Notes on the Nervous System

Notes on the Nervous System

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The nervous system
8.1 Organising the nervous system and understanding the human brain
Organising the nervous system
There are a number of elements to the nervous system. The central nervous system (CNS) comprises the brain and the
spinal cord, and is made of white matter and grey matter. The peripheral nervous system (PNS) is made up of all the
neurones which carry nerve impulses into and out of the central nervous system.
The peripheral nervous system
central nervous system peripheral nervous system
can be broken down into two
subcategories: the sensory
system which involves
receptors detecting change in
brain spinal cord motor system sensory system
the environment, and sending
(messages from CNS (messages from
messages to the CNS; and the to effector) receptor to CNS)
motor system which takes
messages from the CNS to the
effector tissue.
somatic system autonomic system
The motor system can be broken down controls striated controls smooth and
further into two categories. The somatic (voluntary) muscles cardiac muscle
nervous system is responsible for sending
messages to voluntary muscle (also known as
skeletal muscle or striated muscle). The sympathetic system parasympathetic system
autonomic nervous system sends messages generally has an excitatory generally has a depressive
effect, most active during effect, most active during
to all involuntary muscle (cardiac and
times of stress sleep and relaxation
Once again, the autonomic nervous system can be broken down into to final subcategories. These are the sympathetic
nervous system and the parasympathetic nervous system. These two systems are antagonistic, whilst the sympathetic
system is most active during times of stress (involved in the fight-or-flight response) and has an excitatory effect; the
parasympathetic system is active when the organism is relaxed, and has an inhibitory (depressive) effect.
The brain
The brain is one of two core components of the central nervous system. The largest part of the human brain is the
cerebrum, which is divided into two hemispheres, the right and left. The cerebrum is also split into four separate lobes.
The diagram below shows the lobes and what they are most associated with:
The cerebrum contains a very large
parietal lobe number of areas, which fit into three
motor categories: sensory areas receive
frontal lobe cortex indirect impulses from receptors,
taste somatosensory association areas (such as those
association area shown) use what has been learnt from
association speech
area past experiences to interpret the
speech message and decide on an appropriate
hearing response, and motor areas which send
smell visual out the nerve impulses to the effectors
association (muscles and glands).
auditory area
association vision The brain is involved in muscular
area movement, and voluntary muscular
occipital lobe movement is initiated in the cerebrum,
temporal lobe

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These coordinated motor responses
require the involvement of the cerebellum (which lies just beneath the occipital lobe of the cerebrum). Nerves from the
cerebellum carry impulses to the motor areas of the cortex, so that motor output to the effectors can be adjusted,
depending on the requirements.…read more


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