Biology Chapter 5 and 43

Describe what is happening

- The pump moves three Na+ outside for every two K+ inside, which creates a small imbalance in cations outside the cell - The higher concentration of K+ inside the cell leads to diffusion of K+ through K+ leakage channels - positive charge builds up outside the membrane and negative charge inside the membrane - This electrical potential then is an attractive force pulling K+ ions back inside the cell - the balance between the diffusional force and the electrical force produces an equilibrium potential

Structure of a neuron

- cell body is an enlarged region containing the nucleus - Extending from the cell body are one or more cytoplasmic extensions called dendrites that receive information and carry it to the cell body - Some neurons have extensions from the dendrites called dendritic spines that increase the surface area available to receive stimuli - axon extends out from a neuron that conducts impulses away from the cell body.

Why is active transport important?

- enables a cell to take up additional molecules of a substance that is already present in its cytoplasm in concentrations higher than in the extracellular fluid - active transport also enables a cell to move substances out of its cytoplasm and into the extracellular fluid, despite higher external concentrations

What are neuroglia like? What functions do they serve?

- one-tenth as big - 10 times more numerous than neurons - serve a variety of functions, including supplying the neurons with nutrients, removing wastes from neurons, guiding axon migration, and providing immune functions

Resting membrane potential is ____ mV.

-70

Nervous system organization & Resting potential Learning Outcomes

1. As review, describe the structure and function of ion channels, pumps, and membrane potential from last semester. 2. Distinguish between the subdivisions of the nervous system, and the different types of neurons. 3. Draw and label a figure depicting the structure of a "typical" neuron and what is occurring in the specific parts. 4. Describe the various functions of neuroglial cells. 5. Define membrane, resting, and graded potentials, and describe how they are each established, including the relative concentrations of specific ions inside and outside the cell. 6. Draw a picture of a membrane showing how resting and graded potentials are created and maintained.

uniporters

A carrier protein in a cell's membrane that transports only a single type of molecule or ion.

antiporters

A carrier protein in a cell's membrane that transports two molecules in opposite directions across the membrane.

Symporters

A carrier protein in a cell's membrane that transports two molecules or ions in the same direction across the membrane.

myelin sheath

A fatty layer surrounding the long axons of motor neurons in the peripheral nervous system of vertebrates.

aquaporins

A membrane channel that allows water to cross the membrane more easily than by diffusion through the membrane.

Carrier proteins

A membrane protein that binds to a specific molecule that cannot cross the membrane and allows passage through the membrane.

solute

A molecule dissolved in some solution; as a general rule, solutes dissolve only in solutions of similar polarity; for example, glucose (polar) dissolves in (forms hydrogen bonds with) water (also polar), but not in vegetable oil (nonpolar).

isotonic

A solution having the same concentration of solutes as the cell. A cell in an isotonic solution takes in and loses the same amount of water.

hypertonic

A solution with a higher concentration of solutes than the cell. A cell in a hypertonic solution tends to lose water by osmosis.

hypotonic

A solution with a lower concentration of solutes than the cell. A cell in a hypotonic solution tends to take in water by osmosis.

Action potentials

A transient, all-or-none reversal of the electric potential across a membrane; in neurons, an action potential initiates transmission of a nerve impulse.

Channel proteins

A transmembrane protein with a hydrophilic interior that provides an aqueous channel allowing diffusion of species that cannot cross the membrane. Usually allows passage of specific ions such as K+, Na+, or Ca2+ across the membrane.

hyperpolarization

Above-normal negativity of a cell membrane during its resting potential. makes the membrane potential more negative

selectively permeable

Condition in which a membrane is permeable to some substances but not to others.

Why is the inside of the cell is more negatively charged in relation to the outside?

Contributors to membrane potential 1. the sodium potassium pumps brings 2 K+ in for every 3 Na+ it pumps out which establishes a concentration difference that results in high k+ and low Na+ concentrations inside the cells and high Na+ and low K+ concentrations outside the cell 2. More ions channels in cell membrane for K+ than Na+ which makes membrane more permeable to K+ 3. There is a differential distribution of other ions and molecules across the membrane, especially negatively charged proteins, which are at a much higher concentration inside the cell than outside.

Which molecules act as ligands? What do they do?

Hormones and neurotransmitters act as ligands, inducing opening of ligand-gated channels, and causing changes in plasma membrane permeability that lead to changes in membrane voltage

What do ligand-gated channels lead to?

Ligand-gated channels lead to graded potentials that determine whether an axon will fire

Examples of facilitated diffusion in RBCs

One RBC carrier protein transports a different molecule in each direction: chloride ion (Cl−) in one direction and bicarbonate ion (HCO3−) in the opposite direction-- this carrier is important in the uptake and release of carbon dioxide. The glucose transporter - Red blood cells keep their internal concentration of glucose low by immediately adding a phosphate group to any entering glucose molecule, converting it to a highly charged glucose phosphate that can no longer bind to the glucose transporter, and therefore cannot pass back across the membrane - maintains a steep concentration gradient for unphosphorylated glucose, favoring its entry into the cell

Schwann cells produce myelin in the ____, and oligodendrocytes produce myelin in the ____.

PNS CNS

Two of the most important kinds of neuroglia in vertebrates are ______ ______ and __________, which produce _____ _______ that surround the axons of many neurons.

Schwann cells oligodendrocytes myelin sheaths

Nodes of Ranvier

Small gaps that interrupt the myelin sheath at intervals of 1 to 2 µm

Steps of sodium potassium pump

Step 1. Three Na+ bind to the cytoplasmic side of the protein, causing the protein to change its conformation. Step 2. In its new conformation, the protein binds a molecule of ATP and cleaves it into adenosine diphosphate (ADP) and phosphate (or Pi for inorganic phosphate). ADP is released, but the phosphate group is covalently linked to the protein. The protein is now phosphorylated. Step 3. The phosphorylation of the protein induces a second conformational change in the protein. This change translocates the three Na+ across the membrane, so they now face the exterior. In this new conformation, the protein has a low affinity for Na+, and the three bound Na+ break away from the protein and diffuse into the extracellular fluid. Step 4. The new conformation has a high affinity for K+, two of which bind to the extracellular side of the protein as soon as it is free of the Na+. Step 5. The binding of the K+ causes another conformational change in the protein, this time resulting in the hydrolysis of the bound phosphate group. Step 6. Freed of the phosphate group, the protein reverts to its original shape, exposing the two K+ to the cytoplasm. This conformation has a low affinity for K+, so the two bound K+ dissociate from the protein and diffuse into the interior of the cell. The original conformation has a high affinity for Na+. When these ions bind, they initiate another cycle.

osmosis

The diffusion of water across a selectively permeable membrane (a membrane that permits the free passage of water but prevents or retards the passage of a solute); in the absence of differences in pressure or volume, the net movement of water is from the side containing a lower concentration of solute to the side containing a higher concentration.

autonomic nervous system

The involuntary neurons and ganglia of the peripheral nervous system of vertebrates; regulates the heart, glands, visceral organs, and smooth muscle. think autonomic= any other muscle

solvent

The medium in which one or more solutes is dissolved.

depolarization

The movement of ions across a plasma membrane that locally wipes out an electrical potential difference makes the membrane potential less negative (more positive)

osmotic pressure

The potential pressure developed by a solution separated from pure water by a differentially permeable membrane. The higher the solute concentration, the greater the osmotic potential of the solution; also called osmotic potential.

osmotic concentration

The property of a solution that takes into account all dissolved solutes in the solution; if two solutions with different osmotic concentrations are separated by a water-permeable membrane, water will move from the solution with lower osmotic concentration to the solution with higher osmotic concentration.

active transport

The pumping of ions or other molecules across a cellular membrane from a region of lower concentration to one of higher concentration (i.e., against a concentration gradient); this transport process requires energy.

Schwann cells

The supporting cells associated with projecting axons, along with all the other nerve cells that make up the peripheral nervous system.

sodium-potassium pump

Transmembrane channels engaged in the active (ATP-driven) transport of Na+, exchanging them for K+, where both ions are being moved against their respective concentration gradients; maintains the resting membrane potential of neurons and other cells.

What is a concentration gradient?

a difference between the concentration on the inside of the membrane and that on the outside

Nernst equation

a mathematical relationship used to calculate an ionic equilibrium potential

Sensory neurons

also called afferent neurons carry impulses from sensory receptors to the central nervous system

Interneurons

also called association neurons A nerve cell found only in the middle of the spinal cord that acts as a functional link between sensory neurons and motor neurons. located in the brain and spinal cord where they help provide more complex reflexes, and higher associative functions, including learning and memory

Motor neurons

also called efferent neurons carry impulses from the CNS to effectors

The mixture of these substances and water is called an _______ _______.

aqueous solution

How does the relationship between concentration and rate of transport differ between simple diffusion and carrier protein transport?

as the concentration increases, transport by simple diffusion shows a linear increase in the rate of transport but when a carrier protein is involved, a concentration increase means that more of the carriers are bound to the transported molecule and at high enough concentrations all the carriers will be occupied and the rate of transport will be constant this means that carriers exhibit saturation

What is the CNS composed of?

brain and spinal cord

However, a plasma membrane by itself cannot withstand large internal pressures, and an isolated cell under such conditions would...

burst

Can ions only go in one direction ?

can diffuse through the channel in either direction, depending on their relative concentration across the membrane

Ligand gates channels

channels that respond to a chemical signal

Permeability changes are measurable as ____________ or ___________ of the membrane potential.

depolarizations hyperpolarizations

What happens to these potentials as they spread from their point of origin?

diminish in amplitude as they spread from their point of origin

How can some ions and molecules pass through the membrane fairly easily?

due to a concentration gradient

What happens when a neuron is stimulated?

electrical changes in the plasma membrane spread or propagate from one part of the cell to another

The balance between the diffusional force and the electrical force produces an ______ ______.

equilibrium potential

T or F: axons are short

false, they can be quite long

sympathetic nervous system

fight or flight

In most neurons, _____ ____ _____ in dendrites respond to the binding of signaling molecules.

gated ion channels

These small changes in membrane potential result in ______ _______. Why?

graded potentials because their size depends on either the strength of the stimulus or the amount of ligand available to bind with their receptors

What are the two types of changes observed in neurons?

graded potentials and action potential

What do motor and association neurons possess lots of?

highly branched dendrites, enabling those cells to receive information from many different sources simultaneously

What do ions use for transport?

ion channels which have a hydrated interior that spans the membrane

The cytoplasm of a cell contains...

ions and molecules, such as sugars and amino acids, dissolved in water

What parts of the body act as effectors?

muscles and glands

Axons that have myelin sheaths are said to be _______, and those that don't are ________.

myelinated unmyelinated

In the PNS, myelinated axons are bundled together, much like wires in a cable, to form ______.

nerves

Neurons are supported both structurally and functionally by supporting cells, which are collectively called _______.

neuroglia

The nervous system consists of ______ and ______ ____.

neurons supporting cells

Can ions move between the cytoplasm of a cell and the extracellular fluid easily?

no, because their charge, ions interact well with polar molecules such as water, but are repelled by nonpolar molecules like the interior of the plasma membranes so they need membrane transport proteins to pass

It is important for animal cells, which only have plasma membranes, to maintain _______ _______. In contrast, the cells of prokaryotes, fungi, plants, and many protists are surrounded by strong ______ _____, which can withstand high internal pressures without bursting.

osmotic balance cell walls

The concentration of all solutes in a solution determines the ________ _______.

osmotic concentration

Together, sensory and motor neurons constitute the _______ ______ _______.

peripheral nervous system

voltage-gated channels

respond to changes in membrane potential

parasympathetic nervous system

rest and response

These channels and carriers are usually selective for one type of molecule, and thus the cell membrane is said to be ________ ________.

selectively permeable

What are the three types of neurons?

sensory neurons motor neurons interneurons

How are cotransport and countertransport similar and different?

similar: the potential energy in the concentration gradient of one molecule is used to transport another molecule against its concentration gradient different: they differ only in the direction that the second molecule moves relative to the first - same direction-- cotransport - different direction-- countertransport

Each neuron has a _____ axon leaving its cell body, although an axon may also ______ to stimulate a number of cells.

single branch

Graded potenitals

small continuous changes to membrane potential

Some channel proteins can be opened or closed in response to a ________. These channels are called ______ _______, and depending on the nature of the channel, the stimulus can be either ______ or _______.

stimulus gated channels chemical electrical

What do neurons experience?

sudden temporary disruptions to the resting membrane potential that occur in response to stimuli

Depolarizing and hyperpolarizing potentials can add together to either amplify or reduce their effects which is called _______.

summation

What is the autonomic nervous system further broken down into?

sympathetic and parasympathetic divisions

What does neuronal function depends on?

the ability to create an electric potential across the plasma membrane and then alter this potential to propagate signals

The resting potential arises primarily due to what two factors?

the action of the sodium potassium pump and the greater permeability of the membrane to K+

If the membrane is strong enough what happens?

the cell reaches an equilibrium, at which the osmotic pressure, which tends to drive water into the cell, is exactly counterbalanced by the hydrostatic pressure, which tends to drive water back out of the cell

Net movement driven by diffusion will continue until...

the concentration is the same in all regions

What is facilitated diffusion?

the diffusion of molecules or ions through carrier proteins or ion channels requires a concentration gradient, but not any input of energy

Coupled transport

the energy released as one molecule moves down its concentration gradient is captured and used to move a different molecule against its gradient ex: The active glucose transporter uses the Na+ gradient produced by the Na+/K+ pump as a source of energy to power the movement of glucose into the cell. In this system, both glucose and Na+ bind to the transport protein, which allows Na+ to pass into the cell down its concentration gradient, capturing the energy and using it to move glucose into the cell.

What is the major barrier to crossing a biological membrane?

the hydrophobic interior that repels polar molecules but not nonpolar molecules the plasma membrane has limited permeability to small polar molecules and very limited permeability to large polar molecules and ions

Countertransport

the inward movement of substance like Na+ is coupled with the outward movement of another substance, such as Ca2+ or H+ in countertransport, the cell uses the energy released as Na+ moves down its concentration gradient into the cell to eject a substance against its concentration gradient.

What is passive transport?

the movement of substances across a cell's membrane without the expenditure of energy

diffusion

the net movement of dissolved molecules or other particles from a region where they are more concentrated to a region where they are less concentrated

somatic nervous system

the neurons of the peripheral nervous system that control skeletal muscle think somatic = skeletal

In every cycle, _____ Na+ leave the cell and ___ K+ enter.

three two

If not through a concentration gradient, how do other substances move?

through specific channels formed by proteins in the membrane

T or F: the membrane is not permeable to the negative counterions that could balance the movement of K+ (mainly organic phosphates, amino acids, and proteins)

true

What do voltage-gated channels lead to?

voltage-gated channels produce action potentials

In the CNS, myelinated axons form the ______ matter, and the unmyelinated dendrites and cell bodies form the _____ matter.

white gray

During development, what do these cells do?

wrap themselves around each axon several times to form the myelin sheath—an insulating covering consisting of multiple layers of compacted membrane