Ch 41 Flashcards
What are the roles of the nervous system?
reception, transmission, integration, response
What are the steps to the flow of information through the nervous system?
stimulus, reception, transmission, integration
What are the types of cells in the nervous system?
afferent/sensory (meaning “to carry toward” they carry neural messages to the CNS), efferent/motor (efferent means “to carry away” so they carry neural messages away from the CNS to muscles and glands), association/interneurons (they sort the incoming information and determine the correct response)
Describe the structure of a typical neuron and give the function of each of its parts.
Neurons are specialized to recieve stimuli and transmit electrical and chemical signals. In a typical neuron, a cell body contains the nucleus and most of the organelles. Many branched dendrites extend from the cell body; they are specialized to recieve stimuli and send signals to the cell body. The single long axon extends from the cell body and forms branches called axon collaterals. The axon transmits signals into its terminal branches, which end in synaptic terminals. Many axons are surrounded by an insulating myelin sheath. In the PNS the myelin sheath is formed by Schwann cells. In the CNS the sheath is formed by other glial cells. Nodes of Ranvier are gaps in the sheath between successive Schwann cells. A nerve consists of several hundred axons wraped in connective tissue; a ganglion is a mass of neuron cell bodies in the PNS.
Name the main types of glial cells.
Astrocytes, oligodendrocytes, ependymal cells, and microglia
What is the function of glial cells?
They support and nourish neurons and are important in neural communication
What is the function of astrocytes?
the are glial cells that physically support neurons. they help regulate the composition of the extracellular fluid in the CNS by taking up excess potassium ions. Astrocytes communicate with one another and with neurons; they also induce and stabilize synapses.
What is the function of oligodendrocytes?
they are glial cells that form myelin sheaths around axons in the CNS; schwann cells form sheaths around axons in PNS.
What is the function of ependymal cells?
line cavities in the CNS and help produce and circulate cerebrospinal fluid. they may also serve as neural stem cells.
What is the function of microglia?
they are phagocytic, they “eat” any debris, they are very mobile
What are bundles of axons called in the CNS? In the PNS? What about groups of nerve cell bodies?
In the CNS, budles of axons are called tracts. In the PNS, bundles of axons are called nerves. Groups of nerve cell bodies are called nuclei in the CNS, but ganglia in the PNS.
What do dendrites do?
Dendrites recieve stimuli and send signals to the cell body. The axon then transmits the signals into its terminal branches that end in synaptic terminals.
With the sodium-potassium pump, what is the ratio of each pumped?
For every 3 sodium pumped out of the cell, two potassium are pumped in.
Which is more likely to cross the cell membrane without the pump, sodium or potassium?
potassium leaks out more easily than sodium gets in
What is the resting potential of the cell?
-70mV
What is the threshold potential of the cell?
-55mV
What happens when the cell gets to threshold?
The activation gate opens for sodium
When will the potassium gates open?
When the cell membrane’s charge is any positive number
What is a depolarized membrane? A hyperpolarized membrane?
A depolarized membrane is when a stimulus causes the membrane’s potential to become less negative. A hyperpolarized membrane is when the membrane’s potential becomes more negative than the resting potential.
What is the graded potential? The action potential?
Graded potential is the local response that varies in magnitude depending on the strength of the applied stimulus; it fades out within a few mm of its point of origin. Action potential is a wave of depolarization (less negative) that moves down the axon (when the cell goes from -70mV to +30mV)
What are the two refractory periods and when do they occur?
Absolute refractory period (ARP): same as repolarization phase (when the cell is adjusting from +30mV back to resting potential), it’s impossible to start another action potential. Relatively refractory period (RRP): it’s harder to get an action potential started, but not impossible, when the cell is recovering from undershoot trying to get back to resting potential
What is continuous signal conduction?
it involves the entire axon plasma membrane, it takes place in unmyelinated neurons
What is saltatory signal conduction?
it’s more rapid than continuous conduction, it takes place in myelinated neurons, it’s when depolarization skips along the axon from one node of Ranvier to the next (saltatory=skipping/jumping)
What are synapses?
the junction between two neurons or between a neuron and effector, most synapses are chemical, transmission depends on the release of neurotransmitter from synaptic vesicles in the synaptic terminals of a presynaptic neuron
