c2.2 HL neural signalling

what are nerve impulses caused by

transitory changes in electrical charge across the neurone membrane which is caused by movement of sodium and potassium ions

what does the neuron membrane contain

sodium potassium pump and voltage sensitive ion channels

action potential steps

1. the sodium potassium pump maintains the electrochemical gradient of the resting potential. some potassium ions leak out of the neuron making the membrane potential negative

2. in response to stimulus in an adjacent section of the neuron, some voltage gated sodium ion channels open and sodium ions enter via diffusion. if a threshold potential is achieved, all the voltage gated sodium ion channels open which causes the membrane potential to become positive

3. the depolarization of the membrane potential causes the voltage gated sodium ion channels to close and the voltage gated potassium ion channels open. K ion diffuses out and the membrane is negative again

4. before neuron is ready to propgate another impulse, distribution of sodium out and potassium in needs to be reset by the na-k pump, returning the neuron to resting potential. this enforced rest (refractory period) ensures impulses can only travel in a single direction

myelinated neurones v non myelinated neurones in humans

myelinated conduct at 100ms-1 (faster)

non myelinated conduct at 0.5 ms-1(slower)

why are myelinated faster

have a myelin sheath composed of Schwann cells that is wrapped around the neurone (axon) which prevents the movement of ions so depolarization can only happen at the nodes of ranvier (uncovered by myelin sheath)

cytoplasm in the neurone

rich in lipids which helps insulate and ensures that depolarization occurs only at nodes of ranvier

define exogenous chemicals

chemicals produced outside the body (many capable of affecting transmission of signals at synapses)

define endogenous chemicals

chemicals produced inside the body

define neonicotinoids

new group of chemicals similar to nicotine used in insecticides

how do neonicotinoids work

bind to receptors on post synaptic membrane that usually accept acetylcholine. the bind prevents the formation of a new action potential. the chemical is not broken down and remains in the receptor meaning that the synapse becomes permanently blocked, leading to death

define cocaines function

prevents the removal of dopamine (a neurotransmitter) from the synapse and causes the stimulation neurons to release their reserve dopamine supplies

how does cocaine work

usually dopamine is removed by a dopamine transporter but the chemical attaches to this and renders it inactive causing dopamine to build up so the brain feels an exaggerated response making it highly addictive. repeated use makes it more likely that the user will become highly dependent on this and less interested in relationships, food and other natural rewards

what do presynaptic neurons do

some excite post synaptic transmission while others inhibit post synaptic neurons

what are decisions in the CNS caused by

interaction between excitatory and inhibitory neurotransmitters

define excitatory neurotransmitters

stimulate the next neurone to pass a message. increase permeability of the post synaptic membrane to the ions so the +ve ions move in quicker (eg. acetylcholine)

define inhibitory neurotransmitters

cause +ve ions to move out of the postsynaptic cell making it harder to excite (eg. GABA - gamma aminobutyric acid)

how many signals can a post synaptic neuron recieve

many excitatory and inhibitory signals simultaneously. if the sum of the signals is excitatory, the signal continues forward

what is stimuli detected by

specialized receptors

class and function of different specialized receptors

thermoreceptors - detect changes in temp

nociceptors - detect actual or potential tissue damage

electromagnetic receptors - detect electrical currents and magnetic fields

photoreceptors - detect light waves

baroreceptors - detect blood pressure

chemoreceptors - detect chemicals, allowing taste and smell senses

nociceptors adaptations

channels for positively charged ions that open in receptors to stimuli such as temp. (eg. hot chili peppers contain the chemical capsaicin which binds to the receptor and casues it to reach threshold potential)

define reductionsism

understanding the complex system by understanding basic parts

define emergence

looks at the systems whole system and proposed that the system is more than the sum of their parts (eg. consciousness)