The Brain

Copyright © 2010 Pearson Education, Inc.

The Brain


Cerebral Hemispheres

How is the brain organized?– Define the major lobes– Distinguish between gyri and sulci– Compare the functional areas of the cerebral

cortex


The cerebrum is divided into three major areas:• Cerebral Cortex• Internal White Matter• Basal Nuclei


The cerebral hemispheres form the superior part of the brain. It makes up most of the mass of the brain.


A. The Cerebral Cortex

The cortex is composed of gray matter which contains neuron cell bodies, dendrites, glial cells and blood vessels. It is only 2 to 4 mm in thickness. The folds increase the surface area.


The surface of the hemispheres is marked by elevated ridges called gyri and shallow grooves called sulci.


Lissencephaly, which literally means smooth brain, is a rare brain formation disorder caused by defective neuronal migration during the 12th to 24th weeks of gestation resulting in a lack of development of brain folds (gyri) and grooves (sulci).


Normal Brain Lissencephaly


Lissencephaly Normal Brain


The prognosis for children with lissencephaly varies depending on the malformation.

Many individuals remain in a 3-5 month developmental level, while others may appear to have near normal intelligence and development.

Some children with lissencephaly will be able to roll over, sit, reach for objects, and smile socially.


The cortex contains three kinds of functional areas:– Motor area– Sensory areas– Association areas


Each hemisphere is primarily concerned with sensory and motor function on the opposite (contralateral) side of the body.


Each hemisphere is not equal in function. There is lateralization (specialization) of cortical functions.Left hemisphere is logical while the right is creative


The motor areas control voluntary movement and are found primarily in the posterior part of the frontal lobes and include:– the primary motor cortex, – premotor cortex, – Broca’s area and – the frontal eye field.


Figure 12.8a Functional and structural areas of the cerebral cortex.

Gustatory cortex(in insula)

Primary motor cortexPremotor cortexFrontal eye field

Working memoryfor spatial tasksExecutive area fortask managementWorking memory forobject-recall tasks

Broca’s area(outlined by dashes)

Solving complex,multitask problems

(a) Lateral view, left cerebral hemisphere

Motor areas

Prefrontal cortex

Sensory areas and relatedassociation areas

Central sulcus

Primary somatosensorycortexSomatosensoryassociation cortex

Somaticsensation

Taste

Wernicke’s area(outlined by dashes)

Primary visualcortexVisualassociation area

Vision

Auditoryassociation areaPrimaryauditory cortex

Hearing

Primary motor cortex Motor association cortex Primary sensory cortexSensory association cortex Multimodal association cortex


Primary motor cortex is located in the precentral gyrus of the frontal lobe.

Their function is to control the precise voluntary movements of the skeletal muscles.


Figure 12.9 Body maps in the primary motor cortex and somatosensory cortex of the cerebrum.

GenitalsToes

Intra-abdominalSwallowing

Tongue

Jaw

Primary motorcortex(precentral gyrus)

Primary somato-sensory cortex(postcentral gyrus)

MotorMotor map inprecentral gyrus

SensorySensory map inpostcentral gyrus

Posterior

Anterior


Common disorders include stroke, tumors or traumatic brain injury.Effects include loss of specific motor functions.

Stroke

http://www.youtube.com/watch?v=KJe7U32lnpo


Premotor cortex is located just anterior precentral gyrus of the frontal lobe.

It's function is to control learned motor skills of a repetitive or patterned nature, for example typing.


Disorders of the premotor cortex are commonly due to stroke, tumors or trauma.One condition is known as Apraxia or the inability to recognize objects by touch.

http://www.youtube.com/watch?v=vTFdNk7JIoo


Broca’s Area lies anterior and inferior to the premotor cortex. It is typically found only in the left hemisphere and is the motor speech area.


Aphasia is a disorder caused by damage to the parts of the brain that control language. It can make it hard for you to read, write, and say what you mean to say.


There are four main types:• Expressive aphasia - you know what you

want to say, but you have trouble saying or writing what you mean


There are four main types:• Expressive aphasia• Receptive aphasia - you hear the voice or

see the print, but you can't make sense of the words


There are four main types:• Expressive aphasia • Receptive aphasia • Anomic aphasia - you have trouble using

the correct word for objects, places, or events


There are four main types:• Expressive aphasia • Receptive aphasia • Anomic aphasia • Global aphasia - you can't speak,

understand speech, read, or write Aphasia

http://www.youtube.com/watch?v=1aplTvEQ6ew


Frontal eye field is located on or near the premotor cortex and is above Broca’s area. This region controls the voluntary movement of the eyes.


The sensory area of the cerebral cortex is concerned with conscious awareness.

Areas involved with this function are found in the parietal, temporal and occipital lobes.


Primary somatosensory cortex receive information from the sensory receptors in the skin and proprioceptors (position receptors) in the skeletal muscles, joints and tendons.


Figure 12.9 Body maps in the primary motor cortex and somatosensory cortex of the cerebrum.

GenitalsToes

Intra-abdominalSwallowing

Tongue

Jaw

Primary motorcortex(precentral gyrus)

Primary somato-sensory cortex(postcentral gyrus)

MotorMotor map inprecentral gyrus

SensorySensory map inpostcentral gyrus

Posterior

Anterior


• Somatosensory association cortex serves to integrate sensory information such as temperature, pressure to produce an understanding of what is being touched.


Association Areas

Multimodal association areas receive input from multiple senses and sends outputs to multiple areas. There are 3 main areas:

• Anterior association area • Posterior association area • Limbic association area


Anterior association area

Is located in the frontal lobe. It is considered the most complicated and is involved with learning (cognition), recall and personality. Additional functions include working memory, abstraction and planning.


Posterior association area

Covers the temporal, parietal and occipital lobes. This area is involved with pattern recognition. It is what allows us to recognize familiar places. An additional function understands of written and spoken language.


Isolated problems with these association areas are rare.Trauma or stroke often leads to large areas of affliction.

The case of Phineas Gage

http://www.youtube.com/watch?v=MvpIRN9D4D4


Limbic association area

This area is sometimes called the pleasure center. In animal studies it is correlated with sexual arousal, behavior and olfaction (think about this last one). Big Bang

http://www.youtube.com/watch?v=u76jBk59RFk


B. Cerebral White Matter

The cerebral white matter is responsible for communicating between the cerebral areas and the lower CNS centers. This area consists largely of myelinated fibers bundled into large tracts.


The white fibers or tracts are classified based on which direction they run.– Commissural fibers connect gray areas of

the two hemispheres allowing them to coordinate.

– Association fibers connect different parts of the same hemisphere

– Projection fibers either enter the cerebral cortex from the lower brain or descend to the lower areas from the cortex.


Corpus Callosum (Commissures)

http://www.youtube.com/watch?v=ZMLzP1VCANo


Association Fibers


Figure 12.10 Types of fiber tracts in white matter.

Coronaradiata

Projectionfibers

Longitudinal fissure

Gray matter

White matter

Association fibers

Lateral ventricle

Fornix

Thirdventricle

Thalamus

Pons

Medulla oblongataDecussationof pyramids

Commissural fibers(corpus callosum)

Internalcapsule

Superior

Basal nuclei• Caudate• Putamen• Globus

pallidus

(a) (b)


C. Basal Nuclei

These represent the third region of the cerebral hemisphere. The basal nuclei consist of the:– caudate nucleus, – putamen and – the globus pallidus.


The basal nuclei receive input from the entire cerebral cortex. They appear to be important in starting and stopping the intensity of movements initiated by the cerebral cortex. They are important in our ability to multitask.


Together the putamen and globus pallidus form the lentiform nucleus that flanks the internal capsule


Figure 12.11b Basal nuclei (1 of 2).

Corpus callosumAnterior hornof lateral ventricleCaudate nucleusPutamen

Lentiformnucleus

(b)

Globuspallidus ThalamusTail of caudate nucleusThird ventricle

Cerebral cortexCerebral white matter

Anterior

Posterior

Inferior hornof lateral ventricle


Figure 12.11b Basal nuclei (2 of 2).

Corpus callosumAnterior hornof lateral ventricleCaudate nucleus

Lentiform nucleus

(b)

Thalamus

Third ventricle

Cerebral cortexCerebral white matter

Inferior hornof lateral ventricle


Disorders of the Basal Nucleus

The basal ganglia play a central role in a number of neurological conditions. The most notable are, Parkinson’s disease and Huntington's disease.

Basal ganglia dysfunction is also implicated in some other disorders of behavior control such as Tourette’s syndrome, and obsessive compulsive disorder (OCD),

http://www.youtube.com/watch?v=ECkPVTZlfP8


Question

1. What is meant by lateralization?


Question

2. How thick is the cerebral cortex?


Question

3. What are the three types of functional areas found in the cerebrum?


Question

4.

The Brain

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