BIO 210 LabInstructor: Dr. Rebecca Clarke

Chapter 14: The Brain

Human BrainContains almost 98% of body’s neural

tissueAverage weight about 3 lb (1.4 kg)

6 Major Regions of the BrainCerebrumCerebellumDiencephalonMesencephalonPonsMedulla oblongata

The BrainEmbryological Development

Determines organization of brain structures

Neural tubeOrigin of brain

Enlarges into three primary brain vesicles

prosencephalon

mesencephalon

rhombencephalon

The BrainFive Secondary Brain Vesicles

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon

The BrainOrigins of Brain Structures

Diencephalon and mesencephalon persist

Telencephalon:

Becomes cerebrum

Metencephalon

Forms cerebellum and pons

Myelencephalon

Becomes medulla oblongata

The Brain

CerebrumControls higher mental functionsLargest part of brain (80% of volume)

CerebrumDivided into large L and R cerebral

hemispheresLongitudinal fissure:Separates upper part of R & L hemispheres

Corpus callosum:Thick, crescent-shaped band of white matterConnects R & L hemispheres

Figure 14–11a

CerebrumCorpus Callosum

Cerebral CortexSurface layer of gray matter on cerebrumAlso called neural cortexFolded surface:

Increases surface areaProvides space for more cortical

neurons

Cerebral Cortex

Folded surface has:Gyri (sing: gyrus) =

elevated ridgesSulci (sing: sulcus)

= hollow depressions

Fissures = deep grooves

CerebrumSulci and fissures divide cerebral

hemispheres into distinct lobes (regions) (named for overlying bones of skull)

Cerebral StructuresCentral sulcus

Groove across hemi-sphere

Separates motor and sensory areas

Postcentral gyrusUpfold posterior to

central sulcusPrimary sensory cortex

Precentral gyrusUpfold anterior to

central sulcusPrimary motor cortex

Cerebral LobesFrontal lobe

Motor cortexParietal lobe

Sensory cortex Occipital lobe

Visual cortex Temporal lobe

Auditory cortexOlfactory cortex

Cerebral Structures: Insula

“5th lobe;” deep “island” of cortex medial to lateral sulcus

Exposed when temporal lobe pushed to side

Site of gustatory cortex

Cerebral Gray MatterFound in:

Cerebral cortexCerebral nuclei

Cerebral White MatterMyelinated nerve fibersMakes up most of interior of cerebrum Located:

Deep to cerebral cortexAround cerebral nuclei

Ventricles of the BrainChambers lined with ependymal cells CSF4 ventricles: 2 lateral (R & L), 3rd, 4th

Ventricles of the Brain:Lateral Ventricles (First 2)

1/cerebral hemisphere

Ventricles of the Brain:3rd Ventricle

In diencephalon between R & L thalamiConnects to lateral ventricles via

interventricular foramen (of Monro)

Ventricles of the Brain:4th Ventricle

Extends between pons and cerebellum into medulla oblongata; becomes continuous with central canal of spinal cord

Connects to 3rd ventricles via mesencephalic (cerebral) aqueduct

CSF CirculationChoroid PlexusThrough ventriclesTo central canal of spinal

cordInto subarachnoid space

around brain, spinal cord, and cauda equina

Enters venous circulation

Cranial MeningesHave 3 layers (like spinal meninges):

Dura materArachnoid materPia mater

Are continuous with spinal meningesProtect the brain from cranial trauma (act

as “air bags”)

Cranial Meninges: Dura Mater2 Fibrous layers

Outer (endosteal) layerFused to periosteum of

cranial bonesNo epidural space (vs.

spinal cord)Inner (meningeal)

layerIn some locations folds

into cranial cavity between hemispheres dural folds

Venous (dural) sinus between layers

Cranial Meninges: Dural FoldsFolded inner layer of

dura materExtend into cranial

cavityStabilize and support

brain (act like “seat belts”)

Contain collecting veins (dural sinuses)

[FYI: falx cerebri, tentorium cerebelli, falx cerebelli]

Cranial Meninges: Arachnoid Mater

Consists of:Arachnoid membrane

Epithelial layerCovers brain (does

not follow folds)Arachnoid trabeculae

Cells and fibers that cross subarachnoid space to pia mater

Cranial Meninges: Pia Mater

Attached to brain surface by astrocytes

CerebellumCoordinates repetitive body movementsSecond largest part of brain

10% of volume but 50% of neurons

CerebellumR & L cerebellar hemispheres:

Separated at midline by vermisVermis:

Narrow band of cortex

CerebellumHighly folded cerebellar cortex

folia (less prominent than gyri)Arbor vitae: central, tree-like branching

mass of white matter deep to cortex

DiencephalonLocated in central region of brain deep to

cerebrumLinks cerebrum with brain stem

Diencephalon4 Regions:

Thalamus – L & R:Masses of gray matter

(nuclei)Forms walls of third

ventricleHypothalamus:

Below thalamusForms floor and part of

walls of thalamus

DiencephalonThird ventricle:

Separates L & R thalamus

Pineal gland:Secretes hormone

melatonin

DiencephalonIntermediate mass:

Projection of gray matter Extends into ventricle from each side of

thalamus

HypothalamusHas neural and endocrine functionsInfundibulum

Stalk that connects pituitary gland to hypothalamus

Pituitary Gland

Brain StemProcesses information between:

Spinal cord and cerebrum or cerebellumIncludes: mesencephalon, pons, medulla

oblongata

Mesencephalon (Midbrain)2 pairs of sensory nuclei (corpora

quadrigemina):Superior colliculi (visual)Inferior colliculi (auditory)

PonsLinks cerebellum with mesencephalon,

diencephalon, cerebrum, and spinal cordInvolved in motor control

Medulla OblongataConnects brain to

spinal cordRegulates complex

autonomic functions: Heart rate, blood

pressure, respirationContinuous with spinal

cord