nervous system Flashcards
macroscopic structure of the brain
-gyri are the mountains and sulci are the valleys between.
-they are widened due to loss of tissue (polio (grey), or malaysia (necrosis)
- if there is brain edema the brain will appear more flat.
meninges
made of:
-dura mater: adhered to periosteum of cranium bone.
-arachnoid mater: below there is subarachaoid fluid between the pia matter. sends vili into the fluid which absorb fluid and absorb back into circulation. cushion. if excess fluid brain can herniate.
-pia mater
grey and white matter
-grey matter (outside): neuronal cell bodies
-white matter (inside): axons and myelin. containing cell bodies known as nuclei
in spinal cord:
-grey matter (inside) composed of two dorsal and two ventral horns. dorsal (sensory) and ventral roots (motor)
-white matter: outside (dorsal, ventral
and lateral funiculi)
cells in brain
- Astrocytes
Functions:
1. Repair: Astrocytes swell and divide and produce too many foot process
(glial scar)
2. Support + important component of the blood brain barrier)
Oligodendroglia
- Function: The myelinating cells within the CNS
- Microglial cells
- Function: The phagocytic cells of
the CNS
the BBB
- Allows oxygen carbon
dioxide and water to
pass - Prevents
neurotransmitters
hormones, toxins ..etc
from entering the brain
-made of tight junctions, basement membrane where endo cells sit is very thick, astrol cell foot processes which cover things as they enter brain.
brain response to injruy
-very suspectable due to long neurons (most suseptible, BV are least)
-in CNS if you cut axon there is no regeneration, but in PNS there is regeneration.
5. There are few fibroblasts in the brain. Brain wounds heal by proliferation of astrocytic foot processes.
6. The cranial cavity is nearly filled by the brain, its coverings, and fluids.
There is very little room for expansion
how do neurons of the brain respond to injury
Neurones
* If there is degeneration within
axons, neuronal cell body
respond by
CHROMATOLYSIS
- Chromatolysis: is a change in appearance of the cell body brought about by the dispersal of the rough endoplasmic reticulum
(Nissl granules) gets a glassy appearance.
injured axons response to injruy
- Injured axons undergo
Wallerian degeneration** - Axons form linear and
bulbous swellings distal to
the site of injury. These
enlargements are termed
axonal spheroids. - The myelin sheath also
becomes dilated. - The site of injury is invaded
by macrophages which
remove debris - Schwan cells proliferate to
bridge the gap
how are necrotic neurons removed
- Necrotic neurones
are removed by
process known as
neurophagia
(microglial cells) or
by cell lysis
astrocyte response to injury
- Cytoplasmic swelling
and hypertrophy - cell division, and the
laying down of
intermediate filaments in cell processes
-histo: you will see astrocytes with cytoplasm so (activated) = Gemistocytic astrocytes= damage to brain.
-Alzheimer’s type II astrocytes: in hepatic encepholatophy
olgiodendrocytes response to injury
Oligodendrocytes are cells responsible for mylenating axons
- Respond to injury by cell swelling and hypertrophy.
- Degeneration and necrosis
of oligodendrocytes leads to
demyelination
Demyelination: Two types
1. Primary: due to loss of
oligodendrocytes (ex. canine distemper)
2. Secondary: due to loss
of axons (most common)
microglial cells response to injury
- Become gitter cells
- Gitter cells: swollen lipid laden macrophages that are formed after microglial
cells and monocytes phagocytize dead neurons and myelin
brain infarction (necrosis)
-There is low connective tissue in the brain and lot of lipid
* This causes infarcted areas to become soft.
* Infarcted areas within the grey matter tend to be red (more vascularized) while infarction within the white matter tends to be pale (less vascularized)
* After the removal of necrotic debris; if infarcted area is less then 1mm
it is filled with a glial scar. If larger than 1mm it becomes cystic
brain edema
-4 mechanims all look the same, brain appears flattened, sulci and gyri seem same level
Brain swelling with swollen
flattened gyri and less distinct
sulci
* Brain edema is always very
significant clinically as there is
very little space for the brain to
expand
* It can lead to herniation
Brain edema (4 types, mechanisms)
- Vasogenic edema:
- Extracellular accumulation of fluid
- Most common type of edema in the CNS
- The underlying mechanism is
a breakdown of the blood-
brain barrier - Cytotoxic edema:
- Accumulation of fluid intracellularly
in neurons, astrocytes,
oligodendroglia, and endothelial cells
- BBB is intact - Hydrostatic edema
Elevated ventricular hydrostatic pressure.
Fluid moves across the ependyma of the ventricular wall and
accumulates extracellularly in the periventricular white matter. - Hypo-Osmotic Edema
* Occurs after overconsumption of water (water intoxication), leading to
dilution of the osmolality of the plasma, happens when osmolarity changes.
