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Summary 15 Nervous coordination and muscles
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Concise nervous coordination and muscles summary notes for the new linear A-level biology 7401/7402
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Nervous coordination and musclesCoordination
Being able to perform multiple functions
® Nervous coordination: controls and coordinates functions throughout the body, responding
to internal and external stimuli.
® Hormonal coordination: produces hormones in the blood to signal other cells to behave in
certain ways
® Chemical mediators: chemical released from certain cells affects cells right next to them
Nervous coordination Hormonal coordination
? Transmission by neurones ? Transmission by blood system
? Rapid communication ? Slower communication
? Responses are short ? Responses last longer
? Target specific body part ? Less specific
? Response is localised ? Response is widespread
Myelinated motor neurone
® Cell body: contains nucleus and RER for synthesis of neurotransmitters
® Dendrons/dendrites: carry nerve impulses towards cell body
® Axon: single long fibre carries nerve impulses away from cell body
® Schwann cells: surround axon, protecting it and providing electrical insulation
® Myelin sheath: made of membranes of Schwann cells, speed up transmission
® Nodes of Ranvier: gaps between Schwann cells where action potentials occur
Types of neurones
® Sensory neuron: carries impulses from receptors to the CNS
® Intermediate neuron: transmits impulses between neurones
® Motor neuron: carries impulses from the CNS to muscles
The Nerve Impulse
The electrical message that is transmitted down the axon of a neuron by being regenerated at points
along the axon.
® Potential difference: the difference in electrical charge between the interior and exterior of
a cell (across the plasma membrane)
® Resting potential: the state of the neuron prior to the sending of a nerve impulse (potential
difference is -70mV)
® Action potential: occurs when the potential difference across an axon is temporarily
reversed (potential difference is -35mV). Membrane is depolarised.
Resting potential
At rest the membrane is polarised
The inside of the membrane is slightly negative (approx. -65mV)
Controlled by channels containing voltage-sensitive gates
During the resting state:
® An axon is at resting potential when no impulse is present
® The potential difference across the axon membrane is created by the distribution of charged
ions.
How is the resting state established in a neuron?
® Sodium-potassium pumps in the axon membrane transport 3 Na+ ions out of the axon for
every 2 K+ it moves inside, via active transport
® As more positive ions pumped out than in, inside becomes negative and outside positive
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