Test #32 (BsPN Week 3N Block 2: Neuro Physio)

Question 1

(1) In what part of brain stem does CN V arise & via what route (2) What 2 s/sx can infarcts of the anterior portion of this strx cause

Answer 1

(1) Arises at level of middle cerebellar peduncle at lateral aspect of mid-pons (2) Infarcts involving anterior portion of medial pons can produce dysarthria and contralateral ataxic hemiparesis

Question 2

(1) Dx/Explain: 24 yo chronic headaches and visual changes, intracranial calcified mass detected on MRI, gross inspection shows cystic spaces filled with thick brownish fluid that is rich in cholesterol (2) Embryologic origin & important strx shares same origin

Answer 2

(1) Craniopharyngioma - calcified cystic tumors. commonly cause headaches, growth failure, and bitemporal hemianopia (2) Arise from remnants of Rathke’s pouch (an embryonic precursor of anterior pituitary)

Question 3

(1) Where morphine acts (2) Mechanism these receptors

Answer 3

(1) selectively binds mu opioid receptors (2) Mu receptors = G-protein linked receptors, actions mediated through 2nd messenger pathways. One identified pathway = increased potassium efflux. Binding of morphine to mu receptors results in Gpr coupled activation of K conductance. K efflux increases and causes hyperpolarization of postsynaptic neurons, effectively blocking pain transmission.

Question 4

(1) Dx: 14 yo male, mild mental retardation, cytogenetic studies show small gap near tip of long arm of X chromosome (2) PE s/sx associated with this dx

Answer 4

(1) Fragile X syndrome (common cause of inherited mental retardation, X-linked, affects males) (2) Mental retardation, dysmorphic facial features (large jaw, large protruding ears), & macroorchidism

Question 5

Give 2 categories of disease that may be indicated by progressively weakening diaphragmatic contractions during maximal voluntary ventilation with intact phrenic nerve stimulation & at least one example of each category

Answer 5

Indicates (1) Neuromuscular junction pathology (eg., myasthenia gravis) and/or (2) Abnormally rapid diaphragmatic muscle fatigue (eg, restrictive lung or chest wall disease)

Question 6

(1) DNA replication enzyme with 5’ to 3’ exonuclease activity (2) Other activities it has (3) Purpose of 5’ to 3’ exonuclease activity

Answer 6

(1) DNA polymerase I (2) has 5’ to 3’ exonuclease activity in addition to its 5’ to 3’ polymerase and 3’ to 5’ exonuclease activities. (3) This 5’ to 3’ exonuclease activity is used to remove RNA primer (which initiates DNA polymerization) and to remove damaged DNA

Question 7

(1) Purpose of 3’ to 5’ exonuclease activity of DNA polymerase III (2) Important note regarding exonuclease activity of DNA polymerases

Answer 7

(1) Removes improper base-pair nucleotide during replication (2) All 3 prokaryotic DNA polymerases have proof reading activity and remove mismatched nucleotides via 3’ to 5’ exonuclease activity. Only DNA polymerase I has 5’ to 3’ exonuclease activity which is used to excise and replace RNA primers.

Question 8

(1) Mechanism of Huntington disease of altered gene expression (2) Result

Answer 8

(1) Alteration of gene expression in Huntington disease believed to occur due to hypermethylation of histones. Hypermethylated histones bind DNA and prevent transcription of certain genes. This leads to disruption of synthesis of some neurotrophic proteins.

Question 9

34 yo swimmer presents to office with external ear infection, faints upon inserting speculum into external auditory meatus in close contact with posterior wall: (1) irritation of what nerve (2) explain

Answer 9

(1) Vagus nerve (2) provides some cutaneous sensation to posterior external auditory canal via small auricular branch. Sensation to rest of canal from CN V3. Vasovagal syncopal episode results from stimulation of vagus nerve, leading to decrease in bp and HR.

Question 10

(1) Relate thiamine B1 deficiency to brain (2) Mechanism (3) How is thiamine deficiency dx

Answer 10

(1) Chronic thiamine (B1) deficiency leads to diminished ability of cerebral cells to utilize glucose (2) Decreased function of enzymes that use vitamin B1 as a cofactor (pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase) (3) Meas. erythrocyte transketolase activity

Question 11

(1) Dx/Explain: 5 yo boy with development delay, frequent squinting, dx with bilateral lens subluxation, 4 years later, dies of massive stroke, Autopsy shows MCA thrombosis and old renal infarcts (2) Diet supplementation that may have helped & why

Answer 11

(1) Homocystinuria caused by cystathione synthetase deficiency. S/sx resemble Marfan syndrome, particularly ectopia lentis, and may experience some form of developmental delay. High risk of developing thromboembolism. (2) About 50% of affected respond to high doses of vitamin B6 (pyridoxine - cofactor for cystathione synthetase)

Question 12

(1) Dx/Defect: 3 yo boy, not yet begun to walk or speak, severe intellectual disability, dies 6 mo. later from refractory seizures resulting in respiratory failure, autopsy shows pallor of substantia nigra, locus cereleus, and vagal nucleus dorsalis (2) Explain

Answer 12

(1) Deficiency of enzyme phenylalanine hydroxylase or its cofactor tetrahydrobiopterin (2) causes accumulation of phenylalanine in body fluids and CNS. Homozygous infants normal at birth but gradually develop severe intellectual disability and seizures if left untreated. Hypopigmentation of skin, hair, eyes, and catecholaminergic brain nuclei also frequently seen

Question 13

Source of Nitrogen atoms in urea cycle

Answer 13

N atoms in urea molecule derived from NH3 and aspartate in urea cycle

Question 14

(1) Dx/Explain: recent onset mild headaches, left leg weakness, nuermous fleshy, dome-shamed pedunculated lesions on skin, also hyperpigmented lesions with smooth or irregular borders (2) Mode of inheritance, mutation, & chromosome

Answer 14

(1) Neurofibromatosis type 1: neufibromas, cafe-au-lait spots, & assoc. brain tumors (most likely source of patient’s headaches, left leg weakness). Also Lisch nodules common s/sx. (2) Single-gene autosomal dominant disorder due to mutation of NF1 gene located on chromosome 17

Question 15

(1) Dx/Explain: 22 yo male complaining of occasional headaches, pigmented spots on trunk, few rubbery cutaneous tumors on neck (2) Embryologic origin of skin tumors

Answer 15

(1) Neurofibromatosis type I (NF1, or von Recklinghausen disease) common autosomal-dominant disorder resulting from defect in the NF1 gene on chromosome 17. (2) Cutaneous and subcutaneous neurofibromas are common in this condition & are tumors of Schwann cells, which are embryologically derived from neural crest

Question 16

(1) Dx: 6 mo old boy, not interactive with other children his age, delayed developmental milestones and hypotonia, 2 years later has involuntary dystonic movements & demonstrates tendency to aggressively bite his own lips and fingers, elevated blood uric acid level (2) Explain disorder/defect (3) Compensational increase

Answer 16

(1) Lesch-Nyhan syndrome: (2) X-linked recessive disorder caused by defect in hypoxanthine-guanine phosphoribosyltransferase (HGPRT). Results in failure of purine salvage pathway. (3) Because they are not recycled, increased amounts of purine bases hypoxanthine and guanine degraded to uric acid. De novo purine synthesis (e.g., phosphophoribosyl pyrophosphate amidotransferase activity) must be increased to replace lost bases.

Question 17

Provide following on each of 3 important Dopaminergic systems: Pathway, Function, Assoc. disease

Answer 17

(1) Mesolimbic-mesocortical: Regulations behavior (Schizophrenia) (2) Nigrostriatal: Coordination of voluntary movements (Parkinson disease) (3) Tuberoinfundibular: Controls prolactin secretion (Hyperprolactinemia)

Question 18

Kinesin: definition & role

Answer 18

Microtubule-associated, ATP-powered motor protein that facilitates anterograde transport of neurotransmitter-containing secretory vesicles down axons to synaptic terminals