Anatomy & Physiology 34A
Chapter 11 - Neurophysiology
I. Overview
A. Electrical Signals in Neurons
B. Cell to Cell Communication
C. Integration of Neural Information Transfer
II. Electrical Signals in Neurons
A. Neurons are ___________ (responsive to stimuli) cells, able to generate electrical signals
as ___ move across their cell membranes.
B. Membrane ________ (voltage) results from the uneven distribution of _____ across the cell
membrane, and is influenced by
1. Ion _____________ gradients in a resting neuron
a. A higher concentration of ___, Cl-, and Ca2+ in the ____ results in a more __________
charge outside the neuron
b. A higher concentration of _______ and K+ in the _____ results in a more
___________ charge inside the neuron
c. The difference in charge is the membrane’s _________ (voltage)
2. Membrane ____________ to the ions
a. A resting neuron’s membrane is more permeable to ___ than to Na+ or Ca2+ (K+ leaks
slowly out of K+ ion channels)
b. ___ is the major ion that contributes to the ________ membrane potential
c. In an average neuron, the _________ membrane __________ (difference in charge
across the membrane) is about ____ mV
C. Ion movement across cell membranes creates _________ signals
1. Electrical currents in the body are created by the flow of _____ (esp. sodium [___] and
potassium [___]) through openings (ion channels) in the plasma membrane
a. A cell with a difference in charge across it membrane is said to be ____________
b. If the neuron membrane increases its permeablilty to Na+, ___ moves _____ the cell,
which ____________ the membrane (the potential becomes more __________)
c. If the membrane becomes more permeable to K+, ____ moves _____ of the cell,
which ______________ the membrane (the potential becomes more ___________)
D. Three types of gated _________ control neuronal ion permeability
1. _____________ gated ion channels in sensory neurons open due to pressure or
__________
2. ___________ (ligand) gated ion channels in most neurons open in response to
_________ (e.g., neurotransmitter) binding
3. __________-gated ion channels open or close in response to changes in membrane
__________
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E. Electrical ________ may be graded potentials or action potentials
1. _________ (local) potentials are variable strength signals that travel ______ distances
and gradually lose strength
2. ______ potentials are strong, uniform depolarizations that travel from the cell body to
the axon ________ without losing strength
F. Graded Potentials reflect the strength of the ___________ that initiates them
1. _______ potentials are __polarizations or ______polarizations that usually occur in
__________ or the cell body
2. Neurons can be stimulated by __________, light, heat, voltage, or mechanical
distortion of the plasma membrane
3. When stimulated, neuronal ion ________ open or close, causing _____ to enter or
leave the neuron
4. The resulting change in membrane ____________ is directly proportional to the
strength of the initial stimulus
a. A weak stimulus will initiate a weak _________ potential that will not travel far
b. A strong stimulus will stimulate a strong graded potential that may be converted to
an _________ potential
5. Example of a depolarizing ________ potential:
a. A chemical binds to _______ in the neuron plasma membrane (usually in the
dendrites or cell body)
b. The receptors are _______-gated sodium channels that open and allow ____ to
diffuse into the neuron
c. Na+ _______ causes the neuron’s internal negative charge to become more positive
(__________), thus the voltage moves from –70 mV toward ______
d. Incoming Na+ ions produce a _________ that travels to the cell body, then to the
cell’s trigger zone (axon _________)
e. This limited short range change in voltage in the neuron is called a ________
potential
f. If the graded potential depolarizes the membrane to the ____________ voltage
(about ____ mV), voltage-gated Na+ channels are opened, and an ______
potential is initiated
6. Two types of ________ potentials are inhibitory & excitatory post synaptic
potentials
a. ___________ post synaptic potentials (_____s) result from _______polarization
of the post synaptic neuron’s membrane; IPSPs make the neuron_____ likely to fire
an action potential
b. ____________ post synaptic potentials (_____s) result from ___polarization of
the post synaptic neuron’s membrane, which makes the neuron _____ likely to fire
an action potential
1) If the depolarization is not strong enough to reach _______, the graded potential
will ____ out
2) If the depolarization does reach __________, an ________ potential will be
generated
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G. Action Potentials travel ______ distances without losing strength
1. Action potential _______ from graded potentials in that
a. All action potentials have the same _________
b. Action potentials do not diminish in _________ as they travel
c. Action potentials are “____ or ______” – they will only be generated if _________ is
reached in the neuron’s trigger zone
H. Action Potentials result from the movement of ____ and ____ through voltage-gated ion
channels in the membrane
1. ___________-gated ion channels are found in the highest concentration in the
________ zone (axon hillock) of a neuron
2. If an ___________ graded potential is strong enough when it reaches the trigger zone,
it can open these ion channels and generate an _______ potential down the axon
3. The __________ of events that cause an action potential include:
a. Prior to the action potential, the neuron has a resting potential of about ____mV, and
voltage-gated ion channels are _______
b. A stimulus in the neuron initiates a ________ potential, which travels toward the
axon ________, and may generate an action potential, depending on the _________ of
the local potential
c. If enough ____ ions enter the axon hillock to reach _________ voltage (about ___
mV), _________-gated Na+ channels open, and more Na+ ions rush into the neuron
d. An ______ potential is generated down the axon as more voltage-gated ____ channels
are opened (like a row of dominos falling), as the ___polarization wave rises to about
____ mV
e. Voltage-gated Na+ channels ____ as voltage-gated ___ channels open, causing K+ to
move ___ of the neuron, and __polarization occurs (voltage moves back towards the
________ potential)
f. ______polarization, a decrease in membrane voltage slightly below the resting
potential (___ mV), often occurs because voltage-gated K+ channels are _____ to close
4. The ___/___ pump restores the ion balance of the neuron by pumping Na+ ions ___ and
K+ ions ____ the neuron
I. Action potentials will ____ fire during the Absolute Refractory Period
1. The ___________ period is a period of neuronal insensitivity to restimulation during
and after the action potential
2. ___________ refractory period – occurs from start to end of the action potential, when
the ____ channels are still open
a. During this time (about 1msec) the neuron cannot be further __________, regardless
of the stimulus strength
b. Ensures ____ ___ transmission of the action potential
3. ________ refractory period – lasts until _____polarization ends, when ____ channels
are still open, but Na+ channels are closed
a. During this time an exceptionally _______ stimulus can trigger another action
potential
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J. Stimulus _________ is coded by the frequency of action potentials
1. A stronger stimulus will generate a greater __________ of action potentials (no. of APs
fired per second) in a neuron than a weaker stimulus
K. _________ neurons and those with myelinated axons conduct action potentials faster
1. Neurons with larger diameters have decreased ___________ to electrical current flow,
thus ________ action potentials
2. ______________ axons have voltage-gated Na+ channels along their whole ______,
thus depolarization of one part of the neuron membrane propagates the action potential
from axon hillock to axon __________ like a row of dominos falling over
3. ___________ axons have the majority of their voltage-gated Na+ channels in the nodes
of _________ between the myelin sheaths
a. Na+ ions ________ inside the membrane between the nodes, then open the voltagegated ____ channels at the nodes to propagate the action potentials (__________
conduction)
b. The result is ________ nerve conduction than in unmyelinated axons
L. Electrical activity can be altered by _________
1. Some chemicals ______ action potential conduction by binding to Na+, K+, or Ca2+
_________ in the neuron membrane
a. ____________ (e.g., tetrodotoxin from puffer fish) and local ___________ bind to
and block ____ channels
b. If Na+ channels are blocked, ____ cannot enter the axon. How would this affect
nerve conduction?
2. Changes in ECF concentrations of ____ and Ca2+ alter the electrical activity of the
nervous system
a. _____kalemia (high blood [___]) shifts the resting membrane potential toward
_________, causing neurons to fire ______ potentials in response to smaller graded
potentials, which can cause heart failure
b. _____kalemia (low blood [___] ______polarizes neurons, making them ____
likely to fire action potentials, which results in muscle weakness
III. Cell-to-Cell Communication
A. The _____________ of neural communication depends on:
1. ________ molecules secreted by neurons
2. Target cell ___________ for the chemicals
3. _________ – the connections between neurons and their effectors
B. ___________ passes from cell to cell at the synapse
1. A __________ is the place where a neuron meets its _________ (another neuron,
muscle or gland cell). Each synapse has 3 parts:
a. ____synaptic neuron axon terminal
b. Synaptic ______ – minute gap between presynaptic axon and
c. _____synaptic cell membrane
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2. _________ synapses are those in which adjacent cells are joined by ___ junctions,
which allow ___ to diffuse directly from cell to cell. These synapses are found in glia,
_______ & smooth muscle
3. ___________ synapses are those in which neurons communicate with effectors via
neuron_________. These synapses are the most common in the nervous system
C. _______ is the signal for neurotransmitter release at the synapse
1. Axon _________ contain many mitochondria and synaptic _______ that house
neurotransmitter chemicals
2. Neuro_____________ are released from the ____synaptic axon terminal to the
______synaptic cell membrane as follows
a. An action potential __________ the axon terminal
b. Depolarization opens voltage gated ____ channels, and Ca2+ enters the axon
_________
c. Calcium binds to intracellular regulatory _________ and initiate ___________
d. Neuro___________ released from the vesicles diffuse across the synaptic ______
and bind to ligand-gated __________ on the postsynaptic cell membrane
e. A response (e.g., ____ potential) is initiated in the postsynaptic cell
3. Neuro________ (e.g., tetanus and botulinum) can inhibit certain proteins (e.g., voltagegated Ca2+ __________) in the neuron’s exocytotic apparatus, thus ___________
nerve transmission
D. Neuro________ convey information from neurons to other cells
1. __________ molecules released from neurons may function as neurotransmitters,
neuromodulators, or neurohormones
2. Neurotransmitters and neuromodulators act as _________ and/or ___________, with
target cells near by
a. Neurotransmitters act at a _______ and elicit _____ responses
b. Neuromodulators act at synaptic and _________ sites, and are ___________ acting
3. Neurohormones are secreted into the _____ where they travel to distant target cells
E. Neurotransmitters are grouped into several _______, according to their structures. The
classes are: ACh, amino acids and amines, polypeptides, purines, gases, and lipids
1. Acetylcholine (____) – synthesized from acetylCoA and ______, and used in the PNS
a. Neurons that secrete ACh, and ACh receptors are called _________
b. ACh is _________ in skeletal muscle and neurons, but __________ in cardiac muscle
c. ACh may be excitatory or inhibitory in _______ muscles and glands, depending on
their types of __________
2. ______ _____, such as glutamate, aspartate, glycine, and gamma-aminobutyric acid
(GABA)
a. _____________ AAs in the CNS are glutamate and aspartate
b. _____________ AAs in the CNS include glycine and GABA
3. Amino acid derived ______ are mostly made from ________, such as epinephrine
(__________) and norepinephrine (catecholamines), and dopamine, which also function
as neurohormones
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a. Neurons that secrete ___epinephrine, and the NE receptors are called __________.
NE is the main neurotransmitter of the __________ NS.
b. Catechol______ are used in the _____; they are excitatory in _______ muscle and
excitatory or inhibitory in ______ muscle and glands
c. __________ inhibits involuntary skeletal _______ movements; lack of dopamine
leads to ___________ disease
d. Indol_______ include
1) ___________, made from tryptophan in the ____ is involved in sleep, alertness,
thermoregulation and _______
2) __________ is a vasodilator
4. Poly_________ include
a. Substance __ involved in some ______ pathways
b. ________ peptides (endorphins & enkaphalins) are _________ (suppress pain)
F. Multiple _________ types amplify the effects of neurotransmitters
1. Neurotransmitter receptors are either ______-gated ion channels or ___ _________linked receptors that stimulate 2nd messengers
2. ___________ receptors, to which ____ binds, have two subtypes
a. ___________ receptors (nicotine is an agonist) are _____-gated ion channels found on
skeletal ________, in the sympathetic NS and in the CNS
1) ACh binds to and opens ____ channels in the postsynaptic neuron, allowing Na+ to
enter and K+ to leave the neuron
2) Na+ influx ________ the neuron, causing a ______ potential. If the depolarization
is strong enough, an _______ potential is triggered in the postsynaptic cell.
3) Ligand-gated ion channels are _________ – they open ion channels
b. _________ receptors (fungal muscarine is an agonist) are found in the
____sympathetic NS and CNS; they are linked to __ _______ with 2nd messengers
1) ACh binds to the G protein-linked receptor, which activates a ___ _______,
which activates a ____ messenger
2) __________ vary according to the receptor subtype
3. __________ receptors include alpha (__) and beta (__), which are also ___ ________linked receptors and initiate 2nd messenger cascades
4. ________ and neuropeptides have ____________ effects that use a second messenger,
such as _____, to change the metabolism of the postsynaptic cell.
a. When the ligand binds to the _______, it activates the production of a ____ messenger,
which causes the following effects in the postsynaptic cell
b. Metabolic _________ can be turned on and off
c. Other internal messengers can enter the _________ and trigger the synthesis of new
________
d. Intracellular messengers can bind to another ____ ___________ and open it
G. Neurotransmitter activity is quickly __________ in several ways
1. ACh is broken down by acetylcholinesterase (______), then ________ is actively
_________ back into the presynaptic axon to make more ACh
2. Norepinephrine (____) is actively ___________ back into the presynaptic axon, to be
used again or broken down by monoamine oxidase (_____)
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3. _______, polypeptides, and amino acid neurotransmitters in the CNS move into the
_____ or are actively _________ back into the presynaptic axon to be metabolized or
used again
IV. ____________ of Neural Information Transfer
A. Neural pathways may involve ______ neurons simultaneously
1. Neuronal ______ are the pathways among neurons, like a circuit board of an electrical
appliance. Types of neuronal circuits are
a. __________ circuit – one nerve fiber branches and synapses with _________
postsynaptic cells; allows one neuron to control _____ other cells (e.g., 1 motor
neuron controls many skeletal muscle cells)
b. __________ circuit – several neurons synapse with ___ neuron or a neuronal pool;
allows input from several body regions (e.g., eyes, inner ear) to another area (e.g.,
brain area for equilibrium)
2. Summation and inhibition – a neuron may receive input from ___________ of
presynaptic neurons at one time, causing the following effects
a. ____________ – the process of “_________ up” postsynaptic potentials (+____s
and –_____s) and responding to their ____ effect; if the EPSPs override the IPSPs, a
nerve impulse may be generated. Two types of summation are:
1) ___________ (time) summation – occurs when one presynaptic neuron generates
EPSPs so _________ that each is generated before the other decays; which can
add up to __________ and cause an action potential
2) __________ (space) summation – occurs when EPSPs from _______ presynaptic
neurons add up to ___________ at the axon hillock of one postsynaptic neuron
3. Postsynaptic __________ occurs when one neuron suppresses the effect of a another
neuron (e.g., a neuron that generates ____s prevents neurotransmitter release by another
neuron)
B. Synaptic activity can be _______________
1. ___________ modulation allows selective modulation of axon __________ and their
target cells
a. Presynaptic ___________ occurs when a presynaptic neuron __________
neurotransmitter release by a postsynaptic cell
b. Presynaptic __________ occurs when the presynaptic neuron ___________
neurotransmitter release by the postsynaptic cell
2. ______synaptic modulation occurs when a modulatory neuron, usually _________,
synapses with the _________ or cell body of a postsynaptic cell
C. Disorders of _________ transmission are responsible for many diseases
1. Synaptic ________ are exposed to the ______cellular fluid, thus are more accessible to
_______ than intracellular receptors
2. Common drugs that act on synaptic activity include ________ and nicotine (stimulants),
and _________ (a depressant)
3. Nervous system disorders related to faulty synaptic transmission include _____________,
schizophrenia, and depression
a. Drugs used to treat schizophrenia, anxiety, and ________ act by influencing activity at
the synapse