How the cerebral cortex works and its major innervations and function.
Principles of cortical function
Primary and belt regions
Belt regions are most of the areas
Belt regions give higher knowledge of visual stimulus
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.
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.
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.