Neural Tissues Flashcards
In the brain:
- dorsal
- ventral
- rostral
- caudal
- up
- back
- front
- downward toward spinal cord
Reticular theory vs Neuronal Doctrine:
everything in the nervous systems is a single continuous network vs nervous system is made up of a discrete, individual cells which are mutually dependent upon one another
Brodmann Areas of the Cortex:
- 52 regions of the cortex (starting at 1)
- ***determined by histological architecture and each area has a particular set of inputs and outputs
- generally has a distinct functions
What is the basic cellular unit of the CNS?
Neruons
CNS Neuron structure:
nucleus within the cell body and extends one or more processes separate electrically active cells that communicate across a synapse without glia?
Each neuron is a separate entity with a limiting cell membrane
Neuron
Morphology (shape and size) is linked to
the function undertaken by neuron subtype
Multipolar neuron description, types and locations:
- single axon extending from one end of the soma and several dendrites branching from the other side
- both motor and interneurons
- most predominant in the CNS
Bipolar neuron description, types and locations:
- single axon from one end of an oval soma and a lone dendritic tree extending from the other end
- only associated with afferent impulses to the brain
- found in vestibulocochlear, olfactory and ocular systems
Unipolar neuron description and location:
- single axon projection from one end of a spherical soma and no dendritic branches
- generally found in the PNS and sensory ganglia
Pseudo-unipolar description, locations, functions:
- soma found in dorsal root ganglia and has one single process that serves the roles of the axon and dendrite
- the process bifurcates close to the cell body and the central/axonic branch travels from the soma to the spinal cord, which the peripheral/dendritic branch travels from the periphery to the cell body
- associated with movement and joint position
Neuron Morphology:
Dendrites:
- are
- function
- branched protoplasmic extensions with a primary role to propagate the electrochemical input from other cells to the soma
- branching processes which receive incoming signals (action potentials) from other neurons via dendritic spines
Soma:
- is
- function
- axon hillock
- contains the nucleus, cytoplasm, metabolic activity, ATP generation and protein synthesis. Prodces NT’s, subsequently stored in synaptic vessels
- cell functions
- axon hillock is a specialised part of the cell body
Axon Hillock:
- specialised part of cell body, at the interface between the soma and the axon
- section of the soma that has clusters of microtubules and ribosomes, very few Nissil bodies
- known as the trigger zone due to the density of voltage gated Na+ channels
Axon:
- can be —- or —–
- myelinated (>1 micrometer diameter) (120m/s)
- unmyelinated (<1micrometer diameter) (<1.5m/s)
Saltatory Conduction:
The transmission of an electrical impulse along the axon from node to node making the impulse speed faster; rate of conduction increases with diameter. Large axons are typically more heavily myelinated than smaller axons, consequently transmitting impulses faster
Basic Types of Neurons (3):
- sensory (afferent -> inward): send info from the sensory receptors, through nerves into the CNS
- motor (efferent -> outward): carry messages from CNS, through nerves, to operate muscles and glands
- interneurons: carry messages from one set of neurons to another. They can bring info from different sources together into one location in the CNS
Neurons have three divisions:
nuclei, laminae, ganglia
Three Divisions of Neurons: Nuclei:
- in the CNS
- neurons located in clusters (clusters = nuclei)
Three Divisions of Neurons: Laminae:
- in the CNs
- neurons are located in layers (laminae)
Three Divisions of neurons: Ganglia:
in the PNS
Partnerships in the brain: Neurons are the functional unit of the brain, but
do not exist in isolation and rely upon neuron-glial interactions
Neuroglia of the CNS:
Neuroglia = glia = glial cells
These are non-neuronal cells responsible for supporting the neurons and providing a suitable environment in which the neurons can function
provide a homeostatic environment for the neurons to function
Three main types: astrocytes, oligodendrocyte, microglia
Oligodendrocytes:
- found where?
-
- function
- allows development of
Without oligodendrocytes, effect
- found only in the CNS
- each cell myelinates multiple axons (found between axons)
- function: produce and maintain myelin sheath to create white matter
Allows development of the computing power of the vertebrate brain because:
- great increase in nerve conduction velocity
- profound decrease in the size of the nerves
Without myelination each human optic nerve would have a diameter of 0.75nm
Relationship between oligodendrocytes and axon
- complimentary relationship
- axonal development is dependent on oligodendrocytes and olidgodendrocyte development is dependent on axons
- therefore oligodendrocytes and axons are interdependent functional units
Loss of myelin affect on axon
- leads to axon dysfunction
- axon degeneration leads to loss of oligodendrocytes
Microglia:
- are a network of
- status
- found and pattern distributions
- functions (3)
- core functions (2)
- microglia are a network of delicately ramified (resting) cells, activated by pathogens
- resident immune cells
- transform from quiescent (resting?) to activated status
- distributed in regular mosaic patterns throughout the CNS
- phagocytic, immune cells that promote repair
- core functions are: apoptotic clearance, selective killers as well ‘dustmen’
Microglia:
- when do they appear?
- what are they called when they appear?
- when do microglia mature?
- how do microglia mature?
- appear in great numbers shortly before birth
- known as amoeboid (active) microglia
- mature at birth when the blood brain barrier form, hence more ramified
- when macrophage functional antigens are downregulated and microglia assume ramified (resting) process-bearing morphology
Overview of astrocyte functions (6):
- providing structural support
- supply nutrients (glucose)
- maintain ionic environment (remove K+)
- neurotransmitter uptake
- repair of the nervous system
- form protective barrier around the vessels (the blood brain barrier)
SGKNRBBB
Astrocyte functions: Developmental:
- regulation of neuro and gliogenesis (astroglia are stem elements of the CNS)
- neuronal pathfinding
- regulation of synaptogenesis (development of synapses between neurones)
Astrocyte functions: structural:
- astroglia form the scaffold of the nervous system, thus defining the functional architecture of the brain and spinal cord
- astrocytes form a continuous synncytium and integrate other neural cells into this syncytium
Astrocyte function: formation and regulation of the blood-brain barrier:
- formation of the glial-vascular interface
- regulation of cerebral microcirculation
Astrocytes are morphologically stellate (star-like) cells distributed throughout the CNS.
True or False?
False
Classically stellate shops
Morphologically diverse
Astrocytes: Broadest Classification:
Divided into two susbtypes:
- Fibrous astrocytes are located in white matter
- Protoplasmic astrocytes are located in grey matter
Involvement of astrocytes with shuttle systems:
- Glutamate-glutamine shuttle
- 80% glutamate is released at the synapse is taken up by astrocytes, some may be recyles into pre-synaptic neuron or might sit in synaptic gap for a long time
- if in the gap, the astrocyte has receptors to take up glutamine
- astrocytes convert glutamate to glutamine
- release glutamine
- taken up by the pre-synaptic terminal
- converted back to glutamate
purpose: to ensure no wastage of valuable neurotransmitters in the synaptic gap
What are astrocytes connected by?
gap junctions
can transport Ca2+
?????
CNS: Ependymal Cells:
- Line brain’s ventricles and central canal of spinal cord
- function:
- fluid homeostasis due to direct
contact with CSF and transport of
electrolytes/solutes between CSF
and brain parenchyma - contribute to the formation of CSF
as well as assisting in CSF motility
via cilia movement
- fluid homeostasis due to direct
Blood Brain Barrier:
- is
- advantage
- contains what cells
- highly selective permeable barrier
evolved to determine which
substances enter the brain - offers immune privileged status to
the CNS - consists of astrocytes, pericytes and
blood endothelial cells bound tightly
(neurovascular units)
Effect of ageing on the blood brain barrier:
increased permeability with ageing (<500 Daltons in YA to >500 Daltons in old adulthood)
BBB dysregulation evidenced in Alzheimer’s disease and delirium; and further neurodegenerative disorders; might be due to the natural decline and increased impermeability of the BBB
Schwann Cells:
- are
- function
- importance
- relation to axons
- schwann cells are the neuroglia of the
PNS - myelinate axons in a spiral wrapping
- important for regeneration; provide
substrate for axon to grow along - one schwann cell myelinates one
axon
Schwann cell:
Oligodendrocyte:
Satellite Glial Cells:
- location
- morphology
- function (2)
- located exclusively in the PNS ganglia;
sensory, parasymp and symp ganglia - Satellite Glial Cells have a distinctive
morphology; wrap around neuronal
cell bodies forming a complete
envelope (mostly) - function: unclear, support of
neurons, supply nutrients and
regulate the exchange of materials
between neurons and interstitial fluid; similar to BBB - perform an analogous role in PNS to
what astrocytes do in the CNS
Satellite Glial Cells:
Glial Cells Classification Recap:
How do glia differ from neurons (3)?
neurons (adult) are post-mitotic
Glioma (glial pathology):
- pathology
- location
- largest group of primary tumors
derived from glial cells because most common cell - usually highly malignant with rapid
growth - usually inside cranium, referred to as
intra-axial tumors - intra-axial denotes lesions located
within the brain parenchyma
Neuroblastoma (neural pathology):
- common or rare?
- which ages
- location of pathology
- survival rates
- initial prognosis
- side effects
- rare type of tumour
- most common in children and infants
- located outside the cranium (adrenal
glands, abdo, thoracic cavity, neck,
spine - survival rates vary
- initial prognosis is typically good
- survivors often develop neurological
problems 30 yrs later
Neuron-glial interactions are dynamic than previously considered;
glial cells respond to and release neurotransmitters
Neural cells are post-mitotic;
leading to a potential cascade of irreplaceable neuronal loss
What does myelin mostly consist of?
- MBP: Myelin Basic Protein
- Proteolipid Protein
