Download Spinal Cord/ Reflex Action mainly

Human Responses 2
Nervous system Compared to Endocrine System (hormones)
Spinal Cord
Reflex action
SYNPASE
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 Synapse—region where two neurons come into close contact.
 Synaptic cleft—the gap between two
neurons, bridged by chemicals
(neurotransmitters).
SYNAPSE
 Neurotransmitter
—chemical
released across a
synaptic cleft to
carry a signal
from one neuron
to another e.g.
acetylcholine
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Sequence of events
SYNAPSE
 1. Impulse moves
along neuron as
ions move in/out of
neuron
 2. impulse arrives
at synpatic knob
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 3. Neurotransmitter
vesicles move to edge
of syn.knob
 4. Neurotransmitter
chemical released
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 4. Neurotransmitter
chemical crosses
synaptic cleft by
diffusion
 5. Neurotransmitter
chemical lands on
receptors on next neuron
 6. Impulse sent along
next neuron
 7. The neurotransmitter
chemical is then
inactivated by enzymes
&reabsorbed by
presynaptic neuron –
makes new neurotranmitter
chemical to clear receptor sites
for next impulse
SYNAPSE
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LEARNING CHECK
• Distinguish between synapse and synaptic
cleft.
• What are neurotransmitter chemicals?
• What are neurotransmitter vesicles?
• What would happen if there were no gaps
between neurons?
• What is the refractory period and why does
it occur?
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Spinal chord
structure
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31 pairs of
Spinal
nerves
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Different view
Bone
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 The spinal cord is well
protected by the
vertebrae, meninges
(three membranes) and
cerebrospinal fluid.
 Meninges not shown they are wrapped around
here
 It transmits impulses to
and from the brain and
controls many reflex
actions.
This diagram not needed
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A cross-section through the spinal cord shows a small central
canal, filled with cerebrospinal fluid, surrounded by an area of
grey matter, shaped somewhat like the letter H.
Learn
this
diagram
well
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Grey matter contains cell bodies and dendrites
(regions of a neuron that have no white myelin covering).
Outside the grey matter, the spinal cord consists of white
matter (containing mostly axons) – white due to myelin -fatty.
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In humans, 31 pairs of
spinal nerves branch off
from the spinal cord.
Each spinal nerve has a
dorsal root and a ventral
root.
The dorsal root consists of
nerve fibres carrying
information into the spinal
cord from the senses.
The dorsal root ganglion is
a swelling that consists of
the cell bodies of the
sensory neurons.
hint – Dorsal / sensory/swelling
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The ventral root consists of
nerve fibres carrying
information out from the
spinal cord, to the muscles
and glands. hint - Move out
The cell bodies of the
motor neurons are
positioned within the grey
matter of the cord.
 The spinal cord
transmits impulses to
and from the brain and
controls many reflex
actions.
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Reflex
action
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Go to video clip OF REFLEX ACTION.
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REFLEX ACTION --- The Reflex Arc
 A reflex action is a quick, automatic response to a
particular stimulus.
Interneuron
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REFLEX ACTION --- The Reflex Arc
Suppose you touch a hot flame…..
Interneuron
Pain Receptors detect the heat and send an impulse along
the sensory neuron
Which enters the dorsal root to the GREY matter of spinal
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cord
In the spinal cord, the sensory neuron synapses with the
interneuron and this synapses with the motor neuron,
An impulse is sent along the motor neuron, out the ventral root
into muscles that respond by contracting and pulling your hand
from the flame.
Only now does the brain become aware of what has happened
Interneuron
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This response
saves the body
from injury.
Interneuron
The response is called a reflex action, as it does not
involve conscious control, and is FAST predictable and
automatic.
Many of the activities of the body, such as breathing and
keeping our balance, are regulated by reflex actions.
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SUMMARY OF PATHWAY OF REFLEX ACTION.
Pain receptor (skin) 
sensory neuron 
IN Through dorsal root and dorsal root ganglion TO
Grey matter of spinal cord 
 synpases with interneuron 

Synpases with motor neuron 
Impulse OUT via ventral root 
Muscle to carry out response (move hand or foot etc)
Brain becomes aware of what has happened
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Go to video clip OF REFLEX ACTION.
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Nervous System Disorder
Parkinson’s disease is a nervous system disorder, normally
seen in older people, in which muscles become rigid and
movement is slow and difficult, with persistent tremors [shaking].
It is caused by the brain reducing the normal amount of
dopamine that it makes.
There is at present no means of preventing it, but giving L-dopa
(which the body changes into dopamine) can relieve the
symptoms in many patients.
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LEARNING CHECK
•
•
•
•
•
•
•
How is the spinal cord protected?
Distinguish between grey and white matter.
Distinguish between dorsal and ventral root
What is meant by reflex action?
Give some examples of reflex action>
What is an interneuron?
Distinguish between cell bodies and
ganglions.
• Give cause treatment symptoms of
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parkinson’s disease
Comparison of the endocrine and nervous systems - 1
Endocrine
Cells involved
Gland
Message
Chemical
(Hormone)
Carried by
Blood
Message sent to
Cells throughout
the body
Received by
Target organ
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Comparison of the endocrine and nervous systems - 1
Endocrine
Nervous
Cells involved
Gland
Sense receptor
Message
Chemical
(Hormone)
Electrical(Impulse)
Carried by
Blood
Nerve cell
Message sent to
Cells throughout
the body
A specific cell or
tissue
Received by
Target organ
Effector (muscle or
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gland)
Comparison of the endocrine and nervous systems -- 2
Endocrine
Nervous
Speed of
transmission
Usually slow
Rapid
Effects
Can be widespread Localised usually
Duration
long-lasting
(hours)
Usually brief
(seconds)
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LEARNING CHECK
• Co-ordination of an organism’s activities is
carried out by what 2 body systems?
• Distinguish between the CNS and PNS.
• What is a neuron?
• What is an impulse?
• List the main differences between the
endocrine and nervous systems.
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