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Flashcards in Neuron Notes Deck (49):
1

Neurons

Arise from the ventricular layer of the neural tube

Neurofilaments are sparse in young neurons and cilia and centrioles are found

Very little rna in developing neurons

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Neuron growth

Increase in RER and golgi

Precursors to Nissl bodies on nucleus and cytoplasmic glycogen reduced

Proliferation of mitochondria and ribosomes

Microtubules and neurofilaments increase forming axonal volume

3

Growth cones

Tips of the initial neural outgrowth and branches

4

Axonal growth

Non random process

Grow out in consistent directions, initial overproduction of axons

Intrinsic factors determine axonal termination

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CNS and termination

Chemical affinity

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Dendritic ramification

Believed to be associated with activity sensory stimulation and developing cognitive facility

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CNS

Brain and spinal cord

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PNS

Ganglia and peripheral nerves

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Sensory neurons

Detect events in periphery through receptors

Located in dorsal root ganglion of spinal cord

Cell body, peripheral nerve innervate receptor and central axon conveys signal to spinal cord or brain

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Motor neurons

CNS gray matter of spinal cord and brain

Axons enter PNS through spinal or cranial nerves and innervate striated muscle

Innervated by postganglionic axons

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Interneurons

Majority of neurons in brain and spinal cord

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Projection neurons

Interneurons that leave one brain region and travel to another

Many are excitatory

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Upper motor neurons

Projection neurons that strongly influence motor neuron

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Local interneurons

Axons that ratify in immediate vicinity of their cell body

Most local release inhibitory neurotransmitters

15

Neuroglia

Non neuronal CNS cells

Supportive function for neurons

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Ependymal cells

Line the ventricles which contain CSF

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Meninges

Connective tissue in CNS that envelops the ventricle system

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PNS derivation

From embryonic neural crest

Dorsal root ganglion and autonomic postganglionic cells

Supporting cells are satellite cells and Schwann cells analogous to neuroglia

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Dorsal root ganglion

Primary sensory neurons in PNS

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Autonomic postganglionic cells

Innervate smooth muscles and glands, PNS

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Motoneuron

Innervates skeletal muscle

Nucleus with single nucleotide and cytoplasm with organelles

Cell body, soma and perikaryon are contained in nucleus of neuron

22

Cell body

Metabolic center of the cell

Membrane surrounds entire cell including cytoplasmic processes- axons and dendrites

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Dendritic spines

Projections off dendrites

24

Axons

Each neuron has only 1 axon

Axon collaterals are the branches of axons

Axon originates from axon hillock in cell body

25

Initial segment

Region between axon hillock and myelin sheath

Initiation of action potential

26

Boutons

Specialized to form functional contacts with other cells

Contact areas are synapses if interact with muscle are neuromuscular junctions

27

Nissl bodies

Cytoplasm of neurons filled with clumps of intensely staining bodies

Aggregates of RER in nucleus and proximal parts of dendrites

Axons have no ER so no stain so if numerous axons appear white

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Silver stain

Has affinity for neurofibrils , nuclear membrane and nucleolus attract

Shows axons and cell bodies

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Golgi stain

Only stain which shows neuron will all processes, entire trajectory and dendritic spread

30

Neuron plasma membrane

Three layers, differs in thickness in region of synapse where membrane is thickened and ER is elaborate

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Two abundant filamentous structures

Microtubules in dendrites and neurofilaments in axons

Transport and forms scaffolding to maintain neuron complexity

32

Chemical synapses

Most common in mammalian nervous system

Presynaptic complement of membrane bound vesicles
Aggregations in cytoplasm adjacent to membrane
Distinct synaptic cleft or intercellular space
Mitochondria

33

Synaptic vesicles

Feature of chemical synapse

Contain neurotransmitters and shape can vary

Synaptic density can be on one or both sides

34

Synaptic cleft

Distinct gap between pre and post synaptic cell membranes

Clear or striated

Contains glycoproteins and can be involved in specificity

Mitochondria presynaptic and use ATP for energy

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Electrical synapse

Rarer

Close apposition of pre and postsynaptic membranes

No intracellular cleft

36

Neuroglia cell types

Astrocytes, oligodendrocytes, and microglia

Differ from neurons because unpolarized, proliferate, no synapses and do not transmit action potentials

37

Astrocytes

Star shaped

Processes extend around neural cell bodies and fibers

Irregular nucleus

Fibrous in white matter and protoplasmic is grey matter

Regulate blood flow, vasodilation and constriction and neurotransmitter action

Form scar tissue

38

Oligodendrocytes

Myelin in CNS, predominant cell type in white matter

In grey matter are perineuronal satellite cells

Extensive cytoplasmic processes

Chief function= maintenance of myelin sheath around axons, segments of myelin are nodes of ranvier

39

Internode

Myelin segment between two nodes

40

Ependyma

Microvilli and cilia form specialized junctions with one another

Vascular regions known as choroid plexus, associated with meninges

Tanycyte

41

Tanycyte

Cell with basal processes through nervous tissue to blood vessels or Pia

Hypothalamic hormones to pituitary

42

Microglia

Macrophages of the Brain

First line of defense

From hematopoietic stem cells


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Ganglia

PNS neuron cell body aggregates

44

Dorsal root ganglia

Unipolar, connected to spinal cord by dorsal root which is purely sensory

Motor fibers from ventral root and form peripheral nerves by joining in intervertebral foramen

45

Schwann cells in PNS

Neural crest derivation

Produce myelin

In CNS oligodendroglial cells will myelinate

Myelinate sensory then as reach CNS oligo myelinates

46

Endoneurium

Schwann cells here in connective tissue matrix

Wrapped with perineurium which have tight junctions and are wrapped by epineurium which contains fat and blood vessels

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Retrograde degeneration

Of cut nerve fibers simultaneously from both ends

Peripheral nerves within 7 days regenerate and grow into scar, Schwann cells remylinate

48

Regenerative nerve fibers

Can grow into mass if misdirected- neuromas

49

CNS NEURONS

No neuronal replacement