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The Exchange of Information - Lecture Slides | PSYC 771, Study notes of Psychology

Wheaton College Psychology

Material Type: Notes; Class: Biol Bases of Behavior; Subject: Psychology; University: Wheaton College; Term: Unknown 1989;

Typology: Study notes

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Communication Within the Nervous

System: The Exchange of Information

zTypes of information exchange:

–axodendritic—from the axon of one neuron to the

dendrite of another

–axosomatic—from axon to cell body

–axoaxonic—from axon to axon

–dendrodendritic—from dendrite to dendrite

The Resting Membrane Potential

zFactors involved in the resting membrane

potential:

–Channel proteins—provide channels for the

passage of substances from one side of th e

membrane to the other

–Receptor proteins—recognize and bind to

neurotransmitters or other chemicals

–Pump proteins—exchange one type of substance

for another

zFactors involved in the resting membrane

potential (cont.):

–Polarity—The cell membrane is polarized and the

resulting difference between the outside and

inside of the membrane is -70mv. This difference

in polarity is called the resting memb rane

potential.

–There is a greater concentration of positive ions

(charged particles) on the outside of membrane

as compared to the inside.

The Resting Membrane Potential

Partial preview of the text

Download The Exchange of Information - Lecture Slides | PSYC 771 and more Study notes Psychology in PDF only on Docsity!

Communication Within the Nervous

System: The Exchange of Information

z Types of information exchange:

axodendritic—from the axon of one neuron to the

dendrite of another

axosomatic—from axon to cell body
axoaxonic—from axon to axon
dendrodendritic—from dendrite to dendrite

The Resting Membrane Potential

z Factors involved in the resting membrane

potential:

Channel proteins—provide channels for the

passage of substances from one side of the

membrane to the other

Receptor proteins—recognize and bind to

neurotransmitters or other chemicals

Pump proteins—exchange one type of substance

for another

z Factors involved in the resting membrane

potential (cont.) :

Polarity—The cell membrane is polarized and the

resulting difference between the outside and

inside of the membrane is -70mv. This difference

in polarity is called the resting membrane

potential.

There is a greater concentration of positive ions

(charged particles) on the outside of membrane

as compared to the inside.

The Resting Membrane Potential

Recording the Resting Membrane

Potential of a Neuron

The Resting Membrane Potential

z Forces affecting the membrane potential

Diffusion
Electrostatic pressure
Sodium-potassium pump

Resting Membrane Potential: Diffusion

z Diffusion—refers to the movement of

molecules from an area of higher

concentration to an area of lower concentration

(difference in concentration produces a

concentration gradient which causes the

diffusion)

There is a higher concentration of sodium ions

(Na+^ ) outside the cell membrane and a higher

concentration of potassium ions (K+)^ and chloride

(Cl - ) inside the cell.

Resting Membrane Potential:

Sodium-Potassium Pump

z Sodium-potassium pump—an active

mechanism which excludes 3 Na +^ ions for

every 2 K+^ ions taken into the cell

z Requires energy supplied by adenosine

triphosphate (ATP), which is converted to

ADP.

Resting Membrane Potential:

Forces Acting While at Rest

The Action Potential

z The action potential is also called the spike

potential or firing of the neuron.

z The action potential only refers to

depolarization of axon, not to dendrites or

cell bodies.

z Excitatory stimulus—A stimulus which

causes depolarization in the axon when the

inside becomes more positively charged due

to the influx of Na+^ ions.

The Action Potential

z Threshold—The level of stimulation required

for the neuron to fire (about -55 mv).

z Voltage-gated ion channels—Channels

sensitive to changes in cell membrane

potential.

z These ion channels open to Na +^ ions when

threshold is reached, followed by the opening

of K+^ channels. The K+^ ions are expelled by

the electrostatic charge from the Na +^ ions

which have entered the cell.

Action Potential:

Repolarization and the Refractory Period

z Absolute refractory period—The time during

which the neuron is insensitive to further

stimulation.

z Relative refractory period—The time

following the absolute refractory period

during which a neuron can generate another

action potential but only by a stronger than

normal stimulus.

z Hyperpolarized—A cell is hyperpolarized

when it’s negative potential becomes larger

than normal (e.g., -80 mv instead of -70 mv).

z Repolarization—The process of recovery of

the resting membrane potential.

Action Potential:

Repolarization and the Refractory Period

The Neural Impulse

z Neural impulse—The propagation of an action potential along an axon.

z The axon depolarizes in a sequential fashion from the axon hillock to the presynaptic terminal.

z A graded depolarization is a depolarization which has not reached threshold.

z The neural impulse occurs only one way because of the absolute refractory period.

z Speed of transmission varies due to thickness of the axon, presence or absence of myelination, and number of synapses.

Propagation

of the Action

Potential

along an

Unmyelinated

Axon

The Neural Impulse:

Saltatory Conduction

z Saltatory Conduction—from the Latin saltare

(“to jump”)

Occurs on myelinated neurons at the nodes of

Ranvier.

Faster than unmyelinated neurons (a neuron of 1.

mm conducts about 1 m/sec whereas a myelinated

neuron of the same size conducts about 100 m/sec).

Requires less energy than unmyelinated neurons

since depolarization only occurs at the nodes of

Ranvier.

Propagation

of the Action

Potential

Along a

Myelinated

Axon

Synaptic Transmission:

Neurotransmitter Release

z Action potentials arriving at the presynaptic terminal

cause calcium ion channels to open and Ca2+^ ions to

enter the cell.

z Calcium entry causes the synaptic vesicles to move to

the release site on the presynaptic membrane where

they release neurotransmitter molecules into the

synaptic cleft.

z Synaptic transmission occurs when neurotransmitter

molecules pass across the synaptic cleft and depolarize

or hyperpolarize the postsynaptic membrane.

z Neurotransmitter molecules are carried across the

synaptic cleft by diffusion.

Overview of Synaptic Transmission

Spatial Summation and Temporal Summation

Synaptic Transmission:

Presynaptic Effects

z Release of neurotransmitters is not

automatic and can be influenced by several

processes:

Presynaptic inhibition
Presynaptic facilitation
Autoreceptors (inhibition)

Synaptic Transmission:

Presynaptic Effects

z Presynaptic inhibition

A decrease in the release of neurotransmitters

from the presynaptic membrane (despite the

occurrence of an action potential) caused by the

action of another neuron.

z Presynaptic facilitation

The enhanced release of neurotransmitters from

the presynaptic membrane caused by the action

of another neuron.

Axoaxonic

Synapse and

Presynaptic

Inhibition

and

Facilitation

Synaptic Transmission:

Presynaptic Effects

z Autoreceptors—

stimulation of

autoreceptors by a

released

neurotransmitter

causes a decrease

in subsequent

neurotransmitter

release

Synaptic Transmission:

Postsynaptic Receptors

z Types of postsynaptic receptors:

Ionotropic—These receptors’ ion channels are

opened quickly by the direct action of a

neurotransmitter.

Metabotropic—These receptors’ ion channels are

opened indirectly by a second messenger.

Second messenger—A chemical that causes

changes inside the cell in response to a

neurotransmitter that leads to ion channel

changes.

Agents of Synaptic Transmission:

Small-Molecule Neurotransmitters

z Amino acids

glutamate
gamma-amino butyric acid (GABA)
aspartate
glycine

z Monoamines

catecholamines z epinephrine (adrenalin) z norepinephrine (noradrenalin) z dopamine
indoleamines z serotonin z melatonin

z Soluble gases

nitric oxide
carbon monoxide

z Acetylcholine

Agents of Synaptic Transmission:

Small-Molecule Neurotransmitters

z endogenous opioids

z substance P

z oxytocin

z antidiuretic hormone (ADH)

z cholecystokinin (CCK)

Agents of Synaptic Transmission:

Large-Molecule Neurotransmitters

z Glutamate is the most common excitatory

neurotransmitter in the CNS. Synapses that use

glutamate are called glutamatergic. Termination of action

is by reuptake.

z Gamma-aminobutric acid (GABA) is the most common

inhibitory transmitter in the brain. It is produced from

glutamate by the enzyme glutamate decarboxylase. Its

synapses are called GABAergic and it is terminated by

reuptake.

z Both these transmitters are implicated in Huntington’s

disease. Extreme anxiety, linked to below normal GABA

levels, may be treated with Valium. Both transmitters

appear to be involved with memory storage and retrieval.

Small-Molecule Neurotransmitters:

Amino Acids

A GABAergic Synapse

z The monoamines are classified into two

subclasses: the catecholamines and

indoleamines

Catecholamines—norepinephrine (NE) and

dopamine (DA)

z NE transmission is called adrenergic. z NE is terminated by reuptake and degradation of NE within the cytoplasm, not in synaptic vesicles, by monoamine oxidase (MAO). z NE is the transmitter in the sympathetic nervous system and is involved in regulating attention, concentration, arousal, sleep and depression.

Small-Molecule Neurotransmitters:

Monoamines

z Indoleamines

Serotonin (5-HT) z Synthesized from tryptophan z Synapses called serotonergic z Terminated by reuptake and MAO breakdown z Involved in regulation of sleep, depression, and mood disorders z Prozac is a drug which is an agonist for 5-HT

The Exchange of Information - Lecture Slides | PSYC 771, Study notes of Psychology

Related documents

Partial preview of the text

Download The Exchange of Information - Lecture Slides | PSYC 771 and more Study notes Psychology in PDF only on Docsity!

Communication Within the Nervous

System: The Exchange of Information

z Types of information exchange:

dendrite of another

The Resting Membrane Potential

z Factors involved in the resting membrane

potential:

passage of substances from one side of the

membrane to the other

neurotransmitters or other chemicals

for another

z Factors involved in the resting membrane

potential (cont.) :

resulting difference between the outside and

inside of the membrane is -70mv. This difference

in polarity is called the resting membrane

potential.

(charged particles) on the outside of membrane

as compared to the inside.

The Resting Membrane Potential

Recording the Resting Membrane

Potential of a Neuron

The Resting Membrane Potential

z Forces affecting the membrane potential

Resting Membrane Potential: Diffusion

z Diffusion—refers to the movement of

molecules from an area of higher

concentration to an area of lower concentration

(difference in concentration produces a

concentration gradient which causes the

diffusion)

(Na+^ ) outside the cell membrane and a higher

concentration of potassium ions (K+)^ and chloride

(Cl - ) inside the cell.

Resting Membrane Potential:

Sodium-Potassium Pump

z Sodium-potassium pump—an active

mechanism which excludes 3 Na +^ ions for

every 2 K+^ ions taken into the cell

z Requires energy supplied by adenosine

triphosphate (ATP), which is converted to

ADP.

Resting Membrane Potential:

Forces Acting While at Rest

The Action Potential

z The action potential is also called the spike

potential or firing of the neuron.

z The action potential only refers to

depolarization of axon, not to dendrites or

cell bodies.

z Excitatory stimulus—A stimulus which

causes depolarization in the axon when the

inside becomes more positively charged due

to the influx of Na+^ ions.

The Action Potential

z Threshold—The level of stimulation required

for the neuron to fire (about -55 mv).

z Voltage-gated ion channels—Channels

sensitive to changes in cell membrane

potential.

z These ion channels open to Na +^ ions when

threshold is reached, followed by the opening

of K+^ channels. The K+^ ions are expelled by

the electrostatic charge from the Na +^ ions

which have entered the cell.

Action Potential:

Repolarization and the Refractory Period

z Absolute refractory period—The time during

which the neuron is insensitive to further

stimulation.

z Relative refractory period—The time

following the absolute refractory period

during which a neuron can generate another

action potential but only by a stronger than

normal stimulus.

z Hyperpolarized—A cell is hyperpolarized