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Unit 12 – Assignment 2 – P3
The nervous system
There are three parts of the nervous system:
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The Central Nervous System (CNS) - This is made up of the nervous tissues in the brain and
spinal cord
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The Peripheral Nervous System (PNS) - This is made up of the spinal nerves and sensory
receptors in the rest of the body
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The Autonomic Nervous System (ANS) - This is made up of nervous tissues that are not
under conscious control
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http://www
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edu/ANATOMY/AnatomyManual/nervous_system
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ivyroses
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php

The nervous system controls out lives and all of our body functions
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Internal changes
are also coordinated by the nervous system, e
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in response to changes in body temperature to
maintain homeostasis (this is done by the internal organs and the involuntary muscles)
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It controls and coordinated all the activities of the
muscles in response to the changes outside
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It conducts messages between different parts of the
body
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To carry
out this function, the neurones must be very diverse
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The system transfers information throughout the body through
impulses called nerve impulses
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Each neurone receives an impulse and must pass it on to the
next neuron and ensure that the correct impulse continues on its path
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At rest, the voltage-sensitive sodium and potassium gated in the channels in 3 Na+ ions
to the ECF and 2 K+ ions to the ICF
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The sodium/potassium pump contributes to the resting membrane potential by pumping
out three sodium ions to the ECF and pumping in two potassium ions to the ICF
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At rest, the ICF of an axon had a voltage of about –70mV
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This causes the
voltage to change to a less negative state
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As sodium gated open, Na+ flow through sodium channels increases and quickly
changes the voltage from a resting level of –70mV to 30mV
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At 30mv, the sodium gates will close; after this, the
depolarisation process will stop
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The potassium flow quickly reverses the potential from
30mV to about –70mV
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This rapid depolarisation and repolarisation
process generated a voltage pulse peak which is called the action potential or the nerve impulse
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Reflex reactions in humans are controlled by the reflex arc
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, via a relay
neurone, to a motor neuron
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A reflex arc is the nerve pathway which makes a
very fast automatic response; it in inevitable behaviour
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2
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4
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Reflex arc – Your hand touching a hot plate
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The nervous impulse or signal, travels along the sensory nerves towards the spinal cord
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The nervous impulse travels from the spinal cord, along the motor nerves to the hand
muscles which contract to pull your hand away from the stove
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Later, the nervous impulse from the spinal cord travels the longer distance to the brain and
is interpreted as: "Ouch! That was hot!"

Stimulus --> Receptor --> Sensory Nerve --> Relay Neurone --> Motor Neurone --> Effector -->
Response

Conscious actions:
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3
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5
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A message travels down your optic nerve to your brain
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A message is sent from the brain to the CNS
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Unit 12 – Assignment 2 – M2
The Central Nervous System
The Central Nervous System (CNS) is made up of the nervous tissues in the brain and spinal cord and
contains millions of neurones
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In the brain there are grey areas
and white areas
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The white matter is white as it contains a lot
of fatty material called myelin
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This means
that nerve cells are able to conduct electrical messages without interfering with each other
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This area is mainly cytoplasm of nerve cells
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For example: speech, hearing, smell, sight, movement, salivating, etc
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The spinal cord is connected to a
section of the brain called the brainstem and runs through the spinal canal
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Nerve roots exit the spinal cord to both sides of the body
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Cerebrospinal fluid surrounds
the brain and the spinal cord and also circulates within ventricles of the central nervous system
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The cerebrospinal fluid circulates between two
meningeal layers called the pia matter and the arachnoid
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The Sympathetic Nervous System
The sympathetic nervous system allows the body to function under stress
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The sympathetic fibres that end in the adrenal medulla secrete acetylcholine (which functions as a
neurotransmitter), activates the secretion of adrenaline
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This is moderated directly through impulses which are transmitted through
the sympathetic nervous system
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The catecholamines include a number of neurotransmitters such
as adrenaline and dopamine
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The parasympathetic
nervous system has many functions:

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It conserves energy
It decreases the heart rate
Increases the intestinal and gland activity
It relaxes sphincter muscles that are located in the gastrointestinal tract
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An example of this when the
heart rate increases, it will result in a sympathetic reaction
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The afferent (sensory) and efferent (motor) pathways
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They are classified as pseudounipolar
neurones with a single long dendrite and short axon
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However the central axon passing into the
spinal cord
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The aggregation of
afferent neurons can be found in a swelling called dorsal root ganglion, which is located just outside
the spinal cord
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Efferent neurons are bipolar with dendrites on one end and axons on the other
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The impulse enters the cell body through several dendrites and then leaves it through the single
axon at the other end
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The efferent neuron forms an electrochemical pathway towards the effector
organ

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