Download Support Systems of the Nervous System

Support Systems of the Nervous
System
• Lundy-Ekman
– Chapter 1
• Pp. 11-19
– Chapter 19
Meninges
Meninges
• Dura mater
– Periosteal layer – attaches to skull
– Meningeal layer – attaches to arachnoid
• Two layers attached except at dural venous
sinuses
• Projections of inner layer
– Falx cerebri – L and R cerebral hemispheres
– Tentorium cerebelli – Cerebellum and posterior
cerebrum
• Arachnoid mater
– Trabeculae – bars of tissue deep to arachnoid
membrane
• Pia mater
– Thin layer
– Firmly attached to brain and spinal cord
Meningeal spaces
• Subarachnoid space
– Space filled with CSF and blood vessels
• Subdural space
– Between dura and arachnoid
– Virtual space
• Epidural space
– Between skull and dura
– Virtual space
CSF System
• Ventricles
– Lateral (2)
– Third
– Fourth
• Cerebral aqueduct
• Telencephalon: Lateral ventricles
• Diencephalon: Third ventricle
• Midbrain: Cerebral aqueduct
• Pons/medulla/cerebellum: 4th ventricle
• 4th ventricle opens to subarachnoid space
Cerebrospinal Fluid
• Choroid plexus
– All named ventricles
• CSF travels through the ventricles and out
– Lat  3rd  Cerebral aqueduct  4th ventricle
 Subarachnoid space
• CSF in subarachnoid space surrounds
outside of brain and spinal cord
Absorption of CSF
• CSF travels through the arachnoid villi into
the dural venous sinuses
• The CSF enters general circulation
Blood supply to the brain
• Our brain needs a constant supply of O2
– 10 seconds: lose consciousness
– 20 seconds: electrical activity stops
– Few minutes: irreversible injury to brain starts
• Two main pairs of arteries
– Vertebral arteries – posterior brain
– Internal carotid arteries – anterior brain
Blood vessels (ventral view) p. 17
Vertebral arteries
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Superior spinal cord
Brainstem
Cerebellum
Posterior occipital and temporal lobes of the
cerebrum
Internal carotid arteries
• Most of the telencephalon
• Most of the diencephalon
Vertebral arteries
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Arise off subclavian arteries
First 6 cervical vertebrae –
Enter skull and travel along medulla
Branches in medulla – page 17
– Posterior spinal arteries – posterolateral cord
• Posterior 1/3rd of cord
– Anterior spinal artery – anterior median cord
• Anterior 2/3rd of cord
– Posterior inferior cerebellar artery (PICA)
• Inferior cerebellum
Blood supply to the spinal cord
• The anterior and posterior spinal arteries do
not receive enough blood to supply the
whole spinal cord
• Radicular arteries enter the spinal cord with
the nerve roots
– Supplement vascular supply
– Most are small, only a few are significant
– Blockage of a radicular artery can damage the
spinal cord at that level, but also axons passing
through that region
Basilar artery
• The 2 vertebral arteries join at the pons
• Branches
– Anterior inferior cerebellar artery (AICA)
– Superior cerebellar artery
• Basilar artery and branches supply:
– Pons
– Most of cerebellum
Posterior Cerebral Artery
• At the rostral pons the basilar artery forks to
form the 2 posterior cerebral arteries
• They supply
– Midbrain
– Occipital lobe
– Medial and inferior temporal lobes
Internal Carotid artery
• Around optic chiasm it splits
– Anterior cerebral artery
• Travels in longitudinal fissure
• Supplies medial frontal and parietal lobe
– Primary motor and somatosensory cortex for LE
– Middle cerebral artery
• Passes through lateral sulcus
• Supplies most of lateral cerebral hemispheres
Circle of Willis
• Contains all 3 pairs of cerebral arteries
• Communicating arteries connect:
– Left and right anterior circulation
• Anterior communicating artery between the L and R
anterior cerebral artery
– Anterior and posterior circulation
• Posterior communicating arteries between the
posterior cerebral artery and the internal carotid
artery on each side
• Many variations on the standard pattern
Circle of Willis (cont)
• The circle is a common site for aneurysms
– They can form at branch points in arteries
• Blood flow in the communicating arteries
– Usually not a lot
• Blood vessels are small
• Similar pressure on each end of the artery
– They arteries can expand to adapt to slowly
developing occlusions in one of the main
cerebral arteries
Watershed regions – p. 470
• Regions where small anastomoses link the ends of
the cerebral arteries
• With strokes that affect one artery, watershed
regions are relatively spared
• When the blood supply in two adjacent arteries is
affected, watershed regions are most affected
Watershed regions
• Events which can affect blood flow in two
(or more adjacent arteries)
– Severe drop in systolic blood pressure
– Blockage or restriction in internal carotid artery
• Supplies both ACA and MCA
Watershed regions
• For ACA and MCA
– Often includes the trunk and proximal limbs
• Man in a barrel syndrome
– Transcortical aphasia syndromes
• Between MCA and PCA
– Difficulties in higher order visual processing
Deep Cerebral Structures
• Branches of cerebral arteries
– Dive deep into brain
• Anterior choroidal artery
– Choroid plexus in lateral ventricles
– Parts of optic tract, putamen, thalamus, internal
capsule and hippocampus
• Posterior choroidal artery
– Choroid plexus in third ventricle
– Parts of hippocampus and thalamus
Brain Stem Syndromes
• https://www.youtube.com/watch?v=JjcAyV
K7d5A&nohtml5=False
• Medial Medullary Syndrome
• http://www.youtube.com/watch?v=kT7buN
vftQw
Veins
• Not paired with arteries
• Valveless
– How might this affect the brain during
infections?
• Frequent anastomoses
• Superficial and deep veins
Superficial veins
• On surface of cerebral hemispheres
• Most empty into superior sagittal sinus
– Some connect to other sinuses located between
the two layers of the dura
• Bridging veins connect these veins with the
dural sinuses
– What happens if these bridging veins are
damaged?
Deep veins
• Drain deeper regions of telencephalon and
diencephalon
Venous blood
• Returned to internal jugular vein
• Pathology
– Usually few disorders
– Low pressure system so occlusions and
hemorrhages occur less frequently
– Large number of functional anastomoses
Cerebral Blood Flow
• Index of brain activity
• Brain requires glucose and oxygen, but
cannot store either
• Regions differ in their sensitivity to hypoxia
– Cerebral cortex more sensitive than brainstem
– Persistent vegetative state
Autoregulation of Blood Vessels
• Artery dilation
– Low BP, Oxygen or pH
– High CO2 or lactate
• Artery constriction
– High pH, Oxygen or BP
– Low CO2 or lactate
• Autoregulation important to ensure
adequate blood flow and prevent edema