the nervous system 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
what is the function of the synoptic end walls?
swelling at end of axon in which neurotransmitter is stored
26
what is the function of the axon endings?
secretes neurotransmitter by exocytosis into synaptic cleft
27
what is the function of the schwann cells?
surround peripheral neurones in vertebrates and grow around the axon to form a multi-layered myelin sheath
28
what is the function of the myelin sheath?
provide electrical insulation to speed up nerve impulse transmission
29
what is the function of the nodes of ranvier?
intervals in the myelin sheath **between** adjacent schwann cells
30
what is the spinal cord?
a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain
31
what is the spinal cord protected by?
spinal column
32
what are peripheral nerves and where do they originate from?
- nerves which connect the CNS to the other organs of the body - originate from spinal cord
33
what is the function of the spinal cord?
transmission of neural signals between the brain and the rest of the body
34
what are neural circuits and where are these found?
- found in spinal cord - independently control numerous reflexes
35
what is the spinal cord made up of?
- 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
what is the spinal cord surrounded by?
membranes called meninges
37
- where do the sensory fibres enter the spinal cord from? - where are cell bodies of sensory fibres found? - where do motor fibres leave by?
- 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
how can the potential difference across membranes be measured?
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
describe the experiment for measuring potential difference
- 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
how do neurones transmit electrical impulses along the cell membrane?
they do this by changing the potential difference across the axon membrane of the neurone
41
what is resting potential?
when no impulse is being sent, the inside of the cell has a negative electrical charge compared to the outside
42
how is resting potential maintained?
- the movement of sodium and potassium ions - large protein anions and organic phosphates remain in the cytoplasm producing a negative potential difference
43
what is resting potential? VALUE
-70mV
44
outline what occurs at resting potential
- **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
what is depolarisation?
when the nerve impulse is initiated the action potential is created
46
outline what occurs at depolarisation
- 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
outline what occurs at repolarisation and hyperpolarisation
- 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
describe the refractory period
- 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
state the All or Nothing Law
"an action potential is either initiated or it is not and it is always the same size"
50
describe the All or Nothing Law
- 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
outline nerve impulse transmission in a non-myelinated neurone
- 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
outline nerve impulse transmission in a myelinated neurone.
- 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
what factors affect the speed of conduction of an impulse?
- temperature - the diameter of the axon - myelination
54
how does temperature affect the speed of conduction of an impulse?
- 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
how does the diameter of the axon affect the speed of conduction of an impulse?
- 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
how does myelination affect the speed of conduction of an impulse?
- 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
what is Cnidaria?
a phylum containing aquatic animals such as hydra, jellyfish and sea anemone
58
what is the simplest type of nervous system?
nerve net
59
describe nerve net
- 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
are hydra able to regenerate neurones?
yes
61
what are neurones seperated by?
synapses
62
how many types of synapses and what are they?
TWO TYPES 1. electrical 2. chemical
63
describe an electrical synapse
a tiny gap (approx 3nm) that is small enough for an electrical impulse to be transmitted directly across, an electrical impulse
64
describe a chemical synapse
- 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
name some neurotransmitters
- dopamine - serotonin - endorphins - glycine
66
describe the mechanism involved in a synaptic transmission
- 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
what are organophosphates?
organophosphorus insecticides are acetylcholinesterase inhibitors - they cause repeated firing of the post synaptic neurone - results in repeated, uncontrolled contractions of he muscle
68
what are psychoactive drugs?
- act on CNS and can alter brain function resulting in temporary changes in perception, mood, consciousness and behaviour
69
what do excitatory drugs do?
what do they do : stimulate the nervous system - increase number of action potentials
70
what are some possible methods of action of excitatory drugs?
- 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
name some examples of excitatory drugs
- nicotine - organophosphates - insecticides - herbicides - cocaine / ecstasy
72
what do inhibitor drugs do?
inhibit the nervous system - decrease the number of action potentials
73
what are some possible methods of action for inhibitor drugs?
- blocking receptors in post-synaptic membrane preventing NT binding to them, antagonist - blocking calcium ion uptake - inhibit exocytosis of neurotransmitters
74
name some examples of inhibitor drugs
- alcohol - benzodiazepines
75
exa
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exa
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