Psychoactive Substances Ch 2

Includes cells of the nervous system and communication within/between a neuron(s)

What are the types of neurons?

Sensory, interneurons, and motor neurons

Sensory neuron

Detect changes in the internal or external environment

Motor neuron

Controls muscular contraction or glandular secretion

Interneuron

Between sensory and motor neurons, located entirely within the CNS

What are the divisions of the nervous system?

Central and peripheral nervous system

Central nervous system (CNS)

Made up of the brain and spinal cord

Peripheral nervous system

Includes the nerves outside the skull/spinal cord and the sensory organs

Soma

• The cell body of a neuron, which contains the nucleus

• Its shape varies considerably in different kinds of neurons

• integrates information

Dendrite

• a branched, treelike structure attached to the soma of a neuron

• receives information from the terminal buttons of other neurons

Synapse

The junction between the terminal buttons of one neuron and the somatic or dendritic membrane of the receiving cell

Axon

• the long, thin, cylindrical structure covered with myelin

• carries the action potential and transmits information from the cell body to the terminal buttons

Action potential

The basic message carried by the axon

How are neurons classified?

Based on axons and dendrites leaving the soma

• multipolar

• bipolar

• unipolar

Multipolar neuron

• 1 axon

• many dendrites attached to the soma

• motor and interneurons neurons

Bipolar neuron

• 1 axon

• 1 dendrite attached to its soma

• transmits smell, sight, taste, and hearing

Unipolar neuron

• 1 axon attached to its soma

  • the axon divides, one branch receiving sensory information and the other sending information into the CNS

  • fastest transmission of information

• transmits somatosensory information

  • sensory neuron

Nerves

Bundles of individual neurons/axons contained within a protective membrane

What are the sites of neurotransmitter release?

Terminal buttons and synaptic connections

Terminal button

• the bud at the end of a branch of an axon

• forms synapses with another neuron and sends information to that second neuron

• calcium channels are embedded here

Neurotransmitter

• A chemical that is released by a terminal button

• has an excitatory or inhibitory effect on another neuron

Cell membrane

• a structure consisting principally of lipid molecules that defines the outer boundaries of the cell

• contains proteins

Cytoplasm

• jelly-like fluid containing organelles

• contains mitochondria

How do mitochondria work within the cytoplasm of a neuron?

• extract energy from nutrients

• synthesize adenosine triphosphate (ATP)

• contain their own genetic material

• replicate independently of the rest of the cell

ATP (adenosine triphosphate)

• a molecule of prime importance to cellular energy metabolism

• its breakdown liberates energy

Nucleus

A structure in the central region a cell, containing the chromosomes

Describe chromosomes within the nucleus of neurons

• consist of long strands of DNA

• contain genes (which code for proteins)

Where are proteins found in the neuron?

• cytoskeleton

• enzymes

• microtubules involved in axoplasmic transport

DNA (deoxyribonucleic acid)

• a long, complex macromolecule consisting of 2 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

Enzyme

A molecule that controls a chemical reaction, combining 2 substances or breaking a substance into 2 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

• includes anterograde and retrograde transport

Anterograde transport

Runs from the soma to the terminals

Retrograde transport

Runs from the terminals to cell body

Where are glia cells located?

central nervous system

What are the types of glia?

• astrocytes

• oligodendrocytes

• microglia

Astrocyte

• controls chemical composition around neurons

• processes area around neurons and blood vessels

• help nourish neurons

• acts as “glue”

• surrounds and isolates synapses

• removes debris via phagocytosis

Phagocytosis

The process by which cells engulf and digest other cells or debris caused by cellular degeneration

How do astrocytes help nourish neurons?

• convert bloodstream glucose into lactate, which is then used by neurons

• stores glycogen

Oligodendrocytes

• produce the myelin sheath IN THE CNS

  • one cell makes up to 50 myelin segments

Myelin sheath

• Surrounds axons and insulates them

• speeds up the transmittance of information

• prevents messages from spreading between adjacent axons

How do oligodendrocytes form myelin sheaths?

1. form processes shaped like canoe paddles

2. each of these paddle-shaped processes then wraps itself many times around a segment of an axon, producing layers of myelin

3. each paddle becomes a segment of an axon’s myelin sheath

Node of Ranvier

A naked portion of a myelinated axon, between adjacent oligodendroglia or Schwann cells

Microglia

• the smallest of glial cells

• phagocytes

• protects the brain from invading organisms (immune system function)

Where are Schwann cells located?

peripheral nervous system

Schwann Cells

• produce myelin IN THE PNS

  • each segment of myelin is one Schwann cell

True or False? The chemical composition of myelin in the PNS is the same as that of the CNS

False

Describe the BBB (Blood-Brain Barrier)

• selectively permeable

• more permeable in some areas (e.g., area postrema)

• capillaries within the brain do not have gaps

How do molecules pass through the BBB?

• active transport carries many molecules into the CNS

  • drugs are inert (non-effective) if they cannot pass through

Area postrema

• part of the brain that controls vomiting

• BBB is much weaker here, permitting neurons in this region to detect the presence of toxic substances in the blood

Describe Ehrlich’s experiment

• discovered the BBB

• if a blue dye is injected into an animal’s bloodstream, all tissues except the brain and spinal cord will be tinted blue

Membrane potential

• the electrical charge across a cell membrane

• the difference in electrical potential inside and outside the cell

Resting potential

• The membrane potential of a neuron when it is not being altered by excitatory or inhibitory postsynaptic potentials

• -60 to -70 mV

What is the charge of the resting potential?

Approximately 70 mV in the giant squid axon

At rest, what molecules have the highest concentration OUTSIDE the cell?

Chloride and sodium

At rest, what molecules have the highest concentration INSIDE the cell?

Potassium and anion proteins

Depolarization

Reduction (toward 0) of the membrane potential of a cell from its normal resting potential

Hyperpolarization

• An increase in membrane potential, making it more negative than the resting potential.

• refractory period at -90 mV

Action potential

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

Threshold of excitation

The value of the membrane potential that must be reached to produce an action potential

Force of diffusion

When there are no forces or barriers to prevent them from doing so, molecules will diffure from regions of high concentration to regions of low concentration

Electrolytes

An aqueous solution of a material that ionizes (namely, a soluble acid, base, or salt)

Ions

A charged molecule (cations vs. anions)

Cations

Positively charged ions

Anions

Negatively charged ions

Electrostatic pressure

The attractive force between atomic particles charged with opposite signs or the repulsive force between atomic particles with the same sign

When at rest, what ion has force of diffusion and electrostatic pressure going in the same direction?

Sodium ions move into the cell

Which is the stronger force; force of diffusion or electrostatic pressure?

Force of diffusion

How is the resting potential of the cell restored?

Sodium potassium pump (321 NOKIA)

Intracellular fluid

The fluid contained within cells

Extracellular fluid

Fluids located outside of cells

Sodium-potassium transporters

A protein found in the membrane of all cells that extrudes sodium ions out of the cell and transports potassium ions into the cell

Ion channels

A specialized protein molecule that form pores through the membrane that permits specific ions to enter or leave cells

TRUE or FALSE? When an action potential is triggered, its size decreases

False; it remains the same as it travels down the axon

All-or-none law

The principle that once an action potential is triggered in an axon, it is propagated, without decreasing, to the end of the fiber

Rate law

• The principle that variations in the intensity of a stimulus are represented by variations in the firing rate of action potentials, NOT the amplitude of the action potential.

• rate of firing is the basic element of information

Where is the only place where a myelinated axons comes into contact with the extracellular fluid?

At the node of Ranvier, where the axon is naked

Why is there no inward flow of Na+ when the sodium channels open in the myelinated areas?

Because there is no extracellular sodium

Saltatory conduction

• conduction of action potentials by myelinated axons

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

What are some advantages to saltatory conduction?

• the neuron expands less energy (ATP) to maintain ion balance

• faster conduction

Synaptic transmission

• the primary means of communication between neurons

• the transmission of messages from one neuron to another through a synapse

  • relies on neurotransmitters

Postsynaptic potential

Alterations in the membrane potential of a postsynaptic neuron, produced by liberation of neurotransmitter at the synapse

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

Dendritic spine

A small bud on the surface of a dendrite, with which a terminal button of another neuron forms a synapse

What strutures make up the synapse?

• presynaptic membrane

• postsynaptic membrane

• synaptic cleft

• synaptic vesicles

• release zone

• postsynaptic density

Presynaptic membrane

• membrane of the terminal button that lies adjacent to the postsynaptic membrane

• neurotransmitter is released here

Postsynaptic membrane

• the cell membrane opposite the terminal button in a synapse

• the membrane of the cell that receives the message

Synaptic cleft

The space between the presynaptic membrane and the postsynaptic membrane

Synaptic vesicles

Contain neurotransmitter

Release zone

The location of neurotransmitter release

Postsynaptic density

Contains receptors and the proteins that hold them in place

Describe how neurotransmitters are released

Several synaptic vesicles located just inside the presynaptic membrane fuse with the menbrane and then break open, spilling their contents into the synaptic cleft

Omega structure

Synaptic vesicles fused with the membrane during neurotransmitter release

Postsynaptic receptor

A receptor molecule in the postsynaptic membrane of a synapse that contains a binding site for a neurotransmitter

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 a neurotransmitter and an ion channel that opens when a molecule of the neurotransmitter attaches to the binding site

  • can only open ONE ion channel

• glutamate, GABA, etc.

What’s another term for ionotropic receptor?

Ion channel

Is an ionotropic receptor or metabotropic receptor fast acting/short lasting?

Ionotropic receptor