BHSC 1200 midterm 2 Exam questions and answers graded a+

BHSC 1200 midterm 2 Exam questions and answers graded a+ discuss the role of the Na/K pump in establishing the resting membrane potential - ANSWERS-stabilizes resting membrane potential -maintains concentration gradient for Na+ and K+ -3 Na+ pumped out of cell; 2 K+ pumped in graded potential vs action potential - ANSWERS graded potential: small deviation from the resting membrane potential that makes the membrane either more polarized or less polarized; occurs when a stimulus causes mechanically-gated or ligand-gated channels to open or close in an excitable cell's plasma membrane -action potential (aka impulse): a sequence of rapidly occurring events that decrease and reverse the membrane potential and then eventually restore it to the resting state; occurs in the axon of a neuron when depolarization reaches a certain level termed the threshold (-55mV) define threshold, depolarization, repolarization, and hyperpolarization - ANSWERS-threshold: -55mV in most neurons; action potential occurs when this level is reached -depolarization: negative membrane potential becomes less negative, reaches zero, and then becomes positive -repolarization: membrane potential is restored to resting state of -70mV -hyperpolarization: membrane potential temporarily becomes more negative than the resting level role of voltage-gated Na+ channels in the depolarization phase - ANSWERSNa+ channels open first, allowing Na+ to rush into the cell, causing the depolarizing phase role of voltage-gated K+ channels in the repolarization phase - ANSWERSafter depolarization, K+ channels open, allowing K+ to flow out, causing the repolarizing phase define absolute and relative refractory periods and explain their significance - ANSWERS-absolute refractory period = when voltage-gated Na+ channels open, neuron cannot respond to another stimulus; time from opening of Na+ channels to resetting of the channels; ensures that each AP is an all-or-none event; enforces one-way transmission of nerve impulses -relative refractory period = period of time during which a second AP can be initiated, but only by a larger-than normal stimulus; coincides with the period when the voltage-gated K+ channels are still open after inactivated Na+ channels have returned to their resting state significance: act as a protective mechanism so we can't have multiple AP constantly firing discuss how an action potential is propagated - ANSWERS-depends on positive feedback loop -travel from where they arise at the trigger zone to the axon terminals -action potential keeps its strength as it spreads along the membrane (propagation) -sodium flows in, voltage gated ion channels open -action potential travels along membrane, regenerating over and over at adjacent regions of membrane from the trigger zone to the axon terminals -can only propagate in this direction because the regions it has already passed are in their absolute refractory period compare continuous and saltatory conduction - ANSWERS-continuous conduction: step-by-step depolarization of each adjacent segment of the plasma membrane; occurs in unmyelinated axons and in muscle fibres -saltatory conduction: impulse jumps from one Ranvier's node to the next; occurs along myelinated axons due to the uneven distribution of voltage-gated channels describe the components of the synapse - ANSWERS presynaptic neuron: a nerve cell that carries a nerve impulse toward a synapse -postsynaptic neuron: a cell that receives the signal -synaptic cleft: fluid-filled space separating the presynaptic and postsynaptic neurons steps involved in neurotransmission - ANSWERS1) nerve impulse arrives at synaptic end bulb of a presynaptic axon 2) depolarizing phase opens voltage-gated Ca2+ channels, causing Ca2+ to flow inward 3) increase in concentration of Ca2+ inside the presynaptic neuron serves as a signal that triggers exocytosis of synaptic vesicles. vesicle membranes merge with plasma membrane, releasing neurotransmitter molecules into the synaptic cleft 4) neurotransmitter molecules diffuse across the synaptic cleft and bind the neurotransmitter receptors in the postsynaptic neuron's plasma membrane 5) binding of neurotransmitter molecules to their receptors on ligand-gated channels opens the channels and allows particular ions to flow across the membrane 6) as ions flow through the opened channels, the voltage across the membrane changes (called a postsynaptic potential). depending on which ions the channels admit, this could be a depolarization or a hyperpolarization 7) when a depolarizing postsynaptic potential reaches threshold, it triggers an action potential in the axon of the postsynaptic neuron discuss how neurotransmitters excite or inhibit postsynaptic structures - ANSWERS-excitatory postsynaptic potential: a neurotransmitter that causes depolarization of the synaptic membrane, bringing it closer to the threshold organization of nervous system - ANSWERS1) central nervous system = brain and spinal cord -processes many different kinds of incoming sensory information -source of thoughts, emotions and memories -produces signals causing muscles to contracts and glands to secrete 2) peripheral nervous system = consists of all nervous tissue outside the CNS -further divided into sensory (afferent) division [provides information about somatic senses] and motor (efferent) division [conveys output from CNS to effectors] -efferent division is further divided: somatic nervous system (conveys output from CNS to skeletal muscle) and autonomic nervous system (conveys output from CNS to smooth muscle, cardiac muscle, and glands) -autonomic nervous system is further divided: sympathetic nervous system and parasympathetic nervous system (usually have opposing actions) functions of nervous system - ANSWERS-sensory function: sensory receptors detect internal stimuli; sensory information is carried to brain and spinal cord -integrative function: nervous system processes sensory information by analyzing it and making decisions -motor function: nervous system activates effectors causing muscles to contract and glands to secrete