Organization Of The NS Flashcards
Incoming signals
enter this neuron through synapses located mostly on the
neuronal dendrites, but also on the cell body.
output signal travels by way of
several axon leaving the neuron.
True or False
False. Single axon only
information enters the central nervous system through peripheral nerves and is con
ducted immediately to multiple sensory areas in
(1) the spinal cord at all levels;
(2) the reticular substance of the medulla, pons, and mesencephalon of the brain;
(3) the cerebellum;
(4) the thalamus; and
(5) areas of the cerebral cortex.
skeletal muscles can be controlled from many levels of the central nervous system, including
(1) the spinal cord;
(2) the reticular substance of the medulla, pons, and mesencephalon; (3) the basal ganglia;
(4) the cerebellum; and
(5) the motor cortex.
junction point from one neuron to the next.
determine the directions that the nervous signals will spread through the nervous system
synapse
function of the synapses
memory
Facilitation
Each time certain types of sensory signals pass through sequences of synapses, these synapses become more capable of transmitting the same type of signal the next time, a process called
facilitation
neuronal circuits in the cord can cause
(1) walking movements, (2) relexes that withdraw por tions of the body from painful objects,
(3) relexes that stifen the legs to support the body against gravity, and (4) relexes that control local blood vessels, gastrointesti nal movements, or urinary excretion.
True or False
upper levels of the nervous system often operate by sending signals directly to the periphery of the body
False. by sending signals to the control centers of the cord, simply “com manding” the cord centers to perform their functions.
subconscious control of arterial pressure and respiration is achieved mainly in
the medulla and pons.
combined function of the older portions of the cerebellum and the reticular substance of the medulla, pons, and mesencephalon.
Control of equilibrium
Feeding relexes, such as salivation and licking of the lips in response to the taste of food, are controlled by areas in the
medulla, pons, mesencephalon, amygdala, and
hypothalamus
emotional patterns such as anger, excitement, sexual response, reaction to pain, and reaction to pleasure can still occur after destruction of much of the cerebral cortex
True or False
True
an extremely large memory storehouse.
Fxns in association with lower centers of the nervous system.
cerebral corte
it is the cerebral cortex, that initiate wakefulness
True or False
False. it is the lower brain centers, not the cortex, that initiate wakefulness in the cerebral cortex
lower brain centers opens the cortex’s bank of memories to the thinking machinery of the brain
True or False
True
All these functions can
be classiied as synaptic functions of neurons.
each impulse (1) may be
blocked in its transmission from one neuron to the next,
(2) may be changed from a single impulse into repetitive
impulses, or
(3) may be integrated with impulses from
other neurons to cause highly intricate patterns of
impulses in successive neurons.
important neurotransmitters
acetylcholine, norepinephrine, epinephrine,
histamine,
gammaaminobutyric acid (GABA), glycine,
serotonin, and
glutamate.
useful in detecting the coincidence of simultaneous subthreshold depolarizations within a group of interconnected neu
rons; this enables increased neuronal sensitivity and pro
motes synchronous iring of a group of interconnected neurons
bidirectional transmis
sion of electrical synapses
it is this speciic transmission of signals to discrete and highly focused areas both within the nervous system and at the terminals of the peripheral nerves that allows the nervous system to perform its myriad functions of sensation, motor control, memory, and many other functions.
principle of one-way conduction
These diferences make neurons in diferent parts of the nervous system react diferently to incoming synaptic signals and, therefore, perform many diferent functions.
- the size of the cell body;
(2) the length, size, and number of dendrites
(3) the length and size of the axon; and
(4) the number of presynaptic terminals
structural changes of appropri
ately activated neurons do not occur, especially in long
term memory processes.
True or False
False. Do occur
he importance of having inhibitory, as well as excitatory, types of receptors is that
this feature gives an additional dimension to nervous function, allowing restraint of nervous action and excitation.
It is by far the most widely used means for causing excitation.
Opening of sodium channels to allow large numbers
of positive electrical charges to flow to the interior of the postsynaptic cell.
Depressed conduction through chloride or potas-
sium channels, or both make the internal membrane potential more posi
tive than normal, which is inhibitory.
True or False
False. Excitatory
two groups of synaptic transmitters.
small-molecule, rapidly acting transmitters. he other is made up of a large number of neuropeptides of much larger molecular size that usually act much more slowly.
neuropeptides prolonged actions
changes in numbers of neuronal receptors,
opening or closure of certain ion channels,
changes in numbers of synapses or sizes of synapses.
present in the proteoglycan reticulum that ills the space of the synaptic cleft.
cholinesterase
Acetylcholine is secreted by neurons in many areas of the nervous system but speciically by
1) the terminals of the large pyramidal cells from the motor cortex,
2) several diferent types of neurons in the basal ganglia
3) the motor neurons that innervate the skeletal muscles
4) the preganglionic neurons of the autonomic nervous system
5) the postganglionic neurons of the parasympathetic nervous system, and
6) some of the postganglionic neurons of the sympathetic nervous system
inhibitory efect of acetylcholine
inhibition of the heart by the vagus nerves.
Norepinephrine is secreted by
brain stem and hypothalamus
locus ceruleus
secreted by neurons that originate in the substantia nigra.
Dopamine
It is believed to always act as an inhibitory transmitter.
Glycine
GABA
secreted by the presynaptic terminals in many of the sensory pathways entering the central nervous system, as well as in many areas of the cerebral cortex
Glutamate
originate in the median raphe of the brain stem and project to many brain and spinal cord areas and to the hypothalamus.
Serotonin
especially secreted by nerve terminals in areas of the brain responsible for longterm behavior and memory.
Nitric oxide
the action potential begins adjacent to the excit
atory synapses.
True or False
False. it begins in the initial segment of the axon
Time required for the excess positive charges to leak out of the excited neuron and to reestablish the normal resting membrane potential.
15 sec
change in potential at any single point within the soma will cause the potential to change everywhere inside the soma almost equally.
True or False
True
successive discharges from a single presynaptic terminal, if they occur rapidly enough, can add to one another
temporal summation.
Part of the fatigue process probably results from two other factors as well:
1) progressive inactivation of many of the postsynaptic membrane receptors and (2) slow development of abnor mal concentrations of ions inside the postsynaptic neuro nal cell.
from the axon of a preceding neuron to dendrites on cell mem-
branes of subsequent neurons. his feature forces the signal to travel in required directions to perform speciic nervous functions.
forward direction
transmits sensory information from
the receptors of the entire body surface and from some
deep structures
somatic portion of the sen-
sory system
he most important eventual role of the nervous sys-
tem is to control the various bodily activities achieved by controlling collectively called motor functions of the nervous system
1) contraction of appropriate
skeletal muscles throughout the body;
2) contraction of
smooth muscle in the internal organs; and
3) secretion
of active chemical substances by both exocrine and endo-
crine glands in many parts of the body
lower regions (of the levels of the CNS) are concerned primarily with
Automatic, instantaneous muscle responses to sensory stimuli,
higher regions are concerned with
deliberate complex muscle movements controlled by thought processes of the brain.
when important sensory information excites the mind, it is immediately channeled into proper inte-
grative and motor regions of the brain to cause desired responses. This channeling and processing of information is called the
integrative function of the nervous system.
determine the directions that the nervous sig- nals will spread through the nervous system.
Synapses
much of the information is stored for future control of motor activities and for use in the thinking processes
True or False
True
his process gives the person a perception of experiencing the original sensa-
tions, although the perceptions are only memories of the sensations.
the syn-
apses become so facilitated that signals generated within the brain itself can also cause transmission of impulses through the same sequences of synapses, even when the sensory input is not excited
three major levels
of the central nervous system have speciic functional
characteristics
(1) the spinal cord level; (2) the lower
brain or subcortical level; and (3) the higher brain or cor-
tical level.
the cytoplasms of adjacent cells are directly connected by clusters of ion channels called ?
They allow free movement of ions from the interior of one cell to the interior of the next cell.
Gap junctions in electrical synapses
he presyn- aptic terminal is separated from the postsynaptic neuro- nal soma by a
synaptic cleft
he terminal has two internal structures impor- tant to the excitatory or inhibitory function of the syn- apse:
transmitter vesicles and the mitochondria
provide adenosine triphosphate (ATP), which in turn supplies the energy for synthesizing new transmitter substances.
mitochondria
contain the neurotransmitter that when released into the synaptic cleft, excites or inhibits the postsynaptic neuron.
transmitter vesicles
he quantity of neurotransmitter that is then released from the terminal into the synaptic cleft is directly related to the number of calcium ions that enter
True or False
True
Receptor activation controls the opening of ion chan- nels in the postsynaptic cell in one of two ways:
- by gat- ing ion channels directly and allowing passage of speciied types of ions through the membrane; or
- by activating a “second messenger” that is not an ion channel but, instead, is a molecule that protrudes into the cell cytoplasm and activates one or more substances inside the postsynaptic neuron.
Neurotransmitter receptors that directly gate ion channels are often called
ionotropic receptors,
those that act through second messenger systems are called
metabotropic receptors.
a neurotransmitter that opens cation channels is called an
excitatory transmitter
prolonged postsynaptic neuronal excitation or inhibition is achieved by activating ION CHANNELS chemical system inside the postsynaptic neu-
ronal cell, and then it is the second messenger that causes
the prolonged efect.
True or False
SECOND MESSENGER
As long as the G protein complex is bound to
GDP, it remains active
True or False
False. Bound - Inactive
The following four changes that can occur when G protein complex is unbounded
- Opening specific ion channels through the postsyn-
aptic cell membrane - Activation of cyclic adenosine monophosphate
(cAMP) or cyclic guanosine monophosphate (cGMP) in the neuronal cell. - Activation of one or more intracellular enzymes
- Activation of gene transcription.
synthesized as integral parts of large- protein molecules by ribosomes in
the neuronal cell body.
Not in the cytosol
Neuropeptides
Another important characteristic of the neuropeptides is that they
often cause much more prolonged actions. Some of these
actions include
-prolonged closure of calcium channels,
-prolonged changes in the metabolic machinery of cells,
-prolonged changes in activation or deactivation of spe-
ciic genes in the cell nucleus, and/or
-prolonged altera-
tions in numbers of excitatory or inhibitory receptors.
the action potential does not begin adjacent to the excita-
tory synapses. Instead, it begins in
the initial segment of the axon where the axon leaves the neuronal soma.
True or False
the soma has relatively few voltage- gated sodium channels in its membrane
True. which makes it dicult for the EPSP to open the required number of sodium channels to elicit an action potential. Conversely, the membrane of the initial segment has seven times as great a concentration of voltage- gated sodium channels as the soma
he inhibitory synapses mainly open what channels
Cl channels
both chloride influx and potas-
sium efflux increase the degree of intracellular negativity,
hyperpolarization.
An increase in negativity beyond the normal resting membrane potential level is called an
inhibitory postsynaptic potential (IPSP).
caused by release of an inhibi-
tory substance onto the outsides of the presynaptic nerve
ibrils before their own endings terminate on the post-
synaptic neuron.
Presynaptic inhibition
opens anion channels, allowing
large numbers of chloride ions to difuse into the terminal
ibril. he negative charges of these ions inhibit synaptic transmission because they cancel much of the excitatory efect of the positively charged sodium ions that also enter
the terminal ibrils when an action potential arrives.
GABA
summing simultaneous postsynaptic potentials by activating multiple terminals on widely spaced areas of the neuronal membrane
spatial summation.
the summated postsynaptic potential is excitatory but has not risen high enough to reach the threshold for iring by the postsynaptic neuron.
another excitatory signal entering the neuron from some other source can then excite the neuron very easily
When this situation occurs, the neuron is said to be facilitated.
It is also important that between 80% and 95% of all the presynaptic terminals of the anterior motor neuron terminate on dendrites, in contrast to only 5% to 20% ter-
minating on the neuronal soma.
True or False
True
direct spread of electrical cur-
rent by ion conduction in the luids of the dendrites but without the generation of action potentials
electrotonic current
before the excitatory potentials can reach the soma, a large share of the potential is lost by leakage through the membrane. his decrease in mem-
brane potential as it spreads electrotonically along den-
drites toward the soma is called
decremental conduction.
True or False
The farther the excitatory synapse is from the soma of the neuron, the lesser will be the decrement and the greater will be excitatory signal reaching the soma.
False. The farther the excitatory synapse is from the soma of the neuron, the greater will be the decrement and the lesser will be excitatory signal reaching the soma.
number of discharges by the postsynaptic neuron is at
irst very great, but the iring rate becomes progressively
less in succeeding milliseconds or seconds
fatigue of synaptic transmission.
he mechanism of SUMMATION is mainly exhaustion or partial exhaustion of the stores of transmitters in the presynaptic terminals.
True or False
FALSE. FATIGUE
Nor-
mally, alkalosis greatly increases neuronal excitability.
acidosis greatly depresses neuronal activ-
ity; a fall in pH from 7.4 to below 7.0 usually causes a
comatose state.
True or False
TRUE ALL
increase neu-
ronal excitability, presumably by reducing the threshold for excitation of neurons.
caffeine, theophylline, and theobromine,
it inhibits the action of some normally inhibitory transmitter substances, especially the inhibitory
efect of glycine in the spinal cord.
Strychnine
the efects of the excitatory transmitters become overwhelming, and the neurons become so excited that they go into rap-
idly repetitive discharge, resulting in severe tonic muscle spasms.
