Chapter 10 A2 Biology Communication revision notes

I haven't explained 10.7, synapses in detail, the book explains it so much better.

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  • Created on: 05-03-13 21:36
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Coordination
Hormonal system Nervous system
Communication by hormones Communication by nerve impulses
Transmission is by blood system Transmission by neurones
Transmission and response slow Transmission and response rapid
Hormones travel across body but only target Nerve impulses travel to specific parts of body=
organs respond = response widespread response localised
Response long- lasting Response short lived
Effect may be permanent and irreversible Effect temporary and reversible
HISTAMINE ­ stored in WHITE BLOOD CELLS. Released after INJURY or in response to an
ALLERGEN. Causes increase in permeability of capillaries, leading to localised swelling,
redness and itching.
PROSTAGLANDINS ­ found in CELL MEMBRANES. Release following INJURY. And causes
increase in permeability. Affect blood pressure and neurotransmitters, and therefore pain
sensation.
Plant growth factors
Plants respond to:
Light
Gravity
Water
Plants respond to external stimuli by means of plant growth factors.
" plant growth factors" correct term, not " plant hormones" because:
Exert influence by affecting growth.

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Made by cells located throughout the plant
Some plant growth factors affect tissues that release them, not a distant target organ
Indoleacetic acid (IAA) causes plant cells to ELONGATE.
1. Cells in tip of shoot produce IAA, transported downwards
2. IAA initially transported to all sides of shoot
3. Light causes movement of IAA from light to shaded side
4. Greater conc of IAA on shaded side = shaded cells elongate
5.…read more

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Structure of neurons
CELL BODY ­ contains nucleus. Has lots of RER which produces proteins and
neurotransmitters.
DENSDRONS ­ small extensions of body cells which subdivide into dendrites that carry nerve
impulses TOWARDS cell body.
AXON ­ single long fibre that carries nerve impulses AWAY from cell body
SCHWANN CELLS ­ surround axon, protecting and insulating it. Carry out PHAGOCYTOSIS and
regeneration of nerves.
MYELIN SHEATH ­ covering of axon, made up of membranes of Schwann cells. Membranes
myelin ­ rich.…read more

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SENSORY NEURONES ­ transmit nerve impulses from receptor to intermediate or motor
neurone. Contain of dendron and axon
o INTERMEDIATE NEURONES ­ transmit impulses between neurones.
o MOTOR NEURONES - transmit nerve impulses from intermediate or sensory neurones to
and effector. Have long axon and many short dendrites.…read more

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Most Na+ channels closed, most K+ channels open = axon membrane more permeable to K+
which diffuse out faster = increases p.d between ­ive inside and +ive outside.
7. Electrical gradient established. Further outward K+ movement more difficult because they
are attracted to overall negative state inside axon = move into axon and can't move out
again because repelled
8.…read more

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Passage of action potential
Moves rapidly down axon by the reversal of electrical charge reproduced at different points along
axon. Size constant.
As one region produces action potential, it acts as stimulus for the depolarisation of next region, and
it's previous region undergoes repolarisation.
Action potentials are regenerated along each small section of axon.
Passage of action pot in UNMYELINATED NEURON
1. At restinf potenetial, concentration of Na+ outside axon is
higher and K+ concentration higher on inside axon.…read more

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Sheath of myelin acts as electrical insulator, preventing action potentials forming. Action potentials
occur at nodes of Ranvier = localised circuits between nodes. Action potentials jump from node to
node in SALTATORY CONDUCTION.
Action potentials pass down myelinated axon faster.
Factors that affect speed at which action potential travels:
MYELIN SHEATH ­ saltatory conduction increases speed of conductance
DIAMETER OF AXON - greater the diameter, the greater speed
TEMPERATURE - affects rate of diffusion. The higher the temp = faster nerve impulse.…read more

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Ensures that action potential is propagated in
one direction only
o It produces discrete impulses ­ action potentials not merged together
How can an organism perceive the size of the stimulus?
o Number of impulses passing
in a given time. The larger the stimulus, the more impulses
o Different neurones with different threshold values. Brain intercepts number and type of
neurones that pass impulses to stimulus and determines size.…read more

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Functions of synapses
Transmtiing impulses from one neurone to another, and in doing so act as junctions, allowing:
o Single impulse along one neurone to be transmitted to lots of different neurones at a
synapse = simultaneous responses
o Number of impulses combined at synapse to produce single response.
Transmitting across synapse ( simple):
1. Neurotransmitters are made ONLY in presynaptic neurone
2. Neurotransmitter, stored in synaptic vescicles released only when action potential reaches
synaptic knob
3.…read more

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Inhibition: on POSTSYNAPTIC membrane of some synapses, protein channels with Cl- can be made to
open which makes inside postsynaptic membrane more negative at resting potential
hyperpolarisation) = less likely new action potential will be created.…read more

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