4.2 Organisation of the nervous system Flashcards
What does the diencephalon contain?
contains the thalamus and hypothalamus, pineal gland (epithalamus) and subthalamus
Thalamus: lies superiorly; relay station for information travelling between the cerebral cortex and other parts of the CNS in both directions (injury causes __________-)
sensory deficits
Hypothalamus: lies below the thalamus; regulates ________________ (controls homeostasis) + possesses connections with structures in the forebrain (controlling behaviour → directed towards self-preservation)
ANS and endocrine system
What does cerebral hemispheres contain?
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)
what is the role of the primary motor cortex?
Control of movement in the opposite side of the body
what is the role of the primary somatosensory cortex?
Reception and analysis of sensory information from the opposite side of the body
what is the role of the primary auditory cortex?
Reception and analysis of information from the ear
what is the role of the Wernicke’s area?
Understanding of speech (loss results in receptive aphasia)
what is the role of the Broca’s area?
Putting together (organising) speech (loss results in expressive aphasia)
What is the role of the primary visual cortex?
Reception and analysis of information from the retina
what is the role of the cerebellum?
Involved in coordinating motor function (receives sensory input from the part of the brain which plans movement)
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
interventricular foramen of Monro;
middle of the diencephalon;
cerebral aqueduct;
foramina of Luschka and Magendie
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
epithelial cells of the choroid plexuses;
ventricular system and subarachnoid space;
arachnoid villi;
[CSF] < [blood]
K+, Ca2+
Glucose, amino acids
pH
Cholesterol, protein (negligible)
[CSF] = [Blood]
Na+, Cl-, HCO3-
Osmolarity
[CSF] > [Blood]
Mg2+
Creatinine
Epidural space : Between the _______________
• Trauma to skull causes ____________ which is rapidly fatal
bone and dura mater;
arterial bleed
Subdural space: Between the _____________ (does not contain CSF):
• Contains _________ (often tear in elderly when they fall, causing blood to accumulate in dural sinuses)
dura mater and arachnoid;
cerebral veins
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)
arachnoid and pia mater
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 ____________
middle meningeal artery ;
cranial sutures;
cerebral sulci (bright)
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
central sulcus/fissure;
Sylvian fissure;
parieto-occipital sulcus;
Tentorium cerebelli
What is the function of the frontal lobe?
Precentral gyrus (primary motor cortex) → movement • Also involved in higher intellect, personality, mood, social conduct and language (dominant hemisphere)
What does damage of the frontal lobes cause?
Diverse presentation (usually personality and behavioural changes, impaired problem solving)
What is the function of the parietal lobes?
Postcentral gyrus (primary somatosensory cortex) → analysing sensory information • Control of language and calculation (dominant hemisphere) and visuospatial functions (non-dominant hemisphere)
What does damage of the parietal lobes cause?
Typically attention deficits
What are the functions of the occipital lobes?
Primary visual cortex → vision
What does damage of the occipital lobes cause?
Visual field defects (e.g. contralateral hemianopia)
What are the functions of the temporal lobes?
Primary auditory cortex → hearing
what does damage of the temporal lobes cause
Recognition deficits (agnosia) (e.g. auditory agnosia)
What does the basal ganglia consist of?
various subcortical nuclei which serve as feedback mechanisms to modulate and refine cortical activity (mainly control of descending motor tracts):
what are components of input nuclei (receive information)?
Caudate nucleus and putamen (neostriatum)
what are components of intrinsic nuclei (processing information)?
External globus pallidus, Subthalamic nucleus, Pars compacta (substantia nigra)
what are components of the output nuclei?
Internal globus pallidus, Pars reticularis (substantia nigra)
Caudate nucleus: Ventricular C-shape and is separated from the putamen by _____________
• Receives input from cortical association areas and projects to _____________
descending white matter fibres (internal capsule);
prefrontal areas
Subthalmic nucleus: Lies inferior to _________ and directly superior to ______________
thalamus ;
substantia nigra
Substantial nigra: In the _________ (involved in coordinating motor functions)
midbrain
Globus pallidus: Divided into external and internal by the ____________
• Involved in regulation of voluntary movement
medial medullary lamina
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)
lentiform nucleus
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)
incontinence and loss of sensation;
no CNS axonal regeneration
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 _______________________
loss of control of voluntary movement and loss of sensation on the opposite side (primary motor cortex and primary somatosensory cortex affected)
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)
gliomas (neuroglial cells) or meningiomas (meninges)
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)
blood-brain barrier
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
diabetic coma ;
Peripheral neuropathies
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)
basal ganglia of the brain
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
demyelination of axons
