Central Nervous System

Question 1

Diagram to show major divisions of CNS

picture 1, lecture 9

Answer 1

The deep folded part is the cerebral cortex and the
‘bendy’ bit of white matter in the middle is the corpus
callosum (consists of mainly axons).
▪ The corpus callosum interconnects the two
hemispheres to maintain communications – it’s made
of white matter.
▪ The area under the corpus callosum is then the
diencephalon (consisting of the thalamus and
hypothalamus).
o The diencephalon is strongly attached to both
hemispheres and below the diencephalon you
find the midbrain.
▪ The pons is characterised from the bulge it gives.
▪ The medulla then merges with the top of the spinal
cord and goes through the base of the skull

Question 2

Brainstem consists of:

Functions?

Answer 2

Midbrain
Pons
Medulla

▪ Contains a number of nuclei which control vital functions such as respiration and cardiac control.
▪ There are lots of ascending (sensory information to brain) and descending (motor information to the spinal cord) pathways.
▪ There are a number of cranial nerves attached to the brain stem which provide sensory and motor innervation for the head region (i.e. hearing and vision) – 10/12 cranial nerves.
▪ The reticular activating system controls the level of
consciousness.

Question 3

List the functions of the 2 main structures in the diencephalon

Answer 3

▪ Thalamus – A relay station for information going between the
cerebral cortex and other parts of the CNS (lower structures).
o This occurs in both directions.
o Found in the upper area of the diencephalon.

▪ Hypothalamus – Controls homeostasis.
o Interfaces between the limbic system, ANS and
endocrine system.
o Found below the thalamus.

Question 4

Basal ganglia found?

Function?

Answer 4

Basal Ganglia – Movement Control.
▪ Found deep inside the cerebral cortex and
is one of the main nuclei.
▪ Basal Ganglia – group of nuclei which
produce the pattern of movement and
work together with the motor cortex.

Question 5

Cerebellum found?

Function?

Answer 5

Cerebellum – Movement Control.
▪ Found towards the back of the brain and
below the cerebral hemispheres.
▪ It doesn’t initiate movement but it
coordinates movement and is important for
learning new motor skills such as riding a
bike or playing the piano.

Question 6

Cranial fossae types

Answer 6

Frontal fossa protects front, sides and top by parietal and occipital fossa at back

On base, anterior cranial fossa protects the front, followed by the sphenoid cranial fossa

Temporal fossa protects temporal lobes and foramen magnum hole allows nervous entry

Question 7

Ventricular system
Structure
(picture 2, lecture 9)

Answer 7

NOTE: These are AREAS, not bones.
▪ There are TWO (one in each hemisphere of the
brain) large C-shaped ventricles with a spur at the
back, these are the lateral ventricles.
▪ The two lateral ventricles, via a tiny foramen, join
up with a single midline ventricle called the 3rd
ventricle located in the middle of the diencephalon.
▪ At the base of the 3rd ventricle, there is a narrowing
to form a fine channel called the cerebral aqueduct.
▪ The aqueduct passes through the midbrain and at
the top of the midbrain it opens up again into a
tent-shaped 4th ventricle.
▪ The pons and medulla is in front of the 4th ventricle
and the cerebellum is behind it.
▪ At the lower part of the medulla, the 4th ventricle
narrows again to form a very fine channel called the
central canal which goes down the spinal cord.

Question 8

CSF Composition

Answer 8

▪ Produced by ependymal cells found in the ventricles called the choroid plexus.
▪ The choroid plexus filters the blood, takes out most of the cells and then secretes it.
▪ Compared to blood:
o Fewer cells, less protein, reduced concentration of sodium and potassium and a
higher concentration of magnesium and chloride ions.

Question 9

CSF Circulation

Answer 9

▪ CSF then circulates through the ventricular system and gets to the 4
th ventricle which has
holes in it so the CSF can exit the 4th ventricle and spread across the outside of the brain.
▪ The CSF can then circulate in the sub-arachnoid space between the meninges.
▪ It is then reabsorbed into the venous system by arachnoid villi.

Question 10

CSF Functions

Answer 10

▪ To cushion the brain within the skull by acting as a shock absorber.
▪ To circulate nutrients and chemicals filtered from the blood.
▪ To remove waste products from the brain.

Question 11

CSF total volume

Answer 11

Volume = 150ml (turned over 3-4 times a day)

Question 12

CSF flow rate

Answer 12

Flow rate = 500ml/day.

Question 13

Hydrocephalus definition

Answer 13

Hydrocephalus = a blockage of the sub-arachnoid space (e.g. by meningitis), a build up of CSF.

Question 14

Hydrocephalus treatment
Types of stroke caused?
What does each involve?
Treated by?

Answer 14

Bleeding between the layers may then cause a type of stroke. There are two types:
▪ Communicating.
▪ Non-communicating.
The non-communicating presents with blackouts whereas communicating presents with headaches.
Treated with a shunt (divert CSF) or by removing the cause.

Question 15

Intracranial haemorrhage types

Clinical presentation of each?

Answer 15

Epidural Haemorrhage = Between skull and dura (membrane) of the brain. Caused by rupture of middle meningeal artery.

Subdural Haemorrhage = Between the inside of the dura (inside brain) and the brain itself

Question 16

Meninges layers

slide 14, lecture 1

Answer 16

-

Question 17

Membranes enclosing brain+ spinal cord+ layers in between

Answer 17

There are THREE membranes enclosing the brain and
spinal cord:
1. Dura mater – Tough membrane attached to bone
or forming partitions (Dural folds) with venous
sinuses in their margins.
2. Arachnoid membrane – Thin membrane attached
to underside of the Dura.
3. Pia mater – Delicate membrane closely adherent to
the surface of the brain and spinal cord.

▪ Between the arachnoid and the pia, you have the
sub-arachnoid space where the CSF circulates.
▪ There are venous sinuses over the surface of the
brain which are occasionally penetrated by
protrusions of arachnoid membrane that allow the
reabsorption of CSF – These are arachnoid villi.

Question 18

Spinal cord structure

Answer 18

▪ The spinal cord is a column of neural tissue which is segmental.
▪ Each segment has a pair of spinal nerves attached to it.
▪ The core consists of grey matter (mainly neuronal soma).
▪ There is a wrapping around of the white matter (contains axons).
▪ The grey matter is then divided into sensory and motor areas.

NOTE: Dorsal = Towards the CNS, Ventral = Away from the CNS and Spinal Nerves = Both directions.
The spinal cord also mediates reflexes.

Question 19

Dorsal Horns

Answer 19

Sensory centres (The horn is the grey matter).
▪ Dorsal horns of the grey matter are SENSORY.
▪ The soma of the sensory axons lies in the dorsal root ganglion. The axon then continues via the dorsal root and enters the dorsal horn.
▪ The sensory information is then carried up ascending pathways in the white matter to the brain for analysis.

Question 20

Ventral Horns

Answer 20

Motor centres (The horn is the grey matter).
▪ The ventral part of the grey matter consists of motor neurones.
▪ Axons of the motor neurones go out via the ventral roots and to the muscles.

Question 21

Along sides of vertebral column?

Answer 21

Along the sides of the vertebral column, you have a series of holes called intervertebral foramina (with each of these foramina having a spinal nerve coming from them).

Question 22

Levels of vertebral column

Answer 22

▪ Cervical – C1-C7 → 7 vertebrae.
▪ Thoracic – T1-T12 → 12 vertebrae.
▪ Lumbar – L1-L5 → 5 vertebrae.
▪ Sacral – S1-S5 → 5 vertebrae (varies)

Question 23

Number of spinal nerves vs vertebrae

Answer 23

There is an equal number of nerves and vertebrae EXCEPT there is an extra nerve above C1 so there are 8 cervical nerves.

Question 24

Positioning of spinal cord vs vertebral column

Answer 24

The spinal cord is MUCH SHORTER than the vertebral column.
o This is because the spinal cord finishes growing earlier in development compared to the vertebral column.
o Cervical and thoracic segments of the spinal cord is more-or-less corresponding to the vertebral column levels.
o The lumbar and sacral spinal segments are considerably above the vertebrae where the spinal nerves come out.

Question 25

Area with no spinal cord in vertebral column

Answer 25

Lumbar cistern.

o This area contains CSF and a needle can be inserted to obtain CSF sample between L3+ L4