Basics and anatomy lectures
Lecture 1 – 5th of September 2022
Anatomy of the Central Nervous System
There are around 100 billion neurons in the brain. Each
neuron is connected to 1000 - 200.000 other neurons.
15000 synapses /neuron.
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. Chemical information is translated to
an electric signal, which is the 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.
Synaptic transmission via:
◦ Receptive: receives information from other
neurons on their dendrites + soma.
◦ Conducting: axons can conduct information
via action potentials.
◦ Effector: releases signal transduction via
neurotransmitters (= chemical messengers) which happens on the axon terminal via bouton terminal
synapse.
The brain also exists out of glial cells which are 10x more present than neurons. Glial cells protect the neurons:
◦ The microglia have a function for defence, they are a sort of macrophages acting as the first and main
form of active immune defence in the central nervous system (CNS). Located throughout the brain and
spinal cord. They are small cells with longer extensions.
◦ The astrocytes have very elongated broad end feet which they cover capillaries with. Together with the
endothelial cells they form the blood brain barrier (BBB). They decide which components can be
transported from the blood in- and out of the tissue (blocking entrance of toxic substances into the
brain). They also produce NGF (nerve growth factors) for repair and growth of neurons. They provide
nutrients and other substances to neurons, regulate the concentrations of ions and chemicals in the
extracellular fluid, and provide structural support for synapses.
◦ The oligodendrocytes have very long extensions which they wrap around the axons forming the myelin
sheets of the neurons.
,The nervous system has two main parts: a central nervous system (CNS) and a
peripheral nervous system (PNS). The CNS consists out of the brain and spinal cord,
the PNS consists out of cranial nerves and spinal nerves that branch off from the
spinal cord and extend to all parts of the body.
Cranial nerves: There are 12 pairs of nerves that connect directly to your brain, and
11 of them are part of your peripheral nervous system (the second cranial nerve,
which controls your vision, is part of your central nervous system). These 11 nerves
are part of your senses of smell, sound, taste, and the sense of touch you have in
the skin on your head, face and neck. One of the 11, the vagus nerve, extends down
and attaches to all vital organs from your neck to your colon.
Spinal nerves: These are 31 pairs of nerves that attach to your spine at about the
same level as each segment bone (vertebra) in your spine.
The CNS are in the skull and vertebral column and have a variety of functions:
perception, movement, learning memory, personality, emotional behaviour, consciousness and language. 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%) (schakelneuronen) and then to
efferent/motor output to give a reaction to the sensory input.
Your nerves consist of bundles of nerve cells, which have long, arm-like extensions called axons. The nerve cells
and their axons twist and intertwine together to form nerve fibres. Some of the nerves in that bundle carry
information into your brain, while others carry information out of your brain.
Sensory: These nerves carry information to your brain and spinal cord. They either connect directly to your brain
through your cranial nerves or carry information to your spinal nerves, which then feed into your spinal cord.
The sensory nerve connections to your spinal cord are on the back of your spinal cord.
Motor: These nerves carry command signals from your brain to various parts of your body. They only carry
information away from your brain. The motor nerve connections are on the front of your spinal cord; meaning,
these nerves are for sending muscle movement commands only.
Autonomic: These nerves control the automatic functions of the organs and systems in your body. Your
autonomic nerves often involve mixed nerve fibres, some of which carry commands from your brain to their
destination, and others that carry information about an organ’s function back to your brain.
The brain is protected by the bones of the skull and by a covering of three thin membranes called meninges. The
brain is also cushioned (buffered) and protected by cerebrospinal fluid (CSF). This watery fluid is produced by
special cells in the four hollow spaces in the brain, called ventricles. The delicate inner layer is the pia mater. The
middle layer is the arachnoid, a web-like structure filled with fluid that cushions the brain. The tough outer layer
is called the dura mater.
Arachnoid granulations are small protrusions of the arachnoid mater (the thin 2nd layer covering the brain) into
the outer membrane of the dura mater (the thick outer layer). They protrude into the dural venous sinuses of
the brain, and allow cerebrospinal fluid (CSF) to exit the subarachnoid space and enter the blood stream.
, In neuroanatomy, a nucleus (plural form: nuclei) is a cluster of neurons in
the central nervous system, located deep within the cerebral hemispheres
and brainstem.
In the brain you have grey matter on the outside, white matter on the
inside. The grey matter consists out of six layers, the white matter contains
the axons which are myelinated (this gives the white colour). 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
and contains ascending as well as descending fibre tracts. The grey
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:
◦ Telencephalon
◦ Diencephalon
◦ Mesencephalon
◦ Metencephalon
◦ Myelencephalon
+ spinal cord (medulla spinalis)
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 there are problems with closing the neural tube (= spina
bifida). When the neural tube is not closing on the place where the brain is developing, it
can lead to death of the embryo. In the neural tube the cells in the wall are dividing very
fast (~2 million cells/hour). The neuroepithelial cells will go into mitosis and will form
neuroblasts, neurons, glioblasts, ependymal and radial glia cells. Outside of the neural
tube (dorsal (= upper) part of spinal cord) 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 (forming the hemispheres) and the diencephalon. The cavities are forming the lateral
