+ All Categories
Home > Documents > Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving...

Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving...

Date post: 04-Jan-2016
Category:
Upload: kelley-burke
View: 216 times
Download: 0 times
Share this document with a friend
108
Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR
Transcript
Page 1: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 1

FEM 4100

BRAIN &

HUMAN BEHAVIOR

Page 2: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 2

Topic 3

Neurotransmission: Sending & Receiving

Messages

Page 3: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 3

The basic unit of the nervous system A specialized cell that conducts impulses through the

nervous system and contains three major parts—a cell body, dendrites, and an axon

Receives signals from neurons or sensory organs Processes information Sends signals to other neurons, muscles, or organs

The brain contains an average of one hundred billion neurons (50b – 300b)

The Neuron

Page 4: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 4

Afferent neurons relay messages from the sense organs and receptors—eyes, ears, nose, mouth, and skin—to the brain or spinal cord

Efferent neurons convey signals from the central nervous system to the glands and the muscles, enabling the body to move

The Neuron

Page 5: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 5

There are three general types of neurons

Sensory neuron• A neuron that detects changes in the external or

internal environment and sends information aboutthese changes to the central nervous system.

Motor neuron• A neuron located within the central nervous system

that controls the contraction of a muscle or thesecretion of a gland.

Interneuron• A neuron located entirely within the central nervous

system.• Interneurons carry information between neurons in the

brain and between neurons in the spinal cord

Cells of the Nervous System

Page 6: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 6

Three classifications of neurons Multipolar neurons

• A neuron with one axon and many dendrites.

Bipolar neurons• A neuron with one axon and one dendrite attached

to its soma.

Unipolar neurons• A neuron with one axon attached to its soma; the

axon divides, with one branch receiving sensory information and the other sending the information into the central nervous system.

Cells of the Nervous System

Page 7: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 7

Three classifications of neurons

Page 8: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 8

Neuron Basic Structure

Page 9: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 9

Neuron Basic Structure Soma or “cell body”

• The part of the neuron that contains the nucleus and carries out the neuron’s metabolic functions

Dendrite• A branched treelike structure attached to the soma of a

neuron; • Receives signals / information from the terminal button of

other neurons.• Back propagating - when dendrites relay messages from the

cell body to their own branches

Axon• The long, slender, tail-like extension of the neuron that

transmits signals / conveys information from the soma of a neuron to its terminal button, to be received by the dendrites or cell body of the other neurons or to muscles or glands

Cells of the Nervous System

Page 10: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 10

Neuron Basic Structure

Page 11: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 11

Neuron Basic Structure Synapse

• A junction where the terminal button of a sending axon communicates with a receiving neuron across the synaptic cleft

Terminal button• The bud at the end of a branch of an axon; forms

synapses with another neuron; sends information

to that neuron.

Page 12: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 12

Page 13: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 13

Page 14: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 14

Neuron Basic StructureNeurotransmitter

• Chemical messengers that relay neural messages across the synapse

• A chemical that is released into the synaptic cleft from a terminal button (axon) of a sending neuron, crosses a synapse, and binds to appropriate receptor sites on the dendrites or cell body of a receiving neuron, influencing the cell either to fire or not to fire;

• Has an excitatory or inhibitory effect on another neuron. Receptors

• Protein molecules on the dendrite or cell body of a neuron that will interact only with specific neurotransmitters

Action of neurotransmitters• Excitatory

Influencing the neurons to fire• Inhibitory

Influencing neurons not to fire

Page 15: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 15

Internal structure Membrane

• A structure consisting principally of lipid molecules that defines the outer boundaries of a cell and also constitutes many of the cell organelles.

Cytoplasm• The viscous, semi-liquid substance contained in the

interior of a cell.

Mitochondria• An organelle that is responsible for extracting

energy from nutrients.

Cells of the Nervous System

Page 16: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 16

Internal Structure

Page 17: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 17

Internal structure Adenosine triphosphate (ATP)

• A molecule of prime importance to cellular energy metabolism; its breakdown liberates energy.

Nucleus• A structure in the central region of a cell, containing

the nucleolus and chromosomes.

Chromosome• A strand of DNA, with associated proteins, found in

the nucleus; carries genetic information.

Page 18: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 18

Internal structure Deoxyribonucleic acid (DNA)

• A long complex macromolecule consisting of two interconnected helical strands; along with associated proteins, strands of DNA constitute the chromosomes.

Gene• The functional unit of the chromosome, which directs

synthesis of one or more proteins.

Cytoskeleton• Formed of microtubules and other protein fibers,

linked to each other and forming a cohesive mass that gives a cell its shape.

Page 19: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 19

Internal structure Enzyme

• A molecule that controls a chemical reaction,

combining two substances or breaking a substance

into two parts.

Microtubule• A long strand of bundles of protein filaments

arranged around a hollow core; part of the

cytoskeleton and involved in transporting

substances from place to place within the cell.

Axoplasmic transport• An active process by which substances are propelled

along microtubules that run the length of the axon.

Page 20: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 20

Supporting Cells Glial cells

• Also known as neuroglia or “neural glue”.• The supporting cells of the central nervous system. • Fills the gaps between neurons• Supports and feeds neurons• 10 times more glial cells than neurons• Gial cells help to make the brain more efficient by holding neurons

together, removing waste products such as dead neurons, making the myelin coating for the axons, and performing other manufacturing, nourishing, and cleanup tasks

• Myelin producers

Oligodendrocytes (CNS)

Schwann cells (PNS)• Astrocytes – largest glia, many functions• Microglia – involved in response to injury or disease

Cells of the Nervous System

Page 21: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 21

Glial cells Astrocyte or “star cell”

• A glial cell that provides support to neurons of the

central nervous system, provides nutrients and other substances, and regulates the chemical composition of the extracellular fluid.

Phagocytosis• The process by which cells engulf and digest other

cells or debris caused by cellular degeneration.

Oligodendrocyte• A type of glial cell in the central nervous system that

forms myelin sheaths

Cells of the Nervous System

Page 22: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 22

Page 23: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 23

Supporting cells Myelin sheath

• A white, fatty coating wrapped around axons • Acts as an insulator, preventing messages from spreading

between adjacent axons.• Enables impulses to travel much faster and more efficiently• Multiple Sclerosis (MS) involves deterioration of the myelin

sheath

Node of Ranvier• A naked portion of a myelinated axon, between adjacent

oligodendrocytes or Schwann cells. Microglia

• The smallest glial cells; act as phagocytes and protect the brain from invading microorganisms.

Schwann cell• A cell in the peripheral nervous system that is wrapped

around a myelinated axon, providing one segment of its myelin sheath.

Page 24: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 24

Page 25: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 25

Page 26: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 26

Page 27: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 27

TerminologyCNS PNS

Myelin-providing glia

Oligodendrocytes Schwann Cells

Clusters of cell bodies

Nuclei (singular nucleus)

Ganglia(singular ganglion)

Bundles of axons

Tracts Nerves

Page 28: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 28

Features of the blood-brain barrier• Regulates the chemicals that can enter the CNS

from the blood.• Helps the CNS maintain the proper composition of

fluids inside and outside the neurons.

Blood-brain barrier• A semipermeable barrier between the blood and

the brain produced by cells in the walls of the brain’s

capillaries.

Area postrema• A region of the medulla where the blood-brain barrier

is weak; poisons can be detected there and can initiate

vomiting.

The Blood-Brain Barrier (BBB)

Page 29: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 29

Page 30: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 30

The Neural Impulse

Neural impulse –Brief electric surge that carries the neuron’s message

Ions –Charged particles that are moved across the cell membrane

Page 31: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 31

Measuring electrical potentials (Neural Impulses) of axons Axons have two basic electrical potentials

• Resting membrane potential• Action potential

The membrane potential can change• Depolarization• Hyperpolarization• Threshold of excitation

Electrode• A conductive medium that can be used to apply

electrical stimulation and record electrical potentials.

Communication Within a Neuron

Page 32: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 32

Measuring electrical potentials of axons Microelectrode

• A very fine electrode, generally used to record activity

of individual neurons.

Membrane potential• The electrical charge across a cell membrane; the

difference in electrical potential inside and outside the cell.

Oscilloscope• A laboratory instrument that is capable of displaying a

graph of voltage as a function of time on the face of a cathode ray tube.

Page 33: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 33

Page 34: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 34

Measuring electrical potentials of axons Resting membrane potential

• Inside of the neuron is negative with respect to the outside• Resting membrane potential is approximately -70 mV in the

giant squid axon. • Membrane is polarized, it carries a charge• The membrane potential of a neuron at rest, about 270

millivolts• The resting membrane potential of a neuron when it is not

being altered by excitatory or inhibitory postsynaptic potentials;

Depolarization• Reduction (toward zero) of the membrane potential

of a cell from its normal resting potential.

Hyperpolarization• An increase in the membrane potential of a cell,

relative to the normal resting potential.

Page 35: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 35

Ionic Basis of the Resting Potential Ions, charged particles, are unevenly

distributed Factors contributing to uneven distribution

• Homogenizing– Random motion – particles tend to move down their

concentration gradient– Electrostatic pressure – like repels like, opposites

attract• Membrane is selectively permeable• Sodium-potassium pumps

Page 36: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 36

Ions Contributing to Resting Potential Sodium (Na+) Chloride (Cl-) Potassium (K+) Negatively charged proteins (A-)

• synthesized within the neuron• found primarily within the neuron

The Neuron at Rest Ions move in and out through ion-specific channels K+ and Cl- pass readily Little movement of Na+ A- don’t move at all, trapped inside

Page 37: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 37

Equilibrium Potential The potential at which there is no net movement of an

ion – the potential it will move to achieve when allowed to move freely

Na+ = 120mV K+ = -90mV Cl- = -70mV (same as resting potential)

The Neuron at Rest Na+ is driven in by both electrostatic forces and its

concentration gradient K+ is driven in by electrostatic forces and out by its

concentration gradient Cl- is at equilibrium Sodium-potassium pump – active force that exchanges 3

Na+ inside for 2 K+ outside

Page 38: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 38

The Ionic Basis of Action Potentials When summation at the axon hillock results in the

threshold of excitation (-65mV) being reached, voltage-activated Na+ channels open and sodium rushes in.

Remember, all forces were acting to move Na+ into the cell.

Membrane potential moves from -70 to +50mV.

Page 39: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 39

Measuring electrical potentials of axons Action potential

• The brief electrical impulse that provides the basis for conduction of information along an axon.

• The sudden reversal of the resting potential, which initiates the firing of a neuron

Threshold of excitation• The value of the membrane potential that must be

reached to produce an action potential.

Page 40: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 40

Difference between a strong and weak stimulus A weak stimulus may cause few neurons to

fire and at a slow rate A strong stimulus may cause thousands of

neurons to fire at the same time and at hundreds of times per second

Page 41: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 41

Page 42: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 42

Page 43: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 43

The force of diffusion

Diffusion• Movement of molecules from a region of

high concentration to regions of low concentration.

Communication Within a Neuron

Page 44: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 44

The force of electrostatic pressure Electrolyte

• An aqueous solution of a material that ionizes a soluble acid, base, or salt.

Ion• A charged molecule.• Cations are positively charged, and anions are

negatively charged.

Electrostatic pressure• The attractive force between atomic particles charged

with opposite signs or the repulsive force between two atomic particles charged with the same sign.

Communication Within a Neuron

Page 45: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 45

Page 46: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 46

Ions in the extracellular and intracellular fluid Intracellular fluid

• The fluid contained within cells.

Extracellular fluid• Body fluids located outside cells.

Sodium-potassium transporter• A protein found in the membrane of all cells that

extrudes sodium ions.

Communication Within a Neuron

Page 47: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 47

Page 48: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 48

Page 49: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 49

The action potential Ion channel

• A specialized protein molecule that permits

specific ions to enter or leave the cell.

Voltage-dependent ion channel• An ion channel that opens or closes according

to the value of the membrane potential.

Communication Within a Neuron

Page 50: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 50

The Ionic Basis of Action Potentials Rising phase: Na+ moves membrane potential from -70

to +50mV. End of rising phase: After about 1 millisec, Na+

channels close. Change in membrane potential opens voltage-activated

K+ channels. Repolarization: Concentration gradient and change in

charge leads to efflux of K+. Hyperpolaization: Channels close slowly - K+ efflux

leads to membrane potential <-70mV.

Communication Within a Neuron

Page 51: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 51

Conduction of the action potential All-or-none law

• The principle that once an action potential istriggered in an axon, it is propagated withoutdecrement to the end of the fiber.

• When threshold is reached the neuron “fires” and the action potential either occurs or it does not.

• When threshold is reached, voltage-activated ion channels are opened.

Rate law• The principle that variations in the intensity of a

stimulus or other information being transmitted inan axon are represented by variations in the rateat which that axon fires.

Communication Within a Neuron

Page 52: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 52

Page 53: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 53

Page 54: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 54

Conduction of the action potential

Cable properties• The passive conduction of electrical current, in a

decremental fashion, down the length of an axon.

Saltatory conduction• Conduction of action potentials by myelinated axons.

The action potential appears to jump from one node of Ranvier to the next.

Page 55: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 55

Page 56: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 56

Page 57: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 57

Page 58: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 58

The concept of chemical transmission Postsynaptic potentials

• Alterations in the membrane potential of a

postsynaptic neuron, produced by the liberation

of a neurotransmitter at the synapse.

The concept of chemical transmission Binding site

• The location on a receptor protein to which a ligand

binds.

Ligand• A chemical that binds with the binding site of a receptor.

Communication Within a Neuron

Page 59: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 59

Structure of synapses Presynaptic membrane

• The membrane of a terminal button that liesadjacent to the postsynaptic membrane andthrough which the neurotransmitter is released.

Postsynaptic membrane• The membrane located on the dendrite of the

neuron that receives the information. Synaptic cleft

• The space between the presynaptic membraneand the postsynaptic membrane that is about20 nm wide.

Communication Within a Neuron

Page 60: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 60

Structure of synapses Synaptic vesicle

• A small, hollow, beadlike structure found in the

terminal buttons; contains molecules of a

neurotransmitter.

Release zone:• A region of the interior of the presynaptic membrane

of a synapse to which synaptic vesicles attach and

release their neurotransmitter into the synaptic cleft.

Page 61: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 61

Page 62: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 62

Activation of receptors Postsynaptic receptor

• A receptor molecule in the postsynaptic membraneof a synapse that contains a binding site for aneurotransmitter.

Neurotransmitter-dependent ion channel• An ion channel that opens when a molecule of a

neurotransmitter binds with a postsynaptic receptor. Ionotropic receptor

• A receptor that contains a binding site for aneurotransmitter and an ion channel that openswhen a molecule of the neurotransmitter attachesto the binding site.

Communication Within a Neuron

Page 63: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 63

Receptors

Page 64: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 64

Activation of receptors Metabotropic receptor

• A receptor that contains a binding site for a neurotransmitter; activates an enzyme that begins a series of events, opening an ion channel elsewhere in the membrane of the cell when a molecule of the neurotransmitter attaches to the binding site.

G protein• A protein coupled to a metabotropic receptor; conveys

messages to other molecules when a ligand binds with and activates the receptor.

Second messenger• A chemical produced when a G protein activates an

enzyme; carries a signal that results in the opening of the ion channel or causes other events to occur in the cell.

Page 65: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 65

Postsynaptic potentials Excitatory postsynaptic potential (EPSP)

• An excitatory depolarization of the postsynaptic membrane of a synapse caused by the liberation of a neurotransmitter by the terminal button.

Inhibitory postsynaptic potential (IPSP)• An inhibitory hyperpolarization of the postsynaptic

membrane of a synapse caused by the liberation of a neurotransmitter by the terminal button.

Communication Within a Neuron

Page 66: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 66

Generation and Conduction of Postsynaptic Potentials (PSPs) Neurotransmitters bind at postsynaptic receptors These chemical messengers bind and cause

electrical changes• Depolarizations (making the membrane potential less

negative)• Hyperpolarizations (making the membrane potential more

negative) Postsynaptic depolarizations = Excitatory PSPs (EPSPs) Postsynaptic hyperpolarizations = Inhibitory PSPs (IPSPs) EPSPs make it more likely a neuron will fire, IPSPs make it less

likely PSPs are graded potentials – their size varies

Communication Within a Neuron

Page 67: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 67

EPSPs and IPSPs Travel passively from their site of origination Decremental – they get smaller as they travel 1 EPSP typically will not suffice to cause a neuron to

“fire” and release neurotransmitter – summation is needed

Integration of PSPs and Generation of Action Potentials (APs) In order to generate an AP (or “fire”), the

threshold of activation must be reached at the axon hillock

Integration of IPSPs and EPSPs must result in a potential of about -65mV in order to generate an AP

Page 68: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 68

Page 69: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 69

Integration Adding or combining a number of individual

signals into one overall signal Temporal summation – integration of events

happening at different times Spatial - integration of events happening at

different places

Page 70: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 70

Page 71: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 71

How synaptic vesicles can continually pour out neurotransmitters - Termination of postsynaptic potentials The cell body of the neuron is always working to

manufacture more of the neurotransmitter substance Unused neurotransmitters in the synaptic cleft may be

broken down into their component molecules and reclaimed by the axon terminal to be recycled and used again

Reuptake• The process by which neurotransmitter molecules

are taken from the synaptic cleft back into the axon terminal for later use, thus terminating their excitatory or inhibitory effect on the receiving neuron

Communication Within a Neuron

Page 72: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 72

Termination of postsynaptic potentials Enzymatic deactivation

• The destruction of a neurotransmitter by an enzyme

after its release, for example, the destruction of acetylcholine by acetylcholinesterase.

Neural integration• The process by which inhibitory and excitatory

postsynaptic potentials summate and control the

rate of firing of a neuron.

Communication Within a Neuron

Page 73: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 73

Page 74: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 74

Autoreceptor• A receptor molecule located on a neuron

that responds to the neurotransmitter released by that neuron.

• Autoreceptors have a variety of functions:– Regulate internal processes of the cell– Regulate synthesis of the neurotransmitter– Regulate the release of a neurotransmitter– Generally serve to inhibit the activity of a

transmitter

Communication Within a Neuron

Page 75: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 75

Other types of synapses Presynaptic inhibition

• The action of a presynaptic terminal button in an axoaxonic synapse; reduces the amount of neurotransmitter released by the postsynaptic terminal button.

Presynaptic facilitation• The action of a presynaptic terminal button in an

axoaxonic synapse; increases the amount of neurotransmitter released by the postsynaptic terminal button.

Communication Within a Neuron

Page 76: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 76

One neuron fires rapidly? Multiple neurons fire at the same time? Several neurons fire repeatedly? Both temporal and spatial summation occur

simultaneously

What type of summation occurs when:

Page 77: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 77

Page 78: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 78

Page 79: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 79

EPSPs/IPSPsDecrementalFastPassive (energy is not

used)

Action Potentials NondecrementalConducted more

slowly than PSPsPassive and active

PSPs Vs Action Potentials (APs)

Page 80: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 80

Passive movement of AP within myelinated portions occurs instantly

Nodes of Ranvier (unmyelinated) Where ion channels are found Where full AP is seen AP appears to jump from node to node

• Saltatory conduction• http://www.brainviews.com/abFiles/AniSalt.htm

Conduction in Myelinated Axons

Page 81: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 81

Most common Axodendritic – axons on dendrites Axosomatic – axons on cell bodies

Dendrodendritic – capable of transmission in either direction

Axoaxonal – may be involved in presynaptic inhibition

Structure of Synapses

Page 82: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 82

NT molecules Small

• Synthesized in the terminal button and packaged in synaptic vesicles

Large• Assembled in the cell body, packaged in vesicles,

and then transported to the axon terminal

Synthesis, Packaging, and Transport of Neurotransmitter (NT)

Page 83: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 83

Release of NT Molecules

Exocytosis – the process of NT releaseThe arrival of an AP at the terminal opens

voltage-activated Ca++ channels.The entry of Ca++ causes vesicles to fuse with

the terminal membrane and release their contents

http://www.tvdsb.on.ca/westmin/science/sbioac/homeo/synapse.htm

Page 84: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 84

Released NT produces signals in postsynaptic neurons by binding to receptors.

Receptors are specific for a given NT. Ligand – a molecule that binds to another. A NT is a ligand of its receptor.

Receptors There are multiple receptor types for a given NT. Ionotropic receptors – associated with ligand-activated

ion channels. Metabotropic receptors – associated with signal proteins

and G proteins.

Activation of Receptors by NT

Page 85: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 85

NT binds and an associated ion channel opens or closes, causing a PSP.

If Na+ channels are opened, for example, an EPSP occurs.

If K+ channels are opened, for example, an IPSP occurs.

Metabotropic Receptors Effects are slower, longer-lasting, more diffuse, and

more varied. NT (1st messenger) binds > G protein subunit breaks

away > ion channel opened/closed OR a 2nd messenger is synthesized > 2nd messengers may have a wide variety of effects

Ionotropic Receptors

Page 86: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 86

Page 87: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 87

As long as NT is in the synapse, it is active – activity must somehow be turned off.

Reuptake – scoop up and recycle NT.Enzymatic degradation – a NT is broken

down by enzymes.

Reuptake, Enzymatic Degradation, and Recycling

Page 88: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 88

Amino acids – the building blocks of proteins Monoamines – all synthesized from a single amino acid Soluble gases Acetylcholine (ACh) – activity terminated by enzymatic

degradation

Amino Acid Neurotransmitters Usually found at fast-acting directed synapses in the CNS Glutamate – Most prevalent excitatory neurotransmitter in

the CNS GABA –

synthesized from glutamate Most prevalent inhibitory NT in the CNS

Aspartate and glycine

Small-molecule Neurotransmitters

Page 89: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 89

Monoamines

Effects tend to be diffuseCatecholamines – synthesized from tyrosine

Dopamine Norepinephrine Epinephrine

Indolamines – synthesized from tryptophan Serotonin

Page 90: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 90

Soluble-Gases and ACh

Soluble gases – exist only briefly Nitric oxide and carbon monoxide Retrograde transmission – backwards communication

Acetylcholine (Ach) Acetyl group + choline Neuromuscular junction

Page 91: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 91

Neuropeptides

Large moleculesExample – endorphins

“Endogenous opiates” Produce analgesia (pain suppression) Receptors were identified before the natural

ligand was

Page 92: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 92

Pharmacology of Synaptic Transmission

Many drugs act to alter neurotransmitter activity Agonists – increase or facilitate activity Antagonists – decrease or inhibit activity A drug may act to alter neurotransmitter activity

at any point in its “life cycle”

Page 93: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 93

Page 94: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 94

Agonists – 2 examples

Cocaine - catecholamine agonist Blocks reuptake – preventing the activity of the

neurotransmitter from being “turned off”

Benzodiazepines - GABA agonists Binds to the GABA molecule and increases the

binding of GABA

Page 95: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 95

Page 96: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 96

Antagonists – 2 examples

Atropine – ACh antagonist Binds and blocks muscarinic receptors Many of these metabotropic receptors are in the brain High doses disrupt memory

Curare - ACh antagonist Bind and blocks nicotinic receptors, the ionotropic

receptors at the neuromuscular junction Causes paralysis

Page 97: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 97

Page 98: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 98

Demo: How Fast Are Neurons?

Page 99: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 99

Seven Important Neurotransmitters

DopamineDopamine

SerotoninSerotonin

AcetylcholineAcetylcholine

GlutamineGlutamine

NorepinephrineNorepinephrine

GABAGABA

EndorphinsEndorphins

Page 100: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 100

Neurotransmitters

DopamineDopamine

Serotonin

Acetylcholine

Glutamine

Norepinephrine

GABA

Endorphins

Normal Function:

A neurotransmitter that plays a role in learning, attention, and movement

Produces sensations of pleasure and reward; used by CNS neurons

in voluntary movement

Problems with Imbalance:Problems with Imbalance:

Schizophrenia, Parkinson’s Schizophrenia, Parkinson’s diseasedisease

Substances that Affect:Substances that Affect:

Cocaine, amphetamines, Cocaine, amphetamines, Ritalin, alcoholRitalin, alcohol

Page 101: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 101

Neurotransmitters

Dopamine

SerotoninSerotonin

Acetylcholine

Glutamine

Norepinephrine

GABA

Endorphins

Normal Function:

A neurotransmitter that plays an important role in regulating mood, sleep (and dreaming), aggression,

and appetite Also regulates pain, and sexual

behavior

Problems with Imbalance:Problems with Imbalance:

Depression, certain anxiety Depression, certain anxiety disorders, obsessive-compulsive disorders, obsessive-compulsive

disorderdisorder

Substances that Affect:Substances that Affect:

Prozac, hallucinogenics (e.g. LSD)Prozac, hallucinogenics (e.g. LSD)

Neurotransmitters

Page 102: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 102

Neurotransmitters

Dopamine

Serotonin

Acetylcholine

Glutamine

NorepinephrineNorepinephrine

GABA

Endorphins

Normal Function:A neurotransmitter affecting eating

(appetite) and sleep

Also controls heart rate, sexual responsiveness, stress, and

vigilance

Problems with Imbalance:Problems with Imbalance:

High blood pressure, High blood pressure, depressiondepression

Substances that Affect:Substances that Affect:

Tricyclic antidepressants, beta Tricyclic antidepressants, beta blockersblockers

Neurotransmitters

Page 103: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 103

Neurotransmitters

Dopamine

Serotonin

AcetylcholineAcetylcholine

Glutamine

Norepinephrine

GABA

Endorphins

Normal Function:

Primary transmitter used by neurons carrying messages from CNS;

involved in some kinds of learning and memory

Problems with Imbalance:Problems with Imbalance:

Certain muscular disorders, Certain muscular disorders, Alzheimer’s diseaseAlzheimer’s disease

Substances that Affect:Substances that Affect:

Nicotine, botulism toxin, curare, Nicotine, botulism toxin, curare, atropineatropine

Neurotransmitters

Page 104: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 104

Neurotransmitters

Dopamine

Serotonin

Acetylcholine

Glutamine

Norepinephrine

GABAGABA

Endorphins

Normal Function:

Most prevalent inhibitory neurotransmitter in neurons of

CNS

Problems with Imbalance:Problems with Imbalance:

Anxiety, epilepsyAnxiety, epilepsy

Substances that Affect:Substances that Affect:

Barbiturates, tranquilizers (e.g. Barbiturates, tranquilizers (e.g. Valium, Librium), alcoholValium, Librium), alcohol

Neurotransmitters

Page 105: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 105

Neurotransmitters

Dopamine

Serotonin

Acetylcholine

GlutamineGlutamine

Norepinephrine

GABA

Endorphins

Normal Function:

Primary excitatory neurotransmitter in CNS; involved in learning and

memory

Problems with Imbalance:Problems with Imbalance:

Brain damage after strokeBrain damage after stroke

Substances that Affect:Substances that Affect:

PCP (“angel dust”)PCP (“angel dust”)

Neurotransmitters

Page 106: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 106

Neurotransmitters

Dopamine

Serotonin

Acetylcholine

Glutamine

Norepinephrine

GABA

EndorphinsEndorphins

Normal Function:

Pleasurable sensations and control of pain

Problems with Imbalance:Problems with Imbalance:

Lowered levels resulting from Lowered levels resulting from opiate addictionopiate addiction

Substances that Affect:Substances that Affect:

Opiates: opium, heroin, Opiates: opium, heroin, morphine, methadonemorphine, methadone

Neurotransmitters

Page 107: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 107

Endorphins Chemicals produced naturally by the brain that

reduce pain and positively affect mood “Runner’s high” is attributed to the release of

endorphins Candace Pert and her fellow researchers:

• Demonstrated that a localized region of the brain contains neurons with receptors that respond to the opiates

• The brain produces opiate-like substances known as endorphins

Epinephrine A neurotransmitter that affects the metabolism of

glucose and energy stored in muscles to be released during exercise

Page 108: Page 1 FEM 4100 BRAIN & HUMAN BEHAVIOR. Page 2 Topic 3 Neurotransmission: Sending & Receiving Messages.

Page 108

Drugs and the Brain

• Agonist• Antagonist• Selective serotonin-reuptake inhibitor

(SSRI)


Recommended