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Gross Brain Organization and Development
Development
1. The nervous system forms out of the embryonic ectoderm.
a. The primitive ectoderm folds over on itself, forming the neural groove, and eventually, the
neural tube.
i. During this process, a subset of cells, neural crest cells, migrate to form the dorsal
root ganglia and some cells of the adrenal gland.
2. Proliferation of cells in the neural tube leads to formation of three brain vesicles:
a. Hindbrain
i. Includes myelencephalon (the future medulla)
ii. Includes metencephal on (the future pons and cerebellum)
b. Midbrain
i. Includes the mesencephalon (the future midbrain)
c. Forebrain
i. Includes the diencephalon (the future thalamus, hypothalamus, and retina)
ii. Includes the telencephalon (the future cortex)
3. The nervous system in humans must make a number of “bends” or “flexures” to accommodate our
forward-facing, upright posture:
a. Cervical flexure bends neuraxis ventrally caudal to the hindbrain.
b. Pontine flexure bends neuraxis dorsally at the level of the pons.
c. Cephalic flexur e bends the neuraxis ventrally at the level of the midbrain.
Basic Brain Functions
1. There will be plenty more detail later in the course, but in simple terms, there are some generalizations
that can be made about the function of various brain regions:
a. Cerebellum: mediates coordinated movements.
b. Medulla: mediates basic bodily functions, such as breathing.
c. Pons: is the “bridge” between cerebrum and cerebellum.
d. Midbrain: has both sensory and motor functions.
e. Thalamus: the “gateway” by which sensory stimuli (sights, sounds, smells, etc) enter the
cortex.
f. Hypothal amus: a collection of nuclei that mediate thirst, hunger, and other critical “drives.”
g. Corpus callosum: the main (but not only) connection between left and right brain
hemispheres.
h. Basal ganglia: Involved in movement.
Brain Orientation Terms
1. Rostral/anterior: toward the nose.
a. Mnemonic: “rostril = toward the nostril.”
2. Caudal/posterior: toward the tail.
3. Dorsal/superior: Toward the top of the skull (if talking about the brain) or vertebral column (if
talking about the spinal cord).
4. Ventral/inf erior: Toward the bottom of the skull (if talking about the brain) or vertebral column (if
talking about the spinal cord).
a. In rare instances in the spinal cord, the term “anterior” may be used (the “anterior horn of the
spinal cord,” which you will learn about later, is the only example I can think of).
4-5-09 Gross Dissection 1
Note: I have included some info that was not covered in class yet, but will be eventually. I’ve just put it in so
that you can start thinking about it.
Blood Supply
1. Vertebral Art ery
a. Branches off of the subclavian artery.
b. One of the two major blood supplies to the brain (internal carotid being the other).
c. Gives rise to:
i. Anterior Spinal Artery
1. Supplies the ventral 2/3 of spinal cord with blood.
ii. Posterior Inferior Cerebellar Artery (PICA)
1. First of three vessels to supply the cerebellum.
2. Basilar Artery
a. Formed by the confluence of the vertebral arteries.
b. Gives rise to:
i. Anterior Inferior Cerebellar Artery (AICA)
1. Second of three vessels to supply the cerebellum.
ii. Pontine Artery
1. Supplies the pons.
iii. Superior Cerebellar Artery
1. Third of three vessels to supply the cerebellum.
iv. Posterior Cerebral Artery (PCA)
1. Supplies the posterior part of the cerebrum, namely the occipital lobe.
2. Gives rise to the Posterior Choroidal Artery
a. Supplies the choroid plexus within the lateral ventricles as well as the
thalamus.
3. Internal Carotid Artery
a. The second of two major blood supplies to the brain (vertebral arteries being the other).
b. Gives rise to:
i. Middle Cerebral Artery (MCA)
1. Supplies most of the lateral surface of the brain including temporal lobe, parietal
lobe, and frontal lobe.
2. Gives rise to the Lenticulostriate Perforati ng Arteries.
a. Supply the basal ganglia.
b. Particularly susceptible to stroke.
c. THE INSTRUCTORS LOVE ASKING ABOUT THIS ONE!
3. Gives rise to the Anterior Choroidal Artery
a. Supplies the choroid plexus within the lateral ventricles, as well as the
hippocampus and amygdala.
ii. Anterior Cerebral Artery (ACA)
1. Supplies the medial surfaces of the brain (i.e those within the longitudinal fissure)
such as the cingulate cortex.
iii. Anterior Communicati ng Artery
1. Part of the Circle of Willis connecting the two anterior cerebral arteries together.
iv. Posterior Communicating Artery
1. Part of the Circle of Willis connecting the posterior cerebral artery to the internal
carotid/middle cerebral artery/anterior cerebral artery.
Cranial Nerves
1. CN I (Olfactory nerve)
a. Carries smell information from olfactory epithelium/olfactory bulb to olfactory cortex.
2. CN II (Optic nerve)
a. Carries visual information from the retina to higher brain levels.
3. CN III (Occulomotor nerve)
a. Innervates 4 of 6 extraoccular eye muscles (medial rectus, superior rectus, inferior rectus,
inferior oblique).
b. Required for pupillary light reflex.
c. Helpful hint for locating it: usually pokes out between the superior cerebellar artery and the
posterior cerebral artery.
4. CN IV (Trochlear nerve)
a. Innervates 1 of 6 extraoccular eye muscles (superior oblique)
b. Is unique in that it is the only cranial nerve t o protrude from the dorsum of the
brainstem (eventually loopi ng around to t he ventral surface). All other cranial
nerves protrude from the brainstem on the ventral surface.
5. CN V (Trigeminal nerve)
a. Contains a motor component, which provides innervation to some muscles of mastication.
b. Contains a sensory component, which carries sensory information from the face to the CNS.
There are three divisions of the nerve that do this.
i. VI = Ophthalmic nerve
ii. VII = Maxillary nerve
iii. VIII = Mandibular nerve
6. CN VI (Abducens nerve)
a. Innervates 1 of 6 extraoccular muscles (lateral rectus).
b. Helpful hint for locating it: appears right at the junction of the pons and medulla.
7. CN VII (Facial nerve)
a. Contains a motor component that provides innervation to muscles of the face.
b. Contains a sensory component that carries taste information from the anterior 2/3 of tongue back
to the CNS.
8. CN VIII (Vestibulocochlear nerve)
a. Provides hearing and vestibular information from the inner ear back to the brainstem.
9. CN IX (Glossopharyngeal nerve)
a. Carries sensory information from the pharynx back to the CNS.
b. Carries taste information from the posterior 1/3 of tongue back to the CNS.
c. Helpful hint for locating: CN IX, X, XI are located dorsal to the olives.
10. CN X (Vagus nerve)
a. Provides innervation to muscles of the palate, pharynx, and larynx.
b. Provides parasympathetic innervation to structures down to the transverse colon.
c. Helpful hint for locating: CN IX, X, XI are located dorsal to the olives.
11. CN XI (Accessory nerve)
a. Provides innervation to the trapezius and sternocleidomastoid (SCM) muscles.
b. Helpful hint for locating: CN IX, X, XI are located dorsal to the olives.
12. CN XII (Hypoglossal nerve)
a. Provides innervation to the tongue.
b. Helpful hint for locating: Located just ventral to the olives.
Gross Brain Structures
1. Pons
a. A connection point for communications between the cerebrum and cerebellum.
2. Cerebral peduncle
a. A bundle of axons transmitting information from motor cortex down to the spinal cord.
i. This bundle is called “the pyramids” as it travels through the medulla along the way.
3. Medulla
a. The most caudal part of the brainstem.
b. Controls basic functions such as breathing.
4. Cerebellum
a. Important for coordinated movements.
5. Fourth Ventricl e
a. CSF-filled cavity at the level of the cerebellum.
6. Midbrain
a. Contains structures involved in a variety of things, including:
i. Motor function
ii. Vision (superior colliculus)
iii. Hearing (inferior colliculus)
7. Cerebral Aqueduct—connects the third and fourth ventricles.
8. Thalamus
a. Gateway for sensory information from the periphery to enter the cortex.
9. Hypothal amus
a. Located just inferior to the thalamus, thus its name.
b. Controls basic drives such as hunger, thirst, anger, etc.
c. The pituitary gland (hypophysis) is a protrusion off the bottom of the hypothalamus.
10.
Third Ventricle
a. Small CSF-filled cavity in between the two lobes of the thalamus.
11.
Corpus Callosum
a. White matter tract that is the major connection from one brain hemisphere to the other.
b. Anterior and Posterior Commissures are minor connections from one hemisphere to the
other.
12.
Fornix
a. A white matter tract carrying information from the hippocampus to the mammillary bodies.
b. Involved in learning and memory.
13.
Frontal lobe
a. Involved in “higher-order” thinking.
14.
Temporal lobe
a. Involved in learning and memory.
15.
Parietal lobe
a. Involved in a variety of things including bodily sensation and attention.
16.
Occipit al lobe
a. Involved in vision
17.
Insula
a. Cortex located at the very bottom of the lateral (Sylvian) sulcus.
b. Involved in a variety of things including emotion.
18.
Longitudinal fissure
a. Fissure dividing the left and right hemispheres of the brain.
19.
Lateral (Sylvian) sulcus
a. Separates the temporal and parietal lobes.
20.
Central sulcus
a. Separates the frontal and parietal lobes.
b. Motor cortex is located just anterior to the sulcus (i.e. in the frontal lobe).
c. Somatosensory cortex is located just posterior to the sulcus (i.e. in the parietal lobe).
21.
Cingulate sulcus
a. Located on the medial surface of the frontal and parietal lobes (i.e. within the longitudinal
fissure).
b. The cingulate gyrus, which is involved in emotion, is located just inferior to the sulcus.
22.
Calcarine sulcus
a. Located on the medial surface of the occipital lobe (i.e. within the longitudinal fissure).
b. Cortex on either side of the sulcus is involved in vision.
CSF Flow
1. CSF flow proceeds like this:
a. It is made in the choroid plexus of the lateral ventricles.
b. It flows into the third ventricle via the foramen of Monro.
c. It flows into the 4th ventricle via the cerebral aqueduct.
d. It exits the 4th ventricle into the subarachnoid space via the medial foramen of Magendie and
lateral foramen of Lushka.
i. Mnemonic: “Magendie = medial; Lushka = lateral.”
e. CSF travels in the subarachnoid space, bathing the brain until it reaches the arachnoid
granulations, which protrude into the brain’s venous sinuses, thus allowing CSF to be passed
into venous drainage.
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