1.1 Introduction to nervous system

Question 1

What are the components of the CNS and PNS

Answer 1

CNS = cerebral hemispheres, brainstem and spinal cord

PNS = Dorsal and ventral roots, spinal nerves and peripheral nerves (cauda equina is part of the PNS)

Question 2

Function of the Cerebral hemispheres

Answer 2

Higher functions, motor and sensory (conscious), emotion, memory

Question 3

Function of the Brainstem and Cerebellum

Answer 3

Communication via cranial nerves including functions such as eye movement, swallowing and cardiorespiratory homeostasis
Cerebellum involved with motor sequencing and co-ordination

Question 4

Function of the Spinal Cord

Answer 4

Ascending (sensory) and descending (motor) pathways
Spinal reflex arcs
Control of upper and lower limbs at level of cervical and lumbosacral enlargements

Question 5

Outline the structure and function of Grey matter

Answer 5

Composed of cell bodies and dendrites, with a rich blood supply (highly vascular)
There are axons present in grey matter, but volume is predominantly composed of cell bodies and dendrites
Most of the computation occurs here
‘grey matter’ in the PNS = ganglion (collection of cell bodies in PNS)

Question 6

Outline the structure and function of White matter

Answer 6

Composed of (myelinated and non-myelinated) axons with no cell bodies. Myelin (lipid emulsion) is white.
White matter pathways connect areas of grey matter.
'white matter' in the PNS = a nerve (or root)

Question 7

Consider the basics of the Spinal cord

Answer 7

31 segments, each supplying a dermatome and myotome on each side.
Central core of grey matter, outer shell of white matter.
Spinal nerve connects through dorsal (sensory) and ventral (motor) roots. (roots are formed through multiple rootlets, which directly plug into the cord).
Sensory deficit caused by lesion at level of dorsal roots or spinal nerves.
Sensory deficit across multiple segments = cord lesion
Sensory deficit in homuncular pattern = lesion above thalamus

Question 8

Describe the organisation of white matter in the spinal cord.

Answer 8

Funiculus = Segment of white matter containing multiple distinct tracts. Impulses travel in multiple directions (e.g. Lateral funiculus contains lateral corticospinal tract (descending) and spinothalamic tract (ascending)

Tract = an anatomically and functionally defined white matter pathway connecting two distinct regions of grey matter. Impulses travel in one direction. (e.g. spinothalamic tract, corticospinal tract)

Fasciculus = a subdivision of a tract supplying a distinct region of the body. (Way of splitting up tracts) (e.g. Gracile/Cuneate fasciculus)

Question 9

Describe the organisation of grey matter in the spinal cord.

Answer 9

Grey matter of the cord is organised into cell columns (equivalent of tracts in white matter)
These columns are given numbers - Rexed Laminae. These Rexed Laminae are different histiologically and functionally.

Nucleus = Collection of cell bodies inside the CNS

Ventral horn = long cylinder going down supplying different sets of muscles

Question 10

Define Cortex

Answer 10

Cortex (grey matter) = folded sheets of cell bodies found on the surface of the brain structure (typically 1-5mm thickness - cerebral cortex)

Question 11

Define Fibre

Answer 11

Fibre (white matter) = term relating to an axon in association with it’s supporting cells (e.g. oligodendrocytes). Used synonymously with ‘axon’.

Question 12

Give the 3 different types of Fibres

Answer 12

1. Association fibre - connects cortical regions within the same hemisphere (e.g. U fibre)
2. Commissural fibres - connect left and right hemispheres or cord halves (e.g. Corpus Callosum)
3. Projection fibres - connect the cerebral hemispheres with the cord/brainstem and vice versa

Question 13

Define Nucleus

Answer 13

Nuclues (grey matter) = collection of functionally related cell bodies (in the CNS)

Question 14

What are the roles of the Midbrain

Answer 14

Eye movements and reflex responses to sound and vision.

Question 15

What are the roles of the Pons

Answer 15

Feeding (due to trigeminal nerve) and sleeping (due to reticular formation)

Question 16

What are the roles of the Medulla

Answer 16

Cardiovascular and Respiratory centres found in the medulla

Also contains major motor pathways (medullary pyramids)

Question 17

What does the central sulcus separate?

Answer 17

Central sulcus is a key landmark sitting in the coronal plane and separates the frontal and parietal lobes

Question 18

What is the role of the precentral gyrus?

Answer 18

Contains the primary motor cortex

Question 19

What is the role of the postcentral gyrus?

Answer 19

Contains the primary sensory cortex

Question 20

What does the lateral fissure separate?

Answer 20

Lateral fissure (aka Sylvian fissure) separates the temoral from the frontal/parietal lobes

Question 21

What does the Parieto-occipital sulcus separate

Answer 21

Separates the parietal from the occipital lobes

Question 22

State an important structure near the Calcarine Sulcus

Answer 22

Primary visual cortex surrounds the calcarine sulcus

Question 23

Name the key features of the Midbrain (theres a lot)

Part 1/3

Answer 23

Cerebral peduncles (white matter) - contain descending corticospinal fibres (from ipsilateral hemisphere)

Substantia nigra (grey matter) - dopaminergic neurones that project to the striatum (nigrostriatal fibres)

Red nucleus (grey matter) - Axons travel to the cord in the vestigial rubrospinal tract (less important motor functions)

Question 24

Name the key features of the Midbrain (theres a lot)

Part 2/3

Answer 24

Oculomotor nucleus (grey matter)

Edinger-Westphal nucleus (grey matter) - contains parasympathetics which travel to the Ciliary Ganglion

Periaqueductal grey matter - surrounds the cerebral aqueduct, important role in pain transmission and micturition

Cerebral aqueduct - connects the third ventricle (between halves of the thalamus) and the fourth ventricle (beneath cerebellum)

Question 25

Name the key feautres of the Midbrain (theres a lot)

Part 3/3

Answer 25

Medial Lemniscus - connects gracile/cuneate nucleus to the thalamus - part of DCML pathway

Spinothalamic tract - connects the spinal dorsal horn to the thalamus

Superior/inferior colliculus (grey matter) - regulate reflex responses to visual (superior) and auditory (inferior) stimuli

Question 26

Name the key features of the Pons

Answer 26

Trigeminal nerve exits from it’s lateral aspect (CN V, VI, VII, VIII)

Corticospinal fibres travel ventrally (hence susceptible to damage by basilar artery occlusion causing locked in syndrome)

Sits beneath the fourth ventricle so can get compressed if ventricle expands

Contains reticular formation (grey matter) regions important for sleep

Question 27

Name the key features of the Medulla

Answer 27

Pyramids (white matter) - ventral swellings on each side containing corticospinal fibres from the ipsilateral hemisphere - decussate in the caudal medulla at the decussation of the pyramids.

Gracile and cuneate nuclei (grey matter) - relay to second order neurones in DCML

Nuclei (grey matter) for cardiorespiratory homeostasis - such as solitary nucleus and dorsal motor nucleus of the vagus

Question 28

What are the features of the brain seen from the inferior view

Answer 28

1. Optic chiasm - Visual fibres cross over
2. Uncus - Olfactory role, herniates compressing midbrain
3. Medullary pyramids - descending motor fibres
4. Parahippocampal gyrus - memory encoding

Question 29

Features of the brain seen from the midline

Answer 29

1. Corpus callosum
2. Thalamus - sensory relay station projects to sensory cortex
3. Cingulate gyrus - important for emotion and memory
4. Hypothalamus - homeostasis
5. Fornix - Major output pathway from the hippocampus (Papez circuit)
6. Tectum - Dorsal part of the midbrain - inferior = auditory reflexes; superior = visual reflexes
7. Cerebellar tonsil - can herniate and compress medulla

Question 30

Where is most CSF made?

Answer 30

CSF is made in all the ventricles however most CSF is made in the lateral ventricles.
The ventricles contain choroid plexus cells which produce 600-700ml of CSF per day.

Question 31

What are the functions of CSF

Answer 31

CSF has mechanical and metabolic functions.

• CSF supports the brain - holding it up, without CSF the brain would sag.
• CSF also protects the brain (acts as a cushion)
• CSF contains glucose (in bacterial meningitis glucose levels are affected)

Question 32

What is the pathway of CSF flowing through ventricles

Answer 32

Lateral ventricle > Interventricular foramen > 3rd ventricle > cerebral aqueduct > 4th ventricle > LUSCHKA, magendie, central canal

Question 33

Where does the 4th ventricle drain to?

Answer 33

4th ventricle drains via the apature’s:
Luschka (lateral apature)
Magendia (medial apature)

Negligible drainage via the spinal cord (central canal)

Question 34

Where is CSF reabsorbed?

Answer 34

CSF circulates through the ventricular system and subarachnoid space before being reabsorbed at the arachnoid granulations (and some other sites).

Arachnoid granulations drain into dural venous sinuses (e.g. Superior sagittal sinus)

Question 35

Where is a common site of occlusion of the ventricular system and what can cause such occlusion

Answer 35

Cerebral aqueduct is a common site of occlusion (by congenital stenosis or tumours)

Question 36

What condition occurs when there is insufficient drainage of the CSF and where can occlusions occur?

Answer 36

Condition = Hydrocephalus;

Occlusions can occur at the magendie, luschka and cerebral aqueduct by a congenital stenosis or tumours.