1 - Nervous System Flashcards
Brain macroscopic structure
- Brain and SC
o Gyri: mountains
o Sulci: valleys
*If there is edema, what will you see grossly in the brain?
- LOSS of distinction b/w gyri and sulci
- “flattened”
*If there is loss of tissue, what will you see grossly in the brain?
- THIN gyri
- WIDENED sulci
- Ex. polio-encephalomalacia
What are the 3 meninges?
- Dura mater
- Arachnoid mater
- Pia mater
- “bottom to top”: PAD
Dura mater
- Continuous with periosteum of cranium
- Intervertebral canal=no longer adhered to periosteum and there is SPACE=epidural space
Arachnoid mater
- Fluid below it=sub-arachnoid fluid
o The brain will ALWAYS LOOK WET - Sends villi into fluid and absorb fluid and return it back to CIRCULATION
- “brain encircled by a fluid-filled cushion”
Ventricular system of the brain
- CONTINUOUS with the subarachnoid space
o Communicate with each other - Ependymal cells and choroid plexus=use blood to create CSF
- ‘ABSORPTION OF FLUID’
- “brain is hugging this cushion”
What happens if there is something causing the brain to expand?
- No where for brain to go=’herniation’
- Get necrosis and permanent damage OR DEATH
Grey and white matter: brain
- grey outside: neuronal cell bodies
- white inside: axons and myelin
o areas containing cell bodies=nuclei
Grey and white matter: SC
- grey inside: 2 dorsal (sensory, ascending) and 2 ventral (motor, descending) horns
- white outside: dorsal, ventral and 2 lateral funiculi
- *dorsal route ganglia
Neurons
- composed of dendrites, cell body and single axon
- energy dependent transport system
- Nissl substance (protein factory)
- *most vulnerable cells in the body
o Once loss it=loss it forever
Axon and processes length (over 20km!)
- Can be VERY LONG
- Very fast conduction system!
o Anterograde: cell body to dendrites
o Retrograde: dendrites to cell body
o *transport: signals, viruses, toxins, bacteria - *requires LOTS OF ENERGY=very susceptible to hypoxia
What are the 2 functions of astrocytes?
- Repair: astrocytes swell and divide and produce too many foot process (glial scar)
o If less than 1mm
o If larger than 1mm=cyst (empty space) - Support + important component of BBB
- NO FIBROBLASTS IN THE BRAIN
What is the function of oligodendroglia?
- Myelinating cells within the CNS
What is the function of microglial cells?
- Phagocytic cells of CNS
What makes the BBB tight? (3)
- Basement membrane is thicker
- Tight junctions are tighter
- Astrocyte foot processes
What is the function of the BBB?
- Allows O2, CO2 and water to pass
- Prevents NTs, hormones, toxins from entering brain
What is the level of susceptibility of different aspects of the CNS? (most to least)
- MOST: neurons
- Oligodendroglia
- Astrocytes
- Microglia
- Blood vessels
Fibers ‘cut’ in the CNS
- Do NOT regenerate=leads to paralysis or neurological deficit
Fibers ‘cut’ in PNS
- can regenerate if basal lamina is INTACT
How do brain wounds heal?
- Proliferation by astrocytic foot processes=glial scar OR empty space
- NO or a few fibroblasts in brain
What is the name of response that neuronal cell bodies do if there is degeneration within the axons?
- Chromatolysis
- *if cut or damage cell body=NO regeneration
*Chromatolysis (no lysis or chromatin)
- change in appearance of the CELL BODY brought about by dispersal of rER (Nissl granules)
- *chromatin colour: due to Nissl substance being dispersed
What kind of degeneration do injured axons undergo?
- Wallerian degeneration
*Wallerian degeneration
- Axons form linear and bulbous swellings distal to site of injury=AXONAL SPHEROIDS
- Myeline sheath becomes DILATED
- Site of injury is invaded by macrophages which remove debris
- Schwan cells proliferate to bridge gap
What is the name of the process of how necrotic neurones are removed?
- Neurophagia OR by cell lysis
How do astrocytes respond to injury?
- Cytoplasmic swelling and hypertrophy
o Normal=only see nucleus, not cytoplasm
o If activated=see cytoplasm and eccentric nuclei - Cell division and laying down of intermediate filaments in cell processes
- KNOW THE 2 NAMES
*What are gemistocytic astrocytes and what does it mean?
- Damage to the brain
- See cytoplasm and eccentric nuclei
*Hepatic encephalopathy and astrocytes seen in brain
- Get Alzheimer’s type II astrocytes
o Swollen astrocytes that are ‘clumped’ together
How do oligodendrocytes response to injury?
- Cell swell and hypertrophy
What does degeneration and necrosis of oligodendrocytes lead to?
- Demyelination
What are 2 types of demyelination?
- Primary: due to loss of oligodendrocytes
- Secondary: due to loss of axons (MOST COMMON)
a. Ex. canine distemper
What happens to microglial cells with damage?
- Become GITTER CELLS
- Swollen, lipid laden macrophages that are formed AFTER MICROGLIAL CELLS and MONOCYTES phagocytize dead neurons and myelin
What does infarction mean?
- Necrosis, secondary to LOSS OF BLOOD SUPPLY
Brain infarction
- Low connective tissue in brain and a lot of LIPID
o INFARCTED AREAS=BECOME SOFT - *differences in colour between grey and white mater
- *after removal of NECROTIC debris
o If less than 1mm=filled with glial scar
o If larger than 1mm=cystic
Infarcted areas within grey matter: grossly
- Tend to be RED (more vascularized)
Infarcted areas within white matter: grossly
- Tend to be PALE (less vascularize)
Brain edema grossly and significance
- Always the same regardless of mechanism
- *loss of distinction=flattened
- Always significant=can lead to herniation
What are the 4 types of brain edema?
- Vasogenic edema: most important and common
- Cytotoxic edema
- Hydrostatic edema
- Hypo-osmotic edema
Vasogenic edema
- Extracellular accumulation of fluid
- MOST COMMON type of edema in CNS
- *underlying mechanism=breakdown of BBB
Cytotoxic edema
- Accumulation of fluid INTRACELLULARLY in neurons, astrocytes, oligodendroglia and endothelial cells
- *BBB is intact
What is the mechanism of cytotoxic edema?
- Hypoxia
- Loss of NA extrusion mechanism (active)
- Na enters cells and EC water follows
- Depletion of EC space of Na and water
- Fluid moves from systemic circulation to brain through intact BBB
- *Brain edema
Hydrostatic edema
- Elevated ventricular hydrostatic pressure
- Fluid moves across ependyma of ventricular wall and ACCUMULATES extracellularly in the periventricular white matter
What is the osmolality of the CSF compared to ECF in the CNS under normal conditions?
- Osmolality of CSF is slightly greater than the ECF in the CNS
When does hypo-osmotic edema occur?
- After OVER consumption of water (water intoxication) leading to dilution of osmolality of the plasma
- *osmolality of plasma is further decreased=water moves from the vasculature into brain along the osmotic gradient=OSMOTIC EDEMA
