Module 3: Cells of the Nervous System, and the Effects of Drugs on the Nervous System Flashcards
(59 cards)
Contrast the location of the central and peripheral nervous systems.
The CNS is located in the brain and spinal cord. The PNS is outside the brain and spinal cord. The PNS communicates with the CNS via nerves that relay sensory and motor information between the brain and spinal cord, and the rest of the body.
Describe the structures of a neuron, including their general function.
Neurons include four basic structures: the soma, dendrites, axon, and terminal buttons. The soma contains the nucleus and many of the organelles. The dendrites are branched structures attached to the soma that receive messages from other neurons. The axon is a long thin extension of the soma that conveys an electrical message to the terminal buttons. The terminal buttons are extensions of the axon that receive an electrical message and convert it to a chemical message by releasing neurotransmitters into the synapse. Other important structures include the cell membrane, cytoskeleton, and cytoplasm for providing shape and support to the cell. Internal organelles help the cell survive and include the nucleus, endoplasmic reticulum, Golgi apparatus, and mitochondria.
Differentiate the functions of supporting cells of the central and peripheral nervous systems.
In the CNS, astrocytes, oligodendrocytes, and microglia support neurons by creating an environment conducive to neuronal function, providing myelin sheath, and activating immune responses. In the PNS, Schwann cells provide myelin and assist with neural regeneration.
Discuss the features and importance of the blood-brain barrier.
The blood-brain barrier protects the CNS, selectively permitting only certain substances to enter. The barrier is made of capillary walls and helps regulate the composition of fluids in the brain, protecting neural transmission. The blood-brain barrier is more permeable in the area posterma, permitting neurons in this region to detect the presence of toxic substances in the blood.
Compare neural communication in a withdrawal reflex with and without inhibition of the reflex.
A simple withdrawal reflex is made up of a sensory neuron that detects the stimulus, a spinal interneuron that excites a motor neuron, and a motor neuron that causes the withdrawal behaviour. This relfex can be inhibited by input from the brain that can prevent the withdrawal behaviour by inhibiting the motor neuron.
Contrast the changes in electrical potential within a neuron when it is experiencing resting potential, hyperpolarization, depolarization, and an action potential.
Resting potential in most neurons is about -70mV, or 70 units more negative inside the neuron compared to outside of it. Hyperpolarization occurs when the inside of a neuron becomes more negative and depolarization occurs when the inside of the cell becomes more positive. An action potential is a burst of depolarization followed by hyperpolarization that proceeds like a wave along the axon, starting at the point where the axon meets the soma and proceeding to the terminal buttons.
Summarize the contributions of diffusion, electrostatic pressure, and the sodium-potassium pump to establishing membrance potential.
The differnece in charge between the inside and outside of the axonal membrane is generated by the force of diffusion, electrostatic pressure, and the activity of sodium-potassium pumps. The force of diffusion describes the process by which molecules distribute themselves evenly throughout the medium they are dissolved in. Electrostatic pressure describes the phenomenon in which similar charges repel and opposite charges attract each other. The sodium-potassium pump helps maintain the resting membrane potential by pumping three sodium ions out and two potassium ions into the cell with each molecule of ATP.
Summarize the series of ion movemements during an action potential.
After reaching the threshold of excitation, the voltage-gated sodium channels open, allowing sodium to enter the cell. Sodium’s movement into the cell is driven by the force of diffusion and electrostatic pressure. This depolarises the axonal membrane. After approximately one msec, the sodium channels become refractory. The positive charge inside the cell opens voltage-gated potassium channels. Potassium exits the cell due to the force of diffusion and electrostatic pressure due to the now positive charge on the inside of the cell. As potassium exits and diffuses away from the cell, the cell becomes more hyperpolarised and eventually becomes even more negatively charged inside the cell than resting potential. The potassium channels close, halting exit of potassium ions from the cell. The sodium-potassium pumps become active, moving three sodium ions out of the and two potassium ions in.
Describe the propogation of an action potential.
After initiating at the point where the axon joins the soma, the action potential propogates towards the terminal buttons according to the all-or-nothing law. The all-or-nothing law states that an action potential either occurs or doesn’t occur, and, once triggered , it is transmitted down the axon to it’s end. In an unmyelinated axon, the action potential proceeds along the axon but is subject to decremental conduction. In a myelinated axon, the action potential is conducted via salutatory conduction, which speeds the message, reduces decremental conduction, and renews the action potential at nodes of Ranvier. To vary the strength of the message conveyed by an action potential, the rate law explains that although each action potential event is identical, a stronger message can be conveyed by firing action potentials at a higher rate.
Describe the structures and functions of presynaptic cells that are involved in synaptic communication.
Presynaptic cells contain synaptic vesicles filled with neurotransmitters. Transport proteins fill vesicles with the neurotransmitters, and trafficking proteins are involved in the release of neurotransmitters and recycling of the vesicles. The presynaptic membrane faces the postsynaptic membrane across the synaptic cleft.
Describe the process of neurotransmitter release.
Following an action potential, a neurotransmitter is released from vesicles in the presynaptic cell that move and dock with the terminal membrane. Docking and creation of a fusion pore is triggered by the influx of calcium ions. The neurotransmitter is released into the synaptic cleft through the fusion pore. Following release, the membranes of the vesicles are recycled and return to the pool of available vesicles for future neurotransmitter release.
Contrast ionotropic and metabotropic receptors.
Ionotropic receptors open ion channels in direct response to the binding of a ligand. Metabotropic receptors can indirectly open ion channels through use of a G protein. Metabotropic receptors can also activate a second messenger system that can travel to the nucleus or other regions of the neuron and initiate biochemical changes that affect the functions of the cell. Second messengers can also turn specific genes on or off, thus initiating or terminating production of particular proteins.
Compare the functions of EPSPs and IPSPs in postsynaptic cells.
In the postsynaptic cell, an EPSP is a depolarisation resulting from the entry of sodium or calcium ions into the cell through a neurotransmitter-dependent ion channel. In the dendrites of the postsynaptic cell, calcium can also bind with enzymes that have a variety of effects. An IPSP is a hyperpolarisation resulting from the exit of potassium ions from or the entry of chloride ions into the cell through a neurotransmitter-dependent ion channel.
Explain the roles of reuptake and enzymatic deactivation in terminating postsynaptic potentials.
Postsynaptic potentials can be terminated by removing a neurotransmitter from the synapse through reuptake transporters or through breakdown by enzymatic deactivation.
Summarise the process of neural integration of EPSPs and IPSPs.
Neurons recieve multiple subthreshold EPSPs and IPSPs. The neuron integrates these messages. If the integrated messeges result in depolarisation beyond the threshold of excitation for the cell, the neuron will fire an action potential. If the messages are IPSPs or do not reach the threshold of excitation, the neuron will not fire an action potential.
Differentiate between the locations and functions of autoreceptors and postsynaptic receptors.
Postsynaptic receptors are located on the postsynaptic membrane and serve to relay a message to the postsynaptic cell. Postsynaptic receptors can be ionotropic or metabotropic. Autoreceptors are metabotropic receptors located on the presynaptic membrane that help regulate the amount of neurotransmitter that is released.
Identify synapses other than those involved in neural integration.
Other types of neural synapses include axoaxonic or dendrodendritic synapses and gap junctions.
Describe examples of nonsynaptic communication.
Neuromodulators are chemicals released by neurons that travel further and are dispersed more widely than neurotransmitters. Hormones are secreted by cells of endocrine glands or by cells located in various organs. The hormones are then distributed to the rest of the body through the bloodstream.
Central nervous system (CNS)
The brain and spinal cord.
Peripheral nervous system (PNS)
The nervous system outside the brain and spinal cord.
Efferent
Away from
Afferent
Towards
Axon
The long, thin, cylindrical structure that conveys information from the soma of a neuron to its terminal buttons.
Area postrema
A region of the medulla where the blood-brain barrier is weak; poisons can be detected there and can induce vomiting.
