0-1 chapter 12 Nervous Tissue Flashcards Preview

2 - Keiser A&P 2 > 0-1 chapter 12 Nervous Tissue > Flashcards

Flashcards in 0-1 chapter 12 Nervous Tissue Deck (174):
1

Overview of Nervous System

endocrine and nervous system maintain internal coordination

2

endocrine system

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

3

nervous system

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

4

nervous system carries out its task in three basic steps

-receive information and transmits coded messages
• processes this information
• issue commands

5

-receive information and transmits coded messages

•sense organs receive information about changes in the body and the external environment, and transmits coded messages to the spinal cord and the brain

6

• processes this information

•brain and spinal cord processes this information, relates it to past experiences, and determine what response is appropriate to the circumstances

7

• issue commands

brain and spinal cord issue commands to muscles and gland cells to carry out such a response

8

Two Major Anatomical Subdivisions of Nervous System

central nervous system (CNS)
peripheral nervous system (PNS)

9

central nervous system (CNS)

central nervous system (CNS)
–brain and spinal cord enclosed in bony coverings
•enclosed by cranium and vertebral column

10

peripheral nervous system (PNS)

–all the nervous system except the brain and spinal cord
–composed of nerves and ganglia

11

nerve

a bundle of nerve fibers (axons) wrapped in fibrous connective tissue

12

ganglion

a knot-like swelling in a nerve where neuron cell bodies are concentrated

13

Sensory Divisions of PNS

sensory (afferent) division
motor (efferent) division

14

sensory (afferent) division

carries sensory signals from various receptors to the CNS
–informs the CNS of stimuli within or around the body
–somatic sensory division –
–visceral sensory division

15

somatic sensory division

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

16

visceral sensory division

carries signals from the viscera of the thoracic and abdominal cavities
•heart, lungs, stomach, and urinary bladder

17

motor (efferent) division

carries signals from the CNS to gland and muscle cells that carry out the body‟s response
-somatic motor division
-visceral motor division (autonomic nervous system)

18

somatic motor division

carries signals to skeletal muscles
•output produces muscular contraction as well as somatic reflexes –involuntary muscle contractions

19

visceral motor division (autonomic nervous system)

carries signals to glands, cardiac muscle, and smooth muscle
-sympathetic division
-parasympathetic division

20

sympathetic division

–tends to arouse body for action
–accelerating heart beat and respiration, while inhibiting digestive and urinary systems

21

parasympathetic division

–tends to have calming effect
–slows heart rate and breathing
–stimulates digestive and urinary systems

22

effectors

cells and organs that respond to commands from the CNS

23

Universal Properties of Neurons

excitability(irritability)
conductivity
secretion

24

secretion

when electrical signal reaches end of nerve fiber, a chemical neurotransmitter is secreted that crosses the gap and stimulates the next cell

25

Functional Types of Neurons

3

sensory (afferent) neurons
interneurons(association) neurons
motor (efferent)neuron

26

sensory (afferent) neurons

–specialized to detect stimuli
–transmit information about them to the CNS
•begin in almost every organ in the body and end in CNS
•afferent–conducting signals toward CNS

27

afferent

conducting signals toward CNS

28

interneurons(association) neurons

–lie entirely within the CNS
–receive signals from many neurons and carry out the integrative function
•process, store, and retrieve information and „make decisions‟ that determine how the body will respond to stimuli
–90% of all neurons are interneurons
–lie between, and interconnect the incoming sensory pathways, and the outgoing motor pathways of the CNS

29

motor (efferent)neuron

–send signals out to muscles and gland cells (the effectors)
•motor because most of them lead to muscles
•efferent neurons conduct signals away from the CNS

30

efferent

neurons conduct signals away from the CNS

31

motor

because most of them lead to muscles

32

soma

the control center of the neuron
–also called neurosoma, cell body, or perikaryon
–has a single, centrally located nucleus with large nucleolus

33

cytoplasm

cytoplasm contains mitochondria, lysosomes, a Golgi complex, numerous inclusions, and extensive rough endoplasmic reticulum and cytoskeleton

34

cytoskeleton

consists of dense mesh of microtubules and neurofibrils (bundles of actin filaments)
•compartmentalizes rough ER into dark staining Nissl bodies

35

no centrioles

no further cell division

36

Inclusions

glycogen granules, lipid droplets, melanin, and lipofuscin

37

lipofuscin

lipofuscin(golden brown pigment produced when lysosomes digest worn-out organelles)
•lipofuscin accumulates with age
•wear-and-tear granules
•most abundant in old neurons

38

dendrites

vast number of branches coming from a few thick branches from the soma
–primary site for receiving signals from other neurons

39

axon

axon(nerve fiber) –originates from a mound on one side of the soma called the axon hillock
–cylindrical, relatively unbranched for most of its length

40

axoplasm

cytoplasm of axon

41

axolemma

plasma membrane of axon
–only one axon per neuron

42

synaptic knob

(terminal button) –little swelling that forms a junction (synapse) with the next cell
•contains synaptic vesicles full of neurotransmitter

43

axon collaterals

branches of axon

44

terminal arborization

distal end, axon has terminal arborization –extensive complex of fine branches

45

multipolar neuron

–one axon and multiple dendrites
–most common
–most neurons in the brain and spinal cord

46

bipolar neuron

–one axon and one dendrite
–olfactory cells, retina, inner ear

47

unipolar neuron

–single process leading away from the soma
–sensory from skin and organs to spinal cord

48

anaxonic neuron

–many dendrites but no axon
–help in visual processes

49

axonal transport

two-way passage of proteins, organelles, and other material along an axon

50

anterograde transport

movement down the axon away from soma

51

retrograde transport

movement up the axon toward the soma

52

microtubules

microtubules guide materials along axon
–motor proteins (kinesin and dynein) carry materials “on their backs” while they “crawl” along microtubules

53

kinesin

motor proteins in anterograde transport

54

dynein

motor proteins in retrograde transport

55

fast axonal transport

occurs at a rate of 20 –400 mm/day

56

fast anterograde transport

(up to 400 mm/day)
•organelles, enzymes, synaptic vesicles and small molecules

57

fast retrograde transport

•for recycled materials and pathogens -rabies, herpes simplex, tetanus, polio viruses
–delay between infection and symptoms is time needed for transport up the axon

58

slow axonal transport or axoplasmic flow

-0.5 to 10 mm/day
–always anterograde
–moves enzymes, cytoskeletal components, and new axoplasm down the axon during repair and regeneration of damaged axons
–damaged nerve fibers regenerate at a speed governed by slow axonal transport

59

Neuroglial Cells

•about a trillion (10-12) neuronsin the nervous system
•neurogliaoutnumber the neurons by as much as 50 to 1

60

neuroglia or glial cells

–support and protect the neurons
–bind neurons together and form framework for nervous tissue

61

six Types of Neuroglial Cells
•four types occur only in CNS

oligodendrocytes
ependymal cells
microglia
astrocytes

62

oligodendrocytes

•form myelin sheaths in CNS
•each arm-like process wraps around a nerve fiber forming an insulating layer that speeds up signal conduction

63

ependymal cells

•lines internal cavities of the brain
•cuboidal epithelium with cilia on apical surface
•secretes and circulates cerebrospinal fluid (CSF)
–clear liquid that bathes the CNS

64

microglia

•small, wandering macrophages formed white blood cell called monocytes
•thought to perform a complete checkup on the brain tissue several times a day
•wander in search of cellular debris to phagocytize

65

astrocytes

•most abundant glial cell in CNS
•cover entire brain surface and most nonsynaptic regions of the neurons in the gray matter of the CNS

66

astrocytes

diverse functions

–form a supportive framework of nervous tissue
–have extensions (perivascular feet) that contact blood capillaries that stimulate them to form a tight seal called the blood-brain barrier
–convert blood glucose to lactate and supply this to the neurons for nourishment

67

nerve growth factors

secreted by astrocytes promote neuron growth and synapse formation

68

astrocytosis or sclerosis

when neuron is damaged, astrocytes form hardened scar tissue and fill space formerly occupied by the neuron

SCAR TISSUE

69

Six Types of Neuroglial Cells

•two types occur only in PNS

Schwann cells
satellite cells

70

Schwann cells

•envelop nerve fibers in PNS
•wind repeatedly around a nerve fiber
•produces a myelin sheath similar to the ones produced by oligodendrocytes in CNS
•assist in the regeneration of damaged fibers

70

Neurilemmocytes

Schwann cells

71

satellite cells

•surround the neurosomas in ganglia of the PNS
•provide electrical insulation around the soma
•regulate the chemical environment of the neurons

72

tumors

masses of rapidly dividing cells
–mature neurons have little or no capacity for mitosis and seldom form tumors

73

brain tumors arise from:

–meninges (protective membranes of CNS)
–by metastasis from non-neuronal tumors in other organs
–most come from glial cells that are mitotically active throughout life

74

gliomas

gliomas grow rapidly and are highly malignant
–blood-brain barrier decreases effectiveness of chemotherapy
–treatment consists of radiation or surgery

75

myelin sheath

an insulating layer around a nerve fiber
–formed by oligodendrocytes in CNS and Schwann cells in PNS
–consists of the plasma membrane of glial cells
•20% protein and 80 % lipid

76

myelination

production of the myelin sheath
–begins the 14thweek of fetal development
–proceeds rapidly during infancy
–completed in late adolescence
–dietary fat is important to nervous system development

77

Schwann cell

in PNS, Schwann cell spirals repeatedly around a single nerve fiber
–lays down as many as a hundred layers of its own membrane
–no cytoplasm between the membranes

78

neurilemma

thick outermost coil of myelin sheath
•contains nucleus and most of its cytoplasm

79

endoneurium

external to neurilemma is basal lamina and a thin layer of fibrous connective tissue

80

oligodendrocytes

in CNS –oligodendrocytes reaches out to myelinate several nerve fibers in its immediate vicinity
–anchored to multiple nerve fibers
–cannot migrate around any one of them like Schwann cells
–must push newer layers of myelin under the older ones
•so myelination spirals inward toward nerve fiber
–nerve fibers in CNS have no neurilemma or endoneurium

81

myelin sheath

segmented
nodes of Ranvier
internodes

82

nodes of Ranvier

gap between segments

83

internodes

myelin covered segments from one gap to the next

84

initial segment

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

85

trigger zone

the axon hillock and the initial segment
•play an important role in initiating a nerve signal

86

Diseases of Myelin Sheath

multiple sclerosis
Tay-Sachs disease

87

multiple sclerosis

•oligodendrocytes and myelin sheaths in the CNS deteriorate
•myelin replaced by hardened scar tissue
•nerve conduction disrupted (double vision, tremors, numbness, speech defects)
•onset between 20 and 40 and fatal from 25 to 30 years after diagnosis
•cause may be autoimmune triggered by virus

88

Tay-Sachs disease

a hereditary disorder of infants of Eastern European Jewish ancestry
•abnormal accumulation of glycolipid called GM2in the myelin sheath
–blindness, loss of coordination, and dementia
•fatal before age 4

89

mesaxon

neurilemma wrapping of unmyelinated nerve fibers

90

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

–diameter of fiber
–presence or absence of myelin

91

conduction speed

–small, unmyelinated fibers -0.5 -2.0 m/sec
–small, myelinated fibers -3 -15.0 m/sec
–large, myelinated fibers -up to 120 m/sec
–slow signals supply the stomach and dilate pupil where speed is less of an issue
–fast signals supply skeletal muscles and transport sensorysignals for vision and balance

92

Regeneration of Peripheral Nerves

regeneration of a damaged peripheral nerve fiber can occur if:
–its soma is intact
–at least some neurilemma remains

93

regeneration tube

formed by Schwann cells, basal lamina, and the neurilemma near the injury
–regeneration tube guides the growing sprout back to the original target cells and reestablishes synaptic contact

94

denervation atrophy

of muscle due to loss of nerve contact by damaged nerve

95

electrophysiology

cellular mechanisms for producing electrical potentials and currents
–basis for neural communication and muscle contraction

96

electrical potential

a difference in the concentration of charged particles between one point and another

97

electrical current

a flow of charged particles from one point to another

98

Resting Membrane Potential

RMP exists because of unequal electrolyte distribution between extracellular fluid (ECF) and intracellular fluid (ICF)

99

RMP results from the combined effect of three factors

–ions diffuse down their concentration gradient through the membrane
–plasma membrane is selectively permeable and allows some ions to pass easier than others
–electrical attraction of cations and anions to each other

100

potassium ions (K+)

have the greatest influence on RMP
–plasma membrane is more permeable to K+ than any other ion
–leaks out until electrical charge of cytoplasmic anions attracts it back in and equilibrium is reached and net diffusion of K+ stops
–K+ is about 40 times as concentrated in the ICF as in the ECF

101

cytoplasmic anions

can not escape due to size or charge (phosphates, sulfates, small organic acids, proteins, ATP, and RNA)

102

Na+/K+ pumps out

3 Na+ for every 2 K+ it brings in

103

cellIonic Basis of Resting Membrane Potential

•Na+ concentrated outside of cell (ECF)
•K+ concentrated inside cell (ICF)

104

local potentials

disturbances in membrane potential when a neuron is stimulated

105

depolarization

case in which membrane voltage shifts to a less negative value

106

differences of local potentials from action potentials

are graded
decremental
reversible
either excitatory or inhibitory

107

graded

vary in magnitude with stimulus strength
•stronger stimuli open more Na+gates

108

decremental

get weaker the farther they spread from the point of stimulation
•voltage shift caused by Na+ inflow diminishes rapidly with distance

109

reversible

when stimulation ceases, K+ diffusion out of cell returns the cell to its normal resting potential

110

either excitatory or inhibitory

some neurotransmitters (glycine) make the membrane potential more negative –hyperpolarize it –becomes less sensitive and less likely to produce an action potential

111

action potential

more dramatic change produced by voltage-regulated ion gates in the plasma membrane
–only occur where there is a high enough density of voltage-regulated gates

112

soma

soma (50 -75 gates per m2 ) -cannot generate an action potential

113

trigger zone

(350 –500 gates per m2 ) –where action potential is generated

114

threshold

critical voltage to which local potentials must rise to open the voltage-regulated gates
•-55mV

115

action potential

process

look at slides

116

spike

action potential is often called a spike–happens so fast

117

characteristics of action potential versus a local potential

–follows an all-or-none law
•if threshold is reached, neuron fires at its maximum voltage
•if threshold is not reached it does not fire
–nondecremental-do not get weaker with distance
–irreversible-once started goes to completion and can not be stopped

118

refractory period

the period of resistance to stimulatio

119

two phases of the refractory period

–absolute refractory period
•no stimulus of any strength will trigger AP
•as long as Na+gates are open
•from action potential to RMP
–relative refractory period
•only especially strong stimulus will trigger new AP
–K+gates are still open and any effect of incoming Na+ is opposed by the outgoing K+

120

unmyelinated fiber

has voltage-regulated ion gates along its entire length

121

saltatory conduction

the nerve signal seems to jump from node to node(

122

presynaptic neuron

1st neuron in the signal path is the presynaptic neuron
•releases neurotransmitter

123

postsynaptic neuron

2nd neuron is postsynaptic neuron
•responds to neurotransmitter

124

presynaptic neuron may synapse with

a dendrite, soma, or axon of postsynaptic neuron to form axodendritic, axosomaticor axoaxonic synapses

125

Discovery of Neurotransmitters

synaptic cleft

gap between neurons was discovered by Ramón y Cajal through histological observations

126

Discovery of Neurotransmitters

Otto Loewi, in 1921, demonstrated that neurons communicate by releasing chemicals
later renamed acetylcholine, the first known neurotransmitter

127

electrical synapses

–some neurons, neuroglia, and cardiac and single-unit smooth muscle
–gap junctions join adjacent cells
•ions diffuse through the gap junctions from one cell to the next

128

electrical synapses

Advantages and disadvantages

advantage of quick transmission
•no delay for release and binding of neurotransmitter
•cardiac and smooth muscle and some neurons
–disadvantage is they cannot integrate information and make decisions
•ability reserved for chemical synapses in which neurons communicate by releasing neurotransmitters

129

Structure of a Chemical Synapse

•synaptic knob of presynaptic neuron contains synaptic vesicles containing neurotransmitter
•postsynaptic neuron membrane contains proteins that function as receptors and ligand-regulated ion gates

130

Neurotransmitters

4 classes

acetylcholine
amino acid neurotransmitters
monoamines
neuropeptides

131

acetylcholine

in a class by itself
•formed from acetic acid and choline

132

amino acid neurotransmitters

•include glycine, glutamate, aspartate, and -aminobutyric acid (GABA)

133

monoamines

•synthesized from amino acids by removal of the –COOH group
•retaining the –NH2(amino) group
•major monoamines are:
–epinephrine, norepinephrine, dopamine(catecholamines)
–histamine and serotonin

134

neuropeptides

chains of 2 to 40 amino acids
–beta-endorphin and substance P
•act at lower concentrations than other neurotransmitters
•longer lasting effects

135

Function of Neurotransmitters at Synapse

•they are synthesized by the presynaptic neuron
•they are released in response to stimulation
•they bind to specific receptors on the postsynaptic cell
•they alter the physiology of that cell

136

Effects of Neurotransmitters

•a given neurotransmitter does not have the same effect everywhere in the body
•multiple receptor types exist for a particular neurotransmitter
–14 receptor types for serotonin
•receptor governs the effect the neurotransmitter has on the target cell

137

neurotransmitters are diverse in their action

–some excitatory
–some inhibitory
–some the effect depends on what kind of receptor the postsynaptic cell has
–some open ligand-regulated ion gates
–some act through second-messenger systems

138

synaptic delay

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
–0.5 msec for all the complex sequence of events to occur

139

three kinds of synapses with different modes of action

–excitatory cholinergic synapse
–inhibitory GABA-ergic synapse
–excitatory adrenergic synapse

140

Excitatory Cholinergic Synapse

cholinergic synapse –employs acetylcholine (ACh) as its neurotransmitter
–ACh excites some postsynaptic cells
•skeletal muscle
–inhibits others

141

Inhibitory GABA-ergic Synapse

•GABA-ergic synapse employs -aminobutyric acid as its neurotransmitter
•nerve signal triggers release of GABA into synaptic cleft
•GABA receptors are chloride channels
•Cl-enters cell and makes the inside more negative than the resting membrane potential
•postsynaptic neuron is inhibited, and less likely to fire

142

Excitatory Adrenergic Synapse

•adrenergic synapse employs the neurotransmitter norepinephrine(NE) also called noradrenaline
•NE and other monoamines, and neuropeptides acts through second messenger systems such as cyclic AMP (cAMP)
•receptor is not an ion gate, but a transmembrane protein associated with a G protein

143

Cessation of the Signal

stop adding neurotransmitter and get rid of that which is already there
–stop signals in the presynaptic nerve fiber
–getting rid of neurotransmitter

144

getting rid of neurotransmitter by:

•diffusion
•reuptake
•degradation in the synaptic cleft

145

neuromodulators

hormones, neuropeptides, and other messengers that modify synaptic transmission
–may stimulate a neuron to install more receptors in the postsynaptic membrane adjusting its sensitivity to the neurotransmitter
–may alter the rate of neurotransmitter synthesis, release, reuptake, or breakdown

146

neural integration

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

147

neural integration is based on

the postsynaptic potentials produced by neurotransmitters

148

excitatory postsynaptic potentials (EPSP)

excitatory postsynaptic potentials (EPSP)
–any voltage change in the direction of threshold that makes a neuron more likely to fire
glutamate and aspartate

149

inhibitory postsynaptic potentials (IPSP)

any voltage change away from threshold that makes a neuron less likely to fire
glycine and GABA produce IPSPs and are inhibitory

150

acetylcholine (ACh) and norepinephrineare

excitatory to some cells and inhibitory to others

151

summation

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

152

temporal summation

occurs when a single synapse generates EPSPs so quickly that each is generated before the previous one fades
–allows EPSPs to add up over time to a threshold voltage that triggers an action potential

153

spatial summation

occurs when EPSPs from several different synapses add up to threshold at an axon hillock.
–several synapses admit enough Na+ to reach threshold
–presynaptic neurons cooperate to induce the postsynaptic neuron to fire

154

facilitation

a process in which one neuron enhances the effect of another one
–combined effort of several neurons facilitates firing of postsynaptic neuron

155

presynaptic inhibition

process in which one presynaptic neuron suppresses another one
–the opposite of facilitation

156

neural coding

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

157

qualitative information

depends upon which neurons fire
–labeled line code –each nerve fiber to the brain leads from a receptor that specifically recognizes a particular stimulus type

158

quantitative information

information about the intensity of a stimulus is encoded in two ways:
–one depends on the fact that different neurons have different thresholds of excitation
–other way depends on the fact that the more strongly a neuron is stimulated, the more frequently it fires

159

Kinds of Neural Circuits

4

diverging circuit
converging circuit
reverberating circuits
parallel after-discharge circuits

160

diverging circuit

–one nerve fiber branches and synapses with several postsynaptic cells
–one neuron may produce output through hundreds of neurons

161

converging circuit

–input from many different nerve fibers can be funneled to one neuron or neural pool
–opposite of diverging circuit

162

reverberating circuits

–neurons stimulate each other in linear sequence but one cell restimulates the first cell to start the process all over
–diaphragm and intercostal muscles

163

memory trace

physical basis of memory is a pathway through the brain called a memory trace or engram

164

synaptic plasticity

the ability of synapses to change

165

synaptic potentiation

the process of making transmission easier

166

kinds of memory

immediate, short-and long-term memory

167

immediate memory

the ability to hold something in your thoughts for just a few seconds
–essential for reading ability

168

short-term memory (STM)

lasts from a few seconds to several hours
–quickly forgotten if distracted
–calling a phone number we just looked up
–reverberating circuits

169

types of long-term memory

declarative
procedural

170

declarative

retention of events that you can put into words

171

procedural

retention of motor skills

172

Alzheimer Disease

memory loss for recent events, moody, combative, lose ability to talk, walk, and eat
•show deficiencies of acetylcholine (ACh) and nerve growth factor (NGF)

173

Parkinson Disease

progressive loss of motor function beginning in 50‟s or 60‟s -no recovery
–degeneration of dopamine-releasing neurons in substantia nigra
•dopamine normally prevents excessive activity in motor centers (basal nuclei)
•involuntary muscle contractions