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Block 1 - Week 6 > Introduction to the Nervous System and Neurocytology > Flashcards

Introduction to the Nervous System and Neurocytology Flashcards

1
Q

Central Nervous System (CNS)

A

Consists of the:

  • Brain
  • Spinal cord
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2
Q

Peripheral Nervous System (PNS)

A

Consists of:

  • Cranial nerves and their derivatives from the brainstem
    • Except for CN I (Olfactory) and CN II (Optic) which are parts of the CNS
  • Spinal nerves and their derivatives from the spinal cord
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3
Q

What are the two divisionsof the peripheral nervous system?

A
  • Afferent (sensory) division
  • Efferent (motor+) division
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4
Q

Subdivisions of the afferent (sensory) division on the PNS

A
  • Somatic: signals from special sensory organs (except olfactory and retina epithelium), skin, skeletal muscles, joints, and tendons
  • Visceral: signals from internal organs and tissues
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5
Q

Afferent Neurons

A
  • Part of the Peripheral Nervous System
  • Are neurons that receive information from our sensory organs and transmit this input to the CNS
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6
Q

Efferent Neurons

A
  • Part of the Peripheral Nervous System
  • Are neurons that send impulses from the central nervous system to your limbs and organs
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7
Q

Subdivisions of the efferent (motor+) division on the PNS

A
  • Somatic: voluntary, innervating skeletal muscle
  • Visceral: involuntary, innervating smooth and cardiac muscles, glands, and adipose tissue. This subdivision is also known as the autonomic nervous system (ANS)
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8
Q

Neurons

A
  • Electrogenic cells that allow for rabid signaling throughout the body
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9
Q

Glia (AKA neuroglia or glial cells)

A
  • “Glue” of the nervous system
  • Involved in structural support, nutrient and O2 delivery, insulation, immune function, synaptic signaling, formation, and plasticity
  • Don’t fire action potentials
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10
Q

The full nervous system can be classified into which two groups?

A
  • Grey matter
  • White matter
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11
Q

Grey matter

A
  • Neuronal and glial cell bodies (somata)
  • Dendrites and unmyelinated axons
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12
Q

White matter

A
  • Myelinated axons
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13
Q

Nuclei

A

Functionally homogeneous grey-matter densities of the CNS

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14
Q

Ganglia

A

Functionally homogeneous grey-matter densities of the PNS

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15
Q

Tracts

A

Bundles of axons (white matter) of the CNS

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16
Q

Nerves

A

Bundles of axons (white matter) of the PNS

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17
Q

Neuron Structure

Cell Body/Soma/Perikaryon

A
  • Contains organelles
  • Blue arrows in picture
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18
Q

Neuron Structure

Dendrites

A
  • Shorter projections (yellow arrowheads in picture)
  • Afferent: receive signals and sends them to soma
  • Dendritic spines: increase surface area
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19
Q

Neuron Structure

Axon

A
  • Much longer projection (green triangle in picture)
  • Efferent: sends signals away from soma to synapse
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20
Q

Neuron Structure

Nucleus and Nucleolus

A
  • Large central nucleus
  • Strong nucleolus
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21
Q

Neuron Structure

Nissl Bodies/Nissle Substance

A
  • Dark staining endoplasmic reticulum/ribosomes
  • Soma makes tons of proteins
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22
Q

Neuron Structure

Axon Hillock

A
  • Initiates action potential
  • Lots of ion channels and microtubles
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23
Q

Neuron Structure

Myelin Sheath

A
  • Fatty wrapping around axon
  • Increases speed of impulse conduction
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24
Q

Neuron Synapse

A

Communication point between neuron and target

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25
Q

Multipolar Neuron

A
  • Single axon and many dendrites
  • Most common
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26
Q

Bipolar Neuron

A
  • Single axon and single dendrite
  • Seen in sensory organs
27
Q

Unipolar/Pseudounipolar Neuron

A
  • Single projection splits into axon and dendrite
  • Common in the spinal ganglia
28
Q

Neuroglia (glial cells) of the CNS

A
  • Astrocytes
  • Oligodendrocytes
  • Microglia
  • Ependymal cells
29
Q

Neuroglia (glial cells) of the PNS

A
  • Satellite cells
  • Schwann cells
30
Q

Astrocytes

A
  • CNS Glial cells
  • Large star-shaped cells
  • Filled with intermediate GFAP filaments
  • Large irregular neclei (arrows in picture)
  • 2 subcategories:
    • Protoplasmic (grey matter)
    • Fibrous (white matter)
  • Functions:
    • Structural and metabolic support
    • Scavenge NT and ions in synapse
    • Form neural scar (glial scar)
    • Form the blood brain barrier
31
Q

Blood Brain Barrier

A
  • Endothelial cells of capillaries have tight junctions
  • Continous basal lamina/basement membrane
  • Astrocyte foot processes form outer layer
  • Small molecules can cross (gases, hormones, ethanol)
  • Large molecules must be transported (glucose, amino acids)
  • Functions:
    • Protects the brain from compounds or pathogens in blood
    • Restricts ion transport to protect neuronal activity
    • Neutralizes drugs and toxins
32
Q

Oligodendrocytes

A
  • Smaller glial cells of the CNS
  • Small, round dense nucleus with small halo (arrow in picture)
  • Functions:
    • Produce myelin sheath for brain and spinal cord
    • Each oligodendrocyte wraps multiple axons
33
Q

Microglia

A
  • Very small glial cells of the CNS
  • Derived from monocyte precursors in the bone marrow
  • Small, cigar shaped nuclei (arrows in picture)
  • Functions:
    • Immune defense for CNS
    • Antigen presenting cell
    • Initiate inflammatory response
    • Phagocytose cell debris after injury
    • Glial scar formation
34
Q

Ependymal Cells

A
  • Glial cells of the CNS
  • Line the ventricles and central canal (arrows in picture)
  • Act as epithelium, lots of tight junctions
  • Cilia and microvilli on apical ssurfaces
  • Functions:
    • Move and absorb cerebrospinal fluid (CSF)
    • Help form the blood–CSF barrier
    • Specialized ependymal cells form the choroid plexus in third ventricle of brain
35
Q

Satellite Cells

A
  • Small glial cell of the PNS
  • Surrounds neuron somata in spinal ganglia (arrows in picture)
  • Functions:
    • Insulate neurons from electrical impulses
    • Metabolic support
36
Q

Schwann Cells

A
  • Small glial cell of the PNS
  • Extends cytoplasm around developing axon (each schwann cell wraps a single axon)
  • Multiple layers of cell membrane form the myelin sheath
  • Node of Ranvier: point between two Schwann cells
  • Function:
    • Form myelin sheath for peripheral nerves
    • Insulate axons from each other
37
Q

Synaptic Vesicle

A
  • Filled with neurotransmitters
  • Fuse with membrane to release NTs after calcium influx via opening of voltage gated Ca2+ channels
38
Q

Pre-Synaptic Membrane

A
  • Releases neurotransmitters
  • Recycles membrane for new vesicles
39
Q

Synaptic Cleft

A
  • Space between pre-synaptic membrane and post-synaptic membrane
  • 20-30 nm gap
40
Q

Post-Synaptic Membrane

A
  • Where neurotransmitter binds receptors
  • This causes ion channels to change membrane potential
  • Causing new action potential in target neuron
41
Q

Axodendritic Synaptic Connections

A

Axon synapses on dendrite

42
Q

Axosomatic Synaptic Connections

A

Axon synapses on soma

43
Q

Axoaxonic Synaptic Connections

A

Axon synapses on axon

44
Q

Excitatory Signals

A
  • Open Na+ channels to depolarize neuron
  • Makes it easier to reach threshold and fire action potential
45
Q

Inhibitory Signals

A
  • Open Cl- channels to hyperpolarize neuron
  • Makes it harder to reach threshold and fire action potential
46
Q

Electrical Synapses

A
  • Contains gap junctions linking cytoplasm together for direct cell to cell contact
  • Instant transmission; no neurotransmitters
  • Examples: smooth muscle and cardiac muscle
47
Q

Chemical Synapses

A
  • Cells do not physically touch
  • Requires neurotransmitters
  • Delayed transmission (~0.5 ms)
  • Examplse: neuromuscular junction, most neurons
48
Q

Peripheral Nerve Structure

Epineurium

A
  • Dense outer connective tissue covering (arrow in picture)
  • Can contain blood vessels or adipose
49
Q

Peripheral Nerve Structure

Perineurium

A
  • Wraps of bundle (fascicle) of axons together
  • (Golden arrowhead in picture)
50
Q

Peripheral Nerve Structure

Endoneurium

A
  • Innermost layer of reticular fibers
  • Surrounds individual axon; red substance between axons
  • Secreted by fibroblasts and Schwann cells
  • (Green triangle in picture)
51
Q

Axon Histology

A
  • Round, central region
  • (Blue arrow in picture)
52
Q

Myelin Shealth Histology

A
  • Dense lines surrounding axons
  • (Yellow arrowhead in picture)
53
Q

Schwannn Cell Nucleus Histology

A
  • Folden around the myelin sheath
  • (Green triangle in picture)
54
Q

Endoneurium Histology

A
  • Innermost layer of reticular fibers
  • Surrounds individual axon; red substance between axons
  • Secreted by fibroblasts and Schwann cells
55
Q

Nodes of Ranvier

A
  • Unmyelinated spaces between adjecent glia on axons
  • Lots of ion channels
  • Location where action potentials are propagated down myelinated nerves
56
Q

How does myelin increase speed of nerve impulse

A
  • Saltatory Conduction: action potential “jumps” to noes of ranvier
  • Only small areas of axon membrane depolarize
  • Unmyelinated Rate: 0.5-10 m/sec
  • Myelinated Rate: up to 150 m/sec
57
Q

What myelinatess the CNS?

A
  • Oligodendrocytes
  • A single oligodendrocyte wraps around multiple axons
58
Q

What myelinates the PNS?

A
  • Schwan cells
  • A single schwann celll wraps one axon
59
Q

Chemical Synapse Steps

A
  1. Action potential arrives
  2. Voltage gated calcium channels open; calcium influx
  3. synaptic vesicles fuse to pre-synaptic membrane; NT is released and diffuses across synapse
  4. Neurotransmitters bind receptors on post synaptic membrane
  5. Target cell membrane potential changes
60
Q

Nerve Injury Process (Basics)

A
  • Damage to axons can heal; damage to cell bodies is irreversible (neurons are post-mitotic/cannot replicate)
  • Axonal damage triggers rapid electrical injury signal; can kill the neuron if strong enough
  • Injury signal proteins slowly move via retrograde transport to soma via dynein
  • Wallerian degeneration and chromatolysis occur
  • Soma produces proteins and lipids, ships them down axon via anterograde transport (kinesin)
61
Q

Wallerian (anterograde) degeneration

A
  • Axon segment distal to injury degrades
  • A short piece of the proximal segment also degrades (retrograde degeneration)
62
Q

Chromatolysis

A
  • Nucleus and Nissle bodies move to periphery, soma swells
63
Q

Peripheral Nerve Regeneration

A
  • High regeneration potential
  • Macrophages eliminate degraded axon/myelin
  • Schwann cells proliferate to form a channel
  • Axon growth cone sprouts from soma and travels down channel to re-establish synapse with target
64
Q

CNS Nerve Regeneration

A
  • Low regeneration portential
  • Oligodendrocytes undergo apoptosis
  • Blood brain barrier blocks macrophages
  • Microglia can’t clear debris (inflamation increases)
  • Left over myelin blocks regrowth
  • Gliosis: Hypertrophy of astrocytes
  • Glial scar forms and blocks growth cone

Block 1 - Week 6 (6 decks)

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