Lobes of the cerebrum and their functions

025 The 4 Lobes of the

Each cerebral hemisphere is divided into four lobes; the frontal, parietal, temporal, and the occipital.

The Frontal Lobe is the most anterior lobe of the brain. Its posterior boundary is the fissure of Rolando, or central sulcus, which separates it from the parietal lobe. Inferiorly, it is divided from the temporal lobe by the fissure of Sylvius which is also called the lateral fissure.

This lobe deals with with higher level cognitive functions like reasoning and judgment. Sometimes called executive function, it is associated with the pre-frontal cortex. Most importantly the frontal lobe contains several cortical areas involved in the control of voluntary muscle movement, including those necessary for the production of speech and swallowing.

Broca's Area is found on the inferior third frontal gyrus in the hemisphere that is dominant for language. This area is involved in the coordination or programming of motor movements for the production of speech sounds. While it is essential for the execution of the motor movements involved in speech it does not directly cause movement to occur. The firing of neurons here does not generate impulses for motor movement instead it generates motor programming pattern. This motor plan is sent to upper motor neurons in the precentral gyrus (motor strip) which in turn send the signals to to the lower motor neurons (cranial and spinal nerves) which take the signals to muscle end plates.

Injuries to Broca's area may cause or .

The precentral gyrus, which may also be called the primary motor area or, most commonly, the motor strip is immediately anterior to the central sulcus. It controls the voluntary movements of skeletal muscles; cell bodies of the pyramidal tract are found on this gyrus.

The amount of tissue on the precentral gyrus that is dedicated to the innervation of a particular part of the body is proportional to the amount of motor control needed by that area, not just its size. For example, much more of the motor strip is dedicated to the control of speech (tongue, lips, jaw, velum, pharynx, and larynx) than to the trunk.

The premotor area or supplemental motor area is immediately anterior to the motor strip. It is responsible for the programming for motor movements. It does not, however program the motor commands for speech as these are generated in Broca's area which is also located in the frontal lobe.

The most anterior part of the frontal lobe is involved in complex cognitive processes like reasoning and judgment. Collectively, these processes may be called biological intelligence. A component of biological intelligence is executive function. According to Denckla, 1996, executive function regulates and directs cognitive processes, decision making, problem solving, learning, reasoning and strategic thinking. Some characteristics of right hemisphere syndrome may be considered problems of the executive function. They include left side neglect where there is a lack of awareness of the left side of the body.

The Parietal Lobe is immediately posterior to the central sulcus. It is anterior to the occipital lobe, from which it is not separated by any natural boundary. Its inferior boundary is the posterior portion of the lateral fissure which divides it from the temporal lobe.

The parietal lobe is associated with sensation, including the sense of touch, kinesthesia, perception of warmth and cold, and of vibration. It is also involved in writing and in some aspects of reading.

The postcentral gyrus which is also called the primary sensory area or the sensory strip is immediately posterior to the central sulcus. This area receives sensory feedback from joints and tendons in the body and is organized in the same manner as the motor strip.

Like the motor strip, the sensory strip continues down into the longitudinal cerebral fissure and so has both a lateral and a medial aspect.

The presensory, secondary sensory, or sensory association areas are located behind the postcentral gyrus. These areas are capable of more detailed discrimination and analysis than is the primary sensory area. They might, for example, be involved in sensing how hot or cold something is rather than simply identifying it as hot or cold. Information is first processed in the primary sensory area and is then sent to the secondary sensory areas.

The angular gyrus lies near the superior edge of the temporal lobe, immediately posterior to the supramarginal gyrus. It is involved in the recognition of visual symbols. Geschwind described this area as "the most important cortical areas for speech and language" and the "association cortex of association cortices." He also claims that the angular gyrus is not found in non-human species.

Fibers of many different types travel through the angular gyrus, including axons associated with hearing, vision, and meaning. The arcuate fasciculus, the group of fibers connecting Broca's area in the frontal lobe to Wernicke's area in the temporal lobe also connects to the angular gyrus.

The following disorders may result from damage to the angular gyrus in the hemisphere that is dominant for speech and language: anomia, alexia with agraphia, left-right disorientation, finger agnosia, and acalcula.

Anomia according to Webb, Adler, and Love, 2008 is the loss of power to name objects and people. It is difficulty with word-finding or naming. Someone suffering just from anomia can list the functions of an object and explain it meaning, but cannot recall its name.

Alexia with agraphia refers to difficulties with reading and writing.

Left-right disorientation is an inability to distinguish right from left.

Finger agnosia is the lack of sensory perceptual ability to identify which finger is which.

Acalcula refers to difficulties with arithmetic.

The Temporal Lobe is inferior to the lateral fissure and anterior to the occipital lobe. It is separated from the occipital lobe by an imaginary line rather than by any natural boundary.

The temporal lobe is associated with auditory processing and olfaction. It is also involved in semantics, or word meaning. Wernicke's area is located there on the first temporal gyrus.

Wernicke's Area located on the posterior portion of the superior temporal gyrus in the hemisphere that is dominant for language. This area plays a critical role in the ability to understand and produce meaningful speech. A lesion here will case Wernicke's aphasia.

Heschl's Gyrus, is the area in the temporal where sound first reaches the brain. It is is also known as the anterior transverse temporal gyrus, and is the primary auditory area.

There are two secondary auditory or auditory association areas which make important contributions to the comprehension of speech. They are part of Wernicke's area..

The Occipital Lobe, which is the most posterior lobe has no natural boundaries on its lateral aspect. It is involved in vision.

The primary visual area receives input from the optic tract via the thalamus.

The secondary visual areas integrate visual information, giving meaning to what is seen by relating the current stimulus to past experiences and knowledge. A lot of memory is stored here. These areas are superior to the primary visual cortex.

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