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The Nervous System
SMS 1084
Dr. Mohanad R. Alwan
IMS-MSU.MY
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Protection & Nutrition of CNS
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Protection
Bone
Cranial bones & vertebral arches
MeningesDura mater
Arachnoid mater
Pia mater
Cerebrospinal fluid (CSF)
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Definition
Meninges = membranes covering the brain
and spinal cordThey are
1. Duramater
2. Arachnoid mater3. Pia mater
Meninges
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Meninges
Dura mater Arachnoid mater
Pia mater
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Duramater
Two layers of dense fibrous tissueIn the skull outer layer takes the place of periosteum
on the inner surface of the skull
Inner layer covers the brain
Forms a partition between the two cerebralhemispheres called the falx cerebri
Between the cerebellar hemispheres falx cerebelli
Between the cerebrum and cerebellum tentoriumcerebelli
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Spinal Dura mater
Foms a loose sheath around the spinal cord
Extends from the foramen magnum to the S2vertebra Then it invests the filum terminale
Fuses with the periosteum of the coccyx
It is an extension of the cerebral dura It is separated from the periosteum of the vertebraeand ligaments within the neural canal by the epiduralspace.
Applied anatomy : epidural space epiduralanaesthesia
Subarachnoid space of the spinal canal spinalanaesthesia
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Arachnoid mater
Middle layer of the three membranes covering the
brain and spinal cord
Separated from the dura mater by the subdural space
and from the pia mater by the subarachnoid space Subarachnoid space contains the cerebrospinal fluid
Covers the spinal cord also and ends by merging with
the dura mater at the level of S2
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Pia mater
Inner most layer of the meninges
Fine connective tissue
Contains minute blood vessels
Closely invests the brain
Completely covers the convolutions Dips into fissures
Invests the spinal cord
Beyond the end of the spinal cord continues as thefilum terminale
Pierces arachnoid mater and with dura mater fuseswith periosteum of the coccyx
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Meninges - Arachnoid and Pia
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Cerebrospinal Fluid
Slide 7.46
Similar to blood plasma
composition Formed by the choroid
plexus
Forms a watery
cushion to protect thebrain
Circulated in arachnoidspace, ventricles, and
central canal of thespinal cord
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Cerebrospinal fluid (CSF)
Production: floor of the lateral ventricle
and third ventricle, by choroid plexus.
Circulation: L.V. -> III.V. -> IV.V. -> exitventricular system into various basalcisterns and then to subarachroid space
Circulates in through ventricles, canals, &between meninges
Drain back to blood via arachnoidgranulation to superior sagittal sinus, or via
spinal nerve roots, or via olfactory tracts
From Johanson CE
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CSF volume in human
Total: 164.5 47.8 ml
Ventricles: 31.9 17.8 ml
IIIrd ventricle: 0.95 0.62 ml Extraventricular: 132.6 43.2 ml
Total cranium: 1051.7 86.9 ml
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Function of CSF
Maintenance of a constant external
environment for neurons and glia
Mechanical cushion to protect the brainand buoyant to the heavy brain (1400 g)
Serve as a lymphatic system and a conduit
for neuropeptides pH of CSF regulates pulmonary ventilation
and CBF
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Cerebrospinal fluid (CSF)
Supports (buoys) mass Cushions CNS - like
waterbed
Nourishes brain tissue Contains proper
electrolytes for CNS
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Cerebrospinal fluid (CSF)
Filtered from blood
plasma in choroid
plexuses
Circulates in throughventricles, canals, &
between meninges
Returned to blood at
superior sagittal sinus
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Circulation of cerebrospinal fluid
CSF drains from lateral ventricle interventricular foramina third ventricle
mesencephalic aqueductfourth ventricle
median and two lateral apertures
subarachnoid space arachnoid granulations superior sagittal sinus vein
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Ventricular System
Within the brain is a communicating system of
cavities that are lined with ependyma cells and filled
with cerebrospinal fluid (CSF)
There are: two lateral ventricles,
the third ventricle,
the cerebral aqueduct,
and the fourth ventricle within the brain stem.
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Ventricles of the Brain
2 Lateral ventricles (1, 2) in cerebral hemispheres Third ventricle (3) between hemispheres
Fourth ventricle (4) in midbrain and medulla
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Ventricles and Location of the CerebrospinalFluid
Slide
Figure 7.17a
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What is the Blood Brain Barrier?
Structural and functional barrier whichimpedes and regulates the influx of
most compounds from blood to brain.
Formed by brain microvascularendothelial cells (BMEC), astrocyte endfeet and pericytes
Essential for normal function of CNS.
Regulates passage of molecules in andout of brain to maintain neuralenvironment.
Responsible for metabolic activitiessuch as the metabolism of L-dopa toregulate its concentration in the brain.
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Blood-brain barrier CNS is sensitive to chemicals
Capillaries have thicker, non-leaky walls.
Protects brain from drugs, metabolites, toxins
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Functions and Properties of the BBB
The BBB has several important functions:
1. Protects the brain from "foreign substances" in the blood that may injure the brain.
2. Protects the brain from hormones and neurotransmitters in the rest of the body.
3. Maintains a constant environment for the brain.
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Functions and Properties of the BBB
General Properties of the BBB
1. Large molecules do not pass through the BBB easily.
2. Low lipid (fat) soluble molecules do not penetrate into the brain.
However, lipid soluble molecules rapidly cross the BBB into the
brain.3. Molecules that have a high electrical charge to them are slowed.
Therefore:
The BBB is selectively permeable to :Oxygen, Carbon dioxide and
glucose The BBB is not permeable to
hydrogen ions
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Structure of Blood Brain Barrier
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Transport of substances across the BBB
Ions
Amino Acids and organic acids
Glucose and other carbohydrates
Biogenic amines
Nucleotide precursors
Peptides, proteins and lipoproteins
Steroid and thyroid hormones Vitamins, trace metals
Chemotherapy agents, antibiotics
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Transport at the BBB
There are five basic mechanisms by which solute
molecules move across membranes:
1. simple diffusion
2. facilitated diffusion3. simple diffusion through an aqueous channel
4. active transport through a protein carrier
5. Endocytosis
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Blood supply & Nutrition
Brain is highly vascular
blood delivers O2and glucose supply
Can't be deprived of O2. No capacity foranaerobic respiration.
Brain cells die w/in 5-6 minutes when deprived
Requires glucose (or ketone bodies) as fuelCan't use fats, amino acids.
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