[PHYSIOPSYC Carson] Chapter 2

amount of neurons

86 billion

- same number of non-neurons

nervous system

- has to be efficient and accurate

- major control over the operation of our body's systems

- our actions are made possible by its integrated activity

types of nervous system

central and peripheral

Sensory neuron

- detects changes in the external or internal environment and sends information about these changes to the central nervous system

nerves

bundles of thousands of individual neurons, all wrapped in protective membrane

nerve fibers

transmit messages through the nerve, from a sense organ to the brain or from the brain to a muscle

peripheral nervous system

- the rest of the body

- communicates via neurons

Central nervous system (CNS)

The brain and the spinal cord

- communicates with the rest of the body via nerves

Motor neuron

- controls the contraction of a muscle or the secretion of a gland

- CNS

Interneuron

A neuron located entirely within the central nervous system

- local; form circuits with nearby neurons and analyze small pieces of information

- Relay: connect circuits of local interneurons in one region of the brain with those in other regions

divisions of PNS

somatic and autonomic

somatic nervous system

- has afferent and efferent neurons

- afferent; sensory conscious

- efferent; motor voluntary

autonomic nervous system

- motor efferent

- somatic afferent

Soma

The cell body of a neuron

- contains the nucleus

Dendrite

- communicate with one another

- A branched, treelike structure attached to the soma of a neuron; - receives information from the terminal buttons of other neurons

- receive neural messages that are transmitted acorss the synapse

Synapse

- synaptic cleft

- A junction between the terminal button of an axon and the membrane of receiving cell

Axon

The long, thin tube

- conveys information from the soma of a neuron to its terminal buttons

- carries AWAY from the cell body to TB

- basic message; action potential

action potential

Brief Electrical and chemical event that starts at the end of the axon near the cell body in axon hillock and travels to the ends of terminal buttons

Always the same size and duration

Each branch receives a full-strength AP

axoplasmic transport

AP occur along the surface of the axon, but AT moves substances along tracks that run inside axon

Protein; kinesin -> walks down microtubule -> energy from ATP

ATP is provided by mitochondria

Dynein: carries substances from the terminal buttons to soma = retrograde axoplasmic transport

Anterograde is faster

myelin sheath

- Axon is covered by myelin sheath

Myelin: fatty substance that provides insulation for the electrical message carried along the exon membrane

Bundles of myelinated axons: white matter -> tracts

Terminal button

The bud at the end of a branch of an axon

- little knobs

- forms synapses with another neuron; sends information to that neuron

- When AP is travelling down the axon, secrete a neurotransmitter

Neurotransmitter

A chemical that is released by a terminal button;

- has an excitatory or inhibitory effect on another neuron

cell/neural Membrane

Defines the boundary of the neuron

Consists of phospholipid bilayer

Embedded in are variety if protein molecules + carbohydrates that have special functions

protein detects substances outside the cell

Nucleus

- enclosed in nuclear membrane

A structure in the central region of a cell, containing the nucleolus and chromosomes

Nucleolus

ribosome synthesis

Ribosome

A cytoplasmic structure, made of protein, that serves as the site of production of proteins translated from mRNA

proteins

enzymes which direct the chemical processes of a cell by controlling chemical reactions

Chromosome

A strand of DNA, with associated proteins, found in the nucleus; carries genetic information

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

- individual recipes for individual proteins -> responsible for initiating the process of protein synthesis in the cell

Messenger ribonucleic acid (mRNA)

- delivers genetic information concerning the synthesis of a protein from a portion of a chromosome to a ribosome

Enzyme

controls a chemical reaction, combining two substances or breaking a substance into two parts

Non-coding RNA (ncRNA)

A form of RNA that does not encode for protein but has functions of its own

Cytoplasm

The viscous, semiliquid substance contained in the interior of the cell

Mitochondrion

An organelle that is responsible for extracting energy from nutrients, source of ATP

Adenosine triphosphate (ATP)

A molecule of prime importance to cellular energy membrane; its breakdown liberates energy

Endoplasmic reticulum (ER)

Parallel layers of membrane found within the cytoplasm of a cell; has a rough and a smooth section, (ribosomal protein synthesis)

- rough; contains ribosomes

- smooth; lipid synthesis and golgi apparataus

Golgi apparatus

has lysosomes -> waste disposal

pack and wrap neurotransmitters in vesicles -> microtubules brings it

Lysosome

An organelle surrounded by a membrane; contains enzymes that break down waste products

Exocytosis

The secretion of a substance by a cell through means of vesicles; the process by which neurotransmitters are secreted

Cytoskeleton

Formed of microtubules and other protein fibers, linked to each other and forming a cohesive mass that gives a cell its shape

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

Anterograde

In a direction along an axon from the cell body toward the terminal buttons

- forward movement

Retrograde

In a direction along an axon from the terminal buttons toward the cell body, dynein

- backward movement

transcription

information from DNA is transcribed into mRNA

translation

Taking it to the ribosomes and use it to create proteins from sequences of amino acids

supporting cells

- work more efficiently

- Neurons must be supplied with nutrients & oxygen

Neuroglia

The supporting cells of the central nervous system

Astrocyte

- star-shaped

- provides physical support for neurons of the central nervous system and clean up debris in brain

- provides nutrients and other substances

- regulates the chemical composition of the extracellular fluid

Phagocytosis

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

Myelin sheath

A sheath that surrounds axons and insulates them, preventing messages from spreading between adjacent axons

- series of segments

Node of Ranvier

bare portion of a myelinated axon between adjacent oligodendroglia or Schwann cells

Microglia

The smallest of glial cells;

act as phagocytes and protect the brain from invading microorganisms

immune system in the brain

inflammatory action

cleans via phagocytosis

Schwann cell

- PNS

- that is wrapped many times around a myelinated axon

- providing one segment of its myelin sheath

- aids in the digestion of dead and dying neurons and guide regrowth of axons

- re-establish connections with muscles and sense organs

Blood-brain barrier

A semipermeable barrier

- small gaps permit free exchange of most substances between the blood and fluid outside the capillaries that surrounds the cells of the body

- function: transmitting messages and protects the brain

Area postrema

A region of the medulla where the blood-brain barrier is weak; poisons can be detected there and can initiate vomiting

Membrane potential

The electrical charge across a cell membrane

- the difference in electrical potential inside and outside the cell

- can be + or -

potential

stored-up source of electrical energy

Resting potential

The membrane potential of a neuron when it is not being altered by excitatory or inhibitory post-synaptic potentials

- approximately -70 mV in the giant squid axon

Depolarization

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

- more likely to send electrical message

Threshold of excitation

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

- trigger the action potential

Hyperpolarization

An increase in the membrane potential of a cell, relative to the normal resting potential

- inside of axon becomes more negative relative to outside

- less likely to send an electrical message

Action potential

burst of rapid depolarization followed by hyperpolarization

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

- where soma meets the axon (axon hillock) --> terminal buttons

voltageactivated

Ca++ channels

- Ca++ ions flow into the axon

- Ca++ ions stimulate the movement of synaptic vesicles to

the presynaptic membrane and stimulate fusion pore

- A fusion pore is opened, which results in the merging of

the vesicular and presynaptic membranes

• The vesicles release their contents into the synapse

- Released transmitter then diffuses across cleft to interact

with postsynaptic membrane receptors

Diffusion

Movement of molecules from regions of high concentration to regions of low concentration

Electrolyte

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

Ion

A charged molecule

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 charged with the same sign

- like charges repel

- opposite charges attract

Intracellular fluid

The fluid contained within cells (organic anions only contained in intracellular fluid; K+ predominantly)

Extracellular fluid

Body fluids located outside of cells (predominantly Na+ and Cl-, resembles seawater)

Sodium-potassium pump/transporters

A protein found in the membrane of all cells that exchanges 3 sodium ions out of the cell for every 2 potassium ions into the cell

Uses energy (ATP)

- transporters effectively keep the intracellular concentration of Na low

- increase K intracellular

Ion channel

A specialized protein molecule that permits specific ions to enter or leave cells

Voltage-dependent ion channel

An ion channel that opens or closes according to the charges/changes of the membrane potential

All-or-none law

- AP either occurs or does not occur

- when triggered, travels down the axon to its end

- remains exact same size

Rate law

The principle that variations in the intensity of a stimulus or other information being transmitted in an axon are represented by variations in the rate at which that axon fires

Saltatory conduction

Conduction of action potentials by myelinated axons; the action potential appears to jump from one node of Ranvier to the next

AP's are propagated down the axon

AP depolarizes each successive patch of membrane

in nonmyelinated axons and speed based on axonal

diameter

In myelinated axons, the AP "jumps" from node to

node: AP depolarizes membrane to threshold at

each node

synaptic transmission

the transmission of messages from one neuron to another across a synapse

Postsynaptic potential

brief depolarizations or hyperpolarizations that increase or decrease the rate of firing of the axon of the postsynaptic neuron

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

- only bind to receptors

synapses

junctions between the terminal buttons at the ends of axonal branches of one neuron and the membrane of another

Dendritic spine

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

Presynaptic membrane

The membrane of a terminal button that lies adjacent to the post-synaptic membrane and

- where the neurotransmitter is released

Post-synaptic 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 post-synaptic membrane

Synaptic vesicle

A small circle structure found in terminal buttons

- contains molecules of a neurotransmitter

transport & trafficking proteins

fill vesicles with the NTM

release of NTM and recycling of vesicles

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

- contains voltage-dependent calcium channels

docking

clusters of protein molecules attach to other protein molecules located in the presynaptic membrane

fusion pore

a hole through both membranes that enables them to fuse together

release-ready vesicles

docked against the inside of the presynaptic membrane, ready to release their contents when an action potential arrives

less than 1% of total number

- kiss and run: release then get filled

recycling pool

10-15% of the total pool of vesicles

- merge and recycle and lose their identity

reserve pool

85-90% of the vesicles

- recycled via bulk endocytosis; entering a cell

Post-synaptic receptor

A receptor molecule in the post-synaptic membrane of a synapse that contains a binding site for a neurotransmitter

- open neurotransmitter-dependent ion channels (ligand-gated ion channels)

Neurotransmitter-dependent ion channel

An ion channel that opens when a molecule of a neurotransmitter binds with a post-synaptic 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

DIRECT

GABA and glutamate

Metabotropic receptor

A receptor that contains a binding site for a neurotransmitter; activates an enzymes that begins a series of events that opens an ion channel elsewhere in the membrane of the cell when a molecule of the neurotransmitter attaches to the binding site

INDIRECT

G protein