The Brain Body Movement

The motor cortex is located in the most posterior part of the frontal lobe, just anterior to the central sulcus.

A Brodmann area is a region of the cerebral cortex defined by its particular cellular structure and organization.

Brodmann areas are named with specific numbers.

Areas 4 and 6

Area 4 is located just anterior to the central sulcus (precentral gyrus), while area 6 is just anterior to area 4.

Brodmann area 4

Contralateral describes the characteristic of the brain that each cerebral hemisphere corresponds to the movements and the sensations of the opposite side of the body.

Somatotopic describes the characteristic of the brain that every area of the body corresponds to a specific point on the brain.

In motor function, this point is located on the primary motor cortex (precentral gyrus).

In sensory function, this point is located on the primary somatosensory cortex (postcentral gyrus).

The motor homunculus is a complete map of the motor cortex that pinpoints the exact location of the cortex that corresponds to the movement of each body part.

There is also a sensory homunculus that maps out the somatosensory cortex.

The areas of the motor homunculus are proportional to the complexity of the movements they perform, not to the size of the body part.

For example, the areas of the homunculus that correspond to the hands and face are very large compared to those for the legs and arms.

1. The premotor area (PMA)

2. The supplementary motor area (SMA)

The premotor area (PMA ) is located in the lateral portion of Brodmann area 6 and is responsible for integrating sensory information with motor movements, as well as controlling the muscles closest to the body’s main axis.

The supplementary motor area (SMA) is located on the medial aspect of Brodmann area 6 and is responsible for planning complex movements, as well as coordinating movement of the body’s extremities.

The posterior parietal cortex functions to assist the motor cortex in regulating voluntary movement by receiving somatosensory, proprioreceptive, and visual imputs, and using this information to determine body position and plan for body movement.

The nerve bundles of the basal ganglia include:

1. The caudate nucleus

2. The putamen

3. The globus pallidus

4. The subthalamic nucleus

Although the substantia nigra is closely associated with the basal ganglia, it is not considered to be part of the grouping.

The basal ganglia work as part of a complex loop involving the cortex and the thalamus, in which voluntary motor functions become initiated, coordinated, and regulated.

The basal ganglia also work in conjunction with a similar loop in the cerebellum.

Both the caudate nucleus and the putamen, which together form the striatum, are targets for cortical afferents into the basal ganglia.

The globus pallidus emits efferents from the basal ganglia to the thalamus.

The order in which information passes through the basal ganglia motor loop is the following:

1. Cortex

2. Striatum (caudate nucleus, putamen)

3. Globus Pallidus

4. Thalamus

5. Cortex (supplementary motor area)

Parkinson’s disease and Huntington’s disease

Symptoms of Parkinson’s disease often include difficulty starting planned movements, as well as trembles and slowness during movement.

Parkinson’s patients show a deficiency in dopamine in the basal ganglia.

The symptoms of Huntington’s disease related to movement include the following:

1. Involuntary jerking

2. Involuntary and sustained muscle contraction

3. Slow and uncoordinated movements

4. Muscle rigidity

5. Impaired balance, posture, and gait

The functions of the cerebellum include:

1. Storing previously learned movements

2. Assisting in the fine-tuning and coordination of movements

3. Analyzing visual signals associated with movements

4. Determining the speed and fluidity of movements, in order to adjust motor signals accordingly

The cerebellum is divided into three regions, each of which has a particular function.

The cortex projects its axons to the pons, before the pons projects its axons to the cerebellum.

The cerebellum sends its axons to the thalamus, specifically the ventrolateral nucleus, before reaching the motor cortex.

The vermis is the midline structure between the two hemispheres of the cerebellum that closely resembles a worm.

1. vestibulocerebellum

2. spinocerebellum

3. cerebrocerebellum

The vestibulocerebellum is closely involved with balance because it is connected to the vestibule of the inner ear.

The spinocerebellum, because of its close association with the spinal cord, functions to maintain body posture, control muscle tension, and relax the muscles required for planned movements.

The cerebrocerebellum, because of its close connection with the cortex, functions to coordinate voluntary muscle movements.

It controls both the muscles causing the action, and relaxes muscles opposing the planned action.

1. fastigial

2. emboliform

3. globose

4. dentate

A person with cerebellar damage will experience difficulties coordinating balance and posture, have an uncertain gait, and often times when reaching for an object, hand movement will begin too slowly and quickly accelerate past the intended object.

Regardless of the origin of the damage, the associated manifestations of cerebellar damage is called cerebellar syndrome.