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the nervous system Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

define central nervous system

A

brain and spinal cord

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2
Q

define peripheral nervous system

A

the nerves and ganglia on the outside of the CNS

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3
Q

define somatic nervous system

A

associated with skeletal muscle to provide voluntary control of body movements (part of PNS)

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4
Q

define autonomic nervous sytem

A

provides unconscious control of functions of internal organs
e.g heartbeat, digestion (part of PNS)

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5
Q

define reflex arc

A

an inborn response to a stimulus and is rapid, automatic and beneficial

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6
Q

define resting potential

A

the potential difference across the membrane when no nervous impulse is being conducted

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7
Q

define excitable cell

A

a cell which can change its resting potential

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8
Q

define the All or Nothing Law

A

law stating that :
“an action potential is either initiated or it is not, and it is always the same size”

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9
Q

define saltatory conduction

A

jumping of action potentials from one Node of Ranvier to the next due to electrical insulation of myelin

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10
Q

define nerve net

A

the most simple type of nervous system found in simple organisms such as hydras, jellyfish and sea anemones

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11
Q

define synapse

A

tiny gap between neurones
an impulse can be transmitted across electrically or chemically

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12
Q

define excitatory drug

A

a substance which increases the likelihood of depolarisation at a post-synaptic membrane

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13
Q

define inhibitory drug

A

a substance which decreases the likelihood of depolarisation at a post-synaptic membrane

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14
Q

what is the human nervous system composed of?

A

composed of two parts
- central nervous system (brain and spinal cord)
- peripheral nervous system (nerves and ganglia on outside of CNS)

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15
Q

define stimulus and give examples

A

a detectable change in the external or internal environment of an organism
examples:
- pressure on skin
- chemicals in food
- light turning on

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16
Q

define receptor and give examples

A

detects stimulus (one form of energy) and converts this to electrical energy to send the information as an electrical impulse to the central nervous system via neurones
examples :
- photoreceptor
- thermoreceptor
- mechanoreceptor
- osmoreceptor
- chemoreceptor

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17
Q

define effector and give examples

A

recieves electrical impulses from the CNS and brings about a response
example:
- muscles
- glands

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18
Q

what are neurones?

A

highly specialised cells that generate and transmit nerve impulses

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19
Q

what are the three types of neurones and describe them

A
  1. sensory - carry impulse from the receptor to the cells
  2. motor - carry impulses from the CNS to effector organs (muscles / glands)
  3. relay - found within the spinal cord, recieves impulse from sensory neurones or other intermediate neurones and relay them to motor neurones or other intermediate neurones
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20
Q

compare the structure of three main types of neurones

A

SENSORY : cell body in middle of neurones, long axon

MOTOR : long axon, cell body at start of neurone

RELAY : cell body at start of neurone

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21
Q

identify the components of a neurone

A
  • axon
  • dendrites
  • cell body
  • synoptic end bulb
  • axon ending
    these are found only in PNS:
  • schwann cells
  • myelin sheath
  • nodes of ranvier
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22
Q

what is the function of the axon?

A

extension of the cytoplasm that transmit impluse away from the cell body to the axon endings

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23
Q

what is the function of the dendrites?

A

many thin extensions of cytoplasm that receives impulses from other nerve cells and transmit impulses towards the cell body

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24
Q

what is the function of the cell body/centron?

A

contains the nucleus and groups of ribosomes in the cytoplasm (Nissl granules) that synthesise neurotransmitters

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25
Q

what is the function of the synoptic end walls?

A

swelling at end of axon in which neurotransmitter is stored

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26
Q

what is the function of the axon endings?

A

secretes neurotransmitter by exocytosis into synaptic cleft

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27
Q

what is the function of the schwann cells?

A

surround peripheral neurones in vertebrates and grow around the axon to form a multi-layered myelin sheath

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28
Q

what is the function of the myelin sheath?

A

provide electrical insulation to speed up nerve impulse transmission

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29
Q

what is the function of the nodes of ranvier?

A

intervals in the myelin sheath between adjacent schwann cells

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30
Q

what is the spinal cord?

A

a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain

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31
Q

what is the spinal cord protected by?

A

spinal column

32
Q

what are peripheral nerves and where do they originate from?

A
  • nerves which connect the CNS to the other organs of the body
  • originate from spinal cord
33
Q

what is the function of the spinal cord?

A

transmission of neural signals between the brain and the rest of the body

34
Q

what are neural circuits and where are these found?

A
  • found in spinal cord
  • independently control numerous reflexes
35
Q

what is the spinal cord made up of?

A
  • made up of a central area of grey matter which mainly contain nerve cell bodies
  • surrounded by white matter which consists of nerve fibres surrounded by myelin sheath (axons)
36
Q

what is the spinal cord surrounded by?

A

membranes called meninges

37
Q
  • where do the sensory fibres enter the spinal cord from?
  • where are cell bodies of sensory fibres found?
  • where do motor fibres leave by?
A
  • sensory fibres from the peripheral nervous system enter the spinal cord on the dorsal root
  • found in dorsal root ganglia
  • motor fibres leave via ventral roots
38
Q

how can the potential difference across membranes be measured?

A

can be measured in experiments involving inserting micro electrodes into axons and measuring the changes in electrical potential which can be read on a cathode ray oscilloscope

39
Q

describe the experiment for measuring potential difference

A
  • when the two microelectrodes are both outside the neurone no difference in electrical potential is recorded
  • when two microelectrodes are placed on either side of the axon of the neurone and the difference between outside and inside of the axon is measured : this is known as potential difference
40
Q

how do neurones transmit electrical impulses along the cell membrane?

A

they do this by changing the potential difference across the axon membrane of the neurone

41
Q

what is resting potential?

A

when no impulse is being sent, the inside of the cell has a negative electrical charge compared to the outside

42
Q

how is resting potential maintained?

A
  • the movement of sodium and potassium ions
  • large protein anions and organic phosphates remain in the cytoplasm producing a negative potential difference
43
Q

what is resting potential?
VALUE

A

-70mV

44
Q

outline what occurs at resting potential

A
  • three sodium ions are pumped (actively transported) out of the axon for every two potassium ions that are pumped in by the sodium-potassium pump
  • voltage-gated potassium ion channels, some of which are open, allow K+ to **diffuse **back out of the axon
  • as the voltage-gated** sodium ions channels** are closed the membrane is much more permeable to K+ than Na+
  • the neurone has a resting potential of -70mV
  • some K+ channels allow K+ ions to leave the axon through** LEAKAGE**
45
Q

what is depolarisation?

A

when the nerve impulse is initiated the action potential is created

46
Q

outline what occurs at depolarisation

A
  • the energy of a stimulus causes some sodium voltage gated channels to open. the voltage gated potassium ions close
  • if a threshold voltage is reached, the permeability of the membrane to sodium ions increases, and they rush into the axon, depolarising the membrane
  • the negative charge of -70mV inside the axon rapidly becomes a positive charge of +40mV
  • the membrane is said to be depolarised
47
Q

outline what occurs at repolarisation and hyperpolarisation

A
  • the voltage-gated sodium ion channels close. the voltage-gated potassium ion channels open
  • this causes K+ to rapidly diffuse out of the axon, reducing the potential difference across the membrane
  • an overshoot causes the membrane to become hyperpolarised
48
Q

describe the refractory period

A
  • during this time the concentrations of K+ and Na+ are restored to that of the resting potential
  • during this time, this portion of the axon cannot transmit another action potential, ensuring that transmission is in one direction only
49
Q

state the All or Nothing Law

A

“an action potential is either initiated or it is not and it is always the same size”

50
Q

describe the All or Nothing Law

A
  • the size of the impulse is independent of the size of the stimulus
  • the speed of the conduction of the stimulus is not altered by the intensity of the stimulus
  • a large stimulus will simply produce a greater frequency of impulses
51
Q

outline nerve impulse transmission in a non-myelinated neurone

A
  • sodium ions rapidly diffuse into axon during depolarisation and diffuse down their concentration gradient to the next part of the axon
  • this begins to depolarise the adjacent section of the membrane causing voltage gated sodium ions channels to open in these regions
  • this allows more sodium to diffuse in, creating an action potential and depolarising this part of the membrane
  • this spreads a wave of depolarisation along the axon
52
Q

outline nerve impulse transmission in a myelinated neurone.

A
  • the axon is surrounded by schwann cells that form a myelin sheath to act as an electrical insulator
  • the nerve impulse jumps from one node of ranvier to the next, as myelin is a lipid-type substance that is impermeable to ions
  • depolarisation and an action potential can only take place at the nodes of ranvier, where there is an abundance of ion channels and Na+/K+ pumps
  • local currents caused by the diffusion of the sodium ions are elongated and the speed of transmission increases
  • this is called SALTATORY PROPAGATION
53
Q

what factors affect the speed of conduction of an impulse?

A
  • temperature
  • the diameter of the axon
  • myelination
54
Q

how does temperature affect the speed of conduction of an impulse?

A
  • ions move faster at higher temperatures as they have more kinetic energy.
  • warm blooded animals (mammals/birds) transmit nervous impulses more quickly and have faster responses
55
Q

how does the diameter of the axon affect the speed of conduction of an impulse?

A
  • the larger the diameter, the greater its volume in relation to the area of the membrane
  • more Na+ can flow along the axon so impulses travel faster
56
Q

how does myelination affect the speed of conduction of an impulse?

A
  • electrical insulation of axon speeds up the rate of transmission
  • the action potential jumps from node to node in a process called saltatory propagation
57
Q

what is Cnidaria?

A

a phylum containing aquatic animals such as hydra, jellyfish and sea anemone

58
Q

what is the simplest type of nervous system?

A

nerve net

59
Q

describe nerve net

A
  • the sense receptors only respond to a limited number of stimuli and there is only a small number of effectors
  • their nerve net system consists of simple nerve cells with short extensions joined to each other and branching in a number of different direction
60
Q

are hydra able to regenerate neurones?

A

yes

61
Q

what are neurones seperated by?

A

synapses

62
Q

how many types of synapses and what are they?

A

TWO TYPES
1. electrical
2. chemical

63
Q

describe an electrical synapse

A

a tiny gap (approx 3nm) that is small enough for an electrical impulse to be transmitted directly across, an electrical impulse

64
Q

describe a chemical synapse

A
  • involves a gap of around (20nm)
  • branches of axons lie close to dendrites and the impulse is transmitted across the synaptic cleft chemically as a neurotransmitter before being converted back into an electrical impulse
65
Q

name some neurotransmitters

A
  • dopamine
  • serotonin
  • endorphins
  • glycine
66
Q

describe the mechanism involved in a synaptic transmission

A
  • an action potential arrives at the axon terminal. this causes voltage-gated Ca+ ion channels to open. calcium ions diffuse rapidly into the presynaptic knob
  • the influx of Ca2+ causes vesicles containing acetylcholine (neurotransmitter) to fuse with the presynaptic membrane
  • the acetylcholine is released into the synaptic cleft by exocytosis diffuses over the synaptic cleft and binds to specific receptor on the post synaptic membrane
  • this causes sodium ion channels in the post synaptic membrane to open and Na+ diffuses in depolarising the post synaptic membrane. If the depolarisation reaches the threshold value an action potential is generated
  • acetylcholine in the receptors is broken down by acetylcholinesterase into ethanoic acid and choline which diffuse back into the axon termical through the presynaptic membrane
  • ATP is required to re-synthesise and package the neurotransmitters into vesicles
  • Ca2+ ions use a different protein to be actively transported back out of the synpatic knob to rest its electrochemical gradient
67
Q

what are organophosphates?

A

organophosphorus insecticides are acetylcholinesterase inhibitors
- they cause repeated firing of the post synaptic neurone
- results in repeated, uncontrolled contractions of he muscle

68
Q

what are psychoactive drugs?

A
  • act on CNS and can alter brain function resulting in temporary changes in perception, mood, consciousness and behaviour
69
Q

what do excitatory drugs do?

A

what do they do :
stimulate the nervous system - increase number of action potentials

70
Q

what are some possible methods of action of excitatory drugs?

A
  • mimic the action of natural NT, have a similar shape and bind to the post-synaptic neurone, agonist
  • prevent breakdown of NT by inhibiting ACHesterase
  • block reuptake of natural NT
71
Q

name some examples of excitatory drugs

A
  • nicotine
  • organophosphates
  • insecticides
  • herbicides
  • cocaine / ecstasy
72
Q

what do inhibitor drugs do?

A

inhibit the nervous system - decrease the number of action potentials

73
Q

what are some possible methods of action for inhibitor drugs?

A
  • blocking receptors in post-synaptic membrane preventing NT binding to them, antagonist
  • blocking calcium ion uptake
  • inhibit exocytosis of neurotransmitters
74
Q

name some examples of inhibitor drugs

A
  • alcohol
  • benzodiazepines
75
Q

exa

A
76
Q

exa

A
77
Q
A

biology - component 3 (8 decks)

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