Transcript Neurophysiology

Neurophysiology
Electrical Activity
in the Body
Review of basic principles of
electricity
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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
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
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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)
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 smaller 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.
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
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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
• http://www.mind.ilstu.edu/flash/synapse_1.
swf
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
Monoamine
Can be used to manage hypertension
Dopamine
• Released from brain (CNS)
– hypothalamus
• Receptors: heart, kidneys, bld
vessels
• Inhibitory
• sense of feeling good
• Parkinson’s Disease
• amine
Serotonin
• Brain (CNS)
• Regulates endocrine activity
(hormonal controls)
• Leads to sleepiness
– 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: inhibitory
Released in times of pain or stress
Elevated levels cause disease known as
Addison’s disease
• Structure is similar to???
– morphine
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