Lecture 1 - Transmission and Integration of Neuronal Signals

Question 1

Explain what is happening in the diagram below, from the hammer tapping the knee to the leg extending.

Answer 1

1. Hammer tap stretches tendon, which, in turn, stretches sensory receptors in leg extensor mucle.
2. Sensory neuron synapses with and excites motor neurons in the spinal cord. Sensory neuron also excites spinal interneuron. Interneuron synapse inhibits motor neuron to flexor muscles.
3. Motor neuron conducts action potential to synapses on extensor (quadricep) muscle fibres, causing contraction. Flexor (hamstring) muscle relaxes because the activity of its motor neurons has been inhibited.
4. Leg extends.

Question 2

What is defined as the following?:

The electrical signal generated and conducted along axons by which information is conveyed from one place to another in the nervous system.

Answer 2

Action Potential

Question 3

Is an axon pre-synaptic or post-synaptic?

Answer 3

Pre-Synaptic

Question 4

Define:

Dendrites

Answer 4

Neuronal processes arising from the nerve cell body that receive synaptic input.

Question 5

What are 3 advantages of EEG?

Answer 5

1. High temporal (msec) resolution.
2. Relatively non-invasive.
3. Sensitive to coherent cortical activity in 1-30 Hz range.

Question 6

What is the value of the resting membrane potential?

Answer 6

Typically, the cytoplasm rests at about -65 to -80 mV relative to the extracellular space.

Question 7

True or False?:

All action potentials have the same exact shape and size for a given neuron.

Answer 7

True

Question 8

What are the four main roles of the neuron (in terms of conducting information)?

Answer 8

1. Receive and respond to inputs from other neurons or the periphery.
2. Integrate signals and “decide” whether to transmit or not.
3. Rapidly conduct electrical signals long distances along their axons.
4. Activate other brain cells either electrically or by releasing chemical transmitters.

Question 9

True or False?:

Neurons are the excitable cells in the brain.

Answer 9

True

Question 10

Would you describe the signal in dendrites as digital and axons as analog or in dendrites as analog and axons as digital.

Answer 10

The dendrites are regularly recieving graded inputs from the axons of other pre-synaptics cells while the axon is only capable of sending a signal that is “all-or-nothing”. As such, it can be said that a neuron converts an analog signal from the dendrites into a digital signal at the point where you transfer from the soma to the axon. It is right at this axonal intitial segment where the “all-or-nothing” decision is made.

Question 11

What is defined as the following?:

Neuronal processes arising from the nerve cell body that receive synaptic input.

Answer 11

Dendrites

Question 12

Define:

Axon

Answer 12

The neuronal process that conveys the action potential from the nerve cell body to its terminals.

Question 13

What is the name of the signal that is propgrated along an axon?

Answer 13

Action Potential

Question 14

How is extracellular field recording done?

Answer 14

You take a fine tungsten, platinum, or silicone wire, insulate it up to the very tip, and then place the sharp tip into the cortex of the brain in order to record the extracellular field generate by single cells or a group of a few cells. This allows you to pick up action potentials generated by single cells.

Question 15

What are the four types of patch clamp recordings and how are they done?

Answer 15

1. Cell-Attached Recording: The pipette is sealed onto the membrane without tearing it.
2. Whole-Cell Recording: The pipette is sealed onto the mebrane, with a tiny tear formed. Every channel in the cell is measured. The whole cell becomes the tip of the electrode.
3. Inside-Out Recording: A bit of membrane is ripped off with a few individual channels still attached.
4. Outside-Out Recording: Similar to inside-out but the membrane is inverted so that the outside of the cell is facing the outside of the electrode.

Question 16

True or False?:

The membrane has no permeability to charge.

Answer 16

False

Due to the existence of ion channels, membranes are said to have a low permeability to charge.

Question 17

What creates current in neurons?

Answer 17

Current is produced by the movement of charge, which in this case is due to the movement of ions across the membrane.

Question 18

What is EEG short for?

Answer 18

Electroencephalography

Question 19

How do neurons differ from other cells in the body?

Answer 19

All cells have a soma (cell body), where proteins are made, and a nucleus, where DNA is transcribed into RNA. But unlike other cells, neurons have fine, elongated processes called dendrites and axons. They form an elaborate network that allows neurons to contact other cells in the brain. This causes there to be a high degree of interconnectivity that makes the brain a powerful computational device.

Question 20

What allows ions to cross the membrane?

Answer 20

Protein Ion Channels

Question 21

True or False?:

The inside and the outside of the cell are electrotonically seperate due to the membrane’s insulating properties.

Answer 21

True

Question 22

Where are graded inputs integrated into an “all-or-nothing” temporal code to transmit information?

Answer 22

Somatodendritic Compartment

Question 23

True or False?:

Neurons have one dendrite but many axons.

Answer 23

False

Neurons have one axon and many dendrites.

Question 24

From the following diagram, explain why in the knee-jerk reflex circuit the increased firing rate of the sensory neuron leads to the extensor motor neuron and the interneuron having a higher firing rate while the flexor motor neuron has a slower firing rate.

Answer 24

The sensory neuron synapses with and excites both the extensor motor neuron and the interneuron, which is why they both see an increased firing rate. Though, the interneuron is inhibitory, so its action potentials result in inhibitory signals (IPSPs) being propagated to the flexor motor neuron. These IPSPs summate with the EPSPs it is regularly excited with to result in a temporary decrease in its firing rate.

Question 25

Define:

Action Potential

Answer 25

The electrical signal generated and conducted along axons by which information is conveyed from one place to another in the nervous system.

Question 26

Define:

EEG

Answer 26

The study of electrical potentials generated in the brain recorded from electrodes placed on the scalp.

Question 27

True or False?:

EEGs have a high spatial resolution but poor temporal resolution.

Answer 27

False

EEGs have a high temporal resolution but poor spatial resolution.

Question 28

What are 3 common uses of EEG?

Answer 28

1. For the diagnosis and categorization of epileptic seizures.
2. For monitoring anesthesia depth.
3. Diagnosing abnormal brain development in infants.

Question 29

How do neurons conduct information?

Answer 29

Neurons conduct information electrically through the movment of ions across the membrane in response to the opening of ion channels.

Question 30

What is defined as the following?:

The neuronal process that conveys the action potential from the nerve cell body to its terminals.

Answer 30

Axon

Question 31

What is a property that affects the strength of an EPSP or IPSP on a post-synaptic cell? Provide one example of this property at work.

Answer 31

The axon intial segment is responsible for taking all the EPSPs and IPSPs and summating them in order to “decide” whether or not to fire an action potential. As such, the location of the input on the cell relative to this segment can have a huge impact on how much it is capable of depolarizing or hyperpolarizing the membrane. For example, some inhibitory synapses that form right onto the cell body can often inhibit a neuron every time they fire. This is found in the cortex.

Question 32

Is a dendrite pre-synaptic or post-synaptic?

Answer 32

Post-Synaptic

Question 33

Define:

Resting Membrane Potential

Answer 33

The inside-negative electrical potential that is normally recorded across all cell membranes.

Question 34

What is the value of the threshold for firing an action potential?

Answer 34

An action potential will typically fire at around -40 mV.

Question 35

What does patch clamp recording allow you to do?

Answer 35

Patch clamp recording allows you to measure very small synaptic and channel events in a neuron. This is done by using a larger pipette with a slight amount of suction applied.

Question 36

What is defined as the following?:

The inside-negative electrical potential that is normally recorded across all cell membranes.

Answer 36

Resting Membrane Potential

Question 37

How does a cell convey that it has recieved a strong input as opposed to a weak input?

Answer 37

The cell converts the graded analog inputs into a temporal digital signal where the firing rate of the cell increases the more depolarizing the current gets. As such, if you inject more and more depolarizing current into the cell, the cell will fire at higher and higher frequencies.

Question 38

What does intracellular “sharp” electrode recording allow you to do?

Answer 38

This technique allows you to visualize EPSPs, IPSPs, and action potentials within a single cell by measuring the membrane voltage using a very fine glass pipette.

Question 39

True or False?:

As ions flow across the membrane, they generate both electrical and magnetic fields. These can be measured as coarse changes in the extracellular field.

Answer 39

True

Question 40

What are 2 limitations of EEG?

Answer 40

1. Poor spatial resolution.
2. Limited to superficial cortical activity.

Question 41

True or False?:

Inputs induce graded changes in membrane voltage, which are converted to all-or-none “action potentials” as output.

Answer 41

True

Question 42

What electrophysiological technique is photographed below?

Answer 42

EEG

Question 43

What is defined as the following?:

The study of electrical potentials generated in the brain recorded from electrodes placed on the scalp.

Answer 43

EEG

Question 44

True or False?:

An EPSP will always depolarize the membrane to the threshold.

Answer 44

False

EPSPs typically depolarize the membrane by about 10 mV. It is the summation of EPSPs that cause enough of a depolarization for an action potential to be fired.

Question 45

True or False?:

An inhibitory postsynaptic potential depolarizes the membrane.

Answer 45

False

An excitatory postsynaptic potential depolarizes the membrane while an inhibitory postsynaptic potential hyperpolarize the membrane.