Nervous Tissue I Flashcards
Dendrites Appearance
Large diameter compared to axons
- irregular contours and specialized appendages
- typically does not extend far from the cell body
- ALMOST NEVER MYELINATED
Dendrites: Branching
Forms dendritic trees
- increases receptor surface area
- can branch repeatedly
- branches at acute angles
- branches often vary in diameter
Dendrites unique differences in organelles
Contents of soma and dendrites are similar
- golgi can extend into dendrites, not far but can
- can contain ribosomes
- microtubules PREVELANT- evenly spaced
Dendrites: Function
INPUT
Graded potentials-little or much acts like a dimmer switch
Receiving synapses
Axons: Appearance
Small diameter compared to dendrites
- smooth contours and cylindrical shape
- may extend great distances from cell body; 1-2 ft or more
- can be myelinated
Axons Branching
Branches infrequently
- obtuse angles
- typically same diameter
Axons: Unique differences in organelles
- Lacks Nissl bodies and Golgi
- never contain ribosomes
Axons: Function:
OUTPUT
- action potential-all or none
- conduction and transmission-carry information away from cell body
Dendritic Spines
SER and filamentous proteins extend into spines
-no ribosomes
Dendritic Spines Function
Increase Receptive area
Synapse
to fasten together/union
-enlarge part of a nerve fiber
Bipolar Neurons
In vestibular system
-sensory system essential to normal movement and equilibrium
Pseudounipolar neuron
Most are sensory
-associated with pain near skin
Multipolar neuron
most of the neurons in the body
-cell body has multiple dendrites
Axosomatic synapse
axon-> cell body
Ganglion
a collection of neuron cell bodies outside of CNS
Axoaxonic synapse
axon-> axon
-less frequent
Axodendritic synapse
axon-> dendrite or dendrite spine
Dendrodendritic
dendrite-> dendrite
Chemical Synapses
use Neurotransmitters
2 types: with or without uptake
-20% are broken down by enzyme
-80% NTs taken back up into presynaptic membrane
Without reuptake example- acetylcholine
with reuptake: catecholamines include epinephrine, norepinephrine, dopamine
Electrical Synapses
Gap junction like
- very rare
- no Neurotransmitters required
- slow acting process
- use ion channels instead of clefts
- found in smooth muscle, cardiac muscle, and retina of the eye
- more common in invertebrates
appearance Characteristic of synaptic vesicles containing: Acetycholine
Very small
- about 40-50 nm diameter
- clear color
appearance Characteristic of synaptic vesicles containing: Norepinephrine
40-60 nm diameter
-small dot in center
appearance Characteristic of synaptic vesicles containing: Inhibitory
Filamentous and flat
-different sizes
-usually about 50 nm
Ex; GABA
appearance Characteristic of synaptic vesicles containing: Serotonin
aka 5HT
- very large, about 80-150 nm
- dense core on the inside
GABA
Gamma-amino bytyric acid
- most abundant inhibitory neurotransmitter in CNS
- 30-40% of all synapses
Dopamine
Associated with pleasure centers
Glutamate
Most abundant excitatory neurotransmitter in CNS
-ubiquitous (found everywhere)
Substance P
pain transmission
Non-directed synapses
Synapses without distinct postsynaptic targets
- slow acting mechanism
- more energy efficient
Parasympathetic
stimulation of smooth muscles such as in GI tracts
-Ach dumped in area and diffuses to smooth muscle
Glia
or Neuroglia
- 10:1 glia to neurons
- provide protection and support for neurons
- proliferation/constant slow turnover
- no conduction
What are the 4 types of Glia
Astrocytes
Meyline producing cells
Microglia
Ependymal Cells
Astrocytes
-morphological subtypes
large and Most numerous
-functional diversity
Morphological Subtypes:
- fibrous in white matter
- Protoplasmic in gray matter
- others in unique brain regions
-10-20 micrometer soma
Common markers for Astrocytes
- Glial Fibrillary acidic protein (GFAP)
- Glutamate Synthetase
What are astrocyte tumors called
Astrocytomas
Astrocytes Function
Physical and metabolic support
Metabolic:
- store glycogen
- K+ sink-control ionic and chemical environment
- store neurotransmitter enzymes
- processes surround neurons and can extend 100 micrometers
- have perivascular end feed that cover blood vessels and neurons
Reaction to injury:
- increase in size=hypertrophy
- increase in number=hyperplasia
- glial scar from dead astrocytes, casques decreased or lack of conduction for neurons
Myelin Producing cells
Oligodendocytes-CNS ONLY
Schwann Cells-PNS
Oligodendrocytes
CNS only
- 10-12 micrometer soma
- small dark, round nucleus
- cytopaslm difficult to see at LM level without markers
- stain light- dark (EM) deepening on age of oligo
- Produces myelin for serve CNS axons
Myelin
Lipid rich cellular extension, acts as insulator
Common markers for oligodendrocytes
Myelin basic proteins
Galactocerebroside (Gal C)
Oligodendrocyte tumors are called?
oligodendrocytomas
Schwann Cells
PNS
-surround myelinated (one) or unmyelinated (several) PNS axons
Common Markers for Schwann cells
Rail
Microglia
Microphagic=phagocytic part of immune system, ingest cellular debris/invaders
- act as antigen present cells to prevent antigens to newly activated T cells
- 10 um soma
- Mesodermal origin (bone marrow)- all other glia ectodermal (neural tube)
- created from blood monocytes (same as macrophages)
- normally found near blood vessels
- increase in size and number with disease
- normally inactive but respond to injury
- release interferon to wctiavert cells nearby
- release cytokines to attract T cells
Common markers for microglia
MAC-1, MAC-3, OX42
Ependymal Cell
Cuboidal/columnar epithelia
- line ventricles, central canal of brain
- helps CSF movement through ventricular system
- Ciliated and also have microvilli
- Processes can extend far into the CNS
Markers of Ependymal cells
Vimentin
Function of Ependymal cells
Monitor CSF
Ependymal cell tumor is called
Ependymona
Central Nervous system
Brain (cerebrum and cerebellum) and Spinal Cord
-contains white matter (axons) and gray matter (cell bodies)
White matter contains
No or few neuron cell bodies
- many myelinated axons
- Glia (oligodendrocytes, astrocytes, and microglia)
Gray Matter contains
Neuron cell bodies
- netowrk of unmyelinated axons and dendrites
- glia
- many blood vessel compared to white matter
Peripheral nervous system
Cell bodies and nerve process outside the brain and spinal cord
