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9.2 Flashcards

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1
Q

what is a neuron

A

cells specialized for the rapid transmission of impulses throughout an organism

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2
Q

what are receptor cells

A

specialized neurons that respond to changes in the environment

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3
Q

what are effector cells

A

specialized cells that bring about a response when stimulated by a neuron

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4
Q

what are sense organs

A

groups of receptors working together to detect changes in the environment

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5
Q

what is a sensory neuron

A

neurons that only carry information from the internal or external environment into the central processing areas

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6
Q

what is the CNS

A

central nervous system - specialised concentration of nerve cells where incoming information is processed and from where impulses are sent out through motor neurons

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7
Q

what are motor neurons

A

carry impulses to the effector organs

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8
Q

what is an axon

A

the long nerve fiber of a motor neuron which carries the nerve impulse

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9
Q

what is a dendron

A

the long nerve fiber of a sensory neuron which carries the nerve impulse

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10
Q

what is the peripheral nervous system

A

the parts of the nervous system that spread through the body that are not involved in the central nervous system

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11
Q

draw a motor neuron

A
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12
Q

draw a sensory neuron

A
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13
Q

draw a relay (connector) neuron

A
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14
Q

what are nerve impulses

A

minute electrical event that depend on the nature of the axon membrane and the maintenance if the sodium ion and potassium ion gradients across that membrane

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15
Q

what are dendrites

A

slender, finger-like processes that extend from the body cell of a neuron and connect with neighboring neurons

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16
Q

what is a schwann cell

A

specalised type of cell associated with myelinated neurons and the formation of myelin sheath

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17
Q

what is myelin sheath

A

fatty insulating layer around some neurons produced by Schwann cell

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18
Q

what are the nodes of ranvier

A

gaps between schwann cells that enable saltatory conduction

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19
Q

why is myelin sheath important

A

protects nerves from damage
speeds up transmission of the nerve impulses

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20
Q

what factors effect the speed at which electrical impulses travel across a neuron

A

diameter of nerve fiber - thicker fiber = impulse travels faster
absence or presence of myelin sheath

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21
Q

where are myelinated cells commonly found in vertebrates

A

neurons which transmit impulses to voluntary muscles (control movement)

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22
Q

where are unmyelinated cells commonly found

A

invertebrates
autonomic neurons in vertebrates (digestive system)

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23
Q

why are sensory nerve fibers hard to use for investigations

A

they are often connected to the brain or spinal cord making them difficult to access

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24
Q

why are motor axons good to use in investigations

A

they run directly to muscles in large motor nerves and the effect of stimulating them can be seen immediately

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25
Q

how is the axon membrane permeable to sodium and potassium ions

A

relatively impermeable to sodium ions
freely permeable to potassium ions

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26
Q

when is the axon at rest

A

when it is not conducting a nerve impulse and the extracellular concentration of ions is greater than the concentration in the axons cytoplasm

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27
Q

what is the sodium/potssium ion pump

A

contains enzyme Na+/K+ ATPase which uses ATP to move sodium ions out of the axon and potassium ions into the axon through active transport

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28
Q

what causes the membrane to become polarised

A
  • NA+/K+ pump pumps sodium ions out of the axon lowering the concentration of sodium ions inside the axon
  • due to the relative impermeability of the membrane to sodium ions they cannot diffuse back into the axon
  • potassium ions are actively pumped into the axon but passively diffuse back out again along the concentration gradient through open potassium ion channels
  • as a result the inside of the cell is left slightly negatively charged and so the membrane is polarised
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29
Q

what is the potential difference of the membrane at resting potential

A

-70mV

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30
Q

define polarised

A

the condition of a neuron when the movement of positively charged potassium ions out of the cell down the concentration gradient is opposed by the actively produced electrochemical gradient leaving the inside of the cell slightly negative to the outside

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31
Q

define resting potential

A

the potential difference across the membrane (roughly -70mV) when the neuron is not transmitting an impulse

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32
Q

what is a neurotransmitter

A

a chemical which transmits an impulse across a synapse

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33
Q

what are sodium gates

A

specific sodium ion channels in the nerve fiber membrane that open up, allowing sodium ions to diffuse rapidly down their concentration and electrochemical gradients

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34
Q

define depolarisation

A

the condition of the neuron when the potential difference across the membrane is briefly reversed during an action potential, with the cell becoming positive on the inside with respect to the outside for about 1 millisecond

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35
Q

what is action potential

A

when the potential difference across the membrane is briefly reversed to about +40mV on the inside with respect to the outside for about 1 millisecond

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36
Q

what is the threshold

A

the point when sufficient sodium ion channels open for the rush of sodium ions into the axon to be greater than the outflow of potassium ions resulting in an action potential

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37
Q

what is the refractory period

A

the time it takes for ionic movement to repolarise an area of the membrane and restore the resting potential after action potential

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38
Q

what is the absolute refractory period

A

the first millisecond after the action potential when is it impossible to re-stimulate the fiber as the sodium channels are completely blocked and the resting potential has not been restored

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39
Q

what is the relative refractory period

A

a period of several milliseconds after an action potential and the absolute refractory period when an axon may be re-stimulated but only by a much stronger stimulus than before

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40
Q

explain depolarisation (the cause of an action potential)

A
  • when a neuron is stimulated the axon membrane shows a sudden and dramatic increase in permeability of sodium ions
  • specific sodium gates open allowing sodium ions to diffuse rapidly across their concentration and electrochemical gradient
  • this results in the potential difference across the membrane across the membrane to be briefly reversed
  • the inside of the cell becomes positive with respect to the outside
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41
Q

where does an action potential occur

A

any nerve fiber

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42
Q

explain repolarisation

A
  • at the end of depolarisation sodium ion channels close and excess sodium is rapidly pumped out by the active sodium pump
  • permeability of the membrane to potassium ions temporarily increases because voltage-dependent potassium channels open
  • potassium ions diffuse out of the axon down their concentration and electrochemical gradient attracted by the negative charge outside the axon
  • inside of the axon becomes negatively charged again and resting potential is restored
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43
Q

what is the oscilloscope trace

A

the rapid increase (spike) in potential difference on a graph

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44
Q

does action potential change depending on the stimulus after the threshold

A

no the size of the action potential is always the same after the threshold

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45
Q

how does the action potential cause the movement of an impulse across a nerve fiber of an unmyelinated fiber

A

depolarisation of the membrane in front of the action potential causes sodium ion channels to open, sodium channels behind the action potential can’t open due to the refractory period so the impulse is continually conducted in the required direction

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46
Q

what is saltatory conduction

A

the process by which action potentials are transmitted from one node of Ranvier to the next in a myelinated nerve

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47
Q

why are synapses needed

A

receptors must pass their information into the sensory nerves and sensory nerves must then pass their information to the CNS
information needs to be able to move freely around the CNS and be passed to motor neurons then to effector organs

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48
Q

define synapse

A

the junction between two neurons that nerve impulses cross via neurotransmitters

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49
Q

what is the synaptic knobs

A

bulges at the end of the presynaptic neurons where neurotransmitters are made

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50
Q

summarise the creation and movement of an impulse along a neuron fiber

A
  • at resting potential there is a potential charge on the outside of the membrane and a negative charge on the inside due to high Na+ concentration outside and high K+ concentration inside
  • when stimulated voltage gated Na+ channels open and sodium flows into the axon depolarising the membrane
  • localised electric currents are generated in the membrane
  • the potential difference of the adjacent membrane to the first action potential changes inititating a second action potential
  • at the site of the first action potential voltage gated Na+ channels close and K+ channels open
  • K+ leaves the membrane and it is repolarised
  • a third action potential is initiated by the second causing the current to move along the axon
  • at the site of the first action potential K+ ions diffuse back into the axon restoring resting potential
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51
Q

what is the presynaptic membrane

A

the membrane on the side of the synapse where the first impulse arrives from which neurotransmitters are release

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52
Q

what are the synaptic vesicles

A

membrane-bound sacs in the presynaptic knob which contain around 3000 molecules of neurotransmitter and move to fuse with the presynaptic membrane when an impulse arrives at the presynaptic knob

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53
Q

what is the synaptic cleft

A

the gap between the pre and post synaptic membranes in the synapse

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54
Q

what does the functioning of a synapse depend upon

A

movement of calcium ions

55
Q

explain a synapse

A
  • arrival of impulse at synaptic knob increases permeability of presynaptic membrane to calcium ions as calcium channels open
  • calcium ions move into synaptic knob down their concentration gradient causing synaptic vesicles to move to the presynaptic membrane
  • vesicles fuse with presynaptic membrane and release transmitter substance into synaptic cleft
  • these molecules diffuse across the gap and become attached to specific protein receptors on the sodium channels of the post-synaptic membrane
  • this opens the sodium ion channels in the membrane resulting in an influx of sodium ions into the nerve fiber
  • which causes a change in potential difference across the membrane and an excitatory post-synaptic potential (EPSP) to be set up
  • if sufficient EPSPs the positive charge in the post synaptic cell exceeds the threshold level and an action potential is set up which then travels along the post synaptic neuron
56
Q

what happens if the neurotransmitters have an inhibiting effect

A

when the transmitter substance bonds to specific protein receptor sites different ion channels open allowing the inwards movement of negative ions which makes the inside more negative than resting potential and an inhibitory post-synaptic potential results (IPSP)

57
Q

draw a synapse

A
58
Q

what is the excitatory post-synaptic potential (EPSP)

A

the potential difference across the post synaptic membrane caused by an influx of sodium ions into the nerve fiber as the result of the arrival of a molecule of neurotransmitter on the receptors of the post-synaptic membrane that makes the inside more positive than resting potential increasing the chances of an action potential

59
Q

what is the inhibitory post-synaptic potential (IPSP)

A

the potential difference across the post-synaptic membrane caused by an influx of negative ions as a result of the arrival of a molecule of neurotransmitter on the receptors of the post-synaptic membrane which makes the inside more negative than resting potential decreasing the change of a new action potential

60
Q

what is acetylcholine (ACh)

A

a neurotransmitter found in the synapses of motor neurons, the parasympathetic nervous system and cholinergic synapses in the brain synthesised in the synaptic knob using ATP

61
Q

what are cholinergic nerves

A

nerves using acetylcholine as their transmitter

62
Q

what is acetylcholinesterase

A

an enzyme found embedded in the post-synaptic membrane to cholinergic nerves that break down acetylcholine in the synapse after it has triggered a post-synaptic potential

63
Q

what is noradrenaline

A

a neurotransmitter found in the synapses of the sympathetic nervous system and adrenergic synapses of the brain

64
Q

what are adrenergic nerves

A

use noradrenaline as the neurotransmitter in their synapses

65
Q

how can drugs increase response

A
  • increase the amount of neurotransmitter synthesised
  • increase the release of neurotransmitter from the vesicles at the presynaptic membrane
  • binds to post-synaptic receptors and activates them or increases the effect of the normal neurotransmitter
  • prevents the degradation of neurotransmitter by enzymes or prevents reuptake into presynaptic knob
66
Q

how can drugs decrease response

A
  • blocks synthesis of neurotransmitter
  • causes neurotransmitter to leak from vesicles and be destroyed by enzymes
  • prevents release of neurotransmitter from vesicles
  • blocks the receptor and prevents neurotransmitter binding
67
Q

how does nicotine work

A

mimics effect of acetylcholine and binds to specific acetylcholine receptors in post-synaptic membrane (nicotine receptors)
triggers an action potential in the post synaptic neuron but then the receptor remains unresponsive to more stimulation for some time

68
Q

what effects does nicotine have in general

A

raises heart rate & blood pressure
triggers release of dopamine

69
Q

what are the effects of nicotine in small and large doses

A

small dose - stimulating
large dose - blocks acetylcholine receptors and can be deadly

70
Q

what is lidocaine used as

A

local anaesthetic

71
Q

how does lidocaine work

A

lidocaine molecules block voltage gates sodium channels so raises the depolarisation threshold and prevents the production of an action potential in sensory nerves so prevents you from feeling pain

72
Q

how is cobra venom fatal

A

it binds to acetylcholine receptors in the post-synaptic membranes and neuromuscular junctions and prevents the transmission of impulses across the synapse so muscles are not stimulated to contract and gradually the person affected becomes paralyzed and when it reaches muscles involved in breathing it causes death

73
Q

when can cobra venom be beneficial

A

in very low concentrations it can be used to relax the muscles in the trachea and bronchi in severe asthma attacks

74
Q

what is a primary receptor

A

simple sensory receptors where the dendrite receives a stimulus, chemical events occur that result in an action potential in the nerve fiber of the neuron

75
Q

what are secondary receptors

A

consist of one or more completely specialised cells that are sensitive to a particular type of stimulus which synapse with a normal sensory neuron which carries impulses to the CNS

76
Q

how do sensory receptors work (in depth)

A

receptor cells have a resting potential that depends on maintaining the charge of the cell interior negative in relation to the outside using membrane sodium pumps
when a receptor receives a stimulus sodium ions move rapidly across the cell membrane along the concentration and electrochemical gradient which sets up a generator potential
a large stimulus = a large generator potential
a small stimulus = a small generator potential
if the generator potential produced is large enough to reach the threshold of the sensory neuron an action potential will occur

77
Q

summarise the stimulation of a sensory neuron

A

stimulus -> local change in permeability -> generator potential -> action potential

78
Q

what is convergence

A

when several receptor cells synapse with a single sensory neuron so that if the generator potential from an individual receptor cell is insufficient to trigger an action potential several generator potentials may add together to trigger an action potential

79
Q

why is convergence useful

A

because it increases sensitivity of a sensory system to low-level stimulus

80
Q

how does the eye make us aware of varying degrees of light and shade not just light and dark

A

a weak stimulus results in a low frequency of action potential whereas a strong stimulus results in a rapid stream of action potentials therefor a graded response is still possible giving information about the strength of the stimulus in the eye

81
Q

what is the range of wavelength of light that human eyes are sensitive to

A

400 - 700nm

82
Q

what do the ciliary muscles do

A

change the shape of the lens

83
Q

what is the cornea

A

clear layer involved in focusing light and protecting the eye

84
Q

what is the pupil

A

circular hole in the iris which light enters the eye

85
Q

what is the iris

A

a circular sheet of muscle that controls the amount of light entering the eye

86
Q

what is the lens needed for

A

focusing light onto the retina

87
Q

what is the choroid

A

pigmented cells that prevent internal reflection of light

88
Q

what is the retina

A

layer of light sensitive cells (rods & cones)

89
Q

what is the fovea

A

area of the retina containing only cones, region of highest visual acuity

90
Q

what is the optic nerve

A

bundle of nerve fibers carrying impulses from the retina to the brain

91
Q

what is the blind spot

A

the point where the optic nerve leaves the eye so there are no photoreceptor cells so no vision

92
Q

what are secondary exteroceptors (e.g. rods & cones)

A

they signal changes in the external environment

93
Q

what are rods

A

photoreceptors found in the retina which contain the visual pigment rhodopsin and respond to low light intensities, gives black and white vision and are very sensitive to movement

94
Q

what are cones

A

photoreceptors found in the fovea of the retina which contain the visual pigment iodopsin which respond to bright light, give clarity of vision and colour

95
Q

what are the benefits and drawbacks of rod cells not being tightly packed together

A

-/ they don’t give a very clear picture
+/ they are extremely sensitive to low light levels and movement because several of them synapse to the same neuron

96
Q

what is the outer segment of a rod or cone cell

A

light-sensitive region that contains flattened membranous vesicles filled with photosynthetic pigments

97
Q

what is the constriction section of a rod or cone cell

A

narrow region between the outer and inner segments

98
Q

what is found in the inner segment of rod and cones cells

A

mitochondria and ribosomes

99
Q

what forms rhodopsin

A

opsin and retinal

100
Q

what vitamin effects site and why

A

vitamin A because it is needed for the formation of retinal which then forms rhodopsin

101
Q

which geometric isomer of retinal prefers the dark

A

cis-retinal

102
Q

what is bleaching

A

when a photon of light hots a molecule of rhodopsin it converts the cis-retinal into trans-retinal which changes its shape and puts strain on the bonding between opsin and retinal and the rhodopsin breaks into opsin and retinal

103
Q

how is a generator potential geneorated in a rod cell

A
  • rod cells are usuallt very permeable to Na+ ions
  • when rhodopsin is bleached it closes sodium ion channels but the sodium pump continues to work so the interior becomes more negative
  • this is hyperpolarisation and causes generator potential
104
Q

how is generator potential passed on to action potential

A

if the generator potential is above the threshold neurotransmitter substances are released into the synapse with the bipolar cell and an action potential is set up in the bipolar cell that passes across the synapse and causes an action potential in the sensory neuron

105
Q

why do rod cells need a lot of mitochondria

A

once rhodopsin has been bleached the rod cannot be stimulated again so it must be resynthesised using ATP

106
Q

why do you become almost blind when you walk from a sunny garden into a house

A

the bright light has completely bleached rhodopsin you need to see in dimmer light and as rhodopsin reforms your vision returns as your eyes become dark-adapted again

107
Q

why are cone cells less sensitive to low light intensities

A

it requires more energy to break down iodopsin than rhodopsin

108
Q

what pigment so cone cells have and how does it allow us to see in colour

A

iodopsin
there are three types which are sensitive to one of the primary colours of light

109
Q

what is the role of the brain

A

information can be processed, instructions can be issued to give fully coordinated responses to situations

110
Q

what is the role of the spinal cord

A

carries nerve fibers into and out of the brain
coordinates unconscious reflex actions

111
Q

what is the forebrain in embryos

A

old factory lobes which forms the cerebral hemispheres

112
Q

what is the midbrain

A

contains optic lobes

113
Q

what is the hindbrain

A

forms cerebellum and the medulla

114
Q

what is the cerebrum

A

the area of the brain responsible for conscious thought, personality and control of movement

115
Q

what are the cerebral hemispheres

A

two parts of the cerebrum joined by the corpus callosum

116
Q

what is grey matter

A

consists of the cell bodies of neurons in the CNS

117
Q

what is white matter

A

consists of the nerve fibers of neurons in the CNS

118
Q

what is the corpus callosum

A

band of axons (white matter) that join the left and right cerebral hemispheres of the brain

119
Q

what is the hypothalamus

A

the area of the brain that coordinates the autonomic (unconscious) nervous system, thermoregulation, osmoregulation

120
Q

what is the cerebellum

A

the area of the brain that coordinates smooth movements (balance and posture)

121
Q

what is the medulla oblongata

A

the most primitive part of the brain that controls reflex centers controlling functions such as breathing and heart rate

122
Q

what is a reflex response

A

rapid responses that take place with no conscious thought involved

123
Q

where do impulses enter the spinal cord from

A

dorsal roots

124
Q

where do impulses leave the spinal cord

A

ventral roots

125
Q

what is the function of a reflex arc

A

brings about an appropriate response to a particular stimulus as rapidly as possible

126
Q

what is a relay neuron

A

relays impulses from sensory neurons to motor neuron

127
Q

what is the voluntary nervous system

A

involves motor neurons that are under voluntary or conscious control involving the cerebrum

128
Q

what is the autonomic nervous system

A

the involuntary nervous system involved in controlling bodily functions not involving conscious area of the brain

129
Q

give similarities and differences in the structure of the sympathetic and parasympathetic nervous system

A

similarities/ myelinated preganlionic fibers leave the CNS and synapse in ganglion with unmyelinated post-ganglionic fibers
sympathetic/ ganglia very close to CNS
short preganglionic fibers & long post ganglionic fibers
parasympathetic/ ganglia close to CNS
long preganglionic fibers & short post ganglionic fibers

130
Q

what is the neurotransmitter produced in the synapse of the sympathetic nervous system

A

noradrenaline

131
Q

what is the neurotransmitter produced in the synapse of the parasympathetic nervous system

A

acetylcholine

132
Q

what is the function of the sympathetic nervous system

A

produces a rapid response
fight or flight

133
Q

what is the function of the parasympathetic nervous system

A

slower inhibitory effect
maintains normal functioning of the body & restores calm after a stressful situation

Biology (33 decks)

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