HISTOLOGY

Question 1

List the three (3) true barrier systems that contribute to the physiological blood-brain barrier, and name the cell type that mediates the barrier function in each system (3)

Answer 1

Cerebral capillarie – endothelium; choroid plexus – choroid epithelium; arachnoid mater/meninges – arachnoid barrier, trabecular and pial cells

Question 2

Describe the structural specializations of cerebral capillaries and explain how these contribute to their function related to the blood-brain barrier (4)

Answer 2

Endothelium with tight junctions, lack of fenestrations and few pinocytotic vesicles; thick basement membrane – block non-selective exchange of substances; pericytes; astrocyte foot processes – contribute to development and maintenance of the BBB

Question 3

Name the anatomical structure that contains the cell bodies (somata) of primary somatosensory neurons, and state how these neurons are classified in terms of their morphology (2)

Answer 3

Spinal/dorsal root ganglion; pseudo-unipolar

Question 4

Briefly describe the structure and function of the cell type after which the “Substantia Nigra” is named, give a unique diagnostic feature of these cells and state in what neurological disorder these cells play a key role (4)

Answer 4

Multipolar, dopamine-releasing neurons; modulate the activity of the direct and indirect pathways involved in motor control in the basal nuclei; contain neuromelanin pigment inclusions; Parkinson’s disease

Question 5

Explain the role of bone-forming cells in the process of expansion of the skull vault in an infant with raised ICP (2)

Answer 5

Osteoclasts remove bone matrix on inside, osteoblasts deposit matrix on outside

Question 6

With the aid of a labelled diagram, describe the histological structure of the cranial meninges (4)

Answer 6

Endosteal dura, meningeal dura, dural border cells, arachnoid barrier cells, subarachnoid space with arachnoid trabecular cells and blood vessels, pia (½ each feature)

Question 7

List the three (3) true barrier systems that contribute to the physiological BBB [x7], and name the cell type that mediates the barrier function in each system (3)

Answer 7

Cerebral capillaries (continuous endothelium), Choroid plexus (choroid epithelium), Arachnoid mater/meninges (arachnoid barrier, trabecular & pial cells)

Question 8

Describe the structural specializations of cerebral capillaries & explain how these contribute to their function related to the BBB (3)

Answer 8

Endothelium with tight junctions, lack of fenestrations & few pinocytotic vesicles; thick basement membrane – block non-selective exchange of substances; pericytes; astrocyte foot processes – contribute to development & maintenance of BBB

Question 9

In a labelled plan diagram of a cross-section through a typical blood capillary in the CNS, indicate the structures that contribute to the BBB (4)

Answer 9

Astrocyte endfeet, non-fenestrated endothelium, endothelial tight junctions, thick basement membrane (2 for diagram, 0.5 for each structure)

Question 10

In a labelled diagram, indicate how astrocytes contribute to the BBB (4)

Answer 10

Astrocyte end-feet surrounding cerebral capillary, which has a thick basal lamina and non-fenestrated endothelium

Question 11

With the aid of a labelled diagram, explain the structure of the choroid plexus (5)

Answer 11

Should show fenestrated blood capillaries, matrix & choroid epithelium

Question 12

Name the primary functions of the choroid plexus. Which structural features perform these functions? (3)

Answer 12

Part of BBB, secretion of CSF, clearance; tight junctions in epithelium, increased surface area by villi & microvilli

Question 13

Which fluid compartments are separated by the choroid plexus? (1) [x2]

Answer 13

Blood & CSF

Question 14

Name the mechanism that enables large, polar molecules to cross the choroid plexus (½)

Answer 14

Transmembrane transport systems

Question 15

Where are the choroid plexuses found? Are the choroid plexuses continuous or separate entities? (2)

Answer 15

In 3rd, 4th and lateral ventricles; choroids plexus in ventricles 1/2/3 are continuous

Question 16

Name one substance that readily crosses the BBB & one substance that requires an active transport mechanism, & explain what chemical characteristics result in this difference (2)

Answer 16

Gas (O2) – readily crosses. Glucose – requires active transport. Small and non-polar molecule vs. large polar molecule

Question 17

What are arachnoid villi, and what is their function? (2)

Answer 17

Extensions of arachnoid through dura into superior sagittal sinus - drainage of CSF back into blood stream

Question 18

What would be the consequence if the arachnoid villi had difficulty in performing this function? (1)

Answer 18

Obstruction of CSF flow & resorption, thus raised intracranial pressure

Question 19

Draw a labelled diagram of a villus of the choroid plexus. In this diagram, indicate the cells that form the BBB & the subcellular structures relevant to this function and their role in CSF production (4)

Answer 19

Blood vessel, matrix, basement membrane, choroid epithelium. Epithelial cells to show tight junctions, microvilli, mitochondria