Chapter 8: Neurons – Flashcards
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Sensory Neurons
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-pseudounipolar -bipolar -are afferent
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Interneurons
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-cell body is completely housed in nervous -anaxonic -multipolar
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Efferent Neuron
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-take information from brain to body -multipolar shape
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Glial Cells
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-provide physical and biochemical support for neurons -found in peripheral nervous system -Schwann cell forms myelin sheaths
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Schwann cells
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-glial cell -in peripheral nervous system -form myelin sheath which insolates axon and speeds up signal
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Oligodendrocytes
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-glial cells -CNS -forms myelin sheath
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Microglia
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-glial cells -CNS -acts as scavengers
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Astrocytes
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-glial cells -CNS -provide substrates for ATP production -helps form blood brain barrier -secrete neurotrophic factors -takes up potassium, water, and neurotransmitters -source of neural stem cells
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Ependymal cells
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-glial cells -CNS -source of neural stem cells -create barriers between compartments
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Node of ranvier
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-a section of unmyelinated axon membrane between two schwann cells
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What is the resting membrane potential of a neuron?
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-70 millivolts
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What is the membrane potential influenced by?
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-concentration gradient of ions -membrane permeability to ions
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Nernst Equation
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-equation to determine membrane potential -only takes into account one type of ion at a time
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GHK Equation
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-equation that predicts membrane potential that results from the contribution of all ions that can cross the membrane
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Graded potential
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-change in membrane potential due to fact of receiving a stimulus -occurs in dendrites -Sodium is involved -sodium depolarizes the cell -decrease in strength as they spread out from the point of origin
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Action Potential
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-all or none. -55mV -occurs on axon hillock -depolarizing signal
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Nerve cells in the central nervous system are primarily
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interneurons
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The cells that we are capable of controlling consciously are the _____ neurons
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somatic motor (somatic efferent)
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Somatic motor neurons control
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skeletal muscle
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Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?
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resting membrane potential RMP
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Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel
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leak channels
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On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?
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The inside surface of the plasma membrane is much more negatively charged than the outside surface.
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The plasma membrane is much more permeable to K+ than to Na+. Why?
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There are many more K+ leak channels than Na+ leak channels in the plasma membrane.
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The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.
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The presence of concentration gradients and leak channels
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What prevents the Na+ and K+ gradients from dissipating?
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Na+-K+ ATPase
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Where do most action potentials originate?
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initial segment -the first part of the axon adjacent to the tapered end of the cell body known as the axon hillock
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What opens first in response to a threshold stimulus?
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Voltage-gated Na+ channels
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What characterizes depolarization, the first phase of the action potential?
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The membrane potential changes from a negative value to a positive value.
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What characterizes repolarization, the second phase of the action potential?
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Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
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What event triggers the generation of an action potential?
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The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
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What is the first change to occur in response to a threshold stimulus?
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Voltage-gated Na+ channels change shape, and their activation gates open.
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What type of conduction takes place in unmyelinated axons?
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Continuous conduction -The term continuous refers to the fact that the action potential is regenerated when voltage-gated Na+? channels open in every consecutive segment of the axon, not at nodes of Ranvier.
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An action potential is self-regenerating because __________.
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depolarizing currents established by the influx of Na+? flow down the axon and trigger an action potential at the next segment
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Why does regeneration of the action potential occur in one direction, rather than in two directions?
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-The inactivation gates of voltage-gated Na+? channels close in the node, or segment, that has just fired an action potential. -the voltage-gated Na+? channels become absolutely refractory to another depolarizing stimulus.
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What is the function of the myelin sheath?
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-The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals - insulates the axon, reducing the loss of depolarizing current across the plasma membrane
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What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?
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Inactivation gates of voltage-gated Na+? channels close, while activation gates of voltage-gated K+? channels open.
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In which type of axon will velocity of action potential conduction be the fastest?
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Myelinated axons with the largest diameter
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The small space between the sending neuron and the receiving neuron is the
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synaptic cleft.
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A molecule that carries information across a synaptic cleft is a
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neurotransmitter.
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When calcium ions enter the synaptic terminal,
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they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.
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When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron,
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ion channels in the plasma membrane of the receiving neuron open.
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If a signal from a sending neuron makes the receiving neuron more negative inside,
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the receiving neuron is less likely to generate an action potential.
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Leak channels
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-are always open
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Saltatory conduction
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when activations jump from each node of ranvier
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Seven classes of neurotransmitters
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Acetylcholine Amines Amino acids Purines Gases Peptides Lipids
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Which amino acids are excitatory
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-glutamate (CNS) -aspartate (brain)
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Which amino acids are inhibitory?
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-GABA (brain) -Glycine (spinal cord)
