A & P 1 Ch 12 Nervous Tissue

Front 1

two organ systems dedicated to maintaining internal coordination

Back 1

endocrine system

nervous system

Front 2

endocrine system

Back 2

communicates by means of chemical messengers (hormones) secreted into the blood.

Front 3

nervous system

Back 3

employs electrical and chemical means to send messages very quickly from cell to cell

Front 4

The nervous system carries out its coordinating task in three basic steps:

Back 4

1. Through sense organs and simple nerve endings, it receives information about changes in the body and the external environment and transmits messages to the central nervous system (CNS).

2. The CNS processes this information and determines what response, if any, is appropriate to the circumstances.

3. The CNS issues commands primarily to muscle and gland cells to carry out such responses.

Front 5

The nervous systems two anatomical subdivisions

Back 5

Central nervous system

peripheral nervous system

Front 6

Central nervous system

Back 6

the brain and spinal cord

Front 7

peripheral nervous system

Back 7

composed of nerves and ganglia

Front 8

nerve

Back 8

a bundle of nerve fibers (axons) wrapped in fibrous connective tissue. Nerves emerge from the CNS through foramina of the skull and vertebral column and carry signals to and from other organs of the body.

Front 9

ganglion

gangli = knot

Back 9

a knotlike swelling in a nerve where the cell bodies of neurons are concentrated.

Front 10

The peripheral nervous system is functionally divided into sensory and motor divisions, and each of these is further divided into somatic and visceral subdivisions.

Back 10

Sensory (afferent) division

somatic sensory division

visceral sensory division

motor (efferent) division

somatic motor division

visceral motor division (autonomic nervous system, ANS)

ANS

sympathetic division

parasympathetic division

Front 11

define somatic

Back 11

of or relating to the body, especially as distinct from the mind

Front 12

define visceral

Back 12

of or relating to viscera.

viscera is the organs in the cavities of the body

Front 13

sensory (afferent) division

af = ad = toward; fer = to carry

Back 13

carries signals from various receptors (sense organs and simple sensory nerve endings) to the CNS. This pathway informs the CNS of stimuli within and around the body.

Front 14

somatic sensory division

somat = body; ic = pertaining to

Back 14

carries signals from receptors in the skin, muscles, bones, and joints.

Front 15

visceral sensory division

Back 15

carries signals mainly from the viscera of the thoracic and abdominal cavities, such as the heart, lungs, stomach, and urinary bladder.

Front 16

The motor (efferent) division

ef = ex = out; fer = to carry

Back 16

carries signals from the CNS to gland and muscle cells that carry out the body's responses. Cells and organs that respond to these signals are called effectors

Front 17

somatic motor division

Back 17

carries signals to the skeletal muscles. This produces voluntary muscle contractions as well as involuntary somatic reflexes.

Front 18

visceral motor division (autonomic nervous system, ANS)

auto = self; nom = law, governance

Back 18

carries signals to glands, cardiac muscle, and smooth muscle. We usually have no voluntary control over these effectors, and the ANS operates at an unconscious level. The responses of the ANS and its effectors are visceral reflexes. The ANS has two further divisions.

Front 19

ANS sympathetic division

Back 19

tends to arouse the body for action--for example, by accelerating the heartbeat and increasing respiratory airflow--but it inhibits digestion.

Front 20

ANS parasympathetic division

Back 20

tends to have a calming effect--slowing the heartbeat, for example--but it stimulates digestion.

Front 21

what is a receptor?

Back 21

1. A cell or organ specialized to detect a stimulus, such as a taste cell or the eye.

2. A protein molecule that binds and responds to a chemical such as a hormone, neurotransmitter, or odor molecule.

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what is an effector?

Back 22

A molecule, cell, or organ that carries out a response to a stimulus.

Front 23

nerve cells (neurons) three fundamental physiological properties that enable them to communicate with other cells

Back 23

1. Excitability. All cells are excitable--that is, they respond to environmental changes (stimuli). Neurons exhibit this property to the highest degree.

2. Conductivity. Neurons respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations.

3. Secretion. When the signal reaches the end of a nerve fiber, the neuron secretes a neurotransmitter that crosses the gap and stimulates the next cell.

Front 24

Three general classes of neurons corresponding to the three major aspects of nervous system function.

Back 24

1. Sensory (afferent) neurons

2. Interneurons (association neurons)

3. Motor (efferent) neurons

Front 25

Sensory (afferent) neurons

Back 25

specialized to detect stimuli such as light, heat, pressure, and chemicals, and transmit information about them to the CNS. Such neurons begin in almost every organ of the body and end in the CNS; the word afferent refers to signal conduction toward the CNS. Some receptors, such as those for pain and smell, are themselves neurons. In other cases, such as taste and hearing, the receptor is a separate cell that communicates directly with a sensory neuron.

Front 26

Interneurons (association neurons)

inter = between

Back 26

lie entirely within the CNS. They receive signals from many other neurons and carry out the integrative function of the nervous system--that is, they process, store, and retrieve information and "make decisions" that determine how the body responds to stimuli. About 90% of our neurons are interneurons. The word interneuron refers to the fact that they lie between, and interconnect, the incoming sensory pathways and the outgoing motor pathways of the CNS.

Front 27

Motor (efferent) neurons

Back 27

send signals predominantly to muscle and gland cells, the effectors. They are called motor neurons because most of them lead to muscle cells, and efferent neurons to signify signal conduction away from the CNS.

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soma, neurosoma or cell body

soma = body

Back 28

The control center of the neuron

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lipfuscin

Back 29

lipo = fat, lipid

fusc = dusky, brown

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dendrites

Back 30

dendr = tree, branch; its = little

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Multipolar neurons

Back 31

those that have one axon and multiple dendrites. This is the most common type and includes most neurons of the brain and spinal chord.

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Bipolar neurons

Back 32

have one axon sand one dendrite. Examples include olfactory cells of the nose, certain neurons of the retina, and sensory neurons of the ear.

Front 33

Unipolar neurons

Back 33

have only a single process leading away from the soma. They are represented by the neurons that carry sensory signals to the spinal cord.

Front 34

Anaxonic neurons

Back 34

have multiple dendrites but no axon. They communicate locally through their dendrites and do not produce action potentials. Some anaxonic neurons are found in the brain, retina, and adrenal medulla. In the retina, they help in visual processes such as the perception of contrast.

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axonal transport

Back 35

the two-way passage of proteins, organelles, and other materials along an axon.

Front 36

anterograde transport

antero = forward; grad = to walk, to step

Back 36

movement away rom the soma down the axon

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retrograde transport

retro = back; grad = to walk, to step

Back 37

movement up the axon toward the soma.

Front 38

kinesin

kine = motion; in = protein

Back 38

a motor protein employed in anterograde transport.

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dynein

dyne = force; in = protein

Back 39

a motor transport employed in retrograde transport.

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There are two types of axonal transport:

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fast axonal transport

slow axonal transport

Front 41

Fast axonal transport

Occurs at a rate of 20 to 400 mm/day and may be either anterograde or retrograde

Back 41

Fast anterograde transport: moves mitochondria; synaptic vesicles; other organelles; components of the axolemma; calcium ions; enzymes such as glucose, amino acids, and nucleotides toward the distal end of the axon

Fast retrograde transport: returns used synaptic vesicles and other materials to the soma and informs the soma of conditions at the axon terminals. Some pathogens exploit this process to invade the nervous system. They enter the distal tips of an axon and travel to the soma by retrograde transport. Examples include tetanus toxin and the herpes simples, rabies, and polio viruses. In such infections, the delay between infection and the onset of symptoms corresponds to the time needed for the pathogens to reach the somas.

Front 42

Slow axonal transport

Back 42

an anterograde process that works in a stop-and-go fashion. If we compare fast axonal transport to an express train traveling nonstop to its destination, slow axonal transport is like a local train that stops at every station. When moving, it goes just as fast as the express train, but the frequent stops result in an overall progress of only 0.5 to 10 mm/day. It moves enzymes and cytoskeletal components down the axon, renews worn-out axoplasmic components in mature neurons, and supplies new axoplasm for developing or regenerating neurons. Damaged nerves regenerate at a speed governed by slow axonal transport.

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neuroglia, or glial cells

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Glial cells protect the neurons and help them function. The word glia, which means "glue," implies one of their roles--to bind neurons together and provide a supportive framework or the nervous tissue.

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There are six kinds of neuroglia, each with a unique function. Four types occur only in the central nervous system

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1. Oligodendrocytes

2. Ependymal

3. Microglia

4. Astrocytes

5. Schwann cells, or nruilemmocytes

6. Satellite cells

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Oligodendrocytes (CNS)

oligo = few; dendro =branches; cite = cell

Back 45

Form myelin in brain and spinal cord

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Ependymal cells (CNS)

ependyma = upper garment

Back 46

Line cavities of brain and spinal cord; secrete and circulate cerebrospinal fluid

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Microglia (CNS)

Back 47

Phagocytize and destroy microorganisms, foreign matter, and dead nervous tissue.

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Astrocytes (CNS)

astro = star; cyte = cell

Back 48

Cover brain surface and non synaptic regions of neurons; form supportive framework in CNS; induce formation of blood-brain barrier; nourish neurons; produce growth factors tha stimulate neurons; communicate electrically with neurons and may influence synaptic signaling; remove K+ and some neurotransmitters from ECF of brain and spinal cord; help to regulate composition of ECF; form scar tissue to replace damaged nervous tissue.

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Schwann cells (PNS)

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Form neurilemma around all PNS nerve fibers and myelin around most of them; aid in regeneration of damaged nerve fibers

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Satellite cells (PNS)

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Surround somas of neurons in the ganglia; provide electrical insulation and regulate chemical environment of neurons

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myelin sheath

Back 51

a spiral layer of insulation around a nerve fiber, formed by oligodendrocytes int eh CNS and Schwann cells in the PNS. About 20% protein and 80% lipid.

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myelination

Back 52

production of the myelin sheath.

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neurilemma

neuri = nerve; lemma = husk, peel, sheath

Back 53

a thick outermost coil of the Schwann cell. This is where the bulging body of the Schwann cell contains its nucleus and most of its cytoplasm.

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endoneurium

Back 54

a thin sleeve of fibrous connective tissue external to the neurilemma

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nodes of Ranvier

Back 55

The gaps between the segments in myelin sheath

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internodes

Back 56

the myelin covered segments from one gap to the next.

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initial segment

Back 57

the short section of nerve fiber between the axon hillock the the first glial cell.

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trigger zone

Back 58

Since the axon hillock and initial segment play an important role in initiating a nerve signal, they are collectively called the trigger zone.

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centrifugal myelination

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away from the center (PNS)

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centripetal myelination

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toward the center (CNS)

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The speed at which a nerve signal travels along a nerve fiber depends on two factors:

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the diameter of the fiber

the presence or absence of myelin.

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electophysiology

Back 62

cellular mechanisms for producing electrical potentials and currents. This is what neural communication, like muscle excitation, is based upon.

Front 63

electrical potential

Back 63

a difference in the concentration of charged particles between one point and another. It is a form of potential energy that, under the right circumstances, can produce a current.

Front 64

electrical current

Back 64

a flow of charged particles from one point to another.

Front 65

polarized

Back 65

A new flash light battery, for example, typically has a potential, or charge, of 1.5 volts. If the two poles of the battery are connected by a wire, electrons flow through the wire from one pole of the battery to the other, creating a current that lights the bulb. As long as the battery has a potential (voltage), we say it is polarized.

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resting membrane potential (RMP)

Back 66

the charge difference across the plasma membrane

Front 67

Why does a cell have a resting membrane potential?

Back 67

because electrolytes are unequally distributed between the extracellular fluid (ECF) on the outside of the plasma membrane and the intracellular fluid (ICF) on the inside.

Front 68

The resting membrane potential results from the combined effect of three factors:

Back 68

1. the diffusion of ions down their concentration gradients through the membrane.

2. selective permeability of the membrane, allowing some ions to pass more easily than others

3. the electrical attraction of cations and anions to each other.

Front 69

Potassium ions (K+) have the greatest influence on the RMP, because the plasma membrane is more permeable to K+ than to anty other ion.

Back 69

True

Front 70

What is the functional disadvantage of an unmyelinated nerve fiber? What is its anatomical advantage?

Back 70

Its conduction speed is relatively slow, but it has a small diameter and contributes relatively little bulk to the nervous tissue

Front 71

If we suddenly increased the concentration of CL- ions in the ICF, would the membrane potential become higher or lower?

Back 71

The membrane potential will become lower (more negative).

Front 72

depolariztion

Back 72

any case in which the voltage shifts to a less negative charge

Front 73

local potential

Back 73

short-range change in voltage

Front 74

There are four characteristics that distinguish local potentials from the actio potentials

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1. Local potentials are graded

2. Local potentials are decremental

3. Local potentials are reversible

4. Local potentials can be either excitatory or inhibitory

Front 75

local potentials are graded

Back 75

meaning they vary in magnitude 9voltage) according to the strength of the stimulus. An intense or prolong stimulus opens more ion channels than a weaker stimulus. Thus, more Na+ enters the cell and the voltage changes mere that it does with a weaker stimulus.

Front 76

Local potentials are decremental

Back 76

meaning they get weaker as they spread from the point of stimulation. The decline in strength occurs partly because as Na+ spreads out under the plasma membrane and depolarizes it, K+ flows out an reverses the effect of the Na+ inflow, and partly because the Na+ leaks back out of the cell through channels along its path. Therefore, the voltage shift caused by Na+ diminishes rapidly with distance. This prevents local potentials from having long-distance effects.

Front 77

local potentials are reversible

Back 77

meaning that if stimulation ceases, cation diffusion out of the cell quickly returns the membrane voltage to its resting potential.

Front 78

local potentials can be either excitatory or inhibitory.

Back 78

excitatory local potentials depolarize a cell and make a neuron more likely to produce an action potential. Acetylcholine usually has this effect. Other neurotransmitters, such as glycine, cause an opposite effect--they hyper polarize a cell, or make the membrane more negative. This inhibits a neuron, making it less sensitive an less likely to produce and action potential. A balance between excitatory and inhibitory potentials is very important to information processing in the nervous system.

Front 79

actio potential`

Back 79

a more dramatic change produced by voltage-gated ion channels in the plasma membrane. Action potentials occur only where there is a high enough density of voltage-gated channels. Most of the soma has only 50 to 75 channels per square micrometer and cannot generate action potentials. The trigger zone, however, has 350 to 500 channels per square micrometer.

The action potential is a rapid up-and-down shift in voltage.

Front 80

threshold

Back 80

the minimum needed to open voltage-gated channels, typically about -55mV

Front 81

Local potentials

-produced by gated channels on the dendrites and soma

-may be a positive (depolarizing) or negative (hyper polarizing) voltage change

-Graded; proportional to stimulus strength

-Reversible; returns to RMP if stimulation ceases before threshold is reached

-Local; has effects for only a short distance from point of origin

-Decremental; signal grows weaker with distance

Back 81

Action potentials

-Produced by voltage-gated channels on the trigger zone and axon

-Always begins with depolarization

-All or none;either does not occur at all or exhibits the same peak voltage regardless of stimulus strength

-Irreversible; goes to completion once it begins

-Self-propagating; has effects a great distance form point of origin

-Nondecremental; signal maintains same strength regardless of distance

Front 82

refractory perid

Back 82

the period of resistance to restimulation during and for a few milliseconds after an action potential.

It is divided into two stages: an absolute refractory period in which no stimulus of any strength will trigger a new action potential, followed by a relative refractory period jun which it is possible to trigger a new actio potential, but only with an unusually strong stimulus.

Front 83

the nerve signal

Back 83

a traveling wave of excitation produced by self-propagating action potentials. This is a chain reaction of action potentials

Front 84

Why is conduction in myelinated fibers called saltatory conduction ?

saltare = to leap, to dance

Back 84

because action potentials occur only at the nodes. This mode of conduction creates a false impression that the nerve signal jumps from node to node.

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Signals arrive at the synapse by way of the presynaptic neuron, which releases a neurotransmitter.

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The next neuron, which responds to it, is called the postsynaptic neuron.

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neurotransmitters

Back 86

small organic molecules that are released when a nerve signal reaches a synaptic knob or varicosity of the nerve fiber, then bind to a receptor on another cell and alter that cell's physiology.

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The four categories of neurotransmitters

Back 87

1. Acetylcholine is in a class by itself. It is formed from acetic acid (acetate) and choline.

2. Amino acid neurotransmitters include glycine, glutamate, aspartate, and y-aminobutyric acid (GABA)

3. Monoamines (biegenic amines) are synthesized from amino acids by removal of the -COOH group. They retain the -NH2 (amino group), hence their name. some monoamine neurotransmitters are epinephrine, norepinephrine, dopamine, histamine, ATP, and serotonin (5-hydroxytryptamine, or 5-HT). The first three of these are in a subclass called catecholamines.

4. Neuropeptides are chains of 2 to 40 amino acids. Some examples are cholecystokinin (CCK) and substance P. Neuropeptides are stored in secretory granules(dense core vesicles) that are about 100 nm in diameter, twice as large as typical synaptic vesicles. Some neuropeptides also function as hormones or as neuromodulaors. Some are produced not only by neurons but also by the digestive tract; thus they are known as gut-brain peptides. Some of these cause cravings for specific nutrients such as fat, protein, or carbohydrates and may be associated with certain eating disorders.

Front 88

Acetylcholine (ACh)

Back 88

Neuromuscular junctions, most synapses of autonomic nervous system, retina, and mny parts of the brain; excites skeletal muscle, inhibits cardiac muscle, and has excitatory or inhibitory effects on smooth muscle and glands depending on location.

Front 89

Glutamate (amino acid)

Back 89

Cerebral cortex and brainstem; accounts for about 75% of all excitatory synaptic transmission in the brain; involved in learning and memory.

Front 90

Aspartate (amino acid)

Back 90

Spinal cord; effects similar to those of glutamate

Front 91

Glycine (amino acid)

Back 91

Inhibitory neurons of the brain, spinal cord and retina; most common inhibitory neurotransmitter in the spinal cord

Front 92

GABA (amino acid)

Back 92

Thalmus, hypothalamus, cerebellum, occipital lobes of cerebrum, and retina; the most common inhibitory neurotransmitter in the brain

Front 93

Norepinephrine (monoamine)

Back 93

Sympathetic nervous system, cerebral cortex, hypothalamus, brainstem, cerebellum, and spinal cord; involved in dreaming, waking, and mood; excited cardiac muscle; can excite or inhibit smooth muscle and glands depending on location

Front 94

Epinephrine (monoamines)

Back 94

Hypothalmus, thalamus, spinal cord, and adrenal medulla; effects similar to those of norepinephrine

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Dopamine (monamine)

Back 95

Hypothalmus, limbic system, cerebral cortex, and retina; highly concentrated in substantia nigra of midbrain; involved in elevation of mood and control of skeletal muscles

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serotonin (monoamine)

Back 96

Hyupothalmus, limbic system, cerebellum, retina, and spinal cord; also secreted by blood platelets and intestinal cells; involved in sleepiness, alertness, thermoregulation, and mood

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Histamine (monamine)

Back 97

Hypothalmus; also a potent vasodilator released by mast cells of connective tissue and basophils of the blood

Front 98

Substance P (neuropeptide)

Back 98

Basal nuclei, midbrain, hypothalmus, cerebral cortex, small intestine, and pain-receptor neurons; mediated pain transmission

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Enkephalins (neuropeptide)

Back 99

Hypothalamus, limbic system, pituitary, pain pathways of spinal cord, and nerve endings of digestive tract; act as analgesics (pain relievers) by inhibiting substance P; inhibit intestinal motility; secretion increases sharply in women in labor

Front 100

B-endorphin (neuropeptide)

Back 100

Digestive tract, spinal cord, and many parts of the brain; also secreted as a hormone by the pituitary; suppresses pain; reduces perception of fatigue and may produce "runner's high" in athletes

Front 101

Cholecystokinin (neuropeptides)

Back 101

Cerebral cortex and small intestine; suppresses appetite

Front 102

a cholinergic synapse

cholin = acetylcholine; erg = work, action

Back 102

employs acetylcholine as its neurotransmitter. ACh excites some postsynaptic cells (such as skeletal muscle) and inhibits others.

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GABA-ergic synaps

Back 103

employs y-aminobutyric acid (GABA) as it neurotransmitter. Amino acid neurotransmitters work by the same mechanism as ACh--binding to ion channels and causing immediate changes in membrane potential. The GABA receptor is a chloride channel. When it opens, CL- enters the cell and makes the inside even more negative than the resting membrane potential. The neuron is therefore inhibited, or less likely to fire.

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adrenergic synapse

Back 104

employs the neurotransmitter norepinephrine (NE), also called noradrenaline. NE, other monoamines, and neuropeptides act through second-messenger systems such as cyclic AMP (cAMP). The receptor is not an ion channel but a transmembrane protein associated with a G protein.

Front 105

synaptic delay

Back 105

the time from the arrival of a signal at the axon terminal of a presynaptic cell to the beginning of an action potential in the postsynaptic cell, typically only0.5ms or so.

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Diffusion (cessation of the signal)

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neurotransmitter escapes from the synapse into the nearby ECF. In the CNS, astrocytes absorb it and return it to the neurons.

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Reuptake (cessation of the signal)

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The synaptic knob reabsorbs amino acids and monoamines by endocytosis and breaks them down with an enzyme called monoamine oxidase (MAO). Some antidepressant drugs work by inhibiting MAO.

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Degradation in the synaptic cleft (cessation of the signal)

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The enzyme acetlcholinesterase (AChE), located int eh synaptic cleft and on the postsynaptic membrane, breaks ACh down into acetate and choline. These breakdown products have no stimulatory effect on the postsynaptic cell. The synaptic knob reabsorbs the choline and uses it to synthesize more ACh.

Front 109

neuromodulators

simplest is nitric oxide

others are neuropeptides. Among neruopeptides there are enkephalins and endorphins.

Back 109

chemical signals that have long-term effects on entire groups of neurons instead of brief, quick effects at an individual synapse. These adjust, or modulate, the activity of neuron groups in various ways--increasing the release of neurotransmitters by presynaptic neurons; adjusting the sensitivity of postsynaptic neurons to neurotransmitters; or altering the rate of neurotransmitter reuptake or breakdown to prolong their effects.

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enkephalins and endorphins

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inhibit spinal neurons from transmitting pain signals to the brain.

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The terms neurotransmitter, hormone, and neuromodulator define not so much the chemical itself, but the role it plays in a given instance.

Back 111

True.

One chemical can play two or more of these roles under different circumstances.

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cerebral cortex

Back 112

the main information-processing tissue of your brain. It is estimated to have 100 trillion synapses.

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neural integration

Back 113

the ability of you neurons to process information, store and recall it, and make decisions.

Front 114

excitatory postsynaptic potential (EPSP)

Back 114

any voltage change towards depolarization (-55mV) makes a neuron more likely to fire.

Wikipedias says "a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening of ligand-gated ion channels.

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inhibitory postsynaptic potential (IPSP)

Back 115

a neurotransmitter hyper polarized the postsynaptic cell and makes it more negative than the RMP. This makes the postsynaptic cell less likely to fire.

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Summation

Back 116

the process of adding up postsynaptic potentials and responding to their net effect. It occurs in the trigger zone.

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Temporal summation

Back 117

This occurs when a single synapse generates EPSP's so quickly that each is generated before the previous one fades. This allows the EPSPs to add up over time to a threshold voltage that triggers and action potential. Temporal summation can occur if even one presynaptic neuron stimulates the postsynaptic neuron at a fast enough rate.

Front 118

Spatial summation

Back 118

This occurs when EPSPs from several synapses add up to threshold at the axon hillock. Any one synapse may admit only a moderate amount of Na+ into the cell, but several synapses acting together admit enough Na+ to reach threshold. The presynaptic neurons collaborate to induce the postsynaptic neuron to fire.

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Facilitation

Back 119

a process in which one neuron enhances the effect of another.

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Presynaptic inhibition

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the opposite of facilitation, a mechanism in which one presynaptic neuron suppresses another one. This mechanism is used to reduce or halt unwanted synaptic transmission.

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Why is a single EPSP insufficient to make a neuron fire?

Back 121

One EPSP is a voltage change of only 0.5 mV or so. A change of about 15 mV is required to reach threshold and make a neuron fire.

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neural coding (sensory coding when it occurs in the sense organs)

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the way in which the nervous system converts information to a meaningful pattern of action potentials.

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labeled line code (most important mechanism for transmitting qualitative information)

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This code is based on the fact that each nerve fiber to the brain leads from a receptor that specifically recognizes a particular stimulus type.

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quantitative information

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information about the intensity of a stimulus.

encoded in two ways:

1. depends on the fact that different neurons have different thresholds of excitation.

2. depends on the fact that the more strongly a neuron is stimulated, the more frequently it fires.

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recruitment

Back 125

bringing additional neurons into play as the stimulus becomes stronger

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neural pools

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ensembles which consists of thousands to millions of interneurons concerned with a particular body function.

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neural circuit

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the pathways among the neural pools neurons

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four principal kinds of neural circuits:

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1. diverging circuit--on nerve fiber branches and synapses with several postsynaptic cells.

2. converging circuit--input from many nerve fibers is funneled to one neuron or neural pool.

3. reverberating circuit--neurons stimulate each other in a linear sequence from input to output neurons, but some of the neurons late in the path send axon collaterals back to neurons earlier int eh path and restimulate them.

4. parallel after-discharge circuit--an input neuron diverges to stimulate several chains of neurons.

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memory trace (engram)

en = inner; gram = mark, trace, record

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the physical basis of memory, a pathway throughout the brain which new synapses have formed or existing synapses have been modified to make transmission easier.

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synaptic plasticity

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The ability of synapse to change

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synaptic potentiation ( one form of synaptic plasticity)

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the process of making transmission easier

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Immediate memory

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the ability to hold something in mind for just a few seconds.

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Short-term memory (STM)

Back 133

lasts from a few seconds to a few hours. Information stored in STM may be quickly forgotten if we stop mentally reciting it, we are distracted, or we have to remember something new.

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Working memory

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a form of STM that allows us to hold an idea in mind long enough to carry out an action such as calling a telephone number we just looked up, working out the steps of a mathematics problem, or searching for a lost set of keys while remembering where we have already looked.

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tetanis stimulation

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the rapid arrival of repetitive signals at a synapse.

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long-term memory (LTM)

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lasts up to a lifetime and is less limited than STM in the amount of information it can store. LTM allows you to memorize the lines of a play, the words of a favorite song, or (one hopes!) textbook information for an exam. On still a longer timescale, it enables you to remember your name, the route to your home, and your childhood address.

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two forms of LTM

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declarative--the retention of events and facts that you can put into words--numbers, names, dates, and so forth.

Procedural memory--the retention of motor skills--how to tie your shoes, play a musical instrument, or type on a keyboard.

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LTM can also be grounded in molecular changes called long-term potentiation

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This involves NMDA (N-methyl-D-aspartate, a chemical similar to glutamate) receptors, which are glutamate-binding receptors found on the dendritic spines of pyramidal cells.