Lecture 20 Nervous Tissue II Flashcards
Glial Cells
Non-neuronal cells typically derived from embryonic neural crest tissue (except microglia)
“Glue Cells”
Where do Glial cells serve in various support functions?
In the PNS and esp. in the CNS
True or False:
Glial cells are capable of cell division under appropriate conditions.
TRUE
Types of Glial Cells
Astrocytes Oligodendrocytes Schwann cells Microglial cells Ependymal cells
Astrocytes are derived from:
Neural crest (neuroepithelium)
Where are astrocytes found?
Only in the CNS
Astrocytes have numerous ________ with expanded feet (pedicles) that terminate on _____ or the ____ _____.
Have numerous PROCESSES
Terminate on CAPILLARIES or the PIA MATER
Fibrous astrocytes
Found predominately in white matter
Have long processes with few branches
Protoplasmic astrocytes
Found predominantly in gray matter
Have short processes with many short branches
Name the functions of astrocytes
Regulate composition of intercellular environment or entry or substances into it Structural support Blood-brain barrier Development of cerebral cortex Potassium sink Secretion of neuron trophic factors Uptake/metabolism of neurotransmitters Help form noncollagenous scar tissue after injury to CNS
Oligodendrocytes are derived from:
neural crest (neuroepithelium)
Where are oligodendrocytes found?
Only in CNS
Name the functions of Oligodendrocytes
Closely associated w/ neuron cell bodies in gray matter & function as satellite cells
Surround axons of unmyelinated fibers in gray matter
Myelinate axons in the CNS
Schwann cells are derived from:
neural crest
Function of Schwann Cells
Myelinate axons in the PNS - each one myelinates a section of a single axon
Microglial cells are derived from:
macrophage precursors (bone marrow)
Functions of Microglial Cells
Phagocytic in the PNS
Recruit leukocytes across the blood-brain barrier
Modulate initiation & progression of immune responses along with astrocytes
Ependymal Cells
Ciliated cuboidal cells
Ependymal cells are derived from:
neuroepithelium
Where are ependymal cells found?
Found lining the ventricular system of the CNS
Functions of Ependymal Cells
Function in transport
In choroid plexus, may be principal cell type that secretes cerebrospinal fluid
Satellite cells are derived form:
neural crest
Satellite Cells Form:
moons (crescents) around cell bodies in ganglia
Function of Satellite Cells
Function as insulators
Myelination of the PNS
Schwann cell plasma membrane wraps around axon
Schwann cell cytoplasm is “squeezed” out, leaving behind concentric layers of membranes
Internal and External Mesaxon of Myelinated layer
Outer and innermost points of fusion between the outer leaflets (extracellular leaflets)
Intraperiod Line of Myelinated Layer
Electron-dense line created by extracellular space between adjacent outer leaflets
Major protein zero (PNS)
Major dense lines of myelinated layer
Electron-dense line created by cytoplasmic space remnant between adjacent leaflets
Myelin basic protein (found in PNS)
Major protein zero
Transmem. protein that forms homodimers
Only in the PNS
Homodimers form homotetramers w/ opposing outer leaflets
Cyto. domains may have signaling function
Charcot-Marie-Tooth disease
See slide 21
Myelin basic protein
Found in PNS & CNS
Abundant protein associated w/ inner leaflets
May function to stabilize lipid in the leaflet
Number of forms created by splicing of a single gene
See slide 21
Schmidt-Lanterman Clefts (incisures)
Residual areas of cytoplasm within the major dense lines
Components of the Presynaptic Membrane
V-gated calcium channels
SNAPs bind synaptic vesicles to presynaptic membrane
Vesicle docking proteins
Syapsins
SNAPs
Souluble NSF (N-ethylmaleimide-sensitive fusion protein) Found in cytosol of terminal
Vesicle docking proteins
SNAP receptors found in presynaptic and synaptic vesicular membranes
Synapsins
Filaments in the presynaptic membrane
Component of postsynaptic membrane
Neurotransmitter receptors
Types of Synapses
Axosomatic Axoaxonic Axodendritic Axospinous Excitatory Inhibitory
Axosomatic Synapses
Axon terminal synapses with the neuron cell body
Axoaxonic Synapses
Axon terminal synapses with another axon terminal
Axodendritic Synapses
Axon terminal synapses with a dendrite
Axospinous Synapses
Axon terminal synapses with dendritic spine
Excitatory Synapses
More positive end-plate potential (closer to threshold)
Inhibitory Synapses
More negative end-plate potential (farther from threshold)
Meninges and Spaces from Superficial to Deep:
Epidural space (absent around brain)
Dura Mater
Subdural Space
Leptomeninx (Arachnoid membrane, arachnoid villi, pia mater)
Describe the dura mater
“tough mother”
Tough, thick sheet of dense fibrous CT
Describe the dura mater around the cranial cavity
Lines the inside of the cranial vault bone and serves as the periosteum
Describe the dura meter around the spinal cord
Forms a CT tube that is separated from the bone or the vertebral foramina by a space referred to as the epidural space
What is within the dura mater?
Large, endothelial-lined venous sinuses that receive blood from the cerebral drainage as well as cerebrospinal fluid via arachnoid villi
What separates the dura mater from the subdural space?
A layer of dural border cells
Describe the Arachnoid
Meninx composed of delicate CT
Describe the outer layer of the arachnoid
Faces the subdural space and is made up of a single layer of arachnoid barrier cells
How is the arachnoid attached to the underlying pia mater?
By delicate strands of CT called arachnoid trabeculae
The spaces between the arachnoid and the pia mater are collectively referred to as the ______ ______
Subarachnoid space
What fills the subarachnoid space?
Cerebrospinal fluid
Describe Arachnoid Villi
Made up of arachnoid barrier cells
Extend from the outer surface of the arachnoid into the overlying venous sinuses of the dura mater
Allow cerebrospinal fluid to flow form the subarachnoid space into the dural sinuses
Describe Pia Mater
Thin, delicate sheet of CT that lies directly on the surfaces of the brain and spinal cord
Follows the contours of the brain and dips into the sulci, lining them well
Describe the relationship of pia mater CT and perivascular CT of cerebral and spinal cord BVs.
The CT of pia mater is continuous with the perivascular CT
Describe how the pia mater is attached to the brain and spinal cord.
Pia mater is very tightly attached to the nervous tissue of the brain and spinal cord and cannot be removed w/out damaging the nervous tissue
What are perivasular spaces?
Tunnels covered with pia mater
Choroid Plexus
Highly infolded simple cuboidal epithelium that extend into the ventricles from the roof plate
How are cuboidal cells of the choroid plexus linked?
Linked by tight junctions which form part of the cerebrospinal fluid barrier
What do the apical microvilli and infolding of basal membranes with mitochondria in the choroid plexus indicate?
Indicate active transport mechanisms
Describe the capillaries in the choroid plexus
Formed from endothelial cells and lack tight junctions
Fenestrated (leaky)
___,___,_____ pumps in the apical membranes of the choroid plexus cells pump fluid into the ventricular lumen causing a flow of ____, _____, and _____ from the capillaries through the choroid plexus epithelium into the ventricles –> CSF
Na+, K+, ATPase pump
Water, solutes, and proteins
Ependyma
Layer of simple cuboidal epithelium that lines the ventricular walls
Describe the cuboidal epithelial cells of the ependyma.
Linked by zonula adherens and have apical microvilli, cilia, and abundant microvilli
Describe the basal domains of the ependymal cells
In contact with astrocytic processes, forming the glia limitans, which is part of the blood-brain barrier
The basal domains of the ependymal cells are in contact with astrocytic processes. These astrocytes send processes to the surrounding ______ ______, which is part of the blood-brain barrier.
Non-fenestrated capillaries
Describe Tanycytes in the third ventricle
Tightly linked to the adjacent ependymal cells and send processes through the glia limitans to form end-foot processes on underlying BVs
Characteristics of the Sensory (Dorsal Root) Ganglia
Capsule of CT (epineurium)
Clustered pseudounipolar neurons lies within the capsule
Postganglionic axons are myelinated
Satellite Cells
Satellite Cells
Similar to Schwann cells & derived from neural crest
Form single layer around cell body of each neuron
Surfaces of cells facing away from neurons are in contact with basal lamina
Characteristics of Autonomic Ganglia
Capsule of epineurium
Clustered multipolar neurons (receive input from myelinated preganglionic neurons.)
Postganglionic axons are not myelinated
Satellite cells (similar to those in dorsal root ganglia but less numerous)