BSC2085 Exam 3 Checklist Lesson 13 Ch 12 Membrane Potential the Action Potential 1 Describe the main membrane processes in neurons a Five Main Membrane Process in Neural Activities i Resting potential membrane potential of resting cell ii Graded potential 1 Temporary localized change in resting potential 2 Caused by stimulus 3 Can make inside more positive or more negative iii Action potential electrical impulse 1 Produced by graded potential 2 Propagates along surface of axon synapse iv Synaptic activity 1 Releases neurotransmitters presynaptic membrane 2 Neurotransmitter diffused across synaptic cleft binds to receptors on postsynaptic cell 3 Produces graded potentials in postsynaptic membrane v Information processing 1 Response integration of stimuli of postsynaptic cell 2 Explain the trans membrane potential Why is it important a What are the main ions molecules that generate this potential b Membrane potential is particularly important to neurons i Membrane potential caused by difference of charge between the inside and outside of the cell ii Changes Rises or falls 1 In response to temporary changes in membrane permeability physical or chemical stimuli a Resulting from opening or closing specific membrane channels b The channels only allow their specific ion to enter leave c Membrane Potential 3 Concepts i Extracellular fluid ECF intracellular fluid cytosol differ greatly in chemical ionic composition passive force 1 Concentration gradient of ions Na K chemical gradient 2 More Na outside more K inside negatively charged proteins ii Cells have selectively permeable membranes 1 Remember water soluble substances including ions CANNOT pass through hydrophobic region of lipid bilayer need channel carrier protein iii Membrane permeability varies by ion 1 Due to the presence of specific passive leak channels d Electrical Currents Resistance i Electrical Current 1 Movement of charges to eliminate potential difference 2 Opposite charges attract like charges repel ii Resistance 1 BSC2085 Exam 3 Checklist 1 Amount of current a membrane restricts 3 Explain the electrochemical gradient Why is it important a Electrochemical Gradient i For a particular ion Na K is the sum of chemical and electrical forces acting on the ions across a plasma membrane potential energy 1 A form of 4 Explain the role of sodium and potassium ions on the membrane potential a Do they enter leave through active or passive channels b Active Forces Across the Membrane i Sodium Potassium ATPase exchange pump 1 Powered by ATP 2 Carries 3 Na out 3 Balances passive forces of diffusion occurs through passive and 2 K in channels 4 Maintains resting potential 70mV c Passive Forces across Plasma Membrane i Chemical gradients concentration gradients of ions Na K ii Electrical gradients separate charges of positive negative ions result in potential difference d Sodium and Potassium Channels i Membrane permeability to Na and K determines membrane potential ii They are either passive or active 1 Passive Channels Leak Channels a Are always OPEN b Permeability changes with conditions i Net flow always from greater to lesser 2 Active Channels Gated Channels concentration a Open close in response to stimuli b Resting potential most gated channels are CLOSED 5 Explain how gated channels function a What are the different types of gated channels i 3 Classes of Gated Channels 1 Chemically gated channels a Open in presence of specific chemicals i e ACh acetylcholine at a binding site b Found on neuron cell body dendrites 2 Voltage gated channels a Respond to changes in membrane potential i A change in membrane potential causes the channels to open or close b Have activation gates open and inactivation gates close i Some have 2 gates such as Na others such as K only have 1 gate c Characteristic of excitable membrane 2 BSC2085 Exam 3 Checklist d Found in neural axons skeletal muscle sarcolemma cardiac muscle 3 Mechanically gated channels a Respond to membrane distortion b Found in sensory receptors touch pressure vibration b What are the different states to a gated channel i 3 States of Gated Channels 1 Closed but capable of opening 2 Open activated 3 Closed but not capable of opening inactivated 6 Describe the difference between action potentials and graded potentials local potentials AKA a Graded Potentials i Changes in membrane potential cannot spread far from site of stimulation ii Includes any stimulus that OPENS a gated channel produces a graded potential iii The Resting State 1 Opening Na channel produces graded potential a Resting membrane exposed to chemical b Na channels OPEN c Na enters cell d Membrane potential rises e Depolarization occurs why i Becomes more positive b c Na is positive iv Depolarization 1 Shift in membrane potential toward 0 mV a Movement of Na through channel b Produces local current c Depolarized nearby plasma membrane graded potential d Change in potential is proportional to stimulus 1 When the stimulus is removed membrane potential returns to v Repolarization normal vi Hyperpolarization Increasing the negativity of the resting potential 1 2 Result of opening a potassium channel 3 Opposite effect of opening sodium channel 4 Net movement of positive ions out not into cell why a B c the inside of the cell is becoming even more negative vii Effects of graded potentials 1 At cell dendrites or cell bodies trigger specific cell functions a i e Exocytosis of glandular secretions 2 Motor end plate at the axon terminal a Release ACh into synaptic cleft b Action Potentials i Propagated changes in membrane potential ii Affect an entire excitable membrane iii Link graded potentials at cell body with motor end plate actions 3 BSC2085 Exam 3 Checklist c Are they always depolarizing or hyperpolarizing d Graded Potentials depolarizing or hyperpolarizing share 4 basic characteristics i Membrane potential is most changed at site of stimulation effect decreases with distance i e Ripples in a pool of water ii The effect spreads passively due to local currents 1 Spread is in all directions not just in one direction i e Creating ripples in a pool of water ripples travel in all directions iii The graded change in membrane potential may involve either depolarization or hyperpolarization 1 The properties distribution of the membrane channels involved determine the nature of the change a i e In a resting membrane the OPENING of Na channels depolarization whereas the OPENING of K channels hyperpolarization i Change in membrane
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