Lesson 6 Flashcards
(26 cards)
1
Q
Brain stem
A
- continuous with spinal cord
- medulla oblongata
- pons
- midbrain
2
Q
Cerebellum
A
posterior to brain stem
3
Q
Diencephalon
A
- superior to brain stem
- thalamus
- hypothalamus
- epithalamus
4
Q
Cerebrum
A
- largest part of the brain
- sits on diencephalon
5
Q
Protective Coverings of the Brain
A
- Cranium & cranial meninges surround and protect the brain
- Cranial meninges are continuous with the spinal meninges
6
Q
Dura Mater (brain)
A
- outer meningeal layer
- made up of 2 layers:
1. periosteal layer (external)
2. meningeal layer (internal) - these 2 layers are fused together except where they separate to enclose the dural venous sinuses
7
Q
3 extensions of dura mater separate parts of the brain
A
- Falx cerebri
- Falx cerebelli
- Tentorium cerebelli
8
Q
Falx cerebri
A
- Separates the 2 hemispheres of the cerebrum
9
Q
Falx cerebelli
A
- Separates the 2 hemispheres of cerebellum
10
Q
Tentorium cerebelli
A
- Separates the cerebrum from the cerebellum
11
Q
blood flows to brain mainly via
A
- the internal carotid
- vertebral arteries
12
Q
Brain blood flows out via
A
- dural venous sinuses which drain into the internal jugular veins
13
Q
Brain body weight %
Brain oxygen/glucose consumption %
A
- in adults, brain is 2% of total body weight but consumes 20% of all the oxygen and glucose
14
Q
How brain ATP made
A
- neurons use glucose and oxygen to make ATP in the brain
15
Q
Brain blood flow deprivation
A
- even a brief slowing of brain blood flow can cause disorientation or a lack of consciousness
- usually an interruption in blood flow for 1 or 2 minutes impairs neuronal function
- total deprivation of oxygen for about 4 minutes may cause permanent injury
16
Q
Brain glucose storage
A
- no glucose is stored in the brain so the supply of glucose
must be continuous - if blood entering the brain has a low level of glucose:
⬥mental confusion ⬥dizziness ⬥convulsions ⬥loss of consciousness
17
Q
Blood brain barrier
made up of
A
- tight junctions that seal together endothelial cells of capillaries in the brain +
- a thick basement layer that surrounds the capillaries +
- astrocytes (their processes press up against the capillaries and secrete chemicals that maintain the permeability characteristics of tight junctions)
18
Q
Blood brain barrier
What crosses it?
A
- some water-soluble substances cross by active transport
(ie glucose) - creatinine, urea, ions cross slowly
- lipid-soluble substances (O2, carbon dioxide, alcohol, most anesthetic agents)
- proteins and most antibiotic drugs do not cross
- trauma, certain toxins and inflammation can cause a
breakdown of the BBB
19
Q
CSF
A
- clear, colourless liquid
- mainly water
- protects the brain and spinal cord from chemical and physical injuries
- also carries a small amount of O2, glucose and other needed chemicals in blood to the neurons and neuroglia
- CSF continuously circulates through the cavities in the brain + spinal cord andaround the brain + spinal cord in the subarachnoid space
20
Q
CSF
Total volume and contents
A
- total volume = 80-150 mL in adult
- contains – small amounts of glucose, proteins, lactic acid, urea, cations, anions and some WBCs
21
Q
CSF Ventricles
A
- cavities within the brain filled with CSF
- 2 lateral ventricles
- 1 in each hemisphere of the cerebrum
- septum pellucidum: thin membrane that separates the lateral ventricles
- third ventricle
- fourth ventricle
22
Q
CSF
functions
A
- Mechanical protection
* shock absorbing medium that protects brain + SC from jolts
fluid also keeps brain floating in the cranial cavity - Homeostatic function
* the pH of CSF affects pulmonary ventilation & cerebral blood flow - Circulation
* minor exchange of nutrients + waste products btw blood and nervous tissue
23
Q
Formulation of CSF in Ventricles
A
- CSF is formed in choroid plexus
- choroid plexuses are networks of blood capillaries in the walls of the ventricles
- ependymal cells joined by tight junctions cover the capillaries
- substances from blood plasma (mostly water) are filtered from the capillaries through the ependymal cells to produce CSF
- because of the tight junctions btw ependymal cells, fluid must pass through the ependymal cells, creating a blood-cerebrospinal fluid barrier
- this protects the brain + SC from harmful blood-borne substances
24
Q
BBB made up of?
Blood CSF barrier made up of?
A
- so BBB is made up of tight junctions btw brain capillary endothelial cells
- and the blood-CSF barrier is made up of tight junctions btw ependymal cells
25
Circulation of CSF
Lateral Ventricles
--->
Interventricular foramina
--->
Third ventricle
--->
Cerebral aqueduct/aquaduct of midbrain
--->
Fourth ventricle
--->
2 lateral apertures + 1 media aperture
--->
Central canal/subarachnoid space
--->
arachnoid villi
26
Arachnoid villi
* CSF is reabsorbed into blood through arachnoid villi
* arachnoid villi are fingerlike extensions of arachnoid that project into dural venous sinuses
* a cluster of arachnoid villi = granulation