Transmission and Integration of Neuronal Signal

Question 1

What are neurons?

Answer 1

Neurons are the excitable cells in the brain.

Question 2

What are the functions of neurons?

Answer 2

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

Question 3

What is a morphological sign that neurons are specialized for communication?

Answer 3

Their extensive branching

Question 4

What it the role of the soma (cell body)?

Answer 4

• Collecting information
• Deciding if it should act on it (if it reaches the threshold then the spike will propagate down the axon.

Question 5

What is the role of the dendrites? What are found there?

Answer 5

• They are where electric inputs are
• Where synapses form
• They have a high content of ribosomes and have specific cytoskeletal proteins.
• They are the primary target for synaptic input.

Question 6

What happens at the axon terminal (synapse)?

Answer 6

The action potential ends here and propagates the signal further.

Question 7

Name the parts of the neuron

Answer 7

Question 8

What are neurons distinguished by?

Answer 8

• Their specialization for long-distance electrical signalling.
• Intracellular communication via synapses.

Question 9

How do neurons conduct information? What can this be measured as?

Answer 9

Neurons conduct information by the movement of ions across the membrane in response to the opening of ion channels (Na, K, Ca).

This can be measured as electrical impulses. Where the ions = the charge and the charge movement = current.

Question 10

What are the inputs and outputs of information conduction of a neuron?

Answer 10

Input = induced graded changes in membrane voltage.

converted to

Output = all-or-none action potentials (spikes)

Question 11

What is an action potential?

Answer 11

A self-generating wave of electrical activity (either fire or not fire).

Question 12

What is resting potential?

Answer 12

Neuronal resting potential is the voltage difference between the inside and outside of a neuron not receiving inputs (resting). Usually, the cytoplasm rest at about -65 to -80 mV relative to the extracellular space in a mature neuron.

Question 13

What is the threshold for firing an action potential?

Answer 13

The threshold for firing an action potential (AP) is usually around -40mV. If EPSPs sum up to bring the membrane potential to the threshold, the cell will fire.

Question 14

Excitatory Postsynaptic Potential

Answer 14

Excitatory Postsynaptic Potential (EPSP): a small excitatory event that makes the membrane depolarize, typically by about 10mV.

Excitatory causes cell to depolarize, become more positive.

Question 15

Inhibitory Postsynaptic Potential

Answer 15

Inhibitory Postsynaptic Potential (IPSP): a small inhibitory event that males it harder for the membrane to reach the threshold for an action potential.

Inhibitory causes cell to become more negative.

Question 16

Hyperpolarization

Answer 16

When the membrane potential becomes more negative.

When hyperpolarization occurs, the membrane potential changes in proportion to the magnitude of the current. This does not require any unique property of the neurons and is called passive electrical response.

Question 17

Depolarization

Answer 17

The membrane potential becomes more positive.

Question 18

How many different neurons are involved in the knee jerk response? Name them

Answer 18

There are 4 neurons involved in the knee jerk response.

Sensory neuron, interneuron and 2 motor neurons.

Question 19

How many synapses are involved in the knee jerk reflex?

Answer 19

3 synapses

Question 20

What are the steps in the knee jerk response?

Answer 20

Extensor muscle = quad, Flexor muscle = hamstring

When you tap a hammer to your knee, your leg will kick out. In order for your leg to kick out, the quad muscle has to flex (aka get shorter) and the hamstring muscle has to do nothing (not object).

1. The sensory neuron (DRG neuron) detects the tap and sends the signal down the axon, in the form of action potentials, to the spinal cord.
2. In the spinal cord, it synapses onto two cells. One of them is the motor neuron that innervates your quad muscle (the one that has to flex) and the other one will innervate an inhibitory interneuron.
3. In both these cases, the sensory neuron will release glutamate to excite both the cells. It will cause the motor neuron to be excited and flex the quad muscle. It will also cause the interneuron to be excited and release GABA or glycine (inhibitory neurotransmitters) onto the motor neuron that innervates the hamstring muscle. Therefore, it causes a large IPSP in the motor neuron that innervates the hamstring muscle causing it to not fire.
4. The neurotransmitter that is released in the neuromuscular junction is acetylcholine (hamstring muscle)- excitatory.

Question 21

How do the synaptic EPSPs and IPSPs translate into changes in action potential firing rates?

Answer 21

• EPSPs can summate in space or in time to depolarize the neuron to the threshold to fire an action potential.
• IPSPs can impede the cell from reaching threshold for firing an action potential.

Question 22

Excitatory neurons release…

Inhibitory neurons release…

Answer 22

Excitatory neurons release excitatory neurotransmitters.

Inhibitory neurons release inhibitory neurotransmitters.

Question 23

Inputs from the environment are most oftern…

Answer 23

Excitatory

Question 24

Most neurons integrate ____________ onto their somatodendritic compartments into an all or nothing ________ code to ___________.

Answer 24

1. graded inputs
2. temporal
3. transmit information

Question 25

What are the two techniques to do electrophysiological recordings?

Answer 25

You can either read the electricity from outside the cell (crude extracellular technique) or from within the cell (intracellular technique).

Question 26

What are the two extracellular electrophysiological techniques?

Answer 26

Recording change in current or potential outside of the cell. This informs you of activity inside the cell (not direct).

• Electroencephalogram (EEG) - recorded on skin
• Field/single unit recording - recorded by inserting electrodes into tissue. Physically next to neurons. Most common method.

Question 27

Intracellular electrophysiological techniques

Answer 27

Record activity either directly inside the cell or near/in the membrane of cell.

• “Sharp” electrode recording: The electrode goes directly inside the neuron and records the interior of the neuron (not very comon).
• Patch clamp recording - directly at the membrane (4 different ways). Common method

Question 28

How do you use the patch clamp technique?

Answer 28

1. Lower an electrode using a tiny thing called a micromanipulator (joystick that allows you to control your electrode) to the surface of the cell.
2. Use your breath through a tube to suction the membrane gently and create a gigaohm seal.
3. Once you are in this gigaseal, which has a resistance value of 1 giga ohm, you can either record the change in current going through the patch of membrane that you have sealed or you can make a few changes to go into different configurations.

Question 29

What is a gigaseal?

Answer 29

A gigaseal is when you have a perfect seal between the electrode and your membrane and nothing can flow in or out between the two.

Question 30

Name and explain the 4 different patch clamp configurations.

Answer 30

1. Cell-attached recording: allows you to record from an intact cell. But from outside of the cell and recording the flow where you’re directly contacting the outside of proteins/channels.
2. Inside-out recording: you would pull back very gently the joystick and you would break the membrane while keeping that little piece of membrane that you have the gigaseal with intact. You can now apply different compounds to the inside of the channels to record the change in current.
3. Whole-cell recording: You use your breath to apply a sharp pulse of negative or positive pressure to break the membrane. The inside of your electrode (filled with a salt solution) is continuous with the inside of your cytoplasm, but you still have a perfect seal with the membrane. Allows you to record all of the current coming into the cell at once because inside of your recording electrode is continuous with cytoplasm. Have access to record the change in membrane potential of the entire cell. You can only record action potential in whole-cell recordings.
4. Outside-out recording: Take the joystick and back up electrode to now break the membrane at 2 spots. The part you break has a channel and since they are lipids and hydrophobic, they are looking for each other in solution. The two flaps of membrane will bind to each other. Now you have access to the inside of the channel and the extracellular domain of the channel.

Question 31

Electroencephalographic recording (EEG)

Answer 31

• Relies on scalp electrodes to detect changes in electrical activity.
• Records the location of electrical fields across neurons (allows you to see where activity is occurring).
• Measurement of brain activity patterns using an array of scalp electrodes.

Question 32

What are the advantages and limitations of EEG recordings?

Answer 32

Advantages:

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

Limitations:

• Poor spatial resolution
• Limited to superficial cortical activity (only see activity in cortex).

Question 33

What are the uses of the EEG?

Answer 33

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

Question 34

What were the findings of Benjamin Libet’s “W” and the readiness potential?

Answer 34

• Libet’s experiment showed that the brain makes its decision to act before an individual is even aware of the decision.
• they have been raised as arguments against the existence of human free will.
• He used the EEG to understand consciousness.

Question 35

Extracellular Field Recording

Answer 35

• It is like a very local EEG - electrode is placed near the nerve cell of interest
• It has high spatial resolution
• Does not need to pierce through the membrane
• Useful for detecting temporal patterns of action potential activity and relating those patterns to stimulation by other inputs.

Question 36

Extracellular single unit recording (single cell firing)

Answer 36

• Most often used
• Records from several nearby cells in addition to the one selected.
• Use of microelectrodes to record action potential activity allows cell-by-cell analysis of the organization of topographic maps and can give specific insights into the type of stimulus to which the neuron is “tuned” (the stimulus that elicits a maximal change in neuronal activity from a baseline stat.

Question 37

What is a receptive field? What are the differences in activity in a cortical neuron in a single unit recording?

Answer 37

A receptive field is the region in a sensory space within which a specific stimulus elicits and action potential response.

• If you touch in the center of receptive field it increases cell firing.
• If you touch the surround of receptive field it decreases cell firing.
• If you touch outside of the receptive field it has no effect.

Question 38

Intracellular (“sharp” electrode) recording

Answer 38

• Most common in this class
• Where the electrode is placed inside the cell of interest.
• Can detect the smaller, graded changes in electrical potential that trigger action potentials and thus allow a more detailed analysis of communication among neurons within a circuit.