Structure and Functions of Cells of the Nervous System Flashcards
1
Q
how many nerve cells, or neurons, are there in the human brain?
A
around 86 billion neurons
2
Q
central nervous system (CNS)
A
consists of the brain and the spinal cord
3
Q
peripheral nervous system (PNS)
A
The part of the nervous system outside the brain and spinal cord, including the nerves attached to the brain and spinal cord.
4
Q
How does the CNS communicate with the rest of the body?
A
through nerves
5
Q
nerves
A
Bundles of individual neurons contained within a protective membrane; that relay sensory to the CNS from the body and relay motor information from the CNS to the rest of the body.
6
Q
sensory neuron
A
A neuron that detects changes in the external or internal envi- ronment and sends information about these changes to the central nervous system.
7
Q
motor neuron
A
A neuron located
within the central nervous system that controls the contraction of a muscle or the secretion of a gland.
8
Q
interneuron
A
A neuron located entirely within the central nervous system.
9
Q
4 structures of a neuron
A
(1) cell body, or soma; (2) dendrites; (3) axon; and (4) terminal buttons
10
Q
soma
A
The cell body of a neuron, which contains the nucleus.
11
Q
dendrite
A
A branched, treelike structure attached to the soma of a neuron; receives information from the terminal buttons of other neurons.
12
Q
synapse
A
A junction between the terminal button of an axon and the membrane of another neuron.
13
Q
axon
A
The long, thin, cylindrical structure that conveys information from the soma of a neuron to its terminal buttons.
14
Q
axoplasmic transport
A
An active process by which substances are propelled along microtubules that run the length of the axon.
15
Q
anterograde
A
In a direction along an axon from the cell body toward the terminal buttons. Very fast, up to 500mm/day
16
Q
retrograde
A
In a direction along an axon from the terminal buttons toward the cell body. Half as fast
17
Q
myelin sheath
A
A sheath that surrounds axons and insulates them, preventing messages from spreading between adjacent axons.
18
Q
tracts
A
bundles of myelinated axons
19
Q
terminal button
A
The bud at the end of a branch of an axon; forms synapses with another neuron; sends information to that neuron.
20
Q
neurotransmitter
A
A chemical that is released by a terminal button; has an excitatory or inhibitory effect on another neuron.
21
Q
membrane
A
A structure consisting principally of lipid molecules that defines the outer boundaries of a cell and also constitutes many of the cell organelles.
22
Q
cytoskeleton
A
Formed of microtubules and other protein fibers, linked to each other and forming a cohesive mass that gives a cell its shape.
23
Q
microtubules
A
A long strand of bundles of 13 protein filaments arranged around a hollow core; part of the cytoskeleton and involved in transporting substances from place to place within the cell (tracks).
24
Q
enzyme
A
A molecule that controls a chemical reaction, combining two substances or breaking a substance into two parts.
25
mitochondria
Organelles that are respon- sible for extracting energy from nutrients.
26
adenosine triphosphate (ATP)
chemical produced by mitochondria used as cell source (breaking it down liberates energy)
27
glia
supporting cells of the central nervous system. (glue)
28
astrocyte
- provide support for neurons
- clean up debris within the brain (phagocytosis)
- produce chemicals that neurons need to fulfill their functions
- regulate the chemical composition of the fluid surrounding neurons
- matrix that holds neurons in place and provide nourishment to neurons
- surround and isolate synapses, limiting the dispersion of neurotransmitters that are released by the terminal buttons
29
phagocytosis
The process by which cells engulf and digest other cells or debris caused by cellular degeneration.
30
oligodendrocyte
- provide support to axons and to produce the myelin sheath
- grows paddles shapes arms that wrap around multiple axons
- produces myelin (80% lipid, 20% protein); up to 50 segments
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node of Ranvier
A naked portion of a myelinated axon between adjacent oligodendroglia or Schwann cells.
32
microglia
The smallest of glial cells; they act as phagocytes and protect the brain from invading microorganisms.
- responsible for inflammatory reaction in response to brain damage
33
Supporting cells of the CNS
astrocytes, oligodendrocytes, microglia
34
Supporting cells of the PNS
Schwann cells
35
Schwann cells
A cell in the peripheral nervous system that is wrapped around a myelinated axon, providing one segment of its myelin sheath
36
multiple sclerosis
autoimmune attack of myelin in the CNS
37
blood–brain barrier
A semipermeable barrier between the blood and the brain produced by the cells in the walls of the brain’s capillaries.
38
What is the function of the blood–brain barrier?
- makes it easier to regulate the composition of extracellular fluid surrounding neurons
- prevents chemicals from food reaching the brain
39
area postrema
A region of the medulla where the blood–brain barrier is weak; poisons can be detected there and can initiate vomiting.
40
membrane potential
The electrical charge across a cell membrane; the dif- ference in electrical potential inside and outside the cell.
41
resting potential
The membrane potential of a neuron when it is not being altered by excitatory or inhibitory postsynaptic potentials; approximately -70 mV in many neurons.
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hyperpolarization
An increase in the membrane potential of a cell, relative to the normal resting potential. (inside more negative)
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depolarization
Reduction (toward zero) of the membrane potential of a cell from its normal resting potential. (inside more positive)
44
threshold of excitation
The value of the membrane potential that must be reached to produce an action potential.
45
action potential
The brief electrical impulse that provides the basis for conduction of information along an axon.
- rapid depolarization followed by hyperpolarization
46
electrical charge results from a balance between which two opposing forces?
diffusion and electrostatic pressure
47
diffusion
Movement of molecules from regions of high concentration to regions of low concentration.
48
electrostatic pressure
The attractive force between atomic particles charged with opposite signs or the repulsive force between atomic particles charged with the same sign.
49
ions in intracellular and extracellular fluids
- Organic anions (A-): found only in intracellular fluids
- K+ : found mostly in intracellular (usually stay where they are due to balance of diffusion/electrostatic pressure)
- Na+ & Cl- : found mostly in extracellular
50
sodium-potassium pump
- pushes out Na+ from axon
| - made of protein molecules embedded in membrane and driven by ATP
51
sodium–potassium transporters
exchange Na+ for K+, pumping 3 Na+ ions out for every 2 K+ ions they pump in
- use up 40% of neutrons metabolic resources
52
production of Action potential steps
1. membrane potential reaches threshold
2. voltage-dependent sodium channels open and Na+ rushes in (interior of cell becomes more positive aka depolarization)
3. voltage-dependent potassium channels open and K+ goes out
4. 1 sec later, sodium channels become refractory (blocked)
5. outflow of cations causes membrane potential to return to resting value (even a bit more negative)
6. potassium channels close again and sodium channels reset
7. sodium-potassium transporters remove Na+ ions and retrieve K+ ions
53
conduction of the action potential
1. axon conducts the electrical message from the action potential to the next node of Ranvier
2. electrical message is conducted passively; gets smaller as it passes down the axon, but it is still large enough to trigger a new action potential at the next node
3. action potential gets retriggered at each node of Ranvier, and the electrical message that results is conducted decrementally along the myelinated area to the next node
54
all-or-none law
The principle that once an action potential is triggered in an axon, it is propagated, without decrement, to the end of the fiber.
55
rate law
The principle that variations
in the intensity of a stimulus or other information being transmitted in an axon are represented by variations in the rate at which that axon fires.
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decremental conduction
decrease in the size of the electrical message
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saltatory conduction
Conduction of action potentials by myelinated axons. The action potential appears to jump from one node of Ranvier to the next.
58
2 advantages of saltatory conduction
1. More economic: Na+ can only enter at nodes of Ranvier so there is only need for sodium-potassium transporters there
2. More speed: transmission between the nodes is very fast
59
Except for saltatory conduction, what is another way to increase the speed of conduction of the AP?
having a larger diameter; but still slower than myelinated neuron
60
postsynaptic potential
Alterations in the membrane potential of a postsynaptic neuron, produced by liberation of neu- rotransmitter at the synapse.
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binding site
The location on a receptor protein to which a ligand binds.
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ligand
A chemical that binds with the binding site of a receptor. (ex: neurotransmitters, poisonous chemicals, artificial ligands)
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dendritic spine
A small bud on the surface of a dendrite, with which a terminal button of another neuron forms a synapse.
64
Where are synapses located?
smooth surface of a dendrite, dendritic spines, on soma, or even other axons
65
synaptic cleft
contains extracellular fluid through which the neurotransmitter diffuses
66
synaptic vesicle
A small, hollow, beadlike structure found in terminal buttons; contains molecules of a neurotransmitter.
67
how many synaptic vesicles can a terminal button hold?
100 to a million
68
Release of neurotransmitters
- synaptic vesicles located just inside presynaptic membrane fuse with membrane and break open, spilling contents into synaptic cleft
- neurotransmitters move away from vesicle to disperse across synapse
69
neurotransmitter-dependent ion channel (aka ligand-gated ion channels)
An ion channel that opens when a molecule of a neurotransmitter binds with a postsynaptic receptor.
70
How do neurotransmitters open ion channels?
- directly (ionotrpic receptor): neurotransmitter-dependent ion channel has its own binding site; when binded, channel opens
- indirectly (metabotropic receptors): neurotransmitter binds to receptor, activating G protein; G protein activates enzyme that stimulates production of second messenger; these molecules travel though cytoplasm and attach to nearby ion channels to open them
71
G protein
A protein coupled to a metabotropic receptor; conveys messages to other molecules when a ligand binds with and activates the receptor.
72
second messenger
A chemical produced when a G protein activates an enzyme; carries a signal that results in the opening of the ion channel or causes other events to occur in the cell.
73
four major types of neurotransmitter-dependent ion channels found in the post- synaptic membrane
sodium, potassium, chloride, and calcium
74
most important source of excitatory postsynaptic potentials
neurotransmitter-dependent sodium channel
75
excitatory postsynaptic potential (EPSP)
An excitatory depolarization
| of the postsynaptic membrane of a synapse caused by the liberation of a neurotransmitter by the terminal button.
76
inhibitory postsynaptic potential (IPSP)
An inhibitory hyperpolarization of the postsynaptic membrane of a synapse caused by the liberation of a neurotrans- mitter by the terminal button.
77
inhibitory neurotransmitters often open which channels?
chloride
78
What happens when sodium channels open?
depolarization --> EPSP
79
effect of opening chloride channels
- depends on membrane potential:
- -> at resting potential nothing happens
- -> depolarized, influx of Cl- will bring membrane potential back to normal resting condition (helps neutralize EPSPs)
80
What happens when potassium channels open
hyperpolarization --> IPSP
81
What happens when calcium channels open?
- same as sodium
- also trigger migration of synaptic vesicles & release of neurotransmitters
- activates special enzymes in postsynaptic cell (induce biochemical and structural changes)
82
Reuptake
- most common form of termination of postsynaptic potentials
| - reentry of a neurotransmitter released from a terminal button back through its membrane
83
Enzymatic deactivation
The destruction of a neurotransmitter by an enzyme after its release—for example, the destruction of acetylcholine by acetylcholinesterase.
84
neural integration
The process
| by which inhibitory and excitatory postsynaptic potentials summate and control the rate of firing of a neuron.
85
autoreceptor
A receptor molecule located on a neuron that responds to the neurotransmitter released by that neuron.
- usually inhibitory, as a way to control rates of release
86
Axoaxonic synapses
- do not contribute directly to neural integration
- alter the amount of neurotransmitter released by the terminal buttons of the postsynaptic axon
- produce presynaptic modulation: presynaptic inhibition or presynaptic facilitation
87
presynaptic inhibition
The action of a presynaptic terminal button in an axoax- onic synapse; reduces the amount of neu- rotransmitter released by the postsynaptic terminal button.
88
presynaptic facilitation
The action
of a presynaptic terminal button in an axoaxonic synapse; increases the amount of neurotransmitter released by the postsynaptic terminal button.
89
neuromodulator
A naturally secreted substance that acts like a neurotransmitter except that it is not restricted to the synaptic cleft but diffuses through the extracellular fluid.
- secreted in larger amounts and diffuse for longer distances, modulating the activity of many neurons in a particular part of the brain
- affect general behavioral states such as vigilance, fearfulness, and sensitivity to pain
90
peptide
A chain of amino acids joined together by peptide bonds. Most neuro- modulators, and some hormones, consist of peptide molecules.
91
hormone
A chemical substance that is released by an endocrine gland that has effects on target cells in other organs.
92
endocrine gland
A gland that releases chemical messengers into the extracellular fluid around capillaries and hence into the bloodstream.
93
target cell
The type of cell that is directly affected by a hormone or other chemical signal.
