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Flashcards in Nervous Tissue Deck (124):
1

Major components of nervous tissue

Neurons
Neuroglia

2

Neurons

specialized cells
electrically excitable
average of 100,000,000 in the human body

3

Neuroglia

support cells of the nervous system

4

Functional Categories of neurons

Sensory
Interneuron
Motor

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Sensory Neurons

gather information from receptors

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Internerurons

form a communicating network between neurons

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Motor neurons

convey impulses from nervous system to effector cells

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Neuron structure (body and cytoplasm)


What is the relevance of this structure?

Perikaryon with round euchromatic nucleus and prominent nucleolis, well developed RER and Golgi complexes and lots of mitochondria that form Nissl bodies. Many lysosomes in the cytoplasm. Lack centrioles and are unable to divide/replicate. Well developed cytoskeleton with neurofilaments (IF), microfilaments (actin) and microtules

*** need euchromatin, nucleolus, RER and mitochondria because they are producing neurotransmitter products , need to synthesize, need energy, need to get them where they need to go

9

Discuss the lack of centrioles in the neuron

Neurons are unable to replicate. Very few neuroblasts in the adult brain

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Centrosomes in neurons

Research shows that some neurons retain a centrosome which plays a role in microtubule nucleation

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Centrosome

Microtuble organizing center

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Microtuble Nucleation

spontaneous event that initiates the formation of microtubles

13

Clinical significane of the lack of centrioles in neurons

Can be assumed that a large majority of brain cancers arise from support cells rather than neurons in adults
(Astrocytoma most prevalent in adults)

In children there are more neuroblasts present and therefore it is more of a possibility that brain tumors arise from neurons (neuroblastoma)

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Neuron cell processes

1.) Axons
2.) Dendrites

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Axons

- ONLY one per neuron
- Take information from the perikaryon to the next neuron or axon terminal
-Fairly long
- Constant diameter throughout length
- Begin at axon Hillock
- Myelinated or unmyelinated

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Axon Hillock

Beginning of axons
Lack Nissl bodies

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Purpose of Myelin sheath

allows electrical impulses to travel rapidly through the axon

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Axeloma

Plasma membrane of the axon

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Axoplasm (definition and content)

Cytoplasm of the axon

- No nissl bodies
- No ribosomes
- Well developed SER

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Axon cytoskeleton

contains microtubules and neurofilaments

21

Dendrites

- Most neurons have several per cell
- Deliver information from the periphery to the perikaryon
- Short thick and tapered processes
- Profuse branching
- NOT myelinated

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Dendritic tree

result or profuse dendritic branching - increase the surface area for synaptic contacts

23

Dendritic spines

cover the dendritic branches to increase synaptic contacts
- Mushroom shaped head faces toward where most postsynaptic cells are located

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Dendritic cytoplasm

Similar to perikaryon cytoplasm

EXEPT no golgi complexes

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Antegrade Flow

Perikaryon ---> Periphery

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Types of Antegrade flow

Slow Axonal Transport
Fast Axon Transport

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Slow Axonal transport

type of antegrade flow

- 1-6 mm/day
- Moves smaller building blocks (Tubulin molecules, actin molecules)

28

Fast Axonal transport

type of antegrade flow

- 100-400 mm/day
- Moves larger cargo (SER vesicles, Neurotransmitters, Mitochondria)

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What gets moved by slow axonal transport

smaller building blocks
- Tubulin molecules
- Actin molecules
- Neurofilaments

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What gets moved by fast axonal transport

larger cargo
- SER vesicles
- Neurotransmitter vesicless
- Mitochondria

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Antegrade flow motor protein

Kinesisn

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Retrograde Flow

Axon terminal ---> Perikaryon

Dynin is the motor protein

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Types of Retrograde Flow

Fast Retrograde Flow

34

Clinical relevance of Retrograde Flow

this is the path that some viruses (Herpes simplex) and toxins (Tetanus) use to ender the CNS

35

Types of Neurons

1.) Pseuodunipolar
2.) Bipolar
3.) Multipolar

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Psuedounipolar Neurons

One process off of the cell body. T branches in to central and peripheral process. Both act as one axon

37

Location of Pseudounipolar Neurons

- Dorsal Root Ganglion
- Cranial Ganglion

38

Peripheral Processes of Psuedounipolar neurons

- Collect information from the sensory areas and brings it to the central process

39

Central Process of Psuedounipolar neurons

Delivers informatio to the CNS

40

Why psuedounipolar vs unipolar

In development it starts as two processes (axon and dendrite) but later fuse to form a larger single process off the perikaryon

41

Bipolar Neurons

Two processes
Axon
Dendrites: Act as sensory receptors

Sensory Neurons with limited location

42

Bipolar Neurons location

Major sense organs
(eye retina, olfactory mucosa, cochlea and semicircular canals of inner ear)

43

Multipolar neurons

most common type of neuron
Motor and Interneurons
One axon and many dendrites

44

Types of mutipolar neurons

Golgi Type I
Golgi Type II

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Golgi Type I neurons

Motor neurons (larger)
Long axons

46

Golgi Type II neruons

Interneurons (smaller)
Short axons

47

Innerplasma membrane potential

~ -70 mV

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What causes a negative resting membrane potential

10X more Na+ outside the cell than inside

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Depolarization

occurs when Na channels are opened by action potential traveling own the axon

Na diffuses through the membrane ( positive charges decrease the negative charge and depolarize the membrane)

50

Hyperpolarized

membrane can become more negative making it difficult for for the membrane to become depolarized

51

Types of Synapses

Electrical
Chemical

52

Electrical Synapse

Gap junctions in animals
Allow direct passage of ions from one cell to another causing neighbor to depolarize

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Chemical Synapse

- Primary type in mammals
- No protoplasmic connectivity
-Signal transmitted by the release of neurotransmitters

54

Excitatory chemical synapse

neuotransmitter binds postsynaptic cell and depolarizes the membrane. Likely to cause generation of action potential

55

Inhibitory chemical synapse

neurotransmitter binds postsynaptic cell and hyperpolarizes the postsynaptic cell making it less likely t create an actin potential

56

Chemical Synapse components

- Presynaptic Knob (with synaptic vesicles and neurotransmitters)
- Synaptic cleft
-Postsynaptic membrane

57

Release of neurotransmitters

Ca++ channels opened as the action potential reaches the presynaptic terminal which results in synaptic vesicles containing neurotransmitters to fuse to the membrane and be released into the cleft where neurotransmitter can bind postsynaptic receptor causing depolarization or hyperpolarization of the postsynaptic membrane

58

Types of Neurotransmitter deactivation

1.) High affininty reuptake
2.) Enzyme degradation

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High Affinity Reuptake

80% of neurotransmitters such as catecholamines (dopamine, norepinephrine)

Reincorporated via endocytosis into vesicles ready for repackaging

60

Enzyme degradation of neurotransmitters

Breakdown of neurotransmitter within the cleft

Acetylcholine ---> Acetate and Choline

61

Clinical Significance of neurotransmitter degradation

Inhibition of enzymes that breakdown norepinephrine or bloc high affinity reuptake has a beneficial effect on the treatment of depression

62

Synapse morphotype

Axodendritic (Axon to dendrite)
Axoaxonic (Axon to axon)
Axosomatic (Axon to Perkikaryon)
Motor end plate (Neuromuscular junction)

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Motor Endplate

Specialized type of synapse
Axon terminal releases acetylcholine into the cleft
Acetylcholine binds to receptors located in junctional folds of the sarcolema

64

Junctional folds

Area of the sarcolema of muscle cells that contain acetylcholine receptors

65

Curare Toxin

Found on skin of frogs
Toxin binds acetylcholine receptors (competitive inhibitor) and acts as a muscle relaxant (acetylcholine is still released but had nowhere to bind and therefore cannot cause contraction)
Death by asphyxiation due to paralysis of diaphragm

66

Botulism Toxin

Prevents the release of Acetylcholine from synaptic vesicles

67

Myasthania Gravis

Autoimmune disease in which autoantibodies bind acetylcholine receptors thereby weakening the muscles response to nerve stimuli (muscle weakness)

68

Rabies Virus (course of infection)

Animals carry virus in salivary glands
When bite occurs the muscle fibers break and virus begins to repilcate in the muscle (1-2 weeks, vaccination still effective at this point) after replication the virus moves to the motor endplate where it crosses the cleft and is taken into the CNS via retrograde transport. Once in the CNS it causes severe inflamation (small sounds or slight increases in light cause seizures) Virus ends up in the salivatory glands

** Generally after symptoms show up there is no cure

69

PNS support cells

- Schwann cells
- Satellite cells

70

Satellite cells

Found in ganglia of PNS
Surround individual neurons creating a microenvironment and providing electrical insulation
Provide a pathway for metabolic exchange
DO NOT have myelin

71

Schwann cells

Myelin secreting cells of the PNS
Envelop myelinated neurons and create clefts for unmyelinated neurons

Provide insulation (for rapid impulse) and isolation from the surrounding environment

72

Nodes of Ranvier

gaps between myelin sheaths

73

Saltatory conduction

Myelinated fibers
Fast conduction

axolema of nerve fibers near node of Ranvier have high concentration of Na channels

Membrane only depolarizes at the node and is suffiencient to elevate voltage of the next node allowing action potential to jump and continue down the axon

74

Schwann cells and myelinated axons

wraps all the way around the axon

Axon in the middle, Schwann cell around

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Schwann cells and unmyelinated axons

Schwann cells create clefts for nonmyelinated axons to sit in

Schwann in middle, axons surrounding

76

Action potential of unmyeliated fibers

travels like a wave

77

CNS Support Cells

Astrocytes
Oligodendrocytes
Microglia
Ependymal cells

78

Astrocytes

largest neuroglial cell (8-10 um)

Granular cytoplasm, large nuclei, numerous mitochondria

Processes extend between neurons and blood capillaries to form blood brain barrier

Play a role in moving metabolites between blood and nerve cells

Stain positively for GFA

79

Types of Astrocytes

Protoplasmic
Fibrous

80

Protoplasmic Astrocytes

Found in Gray matter
Numerous short branching processes that form perivascular feet

81

Blood brain barrier

formed by astrocytes and endothelium of capillaries

82

Fibrous Astrocytes

Found in white matter
More prominent cytoskeleton
Less branching
Fewer processes

83

Astrocytoma

most common tumor in the brain (20% of all brain tumors including those that have metastasized elsewhere)

80% of all tumors that originate in the brain

84

Astrocytes and local damage

Astrocytes responsible for forming glial scars through gliosis

85

Oligodendrocytes

Most common neuroglia of CNS

6-8 um

small nuclei, abundant SER, prominent golgi

Myelin sheath of the CNS

86

Myelin sheath formation (Schwanns vs Oligodendrocytes)

Oligodendrocytes- processes extend out of the cell and wrap around the CNS neuron

Schwanns wrap cell itself around or form clefts

87

Multiple sclerosis

damage to the myelin sheath of the CNS caused by immune cells resulting in the loss of myelin sheaths

symptoms: loss of sensitivity, partial paralysis (depends on area damaged)

88

Microglia

Phagocytic cells of CNS
Derived from monocytes
Smalles neuroglia (5-7 um)
Dark indented nucleus
Cytoplasm contains lysosome
short twisted processes covered in spikes
number of microglial cells increases with injury (believed to remove CNS debris)

89

Microglia clinical significance

Abundant in Alzheimers and parkinsons

possible that they contribute to plaque formation, demyelination, and destruction of CNS nerve fibers

90

Ependymal Cells

Simple cuboidal epithelium cells line the ventricles of the brain and cavities of the spinal cord

Produce and absorb CSF (microvilla to absorb and cilia to move CSF)

Contain GFAP

91

Are ependymal cells epithelial cells?

No, unlike true epithelia the ependymal cells lack a basement membrane. Instead the basal processes interdigitate with astrocyte processes to allow for exchange of metabolites

92

PNS components

Nerves (sensory and motor, myelinated and unmyelinated)
Ganglia

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Endoneurium

connective tissue covering individual nerve fibers

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Perineurium

Surround nerve fascicles

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Epineurium

surrounds individual nerves and extends into spaces between fascicles

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Ganglia

cluster of neuron cell bodies outside the CNS
Covered by connective tissue capsule
Associated with satellite cells

97

Types of Ganglia

1.) Sensory Craniospinal Ganglia
2.) Motor Ganglia of Autonomic NS

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Sensory Craniospinal Ganglia

Psuedounipolar neurons
- central processes (short) go to spinal cord (dorsal
root ganglia) or brain (cranial ganglia)
- peripheral processes go to receptor organ

99

Motor ganglia of Autonomic nervous system

Multipolar neurons and their satellite cells

100

Types of special nerve endings

1.) Motor Special endings
2.) Sensory nerve endings
3.) Proprioceptors

101

Types of special nerve endings

1.) Special senses nerve endings
2.) Somesthetic receptors

102

Types of somesthetic receptors

Free nerve endings
Encapsulated nerve endings (Pacinian and Meissner Corpuscles)

103

Special senses nerve endings

Sensory Nerve Endings

Specialized for smell, sight, hearing, and equilibrium

104

Somesthetic receptor locations

found throughout the body in epithelial tissue, connective tissue, muscles and joints

105

Free nerve endings

Somesthetic receptor

Branches sensory endings that mediate pain

106

Types of encapsulated nerve endings

Meissner's Corpuscle
Pacininian Corpuscles

107

Meissner's Corpuscle

Cylindrical stacks of lamellae that surround one or two sensory nerve endings

Sense of touch

Common in fingers and toes

108

Pacinian Corpuscles

Largest encapsulated nerve ending ( up to 2 mm)

Spherical shape formed up up to 30 concentric sheets of collagen with fluid and fibroblasts between them. Surround a single nerve fiber

respond to vibrations and deep pressure

Location: Dermis of skin, mesentaries, and inside of internal organs (pancreas)

109

Proprioceptors

collect information about the angulation of joints and muscle tension

110

Muscle spindle

specialized receptor unit located in skeletal muscle

Covered in two capsules with fluid space separating them.

Intrafusal fiber located in spindle

111

Intrafusal fiber

thin skeletal muscle muscle fiber within the muscle spindle surrounded by sensory and motor nerve fibers

Sensory nerve fiber wraps around intrafusal fiber to transmit information about degrees of stretching

Motor nerve fiber regulates the sensitivity of the stretch receptor

112

sensory nerve fibers and intrafusal fibers

sensory nerve fibers wraps around the intafusal fiber to transmit information about degrees of stretching

113

motor nerve fibers and intrafusal fibers

associated with intrafusal fiber and regulate the sensitivity of the stretch receptor

114

Gray matter

consists of neuron cell bodies and unmyelinated fibers
extensive blood supply

In brain: external
In spinal cord: Internal

115

Organization of grey matter in the spinal cord

organized into ventral and dorsal horns connected by gray commissure

116

Ventral horns of spinal cord

contain large neuron cell bodies

117

Dorsal horns of spinal cords

recieve information from sensory neurons

(** Sensory cell body is located outside the horn on the dorsal root ganglia)

118

Organization of gray matter in the brain

- external to white matter

- organized into deep folds called gyri (folds called folia in the cerebellum)

119

Organization of grey matter in cerebellum (and associated cell types)

three layers
1.) Molecular layer (basket cells)
2.) Purkinje layer (purkinje cells)
3.) Granular layer (Granule cells)

120

Purkinje cells

exhibit characteristics of multipolar neurons (many dendtrites, well expressed nucleoli, nissl bodies)

Cell processes extend all the way into the molecular layer

121

Central Nervous system

Brain and Spinal cord

122

White matter

myelinated axons and glial cells
limited blood supply
dense tissue
limited extracellular space
generally no synaptic contacts

123

White matter in the spinal cord

external to gray matter

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White matter in the brain

internal to gray matter