Lecture 2: Neurons

Question 1

The processing of perceptions, thoughts and actions in the brain is accomplished by networks of small cells called neurons.

Answer 1

The essential activities of all neurons, including those involved in sensory processes, are chemical and electrochemical.

Question 2

The Structure of Neurons

Answer 2

Neurons communicate with each other through neurotransmitters, molecules that cross the synapse from the axon of one neuron to the dendrite of the next.

Nerve impulses are electrochemical; voltages change along the axon as electrically charged ions (sodium and potassium) pass in and out of the membranes of nerve cells.

Question 3

Dendrites

Answer 3

Receive information from other neurons

Question 4

Axon

Answer 4

Conducts that information to other parts of the brain, sometimes over great distances

Question 5

The Electric Neuron

Answer 5

Molecules in neural tissue are “charged”: + or -

Charged Ions are potassium K+, sodium Na+, chlorine Cl-, and Proteins-

In the absence of stimulation, the inside of the neuron is slightly more negative than the outside (-70 mv). This is called the resting potential.

Question 6

The Electric Neuron

Answer 6

Molecules in neural tissue are “charged”: + or -

Charged Ions are potassium K+, sodium Na+, chlorine Cl-, and Proteins-

In the absence of stimulation, the inside of the neuron is slightly more negative than the outside (-70 mv). This is called the resting potential.

Question 7

resting potential

Answer 7

-70 mv

In the absence of stimulation, the inside of the neuron is slightly more negative than the outside.

Question 8

Ion channels in a segment of neuronal membrane and measuring resting membrane potential.

Answer 8

Idealized neuron shown with intracellular recording electrode penetrating the neuron.

The electrode measures the difference between the voltage inside versus outside the neuron, and this difference is amplified and displayed on an oscilloscope screen.

The oscilloscope screen shows voltage over time, and shows that prior to the electrode entering the neuron, voltage between the electrode and the extracellular reference electrode is zero, but when the electrode is pushed into the neuron, the difference becomes –70 mV, which is the resting membrane potential.

The resting membrane potential arises from the asymmetric distribution of ions of sodium (Na+), potassium (K+), and chloride (Cl–), as well as of charged protein molecules (A–), across the neuron’s cell membrane.

Question 9

Ion channels pump ions across the membrane.

Answer 9

The Na+–K+ pump preserves the cell’s resting potential by maintaining a larger concentration of K+ inside the cell and Na+ outside the cell. The pump uses ATP as energy.

Question 10

synapse

Answer 10

The concentration of ions inside and outside of a neuron can be affected by neurotransmitters that are released into the synapse.

Question 11

Within the axon terminals, the relative charge between the inside and outside of a neuron is called the ______ .

Answer 11

presynaptic potential.

Question 12

Within the dendrites and soma, the relative charge between the inside and outside of a neuron is called the ____ .

Answer 12

postsynaptic potential.

Question 13

Neural Transmission

Answer 13

When neurotransmitters are absorbed by the dendrites or soma, they can alter the postsynaptic potential.

Excitatory neurotransmitters cause the charge to become depolarized (more positive). This change is called an excitatory postsynaptic potential (EPSP).

Inhibitory neurotransmitters cause the charge to become hyperpolarized (more negative). This change is called an inhibitory postsynaptic potential (IPSP).

Both EPSPs and IPSPs are produced by altering the relative concentration of ions between the inside and outside of the cell membrane.

Question 14

Excitatory Neural Transmission

Answer 14

Excitatory neurotransmitters cause the charge to become depolarized (more positive).

This change is called an excitatory postsynaptic potential (EPSP).

Question 15

Inhibitory Neural Transmission

Answer 15

Inhibitory neurotransmitters cause the charge to become hyperpolarized (more negative).

This change is called an inhibitory postsynaptic potential (IPSP).

Question 16

hyperpolarized

Answer 16

Inhibitory neurotransmitters cause the charge to become hyperpolarized (more negative).

Question 17

depolarized

Answer 17

Excitatory neurotransmitters cause the charge to become depolarized (more positive).

Question 18

Gated Ion Channels, EPSPs

Answer 18

Gated Na+ Channel

Causes depolarization of Post-synaptic neuron

Question 19

Gated Ion Channels, IPSPs

Answer 19

Gated K+ Channel
K+ leaves, Cl- enters

Causes hyperpolarization of Post-synaptic neuron

Question 20

IPSPs and EPSPs are Graded Potentials

Answer 20

They vary in magnitude based on the quantity of neurotransmitters with which they are stimulated.

They travel passively and are attenuated (weakened) with distance.

Question 21

axon hillock

Answer 21

the base of the axon

At the axon hillock, a cell’s potential is determined by the sum of all the excitatory & inhibitory inputs in the dendrites & soma.

Question 22

action potential.

Answer 22

If the voltage at the axon hillock reaches a threshold of -50 mv, then it will increase rapidly to 50 mv, and then quickly rebound to -70 mv.

This sequence of voltage changes is called an action potential.

Question 23

absolute refractory

Answer 23

During the absolute refractory period it is impossible to generate a new action potential.

Question 24

relative refractory

Answer 24

During the relative refractory period a new action potential can be generated, but it requires a stimulus that is much stronger than usual.

Question 25

The Toilet Metaphor

Answer 25

When you push the handle, water floods the bowl.

This event takes a couple of seconds and you cannot stop it in the middle.

Once the bowl empties, the flush is complete. Now the upper tank is empty.

If you try pushing the handle at this point, nothing happens (absolute refractory period).

Wait for the upper tank to begin refilling. You can now flush again, but the intensity of the flush increases as the upper tank refills (relative refractory period)

Question 26

An action potential (firing) of a neuron

Answer 26

Na+ entry locally depolarizes axon, which sufficiently depolarizes the adjacent region of the axon to open more of the voltage-gated Na+channels, re-creating the action potential there.

This process continues down the length of the axon.

Question 27

The action potential is non-decremental.

Answer 27

That is to say, its magnitude does not change as it travels along the axon.

Question 28

synapse

Answer 28

When an action potential reaches an axon terminal, it causes neurotransmitters to be released into the synapse.

Question 29

graded potentials

Answer 29

Note that this is quite different from graded potentials (EPSPs or IPSPs).

Their magnitudes become diminished as they travel within the dendrites and soma, and are therefore referred to as decremental.

Question 30

Primary Sensory & Motor Cortex and Surrounding Association Cortex.

Answer 30

The blue regions show the primary cortical receiving areas of the ascending sensory pathways and the primary output region to the spinal cord.

The secondary sensory and motor areas are colored pink.

The remainder is considered association cortex.

Question 31

Excitation and Inhibition

Answer 31

Any neuron can excite or inhibit another neuron based on the type of neurotransmitter it releases from its axon terminals.

The stimulation of a neuron modifies the frequency at which it generates action potentials.