Neurophysiology
Electrical Activity
in the Body
Review of basic principles of
electricity
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•
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Two types of electrical charges?
Like charges_________
Opposite charges________
The difference in electrical charged areas is
called____________ __________.
• Electricity is measure in _______.
– In your body measurements are _________.
Apparatus to administer thermal stimuli and record nerve
impulses.
Distribution of charges in the
Nerve Cell
• Outside the cell
– Na+ (150mM), K+ (15mM) and Cl- (120mM)
• Inside the cell
– Na+ (15mM), K+ (150mM) and Cl- (10mM), A(100mM)
Recall the Cell Membrane and membrane transport…
What molecules will diffuse based on diffusion
properties?
Na+/K+ Pump
• http://www.brookscole.com/chemistry_d/te
mplates/student_resources/shared_resources
/animations/ion_pump/ionpump.html
Membrane Potential
• Nerve cells have differences in the
concentration of ions
• The membrane is electrically Polarized
(more – charges on inside than the other)
– Anions are more concentrated inside a cell
– Cations are more concentrated outside the cell
Recall a molecule that is polar…?
Extracellular fluid
Intracellular fluid
Review 10-16-14
1. What are the three types of neurons?
2. Which neuron transmits impulses from sensory
receptors to the brain or spinal cord?
3. Which neuron transmits impulses from the CNS to
effectors?
4. Discuss the function of myelination? Which type
of neurons are myelined? Why?
5. In order to maintain membrane potential, the cell
membrane of neurons are composed of __?
6. The electrical charge of a neuron is __?
Membrane Potential
• How do we measure potential?
– Milivolts
• Resting state: when a nerve is inactive (not
transmitting a signal) the value is –70 mV
Changes in the Membrane Potential of a
neuron give rise to nerve impulses
•
How are the membrane potentials
changed?
1. Response to stimuli (ion concentrations)
Ex: temperature, light, or pressure
2. Chemical stimuli (neurotransmitters)
Ex: dopamine, serotonin, amino acids
• http://www.biology4all.com/resources_library/s
ource/63.swf
Phases of an action potential
1. Resting State: Neither channel is open
2. Depolarization: Na+ channels open, K+
remain closed
3. Repolarization: Na+ channels close, K+
channels open
4. Undershoot: K+ channels remain open
(slow to close)
• http://highered.mheducation.com/sites/0072
495855/student_view0/chapter14/animation
__the_nerve_impulse.html
Nerve Impulse Conduction
• The resulting action potential causes an
electric current that stimulates adjacent
portions of the membrane
• Series of action potentials occurs
sequentially along the length of axon as a
nerve impulse
Factors that determine speed of
Nerve Impulses
• Temperature: The higher the temperature, the faster the
speed.
• Axon diameter - The larger the diameter, the faster the
speed
• Myelin sheath –
– Only vertebrates have a myelin sheath surrounding their neurons.
– The voltage-gated ion channels are found only at the nodes of
Ranvier, and between the nodes the myelin sheath acts as a good
electrical insulator.
– The action potential can therefore jump large distances from node
to node (1mm), a process that is called saltatory propagation.
– This increases the speed of propagation dramatically, so while
nerve impulses in unmyelinated neurones have a maximum speed
of around 1 m/s, in myelinated neurones they travel at 100 m/s.
Review of Action Potentials
1. How are the membrane potentials changed?
2. What factors may affect the speed/rate of a nerve
impulse?
3. The potential difference between cell membrane
is called ______ ________.
4. Describe the conditions of a neuron that is at rest.
5. What occurs during Depolarization?
6. Suggest Why a refractory period is necessary
after action potential has been reached?
Characteristics of Nerve Impulses
• Refractory period
• All or none response
• Impulse conduction
Refractory Period
aka: Rest Time
• For an action potential to begin, then the
depolarization of the neuron must reach the
threshold value, i.e. the all or nothing law.
• refractory period,
– After an ion channel has opened, it needs a “rest period”
before it can open again/ lasts about 2 ms.
• One Way Street: although the action potential
affects all other ion channels nearby, the upstream
ion channels cannot open again since they are in
their refractory period
– only the downstream channels open, causing the action
potential to move one-way along the axon.
Refractory Period
•
•
The refractory period is necessary as it allows the
proteins of voltage sensitive ion channels to
restore to their original polarity.
2 periods of refractory period
1. absolute refractory period = during the action
potential, a second stimulus will not cause a new
action potential.
2. Exception: There is an interval in which a
second action potential can be produced but only
if the stimulus is considerably greater than the
threshold = relative refractory
Refractory…Why?
• Limits how many action potentials may be
generated
Neurotransmitters
• Chemicals released
from pre-synaptic
neuron
• Act to assist, stimulate
or inhibit postsynaptic
neurons
• Where do they come
from?
– Synthesized in
cytoplasm of synaptic
knobs
– Or stored in vesicles
•http://intro.bio.umb.edu/111-112/112s99Lect/neuro_anims/s_t_anim/WW36.htm
How NTs are released
• http://highered.mheducation.com/sites/9834
092339/student_view0/chapter44/chemical_
synapse.html
• https://www.youtube.com/watch?v=p5zFgT
4aofA
Acetylcholine
Categories of NT
• Monoamines
– Epinephrin, dopomine, and serotonin
• Amino acids
– Glycine, glutamic acid and gamma aminobutyric acid:
GABA
• Peptides
– Made in RER
• Neuropeptide
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–
–
–
Alter response to a NT or block release of NT
Act as NTs
Released during stress
Ex: beta endorphin: pain reliever…similar to morphine
Norepinephrine
aka: adrenalin
• Released from brain and ANS
– Adrenal gland
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Excitatory
Sense of feeling good, alertness
Increases heart rate and Bld pressure
Monoamine
Can be used to manage hypertension
Glutamate
• Found in CNS and concentrated in brain
• Excitatory
Dopamine
• Released from brain (CNS)
– hypothalamus
• Receptors: heart, kidneys, bld
vessels
• Inhibitory (can be excitatory)
• sense of feeling good, reward
pathway
• Parkinson’s Disease
• amine
Serotonin
• Brain (CNS)
• Regulates endocrine activity
(hormonal controls)
• Leads to sleepiness
• Involved with mood and perception
– Controls sleep/wake cycles
• amine
• Inadequate amounts:
– Severe depression and
obsessive/compulsive disorders, anger
issues, and eating disorders
Endorphins
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Neuropeptide
Produced in brain (CNS)
Pain relief and pleasure
Released in times of pain or stress
Elevated levels cause disease known as
Addison’s disease
• Structure is similar to???
– morphine
GABA
gamma amino butyric acid
• Inhibitory
• Prevents NT that can cause
sensitivity/anxiety
Review of NTs
___1. dopamine
___ 2. norepinephrine
___ 3. serotonin
___ 4. acetylcholine
___ 5. endorphins
a.
b.
c.
d.
e.
excitatory; involved in control of skeletal muscles
associated with reward mechanisms
chemical structure related to morphine
inadequate amounts may lead to depression
excitatory; vasoconstrictor
6. Define a synapse.
7. Predict What would happen if Ca+ ions were not
stimulated by a nerve impulse at a chemical synapse?
8. What causes a person to become dependent on drugs?
9. What might occur if a NT remains in the synapse after
communicating with a post-synaptic neuron?
10. Draw and label a chemical synapse.
Disorders Associated with NT
imbalances
SIDS
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NT: excess dopamine
Symptoms: baby stops breathing
Leading cause of death of infants 0-1yr
Factors: smoking, sleeping on belly
Insomnia
• NT: deficient
serotonin
• Symtoms: no sleep!
Alzheimer's
• NT: not enough AcH
• Symptoms: memory
loss, depression,
disorientation
Parkinson’s
• NT: not enough dopamine
• Symptoms: tremors, muscle rigidy
• Inhibitory? Excitatory?
– Over stimulation of neurons controlling muscle
tone
Huntington’s
• NT: deficient GABA
• Symptoms: personality changes, loss of
coordination, muscle control, death
Depression
• NT: serotonin
• Anger, sadness, excess sleep, social
isolation, short tempered….over long period
of time
• http://www.williams.edu/imput/introduction
_main.html