Brain and Behavior - Chapter 2

What influences keep the membrane polarized even in spite of the force of diffusion and electrostatic pressure?

- Anions are too large to pass through the membrane and their negative charge repels the chloride ions and the force of diffusion is unable to move those inside - The Sodium-Potassium Pump

Two Ways that Neurons Regulate Their Own Synaptic Activity

- Autoreceptors on the presynaptic terminals sense the amount of transmitter in the cleft; if the amount is excessive, the presynaptic neuron reduces its output - When there are unusual increases or decreases in neurotransmitter release, postsynaptic receptors change their sensitivity or even their numbers to compensate

What determines whether the effect on the postsynaptic neuron is exciting or inhibiting?

- Depends on a combination of which transmitter is released and the type of receptors on the postsynaptic neurons

What are the characteristics of a neuron's membrane?

- Exceptionally thin - Made up of lipid (fat) and protein - The heads of the molecules are water soluble, making them attracted to the fluid around and inside cells - The tails are water insoluble, so they repel the fluid - As the heads orient toward the fluid and the tails orient away from the fluid, the molecules turn their tails toward each other and form a double-layer membrane

The Three Ways that the Release of Transmitters can Occur

- In corelease, the transmitters are packaged in the same vesicles. However, this doesn't mean they're always released equally. - In cotransmission, the transmitters are in separate vesicles. Vesicles containing different transmitters in the same terminal differ in sensitivity to calcium (Ca2+); a low rate of neural impulses will trigger release of only one of the messengers, whereas a higher rate will release both of them - Finally, the neuron may release different transmitters from its various terminals to produce different effects at separate destinations

What effects does the absolute refractory period have on the neuron?

- Limits how fast the neuron can generate new action potentials - The impulse can propagate only down the axon toward the dendrites, not back toward the cell body, making neural transmission unidirectional which privates the neuron from locking up

What is the overall permeability of a neuron's membrane?

- Some molecules (water, oxygen, and most gases) can diffuse through the membrane freely, but many other substances cannot - Other substances are allowed limited passage through protein channels that open and close under specific circumstances - The selective permeability contributes to the most fundamental characteristic of neurons, polarization, which means that there is a difference in electrical charge between the inside and outside of the neuron

Three Benefits of nodes of Ranvier

- The insulating effect of myelin reduces an electrical effect of the membrane called capacitance, which slows the movement of ions down the axon, boosting the graded potential in speed - The breaks in the myelination mean that the signal is regenerated by an action potential at every node of Ranvier - Myelinated neurons use much less energy because there is less work for the sodium-potassium pump to do

In what two ways does the action potential differ from the local potential initiates it?

- The local potential is a graded potential, which means that it varies in magnitude with the strength of the stimulus that produced it - - The action potential is ungraded; it operates according to the all-or-none law - The action potential is nondecremental; it travels down the axon without any decrease in size, propagated anew and at full strength at each successive point along the way - - The action potential thus makes it possible for the neuron to conduct information over long distances - - Cannot carry information about the intensity of the initiating stimulus - - - One way stimulus intensity is represented is in the number of neurons firing

The Value of Inhibition

- The message becomes more complex because input from one source can partially or completely negate input from another. - In addition, inhibition helps prevent runaway excitation; one cause of the uncontrolled neural storms that sweep across the brain during an epileptic seizure is a deficiency in receptors for the inhibitory transmitter GABA

How do glial cells (astrocytes) contribute to the regulation of synaptic activity?

- They surround the synapse and prevent neurotransmitter from spreading to other synapses, but some also remove neurotransmitter from the synaptic cleft and recycle it for the neuron's reuse - By varying the amount of transmitter they remove, glial cells influence postsynaptic excitability - They can even respond to the neurotransmitter level in the synapse by releasing transmitters of their own. T -hese gliotransmitters regulate transmitter release from the presynaptic neuron or directly stimulate the postsynaptic neuron to excite or inhibit it - Thus, rather than simply being neural "glue" as the name implies, glia should be considered active partners in neural transmission.

Steps: A Presynaptic Terminal Releases the Neurotransmitter at the Synapse

- When the action potential arrives at the terminals, it opens channels that allow calcium ions to enter the terminals from the extracellular fluid - The calcium ions cause the vesicles clustered nearest the membrane to fuse with the membrane - The membrane opens there, and the transmitter spills out and diffuses into the cleft in a process called exocytosis - On the postsynaptic neuron, the neurotransmitter docks with specialized protein receptors that match the molecular shape of the transmitter molecules like a key in a lock. - Activation of these receptors opens the ion channels, allowing ions to flow across the membrane.

Santiago Ramon y Cajal

-Used the golgi method to study neuron structure -Decisively showed that neurons were not all interconnected, and had distinct structures

Otto Loewi

-conducted an experiment with frogs hearts to demonstrate a chemical interaction between nerves -This experiment demonstrated that transmission at the synapse is chemical and that neurons release at least two different chemicals with opposite effects

What are the two possible results of opening ion channels on the dendrites and cell body?

1. It can cause the local membrane potential to shift in a positive direction toward zero, partially depolarizing the membrane Or 2. It can shift the potential farther in the negative direction.

What speed do the fastest neurons approach?

270mph

Absolute Refractory Period

A brief period following the peak of the action potential when the sodium ion channels are inactivated and the neuron cannot be fired again

Polarization

A difference in electrical charge between the inside and outside of the neuron

Myelin

A fatty tissue that wraps around an axon to insulate it from the surrounding fluid and from other neurons.

nodes of Ranvier

A gap in the myelin sheath covering an axon

Neural Network

A group of neurons that function together to carry out a process - Where the most complex neural processing occurs - Sometimes involve a relatively small number of neurons in a single area, such as groups of neurons in a part of the brain called the hippocampus

Norepinephrine

A hormone released during stress. Functions as a neurotransmitter in the brain to increase arousal and attentiveness to events in the environment. Diminished norepinephrine transmission is involved in depression

Inhibitory Postsynaptic Potential (IPSP)

A hyperpolarization of the dendrites and cell body, which makes a neuron less likely to fire.

Human Connectome Project

A large-scale cooperative effort to map the circuits in the human brain

Vesicle

A membrane-enclosed container that stores neurotransmitter in the neuron terminal.

How are motor and sensory neurons configured differently?

A motor neuron's axon and dendrites extend in several directions from the cell body, which is why it is called a multipolar neuron, while sensory neurons can be either unipolar or bipolar

Hyperpolarization

A negative change in a neural membrane's voltage, which is inhibitory and makes an action potential less likely to occur.

Bipolar Neuron

A nerve cell that has a single dendrite at one end and a single axon at the other end

How is a neuron stimulated?

A neuron is usually stimulated by inputs that arrive on the neuron's dendrites and/or cell body from another neuron or from a sensory receptor; the effect may excitatory or inhibitory, depending on the liband and the characteristics of the receptors

Motor Neuron

A neuron that carries commands to the muscles and organs

Sensory Neuron

A neuron that carries information from the body and from the outside world into the central nervous system.

Interneurons

A neuron that has a short axon or no axon at all and connects one neuron to another in the same part of the central nervous system. - Multipolar - Make connections over very short distances - In the spinal cord, interneurons bridge sensory neurons and motor neurons to produce a reflex - In the brain, they connect adjacent neurons to carry out the complex processing that the brain is noted for - The most numerous neuron

Glial Cells

A nonneural cell that provides several supporting functions to neurons, including myelination. - Hold neurons together and increase the speed of conduction in neurons

Excitatory Postsynaptic Potential (EPSP)

A partial depolarization of the dendrites and cell body, which makes the neuron more likely to fire.

Partial Depolarization

A positive change in a neural membrane's voltage, which is excitatory and makes an action potential more likely to occur.

Rate Law

A principle that the intensity of a stimulus is represented in an axon by the frequency of action potentials.

Metabotrophic Receptor

A receptor on a neuron membrane that opens ion channels slowly via a second messenger and produces long-lasting effects.

Autoreceptor

A receptor on a neuron terminal that senses the amount of transmitter in the synaptic cleft and reduces the presynaptic neuron's output when thHe level is excessive.

Ionotropic Receptor

A receptor that is part of the ion channel and opens the channel immediately to produce quick reactions required for muscle activity and sensory processing.

Neurons

A specialized cell that conveys sensory information into the brain, carries out the operations involved in thought and feeling and action, or transmits commands out into the body to control muscles and organs A single neural cell, in contrast to a nerve.

Epinephrine

A stress hormone related to norepinephrine; plays a minor role ass a neurotransmitter in the brain

Axon Terminal

A swelling on the branches at the end of a neuron that contains neurotransmitters; also called an end bulb.

Postsynaptic

A term referring to a neuron that receives transmission from another neuron

Presynaptic

A term referring to a neuron that transmits to another neuron.

Oligodendrocyte

A type of glial cell that forms myelin in the central nervous system

Schwann Cell

A type of glial cell that forms the myelin covering on neurons outside the brain and spinal cord.

How many neurons are in the human brain?

About 86 billion

Action Potential

An all-or-none electrical signal of a neuronal membrane that contains an abrupt voltage depolarization and return to resting potential; allows the neuron to communicate over long distances.

What does an excitatory signal do to a neuron?

An excitatory signal causes a slight partial depolarization, which means that the polarity in a small area of the membrane is shifted toward zero - Disturbs the ion balance in the adjacent membrane - Dies out over distance - The partial depolarization is often called the local potential - If the local potential exceeds the threshold for activating those channels, typically about 10 mV more positive than the resting potential, it will initiate an action potential

Axon

An extension from a neuron's cell body that carries information to other locations.

What happens when myelin is lost?

As myelin is lost, the capacitance rises, reducing the distance that graded potentials can travel before dying out

What happens at axoaxonic synapses?

At axoaxonic synapses, a third neuron releases transmitter onto the terminals of the presynaptic neuron

What happens at each node of Ranvier?

At each node of Ranvier, whether the membrane is exposed and there are plenty of sodium channels, the graded potential triggers an action potentia

Ions

Atoms that have lost or gained one or more electrons

Physical Description of Sensory Neuron (Bipolar)

Axon and dendritic processes are on opposite sides of cell body

Physical Description of Motor Neuron

Axon, dendrites extend in several directions from cell body

Function of Sensory Neuron

Carries information from body and world to brain and spinal cord

How are chemically gated ion channels opened?

Chemically gated channels can be opened by ligands (neurotransmitters or hormones)

What increases conduction speed?

Conduction speed increases not in direct proportion to axon sixe, but closer to the square of the diameter - Also myelination

Function of Interneuron

Conducts information between neurons in same

Function of Motor Neuron

Conducts messages from brain and spinal cord to muscles and organs

Function of Dopamine

Contributes to movement control and promotes reinforcing effects of food, sex, and abused drugs. Dysregulation is involved in schizophrenia and Parkinson's disease

Presynaptic Inhibition

Decreased release of neurotransmitter from a neuron's terminal as the result of another neuron's release of neurotransmitter onto the terminal (an axoaxonic synapse).

Radial Glia cells

During fetal development, radial glia form scaffolds that guide new neurons to their destinations.

How are electrically gated ion channels opened?

Electrically gated channels are opened by a change in the electrical potential of the membrane

List the Neuropeptides

Endorphines, Substance P, Neuropeptide Y

Dendrites

Extensions that branch out from the cell body to receive information from other neurons.

List the Amino Acids

GABA, glutamate, glycine

Physical Description of Interneuron

Has short or no axon; communicates locally (with nearby neurons)

How many neurons does the higher brain, cerebellum and spinal cord have?

Higher brain - 17 billion neurons Cerebellum - 69 billion neurons Spinal Cord - 1 billion neurons

Presynaptic Excitation

Increased release of neurotransmitter from a neuron's terminal as the result of another neuron's release of neurotransmitter onto the terminal (an axoaxonic synapse).

Glycine

Inhibitory transmitter in the spinal cord and lower brain. The poison strychnine causes convulsions and death by affecting glycine activity.

Neuropeptide Y

Initates eating and produces metabolic shifts

Function of Serotonin

Involved in mood, sleep, and arousal, aggression, depression, obsessive-compulsive disorder, and alcoholism

Where does the electrical charge in the neurons?

Ions

What ions are mostly in the fluid inside of the neuron?

K+ and A- (organic anions)

Sodium-Potassium Pump

Large protein molecules that move sodium ions through the neuron membrane to the outside and potassium ions back inside, helping maintain the resting potential. - Moves three sodium ions out for every two potassium ions it moves inside, which helps keep the inside of the membrane more negative than the outside - The pump's operation is a metabolic process, which means that it uses energy - Accounts for an estimated 40% of the neuron's energy expenditure

How do larger diameter axons impact the conduction speed of electrical potentials?

Larger diameter axons that provide less resistance to the flow of electrical potentials speeds up conduction speed

What are the two categories of cells that carry messages back and forth in the brain and throughout the rest of the body?

Motor and Sensory Neurons

What are motor and sensory neurons specialized for?

Motor and sensory neurons are specialized for transmission over long distances

Form and Soma Location of Interneuron

Multipolar; central nervous system

Form and Soma Location of Motor Neuron

Multipolar; central nervous system

Muscarinic receptors

Muscarinic receptors are more frequent in the brain, where they have an excitatory effect at some locations and an inhibitory one at others.

What ions are mostly in the fluid outside of the neuron?

Na+ and Cl- ions

What is the charge of Chloride ions?

Negative (Cl-)

Endorphins

Neuromodulators that reduce pain and enhance reinforcement

What are neurons responsible for?

Neurons are responsible for all the things we do - our movements, thoughts, memories, and emotions

Astrocytes

Neurons form seven times as many connections in the presence of the type of glia called astrocytes, and they start to lose their synapses if astrocytes are removed from the culture dish Astrocytes also appear to play a key role in learning

Nictonic receptors

Nicotinic receptors are excitatory; they are found in muscles and, in lesser numbers, in the brain.

List the Gases

Nitric Oxide

What physically happens during a action potential?

Nothing physically moves down the amazon, but a series of actions occur, like a row of falling dominoes

What two types of glial cells produce myelin?

Oligodendrocytes (brain and spinal cord) Schwann cells (the rest of the nervous system)

Nitric Oxide

One of two known gaseous transmitters, along with carbon monoxide. Can serve as a retrograde transmitter, influencing the presynaptic neuron's release of neurotransmitter. Viagra enhances male erections by increasing nitric oxide's ability to relax blood vessels and produce penile engorgement.

What parts of the neuron does the myelin cover?

Only the axon

What are ion channels?

Pores in the membrane formed by proteins and they gate the flow of ions

What is the charge of Potassium ions?

Positive (K+)

What is the charge of Sodium ions?

Positive (Na+)

Microglia cells

Provide energy to neurons and respond to injury and disease by removing cellular debris.

Steps of Action Potential

Resting Potential: Sodium channels and potassium channels are closed and the membrane is at resting potential. Arrival of a local potential partially depolarizes the membrane but does not cause the channels to open unless it reaches the threshold Depolarization/Local Potential/Action Potential: As the local potential reaches the neuron's threshold, the sodium channels' activation gates open. Sodium ions rush in, producing an action potential. The membrane in that area depolarizes and overshoots to positive. Repolarization: Sodium channels' inactivation gates close. Potassium channels' activation gates open; potassium ions move out, depolarizing the membrane. Polarity overshoots beyond resting potential. Hyperpolarization: Potassium channels close. The "excess" displaced ions drift away and the potential returns to resting level. (The sodium channel gates will return to their original state later.)

Physical Description of Sensory Neuron (Unipolar)

Single short stalk from cell body divides into two branches

What is the relationship between spatial summation and temporal summation?

Spatial summation and temporal summation occur differently, bu they have the same result

What happens during the summation of EPSPs?

Summation combines EPSPs so that an action potential is more likely to occur

What happens during the summation of IPSPs?

Summation of IPSPs drives the membrane's interior even more negative and makes it more difficult for incoming EPSPs to trigger an action potential

For the few neurons that communicate electrically by passing ions through channels that connect one neuron to the next, what is their main function?

Synchronizing activity in nearby neurons

Resting Potential

The difference in electric charge between the inside and outside of a neuron's cell membrane at rest

Voltage

The difference in electrical charge between two points

Saltatory Conduction

The flow of electricity down the axon in which action potentials jump from one node of Ranvier to the next.

Electrostatic Pressure

The force by which like-charged ions are repelled by each other and opposite-charged ions are attracted to each other.

What are the charges inside of the neuron versus outside of it?

The inside of the neuron has more negative ions than positive ions, whereas the ions on the outside are mostly positive, and this makes the resting potential negative

Cell Body

The largest part of a neuron, which contains the cell's nucleus, cytoplasm, and structures that produce proteins, convert nutrients into energy, and eliminate waste matters; also called the soma - Largest part of the neuron - The largest of these organelles is the nucleus, which contains the cell's chromosomes. - Other organelles are responsible for converting nutrients into fuel for the cell, constructing proteins and lipids, and removing waste materials

What is the purpose of a neuron's membrane?

The membrane not only holds a cell together, but also controls the environment within and around the cell

What is the most critical factor in the neuron's ability to communicate?

The membrane that encloses the cell

The two types of receptors that detect acetylcholine are __________ and __________ receptors.

The nicotinic receptor, so called because it is also activated by nicotine, and the muscarinic receptor, named for the mushroom derivative that can stimulate it.

Can the output of a single neuron cause a postsynaptic neuron to fire?

The output of a single neuron is not enough by itself to cause a postsynaptic neuron to fire or to prevent it from firing; a typical neuron receives input from approximately 1,000 other neurons because each neuron has numerous terminals

Relative Refractory Period

The period during which a neuron can be fired again following an action potential but only by an above-threshold stimulus - Happens right after the absolute refractory period where the potassium channels remain open for a few milliseconds, making the polarity slightly more negative than the resting potential

Gamma-aminobutyric acid (GABA)

The predominant inhibitory neurotransmitter. Its receptors respond to alcohol and the class of tranquilizers called benzodiazepines. Deficiency in GABA or receptors is one cause of epilepsy.

Force of Diffusion

The pressure exerted by ions from an area of greater concentration to an area where they are less concentrated.

Glutamate

The principal excitatory neurotransmitter in the brain and spinal cord. Vitality involved in learning Glutamate dysfunction is implicated in schizophrenia

Reuptake

The process by which a neurotransmitter is taken back into the presynaptic terminals by transporters.

Temporal Summation

The process of combining potentials that arrive a short time apart on a neuron's dendrites and cell body.

Spatial Summation

The process of combining potentials that occur simultaneously at different locations on the dendrites and cell body.

Many drugs capitalize on what mechanism?

The reuptake of neurotransmitters

Unipolar Neuron

The single short stalk from the cell body divides into two branches, with dendrites on one side and the amazon and terminals on the other

Synaptic Cleft

The small gap between a presynaptic neuron and a postsynaptic neuron.

Synapse

The structure in which a neuron passes electrical or chemical signals to another neuron, muscle, or organ.

Dale's principle

The theory that a neuron is able to release only one neurotransmitter - Old theory

What happens when both excitatory and inhibitory impulses arrive on a neuron?

They will summate algebraically - The combined effect will equal the difference between the sum of the partial depolarizations and the sum of the hyperpolarizations

What is the voltage of a neuron at resting potential?

This voltage is negative and varies anywhere from 40 to -80 millivolts (mV) in different neurons but is typically around -70mV

Function of Acetylcholine

Transmitter at muscles; in brain, involved in learning, etc.

Substance P

Transmitter in neurons sensitive to pain

Form and Soma Location of Sensory Neuron

Unipolar; peripheral nervous system, cranial nerves Bipolar; peripheral nervous system

What are the benefits of using potentials from many neurons to fire?

Using potentials from many neurons ensures that a neuron will not be fired by the spontaneous activity of a single presynaptic neuron, and it allows the neuron to combine multiple inputs into a more complex message

What are the types of glial cells?

astrocytes, oligodendrocytes, microglia, schwann cells, radial cells

The majority of synapses are __________

chemical

Camillo Golgi

developed the Golgi stain which helps anatomists see individual neurons by randomly staining some entire cells without staining others

List the Monoamines

dopamine, norepinephrine, epinephrine, serotonin

Where are chromosomes found?

inside the nucleus

Conduction under myelinated areas is by ___________________

local graded potential