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Central Nervous System, drugs for theIntroduction to CNS diseases and their therapies
All mammals have a cortex that increases due to evolution. An expansion of the cortex is associated
with an increase of complexity and different distinct areas. The big difference between the brain of
the human and that of a monkey is that it is much more complex. Differences between the human
and the primates brain is the language and communication. The bottom of the brain in the back of
the head is called the cerebellum, then the occipital lobe and the parietal lobe as you progress to the
top of the head. From the back of the head to the front of the head, a section is called transverse
section and from the top of the head to the bottom of the head is called a frontal section.
The brain can have different body planes, this can be radial symmetry or bilateral symmetry. Sensory
nerves will cause integration in the brain and will stimulate motor neurons to perform an action
depending on the signals received by the sensory nerves.
In the brain there are specific parts, the closer the parts of the brain
are to the spinal cord the more important they are for the basic
fundamental functions like circulation, digestion and breathing. The
forebrain is for example more important for decision making. During
development of the human the forebrain will become large.
From the spinal cord the medulla oblongata and the pons will follow,
then the cerebellum and the cerebrum which is divided in four
different lobes. The frontal lobe, parietal lobe, the occipital lobe and
the temporal lobe. The frontal lobe is important for decision making
and is the
executive part of the brain. The parietal lobe is
important for sensory function and
interpretation. The occipital lobe important for
vision, this part of the brain makes sense of
what you see. The temporal lobe is for hearing
and memory, in the temporal lobe the
hippocampus is located. The hippocampus is
very important for learning and memory, this
moment of learning is called acquisition,
the saving of the learning is called consolidation
and the memorizing of what is learned
is called retrieval. This is short term
memory when you use your long time memory
you use both the hippocampus and the temporal
lobe.
The parietal cortex has the somatosensory cortex which has all the integration of the sensory part.
The motor cortex is more in the frontal part of the cortex. The sensory nerves get the signal from
outside and transfer the information to the parietal lobe where the somatosensory cortex will
transform the information. The information will then go to the frontal cortex where the motor cortex
will send a signal to the motor nerves causing a reaction to the incoming sensory signal.
,The brainstem has three different parts, the medulla oblongata
which is at the bottom of the brainstem, the pons which is in
the middle of the brainstem and the midbrain is the top part of
the brainstem. The brainstem has 2 main functions, their basic
functions that you do not need to think about and the filtering
and routing of the information that comes from the sensory
and motor nerves.
The cerebellum controls the voluntary movements it is
important for the motor coordination and for the motor
memory. The right part of the cerebellum communicates with
the right part of the spinal cord however, the right part of the cerebellum communicates with the left
part of the cerebral cortex. The right part of the spinal cord is important for the posture and gait.
The thalamus has an important role in sorting the data. The
hypothalamus is important in thermoregulation and the
pituitary gland is important in hormonal activity like the
water balance and oxytocin production.
The cerebrum contains a lot of fibers and is important for
integration of all information, it helps to make sense of all
incoming information and will help you to act accordingly.
This can be measured by using MRI, this technique is used
to obtain high resolution images of the anatomy of the
brain. This is used to determine the thickness of the cortex
and determine the grey and white matter. This technique
enables the measurement for the thickness of the grey matter. This particular matter is important
because here the cell bodies of the neurons are located. During the degeneration a lot of cells die
and the thickness of the grey matter decreases.
Brain activity rapidly decreases when a person has had a stroke. The brain activity of the man and of
the women are different.
DTI allows the tracking of movement of water in the brain. This is normally used to evaluate the
integrity of the white matter, which is formed by myelinated axons. This allows the communication
of different brain areas. Cortical final track is an important part of the white matter, it allows a signal
to be send to mast cells and control the movement of it.
Cerebral cortex consists of five parts and is a six-layered sheet. In total it covers threequarters of the
brain and is essential for consciousness. Frontal cortex is about 50% of the cerebral cortex, the
parietal cortex is for somatosensory, the occipital cortex is for the vision, the temporal cortex is for
the smell and the insular cortex is for taste, visceral and feelings. The cerebral cortex is where the
consciousness happens and where executive functions happen.
The corpus collosum connects the right and the left hemisphere. The right
hemisphere is important for facial recognition and the left hemisphere is for
reasoning and logic.
The Broca, Geschwind and Wernicke neocortical areas, during evolution both
hemispheres share a long direct segment which connects all three areas. These
,areas are of importance in the language. Broca area produces the language and Wernicke area
understands the language.
Basal ganglia is for the involuntary movements. The diseases
huntington and parkinson have dysfunction in the basal area. Basal
ganlia is composed of caudate (in blue), the putamen (in red) and the
internal capsule (in between these) and they form stiatum. In the
frontal part of the caudate there is an important part called the
nucleus acumbens, this is activated for reward, pleasure and
addiction.
The midbrain is part of the brainstem and its function is dopamine
production. The dopaminergic neurons are located in the area and
are called substantia nigra. In parkinson disease the dopaminergic
neurons are dying. The cell body in the substantia nigra communicates with the striatum, this is
called the nigrostriatal pathway. The mesolimbic pathway is communicating with the limbic system.
The mesocortical pathway the neurons communicate with the cortical area. The tubero-hypophyseal
pathway communicate with the hypothalamus and the pituitary gland.
The substantia nigra is functional when it is black.
In parkinsons disease the black area is reduced and
becomes more white.
The hippocampus has an organised structure, it is
located in the temporal lobe. In Alzheimers disease
the hippocampus is much smaller and there are
bigger ventricles. When an ischemia takes place the CA1 area in the hippocampus is very largely
affected.
Primary forebrain regulates two essential forces necessary for survival of the individual and species.
The motivation to obtain food, water, warmth (reward driven) and comfort and the motivation to
escape from threat, heat and cold (misery driven). These very ancient mechanisms regulate
behaviour.
The secondary forebrain regulates the intensity of reward driven behaviour, anhedonia (a lack of
pleasure) or the intensity of distress avoiding behaviour, dysphoria (feeling unhappy). These two
consequences are caused by the nucleus acumbens. The secondary brain thus deals with the
intensity of the behaviour types.
The tertiary forebrain regulates the behaviour linked to the thalamic areas. The tertiary brain is
linked to consciousness, perception and language. It is linked to the inhibition of emotional response.
To execute of voluntary response and to control motor response. The tertiary forebrain contains the
cerebral cortex and the dorsal extrapyramidal system.
The human brain weights about 1.5 kg and it is the
largest compared to its body size.
Dorsal versus ventral functions, the dorsal is the top of
the brain and the ventral is the bottom of the brain. The
dorsal route has afferent neurons and the ventral root
has the efferent neurons. the posterior part of the brain
normally receives the input and the anterior part of the
, brain is sending the output. The dorsal spinal cord and posterior cerebral cortex have afferent
sensory root of spinal nerve, ascending tracts of spinal cord and cerebral processing of sensory input.
The ventral spinal cord and anterior cerebral cortex have the efferent motor root of spinal nerve,
have preganglionic autonomic nervous system, descending tracts of spinal cord and cerebral
generation of behavioural output.
Lower versus higher functions, within the spinal cord specific motor and autonomic control centres
are the central motor pattern generator and the spinal micturition centre. The brainstem controls
and coordinates the autonomic regulation. The cerebellum controls and coordinates movements and
the forebrain controls the complex emotional response, rational behaviour and generates mind
activity and speech.
Cortical versus subcortical function, the cerebral cortex and thalamus process sensory input,
perception, planning and executing rational behaviour and inhibit complex emotional responses. The
subcortex is the extrapyramidal control of rational behaviour and intensity of motor function, this
generates complex emotional responses and causes recognition and memory formation.
Voluntary motor behaviour is initiated by the frontal cerebral cortex, it can be adapted by the
cerebellum (coordinates different movements) and the basal ganglia (coordinates different
contractions). In the frontal cortex there is a lot of glutamate receptors which are responsible for the
initiation for the motor output. In the cerebellum there is the inhibitory neurotransmitter GABA
which will coordinate different movements. In the basal ganglia there is the neurotransmitter
dopamine which coordinates contractions.
The extrapyramidal system, contains specific circuits which starts and ends in the cerebral cortex.
The autonomic nervous system will provide the subconscious and involuntary movements. The
somatic nervous system are the conscious and voluntary movements.
The brain is protected by the skin, bones like the parietal bone covering the parietal lobe. Cranial
meninges are specific membranes such as, dura mater, arachnoid and pia mater. The blood is
supplied to the brain via the arteries which will vascularise the brain. In the case of ischemia or stroke
the blood clot can go to the middle cerebral artery and then the blood supply to that area is
insufficient causing the part of the brain to die. The blood brain barrier has tight junctions between
the blood vessel endothelial cells that limit the flow of substances into the brain.
The blood brain barrier is constituent by the
endothelial cells surrounded by basal lamina
and astrocytes, these communicate directly
with the neurons. Microglia are close to the
astrocyte which can be responsible for
inflammatory processes. The blood brain
barrier is very selective, a lot of substances are
not able to penetrate because of the
selectivity.
Astrocytes are the main component of the
brain tissue. They surround the brain vessels
and carry neurons and vessels. They produce a lot of neurotrophic factors and are neurochemically
competent.
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