Brain Anatomy


Brain Anatomy

The brain is similar to a computer. It has modules that process information and pass information from one module to another for additional processing and analysis. When your eyes read the text on this page the cells in the back of the eye detect the shape and coloof the letters and transmit this information to areas in the brain for the processing of visual information. These other areas of brain re-assemble the feature of the letters to identify the letters, and assemble the letters into words, and words into sentences to give the text meaning. If the text contain instructions on how to construct an object, then nerve cells in other modules of the brain that control movement are activated to send electrical impulses down to cells that eventually control muscles for movement. Information is therefore transmitted in the brain from one modular region to another as electrical impulses for the analysis of this information, and the activation of other modular regions of brain to initiate responses in reaction to this information.

The Neocortex 

 

The brain is encased in the skull and when exposed it appears as a convoluted mass of tissue that makes up the neocortex. The convolutions consist of ridges called gyri, and fissures called sulci. Three sulci, the lateral sulcus, the central sulcus, and the parieto-occipital sulcus form borders that partition the brain into lobes. These lobes are called the frontal lobe in the front of the brain, the occipital lobe in the back of the brain, the parietal lobe in the top of the brain, and the temporal lobe.









Functional Regions of the Neocortex 




 
The lobes can be subdivided into functional regions. These functional areas of the brain were initially identified in studies using electrodes to record the electrical activity of the cells within the brain. Touching the surface of the skin, for example, would elicit electrical responses by cells in specific regions of the neocortex. Less invasive approaches now use magnetic resonance imaging (MRI) to visualize the anatomy of the brain and functional MRI (fMRI) to measure blood flow as a marker for brain activation.

Based on the different approaches for studying brain function, it has been demonstrated that the occipital lobe contains the visual cortex which receives information that originated from the eyes.  The frontal lobe includes the motor cortex which transmits information to cells that control muscle movement; the parietal lobe contains somatosensory cortex which responds to sensations felt on the surface of the skin; and the temporal lobe incudes the auditory cortex that responds to sounds detected by the ear. The temporal lobe also contains the hippocampal formation, a region of the brain that plays an important role in learning and memory.  The neocortex also consists of regions that are involved in language:  Wernicke’s area is involved in the processing of visual and auditory information related to language input; and  Broca’s area is involved in generating speech for language output.



Brain Symmetry 


 

The bilateral symmetry of the brain can be seen when viewing it from the top (dorsal aspect).  The left side of the brain in the somatosensory cortex receives information about touch, pressure, pain, and temperature from the right side of the body, while the somatosensory cortex on the right side of the brain receives this type of information from the left side of the body.  Similarly, information about movement is transmitted from the motor cortex on the left side of the brain to control the muscles on the right side of the body for movement, while movement information from the motor cortex on the right side of the brain controls muscles on the left side of the body.  This bilateral symmetry of brain anatomy and function is also found for other modalities that will be discussed later in the book. 


Although there is substantial symmetry in brain anatomy and function, asymmetry in brain function has been documented.  Language and analytical abilities, for example, appear to be predominantly located in the left hemisphere of the brain while musical and artistic abilities are predominantly localized to the right hemisphere.  The neural mechanisms underlying these asymmetries will be discuss later in the book.

 Because of the functional specificity of different regions of the brain, damage to the brain can result in highly selective deficits.  Patients who experience a stroke, for example, where there is a blockage of blood flow to Broca’s area can exhibit an inability to speak yet are able to write in response to a question. Strokes that occur on right side of the brain can lead to paralysis on the left side of the body and not affect movement on the right side of the body. And patients with Alzheimer disease where there is a loss of nerve cells in the hippocampal formation will experience functional deficits in learning and memory.


Brain Areas Beneath the Neocortex 
 


The structures of the brain that lie beneath the neocortex can be seen by making a slice down the middle of the brain to reveal the brain regions near the midline.  From this perspective, the medial (towards the midline) aspects of the frontal, parietal and occipital cortex can be seen.  Beneath the neocortex are subcortical areas of the brain involved in a variety of different functions. The thalamus for example, relays information from the sense organs to specific sensory cortical areas. Collectively, the sense organs, thalamus, and somaticsensory cortex form the sensory system. Other subcortical areas such as the hypothalamus control the secretion of hormones for growth, reproduction, and metabolism.

The neocortical and subcortical components of the brain rest upon the brain stem--an area that plays important roles in several functions.  By receiving information from the motor cortex and transmitting it to the spinal cord, the brain stem aids in maintaining body posture. It also transmits information to and from the cerebellum, another area involved in locomotor coordination.  Collectively, these areas form the motor system.

Areas within the brain stem also control breathing and the rate and force at which the heart beats.  These changes occur automatically and are not typically under conscious control.  These functions of the brain stem are thus part of the autonomic nervous system

Emerging from the brain stem are cranial nerve fibers.  These cranial nerves are sensory and motor fibers that innervate the face and head.  Sensory nerves transmit information from the internal organs conveying information about their condition or state of function. Motor nerves transmit information to the internal organs to control how they operate.  Located beneath the brain stem is the spinal cord. It also transmits information to and receives information from the body's internal organs, as well as from skeletal muscles and skin.  The spinal cord is the major source of nerve fibers that emerge from the nervous system to innervate muscles for movement, and the first relay station to receive sensory information from the rest of the body.  Details of spinal cord anatomy and function will be discussed in a later section of the book.

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