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Topic 8: Grey matter
8.1 Sensitivity in plants

Photoreceptors: A structure in living organisms, especially a sensory cell or sense organ that
responds to light.

The interaction of cells enables them to coordinate their activities appropriately. Organisms
have specialised cells or molecules that are sensitive to changes in the…

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Long-day plants need an abundance of P(FR) which only happens when they have short nights
because not all of the P(FR) has been converted and the sun begins the conversion of P(R)
back to P(FR) again.

Phytochromes activate other molecules in plant cells which affect various metabolic
pathways. The phytochromes…

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Peripheral nervous system is sub-divided into:
Somatic nervous system ­ voluntary, stimulates skeletal muscle
Autonomic nervous system ­ involuntary, stimulates smooth muscle, cardiac muscle
and glands

Autonomic nervous system divided into:
Sympathetic ­ Prepares body for fight or flight response ­ increases activity e.g.
speeding up heart rate
Parasympathetic ­…

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Relay/connector neurones:
Connect sensory and motor neurones
Mostly in CNS
Large number of connections with other nerve cells
Cell body is in the middle of the axon

Stimulus Receptor cells Sensory neurone CNS Motor neurone Effectors

There are two types of main extensions from the cell body of a…

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1) Depolarisation...
There is a change in permeability, causing Na+ channels to open so Na+ to
enter the cell down the concentration gradient ­ inside of cell becomes more
positive than outside
This reverses the resting potential, the membrane depolarises. The potential
difference is +40mV (action potential)
If this reaches…

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The action potential travels rapidly along the axon or dendron. This is because the
repolarisation of one part of the membrane sets up local currents with the areas either side
of it ­ these regions depolarise too as some Na+ flow sideways.

Propagation of an impulse along an axon:

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Two neurones are not in direct contact, there is a small gap called the synaptic cleft. The
synapse is the junction between the two neurones. The presynaptic neurone has a swelling,
called a synaptic knob which contains vesicles filled with neurotransmitter. The presynaptic
knob has mitochondria to provide energy to…

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Although synapses slow the transmission of impulses, they are useful:
Ensure impulses travel only in one direction because receptors are only on the
postsynaptic membrane
Allows neurones to connect with many other neurones ­ increases range of possible
responses to a particular stimulus
Control nerve pathways an give flexibility of…

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If enough Na+ ions enter, the potential difference changes significantly and will initiate an
impulse or action potential.

Synapses can amplify or disperse information ­ one neurone connects to many other
neurones ­ information dispersed around the body ­ synaptic divergence or many neurones
connect to one neurone ­ information…

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Conjunctiva: Protects the cornea
Cornea: Bends light
Lens: Focuses light on retina
Iris: Controls amount of light entering eye by controlling pupil size
Sclera: Protective layer, allows attachment of external muscles
Blind spot: No light sensitive cells where optic nerve leaves eye
Fovea: Most sensitive part of retina
Retina: Contains…




thanks mate

Former Member


fantastic notes, saved me alot of time and effort thanks!



Thank you! 




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