Medical Physiology Block 2 Week 1

Question 1

Describe the components of the Subdivisions of the Nervous system.

Answer 1

CNS: surrounded by meninges (dura, arachnoid, pia),brain and spinal cord, myelin producing oligodendrocytes, axons do not regenerate; PNS: lies outside the dura mater (ganglia, sensory receptors, peripheral portions of cranial nerves), Schwann cells produce myelin, axons can regenerate; ANS: part of CNS and PNS; control viscera (branchial origin or internal organ) (three divisions: sympathetic, parasympathetic, and enteric)

Question 2

What are the four specialized regions in neurons?

Answer 2

cell body (soma: site of nucleus, ER, and Golgi), dendrites (branches; spines and infoldings increase surface area and allow localization of postsynaptic terminals to be closer to soma (better probability to induce an action potential), axon (begins at soma (hillock) and initial segment is the site where an action potential first arises (distal to hillock)), and presynaptic terminals

Question 3

What is one way that neurons are similar to epithelial cells?

Answer 3

different populations of membrane proteins at each of the distinct domains of the neuronal plasma membrane (presynaptic terminal membrane proteins and dendritic membrane proteins have similar dichotomy to the membrane protein differences in basolateral and luminal surfaces of epithelial cells)

Question 4

What structures are absent from an axon?

Answer 4

mRNA, ribosomes, and Golgi

Question 5

Differentiate the features of axoplasmic transport: fast anterograde, fast retrograde, and slow anterograde

Answer 5

Fast anterograde: similar to movement of myosin on actin filaments in muscles (unidirectional; kinesin plays the role of myosin; carries vesicles and mitochondria); fast retrograde: dynein plays the role of myosin (mostly transports growth factors to soma); slow anterograde: g. The slowest moving proteins are neurofilament and microtubule subunits (0.2 to 1 mm/day) (component of the axonal transport mechanism; primarily utilized in response to nerve damage?)

Question 6

What type of neuronal cell is characterized by the presence of dendritic spines? Which neuronal cell can be spiny or aspiny?

Answer 6

Pyramidal cells; stellate cells

Question 7

What are the three ways that neurons can be classified?

Answer 7

axonal projection (projection neuron v interneuron (affects nearby neurons)); dendritic pattern (pyramidal v stellate (star-shaped); number of processes (unipolar, bipolar, multipolar)

Question 8

Why is a dorsal root ganglion cell considered pseudo-polar?

Answer 8

sensory receptor sends action potential (through myelinated component) which bypasses the soma to innervate neurons (also through myelinated component) in the spinal cord

Question 9

What is a considered to be a functional unit of the CNS?

Answer 9

neuron, glial cell, endothelial cell

Question 10

What are pericytes?

Answer 10

neural stem cell (sit on capillaries) and secrete many growth factors to support the viability of the endothelial cell and neuron

Question 11

What does afferent mean? efferent?

Answer 11

towards the CNS; away from the CNS

Question 12

Describe neurulation. What induces it?

Answer 12

The first step in neurulation is formation of the neural plate at about the beginning of the third fetal week. Initially, the neural plate is only a single layer of neuroectoderm cells. Rapid proliferation of these cells, especially at the lateral margins, creates a neural groove bordered by neural folds. Continued cell division enlarges the neural folds, and they eventually fuse dorsally to form the neural tube. The neural tube is open at both ends, the anterior and posterior neuropores; notochord (mesodermal cells)

Question 13

The lumen of the neural tube, the neural canal, develops into what?

Answer 13

four ventricles of the brain and the central canal of the spinal cord.

Question 14

Neural crest cells give rise to cells for which subdivision of the nervous system?

Answer 14

PNS

Question 15

What are the major divisions of the brain that have developed after the fourth gestastional week?

Answer 15

prosencephalon (forebrain), mesencephalon (midbrain); rombencephalon (hindbrain)

Question 16

What are the major divisions of the brain that have developed after the fifth gestastional week?

Answer 16

prosencephalon gives rise to telencephalon (cerebral cortex; lumen = lateral ventricles) and diencephalon (lumen = third ventricle); mesencephalon (midbrain; lumen = cerebral aqueduct); the rhombencephalon can now be divided into the metencephalon (lumen = rostral fourth ventricle), which will give rise to the pons and cerebellum, and the myelencephalon (caudal fourth ventricle), which becomes the medulla

Question 17

Describe development of the spinal cord.

Answer 17

As the neural tube thickens with cell proliferation, a groove called the sulcus limitans forms on the inner, lateral wall of the neural tube (The sulcus limitans divides the neural tube into a ventral area called the basal plate and a dorsal area called the alar plate (“wings”)); alar plate: produces dorsal horn (associative ;sensory); basal plate: produces intermediolateral column and ventral horn (motor)

Question 18

Where is the origin of glial and neuronal cells?

Answer 18

neuroepithelial cells of the subventricular zone and ventricular zone (SVZ + VZ); PDGF and EGF influence these cells into dividing

Question 19

What is unique to the ventricular zone when compared to the SVZ?

Answer 19

Produces progenitor cells (another cell of origin for neurons, glial cells, and ependymal cells)

Question 20

Is the distribution (and number) of glial cells dependent on neurons?

Answer 20

Yes; determined by signals from nearby neurons or axons.

Question 21

How do neurons move from the VZ (or SVZ) to the cortex?

Answer 21

move along radial glial cells; influenced by cell adhesion molecules (CAMs are calcium dependent), expression of ECM proteins laminin and fibronectin (secreted from cells) and integrins; chemical signals (chemotaxis)

Question 22

How is apoptosis different from necrosis?

Answer 22

apoptosis: feature of neuronal pruning (initiates in the nucleus and requires protein synthesis); necrosis: Necrosis characterized by energy failure, loss of cell membrane integrity, and calcium entry (if mitochondria is dead and nucleus is intact, this suggests necrosis)

Question 23

What is an astrocytic glial scar?

Answer 23

This scar is produced primarily by an enlargement of individual astrocytes, a process called hypertrophy, and increased expression of a particular cytoskeleton protein, glial acidic fibrillary protein

Question 24

Can glial cells be replaced?

Answer 24

Yes; there is some evidence of neuronal replacement in adult brains (very uncommon)

Question 25

What are the four lobes of the brain called? What are three segments of the brainstem called? What are the four segments of the spinal cord (vertebral column) called?

Answer 25

Frontal lobe, parietal lobe, temporal lobe, occipital lobe; midbrain, pons (relays signals from cortex to cerebellum), medulla; cervical (8), thoracic (12), lumbar (5), sacral (5) (coccyx or tailbone is the last vertebral column)

Question 26

The spinal cord runs from the base of the skull to where?

Answer 26

first lumbar vertebra

Question 27

Where is white matter in the spinal cord? Gray matter?

Answer 27

White matter outside of the spinal cord; gray matter, inside

Question 28

What are three functions of the cerebellum?

Answer 28

balance (vestibular); regulates muscle tone; coordinates motor behavior via connections with cortex through thalamus

Question 29

What is the difference between ganglia and nuclei?

Answer 29

Both are a cluster of neuronal cell bodies: ganglia = PNS; nuclei = CNS

Question 30

Describe a peripheral nerve bundle.

Answer 30

Individual axons are surrounded by loose connective tissue called the endoneurium. Within the nerve, axons are bundled together in small groups called fascicles, each one covered by a connective tissue sheath known as the perineurium. The perineurium contributes structural stability to the nerve. Fascicles are grouped together and surrounded by a matrix of connective tissue called the epineurium. Fascicles within a nerve anastomose with neighboring fascicles. Axons shift from one fascicle to another along the length of the nerve, but they tend to remain in roughly the same general area within the nerve over long distances.

Question 31

What is the path that a spinal nerve takes after leaving the CNS that innervates the upper extremity? lower extremity?

Answer 31

Brachial plexus; cauda equina (horse’s tail)

Question 32

Describe how ventricles are interconnected, where CSF is synthesized, secreted, circulated and drained in the brain

Answer 32

The two lateral ventricles each communicate with the third ventricle , which is located in the midline between the thalami, through the two interventricular foramina of Monro. The third ventricle communicates with the fourth ventricle by the cerebral aqueduct of Sylvius. CSF escapes from the fourth ventricle and flows into the subarachnoid space through three foramina: the two laterally placed foramina of Luschka and the midline opening in the roof of the fourth ventricle, called the foramen of Magendie; CSF is synthesized and secreted within the brain by a highly vascularized epithelial structure called the choroid plexus; Arachnoid granulations act as pressure-sensitive, one-way valves for bulk CSF clearance into the SSS; The pial-glial membrane has paracellular gaps through which substances can equilibrate between the subarachnoid space and BECF (same idea for ependymal cells surrounding ventricles)

Question 33

Differentiate the composition of CSF from the plasma

Answer 33

CSF has lower concentrations of K + and amino acids than plasma does, and it contains almost no protein; Similar to plasma: osmolality, Na+, Ca2+, Cl-, HCO3-

Question 34

Describe how CSF is synthesized and secreted into the ventricles

Answer 34

Choroid epithelial cells are cuboidal and have an apical (luminal) border with microvilli and cilia that project into the ventricle (i.e., into the CSF). The plexus receives its blood supply from the anterior and posterior choroidal arteries; The choroid epithelial cells are bound to one another by tight junctions that completely encircle each cell, an arrangement that makes the epithelium an effective barrier to free diffusion.

Question 35

How is sodium secreted from the plasma into CSF?

Answer 35

The Na-K pump in the choroid plexus, unlike in other epithelia, is unusual in being located on the apical membrane, where it moves Na + out of the cell into the CSF—the first step. This active movement of Na + out of the cell generates an inward Na + gradient across the basolateral membrane, energizing basolateral Na + entry—the second step—through Na-H exchange and Na + -coupled HCO 3 − transport.

Question 36

How is chloride secreted from the plasma into CSF?

Answer 36

The first step is the intracellular accumulation of Cl − by the basolateral Cl-HCO 3 exchanger. The second step is efflux of Cl − across the apical border into the CSF through either a Cl − channel or a K/Cl cotransporter.

Question 37

The limiting factor for exchange of sodium at the basolateral membrane is intracellular hydrogen ion. Where does this intracellular hydrogen originate from?

Answer 37

carbonic anhydrase generates H+ and HCO 3−, from CO2 and H2O.

Question 38

How is bicarbonate secreted from the plasma into CSF? Why is this important?

Answer 38

At the basolateral membrane, the epithelial cell takes up HCO 3 − through electroneutral Na/HCO 3 cotransporters and the Na + -driven Cl-HCO 3 exchanger (is already elevated in the epithelial cell as a result of carbonic anhydrase). Movement of bicarbonate at the apical membrane occurs through Na/HCO3 cotransporter and through chloride channels (permeable to bicarbonate); neutralizes acids produced in the CNS

Question 39

How is potassium removed from the CSF?

Answer 39

The epithelial cell takes up K + by the Na-K pump and the Na/K/Cl cotransporter at the apical membrane. Most of the K + recycles back to the CSF, but a small amount exits across the basolateral membrane and enters the blood.

Question 40

How are substances cleared from the brain?

Answer 40

Products of metabolism and other substances released by cells, perhaps for signaling purposes, can diffuse into the chemically stable CSF and ultimately be removed on a continuous basis either by bulk resorption into the venous sinuses or by active transport across the choroid plexus into the blood.

Question 41

Describe the BBB and how it prevents blood constituents from entering the BECF

Answer 41

tight junctions prevent water-soluble ions and molecules from passing from the blood into the brain through the paracellular route (contain many mitochondria); thick basement membrane (basal lamina) underlies the endothelial cells and contains occasional pericytes (communicate with both endothelial and glial cell). Astrocytic endfeet (or processes) provide a nearly continuous covering of the capillaries and other blood vessels.

Question 42

Know the major difference between the circumventricular organs (name them) and other organs/tissues in the brain

Answer 42

The capillaries of the brain are leaky in several areas: the area postrema, the posterior pituitary, the subfornical organ, the median eminence, the pineal gland, and the organum vasculosum laminae terminalis (OVLT) (surround the ventricles) In these regions, the neurons are directly exposed to the solutes of the blood plasma (lack BBB); The ependymal cells that overlie the leaky capillaries in some of these regions (e.g., the choroid plexus) are linked together by tight junctions that form a barrier between the local BECF and the CSF, which must be insulated from the variability of blood composition.

Question 43

Know 3 different types of glial cells [astrocyte, oligodendrocyte, and microglia) in the brain and their functions

Answer 43

Astrocytes: provide lactate for neurons (store glycogen), regulate BECF by uptaking K+, regulate pH, characterized by gap junctions (syncytium), synthesize glutamine, secrete trophic factors, and endfeet regulate cerebral blood flow; oligodendrocytes myelinate axons, metabolize iron; microglia are macrophages of the brain (mesodermal origin, antigen-presenting (attract T cells)) (are normally inactive; when activated, proliferated and become phagocytic)

Question 44

Describe how astrocytes regulate the [K+]o and help to stabilize the neuronal microenvironment

Answer 44

depolarization that is triggered by the increased extracellular [K + ] leads to the influx of HCO 3 − into astrocytes by the electrogenic Na/HCO 3 cotransporter; this influx of bicarbonate in turn causes a fall in extracellular pH that may diminish neuronal excitability; ii. Astrocytes can take up K + in response to elevated [K + ] o by three major mechanisms: the Na-K pump, the Na/K/Cl cotransporter, and the uptake of K + and Cl − through channels. Conversely, when neural activity decreases, K + and Cl − leave the astrocytes through ion channels (spatial buffering)

Question 45

Describe glutamine-glutamate cycle that occurs between astrocytes and neurons

Answer 45

Glutamine is manufactured only in astrocytes by use of the astrocyte-specific enzyme glutamine synthetase to convert glutamate to glutamine (and GABA). Astrocytes release this glutamine into the BECF through the SNAT3 and 5 transporters for uptake by neurons through SNAT1 and 2. In the presynaptic terminals of neurons, glutaminase converts the glutamine to glutamate, for release into the synaptic cleft by the presynaptic terminal. Finally, astrocytes take up much of the synaptically released glutamate to complete this glutamate-glutamine cycle (glutamate clearance by an astrocyte from the synaptic cleft occurs by coupling the Na/K ATPase with a EAAT (excitatory amino acid transporter 1 or 2 (glutamate, hydrogen ion, 2 sodiums enter cell and a potassium molecule leaves the cell)).

Question 46

What is the difference between anoxia and ischemia?

Answer 46

Ischemia prevents transport of both oxygen and glucose to the site of injury (anoxia only prevents oxygen)

Question 47

Do the lateral ventricles communicate with each other?

Answer 47

No

Question 48

Where is the choroid plexus complex in the four ventricles?

Answer 48

Lateral ventricles: inner radius of the inferior arm of lateral ventricles; roof of the third and fourth ventricle (inferior to cerebellum but superior to brainstem)

Question 49

What is the glia limitans?

Answer 49

avascular astrocytic endfeet that abuts the pia from the brain side and is separated from the pia by a basement membrane. The pia adheres so tightly to the associated glia limitans in some areas that they seem to be continuous with each other; this combined structure is sometimes called the pial-glial membrane

Question 50

Can objects move paracellularly through the arachnoid membrane?

Answer 50

No

Question 51

Describe the dura mater.

Answer 51

The dura mater is a thick, inelastic membrane that forms an outer protective envelope around the brain. The dura has two layers that split to form the intracranial venous sinuses. Blood vessels in the dura mater are outside the blood-brain barrier

Question 52

Is the rate of CSF production sensitive to ICP?

Answer 52

No; absorption greatly increases above 70 mm H20

Question 53

If a patient has a tumor in the cerebral aqueduct of Sylvius, you would expect enlarged ventricles in which region(s)?

Answer 53

Both lateral ventricles and third ventricle

Question 54

What is Acetazolamide?

Answer 54

blocks carbonic anhydrase and slows CSF production

Question 55

What can readily pass the BBB?

Answer 55

Uncharged and lipid soluble molecules readily pass the BBB (and water); aquaporins allow single water molecules through (ions are too large due to the hydration cell surround them)

Question 56

What is the resting potential of astrocytes? What channel is responsible for this?

Answer 56

Astrocytes resting membrane potential is about -85 mV (close to reversal potential of potassium suggest relative potassium conductance is greater than in neurons (inward rectifying potassium channels are important in setting resting potential of astrocytes)

Question 57

What protein is found in myelin from oligodendrocytes? Schwann cells?

Answer 57

Oligo: myelin basic protein and proteolipic protein; Schwann cells: protein zero

Question 58

How does glucose cross the BBB?

Answer 58

Glucose exits endothelial cells (through the BBB) via the Glut1 transporter (on both sides of endothelial cells; also found in astrocytes; neuron uses Glut3 transporter)

Question 59

How much CSF is produced per day?

Answer 59

Total CSF: 500 ml/day (30 mL in the ventricles and 120 mL in the subarachnoid spaces of the brain and spinal cord is turned over 3 times a day)

Question 60

Why is CSF absorbed by arachnoid granulations (or villi)?

Answer 60

Net CSF movement into venous blood is promoted by the pressure of the CSF, which is higher than that of the venous blood. When intracranial pressure (equivalent to CSF pressure) exceeds ∼70 mm H 2 O, absorption commences and increases with intracranial pressure

Question 61

What are the two type of astrocytes?

Answer 61

Fibrous astrocytes (found mainly in white matter) have long, thin, and well-defined processes; protoplasmic astrocytes (found mainly in gray matter) have shorter, frilly processes

Question 62

Is lactate the preferred source of energy of a neuron?

Answer 62

No; substrate buffering (difficult to directly uptake glucose)