chapter 15

Question 1

nervous system vs hormonal system

Answer 1

nervous system
involves neurones
less rapid response
longer lasting

hormonal system
chemical messangers carried in bloodstream to target cells
rapid
short lived

Question 2

cell body

Answer 2

contains all organelles, including nucleus and lots of rough ER
proteins e.g. neurotransmitters produced here

Question 3

axon

Answer 3

carries impulse away from cell body and along motor neurone

Question 4

myelin shein

Answer 4

made from memrabne of schwann cells
lipid so does not allow charged ions to diffuse through.

Question 5

schwann cells

Answer 5

surround the axon
provide protection
electrical insulation
involved in phagocytosis/removing cell debris
involved in nerve regeneration.

Question 6

dendrities

Answer 6

branch from cell body
branch into smaller units/dendrons
carry impulses towards cell body

Question 7

nodes of ranvier

Answer 7

axon insulated with fatty sheith
small sections of unisulated sheith along its length.

Question 8

factors which affect speed of impulse transmission

Answer 8

temperature- active transport requires ATP- comes from respiraiton in mitochondria
at higher temperatures- higher enzyme activity
molecules have more KE- faster rate of diffusion

diamter of axon- the larger the diameter of the axon- the higher the rate of impulse transmission as fewer ions leaking out

ions leaking out makes it more difficult to maintain a memrbrane potential

myelinated/non myelinated sheith- myleinated sheith acts as an insulator, preventing the generation of an action potential but increased speed of transmission as impulses can jump from node to node.

Question 9

all or nothing principle

Answer 9

if stimulus meets threshold value- actional potential generated- impulse transmitted

if stimulus doesn’t meet thershold level- no action potential generated- no impulse transmtited.

if threshold value is met- maximal response

Question 10

how can you tell what the size of the stimulus is?

Answer 10

-no of impulses that pass given point in particular time
-different neurones have different threshold values.

Question 11

what is the refractory period and what is the purpose of this?

Answer 11

refractory period- from peak of polarisation- resting potential.

when an AP is generated, the voltage gated sodium ion channels close- no more sodium ions can diffuse in- another action potential cannot be generated.
ensures:
action potentials are only propagated in one direction- they can only pass from an active to resting region.

discrete impulses- new actional potential can’t be generated immediately after the first.
ensures the action potentials are separated.

limits no of action potentials- as actions potentials are separated this limits the number of action potentials that can pass along an axon.

Question 12

parts of synapses

Answer 12

neurotransmitters released by pre synaptic neurone.
neurotransmtiters diffuse across the synapse to post synaptic neurones
they bind with receptor protein on surface of membrane

neurotransmitters are stored in the sympatic vesicle

end of axon has synaptic cleft- has lots of mtiochondria and rough ER for production of neurotransmitter.

Question 13

summation

Answer 13

build up of neurotransmitter in synapse through 2 methods

spatial- different pre synaptic neutransmitters release a lot of neutroansmitter
action potential is generated

tempoarl- one pre SN releases a lot of neorotransmitter in a short period of time.
if this reaches threshold of post SN, an action potential is generated.

Question 14

synapses are unidirectional

Answer 14

impulses are only transmitted in one direction from pre to post synaptic neurone.

Question 15

inhibitory synapses

Answer 15

some synapses are less likely to generate another action potential

1) pre SN releases neutransmitter that binds to chloride protein channel on post SN
2) when neurotransmitter binds, chloride protein channels open and chloride ions diffuse in
3) when neutransmitter binds, potassium ion channels open and potassium ions diffuse out
4) negatively charged chloride ions moving in and positively charged potassium ions moving out means that membrane potential of post SN is more negative on inside compared to outside
this is hyperpolarisation- membrane potential is more negative than resting potential
5) this makes it less likely that another AP will be generated as large influx of sodium ions needed.

Question 16

other key facts

Answer 16

neurotransmtiters always produced by pre SN and not post SN

Question 17

excitatory synapses

Answer 17

when neutraonsmitter binds to protein channels on post SN, this generates another AP.
When another AP is generated in this way, it is called excitatory synapse.

Question 18

choligernic synapsesx

Answer 18

have neurotransmitters called acetlycholine.
common in vertebrates
for central nervous sytem and muscular conjuction.

Question 19

function of a synapse

Answer 19

when action potential reaches synaptic knob- epolarisation of synaptic knob
calcium ion channels open and calcium ions diffuse in.

neurotransmitters in vesicles move towards and fuse with post synaptic membrane.
neutraonsmitters diffuse down tehir concentration gradient across synaptic knob and to post synaptic membrane

they bind to receptor on post synaptic membrane that they are complimentary to.

sodium ion channels open and sodium ions diffuse in.
if there is enough neurotransmitter, enough sodium ions diffuse in, threshold is met and post synaptic neurone is depolarised.

neurotransmitter is degraded and released from receptor
sodium ion channels close
pre synaptic neurone restores resting potential
neurotransmtiter transported back to pre synaptic neurone, where it is recyled

Question 20

what is the synapse?

Answer 20

gap between the axon of one neurone and the dendrites of another.

action potential can be transmitted as neurotransmitters diffuse across the synapse.