Brain and Behavior - University of Texas at Arlington - Chapter One

Mind-Brain Problem (Mind-Body Problem)

Why is some brain activity “conscious” while some is not?

Biological Psychology

The study of the psychological, evolutionary, and developmental mechanisms of behavior and experience.

Monism

The idea that the universe consists of only one type of being.

Dualism

The idea that minds are one type of substance and matter is another.

Physiological Explanation

Relates our behavior to brain activity, i.e., how does the brain regulate body activities. For example, the chemical reactions that enable hormones to influence brain activity and the routes by which brain activity controls muscle contractions.

Ontogenetic Explanation

Describes the development of a structure or a behavior via looking at the influence of genes, nutrition, experience, and the interaction among these influences on behavior. For example, if we want to examine why males and females differ on average in some regard, we might examine behavior at various ages and relate it to changes in the nervous system.

Evolutionary Explanation

An explanation of behavior that reconstructs the evolutionary history of a structure or behavior. They call attention to behavioral similarities between related species.

Functional Explanation

Describe why a structure or organ and associated behavior evolved as it did and what function it serves. For example, explaining how a structure or behavior formed by the prevalence of genes which gave an advantage.

Neurons

Cells that make up the nervous system that receive and transmit information between cells.

Glia Cells

Cells that make up the nervous system that play a supportive role, performing many different functions.

Axon

The tail-like protrusion of a neuron that conveys electrical impulses to other neurons, muscles, and glands.

Myelin Sheath

A fatty insulating cover located on some, but not all axons.

Nodes of Ranvier

Interruptions in myelin sheath that don’t cover the axon.

Dendrites

The branch-like portrusions of a neuron that recieve information using synaptic receptors which line the outside of them.

Spines

Parts of a dendrite that branch out, covering more surface area and allowing dendrites to receive more information.

Motor Neuron

Conducts impulses to a muscle

Sensory Neuron

Specialized at one end to be highly sensitive to a particular type of stimulation like touch, light, smell, taste, sound, etc., seen in the peripheral nerves

Interneuron

Located in the central nervous system and acts as a “middle-man” between neurons, allowing efferent neurons, afferent neurons, and other interneurons to communicate with one another.

Axonal Terminal

Also known as a pre-synaptic terminal, releases neurotransmitters to communicate with other cells

Synapse

Connection between two neurons

Axosomatic Synapse

Connection between axon of one neuron and soma of another neuron

Axodendritic Synapse

Connection between axon of one neuron and dendrites of another neuron

Afferant Axons

Refers to bringing information onto a structure like the Central Nervous System, specifically exists in peripheral sensory neurons

Efferent Axons

Refers to carrying information away from a structure

How many glia cells are there compared to neurons?

Glia cells outnumber neurons in the cerebral cortex but neurons outnumber glia in several other brain areas. Overall, the numbers are nearly equal.

Astrocytes

Primarily responsible for homeostasis of the Central Nervous System. The most important part of this role is helping synchronize the activity of the axon by wrapping around the presynaptic terminal and taking up chemicals (like neurotransmitters).

Microglia

Act as part of the immune system (referred to as “brain immune cells”). They remove waste materials and other microorganisms that could prove harmful to the neuron, prune ineffective synapses, and adjust the effectiveness of other neurons. Recently, its been indicated that they provide negative feedback to brake/control negative feedback.

Oligodendrocytes

Only in the Central Nervous System, build the myelin sheath that surrounds and insulates vertebrate axons.

Schwaan Cells

Only in the Peripheral Nervous System, build myelin sheath around one axon in the peripheral nerve.

Radial Glia

An immature glial cell that guides the migration of neurons and the growth of axons and dendrites during embryonic development. After embryonic development finishes, most differentiate into neurons and a smaller amount differentiate into astrocytes or oligodendrocytes.

How does an astrocyte synchronize associated axons?

The astrocyte is in contact with presynaptic neurons and their axons. If the neurons are active at once, the astrocyte absorbs the neurotransmitters and temporarily inhibits the axons. When the inhibition stops, the axons are primed to respond again in synchrony.

Blood-Brain Barrier

Built up in the brain semi-permeable capillaries and keeps most chemicals out of the vertebrate brain, key structure of it is made up of the junctions between the endothelial cells in the walls of these capillaries which serves as a filter for most molecules

BBB Passive Crossing

Only for uncharged molecules (O2 and CO2) fat-solvable molecules (abused drugs, heroine, nicotine). Neurons need a lot of oxygen so oxygen being able to easily pass through is helpful.

BBB active crossing

A protein-mediated process that consumes energy to pump necessary chemicals (charged molecules, like glucose and amino acids). Vertebrate neurons need a constant flow of glucose because brain tissue has a poor ability to store glucose.

What are the downsides of the BBB?

Chemotherapy has difficulty crossing meanwhile many viruses can cross with ease.

Resting Potential

Represents a polarized status in which the inside of the neuron’s membrane is negative with respect to the outside. This status serves as a kind of stand-by that allows the neuron to react quickly to stimulus. This polarized status is possible because of the high concentration of sodium outside the cell and high concentration of sodium inside the cell.

How does the axon maintain this polarized status while at rest?

While at rest, sodium channels are blocked and potassium channels are only partially blocked, allowing the slow flow of ions. Both electrical and concentration gradient make sodium want to move into the cell, while the concentration gradient makes potassium move out and the electrical gradient makes potassium move in. When the Potassium forces are at equilibrium, they create the base negative charge inside the cell.

Sodium-Potassium Pump

Continually pumps 3 sodium ions out of the cell for every two potassium ions pumped into the cell. Activated after action potential ends in order to repolarize axon and establish normal resting potential.

Hyperpolarization

Occurs when the negative charge inside the axon increases (-70 becomes -90)

Depolarization

A sign of excitation occurring when the negative charge inside the axon decreases (moves to 0).

Threshold of Excitement

Minimum level of depolarization needed to trigger action potential. Threshold varies from neuron to neuron (between -45 and -65 mV)

Action Potential

A rapid depolarization of the neuron and a slight reversal of the membrane’s polarized state.

Voltage Dependent Ionic Channels

Ion channels that open and allow the membrane potential to depolarize rapidly, even causing the polarity to reverse. Both sodium and potassium channels are voltage-dependent in the generation of an action potential.

Voltage-Dependent Sodium Channels

Sodium channels open between -45 to -55 mV and close at +30 to +50 mV.

Voltage-Dependent Potassium Channels

Open at +30 mV which leads to an efflux of potassium ions outside of the cell causing the cell to re-polarize. The cell is temporarily hyperpolarized before returning to its normal resting potential because of the potassium channels being open wider than normal.

Axon Hillock

A swelling located where an axon exits the soma, action potentials occur here because cell body and dendrites don’t have voltage-dependent channels.

Anesthetics’ Effect on Sodium Channels

Local anesthetics (like lidocaine and novacain) block sodium channels in sensory neurons and therefore prevent action potentials from occurring

Anesthetics’ Effect on Potassium Channels

General anesthetics (like ether or chloroform) cause potassium gates to open wider, allowing potassium to flow out very quickly (similar effect to temporary hyperpolarization after action potential)

All-or-None Law

The size, velocity, and amplitude of an action potential is independent of the intensity of the stimulus that initiated it, once it is generated. The result is that action potentials are equal in intensity and speed within a given neuron.

Refractory Period

A period immediately after an action potential occurs when resists the production of another action potential. Absolute refractory is when sodium gates are unable to open, and relative refractory is when sodium gates can open but potassium gates are open wider than normal, meaning it would require a stronger than normal stimulus to initiate a new action potential.

Propagation of The Action Potential

Term used to describe the transmission of action potential down the axon

Re-Generation of Action Potential

Generation of the action potential at one spot triggers depolarization along the entire axon, which allows voltage-dependent sodium channels to open which will allow action potential to travel down the axon. The refractory period prevents the action potential from traveling backwards to the axon hillock.

Saltatory Conduction

Used to describe the “jumping” of the action potential from one Node of Ranvier to another. This is possible because of the insulating properties of myelin and because of the absence of sodium channels in the sections of the axon covered by myelin sheaths. The action potential from the axon hillock travels along the insulated axon until it reaches a voltage-dependent sodium channel that can re-generate the action potential.

Multiple Sclerosis

A self-immune disease in which the immune system attacks myelin sheaths until eventually they’re destroyed. Axons that have myelin sheaths don’t have sodium channels between nodes so when they’re demyelinated, the action potential dies out before it can reach the next node. Can cause blindness or paralysis.