Primary+Motor+Area

The primary motor area serves as a neocortical nodal point where impulses organized in other brain tissues are transferred for expression, as the entire body musculature is represented in this tisse and as it contributes the majority of axons (as compared to any other single brain area) that comprises the corticospinal tract.

-Gross and fine motor functioning including finger movements -The final common pathway where impulses organized in other brain areas are transferred for expression, particularly those involving the fingers, thumb, lips, tongue, and hand.
 * Primary Functions: **

extends beyond the confines of the precentral gyrus (area 4) and includes portions of area 6 and the somatosensory (1, 2, 3, 5) regions. These areas are richly interconnected, the somatosensory projections providing information important in the sensory guidance of movement
 * Broadman's Areas: **

-Premotor cortex -Secondary Motor Area
 * Connections From: **

Axonal projections from the motor and somesthetic regions all give rise to the massive cortico-spinal (pyramidal) tract which innervates cranial nerve and sensory and spinal motor neurons. For these reasons some refer to the somesthetic and motor regions as the sensorimotor cortex.
 * Conections To: **

-Can trigger contractions and movements of tiny muscle groups on the opposite side of the body -Conversely, however, activation of one half of the body can induce bilateral activation of the motor area.
 * Electrical Stimulation: **

-Paralysis: initially results in a flaccid hemiplegia such that the muscles are completely without tone contralateral to the lesion. If the examiner were to raise and release an effected arm, it would drop in a limp rag doll fashion. Over the course of the next several days the muscles develop increased tone and there is resistance to passive movements. Reflexes become very brisk and spasticity and hyperreflexia are manifest. With massive lesions extending into the medial regions (where the leg is represented), the leg will become permanently extended and the arm will assume a flexed position. After several weeks or months a very limited capacity to perform gross movements reappears. Fine movements are usually permanently lost.
 * Injury/Damage: **

<span style="color: #000000; font-family: 'Times New Roman',serif;">The primary motor area is organized in a dual fashion in regard to the control over the body musculature. There is a one to one correspondence between neurons located in the primary motor area and specific muscles, which in turn makes fine motor functioning possible. However, there are also convergent connections as well, such that a single neuron innervates numerous muscle groups which in turn are innervated by yet other motor neurons. In this manner, a neuron innervating a specific group of arm muscles, can also act on other muscles so as to coordinate movement.
 * <span style="color: #000000; font-family: 'Times New Roman',serif;">Notes: **

<span style="color: #000000; font-family: 'Times New Roman',serif;">Hence, a given muscle is also influenced by a number of motor neurons, such that a single muscle is represented by multiple neurons. Multiple representation enables the motor cortex to coordinate a variety of movements, such that wide areas of the motor area become activated during even discrete movements of, for example a single finger.

<span style="color: #000000; font-family: 'Times New Roman',serif;">Hence, the entire musculature of the body is neuronally represented in the motor cortex. Nevertheless, since certain muscle groups play a proportionately greater role in the performance of complex (vs simple) movements, a relatively greater number of neurons are involved in their representation. Thus, the hand and fingers have extensive cortical representation whereas a smaller neuronal field is concerned with the elbow. <span style="color: #000000; font-family: 'Times New Roman',serif;">Like the somesthetic neocortex which maintains a double representation of the body surface (e.g. a double body image) the primary motor area contains multiple representations of the body's musculature (Colebatch et al., 1991; Humphrey, 1986; Sanes et al., 1995; Shinoda, et al., 1981).

<span style="color: #000000; font-family: 'Times New Roman',serif;">Activity begins in the primary motor area following activation of the premotor and SMA and becomes maximally active at the time of movement. However, neurons in the primary motor area also become active just prior to movement, increase their activity during movement, and will become increasingly active in response to direction, velocity, and the amount of force required to perform the movement. These neurons will increase their activity depending on the amount of force involved in the movement, and in reaction to the direction and velocity of movement.

<span style="color: #000000; font-family: 'Times New Roman',serif;">Moreover, the motor area is exceedingly plastic and is capable of learning and memorizing and remembering. If a single muscle is repeatedly activated and/or as an individual becomes increasingly skilled at performing a certain motor tasks, the cortical territory representing those muscles will significantly increase.