The Brain
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Transcript of The Brain
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The Brain
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Cerebral Hemispheres
How is the brain organized?– Define the major lobes– Distinguish between gyri and sulci– Compare the functional areas of the cerebral
cortex
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The cerebrum is divided into three major areas:• Cerebral Cortex• Internal White Matter• Basal Nuclei
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The cerebral hemispheres form the superior part of the brain. It makes up most of the mass of the brain.
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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.
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The surface of the hemispheres is marked by elevated ridges called gyri and shallow grooves called sulci.
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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).
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Normal Brain Lissencephaly
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Lissencephaly Normal Brain
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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.
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The cortex contains three kinds of functional areas:– Motor area– Sensory areas– Association areas
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Each hemisphere is primarily concerned with sensory and motor function on the opposite (contralateral) side of the body.
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Each hemisphere is not equal in function. There is lateralization (specialization) of cortical functions.Left hemisphere is logical while the right is creative
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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.
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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
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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.
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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
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Common disorders include stroke, tumors or traumatic brain injury.Effects include loss of specific motor functions.
Stroke
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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.
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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.
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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.
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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.
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There are four main types:• Expressive aphasia - you know what you
want to say, but you have trouble saying or writing what you mean
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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
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There are four main types:• Expressive aphasia • Receptive aphasia • Anomic aphasia - you have trouble using
the correct word for objects, places, or events
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There are four main types:• Expressive aphasia • Receptive aphasia • Anomic aphasia • Global aphasia - you can't speak,
understand speech, read, or write Aphasia
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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.
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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.
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Primary somatosensory cortex receive information from the sensory receptors in the skin and proprioceptors (position receptors) in the skeletal muscles, joints and tendons.
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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
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• Somatosensory association cortex serves to integrate sensory information such as temperature, pressure to produce an understanding of what is being touched.
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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
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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.
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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.
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Isolated problems with these association areas are rare.Trauma or stroke often leads to large areas of affliction.
The case of Phineas Gage
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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
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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.
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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.
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Corpus Callosum (Commissures)
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Association Fibers
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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)
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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.
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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.
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Together the putamen and globus pallidus form the lentiform nucleus that flanks the internal capsule
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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
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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
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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),
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Question
1. What is meant by lateralization?
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Question
2. How thick is the cerebral cortex?
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Question
3. What are the three types of functional areas found in the cerebrum?
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Question
4.