4.2 Organisation of the nervous system

Question 1

What does the diencephalon contain?

Answer 1

contains the thalamus and hypothalamus, pineal gland (epithalamus) and subthalamus

Question 2

Thalamus: lies superiorly; relay station for information travelling between the cerebral cortex and other parts of the CNS in both directions (injury causes __________-)

Answer 2

sensory deficits

Question 3

Hypothalamus: lies below the thalamus; regulates ________________ (controls homeostasis) + possesses connections with structures in the forebrain (controlling behaviour → directed towards self-preservation)

Answer 3

ANS and endocrine system

Question 4

What does cerebral hemispheres contain?

Answer 4

Consists of the cerebral cortex and basal ganglia:
• Basal ganglia: coordinating motor function (organise movement)
• Cerebral cortex: various functions (housekeeping to higher functions like cognition and perception)

Question 5

what is the role of the primary motor cortex?

Answer 5

Control of movement in the opposite side of the body

Question 6

what is the role of the primary somatosensory cortex?

Answer 6

Reception and analysis of sensory information from the opposite side of the body

Question 7

what is the role of the primary auditory cortex?

Answer 7

Reception and analysis of information from the ear

Question 8

what is the role of the Wernicke’s area?

Answer 8

Understanding of speech (loss results in receptive aphasia)

Question 9

what is the role of the Broca’s area?

Answer 9

Putting together (organising) speech (loss results in expressive aphasia)

Question 10

What is the role of the primary visual cortex?

Answer 10

Reception and analysis of information from the retina

Question 11

what is the role of the cerebellum?

Answer 11

Involved in coordinating motor function (receives sensory input from the part of the brain which plans movement)

Question 12

The ventricular system of the brain is a series of spaces which run through the middle (each part of the system is associated with a particular division of the brain):
• Each cerebral hemisphere contains 1 lateral ventricle (C-shaped), which both communicate with a single 3rd ventricle (receives CSF from lateral ventricles via _____________) in the ______________
• Posterior end of 3rd ventricle narrows to form the ___________ which goes through the middle of the midbrain to open into 4th ventricle (tent-shaped) extending posteriorly (opens into CSF spaces via ________________)
• Lower part of the 4th ventricle narrows to form the central canal of the spinal cord
• Pons and upper part of medulla are anterior to the 4th ventricle, while the cerebellum is posterior to the 4th ventricle

Answer 12

interventricular foramen of Monro;

middle of the diencephalon;

cerebral aqueduct;

foramina of Luschka and Magendie

Question 13

The ventricles are filled with cerebrospinal fluid (CSF) (125 – 150 mL) produced by the _________________ (found in all the ventricles) at rate of 500mL/day:
• Choroid plexus is a vascular structure which filters blood and changes the composition of the filtrate → different cellular & ionic composition from blood
• Continuously produced by the choroid plexuses and is continually circulating through the ________________ (between meninges)
o Some of the CSF continues down the 4th ventricle into the central canal, but most leave through holes in the 4th ventricle to circulate outside of the brain in the subarachnoid space
• Reabsorbed into the venous sinuses via the _______________ (at rate of 500mL/day)

The CSF serves several important functions in protection and waste management:
• Acts as a layer of cushion to protect the brain from trauma
• Removes unwanted waste products from the surface of the brain
• Distribute certain substances (e.g. hormones) to different parts of the brain

Answer 13

epithelial cells of the choroid plexuses;

ventricular system and subarachnoid space;

arachnoid villi;

Question 14

[CSF] < [blood]

Answer 14

K+, Ca2+
Glucose, amino acids
pH
Cholesterol, protein (negligible)

Question 15

[CSF] = [Blood]

Answer 15

Na+, Cl-, HCO3-

Osmolarity

Question 16

[CSF] > [Blood]

Answer 16

Mg2+

Creatinine

Question 17

Epidural space : Between the _______________

• Trauma to skull causes ____________ which is rapidly fatal

Answer 17

bone and dura mater;

arterial bleed

Question 18

Subdural space: Between the _____________ (does not contain CSF):
• Contains _________ (often tear in elderly when they fall, causing blood to accumulate in dural sinuses)

Answer 18

dura mater and arachnoid;

cerebral veins

Question 19

Subarachnoid space: Between the _______________, and contains CSF:
• CSF is reabsorbed into the venous circulation (at specialised veins/venous sinuses in the dura mater) through arachnoid villus
• Arachnoid villi push through the dura mater into the venous sinuses (hydrocephalus may result if reabsorption is blocked)

Answer 19

arachnoid and pia mater

Question 20

Strokes: some strokes (cerebrovascular accidents) may be associated with the meninges
- Epidural (extradural) haemorrhage : from damage to the _________________(e.g. fracture of the pterion or foramen spinosum) symptoms appear very quickly
o CT scan : restricted by ______________ (dura very adherent to –> convex

• Subdural haemorrhage : from damage to a bridging vein (going towards the venous sinuses) between the dura and arachnoid layers (usually weakest in the subdural space , symptoms may take hours or days (still dangerous if not treated)
  o CT scan: not restricted by cranial sutures (with midline shift ) –> concave
• Subarachnoid haemorrhage: arterial bleed into all CSF spaces following the contours of the brain (conduct lumbar puncture if unsure) –> extends into the ____________

Answer 20

middle meningeal artery ;

cranial sutures;

cerebral sulci (bright)

Question 21

The cerebrum (forebrain) consists of sulci (grooves/depressions) and gyri (ridges/elevations), and is divided into two hemispheres (each possessing four main lobes separated by various fissures) by the longitudinal fissure (filled by falx cerebri):

• Frontal lobe is separated from the parietal lobe by the _____________; temporal lobe from the frontal and parietal lobes by the ______________
• Occipital lobe from parietal and temporal lobes by _____________
• _____________ is an extension of the dura mater which separates the cerebellum from the inferior portion of the occipital lobes

Answer 21

central sulcus/fissure;

Sylvian fissure;

parieto-occipital sulcus;

Tentorium cerebelli

Question 22

What is the function of the frontal lobe?

Answer 22

Precentral gyrus (primary motor cortex) → movement
• Also involved in higher intellect, personality, mood, social conduct and language (dominant hemisphere)

Question 23

What does damage of the frontal lobes cause?

Answer 23

Diverse presentation (usually personality and behavioural changes, impaired problem solving)

Question 24

What is the function of the parietal lobes?

Answer 24

Postcentral gyrus (primary somatosensory cortex) → analysing sensory information
• Control of language and calculation (dominant hemisphere) and visuospatial functions (non-dominant hemisphere)

Question 25

What does damage of the parietal lobes cause?

Answer 25

Typically attention deficits

Question 26

What are the functions of the occipital lobes?

Answer 26

Primary visual cortex → vision

Question 27

What does damage of the occipital lobes cause?

Answer 27

Visual field defects (e.g. contralateral hemianopia)

Question 28

What are the functions of the temporal lobes?

Answer 28

Primary auditory cortex → hearing

Question 29

what does damage of the temporal lobes cause

Answer 29

Recognition deficits (agnosia) (e.g. auditory agnosia)

Question 30

What does the basal ganglia consist of?

Answer 30

various subcortical nuclei which serve as feedback mechanisms to modulate and refine cortical activity (mainly control of descending motor tracts):

Question 31

what are components of input nuclei (receive information)?

Answer 31

Caudate nucleus and putamen (neostriatum)

Question 32

what are components of intrinsic nuclei (processing information)?

Answer 32

External globus pallidus, Subthalamic nucleus, Pars compacta (substantia nigra)

Question 33

what are components of the output nuclei?

Answer 33

Internal globus pallidus, Pars reticularis (substantia nigra)

Question 34

Caudate nucleus: Ventricular C-shape and is separated from the putamen by _____________ • Receives input from cortical association areas and projects to _____________

Answer 34

descending white matter fibres (internal capsule); prefrontal areas

Question 35

Subthalmic nucleus: Lies inferior to _________ and directly superior to ______________

Answer 35

thalamus ; substantia nigra

Question 36

Substantial nigra: In the _________ (involved in coordinating motor functions)

Answer 36

midbrain

Question 37

Globus pallidus: Divided into external and internal by the ____________ • Involved in regulation of voluntary movement

Answer 37

medial medullary lamina

Question 38

Putamen: Lateral aspect of _____________(with external capsule lateral to it) • Receives input from motor and somatosensory cortex and projects back to motor areas (involved in motor loop)

Answer 38

lentiform nucleus

Question 39

Neurones are highly differentiated cells which cannot re-enter the cell cycle to proliferate, so the loss of neurones during trauma may lead to severe consequences: • Small trauma may produce disability (e.g. spinal cord injury) • Image (right): white flare (injury to the neck caused the spinal cord to become severed) → entire body below level of the lesion becomes paralysed o Includes ______________ (both ascending and descending tracts are damaged) o Situation will not improve as there is _______________ (though possible in the PNS)

Answer 39

incontinence and loss of sensation; no CNS axonal regeneration

Question 40

Cerebrovascular accidents (strokes) cause disruption of blood supply to a particular part of the brain, causing infarction: • May be due to blockage of blood vessel (occlusive stroke; 87%) or rupture of vessel (haemorrhagic stroke) • Image (right): left hemisphere appears swollen and pushes the midline to the right as the artery supplying that part (middle cerebral artery) was blocked by a clot (causing the affected regions to disintegrate and become oedematous) o Results in _______________________

Answer 40

loss of control of voluntary movement and loss of sensation on the opposite side (primary motor cortex and primary somatosensory cortex affected)

Question 41

42 | N E N T E Tumours in the intracranial cavity are a cause of neurological disorders, and about 50% are not intrinsic to the brain (secondary spread from other tumours): • Tumours rarely develop from neurones (only in children) as neurones lose ability to re-enter cell cycle after maturation • Primary tumours: _________________ • Differentiation from cerebral infarct: via history taking (rapidly developing symptoms after CVA, slowly developing symptoms after tumour)

Answer 41

gliomas (neuroglial cells) or meningiomas (meninges)

Question 42

The brain is protected to a certain extent from infections by the ____________, but certain infections (meningitis) can gain access to cranial cavity (may spread to cerebral cortex): • May be caused by viruses (serious infection but not usually fatal) or bacteria (fall in immune response → pyrexia, white cells invading tissues, so chance of death is much higher)

Answer 42

blood-brain barrier

Question 43

There are various metabolic disorders which can affect the brain (e.g. diabetes mellitus): • If too much insulin is taken, or not enough food is taken with the insulin, the patient may fall into a ____________(reduced blood glucose level) • ______________ may also result along with visual consequences

Answer 43

diabetic coma ; Peripheral neuropathies

Question 44

GENETIC DEFECTS Various genetic defects (e.g. Down’s syndrome, fragile X syndrome → cognitive problems, Huntington’s disease) may affect the development of the nervous system: • Huntington’s disease begins by affecting the _________________ • Affected areas often control movement → first signs are an abnormal pattern of movement (eventually passes to other parts of brain → fatal) • Symptoms only develop in adulthood (may already have had children → may also carry the genetic defect)

Answer 44

basal ganglia of the brain

Question 45

``` Autoimmune diseases (e.g. multiple sclerosis) may result in neurological disorders: • Causes _____________, stopping them from working properly (immunological factors are an important contributory factor) • Image (right): darker areas represent the subcortical white matter, white flares represent the areas of demyelination ```

Answer 45

demyelination of axons