chapter 5 BB

autoreceptor

"self-receptor" in a neural membrane that responds to the transmitter released by the neuron

Cholinergic system

1. active in maintaining attention and waking EEG pattern 2. thought to play a role in memory by maintaining neuron excitability 3. death of cholinergic neurons and decrease in ACh in the neocortex are thought to be related to Alzheimer's disease. acetylcholinesterase (AChE) , the enzyme that breaks down ACh , is located throughout the cortex and is especially dense in the basil ganglia. Many of these ACh synapses are connections from ACh nuclei in the brainstem this system plays a role in normal waking behavior and is thought to function in attention and memory This system is also thought to be one of several things that are associated with Alzheimer's disease.

noradrenergic system

1. active in maintaining emotional tone 2. decreases in NE activity are thought to be related to depression. 3. increases in NE are thought to be related to mania (overexcited behavior) 4. Decreased NE activity associated with hyperactivity and ADD/ADHD

serotonergic system

1. active in maintaining waking EEG pattern 2. Changes in serotonin activity are related to OCD, tics and schizophrenia 3. decreases in serotonin activity related to depression 4. abnormalities in brainstem 5-HT neurons are linked to disorders such as sleep apnea and SIDS

Four criteria for identifying neurotransmitters

1. the chemical must be synthesized in the neuron or otherwise be present in it. 2. when the neuron is active, the chemical must be released and produce a response in some target. 3. the same response must be obtained when the chemical is experimentally placed on the target 4. A mechanism must exist for removing the chemical from its site of action after its work is done Identifying neurotransmitters difficult because In the brain and spinal cord, thousands of synapses are packed around a single neuron making it hard to have access to a single synapse. A chemical that has not yet been shown to meet all the criteria is called a putative transmitter. Staining, stimulating and collecting are used to identify substances thought to be CNS neurotransmitters. Researchers trying to identify new CNS neurotransmitters can use microelectrodes to stimulate and record from single neurons. A glass microelectrode is small enough to be placed on specific targets on neurons . It can be filled with a chemical of interest and, when a current is passed through the electrode, the chemical can be ejected into or onto the neuron to mimic the release of a neurotransmitter onto the cell. Renshaw loop today, the term neurotransmitter applies to chemicals that: (a) carry a message from one neuron to another by influencing the voltage on the postsynaptic membrane. (b) have little effect on membrane voltage but rather have a common message - carrying function, such as changing the structure of a synapse. (c) communicat not only by delivering a message from the presynaptic to the postsynaptic membrane but by sending messages in the opposite direction as well. These reverse-direction messages influence the release or reuptake of transmitter gases.

dopamine (DA)

Amine neurotransmitter that plays a role in coordinating movement, in attention and learning, and in behaviors that are reinforcing linked to motor behavior, some forms of learning and to neural structures that mediate reward and addiction. Parkinson's disease loss of dopamine neurons linked to an array of causes including: genetic predisposition, the flu, pollution, insecticides and herbicides, and toxic drugs.

serotonin (5-HT)

Amine neurotransmitter that plays a role in regulating mood and aggression, appetite and arousal, the perception of pain and respiration derived from the amino acid tryptophan (found in turkey, milk, bananas )

Glutamate (Glu)

Amino acid neurotransmiter that exctes neurons

gamma-aminobutyric acid (GABA)

Amino acid neurotransmitter that inhibits neurons

quantum (pl. quanta)

Amount of neurotransmitter, equivalent to the contents of a single synaptic vesicle, that produces a just observable change in postsynaptic electric potential

Alzheimer's disease

Degenerative brain disorder related to aging that first appears as progressive memory loss and later develops into generalized dementia show a loss of cholinergic neurons at autopsy. autopsies also reveal extensive damage to the neocortex and other brain regions. not clear what cholinergic neurons have to do with the disease, not clear whether death of cholingeric neurons cause neocortex damage or the other way around.

Hebb synapse

Donald O. Hebb (1949). he theorized "When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased". A synapse that physically adapts adapts in this way is called this.

ionotropic receptor

Embedded membrane protein that acts as (1) a binding site for a neurotransmitter and (2) a pore that regulates ion flow to directly and rapidly change membrane voltage. allow the movement of ions such as Na+, K+ and Ca2+ across a membrane. Has two parts: (1) binding site for a neurotransmitter (2) a pore or a channel. When the neurotransmitter attaches to the binding site, the receptor changes shape, either opening or closing the pore and brings about rapid changes in membrane voltage. These receptors are usually excitatory and trigger an action potential.

acetylcholine (ACh)

First neurotransmitter discovered in the peripheral and central nervous systems; activates skeletal muscles in the somatic nervous system and may either excite or inhibit internal organs in the autonomic system

nitric oxide (NO)

Gas that acts as a chemical neurotransmitter- for example, to dilate blood vessels, aid digestion, and activate cellular metabolism

Amino Acid synthesis

Glu and GABA are closely related. Glu has an extra carboxyl (COOH) group . in the forebrain and cerebellum Glu is excitatory, GABA is inhibitory. Glu is widely distributed in CNS neurons, but becomes a neurotransmitter only if it is appropriately packaged in vesicles in the axon terminal. Gly is much more common inhibitory transmitter in the brainstem and spinal cord, where it acts within the renshaw loop.

G protein

Guanyl - nucleotide - binding protein coupled to a metabotropic receptor that, when activated, binds to other proteins consists of three pieces: alpha beta and gamma.

norepinephrine (Ep, or nonadrenaline)

Neurotransmitter found in the brain and in the sympathetic division of the autonomic nervous system; accelerates heart rate in mammals chemical closely related to EP

Histamine (H)

Neurotransmitter that controls arousal and waking; can cause the constriction of smooth muscles and so when activated in allergic reactions, contributes to asthma, a constriction of the airways

Excitatory and Inhibitory messages

Neurotransmitters act in only one of two ways : it influences transmembrane ion flow either to increase or to decrease the probability that the cell with which it comes in contact will produce an action potential as in they are either excitatory or inhibitory. Type I synapses are excitatory in their actions. - typically located on the shafts or the spines of dendrites. Have round synaptic vesicles. The material on the presynaptic and postsynaptic membranes is denser than in type II synapses. The active zone is larger than type II synapses. The dendritic tree is excitatory. (Glu is neurotransmitter) Type II synapses are inhibitory. - typically located on the cell body. Have synapses that are flattened. The material on the presynaptic and postsynaptic membrane is less dense than in type I synapses. The active zone is larger than type I synapses. The cell body is inhibitory. (GABA is neurotransmitter)

transmitter-activated receptor

Protein that has a binding site for a specific neurotransmitter and is embedded in the membrane of a cell

small-molecule transmitter

Quick-acting neurotransmitter synthesized in the axon terminal from products derived from the diet includes ACh, H, 4 amines and 3 amino acids

Acetylcholine synthesis and breakdown

The molecule made up of two substances, choline and acetate. Choline is among the breakdown products of fats in foods such as egg yolk, salmon and olive oil. Acetate is a compound found in acidic foods such as vinegar and lemon juice. synthesis: happens inside the presynaptic membrane where Acetyl CoA carries acetate to synthesis site, ChAT takes acetate and attaches to choline to create ACh breakdown: after ACh has been released into the synaptic cleft and diffuses to receptor sites on the postsynaptic membrane, and a third enzyme acetylcholinesterase (AChE), reverses the synthesis process by removing the acetate from the choline. The breakdown products can be taken back into the presynaptic terminal for reuse.

Amine synthesis

Tyrosine > Enzyme 1 > L-dopa > Enzyme 2 > Dopamine > Enzyme 3 > Norepinephrine > Enzyme 4 > Epinephrine Starting with the chemical tyrosine (amino acid abundant in food like hard cheese and bannanas) enzyme tyrosine hydroxylase changes tyrosine into L-dopa, which is sequentially converted by other enzymes into dopamine, norepinephrine, and finally epinephrine. the supply of the enzyme tyrosine hydroxylase is limited. Consequently, so is the rate at which DA, NE, and EP can be produced regardless of how much tyrosine is present or ingested. The rate-limiting factor can be bypassed by ingesting L-dopa.

Neurotranmission in 4 steps

a neurotransmitter must be... 1. synthesized and stored in the axon terminal - neurotransmitters are synthesized in two ways: (1) in the cell body according to instructions contained in the neuron's DNA, packaged in membranes on the Golgi bodies and transported on microtubules to the axon terminal. Also includes neurotransmitters made within the presynaptic terminal from mRNA transported to the terminal. (2) other neurotransmitters are synthesized in the axon terminal from building blocks derived from food. Transporters absorb the required precursor chemicals from the blood supply. (Some are already made). Mitochondria in the axon terminal provide the energy needed both to synthesize precursor chemicals into the neurotransmitter and to wrap them in membranous vesicles. Regardless of origin, neurotransmitters are usually stored in three locations: attached to microfilaments in the terminal, in storage granules, and on the presynaptic membrane. These sites represent the steps in which a transmitter is transported out of the cell. (I put them in order) 2. transported to the presynaptic membrane and released in response to an action potential - an action potential in the presynaptic membrane starts the neurotransmitter release process. The presynaptic membrane is rich in voltage sensitive calcium (Ca2+) channels and the surrounding extracellular fluid is rich in Ca2+. An action potential in the presynaptic membrane opens these Ca2+ channels allowing an influx of calcium ions into the axon terminal. The incoming Ca2+ binds to the protein calmodulin, and the resulting complex takes part in two chemical reactions: one releases vesicles bound to the presynaptic membrane and the other releases vesicles bound to microfilaments in the axon terminal. The vesicles on the presynaptic membrane release their contents through exocytosis into the synaptic cleft. Other vesicles move up to replace. 3. able to activate the receptors on the target-cell membrane located on the postsynaptic membrane - After the neurotransmitter has been released from vesicles on the presynaptic cleft and binds to specialized protein molecules called transmitter - activated receptors that are embedded in the postsynaptic membrane. Through the receptors, the postsynaptic cell may be affected in one of 3 ways depending on the neurotransmitters and the receptors of postsynaptic membrane. (a) depolarize the postsynaptic membrane and so have an excitatory action on the postsynaptic neuron (b) hyperpolarize the postsynaptic membrane and so have an inhibitory action on the postsynaptic neuron (c) initiate other chemical reactions that modulate either effect, inhibitory or excitatory, or that influence other functions of the receiving neuron. Neurotransmitters also interact with postsynaptic membrane receptors called autoreceptors. The smallest amount of neurotransmitters required to cause the postsynaptic electrical potential to change is equal to the contents of one vesicle called quantum. The number of quanta released from the presynaptic membrane in response to a single action potential depends on two factors: (1) amount of Ca2+ influx (2) the number of vesicles docked at the membrane waiting to be released. 4. inactivated, or it will continue to work indefinitely - Deactivation is accomplished in atleast 4 ways: (a) diffusion - diffuses away from the synaptic cleft and is no longer available to bind to receptors. (b) degradation by enzymes in the synaptic cleft (c) reuptake - membrane transporter proteins specific to that transmitter may bring the transmitter back into the presynaptic axon terminal for subsequent reuse. The by-products of degradation by enzymes also may be taken back into the terminal to be used again in the cell. (d) glial uptake: some neurotransmitters are taken up by neighboring glial cells. Potentially the glial cells can also store transmitters for re-export to the axon terminal. As part of the flexibility of synaptic function, an axon terminal has chemical mechanisms that enable it to respond to the frequency of its own use. If the terminal is very active the amount of neurotransmitter made and stored there increases. If the terminal is not often used, enzymes located within the terminal may break down excess transmitter. by products reused or expelled. axon terminals may even send messages to the neuron's cell body requesting for supplies.

small - molecule transmitters include _______________, _______________, _______________, and _______________. Amines include _______________, _______________, _______________, and _______________. Amino acids include _______________, _______________, and _______________.

acetylcholine (ACh), Histamine (H), Amines, Amino acids Dopamine (DA), Norepinephrine (NE or noradrenaline NA), Epinephrine (EP or adrenaline) serotonin (5-HT). Gluatamate (Glu), Gamma- aminobutyric acid (GABA), Glycine (Gly)

In the PNS, the neurotransmitter at somatic muscles is _____________; in the autonomic nervous system, _____________ neurons from the spinal cord connect to _____________ neurons for parasympathetic activity and with _____________ neurons for sympathetic activity.

acetylcholine; acetylcholine; acetylcholine; norepinephrine

contrast the major characteristics of ionotropic and metabotropic receptors

an ionotropic receptor contains a pore or channel that can be opened or closed to regulate the flow-through of ions, directly bringing about rapid and usually excitatory voltage changes on the cell membrane. Metabotropic receptors are generally inhibitory, are slow acting, and activate second messengers to indirectly produce changes in the function and structure of the cell

rate-limiting factor

any enzyme that is in limited supply, thus restricting the pace at which a chemical can be synthesized

Eric Kandel

awarded Nobel prize in 2000 for his descriptions of the synaptic basis of learning in a way that Hebb envisaged: learning in which the conjoint activity of nerve cells serves to link them. He and his coworkers were able to produce enduring changes in a marine snail (aplysia californica) by stroking or shocking the snails appendages. they used these behavioral response to study underlying changes in the snails nervous system. two kinds of learning that he studied: habituation and sensitization. For humans both are considered unconscious because they do not depend on a person's knowing precisely when and how they occur.

The nervous system has evolved a variety of synapses; ____________ b/w axon terminals and dendrites, ____________ b/w axon terminals and cell bodies, ____________ b/w axon terminals and muscles, ____________ b/w axon terminals and other axons, ____________ b/w axon terminals and other synapses. A(n) ___________ synapse releases chemical transmitters into extracellular fluid, a(n) _____________ synapse releases transmitter into the bloodstream as hormones, and still another, the ______________ synapse, connects dendrites to other dendrites

axodendritic; axosomatic; axomuscular; axoaxonic; axosynaptic; axoextracellular ; axosecretory; dendrodendritic

obsessive-compulsive disorder (OCD)

behaivor disorder characterized by compulsively repeated acts (such as hand washing) and repetitive, often unpleasant, thoughts (obsessions)

schizophrenia

behavioral disorder characterized by delusions, hallucinations, disorganized speech, blunted emotion, agitation or immobility, and a host of associated symptoms increases in DA activity may be related to this changes in serotonin activity are related to this

epinephrine (EP, or adrenaline)

chemical messanger that acts as a hormone to mobilize the body for fight or flight during times of stress and as a neurotransmitter in the central nervous system produced by the adrenal glands located atop the kidneys Loewi identified the chemical that carries the message to speed up heart rate in frogs

neurotransmitter

chemical released by a neuron onto a target with an excitatory or inhibitory effect messenger chemicals released by a neuron onto a target to cause an excitatory or inhibitory effect outside the CNS many of the same chemicals including EP circulate in the bloodstream as hormones. Under the control of the hypothalamus, the pituitary gland directs hormones to excite or inhibit targets such as organs and glands in the autonomic nervous system. because hormones travel through the blood stream to distant targets, their action is slower than that of CNS neurotransmitters prodded by the lightning - quick nerve impulse.

in mammals the principal form of communication between neurons occurs via ________________ even though this structure is slower and more complex than the fused _____________.

chemical synapse; gap junction

second messenger

chemical that carries a message to initiate a biochemical process when activated by a neurotransmitter (the first messenger)

what are the names of the four activating system in the CNS?

cholinergic system dopaminergic system noradrenergic system serotonergic system

the four main activating systems of the brain are _____________, _____________, _____________,and _____________.

cholinergic, dopaminergic, noradrenergic, serotonergic

reuptake

deactivation of a neurotransmitter when membran transporter proteins bring the transmitter back into the presynaptic axon terminal for subsequent reuse

excitatory synapses, known as type 1 are usually located on a(n) ______________, whereas inhibitory synapses, known as type 2, are usually located on a(n) ______________.

dendrite; cell body

varieties of synapses

dendrodendritic - dendrites send messages to other dendrites axodendritic - axon terminal of one neuron synapses on dendritic spine of another axoextracellular - terminal with no specific target. Secretes transmitter into extracellular fluid axosomatic - axon terminal ends on cell body axosynaptic - axon terminal ends on another terminal - can provide exquisite control over another neuron's input to a cell. axoaxonic - axon terminal ends on another axon axosecretory - Axon terminal ends on tiny blood vessel and secretes transmitter directly into blood. axomuscular - axon synapses with a muscle end plate, releasing acetylcholine gap junctions further increase the diversity of signaling between one part of a neuron and another part of the same neuron.

parkinson's disease

disorder of the motor system correlated with a loss of dopamine in the brain and characterized by tremors, muscular rigidity, and reduction in voluntary movement 1817 essay written by James Parkinson, a british physician, reported similar symptoms in six patients. Shaking was the first symptom, first starting in the hands and increasing to the arm and other parts of the body. As it progresses, patients tend to lean forward and walk on the balls of the feet and tended to run forward to prevent themselves from falling. Further, patients had difficulty eating and swallowing. They drooled and their bowel movements slowed. Eventually patients lost all muscular control and were unable to sleep because of the disruptive tremors. 50 years later the disease was officially named by Jean-Martin Charcot. three findings have helped researchers understand its neural basis: 1. 1919 Constantin Treatikoff - autopsy of patients with this condition revealed that the substantia nigra, a small nucleus in the mid-brain, had degenerated. In the brain of one patient who had experienced symptoms on one side of the body only, the substantia nigra had degenerated on the side opposite that of the symptoms. 2. chemical examination of the brains of Parkinson patients showed that symptoms of the disease appear when the level of dopamine was reduced to less than 10 percent of normal in the basal ganglia. 3. confirming the role of dopamine in a neural pathway connecting the substantia nigra to the basal ganglia, Urban Ungerstedt found in 1971 that injecting a neurotoxin called 6-hydroxydopamine into rats selectively destroyed these dopamine-containing neurons and produced the symptoms of this disease.

mania

disordered mental state of extreme excitement may be related to increase in activity of noradrenergic neurons

metabotropic receptor

embedded membrane protein, with a binding site for a neurotransmitter but no pore, linked to a G protein that can affect other receptors or act with second messengers to affect other cellular processes. has binding sites but lacks its own pore. Through a series of steps, activated metabotropic receptors indirectly produces changes in: (a) nearby ion channels - transmitter binds to receptor in both reactions. The binding of the transmitter triggers the activation of a G protein. The alpha subunit of G protein binds to a channel, causing a structural change in the channel that allows ions to pass through it. Influences membranes electrical potential. (b) cells metabolic activity- transmitter binds to receptor in both reactions. The binding of the transmitter triggers the activation of a G protein. The subunit alpha binds to an enzyme, which activates a second messenger that can activate other cell processes like (1) bind to a membrane channel. causing the channel to change its structure and thus alter ion flow through the membrane. (2) initiate a reaction that causes protein molecules within the cell to become incorporated into the cell membrane, for example, resulting in the formation of new ion channels. (3) instruct the cell's DNA to initiate or cease the production of a protein. in addition, these receptors allow for the possibility that a single neurotransmitter's binding to a receptor can activate an escalating sequence of events called an amplification cascade which causes many downstream proteins to be activated or inactivated.

noradrenergic neuron

from adrenaline. Latin for "epinephrine"; a neuron containing norepinephrine

gap junction (electrical synapse)

fused prejunction and postjunction cell membrane in which connected ion channels form a pore that allows ions to pass directly from one neuron to the next prejunction and postjunction cell membranes are fused. Ion channels in one cell membrane connect to ion channels in the other membrane, forming a pore that allows ions to pass directly from one neuron to the next. This eliminates the brief 5 millisecond delay of chemical synapses. Found in mammalian brain, and in some regions allow groups of interneurons to synchronize their firing rhythmically. allow glial cells and neurons to exchange substances

synaptic cleft

gap that separates the presynaptic membrane from the postsynaptic membrane the axon terminal and the dendrite are separated by this small space which is central to synapse function because neurotransmitter chemicals must bridge this gap to carry a message from one neuron to the next

carbon monoxide (CO)

gas that acts as a neurotransmitter in the activation of cellular metabolism

Aplysia's synaptic function mediates two basic forms of learning: _____________ and _____________.

habituation, sensitization

peptide transmitters

includes: Opioids, Neurohypophyseals, Secretins, Insulins, Gastrins, Somatostatins, Corticosteroids aka neuropeptides, more than 50 amino acid chains of various lengths make up a neuropeptide. Synthesized through the translation of mRNA from instructions contained in the neuron's DNA. Some can be made at the axon terminal, but most is assembled in the neuron's ribosomes, packaged by the Golgi bodies and transported by the microtubules to the axon terminals. This process is slow compared to small molecule neurotransmitters and therefore act slowly and are not replaced quickly. neuropeptides perform an enormous range of functions in the nervous system: hormones that respond to stress, enable a mother to bond with her infant, regulate eating and drinking and pleasure and pain and probably learning. met-encephalin, leu-enkephalin, and beta-endorphin are naturally occurring opioids. one or two may take part in pain management. Appear in a number of locations and perform a variety of functions in the brain including the inducement of nausea. some neuropeptides take part in specific behaviors, each month or year. neuropeptides do not bind to ion channels, so they have no direct effects on the voltage of the postsynaptic membrane. Instead, peptide transmitters activate synaptic receptors that indirectly influence cell structure and function. peptides are amino acids chains that are degraded by digestive processes. They generally cannot be taken orally as drugs.

the sensitization response is amplified by _____________ that release serotonin onto the presynaptic membrane of the sensory neuron, changing the sensitivity of presynaptic _____________ channels and increasing the influx of _____________.

interneurons; potassium; calcium ions, or Ca2+

two classes of receptors

ionotropic receptors - allow the movement of ions such as Na+, K+ and Ca2+ across a membrane. Has two parts: (1) binding site for a neurotransmitter (2) a pore or a channel. When the neurotransmitter attaches to the binding site, the receptor changes shape, either opening or closing the pore and brings about rapid changes in membrane voltage. These receptors are usually excitatory and trigger an action potential. metabotropic receptor - has binding sites but lacks its own pore. Through a series of steps, activated metabotropic receptors indirectly produces changes in: (a) nearby ion channels - transmitter binds to receptor in both reactions. The binding of the transmitter triggers the activation of a G protein. The alpha subunit of G protein binds to a channel, causing a structural change in the channel that allows ions to pass through it. Influences membranes electrical potential. (b) cells metabolic activity- transmitter binds to receptor in both reactions. The binding of the transmitter triggers the activation of a G protein. The subunit alpha binds to an enzyme, which activates a second messenger that can activate other cell processes like (1) bind to a membrane channel. causing the channel to change its structure and thus alter ion flow through the membrane. (2) initiate a reaction that causes protein molecules within the cell to become incorporated into the cell membrane, for example, resulting in the formation of new ion channels. (3) instruct the cell's DNA to initiate or cease the production of a protein. in addition, these receptors allow for the possibility that a single neurotransmitter's binding to a receptor can activate an escalating sequence of events called an amplification cascade which causes many downstream proteins to be activated or inactivated.

synaptic vesicle

irganelle consisting of a membrane structure that encloses a quantum of neurotransmitter in the axon terminal, round granular substances

chemical synapse

junction at which messenger molecules are released when stimulated by an action potential a synapse consists of an axon terminal, the synaptic cleft and dendritic spine. Presynaptic membrane forms the axon terminal and postsynaptic membrane forms the dendritic spine. Within the axon terminal: mitochondria, storage granules, large compartments that hold several synaptic vesicles; and microtubules that transport substances, including the neurotransmitter to the terminal. Dark patches on the axon terminal membrane are protein molecules that serve largely as ion channels and pumps to release the transmitter or to recapture it after its release. dark patches on the dendrite consist mainly of protein receptor molecules that receive chemical messages. this synapse is preferred in mammals because they are flexible in controlling whether a message is passed from one neuron to the next, they can amplify or diminish a signal sent from one neuron to the next, and they can change with experience to alter their signals and so mediate learning.

habituation

learning behavior in which a response to a stimulus weakens with repeated stimulus presentations develops with all our senses. Brain habituates customary background stimulation In Kandel's experiment Aplysia's siphon is introduced to a water jet and the movement of the gill is recorded. If the jet of water is present to the siphon 10 times, the gill-withdrawal response is weaker, even after a few minutes. (vocab word here) can last as long as 30 minutes. The jet of water stimulates the sensory neuron, which in turn stimulates the motor neuron responsible for the gill withdrawal. (vocab word here) does not result from an inability of either the sensory or motor neuron to produce action potentials. In response to direct electrical stimulation direct electrical stimulation, both sensory and motor neurons retain the ability to generate action potentials even after habituation. Electrical recording from the motor neuron show that, as habituation develops, the excitatory postsynaptic potentials in the motor neuron become smaller. The reason why EPSPs decrease in size is that the motor neuron is receiving less neurotransmitter from the sensory neuron across the synapse. And if less neurotransmitter is being received then the changes accompanying habituation must be taking place in the presynaptic axon terminal of the sensory neuron. calcium channels - As (vocab word) takes place, Ca2+ influx decreases in response to the voltage changes associated with an action potential. With repeated use voltage sensitive calcium channels become less responseive to voltage changes and more resistant to the passage of calcium ions. the neural basis of (vocab word) lies in the change in presynaptic calcium channels. Reduced sensitivity of Ca2+ channels and a consequent decrease in the release of a neurotransmitter - (vocab word) can be linked to specific molecular change less Ca2+ influx = less neurotransmitter release change happens in calcium channels

sensitization

learning behavior in which the response to a stimulus strengthens with repeated presentations of that stimulus because the stimulus is novel or because the stimulus is stronger than normal - for example, after habituation has occurred. Enhanced response to some stimulus, opposite of habituation, organism becomes hyperresponsive to a stimulus rather than accustom to it. Occurs within a context. Also makes you more responsive to other things in your environment. An interneuron that receives input from a sensory neuron in the tail makes an axoaxonic synapse with a siphon sensory neuron. The interneuron's axon terminal contains serotonin and when shocked, releases it. Information from the siphon still comes through the siphon sensory neuron to activate the motor neuron leading to the gill muscle, but the gill-withdrawal response is amplified by the interneuron's action in releasing serotonin onto the presynaptic membrane of the sensory neuron. at the molecular level, serotonin released from the interneuron binds to a metabotropic serotonin receptor on the axon of the siphon sensory neuron. This binding activates second messengers in the sensory neuron. Specifically, the serotonin receptor is coupled through its G protein to the enzyme adenyl cyclase which increases the concentration of the second messenger cyclic adenosine monophosphate (cAMP) in the presynaptic membrane of the siphon sensory neuron. Through a number of chemical reactions cAMP attaches a phosphate molecule (PO4) to potassium channels which renders the potassium channels less responsive. Consequently, K+ ions cannot repolarize the membrane as quickly, and so the action potential lasts longer than it usually would. K+ channels being slower to open prolongs the inflow of Ca2+ into the membrane. Ca2+ is required to release neurotransmitters. More Ca2+ results in more release of neurotransmitters from sensory synapse onto the motor neuron. Increased release of neurotransmitter produces greater activation of the motor neuron and thus a larger than normal gill withdrawal response. The gill withdrawal can also be enhanced by the fact that cAMP may mobilize more synaptic vesicles making more neurotransmitters ready for release into the sensory motor synapse. more Ca2+ influx = more neurotransmitter released change takes place in potassium channels

postsynaptic membrane

membrane on the transmitter-input side of a synapse (dendritic spine)

presynaptic membrane

membrane on the transmitter-output side of a synapse (axon terminal) rich in voltage sensitive calcium (Ca2+) channels

storage granule

membranous compartment that holds several vesicles containing a neurotransmitter

major depression

mood disorder characterized by prolonged feelings of worthlessness and guild, the disruption of normal eating habits, sleep disturbances, a general slowing of behavior, and frequent thoughts of suicide. may be related to decreases in the activity of noradrenergic neurons.

neuropeptide

multifunctional chain of amino acids that acts as a neurotransmitter; synthesized from mRNA on instructions from the cell's DNA. Peptide neurotransmitters can act as hormones and may contribute to learning

learning as a change in synapse number

neural changes associated with learning must last long enough to account for a relatively permanent change in an organism's behavior. repeated stimulation produces habituation and sensitization that can persist for months Craig Bailey and Mary Chen found that the number and size of sensory synapses change in well-trained habituated and sensitized Aplysia. Found that the number of and size of synapses decrease in habituated animals and increase in sensitized animals. Apparently synaptic evens associated with habituation and sensitization can also trigger processes in the sensory cell that result in the loss or formation of new synapses. a mechanism through which these processes can take place begins with calcium ions that mobilize second messengers to send intructions to nuclear DNA. The transcription and translation of nuclear DNA, in turn, initiate structural changes at synapses, including the formation of new synapses and new dendritic spines. cAMP plays an important role in carrying instructions regarding these structural changes to nuclear DNA. Fruit fly mutations caused some to produce too much cAMP (dunce) and another produced to little cAMP(rutabaga). These fruit flies are impaired in acquiring habituated and sensitized responses because their levels of cAMP cannot be regulated. More lasting habituation and sensitization are mediated by relatively permanent changes in neuronal structure - more or less synaptic connections - and effects can be difficult to alter. Like in PTSD - which is sensitization at its worst.

activating system

neural pathways that coordinate brain activity through a single neurotransmitter; cell bodies are located in a nucleus in the brainstem and axons are distributed through a wide region of the brain

Cholinergic neuron

neuron that uses acetylcholine as its main neurotransmitter. The term cholinergic applies to any neuron that uses ACh as its main transmitter

Although neurons can synthesize more than one _____________, they are usually identified by the principal _____________ in their axon terminals.

neurotransmitter; neurotransmitter

dopaminergic system

nigrostriatial pathways 1. active in maintaining normal motor behavior 2. loss of DA is related to muscle rigidity and dyskinesia in Parkinson's disease mesolimbic pathways 1.. dopamine release causes feelings of reward and pleasure 2. thought to be the neurotransmitter system most affected by addictive drugs and behavioral addictions 3. increases in DA activity may be related to schizophrenia 4. decreases in DA activity may be related to deficits of attention

transmitter gases

nitric oxide (NO) and carbon monoxide (CO), synthesized in the cell. after synthesis each gas diffuses away, easily crossing the cell membrane and immediately becoming active. Both activate metabolic processes in cells, including processes modulating the production of other neurotransmitters. NO serves as a chemical messenger in many parts of the body. Controls the muscles in intestinal walls and dilates blood vessels in brain regions that are in active use allowing more blood. also active in producing penile erections - Viagra acts by enhancing the chemical pathways influenced by NO but NO does not itself produce sexual arousal.

Otto Loewi

nobel prize in 1936 his successful experiment on the neural communication in a heart beat marked the beginning of research into how chemicals carry info from one neuron to another. He was the fist to isolate a chemical messenger. He discovered acetylcholine (ACh), epinephrine (EP), norepinephrine (NE). The results of his complementary experiments showed that ACh from the vagus nerve inhibits heartbeat and EP from the accelerator nerve excites it. his discoveries lead to a search for neurotransmitters and their functions.

describe the benefits and/or drawbacks of permanent habituation and sensitization

permanent response to frequently occurring stimuli are biologically (or behaviorally and/or metabolically) efficient, but if stimuli change suddenly, a lack of flexibility becomes maladaptive.

one characteristic of _____________, defined as physiological arousal related to recurring memories and dreams surrounding a traumatic event that persist for months or years after the event, is a heightened response to stimuli. This suggests that the disorder is in part related to _____________.

posttraumatic stress disorder (PTSD) ; sensitization

changes that accompany habituation take place within the _____________ of the _____________ neuron, mediated by _____________ channels that grow _____________ sensitive with use

presynaptic axon terminal; sensory; calcium; less

to generate an action potential that travels from the ______________ across the synaptic cleft onto a _______________ requires the simultaneous release of many _____________ of chemical transmitter

presynaptic cell membrane; postsynaptic cell membrane; quanta

transporter

protein molecule that pumps substances across a membrane

learning

relatively permanent change in behavior that results from experience experience alters the synapse - provides a neural basis of __(vocab word here)__.

three classes of neurotransmitters

small-molecule transmitters peptide transmitters transmitter gases

the three broad classes of chemically related neurotransmitters are _____________, ____________, and _____________. All three classes, encompassing the approximately 100 likely neurotransmitters active in the nervous system, Are associated with both _____________ and _____________ receptors.

small-molecule transmitters, peptide transmitters, transmitter gases ionotropic, metabotropic

Renshaw loop

some spinal cord motor neurons have axon collaterals that synapses on a nearby CNS interneuron. The interneuron, in turn, synapses back on the motor neuron's cell body. the loop made by the axon collateral and the interneuron in the spinal cord forms a feedback circuit that enables the motor neuron to inhibit itself from becoming overexcited if it receives a great many excitatory inputs from other parts of the CNS. if the renshaw loop is blocked (strychnine) motor neurons become overactive, resulting in convulsions that can choke off respiration and so cause death.

two activating systems of the ANS

sympathetic and parasympathetic divisions of the ANS regulate the body's internal environment sympathetic - rouses the body for action, producing the fight or flight response. Heart rate ramps up, digestive functions ramp down. Ach neurons in the CNS synapse with sympathetic NE neurons to prepare the body's organs for fight or flight. Norepinephrine turns up heart rate and turns down digestive functions because NE receptors on the heart are excitatory, whereas NE receptors on the gut are inhibitory. parasympathetic - calms the body down, producing an rest and digest response. Digestive functions are turned up, heart rate is turned down, and the body is made to relax. Cholinergic (ACh) neurons in the CNS synapse with autonomic ACh neurons in the parasympathetic division to prepare the body's organs to rest and digest. ACh turns down heart rate and turns up digestive functions because its receptors on these organs are different. ACh receptors on the heart are inhibitory, whereas those on the gut are excitatory. these opposite effects allow the two divisions to form a complementary ANS that maintains the body's internal environment under differing circumstances.

experience alters the _____________, the site of neural basis of _____________, a relatively permanent change in behavior results from experience.

synapse; learning

posttraumatic stress disorder (PTSD)

syndrome characterized by physiological arousal symptoms related to recurring memories and dreams related to a traumatic event for months or years after the event

neurotransmitters are identified using four experimental criteria: ____________, _____________, _____________, and _______________.

synthesis, release, receptor action, inactivation

how would you respond to the comment that a behavior is caused solely by a "chemical imbalance in the brain"?

this idea has been attractive for a long time because there is a clear relationship between DA loss and Parkinson's disease, and acetylcholine and norepinephrine are clearly related to somatic and autonomic behaviors. But for other neurotransmitter systems in the brain, establishing clear one -to -one relationships has proved difficult

describe the four steps in chemical neurotransmission

when an action potential is propagated on an axon terminal, (1) a synthesized and stored in the axon terminal (2) is released from the presynaptic membrane into the synaptic cleft. The transmitter (3) diffuses across the cleft and binds to receptors on the postsynaptic membrane. (4) then the transmitter is deactivated

neurotransmission in the SNS

without SNS neurons, movement would not be possible. Also called cholinergic neurons because ACh is their main neurotransmitter. Transmitter-activated channel called a nicotinic ACh receptor (nAChr) is the main receptor of the SNS. When ACh binds to this receptor, its pore opens to permit ion flow, thus depolarizing the muscle fiber. The pore of nAChr is large and permits the simultaneous efflux of K+ and influx of Na+ . another neurotransmitter - a neuropeptide called calcitonin - gene- related peptide (CGRP) that acts through the CGRP metabotrophic receptors to increase the force with which a muscle contracts