Cognitive process and structures of the brain includes:
The nervous system encompasses a large range of sub-systems, as shown below (click for larger image).
The central nervous system comprises of the brain and the spinal cord. The spinal cord is used as a messenger between the brain and the rest of the body, sending messages between the brain and the peripheral nervous system. The brain will be examined later in greater detail.
Conversely, the peripheral nervous system sends messages from the body (organs, muscles etc.) to the central nervous system in the brain. It also sends messages from the brain to the body, allowing us to move. There are two subsystems of the peripheral nervous system: the somatic nervous system and the autonomic nervous system.
The somatic nervous system is used to control (voluntary) movement of the body. As suggested in the diagram above, the somatic nervous system makes use of both sensory and motor neurons. Sensory neurons send sensory information (that is, stimuli relating to senses such as touch, smell, taste etc.) toward the central nervous system. This information is then processed by the basal ganglia – part of the forebrain – before motor neurons are sent to particular parts of the body required to respond to the sensory information.
For example, imagine that you accidentally touch a hot stove. Sensory neurons in, let’s say, your fingers, would be sent via the peripheral nervous system to the brain, whereby they would indicate that the stove was painfully hot. In response, motor neurons would be sent back to the fingers to allow them to move away from the stove.
Conversely, the autonomic nervous system is responsible for keeping the automatic processes of internal organs and glands (such as our heartbeat, blinking and breathing, although some of these can be influenced voluntarily) running smoothly. It also partly controls emotion. The autonomic nervous system includes two branches which work exclusively (not at the same time): the sympathetic nervous system and the parasympathetic nervous system.
Sympathetic nervous system
You may have heard of the ‘fight or fight’ (sometimes ‘fight, flight or freeze’) response. This is a big part of the sympathetic nervous system, which activates when an organism perceives itself to be in threat (whether or not they actually are in threat is immaterial). When this response is activated, numerous physiological changes in the body occur. These may include:
Parasympathetic nervous system
Conversely, the parasympathetic nervous system is in action when an individual is relaxed and does not think that they are in immediate threat. Following the fight or flight response of the sympathetic nervous system, the parasympathetic nervous system takes hold to return the body’s processes to regular functioning (homeostasis). The physiological consequences of the parasympathetic nervous system are inverse to those of the sympathetic nervous system:
The cerebral cortex is a thin (around 2-4m.m. thick), outer layer of the brain which allows higher order intellectual functioning. Despite its size, the cerebral cortex accounts for about 75% of the brain’s total neurons. It is divided into two hemispheres – left and right – and four lobes – the frontal lobe, parietal lobe, temporal lobe and occipital lobe. Although each is largely responsible for different areas, they all work smoothly in an integrated fashion.
The frontal lobe is largely responsible for functions of thinking, decision-making, motor function, planning, language and memory. The frontal lobe is, arguably, the most important of the four, as it is involved in both personality and executive functioning. That is, it guides information to the other three lobes.
Primary motor cortex
The primary motor cortex is located to the immediate left (when viewing the right hemisphere) of the central fissure which separates the frontal lobe and the parietal lobe. It is responsible for voluntary movement of skeletal muscles. Specific parts of the primary motor cortex are responsible for movement of specific parts of the body. Interestingly, the left side of the primary motor cortex is responsible for the right side of the body, and vice versa. Similarly, the top of the primary motor cortex is responsible for the bottom of the body, and vice versa. This is indicated in the diagram below, whereby the typography which makes up the primary motor cortex shows roughly is responsible for which part of the body.
It may surprise you which parts of the body require most of the primary motor cortex. Whilst we may initially think that the largest parts of the body would require the most cortical space, this is untrue: it actually depends on how precise required motor control is. For example, parts of the body such as fingers and lips, which are capable of very fine and precise movements, tend to require the most cortical space.
The prefontal cortex is responsible for control of emotions, planning, decision-making, self-awareness and language, amongst other things. In the left hemisphere, the prefrontal cortex includes Broca’s area, which is particularly necessary in the production of speech. The prefrontal cortex also receives messages from the three other lobes.
The parietal lobe is heavily involved in the perception of space. The parietal lobe in the right hemisphere tends to specialise in the perception of 3D shapes, whilst the left hemisphere tends to specialise in mental arithmetic and reading. The parietal lobe is involved in recognising pain, pressure and temperature.
Primary somatosensory cortex
The primary somatosensory cortex is almost a mirror image of the primary sensory cortex; it is located to the immediate right (when viewing the right hemisphere) of the central fissure which separates the parietal lobe and the frontal lobe. The primary somatosensory cortex receives sensory information from parts of the body in order to recognise pain, pressure and temperature.
Like the primary motor cortex, the left side of the primary somatosensory cortex is responsible for the right side of the body, and vice versa.
Information from the parietal lobe is important in spatial reasoning, and is combined with the other lobes to form a holistic experience.
The temporal lobe mainly works with auditory sensory information. It is essential in understanding language, speech and other sounds. The temporal lobe in the left hemisphere tends to specialise in words, whereas the right cortex tends to specialise in other sounds. Together, they work to allow for understanding of speech. Understandably, damage to the temporal lobe may lead to partial or total deafness.
Wernicke’s area – required for understanding language – is found in the temporal lobe (usually in the left hemisphere, but found in the right hemisphere on occasion).
Whilst the temporal lobe is mainly concerned with auditory information, it also contributes to the development of long-term memories, recognition, personal perceptions and emotional responses.
The occipital lobe deals with visual sensory information. Different parts of the occipital lobe are responsible for various functions, including recognition of size, colour, motion, shape etc. The association area in the occipital lobe works with the other three lobes to combine visual information with thoughts, feelings, sound, language and memory, which allows for greater understanding.
Association areas within each of the four lobes are used to combine information from all senses.
Hemispheric specialisation refers to the suggestion that the left and right hemispheres of the brain specialise in particular areas, and have greater control over these areas than the other hemisphere. It suggests that the left hemisphere has more control over verbal functions, whereas the right hemisphere has more control over non-verbal functions.
However, it should be noted that the two hemispheres do not work exclusively and, whilst they are separated by the corpus callosum, heavily interact, complement and depend on each other for higher-order processing. Both hemispheres are usually involved in all functions of the brain to some degree.
According to the theory of hemispheric specialisation, the left hemisphere of the brain has more control over processes such as:
According to the theory of hemispheric specialisation, the right hemisphere of the brain has more control over processes such as:
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