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بسم هللا الرحمن الرحيم
Lecture 2- Neurophysiology Dr. Noor Jawad
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nd
stage Sunday 7 / 10 / 2018
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Cortical areas
Objectives :
1. what are cortical areas?
2. what are the areas for language comprehension, word formation?
The cortex is commonly described as comprising three parts:
sensory, motor, and association areas.
Sensory areas
The sensory areas are the cortical areas that receive and process
information from the senses. Parts of the cortex that receive
sensory inputs from the thalamus are called
primary sensory areas
.
The senses of vision, audition, and touch are served by the
primary visual
primary auditory
cortex and
primary somatosensory cortex respectively.
In general, the two hemispheres receive information from the
opposite (contralateral) side of the body. For example, the right
primary somatosensory cortex receives information from the left
limbs, and the right visual cortex receives information from the left
visual field. The organization of sensory maps in the cortex reflects
that of the corresponding sensing organ, in what is known as
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Motor areas
The motor areas are located in both hemispheres of the cortex. The
motor areas are very closely related to the control of voluntary
movements, especially fine fragmented movements performed by
the hand. The right half of the motor area controls the left side of
the body, and vice versa.
The motor cortex can be divided into
three areas:
is the main contributor to generating
neural impulses that pass down to the spinal cord and control the
execution of movement. However, some of the other motor areas
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in the brain also play a role in this function. It is located on the
anterior paracentral lobule on the medial surface.
is responsible for some aspects of motor
control, possibly including the preparation for movement, the
sensory guidance of movement, the spatial guidance of reaching,
or the direct control of some movements with an emphasis on
control of proximal and trunk muscles of the body. Located
anterior to the primary motor cortex.
3. The
functions including the internally generated planning of movement,
the planning of sequences of movement, and the coordination of
the two sides of the body such as in bi-manual coordination.
Located on the midline surface of the hemisphere anterior to the
primary motor cortex.
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Association areas
The association areas are the parts of the cerebral cortex that do not
belong to the primary regions. They function to produce a
meaningful perceptual experience of the world, enable us to
interact effectively, and support abstract thinking and language.
The parietal, temporal, and occipital lobes - all located in the
posterior part of the cortex - integrate sensory information and
information stored in memory. The frontal lobe or prefrontal
association complex is involved in planning actions and
movement, as well as abstract thought.
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Globally, the association areas are organized as distributed
networks. Each network connects areas distributed across widely
spaced regions of the cortex. Distinct networks are positioned
adjacent to one another yielding a complex series of interwoven
networks. Cortical association areas include:
1. Parieto- occipito temporal Association Area
2. Prefrontal Association Area
3. Limbic Association Area
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1. Parieto-occipitotemporal Association Area
The parieto-occipitotemporal association area lies in the large
parietal and occipital cortical space bounded by the somatosensory
cortex anteriorly, the visual cortex posteriorly, and the auditory
cortex laterally. As would be expected, it provides a high level of
interpretative meaning for signals from all the surrounding sensory
areas.
Wernicke’s Area Is Important for Language Comprehension.
The major area for language comprehension, called Wernicke’s
area, lies behind the primary auditory cortex in the posterior part
of the superior gyrus of the temporal lobe.
The Angular Gyrus Area
Is Needed for Initial Processing of Visual Language (Reading).
Posterior to the language comprehension area, lying mainly in the
anterolateral region of the occipital lobe, is a visual association
area that feeds visual information conveyed by words read from a
book into Wernicke’s area, the language comprehension area. This
so-called angular gyrus area is needed to make meaning out of the
visually perceived words. In its absence, a person can still have
excellent language comprehension through hearing but not through
reading.
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Area for Naming Objects.
In the most lateral portions of the anterior occipital lobe and
posterior temporal lobe is an area for naming objects. The
names are learned mainly through auditory input, whereas the
physical natures of the objects are learned mainly through visual
input. In turn, the names are essential for both auditory and
visual language comprehension.
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2.
Prefrontal Association Area
Prefrontal association area functions in close association with
the motor cortex to
plan complex patterns and sequences of
motor movements
. To aid in this function, it receives strong
input through a massive subcortical bundle of nerve fibers
connecting the parieto-occipitotemporal association area with
the prefrontal association area.
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Through this bundle, the prefrontal cortex receives much
preanalyzed sensory information, especially information on the
spatial coordinates of the body that is necessary for planning
effective movements. Much of the output from the prefrontal
area into the motor control system passes through the caudate
portion of the basal ganglia–thalamic feedback circuit for motor
planning, which provides many of the sequential and parallel
components of movement stimulation.
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The prefrontal association area is also essential to carrying out
“thought” processes.
This characteristic presumably results from
some of the same capabilities of the prefrontal cortex that allow it
to plan motor activities. It seems to be capable of processing
nonmotor and motor information from widespread areas of the
brain and therefore to achieve nonmotor types of thinking, as well
as motor types. In fact, the prefrontal association area is frequently
described simply as important for elaboration of thoughts, and it is
said to store on a short-term basis
“working memories”
that are
used to combine new thoughts while they are entering the brain.
Broca’s Area Provides the Neural Circuitry for Word
Formation
Broca’s area, is located partly in the posterior lateral prefrontal
cortex and partly in the premotor area. It is here that plans and
motor patterns for expressing individual words or even short
phrases are initiated and executed. This area also works in close
association with the Wernicke language comprehension center in
the temporal association cortex.
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3. Limbic Association Area
This area is found in the anterior pole of the temporal lobe, in the
ventral portion of the frontal lobe, and in the cingulate gyrus lying
deep in the longitudinal fissure on the midsurface of each cerebral
hemisphere. It is concerned primarily with behavior, emotions, and
motivation. This limbic system provides most of the emotional
drives for activating other areas of the brain and even provides
motivational drive for the process of learning itself.
Thank you
References : Guyton and Hall textbook of medical physiology,
thirteen edition