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
What is ligand-gated?
a gate that opens or closes depending on whether there’s a neurotransmitter bound to it
What signals the release of neurotransmitters?
Ca2+
What are the types of neurotransmitters?
Acetylcholine, glutamate, GABA, biogenic amines, neuropeptides, and nitric oxide
What are some kinds of biogenic amines and what do they do?
Norepinephrine, serotonin, dopamine, they play important roles in regulating mood
What are some types of neuropeptides and what do they do?
endorphins, enkephalins, they control pain regulation
What is nitric oxide and what does it do?
nitric oxide is a neurotransmitter that goes the wrong way, from post- to pre- synaptic, it talks back to the cell that sent the signal (nitric oxide=NO)
What does glutamate do?
it is an amino acid that is the main excitatory neurotransmitter in the brain
What does GABA do?
it is the main inhibitory neurotransmitter in the brain
What is the process of a chemical synapse?
Calcium enters the cell, exocytosis occurs, it triggers a neurotransmitter of some kind to be released that then diffuses across the cleft, the neurotransmitter opens up the sodium ion channel, sodium enters and depolarizes the cell, cholinesterase (an enzyme that breaks down neurotransmitters) then degrades the neurotransmitter
What does acetylcholine do?
triggers contractions of skeletal muscle
What are the kinds of graded potentials?
Excitatory Postsynaptic Potential (EPSP): excitatory DEpolarizes, excitatory is a change in membrane potential that brings the neuron closer to firing, and Inhibitory Postsynaptic Potential (IPSP): inhibitory HYPERpolarizes, makes the membrane potential more negative and takes it farther away from firing
What is summation? What are the two types of summation?
Summation is when graded potentials are added together, the two types are spatial (simultaneous excitations at two locations on the neuron which increases the membrane potential above resting) and temporal (stimulates/excites the same place twice which results in an increase in the membrane potential above resting)
What is convergence?
when a single neuron is controlled by converging signals from two or more presynaptic neurons, this permits the CNS to integrate incoming information from various sources; multiple neurons talk to one neuron
What is divergence?
when one neuron talks to multiple, a single presynaptic neuron stimulates many postsynaptic neurons which allows for a widespread effect; one neuron talks to multiple neurons
What is reverbation?
when a neuron talks to itself; axon collaterals provide positive feedback
