Anatomy & Physiology chapter 12
Neuroglia in the CNS that remove cell debris, wastes, and pathogens by phagocytosis
Microglia
What are the least numerous and smallest neuroglia in the CNS?
Microglia
This serves as electrical insulation and increases the speed at which an action potential travels along the axon
Myelin
depolarization results from the influx of ______
Na+, sodium
Whenever a Schwann cell covers an axon, the outer surface of the Schwann cell is called the ______________
Neurilemma
The small, unmyelinated gaps between internodes
Nodes of Ranvier
Where do an axon's collateral branches originate?
Nodes of Ranvier
Which neuroglial cell forms the myelin sheath?
Oligodendrocytes
What makes white matter white?
Regions consisting of heavily-myelinated axons The axons appear glossy white bc of lipids in the myelin
Neuroglia in the PNS that surround neuron cell bodies in ganglia, regulate O2 and CO2, nutrient, & neurotransmitter levels around neurons in ganglia
Satellite cells
What are the two types of neuroglia in the PNS?
Satellite cells and Schwann cells
Neuroglia in the PNS that form myelin sheaths or indented folds of plasma membrane around peripheral axons
Schwann cells
which cells in the PNS play a role in repairing damaged nerves
Schwann cells
The membrane potential is the electrical potential of the cell's interior relative to its _________________
Surroundings
what is a current?
a movement of charges to eliminate a potential difference (btwn ions)
part of refractory period where the membrane cannot respond to further stimulation
absolute refractory period
the most widespread neurotransmitter
acetylcholine
if a graded potential is large enough, it triggers an _______________________ in the membrane of the axon
action potential
membrane channels that open or close in response to specific stimuli
active channels
synapses that release norepinephrine are called __________________
adrenergic synapses
what two FUNCTIONAL divisions can the PNS further divide into?
afferent and efferent
principle that states a given stimulus either triggers a typical action potential, or none at all
all-or-none principle
what is an axon potential?
an electrical impulse that is propagated along the surface of an axon and does not diminish as it moves away from its source
the flow of materials from the cell body to the axon is ___________________ flow, carried by _________.
anterograde; kinesin
at an ____________ synapse, a synapse occurs between the axons of two neurons
axoaxonic
specialized portion of the plasma membrane that surrounds the axoplasm
axolemma
an __________ is a long cytoplasmic process capable of propagating an electrical impulse known as an action potential
axon
the base of an axon in a multipolar neuron joins the cell body at a thickened region known as the __________________
axon hillock
bundles of ___________, or nerve fibers, carry sensory information & motor commands in the PNS
axons
the cytoplasm of an axon
axoplasm
the movement of materials between the cell body and axon terminals is called __________________
axoplasmic transport
the CNS consists of the _________ and the ________________
brain; spinal cord
what does the enzyme acetylcholinesterase do?
breaks down molecules of ACh by hydrolysis into acetate and choline
what is the afferent division of the PNS?
brings sensory information to the CNS
the arrival of what ion in the axon terminal triggers the exocytosis of ACh?
calcium
what is the efferent division of the PNS?
carries motor commands from the CNS to muscles, glands, & adipose tissue
the most abundant types of synapses
chemical synapses
what type of gated ion channels are the ACh receptors on the postsynaptic neuron?
chemically gated ion channels
after ACh is broken down into acetate and choline by acetylcholinesterase, what does choline do? what does acetate do?
choline: absorbed by the axon terminal & used to synthesize more ACh (with coenzyme A) acetate: absorbed by postsynaptic cell/other cells/tissues
synapses that release acetylcholine
cholinergic synapses
an axon may branch along its length, producing side branches known as _______________
collaterals
in an unmyelinated axon, an action potential moves along by ________________________
continuous propagation
nerves connected to the brain
cranial nerves
what is the intracellular fluid of a cell called?
cytosol
mechanically gated channels are typically located only on the __________ of sensory neurons
dendrites
materials that travel slowly from the cell body to the axon terminal, called the _____________
"slow stream"
the threshold for an axon is typically between ____ mV and _____ mV
-60; -55
slender, sensitive processes that extend out from the cell body (of the neuron)
dendrites
what are unipolar neurons?
dendrites & axons are continuous (fused) & cell body lies off to one side
where are chemically gated channels most abundant?
dendrites & cell body of neurons (areas where most synaptic communication occurs)
any shift from the resting membrane potential toward a more positive potential is called a _________________.
depolarization
what is the normal stimulus for neurotransmitter release?
depolarization of the axon terminal by the arrival of an action potential
a neurotransmitter of the CNS that has inhibitory and excitatory effects
dopamine
organs targeted by the efferent division of the PNS are called ______________.
effectors
neurotransmitter release is triggered by _____________________
electrical events
a synapse may be ______________ or _________________.
electrical; chemical
the membrane potential at which there is no net movement of a particular ion across the plasma membrane
equilibrium potential
neurotransmitters that cause depolarization and promote the generation of action potentials
excitatory neurotransmitters
a graded depolarization caused by the arrival of a neurotransmitter at the postsynaptic membrane
excitatory postsynaptic potential
what are the two major types of postsynaptic potentials?
excitatory postsynaptic potentials (EPSP) and inhibitory postsynaptic potentials (IPSP)
another way of saying a neuron is close to threshold
facilitated
in presynaptic ______________, the activity at an axoaxonic synapse increases the amount of neurotransmitter released when an action potential arrives at the axon terminal
facilitation
true or false; neurons come in only one shape/size
false
true or false; the properties of the action potential are dependent of the relative strength of the depolarizing stimulus
false
true or false; dendritic spines represent 30-40% of a neuron's total surface area
false; 80-90%
true or false; an action potential that reaches a chemical synapse will always be propagated to the next cell
false; an arriving action potential may or may not release enough neurotransmitter to bring the postsynaptic neuron to threshold
true or false; at resting membrane potential, most gated channels are open
false; closed
true or false; electrical synapses are very common
false; extremely rare
true or false; all stimuli that bring the membrane to threshold generate different action potentials
false; identical action potentials
true or false; the chemical gradient is not strong enough to overpower the electrical gradient
false; the chemical gradient is strong enough to overpower the electrical gradient, but the electrical gradient weakens the force
true or false; the effect of a neurotransmitter on the postsynaptic membrane depends on the nature of the neurotransmitter
false; the effect depends on the properties of the receptor
true or false; the postsynaptic cell can only be a neuron
false; the post synaptic cell can either be a neuron or another type of cell
true or false; the presynaptic membrane bears receptors for neurotransmitters
false; the presynaptic membrane is where neurotransmitters are released
true or false; the sympathetic & parasympathetic division of the autonomic nervous system have the same effect
false; they have opposite effects
what does GABA stand for?
gamma-aminobutyric acid
at electrical synapses, the presynaptic and postsynaptic membranes are locked together at ________ junctions. the opposing membranes are held in position by proteins called _______________, which form pores that allow ions to pass between the cells.
gap; connexons
active channels are also known as _____________ channels
gated
compounds that have direct effects on membrane potential open or close ______________ channels
gated ion
a typical stimulus produced a temporary, localized change in the resting membrane potential, this effect is called a _________________________.
graded potential
aka local potentials, are changes in the membrane potential that cannot spread far from the site of stimulation
graded potentials
what are bipolar neurons?
have one dendrite that branches extensively into dendritic branches at its distal tip & one axon, with cell body in between the two -rare -occur in special sense organs -small
what are multipolar neurons?
have two or more dendrites and a single axon -most common neurons in CNS
-70 mV --> -80 mV is an example of: _____________________
hyperpolarization
an increase in the negativity of the resting membrane potential; the loss of positive ions from inside the cell
hyperpolarization
in presynaptic ______________, activity at an axoaxonic synapse decreases the amount of neurotransmitter released when an action potential arrives at the axon terminal
inhibition
neurotransmitters that cause hyperpolarization and suppress the generation of action potentials
inhibitory neurotransmitters
a graded hyperpolarization of the postsynaptic membrane caused by the arrival of a neurotransmitter at the postsynaptic membrane
inhibitory postsynaptic potential
what are the general functions of the CNS?
integrating, processing, & coordinating sensory data & motor commands
neurons are nerve cells specialized for _____________________
intercellular communication
neurotransmitters that alter ion movement across the membrane are said to have _____________ effects
ionotropic
materials, such as neurotransmitters, enzymes, & lysosomes travel the length of the axon on neurotubules pulled by ______ and ________; "molecular motors" that run on ATP
kinesin, dynein
at resting membrane potential, ions move through ___________ channels
leak
movement of positive charges parallel to the inner and outer surfaces of a membrane: _________________
local current
gated channels that open or close in response to physical distortion of the membrane surface
mechanically gated channels
neurotransmitters that indirectly affect the postsynaptic cell by changing metabolic activity are said to have _____________ effects
metabotropic
why is the inner surface of a neuron negatively charged?
negatively charged proteins inside the cell are too large to cross the membrane and get out
an action potential in a neuron plasma membrane is also known as a ________________
nerve impulse
bundles of axons with associated blood vessels and connective tissues are called ____________
nerves
bundles of neurofilaments, called __________________, extend into the dendrites and axon, providing internal support for them
neurofibrils
the cytoskeleton of the perikaryon contains ______________ and ______________, which are similar to the intermediate filaments & microtubules of other types of cells
neurofilaments, neurotubules
synapse between a neuron & a glandular cell
neuroglandular junction
a compound released by a neuron that alters the rate of neurotransmitter released by the presynaptic neuron or change the postsynaptic cell's response to neurotransmitters
neuromodulator
synapse between a neuron & a muscle cell
neuromuscular junction
the basic functional units of the nervous system are individual cells called ____________.
neurons
neuromodulators are typically _____________, small peptide chains synthesized & released by the axon terminal
neuropeptides
which two gasses are known to be important neurotransmitters?
nitric oxide (NO) carbon monoxide (CO)
will a stimulus that shifts the resting membrane potential from -70 mV to -62 mV produce an action potential?
no
norepinephrine (NE) is also called _________________
noradrenaline
neurotransmitter that is widely distributed in the brain and ANS, typically has an excitatory (depolarizing) effect on the postsynaptic membrane
norepinephrine
neuromodulators that inhibit the release of the neurotransmitter substance P at synapses that relay pain sensations
opioids
leak channels are also known as ____________ channels
passive
membrane channels that are always open
passive channels
the cytoplasm surrounding the nucleus (in neurons) is the __________________
perikaryon
what is a synaptic delay?
period between arrival of a nervous impulse at the presynaptic membrane and the initiation of an action potential in the postsynaptic membrane
this includes all the neural tissue outside the CNS
peripheral nervous system
the cell involved in a synapse that receives the message
postsynaptic cell
membrane in a synapse that bears receptors for neurotransmitters
postsynaptic membrane
graded potentials that develop in the postsynaptic membrane in response to a neurotransmitter
postsynaptic potentials
the cell involved in a synapse that sends a message & includes the axon terminal
presynaptic cell
sensory structures that either detect changes in the environment (internal or external) or respond to specific stimuli
receptors
the time an action potential begins until the normal resting membrane potential has stabilized
refractory period
what are Nissl bodies?
regions of the perikaryon of a neuron that contain clusters of rough endoplasmic reticulum and free ribosomes -stain darkly -give gray color to areas containing neuron cell bodies (gray matter)
part of refractory period where the membrane can respond to further stimulation but only if it is larger than normal
relative refractory period
the primary function of opioids is probably to __________________.
relieve pain
the process of restoring the normal resting membrane potential after depolarization is called ________________
repolarization
the ______________ of the membrane is a measure of how much the membrane restricts ion movement
resistance
all neural activities begin with a change in the _______________________ of a neuron
resting membrane potential
the flow of materials from the axon terminal to the cell body is ______________ flow, carried by ________.
retrograde; dynein
which carries axon potentials faster? saltatory or continuous propagation?
saltatory
in a myelinated axon, an action potential moves along by _________________________.
saltatory propagation
the PNS delivers ___________ information to the CNS and carries _________ commands to peripheral tissues/systems
sensory; motor
a CNS neurotransmitter that is related to depression
serotonin
what are anaxonic neurons?
small neurons with many dendrites and no axon -located in brain & special sense organs
if the resistance of a membrane is high, then the current is ______. if the resistance is low, then the current is _____.
small; large
the ECF contains high concentrations of ______________ and _____________, whereas the cytosol contains high concentrations of ________________ and ________________.
sodium ions (Na+) chloride ions (Cl-); potassium ions (K+), negatively charged proteins
ion pump that exchanges THREE intracellular sodium ions for TWO extracellular potassium ions during normal resting potential of the cell
sodium-potassium ATPase
also called the cell body of a neuron
soma
what can the efferent division of the PNS be further divided into?
somatic nervous system & autonomic nervous system
what is the difference between the somatic nervous system & the autonomic nervous system?
somatic: controls SKELETAL muscle contractions (both subconscious & conscious) autonomic: controls smooth & cardiac muscle, glandular secretions, & adipose tissue (SUBCONSCIOUS)
multiple synapses that are active simultaneously at different locations have a cumulative effect on the membrane potential
spatial summation
nerves attached to the spinal cord
spinal nerves
what is the electrochemical gradient?
sum of the chemical and electrical forces acting on that ion across the plasma membrane
the effects of all the graded potentials that affect one portion of the plasma membrane
summation
what are neuroglia?
supporting cells to the neurons -preserve neural tissue -separate/protect neural tissue -act as phagocytes -help regulate composition of interstitial fluid
what can the autonomic nervous system of the PNS be further divided into?
sympathetic division & parasympathetic division
the activity of the _____________ division accelerates the heart rate, whereas _________________ activity slows the heart rate
sympathetic; parasympathetic
a specialized site where a neuron communicates with another cell
synapse
during a synapse, a narrow space called the ___________________ separates the two cells
synaptic cleft
_____________ occurs when resynthesis and transport mechanisms cannot keep up with the demand for neurotransmitter and the synapse weakens until ACh is replenished
synaptic fatigue
inside the axon terminal of the presynaptic cell, neurotransmitters are contained in ______________
synaptic vesicles
most of the ACh in the axon terminal of the presynaptic neuron is packaged in ____________________.
synaptic vesicles
the main axon trunk and any collaterals end in a series of fine extensions called _______________
telodendria
the addition of stimuli occurring in rapid succession at a single synapse that is active repeatedly
temporal summation
what is resting membrane potential?
the membrane potential of an unstimulated, resting cell
why can typical CNS neurons not divide?
they lack centrioles (organelles important in moving chromosomes during mitosis)
the membrane potential at which an action potential begins
threshold
true of false; a multipolar neuron is the most common type of neuron in the CNS
true
true or false; a cell's membrane permeability varies by ion
true
true or false; an action potential that reaches an electrical synapse is always propagated to the next cell
true
true or false; axoplasmic transport occurs in both directions
true
true or false; dynorphins have far more powerful pain-relieving effects than morphine or the other opioids
true
true or false; neuroglia far outnumber neurons
true
true or false; one neuron may communicate with another at a synapse on a dendrite, on the cell body, or along the length of the axon of the receiving cell
true
true or false; roughly half of the ACh released at the presynaptic membrane is broken down before it reaches receptors on the postsynaptic membrane
true
true or false; sodium and potassium ions are the primary determinants of the membrane potential of many cell types, including neurons
true
true or false; sodium-potassium ATPase pump ejects sodium ions as quickly as they enter the cell
true
true or false; the all-or-none principle applies to all excitable membranes
true
true or false; the degree of depolarization (in graded potential) decreases with distance away from the stimulation site
true
true or false; the diameter of the axon has effects on the propagation speed of an action potential
true
true or false; vesicles containing neurotransmitters move much more rapidly (from soma to axon terminal)
true
what are the 3 classes of gated channels?
1. chemically (ligand) gated channels 2. voltage-gated channels 3. mechanically gated channels
what are the four classes of opioids in the CNS?
1. endorphins 2. enkephalins 3. endomorphins 4. dynorphins
why is regeneration of axons limited in the CNS?
1. many more axons are likely to be involved in an injury 2. astrocytes produce scar tissue that can prevent axon growth across the damaged area 3. astrocytes release chemicals that block the regrowth of axons
How man types of neuroglia are in the PNS?
2
viewed anatomically, how many divisions does the nervous system have? what are they?
2; central nervous system & peripheral nervous system
the average number of ACh molecules in a single vesicle is _____________.
3000
What is the difference between myelination by Schwann cells and myelination by oligodendrocytes?
A myelinating Schwann cell can myelinate only one segment of a single axon, whereas an oligodendrocyte in the CNS may myelinate portions of several adjacent axons
the sodium-potassium pump requires energy in the form of _______
ATP
most sensory information arrives over type ___ fibers
C
True or false; all axons in the CNS are myelinated
False
True or false; each oligodendrocyte can only myelinate one axon
False; each oligodendrocyte myelinates segments of several axons
True or false; the cell bodies of astrocytes are smaller than that of the oligodendrocyts
False; the cell bodies of oligodendrocytes are smaller & have fewer processes
Are ependymal cells found in the CNS or PNS?
CNS
the _______ is the seat of higher functions, such as intelligence, memory, learning, & emotion
CNS
neurotransmitter of the CNS with generally inhibitory effects ; seems to reduce anxiety
GABA
What makes up the gray matter of the CNS?
Areas containing neuron cell bodies, dendrites, & unmyelinated axons
Neuroglial cells of the CNS that: 1. Maintain BBB 2. Provide structural support 3. Regulate ion, nutrient, and dissolved gas concentrations 4. Absorb & recycle neurotransmitters 5. Form scar tissue after injury 6. Guiding neuron development
Astrocytes
Which type of neuroglial cells provide a 3D framework for the CNS?
Astrocytes
Neuroglial cells of the CNS that line ventricles (brain) and central canal ( spinal cord); assist in producing, circulating, and monitoring cerebrospinal fluid
Ependymal cells
The areas of an axon that are wrapped in myelin are called ______________.
Internodes
in an action potential, repolarization involves loss of ______
K+, potassium
True or false; internodes are typically 1-2 mm in length
True
what are type A, B , and C fibers?
type A: largest myelinated axons, diameters 4-20 micrometers, carry action potentials up to 120 meters per second (268 mph) -sensory information about position balance, touch & pressure -also motor neurons that control skeletal muscles type B: smaller myelinated axons, diameters 2-4 micrometers, carry action potentials up to 18 meters per second (40 mph) -carry info to/from CNS -temperature, pain type C: unmyelinated axons, less than 2 micrometers in diameter, carry action potentials up to 1 meter per second (2 mph) -carry info to/from CNS -temperature, pain
gated channels that open or close in response to changes in the membrane potential; often found in areas of excitable membrane
voltage-gated channels
