Download Nervous System • Steers, controls and watches over our bodily

Nervous System
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Steers, controls and watches over our bodily functions and processes
WHY?– to protect us, to keep us alive, and to fit in with the environment
It is divided into a central nervous system (brain and spinal cord) – and a peripheral nervous
system (periphery nerves)
The peripheral system collects information about the inner body and about the world around
us via sensors, and delivers the messages from the central nervous system back to all parts of
the body
The sensors are our senses (conscious processes), as well as unconscious processes
This information (signals inside the body) is either of a physical or chemical nature
The information is carried by electric impulses on AFFERENT pathways in the peripheral
nervous system to the central nervous system = this gives our brain a “screenshot“
This information is then matched to a „I need” or “it should be“ snapshot
When differences are noticeable between these two snapshots, a plan is formed by the
brain, then transmitted back out from the centre to the periphery by the EFFERENT pathways
These pathways end in organs or muscles which must then react in order to change the
situation and make it more desirable
Somatic or animalistic System (Organism – Environment)
the functions of the somatic nervous system are:
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Conscious movement (supply the striated muscles with their innervation = orders to
work
Quick processing of information
Conscious perception
Autonomic or vegetative nervous system (Organism – internal organs)
Is divided into a sympathetic subsection and a parasympathetic subsection:
1 PARASYMPATHETIC SYSTEM:
conserves energy, and builds up reserves
2 SYMPATHETIC SYSTEM:
mobilizes body systems during activity, „Fight or Flight“ reaction
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Both systems work hand in hand, to maintain a balance which provides the best
conditions for the body (homeostasis)
and to regulate organ functions dependant on the demands of the environment.
AFFERENT
chemical and
physical information
Central control
(=brain)
calculates a
screenshot
Muscle/Organ/
Adaption/Change
Orders to bring
about change
given, if the
screenshot is
not ideal =
EFFERENT
Compares screenshot
with an ideal situation
Example:
Skin temperature measures 30°
Messages sent to brain „Here it is 30°“ = Afferent information
Brain compares the information to its ideal of 22°, and has to react to the difference
Brain’s plan: Open the capillaries = Vasodilatation, sent as Efferent information back to the
skin
Capillaries opened, more blood flows near the surface, warmth given off from the surface,
body cools down, which is in turn monitored so as not to cool down too much.
Brain receives new messages, “Here it is now 22°”, the balance is restored.
One problem is that to constantly control so many structures, an incredible amount of information
must be constantly sent to the brain. How does the brain sort through all this information to find out
what is important to react to? Priorities must be laid down, and the most important priority is
CHANGE. Therefore the body reacts to these changes.
The most important of all change is damage, or even danger of damage being done.
 This causes an immediate red alert situation.
The cells of the Nervous System (Neurons)
In order to make the system run smoothly, there must be different types of cells for different
functions within the system. First a message must be registered, then conveyed, and computed in
the brain before the plan is then conveyed back to the specific part of the body.
Sensory Cells
Quelle: http://upload.wikimedia.org/wikipedia/commons/1/17/Structure_of_sensory_system_(4_models)_E.PNG
All sensory cells have receptors of some sort,
some more refined and specialized than others.
Some react to any stimulus, others react only to
certain stimuli.
Having received this information, the cell then
must convey its information to the nerve cell
(Nucleus). Here the first processing takes place,
and the message is either conveyed further, or
ignored.
Having reached the central nervous system, the
message is then passed onto another
(transmitter) cell, and conducted inside the
spinal cord to the brain.
Quelle: http://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Neuron.svg/1280pxNeuron.svg.png
The Axon is the „cable” along which an electric impulse can be sent. Because some neurons can be
up to 1m long, the message needs to be carried as quickly as possible. This happens in the neurons
that have a myelin sheath, built of other cells (Schwann cells), which wrap themselves around the
cable, as a form of insulation. The electric impulse now travels not along the entire axon, but
“springs” from one gap to another between the Schwann cells. This is called saltatorish movement.
The afferent pathway consists of two neurons – one sends information from the periphery to the
dorsal section of the spinal cord, the second neuron runs from here to the brain.
The efferent pathway also consists of two neurons – one down the spinal cord to the required level
of the spine, the second from the ventral section of the spinal cord to the effector tissue (muscle,
organ or gland).
The final connection between this second effector neuron (motor neuron) and the required muscle is
called a motoric unit. Each motor unit has contact to many muscle fibres (= cells), and causes those
fibres to contract when the impulse comes along the motor neuron’s (ὰ-Neuron) axon. Some muscles
have larger motor units than other muscles. Muscles which must do fine tuning of movement (the
eye muscles) have small motor units and innervate relatively few muscle fibres – as few as 3! (mostly Slow Twitch muscle fibres). Muscles which need to work quicker and more powerfully (Quick
Twitch fibres) have large motor units – as many as 5000 – e.g. M. gastrocnemius (calf muscle), M.
biceps brachii (arm flexor).
The connections between the Neurons are called Synapses, and the gap is bridged by chemicals
being sent from one cell to the next across this synapse. The Sympathetic system uses the chemicals
Acetylcholin and Noradrenalin – the Parasympathetic system uses only Acetylcholin.
Functions of the autonomous nervous system:
Parasympathetic System–
regeneration and building of resources
for example:
Blood pressure sinks
Reduction of Heartbeat
Reduction of breathing rate
Increase of digestion
Increase of saliva production
Closing of the pupils
Tendency to empty the bladder and bowels
Sympathetic System –
mobilization of resources
for example:
Increase of blood pressure
Quickening of heartbeat
Quickening of breathing rate
Widening of the Bronchia (airtubes)
Increased blood flow to the muscles
Widening of the pupils
Hairs stand on end
More sweat production
Reduction of bowel activity
Increase of energy production
Spinal Cord
The spinal cord is made of nerve cells in a butterfly formation (grey matter) inside a circle made up of
axons (white matter).
Peripheral Nerves enter the Spinal Cord from all over the body, via the dorsal root. In the dorsal horn
is a synaptic connection to the cell of the Central Nervous System, from where the information from
the body or environment is directed to the brain to be controlled. After processing, the brain sends a
return message (efferent pathway) back
down the spinal cord, which then arrives
at the ventral horn and is passed onto the
efferent nerve via a sysnapsis. This
efferent nerve then exits the Central
Nervous System via the ventral root.
Ventral and dorsal roots join after a very
short distance to form the peripheral
nerve. Therefore every peripheral nerve
has afferent nerves, efferent nerves and
vegetative nerves.
Retrieved from - http://www.newhealthadvisor.com/Spinal-Cord-Cross-Section.html
There are 31 pairs of spinal nerves:
8 cervical nerve pairs
12 thoracic nerve pairs
5 lumbar nerve pairs
5 sacral nerve pairs
1 coccygeal nerve pair
These form the following Plexuses:
Plexus cervicalis (C1-C4)
Plexus brachialis (C5-Th1)
Plexus lumbalis (Th12 – L4)
Plexus sacralis (L5 – S4)