Neuroanatomy
An introduction to the neuroanatomy of the brain
The brain hemispheres
• Oval-shaped mass built up out of fatty proteins
• Asymmetrical
• Inter-hemispheric fissure
Body is controlled contralateral
In 10% percent it is Ipsilateral (due to neuroanatomy of upper and
lower limbs)
• Hemispheres are assymetrical → left is more developed → greater volume
• Separated by interhemispheric fissure
Hemispheres consist of :
→ GREY matter (cortex, basal ganglia= deep in the hemisphere (black white picture)) :
Numerous neuronal cell bodies, dendrites, many unmyelinated and few myelinated axons, glial cells,
synapses, and capillaries.
→ WHITE matter (subcortical areas) : (collored white on the MRI)
Areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called
tracts (e.g., corticospinal tract, corticobulbar tract, pyramidal tract, ...).
Neurons : basic (functional and structural) units of our nervous system.
→ they form a circuit → connected to from long fibers since they are all connected
→ neurons transmit information from one part to the other part and to the body
→ they appear in white because of mylean sheat → they enable the information to be transferred
much faster
,- Electrically excitable cells that communicate with other cells via specialized connections called
synapses. –
White appearance of the axon: myelin sheaths enhances the electrical signal of the neuron that
moves from the cell body towards the axon → hishways of the brain
terminal synapses. (so info transformation is much faster)
• Axons without myelin sheath: signal travels at 1 m / sec
• Myelinated axons: signal travels at 80 to 140 m / sec
Axons: the white matter or “the brain’s highways”
• The axons are critical to the information transfer as they guide information from one place to
another.
• Combined neuronal bundles are also referred to as fiber tracts. (transformation within the same
hemisphere)
• We distinguish between efferent (motor) and afferent (sensory) tracts,
e.g.:
• Projection tracts (e.g., corticospinal tract vs. corticobulbar tract);
• Association tracts within a single hemisphere (e.g., arcuate fasciculus);
• Commissural tracts connecting both hemispheres with each other (e.g., corpus callosum).
→ so brain hemispheres can communicate with each other
→ they may be efferent
→ afferent → coming from the body to the brain
Motor neurons :
• An important type of neuron is the motor neuron. The cell body can be
found in the motor cortex, brainstem, or spinal cord.
• There are two types of motor neurons:
• Upper motor neuron (UMN) (connects brain cortect with the spinal
cord)
• Lower motor neuron (LMN) (connects nerve cell with the peripheral
musculature)
• UMNs communicate signal to LMNs via their axons.
• Axons of LMNs send information from the spinal cord to effectors
(muscles).
(picture of tractography → showing connections → fibers tracts)
,Hemispheres consist of :
GREY matter (cortex, basal ganglia) :
Numerous neuronal cell bodies, dendrites, many unmyelinated and few myelinated axons, glial cells,
synapses, and capillaries.
WHITE matter (subcortical areas) :
Areas of the central nervous system (CNS) that are mainly
made up of myelinated axons, also called tracts (e.g.,
pyramidal tract).
Pyramidal tract includes both the :
• Corticobulbar tract : a white matter motor pathway
connecting the brain’s motor cortex to the medullary
pyramids, which are part of the brainstem's medulla
oblongata (also called "bulbar")
region.
→ contains the cranial nerves
• Corticospinal tract
Pyramidal tract includes both the :
• Corticobulbar tract
• Corticospinal tract : a white matter motor pathway starting at the
cerebral cortex that terminates on lower motor neurons in the
spinal cord.
• The corticobulbar and corticospinal tracts constitute the
pyramidal tracts, and are involved in the control of motor functions
of the body.
• The “pyramidal” tracts : because they pass through the pyramids
of the medulla oblongata.
• The (medullary) pyramids are paired white matter structures of
the brainstem's medulla oblongata that contain motor fibers of the
corticospinal and corticobulbar tracts. The lower limit of the
pyramids is marked when the fibers cross (decussate).
Majority of all fibers are crossing, and 10 precent remain uncrossed
, Pyramidal decussation:
• About 90% of pyramidal fibers decussate (cross over) in the brainstem, 10% remain uncrossed (or
ipsilateral).
The pyramidal system:
Consists of a chain of two motor neurons :
• upper motor neuron (UMN or central motor neuron) = corticobulbar tract
and corticospinal tract;
>> when lesioned, causes a contralateral paralysis with spasticity + increased
reflex + increased muscular tone (hypertonia).
→ when damaged there will be a paraylsis of the body → controlateral to the
location of the lesion, because of the crossing over at the level of the brain
stem, (increased spaticity, increased musculare tone → very difficult for a
physiotherapist to have the paralysed part of the body to move )
(first motor neuron)
- Increased spaticity And reflexes
• lower motor neuron (LMN or peripheralmotor neuron) = acts as a link between upper motor
neurons and muscles;
>> when lesioned, causes a peripheral paralysis with flaccidity + hyporeflexia + decreased muscular
tone (hypotonia) + muscle atrophy + fasciculations.
→ paralysis in the lmn = flaccid → very easy to have a paralysed part of the body to move, because no
spaticity that hinders the movement (second pheripheral motor neuron)
• Motor neuron lesions lead to a typical set of symptoms.
• Based on the symptoms, it is possible to identify damage to the UMN or LMN.
* Muscle twitch; a small, local, involuntary muscle contraction and relaxation which may be visible under the
skin. (the result of degeneration of the nerve pathways)
** A decrease in the mass of the muscle; it can be a partial or complete wasting away of muscle. (wasting away
of muscle → volume is getting down)
Subsystem of the nervous system that is damaged can be seen
An introduction to the neuroanatomy of the brain
The brain hemispheres
• Oval-shaped mass built up out of fatty proteins
• Asymmetrical
• Inter-hemispheric fissure
Body is controlled contralateral
In 10% percent it is Ipsilateral (due to neuroanatomy of upper and
lower limbs)
• Hemispheres are assymetrical → left is more developed → greater volume
• Separated by interhemispheric fissure
Hemispheres consist of :
→ GREY matter (cortex, basal ganglia= deep in the hemisphere (black white picture)) :
Numerous neuronal cell bodies, dendrites, many unmyelinated and few myelinated axons, glial cells,
synapses, and capillaries.
→ WHITE matter (subcortical areas) : (collored white on the MRI)
Areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called
tracts (e.g., corticospinal tract, corticobulbar tract, pyramidal tract, ...).
Neurons : basic (functional and structural) units of our nervous system.
→ they form a circuit → connected to from long fibers since they are all connected
→ neurons transmit information from one part to the other part and to the body
→ they appear in white because of mylean sheat → they enable the information to be transferred
much faster
,- Electrically excitable cells that communicate with other cells via specialized connections called
synapses. –
White appearance of the axon: myelin sheaths enhances the electrical signal of the neuron that
moves from the cell body towards the axon → hishways of the brain
terminal synapses. (so info transformation is much faster)
• Axons without myelin sheath: signal travels at 1 m / sec
• Myelinated axons: signal travels at 80 to 140 m / sec
Axons: the white matter or “the brain’s highways”
• The axons are critical to the information transfer as they guide information from one place to
another.
• Combined neuronal bundles are also referred to as fiber tracts. (transformation within the same
hemisphere)
• We distinguish between efferent (motor) and afferent (sensory) tracts,
e.g.:
• Projection tracts (e.g., corticospinal tract vs. corticobulbar tract);
• Association tracts within a single hemisphere (e.g., arcuate fasciculus);
• Commissural tracts connecting both hemispheres with each other (e.g., corpus callosum).
→ so brain hemispheres can communicate with each other
→ they may be efferent
→ afferent → coming from the body to the brain
Motor neurons :
• An important type of neuron is the motor neuron. The cell body can be
found in the motor cortex, brainstem, or spinal cord.
• There are two types of motor neurons:
• Upper motor neuron (UMN) (connects brain cortect with the spinal
cord)
• Lower motor neuron (LMN) (connects nerve cell with the peripheral
musculature)
• UMNs communicate signal to LMNs via their axons.
• Axons of LMNs send information from the spinal cord to effectors
(muscles).
(picture of tractography → showing connections → fibers tracts)
,Hemispheres consist of :
GREY matter (cortex, basal ganglia) :
Numerous neuronal cell bodies, dendrites, many unmyelinated and few myelinated axons, glial cells,
synapses, and capillaries.
WHITE matter (subcortical areas) :
Areas of the central nervous system (CNS) that are mainly
made up of myelinated axons, also called tracts (e.g.,
pyramidal tract).
Pyramidal tract includes both the :
• Corticobulbar tract : a white matter motor pathway
connecting the brain’s motor cortex to the medullary
pyramids, which are part of the brainstem's medulla
oblongata (also called "bulbar")
region.
→ contains the cranial nerves
• Corticospinal tract
Pyramidal tract includes both the :
• Corticobulbar tract
• Corticospinal tract : a white matter motor pathway starting at the
cerebral cortex that terminates on lower motor neurons in the
spinal cord.
• The corticobulbar and corticospinal tracts constitute the
pyramidal tracts, and are involved in the control of motor functions
of the body.
• The “pyramidal” tracts : because they pass through the pyramids
of the medulla oblongata.
• The (medullary) pyramids are paired white matter structures of
the brainstem's medulla oblongata that contain motor fibers of the
corticospinal and corticobulbar tracts. The lower limit of the
pyramids is marked when the fibers cross (decussate).
Majority of all fibers are crossing, and 10 precent remain uncrossed
, Pyramidal decussation:
• About 90% of pyramidal fibers decussate (cross over) in the brainstem, 10% remain uncrossed (or
ipsilateral).
The pyramidal system:
Consists of a chain of two motor neurons :
• upper motor neuron (UMN or central motor neuron) = corticobulbar tract
and corticospinal tract;
>> when lesioned, causes a contralateral paralysis with spasticity + increased
reflex + increased muscular tone (hypertonia).
→ when damaged there will be a paraylsis of the body → controlateral to the
location of the lesion, because of the crossing over at the level of the brain
stem, (increased spaticity, increased musculare tone → very difficult for a
physiotherapist to have the paralysed part of the body to move )
(first motor neuron)
- Increased spaticity And reflexes
• lower motor neuron (LMN or peripheralmotor neuron) = acts as a link between upper motor
neurons and muscles;
>> when lesioned, causes a peripheral paralysis with flaccidity + hyporeflexia + decreased muscular
tone (hypotonia) + muscle atrophy + fasciculations.
→ paralysis in the lmn = flaccid → very easy to have a paralysed part of the body to move, because no
spaticity that hinders the movement (second pheripheral motor neuron)
• Motor neuron lesions lead to a typical set of symptoms.
• Based on the symptoms, it is possible to identify damage to the UMN or LMN.
* Muscle twitch; a small, local, involuntary muscle contraction and relaxation which may be visible under the
skin. (the result of degeneration of the nerve pathways)
** A decrease in the mass of the muscle; it can be a partial or complete wasting away of muscle. (wasting away
of muscle → volume is getting down)
Subsystem of the nervous system that is damaged can be seen
