FINAL PHYSIOLOGY EXAM 3

PNS made up of nerve cell fibers (axons) (grouped into _______) outside the CNS that transmit information to and from the CNS

nerves

The 12 pairs of nerves that connect the PNS with the brain are called __________ nerves, and the 31 pairs that connect with the spinal cord are called _________ nerves

cranial, spinal

All spinal nerves of the PNS and most cranial nerve contain both sensory and efferent fibers (a few cranial nerves carry only _______ fibers)

sensory

I. Afferent (sensory) division II. Efferent (motor) division A. somatic nervous system B. autonomic nervous system (ANS) 1. sympathetic division 2. parasympathetic division (3. enteric division?)

Divisions of the PNS

Afferent Division is made up of sensory neurons that carry info from receptors in the periphery to the CNS, the cell bodies of these neurons are located outside the CNS in groups called ____

ganglions

From the cell body, one process extends (within a cranial or spinal nerve) out to the receptor; another process passes into the _____. The receptors sense the external (e.g., eye or ear) or internal (e.g., blood pressure) environment

CNS

Somatic nervous system made up of all the axons of neurons (called motor neurons) going from the CNS (via cranial or spinal nerves) to ______ muscles

skeletal

The cell bodies of the neurons in somatic nervous system are in groups in the ______ or ________--- their axons are myelinated

brain, spinal cord

There is only a ___ ____ ___ between the CNS & the skeletal muscle cell in the somatic nervous system

single motor neuron

The transmitter released onto the muscle cell in somatic nervous system is always ___________--- always excite (never inhibit) the muscle cell

Acetylcholine

Autonomic nervous system made up of all the axons of neurons going from the CNS (via cranial or spinal nerves) to smooth muscle, cardiac muscle, and _____

glands

A given cranial or spinal nerve in autonomic nervous system may carry either sympathetic or parasympathetic fibers, but not ___

both

Autonomic nervous system fibers can lead to excitation or inhibition of the effector organ--- always involves a _____________ (connected by a synapse) between the CNS & the effector organ

two neuron chain

In the autonomic nervous system, the cell body of the first neuron in the chain is located in the ________

CNS

In the autonomic nervous system, the cell body of the second neuron in the chain (& the synapse between the first and second neurons) is located outside the CNS in a ____ (called an autonomic ganglion) of cell bodies

cluster

Usually, the ganglia of the sympathetic fibers (sympathetic ganglia) lie close to the _________, forming chains of ganglia known as sympathetic chains or trunks (exceptions: prevertebral ganglia such as celiac ganglion)

spinal cord

The parasympathetic ganglia lie _____________ the effector organ (with a few exceptions in the head)

atop, within

In both sympathetic and parasympathetic sympathetic fibers running between the CNS and a ganglion are called preganglionic fibers; those running from the ganglion to the effector organ are known as ____ fibers

postganglionic

Fibers releasing acetylcholine as their neurotransmitter are called ______fibers, and include: i. somatic NS fibers (not part of the ANS) ii. most preganglionic fibers of both the sympathetic and parasympathetic divisions of the ANS iii. most postganglionic fibers of the parasympathetic division of the ANS

cholinergic

Fibers releasing norepinephrine as their neurotransmitter are called _____ fibers, and include most post ganglionic fibers of the sympathetic division of the ANS

adrenergic

one set of postganglionic cells in the sympathetic division never develops axons; instead, the cells of this “ganglion” release their “transmitter” directly into the _____

bloodstream

this “ganglion,” called the adrenal medulla, is thus an endocrine gland the secretion of which is controlled by the _____ _____ ____

sympathetic preganglionic fibers

the adrenal medullae release both ____ ___ _____ , which are transported all over the body and which here are properly called hormones rather than neurotransmitters

epinephrine & norepinephrine

These hormones may effect (1) the same receptors as the norepinephrine released from other________ ____ ____ , or (2) other receptors far from the sympathetic postganglionic fibers (thus these latter receptors are activated only by the circulating epinephrine & norepinephrine)

sympathetic postganglionic fibers

some (not all) organs are reached by both sympathetic postganglionic & parasympathetic postganglionic fibers; whatever effect one ANS division has, the other division (with a few exceptions) has the ____ ____

opposite effect

A generality regarding the actions of the two ANS divisions is that the sympathetic division mobilizes the body during activity or stress, whereas the _____ _____ promotes maintenance functions and conserves body energy

parasympathetic division

A group of “___ ___ ____” mechanisms controls the kinds of substances that leave the blood and enter the interstitial fluid of the brain, thus precisely regulating the chemical composition of this fluid.

blood brain barrier

____ ___ ___ fills cavities within the brain and surrounds the brain & spinal cord, providing a cushion against jolts

Cerebrospinal fluid (CSF)

All molecules contain negatively and positively charged particles _____ and _____

electrons, protons.

Some molecules have more _______________________, or vice versa, giving them a net electric charge.

electrons than protons

The most notable of these in solution in the body are inorganic ions, especially ___, ____, and ____

Na+, K+, Cl-.

The ___ and intracellular fluid both contain many charged particles, and the distribution of these are important in neuron function.

ECF

An ___ ____ draws + and – charges together; like charges repel each other.

electric force

When oppositely charged particles come together, the force of attraction can be used to _________________. (To separate oppositely charged particles, energy must be used.)

perform work

Thus, separated electrical charges of opposite sign have the “potential” of doing work (if they are allowed to ________________)

come back together again

This potential to do work is called an electric potential, or the potential difference, often shortened to just ____________.

Potential

It is measured in _______ (V), but in living systems the separated charge is so small that the potentials are measured in millivolts (mV); one mV = 0.001 V.

Volts

The attraction between opposite charges tends to make them flow; the movement of electric charge is called ______________.

Current

The amount of current depends on: • the potential difference (voltage) • the nature of the material lying between the separated charges; the hindrance to the movement of charge through a material is called ________

resistance

Materials with high resistance to current flow are insulators, Materials with low resistance to current flow are _____________

conductors (iron, steel)

more current is achieved by raising the voltage or by lowering the resistance, as given by Ohm’s law

current = voltage/resistance

Pure water is a poor conductor of electricity because it contains few ___________________.

charged groups

When salt is added to the water (as in the body), it becomes a good _____________ (with a low resistance) as the Na+ and Cl- ions provide charges that can carry the current.

conductor

Lipids, which contain very few charged groups, have a high electrical resistance; thus, the lipid plasma membrane is a region of __ ___ ___that separate two water compartments of low resistance -- the membrane is good at separating opposite charges.

high electrical resistance

All cells at rest have a potential difference, called the resting membrane potential (RMP), across their membrane such that the inside of the cell is ________ with respect to the outside.

negative

By convention, the polarity (“positiveness” or “negativeness”) is always stated in terms of the kind of charge – plus or minus – that is in excess on the _____ of the cell.

inside

In nerve & muscle cells, this membrane potential can change _____ in response to stimulation.

rapidly

Why does the membrane potential occur? there is a slightly greater number of negative charges than positive charges inside the cell, and a slightly greater number of + charges than – charges outside the cell • the excess negative charges inside are attracted to the excess positive charges outside the cell; thus, these excess charges collect in a thin shell on the two surfaces of the plasma membrane (see next slide) • the ___ of the intracellular fluid and ECF, however, is neutral

Bulk

The total number of + and – charges that have to be separated across the membrane to account for the ___ is an insignificant fraction of the total number of charges actually within the cell

RMP

The magnitude of the RMP is determined by: • differences in numbers of ions in the intracellular fluid and ECF • the _______________ of the plasma membrane to the different ions

permeability

Of the many charged particles in and around a neuron, Na+, K+, and Cl- are present in the highest concentrations and thus have the greatest _____ to play roles in generating the RMP

potential

there is about 10-26 times as much Na+ and Cl- outside a neuron (in ECF) as inside the cell • there is about 30-35 times as much ____ inside a neuron as outside

K+

the Na+ and K+ differences are due to the operation of the _______________, an active transport mechanism that pumps Na+ out of the cell and K+ into the cell

Na+/K+ Pump

How do the concentration differences of Na+ and K+ create membrane potentials? • assumption 1: what if the membrane were completely permeable to K+ and not at all _____ to Na+?

permeable

initially, assume no potential difference across the membrane because the solutions contain equal numbers of positive ions: but the membrane is permeable to K+, so potassium ions will diffuse down their concentration gradient from inside to outside

(a concentration gradient favors Na+ diffusion in the other direction, but the membrane is not permeable to Na+)

after a few ions have moved to the outside, the outside will have an excess of positive charge; that is, a potential difference (voltage) will ___ ___ __ ___

exist across the membrane

however, a second factor (the attraction of opposite charges) can influence ion movement across the membrane; as K+ moves to the outside of the cell, the outside becomes more positive, and the membrane potential itself begins to influence the movement of K+ ions (they are attracted by the negative charge on the inside and repulsed by the positive charge on the outside) this (second factor) slows the ____ ____ ___ ____

outward movement of potassium

as long as the force driving K+ due to its concentration gradient is greater than the electric force driving it the other direction, K + will continue to move out of the cell, and the membrane potential will____ ___ ___

increase in magnitude

the outside will become more and more positive until the electric force opposing the movement of K+ out equals the force due to the concentration gradient favoring movement out; the membrane potential at which the two forces are equal in magnitude but opposite in direction is called:

the equilibrium potential for that ion (in this case, for K +)

the equilibrium potential for an ion can be determined using the _____ _____

Nernst equation

equilibrium potential for an ion = 61 x log (ion concentration outside/ion concentration inside) z where z = the valence (electrical charge) of the ion (e.g., +1 for potassium and sodium; -1 for chloride; +2 for calcium)

Nernst equation simplified

the greater the concentration difference across the membrane for any ion, the greater will be the equilibrium potential for that ion, since a larger electric force will be required to balance the larger flux due to the _____ ____

concentration gradient

if the membrane potential for a cell were at the potassium equilibrium potential (that is, at -94 mV), the forces trying to move K+ due to the concentration and electric gradients would be ____

equal

a normal neuron, however, has a RMP of about -90 mV (neurons and muscle cells range from -90 to -65); thus, in a normal neuron at rest, the concentration force trying to move K+ out is slightly stronger than:

the electric force trying to move K+ in

assumption 2: what if the membrane were completely permeable to Na+ but not at all to K+ ?--- initially, as in assumption 1, there is no potential difference___ ____ ___

across the membrane

the net flow of Na+ will be from outside to inside, and the inside of the membrane will become ____

positive

this movement of Na+ down its concentration gradient will be opposed by the electric force generated by that _____

movement

a sodium equilibrium potential will be established with the inside positive relative to the outside, at which point the concentration and electric forces will balance, and net movement of Na + will ____

cease

for a normal neuron, the sodium equilibrium potential is about +61 mV

(with the inside of the cell positive)

because a normal neuron has a RMP much different from the Na+ equilibrium potential, the two forces trying to move Na+ (in a real, are not at all cancelling each other out; in fact, the concentration force is trying to move Na+ in and the electric force is trying to move Na+ in also

(the membrane potential of a cell would have to be a positive value for the electric force to favor the movement of Na+ out)

- the farther away an ion is from its equilibrium potential, the greater will be the overall force trying to drive it across the membrane

(Na+ “wants” very badly to cross the membrane of a resting neuron)

the actual situation--- actual resting neurons are about 100 times more permeable to K+ than to Na+; thus, the potential that is generated at rest is due largely to the diffusion of K + down its concentration gradient--- this outward K+ movement makes the

inside of the cell negative

the actual RMP (-90 mV) is not equal to the K+ equilibrium potential (-94 mV), however, because a small number of sodium ions are able to continually move into the cell, cancelling the effect of an equal number of

potassium ions that have moved out

thus, when more than one ion can cross the membrane, the permeability for each ion as well as its concentration gradient must be considered when accounting for the RMP (for a given concentration gradient, the greater the permeability to an ion, the greater

contribution that ion will make to the RMP)

Why is Vm so close to EK?

The membrane is far more permeable to K+ than Na +

the Cl- equilibrium potential (-86 mV) is very close to the RMP, and the resting membrane is much less permeable to Cl- than to potassium; thus, the chloride ion normally makes very

little contribution to the RMP

Because a real neuron at -90 mV is at neither K+’s nor Na+’s equilibrium potential, there must be a net movement (leak) of Na+ into the cell and K+ out. Why doesn’t the concentration of Na+ inside the cell progressively increase and that of K + decrease?

at rest, the ______________ of the neuron moves sodium out and potassium in just fast enough to compensate for their diffusion the other way

actually, the pump moves _____ sodium ions out for every _____ potassium ions it moves in and thus makes a contribution to the RMP by making the outside of the cell even more positive (= making the inside even more negative); this contribution is minor in most neurons

3, 2

Because the pump is not electrically neutral, it is called an ____________ pump

electrogenic

Depolarization – change in which the membrane potential becomes ___________________ (closer to 0 or even positive) than the RMP

less negative

Hyperpolarization – change in which the membrane potential becomes __________________________ than the RMP

more negative

Repolarization – when a membrane potential that has been depolarized or hyperpolarized ___________________________

returns to its resting value

Graded potentials (GPs) are local changes in membrane potential in either a _____________ or a _______________ direction.

depolarizing, hyperpolarizing

A GP is usually caused by a specific change in the cell’s ______ _____ acting on a specialized region of the membrane

immediate environment

It is called “graded” because the size of the potential change is _____ (graded) and related to the _____ of the event that produces it; for example, a slightly painful stimulus produces a small GP at the peripheral ending of a sensory neuron, whereas a very painful stimulus produces a larger GP in the same neuron.

variable, magnitude

receptor potential, produced at the peripheral end of a sensory neuron in response to an ____________________

external stimulus

postsynaptic potential, produced in a postsynaptic cell in response to ____________________ by a presynaptic axon terminal

transmitter release

pacemaker potential, produced spontaneously (__ ____ ___ )

by ion leakage

whenever a local change in membrane potential occurs, current flows between this region and adjacent regions of the membrane (this is not flow across the membrane) that are still at the ____ (current always flows between two points if there is a difference in potential between the points and if a conducting material lies between them)

RMP

Thus, GPs cause current to flow in the intracellular and extracellular fluids around them; the greater the potential change, the greater the ____ ____

current flow

imagine a small region of membrane that has been depolarized by a stimulus; this area now has a potential ___ than that of adjacent areas (that is, it is closer to being neutral)

less

Inside the cell, positive ions will flow away from the ____ ____ and toward the more negative, resting regions of the membrane

depolarized region

At the same time, outside the cell, positive ions will flow from the more positive regions of the resting membrane toward the less positive region of (initial)

depolarization

this local current flow removes positive charges from nearby regions along the outside of the membrane and adds positive charges to adjacent sites along the inside of the membrane; thus, it produces a decrease in the amount of charge separation (that is, in the amount of depolarization) of the adjacent membrane sites

the graded potential has spread

note that near the initial stimulus there is much current flow whereas farther away there is less current flow – the magnitude of the current flow ____ ____ ___ away from the initial site of potential change

decreases with distance

Because they die out within a few millimeters, ___ can function as signals only over very short distances

GPs

Summary so far: GPs can be either depolarizations or __________________, they can vary in size, and they decrease in amplitude as they are conducted along the membrane.

Hyperpolarization

of depolarizing GPs: make the neuron more likely to produce an ______________________

action potential

of hyperpolarizing GPs: make the neuron ____________________________________

less likely to produce an action potential

Initiation of GPs: by a stimulus (at a sensory receptor), by a neurotransmitter (at a ___________), or spontaneously

synapse