08 - Brain Protection & Vasculature Flashcards
What is part of the central nervous system?
Brain
Spinal Cord
What is part of the peripheral nervous system?
Mixed spinal nerves carrying
1. Sensory info from the body to CNS
2. Motor info from CNS to the body
Are sensory info afferents or efferents?
AFFERENTS
- Input to CNS
- Body to CNS (entering the CNS)
Are motor info afferents or efferents?
EFFERENTS
- Output from the CNS
- CNS to body (exiting the CNS)
What are the 3 functional classes of neurons?
Afferent neurons
- cell body in the peripheral NS
- peripheral axon endings terminate in the peripheral organ
- central axon terminates in the CNS
Efferent neurons
- the cell body and dendrites are in the CNS
- enters the PNS as it travels to the effector organ
Interneurons
- 99% of all neurons in the body
- all are in the CNS or in the brain
Where do sensory info messages go?
Messages ENTER the CNS through the BACK of the spinal cord
Where do sensory info messages go?
Messages LEAVES the CNS through the FRONT of the spinal cord
Where do sensory info messages go?
Messages LEAVE the CNS through the FRONT of the spinal cord
Can neurons switch what they do?
No
Once the neurons are established & created the circuitry, they NEVER switches
- An afferent neuron will always be an afferent neuron (vice versa)
What do interneurons do?
Does the integration of signals that determine the appropriate output
What are PNS & CNS responsible for?
PNS brings info in & out of the CNS to the rest of the body
CNS is largely responsible for integration of that info
Why are spinal nerves “mixed”
B/c it’s a mixture of afferent & efferent neurons that are running through those spinal nerves
- Sensory neurons and motor neurons are wrapped together
- They’re glued together but info is either travelling in or out through them
What is the dorsal root ganglion?
- Sensory neuron
- A collection of nerve cell bodies out of the CNS
- Most of its axon is out in the PNS and some is in the spinal cord (CNS)
Do afferent neurons send sensory messages from the back or front of the spinal cord?
Afferent neurons send sensory messages from the body to the spinal cord through the BACK
Do efferent neurons send motor messages from the back or front of the spinal cord?
Efferent neurons send motor messages out to the effectors in the body through the FRONT of the spinal cord
Where are the axons of motor neurons?
Axons go out into the PNS to interact with the effector
What are the cell types in the central nervous system?
Ependymal cells (CSF)
Astrocytes (blood-brain barrier)
Neurons (signals)
Microglia (immune)
Glial cells (support cells)
What are ependymal cells?
- Lines all the ventricles (sites of CSF production) of your brain
- Dialyzing/purifying the plasma of the blood to create CSF
What are astrocytes?
- Foot-like processes go out and touch BVs where exchange of nutrients is going to occur
- Signal to the cell of the BVs (the endothelium) to say which substance should be permitted to pass and which ones not
- Creates the blood-brain barrier)
- Many substances in the blood never enter the brain to protect the brain from potentially noxious stimuli
What are neurons?
- Signalling cells
- The smallest # of cells that we have in the CNS
What are microglia?
- The immune cells in the brain
- Has limited ability to do phagocytosis
- All other immune cells that provide protection are stuck in the blood & can’t go to the brain due to the blood-brain barrier)
- Those other immune cells can only get into the brain if there’s a problem with the blood-brain barrier
Microglia
- micro - small
- glia - glue
What are oligodendrocytes?
- Has a few branches and arms hanging out
- Those branches & arms are creating myelin sheaths around the axons of neurons in the CNS
- Myelinate more than 1 axon
Oligodendrocytes
- oligo - few
- dendro - branches
- cytes - cells
What do glial cells do?
Glial cells hold everything together
- Includes all the types of cells
Glial - glue
What is the grey matter?
Area where the soma/cell bodies of neurons are found
- Nucleus
- Cellular machinery
What is the white matter?
Area where the axons of the neurons are the myelin that’s wrapped around it are found
- Myelin is essentially plasma membrane (fat) wrapped around the axons
- Fat –> light in colour
What are the glial cells involved in myelination?
Oligodendrocyte
Schwann cells
What are the differences between oligodendrocytes and Schwann cells?
Oligodendrocyte:
- Forms several myelin sheaths for the axons around it
- Myelinates sections of several axons
- Found in the CNS
Schwann cell:
- Forms one myelin sheath
- Myelinates one section of an axon
- Found in the PNS
Do both the Oligodendrocytes and Schwann cells have Node of Ranvier?
Yes both types of cells have it
How does node of Ranvier help conduction?
They speed up the neural conduction?
Can CNS regenerate? Why?
Very limited
- regeneration is extremely limited
- Once the neurons has formed and created their circuitry, they do not change
- They do not divide or create new neurons
- B/c we cannot have a lot of new, weird connections forming in the brain
- neurons are postmitotic and glia inhibit axon growth
- Largely due to the influences –> the inhibiting factors secreted by the glial cells
- Only a few specific areas where there is the possiblility for neurons to regrow and make new connections
- Largely in the memory centers
Can PNS regenerate? Why?
Yes - 1mm of regrowth of axon that was damaged per day
- neurons can sprout collaterals & regenerate
- There’s a 1:1 ratio b/w a Schwann cell and an axon making myelin sheath thus regeneration can happen
- Schwann cells secrete growth factors and promote axonal growth
- No inhibitory factors (b/c they’re not in the PNS)
- glia produce growth factors
- macrophages remove debris
- from the blood out in our body which can remove debris and set the stage for healing & repair
What are the bony protections for the CNS?
Brain - Bony encasement (skull)
Spinal cord - Protection (vertebrate & veretbral column)
What are meninges?
Another layer of protection for the brain
What is the dura mater?
Part of the meninges
- A leathery matter that is very durable
- Firmly attached to skull (glued to the skull)
- Keep the skull in place so there’s no space b/w the dura mater and the skull
What’s running through the meninges and the dura mater?
Meningeal veins, arteries & nerves
- Plastered between the dura mater and the skull
What’s under the dura mater?
The arachnoid mater
What is the arachnoid mater?
Tiny spider-like projections coming down from the dura mater
- Lines inner surface of the dura mater
What does the arachnoid mater form?
Subarachnoid Space
Those spider-like webs span the gap b/w the dura mater and the surface of the brain
- There’s potential space there
- Where CSF are found
Where are cerebral BVs found?
Right under the pia mater
- The BVs that supplies blood to the brain
What is the pia mater?
Covers the surface of the brain and cerebral vessels
Do cerebrum BVs and Meningeal BVs have the same blood supply?
NO they have different blood supply
What are the meningeal layers of the brain?
Scalp
Skull
Periosteal dura mater (attached to the skull)
- peri- around
- osteal - bone
Meningeal dura mater
Arachnoid mater
Subarachnoid space
Pia mater
Cerebral cortex (brain)
How many layers does the dura mater have? What are they called?
2
Periosteal dura mater
- peri - around
- osteal - bone
Meningeal dura mater
What are the 2 dura mater layers?
Periosteal dura mater - attached to skull
- The layer intimately glued to the skull
Meningeal dura mater
- Dive away from the skull and create little invaginations/cavities that create compartments within the skull
What separates the left & right cerebral hemispheres?
Flax cerebri
- Sickle-shaped
What divides the cranium into compartments?
The inward extensions of the dura mater
- Dura mater can create little flaps & folds (invaginations) in the skull to create compartments
What creates the SPACES for the hemispheres?
Dural extensions
- Separates the hemisphere above from the cerebellum below
What is the tentorium cerebelli
A flap (a dura) that sits on top of the cerebellum
- Forms a tent-like shape
What are the 2 types of damages to the brain or cranial by extreme movements of the CNS?
Herniation
Coning
- Extreme movements of the CNS may be restricted by the dural extensions, resulting in damage to the brain or cranial nerves
What does a hematoma do in the brain?
Compresses the brain and move it around
What happens if you have a space-occupying lesion in your brain (eg. hematoma)?
- Can lead to the brainstem to move out of the way, to exit the skull through the foramen magnum
- Can move the brain from one compartment to another within the skull
What is it called if the brainstem moves out of the way due to a space-occupying lesion in the brain and exit the skull through the foramen magnum?
Coning
- B/c the brainstem look like an ice cream cone
What happens to the brainstem in coning?
- If you force it through that hole to exit the skull, you will shear off all the cranial nerves
- Lead to an inability to do things like having any sensations, moving muscles, etc
- The brainstem is where all the cranial nerves arise from
- Cranial nerves: All the nerves that’s control all the muscles, the skin and everything attached to the skull
What is it called if the brain moves to another compartment within the skull due to a space-occupying lesion in the brain?
Herniation or Pouching
What is the meningeal artery between?
The dura and skull
What are cerebral vessels supplied by?
Internal carotid
What are meningeal arteries supplied by?
External carotid artery
What do cerebral veins do?
Drain blood away from the brain
What are some of the trigeminal nerves?
Some of the trigeminal nerves are cranial nerves
Does the brain itself have sensory receptors on its surface?
NO
What is the trigeminal nerve?
Cranial nerve # 5
What are the 3 branches of the trigeminal nerve?
- Mandibular branch
- For the mandible - Maxillary branch
- For the maxilla - Ophthalmic branch
- For the eyes
True or false?
Some headaches are referred pain
True
What is the superior sagittal sinus?
The space between the dura mater where it created the flax cerbri
What is the superior sagittal sinus?
The space between the dura mater where it created the flax cerbri
Superior sagittal sinus
- superior - the uppermost part of the skull
- sagittal - right on the midline
- There’s only one superior sagittal sinus but there are other dural sinuses
What drains the blood in the brain?
Cerebral veins
- Empty into sinuses
- BVs that are draining the surface of the brain across the CSF space, go into the dural sinus and dump their blood there
What supplies the blood in the brain?
Cerebral arteries
- From internal carotid artery
- Supply the blood from the base of skull, through the brain tissue and get collected at the top of the surface with the cerebral veins
Steps in blood draining from brain
- Drains blood from the brain
- Has to cross the subarachnoid space (CSF space)
- Dumps the blood into the sinus
There are a lot of _______ ____ and they are very thin-walled
Think in terms of the meninges
Bridging vein
What is an Epidural hematoma?
- Rupture of meningeal vessel
- Blood between the skull and the dura mater
Epidural
- epi - upon or above
- upon or above the dura mater
What is a Subdural hematoma?
- Rupture of bridging vein
- Blood in the arachnoid space (CSF space)
- Blood gets mixed up with CSF
Subdural
- sub - below
- below dura mater
- arachnoid mater is below dura mater
What is a Subarachnoid hematoma?
- Rupture of cerebral artery
- Blood in the subarachnoid space (CSF space)
Subarachnoid
- below the arachnoid mater
- pia mater is below the arachnoid mater
What cause an epidural hematoma?
- Caused by blunt force to skull
- Peels the dura mater away from the bone
- Blood gets captured there in the space between
What cause a subdural hematoma?
- Caused by sudden movement of the head which causes the brain to move inside the skull
- Cause traction on those bridging veins which caused them to tear
What cause a subarachnoid hematoma?
- Caused by aneurism: the weakening of cerebral artery walls which led to them bursting
- The bursting of cerebral artery will tear the pia mater on top of it
Is the dura mater glued to the bones of the vertebrae? Why?
No
The dura mater is not glued to the bodies of the vertebrae to prevent tearing during movements
B/c all the bones in your skull are fused together & do not move
But your vertebral column are bones that are separate and have articulations b/w them which allows them to move
What is the purpose of the epidural fat space?
Acts to cushion the dura mater from the bone as its moving around in the vertebral canal
What are the 2 reasons why lumbar puncture are performed?
- To deliver an anesthetic to numb neurons
- To gain a sample of the CSF in the subarachnoid space in the spinal column
Where to aim for in a lumbar puncture when doing an epidural?
The epidural fat space
What is the epidural lumbar puncture?
A procedure that involves injecting a med (eg. anesthetic) into the epidural fat space
What is it called when getting a sample of the CSF in the spinal column (lumbar puncture)?
Spinal tap
What is the conus medullaris?
The terminus where the spinal cord end around the L1 vertebrae
- Look like a cone shape
Does spinal nerves end where the spinal cord end?
No
The spinal nerves continue down and exit through the openings at the side of the spinal cord in order to get out to the tissues
- Go all the way down to the sacral regions
Spinal cord ends at the conus medullaris
What is cauda equina?
Spinal nerves running through the inter-vertebral canal
- kind of look like a horse’s tail
- cauda - tail
- equina - horse
What is the brain formed as during development?
A tube-like structure
- Started as a flat sheet and the edges of the sheet curl up to form a tube-like structure
How many ventricles do we have in the brain?
4
What are the 4 ventricles in the brain?
2 lateral ventricles (one in each hemisphere in the brain)
third ventricle
fourth ventricle
What are specialized tufts of BVs within the ventricles that produces CSF?
Choroid plexus
What’s the cell that’s lining the ventricular system?
Ependymal cells
What are the portions of a lateral ventricle?
A frontal portion
- associated with the frontal lobe
A body portion
An occipital portion
- a little tail that goes into the occipital lobe
A temporal portion
- come out to the temporal lobe
What’s the largest ventricle(s) of the brain?
Lateral ventricles (a pair)
How does the CSF drain from the lateral ventricles to ventricle #3?
Through tiny holes called interventricular foramina
What is ventricle #3?
A single ventricle found on the midline b/w the 2 halves of the diencephalon
Where does the CSF produced in ventricle 3 go?
To ventricle #4
How does the CSF from ventricle #3 go to ventricle #4?
- Have to pass through part of the brainstem called the mid brain
- There’s a straw-like aperture (an opening) running b/w ventricle #3 and #4 called the cerebral aqueduct
What is the straw-like aperture (an opening) running b/w ventricle #3 and #4 called?
Cerebral aqueduct
- A structure to convey water from one region to another
- It continues all the way down to the tip of the spinal cord as the central canal
True or false
CSF is produced in the lateral, 3rd, and 4th ventricles by the ependymal cells of the CHOROID PLEXUS
True
Why do we need CSF?
- delivers nutrients to all the neurons and glial cells within the brain
- a highly buoyant solution
- Denser than water
- Helps to float your CNS in the skull
What are arachnoid granulations?
One way valves to let the CSF go back to the blood
Issues when ppl don’t make enough CSF
Brain starts to droop in their skull
- Results in the brainstem being compressed
- Temporal lobes are compressed
- Thus deficiencies in functions
How do CSF travel through the ventricles in the brain?
Ventricle 1&2 (lateral ventricles) - make CSF
CSF travel through the interventricular foramina
Ventricle 3 - make more CSF
CSF travel through the cerebral aqueduct through the midbrain
Ventricle 4 - more CSF made
Tiny little holes in the roof of ventricle 4 allows CSF to go into the subarachnoid space
CSF composition
Filtered Plasma
+sodium
+chloride
potassium, calcium
proteins (no clotting factors)
glucose (2/3 as much as in the blood)
Very few white blood cells (lymphocytes & monocytes / macros)
No red blood cells
- Similar to the plasma (liquid matrix of the blood)
What will transfer CSF from the subarachnoid space to the superior sagittal sinus?
Arachnoid granulations (villi)
- One way valves
What does stenosis mean?
Narrowing
True or false
Rate of CSF production and drainage are matched.
If rates unmatched, pathology ensues.
True
What is the lumphatics system
The immun system
Where is CSF drained through before returning to the blood near the heart?
Cervical lymph nodes
- Help drain CSF
- Swollen lymph nodes - indication of infection
Blood supplies to the brain
2 paired internal carotid arteries and a set of vertebral arteries
Where does blood go in the brain from?
The base of the brain
What is the one that services all the structures on the outside of the skull including the muscles and the skin? Think of BVs
External carotid
What is the anterior cerebral artery?
- 2 of them (left & right hemispheres)
- Go through the inferior surface of the frontal lobe and curl up to the top parts of the frontal lobe and the parietal lobe
What comes off of the basilar artery and supplies blood to the occipital lobe?
Posterior cerebral
What is basilar artery formed by?
The 2 vertebral arteries
- It’s on the base of the pons
What does the posterior communicating artery do?
Allows blood to be shared b/w the basilar and the internal carotid
Where is the anterior ocmmunication artery?
B/w the 2 anterior cerebral arteries
What is a connection b/w arteries where there’s more than 1 route for blood flow called?
Anastomosis
- The circle of Willis
Where does most of the blood feeding the posterior cerebral arteries come from?
Basilar artery
Where does most of the blood feeding the middle cerebral and the anterior cerebral come from?
The internal carotids
What are the 4 vessels that feeds the Circle of Willis?
2 vertebral
2 internal carotids
True or false?
85% of aneurysms occur in the Circle of Willis
True
Why are congenital (presence from birth) weakening of the BVs more like to occur in the Circle of Willis?
B/c of all the branching points
- They tend to tbe the weakest parts of the vessels
What are the 2 major types of cerebrovascular accidents (strokes)?
Hemorrhagic stroke
Ischemic stroke
When do hemorrhagic stroke happen?
Occur when a cerebral BV tears & breaks
- Bleeding into the brain
- Intracerebral hemorrage
What causes hemorrhagic strokes?
hemorrhage/blood leaks into brain tissue
(intracerebral hematoma)
What causes ischemic strokes?
clot stops blood supply to an area of the brain
What’s the problem in hemorrhagic strokes?
Where the BV is broken, distal (downstream) to it, those tissues are not receiving blood
- B/c the blood is bleeding into the brain, those tissues will die
What’s the problem in ischemic strokes?
Blood clot prevents all the distal regions from receiving blood
- The anterior, middle & posterior cerebral arteries are the only ways to get blook to that region of the brain, thus, blood clot will stop blood flow to that region of the brain
- No anastomosis b/w those arteries
- If one of them is blocked, all the tissues it supplies will die
What’s happening in ischemic strokes?
BVs are intact but there’s a blood clot that’s occluding/stopping blood flow
True of false
Functional deficits due to strokes will depend on the area of brain supplied by the affected artery
True
Functions of the right cerebral cortex
Movements on the left side of the body
Sensations from the left side of the body
Spatial orientation & object recognition
Damage = reduction of emotional component to speech
Functions of the left cerebral cortex
Movements on the right side of the body
Sensations from the right side of the body
Spoken and written language
Damage = aphasia
Which arteries are interconnected via the Circle of Willis?
middle, anterior and posterior cerebral arteries
Do most people have a complete Circle of Willis?
No - most ppl have incomplete Circle of Willis, only minority have complete CoW
