Lesson 6

Question 1

Brain stem

Answer 1

• continuous with spinal cord
• medulla oblongata
• pons
• midbrain

Question 2

Cerebellum

Answer 2

posterior to brain stem

Question 3

Diencephalon

Answer 3

• superior to brain stem
• thalamus
• hypothalamus
• epithalamus

Question 4

Cerebrum

Answer 4

• largest part of the brain
• sits on diencephalon

Question 5

Protective Coverings of the Brain

Answer 5

• Cranium & cranial meninges surround and protect the brain
• Cranial meninges are continuous with the spinal meninges

Question 6

Dura Mater

Answer 6

• 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

Question 7

3 extensions of dura mater separate parts of the brain

Answer 7

1. Falx cerebri
2. Falx cerebelli
3. Tentorium cerebelli

Question 8

Falx cerebri

Answer 8

• Separates the 2 hemispheres of the cerebrum

Question 9

Falx cerebelli

Answer 9

• Separates the 2 hemispheres of cerebellum

Question 10

Tentorium cerebelli

Answer 10

• Separates the cerebrum from the cerebellum

Question 11

blood flows to brain mainly via

Answer 11

• the internal carotid
• vertebral arteries

Question 12

Brain blood flows out via

Answer 12

• dural venous sinuses which drain into the internal jugular veins

Question 13

Brain body weight %

Brain oxygen/glucose consumption %

Answer 13

• in adults, brain is 2% of total body weight but consumes 20% of all the oxygen and glucose

Question 14

How brain ATP made

Answer 14

• neurons use glucose and oxygen to make ATP in the brain

Question 15

Brain blood flow deprivation

Answer 15

• 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

Question 16

Brain glucose storage

Answer 16

• 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

Question 17

Blood brain barrier
made up of

Answer 17

• 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)

Question 18

Blood brain barrier
What crosses it?

Answer 18

• 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

Question 19

CSF

Answer 19

• 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

Question 20

CSF

Total volume and contents

Answer 20

• total volume = 80-150 mL in adult
• contains – small amounts of glucose, proteins, lactic acid, urea, cations, anions and some WBCs

Question 21

CSF Ventricles

Answer 21

• 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

Question 22

CSF
functions

Answer 22

1. Mechanical protection
   * shock absorbing medium that protects brain + SC from jolts
   fluid also keeps brain floating in the cranial cavity
2. Homeostatic function
   * the pH of CSF affects pulmonary ventilation & cerebral blood flow
3. Circulation
   * minor exchange of nutrients + waste products btw blood and nervous tissue

Question 23

Formulation of CSF in Ventricles

Answer 23

• 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

Question 24

BBB made up of?

Blood CSF barrier made up of?

Answer 24

• 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

Question 25

Circulation of CSF

Answer 25

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

Question 26

Arachnoid villi

Answer 26

• 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