The primary motor area of the cerebral cortex is located in the precentral gyrus of the frontal lobe, just in front of the central sulcus, and is concerned mainly with the voluntary initiation of finely controlled movements such as those of the hands, fingers, lips, tongue, and vocal cords. The amount of area in the primary motor cortex devoted to a particular muscle or muscle group is a reflection of the degree of fine motor control required for the proper functioning of these muscles. For example, the muscles that control speech or the use of the fingers are represented by many more neurons within the primary motor cortex than are the larger muscles of the legs or trunk. This disproportionate representation within the primary motor cortex is a reflection of the relative importance the brain places on the proper control of different muscles.

Axons from the primary motor cortex descend through the internal capsule, midbrain, and pons to the medulla. These axons are called pyramidal because of the shape of the structure they form with the medulla. Within the medulla, most of these axons decussate and continue down into the spinal cord via the lateral corticospinal tracts. Fibers that do not decussate in the medulla descend down the spinal cord via the ventral corticospinal tracts. Most of these fibers eventually decussate at lower levels within the cord. Pyramidal cell axons also connect within the brain with the basal ganglia, the brainstem, and the cerebellum. Generally, these pyramidal motor nerves constitute a direct pathway from the primary motor area to the muscles and are concerned mostly with control of discrete, detailed body movements.

The premotor area of each hemisphere is located in the cortex immediately in front of the primary motor cortex in the frontal lobe. On the whole, this area is concerned with movement of the opposite side of the body, especially with control and coordination of skilled movements of a complex nature such as throwing or kicking a ball. In addition to its subcortical connections with the primary motor area, its neurons also have direct connections with the basal ganglia and related nuclei in the brainstem—for example, the reticular formation. Many of the axons from these subcortical centers cross to the opposite side before descending as extrapyramidal tracts in the spinal cord. Collectively, the connections from the premotor area to these related nuclei compose the extrapyramidal system, which coordinates gross skeletal muscle activities that are largely automatic and repetitive in nature. Examples are postural adjustments, chewing, swallowing, gesticulating during speech, and associated movements that accompany voluntary activities. Certain portions of the extrapyramidal tract also have an inhibitory effect on spontaneous movements initiated by the cerebral cortex and serve to prevent tremors and rigidity. Complete structural and functional separation of the pyramidal and extrapyramidal systems is impossible because they are so closely connected in the harmonious work of executing complex coordinated movements.

Of interest to the PACU nurse is that drugs used during the perioperative period can cause extrapyramidal reactions eliciting stereotypical neurologic reactions. More specifically, the neuroleptics such as the phenothiazines (of which chlorpromazine is the prototypal drug), the butyrophenones as typified by Droperidol (Inapsine) and haloperidol (Haldol), and the antiemetic metoclopramide (Reglan) are known to produce extrapyramidal reactions. The following four types of extrapyramidal reactions exist: drug-induced parkinsonism, akathisia, acute dystonic reactions, and tardive dyskinesia.

Drug-induced parkinsonism, which can occur 1 to 5 days after the administration of the neuroleptic drug, is typified by a generalized slowing of automatic and spontaneous movements (bradykinesia) with a mask-like facial expression and a reduction in arm movements. The most noticeable signs of drug-induced parkinsonism syndrome are rigidity and oscillatory tremor at rest. The treatment is an antiparkinsonian agent such as levodopa, trihexyphenidyl, and benztropine.

Akathisia, which can occur immediately or up to 60 days after the administration of a neuroleptic drug, refers to a subjective feeling of restlessness accompanied by a need on the part of the patient to move about and pace back and forth, acute anxiety, and a feeling of impending doom. Treatment requires a reduction in the dosage of the responsible drug and the administration of a benzodiazepine if encountered during the perioperative period.

Acute dystonic reactions may occur after the administration of some psychotropic drugs and are characterized by torsion spasms such as facial grimacing and torticollis. These reactions are occasionally seen when a phenothiazine is first administered, and they are associated with oculogyric crises (involuntary eye movements). Acute dystonic reactions may be mistaken for hysterical reactions or seizures and can usually be reversed with anticholinergic antiparkinsonian drugs such as benztropine or trihexyphenidyl.

This area is only one point in the complicated network needed to form spoken and written words. The motor speech area lies at the base of the motor area and slightly in front of it in the inferior frontal gyrus and is also known as the Broca area. In right-handed people, the language and speech areas are usually located in the left hemisphere. In those who are left-handed, these areas may lie within the right or the left hemisphere.

This area of the frontal lobe lies anterior to the premotor area, has extensive connections with other cortical areas, and is believed to have an important role in complex intellectual activities such as mathematic and philosophic reasoning; abstract and creative thinking; learning; judgment and volition; and social, moral, and ethical values. The prefrontal area also influences certain autonomic functions of the body with the conduction of impulses directly or indirectly through the thalamus to the hypothalamus, which makes possible certain physiologic responses to feelings such as anger, fear, and lust.