1- Anatomy/Physiology Flashcards
What are the types of glial cells and their functions?
Astrocytes - contribute to BBB, participate in neuronal metabolism, scaffolding for growing axons and neurons during development, maintain extracellular ion concentration
Oligodendrocytes - for the myelin sheath around CNS axons
Microglia - phagocytic cell of the CNS
Ependymal cells - line the fluid filled cavities of the brain and cord
Describe the types of integration of synaptic imputs.
Temporal summation - consecutive EPSPs at the same site add together to depolarize the membrane
Spatial summation - simultaneous EPSPs at different synapses on the same neuron sum to depolarize the membrane
** due to decay of the voltage as it travels along dendrites, the axon hillock is an important point of integration and regulation –> it is here that the EPSPs transition to Action Potentials
Define:
1) presynaptic facilitation
2) presynaptic inhibition
3) feed forward processes
4) disinhibition
1) presynaptic facilitation -> neutransmitter (NT) released at the axoaxonic synapse increases Ca at the terminal
2) presynaptic inhibition -> NT released at the azoaxonic synapse decreases Ca at the terminal
3) feed forward processes -> unidirectional flow of signal through a series of neurons causes either excitation or inhibition
4) disinhibition -> 4 neurons in series; 1 & 4 excitatory, 2 & 3 inhibitory => 1 excites 2, which inhibits 3, releasing 4 from inhibition –> excitatory signal
Describe the stages of the neuronal response to PNS injury.
- > Retrograde reaction: occurs proximal to the axonal injury; 1)swelling of cell body/nucleus, 2) nuclear displacement from center of cell, 3)chromatolysis - dispersion of Nissl bodies, 4) RER replaced by polyribosomes
- > Aterograde reaction(Wallerian degeneration): occurs distal to the injury; 1) Schwann cells dedifferentiate and divide, 2) Schwann cells and macrophages phagocytose the debris
- > Regeneration: 1) growth cone develops at site of injury, 2) sprouts from growth cone must grow across site of injury to enter the schwann cell guidance tunnels, 3) schwann cell proliferation (2nd wave) stimulated by contact with growth cone, 4) tunnel and axon extend along previous nerve path to reinnervate original tissue
- *CRUSH injury has better prognosis than TRANSECTION
What are the 5 divisions of the brain?
Forebrain: 1) Telencephalon -> cerebral cortex, subcortical white matter, basal ganglia, etc. 2) Diencephalon -> Thalamus, hypothalamus Midbrain: 3) Mesencephalon -> Midbrain Hindbrain: 4) Metencephalon -> Pons, Cerebellum 5) Myelencephalon -> Medulla
Describe the function of the Precentral Gyrus.
Primary Motor Cortex: contains “upper motor neurons” that travel to the brainstem and spinal cord to control “lower motor neurons” which innervate skeletal muscles of the body
-Somatotropic organization: (from lateral fissure) face, hand, arm and trunk (at longitudinal fissure); Paracentral Lobule controls the motor and sensory innervation of the lower extremeties
Describe the Postcentral Gyrus.
Primary Sensory Cortex: receives and processes somatic sensory information from the opposite side of the body
Somatotropic organization: (from the lateral fissure) face, hand, arm, trunk (at longitudinal fissure)
What is contralateral hemineglect?
Lesion to the non-dominant inferior parietal lobule causes the patient to “ignore” the contralateral half of the external world/body.
ex: not eating food on left side of plate, not drawing left half of clock, not dressing left side of body
What are Brosmann’s Areas?
Schema of organizing the brain based on cytology. Areas frequently correlate with functional region (primary motor cortex, primary auditory cortex)
Describe the flow path of CSF.
Produced by the choroid plexus and emptied into the ventricles (lateral, 3rd and 4th).
Flows through the Intraventricular Forarmen (of Munro) into the 3rd ventricle and then through the Cerebral Aqueduct into the 4th.
Exits the 4th ventricle through the foramina of Lushcka (laterally) and Magendie (medial) into the Subarachnoid Space.
Specific portions of the SAS are the major cisterns: cerebellomedullary (magna), pontine, superior(ambines), interpeduncular, and chiasmatic. These then “drain” into the superior sagital sinus via the arachnoid villi.
How is CSF formed?
75% Formed by the Choroid Plexus in the body of the lateral ventricles, the roofs of the 3rd and 4th ventricles and in the foramina of Luschka and Munro.
The choroid plexus is composed of a capillary network of fenestrated endothelia surrounded by cuboidal, choroid epithelium.
During production of CSF, metabolites are actively transported out of the ventricles into the blood.
25% of CSF is formed from extrachoroidal sources, mostly cerebral capillary walls.
What are the primary functions of the CSF?
1) Maintenance of external environment for neurons and glia
2) Removal of harmful brain metabolites
3) Protection of the brain from trauma by buoyancy effect
What is the composition of normal CSF?
Filtrate of the blood with different concentrations of key components. Compared to serum levels:
- LOW protein (200:1)
- low glucose, Ca++, K+ (2:1)
- low ph (7.33)
- less cells
- SAME Na and Osmolarity
- MORE water (99% v 93%), Cl-, Mg++
Describe Hydocephalus.
Hydrocephalus is an expansion of the ventricle and, frequently, increased intracranial pressure. Due to:
1) over secretion of CSF (tumor of choroid plexus/papillomas)
2) impaired reabsorption of CSF (tumors, malformations, scarring)
3) obstruction of CSF circulation (tumor as channels/foramina)
#3 is Non-Communicating, while #1&2 are Communicating
**Hydrocephalus ex vacuo is enlargement of the ventricles without increase in pressure. Due to CENTRAL ATROPHY allowing expansion, not due to CSF build up.
What are the barriers between the vascular, CSF and extracellular compartments of the CNS?
1) Blood-CSF Barrier: tight junctions of choroid epithelial cells controls the transfer of nutrients that are needed in the brain in small amounts over a long period of time (Vit C, folates)
2) CSF-Blood Barrier: molecules move freely between ventricles and intracellular space of CNS
3) Blood-Brain Barrier: regulates diffusion from blood to preserve CNS environment; actively transports nutrients consumed rapidly (glucose, amino acids, lactate, ribonucloesides); formed by:
a) endothelial cells of capillaries w tight junctions,
b) low vesicular transport of endothelial cells,
c) continuous basement membrane,
d) perivascular foot processes of Astrocytes cover the outer surface of cells
What are circumventricular organs?
- Areas of the CNS that lack a BBB.
- Located in close proximity to ventricles to allow for rapid response to changes in systemic chemical changes
- EX: pineal body, subcommissural organ, subfornical organ, organum vasculosum of the lamina terminalis, median eminence, neurohypophysis, area postrema
What are the layers of the scalp?
Skin - hair bearing with sweat and sebaceous glands
Connective Tissue (dense) - subcutaneous layer of collagen and fat, with vessels and nerves
Aponeurotic Layer - fibro-muscular sheet; epicranial aponeurosis, occipitalis and frontalis
Loose Connective Tissue - mobility of the scalp
Pericranium - periosteum on external surface of the skull; attached loosely except at surtures
Where is the pterion? What is its clinical significance?
On the lateral surface of the skull, it is the intersection of the frontal, parietal, temporal and sphenoid bones. This is a particularly weak area of the skull and it overlies the anterior branch of the Middle Meningeal Artery. A fracture here can result in a life-threatening epidural hematoma.
What are the meninges?
- Dura mater:
1) Periosteal dura is attached to the inner surface of the skull bones
2) Meningeal dura is typically attached to the periosteal layer, but separates from it to form the dural venous sinuses and dural partitions - Arachnoid mater is attached loosely to the surface of the brain, not entering the sulci; the subarachnoid space is filled with the arachnoid trabeculae
- Pia mater is closely attached to the brain surface and DOES enter the sulci
- the meningeal arteries supply the layers and sensory innervation is provided by the trigeminal nerve(V1-3), C2 and C3
What are the classes of intracranial hemorrhage? What is their typical clinical presentation?
Epidural: between the periosteum of the skull and the periosteal dura, commonly from the meningeal arteries (middle)
-> Clinical: trauma w/ temporary loss of consciousness, followed by a period of “recovery,” which is then succeeded by acute onset of symptoms-> headache, confusion, contralateral motor paralysis, COMA
Subdural: between the meningeal dura and the arachnoid mater; due to a rupture of a branching vein as it travels from a sinus back to the subarachnoid space
-> Clinical: low pressure bleed results in a slowly-expanding hematoma which may present in days to weeks
Subarachnoid: between the arachnoid and pia mater; much more acute due to the number of larger vessels that pass in this true space
-> Clinical: frequently associated with aneurysms or HPTN, hemorrhage presents as acute onset of “worst headache of my life”; lumbar puncture will show blood in the CSF
What are the types of brain herniations? What is their typical clinical presentation?
1) Subfalcine: cingulate gyrus is displaced under the falx cerebri; typically due to a unilateral mass and can present as compression of the cingulate gyrus
2) Tentorial: increased supratentorial pressure can push the uncus/temporal lobe segments under the tentorial membrane; also called an Uncal hernuiation, can compress the ventral surface of the midbrain and the CNII causing a “blown pupil”
3) Tonsillar: increased intracranial pressure can push the cerebellum through the foramen magnum, resulting in compression of the respiratory control centers and respiratory arrest; can be congenital in Anrold-Chiari -> foramen usually adapts in development so symptoms are mild, absent or delayed
3) Tonsillar
Describe the venous drainage of the cranium.
CSF is resorbed into the venous system via arachnoid villi in the subarachnoid space. They act as one-way-valves from the SAS into the venous sinuses. These villi frequently group together in “arachnoid granulations.”
The remaining portions of the cranium are drained by 4 types of veins:
1) Cerebral veins - cerebral hemispheres
2) Meningeal veins - meninges
3) Diploic veins - cranial bones
4) Emissary veins - connect the veins of the face and scalp to the dural venous sinuses via openings in the bones
Once in the sinuses, the flow is via the dural sinus system which will eventually drain into the IJV.
What important structures are located in the cavernous sinus?
Vessels -> internal carotid artery travels through and back in the sinus
Nerves -> CN III, CN IV, CN V1, CN V2, CN VI
** since the superior opthalmic artery drains into the sinus, infections can make it into the sinus and present with symptoms related to any one or combination of the nerves that travel through it
What autonomic sensory structures are at the bifurcation of the Common Carotid and Internal Carotid Artieries?
Carotid Sinus -> at the bifurcation, it is a dilation of the proximal ICA wall that contains baroreceptors sensitive to changes in blood pressure -> innervated by CN IX, X and sympathetics -> activation causes reflexive DECREASE in blood pressure
Carotid Body -> body in the cleft between the arteries that are sensitive to changes in PO2, PCO2, and pH -> innervated by CN IX, X and sympathetics -> activation causes reflexive INCREASE in HR, BP and respiration
