Cellular Neuroanatomy Flashcards
1
Q
2 Principle Cells Types of Neuroanatomy
A
1) Neurons & their unique morphology
- cell bodies (soma) & Nissl bodies
- morphology & function of dendrites & axons
- axonal transport
2) Neuroglia: function & morphology of different glia cells
- astrocytes & satellite cells
- Schwann cells, oligodendrocytes, & meylin
2
Q
Connections b/w Neurons
A
- Chemical synapses: Morphology, function, & neurotransmitters
- Electrical Synapses
3
Q
The Neurons
A
- structural & functional unit of the NS
- electrically excitable
- collects sensory information
- integrated information
- controls effector organs like muscles & glands
4
Q
Supporting Cells (glia)
A
- glia = glue
- provide physical support (protection)
- electrical insulation for impulse conductance
- metabolic exchange between the vascular system and the NS
5
Q
The Cell Body (Soma)
A
- cell’s supply station
- produces proteins & provides metabolic function
- houses cell nucleus (light area) & machinery for metabolic functions and the production of proteins
- has nucleoulus (dark spot)
- cytoplasm that contains all cell organelles like rER, Golgi, lysosomes, & mitochondria
- soma in neurons is rich in rER (it produces a large amount of proteins, large stacks appear as islands in Nissl stain)
6
Q
Dendrites
A
- cell’s receiver: imputs
- receives electrical impulses from other neurons
- neuron may have one or many
- synaptic inputs on most cells (especially excitatory synaptic input) are preferentially on to dendrites & dendritic spins
7
Q
Axon
A
- output for the cell
- sends electrical impulses to other neurons
- each neuron has a single axon, originates at soma where it forms an axon hillock (free of cell organelles)
- electrical signals are initiated in axon & travel down the axon to terminal, where neurotransmitters are released for chemical neurotransmission
8
Q
Dendritic Spines
A
- small, membranous protrusions from the dendrite
- receive synaptic inputs (excitatory)
- transmit electrical signals to the dentrite
- serve as anatomical substrate for synaptic transmission
- synaptic plasticity
- memory storage
- hundreds of thousands per dendrites
9
Q
Gray Matter
A
-unmyelinated tissue-primarily somas & dendrites
10
Q
White Matter
A
-tissue containing myelinated axons (myelin = lipid wrapping on axons, appearance is white in unstained tissue)
11
Q
Nissl Stain
A
- stains neuronal somas
- primarily indicates cell bodies & proximal dendrites (not axons)
12
Q
Nissl Bodies
A
- basophilic masses, primarily rough endoplasmic reticulum (rER) and ribosomes
- masses are concerned with protein synthesis, much of which occurs in cell bodies of neurons
13
Q
Nissl Substance Extends into?
A
-proximal dendrites but not into the axon hillock, which gives rise to the axon
14
Q
Pyramidal neuron
A
- pear-shaped soma & prominent apical dendrite (shown extending upwards from soma)
- typically have a group of basal dendrites as well as the apical dendrite & its branches
15
Q
Initial Segment
A
- portion of axon from the hillock to the beginning of myelination
- site of action potential initiation
16
Q
Motoneuron
A
-when axon connects to a effector organ (muscle, gland)
17
Q
Long axons are myelinated because?
A
electrical insulation resulting in faster nerve impulses conduction
18
Q
Collaterals
A
-major branches of an axon
19
Q
Neuron Types
A
- unipolar (pseudo)
- bipolar
- multipolar
20
Q
Unipolar Neurons
A
- have a single neurite (process - axon or dendrite)
- do not exist in mature vertebrate nervous system
21
Q
Pseudounipolar Neurons
A
- sensory neurons with cell bodies in the dorsal root ganglia
- peripheral & central processes of a single axon mostly bypass the soma
22
Q
Bipolar Neurons
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- mostly local circuit interneurons
- 2 primary neurites (dendrites)
- leave the soma at opposite ends of the cell
23
Q
Multipolar Neurons
A
- several primary dendrites leaving the soma
- Ex: pyramidal neurons of cortical regions, Purkinje cells of cerebellum, or motoneurons (spinal cord & brain stem)
24
Q
Silver Stain
A
(Golgi-stained cells)
-stain random subset of cells but show entire morphology of those cells
25
Principle Cells
- are projection neurons
- integrate information & send axons to other brain areas (path of an axon from one brain area to another)
- Golgi Type I cells (long projection axon)
26
Interneurons
- cells that do not send their axon out of the local brain area
- Ex: chandelier cells, basket cells, double bouquet cells (in cortex)
- local circuit neurons
- Golgi Type II cells (either no axon or short, local axon)
27
Synapses
-specialized junctions that allow neural signals to be communicated from one cell to another (or from neuron to another effector)
28
2 Types of synaptic transmission?
1) Chemical
| 2) Electrical: form direct electrical connections b/w neurons, called gap junctions
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Electrical Synapses
- formed as direct connections from one cell to another via gap junctions
- electrical signals & small molecules can pass directly b/w the pre-and-postsynaptic cell at an electrical synapse
- close appositions of the pre/post synaptic membranes
30
Chemical Synapses
-electrical signal in the presynaptic neuron is transduced into release of a chemical transmitter that traverse a synaptic cleft w/w cells to bind to receptors on the postsynaptic neuron (or effector)
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Location of most excitatory synapse in the brain?
dendritic spines
32
Neuromuscular Junction
-when a synapse is formed b/w a neuron and a muscle
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Axosomatic Synapse
contact from an axon to a soma
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Axodendritic Synapse
axon contacting a dendrite (spine or shaft)
35
Most excitatory synapses are formed on?
dendritic spines (axospinous = subset of axodendritic)
36
Axoaxonic Synapse
axon to axon synaptic contact
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Dendrodendritic Synapse
dendrite to dendrite
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Vertebrate Chemical Synapses
-unidirectional
| only transmit information from the presynaptic neuron to the postsynaptic neuron
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Steps of Chemical Synapse
1) Presynaptic bouton (axonal varicosity) contains membranous synaptic vesicles called synaptic vesicles that contain neurotransmitter
2) On an incoming nerve impulse, entry of Ca2+ causes synaptic vesicles to release their contents into the synaptic cleft
3) Specialized receptor proteins located in the postsynaptic density bind the neurotransmitter & generate another electrical signal in the postsynaptic cell
40
3 Types of neurotransmitters?
- Excitatory
- Inhibitory
- Modulatory
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Excitatory Neurotransmitters
- increases the probability that the postsynaptic neuron will fire a nerve impulse
- Ex: synapses containing ACh (at nicotinic receptors) or glutamate (AMPA, NMDA receptors)
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Inhibitory Neurotransmitters
- reduces the probability that the postsynaptic neuron will fire a nerve impulse
- Ex: synapses with glycine or gamma-aminobutyric acid (GABA - at GABAa receptors)
43
Modulatory Neurotransmitters
- influences how excitatory and inhibitory signals are integrated
- Ex: synapses using dopamine or norepinephrine (also acetylcholine at muscarinic receptors & GABA at GABA b receptors)
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Type I Synapse
-Excitatory (excitatory amino acids)
-Asymmetric - pronounced postsynaptic density (denser that presynaptic membrane)
(Gray's type 1)
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Type II Synapse
-Inhibitory (GABA, Glycine)
-Symmetrical (thin postsynaptic density - same density as presynaptic membrane)
(Gray's type 2)
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Excitatory
something that increases the probability for an action potential
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Inhibitory
something that decreases the probability for an action potential
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Where are type I synapses found?
mainly on dendrites & result in an excitatory response in the post-synaptic cell
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Where are type II synapses found?
on the soma & inhibit the receiving cell's activity
50
Connexons
(large channels)
- direct, passive flow of electrical current from one cell to the next is achieved by these
- made up of molecules called connexins (6 form a connexon)
51
Electrical synapses
bi-directional, either cell can be both pre- and postsynaptic
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Gap Junctions are made up of?
-a connexon from each cell
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Axonal Transport
- proteins synthesized in the soma are packed into cargo vesicles & transported along microtubules toward their destination (ratchet-like action)
- kinesin
- dynesin
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Kinesin
-moves cargo vesicles anterograde (away from soma)
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Dynein
-moves cargo vesicle retrograde (toward soma)
56
Supporting Cells
- neuroglia (glia: Schwann cells, Oligodendrocytes, Astrocytes) as well as other cell types (microglia, satellite cells, ependymal cells)
- not "excitable cells" do not generate action potentials
- structural support
- facilitating electrical signaling
- isolating cells electrically & biochemically
- assisting in repair in response to injury
- producing cerebrospinal fluid
57
Schwann Cells
- provide myelination in the peripheral nervous system
- improves electrical insulation, which increases conductance velocity for action potentials
- individual cells wrap around an axon
- where 2 cells touch, form "node of Ranvier" (unmyelinated area), site where action potentials regenerate
- synapses are not myelinated
58
Oligodendrocytes
- provide myelination in the central nervous system
- each process provides myelination for one axon, therefore one oligodendrocte myelinates several axons
- neighboring internodes originate from different oligodendrocytes
- many axons in the CNS are not myelinated
- one forms 30-50 internodes (many different axons, 1 internode per axon)
59
Astrocytes
- there are 2 types: fibrous (white matter)& protoplasmic (grey matter), radial astrocytes "servants of CNS"
- general support
- blood brain barrier
- move metabolites to & from neurons = metabolic exchange
- maintain constant ionic conc. for optimal neuronal function
- radiating processes (astrocyte), contact neurons (perineural feet), endothelial cells of blood vessels (perivascular feet), and myelin
60
Satellite Cells
- function as astrocytes in the autonomic NS/ peripheral ganglia
- small, cubodial cells of neural crest origin
- modified Schwann cells (PNS) or oligodendrocytes (CNS)
- surround the entire soma of ganglion cels, but only their nucleus is visible in H&E stains
61
Microglia
- phagocytosis, inflammation
| - "immune cells of the CNS"
62
Polydendrocytes
stem cells within the brain
63
Ependymal Cells
- ventricles of the brain and the central canal of the spinal cord are lined with ependymal cells
- form a cuboidal to columnar epithelium, ciliated
- lack tight junctions b/w ependymal cells allows a free exchange b/w cerebrospinal fluid and nervous tissue
- apical surface covered with cilia and microvilli
- basal surface is in close contact with astrocytes
64
Neuroglia
- "GLUE"
| - outnumber neurons 10 to 1, make up 50% brain volume
65
Schmidt-Lanterman Clefts
-small folds of cytosol remain to support the myelin
66
Each Schwann Cell forms how many internodes?
1
67
Osmium Stain
-stains individual myelinated axons black
68
Endoneurium
thin layer of connective tissue (stain brownish), that surrounds each nerv fiber
69
Perineurium
-delimits the fascicle
70
Fibrous Astrocytes
-have vascular feet that physically connect them to the outside capillary walls
71
Radial Astrocytes
- oriented in a plane perpendicular to the axis of the ventricles, with one axis towards the pia and the other near the vnetricle
- mostly present during dev. and play a role in neuron migration
72
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Mueller Cells (retina)
Bergmann Glia (cerebellum)
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-examples of radial glia that persist into adulthood
