
CNS Glial Cells-4 Types • Oligodendrite Myelinating Cell (like Schwaan) but can wrap around more than one neuron • Astroglia Make contact with blood vessels and neurons; transfer nutrients, maintain microenvironment; Star Shaped.
CNS Glial Cells • Microglia Small, specialized immune cells -maintain microenvironment like astroglia -remove dead cells & foreign invaders, protect neurons • Ependymal Cells Epithelial cells, create semi-permeable barriers between brain compartments -produce cerebrospinal fluid
Electrical Properties of Neurons • Difference between electrical charge on the inside of the cell and the outside environment creates an electrical gradient across the membrane • There is also an osmotic gradient due to the differences in concentrations of solutes between the inside & outside of cell
Electrical Properties of Neurons • Cell membranes are semi-permeable • Allow free diffusion of small, hydrophobic (non-polar) molecules • Membranes a impermeable to most molecules, Especially charged ions. • Specific protein transporters move these molecules across the membrane
Resting Membrane Potential • Resting Membrane Potential for a neuron is around -70 mV to -90 mV Negative charge compared to environment; mostly due to phosphate (HPO42- ,H2PO4-), and negatively charged proteins & DNA + + + - + - - - + + - - -70 mV - + + + - - + -
Resting Membrane Potential • Know the relative ion concentrations for the neuron at rest: • Na+, Cl-, and Ca2+ have concentrations higher in the extracellular fluid (outside cell) • K+ has a higher concentration inside the cell Na+ Cl- -70 mV Ca2+ K+
Na+/K+ ATPase • Active transport of 3 Na+ out of the cell and 2 K+ into the cell powered by ATP • Pumps ions against gradient (by consuming energy) to maintain cellular concentrations of K+ and Na+ • Compensates for ions leaking into/out of cell along their concentration gradient
Nernst Equation • Equilibrium Potential (Eion) is the electrical potential of the Cell needed to generate an equilibrium state for a KNOWN concentration gradient The electrical gradient needed to balance the concentration gradient • Compare this to known cell potential to predict where ions are likely to flow
Nernst Equation • Know that K+ is found at higher concentrations inside of the cell Concentration gradient dictates K+ would flow out of the cell • Calculated Equilibrium Potential for Potassium is -90 mV. Neuron with membrane potential of -70 mV Neuron with membrane potential of -90 mV - - - - - -70 mV -90 mV - K+ K+ K+ will flow (leak) out of cell Negative charges not enough to attract Positive K+to remain in the cell No NET K+ movement Negative charges attract Positive K+ to balance concentration gradient
Nernst Equation • Know that Na+ is found at higher concentrations outside of the cell Concentration gradient dictates Na+ would flow into the cell • Calculated Equilibrium Potential for Na+ is +60 mV. Neuron with membrane potential of -70 mV Neuron with membrane potential of +60 mV - + + - Na+ Na+ + -70 mV +60 mV + + Na+ will leak into the cell Negative charges not enough to repel Positive Na+to prevent movement into cell No NET Na+ movement Positive charges repel Positive Na+ to balance concentration gradient
Resting Membrane Potential & Ion Permeability • The relative permeability of these ions dictate how important its contribution to the resting membrane potential is • Ions that can move more easily through the membrane contribute greater to the RMP • RMP can be calculated using the Goldman Equation which takes into account the relative permeability of ions • Permeability can be increased by: 1)opening gated protein channels for transport 2) increasing the # of transport proteins
Gated Channels Stretch + + + + Channel Closed Channel Open Channel Closed Channel Open Channel Closed Channel Open Voltage Gated - Respond to membrane potential changes - Involved in initiation and conduction of electrical signals Chemically Gated - Respond to ligand binding (neurotransmitters, neuromodulators) - “most important” for neurons (located in synapses) Mechanically Gated - Respond to physical forces - Found in Sensory neurons
Changes in Membrane Potential Repolarizationis any change in membrane potential which returns it to the Resting Membrane Potential
Action Potential 3 4 2 0 -55 mV 1 6 -70 mV 5
Action Potential-Voltage Gates Na+ + + + Activation Gate Inactivation Gate Sodium (Na+) Channel with Activation Gate (opens at -55 mV), and Inactivation Gate (voltage activated but time delayed)
Action Potential-Voltage Gates + + K+ Potassium (K+) Channel with Voltage Gate which opens later than Na+ channels (fully open at +30 mV)
Action Potential 0 MP = Less than -55 mV + + 1 MP = -55 mV + +
Action Potential Na+ 2 + MP = Between -55 mV and +30 mV + 3 &4 + + MP = +30 mV to -70 mV K+
Action Potential ABSOLUTE REFRACTORY 5 + MP = Less than -70 mV + K+ 5.5 RELATIVE REFRACTORY + MP = Less than -70 mV + K+
Refractory Periods • Set directionality of Signal cannot activate membrane regions which have recently fired Na+ + + + Na+ Na+ Na+
Synapses • Electrical Synapses Gap junctions connect 2 cells allowing direct electrical signalling - CNS; between 2 neurons, or neuron and glial cell - Nervous system development and transmission in adult brain Action Potential Depolarization wave Action Potential Depolarization wave
Chemical Synapse Synaptic Cleft Presynaptic cell Postsynaptic cell Action Potential Depolarization wave Ions Neurotransmitter Receptors can either open ion channel directly, or cause another (long lasting) signal cascade coupled to G proteins etc AP causes Ca+2 entry vesicles release neurotransmitter Ca2+
CNS Somatic neuron Always excitatory ACh Nicotinic ACh receptors Muscle Cell
CNS Parasympathetic 2 Neuron chain Sympathetic 2 Neuron Chain Swollen Terminals Varicosity; stores a lot of neurotransmitter Ganglion Target Cell Target Cell
Muscles • Tissues specialized to convert biochemical reactions into mechanical work • Generate force, motion, & heat • Skeletal attached to skeleton, responsible for movement; has striations • Smooth internal organs; influences movement of materials through body no striations • Cardiac Heart muscles; pumps blood; has striations
Skeletal Muscles • Attach to bones via tendons at 2 points; - Origin at “least” moveable part of body -Insertion at “most” moveable part of body • Flexor Muscles contraction brings bones closer together • Extensor Muscles contractions moves bones away from another • Flexor & Extensor are antagonistic pairs