Case 19 Questions 21-40

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Question 21

Which of the following is true about the ascending pathway?

  1. The spinothalamic tract of the anterolateral system is responsible for pain and temperature and decussates in the medulla
  2. The dorsal column is responsible for fine touch and decussates in the spinal cord
  3. The cuneate fasciculus and the gracile fasciculus are the two sub pathways of the anterolateral system
  4. The spinothalamic tract of the anterolateral system is responsible for pain and temperature and decussates within the spinal cord
  5. The lateral corticospinal tract forms part of the dorsal column and is responsible for fine touch

The correct answer is option 4, The spinothalamic tract of the anterolateral system is responsible for pain and temperature and decussates within the spinal cord

Option 4, This is correct. It enters the spinal cord via the dorsal root, synapses in the dorsal horn, then crosses over to the contralateral side within the spinal cord. It then ascends the spinal cord to the thalamus where it synapses again, and these third order neurones travel to the post central gyrus (primary somatosensory cortex).
Option 1, Whilst this tract is responsible for pain and temperature sensation, it is the dorsal column pathway (responsible for fine touch) which crosses over in the medulla (lowest portion of brainstem).
Option 2, This column is responsible for fine touch, but does not decussate in the spinal cord, it decussates in the medulla.
Option , They are the two sub pathways of the dorsal column. These pathways form from this ascending pathway has entered the medulla. The cuneate fasciculus carries information from hands/arms, and the gracile fasciculus carries information from the legs/lower body. The cuneate pathway termites at the cuneate nucleus, and the gracile pathway at the gracile nucleus; both nuclei are in the medulla. Second order neurones from these nuclei then decussate and ascend to the thalamus where they synapse, travelling via the medial lemniscus. From the thalamus, third order neurones ascend to the post central gyrus.
Option 5, This is actually a descending pathway responsible for voluntary motor control of distal musculature, such as fine control of the fingers or arms. It is a direct pathway, meaning it can directly influence a motor neurone e.g. to twitch a finger.

Question 22

Which signs would we not see in a left sided hemisection at the level of T12?

  1. Loss of fine touch and proprioception on left below lesion
  2. Paralysis and hyperreflexia below lesion, on left side
  3. Deficits in pain and temperature on the right below the lesion
  4. Deficits in balance
  5. Paralysis and hyporeflexia below lesion, on right side

The correct answer is option 5, Paralysis and hyporeflexia below lesion, on right side

Option 5: The lateral corticospinal tract contains UMNs, meaning you would have hyperreflexia, not hyporeflexia. Furthermore, these signs would be on the left hand side, as this pathway has already decussated and thus would be ipsilateral.
Option 1: This is because the dorsal column has not yet decussated to the contralateral side, thus any loss of sensation is on the left side.
Option 2: The lateral corticospinal tract has already decussated, therefore any damage would be ipsilateral and on the left side. It contains UMNs, and would therefore cause hyperreflexia.
Option 3: This would be due to damage to the spinothalamic tract, which decussates straight away and so is travelling on the contralateral side almost immediately.
Option 4: The spinocerebellar tract would be damaged, and is responsible for subconscious proprioception which takes information to the cerebellum. Will lead to unsteady gait.

Question 23

Which statement is the most true of receptive fields?

  1. The receptive fields in the fingertips are larger and there are more of them meaning two point discrimination is better
  2. The back contains small and numerous receptive fields
  3. The receptive fields in the fingertips are much smaller and there are more of them meaning two point discrimination is better
  4. The size of the receptive field is not important when initiating a response
  5. A receptive field is the space occupied by a nociceptor which can elicit a response to a sensory stimulus

The correct answer is option 3, The receptive fields in the fingertips are much smaller and there are more of them meaning two point discrimination is better

Option 3: This means you are more likely to hit two separate receptive fields and thus distinguish between two points.
Option 1: Larger receptive fields would make two point discrimination much worse, as two points may activate the same receptive field, which would send only one signal to the brain, so you only get one input – cannot distinguish between the two points.
Option 2: The back actually contains large and sparse receptive fields, meaning that the two point discrimination is not as good as somewhere like the fingertips.
Option 4: The size is very important when determining how discriminatory the the receptive field is – smaller fields means better two point discrimination.
Option 5: A nociceptor is a sensory receptor responsible for the sensation of pain, but all mechanoreceptors including those responsible for fine touch have their own receptive field.

Question 24

How is a sensory stimulus converted into something the brain can understand?

  1. Deformation of a sensory receptor leads to opening of sodium channels which leads to depolarisation
  2. Deformation of a sensory receptor leads to opening of potassium channels which leads to depolarisation
  3. Rapid adapting receptors will respond to continuous stimulation and these action potentials go to the brain
  4. All sensory receptors have a tonic slow firing rate of action potentials, and the brain can detect changes in this firing rate to decode the sensory information
  5. Stimulation of the sensory receptor causes immediate neurotransmitter release which causes a strong impulse to the brain

The correct answer is option 1, Deformation of a sensory receptor leads to opening of sodium channels which leads to depolarisation

Option 1: Fine touch, pressure or vibration can physically deform the receptor, and leads to opening of mechanically gated sodium channels on surface membrane of the nerve fibre in the centre of the receptor. The channels themselves will deform and open, allowing sodium into the cell, and causing depolarisation.
Option 2: Whilst the other information in this statement is broadly correct, it is the opening of mechanically gated sodium channels, leading to sodium influx, which causes an action potential.
Option 3: Rapid adapting receptors do not respond to continuous stimulation, instead they respond to application/removal of a stimulus, such as a vibration. The brain then receives a frequency of bursts of action potentials. Low vibration means action potentials will be more spaced apart. Examples include the Meissner and Pacinian corpuscles.
Option 4: This is true of slow adapting receptors, such as Merkel cells and Ruffini corpuscles, which activate for the duration of a maintained stimulus. Slight stimuli cause slight increase in firing rate, and increasing this stimulus leads to increased rate of firing. This is not however true for all sensory receptors, as many are rapid adapting.
Option 5: In order for neurotransmitter to be released, we need to first convert this sensory signal into an action potential by deforming the sodium channels to open them. This causes a generator potential, and if there are enough generator potentials, this triggers an action potential, which leads to the release of neurotransmitter at the synapse and will cause further action potentials.

Question 25

What is convergence in relation to the retina?

  1. This is when a single rod synapses onto multiple retinal ganglion cells to increase sensitivity
  2. This is when you get downregulation of activity at the edge of a receptive field
  3. This is when multiple rods converge on to one retinal ganglion cell as opposed to one for each rod
  4. Convergence means one sensory modality can modulate another
  5. This is when multiple retinal ganglion cells synapse on to one rod to increase likelihood of action potential

The correct answer is option 3, This is when multiple rods converge on to one retinal ganglion cell as opposed to one for each rod

Option 3
Option 1: This is divergence, and it means that a very small stimulus can be picked up by multiple neurones, leading to amplified signal and increased activity.
Option 2: This is lateral inhibition, and it means that the neurones at the centre of the receptive field are being highly activated, meanwhile the more peripheral neurones have downregulation in activity. This acts to sharpen sensory input and increase contrast.
Option 4: This is true, but divergence can also do this. An example of convergence doing this is when we consider the gated theory of pain. This is the theory that one sensory modality can modulate another. For example, when you bang your elbow you rub it to ease the pain. By stimulating touch receptors you feed into the pain pathway to dampen it down.
Option 5: It is multiple rods which would synapse onto a singular retinal ganglion cell, as opposed to this way round.

Question 26

  1. T12
  2. L1
  3. T4
  4. T6
  5. T10

The correct answer is option 5, T10

T12 -> This supplies the inguinal/groin region.
L1 -> This supplies the upper aspect of the thigh.
T4 -> This supplies the skin at the level of the nipples.
T6 -> This supplies the skin in the epigastric region.

Question 27

An individual presents with loss of fine touch in the right hand and loss of pain perception on the left hand. What is the most likely place of damage?

  1. The right dorsal column
  2. Left somatosensory cortex
  3. The right dorsal root nerve
  4. The right side of the spinal cord, above entry
  5. Left spinothalamic tract

The correct answer is option 4, The right side of the spinal cord, above entry

The right side of the spinal cord, above entry: The spinothalamic tract has already decussated so damage is most likely to be on the contralateral side to the loss of pain perception. The dorsal column has yet to decussate so the loss of fine touch will be on the same side as the lesion.
The right dorsal column: This would only take out fine touch from the right hand, because any sensation from the left hand would be in the right cortex, and in this case the patient has lost pain perception in the left hand.
Left somatosensory cortex: The patient has lost pain perception in the left hand, and these fibres would enter via the left dorsal root nerve and decussate immediately to the right hand side. Therefore, a lesion here would only cause loss of fine touch in the right hand.
The right dorsal root nerve: The patient has lost pain perception in the left hand, and these fibres would enter via the left dorsal root nerve and decussate immediately to the right hand side. Therefore, a lesion here would only cause loss of fine touch in the right hand.
Left spinothalamic tract: If the lesion was here, the patient would have no deficit in fine touch sensation as this tract is responsible for pain and temperature sensation. Furthermore, we know the patient has lost pain sensation in their left hand, and because this tract decussates immediately in the spinal cord, a lesion in the left hand side of the tract would affect the pain sensation in the right hand, not the left.

Question 28

  1. Extensor plantar response
  2. Fasciculations
  3. Hypotonia
  4. Flaccid paralysis
  5. Hyporeflexia

The correct answer is option 1, Extensor plantar response

Aka a positive Babinski sign, is an example of hyperreflexia. It is normal in babies but in adults indicates UMN damage. Usually reflexes are dampened by the descending pathways, so when the descending pathways are damaged we see exaggerated reflexes.
Option 2: These are twitches of muscle fibres, and occur in LMN damage. They are caused by spontaneous depolarisation of a lower motor unit.
Option 3: This is a LMN sign – the muscle is no longer being innervated, and muscles need innervation in order to contract. Therefore, we will see reduced tone.
Option 4: This is a LMN sign – muscles cannot contract to produce a spastic paralysis (which is an UMN sign).
Option 5: This occurs in LMN damage – you no longer have innervation of the effector limb of that reflex.

Question 29

Which area of the brain is affected in expressive aphasia? (extra bonus points if you can name the area!)

  1. Frontal lobe
  2. Occipital lobe
  3. Parietal lobe
  4. Temporal lobe
  5. Wernicke’s area

The correct answer is option 1, Frontal lobe

Answer: Broca’s area is affected in expressive aphasia (difficulty producing words, no difficulty understanding). This is found in the Frontal Lobe. The frontal lobe contributes to personality, the motor cortex (precentral gyrus) and problems. Receptive aphasia is associated with Wernickes area found in the temporal lobe. Temporal lobe also contains the primary auditory cortex, amygdala, limbic system (associated with memory, emotion, hearing) The Parietal lobe contains the primary somatosensory cortex and special manipulation areas (agnosia commonly in parietal lobe lesions) Occipital lobe is mainly associated with vision (visual cortex found in calcarine sulcus)

Question 30

What is labelled in the cross sectional diagram?

  1. Spinothalamic tract
  2. Rubrospinal tract
  3. Corticospinal tract
  4. Dorsal column
  5. Spinocerebellar tract

The correct answer is option 4, Dorsal column

The dorsal column medial lemniscus pathway is associated with fine touch, pressure, vibration and proprioception. Signals ascend the dorsal column ipsilaterally, terminating in cuneate and gracile nucleus in the medulla. They then ascend to synapse the thalamus (ventroposterolateral nucleus) via medial lemniscus and ascend to the somatosensory cortex in the post central gyrus in parietal lobe. Clinical significance of the dorsal column includes Tabes Dorsalis as a result of tertiary syphilis. The other ascending tract is the anterolateral system (spinothalamic) which is responsible for crude touch, pain, temperature. Clinical significance is syringomyelia, a cyst in the central canal formed from ependymal cells.

Question 31

Which of the following describes features of Treacher Collins syndrome?

  1. Micrognathia, posteriorly displaced tongue, airway obstruction
  2. Bilateral hypoplasia of the zygomatic bone and mandible, external ear malformations and facial clefts
  3. Craniofacial dysmorphology and cardiovascular defects, micrognathia, small mouth, small philtrum, ears rotated
  4. Craniofacial defect with compromised hearing, maxillary process with the frontonasal process affected
  5. 2nd-4th pharyngeal clefts not obliterated remaining as a cervical sinus to form a neck lump

The correct answer is option 4, Craniofacial defect with compromised hearing, maxillary process with the frontonasal process affected

Treacher Collins syndrome involves the underdevelopment of the bones of the face. It is a 1st and 2nd pharyngeal arch neural crest cell defect (TCOF1). Affected individuals may also have colobomas, sparse eyelashes, underdeveloped/misaligned jaw, crowded teeth, small nasal passages, hearing difficulties.

Pierre robin sequence is a neural crest cell genetic defect (SOX9) which results in craniofacial abnormalities (Micrognathia, posteriorly displaced tongue, airway obstruction)

22Q11.2 deletion syndrome/DiGeorge is a neural crest cell genetic defect (deletion on chromosome 22) leading to craniofacial dysmorphology and cardiovascular defects. Features include micrognathia, small mouth, small philtrum, ears rotated. NB the cardiovascular system is developed from 4th/6th arch arteries, thymus 3rd pharyngeal pouch.

Cleft lip and palate is one of the most common craniofacial defects when maxillary process fusion with the frontonasal process is affected. This can lead to feeding problems, compromised hearing.

Branchial cysts occur as a result of 2nd-4th pharyngeal clefts not obliterating, leaving a neck lump.

Question 32

Which pharyngeal arch leads to the development of the muscles of mastication?

  1. 1st
  2. 2nd
  3. 3rd
  4. 4th
  5. 6th

The correct answer is option 1, the 1st pharyngeal arch

The 1st pharyngeal arch involves the muscles of mastication (innervated by the trigeminal nerve)
The 2nd pharyngeal arch involves the muscles of facial expression and stapedius (innervated by cranial nerve 7, facial nerve)
The 3rd pharyngeal arch involves the stylopharyngeus muscle (innervated by glossopharyngeal IX)
The 4th pharyngeal arch involves the muscles of the soft palate and pharynx (superior laryngeal branch of the vagus)
The 6th pharyngeal arch involves the intrinsic muscles of the larynx, except cricothyroid (recurrent laryngeal nerve of the vagus)

Question 33

Which part of the ear is NOT associated with the 1st pharyngeal arch/membrane

  1. Malleus
  2. Incus
  3. Stapes
  4. Tympanic membrane
  5. External acoustic meatus

The correct answer is option 3, Stapes

Stapes is produced by the 2nd pharyngeal arch developing (the stapedius muscle is innervated by cranial nerve 7, facial nerve) Malleus and incus develop from the 1st central rod of the pharyngeal arch and the 1st pharyngeal arch membrane persists to form the tympanic membrane.

Question 34

On examining a patient’s cranial nerves, you notice they have reduced sensation of the forehead. Which branch is responsible for this innervation?

  1. Maxillary nerve
  2. Ophthalmic nerve
  3. Mandibular nerve
  4. Temporal
  5. Zygomatic

The correct answer is option 2, Ophthalmic nerve

The trigeminal nerve is responsible for sensation of the anterior 2/3 of the face. Note that the cranial nerve exam! Ophthalmic branch of trigeminal is responsible for sensation of the upper 3rd of the face, maxillary the middle 3rd and mandibular the lower 3rd. Cervical spine nerves are responsible for innervating the posterior aspect of the scalp.

Facial nerve (CNVII) is responsible for motor innervation to the muscles of facial expression – branches = temporal, zygomatic, buccal, marginal mandibular, cervical

Question 35

Which of the following are the 4 divisions of the anterior triangle of the neck?

  1. Submental, submandibular, subclavian and carotid
  2. Submental, submandibular, subclavian and occipital
  3. Submental, subclavian, occipital and carotid
  4. Submental, submandibular, carotid and muscular
  5. Submental, subclavian, occipital, muscular

The correct answer is option 4, Submental, submandibular, carotid and muscular

Submental, submandibular, carotid and muscular are the subdivisions of the anterior triangle of the neck. The occipital and subclavian triangle are the divisions of the posterior triangle of the neck. Boundaries of the anterior triangle are the inferior border of the mandible, anterior border of sternocleidomastoid, and sagittal line down the midline of the neck. Boundaries of the posterior triangle are the posterior border of the sternocleidomastoid, anterior border of trapezius and middle ½ of the clavicle.

Question 36

Which layer of cervical fascia contains the scalene muscles?

  1. Investing
  2. Prevertebral
  3. Pretracheal
  4. Carotid sheath
  5. Post vertebral

The correct answer is option 2, Prevertebral

Prevertebral layer covers the prevertebral muscles (splenius capitus, levator scapulae, posterior scalene, middle scalene, anterior scalene).
Investing layer – surrounds neck like a collar, encloses the SCM, infrahyoid and trapezius
Pretracheal layer – lies deep to infrahyoid, encloses thyroid, trachea and oesophagus/pharynx
Carotid sheath – encloses the vagus nerve, internal jugular vein, common and internal carotid arteries
Note the post vertebral is NOT a type of cervical fascia

Question 37

Describe the main function of association fibres

  1. Link gyri in the same hemispheres
  2. Link gyri across hemispheres
  3. Link gyri to other CNS structures eg. Basal ganglia
  4. Link gyri to the cerebellum
  5. Link gyri between different lobes

The correct answer is option 1, Link gyri in the same hemispheres

Association fibres link gyri in the same hemispheres.Examples include the arcuate fasciculus connecting Wernickes and Brocas areas.
Commissural fibres link gyri across hemispheres, an example being the corpus callosum.
Projection fibres link gyri to other CNS structures, from layer 5 in the cortex.

Question 38

Which of the following tracts decussate at the level of the medullary pyramids?

  1. Dorsal column medial leminscal pathway
  2. Anterior corticospinal tract
  3. Spinothalamic tract
  4. Lateral corticospinal tract
  5. Corticobulbar tract

The correct answer is option 4, Lateral corticospinal tract

The only one that decussates at that level. Corticobulbar decussates at each relevant cranial nerve nuclei (also not all corticobulbar tracts decussate) anterior corticospinal decussate further down in the spinal cord.

Question 39

Which of the following statements are true?

  1. The lateral corticospinal tract arises exclusively from the primary motor cortex
  2. The corticobulbar tract is an extrapyramidal tract that supplies motor innervation to the musculature of the head and neck
  3. The lateral corticospinal tract primarily innervates the distal musculature
  4. The spinothalamic tract decussates at the level of the medulla
  5. Fibres in the gracile fasciculus contains afferent sensory information from the upper trunk and its extremities

The correct answer is option 3, The lateral corticospinal tract primarily innervates the distal musculature

Option 1: CST can arise from other motor areas e.g. secondary motor cortex, posterior parietal cortex
Option 2: Corticobulbar is a pyramidal tract
Option 4: Spinothalamic tract decussates at the level of the spinal cord
Option 5: Gracile fasciculus contains sensory info from lower half of body and extremities

Question 40

Which of the following neurotransmitters cause muscle contraction after the neuromuscular junction?

  1. Norepinephrine
  2. Acetylcholine
  3. Calcium
  4. Gamma-aminobutyric acid
  5. Glutamate

The correct answer is option 3, Calcium

Calcium released from sarcoplasmic reticulum post action potential at NMJ binds to troponin and causes muscle contraction. Ach is the neurotransmitter released at NMJ to initiate the action potential at sarcoplasmic reticulum

Credits

  • 21-28 (Molly Mercurio, 3rd year)
  • 31-40 (Teresa Snook, 3rd year)