Theme 2: Cranium (NS/AHAN)

Question 1

What two main types of cells exist in the nervous system?

Answer 1

Neurons and Glial cells.

Question 2

What can Glial cells be subdivided into in the CNS?

Answer 2

Astrocytes, Oligodendrocytes, Microglia.

Question 3

Neurons are sensitive to glucose deprivation. How can they compensate for a lack of glucose?

Answer 3

Astrocytes can store glycogen.
Glycogen is a form of long-term storage for glucose.
The astrocytes will convert glucose to lactate (thus they receive some energy).
Lactate can be passed to neurons, which oxidise it into CO2, generating ATP.
This is known as the glucose lactate shuttle.

Question 4

What is the main function of oligodendrocytes?

Answer 4

Myelination of the axons of the CNS.

Schwann cells do the equivalent in the PNS.

Question 5

How do microglia help in the battle against infection?!

Answer 5

They are activated when they recognise foreign material. They remove debris through phagocytosis. They can also act as antigen presenting cells (which T-cells will respond to!)

Question 6

T-cells often have a pro-inflammatory response. Why might this be a problem in the CNS?

Answer 6

The skull is a rigid structure - it will not tolerate volume expansion. The CNS appears to inhibit the pro-inflammatory T-cell response.

Question 7

What is the structure of a Voltage-Gated K+ Channel?

Answer 7

They contain 4 functional subunits (alpha 1,2,3,4).

Each subunit contains 6 transmembrane-spanning helices (the 4th is the voltage sensor).

Question 8

What can the Nernst equation be used to calculate? What is the equation?

Answer 8

The equilibrium potential for an ion.
RT / zF ln ([ion outside] / [ion inside]) or…
61 / z log ([ion outside] / [ion inside])

Question 9

What is the initial segment of a neuron?

Answer 9

It connects the cell body and the axon of the neuron. Physiologically, it is the only portion of the neuron that can generate an action potential.

Question 10

What is the structure of a Voltage-Gated Na+ Channel?

Answer 10

It is one protein with four domains, consisting of six transmembrane spanning helices (the 4th is the voltage sensor). It contains only one functional alpha subunit, often having 3 non-functional beta subunits.

Question 11

How do local anaesthetics work?

Answer 11

They block voltage-gated Na+ channels: this is use-dependent. Therefore there must be ‘activation’ of the desired, anaesthetised area. They affect (in order) small myelinated axons, un-myelinated axons and large myelinated axons.

Question 12

What are the three main types of gated ion channels?

Answer 12

Voltage-gated (e.g. Na+, K+)
Ligand-gated (e.g. ACh)
Mechanically-gated

Question 13

What does the CNS comprise of?

Answer 13

The brain and the spinal cord.

Question 14

What is the CNS surrounded by? What do these offer the CNS?

Answer 14

The meninges, which along with CSF help protect the CNS against damage.

Question 15

What are the layers of the meninges (outermost to innermost)?

Answer 15

The periosteal layer and the meningeal layer of the dura mater. The arachnoid mater (which is fibrous and spider-like). The pia mater (which is like a sheet that covers and is continuous with the brain).

Question 16

Which layers of the meninges reflect?

Answer 16

The dura mater: the periosteal layer is reflected at the foramen magnum as the meningeal layer of the dura mater, arachnoid mater and pia mater pass through with the spinal cord. The meningeal layer of the dura mater is also reflected to form the tentorum cerebelli and the falx cerebri.

Question 17

What is the tentorum cerebelli?

Answer 17

The tentorum cerebelli separates the cerebellum and brainstem from the occipital lobe of the cerebral cortex. It is a crescent-shaped in-folding. It has a gap anteriorly allowing the passage of the midbrain (tentorial incisure).

Question 18

What is the falx cerebri?

Answer 18

The falx cerebri separates the two hemispheres of the cerebral cortex (located in the longitudinal cerebral fissure). It is sickle-shaped.

Question 19

Where is the CSF stored in the CNS?

Answer 19

The subarachnoid space.

Question 20

What is an extradural haematoma and what can commonly cause it?

Answer 20

Blood accumulates in the extradural space (a potential space between the periosteal layer of the dura mater and the skull). Can be caused by a fracture of the pterion (e.g. a blow to the side of the head), which overlies the middle meningeal artery.

Question 21

What is a subdural haematoma and what can commonly cause it?

Answer 21

Blood accumulates in the subdural space (between the dura mater and the brain). It is normally due to the rupture of bridging veins - often seen in the elderly and alcoholics who may display cerebral atrophy.

Question 22

What is the function of the CSF?

Answer 22

Support (cushioning); Buoyancy (less heavy, does not cut off own blood supply); Maintain homeostasis by providing nutrients/eliminating waste (through the ventricular sytem).

Question 23

Regarding cell regeneration, how do the CNS and PNS differ?

Answer 23

Neurons cannot regenerate after birth (despite the fact progenitor/stem cells are found in the brain in later life). Glial cells and many cells of the PNS have a capacity to regenerate after injury.

Question 24

Regarding tumours, how do the CNS and PNS differ?

Answer 24

All tumours in the PNS and neuronal tumours in the CNS are benign. In contrast tumours of the glial cells of the CNS can become malignant.

Question 25

Where does the spinal cord show enlargements?

Answer 25

At the cervical and lumbar levels.

Question 26

Are spinal vertebrae and neuronal segments of the spinal cord different?

Answer 26

Yes. Embryonically, the spinal vertebrae and neuronal segments of the spinal cord develop together, however, by the age of four the spinal cord stops growing. This means the vertebral column is longer than the spinal cord.

Question 27

What is the terminal part of the spinal cord known as?

Answer 27

Conus Medullaris.

Question 28

What is the Cauda Equina?

Answer 28

The sympathetic nerve fibres that travel in the spine below the Conus Medullaris. Sacral nerves originate from the upper lumbar vertebral levels (because the spinal cord stops growing before the vertebral column).

Question 29

What is the Filum Terminale?

Answer 29

Continuation of the Pia Mater below the Conus Meullaris, anchoring the spinal cord to the coccyx.

Question 30

Which sutures are found on the calvaria? What are the points that they meet known as?

Answer 30

Anterior to Posterior: Coronal (fronto-parietal); Saggital; Lambdoid (parieto-occipital). Bregma is where the coronal and saggital sutures meet; Lambda is where the lambdoid and saggital sutures meet.

Question 31

What is the difference between white and grey matter?

Answer 31

White matter contain myelinated axons; the myelin gives the matter their distinctive colour. Grey matter contains unmyelinated axons.

Question 32

How is white matter distributed in the spinal cord?

Answer 32

Around the edges of the spinal cord, in funiculi (dorsal, lateral and ventral).

Question 33

How is grey matter distributed in the spinal cord?

Answer 33

In a butterfly-shaped region in the middle of the spinal cord. It is divided into 10 rexed laminae.

Question 34

What are ascending tracts?

Answer 34

They are fibre tracts which provide the brain with sensory information.

Question 35

How can sensation be divided?

Answer 35

Conscious (pain, temp. crude touch, tactile sensation) and non-conscious (taxtile sensation, muscle length/tension, joint position/angle etc).

Question 36

With which modalities of sensation is the lateral spinothalamic tract involved?

Answer 36

Pain and temperature.

Question 37

Where is the cell body of the primary neuron of all ascending tracts located?

Answer 37

In the dorsal root ganglion.

Question 38

Regarding the lateral spinothalamic tract, what happens to the primary sensory neuron upon reaching the spinal cord?

Answer 38

Divides into branches which supply 1-3 spinal segments rostrally and caudally. The main axon terminates in the dorsal horn of its respective spinal segment.

Question 39

Regarding the primary neuron of the lateral spinothalamic tract, what do its axonal branches traverse rostrally and caudally through?

Answer 39

The Posterolateral Tract of Lissauer.

Question 40

Regarding the lateral spinothalamic tract, what is the classification of the primary neurone?

Answer 40

Sensory neurones with pseudo-unipolar axons - one axon with two branches (no dendrites or additional axons).

Question 41

Where are the cell bodies of secondary neurones of the spinothalamic tract located?

Answer 41

In the dorsal horn of the spinal cord.

Question 42

What is the anterior spinothalamic tract involved in detecting?

Answer 42

Tactile sensation including pressure.

Question 43

Where do fibres of the spinothalamic tract decussate?

Answer 43

At the segmental level that they arise (the secondary neuron dives under the Central Canal, crossing the midline).

Question 44

Where are the cell bodies of the tertiary neurones of the spinothalamic tract found?

Answer 44

In the ventral posterolateral nucleus of the thalamus, having ascended from the spinal cord, pons, medulla, midbrain.

Question 45

What structure does the axon of the secondary neuron of the spinothalamic tract join after decussation?

Answer 45

The lateral funiculus, where it joins fibres of the lateral spino-thalamic tract.

Question 46

Where do the tertiary neurones of the spinothalamic tract terminate?

Answer 46

They terminate in the post-central gyrus of the cerebral cortex (the somatosensory centre), ascending via the internal capsule.

Question 47

Is the spinothalamic tract somatotopically organised (i.e. spatial mapping of body’s surface is preserved within the tract)?

Answer 47

Yes. Fibres from the lowest part of the body travel dorsolaterally within the spinothalamic tract. Fibres arising from the cervical cord ascend ventro-medially.

Question 48

What is syringomyelia?

Answer 48

It is where there is a cyst or cavity within the central cavity. The cyst will expand ventrally into the ventral horn, effectively transecting the spinal cord.

Question 49

For which modalities of sensation is the dorsal column responsible (medial lemniscal)?

Answer 49

Fine touch and conscious proprioception.

Question 50

Where do the axonal branches of the primary neuron of the dorsal column terminate?

Answer 50

The axon from a derma/myotome enters the dorsal horn at the corresponding neural level. One branch immediately joins the dorsal funiculus of the same side, without terminating. The other terminates in the dorsal horn of its neural level of entry (Laminae VII)

Question 51

What is Clarke’s Column?

Answer 51

Lamina VII of the grey matter is the nucleus of Clarke. One nucleus at each neural level, forming a column. The column acts locally as interneurones and sends their axons to the cerebellum.

Question 52

What two structures is the dorsal funiculus composed of?

Answer 52

Fasciculus cuneatus (upper body, above vertebral level of T6, lateral part of dorsal funiculus) and the fasciculus gracilis (lower body, below vertebral level of T6, medial part of dorsal funiculus).

Question 53

Where do fasciculus cuneatus and gracilis terminate?

Answer 53

In the medulla, on the same side of the body, in the nucleus cuneatus and gracilis, respectively.

Question 54

Do the dorsal columns decussate? If so, where?

Answer 54

Yes - at the medulla oblongata. The secondary neuron axon travels ventromedially, crossing the midline to become the medial lemniscus.

Question 55

Where do the secondary neurons of the dorsal column terminate?

Answer 55

Ventral posterolateral nucleus of the thalamus.

Question 56

Where do the tertiary neurons of the dorsal column terminate?

Answer 56

The sensory-motor cerebral cortex, ascending from the ventral posterolateral nucleus of thalamus via the internal capsule.

Question 57

What is Brown-Sequard syndrome?

Answer 57

It is caused by damage to one half of the spinal cord. There will be loss of motor function and pain and temperature sensation on the ipsilateral side to the injury, and loss of fine touch and conscious proprioception on the contralateral side to the injury if it occurs in the dorsal column.

Question 58

Where do the axons of the secondary neurons of the dorsal spinocerebellar tract arise from?

Answer 58

From the nucleus of Clarke (grey matter); the enter the white matter in the lateral funiculus.

Question 59

Where are the secondary neurons of the spinocerebellar tract found? Where do they terminate?

Answer 59

The grey matter of the spinal column. The cerebellum.

Question 60

Is there decussation of the fibres of the spinocerebellar tract?

Answer 60

Dorsal - spinal cord; Ventral - none.

Question 61

What type of sensation is the cerebellum involved in?

Answer 61

Unconscious proprioception.

Question 62

Where are the secondary neurons of the cuneocerebellar tract found? Where do they terminate?

Answer 62

Nucleus cuneatus. The cerebellum.

Question 63

What does the vermis of the cerebellum control?

Answer 63

Balance. It is a midline structure, so damage to it will manifest itself in a patient falling backwards (NOT sideways!).

Question 64

What are the three primary vesicles of the brain?

Answer 64

Forebrain, midbrain and hindbrain.

Question 65

What are the 5 major neuro-anatomical segments of the adult brain (secondary vesicles)?

Answer 65

Telencephalon - Cerebral Cortex; Diencephalon - Thalamus; Mesencephalon - Midbrain; Metencephalon - Pons and Cerebellum; Mylencephalon - Medulla Oblongata.