Neuro Anatomy & CBF Flashcards
What is the organization of the nervous system?
CNS: Brain and Spinal Cord
PNS: Includes the cranial and spinal nerves and their receptors, and it is divided into the somatic and autonomic nervous systems. The somatic nervous system contains sensory neurons for the skin, muscles, and joints. The autonomic nervous system consists of the sympathetic, parasympathetic, and enteric subdivisions and is responsible for involuntary innervation of various organ systems.
What are Neurons?
The basic functional cell of the CNS.
-Responsible for impulse conduction (motor and sensory)
What are Neuroglial cells (Glial)?
5 types:
-Astrocytes
-Ependymal Cells
-Microglia
-Oligodendrocytes
-Schwann Cells
What are Astrocytes?
-Provide structural neuronal support
-Regulate metabolic activity
-Essential in the development of the blood brain barrier.
What are Ependymal Cells?
Form the Choroid Plexus in the 3rd and 4th ventricles to produce CSF.
What are Microglia?
Go to sites of neuronal injury or degeneration and develop into macrophages that phagocytize neuronal debris.
What are Oligodendrocytes?
Form the myelin sheath of axons in the brain and spinal cord (CNS).
What are Schwann Cells?
Produce myelin for the peripheral nervous system.
-If found in CNS it is pathologic (Vestibular or Acoustic Schwannoma)
What is Glutamate?
The primary excitatory transmitter found within the cerebral cortex, the hippocampus, and the substantia gelatinosa of the spinal cord.
-Glutamate plays a significant role in learning and memory (perhaps interactive in memory formation during awareness that occurs during anesthesia) and the appreciation of pain.
-Involved in neuronal injury in TBI as well as ischemic injury.
What is Cerebrospinal Fluid (CSF)?
-Serves to protect the brain and spinal cord
-Contains Na, K, HCO3, glucose, and minimal protein that leak from perivascular fluid
-Normal pressure is 5-15 mmHg
-About 500 mL/day is produced (20-30 mL/hr), mainly in the Lateral Ventricles by the Choroid Plexus
-At any given time, there is only 150 mL of CSF present in adults and 50 mL in children.
-Absorbed in Arachnoid Villi in the Subarachnoid space and absorbed into the blood.
-pH is 7.32
What is the specific gravity of CSF?
1.002 - 1.009
-Can be changed with severe hyperglycemia, hypoglycemia
-Protein levels change SG, this can indicate tumors, infection, bleeds etc.
What are things that can decrease the production of CSF?
-Carbonic anhydrase inhibitors like acetazolamide,
-Vasoconstrictors
-Lasix, steroids
-Isoflurane
Describe the circulation or flow of CSF.
-CSF flows from the lateral ventricles of the cerebral hemispheres through the foramen of Monro into the third ventricle, and through the aqueduct of Sylvius (very tiny - common to obstruct here) in the midbrain into the fourth ventricle. CSF enters the subarachnoid space through the medial foramen of Magendie and the paired lateral foramina of Luschka, opening posterior to the pons and anterior to the cerebellum.
-The cisterna magna, located between the medulla and the cerebellum, is formed from the separation of the arachnoid mater from the pia mater and is filled with CSF. Two additional cisterns exist, the cisterna pontis and the cisterna basalis. CSF drains into the venous blood via the superior sagittal sinus and is absorbed by arachnoid granulations.
How is the Blood-Brain Barrier (BBB) formed?
Collection of Endothelial Cells from the capillary wall that form a very selective semi-permeable membrane plus a capillary basement membrane, a neuroglial membrane, and astrocyte projections.
-These form continuous tight junctions that make the BBB a tight barrier for water soluble molecules.
-Strictly control the passage of substances into and out of the CNS.
-BBB disruption can be caused by traumatic head injury, subarachnoid or intracerebral hemorrhage, or cerebral ischemia. The BBB can be disrupted in several disease processes such as multiple sclerosis, stroke, and brain tumors.
Give an example of one CNS structure NOT protected by the Blood-Brain Barrier?
The Chemoreceptor Trigger Zone (CTZ).
-Allows detection of toxins, emetic agents
How much CO does the brain receive?
~15% (750 mL/min)
-Originates from 2 arterial supplies to form Circle of Willis (Anterior and Posterior)
-The anterior and posterior arterial systems communicate through arterial anastomoses that form the circle of Willis.
Describe the Anterior circulation to the brain.
Receives blood from the Internal Carotid Arteries.
-Form the anterior and middle cerebral arteries.
-Anterior cerebral artery supplies the medial surface of the cerebral hemispheres
-Middle cerebral artery supplies the lateral surface of the cerebral hemispheres.
Describe the Posterior circulation to the brain.
Receives blood from the Vertebral Arteries.
-Form the Basilar artery in the pons.
-Supplies a large portion of the brain and spinal cord.
Nagelhout:
-Branches of the vertebral and basilar arteries supply a wide area, including the cervical region of the spinal cord, the brainstem, the cerebellum, the vestibular apparatus and cochlea of the inner ear, parts of the diencephalon, and the occipital and temporal lobes of the cerebral hemispheres.
The paired anterior, middle, posterior cerebral arteries originate from where?
The paired anterior, middle, and posterior cerebral arteries originate from the circle of Willis.
Thrombosis of the Anterior Cerebral Artery causes what effects?
-Paralysis and loss of sensation of leg and foot
-Personality changes
Thrombosis of the Middle Cerebral Artery causes what effects?
-Hemiplegia and loss of the sensation mainly face and arm
-Aphasia (Broca’s and Wernickes’s area)
