Neurons, Neuron Types

Cranial nerves reach out from the brain but go to the head and neck. They are part of the: A)PNS B)CNS

PNS

True or False? In this image, the same neuron carries sensory and motor information.

False

Does the cerebellum control heart rate? a)yes b)no

no

Using figure 2, neurotransmitter binding at which positions will have the most influence over whether or not the post synaptic neuron reaches threshold? a)1 or 2 b)1 or 4 c)3 or 4 d)2 or 3

1 or 4; Neurotransmitters binding cause graded potentials on the post synaptic cell. Graded potentials die out away from their site of generation. So, the closer the synapse to the trigger zone, the more influence its graded potential will have on the membrane potential of the trigger zone. Conversely, the further the synapse from the trigger zone (like 2 or 3), the less influence the graded potential will have on the trigger zone because the graded potential will die out.

Using figure 2, which trace shows temporal summation? (Figure 2 has numbers not letters.) a)2 b)4 c)1 d)None. e)5 f)3

1;This image shows transmembrane electrodes that are measuring potential at several locations on the neuron. Trace 1 shows multiple building EPSPs occurring at that spot on the postsynaptic neuron. This is most likely temporal summation - the effect of one neuron firing repeatedly and the resulting effect on the postsynaptic cell. Question 3

To create a graded hyperpolarization in the postsynaptic cell, the following events would need to occur in which of the following orders (you may or may not need to use all numbers below). 1. Synaptic vesicles fuse with cell membrane. 2. Action potential depolarizes the terminal end (knob). 3. Chemically gated potassium channels open on the postsynaptic cell. 4. Neurotransmitter released from presynaptic neuron. 5. Neurotransmitter diffuses across synaptic cleft. 6. Chemically gated sodium channels open on the postsynaptic cell. 7. Calcium enters the terminal end (knob). a)3, 5, 4, 1, 7, 2 b)7, 2, 4, 1, 5, 6 c)2, 7, 1, 4, 5, 6 d)2, 7, 1, 4, 5, 3

2, 7, 1, 4, 5, 3

Suppose a neurotransmitter causes Cl- channels to open on the postsynaptic membrane. Which of the following would occur? a)A graded hyperpolarization on the postsynaptic cell b)The postsynaptic neuron would reach threshold c)A graded depolarization on the postsynaptic cell

A graded hyperpolarization on the postsynaptic cell: When Cl- channels open, Cl- ions rush into the cell, making the interior more negative = the transmembrane potential becomes hyperpolarized. This hyperpolarization of the cell membrane is called an IPSP - an inhibitory postsynaptic potential. It brings the postsynaptic transmembrane potential further away from threshold, making it less likely to fire an action potential. IPSPs cause neurons to be inhibited. Graded depolarizations occur when the postsynaptic transmembrane potential becomes less negative, moving towards 0 mV and above. Graded depolarizations of the postsynaptic membranes are called EPSPs (excitatory postsynaptic potentials) and they bring the neuron closer to threshold and thus AP generation. When a neuron moves closer to threshold, it is said to be facilitated.

What is Y? a)A large vessel that delivers nutrients to brain tissue via smaller vessels b)A large vessel that collects waste blood from smaller vessels of the brain c)A large space that protects the brain from blood borne pathogens d)A large space that contains CSF to support the brain against mechanical damage

A large vessel that collects waste blood from smaller vessels of the brain; Y is the superior sagittal sinus located in the dural fold between the two cerebral hemispheres. (Superior for higher on the body in anatomical position, sagittal for being in the midline and sinus for a large opening.) This sinus collects deoxygenated blood and cellular waste from the many veins of the cerebrum. The smaller veins are nearer to the brain tissue. They emerge from the brain tissue carrying the waste blood. These veins end at the superior sagittal sinus, emptying their contents.

Which of the following will cause a graded hyperpolarization on a postsynaptic neuron? a)A neurotransmitter binding to a chemically gated sodium channel b)A neurotransmitter binding to a voltage gated sodium channel c)A neurotransmitter binding to a voltage gated potassium channel d)A neurotransmitter binding to a chemically gated potassium channel

A neurotransmitter binding to a chemically gated potassium channel: At a synapse, the presynaptic cell communicates with the postsynaptic cell. At a chemical synapse, the presynaptic cell releases a chemical (neurotransmitter) that binds to chemically gated channels on the membrane of the postsynaptic cell. When a chemically gated channel opens, specific ions may move down their concentration gradients (from high to low). The concentration gradient for potassium is to move out of the cell. When potassium moves out of the cell, it removes positive ions from the cellular interior, thus leaving the cell more negative. A hyperpolarization is a change in the transmembrane potential from resting values to something more negative (perhaps -70 mV to -90 mV). Neurotransmitters do not bind to voltage gated channels. Opening a sodium channel would lead to a graded depolarization. Because sodium would move down its concentration gradient into the cell, this would make the interior less negative (move closer to 0 or positive values; perhaps from -70mV to -20 mV).

How long is the longest neuron in your body?

About 8ft

What is the role of the sodium-potassium pumps on the neuron cell membrane? a)All of the options b)To move potassium against its concentration gradient c)To establish the proper ionic concentrations of sodium and potassium across the cell membrane d)To move sodium against its concentration gradient

All of the options:The Na+/K+ pump uses ATP to pump 3 Na+ ions out of the cell and 2 K+ ions into the cell. Because it uses energy to move the ions, it does not rely on diffusion for ion movement - meaning, it can push ions uphill against their concentration gradient. In doing this, it actually establishes the concentration gradient of these ions across the cell membrane and then re-establishes it after signals (action potentials) pass through the cell. This is an essential component to neuron function. Without the concentration gradients created and maintained by the Na+/K+ pumps, there could be no action potential.

Where will you find ependymal cells? a)Around blood vessels of the choroid plexuses, creating the blood-CSF barrier. b)Around the Circle of Willis, creating a continuous supply of blood flow. c)Around the trabeculae of the subarachnoid space, moving CSF around. d)Around most blood vessels of the brain, creating the blood brain barrier.

Around blood vessels of the choroid plexuses, creating the blood-CSF barrier; Ependymal cells are a type of glial cell found lining brain ventricles and in choroid plexuses. At choroid plexuses, ependymal cells select ions and nutrients from the blood, moving them into the spaces of the ventricles (this forms CSF). Using their cilia, ependymal cells move CSF throughout the ventricles. However, even though CSF flows through the subarachnoid space, there are no ependymal cells present here to move it. Astrocytes form the blood brain barrier around the smallest of blood vessels. The Circle of Willis does not involve ependymal cells - it is a blending of blood vessels that allows continuous and redundant blood flow to brain tissue cells (oxygenated blood).

Using figure 1, when does the action potential begin? a)At the start of D. b)At the start of C. c)At the start of E. d)At the end of F. e)At the start of B.

At the start of C: AP begins at the beginning of C. B is a graded potential that brings the membrane to threshold.

Why are the most effective anti-depressant medications small and fat soluble? a)Because they use a membrane bound glucose transport protein to enter the brain b)Because ependymal cell cilia can readily remove them from the blood c)Because they are readily phagocytosed by microglia in the brain d)Because they are not regulated by the blood brain barrier

Because they are not regulated by the blood brain barrier; he blood brain barrier (BBB) is a tight boundary that prevents most things from leaving the blood and entering the brain. The exceptions are as follows: -some substances cross the BBB by fitting into transport proteins for glucose or amino acids (facilitated diffusion across the BBB) -substances that are small and fat soluble simply diffuse into the cell membrane of the cells making the BBB - the BBB cannot regulate these to restrict them from getting into the brain -the BBB is absent in a few places and therefore makes the brain vulnerable to infection by pathogens at these places (small sections of the hypothalamus, pineal gland and pituitary gland where water soluble hormones from these tissues leave the brain and enter the blood). For a drug to effectively work in the brain, it must cross the BBB. The less the drug is restricted by the BBB, the more effective it can be in the brain. If microglia phagocytose the medication, it would not be terrible effective. Ependymal cells do not use their cilia to do this.

The subarachnoid space is located where? a)Between the bone & A b)Between B & C c)Between C & the cerebral cortex d)Between A & B

Between B & C; A is the dura mater, B is the arachnoid mater and C is the pia mater. The sub (below) arachnoid (letter B layer in pink above) space contains spider web like projections of the arachnoid down to the pia mater. Blood vessels are in this space as is CSF, the fluid the surrounds the brain to cushion it.

What do you find in the gray matter of the spinal cord? a)Cell bodies of multipolar neurons b)Cell bodies of unipolar neurons c)Both of the above

Cell bodies of multipolar neurons

What do you think? For you to be fully consciously aware of body activities or stimuli in the environment, the ____________ must receive or initiate neural signals. a)Hypothalamus b)Diencephalon c)Cerebellum d)Cerebral cortex e)Brain stem

Cerebral cortex; To accurately perceive stimuli (be consciously aware of stimuli), the sensory information must reach the cerebral cortex. To consciously control skeletal muscle, the motor signal must originate in the primary motor cortex (precentral gyrus) of the cerebral cortex. All other regions of the brain/spinal cord may be involved in signal transmission or motor initiation, but if the signal does not have some component that reaches the cerebral cortex, you have no precise knowledge of the activity and are not able to localize it with specificity.

By mass, the ____ is the largest part of the brain. a)Cerebellum b)Cerebrum c)Brainstem d)Diencephalon

Cerebrum; Perhaps a little more straight foward than I usually ask, but the cerebrum is very well developed in humans. We use our cerebrum for higher level processing and conscious activities. If information originates in or is transmitted to the cerebral cortex, you are consciously aware of that information. We will explore the cerebrum in detail next week. The cerebellum is important for unconscious motor control. The diencephalon is a major relay station and autonomic control center. The brainstem regulates basic life functions (heart, lungs, guts).

During presynaptic inhibition, what type of channels open in response to GABA? a)Chemically gated Ca++ channels b)Voltage gated Cl- channels c)Voltage gated Ca++ channels d)Chemically gated Cl- channels

Chemically gated Cl- channels: During presynaptic inhibition an inhibitory neuron releases neurotransmitter to a presynaptic neuron. This NT binds to chemically gated channels on the terminal end of the presynaptic neuron. For GABA, a chemically gated, Cl- channel opens, Cl- rushes in, causing hyperpolarization. Because the terminal end hyperpolarizes, it moves further from the threshold value that opens the voltage gated Ca++ channels. This causes less Ca++ to rush in, making for less NT release. NT must bind to chemically gated channels. Never voltage gated channels. If NT bound to chemically gated Ca++ channels, these channels would open, more Ca++ would rush in and even more NT would be released. This would be termed presynaptic facilitation. This also does occur, but not with GABA. It may occur with serotonin.

Which of the following would prevent repolarization after the peak of the action potential? a)Closing (or not opening) voltage gated potassium channels at the peak b)Closing sodium voltage gated channel inactivation gate (activation gate still open) at the peak c)Opening potassium voltage gated channels at threshold

Closing (or not opening) voltage gated potassium channels at the peak: The action potential shows depolarization, repolarization and after-hyperpolarization phases due to the opening and timing of sodium voltage gated channels and potassium voltage gated channels. The opening of the sodium voltage gated channel activation gate results in the depolarization phase as Na+ enters the cell. The repolarization and after-hyperpolarization phases occur as the K+ voltage gated channels open allowing K+ to leave the cell and the sodium channel inactivation gate closes, preventing further Na+ entry. Should potassium not be able to leave or Na+ continue to enter, the cell will stay depolarized and will not repolarize.

Using this figure, where does CSF leave the subarachnoid space? a)D b)E c)F d)G

D and E; Letters D & E are the arachnoid granulations. These are where CSF leaves the subarachnoid space into the dural sinuses. Letters F & G are choroid plexuses. They are made of a blood vessel surrounded by ependymal cells. These are located in the ventricles of the brain (one in each lateral, one in the third ventricle, one in the fourth ventricle). CSF is formed in the choroid plexus of the lateral ventricle and moves through the interventricular foramen into the ___third ventricle___ (name of ventricle). More CSF is made by the choroid plexus here and travels through the cerebral aqueduct to the ___fourth ventricle___ (name of ventricle). More CSF is made by the choroid plexus here and travels through the median aperture into the cerebellomedullary cistern of the ___subarachnoid space___ (name of space). Finally, CSF flows out of the brain at the superior aspect into the dural sinuses through ___arachnoid granulations___ structures).

Using figure 1, when is it NOT possible to generate another action potential in a neuron? a)During C, D, E, & F b)During F & G. c)During C & D. d)During E & F e)During A & B

During C & D: This is absolulte refractory period - no additional AP possible because the sodium voltage gated channels are either opened completely or the inactivation channel has not been reset to the resting state (door open).

Using figure 1, when are the potassium voltage gated channels allowing the most ions to flow? a)During F. b)At all time periods. c)During D & E. d)During C. e)During A, B & G.

During D & E: Voltage gated potassium channels open and allow ions to flow, creating the repolarization and hyperpolarization phases of the action potential.

Which of the following most accurately describes what is happening in a resting neuron? a)During rest, no ions are moving across the cell membrane. b)During rest, the membrane is hyperpolarized. c)During rest, the membrane is more permeable to potassium than it is to sodium. d)During rest, all ions are moving across the cell membrane passively. e)During rest, gated channels are open.

During rest, the membrane is more permeable to potassium than it is to sodium: At rest a neuron is more permeable to potassium than sodium because it has more leak channels for potassium than sodium. Ions are crossing a resting neuron (one that is neither sending nor receiving a signal) both passively through leak channels and actively through pumps. This separation of charges on either side of the membrane and the movement of ions across the membrane causes the membrane to be polarized at -70 mV (this number varies for different cells). When the membrane hyperpolarizes, the membrane potential becomes more negative than resting levels (ie: -90 mV, -100 mV etc). Gated channels open when neurons are sending and receiving signals.

Which of the following are essential to the production of the fluid that is found in the central nervous system, but not the peripheral nervous system? a)Dura mater b)Microglia c)Ependymal cells d)Pia mater e)Arachnoid mater

Ependymal cells; Cerebrospinal fluid (CSF) is found in the CNS but not the in the PNS. It functions to protect and support the CNS neural tissue and provide nutrients. It is made in the ventricles by the choroid plexus - a special arrangement of ependymal cells and a blood capillary bed. Microglia are important for pathogen destruction in the CNS. Astrocytes are essential to the blood brain barrier. The meninges, which are protective connective tissues, do not produce CSF.

Using this figure, where is CSF made? a)D, E, F & G b)F & G c)None of these d)D & E

F & G; Letters F & G are choroid plexuses. They are made of a blood vessel surrounded by ependymal cells. These are located in the ventricles of the brain (one in each lateral, one in the third ventricle, one in the fourth ventricle). Letters D & E are the arachnoid granulations. These are where CSF leaves the subarachnoid space. CSF is formed in the choroid plexus of the lateral ventricle and moves through the interventricular foramen into the ___third ventricle___ (name of ventricle). More CSF is made by the choroid plexus here and travels through the cerebral aqueduct to the ___fourth ventricle___ (name of ventricle). More CSF is made by the choroid plexus here and travels through the median aperture into the cerebellomedullary cistern of the ___subarachnoid space___ (name of space). Finally, CSF flows out of the brain at the superior aspect into the dural sinuses through ___arachnoid granulations___ structures).

True or False? Motor and sensory information are carried on the same neuron.

False: Sensory and motor information are carried on two different nerve cells (neurons). Neurons only carry information in one direction. Motor information must go away from the central nervous system, sensory information must come into the central nervous system.

True or False? The terminal end of neurons only contain voltage gated channels.

False: Though we have often only described the voltage gated calcium channels on the terminal end of the neuron (those involved in neurotransmitter release), there are actually also chemically gated channels. These channels allow different (intervening) neurons to synapse from their terminal end to the terminal end of the main neuron, have NT bind and open channels on the main neuron that influence Calcium entry into the main neuron. By manipulating calcium entry, you can influence the amount of NT released. In some cases, the chemically gated channels are ionotropic channels that have the receptor for the intervening neuron's NT on an ion channel. In other cases, it is a second messenger effect (metabotropic) that leads to an ion channel opening. When these additional ion channels open, the membrane potential of the main neuron is changed. This change influences the likelihood that the calcium voltage gated channel will remain open (from the AP) or close (if the NT causes hyperpolarization).

True or False? Facilitated neurons will generate an action potential no matter what neurotransmitter binds next. a)True b)False Right! A facilitated neuron is one in which the membrane potential has been brought closer to threshold by subthreshold stimuli (EPSPs being generated on the postsynaptic cell). The next EPSP may bring a facilitated neuron to threshold and cause AP generation even if very small. However, to state than any neurotransmitter would bring the neuron to threshold and cause an AP is not true because you do not know what channels would be opened and an IPSP could occur. An IPSP would lower the membrane potential further from threshold and never induce an AP.

False; A facilitated neuron is one in which the membrane potential has been brought closer to threshold by subthreshold stimuli (EPSPs being generated on the postsynaptic cell). The next EPSP may bring a facilitated neuron to threshold and cause AP generation even if very small. However, to state than any neurotransmitter would bring the neuron to threshold and cause an AP is not true because you do not know what channels would be opened and an IPSP could occur. An IPSP would lower the membrane potential further from threshold and never induce an AP.

True or False? The two cerebral hemispheres serve the exact same functions, just for opposite sides of the body. a)False b)True

False; The two cerebral hemispheres may look similar, and they can have similar functions in certain regions, but other regions serve very different functions. Specifically, the areas associated with understanding, using and speaking language (Wernicke's and Broca's) are located only in the left hemisphere of almost all people. The region in the right hemisphere serves a different purpose (appreciation of tone of words). This division of cerebral labor is called hemispheric lateralization.

When blockage of the left internal carotid artery occurs, cerebral areas served by that vessel will no longer receive blood. a)True b)False

False; This is false because the left internal carotid artery feeds into the Circle of Willis. The right internal carotid also feeds into this cerebral arterial circle as do the vertebral arteries. Then, from the circle, different arteries branch off and go to the brain tissue. If the internal carotid on one side is blocked, blood will still enter the circle from the other vessels and then provide continuous blood supply to the brain tissue.

Which of the following best matches the texture of fresh brain tissue? A)Olives B)Flan C)Raw Meat

Flan

Using this figure, there are two interfaces shown between blood vessels and specific glial cells. Each of these feature tight junctions. Which is correct? a)For the Blood Brain Barrier, the tight junctions are between the capillary cells; For the choroid plexus, the tight junctions are between the ependymal cells. b)For the Blood Brain Barrier, the tight junctions are between the astrocytes; For the choroid plexus, the tight junctions are between the ependymal cells. c)For the Blood Brain Barrier, the tight junctions are between the astrocytes; For the choroid plexus, the tight junctions are between the capillary cells. d)For the Blood Brain Barrier, the tight junctions are between the capillary cells; For the choroid plexus, the tight junctions are between the capillary cells.

For the Blood Brain Barrier, the tight junctions are between the capillary cells; For the choroid plexus, the tight junctions are between the ependymal cells; Blood capillaries are normally very leaky to allow nutrients to easily leave the blood reaching the tissues, and waste to easily leave the tissues and enter the blood. This ease of movement means that whenever the blood composition fluctuates (such as when you eat), your tissue extracellular fluid composition also significantly fluctuates. However, the brain is a very sensitive environment in which the extracellular fluid composition can significantly impact proper neuron function (think along the lines of changing K+/Na+ concentration variations). As such, the brain uses tight junctions to create a barrier, preventing fluid composition changes. In the choroid plexuses, the capillaries are leaky, but the epedymal cells make tight junctions. In the blood brain barrier, the astrocytes induce the capillary cells to not be leaky and instead form tight junctions. In both conditions, nutrients that are water soluble must pass through the cell membranes (ependymal in the choroid plexuses, capillary cells in the blood brain barrier) using transport proteins. The tight junctions minimize water soluble materials from passing between cell edges (paracellular transport).

Using the graphs above, suppose a very painful stimulus was received by the dendrites of a sensory neuron. Which of the following would occur at the dendrites? (the lines in C & D are action potentials, A & B show graded potentials) a)Graph C b)Graph D c)Graph A d)Graph B

Graph B; Graphs A & B show graded potentials. Graph B is a very large graded potential which you would expect associated with a large stimulus. If we were asking about the axon instead of the dendrites, we would expect graph C to be associated with a large stimulus (many APs).

Where do terminal ends synapse with cell bodies in the central nervous system? a)Nerves b)Meninges c)White matter d)Gray matter

Gray matter: Gray matter are collections of neuron cell bodies in the central nervous system. White matter are collections of axons (similar to nerves of the PNS). Nerves are bundles of axons in the peripheral nervous system. Meninges are connective tissues that protect the brain and spinal cord.

Suppose you open a chemically gated channel. Molecules of X ions rush out of the cell. Where are the X ions more concentrated at rest? a)In synaptic vesicles b)Inside the cell c)There is not enough information presented to answer the question d)In the phospholipid bi-layer e)Outside the cell

Inside the cell: Channels allow ions to move down their concentration gradients - from high to low. If this ion left the cell through a channel, the ion must be more concentrated inside the cell than out.

What is X? a)External carotid artery b)External jugular vein c)Internal jugular vein d)Internal carotid artery

Internal carotid artery; Oxygenated blood travels up to the brain via the internal carotid artery. The common carotid artery branches from the larger vessels nearer to the heart. As the common carotid artery travels upward into the neck, it splits and forms the external carotid artery (provides blood to scalp and external skull bones/muscles) and the internal carotid artery (provides blood to brain tissue).

What would happen if the dural sinuses were not able to collect CSF in the adult? a)The brain would not be anchored in the cranium. b)The blood brain barrier could not form. c)Intracranial fluid pressure would increase. d)Nothing - the dural sinuses contain blood not CSF.

Intracranial fluid pressure would increase; The dural sinuses drain CSF from the CNS. The CNS can hold ~150 ml of CSF, but more than ~500 mls is made everyday by the choroid plexuses. This means that CSF must be continually removed from the CNS - the process of removing CSF occurs in the dural sinuses where projections of the arachnoid mater stick into the dural sinus. If CSF is not continuously removed in the adult, fluid builds inside the cranium and compresses delicate neurons, thus affecting their normal function. Astrocytes make the blood brain barrier effective. While the dura mater does anchor the brain into position, drainage of CSF likely does not affect this function. If CSF was so high as to damage the dura anchoring, increased intracranial pressure would have occurred first and foremost.

Methylphenidate is sold as the medication Ritalin. It has been shown to improve memory and learning in individuals who consume this medication because it increases excitatory signal transmission in certain neural pathways. Which of the following would explain how it acts (its mechanism of action)? a)It acts as an antagonist to EPSP causing neurotransmitters b)It prevents re-uptake of EPSP causing neurotransmitter c)It acts as an inverse agonist for EPSP causing neurotransmitters d)It acts an agonist for IPSP causing neurotransmitters

It prevents re-uptake of EPSP causing neurotransmitter; The prompt suggests that we want to increase the number of EPSPs (or intensity of them) in certain neural pathways. There are two ways to do this: 1) prevent removal of the EPSP causing NT or 2) add an agonist that acts like the EPSP causing NT. Re-uptake is the process by which a presynaptic neuron reabsorbs the NT it released. If we inhibit this re-uptake, we can increase the amount of NT in the cleft and sustain signal transmission in the pathway. Agonists bind to a receptor and cause the same effect as when a NT usually binds to that receptor on that cell. Inverse agonists bind to receptor and cause the opposite effect as when a NT usually binds to that receptor on that cell. So, if the normal response of a certain cell to Ach is opening of Na+ channels --> depolarization, then when the inverse agonist binds to the Ach receptor, the cell hyperpolarizes (perhaps by opening a Cl- channel or K+ channel). Antagonists bind to a receptor for a certain NT and block the receptor - the antagonist itself does not change the activity of the cell, but instead prevents an NT from changing the activity of the cell. Agonists, antagonists and inverse agonists are receptor specific.

If an AP is moving down a neuron to the terminal end, what happens if Ca++ voltage gated channels at the terminal end of the presynaptic neuron do not open? a)More NT will be released b)Less (or no) NT will be released c)Nothing, Ca++ voltage gated channels do not affect NT release

Less (or no) NT will be released

What part of your brain is responsible for motivating you to be here today? a) Premotor cortex b)Limbic system c)Brainstem d)Cerebellum

Limbic system

Using this figure, a neuron dendrite was measured. At time 1, dopamine was released onto the neuron. At time 2, dopamine was still present but a bit of medication X was also added. At time 3, medication Y was added - medication Y acts differently than medication X. How did medication X act? All medications were removed at time 4, including dopamine. (Note: If medication X was not added, the cell would have continued to depolarize) a)Medication X was an agonist for dopamine b)Medication X was an inverse agonist for dopamine c)Medication X was a reuptake inhibitor for dopamine d)Medication X was an antagonist for dopamine

Medication X was an antagonist for dopamine; Dopamine depolarizes the cell, perhaps by opening Na+ or Ca2+ chemically gated channels. According to the passage, dopamine was added at time 1 and remained present. When medication X was added, membrane potential remained unchanged. According to the passage, dopamine was still present and the cell would have continued to depolarize if the medication X was not added. So, medication X could not be an agonist for dopamine - if it were, the cell would have depolarized more (agonists act just like the native compound). The same thing would have happened if the medication were a reuptake inhibitor for dopamine. Reuptake inhibitors prevent removal of neurotransmitter, making the effect of the neurotransmitter last longer and have a greater impact. Therefore, medication X could be an antagonist for dopamine, binding to the same receptors as dopamine, but not causing them to open. If medication X was an antagonist, it would outcompete some dopamine for the receptors, preventing further depolarization. Medication X could perhaps be an inverse agonist. If this were the case, then X would cause hyperpolarization instead of depolarization. If this were the case, I might expect membrane potential to return to resting levels (or lower), as happened when medication Y was added.

Which of the following would most likely inhibit the opening of voltage gated channels on the axon? a)Briefly opening a sodium chemically gated channel on a dendrite far from the trigger zone. b)One EPSP on a dendrite near the trigger zone. c)Multiple IPSPs in rapid succession at the same location on a dendrite far from the trigger zone. d)Multiple EPSPs in rapid succession at the same location on a dendrite far from the trigger zone.

Multiple IPSPs in rapid succession at the same location on a dendrite far from the trigger zone; IPSPs are graded potentials that cause hyperpolarizations. Whenever you hyperpolarize a postsynaptic cell, you make the transmembrane potential less negative than the threshold. Threshold is the membrane potential that causes the voltage gated channels to open. In our discussions, voltage gated channels are what cause action potentials. This is why we call these graded hyperpolarizations inhibitory - they make the neuron less likely to generate an AP.

Using Model 2: Besides Ca2+ entering through chemically gated Ca2+ channels, what other channel would presynaptically facilitate a neuron? a)Opening a chemically gated K+ channel b)Opening a chemically gated Na+ channel c)Neither. Only Ca2+ channels can be opened for presynaptic facilitation

Opening a chemically gated Na+ channel

Using figure 2, what most likely explains numbers 1 & 4? (Figure 2 has numbers not letters.) a)Opening voltage gated potassium channels b)Opening mechanically gated potassium channels c)Opening chemically gated potassium channels d)Opening chemically gated sodium channels e)Opening sodium leak channels

Opening chemically gated sodium channels; Trace 1 4 are depolarizations (EPSPs) - they are created by Na+ or Ca++ entering the cell. Typically on the cell body and dendrites, there are chemically gated channels that open in response to neurotransmitter. Potassium or chloride chemically gated channels would cause hyperpolarizations.

Broca's area is in the premotor cortex. Are the neurons in this area planning for muscle action or are the neurons executing the plan to activate the muscles? a)Planning b)Executing

Planning

Plasma is blood. Which of the following is significantly different between the blood and CSF? a)Protein b)Osmolality c)HCO3- d)Na+

Protein; The CSF has significantly less protein than the blood. The functional consequence of this is the the brain is less able to buffer changes in pH. Proteins are excellent buffers (able to bind or release H+ ions to change pH). With fewer proteins around (proteins are negatively charged), if there are excess H+ ions (pH becomes acidic), the brain is affected. When excess H+ are around (or there are too few H+), enzymes behave differently and therefore cellular function is affected. Our bodies carefully monitor CSF pH to prevent these large changes and brain function.

Which of the following would be found in the Vagus cranial nerve? a)Microglia b)Ependymal cells c)Schwann cells d)Astrocytes

Schwann cells; Nerves are part of the peripheral nervous system. They are composed of neuron axons and specific neuroglia. Neuroglia are supportive cells associated with neurons (all are cells of nervous tissue). They support neurons in different ways and are essential to the proper functioning of neurons. Schwann cells are glial cells of the PNS and function to myelinate axons. Astrocytes, ependymal cells and microglia are glial cells of the CNS and have functions as described in the lecture notes.

Which of the following would most likely trigger the opening of voltage gated channels on the axon? a)Several IPSPs in rapid succession at the same location on a dendrite far from the trigger zone. b)One IPSP on the dendrite adjacent to the trigger zone. c)Several EPSPs in rapid succession at the same location on a dendrite far from the trigger zone. d)Briefly opening a sodium chemically gated channel on a dendrite far from the trigger zone.

Several EPSPs in rapid succession at the same location on a dendrite far from the trigger zone: EPSPs are depolarizations. The more EPSPs you have, the more likely you are to bring the membrane to threshold. IPSPs are hyperpolarizations. They are less likely to bring the membrane to threshold. Proximity to the trigger zone is also important. Because graded potentials die out as they spread away from the site of generation, an EPSP of a given size closer to the trigger zone is more likely to generate an action potential than one far away (of the same size).

In this image, when the muscle tendon is struck, the muscle is pulled long, activating the sensory neuron. In response, the pathway of neurons is activated which eventually causes the skeletal muscle to contract. What type of sensory neuron is shown here? a)Somatic b)Multipolar c)Visceral d)Autonomic

Somatic: The sensory neuron is shown in red - it is a unipolar sensory neuron that is both part of the peripheral nervous system (its axon and cell body are in the PNS) and part of the CNS (its terminal end). It is detecting the degree of stretch (position) of the skeletal muscle which is classified as a somatic sense; visceral senses are for organs in the GI tract, reproductive system, blood vessels etc. Receptors that detect position are called proprioceptors. Proprioceptors are a type of mechanoreceptor that are located in a muscle, joint, tendon or ligament. They send signals to the CNS when the shape of the muscle, tendon, joint or ligament changes. The tendon & stretch reflexes use proprioceptors. The image here shows the stretch reflex, in which the special proprioceptor (a muscle spindle) is located in the muscle itself. When the muscle spindle is stretched, it initiates the stretch reflex, causing the same muscle that contains the muscle spindle to contract. Multipolar neurons look like the black neuron (a somatic motor neuron). Autonomic neurons are motor neurons that activate smooth muscles and cardiac muscle. Visceral sensory neurons are for organs in the GI tract, reproductive system, blood vessels etc. and usually detect pain, stretch, tissue damage, pH etc.

Using figure 2, what is happening during the shown time period? (Figure 2 has numbers, not letters) a)The combined effects of excitatory neurotransmitters only. b)The combined effects of EPSPs and IPSPs that inhibited the neuron. c)Spatial and temporal summation leading to a threshold depolarization at the trigger zone. d)The combined effects of multiple postsynaptic action potentials. e)Spatial summation leading to a subthreshold depolarization at the trigger zone.

Spatial and temporal summation leading to a threshold depolarization at the trigger zone; This image shows transmembrane electrodes that are measuring potential at several locations on the neuron. Trace 1 shows multiple building EPSPs occurring at that spot on the postsynaptic neuron. This is most likely temporal summation - the effect of one neuron firing repeatedly and the resulting effect on the postsynaptic cell. The rest of the numbers show measures of the postsynaptic membrane potential at various locations. Trace 5 shows a measure of the axon. Because traces 1-4 occur simultaneously, but at different points on the neuron, this is spatial summation. The recording at spot 5 shows an action potential. Therefore the best answer here is that spatial and temporal summation lead to a threshold depolarization at the trigger zone.

What is shown on the screen? a)Temporal summation leading to an action potential b)Spatial summation leading to an action potential c)Temporal summation leading to a subthreshold depolarization d)Spatial summation leading to a subthreshold depolarization

Spatial summation leading to a subthreshold depolarization

If the main neuron of model 3 generates an AP, and neurons A & B also generate APs, then....

Target cell 3 will be the most excited

Which of the following will, for sure, without question, stimulate an action potential in a postsynaptic neuron? a)Three IPSPs and two EPSPs occurring at once, near one another, near the trigger zone b)Three rapidly occurring EPSPs at the same spot, far from the trigger zone c)Four IPSPs occurring at once near the trigger zone d)Seven EPSPs, occurring repeatedly near the trigger zone e)The information given is not sufficient to answer the question.

The information given is not sufficient to answer the question: EPSPs bring the neuron transmembrane potential above resting values towards (or above) threshold values. Once threshold is reached at the trigger zone, the voltage gated channels open and an action potential can be generated. IPSPs lower the membrane potential away from threshold and make a neuron less likely to fire an action potential. What you do not know from this question is the magnitude of each stimulus. They could be very small EPSPs and very large IPSPs - it is impossible to know if the postsynaptic neuron generated an action potential without seeing a measure of its membrane potential at the trigger zone.

Using figure 1, what is the cause of the transmembrane potential during E? a)The membrane is more permeable to sodium than it is to potassium b)More sodium is entering the cell than potassium is leaving. c)The membrane is freely permeable to all ions. d)Chemically gated Cl- channels are open. e)The membrane is more permeable to potassium than it is to sodium.

The membrane is more permeable to potassium than it is to sodium; Ions must cross the membrane through membrane proteins, either channels or pumps. Membrane permeability is determined by the activity of these pumps or if ion channels are open. Even at rest, neurons are more permeable to K+ than Na+ due to the high abundance of open K+ leak channels (1 Na+ leak channel: 100 K+ leak channels). The membrane is even more permeable to K+ during time E because the voltage gated K+ channels are also open at this time. This is why the membrane is repolarizing, as K+ flows out of these open voltage gated K+ channels, down its concentration gradient. Cl- is not involved in neuron APs. The other options are inaccurate statements.

Using figure 1, what is happening during time period C? a)More calcium is entering the cell than potassium is leaving. b)More potassium is entering the cell than sodium is leaving. c)The membrane permeability to sodium dramatically increased compared to rest d)The membrane permeability to sodium dramatically decreased compared to rest The membrane is hyperpolarized.

The membrane permeability to sodium dramatically increased compared to rest; During time period C, the voltage gated sodium channels have opened, increasing membrane permeability to sodium dramatically. Because sodium is crossing the membrane, the membrane potential is depolarizing. Potassium enters the cell through the Na+/K+ pump. It moves 2K+ in when moving 3Na+ out. Calcium is not involved in this graph of action potentials for neurons.

What determines the effect of a neurotransmitter (NT) on a cell's transmembrane potential? a)The NT chemical makeup (amino acid, protein etc) b)The type of ion channel it causes to open c)The NT solubility in the cell membrane (fat soluble, water soluble)

The type of ion channel it causes to open

What is the role of vessel X? (Select all that apply) a)To deliver oxygen rich blood to the brain b)To drain CSF from the brain c)To remove deoxygeated blood from the brain

To deliver oxygen rich blood to the brain; Vessel X is the internal carotid artery. Oxygenated blood travels up to the brain via the internal carotid artery. The common carotid artery branches from the larger vessels nearer to the heart. As the common carotid artery travels upward into the neck, it splits and forms the external carotid artery (provides blood to scalp and external skull bones/muscles) and the internal carotid artery (provides blood to brain tissue). The jugular vein drains deoxygated blood from the brain. The dural sinuses collects CSF from the brain, which then drains to the jugular vein.

What is the role of vessel Y? (select all that apply) a)To drain CSF from the brain b)To deliver oxygen rich blood to the brain c)To remove deoxygeated blood from the brain

To drain CSF from the brain and To remove deoxygeated blood from the brain; Vessel Y is a dural sinus (the superior sagittal sinus). It is a large vessel housed in the split of the dura mater. Deoxygenated blood and CSF both drain into the superior sagittal sinus. CSF enters into this via the arachnoid granulations. Eventually, waste blood (mixed with CSF) drains from the superior sagittal sinus into the jugular veins.

True or False? Leak channels and sodium-potassium pumps are present on the cell body, dendrites, axon and terminal ends of the neuron cell membrane.

True: The leak channels and sodium-potassium pumps are responsible for creating and maintaining the cell membrane resting potential. Because the transmembrane potential exists at all parts of the cell membrane, they are located throughout the cell membrane and all its parts (cell body, dendrites, axon, terminal end).

True or False? At rest, the interior of a neuron has more potassium ions than the exterior, but is relatively negative compared to the outside of the cell.

True: The sodium/potassium pumps on every cell establish a high concentration of potassium inside cells and high concentration of sodium outside of cells. This is true of neurons as well. Each turn of the sodium potassium pump moves 3 positively charged sodium ions out of cells and adds 2 positively charged potassium ions into cells. This action contributes to the relatively negative interior of neurons despite the presence of so many positively charged ions. Additionally, the interior of neurons has negatively charged proteins contributing to the relatively negativity (these proteins are not present on the exterior). However, the most important component of the negative interior is the constant outward leakage of potassium ions through membrane leak channels for potassium. When these ions leak out, a positive ion leaves the interior and is added to the exterior, thereby making the interior relatively negative. While there is some inward leakage of positive sodium, it is 100X less than the outward leakage of potassium and overall does not make the interior positive during rest. If you are still not convinced, please check out the animations in the multimedia folder on our BB page, Course Docs.

True or False? The brain has a very high metabolic rate. a)True b)False

True; The brain has a high metabolic rate as evidenced by its impressive blood supply. At any given moment, the brain receives some 15-20% of all the blood delivery in the whole body! It must have a constant source of oxygen and glucose to make ATP for its metabolic processes (mostly sending signals). Furthermore, the brain has limited ability to make ATP from anything other than glucose and oxygen. This means that it must have freshly oxygenated blood (arterial blood) constantly delivered. To accomplish this, the body has multiple delivery routes for blood to the brain (internal carotid artery and vertebral arteries) that meet in the Circle of Willis on the ventral brain.

In terms of generating a depolarizing or hyperpolarizing graded potential on a postsynaptic cell, what do you think will be the most important factor? a)Type of voltage gated channel that binds the neurotransmitter b)Type of ion channel opened c)Type of neurotransmitter released from presynaptic cell d)Overall width of synaptic cleft

Type of ion channel opened: Sometimes a given neurotransmitter can bind to a K+ chemically gated channel and sometimes a given neurotransmitter can bind to a Na+ chemically gated channel. This happens with acetylcholine in the heart versus in the small intestine. Therefore the same neurotransmitter can generate a hyperpolarization if it opens the K+ channel or a depolarization if it opens the Na+ channel. In these cases, the sensitivity and structural make up of the postsynaptic cell really determines if the neurotransmitter will excite (depolarize) or inhibit (hyperpolarize) the postsynaptic cell. It is more important to know the type of channel that opens (in terms of ion allowed to move) than the specific identity of the neurotransmitter. Width of the cleft may affect signal transmission - if the cleft it too big, the neurotransmitter cannot reach the targets. However, this is not something that usually varies among targets and neurons. Voltage gated channels do not bind neurotransmitter - only chemically gated channels can.

Which of the following neuronal pathways would transmit its impulse to the effector slowest? (Assume equal axon diameter and pathway length.) a)Myelinated axon - synapse - myelinated axon - synapse - myelinated axon - effector b)Myelinated axon - synapse - myelinated axon - effector c)Unmyelinated axon - synapse - unmyelinated axon - synapse - unmyelinated axon - effector d)Unmyelinated axon - synapse - unmyelinated axon - effector

Unmyelinated axon - synapse - unmyelinated axon - synapse - unmyelinated axon - effector: Myelinated neurons send signals from beginning to end of the neuron faster than unmyelinated neurons. Unmyelinated axons must regenerate the AP more times to send the signal all the way to the end of the neuron - this means the AP event must occur more often and this takes more time. In myelinated neurons, the AP event is generated less often and the signal reaches the end of the neuron sooner. Neuron pathways with fewer synapses send signals from beginning to end faster than pathways with more synapses (same total pathway length). Synapses take time for neurotransmitter release, binding, EPSP generation and finally AP generation. So, the slowest signal along the path with less myelination and more synapses.

What type of channels, essential to neurotransmitter release, are present at the terminal end of neurons? a)Leak Ca2+ channels b)Chemically gated Ca2+ channels c)Voltage gated Ca2+ channels

Voltage gated Ca2+ channels

After suffering a stroke, your patient awakens. When speaking, his language is filled with made up words and nonsense, though his speech is properly formed (mechanically). You ask him questions and attempt to engage him in conversation, but he responds with meaningless words. He seems to be unaware that his word choices do not make sense. What condition do you think he most likely has? a)Dyslexia b)Word deafness c)Anomia d)Broca's aphasia e)Wernicke's aphasia

Wernicke's aphasia; Your patient, much like Bob in Case 5 from Friday's activity, has symptoms of Wernicke's aphasia. His language is filled with made up words and nonsense, though his speech was properly formed (mechanically). Broca's area is needed for the motor patterns that produce formed words - this is possible with your patient and Bob. However, the words he produces are non sensical and he does not seem to realize that he has a problem. Wernicke's area is used to give meaning to language, both for understanding others and word choice. The other conditions are explained on the Background sheet of the Activity 1.

Which of the following most directly allows you to comprehend simple verbal or written commands? a)Thalamus b)Prefrontal cortex c)Broca's area d)Wernicke's area

Wernicke's area; The Wernicke's area is a region of the cerebral cortex encompassing parts of the parietal, occipital and temporal lobes. When language is spoken, the sounds travel to the primary auditory cortex in the temporal lobe and then are relayed to the auditory association areas; in the association areas the sounds are identified as language (instead of music). When written words are read, the visual information is sent to the primary visual cortex in the occipital lobe and then relayed to the nearby association area; here, the visual information is interpreted as the shapes that make words. From these regions of the brain, information is then sent to the Wernicke's area. When the information is relayed to the Wernicke's area, you become fully able to comprehend that which you saw or heard. If a response is required, you will form the response here, but to speak it, you need to send information to the Broca's area. The Broca's area is the motor speech association area of the premotor cortex (frontal lobe, just anterior to the precentral gyrus). To speak, the motor signals are formulated here and then sent to the appropriate neurons of the precentral gyrus; the neurons in the precentral gyrus control your tongue, pharyngeal muscles and respiratory muscles to form words. In short, Broca's is the motor planning area for speech, not the interpretive area*. The thalamus is important as a relay station for sensory and motor information. The prefrontal cortex influences your appreciation of consequences, personality, reasoning and judgement. Although these may seem like qualities for appropriate conversation, damage to them will not influence your ability to understand spoken or written language.* *In some cases, when words or text are very complex and ambiguous, the Broca's area and other regions of the frontal lobe can become engaged to comprehend the language. This is the amazing concept about the brain, many overlapping functions and an exception to every rule! This question with the given options is not a great test question.

Which of the following will postsynaptically inhibit a neuron? a)Adrenaline b)ATP c)You cannot tell from the information given - the effect of a neurotransmitter depends on the type of channel it causes to open. d)Dopamine e)Acetylcholine Once again, it's not about the neurotransmitter but the type of channel it opens.

You cannot tell from the information given - the effect of a neurotransmitter depends on the type of channel it causes to open.; Once again, it's not about the neurotransmitter but the type of channel it opens.

Which of the following will postsynaptically inhibit a neuron? a)Adrenaline b)Dopamine c)ATP d)Acetylcholine e)You cannot tell from the information given - the effect of a neurotransmitter depends on the type of channel it causes to open.

You cannot tell from the information given - the effect of a neurotransmitter depends on the type of channel it causes to open; A cell is postsynaptically inhibited when it hyperpolarizes in response to a ligand. This IPSP occurs when the ligand opens (for example), a chemically gated Cl- or K+ channel. The effect of a neurotransmitter on a neuron can be an EPSP if it opens a Na+ or Ca2++ chemically gated channel. But, most neurotransmitters open different ion channels on different cells, depending on where the neurotransmitter receptor is located. If it is located on a Cl- or K+ channel, then the cell will hyperpolarize, causing an IPSP. You cannot tell from the information given if an EPSP or IPSP will result, and therefore if the cell will be inhibited or excited.

Which of the following will produce an EPSP? a)You cannot tell from the information given - the effect of a neurotransmitter depends on the type of channel it causes to open. b)Serotonin c)Dopamine d)ATP e)Norepinephrine

You cannot tell from the information given - the effect of a neurotransmitter depends on the type of channel it causes to open;An EPSP is a graded depolarization on a cell. It can be due to opening a Na+ or Ca2+ channels. The effect of a neurotransmitter on a neuron can be an EPSP if it opens a Na+ or Ca2++ chemically gated channel. But, most neurotransmitters open different ion channels on different cells, depending on where the neurotransmitter receptor is located. If it is located on a Cl- or K+ channel, then the cell will hyperpolarize, causing an IPSP. You cannot tell from the information given if an EPSP or IPSP will result.

Which of the following would simply diffuse through the intact blood brain barrier? a)small amino acids b)glucose c)alcohol d)sodium ions

alcohol; Of this list, alcohol is small and fat soluble. The rest are water soluble and do cross through the blood brain barrier, but use transport proteins to do so. The blood brain barrier is a continuous line of blood vessel cells (the cells are joined by tight junctions). Because the cells form a continuous barrier, to enter into the brain, molecules must pass through cell membranes. Molecules that are small and fat soluble can simply diffuse through the cells. Molecules that are too big or water soluble must cross using either transcytosis (endocytosis on one side, exocytosis on the other) or a transport protein.

If ____________ are non-functional, the interstitial fluid environment of the brain cannot be regulated. (Interstitial fluid is the extracellular fluid around tissue cells, here it is the fluid around brain cells). a)astrocytes b)oligodendrocytes c)Schwann cells d)satellite cells

astrocytes; Astrocytes are neuroglia that regulate the interstitial fluid environment of the brain by working with blood vessels to form the blood brain barrier. Blood capillaries are typically very leaky and allow substances to easily pass from the blood to the fluid surrounding tissues (interstitial fluid). But in the brain, the astrocytes make the blood capillaries less leaky and force most substances to move between the blood and brain tissue via tightly regulated cell membrane channels/carriers. Additionally, astrocytes mop up excess ions and neurotransmitter surrounding neurons. Without properly functioning astrocytes, the interstitial environment of the brain cannot be maintained. Schwann cells and satellite cells are cells of the PNS and therefore their function does not influence the brain interstitial environment. Oligodendrocytes are responsible for myelinating axons in the CNS which allows the neurons to send signals faster.

What part of a neuron would you expect to find in the corpus callosum? a)cell body b)axon c)terminal end d)dendrites

axon; The axon is in the white matter & the corpus callosum is a white matter tract. The terminal end will be in some gray matter where it can synapse on another neuron. Dendrites & cell body of the neurons in the corpus callosum (which are multipolar neurons) will be in some gray matter somewhere in the brain.

Consider a ligand that opens a Cl- channel on a neuron dendrite. What does an agonist for this ligand do to the neuron? (Assume no endogenous ligand is present) a)It depolarizes the membrane b)It hyperpolarizes the membrane c)Nothing - it binds but does not change the membrane d)Nothing - it does not bind

b)It hyperpolarizes the membrane

How would action potential frequency change for the postsynaptic neuron if an inverse agonist were given along with NT A at the time of the arrow? a)It would increase b)It would decrease c)It would stay the same

b)It would decrease

Somatic motor neurons: a) transmit proprioceptive (sensory) information b)can be found in cranial nerves c)are usually bipolar in shape

b)can be found in cranial nerves: Somatic motor neurons can be found in either cranial or spinal nerves. The difference is that cranial nerves send neurons to the face, head, neck and internal thoracoabdominal organs, and spinal nerves serve structures below the neck. As a group, these nerves contain axons of sensory (somatic and visceral) neurons, as well as axons of motor (autonomic and somatic) neurons. Somatic motor neurons serve skeletal muscles - you have skeletal muscles in your face served by the facial nerve. Somatic motor neurons do not transmit proprioceptive information - only somatic sensory neurons do. Somatic motor neurons are multipolar in shape - bipolar neurons are restricted to the eyes, ears and nose.

According to this image (same as Model 3 on handout from first class), the dorsal root ganglion contains: a)motor neuron only b)sensory neuron only c)sensory neuron & motor neurons

sensory neuron only: A dorsal root ganglion (located in the dorsal root) contains only sensory neurons. The ventral root contains only motor neurons. This reflects the embryology of the spinal cord in which the dorsal roots are formed from the neural crest cells but the ventral roots are outgrowths from the spinal cord. A dorsal RAMUS is a branch of a spinal nerve that provides innervation to the skin and muscles of the back. It contains both sensory neurons and motor neurons (axons of these).

In the peripheral nervous system (PNS), cell bodies of unipolar neurons associated with spinal nerves cluster together in structures called "dorsal root ganglia". Which of the following CNS structures is most similar to ganglia? a)white matter b)spinal nerves c)subcortical gray matter d)cranial nerves

subcortical gray matter: The ganglia of the PNS contain cell bodies of neurons. In the CNS, clusters of cell bodies are called gray matter. There are many different ways gray matter is found in the CNS. These include outer layers (cortex) and inner masses (subcortical gray matter nuclei, just called nuclei). White matter is made of neuron axons - myelinated axons make white matter, white looking. Cranial and spinal nerves are both structures of the PNS and contain axons.

When the appropriate part of the axon membrane reaches a certain transmembrane potential... a)the leak channels begin to open. b)the chemically gated channels begin to open. c)the sodium-potassium pumps begin to function. d)the voltage gated channels begin to open.

the voltage gated channels begin to open: The certain value of transmembrane potential that opens voltage gated channels is called threshold. When the cell membrane adjacent to voltage gated channels reaches threshold, the gates begin to open. This is the triggering of an action potential. Leak channels are always open (effectively) Chemically gated channels open when a chemical binds (neurotransmitter) The Na+/K+ pumps are always active

The ___________ are fluid filled cavities in the brain that are continuous with one another and the central canal of the spinal cord. a)dural sinuses b)ventricles c)meninges d)cerebral cortex

ventricles; The brain ventricles are formed from the neural tube during development. They are lined by ependymal cells and they contain cerebrospinal fluid which circulates through them and into the central canal of the spinal cord and the subarachnoid space. The cerebral cortex is a region of gray matter that makes up the outer edges of the cerebrum. The meninges are connective tissue layers outside the brain that protect the brain. They are the pia, arachnoid and dura maters. Dural sinuses are places where the bi-layered cranial dura mater is split into two portions. The cavity that forms fills with venous blood (deoxygenated blood leaving neural tissue to return to the lungs for oxygenation). The dural sinuses also act as a place where cerebrospinal fluid is removed from the CNS.