L4 transmission of impulses

recall the threshold value

• - 55mV

why important - action potential is generated - all or nothing principle 

+40 mV action potential threshold 

potassium ion channels allowing potassium ions to leave the axon is important to maintain the resting potential. Describe their primary structure - 2 marks

sequence/order of amino acids joined by peptide bonds 

sodium and potassium ions can only cross the axon membrane through proteins. explain why

2 marks 

cannot pass through phospholipid bilayer 

because water soluble/ not lipid soluble/ charged/ hydrophilic/ hydrated 

summary of events

on L3 - regenerating action potential worksheet

speed of conduction of impulses

the speed of conduction of an impulse refers to how quickly the impulse is transmitted along a neurone

3 factors that can affect the speed of impulse transmitted along a neurone 

• teh presnece or absesne of myelin (whether or not an axon is insulated by myelin sheath 

• temperature 

• the diameter of the axon 

unmyelinated axon

• speed of conduction is very slow

• this is because depolarisation must occur along the whole membrane of the axon with localised electrical currents being established

myelinated axon

• the fatty sheath of myelin acts as an electrical insulator

• this prevents an action potential being formed in the axon covered by the sheath

• action potential being formed in the axon covered by the sheath

• action potentials can occur at the nodes of ranvier

• this means localised circuits arise between adjacent nodes

• as a result the impulse travels down the axon faster (compared to unmyelinated axons) as it is able to ‘jump’ large sections of the axon

• this is salutatory conduction

• nodes of ranvier are the gaps between the myelin

diameter of the axon 

the greater the diameter of the axon the faster the conduction 

thicker axons have an axon membrane with a greater surface area over which the diffusion of ions can occur 

this increases the rate of disunion of sodium ions and potassium ions through protein channels 

this can in turn increase the rate at which depolarisation and action potentials can occur leading to speeding up the impulse of the action potential?? 

because they are faster - axons with a. greater diameter also possess a greater cytoplasm volume (which contains ions). this reduces their electrical resistance so that an action potential can push into the next section faster. 

L5 starter - define the term antigen

molecules (usually a protein) found on the cell surface membrane that can be detected by antibodies that triggers an immune response

MS - a protein found on the cell surface membrane

identifies a cell as a self or non self/ allow recognition of self or non self or triggers an immune response

state the difference between kinesis and taxis

taxis is directional movement 

kinesis is non directional movement 

a kinesis response depends on the intensity of the stimulus whereas the taxis response is simply a movement away or towards the stimulus