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Key Concepts

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

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  1. 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

  2. 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

  3. 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

  4. Tissue Types

  5. Cell to Cell Communication Add Red Dye to left cell Connexon

  6. Cell to Cell Communication Paracrine Target Cell Cell Autocrine Endocrine Blood

  7. 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)

  8. Receptors Biological Signalling Molecule Foreign “drug” molecule Foreign “drug” molecule Antagonist Pathway Without Response Normal Signal Pathway With Response Agonist Pathway With Response

  9. 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

  10. 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

  11. Neurons

  12. Neurons

  13. Nervous System

  14. 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

  15. 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

  16. PNS Glial Cells • Satellite Cells  non-myelinating, support nerve cells

  17. 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.

  18. 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

  19. 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

  20. Electrical Properties of Neurons • Cell membranes are semi-permeable • Allow free diffusion of small, hydophobic (non-polar) molecules • Membranes a impermeable to most molecules, Especially charged ions. • Specific protein transporters move these molecules across the membrane

  21. 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 - + + + - - + -

  22. 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+

  23. 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

  24. 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

  25. Nerst 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

  26. Nerst 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

  27. 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

  28. 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

  29. Changes in Membrane Potential Repolarizationis any change in membrane potential which returns it to the Resting Membrane Potential

  30. Graded & Action Potentials

  31. Action Potential 3 4 2 0 -55 mV 1 6 -70 mV 5

  32. 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)

  33. Action Potential-Voltage Gates + + K+ Potassium (K+) Channel with Voltage Gate which opens later than Na+ channels (fully open at +30 mV)

  34. Action Potential 0 MP = Less than -55 mV + + 1 MP = -55 mV + +

  35. Action Potential Na+ 2 + MP = Between -55 mV and +30 mV + 3 &4 + + MP = +30 mV to -70 mV K+

  36. Action Potential ABSOLUTE REFRACTORY 5 + MP = Less than -70 mV + K+ 5.5 RELATIVE REFRACTORY + MP = Less than -70 mV + K+

  37. Refractory Periods • Set directionality of Signal  cannot activate membrane regions which have recently fired Na+ + + + Na+ Na+ Na+

  38. Action Potential

  39. Action Potential

  40. Synapses • Electrical Synapses Gap junctions connect 2 cellss 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

  41. 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+

  42. Types of Neurotransmitters

  43. Types of Neurotransmitters

  44. Peripheral Nervous System

  45. CNS Somatic neuron Always excitatory ACh Nicotinic ACh receptors Muscle Cell

  46. CNS Parasympathetic 2 Neuron chain Sympathetic 2 Neuron Chain Swollen Terminals Varicosity; stores a lot of neurotransmitter Ganglion Target Cell Target Cell

  47. G Proteins & Ion Channels IONS e.g. Nicotinic cholinergic receptors 1 molecule of neurotransmitter opens 1 ion channel

  48. G Proteins & Ion Channels e.g. Adrenergic receptors 1 molecule of neurotransmitter can have many effects G Protein Coupled Receptor G Protein Coupled Receptor G Protein Trimer Open Ion Channels Activate other proteins Increase cAMP levels

  49. Adrenergic Receptors

  50. Cholinergic Receptors

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