Excitable Cells
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| List and describe the components of a neuron. | Soma: cell body, Dendrites: the receptive process of the neuron, Axon: major outflow of the neuron-leads to the synapse. | |
| Describe a bipolar neuron. | Two processes – one dendrite and one axon (special senses). | |
| Describe a multipolar neuron. | One axon and several dendrites (anterior horn cells of spinal cord). | |
| Describe a pseudounipolar neuron. | One process that splits close to the soma into the dendrite and the axon. | |
| What are the classifications of neurons? | Bipolar, multipolar, and pseudounipolar or sensory neurons, motor neurons, and interneurons. | |
| What are the types of communication between neurons? | Axondendritic, axosomatic, and axoaxonal synapse, en passant, and somatosomatic. | |
| What is an internode? | A single segment of myelin produced by one Schwann cell or oligodendrocyte. | |
| What is a Node of Ranvier? | The gap between internodes. | |
| What is myelin made up of? | Lipids and proteins | |
| What is a myelin sheath? | The layered wrapping of the glial cells around the axons. | |
| What is the role of myelin in nerve conduction? | Acts as an insulator of the nerve cell, enable salutatory conduction, increases the conduction velocity of the action potential. | |
| Give examples of demyelinating diseases. | MS, Guillian Barre, Charcot-Marie-Tooth disease, Adrenoleukodystrophy. | |
| What happens in an action potential? | The cell membrane potential becomes reversed when a stimulus depolarizes the axon. | |
| Name the three protein ion channels that may be present in a cell membrane. | Open, voltage gated, or ligand gated. | |
| What is the sodium-potassium pump? | Actively transports sodium ions out of the cell and potassium ions into the cell to establish and maintain a concentration gradient. | |
| What is the resting membrane potential of a cell? | -70mV, more negative inside the cell, more positive outside the cell. | |
| Describe the process of an action potential. | Stimulus depolarizes the axon->voltage gated sodium ion channels open->sodium enters the axon making the cell more positive->potassium pump also opens and potassium is moved out of the cell->when threshold is reached(inside of cell is positive)the reversal of the membrane potential results in an action potential->depolarization occurs->repolarization begins. | |
| What is an absolute refractory period? | Occurs immediately after the action potential, the cell will not excite regardless of stimulus. | |
| What is a relative refractory period? | Action potential is triggered only if stimulus is stronger than normal. | |
| What determines conduction velocity? | The diameter of the axon and the amount of myelin, bigger axon and more myelin=quicker conduction. | |
| What is saltatory conduction? | Signal jumps from node to node in mylinated fibers. | |
| What is orthodromic conduction? | Signal sent away from the cell body. | |
| What is antidromic conduction? | Signal sent towards the cell body. | |
| Explain the significance of calcium in the passage of a nerve potential across a nerve synapse. | Ca++ ions must be present at the end of the axon for transmission of the impulse. | |
| What is a chemical synapse? | Transmission is accomplished by the release of chemical transmitters by the presynaptic cell across the synaptic cleft and into the postsynaptic cell by transmitter sensitive ion channels. | |
| Define terminal bouton. | The presynaptic/afferent end of the axon. | |
| Name the two types of receptors. | Ligand gated ion channel receptors and G-protein linked receptors. | |
| What is a ligand? | A neurotransmitter/chemical messenger. | |
| What is a ligand gated ion channel? | A ligand binds to a protein receptor molecule which selectively allows ions to pass through the ion channel and therefore in or out of the cell. This generates the postsynaptic potential which alters the membrane potential of the postsynaptic neuron. This potential either excites or inhibits the postsynaptic cell. | |
| What is a G-protein linked receptor? | Evoke action through a regulatory protein – guanosine nucleotide binding protein. When a neurotransmitter binds to a receptor, G-proteins are activated and released from the receptor to bind with target enzymes to form a second messenger. This allows them to affect cell metabolism and act as neuromodulators. | |
| Define EPSP. | An excitatory synapse in which the postsynaptic response to the specific neurotransmitter is for depolarization due to the opening of sodium and potassium channels (more Na++ in). | |
| Define IPSP. | An inhibitory synapse in which the postsynaptic response of hyperpolarization reduces the chance of a postsynaptic action potential due to the opening of chloride channels (more K+ out and Cl- in). | |
| How does the influx of chloride in an IPSP hyperpolarize the cell? | Chloride ions are negative and thus neutralize the positive charge. | |
| What is temporal summation? | Summation of several EPSP’s occurring close together in time due to rapid and successive firing of one or more presynaptic neurons. | |
| What is spatial summation? | The summation of EPSP’s that arrive to one neuron simultaneously from several different presynaptic inputs. | |
| What is presynaptic inhibition? | The sum of all the synaptic currents on a neuron that results in what occurs, modulates the amplitude of IPSP’s and EPSP’s. | |
| What is long term potentiation (LTP)? | Synapses increase their effectiveness with activity, can last minutes to hours. | |
| What is long term depression (LTD)? | Synapses decrease their effectiveness LTP and LTD assist in modulating the function of synapses (important in plasticity and learning). | |
| What are the excitatory neurons? | Acetylcholine (ACh), the amino acids glutamate & aspartate, the neuroactive peptides opioid neuropeptides & substance P. | |
| What are the inhibitory neurons? | The amino acids GABA, glycine, the monoamines norepinephrine, dopamine, and serotonin. | |
| What agent will inhibit choline from crossing the cell membrane for the formation of acetylcholine? | Hemicholinium-3. | |
| What agent will prevent vesicles from taking up acetylcholine at the end of the axon in the region of the synapse? | Vesamicol. | |
| What agent prevents acetylcholine release and the transmission of an impulse? | Botulinum toxin. | |
| What agent prevents the formation and reformation of vesicles for storing acetylcholine? | Black widow spider venom. | |
| What agent prevents Ca+ from entering the cell/being present at the end of the axon for transmission of the impulse? | Metals such as magnesium. | |
| What causes the ligand binding site to be unavailable to the neurotransmitter and prevents uptake? | Curare. | |
| What agent prevents the chemical breakdown of acetylcholine by enzyme cholinesterase and prolongs ACh action? | Neostigmine. | |
| Which toxins act pre-synaptically? | Hemicholinium-3, vesamicol, botulinum toxin, black widow spider venom, and metals such as magnesium. | |
| Which toxins act post-synaptically? | Curare and neostigmine. |
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