Histology: Nerve Tissue Flashcards
1
Q
Central Nervous System
A
Brain and spinal cord
2
Q
Peripheral Nervous System
A
- Cranial Nerves
- Spinal Nerves
- Ganglia
3
Q
Neuron
A
- Functional unit of nervous system
- Specialized to receive and transmit electrical impulses
3 Main Parts:
- Cell body
- Dendrites
- Axon
Classified Based on Shape:
- Multipolar
- Bipolar (one axon and one dendrite)
- Pseudounipolar (one process that divides into two)
4
Q
Cell Body
A
- Nucleus and organelles
- Prominent nucleolus
- Highly developed RER and many free polyribosomes (Nissl substance)
- Basophilic staining
5
Q
Dendrites
A
- Shorter, smaller process
- Typically immerge from soma in multipolar
- Receive information from other neurons
- Unmyelinated
- Can form dendritic trees to increase surface area
- Lack Golgi (do not secrete proteins)
6
Q
Axon
A
- Every neuron has one axon
- Transmit stimuli to other neurons or effector cells
-
Axon Hillock
- Pyramidal-shaped region of the cell body where axon originates
- Where action potentials are generated (high concentration of Na+ ion channels)
- Lack RER or polyribosomes (all proteins must be shipped from cell body)
7
Q
Bipolar Neuron
A
- Dendrite on one end
- Axon on other end
8
Q
Unipolar Neuron
A
- Axons and dendrite arise from same extension of cell body
- Sensory Nerves
9
Q
Multipolar Neuron
A
- Multiple dendrites arise from cell body and single axon
10
Q
Resting Membrane Potential
A
- Nerve plasma membrane contains Na+/K+ ATPase pumps
- Pumps 3 Na+ ions out of the cell
- Pumps 2 K+ ions into the cell
- Creates resting potential
- Difference in voltage across the membrane
- Inside of cell is negatively charged relative to outside (-65 mV)
11
Q
Action Potential
A
- Brief, rapid depolarization of the resting membrane potential due to rapid influx of Na+ ions
- Generated at axon hillock (rich in voltage-gated Na+ channels)
- Propagated along axon as a “wave of depolarization”
- Myelinated fibers use saltatory conduction to increase speed of propagation
12
Q
Synapses
A
- Neuron contacts another neuron or effector signals
- Converts electrical signal into chemical signal
- Presynaptic axon terminal (terminal bouton)
- Contains vesicles with neurotransmitter
- Postsynaptic membrane
- Contains receptors for neurotransmitter and ion channels
Types of Synapses:
- Axosomatic
- Axodendritic
- Axoaxonic
13
Q
Electrical Synapse
A
- Impulse conducted by Gap Junctions
14
Q
Synaptic Transmission
A
- Action potential reaches axon terminal
- Depolarization of axon terminal membrane opens voltage-gated Ca2+ channels
- Ca2+ influx causes fusion of synaptic vesicles with presynaptic membrane
-
Neurotransmitter exocytosed and binds post-synaptic receptors
- Can cause depolarization or hyperpolarization of postsynaptic membrane
- Generation of action potential in posynaptic cell depends on summation of all excitatory and inhibitory impulses
15
Q
Neurotransmitters
A
- Small molecules that bind receptor proteins
- Ionotropic receptors are ligand-gated ion channels
- Metabotropic receptors are G-protein coupled receptors (second messenger cascade)
Excitatory NTs:
- Acetylcholines (e.g. neuromuscular junctions)
- Glutamate
Inhibitory NTs:
- GABA
- Glycine
16
Q
Axonal Transport
A
- Transport of materials between nerve cell body and axon
- Occurs along microtubules by ATP-powered motor proteins
Anterograde Transport
- Transport from cell body to axon via Kinesin
Retrograde Transport
- Transport from periphery toward cell body via Dynein
17
Q
Neuroglia Cells
A
- Support cells
- 10x more abundant than neurons
- Occupy space between neurons (similar to CT)
-
Neuropil
- Resembles ECM of CT
18
Q
Types of Glial Cells
A
CNS:
- Oligodendrocytes
- Astrocytes
- Ependymal Cells
- Microglial
PNS:
- Schwann Cells
- Satellite Cells
19
Q
Oligodendrocytes
A
-
Produce myelin sheath
- Can myelinate many axons via sheet-like processes that wrap around axons multiple times
- Round, condensed nucleus; cytoplasm does not stain in H&E due to abundant golgi
20
Q
Astrocytes
A
- Most numerous glial cells in CNS
- “Have to baby neurons”
- Star-shaped cells with radiating cytoplasmic processes
- Cytoskeleton composed of Glial Fibrillary Acidic Protein (GFAP)
- Allows visualization via staining
Functions:
- Structural and metabolic support
- Recycle NTs
- Maintain blood-brain barrier
21
Q
Ependymal Cells
A
- “Epithelial-like” that line ventricles and central canal
- Cuboidal or columnar cells
- Joined with junctional complexes
- No basal lamina; basal ends extend processes into neuropil
- Surround capillaries to form choroid plexus (produce CSF)
22
Q
Microglia
A
-
Phagocytic cells of CNS
- Originate from monocytes
- Provide immune defense in CNS
23
Q
Schwann Cells
A
-
Produce myelin in the PNS
- Each cell myelinates only one axon
- LM: appear oval nuclei within CT of nerve
Myelinated Nerves
- Multiple concentric layers of Schwann cell plasma membrane
Unmyelinated Nerves
- Axons embedded within cytoplasm of the Schwann cell
24
Q
Myelin Sheath
A
- Plasma membrane concentric layers
- 80% lipids; 20% protein
25
Q
Nodes of Ranvier
A
- Interface between myelin sheaths of adjacent Schwann cells
-
Axolemma exposed to ions in interstitial fluid
- High concentration of voltage-gated Na+ channels
- Saltatory Conduction
26
Q
A
- Myelinated Axon EM
27
Q
A
Unmyelinated Axon EM
- Small-diameter axons
- Conduction is slower
- Within surface invaginations of Schwann cell cytoplasm
28
Q
Satellite Cells
A
- Surround nerve cell bodies in ganglia
- Maintain controlled microenvironment around nerve cells
29
Q
Nerve Regeneration Step One
A
*Exclusive to PNS
-
Degeneration
-
Anterograde Reaction/Wallerian:
- Axons degenerates distal to injury and is phagocytosed
- Retrograde Reaction/Chromatolysis
- Cell body swells and nucleus moves to periphery
- Nissl substance diminishes
-
Anterograde Reaction/Wallerian:
30
Q
Nerve Regeneration Step Two
A
- Regeneration
- Schwann cells form tubes around future axon growth
-
Axon sprouts enter tubes
- Axon sprouts that reach target form synapses
- Schwann cells form myelin sheath around new axons
31
Q
Injury Repair: PNS vs. CNS
A
- No regeneration typically in CNS
- Limited ability to clean up debris in CNS (lack of macrophages due to BBB)
32
Q
A
- Left Side: White Matter
- Mostly myelinated axons
- Right Side: Gray Matter
- Neuron cell bodies and neuropil
33
Q
Meninges
A
- Dura Mater: Dense irregular CT
- Arachnoid Mater: loosely arranged trabeculae
- Pia Mater: flattened cells closely related to surface of CNS
34
Q
Brain: Cerebral Cortex
A
- Gray Matter
- 6 Layers of Neurons
35
Q
Brain: Cerebellar Cortex
A
- Gray Matter
- 3 Layers of Neurons
36
Q
Spinal Cord
A
Gray Matter:
- Dorsal Horns
- Ventral Horns
White Matter:
- Myelinated axon tracts
37
Q
Peripheral Nerve Coverings
A
Endoneurium:
- Loose CT surrounding each axon and its Schwann cell
- Mostly reticular fibers
Perineurium
- Squamous perinueral cells
- Surrounds bundles of axons and Schwann cells
Epineurium
- Dense, irregular CT layer that surrounds nerve
38
Q
Peripheral Nerve Longitudinal Section
A
- Wavy appearance
39
Q
Ganglia
A
Collections of cell bodies in PNS
Autonomic Ganglia
- Multipolar neurons with eccentric neurons
Sensory Ganglia
- Pseudounipolar neurons with central nucleus
- Surrounded by satellite cells
