Neurosciences 1+ Appendix
HC 1
General organization of the CNS and PNS
From a functional point of view, the nervous system is divided into a sensory and motor
system. The sensory system acquires and processes information from the internal and
external environments. The motor system responds to such information by generating
movements. The overlapping cells between these input and output systems are known as
the associational system, which thus mediate the most complex and misunderstood brain
functions.
From an anatomical point of view, the nervous system is divided into a central and
peripheral system. The central nervous system comprises of the brain and the spinal cord.
The peripheral nervous system exists of the rest, so all sensory ganglia and nerves, sensory
receptors, visceral motor system (innervates involuntary muscles) and the somatic motor
system (innervates voluntary muscles). The nerve cell bodies of the PNS accumulate to form
ganglia, while peripheral axons converge together to form nerves – whereby all axons are
encapsulated in myelin by Schwann cells. Regions rich in neuronal bodies are grey matter,
while the regions rich in axons are white matter; in the brain the exterior is grey, in the
spinal cord the exterior is white. Cell bodies in the grey matter can either be organized in
nuclei (local accumulation) or in cortices (sheet-like structure).
In order to understand anatomy, the anatomical orientation must be known:
- Anterior, front
- Posterior, behind
- Superior, top
- Inferior, bottom
- Rostral, nose
- Caudal, tail
- Dorsal = upper portion, brain from above or seen from the back
- Ventral = lower portion, brain from below or seen from the front
- Medial, midline
- Lateral, side
Furthermore, the coronal/frontal axis is from ear to ear, the sagittal axis from nose to back
of the head, thus dividing the two hemispheres. A horizontal, axial or transverse section
runs perpendicular to the longitudinal body axis, or parallel to the rostral-caudal axis of the
brain.
The brain, being one of the most important organs of our body, is well-protected by several
tissue layers. From superficial to deep, these include the skin, skull, dura mater, arachnoid
and pia mater. The last three are also known as the meninges. The dura mater is the most
thick and tough, lying directly beneath the skull – between the two, meningeal arteries run
to supply the brain tissues. The arachnoid has a spider-web like structure with arachnoid
trabeculae through which the cerebrospinal fluid can flow and which contains various
cerebral arteries and veins. Between the dura mater and arachnoid, there are bridging veins
which empty into venous sinuses for drainage of the brain. Beneath the arachnoid, the
thinnest epithelial-like layer, the pia mater, lies. This layer connects to the basement
membrane of glial cells of the outer brain surface. Because there are so many major arteries
and veins in the subarachnoid space, this is often a site of bleeding after trauma – giving rise
, to subdural and subarachnoid haemorrhages. The skull is particularly curved and shaped to
perfectly fit the brain with all its specific lobe structures and portions.
Functional localization of the cerebral cortex
The early brain, during embryogenesis, arises after neurulation in the form of three
swellings at the cephalic end of the neural tube. These swellings develop, loop and divide
further to become the brain, whereas the neural tube becomes the spinal cord. From rostral
to caudal, these swellings include and divide into:
- Prosencephalon
o Telencephalon, becomes cerebral cortex and nuclei
o Diencephalon, becomes (hypo)thalamus and retina
- Mesencephalon, the midbrain which becomes the superior/inferior colliculi, the red
nucleus and the substantia nigra.
- Rhombencephalon
o Metencephalon, becomes cerebellum and pons
o Myelencephalon, becomes medulla oblongata
The term brainstem disregards the embryonic origins and consists of the medulla, pons and
midbrain. As the brain starts out as a neural tube, the lumen remains in the adult brain
becoming a series of connected spaces or ventricles, filled with cerebrospinal fluid. These
ventricles, although continuous, have different names depending on the embryological
subdivisions of the CNS:
- Telencephalon = lateral ventricle
- Diencephalon = third ventricle
- Mesencephalon = cerebral aqueduct
- Met- and myelencephalon = fourth ventricle
- Spinal cord = central canal.
The cerebral hemispheres are characterized by folded cortical tissue segments, gyri, and
fissures or grooves the divide on gyrus from another, sulci. The exact composition of gyri
and sulci differs per individual, there are still some hallmarks we all share. These divide our
cerebral cortex into four lobes.
- Frontal lobe: the central and lateral sulci separate the frontal lobe from the rest.
Bordered by the central sulcus and precentral sulcus, lies the precentral gyrus in the
frontal lobe, which contains the motor cortex. Anterior to the precentral sulcus, the
superior and inferior frontal sulci run horizontally, dividing the frontal lobe into the
superior, middle and inferior frontal gyrus. At the posterior portion of the left
inferior frontal gyrus, Broca’s area resides, which is the brain area that is needed for
the physical expression of speech.
- Parietal lobe: posterior to the central sulcus, lies the parietal lobe. The inferior
border, dividing it from the temporal and occipital lobe, is comprised of the lateral
and parieto-occipital sulcus, respectively. Posterior to the central sulcus, within the
parietal lobe, runs the postcentral sulcus (giving rise to the postcentral gyrus) and
the intraparietal sulcus. The postcentral gyrus is also known as the somatosensory
cortex, thus active in body sensation. The superior and inferior parietal lobules,
derived from the division by the intraparietal sulcus, are both active in making an
image of and understanding the own body.
- Temporal lobe: this portion lies inferior to the frontal and parietal lobe, encircling
the brain stem. The deep lateral fissure separates it from the frontal and parietal
HC 1
General organization of the CNS and PNS
From a functional point of view, the nervous system is divided into a sensory and motor
system. The sensory system acquires and processes information from the internal and
external environments. The motor system responds to such information by generating
movements. The overlapping cells between these input and output systems are known as
the associational system, which thus mediate the most complex and misunderstood brain
functions.
From an anatomical point of view, the nervous system is divided into a central and
peripheral system. The central nervous system comprises of the brain and the spinal cord.
The peripheral nervous system exists of the rest, so all sensory ganglia and nerves, sensory
receptors, visceral motor system (innervates involuntary muscles) and the somatic motor
system (innervates voluntary muscles). The nerve cell bodies of the PNS accumulate to form
ganglia, while peripheral axons converge together to form nerves – whereby all axons are
encapsulated in myelin by Schwann cells. Regions rich in neuronal bodies are grey matter,
while the regions rich in axons are white matter; in the brain the exterior is grey, in the
spinal cord the exterior is white. Cell bodies in the grey matter can either be organized in
nuclei (local accumulation) or in cortices (sheet-like structure).
In order to understand anatomy, the anatomical orientation must be known:
- Anterior, front
- Posterior, behind
- Superior, top
- Inferior, bottom
- Rostral, nose
- Caudal, tail
- Dorsal = upper portion, brain from above or seen from the back
- Ventral = lower portion, brain from below or seen from the front
- Medial, midline
- Lateral, side
Furthermore, the coronal/frontal axis is from ear to ear, the sagittal axis from nose to back
of the head, thus dividing the two hemispheres. A horizontal, axial or transverse section
runs perpendicular to the longitudinal body axis, or parallel to the rostral-caudal axis of the
brain.
The brain, being one of the most important organs of our body, is well-protected by several
tissue layers. From superficial to deep, these include the skin, skull, dura mater, arachnoid
and pia mater. The last three are also known as the meninges. The dura mater is the most
thick and tough, lying directly beneath the skull – between the two, meningeal arteries run
to supply the brain tissues. The arachnoid has a spider-web like structure with arachnoid
trabeculae through which the cerebrospinal fluid can flow and which contains various
cerebral arteries and veins. Between the dura mater and arachnoid, there are bridging veins
which empty into venous sinuses for drainage of the brain. Beneath the arachnoid, the
thinnest epithelial-like layer, the pia mater, lies. This layer connects to the basement
membrane of glial cells of the outer brain surface. Because there are so many major arteries
and veins in the subarachnoid space, this is often a site of bleeding after trauma – giving rise
, to subdural and subarachnoid haemorrhages. The skull is particularly curved and shaped to
perfectly fit the brain with all its specific lobe structures and portions.
Functional localization of the cerebral cortex
The early brain, during embryogenesis, arises after neurulation in the form of three
swellings at the cephalic end of the neural tube. These swellings develop, loop and divide
further to become the brain, whereas the neural tube becomes the spinal cord. From rostral
to caudal, these swellings include and divide into:
- Prosencephalon
o Telencephalon, becomes cerebral cortex and nuclei
o Diencephalon, becomes (hypo)thalamus and retina
- Mesencephalon, the midbrain which becomes the superior/inferior colliculi, the red
nucleus and the substantia nigra.
- Rhombencephalon
o Metencephalon, becomes cerebellum and pons
o Myelencephalon, becomes medulla oblongata
The term brainstem disregards the embryonic origins and consists of the medulla, pons and
midbrain. As the brain starts out as a neural tube, the lumen remains in the adult brain
becoming a series of connected spaces or ventricles, filled with cerebrospinal fluid. These
ventricles, although continuous, have different names depending on the embryological
subdivisions of the CNS:
- Telencephalon = lateral ventricle
- Diencephalon = third ventricle
- Mesencephalon = cerebral aqueduct
- Met- and myelencephalon = fourth ventricle
- Spinal cord = central canal.
The cerebral hemispheres are characterized by folded cortical tissue segments, gyri, and
fissures or grooves the divide on gyrus from another, sulci. The exact composition of gyri
and sulci differs per individual, there are still some hallmarks we all share. These divide our
cerebral cortex into four lobes.
- Frontal lobe: the central and lateral sulci separate the frontal lobe from the rest.
Bordered by the central sulcus and precentral sulcus, lies the precentral gyrus in the
frontal lobe, which contains the motor cortex. Anterior to the precentral sulcus, the
superior and inferior frontal sulci run horizontally, dividing the frontal lobe into the
superior, middle and inferior frontal gyrus. At the posterior portion of the left
inferior frontal gyrus, Broca’s area resides, which is the brain area that is needed for
the physical expression of speech.
- Parietal lobe: posterior to the central sulcus, lies the parietal lobe. The inferior
border, dividing it from the temporal and occipital lobe, is comprised of the lateral
and parieto-occipital sulcus, respectively. Posterior to the central sulcus, within the
parietal lobe, runs the postcentral sulcus (giving rise to the postcentral gyrus) and
the intraparietal sulcus. The postcentral gyrus is also known as the somatosensory
cortex, thus active in body sensation. The superior and inferior parietal lobules,
derived from the division by the intraparietal sulcus, are both active in making an
image of and understanding the own body.
- Temporal lobe: this portion lies inferior to the frontal and parietal lobe, encircling
the brain stem. The deep lateral fissure separates it from the frontal and parietal
