Nervous system

Question 1

Which of the following is the main inhibitory neurotransmitter of the spinal cord?

A Acetylcholine
B Dopamine
C Gama-aminobutyric acid (GABA)
D Glycine

Answer 1

D

Explanation
GABA is the main inhibitory mediator in the brain, where it transmits at 20% of CNS synapses. Glycine is also responsible for direct inhibition in the brainstem and the spinal cord. Note that Glycine can be both inhibitory and excitatory.

Question 2

The vestibular nerve has its nucleus located in which part of the brain?

A Cerebellum
B Pons
C Cortex
D Oculomotor nucleus

Answer 2

B

Explanation
The vestibular nucleus is primarily located in the pons.

The vestibulocochlear nerves (CNVIII) carry fibres concerned with the special senses of hearing, equilibrium and motion. The nerves originate from the grooves of the pons and medulla. They run through the internal acoustic meatus and divide into the cochlear and vestibular nerves

Extra: Vestibular component – arises from the vestibular nuclei complex in the pons and medulla. Cochlear component – arises from the ventral and dorsal cochlear nuclei, situated in the inferior cerebellar peduncle.

Source: https://teachmeanatomy.info/head/cranial-nerves/vestibulocochlear/)

Extra: an easier way to remember

The rule of 4 of the brainstem: a simplified method for understanding brainstem anatomy and brainstem vascular syndromes for the non-neurologist. Internal Medicine Journal 2005; 35: 263-266); Rule of 4s The 4 cranial nerves above the pons are CN 1-4: Olfactory (CN1) Optic (CN2) Oculomotor (CN3) Trochlear (CN4) The 4 cranial nerves in the pons are CN 5-8: Trigeminal (CN5) Abducent (CN6) Facial (CN7) Auditory (CN8) The 4 cranial nerves in the medulla are CN 9-12: Glossopharyngeal (CN9) Vagus (CN10) Spinal accessory (CN11) Hypoglossal (CN12)

Question 3

Which area has the best visual acuity?

A Area with maximal rods
B Retina
C Optic disc
D Fovea centralis

Answer 3

D

Explanation
The fovea is the point where visual acuity is the greatest

Question 4

The hypothalamus is essential for which of the following?

A Hunger
B Sleep
C Visual acuity
D Movement

Answer 4

A

Explanation
Principal hypothalamic regulatory mechanisms include:

Temperature regulation

Neuroendocrine control (Catecholamines, vasopressin, oxytocin, TSH, FSH, ACTH, LH, Prolactin and GRH)

“Appetitive” behaviour (thirst, hunger and sexual behaviour)

Defensive reactions (rage,fear)

Control of body rhythms

Question 5

The kappa receptor is responsible for which of the following?

A Euphoria, dependence, and analgesia
B Sedation, dysphoria and mydriasis
C Dysphoric reactions and modulation of hormone release
D Analgesia, sedation, and dysphoria

Answer 5

D

Explanation
The Kappa receptor is responsible for- analgesia, diuresis, sedation, miosis, slow GIT transit and dysphoria. Kappa can cause psychotomimetic effects as well (actions which mimic symptoms of psychosis including delirium, delusions and hallucinations

The Mu receptor is responsible for- analgesia, respiratory depression, constipation, euphoria, sedation, miosis and modulation of hormone and neurotransmitter release

The Delta receptor- analgesia and and modulation of hormone and neurotransmitter release

Extra:

Kappa receptors mediate supraspinal analgesia, spinal analgesia, psychotomimetic effects, slow gastrointestinal transit, inhibit ADH release, cause miosis, sedation and dysphoria

Mu receptors - decreases respiration, supraspinal and spinal analgesia, sedation, slow GIT transit, modulation of hormone and neurotransmitter release, causes physical dependence, miosis and euphoria

Delta receptors - supraspinal and spinal analgesia, and modulation of hormone and neurotransmitter release

Question 6

Which of the following most easily penetrates the cerebro-spinal fluid (CSF)?

A N2O
B O2
C CO2
D H2O

Answer 6

C

Explanation
Water, CO2 and O2 penetrate the brain with ease, as do lipid soluble free forms of steroid hormones, where as their protein bound form and all protein and polypeptides do not. The rapid passive penetration of CO2 contrasts with the regulated transcellular penetration of H and HCO3 and has physiologic significance in the regulation of respiration.

Note: According to sources CO2 seems to penetrate the CSF the fastest. I think it is because of the need for immediate control of ventilation.

Extra: the solubility of CO-2 being 20 x that of oxygen means that it will diffuse faster. As it is not an active process it does not stem from the need for immediate control of ventilation but rather it is a most efficient/appropriate indicator.

Question 7

Which part of the eye allows for maximum visual acuity?

A Optic disc
B Retina
C Fovea centralis
D Choroid

Answer 7

C

Explanation
In the human eye the term fovea (or fovea centralis FC) denotes the pit in the macular part of the retina, which allows for maximum acuity of vision. The FC is a thin portion of the retina free of rods. It has densely packed cones. The FC provides a direct pathway to the brain. There are very few overlying cell and no blood vessels

Question 8

The major excitatory transmitter in the spinal cord is which of the following?

A Glutamate
B Gama-aminobutyric acid (GABA)
C Aspartate
D Glycine

Answer 8

A

Explanation
Glutamate is the main excitatory transmitter in the brain and spinal cord. Aspartate is also excitatory. GABA and Glycine are inhibitory

Question 9

Which of the following is correct in relation to the sensation for cold stimuli?

A Is an uncrossed sensory modality
B Is mediated by A alpha fibres
C Is transmitted by the dorsal columns
D Is relayed by the thalamus

Answer 9

D

Explanation
The sensation for cold is transmitted by the lateral spinothalamic tracts and is a crossed sensorimodality. Cold is mediated by type A delta fibres

There are two main parts of the spinothalamic tract (STT):

The lateral STT transmits pain and temperature
The anterior STT (or ventral spinothalamic tract) transmits crude touch and pressure.
The dorsal columns transmits fine touch (two point discrimination), proprioception and vibration sense

Question 10

Alpha 1 stimulation will lead to which of the following?

A Pupillary constriction
B Increased atrio-ventricular (AV) conduction
C Bronchial smooth muscle contraction
D Contraction of bladder trigone and sphincter

Answer 10

D

Roles of a1 receptors:

Eyes – mydriasis

Skin & splanchnic vessels – constriction

Skeletal muscle - constriction / dilation

Bronchial glands - increase secretion

GIT motility & tone - decreased - contraction of GIT sphincters

Contraction of urinary sphincter

Contraction of pregnant uterus

Ejaculation in male

Skin pilomotor muscles - contraction

Liver - glycogenolysis - pancreas acini - decrease secretion

Salivary glands - thick, viscous secretion

Question 11

Anterolateral dissection of the spinal cord is associated with which of the following?

A Ipsilateral hyperreflexia
B Contralateral vibration loss
C Ipsilateral loss of temperature
D Ipsilateral loss of pain

Answer 11

A

Explanation

Loss of pain and temperature occurs after damage to the spinothalamic tract which crosses at the spinal cord level and thus will be contralateral. Vibration sense is mediated by the posterior columns and thus is not affected.

Dissection of the lateral spinal cord will also damage the lateral corticospinal tract, which decussates in the pyramids, resulting in loss of cortical control of motor function on the ipsilateral side (ipsilateral hyperreflexia)

Question 12

Which of the following has the most effect on smooth muscle relaxation?

A Noradrenaline
B Dopamine
C lAdrenaline
D Isoprenaline

Answer 12

D

Explanation
Isoprenaline has pure B1 and B2 effects. More so than adrenaline, noradrenaline and dopamine. Isoprenaline will cause pure smooth muscle relaxation. Dopamine in higher doses will activate beta and then alpha receptors. Adrenaline in higher doses will also activate alpha receptors.

Question 13

Monoamine oxidase (MAO) breaks down which of the following?

A Glycine
B Glutamate
C Tryptophan
D Serotonin

Answer 13

D

Explanation
Serotonin, melatonin, noradrenaline, and adrenaline are mainly broken down by MAO-A. Phenethylamine and benzylamine are mainly broken down by MAO-B. Both forms break down dopamine, tyramine, and tryptamine equally

Question 14

In the formation of adrenaline, which of the following is correct?

A Serotonin is a vital intermediate step
B Dopa is formed from dopa decarboxylase
C Phenylalanine is converted to tyrosine
D Catechol-o-methyl transferase (COMT) produces adrenaline from noradrenaline

Answer 14

C

Explanation
Both noradrenaline (NA) and adrenaline are metabolized to inactive products by catechol-o-methyl transferase (COMT) and monoamine oxidase (MAO). Dopa, dopamine and noradrenaline are important steps in the formation of adrenaline. Dopa is formed from tyrosine hydroxylase

Question 15

Which of the following is correct in relation to true acetylcholinesterase?

A Functions in the synaptic cleft
B Is involved in gama-aminobutyric acid (GABA) metabolism
C Is produced by the liver
D Forms acetylcholine from acetate

Answer 15

A

Explanation
Acetylcholinesterase (AChE) breaks down acetylcholine (ACh) by way of hydrolysis of ACh to choline and acetate in the synaptic cleft. AChE is formed in the cytoplasm of nerve endings. AChE in the nerve endings (clustered in the post synaptic membrane of the cholinergic synapses) and in red blood cells is called TRUE AChE. PseudoAChE is found in the serum, plasma as well as in the liver, pancreas and the white matter of the brain. Its physiological role remains unclear-some sources say that pseudo AChE hydrolysis butyrylcholine rather than acetylcholine.

Question 16

All the following are neurotransmitters except?

A Adenosine
B Insulin
C Glutamate
D Serotonin

Answer 16

B

Explanation
Insulin is a hormone; a polypeptide containing 2 chains of amino acids linked by disulfide bridges

Question 17

Inhibitory neurotransmitters increase the post synaptic conductance of which of the following?

A Calcium
B Magnesium
C Chloride
D Sodium

Answer 17

C

Explanation
Chloride conductance is important to both gama-aminobutyric acid (GABA) and glycine functioning as inhibitory neurotransmittors

Question 18

A subject is injected with a substance that: caused slight increase in heart rate, no change in BP, decreased sweating, pupillary dilatation but did not impair erection. It was most likely which of the following?

A An alpha blocker
B A muscarinic antagonist
C A dopamine antagonist
D A nicotinic antagonist

Answer 18

B

Explanation
Anticholinergic drugs acting on the muscarinic receptor giving the classical features of:

• red as a beet (vasodilatation)
• dry as a chip (decreased sweating)
• blind as a bat (pupillary vasodilatation)
• mad as a hater (delirium)

Note: there are no muscarinic receptors on the blood vessels of the penis. Vasodilation occurs via nitric oxide form the endothelium.

Question 19

With regard to the composition of cerbro-spinal fluid (CSF), which of the following statements is correct?

A CSF has a lower concentration of Mg with respect to plasma
B CSF has a higher concentration of Ca with respect to plasma
C Has the same composition as cerebral extracellular fluid (ECF)
D Production is 50-100 mls per day

Answer 19

C

Explanation
Cerebrospinal fluid volume in humans is 150mls and the rate of production is about 550ml/day. Thus the CSF turnover is 3.7 times a day. 50-70% of CSF is formed in the choroid plexuses and the remainder is formed around blood vessels and along ventricular walls. It is absorbed through the arachnoid villi into veins, mainly the cerebral venous sinus. The composition of CSF: it contains electrolytes (Na, K, Mg, Ca, Cl, HCO3), pco2, pH, proteins, glucose, urea, creatinine, uric acid, cholesterol, and inorganic P.
CSF potassium concentration is 2.9 meq/kg H20 and in plasma it is 4.6. Protein concentration in CSF is 20 (mg/dl) and plasma is 6000 (mg/dl). Ca concentration in CSF is 2.3 (meq/kg H2O) and in plasma 4.7(meq/kg H2O).
Mg concentration in CSF is 2.2(meq/kg H2O) and in plasma 1.6(meq/kg H2O).
Osmolality of CSF and plasma is the same. The composition of CSF is essentially the same as brain CSF, which in humans makes up 15% of the brain volume.

Note: The composition of drug preparations, such as IV fluids, is often stated in mmol/L rather than mEq/L. (The molarity refers to the number of moles per liter, and does not account for the number of available charges. For that reason, for an element such as Na, which has a valence of one, 1 mmol/L = 1 mEq/L, whereas for a divalent element (i.e. an element having a valence of two) such as Mg or Ca, 1 mmol/L = 2 mEq/L. Therefore Calcium in plasma is 4.7/2=2.35mmol/l

Question 20

Light crosses (refracts) before the retina in which of the following conditions?

A Hyperopia
B Astigmatism
C Myopia
D Presbyopia

Answer 20

C

Explanation
Hyperopia- Eye too short for refractive power of cornea and lens- Light focused behind retina

Myopia- Eye too long for refractive power of cornea and lens- light focused in front of retina

Astigmatism- Abnormal curvature of cornea- different refractive power at different axes

Presbyopia- Age related impaired accommodation. (Focusing on near objects), primarily due to decrease lens elasticity. Often necessitates “reading glasses.”

Question 21

Which substance penetrates the blood brain barrier rapidly?

A Urea
B HCO3
C Protein bound steroids
D Water

Answer 21

D

Water, CO2 and oxygen penetrate the BBB with ease. So do lipid soluble free forms of steroid hormones, whereas their protein bound forms, and, in general, all proteins and polypeptides don’t. Urea, H and HCO3 penetrates slowly

Question 22

The vestibularcochlear nerve terminates in which part of the central nervous system?

A Pons
B Medulla
C Reticular formation
D Cerebellum

Answer 22

D

Explanation
According to current textbook, each vestibularcochlear nerve terminates in the ipsilateral four-part vestibular nucleus (see below) and in the flocculonodular lobe of the cerebellum.

Not a great question but definitely a recall. There are vestibular nuclei (4) that are the nuclei for the vestibular nerve found in the medulla and pons. Hopefully the stems won’t include pons and medulla (I have seen other stems including occulomotor nuclei, cortex which are wrong-but we would know this)

This question is causing some issues. I gave decided to insert a user thoughts..

The TB-25th ed suggest that the auditory fibres end at dorsal/ventral cochlear nuclei and vestibular fibres end in vestibular nuclei. The accompanying picture with the medulla has the cerebellum removed altogether and a google search seems to imply both nuclei are in the medulla near the pontomedullary junction. The answer would be the medulla

Question 23

Regarding EPSP (excitatory postsynaptic potentials) which is INCORRECT?

A EPSPs is an all or nothing response to the afferent stimulus
B EPSP is produced by depolarization of the post synaptic cell membrane immediately under the presynaptic ending
C Repeated afferent stimuli causing new EPSPs before the old EPSPs has decayed is temporal summation
D Activity present in more than one synaptic knob at the same time creates spatial summation

Answer 23

A

Explanation
EPSP is produced by depolarization of the postsynaptic cell membrane immediately under the presynaptic ending. The excitatory transmitter opens NA or Ca channels in the postsynaptic membrane producing an inward current. The area of current flow is so small that it does not drain enough positive charge to depolarize the whole membrane. Instead an EPSP is created. The EPSP due to activity in one synaptic knob is small, but the depolarizations produced by each of the active knob summate. Activity present in more than one synaptic knob at the same time creates spatial summation- the activity in one knob is said to facilitate activity in another to approach the firing level. Repeated afferent stimuli causing new EPSPs before the old EPSPs have decayed are called temporal summation. EPSPs are therefore NOT all or nothing response but are proportionate in size to the strength of the afferent stimuli.

Question 24

Which dopaminergic systems are important for the understanding of schizophrenia

A Tuberoinfundibular pathway
B Medullary-periventricular pathway
C Nigrostriatal pathway
D Mesolimbic-mesocortical pathway

Answer 24

D

Explanation
Mesolimbic-mesocortical pathway= behaviour and psychosis

Nigrostriatal pathway= coordination of voluntary movement

Tuberoinfundibular pathway= inhibits prolactin form the anterior pituitary

Medullary-periventricular pathway= ?eating behaviour

Incertohypothalamic pathway= regulates the anticipatory motivational phase of copulatory behaviour in rats

Question 25

Demyelination in the CNS affects which of the following?

A Oligodendrocytes
B Schwann cells
C Dendrites
D Nodes of Ranvier

Answer 25

A

Explanation
Demyelination due to multiple sclerosis, an autoimmune disease causing patchy destruction of myelin, occurs in the CNS. This disease affects oligodendrocytes-the cells that form the myelin over the axons in the CNS. In the peripheral nervous system, Schwann cells form the myelin over the axons. Nodes of Ranvier are not enveloped by myelin. Dendrites are not enveloped by myelin.

Question 26

Local anaesthetics work most strongly on which fibres?

A Type C
B Diameter 2-20 (um)
C Type B
D Type A

Answer 26

A

Explanation
Nociceptive fibres (unmyelinated C fibres) are the most sensitive to the blocking effects of local anaesthetics. This is followed by sequential loss of sensitivity to temperature, touch, and deep pressure. Motor nerves fibres (A) are the most resistant to the actions of local anaesthetics.

C (most)»B»A (least)

Question 27

What is the order of the structures conveying visual sensation?

A Optic nerve, optic tract, optic chiasm, lateral geniculate body, occipital cortex
B Optic nerve, optic tract, lateral geniculate body, optic chiasm, occipital cortex
C Optic nerve, optic chiasm, optic tract, lateral geniculate body, occipital cortex
D Optic nerve, optic chiasm, lateral geniculate body, optic tract, occipital cortex

Answer 27

C

Question 28

Which nerve is responsible for the afferent pathway of the corneal reflex?

A CN VII
B CN X
C CN III
D CN V

Answer 28

D

Explanation
The corneal reflex is Involuntary blinking of eyelid in response to a stimulus.

The nasocillairy branch of the ophthalmic branch (V1) of the trigeminal nerve (CN V) sensing the stimulus on the cornea only (afferent fibre).

The temporal and zygomatic branches of the facial nerve (CN VII) initiating the motor response (efferent fibre).

The centre (nucleus) is located in the pons of the brain stem.

Question 29

You are testing a patient’s visual acuity. Which structure in the eye is directly responsible for accommodation?

A Pupil
B Ciliary muscle
C Iris
D Lens

Answer 29

B

Explanation
The ciliary muscle, which is a smooth muscle responsible for lens accommodation, is contained within the ciliary body. Contraction of the ciliary muscle enables the lens to focus light onto the retina by changing its shape.

Interesting thought:

The ciliary muscle of the ciliary body changes the shape of the lens. This active process of changing the shape of the lens for near vision is called accommodation. The thickness of the lens increases with aging so that the ability to accommodate typically becomes restricted after the age of 40. I think the ciliary muscle is the structure directly responsible for accommodation and not the lens. (Even though the lens needs to change to allow for accommodation).

Hopefully this question will not include the lens as an option-to avoid confusion

Question 30

Where is proprioception and vibration transmitted in the spinal cord?

A Anterior column
B Sympathetic afferent fibres
C Lateral spinothalamic tracts
D Dorsal column

Answer 30

D

Explanation
Proprioception and vibration are transmitted via the DCML (dorsal column medial lemniscus) pathway.

Question 31

You test a gentleman’s vibration sense with a 126Hz tuning fork. Where does this travel?

A Spinohypothalamic tract
B Dorsal ventral column pathway
C Ventrolateral pathway
D Medial lemniscal pathway

Answer 31

D

Explanation
Dorsal column (medial lemniscal) pathway mediates touch, vibratory sense, and proprioception. Sensory fibres ascend ipsilaterally via the spinal dorsal columns to medullary gracilus and cuneate nuclei; from there the fibres cross the midline and ascend in the medial lemniscus to the contralateral thalamic ventral posterior lateral (VPL) and then to the primary somatosensory cortex.

That which mediates pain and temperature ascends via the ventrolateral (spinothalamic pathway)

Question 32

A patient suffers peripheral vision loss in both the right and left eyes, with macular sparing. Where is the lesion?

A Optic chiasm
B Occipital lobe
C Lateral geniculate body
D Optic nerve

Answer 32

B

Explanation
Macular sparing or loss of peripheral vision with intact macular vision is also common with occipital lesions because the macular representation is separate from that of the peripheral fields and very large relative to that of the peripheral fields. Therefore, occipital lesions must extend considerable distances to destroy both macular and peripheral vision. The fibers to the pretectal region that subserves the pupillary reflex produced by shining a light into the eye leave the optic tracts near the geniculate bodies. Therefore, blindness with preservation of the pupillary light reflex is usually due to bilateral lesions caudal to the optic tract.”

Ganong’s Review of Medical Physiology 26e

Question 33

A patient suffers peripheral vision loss in both the right and left eyes, with macular sparing. Where is the lesion?

A Optic chiasm
B Occipital lobe
C Lateral geniculate body
D Optic nerve

Answer 33

B

Explanation
Macular sparing or loss of peripheral vision with intact macular vision is also common with occipital lesions because the macular representation is separate from that of the peripheral fields and very large relative to that of the peripheral fields. Therefore, occipital lesions must extend considerable distances to destroy both macular and peripheral vision. The fibers to the pretectal region that subserves the pupillary reflex produced by shining a light into the eye leave the optic tracts near the geniculate bodies. Therefore, blindness with preservation of the pupillary light reflex is usually due to bilateral lesions caudal to the optic tract.”

Ganong’s Review of Medical Physiology 26e

Question 34

What spinal tract is primarily responsible for motor control of voluntary movements?

A Lateral corticospinal tract
B Ventrolateral spinothalamic tract
C Spinocerebellar tract
D Dorsal column-medial lemniscus pathway

Answer 34

A

Explanation
The TB doesn’t explicitly state “motor control,” it mentions the corticospinal tract in relation to descending motor pathways and voluntary movement. The lateral corticospinal tract is the major pathway for voluntary motor control. The other options relate to sensory pathways.

Ganong’s Review of Medical Physiology 26e