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Motor, Sensory, Visual and Olfactory Areas of Lateral Surface of the Brain
The cerebral cortex is demarcated into large number of areas which differ from each other in structure and function. The functional areas of the brain are referred to as the Brodmann’s areas.
In this specimen we can identify the following structures and functional areas (labelled) in the superolateral surface of the cerebrum.
- Primary motor area
- Central sulcus
The central sulcus is a prominent sulcus/ groove that begins by cutting the superomedial border of the cerebral hemisphere about 1 cm behind the mid-point between the frontal and occipital poles. It forms a boundary between the motor area of the cerebral cortex in front and the sensory area is behind.
- Primary sensory area
- Visual area
- Auditory area
- Motor speech area of Broca
A brief description of the functional areas in the superolateral surface of the brain is given below:
Frontal lobe
Motor area or Primary motor area (Broadmann's area 4)
The primary motor area is located in the precentral gyrus and anterior part of paracentral lobule. It produces isolated movements on the opposite side of the body
Premotor area or secondary motor area (Broadmann's area 6)
The premotor area is located anterior to the primary motor area in the posterior parts of superior, middle and inferior frontal gyri. It also extends on to the medial surface of the hemisphere. The premotor area is responsible for successful performance of the voluntary motor activities.
Frontal Eye Field (Broadmann's area 8)
The frontal eye field lies in the middle frontal gyrus in front of precentral gyrus. It causes conjugate movements of the eyes (eyes move to opposite side). It controls voluntary scanning movements of the eyes and is independent of visual stimuli.
Motor Speech area of Broca or Broca's area [Broadmann's area 44 and 45 (on the dominant hemisphere)]
The Broca's area is located in the pars triangularis and pars opercularis of the inferior frontal gyrus. Broca's area is responsible for the production of expressive speech/vocalization.
Prefrontal cortex (Broadmann's area 9, 10, 11 and 12)
The prefrontal cortex is the part of the frontal lobe that lies anterior to the motor and premotor areas. This area is concerned with individual's personality. It influences the initiative and judgement of an individual. It is also concerned with the depth of emotions, social, moral and ethical awareness, concentration, orientation and foresightedness.
Parietal lobe
Primary sensory area (Broadmann's area 3,1 and 2)
The primary sensory area occupies the postcentral gyrus and posterior part of paracentral lobule. It receives fibers from ventral posterior lateral and ventral posterior medial nuclei of thalamus. This area is concerned with perception of exteroceptive (pain, touch and temperature) and proprioceptive (vibration, muscle and joint sense) sensations from the opposite half of the body.
Sensory association areas (Broadmann's area 5 and 7)
The sensory association area occupies the superior parietal lobule. It is concerned with the perception of shape, size, roughness, and texture of the objects. It helps in stereognosis.
Occipital lobe
Primary visual area (Broadmann's area 17)
The primary visual area is situated in the walls and floor of the posterior part of the calcarine sulcus. It receives fibers from lateral geniculate body. The area is concerned with reception and perception of isolated visual impressions such as color, size, form, motion, illumination and transparency.
Secondary visual area (Broadmann's areas 18 and 19)
The secondary visual area surrounds the primary visual area. The area interprets and relates the visual information received by primary visual area. Thus the area is responsible for recognition of the objects seen.
Temporal Lobe
Primary auditory area (Broadmann's areas 41 and 42)
The primary visual area is situated in the inferior wall of posterior ramus of lateral sulcus. The area is concerned with the reception of isolated impressions of loudness, quality and pitch of the sound. It also picks the source of sound.
Secondary auditory area (Broadmann's area 22)
The secondary auditory area is situated posterior to primary auditory area in the lateral sulcus and in the superior temporal gyrus. This area is responsible for the interpretation of the sound heard.
Sensory speech area of Wernicke (Broadmann's areas 39 and 40 on the dominant hemisphere)
The sensory speech area is located in the dominant hemisphere occupying the posterior part of the superior temporal gyrus of temporal lobe and angular and supramarginal gyri of the inferior parietal lobule. The area is concerned with the interpretation of language through visual and auditory input.
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