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Biology > Chapter 15 > Flashcards

Chapter 15 Flashcards

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1
Q

Describe the features of the nervous system

A
  • communication is by nerve impulses
  • transmission is by neurones
  • transmission is rapid
  • nerve impulses travel to specific parts of the body
  • response is localised
  • response is rapid
  • response is short-lived
  • effect is usually temporary and reversible
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2
Q

Describe the features of the hormonal system

A
  • communication is by chemicals
  • transmission is by the blood
  • hormones travel to all areas but only target cells
  • response is widespread
  • response is slow
  • response is long-lasting
    effect may be permenant and irreversible
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3
Q

What is a neurone?

A

specialised cells adapted to rapidly carrying electrochemical changes called nerve impulses from one part of the body to another

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4
Q

what is a motor neurone made up of?

A
  • a cell body
  • dendrons
  • dendrites
  • an axon
  • schwann cells (if myelinated)
  • an axon terminal
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5
Q

what are the purpose of schwann cells

A

protection and providing electrical insulation.
they also carry out phagocytosis

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6
Q

what is a myelin sheath?

A

covers the axon is made up of membranes of schwann cells with nodes of ranvier in between

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7
Q

Describe a sensory neurones function

A

transmitt nerve impulses from a receptor to an intermediate/motor neurone

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8
Q

Describe a motor neurones function

A

transmitt nerve impulses from an intermeidiate or relay neurone to an effector such as a gland or a muscle

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9
Q

Describe an intermeidiate/relay neurones function

A

transmitt impulses between neurones

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10
Q

Explain the process of a resting potential

A
  • Na+ and K+ unable to pass through phospholipid bilayer
  • 3Na+ are actively transported out by Na+K+ pump
  • 2K+ are actively transported in by Na+K+ pump
  • more Na than K so chemical gradient is formed
  • Na+ channels are closed so Na+ cannot move back into the axon
  • K+ channels are open so K+ diffuses back out.
  • results in axon being polarised and inside being charged to -65mV
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11
Q

What factors affect the speed at which an action potential occurs

A
  • the myelin sheath
  • the diameter of the axon
  • temperature
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12
Q

What is saltatory conduction?

A

when a nerve impulse jumps from one node of ranvier to the next increasing the speed of the impulse

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13
Q

Explain the all-or-nothing principle?

A

nerve impulses = all-or-nothing responses
a certain level of stimulus is required to reach the threshold value which triggers an action potential
below the threshold an impulse doesnt occur

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14
Q

What is the refractory period

A

once an action potential occurs there is a period of time afterwards where there is an inward movement of sodium ions prevented by Na voltage-gated channels being closed
- no action potential is able to be generated

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15
Q

What are the purposes of the refractory period?

A
  • ensures action potentials only occur in one direction
  • it produces discrete impulses
  • it limits the number of action potentials
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16
Q

What is a synapse?

A

the point where one neurone communicates with another or with an effector
important in linking different neurones together and coordinating activities

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17
Q

What are neurotransmitters?

A

chemicals transmitted from one neurone to the next
- stored in synaptic vesicles

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18
Q

What is the presynaptic neurone?

A

the neurone that releases the neurotransmitter to the postsynaptic neurone

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19
Q

What are the features of a synapse?

A
  • Unidirectionality
  • Summation (spatial and temporal)
  • Inhibition
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20
Q

Explain unidirectionality

A

synapses can only pass information in one direction - presynaptic to the postsynaptic

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21
Q

Explain spatial summation

A

where a number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone
- triggers an action potential

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22
Q

Explain temporal summation

A

where a single presynaptic neurone releases a neurotransmitter many times over a very short period. if the concentration of neurotransmitter exceeds the threshold value of the postsynaptic neurone then a new action potential is triggered

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23
Q

Explain inhibition

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A

some synapses make it less likely that a new action potential will be created on the postsynaptic neurone
- inhibitory synapses

24
Q

What are the functions of synapses?

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A
  • synapses transmit information from one neurone to another
  • a single impulse along one neurone to initiate new impulses in a number of different neurones at a synapse - allows a stimulus to create a number of simultaneous responses
  • a number of impulses to be combined at a synapse - allows nerve impulses from receptors reacting to different stimuli to contribute to a single response
25
What is a cholinergic synapse?
a synapse where its neurotransmitter is a chemical called acetyl choline - common in vertebrate
26
Describe the process of transmission across a cholinergic synapse
- an action potential arrives at the end of the presynaptic neurone causes calcium ion channels to open and enter the synaptic knob by facilitated diffusion - influx of Ca2+ into the presynaptic neurone causes synaptic vesicles to fuse with the presynaptic membrane releasing acetylcholine - acetylcholine diffuses across the synaptic cleft quickly as the diffusion pathway is short - acetylcholine binds to receptor sites on the sodium ion protein channels in the postsynaptic membrane causes the Na+ channels to open allowing Na+ to diffuse rapidly along a conc gradient - the influx of sodium ions generates a new action potential in the postsynaptic neurone - acetylcholinesterase hydrolyses acetylcholine back into acetyl and choline - these then diffuse across the synaptic cleft into the presynaptic neurone and are recycled = new action potential generated - ATP is released by mitochondria and is used to form acetylcholine again
27
What is a skeletal muscle?
a muscle which is attached to bone and is the only type of muscle under conscious control
28
What are the 3 sections of a sarcomere?
- A-band - I-band - H-zone
29
What is the A-band?
a section of sarcomere containing both myosin and actin
30
What is the I-band?
a section of sarcomere containing just actin
31
What is the H-zone?
a section of sarcomere containing myosin only
32
Explain what a fast twitch muscle fibre is?
- a muscle fibre that has rapid, short term contraction - contains more myosin, more glycogen stores and more enzymes
33
Explain what a slow twitch muscle fibre is?
- a muscle fibre that has slower and more sustained contractions - contains a large myoglobin store
34
What is a muscle fibre
- large bundles of long cells made up of myofibrils
35
What is a myofibril?
- made up of two types of protein filaments - actin and myosin
36
Explain what a neuromuscular junction is?
a synapse between a motor neurone and a muscle cell
37
What is a sarcomere?
- short units that make up a myofibril with A-bands, I-bands and H-zones
38
What is sarcoplasm?
- a muscle cells cytoplasm
39
What is sarcoplasmic reticulum?
a muscle cells endoplasmic reticulum
40
What is a Z-line ?
the end of each sarcomere
41
Describe the main difference between slow and fast twitch muscle fibres?
- slow-twitch muscles have slow, sustained contractions and release energy slowly through aerobic respiration so contain lots of mitochondria - fast-twitch muscles have fast, powerful short-term contractions and release energy quickly through anaerobic respiration as well as having a large phosphocreatine store
42
What is actin?
filament containing 2 actin subunits which are twisted together
43
Explain what an actin-myosin crossbridge is?
myosin globular head binds to the binding site on actin
44
What is myosin?
-thicker and consists of long rod-shaped tails with bulbous heads
45
What is sliding filament theory?
The idea that actin slides over myosin during contraction
46
Explain how a resting potential is maintained across the axon membrane in a neurone.
- increased concentration of K+ inside, increased concentration of Na+ - the membrane is more permeable to K+ - the Na+-K+ pump, pumps 3Na+ out of the membrane and 2K+ into the axon membrane
47
Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon.
- myelination provides electrical insulation - saltatory conduction occurs in a myelinated axon as the nerve impulse jumps from one Node of Ranvier to the next whereas in a non-myelinated axon the action potential has to travel the length of the whole axon
48
Explain how a lower temperature leads to slower nerve impulse conduction.
- slower diffusion of Na+/K+
49
Describe the sequence of events involved in transmission across a cholinergic synapse.
- depolarisation of the presynaptic membrane - Ca2+ channels open and Ca2+ enter the synaptic knob - synaptic vesicles containing acetylcholine bind to the presynaptic membrane releasing acetylcholine into the synaptic cleft - acetylcholine diffuses across the synaptic cleft - acetylcholine binds to the receptors on the channels on the postsynaptic membrane, this allows the channels to open and Na+ to diffuse into the postsynaptic membrane - carrying the action potential along the postsynaptic neurone
50
During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in ability of calcium ions to stimulate muscle contraction.
- low pH changes the shape of Ca2+ - this means that fewer Ca2+ bind to the tropomyosin - fewer binding sites on the actin - so fewer actin-myosin cross bridges form as the binding sites on the actin would still be covered by tropomyosin
51
Describe the roles of calcium ions and ATP in the contraction of a myofibril.
- calcium ions bind to the tropomyosin filament causing the tropomyosin to shift down the actin filament so that the myosin binding site on the actin filament is uncovered - the bulbous head on myosin is moved to the correct position to bind to the actin by ADP - when the myosin head binds to the actin ATP is released - ATP is hydrolysed by ATPase forming ADP + Pi - this allowa the myosin head to detach from the actin and return to its original position
52
give some evidence for sliding filament theory
when a muscle contracts the: - I-band becomes narrower - Z-lines move closer together - H-zone becomes narrower - A-band remains the same width
53
How is the muscle stimulated before a muscle contraction?
- action potential reaches the neuromuscular junction - Ca2+ channels open and Ca2+ cause synaptic vesicles to fuse with the presynaptic membrane - releases neurotransmitter into synaptic cleft - neurotransmitter diffuses across the synaptic cleft and bind to a receptor on a muscle cell = depolarisation
54
Explain the process of muscle relaxation
- Ca2+ are actively transported back into the endoplasmic reticulum using energy from the hydrolysis of ATP - reabsorption of the Ca2+ allows tropomyosin to block the actin filament again - myosin heads are now unable to bind to actin filaments and contractions cease - in this state antagonistic muscles can pull the actin filaments out from between the myosin
55
Where does the energy supply of a muscle contraction come from
- the hydrolysis of ATP to ADP + Pi - ATP is also generated anaerobically through the use of phosphocreatine

Biology (12 decks)

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