Neurophysiology

Electrical Activity in the Body

Review of basic principles of electricity

• 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/templates/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…?

Intracellular fluid

Extracellular 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

• 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/source/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 Periodaka: 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 period1. 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– Alter response to a NT or block release of NT– Act as NTs– Released during stress– Ex: beta endorphin: pain reliever…similar to morphine

Norepinephrineaka: adrenalin

• Released from brain and ANS– Adrenal gland

• 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

• 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

• 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