Brain systems
What Are Brain Systems?
Learning changes the brain
Modern technology allows neuroscientists to study the brain in ways that were not available before. However, many of the historical subdivisions and general classifications used long ago are still used in modern neuroscience.
When we refer to brain systems, we are talking about conceptual frameworks - subdivisions and classifications - that help us understand how different areas of the brain function, process, and respond to input from the world and from our bodies.
The brain is complex, so conceptual frameworks will always be limited, but they help neuroscientists organize and analyze information about brain functions and neuronal pathways, the brain's communication networks.
Sensory and motor systems
Sensory systems send information to the brain about the world outside our bodies and at a distance.
Sensory systems, like the auditory and visual systems, refer to areas of the brain that process information from the senses. Motor systems coordinate motor activity - i.e., movement of the muscles.
Sensory perceptions trigger our brain to formulate both thought and plans about movement.
Auditory and visual systems
Auditory system refers to areas of the brain that process and interpret external input that we experience as hearing.
Visual system refers to areas of the brain that process and interpret external input that we experience as seeing.
The auditory and visual systems are typical sensory systems.They send information about the world outside our bodies and at a distance, triggering the brain to formulate thoughts, actions, and responses.
auditory pathway
The auditory system is the sensory system for the sense of hearing.
Sound waves funnelled into the external ear canal cause the ear drum to vibrate. The ear drum separates the external and middle ears.
Three tiny bones transmit these vibrations on to the cochlea, a snail-shaped, fluid-filled structure in the inner ear. Vibration from structures in the cochlea travel along the auditory nerve fiber, to the cochlear nucleus.
Cells from the cochlear nucleus transmit auditory signals as electrical impulses along complex pathways, eventually stimulating auditory areas of the cortex.
The brain interprets these impulses, and we experience the auditory perception as "hearing."
visual pathway
The eyeball focuses light rays on the retina, a sheet of neurons at the back of the eye.
The cornea is the transparent outer layer through which light passes.
The lens is the transparent flexible structure that brings objects at different distances into focus.
The cornea and the lens bend (refract) the light so that it can be focused on the retina.
The pupil adjusts to light conditions - opening under low light conditions, and closing to protect the retina under bright light conditions.
Magic tricks work because the brain constructs perception.
Another example of the brain making sense of visual stimulus is what we experience when we view ambiguous images that can be "seen" or interpreted in different ways.
Click here for examples of visual ambiguity.
Light is absorbed by receptors at the back of the retina. Different structures in the retina are responsible for colour and high visual acuity (fine, sharp details)
Information - form, motion, colour, etc. - from the eye is transmitted along the optic nerve to the brain, stimulating visual areas of the cortex.
Parts of the eye project to both parts of the brain, so that each hemisphere processes information from the opposite half of the visual field. Information from each eye is kept separate, as is information about form, motion, and colour.
We experience this perception as "seeing."
The information that reaches the brain is not a picture of the world. What we "see" is the brain's interpretation of the information it receives from the eyes.
Motor systems
The motor system is the part of the central nervous system that is involved with movement.
Information reaching the brain from our senses leads our brain to formulate both thought and plans about movement.
The motor system is generally subdivided into subsystems to better describe, explain, and understand it. However, all subsystems work together in normal movement. The diagram below right illustrates the "pyramidal" subsystem.
motor cortex
Movement impulses originate in the motor area of the of the cerebral cortex, shown in the diagram above.
motor pathway
Movement impulses originate in the motor area of the of the cortex. Axons from these cells descend down to the midbrain, further down the lower part of the brain, where they cross (decussate) and descend to the spinal cord to control movement on the opposite side of the body.
Somatosensory system
Somatosensory system refers to areas of the brain that process information received through touch, inform us about the position and movement of our body, and provide information about itchy and tickling stimuli, and pain.
It carries information the brain will use to interpret sensations such as touch and temperature, within the distance of our body, as well as information about our bodies themselves, such as the position and movement of our bodies.
For a simple example, think of a specific stimulus, such as heat. This stimulus triggers activity in a sensory neuron, and this signal eventually passes to an area of the brain connected to that area of the body, allowing the stimulus to be felt at that connected area of the body.
Stimuli from sensory systems trigger the brain to formulate thoughts, actions, and responses.
A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception.
Somatosensory brain map
This image shows a segment of the somatosensory cortex, an area of the parietal lobe.
A somatosensory brain map is a visual representation that relates specific areas of the somatosensory cortex to corresponding parts of the body. One example is the image you're looking at. It is one version of the cortical homunculus devised by Canadian neurosurgeon, Wilder Penfield. It is associated with the interpretation of sensory input from the body - e.g., touch, temperature, pain, etc. It lets us know when we are touched on our body surface.
Different areas of the somatosensory cortex process input from different groups of cells corresponding to different areas of the body. Neuroscientists have come up with somatosensory brain maps of these precise regions, showing, proportionally, how much of the brain corresponds to sensations from specific parts of the body, such as the face, hand, tongue, etc.
Somatosensory cortex
The somatosensory cortex is an area of the parietal lobe. It is associated with the interpretation of sensory input from the body - e.g., touch, temperature, pain, etc. It lets us know when we are touched on our body surface.
Different areas of the somatosensory cortex process input from different groups of cells corresponding to different areas of the body. Neuroscientists have come up with somatosensory brain maps of these precise regions, showing, proportionally, how much of the brain corresponds to sensations from specific parts of the body, such as the face, hand, tongue, etc.
Limbic system
Limbic system refers to areas of the brain involved in emotion, motivation, and associating emotion with memory. The limbic system is sometimes called the emotional brain.
The limbic system allows for memory, learning and emotions, is associated with pain and pleasure sensations, regulates the sleep-wake cycle, relays sensory signals to the cerebral cortex, to mention just a few of its important functions. It is sometimes called the emotional brain.
The image on the left shows the right hemisphere from the inside. The front of the brain is on the left of the image. The limbic areas are shown in red.
The limbic system, evolutionarily much older than the cerebral cortex, is located on top of the brainstem, under the cortex. It is made up of a group of brain structures that form the inner border of the cortex. They include the amygdala, cingulate gyrus, fornix, hippocampus, hypothalamus, olfactory cortex, and the thalamus.