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MN: Basics and Anatomy Summary (MED-BMS24)
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Summary of the course MED-BMS24. This summary encompasses all the lectures from this course in the master Biomedical Sciences.
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fMN: Conceptual basics and neuroanatomyLecture 1
A neuron exists out of a soma, dendrite and axon. Synapses from other neurons go to the soma and
release neurotransmitters into the synaptic cleft. These neurotransmitters bind to receptors on the
soma, letting ions flow into the soma, inducing an action potential. the action potential is
transported through the axon towards the boutons terminal (the synapses from this neuron). This is
called the effector side, the side with dendrites and soma is called the receptive side.
The brain also exists out of glial cells which are 10x more present than neurons. They protect the
neurons:
- The microglia have a function for defense, they are a sort of macrophages.
- The astrocytes have very elongated broad end feet which they cover capillaries with.
Together with the endothelial cells they form the blood brain barrier. They decide what sort
of component can be transported from the blood into the tissue. They also produce NGF
(nerve growth factors) for repair and growth of neurons.
- The oligodendrocytes have very long extensions which they wrap around the axons forming
the myelin sheets of the neurons.
The central nervous system (CNS) consists out of the brain and spinal cord, the peripheral nervous
system (PNS) consists out of cranial nerves and spinal nerves.
The CNS are in the skull and vertebral column and have a variety of functions: perception,
movement, learning memory, personality, and many more. They are well protected in the body (skull
and vertebral column). They are surrounded by three brain membranes (meninges). They form a sac
surrounding the brain and spinal cord. Within the membranes there is cerebral spinal fluid (CSF)
which protects the brain from sudden movements.
CNS is a triptych: in the brain information is stored. In the brain you get afferent/sensory input which
goes to interneurons (99.9%) and then to efferent/motor output to give a reaction to the sensory
input.
In the brain you have gray matter on the outside, white matter on the inside. The gray matter
consists out of six layers, the white matter contains the axons which are myelinated (this gives the
white color). In the white matter there are small organs of grey matter which are called the basal
ganglia (initiation and organization of motor movements).
In the spinal cord the white matter is on the outside, the gray matter forms a butterfly form on the
inside, surrounding the canalis centralis.
The brain is divided into 5 brain vesicles based on the embryological development: you have the
telencephalon, diencephalon, mesencephalon, metencephalon and myelencephalon.
Neural development: at day 19 after fertilization the embryo consists out of two flat layers. The
upper layer (ectoderm) is folding inwards forming the neural folds. The groove is closing from day 22
like a zipper. At day 23 the groove is closed and is forming the neural tube. From this tube the whole
nervous system is derived.
Sometimes the neural tube is not closing which can lead to death of the embryo.
In the neural tube the cells in the wall are dividing very fast.
The neuroepithelial cells will go into mitosis and will form
neuroblasts, neurons, glioblasts, ependymal and radial glia
cells.
Outside of the neural tube two plates will be formed: at the
basal plate the motor neurons will be formed, at the alar plate
the sensory neurons will be formed.
,In the cerebral cortex the mitotic progenitor cells will divide and make neural cells. These neural
progenitor cells will crawl up via the radial glia cells towards their own layer (I-VI).
The neural tube within 4 weeks has four brain vesicles: prosencephalon (forebrain), mesencephalon
(midbrain), rhombencephalon (hindbrain), spinal cord.
The neural tube within 5 weeks is no longer a tube anymore. the brain vesicles divide:
prosencephalon will divide into the telencephalon (forms the hemispheres) and the diencephalon.
The cavities are forming the lateral ventricles (in telencephalon), third ventricle (in diencephalon) and
fourth ventricle (in rhombencephalon). The rhombencephalon will divide in the metencephalon and
myelencephalon.
Within 6 weeks the neural tube is bending. The telencephalon is bending backwards, covering the
diencephalon.
The telencephalon will grow the most and will eventually form the brain. In the picture below you
can see the development.
The corpus callosum, hippocampus, choroid plexus and caudate nucleus are firstly formed at the
front of the brain. They are stretched towards the back of the brain
Telencephalon: cortex exists out of 6 layers with different functions. The corpus callosum binds the
two hemispheres together with thick fiber bundles going in between. The corona radiata go inside
the brain, run between the basal ganglia and the thalamus, and go into the midbrain. When it passes
the corpus callosum, the bundle of fibers is called the internal capsule.
Thanks to DTI all the different fiber tracts can be visualized in vivo. The fibers run into the brain stem
towards the cerebellum.
, The basal ganglia are caudate nucleus, putamen, globus
pallidus (these last two together are called the lentiform
nucleus). Function is initiating and coordinating movement. In
between them runs the white matter (internal capsule). Other
structures here are the amygdala and hippocampus.
In the brain there are windings which are called gyri and
grooves which are called the sulci. In Alzheimer’s Disease the
sulci will become larger and gyri will become smaller (less
brain surface thus). In AD there is a huge loss in white matter,
but also the nerve cell bodies in the cortex. There will be a
huge loss in the hippocampus too.
In the cortex you have the somatic sensory cortex and the primary motor cortex. the sensory cortex
is smaller than the motor cortex. layer IV has afferent fibres from thalamus which means that it is
bigger in the sensory cortex. In layer V there are large pyramid cells which have motor projections to
brainstem and spinal cord which means
that it is bigger in the motor cortex.
layer VI has projections to the thalamus.
Layer I, II and III are almost the same in
both cortices. Layer I is a molecular
layer, layer II and III have a cross
integration of small pyramid cells. layer
III had longer tracks between
hemispheres.
The lobes and important sulci of the
brain can be seen in the picture.
In the frontal cortex there is the
prefrontal cortex where your
personality and motivation are located.
Just before the central sulcus is the
primary motor cortex where all the
motor information is stalled. Behind the
central sulcus is the somatosensory cortex where all
the sensory information is stored. On the back of the
brain there is the primary visual cortex. the primary
auditory cortex is situated below the central sulcus in
the temporal lobe.
Phineas Gage had a metal rod that went through his
prefrontal cortex. He survived the accident, but after a
while he became a very irresponsible person. In this
way they discovered the function of the prefrontal
cortex.
Another patient couldn’t pronounce words very well.
After his death a doctor (Broca) saw aphasia in the left
frontal cortex which is now called Broca’s area.
Damage in this area can cause aphasia (people know what to say but cannot pronounce it). This is an
example of lateralization: only the left side of the brain is altered where Broca’s area is situated.
Damage in Wernicke’s area will cause that a person can perfectly pronounce words but the
sentences don’t make sense (also present in the left hemisphere). The primary auditory cortex is
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