Gross Brain Structure
Brain Structures
cerebral hemispheres largest portion of the brain; with the diencephalon, forms the forebrain
- divided into 4 lobes
:
- (1) frontal lobe
separated from the parietal lobe by the central sulcus
- (2) occipital lobe
separated from the parietal lobe by the parieto-occipital sulcus
- (3) temporal lobe
separated from the frontal lobe by the Sylvian fissure (lateral fissure)
- (4) parietal lobe
- anterior commissure below the lateral ventricle in its anterior portion; connects hemispheres
- corpus callosum
above the lateral ventricle; connects the hemispheres
- fornix
between the lateral ventricles; connects the hypothalamus with the hippocampus
- falx cerebri
fold of the dura mater that lies between the two hemispheres of the cerebrum
diencephalon2nd part of forebrain;contains thalamus, hypothalamus, epithalamus, subthalamus; surrounds 3rd ventricle
- thalamus
(2) 4/5 of the bulk of the diencephalon; lies between the midbrain and the corpus callosum
- hypothalamus
lies under the thalamus
brainstem (aka: hindbrain)
most rostral component of brainstem; cerebral peduncles are prominent on its ventral surface; occulomotor nerve emerges between the two peduncles; trochlear nerve emerges on the dorsal aspect of midbrain; the cerebral aqueduct runs through the midbrain and connects the 3rd and 4th ventricles
- cerebral peduncles
connect the cerebral cortex with the brainstem and spinal cord
- tectum
dorsal portion of the midbrain, contains the superior and inferior colliculi
- pineal gland
lies just superior to the tectum
pons latin for "bridge"; second part of the hindbrain (just caudal to the midbrain); fibers appear to connect the two cerebellar hemispheres, but actually connect the cerebral to the opposite cerebellar hemisphere; cavity of the pons forms part of the 4th ventricle; trigeminal nerve arises from the pons (CN V VIII)
medulla most caudal part of the brainstem; medullary pyramids are two longitudinal prominences on the ventral surface that contain motor axons from the precentral gyrus; inferior olives are prominences on the lateral aspect of the medulla, and are also involved in motor control; cavity forms the inferior part of the 4th ventricle; CN IX XII arise from the medulla (CN XI arises from spinal cord)
spinal cord
cerebellum "little brain"
pituitary stalk lies just posterior to the optic chiasm
sulci grooves on the brain
gyri ridges that are separated by the sulci
- precentral gyrus
(motor cortex) lies just anterior to the central sulcus; involved in motor control
- postcentral gyrus
(somatic-sensory cortex) lies just posterior to the central sulcus
meninges coverings of the brain
- dura mater
tough outer covering
- arachnoid
separated from dura by subdural space; thin, transparent membrane
- does not dip into the sulci during life (collapses with preservation)
- subarachnoid space
: filled with CSF bathing the brain; also contains many arteries and veins
- connected to the pia by thin filaments (which give it its name); closely opposed to the pia at the gyri
- arachnoid granules
: cauliflower-like projections on either side of superior sinus; are formed by many arachnoid villi which serve to release CSF into the sinus
- pia mater
innermost of the meninges; closely opposed to the gyri and sulci; communicates with inner structures of the brain via tubular expansions of the pia that are carried internally by smaller arteries Þ allows CSF to get to the inner structures of the brain
lateral sulcus (Sylvian fissure) (96B) separates the frontal and temporal lobes; the superficial middle cerebral vein runs in this fissure; the superior and inferior anastomotic veins (tempero-occipital sulcus) join with the superficial middle cerebral at the posterior end of the fissure
calacrine sulcus sulcus on medial side of the occipital lobe; runs perpendicular to the parieto-occipital sulcus
Arteries
circle of Willis already covered beautifully in the anatomy section
posterior inferior cerebellar artery branches off of the vertebral a just before the anastamosis
anterior inferior cerebellar artery larger than the posterior; branches off the basilar just after the anastamosis
superior cerebellar artery branches off the basilar just before the circle of Willis
Cranial Nerves
I (olfactory) usually torn off on gross specimens; run from the cribiform plate of the ethmoid to the olfactory bulbs on the underside of the anterior cerebrum
II (optic) protrude from the optic chiasm; beyond the chiasm (closer to brain) are termed the optic tracts
III (oculomotor) emerge from the medial edges of the cerebral peduncles at junction with pons
- oculomotor nucleus Þ superior, medial, inferior rectus, inferior oblique mm of eye; levator palpebrae of eyelid
- Edinger-Wesphal nucleus Þ via cilliary ganglia to pupillary and cilliary mm of eye
IV (trochlear) only cranial nn that arise dorsally and cross the midline; pass ventrally and run medially along the junction of the pons and cerebral peduncles
- motor
: trochlear nucleus Þ superior oblique muscles of eye
V (trigeminal) large nn emerge from lateral border of pons
- sensory
: pain, temp, deep touch, proprioception from face, nose, mouth; sensory to buccinator
- motor
: trigeminal nucleus Þ muscles of mastication (ABD, stylohyoid, obicularis oculi, levator labii superioris, depressor angularis oris, buccinator, zygomaticus major)
VI (abducens) most medial of nerves at juncion of pons and medulla
- motor
: abducent nucleus Þ lateral rectus muscle of eye
VII (facial) just lateral to abducens; usually composed of two rootlets, facial n. and intermediate n.
- sensory
: anterior 2/3 of tongue
- motor
: facial nucleus Þ muscles of facial expression
- parasympathetic
: sup. salivary nucleus Þ glands and vessels of nose and palate, submandibular, lingual, lacrimal glands
VIII (vestibulocochlear) emerge lateral to the facial nerves
- sensory
: incoming auditory and vestibular information
IX (glossopharyngeal) arise dorsal to the olive, inferior to CN VIII
- sensory
: from posterior taste buds and other general somatic and visceral information
- motor
: nucleus ambiguous Þ muscles of pharynx
- parasympathetic
: inferior salivatory nucleus Þ parotid gland
X (vagus) arise on dorsal edge of the olive inferior to the glossopharyngeal
- sensory
: from viscera of the thorax and abdomen
- motor
: nucleus ambiguous Þ muscles of pharynx and larynx
- parasympathetic
: posterior nucleus of vagus Þ visceral motor information to all viscera down to the pelvis
XI (accessory) arises from a series of rootlets posterior to the vagus on the medulla, and also on the spinal cord
- motor
: to trapezius and sternocleidomastoid muscles
XII (hypoglossal) from rootlets between the pyramid and the olive
- motor
: all the intrinsic and extrinsic muscles of the tongue
Other Structures
optic chiasm joining of the optic nerves, then splits to become the optic tract
stalk of the pituitary lies just posterior to the optic chiasm
interventricular foramen (of Monro) connects the lateral ventricles with the 3rd ventricle
choroid plexus lines the ventricles and produces CSF (composes of capillaries, ependyma, pia mater)
thalamus
hippocampus on inferior surface of temporal lobe
hypothalamus
fornix
basal ganglia form lateral wall of the lateral ventricles
corpus callosum
internal capsule lies just lateral to the diencephalon and forms a capsule around it
tectum
lateral ventricles
insula lies under the frontal lobe between it and the temporal lobe
third ventricle