Neural Signaling and Structure of the Nervous System

Physiology 311 with Dujardin at Ohio State University - All Campuses

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By: Alexandra Pawlyszyn
Textbook:

Vander's Human Physiology with Connect Plus Access Card

Vander's Human Physiology: The Mechanisms of Body Function with ARIS (HUMAN PHYSIOLOGY (VANDER))
Created: 2008-10-06
Size: 107 flashcards
Views: 24

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The Nervous system contain 2 integrated parts. what are they?

1. The CNS
2. The PNS

What does the CNS consist of? What does the PNS consist of?

1. brain and spinal cord
2. Nerves that extend between the CNS and the rest of the body

What are the two general types of cells that exist in the nervous system?

1. Neurons (nerve cells)
2. Glial cells (or neuroglia)

How do NEURONS transmit information?

Via electrical and chemical mechanisms

What percentage of cells in the nervous system do NEURONS account for?

10%

What do GLIAL CELLS do?

They support neurons through physical and metabolic mechanisms

What does the term NEUROGLIA mean?

"nerve glue"

What is a NEURON?

The basic unit of the nervous system; the individual nerve cell

What are DENDRITES?

Highly branched outgrowths from the cell body that RECEIVES INFORMATION.

What does a CELL BODY contain?

The cell nucleus and the protein synthesis machinery.

What is the AXON?

A long process that transmits signals to other neurons.

Signals are carried along the ________ to the _________.

axon length, axon terminal

AXONS are sometimes called:

nerve fibers

What is the INITIAL SEGMENT?

The junction between the cell body and the axon

What happens at the INITIAL SEGMENT?

Electrical signals are generated

The AXON TERMINAL releases __________ to __________.

chemical messengers, neighboring cells

The main axon may have branches that also release chemical messengers. What are these called?

AXON COLLATERALS

What is MYELIN?

Insulation that covers some axons.

What is MYELIN made by?

Myelin in made by GLIAL CELLS that wrap around the cell.

In ______, the cells that make myelin are called ______.

In the PNS, Schwann cells

What 2 things do SCHWANN CELLS do?

1. Each Schwann cell makes a small segment of myelin around ONE AXON.
2. Many Schwann cells are needed to insulate an entire axon in the PNS.

In ______, the cells that make myelin are called _______.

In the CNS, oligodendrocytes

What do OLIGODENDROCYTES do?

Each oligodendrocyte makes a small segment of MYELIN around MANY AXONS.

Myelin acts like ______________.

insulation for electrical currects.

What is the purpose of MYELIN?

to permit EFFICIENT SIGNAL CONDUCTION over long distances

What are the three functional classes of neurons?

1. AFFERENT NEURONS
2. EFFERENT NEURONS
3. INTERNEURONS

What do AFFERENT NEURONS do?

They convey information form TISSUES AND ORGANS into the CNS.

AFFERENT NEURONS usually only have __________.

one long process, an axon.

Instead of dendrites, afferent neurons receive signals through _________ on one end of the axon.

sensory receptors

The sensory receptors dtect signals such as ________. (4 things)

1. stretch
2. light
3. touch, or
4. chemicals

Where do EFFERENT NEURONS transmit information? and to what?

- transmit information OUT OF THE CNS
- to MUSCLES, GLANDS AND OTHER NEURONS

EFFERENT NEURONS contain ___________. (2 things)

both axons and dendrites

Where is the bulk of the cell?
What is out in the periphery?

In the CNS, the axon

Where are INTERNEURONS completely contained?

within the CNS

How do INTERNEURONS integrate information?

They integrate information between AFFERENT and EFFERENT NEURONS.

INTERNEURONS account for HOW MUCH of all neurons?

99%

In the periphery, the AXONS of AFFERENT and EFFERENT NEURONS are bundled together to form ______.

NERVES

A synonym for AXON:

NERVE FIBER

What is a SYNAPSE?

A JUNCTION BETWEEN TWO NEURONS, where one neuron affects THE ACTIVITY OF THE OTHER.

At most SYNAPSES, what is the signal between the neurons passed by? What are they called?

chemicals, neurotransmitters

Where do most SYNAPSES occur?

between the AXON TERMINAL of one neuron and the DENDRITE OR CELL BODY of another.

What is a neuron that sends signals TO the synapse called?

a PRESYNAPTIC NEURON (contains neurotransmitters)

What is a neuron that RECEIVES signals called?

a POSTSYNAPTIC NEURON

A neuron can be ________ to one cell and _________ to another cell.

presynaptic, postsynaptic

What are the major types of GLIAL CELLS in the CNS? (4 types)

1. oligodendrocytes
2. astrocytes
3. microglia
4. ependymal cells

What are the myelin forming cells in the CNS called?

oligodendrocytes

What are ASTROCYTES?

Star-shaped cells that provide STRUCTURAL and METABOLIC SUPPORT for neurons.

What are MICROGLIA?

Small cells that provide immune functions.

What do EPENDYMAL CELLS do?

They line fluid-filled cavities within the brain and spinal cord and regulate production of cerebrospinal fluid.

During very early embryonic development, the nervous system arises from the division of undifferentiated precursor cells called? (2 names)

STEM CELLS, or NEURAL PROGENITOR CELLS

What can STEM CELLS give rise to?

NEURONS and GLIAL CELLS.

The correct wiring of the nervous system is a complex process that requires precise guidance of __________ and _________.

neuron MIGRATION, axon GROWTH

After injury or disease, very few new neurons are produced. Therefore, repair in the nervous system depends on WHAT?

AXON growth and regenereation.

If the positive and negatively charges are SEPARATED, what is driving the ions toward each other?

ELECTRICAL POTENTIAL

T/F - The greater the difference in charge across the membrane, the greater is the magnitude of the voltage.

true

What is the difference between GRADIENTS and CURRENTS? (define both)

- GRADIENTS are produced by separating charges.
- CURRENTS are produced by allowing charges to cross a membrane.

What is MEMBRANE POTENTIAL?

THE VOLTAGE DIFFERENCE BETWEEN THE INSIDE AND OUTSIDE OF THE CELL.

Why can't ions move freely from the inside to the outside of the cell or vice versa?

Because they CANNOT DIFFUSE ACROSS A LIPID MEMBRANE.

Under normal conditions in which a neuron is not excited, what is the voltage across the plasma membrane called?

RESTING MEMBRANE POTENTIAL (RMP)

What voltage is the ECF assigned?

zero

What does the resting membrane potential of neurons range between? (numbers)

-40 to -90 mV.

Where do these charges tend to tightly collect?

at the plasma membrane

What is responsible for the ionic differences between the ECF and the ICF?

The Na+/K+ pump

What does the Na+/K+ pump do?

It pumps Na+ ions OUT of the cell and K+ INTO the cell.

Why does the pump have to keep going?

Because the ions do not remain where they are pumped. They are constantly flowing across the cell membrane through OPEN CHANNELS.

The movement of K+ ions is due to differences in both ________ and ________ across the membrane.

concentration, electrical charge differences

What is the equilibrium potential for K+, about?

-90 mV

How much larger is the K+ permeability than the Na+ permeability? This is thr?ugh the action of what>

50 times larger, K+leak channels (they don't let sodium in, only potassium)

What is the typical value of the RMP?

-70 mV

What kind of energy does the Na+/K+ pump require?

ATP

If a cell has a RMP of -70 mV, what is it?

POLARIZED

If A FEW POSITIVE IONS FLOW INTO THE CELL through a channel, what will the inside of the cell NEAR THE CHANNEL become?

LESS NEGATIVE, or DEPOLAIZED

If A FEW POSITIVE IONS FLOW OUT OF THE CELL through another channel, the inside of the cell near that channel will become what?

MORE NEGATIVE, or HYPERPOLARIZED

What happens during DEPOLARIZATION?

The membrane potential BECOMES LESS NEGATIVE THAN RMP (TOWARD ZERO).

What happens during OVERSHOOT?

The membrane potential BECOMES POSITIVE, or >0.

What happens during REPOLARIZATION?

The membrane potential RETURNS TO ITS RESTING VALUE (RMP).

What happens during HYPERPOLARIZATION?

The membrane potential BECOMES MORE NEGATIVE THAN THE RMP.

What two forms of membrane potential occur?

1. Graded potentials
2. Action potentials

What do GRADED POTENTIALS do?

They TRANSMIT INFORMATION ONLY OVER VERY SHORT DISTANCES.

What do ACTION POTENTIALS do?

They CAN TRANSMIT INFORMATION OVER VERY LONG DISTANCES. (WE WOULD RECORD THESE FROM THE AXONS.)

In a very small area of a neuron membrane, if we open a Na+ channel for a very brief (<msec) time, what will happen to the membrane potential?

Some Na+ ions will flow into the cell AND SLIGHTLY DEPOLARIZE THE MEMBRANE AT THAT SPOT.

What will depolarizing the membrane at that spot do to the surrounding membrane?

The LOCAL CURRENT will depolarize ADJACENT REGIONS.

T/F - A larger stimulus can cause greater depolarization that affects a larger region of the membrane.

true.

A characteristic of graded potentials:
They can be _______ or _______, depending on the type of ion flow.

DEPOLARIZING, or HYPERPOLARIZING

A characteristic of graded potentials:
They are ________; they decrease with distance from the stimulus.

decremental

A characteristic of graded potentials:
They are often initiated by _________ channels.

ligand-gated

A characteristic of graded potentials:
Their magnitude ________.

can vary

Graded potential s may be also called what 2 things?

"receptor potentials" or "sunaptic potentials"

What major types of cell can produse action potentials? (name 3)

NERVE, MUSCLE, and ENDOCRINE CELLS

Because the plasma membrane of these cells can produce action potentials, the membranes are referred to as what?

EXCITABLE

Action potentials are very different from graded potentials. Reason: the presence of ____________ in the cell membrane.

VOLTAGE-GATED CHANNELS

What are VOLTAGE-GATED CHANNELS?

-> CLOSED WHEN THE CELL IS AT RMP; THEY ARE OPENED WHEN THE CELL IS SUFFICIENTLY DEPOLARIZED.

What is key to producing action potentials?

VOLTAGE-DEPENDENT NA+ AND K+ CHANNELS.

What would happen if the voltage dependent Na+ channel was inhibited?

We wouldn't get rapid depolarization

What would happen if the voltage dependent K+ channel was inhibited?

Rapid-positive influx; small down repolarization

In an action potential, first, a depolarized stimulus causes what?

A FEW VOLTAGE-GATED NA+ CHANNELS TO OPEN QUICKLY.

What does a few voltage-gated Na+ channels opening quickly in an action potential allow?

This allows NA+ IONS TO FLOW IN RAPIDLY AND DEPOLARIZE THE MEMBRANE SLIGHTLY.

If the membrane becomes depolarized enough in an action potential, what happens?

Then MANY voltage-gated Na+ channels open, and a large influx of Na+ occurs.

What is the membrane potential at which that large influx of Na+ is triggered callled? How many mV is this?

THRESHOLD POTENTIAL, about -55mV

In action potential, in less that 1 msec, the Na+ permeability decreases drastically. What does the membrane now begin to do?

REPOLARIZE

What is the ball-like structure at the end of the channel called that inactivates the Na+ channels to close?

INACTIVATION GATE

Those stimuli that are just large enough to open the voltage-dependent Na+ channels are called what?

THRESHOLD STIMULI

What are those stimuli that are too weak called?

SUBTHRESHOLD STIMULI

What are membrane depolarizers that are too small to produce an action potential called?

SUBTHRESHOLD POTENTIALS

What is needed to generate an action potential?

the threshold potential

All action potentials are (how large?) as those caused by threshold stimuli?

EXACTLY THE SAME SIZE AND SHAPE as those caused by threshold stimuli

How do all action potentials occur? What are they called?

maximally or not at all, "all-or-none"