1
Q
Nervous pathway
A
Receptor - sensory neurone - CNS (brain, spinal chord + relay neurone) - motor neurone - Effector (gland - hormonal + muscle - nervous)
2
Q
Internal stimuli
A
- BGC
- internal temperature
- water potential
- cell pH
3
Q
External stimuli
A
- humidity
- external temperature
- light intensity
- new/sudden sound
4
Q
the need for communication systems in multicellular organisms
A
- organism needs to respond to in/external changes for survival
- occurs by electrical impulses/NS in animals
- chemical/hormones in plants/animals
- diff cells rely on others for materials/removal of waste(gluc+oxygen)
- diff organs work together; ensures homeostasis (brain and skin in temp control)
- cells communicate through cell signalling (cells of pituitary gland secrete ADH acting on cells in kidneys to maintain water balance)
5
Q
How do cells communicate with one another
A
- cell releases a chemical
- which has an effect on a target cell
6
Q
Dendron
A
part of neurone that sends impulse to cell body
7
Q
cell body
A
releases neurotransmitters
8
Q
axon
A
sends impulse away from the cell body
9
Q
myelin sheath
A
layers of plasma membranes (lipids)
10
Q
sensory neurone
A
- transmit impulses from receptor cell to RN, MT or the brain
- dendrite branches
- have one dendron (carries impulse to the cell body)
- one axon (impulse away from cell body)
- cell body in the middle
11
Q
motor neurone
A
- cell body at the start
- dendrite branches on cell body
- Axon after cell body
- Dendrites of the end of axon
12
Q
relay neurone
A
- only cell body in the middle
- dendrite receive the signal from SN
- other branches are axons that send the signal away from cell body to MN.
13
Q
function of myelin sheath
A
- layers of plasma membranes
- insulating layer
- speeds up nerve transmission (saltatory conduction) at nodes of Ranvier
- ## SN + MN have myelin sheath
14
Q
what cell produces myelin sheath
A
- Schwann cells growing around the axon several times
15
Q
what are the nodes of Ranvier + what happens there
A
- between each adjacent SC there is a small gap = NOR
- in myelinated neurones the electrical impulse ‘jumps’ from one node to the next (saltatory conduction)
- impulse transmitted faster compared to unmyelinated
- in non-myelinated the impulse transmits along the nerve at a slower rate
16
Q
features of a SR
A
- specific to a single type of stimulus
- transducer - covert a stimulus into a nerve impulse
17
Q
Mechanoreceptor
- stimulus
- receptor
- sense organ
A
- pressure and movement
- Pacinian corpuscle (pressure)
- skin
18
Q
chemoreceptor
- stimulus
- receptor(detects)
- sense organ
A
- chemicals
- olfactory receptor (smell)
- nose
19
Q
thermoreceptor
- stimulus
- receptor(detects)
- sense organ
A
- heat
- end bubs of Krause
- tongue
20
Q
photoreceptors
- stimulus
- receptor (detects)
- sense organ
A
- light
- cone cell (diff wave-lengths)
- eye
21
Q
role as a transducer
A
- SR converts stimulus into a nervous impulse
- also called generator potential
22
Q
Pacinian corpuscle
A
- detect pressure
- end of SN within the centre of the corpuscle
- surrounded by layers of connective tissue
- each layer is separated by a layer of gel
- neurone ending in PC has stretch mediated Na+ channels
23
Q
how does the PC convert mechanical pressure into a nervous impulse
A
- at resting state the SM Na+ channels in SN membrane are closed
- neurone has a resting potential
- when pressure is applied , PC detects pressure
- PC changes shape
- neuronal membrane stretches
- SM Na+ channels widen
- Na+ diffuses into the neurone down its ECG
- membrane becomes depolarised - less negative
- generator potential formed
- GP creates an action potential
- AP transmitted along the SN to the CNS.
24
Q
How is a resting potential created
A
- sodium potassium pump actively transports Na+/K+ ions (ATP used)
- 3Na+ moved out
- 2K+ moved in
- K+ ions can diffuse out through open K_ ion channels
- Na+ can’t diffuse in as ‘gated’ Na+ channels closed
- outside of axon is more positive (more Na+ and K+)
- axon membrane is polarised
- creates a resting potential across the membrane of -70mV
25
how is an action potential generated
- neurone has a RP
- some K+ channels are open
- VG Na+ closed
- energy of stimulus triggers some Na+ to open
- Na+ diffuses into axon down ECG
- inside of neurone is depolarised
- more VG Na+ channels opens (change in charge)
- more Na+ diffuse in (positive feedback)
- when P.D reaches +40 mV VG Na+ close
- VG K+ open
- membrane now permeable to K+
- K+ diffuses out of axon down ECG
- charge is reduced
- inside of axon becomes more negative than the outside
- Initially lots of K+ diffuse out of axon so inside of axon becomes more negative than RP
- hyperpolarisation
- VG K+ close
- Na+/K+ pump moves Na+ out and K+ in
- axon returns to RP
- repolarised.
26
frequency of impulse link to stimulus
Higher frequency of impulses means a more intense stimulus
27
saltatory conduction
- AP 'jumps' from one node to another as saltatory conduction
- longer localised circuits
- less places where channels open and ions move in/out : speeds up AP transmission
- Repolarisation uses ATP in the pump : reduces repolarisation needed : energy efficient.
28
Factors affecting speed of action potentials
- myelinated
- axon diameter : bigger the diameter = faster. Less resistance to the flow of ions in the cytoplasm compared to smaller axon
- temperature : higher temp = faster. ions diffuse faster at high temp . This only occurs up to 40c ; at high temp proteins (pump) can be denatured.
29
All-or-nothing principle
- Power of stimulus isn’t proportional to power of AP
- If threshold is reached, AP is generated
- If threshold isn’t reached, AP isn’t generated
- More intense stimulus = more frequent AP
30
why is the refractory period important
- prevents the propagation of an AP moving backwards along the axon as well as forwards
- ensures AP are unidirectional
- ensures AP don't overlap and occur as discrete impulses.
31
what would happen if a refractory period did not exist
- axon could be immediately depolarised after an AP
| - AP could travel backwards/not reach target cell
32
what is the synapse
junction between 2 neurones
| impulses are transmitted using neurotransmitters
33
synaptic cleft
gap that separates the axon of one neurone from the dendrite of the next neurone
34
presynaptic neurone
neurone along which the impulse has arrived
35
postsynaptic neurone
neurone that receives the neurotransmitter
36
synaptic knob
- swollen end of preS neurone
- contains mitochondria
- large amounts of endoplasmic reticulum to enable manufacture of neurotransmitters.
37
synaptic vesicles
- vesicles contain neurotransmitters
- vesicles fuse with presynaptic membrane
- release contents into the synaptic cleft.
38
neurotransmitter receptors
- receptor molecules which the neurotransmitter binds to in the postsynaptic membrane.
39
excitatory neurotransmitter
- depolarises the postsynaptic neurone
- if threshold is reached in the postS membrane - AP is triggered
- acetylcholine
40
inhibitory neurotransmitter
- hyperpolarisation of the postsynaptic membrane
- prevents and AP being triggered
- GABA (gamma-aminobutyric acid) in synapses in the brain
41
transmission across a cholinergic synapse
- arrival of AP at presynaptic end
- PreS membrane depolarised
- causes Ca2+ channels to open
- Ca2+ diffuse into the presynaptic knob
- synaptic vesicles fuse with presynaptic membrane
- acetylcholine released into and diffuses across synaptic cleft. (exocytosis)
- AC binds with receptor sites on Na+ channel in postS membrane
- Na+ channels open
- Na+ diffuse in rapidly along CG
- threshold reached
- depolarisation triggers an AP
- effector contracts/secretes
- Acetylcholinesterase hydrolyses AC into choline+ethanoic acid
- they diffuse back across synaptic cleft into preS neurone
- breakdown of AC prevents the continuous generation of a new AP in the postS neurone
- ATP released by mitochondria is used to recombine choline and ethanoic acid into acetylcholine.
- stored in synaptic vesicles for future use
- Na+ channels close in absence of acetylcholine in the receptor sites.
42
role of synapses
- unidirectional transmission
- cause multiple responses from one stimulus
- receive multiple stimuli for one response.
- cell signalling
- filters low level stimuli
- prevents over stimulation
43
what is spatial summation
- Several preS neurones connect to one postS neurone.
- each releases NT
- which builds up to a high level in the synapse
- AP triggered in the single postS neurone
44
what is temporal summation
- single preS neurone
- receives high frequency of AP several times over a short period of time.
- builds up in synapse until quantity is enough to trigger an AP
45
how do synapses ensure impulses are only transmitted in one direction
- NT receptors only present on the postS membrane
| - can only depolarise this membrane to form AP
