Which parts of a neuron are shown by a Golgi stain that are not shown by a Nissl stain?
The axons and the dendrites.
The Nissl stain distinguishes between neurons and glia, but it does not show the axons or dendrites.
What are the three physical characteristics that distinguish axons from dendrites?
1) Length: Axons can be more than 1m, dendrites rarely over 2mm.
3) Structure: Dendrites appear as trees, whereas an axon is usually singular that branches at the end.
Of the following structures, state which ones are unique to neurons and which are not: nucleus, mitochondria, rough ER, synaptic vesicle, Golgi apparatus.
Unique: Synaptic vesicle.
Non-unique: Nucleus, mitochondria, rough ER, Golgi apparatus.
What is myelin? What does it do? Which cells provide it in the central nervous system?
A white fatty substance that is generated by glial cells (Schwann cells and oligodendrocytes). It provides electrical insulation for some axons, and increases the conduction velocity of action potentials by allowing saltatory conduction.
What two functions do proteins in the neuronal membrane perform to establish and maintain the resting membrane potential?
1) They form Sodium-Potassium pumps that exchange extracellular K+ for intracellular Na+
2) They form permeable potassium channels in the membrane that allow the movement of K+ ions across the membrane, down their concentration gradient.
On which side of the neuronal membrane are Na+ ions more abundant?
Outside the cell.
When the membrane is at the potassium equilibrium potential, in which direction (in or out) is there a net movement of potassium ions?
There is no net movement of potassium ions at the equilibrium potential, since equilbrium signifies balance.
There is a much greater K concentration inside the cell than outside. Why, then, is the resting membrane potential negative?
There is an large concentration of Na+ outside the cell, and the sodium-potassium pumps exchange 2 K+ (to inside) for 3 Na+ (to outside).
When the brain is deprived of oxygen, the mitochondria within neurons cease producing ATP. What effect would this have on the membrane potential? Why?
The Sodium-Potassium pump requires ATP to function, so it would no longer be able to keep the resting membrane potential negative and pump out the Na+ as it flows in from the ion channels.
The membrane potential would depolarize.
How is the Nernst equation caclulated?
Define membrane potential (V m) and sodium equilibrium potential (E Na). Which of these, if either, changes during the course of an action potential?
V m: The membrane potential is the voltage across the neuronal membrane at any moment.
E Na: A state in which the diffusional and electrical forces of Na+ are equal and opposite, and there is no net movement of Na+ across the membrane.
The membrane potential changes during the action potential, as the membrane depolarizes. An equilibrium potential is constant.
What ions carry the early inward and late outward currents during the action potential?
Early inward current is caused by Na+ flowing inside the cell. There is a large driving force on Na+ towards the negative side of the membrane (inside the cell).
Late outward current is caused by K+ flowing out of the cell. This is because now that the membrane potential is positive, there is a large force driving K+ out of the cell, towards the negative side of the membrane (outside the cell).
Why is the action potential referred to as "all-or-none"?
What is meant by quantal release of neurotransmitter?
Neurotransmitters are released into a synapse in packaged vesicles called quanta. Quantal release is the mechanism by which most traditional endogenous neurotransmitters are transmitted throughout the body. Electrical synapses do not use quantal neurotransmitter release. The goal of any synapse is to produce either an excitatory postsynaptic potential (EPSP) or an inhibitory postsynaptic potential (IPSP), which generate or repress the expression, respectively, of an action potential in the postsynaptic neuron.
You apply ACh and activate nicotinic receptors on a muscle cell. Which way will current flow through the receptor channels when Vm = -60 mV? When Vm = 0 mV? When Vm = 60 mV? Why?
-Nicotinic ACh receptors are permeable to Na and K
*Vm= -60mV, net current inward toward Ena (causes depolarization)
*Vm= 0mV, would be the reversal potential because these is the point at which the current flow would reverse; right between Ena and Ek; NO CURRENT FLOWS
*Vm= 60mV, outward net current toward Ek (causes hyperpolarization)
This chapter discussed a GABA-gated ion channel that is permeable to Cl. GABA also activates a G-protein-coupled receptor, called the GABAB receptor, which causes potassium-selective channels to open. What effect would GABAB receptor activation have on the membrane potential?
-GABA-gated Cl ion channels would bring the membrane toward Ecl (-65mV)
*if Vm was less, activation would cause hyperpolarization
-activation of GABAb receptors would cause K-selective channels to open and bring the Vm toward Ek (-80mV)
-if Vm was less, activation would cause hyperpolarization
You think you have discovered a new neurotransmitter, and you are studying its effect on a neuron. The reversal potential for the response caused by the new chemical is -60 mV. Is this substance excitatory or inhibitory? Why?
Reversal potential is the critical value of membrane potential at which the direction of current flow reverses.
-if neurotransmitter causes Vm to move toward a value more positive than the action potential threshold, neurotransmitter action would be excitatory, otherwise inhibitory
-reversal potential of -60mV suggests that the neurotransmitter activates ion channels that make the membrane more negative
-movement toward this value is likely to be more negative than the action potential threshold, making it less likely for firing (inhibition)
A drug called strychnine, isolated from the seeds of a tree native to India and commonly used as rat poison, blocks the effects of glycine. Is strychnine an agonist or an antagonist of the glycine receptor?
-blocks the effects of glycine
-high doses eliminate glycine-mediated inhibition in circuits of the spinal cord and brain stem
-leads to paralysis of the respiratory muscles
Why is an excitatory synapse on the soma more effective in evoking action potentials in the postsynaptic neuron than an excitatory synapse on the tip of a dendrite?
-current entering through synapse must spread spike-initiation zone; zone must be depolarized beyond threshold
-depolarization decreases as a function of distance along a dendrite
-soma is closer so it will be more effective
What are the steps that lead to increased excitability in a neuron when NE is released presynaptically?
1. The NE receptor bound to a b receptor activates G-protein in the membrane.
2. G-protein activates the adenylyl cyclase enzyme.
3. Adenylyl cyclase converts ATP into the second messenger cAMP.
4. cAMP activates a protein, kinase.
5. Kinase causes a potassium channel to close by attaching a phosphate group to it. This produces little change in membrane potential but increases the membrane resistance and increases the length constant of dendrites. This enhances the response that a weak or a distant excitatory synapse produces. This effect can last longer than that of the presence of the transmitter.
List the criteria that are used to determine whether a chemical serves as a neurotransmitter. What are the various experimental strategies you could use to show that ACh fulfills the criteria of a neurotransmitter at the neuromuscular junction?
What are three methods that could be used to show that a neurotransmitter receptor is synthesized or localized in a particular neuron?
Compare and contrast the properties of (a) AMPA and NMDA receptors and (b) GABAA and GABAB receptors.
Are the dorsal root ganglia in the central or peripheral nervous system?
Peripheral nervous system.
1) Pointing toward the nose / back (Latin: beak)
2) Pointing toward the nose / back (Latin: beak)
3) Pointing toward the tail / back (Latin: tail)
4) Pointing toward the tail / back (Latin: tail)
1) Pointing up in mammals (Latin: "back")
2) Pointing down in mammals (Latin: "belly")
3) Invisible line running down the middle of the nervous system
4) Structures closer to midline
4) Midsagittal plane
5) Sagittal plane
6) Horizontal plane
7) Coronal plane
1) Structures farther away from the midline
2) Two structures on the same side
3) Two structures on opposite sides
4) The plane of the section resulting from splitting the plane into equal right and left halves
5) Sections parallel to the midsagittal plane
6) Anatomical plane perpendicular to the sagittal plane, and parallel to the ground
7) Anatomical plane perpendicular to the ground and the sagittal plane
1) Part of the peripheral nervous system with which the spinal cord communicates with the body
2) A branch that attaches a spinal nerve to the spinal cord
3) A branch that attaches a spinal nerve to the spinal cord
4) All parts of the nervous system other than brain and spinal cord. Divided into somatic PNS and visceral PNS.
5) All spinal nerves that innervate the skin, the joints, and the muscles under voluntary control
6) Ganglion that contains the somatic sensory cell bodies that innervate and collect somatosensory information from the skin, muscles, and joints
1) Visceral PNS
2) Autonomic nervous system (ANS)
1) Same as ANS. Consists of neurons that innervate internal organs, blood vessels, and glands. Brings information about visceral function to the CNS, such as the pressure and oxygen content of the blood in the arteries.
Commands the contraction and relaxation of muscles that form the walls of the intestines and blood vessels (smooth muscles).
2) Same as Visceral PNS (above)
3) Cranial nerve
1) Moving information toward a particular point (Latin: carry to)
2) Moving information away from a particular point (Latin: carry from)
3) 12 pairs of nerves that arise from the brain stem and innervate (mostly) the head. Some are part of CNS, some somatic PNS, some visceral PNS.
4) Three membranes covering the central nervous system so it does not touch the bone (Greek: covering). Parts: Dura mater, arachnoid membrane, pia mater.
1) Dura mater
2) Arachnoid membrane
3) Pia mater
4) Subarachnoid space
5) Ventricular system
6) Cerebrospinal fluid CSF
1) Meningeal layer. Tough, inelastic bag that surrounds the brain and spinal cord. (Latin: hard mother)
2) Meningeal layer under Dura Mater. Has appearance and consistency resembling a spinder web. Normally there is no space between the dura and the arachnoid, if blood vessels passing through the dura are ruptured, blood can collect here and form a subdural hematoma. (Greek: spider)
3) Meningeal layer that adheres closely to the surface of the brain. Along the pia run many blood vessels that ultimately dive into the substance of the underlying brain. Separated from the arachnoid by a fluid-filled space. (Latin: gentle mother)
4) Fluid-filled space that separates arachnoid membrane and pia mater. Filled with CSF.
5) The fluid-filled caverns and canals inside the brain. Contains CSF.
6) Salty clear liquid that fills the subarachnoid space and the ventricular system. Produced by a special tissue, called the choroid plexus, in the ventricles of the cerebral hemisphere. Exists ventricular system to subarachnoid space by small openings, or apertures, located near the cerebellum's attachment place to brain stem. Absorbed by the blood vessels at special structures called arachnoid villi.
What is the "Primary Vesicle", Forebrain? (Prosencephalon)
Plays a role in the formation of the neural tube in infants. The first of the three primary vesicles of the neural tube: the rostral-most vesicle.
What are the secondary vesicles:
1) Optic vesicle
2) Thalamus (diencephalon)
1) Part of the forebrain, that develops into an eye.
2) Part of the forebrain, "between brain"
3) "Endbrain", formed by the telencephalic vesicles and the diencephalon
What are these adult derivatives:
2) Optic nerve
3) Dorsal thalamus
5) Third ventricle
1) Formed from the optic vesicles -> optic cups, and part of the brain, at the back of the eye
2) Formed from the optic vesicles -> optic stalks, part of the brain
3) Upper part of thalamus (Thalamus: greek for "inner chamber")
4) Formed from the diencephalon
5) Part of the ventricular system
What are these adult derivatives:
1) Olfactory bulb
2) Cerebral cortex
3) Basal telencephalon
4) Corpus callosum
5) Cortical white matter
6) Internal capsule
1) Structure attached to the ventral surface of the cerebral hemisphere, participating in the sense of smell
2) The sheet of neurons found just under the surface of the cerebrum. Gray matter in the telencephalon.
3) Gray matter located in the telencephalon (separate from the cerebral cortex)
4) Continous with cortical white matter, forms an axonal bridge that links the cortical neurons of the two cerebral hemispheres
5) Contains all axons that run to and from the neurons in the cerebral cortex
6) Internal capsule links the cortex with the brain them, particularly the thalamus
Define the primary vesicle
1)a Midbrain (mesencephalon),
And the adult derivatives:
3) Cerebral aqueduct
1a) Midbrain is one of the 3 primary brain vesicles, that differentiates into the tectum and tegmentum
1b) Derived from the dorsal surface of the mesencephalic vesicle (Latin for "roof")
2) Floor of the midbrain
3) CSF-filled space in between the tegmentum and tectum
Define the primary vesicle
1a) Hindbrain (rhombencephalon)
And the adult derivatives
3) Fourth ventricle
1a) The back of the brain, that differentiates into cerebellum, pons, and medulla oblongata (or just medulla)
1b) Part of the brain largely responsible for coordinating movement, derived from rostral hindbrain
2) Structure of the brain differentiated form the rostral hindbrain (metencephalon)
3) CSF-filled space at the core of the hindbrain
4) Medulla oblongata, derived from the caudal half (myelencephalon)
Name eight structures in the eye that light passes through before it strikes the photoreceptors.
2) Aqueous humor
4) Zonule fibers
5) Vitreous humor
6) Ganglion cell layer
7) Inner plexiform layer
8) Outer plexiform layer
9) Inner nuclear layer
How does the membrane potential change in response to a spot of light in the receptive field center of a photoreceptor? Of an ON-center bipolar cell? Of an OFF-center ganglion cell? Why?
Photoreceptors hyperpolarize in response to light. As a result, they release less neurotransmitters at the photoreceptor/bipolar cell synapse. ON-center bipolar cells depolarize in response to light in the receptive field center. This is their response to lessglutamate release at the photoreceptor/bipolar cell synapse. ON-center ganglion cells depolarize in response to light in the receptive field center. These ganglion cells receive direct input from ON-center bipolar cells.
Following a bicycle accident, you are disturbed to find that you cannot see anything in your left visual field. Where has the retinofugal pathway been damaged?
The right optic tract. This is where information from the left visual field converges and is sent to the brain.
What is the source of most input to the left LGN?
Right nasal retina and left temporal retina
List the chain of connections that link a cone in the retina to a blob cell in the striate cortex. Is there more than one path by which cones connect to the blob cell?
1) Parvo-interblob pathway:
-P-type ganglion cells
-Layer IVC-beta in V1
2) Blob pathway:
-nonM-nonP ganglion cells
-Blob in V1
3) Magnocellular pathway (motion)
-M-type ganglion cells
-Layer IVC-alpha in V1
What is meant by the statement that there is a map of the visual world in the striate cortex?
What is parallel processing in the visual system? Give two examples.
Different visual attributes are processed simultaneously using distinct pathways. E.g., viewing the world with two eyes, and independent streams of information about light and dark from ON and OFF-center ganglion cells in each retina. Finally, ganglion cells of both ON and OFF varieties have different types of receptive fields and response properties: M cells can detect subtle contrasts, P cells can see fine detail, P and nonM-nonP cells process red-green and blue-yellow information.
How is the conduction of sound to the cochlea facilitated by the ossicles of the middle ear?
Sound waves move the tympanic membrane, which is at the entrance to the middle ear, at the end of the auditory canal. The tympanic membrane is connected to the 3 ossicles in the middle ear, and two tiny muscles attach to the ossicles.
The 3 ossicles act as levers, and this increases the force on the oval window membrane by the stapes. The muscles attached to the ossicles also have a significant effect on the sound transmission, as they elicit a response called the attenuation reflex when a loud sound occurs, and this makes the sound less loud. The attenuation reflex has a delay of 50-100msec so it does not protect against sudden sounds.
The tympanic membrane movement moves the malleus, which then moves the incus, that then moves the stapes. The stapes pushes at the oval window, and its force is amplified since the area of the oval window is smaller than that of the tympanic membrane. This is required, since the cochlea is filled with fluid instead of air, and has higher inertia.
If inner hair cells are primarily responsible for hearing, what is the function of outer hair cells?
The outer hair cells amplify the sound of the inner hair cells. They amplify the movement of the basilar membrane during low-intensity sound stimuli. This action is called the cochlear amplifier.
Why doesn't unilateral damage to the inferior colliculus or MGN lead to deafness in one ear?
Because the cells in the ventral cochlear nucleus send axons that project to the superior olive on both sides of the brain stem. Each cochlear nucleus receives input from just one ear on the ipsilateral side, so only brain stem damage to the cochlear nucleus or auditory nerve can cause deafness in one ear.
What purpose is served by the encapsulations around some sensory nerve endings in the skin?
The encapsulation around the pacinian corpuscle significantly increases the adaptation speed. Without the capsule, the adaptation rate is slowed down quite a bit.
What lobe of the cortex contains the main somatic sensory areas? Where are these areas relative to the main visual and auditory areas?
The parietal lobe contains all the main somatic sensory areas.
The main visual area is in the occipital lobe, and the main auditory areas are in the superior temporal gyrus on the lateral surface of the brain.
Define, in one sentence, a motor unit. How does it differ from motor neuron pool?
A motor unit is the combination of one alpha motor neuron and the muscle fibers that it innervates. By contrast, a motor neuron pool is a collection of alpha neurons that together operate a single larger muscle.
Your doctor taps the tendon beneath your kneecap and your leg extends. What is the neural basis of this reflex? What is it called?
It is called the stretch reflex. When a weight is placed on a muscle and the muscle starts to lengthen, the muscle spindles are stretched. The stretching of the equatorial region of the spindle leads to depolarization of the Ia axon endings due to the opening of mechanosensitive ion channels. The resulting increased action potential discharge of the Ia axons synaptically depolarizes the alpha motor neurons, which respond by increasing their action potential frequency. This causes the muscle to contract, thereby shortening it.
What is the function of gamma motor neurons?
They innervate intrafusal muscle fibers when the muscle is contracted and shortened and the spindle would otherwise go slack and no longer send information about muscle length.
List the components of the lateral and ventromedial descending spinal pathways. Which type of movement does each path control?
Lateral pathways: Corticospinal tract and rubrospinal tract. Involved in voluntary movement of the distal musculature.
Corticospinal tract: Motor cortex, internal capsule, medulla, pyramidal decussation, spinal cord.
Rubrospinal tract: Right red nucleus, medulla, spinal cord.
Ventromedial pathways:Vestibulospinal tracts, tectospinal tract. Involved in the control of posture and locomotion.
Vestibulospinal tract: Vestibular nucleus, vestibulospinal tract, spinal cord.
Tectospinal tract: Superior colliculus, tectospinal tract, spinal cord.
PET scans can be used to measure blood flow in the cerebral cortex. What parts of the cortex show increased blood flow when a subject is asked to think about moving her right finger?
Area 6, supplementary motor area. If the fingers are actually moved, it would be 4, but just thinking activates 6.
Why is L-dopa used to treat Parkinson's disease? How does it act to alleviate the symptoms?
Parkinsons is caused by damage to the substantia nigra, and impaired production of dopamine. This leads to impairment of the direct motor loop. L-dopa is a dopamine antagonist, and activates the dopamine receptors, providing help with controlling the movements. This works for some time, eventually many neurons are lost and it is no longer effective. Furthermore, L-dopa has some side effects.
What do we mean by saying that the cortex develops "inside out"?
Each new wave of neural precursor cells migrates right past those in the existing cortical plate.
Subplate -> Layer VI formed -> Layer V formed -> Layers IV-I formed
Describe the three phases of pathway formation. In which phase (or phases) does neural activity play a role?
1. The growing axon / pathway selection: The growth cone (growing tip of a neuron) identifies an appropriate path for neurite elongation.
2. Axon guidance / target selection: The axon grows in the correct direction, along the correct paths, to the correct targets. It may receive guidance cues such as chemoattractants and chemorepellents, that "pull" and "push" the axons.
3. Synapse formation / address selection: When the growth cone comes in contact with its target, a synapse is formed. A filopodium extends from a dendrite seeking innervation and touches an axon that might be passing by. This interaction appears to cause a preassembled presynaptic active zone and recruitment of neurotransmitter receptors to the postsynaptic membrane. In addition, specific adhesion molecules are expressed by both membranes that glue the partners together.
Neural activity takes place during step 3.
What are three ways that Ca2+ is thought to contribute to the processes of synapse formation and rearrangement?
1) Basal lamina factors provided by the target cell stimulate Ca2+ entry into the growth cone, which triggers neurotransmitter release.
2) Ca2+ triggers changes in the cytoskeleton that cause it to assume the appearance of a presynaptic terminal.
3) Ca2+ may also play a role in synapse rearrangement.
In what brain areas have neural correlates of working memory been observed?
E:g., the prefrontal cortex and lateral intraparietal cortex LIP. Some areas in the temporal and parietal lobes are also involved in specific types of memory.
What evidence is there that declarative and nondeclarative memory use distinctly different circuits?
Many of these pieces of evidence relate to lesions.Examples:
1) Animals with hippocampus or temporal lobe lesions may be unable to form procedurial memories, but the declarative memory might be intact.
2) In H.M, the medial temporal lobe (8cm length) was bilaterally excised, and he could no longer form declarative memories. His procedural memory was intact, though.
What is the most common cellular correlate of memory formation in the cerebral cortex? What does this say about how memories are stored?
Stimulus selectivity of IT neurons: they respond with a barrage of action potentials to the presentation of some but not all stimuli. With repeated presentations of a novel set of faces, responses on the IT neuron change, and selectivity emerges. Nearby neurons in IT show similar changes, but their responses grow and diminish to different faces. Memory storage seems to be distributed.
How can LTD contribute to memory?
Long-term depression has long been hypothesized to be an important mechanism behind motor learning and memory. Cerebellar LTD is thought to lead to motor learning, and hippocampal LTD is thought to contribute to the decay of memory or spatial memory formation.
Sketch the trisynaptic circuit of the hippocampus.
How can the mechanisms of LTP serve associative memory?
LTP is strengthening of synaptic transmission, that appear to come as a consequence of strong NMDA receptor activation.
LTP can cause increase in EPSP magnitude. For example, a rat may learn to associate a place (dark side of a box) with aversive experience (a foot shock). All types of animals will learn to avoid the place they received the shock after only one trial.
What property of the NMDA receptor makes it well suited to detect coincident presynaptic and postsynaptic activity?
How could Ca2+ entering through the NMDA receptor possibly trigger both LTP and LTD in CA1 and the neocortex?
NMDA receptor can have different types of Ca2+ responses, that selectively activate different types of enzymes.
High-frequency stimulation yields LTP by causing a large elevation of Ca2+ in the postsynaptic membrane, and low-frequency stimulation yields LTD by causing a smaller elevation of Ca2+.