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A2 BIO UNIT3 > 3.8 Nervous System > Flashcards

3.8 Nervous System Flashcards

1
Q

Define stimuli, receptors, reflex arc, effectors and response

A
  • changes that can be detected by the body
  • cells that detect changes
  • pathway of neurones leading to a rapid automatic response
  • muscles or glands that carry out the response
  • how the body reacts to a stimulus
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2
Q

State the main roles of the nervous system

A
  • detects changes in body and environment
  • process and store information
  • initiates responses
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3
Q

Describe the CNS

A
  • brain and spinal cord
  • processes info from stimulus
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4
Q

Structure of spine

A
  • surrounded by meninges
    —> three membranes: dura mater, arachnoid, pia mater)
    —> line brain and spinal cord
  • white matter contains nerve fibres surrounded by myelin
  • grey matter contains nerve fibres of relay neurones and cell bodies of relay and motor neurones
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5
Q

Describe the PNS

A
  • somatic nervous system - pairs of nerves that originate in brain or spinal cord, and their branches
    —> fibres of sensory neurones and motor neurones
  • autonomic nervous system - unconscious control of the functions of internal organs
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6
Q

Draw and label a sensory, relay and motor neurone

A
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7
Q

Draw and label spinal cord

A
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8
Q

Describe a nerve net

A
  • simplest type of nervous system
  • diffuse network of cells that group into ganglia but don’t form a brain
    —> ganglion cells provide connections in several connections
    —> sensory cells detect stimuli
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9
Q

Compare nervous system of hydra v human

A
  • nerve net vs CNS
  • 2 cell types vs many
  • rapid regeneration vs very slow if at all
  • absent myelin sheath vs present myelin sheath
  • slow conduction vs fast conduction
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10
Q

Role of sensory, motor and relay neurones

A

Sensory: carry impulses from receptors to CNS

Motor: carry impulses from CNS to effectors

Relay: carry impulses from sensory to either relay or motor in CNS

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11
Q

Functions of the cell body, cytoplasm, nucleus, nissl granules, dendrite, and axon in nerve cells

A
  • cell body: contains a nucleus and granular cytoplasm
  • cytoplasm: contains many ribosomes
  • nucleus: holds DNA
  • nissl granules: cytoplasmic granules comprising ribosomes grouped on RER
  • dendrite: thin fibre carrying impulses toward cell body
  • axon: thin fibre carrying impulses away from cell body
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12
Q

Functions of Schwann cells & myelin sheath

A
  • glial cells that surround and support nerve fibres
  • wrap around developing axons many times and withdraw their cytoplasm, leaving a multi layered phospholipid myelin sheath
    —> myelin sheath is an electrical insulator that speeds up transmission of impulses
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13
Q

Function of nodes of ranvier

A
  • gaps in myelin sheath where adjacent Schwann cells meet and axon membrane is exposed
  • allows impulses to be transmitted rapidly by saltatory propagation
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14
Q

Function of synaptic end bulb and axon terminal

A
  • synaptic end bulb: swelling at end of axon where NTs are synthesised
  • axon terminal: secretes NT which transmits impulse to adjacent neurone
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15
Q

What is meant by a nerve?

A

A bundle of neurones

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16
Q

Define saltatory propagation/conduction

A
  • transmission of a nervous impulse along a myelinated axon, in which the action potential jumps from one node of ranvier to the adjacent node
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17
Q

Define resting potential

A

The potential difference across the membrane of a cell when no nervous impulse is being conducted

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18
Q

Why can neurones change their resting potential?

A

They are excitable cells

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19
Q

Describe how a resting potential is generated

A
  • inside of cell has higher conc of K+ ions and lower conc of Na+ than outside
  • K+ diffuse out and Na+ in
  • some channels that allow K+ ions to diffuse out are open, whilst most of channels allowing Na+ to move in are closed
  • axon membrane much more permeable to K+ ions which diffuse out faster than Na+ diffuse back in
  • sodium-potassium exchange pumps pump K+ ions back into cell and Na+ ions back out
  • transmembrane proteins with ATPase that transport K+ and Na+ ions against conc gradient by active transport
  • maintain conc and uneven distribution of ions across membrane
  • Na+ ions out faster than K+ in so inside membrane more -ve than outside
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20
Q

Define action potential

A

The rapid rise and fall of electrical potential across a nerve cell membrane as a nervous impulse passes

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21
Q

Define a nervous impulse

A

Transmission of a change in potential along a nerve fibre associated with the movement of sodium ions

22
Q

Describe how action potential is generated

A
  • energy of stimulus causes voltage gated sodium channels in axon membrane to open
  • sudden increase in permeability of membrane to Na+ ions allows them to rapidly diffuse into axon down conc gradient
  • charge from -70mV to 40mV
    —> cell membrane is depolarised
  • sodium channels close to prevent further influx of sodium ions
  • potassium channels open and K+ ions diffuse out down conc gradient
  • cell becomes less positive inside as more diffuse out and membrane is repolarised
  • more K+ ions diffuse out than Na+ in so potential difference across membrane becomes even more -ve than resting potential
    —> membrane is hyperpolarised
  • sodium-potassium pumps pump K+ ions back in and Na+ ions out, restoring ion balance of resting potential
23
Q

Define depolarisation

A

A temporary reversal of potential across the membrane of a neurone such that the inside becomes less negative than the outside as an action potential is transmitted

24
Q

Draw and annotate action potential graph

A
25
Q

Describe how action potential travels along an axon

A
  • at the site of an action potential, Na+ ions diffuse into axon and K+ diffuse out
  • reversal of potential sets up local current as Na+ ions diffuse along axon
  • they depolarise the adjacent section of the membrane
  • this opens more voltage gated sodium channels in those regions and more Na+ flood in, depolarising axon
  • Na+ diffuse further down axon and a self-perpetuating wave of depolarisation spreads along axon
  • at site of initial action potential, sodium channels are inactivated and cannot open again until resting potential reestablished so new action potential cannot be initiated there
  • this is the absolute refractory period
  • ensures action potential is not protracted back in direction from which it came, and nervous potential travels in one direction only
  • relative refractory period then occurs where if an impulse is strong enough, a new action potential may pass
  • occurs while sodium-potassium pumps are restoring resting potential
26
Q

What is meant by the all or nothing law?

A
  • a nervous impulse is either initiated or it is not, and it is always the same size
  • increase in intensity of stimulus does not give greater action potential - frequency of action potential increases instead
  • allows action potential to act as a filter, preventing minor stimuli from setting up nervous impulses so brain is not overloaded
27
Q

How does temperature impact speed of conduction of nervous impulse?

A
  • ions move faster at higher temp as have more KE
  • warm blooded animals transmit nervous impulses quicker than all animals
28
Q

How does diameter of the axon impact speed of conduction of nerve impulse?

A
  • greater diameter of axon = greater volume in relation to area of membrane
  • more Na+ ions can flow through axon so impulses travel faster
29
Q

How does myelination impact speed of conduction of nervous impulses?

A
  • speeds up rate of transmission by insulating axon
  • sodium ions flow through axon but a myelinated nerve fibre only depolarises at the nodes of ranvier
  • voltage gated ions only occur at nodes of ranvier so this is where sodium ions enter
  • action potential therefore jumps from node to node by saltatory propagation
30
Q

Differentiate between an electrical and chemical synapse

A
  • electrical: 3nm across, small enough that electrical impulse is transmitted directly from one neurone to the next
  • chemical: 20nm across, impulse transmitted by NT which diffuses across synaptic cleft
31
Q

Define a neurotransmitter

A

A chemical secreted in response to an action potential which carries a chemical signal across a synapse from one neurone to the next, where a new action potential is limited

32
Q

Define a neurotransmitter

A

A chemical secreted in response to an action potential which carries a chemical signal across a synapse from one neurone to the next, where a new action potential is limited

33
Q

Describe synaptic transmission

A
  • arrival of impulse at synaptic end bulb alters its membrane permeability, opening voltage-dependant calcium channels, so calcium ions diffuse to end bulb down conc gradient
  • influx of calcium ions causes synaptic vesicles to fuse with the presynaptic membrane which releases the NT acetylcholine into the synaptic cleft by exocytosis
  • NT diffuse across synaptic cleft and binds to receptor protein
    —> 2 subunits, 2 molecules of acetylcholine bind with cooperative binding
  • when acetylcholine binds, the receptor protein changes shape, opening a channel for Na+ ions to diffuse in
  • post synaptic neurone is depolarised, and an action potential is initiated
34
Q

3 ways to prevent acetylcholine remaining in the synaptic cleft

A
  • direct uptake of acetylcholine into pre synaptic neurone so none remains in synaptic cleft
  • active transport of calcium ions out of synaptic end bulb, so no more exocytosis of acetylcholine occurs
  • hydrolysis of acetylcholine - destroyed by acetylcholinestarase in cleft to produce chlorine and ethanoic acid which diffuse back to pre synaptic neurone, reforming acetylcholine
35
Q

Why are there mitochondria in axon end bulbs?

A

Energy is required to reform acetylcholine and for exocytosis

36
Q

Why do neurones only transmit an impulse in one direction?

A
  • hyper-polarisation happens behind action potential so depolarisation could not happen at that point
  • synaptic vesicles only occur at end bulb of presynaptic neurone
  • neurotransmitter receptors are only found on post-synaptic neurones
37
Q

Describe the properties of synapses

A
  • transmit information between neurones
  • lass impulses in one direction, generating precision in nervous system
  • act as junctions
  • protect the response system from overstimulation because the impulse is always the same size
  • filter out low-level stimuli
    —> action potential only initiated when depolarisation is large enough to reach a threshold value built by either temporal summation or spatial summation
38
Q

Briefly describe temporal summation and spatial summation

A

Temporal: depolarisation builds up over time to reach the threshold at which action potential is initiated
Spatial: several presynaptic neurones synapse with the same post-synaptic neurone and all contribute to the growing depolarisation which generates a large enough action potential

39
Q

Define a drug and brief overview of their impact

A

Drug: molecule that has a physiological effect on the body when ingested, inhaled, absorbed, or injected
—> act at synapses and disrupt normal functions of NT, producing abnormal patterns of nervous impulse

40
Q

Differentiate between sedatives and stimulants

A

Sedative: inhibit nervous system creating fewer action potentials in post-synaptic neurones
Stimulants: stimulate nervous system by allowing more action potentials in post-synaptic neurones Stimulants

41
Q

Describe how drugs that mimic action of NTs work

A
  • similar shape and bind to post synaptic neurone in same way a NT would, increasing the frequency of action potential
    —> ie nitrogen atoms in nicotine and acetylcholine allow them both to bind to the same receptor, but nicotine cannot be removed by hydrolysis so continues to initiate impulses
    —> body becomes habituated to nicotine so nervous system can’t function without
    —> nicotine leads to increase in dopamine levels
42
Q

Describe how drugs that prevent the breakdown of NTs work

A
  • organophosphate inhibit acetylcholinestarase meaning acetylcholine remains in the synaptic cleft causing repeated firing of the post synaptic neurone
    —> phosphates of esters found in insecticides, herbicides, and nerve gases
    —> nerve gases inhibit acetylcholinestarase at neuromuscular junctions generating repeated, uncontrollable contractions of muscles that can break bones
43
Q

Explain how lidocaine acts as a local anaesthetic

A
  • sodium ions o longer enter axon
  • threshold not reached
  • no action potential align sensory neurone to brain
44
Q

Describe how a chemical that blocks calcium channels on the presynaptic neurone could work as an anaesthetic

A
  • calcium ions don’t diffuse into synaptic end bulb
  • prevents synaptic vesicles fusing w membrane
  • prevents NT release into synapse
45
Q

Name some drugs that mimic NTs by activating receptors

A
  • morphine
  • nicotine
  • marjuana
46
Q

Name some drugs that block dopamine pumps

A
  • cocaine
  • amphetamine
47
Q

Name some drugs that activate or inhibit channels

A
  • alcohol
  • ketamine
48
Q

How do psychoactive drugs affect the brain?

A
  • can increase or decrease release of NTs
  • breakdown reuptake proteins which are responsible for returning used components of NT to presynaptic
  • block reuptake proteins
  • mimic or block NTs binding to the receptors on post synaptic membranes
  • inhibit production of new NTs
49
Q

Explain action of inhibitory drugs

A
  • mimic inhibitory NT
    —> increase hyperpolarisation of post-synaptic neuron leading to fewer action potentials
  • block excitatory NTs
    —> prevent propagation of action potentials
50
Q

Explain action of excitatory drugs

A
  • block reuptake pumps for NTs
    —> NT remains in synapse
  • mimic excitatory NTs
    —> increase depolarisation of post-synaptic neurons
    —> more action potentials
  • block inhibitory NTs
    —> prevent inhibition of action potentials
51
Q

How is a resting potential maintained?

A
  • imbalance of Na and K ions
  • more Na out and more K in
  • Na-K pump actively transports 3Na out and 2K in which creates electrochemical gradient
  • sodium build up outside and potassium build up inside
  • K+ move out and Na+ move in
  • membrane is more permeable to K+ so moves out quicker than Na+ moves in

A2 BIO UNIT3 (8 decks)

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