CNS Flashcards
Meninges
- Singular meninx; composed of specialized epithelial cells (meningothelial cells)
- Supported by connective tissue; have protective function
- Confined to outer layer of brain & cord in CNS
What are the 3 meninges laters?
- Dura Mater
- Arachnoid
- Pia Mater
Thick layer of dense connective tissue, internally lined by ____?
mesothelium
In cranium, fuses with___of skull
periosteum
In spinal cord, dura is surrounded by what?
epidural space
what is beneath the dura? what what does it separate?
subdural space; separates dura from underlying arachnoid mater
subarachnoid space is lined by what?
lined by flattened mesothelial cells
subarachnoid space
contains CSF & is continuous with ventricles of brain
pia mater is ___ to surface of brain and cord?
adherent; it is highly vascular
what makes up of leptomeninges?
pia + arachnoid
Denticulate ligaments
support cord; extend from pia, anchor cord to arachnoid, dura & periosteum
Neurons in CNS are derived from what?
neuroectodermal cells of neural tube
what does the brain and cord contain?
gray and white matter
peripheral gray matter
neuron cell bodies, dendrites & axons
central white matter
contains mostly myelinated axon
what is neuroglia and its structure & function
- Large # of support cells in CNS
- Structure: Highly branched
- Function: provide structural & metabolic support for neurons
Types of neuroglia? (4)
- oligodendrocytes
- astrocytes
- microglia
- ependymal
oligodendrocytes
CNS equivalent of Schwann cells; elaborate myelin sheaths
astrocytes
- most highly branched; largest neuroglial cells
- Provide structural & metabolic support & aid in tissue repair following injury
microglia
- phagocytic, fixed-tissue macrophages
- part of monocyte-macrophage lineage
- smallest neuroglial cells; originally mesodermal, have immune function
ependymal cells
- Frequently ciliated; microvilli for reabsorbtion of CSF
- cuboidal epithelium lining ventricles & central canal of spinal cord
what are the largest neuroglial cells?
astrocytes
what are the smallest neuroglial cells
microglia
Choroid plexus
- secretes CSF
- vascular structure arising from walls of ventricle in brain
- Contains modified ependymal cells
- fluid acts like shock absorber
Cerebrum
=cerebral cortex
- composed of gray matter peripherally; contains large # of neuron cell bodies
-
neocortex
in mammals, evolved to include sensory, motor, and association areas
gyri
grossly organized folds
nuclei in cerebrum
clusters of neuron cell bodies form small islands of gray matter in cerebrum and cerebellum
in gray matter, neuroglial cells include what?
astrocytes and microglial cells
deep to cortex is____
subcortical white matter (=medulla)
white matter
Contains mostly myelinated axons surrounded by oligodendrocytes
tracts
axons leading in and out of gray matter is grouped in bundles
cortical neurons
- Histologically, neurons of neocortex divided into five morphological categories
- Anatomically, divided into six layers, designated with Roman numerals I-VI, from superficial to deep
- Functionally, arranged in vertical columns or units
types of cortical neurons (5)
- pyramidal cells
- stellate cells
- cells of martinotti
- fusiform cells
- horizontal cells of cajal
pyramidal cells
- Largest include upper motor neurons in motor cortex, known as Betz cells
- pyramid-shaped neurons with long, slender axons, varying in size from small to large
Betz cells
upper motor neuron in motor cortex, associated with pyramidal cells
Stellate cells
=(granule)
- small star-shaped neurons with short axons & dendrites
Cells of Martinotti
small neurons with long, horizontal axons
Fusiform cells
vertically oriented, spindle-shaped neurons with vertical axons
Horizontal cells of Cajal
horizontally oriented, spindle-shaped neurons with horizontal axons
- least common type of neuron, found only in superficial layer
what is the least common type of neuron & found only in superficial layer
horizontal cells of Cajal
what are the 6 layers of the neocortex?
I. Plexiform II. Outer granular layer III. pyramidal cell layer IV. inner granular layer V. ganglionic layer VI. multiform cell layer
I. Plexiform
(molecular) layer—most superficial layer
- contains mostly dendrites & axons of cortical neurons
II. outer granular layer
contains large #’s of small pyramidal & stellate cells
III. pyramidal cell layer
larger cells located deeper in layer; Martinotti cells also present
IV. inner granular layer
densely packed stellate cells
V. ganglionic layer
contains large pyramidal cells, stellate cells & cells of Martinotti
VI. multiform cell layer
contains small pyramidal cells, cells of martinotti, stellate cells and fusiform cells
Cerebellum
- Coordinates muscular activity, posture, & equilibrium
* Grossly organized into folia, with central medulla of white matter
what are the 2 layers of the outer cerebellar cortex?
- outer molecular layer
2. inner granular layer
outer molecular layer
contains few neurons & large #’s of unmyelinated axons
inner granular layer
-highly cellular, very basophiic -contains large # of neuroglial cells & granule cells
granules cells
small neurons
Purkinje cells
- Molecular & granular layers separated by single layer of large neurons
- specialized neurons, function in coordination & equilibrium
Spinal cord
Similar structure throughout; prominent ventral median fissure
central canal
contains CSF, lined by ependymal cells; continuous with ventricles of brain
In the spinal cord, gray matter is located____
centrally, white matter peripherally
In the spinal, gray matter contains___
neuron cell bodies & axons
central commissure
connected by 2 dorsal horns & 2 ventral horns
Dorsal horns contain
- afferent (sensory) N tracts
- Cell bodies of somatic sensory neurons lie in dorsal root ganglia of spinal Nn
Dorsal N roots form…
lateral entensions of dorsal horns of gray matter
Ventral horns contain
efferent (motor) N cell bodies- innervate skeletal muscles
In spinal cord, surrounding white matter of cord contains:
ascending & descending fiber tracts (=columns)
-mostly myelinated axons; carry sensory & motor data
In PNS, what forms a bridge between severed ends of nerve?
connective tissue scar and Schwann cells
What are the steps (3) if gap not too big, regeneration of axon possible (PNS)?
- 1st step—Schwann cells multiply to physically bridge gap
- 2nd step—nerve axon sprouts neurites from proximal stump
- 3rd step—neurites grow into distal stump; contact reestablishes function
if damage too old or severe, axon may____
need to regrow its entire length, may take weeks to months
PNS
Anterograde (Wallerian) degeneration
if portion of axon distal to point of injury degenerates
PNS
when does nutrient synthesis occurs in cell body?
interruption of axonal transport
PNS
chromatolysis
Cell body of an injured neuron also swells, becomes brightly eosinophilic, loses Nissl substance
(PNS)
retrograde degeneration
results if injury severe and death of cell body
PNS
In CNS, oligodendrocytes are less efficient than___
Schwann cells; instead neuroglial cells multiply
Scar tissue proliferation from glial cells prevents what?
regeneration, physically blocks contact between cell body & axon (CNS)
When neurons terminally differentiated (Go)….
unable to be replaced (CNS)
ALS (amyotrophic lateral sclerosis)
= Lou Gehrig’s disease; also due to death of motor neurons controlling voluntary muscle
Meningitis
inflammation of meninges; may be bacterial or viral
Encephalitis
inflammation of brain
Myelitis
inflammation of spinal cord
encephalomyelitis
mixed involvement of brain and cord
meningoencephalitis
mixed involvement of meninges & brain
types of mixed involvement (2) and its symptoms?
encephalomyelitis & meningocephalits
Symptons: vary from mild (headaches) to paralysis, debilitation & death
Viral meningitis generally
transient lymphocytic infiltrate
Bacterial meningitis
Meningococcus, Streptococcus) => neutrophilic infiltrate & may be life-threatening
Polio
poliovirus affects α-motor neurons of ventral horn of spinal cord => poliomyelitis
Polio results
- Lower motor neuron paralysis & subsequent Mm atrophy
- Eradicated due to invention of Salk vaccine
Parkinson’sdisease
neurodegenerative disease characterized by muscular tremor due to death of neurons in substantia nigra
substantia nigra
-↓ production of dopaminein brain
-Tx involves administration of L-dopa, a dopamine precursor
(seen in parkinson’s disease)
Alzheimer’s disease
form of dementia characterized by neural plaques & fibrillary tangles within cortex
Multiple sclerosis (MS)
- An autoimmune, inflammatory, demyelinating disease of CNS
- Ab’s destroy myelin sheaths around axons => plaqueformation
- Usually affects women between ages of 20-40 years old
Multiple sclerosis (MS) symptoms
- vary with location of affected neurons & degree of demyelination
- Often multiple episodes, with partial resolution in between
Guillain-Barre syndrome
- Immune-mediated demyelination in PNS
* Often initiated by infection => progressive weakness in peripheral Mm
