Module 32/22 - Neuroanatomy of the development of the brain

Question 1

The nervous system develops from the ___________.

Answer 1

The nervous system develops from the ectoderm = which is the outmost layer.

Question 2

Neural plate invaginates to form ____________….. And ultimately the ______________

Answer 2

Neural plate invaginates to form neural groove…. And ultimately the neural tube.

Question 3

All the tissues of the body are derived from one of the three primary germ layers. What are the three different layers?

Answer 3

• Endoderm
• Mesoderm
• Ectoderm

Question 4

At the earliest stages of development, what composes the ectoderm?

Answer 4

At the earliest stages think of the ectoderm as a sheet of paper.

Question 5

What happens to the ectoderm at day 18 and then at day 20 of development?

Answer 5

Around 18 days of development, a groove forms down the middle of the piece of the paper, forming the neural groove. By 20 days the groove is quite deep.

Question 6

Explain the development of the ectoderm.

Answer 6

• At the earliest stages think of the ectoderm as a sheet of paper. Around 18 days of development, a groove forms down the middle of the piece of the paper, forming the neural groove. By 20 days the groove is quite deep.
• Over the period 21-24 days, the groove seals up forming the neural tube that is separate from the overlying remaining ectoderm. By 24 days 3 swellings or vesicles appears at one end of the tube, the end that will form the brain. They are called the prosencephalon, the mesencephalon, and the rhombencephalon. The region between the rhombencephalon and the other end of the neural tube will form the spinal cord.

Question 7

Over the period 21-24 days, the groove seals up forming the ___________ that is separate from the overlying remaining ectoderm.

Answer 7

Over the period 21-24 days, the groove seals up forming the neural tube that is separate from the overlying remaining ectoderm.

Question 8

By 24 days 3 swellings or vesicles appear at one end of the tube, the end that will form the brain. They are called the _______________, the ______________, and the ________________.

Answer 8

By 24 days 3 swellings or vesicles appear at one end of the tube, the end that will form the brain. They are called the prosencephalon, the mesencephalon, and the rhombencephalon.

Question 9

The region between the rhombencephalon and the other end of the neural tube will form the ___________.

Answer 9

The region between the rhombencephalon and the other end of the neural tube will form the spinal cord.

Question 10

The three primary vesicles are not arranged in a straight line: there are two bends or flexures in the neural tube. One of these, the____________, appears at the level of the mesencephalon and persist in the adult.

Answer 10

The three primary vesicles are not arranged in a straight line: there are two bends or flexures in the neural tube. One of these, the cephalic flexure, appears at the level of the mesencephalon and persists in the adult.

Question 11

At 5 weeks secondary vesicles form, creating a total of 5 vesicles, from which all parts of the brain are derived. What are the 5 secondary vesicles and their corresponding key brain structures?

Answer 11

IMAGE = ANSWER

Question 12

What are the secondary vesicles and corresponding key brain regions of the prosencephalon?

Answer 12

Telencephalon

• Cerebral hemispheres
• Basal ganglia (or nuclei)

Diencephalon

• Thalamus
• Hypothalamus

Question 13

What are the secondary vesicles and corresponding key brain regions of the mesencephalon?

Answer 13

Mesencephalon

• Midbrain

Question 14

What are the secondary vesicles and corresponding key brain regions of the rhombencephalon?

Answer 14

Metencephalon

• Pons
• Cerebrum

Myelencephalon

• Medulla

Question 15

Upright posture and the ______________result in dorsal and ventral being different at the level of the spinal cord and brainstem vs. the long axis of the cerebrum.

Answer 15

Upright posture and the cephalic flexure result in dorsal and ventral being different at the level of the spinal cord and brainstem vs. the long axis of the cerebrum.
Therefore, the terms anterior, posterior, superior, inferior (which are the same on either side of the cephalic flexure) are preferred for human neuroanatomy.

Question 16

The hollow portion of the neural tube ultimately becomes the _____________found deep within the brain.

Answer 16

The hollow portion of the neural tube ultimately becomes the ventricles found deep within the brain.

Question 17

What are the four named ventricles?

Answer 17

• Two lateral ventricles (within the cerebral hemispheres).
• A single third ventricle (single midline cavity within the diencephalon).
• The cerebral aqueduct, a single midline cavity within the midbrain.
• The fourth ventricle (anterior wall formed by the pons and medulla; posterior wall by medulla and cerebellum).

Question 18

What are the four name ventricles and their location/origin?

Answer 18

• Two lateral ventricles (within the cerebral hemispheres).
• A single third ventricle (single midline cavity within the diencephalon).
• The cerebral aqueduct, a single midline cavity within the midbrain.
• The fourth ventricle (anterior wall formed by the pons and medulla; posterior wall by medulla and cerebellum).

Question 19

During development, there is also a cavity within the spinal cord, the ______________. In the adult, it generally becomes occluded (closes off).

Answer 19

During development, there is also a cavity within the spinal cord, the central canal. In the adult, it generally becomes occluded (closes off).

Question 20

What are the 5 parts of the lateral ventricle?

Answer 20

The lateral ventricles are divided into 5 parts: anterior horn (within frontal lobe), body, atrium, posterior horn (occipital lobe), and inferior horn (temporal lobe).

Question 21

The cavities are connected; each lateral ventricle connects with the third ventricle via an _________________( _____________); the third ventricle connects with the fourth ventricle via the ________________.

Answer 21

The cavities are connected; each lateral ventricle connects with the third ventricle via an interventricular foramen (of Monro); the third ventricle connects with the fourth ventricle via the cerebral aqueduct.

Question 22

The ventricular cavities are filled with ________________, produced by choroid plexus, specialized (ependymal) cells that line the walls of the ventricles.

Answer 22

The ventricular cavities are filled with cerebrospinal fluid (CSF), produced by choroid plexus, specialized (ependymal) cells that line the walls of the ventricles.

Question 23

CSF (a filtrate of blood) is produced constantly by choroid plexus. It flows from one ventricle to another, draining out of the fourth ventricle via two (lateral) ____________________(not shown) and one (median) ________________.

Answer 23

CSF (a filtrate of blood) is produced constantly by choroid plexus. It flows from one ventricle to another, draining out of the fourth ventricle via two (lateral) foramina of Luschka (not shown) and one (median) foramen of Magendie.

Question 24

A feature of CNS tissue is that it is protected within the ____________(the brain) … or the ________________(spinal cord).

Answer 24

A feature of CNS tissue is that it is protected within the bony skull (the brain) … or the vertebral column (spinal cord).

Question 25

But the brain does not sit within the skull like a blob of Jello sitting in a bowl! The CNS is contained within meninges, membranous coverings consisting of three layers. What are those three layers? Which one can be grossly seen?

Answer 25

• Dura mater
• Arachnoid mater
• Pia mater
• Grossly, only the tough, outermost layer, the dura mater, can be seen.

Question 26

At certain locations the dura form reflections that help hold the brain in place. What are the two main reflections?

Answer 26

• The falx cerebri between the two hemispheres of the cerebrum.
• The tentorium cerebelli separates cerebrum and cerebellum

Question 27

Adjacent to the brain are the two other layers of the meninges, deep to the dura mater. The _______________mater, in contact with dura, and the _____________mater, intimately opposed to the surface of the brain.

Answer 27

Adjacent to the brain are the two other layers of the meninges, deep to the dura mater. The arachnoid mater, in contact with dura, and the pia mater, intimately opposed to the surface of the brain.

Question 28

There is a space between the arachnoid and pia mater, the ______________space. It is filled with CSF, contains filaments of arachnoid (trabeculae, that connect to the pia mater) and blood vessels that ultimately penetrate (and provide blood supply to) brain tissue.

Answer 28

There is a space between the arachnoid and pia mater, the subarachnoid space. It is filled with CSF, contains filaments of arachnoid (trabeculae, that connect to the pia mater) and blood vessels that ultimately penetrate (and provide blood supply to) brain tissue.

Question 29

The CSF that is contained in subarachnoid space comes from the ventricular system, via the foramina of _______________and the foramen of ____________ …

Answer 29

The CSF that is contained in subarachnoid space comes from the ventricular system, via the foramina of Luschka and the foramen of Magendie …

Question 30

The CSF flows into regions where the subarachnoid space is expanded in size (greater separation of the arachnoid and pia mater) called ____________.

Answer 30

The CSF flows into regions where the subarachnoid space is expanded in size (greater separation of the arachnoid and pia mater) called cisterns.

Question 31

The _______________ is also covered by meninges and the spinal cord subarachnoid space is continuous with the subarachnoid space of the brain.

Answer 31

The spinal cord is also covered by meninges and the spinal cord subarachnoid space is continuous with the subarachnoid space of the brain.

Question 32

The spinal cord ends at the L1/L2 vertebral level (at the conus medullaris). The continuation of spinal nerve roots below this level form the cauda equina, and is contained within an expanded region of _______________space called the __________________.

Answer 32

the spinal cord ends at the L1/L2 vertebral level (at the conus medullaris). The continuation of spinal nerve roots below this level form the cauda equina, and is contained within an expanded region of subarachnoid space called the lumbar cistern.

Question 33

Clinically, the subarachnoid space has high importance… Give an example of when and typically in which region of the spinal cord would we insert a needle to extract a sample of CSF.

Answer 33

This allows for the insertion of a needle into the subarachnoid space (typically at the L2/L3 level) to extract a sample of CSF (lumbar puncture) to look for signs of infection (meningitis) or bleeding. Understand that because the subarachnoid space at this level is continuous with the subarachnoid space in the brain, sampling CSF here can be informative about disease or damage in the brain.

Question 34

Using the same approach, the anesthetic can be injected into the subarachnoid space, a procedure called ________, for pelvic or lower limb surgery.

Answer 34

Using the same approach, the anesthetic can be injected into the subarachnoid space, a procedure called spinal block, for pelvic or lower limb surgery.

Question 35

What is the difference between spinal block and epidural anesthesia?

Answer 35

• A spinal block is not the same as epidural anesthesia. In this case, a catheter is inserted into the space between the dura and the vertebral column. The goal of an epidural is to provide analgesia, or pain relief, rather than anesthesia (total lack of feeling) during, for example, labor and delivery.
• Using the same approach, anesthetic can be injected into the subarachnoid space, a procedure called spinal block, for pelvic or lower limb surgery.

Question 36

As mentioned already, CSF is constantly being produced within the ventricular system, meaning that it is constantly flowing into the subarachnoid space. This means there must be someplace for CSF to go next. CSF flows throughout the subarachnoid space, ultimately draining into a large __________ (superior sagittal sinus) along the superior margin of the _______________.

Answer 36

• As mentioned already, CSF is constantly being produced within the ventricular system, meaning that it is constantly flowing into the subarachnoid space. This means there must be some place for CSF to go next. CSF flows throughout the subarachnoid space, ultimately draining into a large venous sinus (superior sagittal sinus) along the superior margin of the falx cerebri.

Question 37

CSF drains from the subarachnoid space into the superior sagittal sinus via structures called _____________________.

Answer 37

• CSF drains from the subarachnoid space into the superior sagittal sinus via structures called arachnoid villi.

Question 38

CSF fluid is produced constantly within the ventricular system. This means there must continuous flow of CSF within (and out of) the ventricular system, into the subarachoid space, to be drained away into the superior sagittal sinus. If there is blockage of CSF flow within the ventricular system, CSF will accumulate behind the blockage and CSF pressure will rise. The pressure can lead to compression of delicate brain tissue adjacent to the ventricles, a condition called _____________________.

Answer 38

CSF fluid is produced constantly within the ventricular system. This means there must continuous flow of CSF within (and out of) the ventricular system, into the subarachoid space, to be drained away into the superior sagittal sinus. If there is blockage of CSF flow within the ventricular system, CSF will accumulate behind the blockage and CSF pressure will rise. The pressure can lead to compression of delicate brain tissue adjacent to the ventricles, a condition called hydrocephalus.

Question 39

***This slide show = image = a normal brain on the right, revealing portion of the ventricular system. The brain on the left shows what happens when flow out from the third ventricle was blocked, causing an expansion of the lateral ventricles and compression of surrounding brain tissue.

Answer 39

IMAGE

Question 40

What are there are two sources of blood supply to the brain?

Answer 40

• An anterior pair of internal carotid arteries
• A posterior pair of vertebral arteries.

Question 41

The internal carotids arise at the bifurcation of the common carotid artery (giving rise to the external and internal carotid arteries). The internal carotids enter the skull via the ______________. The vertebral arteries are branches of the ___________ arteries and travel through transverse foramina of each cervical vertebrae until reaching the skull, where they enter via the foramen ____________.

Answer 41

The internal carotids arise at the bifurcation of the common carotid artery (giving rise to the external and internal carotid arteries). The internal carotids enter the skull via the carotid canals. The vertebral arteries are branches of the subclavian arteries and travel through transverse foramina of each cervical vertebrae until reaching the skull, where they enter via the foramen magnum.

Question 42

This illustration shows the blood supply to the brain that emerges from the posteriorly positioned vertebral arteries and the anteriorly positioned internal carotids. Note that the two sources of blood appear to be interconnected =forming an _________________

Answer 42

This illustration shows the blood supply to the brain that emerges from the posteriorly positioned vertebral arteries and the anteriorly positioned internal carotids. Note that the two sources of blood appear to be interconnected =forming an anastomosis

Question 43

The vertebral arteries join together to form the ________________artery adjacent (inferior) to the pons. The basilar artery terminates at the base of what is called the ____________________

Answer 43

The vertebral arteries join together to form the single basilar artery adjacent (inferior) to the pons. The basilar artery terminates at the base of what is called the Circle of Willis.

Question 44

Along the way, the basilar artery gives off ____________arteries, providing blood supply to the pons, and …the vertebrals and basilar give rise to 3 arteries for the cerebellum.

Answer 44

Along the way, the basilar artery gives off pontine arteries, providing blood supply to the pons, and …the vertebrals and basilar give rise to 3 arteries for the cerebellum.

Question 45

From each vertebral artery… what arises?

Answer 45

posterior inferior cerebellar artery (PICA)

***The names of these arteries indicate the region of the cerebellum supplied.

Question 46

From each basilar artery… what arises?

Answer 46

anterior inferior cerebellar arteries (AICA) and the superior cerebellar arteries (SCA)

***The names of these arteries indicate the region of the cerebellum supplied.

Question 47

Explain the connections that happen around the Circle of Willis

Answer 47

• Moving around the Circle of Willis:
• First is the posterior cerebral artery (PCA) that then connects to the middle cerebral artery (MCA) via the posterior communicating artery.
• Note that the middle cerebral artery is continuous with the internal carotid
• Several other branches emerge at this location, the ophthalmic artery (blood supply to the structures in the orbit as well as some structures in the nose, face and meninges) and the anterior choroidal artery (that contributes blood supply to numerous brain structures, including the choroid plexus of the lateral ventricle and third ventricle)
• From the internal carotid/middle cerebral artery junction emerges the anterior cerebral artery (ACA), that connect with the anterior cerebral artery on the opposite side via the anterior communicating artery.

Question 48

It has been suggested that the arrangement of the circle of Willis creates ______________: if one part of the circle becomes blocked or narrowed (stenosed) or one of the arteries supplying the circle is blocked or narrowed, blood flow from the other blood vessels may preserve blood supply to the cerebrum, avoiding ischemic stroke.

Answer 48

It has been suggested that the arrangement of the circle of Willis creates collateral cerebral circulation: if one part of the circle becomes blocked or narrowed (stenosed) or one of the arteries supplying the circle is blocked or narrowed, blood flow from the other blood vessels may preserve blood supply to the cerebrum, avoiding ischemic stroke.

Question 49

Explain the blood supply to the cerebrum and how it forms distinct territories related to each cerebral artery.

Answer 49

• Laterally:
• mostly the MCA (portions of frontal, parietal, temporal & occipital lobes) but also
  
  • superior and anterior (frontal & parietal lobes), ACA
  • posterior and inferior (occipital & temporal lobes), PCA
• Continuous with the pattern found Medially:
  
  • Frontal, parietal lobes, ACA
  • Occipital & temporal lobe, PCA; Portion of the temporal lobe, MCA

Question 50

How does blood drain from the brain?

Answer 50

• Blood drains into various sinuses (e.g. superior and inferior sagittal sinus).
• Collects via the confluence of sinuses that drains into the transverse sinus –> sigmoid sinus –> internal jugular vein.

Question 51

These sinuses are embedded in the dura mater. Note the superior sagittal sinus (also into which drain the CSF) located associated with the falx cerebri and the straight and transverse sinuses within the tentorium cerebelli.

Answer 51

IMAGE