APK4114 Exam 1

Rods and cones

**Rods: -low spatial resolution -extremely sensitive to light **Cons -high spatial resolution -less sensitive to light -specialized for acuity and color vision

Explain the difference between action potentials (all-or-none) and synaptic potentials (graded).

*Action Potentials -same amplitude regardless of stimulus frequency and intensity (ALL or NONE) *Synaptic Potentials - amplitude does depend on the stimulus : the number of synapses activated , strength of each synapse and the amount of synaptic activity

Give examples of the two types of postsynaptic potentials (EPSP and IPSP).

*EPSP: depolarization in the membrane of a postsynaptic neuron caused by the binding of an excitatory NT from a presynaptic cell to a postsynaptic receptor - --reversal potential is greater than AP threshold *IPSP: hyperpolarization of postsynaptic membrane caused by the flow of negatively charged ions into the postsynaptic cell --reversal potential is lower than AP threshold

Compare and contrast electrical and chemical synapses. Why is the transmission faster in electrical synapses? What are other advantages of electrical synapses? What are the advantages of chemical synapses?

*Electrical Synapses -Fast signal transmission, growth + maturation. -Bidirectional communication btwn cells connected via an electrical synapse *Chemical Synapses - broad range of postsynaptic responses -Transmission is slower -more specific (neurotransmitters ) -signal can be amplified. -unidirectional through synaptic vesicles -pre and post synaptic specializations

Compare the cause and symptoms of Retinitis Pigmentosa and Macular Degeneration

*Retinitis Pigmentosa: -group of diseases that are marked by the degeneration of photoreceptors -starts with rod degeneration. -loss of night, peripheral and central vision -an effect called '' tunnel vision" *Macular Degeneration -loses some vision usually in the center of their field of vision

What is a center-surround receptive field? For an OFF-center ganglion cell, which stimulus would cause the highest rate of action potential firing?

- A center-surround receptive field is the center of a ganglion cell receptive feild is surrounded by a concentric region that, when stimulated antagonizes the response to stimulation of the receptive field center. -For an OFF-center ganglion cell, retinal ganglion cells increase their discharge rate to luminance. Off center decrements in the receptive field. Light spots on the side and dark spots (absence of light) on the center would cause the highest rate of action potential firing.

which statement(s) about EPSPs in the central nervous system is /are true?

-An IPSP can sum with suprathreshold EPSPs to prevent the postsynaptic neuron from reaching threshold.

Which cell type is thought to be responsible for the antagonistic surround of ganglion cells?

-Antagonistic surround of ganglion cells is a product of interactions in the early stages of retinal processing. A large portion of antagonism arises via lateral connections created by horizontal cells and receptor terminals. --Horizontal cells receive synaptic inputs from photoreceptor terminals

Explain the steps in phototransduction in a photoreceptor. What is the mechanism that accounts for light-induced hyperpolarization of photoreceptors?

-At rest , a rod photoreceptor contains high levels of cGMP in its outer segment. -cGMP binds to cGMP-gated cation channels , keeping them open, thus maintaining a depolarized state -When a photon is absorbed , cGMP levels decrease , cGMP dissociates from the channels and the cGMPgated channels close. -This reduces the flow of Na+ and Ca+ into the cell -K+ channels remain open in the presence of light , so positive charge flows out of the cell more rapidly than it flows in , leading to hyperpolarization

The structural brain imaging technique that relies on atoms behaving like small magnets is called

-MRI

chili peppers seem hot?

-Noxious heat and capsaicin both activate TRPV1 receptors in Ad and C fibers

Which structure(s) contribute(s) to the sensory-discriminative aspect of pain?

-Primary and secondary somatosensory cortex (SI,S11) -Ventral posterior lateral nucleus of thalamus

sensory transduction

-Specialized cells (receptors) convert energy (mechanical forces, light) into afferent sensory signals - conveys information to the brain. -Stimulus alters the permeability of ion channels in the afferent nerve, generating a receptor potential -If sufficient in magnitude, the receptor potential reaches threshold for the generation of action potentials

-What response would you expect to see when an ON-center bipolar cell is exposed to light in the center of its receptive field? -What is the major difference between ON-center and OFF-center bipolar cells that explains their opposite response to light increments?

-When an ON- center bipolar cell is exposed to light in the center of its receptive field, it will produce a burst in action potentials. - ON-center cells: increase their discharge rate to luminance increments in the receptive field. (have g-coupled metabotropic glutamate receptors and causes the cell membrane to hyperpolarize) -OFF-center cells: increase their discharge rate to luminance decrements in the receptive field. (ionotropic receptors and causes the cell membrane to depolarize)

Describe the maps of body surface in the primary somatosensory cortex (S1). Lesions in Brodmann's areas 3b and 1 would result in what kind of sensory deficits? what factors might contribute to the fact that surgical removal of S1 fails to abolish pain

-lesions in Brodmann's areas 3b and 1 would result in tactile sensation. Lesions of area 3b results in deficits in all forms of tactile sensations from cutaneous mechanoreceptors. Lesions of area 1 would result in the inability to discriminate between textures of objects. -surgical removal of S,AKA sensory discriminative, fails to abolish pain because since the anterolateral system is split into 2 projections(sensory-discriminative and affective-motivational), the affective-motivational aspect of pain responsible for "second pain" is still intact. --3b and 1: cutaneous --3a: proprioception --2: both

List the steps involved in chemical neurotransmission, beginning with the arrival of action potential to the presynaptic terminal and ending with the release of neurotransmitters. List the sequence of steps involved in postsynaptic signaling, beginning with neurotransmitter release to postsynaptic potential changes.

-pre 1.Action Potential in the presynaptic cell causes voltage-gated Ca+ channels to open -pre 2. Influx of Ca+ (necessary + sufficient) into the neurotransmitter, which is stored in synaptic vesicles , to be released across synaptic cleft. -post 3.Neurotransmitter diffuses across the synaptic cleft & binds to receptors on the postsynaptic membrane. -post 4. produces a change in membrane potential on the postsynaptic cell .

Which statement(s) about the primary somatosensory cortex(S1) is/ are true?

-somatosensory cortex reorganization after limb amputation contributes to phantom limb sensation -Requiring a monkey to repeatedly use a digit (finger) can alter the monkey's cortical representation of that finger.

Muscle spindles

-specialized to signal muscle length -High density of spindles in eye, neck and hand muscles -type II afferents: slowly adapting response(sustained) -Type Ia afferent: rapidly adapting response

The CNS comprises

-the brain -spinal cord

EPSP VS IPSP

EPSP=cause increase in likelihood of postsynaptic action potential IPSP=they decrease this likelihood

Which afferent fibers conduct pain and temperature information?

A and C fibers

What determines whether the postsynaptic cell fires an action potential?

A postsynaptic neuron adds together, or integrates , all of the excitatory and inhibitory inputs it receives and "decides" whether to fire an AP

Provide examples of abnormal transmission at neuromuscular synapses. How does acetylcholinesterase inhibitors (such as neostigmine) help alleviate the symptoms of myasthenia gravis?

Abnormal Transmission= Myasthenic Syndromes *Myasthenia Graves symptoms -weakness in eye muscles (drooping eyelids+double vision) -difficulty swallowing -slurred speech (first signs) -antibodies produced against ACh receptor -EPPs are much smaller than normal -Acetylcholinesterase Inhibitors : increase the amount of ACh available and so it helps muscle activation and contraction *NeoStigmine works by slowing the breakdown of ACh when it is released from nerve endings .This means that there is more ACh available to attach to the muscle receptors and this improves muscle strength

What prevents action potentials from going back up the axon?

Absolute refractory period : prevents backwards propagation of an action potential

Suppose you are recording a neuron's resting membrane potential. If you add KCl to the external medium, what will happen to the resting potential? Compare this to what will happen if you add the same amount of NaCl. What can be concluded from this comparison?

Adding KCl will cause the resting potential to become less negative . Adding NaCl to the external medium will have a small effect because membrane permeability to Na+ is low. We can conclude that the resting membrane potential is primarily due to/ attributable to the product of K+ permeability

What change could improve the two-point discrimination of a region of skin?

An increase in the density of innervation and reduction of the receptive field size

anterolateral systems in terms of anatomy and sensory modality. Where does each pathway decussate? Is the left side of the body represented in the right or left S1 cortex?

Anteriolateral -also called spinothalamic -pain and temperature -cross midline(decussates) in spinal cord -1st order: *cell body=dorsal ganglion *axon terminates=dorsal horn -2nd order: *cell body=dorsal horn *axon terminates= ventral posterior lateral nucleus in thalamus -3rd order: *cell body=VPL in thalamus *axon terminates= primary somatosensory cortex

What is the main cause of myasthenia gravis symptoms?

Autoimmune reaction against acetylcholine receptors

Which feature of an electrical synapse allows synchronizing the electrical activity of multiple neurons?

Bidirectional transmission of electrical signals

which structure can be found exclusively at an electrical synapse?

Connexon

A person with dichromatic vision would have the most trouble with which task?

Determining when a red light turns green

Dorsal column-medial lemniscal Where does each pathway decussate? Is the left side of the body represented in the right or left S1 cortex?

Dorsal column-medial -Touch +proprioception through mechanosensory receptors -cross midline at medial lemniscus(decussates) -1st order: *cell body=dorsal root ganglion axon terminates --upper body =cuneate nucleus --lower body=gracile nucleus -2nd order: *cell body= cuneate/gracile nucleus *axon terminates= VPL in thalamus -3rd order: *cell body= VPL in thalamus *axon terminates= primary soimatosensory cortex --Upper body= lsteral cortex --lower body= medial cortex

At which point during signal transmission at a chemical synapse is exocytosis occurring?

During neurotransmitter release into the synaptic cleft.

What is the role of interneurons in the knee-jerk reflex?

Interneurons are in charge of relaxation of the flexor muscles

What factors might contribute to the fact that surgical removal of S1 fails to abolish pain?

Multiple regions of the CNS , in addition to SI, are involved in the processing of nociceptive information

Which fibers conduct the sensation of first pain?

Myelinated Aδ

A rise in presynaptic Ca2+ is ________ and ________ for neurotransmitter release.

Necessary and sufficient

What is the magnitude of a typical neuron's resting membrane potential? Why do neurons and other cells have a negative resting membrane potential?

Neurons have a negative resting membrane potential . (approx - 65mV). It is negative because resting membrane is permeable mainly to K+ and there is a concentration gradient for K+ across the plasma membrane with roughly a 13-fold excess of K+ inside the cell

Describe the specialized features that distinguish neurons from other types of cells

Neurons have axons and dendrites , structures for maintaining and transmitting electrical potential , and synapses, all of which allow neurons to establish connections and share info .

What are some differences between photoreceptors and other sensory cells?

Photoreceptors exhibit a graded change in membrane potential in response to light instead of action potential . They also maintain a resting membrane potential around - 40mV and they hyperpolarize in the presence of light

Suppose you are recording action potentials from a neuron. How will the action potential be affected if you remove: a) Na+ , or b) K+ from the external medium?

a) Na+: It will be suppressed ; the rising phase will not occur b) K+ : It will be more difficult to trigger b/c resting potential becomes more neg.

A rise in presynaptic Ca2+ is necessary and sufficient for neurotransmitter release. Which experimental evidence a) supports the claim that Ca2+ is necessary, and b) supports the claim that Ca2+ is sufficient?

a) Presynaptic microinjection of Ca+ Chelators prevents presynaptic Action Potentials from causing Neurotransmitter secretion b) microinjection of Ca+ into presynaptic terminals triggers Neurotransmitter release even in the absence of presynaptic Action Potentials

Which statement best describes the action potential

an action potential occurs when the cell's membrane potential reaches a threshold

The resting potential of a cell is negative because

at rest there is an excess of k+ inside the cell, an the membrane is selectively permeable to K+

Studies of the iconic basis of the action potential in squid giant axon found that.

decreasing sodium outside the cell decreases the size of the action potential.

Hyperpolarization occurs when the membrane potential becomes more positive.

false

Stimulus strength is encoded by the________ of graded potentials. Stimulus strength is encoded by the_________ of action potentials.

frequency, magnitude

Nodes of Ranvier

gaps in the myelination of axons where action potentials are generated

Rods and cones are the photoreceptors of the eye. The rods are:

highly sensitive to light

Light

hyperpolarizes

Structure ______ is the main target for incoming signals received from the axons of other cells.

image

In the sequence of events in neurotransmission at a chemical synapse, which event occurs just after the action potential arrives at the presynaptic terminal?

influx of Ca 2+ into the presynaptic terminal

A patient presents with a wound that has caused left hemisection of the spinal cord at T10. Which sensory loss would you expect to find?

ipsilateral loss of touch and propioception below the level of the lesion; contralateral loss of pain and temperature below the level of the lesion.

what is the action of the neurotransmitter at a chemical synapse?

it acts on receptors in the postsynaptic membrane

which statement best describes the function of neuron with multiple, highly branched dendrites and the one axon?

it integrates information from many neurons

Oligodendrocytes

myelinate axons in the brain and spinal cord (CNS)

Schwann cells

myelinate axons in the periphery of the body (PNS)

Subthreshold current injected into an axon flows______ along the axon and ________with distance from the site of injection

passively; decays

In the phase labeled D (going down,repolarization) ______ ions are moving_______ the cell.

potassium; out of

A neuron that innervates(i.e. makes synaptic contact with) a large number of other neurons

represents divergent neural signaling

If the ______for postsynaptic potentials is more positive than the ______, the effect of a neurotransmitter is excitatory, and it generates EPSPs.

reversal potential; action potential threshold

Which statement about ionic distributions in nerve cells is true?

sodium is higher outside than inside cells

In the phase labeled B (rising trend depolarization ),_______ ions are moving______ the cell.

sodium; into

GTO (golgi tendon organ) receptos

specialized to signal muscle tension

The axons of the medial lemniscus synapse with neurons of the

thalamus

How does the resting membrane potential of typical neuron compare to the equilibrium potential (calculated by the Nernst equation) for potassium?

the resting membrane potential is not exactly equal to the equilibrium potential for potassium because the membrane has some resting permeability to ions other than potassium.

Experiments using vibrators to stimulate muscle leads to the illusion that the elbow is moving to an extended position.

true

The neuron doctrine of Cajal and Sherrington argued that nerve cells are separate entities.

true

Action potential

1)•Initiated when the membrane reaches a certain threshold (-50 mV) 2)•All-of-none event (size and shape does not change) 3)•Frequency of signal (firing rate) determines signal intensity 4)•Signal is kept constant over long distances

Which technique first produced unequivocal support for the neuron doctrine of the nervous system (as opposed to the reticular theory)?

Electron microscopy of nervous tissue

Which technique is first produced unequivocal support for the neuron doctrine of the nervous system (as opposed to the Reticular theory)?

Electron microscopy of nervous tissue

Axons are good conductors of action potentials.

False

Passive potentials maintain the same amplitude as they travel along an axon

False

Hyperpolarization of an off-center bipolar cell would indicate:

Hyperpolarization of the center cone and a bright center display

The fastest conducting of the following sensory fibers is the

Ia sensory afferents

During the knee jerk reflex, the role of the spinal interneuron is to______ the ______ muscle, allowing the leg to_______.

Inhibit; flexor; extend

What is an important difference between the Meissner and Pacinian receptor

Meissner receptors have small receptive fields and pacinian have large receptive fields. -pacinian is rapid and ruffini and merkel are slow

Which touch receptor has both a small receptive field and is slowly adapting?

Merkel

Do we have more rods or cones in the (i) retina and (ii) fovea?

More rods (90 million) than cones (4.5 million) in the retina. However, cone density increases in the fovea , with the foveola being rod - free

After entering the spinal cord, which of the following is true regarding nociceptors and mechanoreceptors coming from the hands via the dorsal root ganglia?

Nociceptors cross the midline in the spinal cord but mechanoreceptors cross the midline in the medulla

What is the major determinant of the permeability of a membrane to a specific ion?

Number of open ion channels specific for that ion

Which part of the eye results in a blind spot?

Optic disc

Due to a spinal injury, a patient has lost pain and temperature sensation on the left half of his body from the waist down. Where is his injury? Where would you expect loss of tactile sensation in this patient?

Patient sustained a spinal cord injury at a lower thoracic level on the right side of his body. Tactile sensation will be lost on the right half of his body from waist down.

Explain the regenerative property of the action potential. Provide an analogy to illustrate how action potentials are generate and actively propagated down an axon.

Regenerative Property : During the AP , an active inward current produced by depolarization spreads passively inside the axon and depolarizes an adjacent membrane region. This results in generation of another AP in this adjacent region, and the cycle repeats. *Analogy : A toilet flushing (all or nothing)

What's the reason that rods do not contribute to photopic vision?

Rods don't contribute to photopic vision b/c their response is saturated

Which cell produces myelin in the nerves of the peripheral nervous system?

Schwann cell

Which sensation would an individual with anesthetized C fibers report when exposed to intense heat?

Sharp pain only

How is stimulus strength encoded by graded potentials? How is stimulus strength encoded by action potentials?

Stimulus strength *Graded Potentials : by amplitude *Action Potentials : in frequency

Give examples of structural and functional analysis of neural systems

Structural -White matter + gray matter -MRI-causes atoms to emit energy -CT scan -DT l (type of MRI) Functional - action potentials -fMRI (tracks 02 levels) ↳ doesn't have good temporal resolution -EEG -MEG-has better spatial property

What causes spontaneous miniature end plate potentials (MEPPs) in the absence of presynaptic stimulation? -What evidence indicates that EPPs are composed of MEPPs? If the distribution of EPP amplitudes has peaks at 0.4 mV, 0.8 mV, 1.2 mV, 1.6 mV, and 2.0 mV, what is the most likely amplitude of the MEPP?

Synchronous release of large numbers of ACh molecules, with roughly the same number being released for each MEPP. -Evidence: The amplitude of the smallest EPPs is similar in size to that of a single MEPP, and increments in the EPP response occur in units about the size of single MEPP. - 0.4mV is the most likely amplitude

What is a somatosensory receptive field?

The surface area over which stimulation results in a significant change in the rate of action potentials of a particular neuron

Golgi believed that:

There is one continuous neuronal cell in the body

On which body part would the two-point discrimination threshold be shortest?

Thumb

What are the main types of glial cells, and what is the main function of each?

a - Astrocytes : maintain an optimal environment for neural signaling b - Microglia : respond to injury within the nervous system C-Oligodendrocytes /Schwann cells: produce myelin in the CNS t PNS

What is the evidence that nociception is mediated by specific nociceptors rather than by strong stimulation of somatosensory receptors or non-nociceptive thermoreceptors?

Transcutaneous nerve recording experiments have revealed that nociceptors and thermo receptors respond differently to the same stimulus. -Thermoreceptors reach their maximum firing rate at a temperature below the pain threshold and maintain that rate even at increasing levels of heat stimulation, whereas nociceptive thermoreceptors begin firing at a higher stimulus intensity and increase their firing rate as the stimulus intensity increases.

which function is a characteristic primarily of neurons only, and not glia

Transmits action potentials

Which tract does facial nerve feedback travel through?

Trigeminal

Applying a negative current will hyperpolarize a neuron.

True

Glia are at least as numerous as neurons in the brain.

True

Miniature end plate potentials (MEPPs) are produced by spontaneous release of neurotransmitters

True

Receptive field size is larger for somatic sensors that are deeper in the skin.

True

When a cone is hyperpolarized, the on-center receptors depolarize and the off-center receptors hyperpolarize.

True

How does variations in the size of afferent receptive fields affect somatic acuity (e.g., twopoint discrimination threshold).

Variations in the average size of afferent receptive fields influence density of fibers . Somatic acuity is much higher in fingers, toes + face

When light stimulates the photoreceptors of the retina, the membrane voltage becomes:

both a and c hyperpolarized more negative

Efferent neurons

carry information away from brain or spinal cord.

Afferent neurons

carry information toward brain or spinal cord.

What do nociceptor neurons and non-nociceptor mechanoreceptor neurons have in common?

cell bodies located in the dorsal root ganglia