Lecture 4: actual lecture Flashcards
SPINAL CORD EXTENT
BASE OF SKULL - Continuous With The Medulla Of The Brain
2nd – 3rd Lumbar Vertebrae
DISTAL END OF THE SPINAL CORD
Nerve Roots that emerge at levels below L2 extend beyond the conus medullaris to reach their exit. This forms fine filaments distal to end of the spinal cord that is called the CAUDA EQUINA.
Conus Medullaris is at level of L2-L3. However, rootlets continue to emerge and descend to exit vertebral canal at appropriate level. Therefore, CSF must still be present below the end of the spinal cord.
Whereas the spinal cord ends at L2-L3, the meninges continue inferiorly to end by attaching to the coccyx. The dura and arachnoid remain as a visible dense sheath. The pia continues beyond the end of the cord as the filum terminale.
FILUM TERMINALE
Extension of pia mater that extends beyond the distal end of the spinal cord (the conus medullaris).
All 3 layers of the meninges fuse in the sacral area to form the coccygeal ligament that anchors the cord to the coccys.
Dura and Arachnoid fuse
around S2 where they are joined by filum terminale
COCCYGEAL LIGAMENT =
FILUM TERMINALE (PIA) + FILUM OF DURA
TELENCEPHALON
FOREBRAIN
Cerebral cortex and subcortical nuclei (e.g., Basal Ganglia).
The largest part of the brain is the telencehalon or forebrain. It consists of the massive cerebral cortex and several nuclei that are buried deep within the telencephalon. These are referred to as subcortical nuclei.
PONS
Latin for “BRIDGE”
Enlargement Rostral to medulla
PONS
Latin for “BRIDGE,” as it has the appearance of planks as on a wooden bridge.
Enlargement Rostral to medulla
MEDULLA
Latin for “Having an oblong shape”
“in the center”
Direct Rostral extension of the Spinal cord
cerebellum
means “little brain”.
neural structure located dorsal to the medulla and pons
EXTERNAL FEATURES OF VENTRAL MEDULLA
On the brainstem there are various “bumps” caused by the presence of underlying nuclei or fiber tracts.
On the ventral surface of the medulla, there is a midline slit called the Anterior Median Fissure.
Immediately adjacent to the anterior median fissure are 2 elevations called the Pyramids because of their shape. They are widest at the junction of the pons and medulla and they taper at the junction of the medulla and spinal cord.
Near this latter junction, the anterior median fissure becomes somewhat obscured due to the fact that axons descending in the pyramids cross from one side to the other forming a decussation or crossing.
Immediately lateral to the pyramids is another depression called the Preolivary Sulcus. This is not as deep as the anterior median fissure.
Continuing laterally, the next small round bump is called the Olivary Eminence. This structure is located around the mid-medullary level.
Lateral to the olivary eminence is another depression called the Post-Olivary Sulcus.
These structures serve as landmarks for several nerves that arise from the brainstem to innervate structures in the head. These are collectively referred to as cranial nerves.
CRANIAL NERVES RELATED TO MEDULLA
Cranial nerves innervate structures in the head. There are a total of 12 pairs of cranial nerves. These nerves are given Roman numerals as well as a name.
In the medulla, we find 6 of the 12 cranial nerves.
Cranial Nerve XII – Hypoglossal
This is the only cranial nerve located in the preolivary sulcus.
Cranial nerve XI – Accessory.
This nerve arises from the upper segments of the cervical spinal, enters the skull through a large opening at the base called the Foramen Magnum, and is joined by a few branches arising from the medulla.
Cranial nerve X – Vagus
Vagis located at the caudal end of the post-olivary sulcus.
Cranial nerve IX – Glossopharyngeal is also located in the post-olivary sulcus.
Cranial nerve VIII – Vestibulocochlear arises from the lateral aspect of the brainstem at the junction of the medulla and pons.
Cranial nerve VII – Facial
Arises at the same level as Cranial nerve VIII, just a bit more rostral.
Cranial nerve VI – Abducens
Located on either side of midline at the junction of the pons and medulla.
CRANIAL NERVES RELATED TO MEDULLA
Cranial nerves innervate structures in the head. There are a total of 12 pairs of cranial nerves. These nerves are given Roman numerals as well as a name.
In the medulla, we find 6 of the 12 cranial nerves.
Cranial Nerve XII – Hypoglossal
This is the only cranial nerve located in the preolivary sulcus.
Cranial nerve XI – Accessory.
This nerve arises from the upper segments of the cervical spinal, enters the skull through a large opening at the base called the Foramen Magnum, and is joined by a few branches arising from the medulla.
Cranial nerve X – Vagus
Vagis located at the caudal end of the post-olivary sulcus.
Cranial nerve IX – Glossopharyngeal is also located in the post-olivary sulcus.
Cranial nerve VIII – Vestibulocochlear arises from the lateral aspect of the brainstem at the junction of the medulla and pons.
Cranial nerve VII – Facial
Arises at the same level as Cranial nerve VIII, just a bit more rostral.
Cranial nerve VI – Abducens
Located on either side of midline at the junction of the pons and medulla.
Cranial Nerve XII
Hypoglossal
This is the only cranial nerve located in the preolivary sulcus.
Cranial nerve XI
Accessory.
This nerve arises from the upper segments of the cervical spinal, enters the skull through a large opening at the base called the Foramen Magnum, and is joined by a few branches arising from the medulla.
Cranial nerve X
Vagus
Vagis located at the caudal end of the post-olivary sulcus.
Cranial nerve IX
Glossopharyngeal
Also located in the post-olivary sulcus.
Cranial nerve VIII
Vestibulocochlear
Arises from the lateral aspect of the brainstem at the junction of the medulla and pons.
Cranial nerve VII
Facial
Arises at the same level as Cranial nerve VIII, just a bit more rostral.
Cranial nerve VI –
Abducens
Located on either side of midline at the junction of the pons and medulla
the dorsal aspect of the medulla.
The large space on the dorsal surface of the medulla is the 4th ventricle. This is filled with cerebral spinal fluid (CSF).
The distal end of the 4th ventricle is called the obex. It serves as an important landmark for several structures in the caudal vs. the rostral medulla.
Lateral to the obex are paired “bumps” called the gracile tubercle. There are 2 other elevations adjacent to the gracile tubercle called the cuneate tubercle.
CEREBELLUM
The cerebellum is located dorsal to the medulla and pons.
It is connected to these brainstem regions by 3 fiber tracts called Cerebellar Peduncles. Think of them as roads allowing information to flow from the brainstem into the cerebellum or from the cerebellum back to the brainstem.
The cerebellum is part of the motor system and is involved in coordinating movement.
CEREBELLAR CORTEX
As for the cerebral cortex, the cerebellar cortex is highly infolded forming deep ridges. If it was completely unfolded it would extend up to 1 meter in length. This clearly reflects the importance of this structure in brain function.
CEREBELLAR PEDUNCLES
Fiber tracts that connect cerebellum to brainstem.
Cerebellar Peduncles are made up of:
- Axons entering the cerebellum that originated in the spinal cord or other parts of the brainstem (e.g., medulla, pons).
- Axons leaving the cerebellum. These are destined for brainstem targets.
VENTRAL PONS =
the “BRIDGE” part
The pons is greatly expanded from right to left compared to the slender medulla.
The large expansion on the ventral surface is called the Basilar Pons. The basilar pons extends from the medulla, caudally, to the midbrain rostrally.
If one follows the “planks” of the bridge laterally, they appear to converge into a large bundle. This is called the Middle Cerebellar Peduncle and is one pathway by which the cerebellum is connected to the brainstem.
Two cranial nerves are related to the pons. The largest cranial nerve is Cranial nerve V – trigeminal. It is located just rostral to the middle cerebellar peduncle on the lateral side of the pons. Cranial nerve IV – Trochlear is the smallest cranial nerve and it appears on the lateral side of the rostral end of the pons.
Cranial nerve IV
Trochlear
The smallest cranial nerve and it appears on the lateral side of the rostral end of the pons.
Cranial nerve V
Trigeminal
The largest cranial nerve. It is located just rostral to the middle cerebellar peduncle on the lateral side of the pons.
MIDBRAIN - VENTRAL
moving rostrally in the brainstem.
Immediately rostral to the pons is the midbrain (aka, the mesencephalon).
It extends from the rostral pole of the pons to two protrusions titled the Mammillary Bodies which actually are part of a nuclear complex in the diencephalon called the hypothalamus.
Laterally, there are large columns called the Cerebral Peduncles. These should not be confused with the cerebellar peduncles. The axons in the cerebral peduncle arose from neurons in the cerebral cortex. These axons course from the cerebral cortex to the brainstem and spinal cord.
The space between the cerebral peduncles is called the Interpeduncular Fossa.
Emerging from the interpeduncular fossa is cranial nerve III – oculomotor N. These paired nerves are located adjacent to the midline and emerge at the junction of the pons and midbrain.
Cranial Nerve III
Oculomotor
These paired nerves are located adjacent to the midline and emerge at the junction of the pons and midbrain.
TECTUM
SUPERIOR AND INFERIOR COLLICULI (“little hill”)
Found in Midbrain
Latin for “ROOF”
BRAINSTEM – SAGITTAL VIEW
The large bulge of the basilar pons is evident, as is a space called the fourth ventricle located between the cerebellum and the brainstem.
Rostrally, the fourth ventricle is continuous with a narrow channel called the Cerebral Aqueduct. The cerebral aqueduct is dorsal to the midbrain.
The roof of the aqueduct is formed by two small bulges called the superior and inferior colliculi (which means little hill in Latin). Collectively they are referred to as the tectum or roof of the midbrain
MIDBRAIN – DORSAL VIEW
Cerebellum and Cerebral Cortex Removed
The tectum, or roof of the midbrain, is visible and the superior and inferior colliculi can be identified.
Several elevations are observed lateral to the colliculus. These actually are part of the diencephalon and are called the Medial and Lateral Geniculate Nuclei.
The inferior colliculus is connected to the medial geniculate nucleus via a fiber tract called the Brachium of the Inferior Colliculus. This pathway is related to the auditory system.
The superior colliculus and the lateral geniculate nucleus, together with other structures, are part of the visual system.
The lateral geniculate nucleus is not connected to the superior colliculus.
The origin of Cranial nerve IV –Trochlear Nerve is seen just below the inferior colliculus. This is the only cranial nerve that arises from the dorsal surface of the brainstem.
After emerging from the midbrain, the nerve courses laterally and ventrally to emerge on the ventral surface of the brainstem at the level of the rostral pons.
Cranial nerve IV
Trochlear Nerve
The origin of the Trochlear Nerve is seen just below the inferior colliculus. This is the only cranial nerve that arises from the dorsal surface of the brainstem.
INFERIOR COLLICULUS
PART OF AUDITORY SYSTEM
SUPERIOR COLLICULUS
PART OF VISUAL SYSTEM
DIENCEPHALON – Sagittal View
Most of the diencephalon is covered by the telencephalon or cerebral cortex. It extends from the mammillary bodies to the optic chiasm.
Thalamus, Hypothalamus
INFUNDIBULUM
STALK OF THE PITUITARY GLAND
Describe the Anatomical Organization of the Cerebral Cortex
- Identify the lobes of the cerebral cortex and their borders including the frontal lobe, parietal lobe, temporal lobe, occipital lobe, cingulate lobe, and insula.
- Identify specific sulci in the cerebral cortex including the central sulcus, lateral sulcus, calcarine sulcus, cingulate sulcus, and parieto-occipital suclus.
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MAJOR SULCI OF LATERAL CORTEX
To define the lobes, we must first identify some of the major depressions or sulci that form the borders of the different lobes.
The most obvious depression is the Lateral Sulcus which seems to split the brain almost in half in the horizontal plane.
Another prominent depression, is the Central Sulcus which seems to divide the brain in half in the transverse plane. The central sulcus does not quite reach the lateral sulcus and there is always a small bridge of cortex that separates them.
The depression rostral to the central suclus is called the Precentral Sulcus, whereas the depression immediately caudal to the central sulcus is the Postcentral Sulcus.
A very short, shallow sulcus near the caudal pole of the cerebral cortex is the Parieto-Occipital Sulcus.
BORDERS of the FRONTAL LOBE
Frontal Pole Of Brain
Central Sulcus
Lateral Sulcus
BORDERS of the PARIETAL LOBE
Central Sulcus
Line Between Preoccipital Notch And Parieto-Occipital Sulcus
BORDERS of the OCCIPITAL LOBE
Line Between Preoccipital Notch And Parieto-occipital Sulcus
BORDERS of the TEMPORAL LOBE
Lateral Sulcus
Line Between Preoccipital Notch And Parieto-occipital Sulcus
No Clear Demarcation Between Parietal Lobe Posteriorly
INSULAR CORTEX
Buried Deep In The Lateral Sulcus.
Covered By Gyri From The Temporal, Parietal, and Frontal Lobes.
Contains Gustatory, Autonomic, Pain, Vestibular Areas.
MAJOR SULCI OF MEDIAL CORTEX
CINGULATE SULCUS
PARIETO-OCCIPITAL SULCUS
CALCARINE SULCUS
TELENCEPHALON – MEDIAL VIEW
The medial extent of the central sulcus is visible and is a landmark for defining the frontal and parietal lobes.
Two additional sulci are evident and further define the lobes of the cerebral cortex. A well defined parieto-occipital sulcus separates the occipital and parietal lobes in this view. In addition, the Cingulate Sulcus separates the frontal and parietal lobes from the cingulate or limbic lobe.
Two other prominent landmarks are prominent fiber tracts. One is the Corpus Callosum which is a large bundle of axons that connects the right and left sides of the cerebral cortex. The other is the Fornix which links structures related to the limbic system.
