Lecture 5- The Brain Flashcards
(26 cards)
Purpose of the meninges
Provide physical support
Name the meninges
Dura Mata
Arachnoid Mata
Pia Mata
Dura Mata
Dense, firm layer of collagenous connective tissue
Outer layer consists of collagen and elastic fibers and a smooth inner surface of simple squamous epithelium
Spinal dura mata
A tube that extending from foramen magnum to S2, pierced by spinal nerves
Separated from wall of spinal canal by epidural space containing adipose tissue and a venous plexus
Cranial dura mata
Firmly attached to periosteum from which it received small blood vessels
Characterized by the dural reflections, flax cerebri, tentorium cerebelli and dural venous sinuses
Leptomeninges constituents and features
Pia mata and arachnoid mata together
Numerous trabeculae passing between the two layers
Pia mata adheres to parenchyma of CNS, therefore cannot be removed or manipulated
Surfaces of both layers are covered by simple squamous epithelium
Leptomeninges development
Initially develop as a single layer from the mesoderm surrounding the embryonic brain and spinal cord
Fluid-filled spaces form within the layer and join to form the subarachnoid space
Leptomeningial trabeculae
Numerous passing between the two layers
Delicate strands of connective tissue with squamous epithelial cells on their surfaces
Zonulae occludentes
Tight junctions that connect adjacent arachnoid epithelial cells, preventing exchange of large molecules between the blood in the dural vasculature and CSF
No tight junctions between pial cells, therefore free exchange of macromolecules between CSF and CNS tissue
Types of cortical tissue
Paleocortex of the olfactory system
Archicortex of the hippocampal formation
Neocortex in the remainder of the cerebral cortex
Layers of the cerebral cortex
Numbers differ according to region
Up to 5 layers in paleocortex, with superficial ones more distinct
No more than 3 layers in the archicortex
Neocortex
6 layers always present at some stage of embryonic or fetal development
Layers not often discernable in adults
Impregnation technique used to decipher histological description of cell
Nissl stain for cell density
Myelin stain for distribution of axons and synapses
Cortical neuron classification criteria
Morphology: shape of neural processes (eg. pyramidal cells)
Function: projection neurons that connect the cerebral cortex to entirety of its distal intracortical, subcortical or subcerebral targets, or interneurons that make local connections within the cortex
Spiny or aspiny (smooth): spiny have dendrites with dendritic spines, mostly excitatory.
Smooth are interneurons that are mainly inhibitory
Pyramidal cells
Projection neurons of the cerebral cortex
Excitatory, glutamatergic neurons
Connect cerebral cortex to the entirety of its distal intracortical, subcortical and subcerebral targets
Make up vast majority of cortical neurons
Spiny
Pyramidal cell characteristics
Prominent apical dendrite orientated towards pial surface of the cortex
Basal dendrites
Both apical and basal dendrites have dendritic spines
Spines are small outgrowths of the dendrite that resembles a thorn
Majority of synaptic contacts received are on the dendritic spines rather than directly on the dendrite shaft or cell body
Cortical interneurons
Represent approximately 20-30% of all cortical neurons
Make local connections within the cortex that can span multiple layers
Classes of cortical interneurons
Spiny pyramidal and stellate cells
Aspiny and nonpyramidal cells
Spiny interneurons
Excitatory glutamatergic neurons locates in 4th layer
Receive sensory inputs from thalamus
Inhibitory GABAergic neurons located in all layers of the cortex
Aspiny interneurons
Main inhibitory component of neocortical circuits
Finely modulate activity of projection neurons
Layers of neocortex
Molecular layer External granular layer External pyramidal layer Internal granular layer Internal pyramidal layer Multiform or fusiform layer
Layer 1: Molecular layer
Most superficial, few nerve cells but many dendritic and axonal processes in synaptic interaction
Consists predominantly of terminal branches of dendrites and axons, which give a “molecular” appearance in sections stained for nerve fibers
Histologically very clear
Layer 2: External granular layer
Contains many small neurons, which establish intracortical connections
Densely packed of small stellate cells and small pyramidal cells whose apical dendrites terminate in the molecular layer and whose axons are sent to lower cortical layers
Layer 3: External pyramidal layer
Contains medium-sized neurons giving rise to association and commissural fibers
Medium to large pyramidal cells whose apical dendrites extend to layer 1
Axons of these cells function as association or intracortical association fibers
Easily identifiable histologically
Layer 4: Internal granular layer
The site of termination of afferent fibers from specific thalamic nuclei
Received thalamocortical connections, especially from the specific thalamic nuclei
The most prominent in the primary sensory cortices
