Neurophysiology - Cells AQ

Question 1

What are the two divisions of the CNS?

Answer 1

The brain and the spinal cord.

Question 2

What are the two divisions of the PNS?

Answer 2

The cranial nerves and the spinal nerves.

Question 3

In which division would sensory receptors be appropriately categorized and what is your rationale?

Answer 3

Sensory receptors would be categorized into the PNS because sensory organs are the most peripheral extensions of sensory neurons.

Question 4

How is it that brain cancer is fairly common, yet neurons do not mitotically divide?

Answer 4

Brain cancer is typically caused by glial cells, not neurons. Glial cells rapidly divide in the brain and they are more abundant then neurons.

Question 5

What are the major differences between oligodendrocytes and Schwann cells?

Answer 5

Oligodendrocytes are found in the CNS and can myelinate several axons. Schwann cells are found in the PNS and can myelinate one segment of an axon at a time.

Question 6

What glial cell in the PNS has a similar function to the astrocyte in the CNS?

Answer 6

Satellite cells

Question 7

What is a node of Ranvier, and are they found in the CNS, PNS, or both?

Answer 7

The node of Ranvier is the region of an axon between myelinated regions (i.e., internodes), and they are found both in the CNS and the PNS.

Question 8

Comparing a neuron (specifically the axon portion) to the charging cord for your cell phone, what biological material surrounding the axon would be analogous to the plastic/rubber coating surrounding the wire of the cord itself?

Answer 8

Myelin sheath surrounds our ‘wires’ (axons).

Question 9

What is the purpose of this material surrounding axons in humans?

Answer 9

To insulate the neurons and increase action potential velocity.

Question 9

What percentage of all neurons are interneurons and where are they located?

Answer 9

99% of all CNS neurons are interneurons and they are located in the brain and the spinal cord.

Question 10

Can you draw out and label a typical motor neuron?

Answer 10

*See Question 6 on AQ sheet

Question 11

What are dendritic spines?

Answer 11

Dendritic spines are elevations on dendrites where presynaptic neurons form a synapse.

Question 12

What is a soma?

Answer 12

A soma is the cell body of a neuron.

Question 13

What are synaptic knobs?

Answer 13

Synaptic knobs are the terminal ends of axons where neurotransmitters are stored and released.

Question 14

What are the three components of a synapse?

Answer 14

Presynaptic cell - synaptic cleft - postsynaptic cell.

Question 15

The synaptic cleft is nothing more than what?

Answer 15

Interstitial fluid (i.e., ISF).

Question 16

How is information transferred from the presynaptic cell to the postsynaptic cell?

Answer 16

Information is transferred in the form of neurotransmitters.

Question 17

In an axo-dendritic synapse, where an axon of one neuron synapses with the dendrite of another, what are the presynaptic and postsynaptic cells?

Answer 17

The presynaptic cell is the axon terminal and the postsynaptic cell is the dendrite.

Question 17

What portion(s) of a neuron do other neurons form synapses with?

Answer 17

Cell body and dendrites.

Question 18

Which MAP transports recycled vesicles from the terminal knob to the soma? Is this in the positive or negative direction?

Answer 18

Dynein is the MAP that goes from the terminal knob to the soma and it travels in a negative direction.

Question 19

Which MAP transports secretory vesicles from the soma to the terminal knob? Is this in the positive or negative direction?

Answer 19

Kinesis is the MAP that goes from the soma to the terminal knob and it travels in a positive direction.

Question 19

Which of the three components of the cytoskeleton do these MAPs “walk” along?

Answer 19

MAPs walk along the microtubules.

Question 20

What is an equilibrium potential?

Answer 20

The equilibrium potential is the membrane potential at which an ion is in equilibrium across the plasma membrane.

Question 21

How do these equilibrium potentials relate to the RMP? In other words, how did we experimentally determine that K+ is the ion primarily responsible for the establishment of an RMP?

Answer 21

If the only ions across the cell membrane are K+ ions, the resultant membrane potential will be -90 mV, very close to the actual RMP of the neuron (-70 mV).

Question 22

What is the equilibrium potential value for Na+ and for K+?

Answer 22

The equilibrium potential for Na is +60 mV and the equilibrium potential for K is -90 mV.

Question 23

In which portion(s) of a neuron does a resting membrane potential (RMP) exist?

Answer 23

It runs through the entirety of the neuron.

Question 24

In which portion(s) of a neuron do graded (local) potentials occur?

Answer 24

Graded potentials occur in the cell body, dendrite, axon hillock, internode, and terminal knob.

Question 25

What type of gated channels would you find in the locations where a graded potential can occur?

Answer 25

Ligand-gated and mechanically-gated channels.

Question 26

In which portion(s) of a neuron do action potentials occur?

Answer 26

Action potentials occur in the initial segment of axon and the node of Ranvier.

Question 26

What type of gated channels would you find in the locations where an action potential can occur?

Answer 26

Voltage-gated channels.

Question 27

What is the primary mechanism responsible for establishing a RMP?

Answer 27

K+ leak channels.

Question 28

Hypothetically, how would your cells’ RMP be affected if this mechanism went offline (i.e., stopped working)?

Answer 28

If K+ leak channels stopped working, the RMP would become more positive, as the K+ would build up in the cell via the action of the Na+/K+ pump.

Question 29

What is the most abundant intracellular cation?

Answer 29

he most abundant intracellular cation is potassium.

Question 30

What is the most abundant extracellular cation?

Answer 30

The most abundant extracellular cation is sodium.

Question 31

What cation has the steepest concentration gradient across the plasma membrane?

Answer 31

Calcium has the steepest concentration gradient across the plasma membrane

Question 31

Why is it crucial that there is a 1 milli-osmolar difference in plasma solute concentration between our blood plasma and interstitial fluid (ISF)?

Answer 31

It is crucial to have a difference in plasma solute concentration between our blood plasma and ISF so that water will go into our bloodstream to keep the blood volume and blood pressure up.

Question 32

If a cell at rest is -70 mV, what happens when sodium enters it?

Answer 32

The cell becomes more positive, or depolarized.

Question 32

If a cell at rest is -70 mV, what happens when potassium leaves it?

Answer 32

The cell becomes more negative, or hyperpolarized.

Question 33

If a cell at rest is -70 mV, what happens when chloride enters it?

Answer 33

The cell becomes more negative, or hyperpolarized.

Question 34

If a cell goes from -70 mV to -60 mV, is that a reduction or increase in membrane potential? Why?

Answer 34

Reduction occurs when the cell goes from -70 to -60 millivolts. The cell is becoming less negative, so the polarity is being reduced.

Question 35

What is a depolarization and how can it be achieved?

Answer 35

A depolarization is a decrease in membrane potential; the membrane potential is becoming less negative or more positive. This can occur by a cation entering the cell or an anion leaving the cell.

Question 36

What is a hyperpolarization and how can it be achieved?

Answer 36

Hyperpolarization is an increase in membrane potential. The membrane potential is becoming more negative. This can occur by an anion entering the cell or a cation leaving the cell.

Question 37

What is a repolarization and how does this term relate to depolarization, hyperpolarization and resting membrane potential?

Answer 37

Repolarization is the return to RMP. During an action potential, a neuron becomes depolarized to its maximum amplitude, is repolarized, reaches RMP, and is hyperpolarized shortly after.

Question 38

Graded potentials are also referred to as local potentials. Why are these potentials referred to as “graded” potentials or “local” potentials?

Answer 38

Graded potentials are referred to as graded because the change in membrane potential is directly proportional to the magnitude of the stimulus. In addition to this, graded potentials are referred to as local potentials because they only occur over small regions of the plasma membrane.

Question 39

What does it mean that the change in membrane potential is directly proportional to the size of the stimulus?

Answer 39

If there is a greater stimulus (i.e., more ions entering the cell) there will be a greater change in membrane potential. Therefore, the change in membrane potential is directly proportional to the stimulus.

Question 40

What does it mean that graded potentials are distance-limited?

Answer 40

They are distance-limited because diffusion is distance-limited.

Question 41

For a patient with hyper-neuronal activity (e.g., anxiety or PTSD), what could you inhibit/block to stop their neurons from generating the graded potentials thereby preventing their neurons from firing (i.e., undergoing action potentials)?

Answer 41

You could block receptors in the neuron that, when opened, lead to a depolarization.

Question 42

What does it mean that action potentials are variable in frequency?

Answer 42

The frequency of APs along an axon is a major way in which information in coded. In general, a strong stimulus would have a greater AP frequency than a weak one.

Question 43

What does it mean that action potentials are fixed in magnitude?

Answer 43

The amplitude of an AP is fixed so the amplitude will stay the same regardless of the stimulus strength (all-or-nothing response)

Question 44

Can you compare and contrast the major differences between graded potentials and action potentials?

Answer 44

Graded potentials may be depolarizing or hyperpolarizing depending on the stimuli, whereas APs always initiate with a depolarization. In graded potentials, the amplitude is proportional to the stimuli, whereas in APs, the amplitude is fixed.

Question 44

What is the RMP value of a typical neuron?

Answer 44

The RMP of a typical neuron is -70 mV.

Question 45

What is a threshold potential (TP)?

Answer 45

A threshold potential, which must be achieved in the axon hillock, is the potential at which the neuron will fire an action potential.

Question 46

What is the peak amplitude (in mV) of a typical neuron?

Answer 46

The peak amplitude of a typical neuron is +30 mV.

Question 46

What is a TP value for a typical neuron?

Answer 46

The typical TP of a neuron is -60 mV.

Question 47

Can a cell fire a second AP after the threshold has been met but the TMP has not yet reached +30 millivolts, why or why not?

Answer 47

No, the cell cannot fire a second AP because voltage-gated sodium channels would still be open from the first AP.

Question 48

Can a cell fire a second AP after the threshold has been met, during the relative refractory period, why or why not?

Answer 48

Potentially, yes, but the stimulus would have to be greater than normal as the cell is becoming hyperpolarized during this period.

Question 49

Why is it important that the heart’s AP frequency is about 1 AP per 200 milliseconds versus skeletal muscle, which has a frequency of about 1 AP per 5 milliseconds?

Answer 49

Heart cell AP frequency is markedly decreased, making it impossible for the summation of muscle tension. Therefore, the heart cannot undergo a sustained contraction.

Question 50

Action potential (AP) propagation along a myelinated neuron can be described as a series of successively regenerated APs linked by a series of successively regenerated graded potentials. Starting with a neuron reaching a threshold in the axon hillock, can you provide a more detailed explanation of how an AP arises in the initial segment and then how the signal is propagated along a neuron? Is the same AP that is generated in the initial segment of axon the signal that is propagated along the entire axon?

Answer 50

An AP arises in the initial segment when enough Na+ comes into the cell to bring it from -70 mV to -60mV. Voltage-gated Na+ channels open, and Na+ flows in until the cell reaches +30 mV, where voltage-gated Na+ channels inactivate and voltage-gated K+ channels open. K+ leaves the cell until it reaches -90 mV, where voltage-gated K+ channels close and the cell returns to its normal state. This process repeats itself as AP propagation continues. New APs are generated at each node, so no, the initial AP generated in the initial segment of axon is not the same AP that is propagated along the axon.

Question 51

What is an excitatory postsynaptic potential (EPSP)?

Answer 51

An EPSP is an excitatory stimulus that causes a depolarization in the postsynaptic cell.

Question 51

In general, what types of potentials are EPSPs and IPSPs?

Answer 51

In general, EPSPs and IPSPs are graded potentials.

Question 52

What is an inhibitory postsynaptic potential (IPSP)?

Answer 52

An IPSP is an inhibitory stimulus that causes hyperpolarization in the postsynaptic cell.

Question 53

What type of channels, neurotransmitters, and ions are involved in EPSPs?

Answer 53

The channel involved in an EPSP is ligand-gated. A typical neurotransmitter involved in an EPSP is glutamate, as it is the most abundant excitatory neurotransmitter in the CNS. The ions involved in an EPSP are typically cations, such a Na+.

Question 53

What type of channels, neurotransmitters, and ions are involved in IPSPs?

Answer 53

The channel involved in an IPSP is ligand-gated. A typical neurotransmitter involved in an IPSP is GABA. The ions involved in an IPSP are typically anions, such a Cl-.

Question 54

What are the two regions of the spike initiation zone of a neuron?

Answer 54

The axon hillock and the initial segment of axon.

Question 55

What types of channels are located in each area?

Answer 55

The axon hillock has ligand-gated and mechanically-gated channels. The initial segment has voltage-gated channels.

Question 56

What type of potentials (action or graded) occurs in each area?

Answer 56

The axon hillock undergoes graded potentials and the initial segment of axon undergoes action potentials.

Question 57

Where does an action potential (AP) first occur in a neuron?

Answer 57

The initial segment of the axon.

Question 58

What are the events that lead up to an AP occurring?

Answer 58

If the current reaching the axon hillock changes the membrane potential to -60 mV, current will spread to the initial segment of axon and open voltage-gated Na+ channels at -60 mV. An action potential will then ensue.

Question 59

If a postsynaptic cell synapses with 32 different EPSPs totaling 42 mV, and one IPSP of -32 mV, would the initial segment of the axon fire an AP? Why or why not?

Answer 59

Yes, because spatial summation is occurring, so you have more EPSPs firing than IPSPs thus causing depolarization of the neuron. 42 mV - 32 mV = +10 mV change in voltage. -70 mV (i.e., RMP) + 10 mV = -60 mv (i.e., threshold). An action potential will ensue.

Question 60

What channels are involved in an AP?

Answer 60

Voltage-gated Na+ channels and voltage-gated K+ channels.

Question 61

At which voltages (in mV) do they open, inactivate, and close?

Answer 61

Voltage-gated sodium channels open at -60 mV, inactivate at +30 mV, and fully close at -90 mV. Voltage-gated potassium channels open at +30 mV, and close at -90 mV.

Question 62

During depolarization in an AP, what channel is open and what channel is closed?

Answer 62

During depolarization,voltage-gated sodium channels are open and voltage-gated potassium channels are closed.

Question 63

During a minor hand surgery, a local anesthetic (e.g., lidocaine) is used to numb the patient’s hand. What is the mechanism by which this drug works?

Answer 63

Lidocaine inhibits voltage-gated Na+ channels. Neurons are still active, but the voltage-gated Na+ channels can’t open, so there are no APs and no signal propagation. Therefore, the perception of pain never occurs in the brain.

Question 64

During repolarization in an AP, what channel is open and what channel is closed?

Answer 64

During repolarization,voltage-gated potassium channels are open and voltage-gated sodium channels are inactivated.

Question 65

Where are voltage-gated sodium and potassium channels found in myelinated axons versus unmyelinated?

Answer 65

In myelinated axons, they are found in the nodes of Ranvier. In unmyelinated axons, they occur continuously down the axon.

Question 66

What other structure must be present in the axolemma for AP formation and propagation?

Answer 66

The sodium-potassium pump.

Question 67

What type of conduction occurs in myelinated and unmyelinated nerve fibers, and what are the relative speeds of conduction?

Answer 67

A myelinated axon does saltatory conduction, which propagates action potentials at about 100 meters per second, while an unmyelinated axon does continuous conduction which propagates action potentials at about 1 meter per second.

Question 68

Nerve fibers are much like electrical wires. Current in electrical wires is generated by the flow of electrons. What is flowing in nerve fibers that creates the current of your neurons?

Answer 68

The potassium flowing through the axons creates the current for the neurons.

Question 69

What are the factors that increase the velocity of an action potential?

Answer 69

An increased axon diameter leads to less resistance in the axon, thus increasing velocity of signal travel; myelination (by reducing the number of APs to occur along the axon via saltatory conduction, by insulating the axolemma, and by reducing the charges at the internodes).

Question 70

In a disease like multiple sclerosis (MS) where the immune system attacks myelin-synthesizing cells, which property or properties of neurons would be affected? How is this so?

Answer 70

The conduction and velocity of action potentials would be affected.

In demyelinating disorders like MS, there is damage to the myelin sheath and the axolemma since the immune system attacks oligodendrocytes. Current can leak out of the axon, meaning cations will no longer be able to depolarize the neuron to reach threshold. Thus, the signal can be lost due to insufficient action potential propagation.

Question 71

A friend explains to you that multiple sclerosis (MS) is analogous to having a phone charging cord that has a broken coating and is frayed. He also explains how some electricity from the outlet is lost through these frayed spots on its way to charge the phone. In other words, there is a short in the wire. How do you compare this to a neuron that is damaged due to multiple sclerosis?

Answer 71

This is analogous to MS since the myelin sheath is attacked by the immune system. The myelin sheath acts as the rubber coating to a wire, and when this sheath is attacked by the immune system, it breaks down over time. Without this sheath, information/current in the form of potassium will leak out of our cells, thus creating a ‘short’ in our wires.

Question 72

You are creating a human-like android. You want to create an android that can react, move and think faster than yourself. How would you construct neurons for your android so that they propagate APs with a greater velocity than your own neurons?

Answer 72

Construct the nodes of Ranvier closer together.

Question 73

The internodes of an axon are a defined length. What is the reason they evolved to be the length that they are?

Answer 73

Diffusion is distance-limited. If the nodes were any further apart, the graded potentials in the internodes would be too weak to reach the nodes.

Question 74

The internodes of an axon are a defined length. What would happen if axons were longer?

Answer 74

The AP initiated in the initial segment could not be regenerated along the axon.

Question 75

What kind of potential occurs in a terminal knob?

Answer 75

A graded potential

Question 76

This change in membrane potential in the synaptic terminal leads to the opening of what type of channel?

Answer 76

A change in membrane potential in the synaptic terminal leads to the opening of the voltage-gated calcium channels.

Question 77

In a synapse, we often say that information is communicated from one neuron to the next in the following way: electrical to chemical to electrical. Can you explain what this means in neurophysiological terms?

Answer 77

The presynaptic neuron undergoes action potentials (electrical) and releases neurotransmitters (chemical) that simulate the postsynaptic neuron to undergo action potentials (electrical).

Question 77

What happens as the result of the influx of these ions into the terminal knob?

Answer 77

As a result of the influx of these irons into the terminal knob, synaptic vesicles undergo exocytosis.

Question 78

What is a ligand?

Answer 78

A ligand is an ion/molecule that binds to a receptor.

Question 79

What is an agonist?

Answer 79

An agonist is an ion/molecule that binds to a receptor and enhances that receptor’s activity or response.

Question 80

What is an antagonist?

Answer 80

An antagonist is an ion/molecule that binds to a receptor and resists that receptor’s activity or response.

Question 81

What is a cholinergic synapse and what is/are the ligand(s) present in this synapse?

Answer 81

A cholinergic synapse contains acetylcholine (ACh), a ligand, and uses this ligand as a neurotransmitter. They may be excitatory or inhibitory. These are abundant in the brain and neuromuscular junctions. Nicotine and muscarine can also act as agonists to their respective receptor.

Question 82

What are the different types of cholinergic receptors?

Answer 82

Nicotinic and muscarinic. Nicotinic receptors are ionotropic, which means they are permissive to ions, and muscarinic receptors are metabotropic, which means they are altered through metabolic changes.

Question 82

Can you provide an example of an excitatory cholinergic synapse and explain how it works?

Answer 82

An example of an excitatory cholinergic synapse is the neuromuscular junction of skeletal muscle. Acetylcholine binds to nicotinic receptors on muscle cells and opens these receptors, allowing Na+ to depolarize the cell.

Question 83

Can you provide an example of an inhibitory cholinergic synapse and explain how it works?

Answer 83

An example of an inhibitory cholinergic synapse is the sinoatrial node on the heart. Acetylcholine binds to muscarinic receptors on the SA node and ultimately decreases cAMP levels, decreasing activity and thus slowing heart rate.

Question 84

What would happen if acetylcholine was not tonically dripped on the heart’s sinoatrial node?

Answer 84

If acetylcholine stopped dripping on the SA node, our heart rate would increase.

Question 85

What would happen if epinephrine (adrenaline) was dripped on the sinoatrial node instead of acetylcholine?

Answer 85

If epinephrine was dripped on the SA node, our heart rate would increase dramatically since it speeds up the rate of APs.

Question 86

Would heart rate (HR) increase or decrease if cAMP levels in the sinoatrial node increased?

Answer 86

If cAMP levels increased in the SA node, heart rate would increase.

Question 87

What is an adrenergic synapse and what is/are the ligand(s) that are used in this synapse?

Answer 87

An adrenergic synapse is a nerve fiber that releases the catecholamines norepinephrine and epinephrine at the synapse.They may be excitatory or inhibitory.

Question 88

What is a catecholamine?

Answer 88

A catecholamine is a hormone that is created by your adrenal glands.

Question 89

What are the different types of adrenergic receptors?

Answer 89

The different types of adrenergic receptors include α1, α2, β1, and β2 adrenergic receptors.

Question 90

What is the Gs signaling pathway?

Answer 90

This is a stimulatory pathway. The neurotransmitter binds to a receptor attached to Gs and activates Gs. This will activate adenylyl cyclase, which converts ATP to cAMP, increasing cellular activity. Protein kinase A will activate, which phosphorylates proteins inside the cell and changes the cell’s metabolism.

Question 91

What is the Gi signaling pathway?

Answer 91

This is an inhibitory pathway. The neurotransmitter binds to a receptor attached to Gi and activates Gi. This will inhibit the activity of adenylyl cyclase, inhibiting production of cAMP. cAMP will be further degraded by cAMP PDE. Protein kinase A will not activate, thus inhibiting protein phosphorylation.

Question 92

What is the Gq signaling pathway?

Answer 92

Activation of Gq activates phospholipase C, which produces diacylglycerol (DAG) and IP3. DAG activates protein kinase C, which phosphorylates proteins inside the cell and changes the cell’s metabolism. IP3 increases calcium levels.

Question 93

What is a GABAergic synapse and what is/are the ligand(s) that are used in this synapse?

Answer 93

A GABAergic synapse contains γ-aminobutyric acid (GABA) which is an inhibitory neurotransmitter in the brain. This is exclusively inhibitory.

Question 94

What are the different types of GABAergic receptors?

Answer 94

GABAA and GABAB.

Question 95

Which one is ionotropic, and which is metabotropic? For the receptor that is ionotropic, which ion is the receptor permissible to?

Answer 95

GABAA is ionotropic and GABAB is metabotropic. GABAA is permissible to Cl-.

Question 96

Is diazepam (Valium) an agonist or antagonist, and for which receptor?

Answer 96

Diazepam is an agonist for the GABAA receptor.

Question 97

What is a glutamatergic synapse and what is/are the ligand(s) that are used in this synapse?

Answer 97

A glutamatergic synapse contains the neurotransmitter glutamate. This is exclusively excitatory. It is the most abundant excitatory neurotransmitter in the CNS.

Question 97

What are the different types of glutamatergic receptors?

Answer 97

NMDA and AMPA.

Question 98

How are AMPA and NMDA gated?

Answer 98

AMPA is a ligand-gated and NMDA is a ligand-gated and voltage-gated.

Question 99

Are these receptors metabotropic or ionotropic? For the receptor(s) that is/are ionotropic, which ion is the receptor permissible to?

Answer 99

Both receptors are ionotropic. AMPA is a ligand-gated Na+ channel, and NMDA is a ligand-gated Ca2+ channel.

Question 100

Can you describe how the AMPA and NMDA receptors work together to mediate the postsynaptic response?

Answer 100

Na+ entering AMPA depolarizes the cell, which ejects the Mg2+ ion in the center of the NMDA.

Question 101

Is ketamine an agonist or antagonist, and for which receptor?

Answer 101

Ketamine antagonizes the NMDA receptor

Question 102

What type of channels would you target to treat depression and anxiety?

Answer 102

One mechanism to treat depression would be to inhibit serotonin reuptake. One mechanism to treat anxiety would be to hold GABAA channels open

Question 103

What are the various mechanisms involved in the cessation of a nerve signal?

Answer 103

The presynaptic neuron can stop firing signals; ligands binding to receptors is only temporary, and the signal can stop when ligands unbind; neurotransmitters can diffuse out of synaptic cleft; neurotransmitters can be degraded in the synaptic cleft; presynaptic knob can reabsorb neurotransmitters and their degraded constituents.

Question 104

What is acetylcholinesterase and what is its function?

Answer 104

Acetylcholinesterase is an enzyme that degrades acetylcholine to acetate and choline; this can be resynthesized in the terminal knob.

Question 105

What is the function of MAOIs?

Answer 105

MAO degrades the catecholamines (dopamine, norepinephrine, and epinephrine). MAOIs inhibit the degradation of these catecholamines. By preventing the degradation of chemicals like dopamine, this can be utilized as an antidepressant.

Question 106

What is a selective serotonin reuptake inhibitor (SSRI) and what is it used to treat?

Answer 106

Selective serotonin reuptake receptors reabsorb serotonin back into the presynaptic terminals. SSRI’s treat depression by limiting serotonin reabsorption into presynaptic cells, thereby increasing serotonin levels in the cleft. Thus, more can bind to the postsynaptic receptors.

Question 107

Of the three structural classes of neurons, which are sensory and which are motor?

Answer 107

Special sensory neurons are bipolar, somatic sensory neurons are unipolar, and motor neurons are multipolar.

Question 108

Explain how temporal and spatial summation affect the threshold potential?

Answer 108

Temporal summation is when the same presynaptic neuron is fired repeatedly over time. Spatial summation is when several presynaptic neurons fire simultaneously. In either case, many ions accumulate in the postsynaptic cell. Positive charge pushes K+ towards the axon hillock. Negative charge draws K+ away from the axon hillock