Introduction to the Nervous System and Neurocytology Flashcards
1
Q
Central Nervous System (CNS)
A
Consists of the:
- Brain
- Spinal cord
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
3
Q
What are the two divisionsof the peripheral nervous system?
A
- Afferent (sensory) division
- Efferent (motor+) division
4
Q
Subdivisions of the afferent (sensory) division on the PNS
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- Somatic: signals from special sensory organs (except olfactory and retina epithelium), skin, skeletal muscles, joints, and tendons
- Visceral: signals from internal organs and tissues
5
Q
Afferent Neurons
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- Part of the Peripheral Nervous System
- Are neurons that receive information from our sensory organs and transmit this input to the CNS
6
Q
Efferent Neurons
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- Part of the Peripheral Nervous System
- Are neurons that send impulses from the central nervous system to your limbs and organs
7
Q
Subdivisions of the efferent (motor+) division on the PNS
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- 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)
8
Q
Neurons
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- Electrogenic cells that allow for rabid signaling throughout the body
9
Q
Glia (AKA neuroglia or glial cells)
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- “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
10
Q
The full nervous system can be classified into which two groups?
A
- Grey matter
- White matter
11
Q
Grey matter
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- Neuronal and glial cell bodies (somata)
- Dendrites and unmyelinated axons
12
Q
White matter
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- Myelinated axons
13
Q
Nuclei
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Functionally homogeneous grey-matter densities of the CNS
14
Q
Ganglia
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Functionally homogeneous grey-matter densities of the PNS
15
Q
Tracts
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Bundles of axons (white matter) of the CNS
16
Q
Nerves
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Bundles of axons (white matter) of the PNS
17
Q
Neuron Structure
Cell Body/Soma/Perikaryon
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- Contains organelles
- Blue arrows in picture
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
19
Q
Neuron Structure
Axon
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- Much longer projection (green triangle in picture)
- Efferent: sends signals away from soma to synapse
20
Q
Neuron Structure
Nucleus and Nucleolus
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- Large central nucleus
- Strong nucleolus
21
Q
Neuron Structure
Nissl Bodies/Nissle Substance
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- Dark staining endoplasmic reticulum/ribosomes
- Soma makes tons of proteins
22
Q
Neuron Structure
Axon Hillock
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- Initiates action potential
- Lots of ion channels and microtubles
23
Q
Neuron Structure
Myelin Sheath
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- Fatty wrapping around axon
- Increases speed of impulse conduction
24
Q
Neuron Synapse
A
Communication point between neuron and target
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Multipolar Neuron
* Single axon and many dendrites
* Most common
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Bipolar Neuron
* Single axon and single dendrite
* Seen in sensory organs
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Unipolar/Pseudounipolar Neuron
* Single projection splits into axon and dendrite
* Common in the spinal ganglia
28
Neuroglia (glial cells) of the CNS
* Astrocytes
* Oligodendrocytes
* Microglia
* Ependymal cells
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Neuroglia (glial cells) of the PNS
* Satellite cells
* Schwann cells
30
Astrocytes
* 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
Blood Brain Barrier
* 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
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Oligodendrocytes
* 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
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Microglia
* 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
Ependymal Cells
* 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
Satellite Cells
* Small glial cell of the PNS
* Surrounds neuron somata in spinal ganglia (arrows in picture)
* Functions:
* Insulate neurons from electrical impulses
* Metabolic support
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Schwann Cells
* 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
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Synaptic Vesicle
* Filled with neurotransmitters
* Fuse with membrane to release NTs after calcium influx via opening of voltage gated Ca2+ channels
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Pre-Synaptic Membrane
* Releases neurotransmitters
* Recycles membrane for new vesicles
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Synaptic Cleft
* Space between pre-synaptic membrane and post-synaptic membrane
* 20-30 nm gap
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Post-Synaptic Membrane
* Where neurotransmitter binds receptors
* This causes ion channels to change membrane potential
* Causing new action potential in target neuron
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Axodendritic Synaptic Connections
Axon synapses on dendrite
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Axosomatic Synaptic Connections
Axon synapses on soma
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Axoaxonic Synaptic Connections
Axon synapses on axon
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Excitatory Signals
* Open Na+ channels to depolarize neuron
* Makes it easier to reach threshold and fire action potential
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Inhibitory Signals
* Open Cl- channels to hyperpolarize neuron
* Makes it harder to reach threshold and fire action potential
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Electrical Synapses
* Contains gap junctions linking cytoplasm together for direct cell to cell contact
* Instant transmission; no neurotransmitters
* Examples: smooth muscle and cardiac muscle
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Chemical Synapses
* Cells do not physically touch
* Requires neurotransmitters
* Delayed transmission (~0.5 ms)
* Examplse: neuromuscular junction, most neurons
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Peripheral Nerve Structure
Epineurium
* Dense outer connective tissue covering (arrow in picture)
* Can contain blood vessels or adipose
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Peripheral Nerve Structure
Perineurium
* Wraps of bundle (fascicle) of axons together
* (Golden arrowhead in picture)
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Peripheral Nerve Structure
Endoneurium
* Innermost layer of reticular fibers
* Surrounds individual axon; red substance between axons
* Secreted by fibroblasts and Schwann cells
* (Green triangle in picture)
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Axon Histology
* Round, central region
* (Blue arrow in picture)
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Myelin Shealth Histology
* Dense lines surrounding axons
* (Yellow arrowhead in picture)
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Schwannn Cell Nucleus Histology
* Folden around the myelin sheath
* (Green triangle in picture)
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Endoneurium Histology
* Innermost layer of reticular fibers
* Surrounds individual axon; red substance between axons
* Secreted by fibroblasts and Schwann cells
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Nodes of Ranvier
* Unmyelinated spaces between adjecent glia on axons
* Lots of ion channels
* Location where action potentials are propagated down myelinated nerves
56
How does myelin increase speed of nerve impulse
* **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
What myelinatess the CNS?
* Oligodendrocytes
* A single oligodendrocyte wraps around multiple axons
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What myelinates the PNS?
* Schwan cells
* A single schwann celll wraps one axon
59
Chemical Synapse Steps
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
Nerve Injury Process (Basics)
* 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
Wallerian (anterograde) degeneration
* Axon segment distal to injury degrades
* A short piece of the proximal segment also degrades (retrograde degeneration)
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Chromatolysis
* Nucleus and Nissle bodies move to periphery, soma swells
63
Peripheral Nerve Regeneration
* 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
CNS Nerve Regeneration
* 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
