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Reception, Transduction, Response
Ligand is the fancy word for signaling
molecule.
Energy can be in the form of ions
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Evolved from nerve net in Cnidarians
Brain evolves giving greater control. Includes
a nerve cord.
Cephalization occurs- development of other
sensory organs in the head.
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A stimulus is a form of energy like light
(electromagnetic) or pressure (mechanical), or
sound waves.
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1. Sensory Input-Sensory receptors receive a
stimulus and send it into the brain/ spinal cord.
2. Integration- the CNS
integrates/interprets/thinks about the sensory
input (stimulus).
3. Motor Output- Impulse sent from the brain to
the muscles to respond. Effector cells in muscles
and glands will respond.
Peripheral Nervous System-has sensory receptors
and motor nerves.
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Cell Body- receives stimuli from all dendrites,
and creates one signal
Dendrites- carry stimuli into the cell body
Axon- carries signal away from cell body and
towards next neuron.
Myelin Sheath- lipid covering over axon for
insulation. Composed of Schwann cells (PNS)
Synaptic Terminal- end of axon
Synapse- gap between neurons or neuron
and effector cell.
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Ganglia- bundle of neurons in the PNS
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Nuclei- bundle of neurons in the CNS
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Glial Cells- give neurons support (framework)
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Oligodendrocytes- aka Schwann Cells of the
CNS
Multiple Sclerosis- MS- Schwann Cells die in CNS &
PNS and causes the signal (electrical current) to burn
muscles into permanent contractions.
Nodes of Ranvier
Layers of myelin
Axon
Schwann
cell
Axon
Myelin sheath
Nodes of
Ranvier
Schwann
cell
Nucleus of
Schwann cell
0.1 µm
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Ions can be considered ___________
Concentration gradients are ________________
and so they can be considered _____________
Active transport requires _______________ .
Diagram a cell pump.
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Ability of the membrane to do work.
Created by electrical gradient (difference) on
either side of the c.m.
Anions inside
Cations outside
CYTOSOL
EXTRACELLULAR
FLUID
[Na+]
15 mM
[Na+]
150 mM
[K+]
150 mM
[K+]
5 mM
[Cl–]
[Cl–]
120 mM
10 mM
[A–]
100 mM
Plasma
membrane
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Resting Potential- Unstimulated neuron, need
to establish the [gradient]
1. NaK Pump responsible for generating nerve
impulse.
◦ NaK Pumps are either ligand gated or voltage gated,
which helps create gradient faster.
EXTRACELLULAR [Na+] high
FLUID
[K+] low
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
CYTOPLASM
[Na+] low
[K+] high
Na+
Cytoplasmic Na+ bonds to
the sodium-potassium pump
P
ATP
P
ADP
Na+ binding stimulates
phosphorylation by ATP.
Phosphorylation causes
the protein to change its
conformation, expelling Na+
to the outside.
Loss of the phosphate
restores the protein’s
original conformation.
K+ is released and Na+
sites are receptive again;
the cycle repeats.
P
P
Extracellular K+ binds
to the protein, triggering
release of the phosphate
group.
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1. Depolarization- destroys membrane
potential, Na floods into cell
◦ Depolarization is “graded”
◦ Threshold potential-minimum Na that must enter
to generate a nerve impulse
◦ Action Potential- “Spike” electrical generated
impulse, ana ction will occur
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2. Repolarization- neuron pumps out K to try
and return to resting potential.
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3. Hyperpolarization- the cell will pull in
some K to get back to resting potential.
◦ Must Hyperpolarize so that the neuron can get back
to resting potential, and to recreate the [gradient]/
polarity
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4. Refractory Period- neuron can’t make new
impulse
Stimuli
Stimuli
+50
–50 Threshold
Resting
potential
Hyperpolarizations
0 1 2 3 4 5
Time (msec)
Graded potential hyperpolarizations
+50
Membrane potential (mV)
0
Membrane potential (mV)
Membrane potential (mV)
+50
–100
Stronger depolarizing stimulus
0
–50 Threshold
Resting
potential
–100
0
–50 Threshold
Resting
potential
Depolarizations
0 1 2 3 4 5
Time (msec)
Graded potential depolarizations
Action
potential
–100
0 1 2 3 4 5 6
Time (msec)
Action potential
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Nerve Impulse Animation
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Propagation: Impulse traveling down the
axon.
Saltatory Conduction: impulse “hopping” over
Schwann Cells. Ions are only exposed at the
nodes.
◦ The jumping makes impulse travel really quick.
Axon
Action
potential
Na+
An action potential is generated as Na+ flows
inward across the membrane at one location.
K+
Action
potential
Na+
K+
The depolarization of the action potential spreads to the
neighboring region of the membrane, re-initiating the
action potential there. To the left of this region, the
membrane isAction
repolarizing as K+ flows outward.
K+
potential
Na+
K+
The depolarization-repolarization process is repeated in the next region of
the membrane. In this way, local currents of ions across the plasma
membrane cause the action potential to be propagated along the length of
the axon.
Schwann cell
Depolarized region
(node of Ranvier)
Cell body
Myelin
sheath
Axon
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1. Sensory Neuron- receive stimulus
2. Interneuron- in CNS (spinal cord) takes
sesory imput and gives signal to motor
neuron
3. Motor Neuron- carries energy to effector
cell. ( ________/__________)
This is why you don’t think about a reflex, the
signal never made it to the brain for
integration.
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Diffusion is _________ and uses no ________
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Ligands bind to receptor proteins and cause a:
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Do you think all ligands cause the same
response?
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Where are synapses located? ______&________
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2 Types of Synapses
◦ 1. Electrical- direct cell contact, in brain
◦ 2. Chemical- most common in animals- requires a
neurotransmitter (chemical ligand)
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The impulse is Electrical energy chemical
energy electrical energy
Nerve Impulse Conversion in Chemical
Impulses:
1. Depolarization- down to the axon terminal of
presynaptic neuron.
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2. Ca rushes into presynaptic cell due to
impulse hitting the axon terminal.
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3. Neurotransmitter vesicles fuse with pre-syn.
cell membrane.
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4. Neurotransmitter released into synapse
5. Neurotransmitter binds to receptor protein
on post syn cell and causes a CSC
6. Na floods into post syn. Cell and causes
depolarization.
Presynaptic
cell
Postsynaptic cell
Synaptic vesicles
containing
neurotransmitter
Na+
K+
Presynaptic
membrane
Neurotransmitter
Postsynaptic
membrane
Ligandgated
ion channel
Voltage-gated
Ca2+ channel
Postsynaptic
membrane
Ca2+
Synaptic cleft
Ligand-gated
ion channels
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IPSP & EPSP
Excitatory Post Synaptic Potential- causes
Post syn. Cell to do act or keep impulse going
Inhibitory Post Synaptic Potential- causes
Post syn. Cell to stop impulse transmission
Summation- adding of all dendrite stimuli to
reach threshold potential
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Neurotransmitters- chemical ligands produced
by neuron to transmit the signal across the
synapse.
Neurotransmitters are released from a presynaptic cell (neuron) and received by a
postsynaptic cell (neuron or effector cell).
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Acetylcholine- (ACh)makes muscles contract
in PNS, can be excitatory or inhibitory in CNS.
Cholinesterase breaks down ACh
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Biogenic Amines
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◦ 1 & 2. Epinephrine and norepinephrine- fight or
flight, speeds up body functions
◦ 3.Dopamine=happy
◦ 4. Serotonin=sleep *both out of whack in
ADD/Schiz
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Amino Acids
◦ 1. Substance P- relays pain stimulus
◦ 2. Endorphins- block Substance P “second wind”
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Gases- work by diffusion
◦ 1. NO
◦ 2. CO
 *both inhibit nerve signaling and muscle contractions
Stimuli
Stimuli
+50
–50 Threshold
Resting
potential
Hyperpolarizations
0 1 2 3 4 5
Time (msec)
Graded potential hyperpolarizations
+50
Membrane potential (mV)
0
Membrane potential (mV)
Membrane potential (mV)
+50
–100
Stronger depolarizing stimulus
0
–50 Threshold
Resting
potential
–100
0
–50 Threshold
Resting
potential
Depolarizations
0 1 2 3 4 5
Time (msec)
Graded potential depolarizations
Action
potential
–100
0 1 2 3 4 5 6
Time (msec)
Action potential
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1. Sensation- action potential is at the brain,
and senses a nerve impulse.
2. Perception- integration of sensation by
brain
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Special neurons detect stimuli.
Stimuli will be detected by their ____________.
Stimuli is defined as _________________
That will cause a _ _ _
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1. Summation will cause Threshold potential
to be reached.
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2. Amplification can occur on the way to the
CNS.
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3. Saltatory conduction is responsible for
signal propagation.
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4. Integration by CNS for appropriate
response.
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Decrease in continuous stimulus coming into
the CNS.
◦ CLOTHING DETECTED BY BODY, BUT IS NOT
RESPONDING.
1. Internorepectors- detect internal stimulipressure, balance, homeostasis
2. Externoreceptors- external stimuli
 Mechanoreceptors- detect bend/stretch of
membranes/hairs
 Nociceptors-detect pain using Substance P
 Thermoreceptors- detect cold
 Chemoreceptors-detect cheimicals: osmo-water,
gustatory-taste, olfactory-smell
 Electromagnetic receptors-detect photo-light,
electro- electrical, magno-magnetic
Heat
Light
touch
Pain
Cold
Hair
Epidermis
Dermis
Hypodermis
Nerve
Connective
tissue
Hair
movement
Strong
pressure
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Accomplished by mechanoreceptors in the
inner ear.
Hairs bend, mechanoreceptors detect this,
cause a depolarization of auditory nerves and
create action potential.
Lateral lines in fish
Tympanum in insects and amphibians
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Accomplished by mechanoreceptors in the
inner ear
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Accomplished by chemoreceptors in the nose
(olfactory) and mouth (gustatory).
Or hairs if you’re a bug!
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Taste is 80% smell and 20% tase
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Five senses of taste:
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Sweet
Sour
Bitter
Salty
Umami
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All animals have photoreceptors- detect
colors
Some photoreceptors contain photopigments
that detect color
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Second biggest consumer of ATP
Must overcome friction and gravity
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Animals move in/on: water, land, air
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Muscles provide a pulling force
Motor Unit= muscle and corresponding
motor nerve
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1. ACh attaches to receptor proteins on
muscle cell.
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2. Depolarization occurs (release of Na)
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3. Na causes Ca to be released. Ca is a
secondary messenger.
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4. Ultimately it causes two different proteins
actin and myosin to slide over one another.
Myosin pulls on actin.
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Acetylcholinesterase breaks down ACh and
actin and myosin slide back to original
position.