2 Cns Protection
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IMS-MSU.MY
The Nervous System SMS 1084 Dr. Mohanad R. Alwan
1
Protection & Nutrition of CNS
2
Protection • Bone – Cranial bones & vertebral arches
• Meninges – Dura mater – Arachnoid mater – Pia mater
• Cerebrospinal fluid (CSF) 3
Meninges Definition Meninges = membranes covering the brain and spinal cord They are 1. Duramater 2. Arachnoid mater 3. Pia mater 4
Meninges • Dura mater • Arachnoid mater • Pia mater
5
Duramater Two layers of dense fibrous tissue In 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 cerebral hemispheres called the falx cerebri Between the cerebellar hemispheres – falx cerebelli Between the cerebrum and cerebellum – tentorium cerebelli
6
7
Spinal Dura mater • • • • • •
Foms a loose sheath around the spinal cord Extends from the foramen magnum to the S2 vertebra 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 vertebrae and ligaments within the neural canal by the epidural space. • Applied anatomy : epidural space – epidural anaesthesia • Subarachnoid space of the spinal canal – spinal anaesthesia 8
9
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
10
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 the filum terminale • Pierces arachnoid mater and with dura mater fuses with periosteum of the coccyx 11
Meninges - Arachnoid and Pia
12
Cerebrospinal Fluid • Similar to blood plasma composition • Formed by the choroid plexus • Forms a watery cushion to protect the brain • Circulated in arachnoid space, ventricles, and central canal of the spinal cord
Slide 7.46
Cerebrospinal fluid (CSF) • Production: floor of the lateral ventricle and third ventricle, by choroid plexus. • Circulation: L.V. -> III.V. -> IV.V. -> exit ventricular system into various basal cisterns and then to subarachroid space • Circulates in through ventricles, canals, & between meninges • Drain back to blood via arachnoid granulation to superior sagittal sinus, or via spinal nerve roots, or via olfactory tracts
From Johanson CE
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
15
Function of CSF • Maintenance of a constant external environment for neurons and glia • Mechanical cushion to protect the brain and 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
Cerebrospinal fluid (CSF) • Supports (buoys) mass • Cushions CNS - like waterbed • Nourishes brain tissue • Contains proper electrolytes for CNS
17
Cerebrospinal fluid (CSF) • Filtered from blood plasma in choroid plexuses • Circulates in through ventricles, canals, & between meninges • Returned to blood at superior sagittal sinus
18
Circulation of cerebrospinal fluid CSF drains from lateral ventricle
mesencephalic aqueduct
interventricular foramina
fourth ventricle
third ventricle
median and two lateral apertures
subarachnoid space arachnoid granulations superior sagittal sinus
vein
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.
Ventricles of the Brain • 2 Lateral ventricles (1, 2) in cerebral hemispheres • Third ventricle (3) between hemispheres • Fourth ventricle (4) in midbrain and medulla
21
Ventricles and Location of the Cerebrospinal Fluid
Figure 7.17a
Slide
What is the Blood Brain Barrier? • Structural and functional barrier which impedes and regulates the influx of most compounds from blood to brain. • Formed by brain microvascular endothelial cells (BMEC), astrocyte end feet and pericytes • Essential for normal function of CNS. • Regulates passage of molecules in and out of brain to maintain neural environment. • Responsible for metabolic activities such as the metabolism of L-dopa to regulate its concentration in the brain.
Blood-brain barrier • CNS is sensitive to chemicals • Capillaries have thicker, non-leaky walls. • Protects brain from drugs, metabolites, toxins
24
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.
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
Structure of Blood Brain Barrier
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
Transport at the BBB There are five basic mechanisms by which solute molecules move across membranes: 1. 2. 3. 4. 5.
simple diffusion facilitated diffusion simple diffusion through an aqueous channel active transport through a protein carrier Endocytosis
Blood supply & Nutrition • Brain is highly vascular – blood delivers O2 and glucose supply
• Can't be deprived of O2. No capacity for anaerobic respiration. – Brain cells die w/in 5-6 minutes when deprived
• Requires glucose (or ketone bodies) as fuel – Can't use fats, amino acids. 30
31
The Nervous System SMS 1084 Dr. Mohanad R. Alwan
1
Protection & Nutrition of CNS
2
Protection • Bone – Cranial bones & vertebral arches
• Meninges – Dura mater – Arachnoid mater – Pia mater
• Cerebrospinal fluid (CSF) 3
Meninges Definition Meninges = membranes covering the brain and spinal cord They are 1. Duramater 2. Arachnoid mater 3. Pia mater 4
Meninges • Dura mater • Arachnoid mater • Pia mater
5
Duramater Two layers of dense fibrous tissue In 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 cerebral hemispheres called the falx cerebri Between the cerebellar hemispheres – falx cerebelli Between the cerebrum and cerebellum – tentorium cerebelli
6
7
Spinal Dura mater • • • • • •
Foms a loose sheath around the spinal cord Extends from the foramen magnum to the S2 vertebra 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 vertebrae and ligaments within the neural canal by the epidural space. • Applied anatomy : epidural space – epidural anaesthesia • Subarachnoid space of the spinal canal – spinal anaesthesia 8
9
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
10
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 the filum terminale • Pierces arachnoid mater and with dura mater fuses with periosteum of the coccyx 11
Meninges - Arachnoid and Pia
12
Cerebrospinal Fluid • Similar to blood plasma composition • Formed by the choroid plexus • Forms a watery cushion to protect the brain • Circulated in arachnoid space, ventricles, and central canal of the spinal cord
Slide 7.46
Cerebrospinal fluid (CSF) • Production: floor of the lateral ventricle and third ventricle, by choroid plexus. • Circulation: L.V. -> III.V. -> IV.V. -> exit ventricular system into various basal cisterns and then to subarachroid space • Circulates in through ventricles, canals, & between meninges • Drain back to blood via arachnoid granulation to superior sagittal sinus, or via spinal nerve roots, or via olfactory tracts
From Johanson CE
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
15
Function of CSF • Maintenance of a constant external environment for neurons and glia • Mechanical cushion to protect the brain and 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
Cerebrospinal fluid (CSF) • Supports (buoys) mass • Cushions CNS - like waterbed • Nourishes brain tissue • Contains proper electrolytes for CNS
17
Cerebrospinal fluid (CSF) • Filtered from blood plasma in choroid plexuses • Circulates in through ventricles, canals, & between meninges • Returned to blood at superior sagittal sinus
18
Circulation of cerebrospinal fluid CSF drains from lateral ventricle
mesencephalic aqueduct
interventricular foramina
fourth ventricle
third ventricle
median and two lateral apertures
subarachnoid space arachnoid granulations superior sagittal sinus
vein
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.
Ventricles of the Brain • 2 Lateral ventricles (1, 2) in cerebral hemispheres • Third ventricle (3) between hemispheres • Fourth ventricle (4) in midbrain and medulla
21
Ventricles and Location of the Cerebrospinal Fluid
Figure 7.17a
Slide
What is the Blood Brain Barrier? • Structural and functional barrier which impedes and regulates the influx of most compounds from blood to brain. • Formed by brain microvascular endothelial cells (BMEC), astrocyte end feet and pericytes • Essential for normal function of CNS. • Regulates passage of molecules in and out of brain to maintain neural environment. • Responsible for metabolic activities such as the metabolism of L-dopa to regulate its concentration in the brain.
Blood-brain barrier • CNS is sensitive to chemicals • Capillaries have thicker, non-leaky walls. • Protects brain from drugs, metabolites, toxins
24
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.
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
Structure of Blood Brain Barrier
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
Transport at the BBB There are five basic mechanisms by which solute molecules move across membranes: 1. 2. 3. 4. 5.
simple diffusion facilitated diffusion simple diffusion through an aqueous channel active transport through a protein carrier Endocytosis
Blood supply & Nutrition • Brain is highly vascular – blood delivers O2 and glucose supply
• Can't be deprived of O2. No capacity for anaerobic respiration. – Brain cells die w/in 5-6 minutes when deprived
• Requires glucose (or ketone bodies) as fuel – Can't use fats, amino acids. 30
31
