2.2.1. Neural Tissue Flashcards
parts of CNS
brain and spinal cord
parts of PNS
cranial, spinal, and peripheral nerves
afferent neurons function
sensory and receptor neurons. Carry nerve impulse from receptors or sense organs toward CNS
efferent neurons function
motor or effector neurons that carry nerve impulses away from CNS to effectors such as muscles or glands
somatic nervous system function
regulates voluntary body movements
autonomic nervous system
regulates involuntary body movements
sympathetic nervous system
part of autonomic nervous system and stimulates fight or flight response as well as homeostasis
parasympathetic nervous system
part of autonomic nervous system and responsible for rest and digest or regulation of internal organs and glands
Neuron components
- cell body (soma)
- axon (transmit)
- dendrites (receive)
- nerve terminals
astrocyte (astroglia)
star shaped glial cell in CNS that provide mechanical/structural support
oligodendrocyte
type of neuroglia. Function is to support and insulate axons of CNS via myelin sheet
glial cells
non-neural cells that maintain homeostasis, form myelin, and provide support and protection for CNS and PNS
steps of neurotransmission
- depolarization of presynaptic membrane which induces opening of calcium channels
- Influx of calcium into presynaptic neuron causes vesicles in presynaptic neuron to release neurotransmitters into synapse
- Neurotransmitters in synapse bind to receptors in postsynaptic region which causes depolarization in postsynaptic membrane
- membrane retrieval occurs by coated vesicles
gray matter composition
mostly cellular elements: cell bodies of neurons and astroglia with dendrites covered by synapses
white matter composition
mostly axons covered by myelin sheet (oligodendrocytes)
Ectoderm is source for this tissue
- epithelial
2. neural
neuron cell body characteristics
- large nucleus
- light cytoplasm with high transcription rate
- contains nissl bodies (granules of RER)
dendrite characteristics
- multiple per neuron and vary in shape
- receptive surface of neurons and form dendritic spines at the postsynaptic element
- motile
- dendrites are extensions of neuronal perikaryon (bulbous part of the neuron with the nucleus)
axon characteristics
- one per neuron but may branch
- thin (.1 to 25 micron) but long (up to several feet)
- highway for neurons: massive macromolecular and organelle movement (axonal transport)
- contain neurofilaments, microtubules, mitochondria
- do not contain ribosomes or golgi
synapse definition
specialized junction enabling communication between pre and postsynaptic neuron
nerve terminal characteristics
- precede a synapse
- communication is chemical and electrical in nature
- presynaptic nerve terminal contain synaptic vesicles that store and release chemical messenger molecules (neurotransmitters)
types of neurotransmitters
- classical
- peptide
- other
classic neurotransmitter
- acetylcholine
- epinephrine
- norepinephrine
- dopamine
- serotonin
- glutamate
- aspartate
- GABA
peptide neurotransmitter
- encephalin
- VIP
- neurotensin
- substance P
- CGRP
other type neurotransmitter
- NO
- CO
- adenosine
- growth factors
Types of neurons
- sensory
- motor
- intermediate
classification of neuron
- unipolar: one dendrite OR one axon
- pseudounipolar: one process that branches into a dendrite AND an axon
- bipolar: one dendrite and one axon
- multipolar: many dendrites and one axon
supporting cells
- astroglia
- oligodendrocytes
- microglial cells
- ependymal cells
function of astroglia
- mechanical/structural support
- react to injuries (gliosis - proliferation of more glial cells)
- metabolic support via nourishing neurons with glucose, taking up toxic metabolites, and regulating access to brain parenchyma
function of oligodendrocyte
wrap axons in the CNS with multiple processes that form multilayer myelin sheets (insulation for fast transmission)
node of Ranvier structure and function
structure: gap between myelin segments that contains a high density of Na ion channels
function: permits signal transduction. Also allows fast efficient travel of impulses via saltatory conduction
saltatory conduction
propagation of action potentials of myelin axons from one node of Ranvier to the next increasing the conduction velocity of action potentials
microglial cell function
resident immune cell of CNS which phagocytose cellular debris. They are of monocytic origin
What makes up a peripheral nerve?
Endoneurium (inner)
Perineurium (around)
Epineurium(outer)
What part of the peripheral nerve must be rejoined in microsurgery for limb reattachment?
Perineurium (permeability barrier): surrounds a fascicle of nerve fibers
Blood-Brain Barrier (BBB)
Prevents circulating blood substances from reaching the CSF/CNS
Formed by 3 structures:
1. Tight junctions b/w non-fenestrated capillary endothelial cells
2. Basement membrane
3. Astrocyte foot processes
What can rapidly diffuse through the BBB?
Non-polar/lipid-soluble substances
glucose and amino acids cross slowly
Histologically, how to distinguish b/w the cell body and the axon?
Axons do not have RER and, therefore, will not stain with the Nissl substance like cell bodies and dendrites will
Wallerian degeneration
If an axon is injured it will undergo degeneration distal to the injury and axonal retraction proximally (allows for potential regeneration of axon if injury occurs in the PNS)
“Fried egg” appearance on H&E stain
Oligodendrocytes (smaller than astrocytes with shorter and fewer processes)
Reactive gliosis
Proliferation/hypertrophy of astrocytes in response to neural injury
Multiple sclerosis, progressive multifocal leukoencephalopathy (PML), and leukodystrophies
Central myelinating diseases that destroy oligodendrocytes
Ependymal cells
Line the cerebral ventricles and central canal; also involved in CSF production and circulation (lined with stereocilia)
Schwann Cells
Derived from the neural crest, myelinate one and only one PNS axon leading to increased conduction velocity via saltatory conduction b/w nodes of Ranvier; also promote axonal regeneration
Guillain-Barre Syndrome
Consequence is schwann cell destruction
Acoustic neuroma
Type of schwannoma (tumor); typically located in internal acoustic meatus (CN VII); if bilateral, strongly associated with neurofibromatosis type 2
Vasogenic edema
infarction and/or neoplasm that destroys endothelial cell tight junctions
Neural Tube
Where neurons and glia of the CNS develop
Neural Crest
Where neurons and glia of the PNS develop
Kinesins and dyneins
Kinesins: involved in the movement of organelles and vesicles down the axon
Dyneins: movement of organelles, vesicles, and possibly microtubule fragments towards the cell body
Neural Development of the Neural Plate
Notochord induces the ectoderm to differentiate into neuroectoderm and form the neural plate, then the notochord becomes the nucleus pulposus of the intervertebral disc
What does the neural plate give rise to?
Neural Tube and Neural Crest cells
Alar plate
Dorsal (sensory)
Basal Plate
Ventral (motor)
What does the neuroectoderm give rise to?
CNS, ependymal cells, oligodendroglia, and astrocytes
What does the neural crest give rise to?
PNS neurons, Schwann cells
What does the mesoderm give rise to?
FIRST AID: Microglia (like Macrophages, originate from Mesoderm)
