📚 Question Bank

The given clinical scenario is suggestive of Parkinson's disease, a disorder involving the destruction of the substantia nigra in the basal ganglia. The most accurate representation of the direct pathway in the basal ganglia is cortex gt; striatum gt; globus pallidusgt; thalamus gt; premotor cortex.

Parkinson's disease is a chronic progressive neurodegenerative disease that is clinically manifested by a triad of cardinal motor symptoms- rigidity, bradykinesia and tremor.

The indirect pathway is represented as follows:

Cortex gt; Striatum gt; Globus pallidus externa gt; Subthalamic nucleus gt; Globus pallidus interna and Substantia nigra reticulata gt;Thalamus gt; Premotor cortex

The direct pathway stimulates the cortex to produce movement and the indirect pathway inhibits movement.

Medial thalamic nuclei are not part of the limbic system. The anterior nucleus of the thalamus is a part of the limbic system.

The limbic system controls emotional behavior and is involved in the conversion of short-term memory to long-term memory. It consists of both the grey mater and white mater. It is located between the cerebral cortex and the hypothalamus.

The given clinical scenario of polyuria and polydipsia along with the investigation findings is suggestive of central diabetes insipidus. It involves the diencephalon, a structure that is derived from the prosencephalon.

The diencephalon forms the thalamus, epithalamus, subthalamus, and hypothalamus.

The MRI given below shows the posterior pituitary bright spot. The arrow points at the posterior pituitary and the arrowhead at the anterior pituitary.

The medial nucleus of the thalamus predominantly receives input from the hypothalamus and sends output to the prefrontal cortex.

The medial thalamic nuclei contain the large dorsomedial nucleus and several smaller nuclei:

• Internally, the dorsomedial nucleus is connected to all other thalamic nuclei.
• Externally, it has 2 major connections—the prefrontal cortex and the hypothalamus. Its functions include integration of somatic, visceral, and olfactory sensory information as well as relation of this sensory information to emotional feelings and subjective states.

The given clinical scenario of contralateral hemiplegia and paralysis of the third cranial nerve is suggestive of Weber syndrome involving the midbrain. In this, the tectum lies posterior to the cerebral aqueduct.

The midbrain connects the pons and cerebellum with the forebrain. Externally, on the posterior surface, there are two pairs of colliculi—the corpora quadrigemina:

• The superior colliculi are centers for visual reflexes. The superior brachium connects the superior colliculi to the lateral geniculate body and the optic tract.
• The inferior colliculi are auditory centres, and the inferior brachium connects the inferior colliculus to the medial geniculate body.

The trochlear nerve emerges in the midline below the inferior colliculi.

Internally, the midbrain comprises two cerebral peduncles. Each one is divided into an anterior crus cerebri and a posterior tegmentum by the substantia nigra. The oculomotor nerve emerges from a groove on the medial side of crus cerebri and passes to the lateral wall of the cavernous sinus.

The given clinical scenario is suggestive of medial lemniscus tract lesion following a high voltage electrical injury. The medial lemniscus is formed by the internal arcuate fibres. It is also called Reil's ribbon.

The internal arcuate fibres are axons of the second-order neurons from nucleus gracilis and nucleus cuneatus. In the upper medulla, they decussate and form the medial lemniscus which synapses in the thalamus.

The image given below depicts the medial lemniscus tract.

The given clinical features are suggestive of lateral medullary syndrome or Wallenberg syndrome, which is seen in thrombosis of the posterior inferior cerebellar artery.

The lateral part of the medulla is supplied by the posterior inferior cerebellar artery, a branch of the vertebral artery. Injury or thrombosis to this artery results in lateral medullary

syndrome leading to:

Signs and symptoms:

Contralateral loss of pain and temperature on the body

Ipsilateral loss of pain and te mperature on the face

Ataxia and intention tremors

Vertigo, nausea, vomiting, an d nystagmus

Dysphagia, dysarthria and ho arseness of voice

Ipsilateral Horner syndrome

Affected structures: Lateral spinothalamic tract

Spinal sensory nucleus of V n erve

Spinocerebellar tract Vestibular nuclei

Nucleus ambiguus Sympathetic fibers

The given clinical scenario is suggestive of post-traumatic cerebellar ataxia presenting with impaired balance. The largest part of the affected structure i.e. the cerebellum is the middle lobe, also known as the posterior lobe. The gait shown in the above video is a cerebellar ataxic

gait. Here, the patient is seen attempting tandem walking and displaying improper heel-toe coordination, erratic foot placement, and truncal swaying.

The cerebellum consists of two hemispheres (right and left) joined by a median vermis. It is divided into three lobes:

• Anterior lobe - lies superiorly above the primary fissure
• Middle lobe - lies inferiorly below the primary fissure
• Flocculonodular lobe - lies posterior to the uvulonodular fissure

It has two surfaces, superior and inferior, separated by a horizontal fissure. It is connected to the other parts of the central nervous system via three peduncles.

The given clinical scenario is suggestive of cerebellar syndrome. Phylogenetically, the oldest part of the atrophied structure i.e. the cerebellum is archicerebellum/ vestibulocerebellum and it is concerned with fastigial nucleus (connected to vestibular nuclei via descending pathways along with medullary/pontine reticular formations).

The image given below shows MRI scans of two brains. The brain on the left shows atrophy of the cerebellum in a person with cerebellar degeneration. The brain on the right shows a normal cerebellum.

Cerebellar glomeruli are seen in the granular layer (layer B) of the cerebellar cortex.

The image shows a histopathological section of the cerebellum. The cells marked with the arrow are Purkinje cells and they inhibit deep nuclei of the cerebellum.

The given slide shows Negri bodies, which are eosinophilic, cytoplasmic inclusions found in the neurons of the Purkinje cells in a patient with rabies. The input to the Purkinje cells of the cerebellum come from the climbing fibers.

The image given below shows Negri bodies.

The given clinical scenario is suggestive of transient ischemic attack due to internal carotid artery stenosis. The cervical part of the internal carotid artery does not give off any branches.

The image given below shows the internal carotid artery.

The clinical scenario of ptosis, down and out eyes and dilated pupils is suggestive of

an oculomotor nerve palsy secondary to a posterior communicating artery aneurysm. The posterior communicating artery is a branch of the cerebral part of the internal carotid artery.

The image given below shows the posterior communicating arteries in the circle of Willis.

These patient's clinical features as well as the CT scan showing blood in the cistern and the xanthochromatic CSF appearance are suggestive of subarachnoid haemorrhage. The affected vessels i.e. the circle of Willis do not get a contribution from the middle cerebral artery.

The circle of Willis is located in the interpeduncular fossa at the base of the brain. It is an anastomosis between the internal carotid arteries and vertebral arteries. It allows the blood entering from either artery to be distributed to both the cerebral hemispheres.

The arteries forming the circle of Willis are:

• Anterior communicating artery
• Anterior cerebral arteries
• Internal carotid arteries
• Posterior communicating arteries
• Posterior cerebral arteries
• Basilar artery

The given clinical scenario with visual field defects and Riddoch phenomenon is suggestive of occipital lobe lesion occurring due to the occlusion of the posterior cerebral artery.

The visual cortex is supplied by the posterior cerebral artery. Its occlusion is commonly seen in head injury and may be associated with visual hallucinations, denial of blindness (Anton syndrome), and the Riddoch phenomenon (only moving visual targets are perceived). These lesions generally spare the central vision/macular vision.

The anatomical reason for this sparing is attributed to the uniqueness in the blood supply. The part of the occipital lobe representing the peripheral field vision is supplied by the posterior cerebral artery. Whereas, the area at the tip of the calcarine cortex representing the central macular vision, is supplied by a branch of the middle cerebral artery.

The marked vessel is posterior cerebral artery. It does not supply the pons, hence a thrombus in this artery will not affect the pons.

The branches of the posterior cerebral artery are:

• Cortical branches
• Occipital lobe - visual cortex
• Temporal lobe - medial and inferolateral surfaces
• Central branches
• Thalamus
• Subthalamus
• Lentiform nucleus
• Midbrain
• Pineal gland
• Superior and inferior colliculi
• Medial and lateral geniculate bodies
• Choroidal branches- choroid plexus of
• Lateral ventricle
• Third ventricle

The image given below shows the posterior cerebral arteries in the circle of Willis.

The given clinical scenario is suggestive of a Charcot-Bouchard aneurysm. The affected artery is the Charcot's artery which is the striate branch of the middle cerebral artery marked as 'C' in the above image.

Charcot-Bouchard aneurysms are located in the lenticulostriate vessels of the basal ganglia and are commonly associated with hypertension. Charcot's artery supplies the internal capsule and basal ganglia. It is also known as the 'Charcot's artery of cerebral haemorrhage'.

The image given below shows the circle of Willis at the base of the brain.

CT image showing a crescent-shaped hyperdense lesion, is suggestive of acute subdural hematoma. The head injury leads to a tear in the cerebral veins (predominantly the bridging veins like the superior cerebral vein) causing the hematoma. The superior cerebral vein drains into the superior sagittal sinus.

Veins of the cerebral hemispheres can be categorized into superficial and deep. The superficial veins chiefly drain the cerebral cortex, while the deep veins return blood from the deep structures of the cerebrum.

Superficial veins:

• Superior cerebral veins:

These veins drain the upper parts of the superolateral and medial surfaces of the cerebral hemisphere. They drain blood into the superior sagittal sinus.

• Inferior cerebral veins:

These veins return blood from the inferior aspect of the cerebral hemisphere into the transverse, superior petrosal, cavernous and sphenoparietal sinuses. Some also drain into the inferior sagittal sinus.

• Superficial middle cerebral vein:

This vein receives blood from veins on the superolateral surface. It terminates in the cavernous sinus.

Deep veins:

• Internal cerebral veins:

This pair of veins originates at the foramen of Munro and eventually anastomoses to form the great vein of Galen.

• Basal veins:

The two basal veins are closely related to the midbrain structures and drain into the great vein of Galen.

• Great cerebral vein:

The two internal cerebral veins unite to form the great cerebral vein before it passes beneath the corpus callosum and anastomoses with the straight sinus.

The procedure shown in the image is a lumbar puncture. In this, the needle is introduced in the subarachnoid space which ends at the lower border of the S2 vertebra.

A lumbar puncture can be done anywhere from L1 to S2 vertebra. Beyond S2, there are only meninges. However, lumbar puncture is most commonly performed at the level of L3 or L4.

Epidural anaesthesia is given during labour and the placement is usually preferred below L1 to avoid injury to the spinal cord. This is because the adult spinal cord terminates at the lower border of the L1 vertebra.

In children, it usually terminates at the upper border of the L3 vertebra.

Note: Coverage from dermatomes T10 to S1 is necessary for epidural analgesia during labor. For a cesarean section, a block from T4 to S1 is needed. However, since the spinal cord ends at the lower border of L1 in most adults, epidural analgesia is given below this level.

There are a total of 31 pairs of spinal nerves.

In contrast, the number of vertebrae is 33. Due to the difference in the number of spinal segments and the number of vertebrae, the spinal segments don't correspond to the respective vertebrae.

The table below shows the vertebral level corresponding to different regions of the spinal cord: The T11 spine overlies the L3 spinal segment.

The T12 spine overlies the S1 spinal segment.

Regions

Upper cervic al

Lower cervic al

Upper thora cic

Lower thora cic

Spinal Segment( s)

C2 C6 T5 T10

Vertebral spi ne

C2 C5 T3 T7

Spinal segment corresponds t o

Same level

One vertebra above Two vertebrae above Three vertebrae above

The grey rami communicantes are not preganglionic fibers. They are postganglionic fibers.

The sympathetic trunks on either side of the vertebral columns consist of a series of ganglia. They are connected to the spinal nerves by white and grey rami communicantes. The cell bodies of the preganglionic sympathetic neurons are located in the lateral horn in the spinal grey matter. They leave the cord in the ventral nerve roots to form spinal nerves. These fibers enter the sympathetic trunk in white rami communicantes. They synapse with the postganglionic sympathetic neurons in the sympathetic ganglia. The axons of the postganglionic neurons return to the spinal nerve through the grey rami communicantes.

Fibers

Location Myelination

Principal neurotransmitte r

White rami communica ntes

Preganglionic Myelinated Acetylcholine

˜rey rami communica ntes

Postganglionic Unmyelinated Noradrenaline

The T10 spinal segments lie at the level of the spinous process of the T7 vertebra.

The table below shows the vertebral level corresponding to different regions of the spinal cord: The T11 spine overlies the L3 spinal segment.

The T12 spine overlies the S1 spinal segment.

Regions

Upper cervic al

Lower cervic al

Upper thora cic

Lower thora cic

Spinal Segment( s)

C2 C6 T5 T10

Vertebral spi ne

C2 C5 T3 T7

Spinal segment corresponds t o

Same level

One vertebra above Two vertebrae above Three vertebrae above

The structure marked as "?" in the above image is ligamentum denticulatum. Its lowest projection lies at the level of T12 and L1 spinal nerves.