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Biology component 3 > The nervous system > Flashcards

The nervous system Flashcards

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1
Q

How does nervous changes differ to hormonal changes

A
  • hormonal changes are more slow, long term response and chemicals being carried by the blood
  • nervous is more rapidly involve short term reponse and information carried by neurones
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2
Q

What is the nervous system responsible for

A

detecting changes within the internal and external environment processing that information and initiating a response

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3
Q

What is the stimulus response model

A

stimulus -> receptor -> coordinator -> effector -> response

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4
Q

What is a stimulus

A

change in the environment

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5
Q

What is a receptor / detector

A

contains cell which can detect stimuli converting energy from one form into an electrical impulse

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6
Q

What is a coordinator

A

central nervouse system consisting of brain and spinal cord coordinates a response

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7
Q

What is an effector

A
  • brings about response
  • either mucle of gland
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8
Q

what is the response

A

change in the organism

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9
Q

What does the peripheral nervous system made up of

A
  • somatic nervous system
  • autonomic nervous system
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10
Q

What is the somatic nervous system made up of

A
  • pair of nerves originate from the brain and spinal cord containing both sensory and motor neurones
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11
Q

What is the autonomic nervous system

A
  • controls involutnary actions
  • digestion and control of heartbeat
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12
Q

What are the three types of neurones and what do they do

A
  • sensory neurones - carry impules from receptors to the CNS
  • relay neurones - within CNS recieve impulses from sensory or other relay neyornes and transmit them onto motor neurones
  • motor neurones - transmit impulses from the CNS to effectors (muscles or glands)
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13
Q

What is the function of the cell body

A
  • contains granular cytoplasm with ribosomes for protein synthesis
  • DNA is present within a nucleus and acts as the site for transcription
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14
Q

What is the function of the axon

A
  • carries the impulse away from the cell body
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15
Q

What is the function of the myelin sheath

A
  • surrounds the axon (and dendron in sensory neuornes)
  • providing electrical insulation resulting in faster impulse transmission
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16
Q

What is the function of the Schwann cell

A
  • surround the axon (and dendrons in sensory neurones) and forms the myelin sheath
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17
Q

What is the function of the nodes of ranvier

A
  • gaps in the myelin sheath between schwann cells where the axon membrane is exposed
  • allow faster nerve impulse conduction (saltatory conduction)
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18
Q

What is the function of the axon endings

A

secrete a neurotransmitter whcih results in depolarisation of the adjacent neurone

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19
Q

What is the function of the synpatic end bulbs

A

swelling found at the end of an axon where the neurotransmitter is synthesised

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20
Q

Describe the process of a reflex arc

A
  • a stimulus is detected by a receptor passed to the CNS along a sensory neurone
  • the impulse is then relayed directly to a motor neurone and its effector by a relay neurone
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21
Q

What is a reflex

A
  • rapid automatic responses to stimuli that could prove harmful to the body and therefore protective in nature
22
Q

What is the response of a reflex usuallly

A
  • contraction of a muscle
  • release of a hormone
23
Q

What are nerve nets and where are they found

A
  • simple animals eg cnidarians like hydra do not possess a nervous system
  • it consists of sensory photoreceptors and touch receptors in the wall fo the body and tentacles
  • ganglion cells provide conncenctions between the neurones in several directions but they do not form a brain
24
Q

What is the difference between a cnidarian nerve net and mammalian nervous systems

A

Cnidarian nerve net
* 1 type of simple neurone
* unmyelinated
* short branched neurones
* impulse transmitted in both directions
* slow impule transmission
Mammalian nervous system
* 3 types of neurones
* myelinated
* long unbranched neurones
* impulse transmitted in one direction
* fast impulse transmission

25
Q

resting potential

A

of a neurone is the potential difference between the inside and outside when a nerve impulse is not being transmitted it is around -70mV the membrane is polarised

26
Q

What happens when neurone is at rest

A
  • no impulses are being transmitted - resting potential
  • at rest charge across membrane is -70mv respect to inside (outside is more positive)
27
Q

How is resting potential created

A
  • phospholipid bilayer is impermeable to Na+ /K+ ions
  • ions are oly able to move across the membrane through intrinsic proteins and sodium potassium poump (active transport)
  • some intrinsic proteins have gates which can be opened or closed to allow/inhibit ion movement
  • Na+ gates allow Na+ ions to pass in K+ gates all K+ ions to pass out
  • most K+ gates are open whereas most Na+ gates are closed making the mebrane more permeable to K+ ions than Na+ ions
  • resting potential is negative as fewer positive inside than outside
28
Q

action potential

A

the rapid rise and fall of electrical potential across a neurone membrane as a nerve impulse passes

29
Q

depolarisation

A

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

30
Q

Describe how action potential is bought about

A
  • at resting potential the Na+ gates are closed and some K+ gates are open which together the sodium potassium pump result in a potential difference across membrane of -70mV
  • energy of stimulus causes Na+ voltage gated gates to open and Na+ ions flood in down their concentration gradient depolarising the neurone
  • now the charge across membrane becomes more positive due to more positive charges inside
  • as more Na+ ions enter more gates open so even more Na+ ions rush in
  • when potential reaches +40mV the neurone is depolarised Na+ gates close preventing further influx of Na+ ions K+ gates then begin to open
  • K+ ions flood out of the neurone down their concentration gradient lowering the positive gradient across the membrane
  • further K+ chaannels open resulting in even more K+ ions leaving the neurone
  • the neurone is repolarised
  • too many K+ ions leave the neurone so the electrical gradient overshoots -70 reaching around -80 - hyperpolarisation
  • restablish the resting potential -70 K+ gates now close and sodium potassium pump restablisshes the resting potential
31
Q

What is the ration for the sodium potassium pump

A
  • 3 Na+ out
  • 2K+ in
32
Q

Describe impulse propagation in unmyelinated neurones

A
  • neuorne membrane is polarised charge across membrane is now -70mV
  • Na+ channels open so Na+ ions rush into the axon cytoplasm. A local circuit is established where Na+ ion are pumped out of the adjacen sodium potassium pump
  • Na+ channels in the adjacent part of the membrane open causin depolarisation
  • meanwhile Na+ channels close K+ channels open causing repolarisation behind it
  • depolarisation continues along neurone membrane the membrane at start is now polarised again
33
Q

Describe how ions travel across myelinated neurones

A
  • ion can only move across at the node of raanvier where there is no myelin present therefore local circuits are etablishes over greater distances (between each node)
34
Q

Where does depolarisation and action potential occur in myelinated neurones

A
  • only occurs at the nodes and the action potential effectivley jumps from node to node increasing the speed of impule transmission
35
Q

What is the total refractory period

A
  • represent the period during which it is not normally possible to send another impulse
36
Q

What is the abolute refractory period

A

i the period during which it is not posible to send another impulse irrespective of how big the stimulus is

37
Q

```

~~~

What is the relative refractory period

A
  • period during which it is possible to send another impulse if th stimulus is big enough to overcome the threshold
38
Q

What is the all or nothing rule

A
  • impulses will pass if a threshold value is exceeded -55mV a large stiulus will result in more impulses passing per second (increased frequency of ction potentials) rather than a greater evel of depolariation
  • impulses either pass or do not and they are always the same size
39
Q

How does myelination effect speed of impulse transmission

A
  • saltatory conduction is faster than impulse trasmission in unmyleinated neurones
  • depolarisation only occur at the nodes of ranvirer
  • so the action potential jumps form node to node
  • rate of tranmission is faster in myelinated neurones
40
Q

How does diameter of the axon affect speed of impulse transmission

A
  • impulse transmission speed increases with axon diameter
  • due to less leakage of ions from larger axons (due to a larger volume to surface area)
41
Q

What are the factors affecting speed of impulse transmission

A
  • myelintion
  • diameter of axon
  • temperature
42
Q

How does temperature affect the speed of impulse transmission

A
  • impulse transmission speed increases with temperatre as the rate of diffusion increases due to increased kinetic energy of ions involved
  • only in organisms which do not control their internal body temperature
43
Q

What is a synapse and it’s function

A
  • gap between two neurones
  • impulse is transmitted from one to other by a neurotransmitted which diffuses acros the synaptic cleft from the pre synaptic membrane to receptors on post synaptic neurone triggering depolarisation in the post synaptic neurone
44
Q

What is the name of the neurotransmitter

A

acetylcholine

45
Q

Outline the functions of synapses

A
  • tranmit information between neurones
  • transmit information in one direction only
  • act as junctions
  • filter out low level stimuli
  • prevent over stimulatio of neurone and fatigue
46
Q

Describe the event of a synaptic transmission

A
  • impulse arrives at the pre synaptic knob
  • calcium channels open causing calcium ions to diffuse rapidly into pre synaptic knob
  • vesicles containing acetylcholine migrate to and fuse with pre synaptic membrane
  • contents of vesicles are released into the synaptic cleft by exocytosis
  • acetylcholine molecules diffuse acros the cleft and bind to receptors on the post synaptic membrane causing sodium ion channels to open
  • sodium ions rush into the post syntaptic neurone resulting in depolarisation of the post synaptic membrane an action potential is initiated
  • acetylcholinesterase splits acetylcholine into ethanoic acid and choline releasing them form the recepetor and sodium channels close the products diffuse back across the cleft
  • products are reabsrobed into the pre synaptic knob
  • ATP is used to reform acetylcholine in the pre synaptic knob
47
Q

Describe how repeated depolrision of the post synaptic neurone is prevented

A
  • hydrolysis of acetylcholine
  • reabsorption of ethanoic acid and choline back into pre synaptic knob
  • active transport of calcium ions out of the pre synaptic knob preventing further exocytosis of neurotransmitter
48
Q

What happens if insufficient acetylcholine is released

A
  • not enough sodium ion channels open on posrt synaptic membrane to exceed threshold potential of -55mV so action potential is not initiated
49
Q

Wht are the two main types of drugs that effect chemicals on the synapse

A
  • excitatory (stimulant of agonists) like caffiene and cocaine whcih result in more action potentials
  • sedatives (inhibitory) like cannabis result in fewer action potentials
50
Q

Describe the effect of organophosphorus insecticides

A
  • are agonists by inhibiting cholinesterase so acetylcholine lingers at the synapse causing repeated depolarisation of the post synaptic membrane
51
Q

Describe the effect of nicotine on the effects of chemicals on synapses

A
  • mimic the action of nerotransmittters unlike acetylcholine nictotine is not removed by cholinesterase
  • over time body produces less acetlycholine and person is more reliant on nicotine for the normal functioning of the synapes
  • increased release of dopamine from the brain resulting in addiction

Biology component 3 (3 decks)

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