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Cerebral Cortex

How the cerebral cortex works and its major innervations and function.

CEREBRAL CORTEX

Principles of cortical function

Primary and belt regions

Belt regions are most of the areas

Belt regions give higher knowledge of visual stimulus

Feature detection

When neurophysiologists study cortical cells, if they study visual cells what they find is that the cortical cells are feature detectors. They respond to a particular configuration of a stimulus.

They respond and recognize specific features.

LESIONS – sensory defecits

Lesions of somatosensory cortex à When post central gyrus is lesioned à Person has difficulty recognizing tactile stimulus (can’t tell the dif b/w dif roughness, shape, hard or soft)

Lesion of the belt area of superior parietal lobule à tactile agnosia (lack of knowledge/understanding)

With finger aagnosia – the person doesn’t have loss of tactile ability. But, he has finger agnosia so he can’t tell you if you point to a finger which finger it is with his eyes closed.

Lesion of visual cortex à blindness

Lesion of area 19 (belt area near visual cortex) à achromatopsia (loss of color vision)

Lesion of inferior temporal cotex à prosopagnosia (unable to recognize faces)

Visual stimuli go to area 17 but everything is processes later in other areas.

LESIONS – apraxia/ motor deficits

Lesion of motor cortex à contralateral spastic paralysis (think of the pyramidal tract)

Lesion of the supplementary motor area (in front of area 4 the motor cortex) à contralateral apraxia (the patient is not paralyzed but they cannot produce certain learned motions. A patient may not be able to strike a match.

LESION – aphagias (language defecits)

Lesion of Broca’s area à there is an area on the frontal lobe involved with speech. This person would have expressive aphasia

Lesion of Wernicke’s area à receptive aphasia associated with a lesion behind the superior temporal gyrus where the gyri of heschl are located. These people can speak and produce words and are very talkative. But they talk nonsense and their comprehension is affected. They can make up words. Speaks fluently and continuously. Wernicke’s area is right behind auditory cortex and is more involved with understanding speech then producing it.

DOMINANT HEMISPHERE – language in most people is restricted to one hemisphere not both. The hemisphere which has the language function is called the dominant hemisphere

All right-handed persons are left hemisphere dominant

50% of left-handed persons are also left hemisphere dominant.

If a person is right-handed and has a right-sided spastic paralysis, it is crucial to know which handed they are. If they are a lefty then the language function will be preserved versus a righty would not have it preserved.

Combination of spastic paralysis and aphagsia is common for right-handed people.

To read something aloud:  Wernicke’s area( comprehension) , angular gyrus à broca’s area (organize) à face area of the motor cortex (to move the lips)

FUNCTION OF NON-DOMINANT HEMISPHERE

Gesture, emphasis and emotional aspects of speech

People that have a lesion of non-dominant hemisphere speak in a flat tone with no gestures

Spatial relationships – rt hemisphere for ability to comprehend something in space while lt hemisphere e is more for linear things like reading.

Musical ability

Lesion à contralateral neglect. (like putting on a jacket and forget the left sleeve)

FRONTAL LOBE SECTIONS

Lesion à frontal lobotomy

Before the discovery of anti-psychotic drugs there was a movement of psycho-surgery where they lesioned the brain to change their personalities.

A person had damage to the frontal lobe and personality had changed.

ARTERIAL SUPPLY

Stroke à leading cause of disability

There are 2 blood supplies that supplies the brain

1. Vertebral (2 which form the basilar arteries  and meet at the circle of Willis)

2. Internal coratid

2 vertebral à basilar à posterior cerebral à posterior communicating à middle certebral à anterior cerebral à anterior communicating

Blood will not go in a circle

It is important to know the major vessels and what part of the brain they serve.

Middle Cerebral artery

Biggest of the cerebtral arteries

Goes into the fissure of sylvius

Supplies most of the lateral part of the hemisphere (except the rim at the top, medial surface, or all of the temperol lobe, or occipital lobe)

Anterior Cerebral artery

Supplies hthe medial surface of the motor cortex, somatosensory area.

Medial surface is the leg

A stroke here will give you the paralysis of the leg not head

Posterior cerebral artery

Curves around midbrain

Supplies occipital lobe

Linked to internal carotid by posterior communicating artery.

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