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Biology Unit 3 > 3.8 The Nervous system 5/6 > Flashcards

3.8 The Nervous system 5/6 Flashcards

1
Q

state the components of a nervous response

A

receptors
effectors
nervous system or hormones transfer info from receptors to effectors

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2
Q

name 2 main divisions of the nervous system

A

CNS Central nervous system
PNS Peripheral nervous system

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3
Q

what is the CNS?

A

brain and spinal cord

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4
Q

What is PNS?

A

pairs of nerves that originate from the CNS and carry nerve impulses into and out of CNS

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5
Q

what is the dorsal root?

A

one of two roots that emerges from the spinal cord
travels to the dorsal root ganglion
sensory neurones enter spinal cord via the dorsal root

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6
Q

what is the ventral root?

A

one of two roots that emerges from spinal chord
motor neurones leave spinal cord via the ventral root

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7
Q

what is a reflex??

A

a rapid automatic response to a sensory stimulus by the body, serves as a protective mechanism

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8
Q

outline a simple reflex arc

A

stimulus -> receptor -> sensory neurone -> relay neurone (in CNS) ->motor neurone -> response

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9
Q

how does a reaction differ from a reflex?

A

reaction is voluntary & coordinated by the brain
reflex is non-voluntary & does not involve the brain

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10
Q

what is a nerve net?

A

simplest form of nervous system found in Cnidarians
consists of interconnected nerve cells with short extensions allowing a response to a limited number of stimuli

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11
Q

3 types of functional neurones

A

sensory neurone
relay neurone
motor neurone

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12
Q

state the function of a sensory neurone

A

carries nerve impulses from receptors to the CNS via the dorsal root

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13
Q

what is the function of the motor neurone?

A

carries nerve impulses from the CNS to the effectors via the ventral root

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14
Q

describe the structure of a motor neurone??

A

short dendrites carry impulses from CNS to cell body
cell body found at one end of neurone
long axon carries impulses from cell body to effectors

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15
Q

state the function of a relay neurone??

A

located in the spinal cord
links sensory neurone to motor neurone

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16
Q

what is the function of dendrites??

A

short branched extensions of the cell body
receive nerve impulses from other neurones

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17
Q

describe the cell body

A

the region of neurone that contains organelles notably the nucleus and rough endoplasmic reticulum

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18
Q

what is the function of the axon?

A

a long fibre tht conducts nerve impulses away from the cell body

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19
Q

what are axon terminals??

A

branched endings of an axon that approach the muscle fibre

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20
Q

what is a synaptic end bulb??

A

the end of an axon that is bulbous shaped contains synaptic vesicles filled with neurotransmitters

21
Q

describe the additional features of a myelinated neurone??

A

schwann cells: wrap around axon involved in electrical insulation, phagocytosis, nerve regeneration
myelin sheath: made from myelin-rich membranes of schwann cells
nodes of ranvier: small gaps between neighbouring schwann cells where there is no myelin sheath

22
Q

action potential??

A

temporary change in electrical potential across the membrane of an axon in response to the transmission of a nerve impulse

23
Q

resting potential??

A

potential difference (voltage) across a neurone membrane when not stimulated (-70mV)

24
Q

how is resting potential established?

A
  • membrane more permeable to K+ than Na+
  • Sodium-potassium pump actively transports 3Na+ out of cell and 2K+ into cell
  • organic phosphates & large protein anions remain in cytoplasm
  • establishes electrochemical gradient: cell contents more -ve than extracellular environment
25
Q

name the stages of an action potential:

A
  1. depolarisation
  2. repolarisation
  3. hyperpolarisation
  4. return to resting potential
26
Q

what happens during depolarisation?

A
  1. stimulus causes a change in the voltage across axon membrane, opening voltage-gated Na+ channels
  2. Na+ diffuse into axon
  3. potential diff across membrane becomes more +ve, membrane depolarises
27
Q

what happens during repolarisation??

A
  1. membrane potential reaches +40mV
  2. voltage-gated Na+ channels close and voltage gated K+ channels open
  3. falicitated diff of K+ ions out of cell down their electrochemical gradient
    4.potential difference across membrane becomes more -ve, membrane repolarises
28
Q

what happens during hyperpolarisation?

A
  1. ‘overshoot’ when K+ ions diffuse out
  2. potential difference becomes move -ve than resting potential
  3. membrane hyperpolarises, preventing another impulse occurring
29
Q

refractory period??

A

time period after an action potential during which further action potentials are prevented

30
Q

why is the refractory period imp??

A

ensures that action potentials can only be propagated in one direction

31
Q

describe the shape of an oscilloscope trace showing the passage of an action potential

A

graph y axis:voltage(mV) x axis:time resting potential -70mV stimulus shoots up depolarisation (dotted line at -55mv threshold potential) peak action potential down repolarisation below -70mV refractory period then back up to resting state

32
Q

describe the ‘all or nothing’ law

A

principle that states that all stimuli above a certain threshold value will generate the same size of action potential regardless of the strength of the stimulus

33
Q

state the factors affecting the speed of conduction of a nervous impulse

A

temp
axon diameter
myelin sheath

34
Q

explain why myelinated axons conduct impulses faster than unmyelinated axons

A

saltatory propagation: impulse ‘jumps’ from one node of Ranvier to another (depolarisation cannot occur where myelin sheath acts as electrical insulator) so impulse doesnt travel along whole axon length

35
Q

how does temp affect speed of conduction of nervous impulses?

A

higher the temp the faster the speed of conduction

36
Q

how does axon diameter affect speed of conduction of nervous impulses?

A

larger diameter faster the speed of conduction

37
Q

synapse??

A

junction bet 2 nerve cells or a nerve cell & an effector

38
Q

what is the function of synapses?

A
  • electrical impulse cant cross junction
    -neurotransmitters send impulses bet neurones or from neurones to effectors
  • summation of sub-threshold impluses
    -new impulses can be initiated in several diff neurones for multiple simultaneous responses
39
Q

parts of a sypanse

A

presynaptic knob
postsynaptic knob
vesicles containing neurotransmitters
receptors
synaptic cleft

40
Q

describe structure of a synapse:

A

-presynaptic neurone ends in synaptic knob
-synaptic knob contains a high conc of mitochondria, endoplasmic reticulum & vesicles of neurotransmitter
- synaptic cleft 20-30nm gap
-postsynaptic neurone has complementary receptors to neurotransmitter (ligand-gated Na+ channels)

41
Q

what is a synaptic cleft??

A

a small gap bet neurones across which a nerve impulse is transmitted via neurotransmitters

42
Q

describe synaptic transmission in the presynaptic neurone:

A
  1. wave of depolarisation travels down presynaptic neurone causes voltage-gated Ca2+ channels to open
    2.Ca2+ cause vesicles of acetylcholine to move towards & fuse w presynaptic membrane
    3.exocytosis of neurotransmitter(e.g. acetylcholine) into synaptic cleft
43
Q

how do neurotransmitters cross the synaptic cleft?

A

via simple diffusion

44
Q

describe synaptic transmission in the postsynaptic neurone:

A
  1. acetylcholine diffuses across synaptic cleft binds to specific receptors on postsynaptic membrane
  2. ligand-gated Na+ channels open
  3. if influx of Na+ ions raises membrane to threshold potential action potential is generated
45
Q

how is the merging of impulses prevented during synaptic transmission?

A

-active transport of Ca2+ out of synaptic knob
-role of cholinesterase
-reabsorption of neurotransmitters

46
Q

describe the role of cholinesterase in synaptic transmission:

A

-hydrolyses acetylcholine in the postsynaptic neurone
-products diffuse back across the cleft

47
Q

what is the effect of organophosphates on the transmission of impulses?

A
  • act as cholinesterase inhibitors, preventing the hydrolysis of acetylcholine in the postsynaptic neurone
    -results in continuous stimulation of the neurone
48
Q

where are organophosphates commonly found?

A

component of insecticides

49
Q

how do psychoactive drugs (e.g. amphetamine) affect the transmission of impulses??

A
  • excitatory drugs
    -stimulate the release of neurotransmitters such as noradrenaline

Biology Unit 3 (8 decks)

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