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A level Biology > Nervous System ( Component 3 ) > Flashcards

Nervous System ( Component 3 ) Flashcards

1
Q

In mammals, what do the responses to many external and internal stimuli involve ? ( main components of a nervous response )

A

the reception of information and its transfer from a receptor to an effector via the nervous system or as hormones via the blood.

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2
Q

What is the dorsal root ? ( back of spinal cord )

A

One of the two roots that emerges from the spinal cord
Travels to dorsal root ganglian
Sensory neurones enter the spinal cord via the dorsal root

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3
Q

What is the ventral root ? ( front of spinal cord )

A

One of the two roots that emerges from the spinal cord
Motor neurones leave the spinal cord via the ventral root

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4
Q

What does the gross structure of the Human Nervous System include ?

A

the central nervous system, composed of the brain and spinal cord (including examination of T.S. spinal cord)
the peripheral nervous system (the basic pattern of spinal nerves in relation to the spinal cord including the dorsal root and ventral root).

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5
Q

What is the Central Nervous System ( CNS ) ?

A

Brain and Spinal Cord

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6
Q

What is the Peripheral Nervous System ( PNS ) ?

A

Pairs of nerves that originate from CNS and carry nerve impulses into and out of CNS - the basic pattern of spinal nerves in relation to the spinal cord including the dorsal root and ventral root

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7
Q

What does the simple reflex arc act as a basis for ?

A

Rapid, protective, involuntary actions

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8
Q

Label a diagram of a transverse section through the spinal cord, showing: central canal, grey matter, white matter, dorsal root, ventral root, sensory neurone, dorsal root ganglion, connector neurone, motor neurone, meninges

A

…

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9
Q

What is a simple reflex an inborn response to ?

A

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

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10
Q

What does the transmission of a nerve impulse along a three-neurone reflex arc involve ?

A

stimulus→receptor→sensory neurone→relay neurone (in CNS)→ motor neurone→effector→response.

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11
Q

How does a reaction differ from a reflex ?

A

Reaction = voluntary and coordinated by the brain
Reflex = non voluntary and doesn’t involve brain

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12
Q

What is a nerve net and describe the structure of a nerve net ?

A

It is the simplest form of nervous system found in Cnidarians
Consists of interconnected nerve cells with short extensions allowing a response to a limited number of stimuli

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13
Q

Describe the sense receptors and The Nerve Net system of simple organisms ( eg Hydra )

A

The sense receptors respond to a limited number of stimuli and so the number of effectors is small.
Their nerve net system consists of simple nerve cells with short extensions joined to each other and branching in a number of different directions.

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14
Q

Compare “ the nervous systems “ of Hydra ( simple organism ) and Humans ( complex mammal )

A

Hydra = Nerve net, one type of nerve cell, short length of cell processes, no myelin insulation, slow conduction speed, impulse travels in both directions from point of stimulation, limited number of stimuli that can be detected by sensory receptors, small number of effectors

Humans = CNS, sensory and motor in the PNS and many different cells in CNS, long length of cell processes, contains myelin insulation- myelinated and unmyelinated, fast conduction speed, impulse travels in one direction from point of stimulation, various/large number of stimuli that can be detected by sensory receptors, large number of effectors - skeletal muscles and glands.

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15
Q

What are the three functional types of neurones in mammals ?

A

sensory, motor and relay (connector or association).

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16
Q

Draw a labelled diagram of a mammalian motor neurone ( include dendrites, cell body/ centron, nucleus, axon, myelin sheath of Schwann cells, nodes of Ranvier, axon endings/terminals, synaptic end bulbs. )

A

…

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17
Q

State the function of a sensory neurone

A

Carries nerve impulses from receptors to CNS via dorsal root

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18
Q

State the function of a motor neurone

A

Carries nerve impulses from CNS to effectors via ventral root

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19
Q

Describe the structure of a motor neurone

A

Short dendrites carry impluses from CNS to cell body
Cell body found at one end of neurone
Long axon carries impulses from cell body to effectors

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20
Q

State the function of a relay neurone

A

Located in the spinal cord
Links the sensory neurone to the motor neurone

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21
Q

What is the function of dendrites ?

A

Short branched extensions of the cell body
Receive nerve impulses from other neurones
Carry impluses from CNS to cell body

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22
Q

What is the function of the cell body / centron ?

A

The region of the neurone that contains the organelles, notably the nucleus and the rough endoplasmic reticulum

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23
Q

What is the function of the nucleus ?

A

the control centre of the cell, containing the genetic material (DNA) that directs the synthesis of proteins necessary for the neuron’s growth, maintenance, and proper functioning

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24
Q

What is the function of the axon ?

A

A long fibre that conducts nerve impulses away from the cell body

25
What is the function of the myelin sheath ?
made from myelin rich membranes of schwann cells insulates nerve fibres and helps electrical signals travel quickly and efficiently between nerve cells.
26
What is the function of schwann cells ?
Wrap around axon, involved in electrical insulation, phagocytosis and nerve regeneration
27
What is the function of the Node of Ranvier ?
Small gaps between neighbouring shwann cells where there is no myelin sheath. Allow for ions to diffuse in and out of the neuron, propagating the electrical signal down the axon.
28
What is the function of axon endings / terminals ?
Branched endings of an axon that approach the muscle fibre Release neurotransmitters
29
What is the function of synaptic end bulbs ?
The end of an axon that is bulbous shaped and contains synpatic vessels filled with neurotransmitters
30
Describe the shape of an oscilloscope trace showing the passage of an action potential
...
31
Define action potential
The temporary change in electrical potentials across the membrane of an axon in response to the transmission of a nerve impulse. A change in the voltage across the axon membrane (a stimulus) opens the Na+ channels so that Na+ flood in and depolarises the axon to about +40mV
32
What is resting potential ?
Potential difference ( voltage ) across a neurone membrane when not stimulated ( -70mV )
33
How is resting potential established ?
Membrane is more permeable to K+ than Na+ Sodium-potassium pump actively transports 3Na+ out of cell and 2K+ into cell Organic phosphates ( eg ATP4- ) and large protein anions remain in cytoplasm thus producing a negative potential difference across the membrane at around -70mV relative to the exterior of the axon; Establishes electrochemical gradient : cell content more negative than extracellular environment
34
Name the 4 stages of action potential
1) Depolarisation 2) Repolarisation 3) Hyperpolarisation 4) Return to resting potential
35
What happens during depolarisation ?
1) Stimulus causes a change in voltage across an axon membrane, opening voltage-gated Na+ channels 2) Na+ ions diffuse into axon 3) Potential difference across membrane becomes more positive, membrane depolarises
36
What happens during repolarisation ?
1) Membrane potential reaches +40mV 2) Voltage-gated Na+ channels close and voltage-gated K+ channels open 3) Facilitated diffusion of K+ ions out of axon down their electrochemical gradient 4) Potential difference across membrane becomes more negative, membrane repolarises
37
What happens during hyperpolisation ?
1) "overshoot" when K+ ions diffuse out 2) Potential difference becomes more negative than resting potential 3) Membrane hyperpolarises, preventing another impulse occuring
38
What is the refractory period ?
Time period after an action potential during which further action potentials are prevented. The concentrations of K+ and Na+ ions are restored to that of the resting potential – during this time the axon cannot transmit another action potential and that this ensures that transmission is in one direction only.
39
Why is the refractory period important ?
Ensures that action potentials can only be propagated in one direction
40
Describe the " all or nothing " law
Principle states that all stimuli above a certain threshold will generate the same size of action potential, regardless of the strength of the stimulus. The size of the action potential is independent of the size of the stimulus, as long as the stimulus exceeds the value of the threshold potential an action potential is generated. Stronger stimuli = higher frequency of action potentials
41
State the factors affecting the speed of conduction of a nervous impulse
Temperature Axon diameter Myelin sheath - only vertebrates have a myelin sheath surrounding their neurones
42
Explain why myelinated axons conduct impulses faster than unmyelinated axons
Saltatory propagation : The voltage gated ion channels are found only at the nodes of Ranvier, and between the nodes the myelin sheath acts as a good electrical insulator. Impulse jumps from one Node of Ranvier to another ( depolarisation cannot occur where myelin sheath acts as electrical insulator ). Therefore, the impulse does not have to travel the whole axon length. This increases the speed of propagation dramatically, so while nerve impulses in unmyelinated neurones have a maximum speed of around 1 m/s, in myelinated neurones they travel at 100 m/s.
43
How does temperature affect the speed of conduction of nervous impulses ?
The higher the temperature, increased ke, the faster the speed of conduction
44
How does axon diameter affect the speed of conduction of nervous impulses ?
The larger the diameter, less resistance, the faster the speed of conduction
45
What is a synapse ?
The junction between two nerve cells or a nerve cell and an effector
46
What is the function of synapses ?
Electrical impulse cannot cross junction Neurotransmitters send impulses between neurones or from neurones to effectors Summation of sub threshold impulses New impulses can be initiated in several different neurones for multiple simultaneous responses Make sure impulses travel in one direction only becuase the vesicles containing the transmitter are only in presynaptic neurone and the receptor molecules are only on the postsynaptic membrane They allow acclimatisation - after repeated stimulation, a synapse might run out of the neurotransmitter, ie synapse is fatigued which allows them to filter out low level stimuli such as bad smell / background noise.
47
Draw and label a diagram of a synapse it should include : pre and post-synaptic membranes; synaptic vesicles, neurotransmitters (e.g. acetylcholine), synaptic cleft, Ca2+ channels; receptors on post-synaptic membrane.
...
48
Describe the structure of a synapse
Presynaptic neurone ends in synaptic knob Synaptic bond contains high conc of mitochondria, endoplasmic reticulum and vesicles of neurotransmitter Synaptic cleft - 20-30nm gap Postsynaptic neurone has complementary receptors to neurotransmitter ( ligated-gated Na+ channels )
49
What is the synaptic cleft ?
A small gap between neurones across which a nerve is transmitted via neurotransmitters
50
Describe the synaptic transmission in the presynaptic neurone
1) Wave of depolarisation travels down presynaptic neurone, causing voltage-gated Ca2+ channels to open 2) Ca2+ cause vesicles of acetylcholine to move towards and fuse with presynaptic membrane 3) Exocytosis of neurotransmitter ( eg acetylcholine ) into synaptic cleft
51
How do neurotransmitters cross the synaptic cleft ?
Via simple diffusion
52
Describe the synaptic transmission in the postsynaptic neurone
1) Acetylcholine diffuses across synaptic cleft and binds to specific receptors on postsynaptic membrane 2) Ligand-gated Na+ channels open 3) If influx of Na+ ions raises membrane to threshold potential, action potential is generated.
53
Describe the whole process of synaptic transmission
1) The arrival of the nerve impulses depolarises the presynaptic membrane causing voltage gated Ca2+ channels to open 2) Ca2+ ions enter the presynaptic cell down a concentration gradient 3) The influx of Ca2+ causes vesicles of neurotransmitter ( eg acetylcholine ) to move towards and fuse with the presynaptic membrane and release their contents into the synaptic cleft 4) Neurotransmitter diffuses across the cleft 5) Neurotransmitter binds to complementary receptors on the post synaptic membrane 6) This causes the ligand-gated Na+ channels to open in the post synaptic membrane, sodium ions diffuse in. This depolarises the post synaptic membrane and initiates an action potential in the post synaptic neurone.
54
How is the merging of impulses prevented during synaptic transmission ?
Active transport of Ca2+ out of synaptic knob Role of cholinesterase Reabsorption of neurotransmitters
55
Describe the role of cholinesterase in synaptic transmission
Hydrolyses acetylcholine ( into choline and ethanoic acid ) in the post synaptic neurone Products diffuse back across the synaptic cleft
56
What is the effect of organophosphates on the transmission of impulses ?
Act as cholinesterase inhibitors, preventing the hydrolysis of acetylcholine in the post synaptic neurone Results in continuous stimulation of the neurone - multiple action potentials
57
Where are organophosphates commonly found ?
Component of insecticides
58
How do psychoactive drugs ( eg amphetamine ) affect the transmission of impulses ?
Excitatory drugs Stimulate the release of neurotransmitters such as noradrenaline

A level Biology (10 decks)

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