chapter 12- nervous tissue Flashcards
1
Q
the spinal cord & brain make up the what nervous system?
A
central
2
Q
a bundle of axons with connective tissue & blood vessels that is connected to the spinal cord is a what?
A
spinal nerve
3
Q
what division of the PNS carries info. coming into the CNS from the internal organs?
A
visceral afferent
4
Q
what nervous system carries info. from the CNS to the skeletal muscles?
A
somatic
5
Q
a large visible nucleolus tells you what about a cell?
A
making lots of ribosomes which it will use to make lots of protein
6
Q
the visible collection of RER & ribosomes in the soma of a neuron are called what?
A
nissl bodies
7
Q
what are the neuron cell processes that carry graded potentials?
A
dendrites
8
Q
the membrane of the axon is called the what?
A
axolemma
9
Q
what are the cells of the CNS that are responsible for the myelin?
A
oligodendrocytes
10
Q
anterograde transport in an axon functions to do what?
A
move neurotransmitters from the soma to the terminal
11
Q
how many axons does an anaxonic neuron have?
A
one, all neurons have one axon
12
Q
most sensory neurons are structurally what neurons with their somas in peripheral sensory what cells?
A
unipolar & ganglia
13
Q
the ependymal cells are responsible for the secretion & circulation of what?
A
cerebrospinal fluid (CSF)
14
Q
if resistance is high, current is what?
A
low
15
Q
ion channels that are always open & allow free flow of ions are called what channels?
A
passive/leak
16
Q
a ligand-gated channel will open in response to a what?
A
chemical bonding
17
Q
why does potassium generate less current than sodium when the ion channels are open on the membrane?
A
movements of sodium ions into the cell is favored by both the diffusion & electrical gradients whereas movement of potassium ions out of the cell its favored only by the diffusion gradient
18
Q
opening of a sodium channel causes a what graded potential?
A
depolarizing
19
Q
during an action potential, what happens at +30mV?
A
sodium channels close &potassium channels open
20
Q
during which period do sodium channels open & the membrane can’t respond to additional stimuli?
A
absolute refractory
21
Q
continuous propagation of action potentials occurs on what axons?
A
unmyelinated
22
Q
what kind of info. is carried on type A axons?
A
somatic motor & sensory
23
Q
inhibitory neurotransmitters cause a what of the post synaptic cell?
A
hyperpolarization
24
Q
what is the neurotransmitter used at cholinergic synapses?
A
acetylcholine
25
if a neurotransmitter works by the direct effect, it will cause what to happen on the post synaptic cell?
open or close ion channels
26
in the indirect effect on the membrane potential, what is created inside the cell to open ion channels?
second messenger
27
what summation occurs when one synapse produces multiple ESPS in a row on one spit to reach the threshold?
temporal
28
a what neurons have been brought closer to the threshold by a depolarizing stimulus?
facilitated
29
the neurotransmitter responsible for our reward feelings is what?
dopamine
30
neurons get ATP through what?
aerobic respiration of glucose
31
neural tissue
-3% of body mass
-cellular, ~20% extracellular space
-two categories: neurons & neuroglia/glial cells
32
neurons
conduct nerve impulses
33
neuroglia/glial cells
"nerve glue", supporting cells
34
central nervous system (CNS)
-spinal cord, brian
-function: integrate, process, coordinate, sensory input & motor output
35
peripheral nervous system (PNS)
-all neural tissue outside CNS
-function: carry info to/from CNS via nerves
36
nerve
bundle of axons (nerve fibers) with blood vessels & CT
-cranial nerves <-> brain
-spinal nerves <-> spinal cord
37
sensory/afferent division (division of PNS)
sensory receptors -> CNS
38
somatic afferent division
from skin, skeletal muscles, joints
39
visceral afferent division
from internal organs
40
motor/efferent division (division of PNS)
CNS -> effectors
41
somatic nervous system
-"voluntary nervous system"
-to skeletal muscles
42
autonomic nervous system (ANS)
-"involuntary nervous system"
-to smooth & cardiac muscle, glands
-both sympathetic & parasympathetic divisions tend to be antagonistic to each other
43
sympathetic division of the autonomic nervous system (ANS)
"fight or flight"
44
parasympathetic division of the autonomic nervous system (ANS)
"rest and digest"
45
neuron
-function: conduct nervous impulses (messages)
-characteristics: extreme longevity, amiotic (except hippocampus & olfactory receptors) & high metabolic rate: need O2 & glucose
46
nissl bodies
visible RER & ribosomes, gray
47
neurofilaments
neurofibrils, neurotubules (internal structures)
48
dendrites (cell extension of a neuron)
-receive info
-carry a graded potential toward soma
-contain same organelles as soma
-short, branched
-end in dendritic spines
49
neuron structure
-large soma/perikaryon
-large nucleus, large nucleolus (rRNA)
-many mitochondria, ribosomes, RER, Golgi (increases ATP & protein synthesis to produce neurotransmitters)
-no centrioles
-2 types of processes
50
axon (cell extension of a neuron)
-single, long
-carry an action potential away from soma
-release neurotransmitters at end to signal next cell
-long ones = "nerve fibers"
51
axon contains:
-neurofibrils & neurotubules (abundant)
-vesicles of neurotransmitter
-lysosomes, mitochondria, enzymes
-no nissl bodies, no golgi (no protein synthesis in axon)
-connects soma at axon hilock
-covered in axolemma
-end in synaptic terminals or knobs
52
axon collaterals
branches of axon
53
axon myelin sheath:
-protein + lipid
-protection
-insulation
-increase speed of impulse
-CNS: myelin from oligodendrocytes
-PNS: myelin from Schwann cells/neurilemma cells
54
axoplasmic transport
-move material between soma & terminal
-along neurotubules on kinesins
-2 transport systems: anterograde & retrograde
-some viruses use retrograde transport to gain access to CNS (Polio, Herpes, Rabies)
55
anterograde transport (axoplasmic transport)
soma -> terminal (neurotransmitters from soma)
56
retrograde transport (axoplasmic transport)
terminal -> soma (recycle breakdown products from used neurotransmitters)
57
synapse
site where neuron communicates with another cell: neuron or effector
58
presynaptic cell
sends message along axon to axon terminal
59
postsynaptic cell
receives message as neurotransmitter
60
neurotransmitter
chemical, transmits signal from pre- to post- synaptic cell across synaptic cleft
61
synaptic knob
small, round, when postsynaptic cell is neuron, synapse on dendrite or soma
62
synaptic terminal
complex structure, at neuromuscular or neuroglandular junction
63
anaxonic neurons (structural classification of neurons)
-dendrites & axons look the same
-brain & special sense organs
64
bipolar neurons (structural classification of neurons)
-1 dendrite, 1 axon
-soma in the middle
-rare: special sense organs, relay from receptor to neuron
65
unipolar neurons (structural classification of neurons)
-1 long axon, dendrites at one end, soma off-side (T shape)
-most sensory neurons
66
multipolar neurons (structural classification of neurons)
-2 or more dendrites
-1 long axon
-99% all neurons
-most CNS
67
sensory/afferent neurons (functional classification of neurons)
-transmit info from sensory receptor to CNS
-most unipolar
-soma in peripheral sensory ganglia
68
ganglia
collection of cell bodies in PNS
69
somatic sensory neurons
receptor monitor outside conditions
70
visceral sensory neurons
receptors monitor internal conditions
71
motor/efferent neurons (functional classification of neurons)
-transmit commands from CNS to effector
-most multipolar
72
somatic motor neurons
-innervate skeletal muscle
-conscious control or reflexes
73
visceral/autonomic motor neurons
-innervate effectors on smooth muscle, cardiac muscle, glands, adipose
74
interneurons/association neurons (functional classification of neurons)
-distribute sensory info & coordinate motor activity
-between sensory & motor neurons
-in brain, spinal cord, autonomic ganglia
-most multipolar
75
neuroglia in CNS
-outnumber neurons 10:1
-half mass of brain
76
ependymal cells (neuroglia in CNS)
-line central canal of spinal cord & ventricles of brain
-secrete cerebrospinalal fluid (CSF)
-have cilia to circulate CSF
77
cererospinal fluid (CSF)
cushion brain, nutrient & gas exchange
78
astrocytes (neuroglia in CNS)
-most abundant CNS neuroglia
-varying functions
79
functions of astrocytes:
a. blood-brain barrier
b. framework of CNS
c. repair damaged neural tissue
d. guide neuron development in embryo
e. control interstitial environment: regulate conc. ions, gasses, nutrients, neurotransmitters
80
oligodendrocytes (neuroglia in CNS)
-create myelin sheath
-1 cell contributes myelin to many neighboring axons
-lipid in membrane insulates axon for faster action potential conductance
-nodes (of ranvier)
-"white matter"
81
myelin sheath
wide flat processes wrap local axons
82
Nodes (of Ranvier)
gaps on axon between processes/myelin, necessary to conduct impulse
83
"white matte" of oligodendrocytes
white, myelinated axons
84
microglia (neuroglia in CNS)
-phagocytic
-wander CNS
-engulf debris, pathogens
-important CNS defense (no immune cells or antibodies)
85
satellite cells (neuroglia in PNS)
-surround somas in ganglia
-isolate PNS cells
-regulate interstitial environment
86
Schwann cells/neurilemma cells
-myelinated axons in PNS
-whole cells wrap axon, many layers, organelles compressed in superficial layer (neurilemma)
-Nodes (of Ranvier) between cells
-vital to repair of peripheral nerve fibers after injury: guide growth to original synapse
87
neurophysiology
-requires transmembrane potential = electrical difference across cell membrane
-cells: positive charge outside (pump cations out) & neg. charge inside (proteins)
88
voltage
measure of potential energy generated by separation of opposite charges
89
current
flow of electrical charges (ions), cell can produce current (nervous impulse) when ions move to eliminate the potential differences (volts) across the membrane
90
resistance
restricts ion movement (current) (high resistance = low current); membrane has resistance, restricts ion flow/current
91
Ohm's law
-current = voltage ÷ resistance
-current highest when voltage high & resistance low
-cell voltage set at -70mV but membrane resistance can be altered to create current
-membrane resistance depends on permeability to ions: open or close ion channels
92
cells must always have what?
resistance or else ions would equalize, voltage = zero, no current generated = no nervous impulse
93
membrane ion channels
-allow ion movement (alter resistance)
-each channel specific to one ion type
94
passive channels (leak channels) (membrane ion channels)
-always open, free flow
-sets resting membrane potential at -70mV
95
active channels (membrane ion channels)
-open/close in response to signal
-3 types: chemically regulated, voltage regulated, mechanically regulated
96
chemically regulated/Ligand-gated (active channel)
-open in response to chemical binding
-located on any cell membrane (dendrites, soma)
97
voltage regulated channels (active channel)
-open/close in response to shift in transmembrane potential
-excitable membrane only: conduct action potentials (axolemma, sarcolemma)
98
mechanically regulated channels (active channel)
-open in response to membrane distortion
-on dendrites of sensory neurons for touch, pressure, vibration
99
when channels opens, ions flow along electrochemical gradient:
-diffusion (high conc. to low)
-electrical attraction
/repulsions
100
sodium-potassium pump
-uses ATP to move 3 Na+ out 2 K+ in (70% of neuron ATP for this)
-runs anytime cell not conducting impulse
-creates high (K+) inside & high (Na+) outside
101
when Na+ channels open in sodium-potassium pump:
-Na+ flows into cell:
1. favored by diffusion gradient
2. favored by electrical gradient
-open channel = decrease in resistance = increase in ion flow/current
102
when K+ channels open in sodium-potassium pump:
-K+ flows out of cell:
1. favored by diffusion gradient only
2. electrical gradient repels K+ exit
-thus less current than Na+
103
channels open = resistance low = ions move until equilibrium potential, what does this depend on?
diffusion gradient & electrical gradient
104
what are the equilibrium potentials for K+ & Na+?
-K+ = -90mV (K+ can't leave cell)
-Na+ = +66mV (too positive in cell, so Na+ can no longer enter)
105
open channel -> current = what?
graded potential
106
graded potential
localized shift in transmembrane potential due to movement of charges into/out of cell (not nervous impulse messages)
107
Na + channel opens (graded potential):
Na+ flows in, depolarization (cell less negative)
108
K + channel opens (graded potential):
K+ flows out, hyperpolarization (cell more negative)
109
graded potentials:
-occur on any membrane: dendrites and somas
-can be depolarizing or hyperpolarizing
-amount of depolarization or hyperpolarization depends on intensity of stimulus: increase channels open = increase voltage change
-passive spread from site of stimulation over short distance
-effect on membrane potential decreases with distance from stimulation site
-repolarization occurs as soon as stimulus is removed: leak channels & Na+/K+ pump reset resting potential
110
action potentials:
-occur on excitable membranes only (axolemma, sarcolemma)
-always depolarizing
-must depolarize to threshold (-55mV) before action potential begins (voltage-gated channels on excitable
membrane open at threshold to propagate action potential)
-action potential at one site depolarizes adjacent sites to threshold
-propagated across entire membrane surface without decrease in strength
111
action potentials "all or none"
all stimuli that exceed threshold will produce identical action potentials
112
generation of an action potential: depolarization to threshold step 1
-a graded potential depolarizes local membrane & flows toward axon
- if threshold is met (-55mV) at the hillock, an action potential will be triggered
113
generation of an action potential: activation of sodium channels & rapid depolarization step 2
- at threshold (-55mV), voltage-regulated sodium channels on excitable axolemma membrane open
-Na+ flows into cell depolarizing it
- transmembrane potential rapidly changes from -55mV to +30mV
114
generation of an action potential: inactivation of sodium channels & activation of potassium channels step 3
- at +30mV Na+ channels close & K+ channels open
-K+ flows out of the cell repolarizing it
115
generation of an action potential: return to normal permeability step 4
- at -70mV K+ channels begin to close
-cell hyper polarizes to -90mV until all channels finish closing
-leak channels restore the resting membrane potential to -70mV
116
restimulation only when Na+ channels closed:
-influx of Na + necessary for action potential
-cell has ions for thousands of action potentials, eventually must run Sodium-Potassium pump (burn ATP) to reset high [K+] inside and high [Na+] outside
117
absolute refractory period
-55mV (threshold) to +30mV, Na + channels open, membrane cannot respond to additional stimulus
118
relative refractory period
+30mV to -70mV (return to resting potential), Na+ channels closed, membrane capable of second action potential but requires larger/longer stimulus (threshold elevated)
119
propagation of action potentials:
-once generated must be transmitted length of axon: hillock to terminal
-speed depends on: degree of myelination (yes or no) & axon diameter
120
continuous propagation
-unmyelinated axons
-whole membrane depolarizes and repolarizes sequentially hillock to terminal
-only forward movement; membrane behind always in absolute refractory period
121
saltatory propagation
-myelinated axons
-depolarization only on exposed membrane at nodes
-myelin insulates covered membrane from ion flow
-action potential jumps from node to node: faster and requires less energy to reset
122
axon diameter (propagation of action potentials)
larger axon -> less resistance -> easier ion flow -> faster action potential
123
type A fibers/axon
- 4-20μm diameter
- myelinated (saltatory propagation)
- action potentials 140m/sec
- carry somatic motor & somatic sensory info
124
type B fibers/axon
- 2-4μm diameter
- myelinated (saltatory propagation)
- action potentials 18m/sec
- carry autonomic motor & visceral sensory info
125
type C fibers/axon
- < 2μm diameter
- unmyelinated (continuous propagation)
- action potentials 1m/sec!
- carry autonomic motor & visceral sensory info
126
myelination
-requires space, metabolically expensive
-only important fibers large and myelinated
-occurs in early childhood
-results in improved coordination
127
multiple sclerosis
genetic disorder, myelin on neurons in PNS destroyed ->numbness, paralysis
128
synapse
-junction between transmitting neuron (presynaptic cell) and receiving cell (postsynaptic cell), where nerve impulse moves from one cell to next
-two types: electrical & chemical
129
electrical synapse
-direct contact via gap junctions
-ions flow directly from pre to post cell
-less common synapse
-in brain (conscious perception)
130
chemical synapse
-most common
-pre and post-cells separated by synaptic cleft
-presynaptic neuron releases neurotransmitter to trigger effect on postsynaptic cell
131
dynamic (of chemical synapses)
facilitate or inhibit transmission, depending on neurotransmitter
132
excitatory neurotransmitter (dynamic of chemical synapses)
-depolarization
-propagate action potential
133
inhibitory neurotransmitter (dynamic of chemical synapses)
-hyperpolarization
-suppress action potential
134
events at a cholinergic synapse with acetylcholine as neurotransmitter: an action potential arrives step 1
-an arriving action potential depolarizes the synaptic knob
135
events at a cholinergic synapse with acetylcholine as neurotransmitter: extracellular Ca2+ enters the synaptic terminal triggering the exocytosis of ACh step 2
-calcium ions enter the cytoplasm of the synaptic knob
-ACh is released through exocytosis of neurotransmitter vesicles
136
events at a cholinergic synapse with acetylcholine as neurotransmitter: ACh binds to receptors & depolarizes postsynaptic membrane step 3
-ACh diffuses across synaptic cleft & binds to receptors in postsynaptic membrane
-chemically regulated sodium channels on postsynaptic surface are activated, producing graded depolarization
-ACh release ceases bc calcium ions are removed from cytoplasm of synaptic knob
137
events at a cholinergic synapse with acetylcholine as neurotransmitter: ACh is removed by AChE (acetylcholinesterase) step 4
-depolarization ends as ACh is broken down into acetate & choline by AChE
-synaptic knob reabsorbs choline from synaptic cleft & uses it to resynthesize ACh
138
direct effect on membrane potential (neurotransmitter mechanism of action)
-open or close channels upon binding to post synaptic cell
-provides a rapid response
- ex: ACh (cholinergic synapse)
139
indirect effect on membrane potential (neurotransmitter mechanism of action)
-binds a receptor that activates a G protein in post-synaptic cell
-active G protein activates a 2nd messenger (cAMP, cGMP, diacyglyceride, Ca++)
-2nd messenger opens ion channels or activates enzymes
-provides slower but long-lasting effects
-ex: norepinephrine (adrenergic synapse)
140
example of indirect action (neurotransmitter mechanism of action)
1. neurotransmitter binds receptor
2. receptor activates G protein
3. G protein activates adenylate cyclase
4. adenylate cyclase converts ATP to cyclic AMP
5. cAMP opens ion channels
141
post synaptic potential
-graded potential caused by a neurotransmitter due to opening or closing of ion channels on postsynaptic cell membrane
-two types: excitatory postsynaptic potential (EPSP) & inhibitory post synaptic potential (IPSP)
142
inhibitory post synaptic potential (IPSP)
-causes hyperpolarization
-inhibits postsynaptic cell (need larger stimulus to reach threshold)
143
excitatory postsynaptic potential (EPSP)
-causes depolarization
-multiple EPSPs needed to trigger action potential in post-cell axon
144
temporal summation (EPSP summation)
-single synapse fires repeatedly: string of EPSPs in one spot
-each EPSP depolarizes more until threshold reaches hillock
145
spatial summation (EPSP summation)
-multiple synapses fire simultaneously
-collective depolarization reaches threshold
146
facilitated
depolarized; brought closer to threshold by some sort of stimulus, less stimulus now required to reach threshold (e.g. caffeine)
147
post synaptic potentiation
repeat stimulation of same synapse conditions synapse, pre-cell more easily stimulates post-cell to threshold (repetition)
148
neuromodulators
chemicals that influence synthesis, release, or degradation of neurotransmitters thus altering normal response of the synapse
149
acetylcholine- cholinergic synapses (common neurotransmitter)
-excitatory
-direct effect
-skeletal neuromuscular junctions, many CNS synapses, all neuron to neuron PNS, all parasympathetic ANS
150
norepinephrine- adrenergic synapses
-excitatory
-second messengers
-many brain synapses, all sympathetic ANS effector junctions
151
dopamine
-excitatory or inhibitory
-second messengers
-many brain synapses, many functions
-responsible for reward feeling
-cocaine: inhibits removal = “high”
-Parkinson’s disease: damaged neurons = ticks, jitters
152
serotonin
-inhibitory
-direct or second messenger
-brain stem for emotion
-anti-depression/ anti-anxiety drugs block uptake
153
gamma aminobutyric acid (GABA)
-inhibitory
-direct effect
-brain: anxiety control, motor coordination
-alcohol: augments effects = loss of coordination
154
pH (factors that disrupt neural function)
pH: normal = 7.4
-pH 7.8 -> spontaneous action potentials = convulsions
-pH 7.0 -> no action potentials = unresponsive
155
ion concentrations (factors that disrupt neural function)
high extracellular [K+] depolarize membranes = death, cardiac arrest
156
temperature (factors that disrupt neural function)
-normal: 37°C
-higher: neurons more excitable (fever = hallucinations)
-lower: neurons non-responsive (hypothermia = lethargy, confusion)
157
nutrient (factors that disrupt neural function)
-neurons: no reserves, use a lot of ATP
-require constant and abundant glucose
-glucose only
158
oxygen (factors that disrupt neural function)
-aerobic respiration only for ATP
-no ATP = neuron damage/death
