Cerebral Cortex

The cerebral cortex plays a critical role in both the planning and ongoing control of voluntary movements, functioning in both the highest and middle levels of the motor control hierarchy. The term sensorimotor cortex is used to include all those parts of the cerebral cortex that act together in the control of muscle movement. A large number of nerve fibers that give rise to descending pathways for motor control come from two areas of sensorimotor cortex on the posterior part of the frontal lobe: the primary motor cortex (sometimes called simply the motor cortex) and the premotor area (Figure 12-10). Different regions of the primary motor cortex are each concerned primarily with movements of one area of the body (Figure 12-11).

Other areas of sensorimotor cortex include the supplementary motor cortex, which lies mostly on the surface on the frontal lobe where the cortex folds down between the two hemispheres (see Figure 12-10b), the somatosensory cortex, and parts of the parietal-lobe association cortex (see Figures 12-10a and b).

Although these areas are distinct anatomically and functionally, they are heavily interconnected, and individual muscles or movements are represented at multiple sites. Thus, the cortical neurons that control movement form a neural network, such that many neurons participate in each single movement, and any one neuron may function in more than one movement. The neural networks can be distributed across multiple sites in parietal and frontal cortex, including the sites named in the preceding two paragraphs. The interaction of the neurons within the networks is flexible so that the neurons are capable of responding differently under different circumstances. This adaptability enhances the possibility of integration of incoming neural signals from diverse sources and the final coordination of many parts into a smooth, purposeful movement. It

Association Cortex

Parietal-lobe association cortex

Parietal-lobe association cortex

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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