PSL300H1 Lecture Notes - Lecture 6: Pia Mater, Dura Mater, Extracellular Fluid
PSL300
Lecture 6: Neurophysiology 6
Blood Brain Barrier
• The brain and the spinal cord are protected from the general circulation and the body
• The ionic composition of the extracellular fluid and the neuron must be carefully controlled:
o Can not change the excitability of the membrane (e.g. with KCl injection → decreased K+ concentration
gradient → depolarization → inactivation of the Na+ channel → no more AP produced)
o Can not have neurotransmitters floating around for no reason
• Thus, the extracellular fluid in the neuronal environment (brain and spinal cord) are carefully regulated through
BBB
o Do not want the brain and spinal cord to come into contact with toxins
• BBB can be thought of as a 2-fold entity
o Between the blood vessels & interstitial fluid and
the blood vessels & the CSF
• There is isolation between each compartment
o Free diffusion happens between the CSF and the
interstitial fluid
• Parkinson’s Disease
o Do not want toxins to reach the brain
o Lack of dopamine
o Results in stiffness and muscle contraction,
twitching
o Dopamine cannot cross the BBB
▪ Need to inject a precursor of dopamine
that CAN cross the BBB
Areas Lacking the BBB
• Most of the brain is protected by the BBB, but it is not continuous
• At some places it is essential for neurons to communicate freely with the blood stream
o Hypothalamus – release hormones into the general circulation
• The pituitary gland (releases hormones) is directly connected to the hypothalamus → thus the BBB is
purposefully broken to allow release of hormones
• In ‘Circumventricular Organs’ (around 3rd ventricle) the BBB is broken so neurons can sense specific chemical
concentrations
o Neurons can send out projections to sense what is going on in the general circulation
• Generally, BBB is broken in areas that interact with the endocrine system or require sensitivity to metabolites in
plasma
Brain Encasing’s
• Skull is one of the strongest parts of the body
o Thick and bony
• Meninges:
o Dura mater (very tough membrane, sac containing the brain
and the spinal cord)
o Arachnoid membrane (much more delicate tissue)
o Pia mater (lies right on top of the brain; tethered to arachnoid
by arachnoid ‘Trabeculae’
o Between the arachnoid membrane and pia matter →
subarachnoid space (filled with CSF)
▪ Brain floats here to protect it from mechanical stress
– shock absorber
▪ Ensures that the head doesn’t shake too much
o The reticular formation is in the back of the head
▪ Area of loose nerves that connect the brain to behaviour
▪ Automatically causes someone to pass out -- -gives the brain the sensation of a missing body
