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biology > 3.5 - the nervous sytem > Flashcards

3.5 - the nervous sytem Flashcards

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1
Q

state the components of a nervous response

A
  • receptors
  • effectors
  • nervous system or hormones transfer information from receptors to effectors
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2
Q

name the 2 main divisions of the nervous system

A
  • central nervous system (CNS)
  • peripheral nervous system (PNS)
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3
Q

outline the gross structure of the mammalian nervous system

A

peripheral:
- voluntary
- automatic:
— sympathetic
— parasympathetic
central:
- spinal cord
- brain

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4
Q

what’s the CNS

A

brain + spinal cord

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5
Q

what’s the PNS

A

pair of nerves originating from CNS + carry nerve impulses into + out of CNS

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6
Q

what’s the dorsal root

A
  • one of 2 roots that emerges from spinal cord
  • travels to dorsal root ganglion
  • sensory neurones enter spinal cord via dorsal root
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7
Q

what’s the ventral root

A
  • one of 2 roots emerging from spinal cord
  • motor neurones leave spinal cord via ventral root
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8
Q

what’s a reflex

A

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

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9
Q

outline a simple reflex arc

A

stimulus → receptor → sensory neurone → relay neurone (in CNS) → motor neurone → effector → response

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10
Q

how does a reaction differ from a reflex

A
  • reaction is voluntary + coordinated by brain
  • reflex is non-voluntary + doesn’t involve the brain
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11
Q

what’s a nerve net

A
  • simplest form of nervous system found in Cnidarians
  • consists of interconnected nerve cells w/ short extensions allowing response to limited number of stimuli
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12
Q

state the 3 types of functional neurones

A
  • sensory neurone
  • relay neurone
  • motor neurone
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13
Q

state the function of a sensory neurone

A

carries nerve impulses from receptors to CNS via dorsal root

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14
Q

state the function of a motor neurone

A

carries nerve impulses from CNS to effectors via ventral root

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15
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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16
Q

state the function of a relay neurone

A
  • located in spinal cord
  • links sensory neurone to motor neurone
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17
Q

what’s te function of dendrites

A
  • short, branched extensions of cell body
  • receive nerve impulses from other neurones
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18
Q

describe the cell body

A

region of neurone that contains organelles, notably nucleus + RER

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19
Q

what’s the function of the axon

A

long fibre that conducts nerve impulses away from cell body

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20
Q

what are axon terminals

A

branched endings of axon that approach muscle fibre

21
Q

what’s a synaptic end bulb

A

end of axon that’s bulbous shaped + contains synaptic vesicles filled w/ neurotransmitters

22
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 theres no myelin sheath

23
Q

define action potential

A

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

24
Q

what’s resting potential

A

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

25
Q

how is resting potential established

A
  • membrane more permeable to K+ than Na+
  • sodium-potassium pump actively transports 3Na+ out of cells and 2K+ into cell
  • organic phosphates + large protein anions remain in cytoplasm
  • establishes electrochemical gradient: cell contents more negative than extracellular environment
26
Q

name the stages of action potential

A
  1. depolarisation
  2. repolarisation
  3. hyperpolarisation
  4. return to resting potential
27
Q

what happens in depolarisation

A
  1. stimulus causes change in voltage across axon membrane, opening voltage-gated Na+ channels
  2. Na+ diffuse into axon
  3. potential difference across membrane becomes more positive, membrane depolarises
28
Q

what happens in repolarisation

A
  1. membrane potential reaches +40mV
  2. voltage-gated Na+ channels close and voltage=gated K+ channels open
  3. facilitated diffusion of K+ ions out of cell down electrochemical gradient
  4. potential difference across membrane becomes more negative, membrane repolarises
29
Q

what happens in hyperpolarisation

A
  1. ‘overshoot’ when K+ ions diffuse out
  2. potential difference becomes more negative than resting potential
  3. membrane hyperpolarises, preventing another impulse occurring
30
Q

what’s the refractory period

A

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

31
Q

why is the refractory period important

A

ensures action potentials can only be propagated in one direction

32
Q

describe the ‘all or nothing’ law

A

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

33
Q

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

A
  • temperature
  • 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 can’t occur where myelin sheath acts as electrical insulator)
impulse doesn’t travel along whole axon length

35
Q

how does temperature affect speed of conduction of nervous impulses

A

higher temp = faster speed of conduction

36
Q

how does axon diameter affect speed of conduction of nervous impulses

A

larger diameter = faster speed of conduction

37
Q

what’s a synapse

A

junction between 2 nerve cells or nerve cell + effector

38
Q

what’s the function of synapses

A
  • electrical impulse can’t cross junction
  • neurotransmitters send impulses between neurones or from neurones to effectors
  • summation of sub-threshold impulses
  • new impulses can be initiated in several different neurones for multiple simultaneous repsonses
39
Q

describe the structure of a synapse

A
  • presynaptic neurone ends in synaptic knob
  • synaptic knob contains high conc of mitochondria, ER, + vesicles of neurotransmitter
  • synaptic cleft, 20-30nm gap
  • postsynaptic neurone has complementary receptors to neurotransmitter (ligand-gated Na+ channels)
40
Q

what’s the synaptic cleft

A

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

41
Q

describe synaptic transmission in presynaptic neurone

A
  1. wave of depolarisation travels down presynaptic neurone, causing 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
42
Q

how do neurotransmitters cross the synaptic cleft

A

via simple diffusion

43
Q

describe synaptic transmission in 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 generated
44
Q

how is merging of impulses prevented during synaptic transmission

A
  • active transport of Ca2+ out of synaptic knob
  • role of cholinesterase
  • reabsorption of neurotransmitters
45
Q

describe the role of cholinesterase in synaptic transmission

A
  • hydrolyses acetylcholine in postsynaptic neurone
  • products diffuse back across cleft
46
Q

what’s the effect of organophosphates on transmission of impulses

A
  • act as cholinesterase inhibitors, preventing hydrolysis of acetylcholine in postsynaptic neurone
  • results in continuous stimulation of neurone
47
Q

where are organophosphates commonly found

A

component of insecticides

48
Q

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

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

biology (24 decks)

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