Exam 3 Flashcards
1
Q
what causes muscle movement
A
stimulation which leads to contraction
2
Q
what are the three types of muscle tissue
A
skeletal
cardiac
smooth
3
Q
skeletal muscle tissue
A
long, cylindrical, stratified fibers arranged parallel and unbranched: fibers are multinucleated; fiber is under voluntary control
primarily responsible for moving skeleton and selected other components of the body
found attaches to bone and sometimes skin
4
Q
cardiac muscle tissue
A
short, stratified cells typically branching; cells contain one or two centrally located nuclei; intercalated discs between cells; under involuntary control
pumps blood through heart
found in heart wall (myocardium)
5
Q
smooth muscle tissue
A
nonstriated cells that are short and fusiform in shape; contain one centrally located nucleus; under involuntary control
moves and propel materials through internal organs, controls size of the lumen
found in walls of hollow internal organs such as intestines, stomach, airways, bladder, uterus, and blood vessels
6
Q
what muscle tissues are involved in involuntary control
A
smooth and cardiac muscle
7
Q
what are the functions of the skeletal muscle
A
body movement (move, facial expressions, speak, breathe)
maintenance of posture (stabilizes joints, maintain body position)
protection and support (package internal organs and hold them in place)
regulating elimination of material (circular sphincters control passage of material at orifices)
heat production (helps maintain body temp)
8
Q
characteristics of skeletal muscle tissue
A
excitability
conductivity
contractibility
elasticity
extensibility
9
Q
excitability
A
ability to respond to a stimulus by changing electrical membrane potential
10
Q
conductivity
A
involves sending an electrical change down the length of the cell membrane
11
Q
contractility
A
exhibited when filaments slide past each other which enables muscle to cause movement
12
Q
elasticity
A
ability to return to original length following a lengthening or shortening
13
Q
extensibility
A
ability to be stretched
14
Q
muscle cells are called muscle fibers and are grouped together, each group of these is called a
A
facet
15
Q
epimysium
A
a connective tissue layer that surrounds entirety of muscle
16
Q
perimysium
A
boundary between each facet
17
Q
endomysium
A
loose areolar connective tissue that surrounds individual muscle fibers
18
Q
plasma membrane of muscle cells is called
A
the sarcolemma
19
Q
sarcomeres consist of
A
bundles of contractile proteins called myofilaments
20
Q
myofilaments are also called
A
contractile proteins
21
Q
myofibrils
A
hundreds to thousands per cell that are bundles of myofilaments (contractile proteins) enclosed in the sarcoplasmic reticulum and make up most of cell’s volume
22
Q
sarcoplasmic reticulum
A
internal membrane complex similar to smooth endoplasmic reticulum that contain terminal cisternae
23
Q
terminal cisternae
A
blind sacs of sarcoplasmic reticulum
serve as resovioir for calcium ions
combine in twos with central T-tubule to form triads
24
Q
Ca2+ pump in sarcoplasmic reticulum
A
has pumps that important calciu into sarcoplasmic reticulum where it binds to calmodulin and calsequestrin
has channels that allow Ca2+ to be released into surrounding sarcoplasm to trigger contraction
25
thick filaments
consist of bundle of many myosin protein molecules
each mysoin molecule has two heads and two intertwined tails
heads have binding site for actin of thin filaments and ATPase site
heads point toward ends of the filament
26
thin filaments
consist mostily of two twisted strands of filamentous actin (F-actin)
each strand is a necklace of hundredsd of actin globules (G-actin)
each G-actin has a myosin binding site to which myosin heads attach during contraction
27
tropomyosin
twisted string like protein covering actin in a noncontracting muscle
28
troponin
globular protein attached to tropomyosin
29
when Ca2+ binds to troponin...
it pulls tropomyosin off actin allowing contraction
30
what are the regulatory proteins of thin filament
tropomyosin and troponin
31
organization of a sarcomere
myofilaments are arranged in repeating units called sarcomeres which are subunits of myofilaments
they are composed of overlapping thick and thin filaments
delinated at both ends by Z dics
the positions of thin and thick filaments give rise to alternating I-bands and A-bands
32
z discs
specialized proteins perpendicular to myofilaments that serve as anchors for thin filaments
33
motor unit
a motor neuron and all the muscle fibers it controls
34
what determines motor unit size
location in the body and what is required of muscle
35
neuromuscular junction
found where motor neuron innervates muscle
usually mid-region of muscle fibers
has synaptic knob, synaptic cleft, motor end plate
36
motor end plate
refers to the segment of plasma membrane of muscle fiber that interacts where neuron meets
37
ACh
the specific neurotransmitter that is going to be released to kick off muscle contraction
diffuses from synaptic cleft into motor end plate
the gray bodies that line the sarcolemma are acetylcholine receptors that transfer it from the synaptic cleft into motor end plate
calcium allows for the exocytosis of ACh
38
muscle fibers exhibit
resting membrane potential (RMP) meaning that fluid inside cell is negative compared to fluid outside of cell
39
what is the RMP of muscle cells
-90mV
40
what sets RMP is skeletal muscle fibers
leak channels and Na+/K+ pumps
(voltage gated channels are closed)
41
where is calcium stored in muscle fibers
in sarcoplasmic reticulum
42
sodium potassium pump (Na+/K+)
ion pumps that actively transport sodium out of cell and actively transport potassium into the cell
43
what is the level of sodium when a muscle cell is at rest?
concentration of sodium is greater outside than in
44
what is the level of potassium when muscle cell is at rest
concentration of potassium is greater inside than outside
45
events in skeletal muscle contraction
1. neuromusclar junction: excitation of skeletal muscle fiber
2. sarcolemma, t-tubules, and sarcoplasmic reticulum: excitation-contraction coupling
3. sarcomere: crossbridge cycling
46
neuromuscular junction: excitation of a skeletal muscle fiber
1. calcium (Ca2+) enter the synaptic knob.
- A nerve signal is propagated down a motor axon and triggers the energy of Ca2+ into the synaptic knob. Ca2+ binds to proteins in synaptic vessicle membrane
2. release of ACh from synaptic knob
-calcium binding triggers synaptic vessicle to merge with the synaptic knob plasma membrane and ACh is exocytosed into the synaptic cleft
3. Binding of ACh receptor at motor end plate
-ACh diffuses across the fluid filled synaptic cleft int he motor end plate to bind with ACh receptors
47
simple version of exciation of muscle fiber
neuron excites muscle fiber
ACh binds to its receptors at motor end plate
ACh diffuses across cleft, binds to receptors, excites fiber
48
sarcolemma, t-tubules, and sarcoplasmic reticulum: excitation contraction coupling
1. development of an end-plate potential (EPP) at the motor end plate
-binding of ACh to ACh receptors in the motor end plate triggers the opening of these chemically gated ion channels. Na+ (sodium) rapidly diffuses into and K+ slowly diffuses out of the muscle fiber
-an end plate potential is produced when sufficient Na+ enters at the motor end plate and the membrane potential changes from -90mV to -65mV
2. initiation and propagation of an action potential along sarcolemma and T-tubules
- the EPP initiates an action potential to be propagated along the sarcolemma and t-tubules
-first, voltage gated Na+ channels open and Na+ moves in to cause depolarization
-second, voltage gated K+ channels open and K+ moves out to cause repolarization
3. release of Ca2+ from the sarcoplasmic reticulum
-the action potential is then propagated along the t-tubules to trigger the opening of Ca2+ channels located in the terminal cisternae of the sarcoplasmic reticulum.
-Ca2+ diffuses out of the cisternae sarcoplasmic reticulum and into the sarcoplasm
49
events of action potential at the sarcolemma
1. the sarcolemma of an unstimulated skeletal muscle fiber has a resting membrane potential of -90mV
2. the threshold is reached when an end=plate potential (EPP) is produced as sufficient Na+ enters the motor end plate to change the RMP from -90mV to -65mV (threshold value)
3. depolarization occurs as voltage-gated Na+ channels on the sarcolemma open and Na+ enters rapidly reversing the polarity from negative to positive
4. repolarization occurs due to closure of voltage-gated Na+ channels and opening of voltage-gated K+ channels on the sarcolemma. K+ moves out of the cell and the polarity is reversed from positive to negative (+30mV to -90mV)
50
sarcomere: crossbridge cycling
1. Ca2+ binding
- Ca2+ binds to troponin's calcium binding sites (regulatory proteins associated with thin filaments) causing a conformational change in troponin. Troponin changes shape and the entire troponin-tropomyosin complex is moved - this tropomyosin no longer covers the myosin binding site on actin
2. Crossbridge Formation
-myosin heads, which are in cocked position, bind to the exposed myosin binding site on actin forming a crossbridge between myosin and actin
3. Power Stroke ("pull")
-the myosin head swivels toward the center of the sarcomere pulling along the attache thin filament. this motion is called a power stroke. ADP and inorganic P are released during this process. myosin head bends forward towards center of sarcomere attached to thin filament. ADP and P are released
4. release of myosin head
-myosin head released from actin. ATP binding site open so ATP binds to site which allows for release of myosin head from actin
5. reset myosin head ("reset")
-ATP is split into ADP and P by myosin ATPase
-provides the energy to reset the myosin head
51
crossbridge cycling
multiple repetitions of attach, pull, release, and reset lead to fully contracted sarcomere
52
as long as ______ and _____ are present cycling continues
Ca2+ and ATP
53
what does crossbridge cycling result in
sarcomere shortening as Z discs move closer together
54
events in muscle relaxation
-termination of nerve signal and ACh release from motor neuron
-hydrolysis of ACh by acetylcholinesterase
-closure of ACh receptor causes cessation of end plate potential
-no further action potential generation
-closure of calcium channels in sarcoplasmic reticulum
-return of Ca2+ to sarcoplasmic reticulum by pumps
-return of troponin to original shape
-return of tropomyosin blockade of actin's myosin binding sites
-return of muscle to original position due to its elasticity
55
how much ATP do muscle cells store
only a small amount, after about 5 seconds of intense exertion stored ATP is spent
56
what are the 3 ways to generate ATP in skeletal muscle fiber
immediate supply via phosphate transfer
short term supply via glyoclysis
long term supply via aerobic cellular respiration
57
immediate supply of ATP: phosphate transfer
myokinase transfer inorganic phosphate from one ADP to another
creatine kinase transfers inorganic phosphate from creatine phosphate to ADP
58
short-term means of supplying ATP: glyoclysis
glucose forms into 2 pyruvate molecules and gives off ATP and NADH to regenerate NAD+
59
long-term means of supplying ATP: aerboic cellular respiration
pyruvate undergoes citric acid cycle and then into the ETC to give off ATP
60
what does the source of ATP depends on
insensity and duration of exercise
61
for a 50 meter sprint (less than 10 seconds) where is ATP coming from
primarily by phosphate transfer system
62
for a 400-meter sprint (less than a minute) where is ATP coming from
ATP supplied primarily by glycolysis after first few seconds
63
for a 1500 meter run (more than a minute) where is ATP coming from
primarily by aerobic processes after first minute
64
what are the two criteria that categorize muscle fibers
type of contraction
primary means used for supplying ATP
65
the type of contraction generated refers to differences in
power, speed, and duration
66
the larger a muscle fiber the ...
more powerful
67
fast-twitch fibers
more powerful and have quicker and briefer contractions than slow-twitch fibers
68
oxidative fibers (fatigue resistant)
use aerobic cellular respiration
contains extensive capillaries, many mitochondria, and has a large supply of myoglobin (red fibers)
69
glycolytic fibers (fatiguable)
use anaerobic cellular respiration
contains fewer capillaries, fewer mitochondria, smaller supply of myoglobin (white fibers), and large glycogen reserves
70
hand muscles have a high percentage of what kinds of fiber types
fast glyoclytic fibers for quickness
71
back muscles have a high percentage of what kinds of fiber types
slow oxidative fibers to continually maintain postural support
72
what determines the distribution of muscle fiber types
primarily genes
73
in long distance runners you are more likely to find what kind of muscle fiber types
a higher proportion of slow oxidative fibers in legs
74
in sprinters you are more likely to find what kind of muscle fiber types
higher percentage of fast glyoclytic fibers
75
muscle twitch
a brief contraction to a single stimulus
76
periods of the twitch
latent period
contraction period
relaxation period
77
latent period
time after stimulus but before contraction begins
no change in tension
78
contraction period
time when tension is increasing
begins as power strokes pull thin filaments
79
relaxation period
time when tension is decreasing to baseline
begins when release of crossbridges
generally lasts a little longer than contraction period
80
as voltage increases more units are
recruited to contract
81
recruitment is also called
multiple motor unit summation
82
multiple motor unit summation
explains how muscle exhibit varying degrees of force
83
treppe
increase in twitch tension when stimuli occur 10-20 times per second
voltage is the same for each stimulus and relaxation is complete for each twitch
84
what causes twitches to get stronger
insufficient time to remove all Ca2+ between twitches
increased heat improves enzyme efficiency
85
wave summation (temporal summation)
if stimulus frequency set at about 20 per second..
-relaxation is not completed between twitches
-contractile forces add up to produce higher tensions
86
incomplete tetany
if frequency is increased further, myogram exhibits incomplete tetany
-tension increases and twitches partially fuse
87
tetany
if ferquency is increased further still (40-50 per second), myogram exhibits tetany
-tension trace is a smooth line without relaxation
88
high frequency stimuli leads to
fatigue or decreased tension production
89
isometric contraction
muscle tension is less than resistance
although tension is generated, the muscle does not shorten and no movement occurs.
90
isotonic contraction
muscle tension is greater than the resistance
the muscle shortens (concentric) or lengthens (eccentric) and movement occurs
91
the tension a muscle produces depends on
its length at time of stimulation
92
fibers at resting length generate
maximum contractile force
optimal overlap of thick and thin filaments
93
fiber at a shortened length generates
weaker force
filament movement is limited (actin already closer to opposite Z dics)
94
fiber at an extended length generates
weaker force
minimal thick and thin filament overlap for crossbridge formation
95
when a muscle contracts we create the
greatest amount of tension
96
cardiac muscle cells
short branching fibers with one or two nuclei that contain sarcomeres and many mitochondria for aerobic respiration
97
intercalated discs
join ends of neighboring fibers and contain desmosomes and gap junctions
98
desmosomes
cell-to-cell attachment
99
gap junctions
cell-to-cell communication
100
what starts contractions of the heart
autoryhtmic pacemaker cells, myogenic contraction
101
heart rate and contraction force is influenced by
autonomic nervous system
102
smooth muscle
have fusiform shape (wide in the middle with tapered ends), are smaller tahn skeletal muscle fibers, don't contain transverse tubules, has a sparse sarcoplasmic reticulum, and lacks sarcomeres and Z discs
smooth
103
what increases the surface area of smooth muscle
caveolae (flask-like invaginations)
104
smooth muscle fibers contrain ____,_____,____ but lack ______
actin, myosin, and tropomyosin .... troponin
105
smooth muscle filaments have myosin heads along
their entire length meaning they can form many crossbridges
106
calmodulin
protein that binds Ca2+ to trigger contraction
107
myosin light-chain kinase (MLCK)
enzyme that phosphorylates myosin heads when activated by calmodulin
108
myosin light-chain phosphate
enzyme that deposhporylates myosin head (required for relaxation)
109
smooth muscle contraction
1. opening of voltage gated Ca2+ channels
2. binding of Ca2+ to calmodulin
3. activation of myosin light chain kinase
4. activation of myosin head
5. crossbridge formation, power stroke, reattachment
110
how is the nervous system organized structurally
structurally: CNS and PNS
functionally: SNS and MNS
111
CNS contains
brain and spinal cord
112
PNS consists of
nerves (fiber bundles) and ganglia (clusters of cell bodies along nerves)
113
sensory nervous system
detects stimuli and transmits information from receptors to the CNS
114
motor nervous system
initirates and transmits information from the CNS to effectors
115
somatic sensory and visceral sensory are part of
the sensory nervous system
116
somatic motor and autonomic motor are part of
motor nervous system
117
somatic sensory
input that is consciously percieved from receptors (eyes, ears, skin)
118
visceral sensory
input that is not consciously percieved from receptors of blood vessels and internal organs (heart)
119
somatic motor
motor output that is consciously or voluntarily controlled; effector is skeletal muscle
120
autonomic motor
motor output is not consciously or is involuntarily controlled; effectors are cardiac muscle, smooth muscle, and glands
121
what are the three main pairs of a neuron
cell body (soma)
dendrites
axon
122
cell body
plasma membrane encloses cytoplasm
contain nucleus
initiates some graded potentials, receives others from dendrites; conducts these potentials to axon
contains chromatophillic substance (Nissl bodies) made of ribosomes
123
dendrites
short, unmyelinated processes branching off cell body
recieve input and transfer it to cell body
124
axon
long process emanating from cell body
makes contact with other neurons, muscle cells, or glands
synaptic knobs house synaptic vessicles containing neurotransmitters
axons function to conduct action potentials and then release neurotransmitter at synaptic knobs
125
where is action potential generated
in the axon hillock
126
where do axons carry strong action potentials
away from cell body to either another neuron or an effector (like a muscle)
127
myelin sheath helps enhance...
the conduction velocity of action potential down the length of axon
128
the first neuron is refered to as
the presynaptic neuron
129
the second neuron is referred to as
the postsynaptic neuron
130
multipolar neuron
multiple processes extend directly from cell body; typically many dendrites and one axon; most common type of neuron
examples: all motor neurons; most interneurons
131
bipolar neuron
two proesses extend directly from the cell body; one dendrite and one axon; relatively uncommon
examples: some special sense neurons (retina of eye, olfactory epithelium of nose)
132
unipolar neuron
single short process extends directly the cell and looks like a T as a result of the fusion of two processes to look like one long axon
examples: most sensory neurons
133
axinomic neuron
processes are only dendrites; no axon present
example: interneurons of the central nervous system (CNS)
134
functional classification of neurons
1. sensory neurons
2. motor neurons
3.interneurons
135
sensory neurons (afferent neurons)
conducts input from somatic and visceral receptors to CNS
most are unipolar ( a few bipolar )
136
motor neurons (efferent neurons)
conduct output from CNS to somatic and visceral effectors
all multipolar
137
interneurons (association neurons)
receive process and integrate information from many other neurons
communicate between sensory and motor neurons
located within CNS; make up 99% of our neurons
generally multipolar
138
nerve
a bundle of parallel axons in the PNS
139
structural classification of nerves
cranial nerves : extend from brain
spinal nerves : extend from spinal cord
140
functional classification of nerves
sensory nerves
motor nerves
mixed nerves
141
sensory nerves
contain sensory neurons sending signals to CNS
142
motor nerves
contain motor neurons sending signals FROM CNS
143
mixed nerves
contain both sensory and motor neurons
most named nerves are in this category
individual axons in these nerves transmit only one type of information
144
pumps
membarne proteins that maintain a concentration gradient by moving substances against their concentration gradient
require cellular energy
145
what kind of pumps are present in neurons
sodium-potassium pumps and calcium pumps
146
channels
protein pores in the membrane that allow ions to move down their concentration gradients (into or out of cell)
when open they allow a specific type of ion to diffuse
147
leak channels
passive channels that are always open for continuous diffusion
148
chemically gated channels
normally closed but open when neurotransmitter binds
149
voltage gated channels
normally closed but open when membrane charge changes
150
glial cells (neuroglia)
nonexcitable support cells found in both the CNS and PNS
smaller but outnumber neurons and account for half the volume of nervous system
capable of mitosis, protect and nourish neurons, provide physical scaffolding for nervous tissue and are critcial for normal function at neural synapses
151
what are the different kinds of glial cells in the CNS
astrocytes
ependymal cells
microglial cell
oligodendrocytes
152
astrocyte
helps form the blood brain barrier
regulates interstitial fluid composition
provides structural support and organization to the CNS
assists with neuronal development
replicates to occupy space of dying neurons
153
ependymal cell
lines ventricles of brain and central canal of spinal cord
assists in production and circulation of cerebrospinal fluid
154
microglial cell
phagocytic cells that move through CNS
protects the CNS by engulfing infectious agents and other potential harmful substances
155
oligodendrocytes
myelinates and insulates CNS axons
allows faster action potential propogation along axons in the CNS
156
glial cells of the PNS
satellite cells
neurolemmocytes
157
satellite cells
arranged around neuronal cell bodies in a ganglion
electricity insulate and regulate the exchange of nutrients and wastes
158
neurolemmocytes (schwann cells)
elongated flat cells that ensheath PNS axons with myelin which allows for faster action potential propagation
159
myelination
process of wrapping an axon with myelin
160
myelin
several layers of membrane of glial cells
contain a high lipid content which gives it a glossy white appearance and insulates axon
161
myelination of PNS axons
1. neurolemocyte starts to wrap around portion of axon
2. neurolemmocyte cytoplasm and plasma membrane begin to form consecutive layers around the axon as wrapping continues
3. the overlapping inner layers of the neurolemmocyte plasma membrane form the myelin sheath
4. eventually the neurolemmocyte cytoplasm and nucleus are pushed to the periphery of the cell to form the neurilemma
162
neurilemma
neurolemmocyte's cytoplasm and nucleus are pushed to periphery
163
neurofibril nodes (nodes of ranvier)
caps between neurolemmocytes
164
myelination of CNS axons
one oligodendrocyte can myelinate 1mm of multiple axons, each at multiple spots
no neurilemma formed
neurofibril nodes between adjacent wrapped segments
165
where are unmyelinated axons present
in both PNS and CNS
166
unmyelinated axons in PNS
axon sits in depressed portion of neurolemmocyte
not fully ensheathed
167
unmyleinated axons in CNS
not associated with oligodendrocytes
168
synapse
place where neuron connects to another neuron or an effector
169
chemical synapse
presynaptic neuron's axon terminal produces signal
postsynaptic neuron recieves signal most commonly with dendrites
170
synaptic cleft
small fluid filled gap between two neurons
171
events in synaptic communication
neurotransmitter molecules released from vesicles of synaptic knob into cleft
transmitter diffuses across cleft and binds to postsynaptic receptors
binding of neurotransmitter to receptor initiates poststynaptic potential
172
synaptic delay
time it takes for all synaptic communication to occur
usually between .3-.5 nanoseconds
173
characteristics of resting neurons
ions are unevenly distributed across the plasma membrane due to the actions of pumps
gated channels are close in the functional segments of cell
there is an electrical charge difference
174
in a resting neuron there is a higher concentration of K+ in
the cytosol versus interstitial fluid
175
in a resting neuron there is a higher concentration of Na+, Cl-, Ca2+ in
interstitial fluid than in cytosol
176
what is resting membrane potential in a resting neuron
-70mV
177
what part of neurons is more negative
cytosol compared to IF
178
what is the most important factor in setting RMP
K+ diffusion
179
K+ diffusion
K+ diffuses out of the cell due to concentration gradient
K+ diffusion is limited by electrical gradient
180
Na+ diffusion
diffuses into the neuron due to its concentration gradient and the electrical gradient
181
role of Na+/K+ pumps
by pushing out 3 positive charges and pushing in only 2 negative, the pump contributes about -3 mV (of the -70 mV total)
more importantly it maintains the concentration gradients for these ions
182
what triggers postsynaptic potential
reception of neurotransmitters
183
what happens when a neurotransmitter binds to a chemically gated ion channel
it opens them
184
what happens when a neurotransmitter binds to a chemically gated ion channel
it opens them allowing ions to flow through the membrane changing its electrical potential
185
graded potential
the voltage change that can vary in size
186
what does the direction of the potential depend on
what type of ion channel opens
187
if na+ channels open...
na+ diffuses IN and membrane becomes LESS negative
188
if Cl- channels open...
Cl- diffuses IN and membrane becomes MORE negative
189
if K+ channels open...
K+ diffuses out and membrane becomes MORE negative
190
depolarized
when a cell is less negative than RMP
191
hyperpolarized
when a cell is more negative than RMP
192
excitatory postsynaptic potentials (EPSPs)
depolarizations caused by cation entry
193
generation of EPSP
1. neurotransmitter released from presynaptic neurons binds to postsynaptic neuron receptors which are chemically gated caiton channels causing them to open
2.na+ flows into neuron faster than K+ flows out
3. inside of neuron becomes more positive (less negative); called EPSP (-68 mV)
4. EPSP proopagates toward the initial segment
194
inhibitory postsynaptic potentials (IPSPs)
hyperpolarizations caused by cation exit or anion entry
195
generation of IPSP
1. neurotransmitter released from presynaptic neurons binds to postsynaptic neuron receptors, which are either chemically gated K+ channels or chemically gated Cl- channels causing them to open
2. either k+ flows out of, or Cl- flows into, the neuron, depending on the type of channel stimulated
3. inside of neuron becomes more negative; called IPSP (-72 mV)
4. IPSP propahates toward the initial segment
196
initial segment
summation of EPSPs and IPSPs
197
where does summation of EPSPs and IPSPs occur
at axon hillock
198
the summation of EPSPs and IPSPs may or may not reach threshold membrane potential which initates
an action potential
199
threshold
minimum voltage change required
200
what is the typical threshold for an action potential
-55 mV
201
if threshold is reached at axon hillock what happens
voltage gated channels open and an action potential is generated
202
all or none law
if threshold is reached action potential is generated and propagated down axon
if threshold isn't reached voltage gated channels stay closed but no action potential
203
does the value of threshold reached show different intensity
no, once threshold is reached the response is the same
204
conductive segment
the axon conducts action potentials
205
action potential
involves depolarization and repolarization
206
depolarization
gain in positive charge as Na+ enter through voltage gated Na+ channels
207
repolarization
return to negative potential as K+ exits through voltage gated K+ channels
208
action potential is propagated down
the axon to synaptic knob where voltage gated channels open sequentially down axolemma
209
propagation
called an impulse or nerve signal
210
action potential: steps in depolarization
1. at RMP voltage gated channels are closed
2. as Na+ enters from adjacent region, voltage gated Na+ channels open (changes MP to -55mV)
3. Na+ enters the axon causing the membrane to have a positive potential
4. Na+ channels close becoming inactive (unable to open) for a time
211
steps in repolarization
1. depolarization slowly opens K+ channels and K+ diffuses out causing negative membrane potential
2. K+ channels stay open for a longer time, so K+ exit makes cell more negative than RMP (-80mV)
3. K+ channels eventually close and RMP is reestablished
212
events of action potential
1. unstimulated axon has RMP of -70 mV
2. graded potentials reach the initial segment and are added together (-70mV - -55 mV)
3. depolarization occurs when the threshold (-55mv) is reached; voltage gated Na+ channels open and Na+ enters rapidly; reversing the polarity from negative to positive (-55mV - +30mV)
4. repolarization occurs due to colsure of voltage gated Na+ channels (inactivation state) and opening of voltage gated K+ channels. K+ moves out of the cell and polarity is reversed from positive to negative (+30mV - -70mV)
5. hyperpolarization occurs when voltage gated K+ channels stay open longer than the time needed to reach resting membrane potential; during this time the membrane potential is less than the resting membrane potential (-70mV - -80mV)
6.voltage gated k+ channels are closed and the plasma membrane has returned to resting conditions by activity of Na+/K+ pumps
213
refractory period
period of time after start of action potential when it is impossible or difficult to fire another action potential
214
absolute refractory period (1ms)
no stimulus can initiate another action potential
na+ channels are open but are ianctive
ensures propagation goes toward synaptic knob; doesn't reverse direction
215
relative refractory period (just after absolute)
another action potential is possible (Na+ channels have reset) but the minimum stimulus strength is now greater
some K+ channels are still open cell is slightly hyperpolarized and further from threshold
216
transmissive segment: release of neurotransmitter
1. nerve signal reaches synaptic knob
2. voltage gated Ca2+ channels open and Ca2+ enters the synaptic knob and binds with proteins associated with synaptic vessicles
3. synaptic vessicles fuse with the synaptic knob plasma membrane and neurotransmitter is exocytosed
4. neurotransmitter diffuses across synaptic cleft and attaches to receptors on a muscle
217
where do graded potentials occur
in neuron's receptive region due to ion flow through chemically gated channels
218
graded potentials
can be positive or negative in charge
are graded: have larger potential change to stronger stimulus
are local (short distance)
219
where do action potentials occur
on neurons conductive region (axon) due to ion flow through voltage gated channels
220
action potentials
involve depolarization (Na+ in) and repolarization (K+ out)
all or none once threshold is reached
propagate down entire axon to synaptic knob
221
what does conduction speed depend on
axon thickness and myelination
222
what fibers are faster
thick axons because they offer less resistance to current flow down the axon
223
where does saltatory conduction
on myelinated axons
224
where does action potential occur
only at neurofibril nodes which is where axon's voltage-gated channels are concentrated
225
conductive segment
after na+ enters at a node it starts a rapid positive current down the inside of the axon's myelinated region
the current becomes weaker with distance but still strong enough to open voltage-gated channels at the next node
full action potential occurs at the node and the process repeats : impilse seemingly jumping from node to node
226
what are the four chemical classes of neurotransmitters
acetylcholine
biogenic amines (monoamines)
-catecholamines
-indoalmines
amino acids
neuropeptides
227
what is an example of catecholamines
dopamine
228
what is an example of indoalines
seratonin
229
amino acids examples
glutamate glycine and GABA
230
neuropeptides examples
endorphins
231
functional classification of neurotransmitters
effect
action
232
excitatory transmitters cause
EPSPs
233
inhibitory transmitters cause
IPSPs
234
classes by action
direct transmitters bind to receptors that are chemically gated channels (immediate postsynaptic potential)
indirect transmitters bind to receptors that involve G-proteins and second messengers in order to cause postsynaptic potential
235
what is the difference between direct and indirect transmitters
indirect transmitter involve G-proteins and a secondary messenger to cause postsynaptic potential
236
acetylcholine is used in the PNS to stimulate
skeletal muscle
237
ACH is used in CNS to
increase arousal and attention, enhances memory
238
what is ach synthesized from
acetate and choline which is stored in synaptic vesicles
239
how is ach cleared from the cleft
by being broken down to acetate and choline by acetylcholinesterase
240
what happens to acetate and choline after it has been used
it is taken up by presynaptic cell for recycling
241
removal of neurotransmitter from the synaptic cleft can occur in varried ways. what are the 3 ways?
enzymes might degrade trasmitter
presynaptic transporters might important transmitter ("reuptake")
some transmitter diffuses away from synapse reabsorbed by glia
242
how do drugs influence transmitter removal
selecttive serotonin reuptake inhibitors treat depression
galantamine hydrobromide is an acetylcholinesterase inhibitor used to treat alzheimer disease
243
what does ACH effect on target cell depend on
the receptor
244
nicotinic receptor
directly causes EPSP
245
muscarinic receptor
engages G protein and 2nd messenger and indirectly leads to EPSP or IPSP
246
neuromodulators
chemicals that alter responses of local neurons
247
faciliation
modulation that causes greater response in postsynaptic neuron
may increase amount of neurotransmitter in cleft or number of postsynaptic receptors
248
inhibition
modulation that causes weaker response
may decrease amount of neurotransmitter in cleft or number of postsynaptic receptors
249
neuronal pools (neuronal circuits)
groups neurons arranged in specific patterns
250
what are the 4 types of circuits
converging
diverging
reverberating
parallel-after-discharge
251
converging circuit
input converges at a single postsynaptic neuron
ex. multiple sensory inputs synapse on neurons in the salivary nucleus. sights, sounds, and smells, or cooking lead to one output: salivation
252
diverging circuit
spreads information from one presynaptic neuron to several postsynaptic neurons
example: neurons in brain that control walking send commands to several different muscles for proper balance, posture, and motion
253
reverberating circuits
use feedback to produce repeated cyclical activity
once started it stays active until there is an inhibitory stimulus or synaptic fatigue
example: circuits that keep us breathing regularly during sleep
254
parallel-after-discharge circuits
input transmitted simultaneously along several paths to a postsynaptic cell
since paths vary in number of synapses, signal arrives at postsynaptic cell at various times
believed to be involved in higher-order thinking
255
reflexes
a rapid involuntary response caused by a stimulus that is preprogrammed, involuntary, and always the same
256
what is the importance of a reflex
we respond to a potentially detrimental stimulus immediately and awareness comes later
257
steps of a reflex
1. stimulus activates receptor
2. nerve signal is propagated through sensory neuron to the spinal cord
3. nerve signal is processed int the integration center by interneurons
4. nerve signal is propagated by motor neuron to effector
5. effector responds
