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What do nerve cell serve?
sensorimotor activities and higher mental functions (e.g., memory, thought, language, reasoning and calculation.)
What are Oligodendroglia?
Equivalent to Schwann Cell in the PNS
lay down the myelin sheath in the CNS
Why are astroglia believed to play a role in transport of substances between capillaries and neurons and in the blood brain barrier?
Because they have end-feet that contact capillaries
What are the cells that remove cell debris generated in normal cell death and in degenerating brain tissue/cell death due to brain injury?
Together with the ___ ___, dendrites constitute the ______ segment of the neuron
Together with the cell body, dendrites constitute the receptive segment of the neuron.
What unit is specialized as a receptor and integrator of info received from other neurons?
Each main axon or its collaterals, terminates by branching into several terminal filaments called _______
What determines if a neuron will have an excitatory or inhibitory effect on the neuron with which it synapses?
Axon length can vary from ___ ____ (in the brain) to as long as __ ______ (in the spinal cord)
Axon length can vary from a few micrometers (in the brain) to as long as 2 meters (in the spinal cord)
What has one process extending from the body and divides into central and peripheral processes?
What kind of neurons are the cells in the dorsal/sensory roots of the spinal cord?
unipolar or pseudopolar
What is the synaptic cleft?
space between the
bouton of one neuron and the cell body, dendrite or axon or another neuron
or the space between the bouton and the cell membrane of a muscle fiber neuron to muscle synapse
What is the cell membrane of the other cell body, dendrite, axon, or muscle fiber?
What is an internode?
distance from one node of ranvier to the next along the course of the axon fiber
What are neurotransmitters?
chemical messengers that transmit signals between neurons and between neurons and muscle
What is the nerve to muscle ratio?
describes how many muscle fibers are innervated by a single motor neuron
The more precise (fine) a movement, the ____ the ratio
The more precise a movement, the smaller the ratio.
i.e. tongue muscle 1:5
What is the termination of a nerve fiber (and its branches) on a muscle?
neuromuscular (myoneural) junction
What is the synapse of each axon terminal (bouton) of a motor neuron on a voluntary muscle fiber?
Neuron fluid inside is more _____ than fluid ____ a neuron
Neuron fluid inside is more negative than fluid outside a neuron.
How is the membrane potential created?
by differences in ion concentrations across the cell membrane (between the intra vs. extracellular fluid)
cell metabolic activity (diffusion of potassium)
selective transport (gated channels in the cell membrane)
What is left behind when potassium (K+) leaks out?
anions (large quantities of (-) charged protein molecules that cannot leak out)
which is why the inside of the cell is negative relative to the outside
When a signal is transmitted over a nerve fiber, the membrane potential goes through a series of changes called the ____ ________
What does an action potential do to the cell membrane?
any factor that suddenly increase the permeability of the membrane to sodium ions
What are two stimuli that can elicit an action potential?
physical stimulus - sensory nerve ending such as pressure on skin
chemical stimulus - neurotransmitter
What happens when the action potential permeates?
positively charged sodium ions leak into the cell in great numbers and membrane becomes more positive/less negative by at least 30 mV
What is the initial positive change in the membrane potential?
depolarization (where the normal negatively polarized state no longer exists)
What is saltatory conduction?
takes place in myelinated axons. the Action potential jumps from node to node
When the the neuron is hyperpolarized, what is happening to the membrane potential?
it becomes more negative from -70 to -90
What is the relative refractory period?
membrane is not fully repolarized but a strong (suprathreshold) stimulus can cause new AP
What are the steps in the process of synapse and neurotransmitter release?
1. AP arrives at the terminal bouton
2. this causes depolarization of presynaptic membrane
3. Influx of calcium (CA++) from synaptic cleft
activates neurotransmitter release from the synaptic vessicles
Generator potential relies on _________ of arriving stimuli, which is a local graded response.
What has to happen for the stimulus to to reach the initial segment (axon hillock) and generate a new AP?
Generator potentials need to sum
What is temporal summation?
several subthreshold stimuli must sum within a critical time period to initiate new AP
What type of neural summation requires many stimuli to converge on postsynaptic membrane simultaneously to initiate new AP?
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