LAB 1: MACRO-ANATOMY OF THE RAT BRAIN
The corpus callosum (cc) connects cortical areas between both hemispheres.
In the anterior part of the brain, the cc splits into the forceps minor (fmi) and
in the posterior part of the brain into the forceps major (fmj). So, the
uttermost posterior cortical part of the right hemisphere connects to its left
counterpart by sending its axons anterior into the right fork of the fmj, until it
reaches the cc. Then, it crosses the midline where the axon follows its route
into the left fork of the fmj in the posterior direction until it reaches its target
cortex.
The anterior commissure (AC) is a fiber bundle that
connects inferior and middle temporal gyri to the
olfactory regions across hemispheres. AC is visible
when the cc splits in the fmi.
AC is divided in anterior (aca) and posterior (acp) in the
Atlas.
The internal capsule (ic) mainly connects cortical areas with the spinal cord, where it gives rise
to the corticospinal tract.
The fimbria (fi) connects the right and left hippocampi. It gives rise to the fornix (f) anterior of
the hippocampus. The fornix fibers travel toward the mammillary bodies in the hypothalamus as
part of the learning and memory system.
1
,NB
It asked me where the cc splits into the fmi. I chose the figure where the fmi is first visible if we
start from the utmost anterior part of the brain. However, if we start from the cc and go anterior,
it splits into the fmi in Figure 13. The wording was not really clear but keep this in mind.
Ventral view of the rat brain:
2
The pyramidal tracts bring motor information to the spinal cord.
The olfactory tracts (I indicated only one of them in the picture) are also known as tractus olfactori.
,Dorsal view of the rat brain:
Sagittal view of the rat brain:
The branching out of the cerebellar white matter is called arbor vitae.
The tectum is composed of the colliculi. Below the tectum there is the tegmentum.
3
, Macro-anatomically, you can discriminate grey and white matter. The white matter consists of
fiber tracts and gets its color from the myelin sheath insulating the axons. The grey matter is pink
of fresh tissue, although it may turn beige when the brain is fixated in formaldehyde. The grey
matter consists of cell bodies, which are arranged in layers (laminae) or groups (nuclei; different
from the nuclei of individual cells).
Adjoining nuclei not separated by fiber tracts cannot be identified macroscopically (e.g., nuclei
of the thalamus).
Atlas of Sagittal view:
When dissecting, it is important to slice at the angle of 90º to midline of the brain, in order to easily locate the structures with the help of the atlas.
GROSS ANATOMY Another way to subdivide the brain is:
Diencephalon: thalamus, hypothalamus, pineal gland
Cerebrum (telencephalon)
Mesencephalon: midbrain Cerebellum
Metencephalon: cerebellum, pons Brainstem (diencephalon, mesencephalon, pons of the
metencephalon, and myelencephalon)
Myelencephalon: medulla
Telencephalon: cortex
Each of the 5 brain divisions houses a ventricle, except for the
mesencephalon which contains the mesencephalic aqueduct. The
cerebrum contains two ventricles (LV), one in each hemisphere.
These structures derive from embryonic development, The diencephalon contains the 3V, and the 4V resides within the
when the brain is composed of three vesicles: hindbrain (both mete- and myelencephalon)
Forebrain (telencephalon, diencephalon)
Midbrain (mesencephalon) 4
Hindbrain (metencephalon, myelencephalon)
The corpus callosum (cc) connects cortical areas between both hemispheres.
In the anterior part of the brain, the cc splits into the forceps minor (fmi) and
in the posterior part of the brain into the forceps major (fmj). So, the
uttermost posterior cortical part of the right hemisphere connects to its left
counterpart by sending its axons anterior into the right fork of the fmj, until it
reaches the cc. Then, it crosses the midline where the axon follows its route
into the left fork of the fmj in the posterior direction until it reaches its target
cortex.
The anterior commissure (AC) is a fiber bundle that
connects inferior and middle temporal gyri to the
olfactory regions across hemispheres. AC is visible
when the cc splits in the fmi.
AC is divided in anterior (aca) and posterior (acp) in the
Atlas.
The internal capsule (ic) mainly connects cortical areas with the spinal cord, where it gives rise
to the corticospinal tract.
The fimbria (fi) connects the right and left hippocampi. It gives rise to the fornix (f) anterior of
the hippocampus. The fornix fibers travel toward the mammillary bodies in the hypothalamus as
part of the learning and memory system.
1
,NB
It asked me where the cc splits into the fmi. I chose the figure where the fmi is first visible if we
start from the utmost anterior part of the brain. However, if we start from the cc and go anterior,
it splits into the fmi in Figure 13. The wording was not really clear but keep this in mind.
Ventral view of the rat brain:
2
The pyramidal tracts bring motor information to the spinal cord.
The olfactory tracts (I indicated only one of them in the picture) are also known as tractus olfactori.
,Dorsal view of the rat brain:
Sagittal view of the rat brain:
The branching out of the cerebellar white matter is called arbor vitae.
The tectum is composed of the colliculi. Below the tectum there is the tegmentum.
3
, Macro-anatomically, you can discriminate grey and white matter. The white matter consists of
fiber tracts and gets its color from the myelin sheath insulating the axons. The grey matter is pink
of fresh tissue, although it may turn beige when the brain is fixated in formaldehyde. The grey
matter consists of cell bodies, which are arranged in layers (laminae) or groups (nuclei; different
from the nuclei of individual cells).
Adjoining nuclei not separated by fiber tracts cannot be identified macroscopically (e.g., nuclei
of the thalamus).
Atlas of Sagittal view:
When dissecting, it is important to slice at the angle of 90º to midline of the brain, in order to easily locate the structures with the help of the atlas.
GROSS ANATOMY Another way to subdivide the brain is:
Diencephalon: thalamus, hypothalamus, pineal gland
Cerebrum (telencephalon)
Mesencephalon: midbrain Cerebellum
Metencephalon: cerebellum, pons Brainstem (diencephalon, mesencephalon, pons of the
metencephalon, and myelencephalon)
Myelencephalon: medulla
Telencephalon: cortex
Each of the 5 brain divisions houses a ventricle, except for the
mesencephalon which contains the mesencephalic aqueduct. The
cerebrum contains two ventricles (LV), one in each hemisphere.
These structures derive from embryonic development, The diencephalon contains the 3V, and the 4V resides within the
when the brain is composed of three vesicles: hindbrain (both mete- and myelencephalon)
Forebrain (telencephalon, diencephalon)
Midbrain (mesencephalon) 4
Hindbrain (metencephalon, myelencephalon)
