Reading:

BCP Chapter 7/7A

Structure-Function I The Cerebrum

Major Divisions of the Brain

Brainstem

Divisions are based on developmental origins; they do not sub-serve discrete

functions.

Cerebrum

A frontal section of the forebrain

reveals that the telencephalon

(cerebrum) surrounds the paired

lateral ventricles, whereas the

diencephalon surrounds the third

ventricle.

The cerebrum comprises three

different areas:

• outer area of neuronal cell

bodies (called gray matter or

cerebral cortex)

• inner area of myelinated

axons (called white matter)

• subcortical areas of gray

matter

The Cerebrum

diencephalon

telencephalon

Neocortex 1

Most areas of cerebral cortex are

organized in a similar manner

(called neocortex): 6 layers deep;

in total, 2-4 mm thick • layer 1, synaptic integration

• layers 2 and 3, input/output to other

cortical areas

• layer 4, input from thalamus

• layer 5,output brainstem/spinal cord

• layer 6 output to thalamus

Features: • layers differ in thickness, cell density

and type

• pyramidal cells (output neurons;

excitatory) vs stellate cells (local

circuit; both excitatory and inhibitory)

• vertical axons and dendrites give

rise to columnar organization

• layer thickness differs from brain

area to area

Neocortex 2

Based on cytoarchitectural

grounds (as observed in Nissl

stained material), the German

anatomist Korbinian Brodmann

defined upwards of 50 distinct

regions of neocortex (1909).

Brodmann areas have been

discussed, debated, refined, and

renamed exhaustively for over a

century but remain the most

widely known and frequently cited

map of human cortex.

Brodmann postulated that these

areas with different structures

performed different functions.

lateral view

medial view

Neocortex is commonly described as

comprising three parts: sensory, motor,

and association (higher-order) areas.

Neocortex 3

Many of the areas Brodmann

defined based solely on their

neuronal organization have since

been correlated closely to diverse

cortical functions. For example,

Sensory

• 1-3: primary somatosensory

• 17: primary visual

• 34: part of primary olfactory (most

olfactory cortex is not neocortex)

• 41-42: primary auditory

• 43: primary taste (gustatory)

Motor

• 4: primary motor

• 6: supplementary motor

Association

• 39-40: language comprehension

(Wernicke’s area)

• 44-45: speech production (Broca’s)

Broca’s area

(areas 44, 45)

Wernicke’s area

(areas 44, 45)

Neocortex 4

Brodmann areas and cortical functions also correlate well with gross anatomical

features of the forebrain.

Central sulcus Primary motor cortex Primary somatosensory cortex

Primary visual

Primary auditory

Superior temporal gyrus

Supplementary motor

Frontal lobe

Broca’s area Wernicke’s area

White Matter 1

White matter is composed of bundles

of myelinated nerve cell axons,

which connect various gray matter

areas of the CNS to each other.

There are three types of fiber tracts: • association – connect gyri in same

hemisphere (short and long)

• commissural – connect corresponding

gyri in opposite hemispheres

• projection – connect cerebrum with other

parts of brain and spinal cord

White Matter 2

White matter fiber tracts connect

gray matter areas of the CNS to

each other.

Within the three types of tracts,

major bundles include: Association

• short (arcuate) fibers: primary

somatosensory with primary motor

• long (fasciculus) fibers: connect

Wernicke’s and Broca’s areas

Commissural

• corpus callosum

• anterior

Projection

• corona radiata

• internal capsule

sensory input from thalamus

motor output to spinal cord

Subcortical Areas 1

Below the cerebral cortex are

a variety of other structures,

called subcortical (literally

"below the cortex") structures.

Collectively, there are three

main groups, but not all the

nuclei in each group serve the

same function.

The three groups organized

roughly anterior to posterior

(and medial to lateral) are the:

• basal forebrain

• basal ganglia

• limbic system

(memory)

Basal

forebrain

Subcortical Areas 2

The basal forebrain is a collection

of structures located to the front

of and below the thalamus (rostral

to the hypothalamus). It includes

a number of structures including

the nucleus accumbens and the

nucleus basalis.

The nucleus accumbens plays a

significant role in the cognitive

processing of motivation and

reward learning, and in addiction.

The nucleus basalis plays a role

in the sleep-wake cycle and

learning and memory (this

nucleus undergoes damage in

Alzheimer’s disease).

(memory)

Nucleus

accumbens

Nucleus

basalis

Subcortical Areas 3

The basal ganglia include several

subcortical nuclei, including the

caudate and putamen (together

called the striatum) and the globus

pallidus, all lateral to the thalamus.

Other components include the

subthalamus (diencephalon) and

substantia nigra (mesencephalon).

The basal ganglia plays a role in

the selection of which of several

motor actions to execute at any

given time. Damage to the basal

ganglia can lead to Parkinson’s or

Huntington’s disease.

The limbic system is a set of brain

structures located on both sides of the

thalamus. Major components include:

Cerebral cortex:

• hippocampus (not neocortex)

• cingulate cortex

Subcortical

• amygdala

• septum

Diencephalon

• hypothalamus

• mammillary bodies

• anterior nuclei of thalamus

The structures of the limbic system

are involved in basic motivations (in

particular, hypothalamus), emotion

(amygdala), learning and memory

(hippocampus)

Subcortical Areas 4

StructureFunction: Cerebrum