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A level biology-CIE > Control And Coordination > Flashcards

Control And Coordination Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are the 5 things which make up the structure of neurons

A

A) cell body
B)Cytoplasmic processes
C)Axon terminal/presynaptic knob
D)Myelin sheath
E)Nodes of Ranvier

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2
Q

Describe the structure of the cell body in neurons

A

The cell body has a nucleus and a cytoplasm.
The cytoplasm has many mitochondria, ribosomes, RER and Golgi

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3
Q

Describe the structure of cytoplasmic processes in neurones

A

Thin, cytoplasmic extension of cell body

1) Dendrites
* Carry impulses towards the cell body
2)Axons
*Carry impulses away from the cell body

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4
Q

Describe the structure of the axon terminal/presynaptic knob in neurones

A

Has many mitochondria, synaptic vesicles containing voltage gates Ca2+ channels
Part of a synapse= junction between neurones/muscles

A synapse also includes:
*Synaptic cleft=gap
→has enzymes to break down neurotransmitters
*postsynaptic membrane
→has receptor proteins for neurotransmitters

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5
Q

What is the function of the myelin sheath?

A

Insulates axons of many neurones and speeds up conduction of nerve impulses.

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6
Q

What is the myelin sheath made of?

A

Made of Schwann cells.

Schwann cells have a nucleus and consist of layers of cytoplasm and plasma membrane spiraling around the axon.

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7
Q

What are the Nodes of Ranvier?

A

Gaps between Schwann cells where there is no myelin.

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8
Q

What are the three types of neurones?

A
  1. Sensory neurone (afferent)
  2. Motor neurone (efferent)
  3. Intermediate / relay neurone
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9
Q

Characteristics of sensory neurones?

A

Longer sensory axon / dendron and shorter axon.

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10
Q

Characteristics of motor neurones?

A

Shorter dendrites and much longer axon.

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11
Q

What is the role of intermediate / relay neurones?

A

They connect sensory and motor neurones.

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12
Q

What is a common feature of all neurones?

A

They have a cell body, dendrites, and an axon.

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13
Q

What is the Reflex Arc?

A

Pathway where impulses are carried along during a reflex action.

E.g. knee jerk reflex, sneezing.

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14
Q

What are the advantages of the Reflex Arc?

A

Fast,
automatic, involuntary, without conscious thought,
innate/instinctive, response is always the same
and protects from harm.

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15
Q

What are impulses?

A

Brief changes to the distribution of electrical charge across membrane (aka membrane potential)

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16
Q

What is the resting potential of a nerve cell?

A

At rest: more negatively charged on inside than outside
Resting potential = -70mV

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17
Q

What happens when impulses are formed?

A

More positive on inside than outside

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18
Q

What is the action potential or depolarization value?

A

Action potential is a brief change in the potential difference from -70mV to +30mV across the cell surface membranes of neurones and muscle cells caused by the inward movement of sodium ions

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19
Q

What is the role of sensory receptor cells?

A
  1. Detect stimuli
  2. Act as transducers
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20
Q

How do sensory receptor cells respond to stimuli?

A

Receptors are specific to one type of stimulus, such as chemical, light, heat, sound, or pressure.

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21
Q

What is the function of transducers in sensory receptors?

A

They convert stimulus energy to electrical energy and produce generator/receptor potential.

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22
Q

What happens after a generator potential is produced?

A

The impulse is passed along the sensory neuron.

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23
Q

What are taste chemoreceptor cells?

A

Sensory receptors that respond to chemical stimuli.
Different chemoreceptors are specific for different chemicals=diff tastes

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24
Q

How do taste chemoreceptor cells function?

A

e.g. NaCl
1. Na+ ions diffuse into cell via microvilli

→Increase in positive charge inside cell
2. Membrane depolarised

→receptor/generator potential generated

  1. Voltage gated Ca2+ channels open

→Ca2+ enter cell

  1. Trigger movement of vesicles containing neurotransmitters

→ exocytosis occurs

→ neurotransmitter released

  1. Neurotransmitter stimulate action potential/impulse in sensory neuron

→ send impulse to taste Centre in brain

25
Q

What occurs after the membrane of a taste receptor cell is depolarized?

A

A receptor/generator potential is generated.

26
Q

Describe the transmission of action potential

A
  1. Resting potential-70mV
  2. Depolarisation-70mV->+30mV
  3. Repolarisation +30mV->-70mV
  4. Hyperpolarisation/Refractory period less than-70mV
27
Q

Describe what resting potential is and how it is maintained

A

At rest=no stimuli, no impulses formed and transmitted
Inside of axon more negatively charged than outside
Neurone is polarised and maintained at -70mV

How is a resting potential maintained?
1. Na+/K+ pump
2. More K= channels open than Na_ channels

28
Q

Describe how the Na+/K+ pump helps to maintain a resting potential gradient?

A

3 Na+ pumped out, 2K+ pumped in
ATP needed
Axon phospholipid bilayer impermeable to K+/Na+
Electrochemical gradient is set up=difference in both charge and chemical ions across membrane
-> so K+ diffuse out, Na+ diffuse in
->via channel proteins

29
Q

Describe how more K+ channels open than Na+ channels helps maintain resting potential

A

Membrane more permeable to K+ than Na+
More K+ leaves than Na+ enter
Leaking K+ is responsible for resting potential
Inside becomes relatively more negative than outside Neurone
P/S: these channel proteins are open all the time. But voltage gated K+ and Na+ channels are closed.

30
Q

Describe what happens during depolarisation (-70mV->+30mV)

A
  1. Voltage-gated K+ channels remain closed
  2. Voltage gated Na+ channels open
    →Channels change shape when membrane potential changes when action potential arrives from previous section
    *Na+ enter cell
    *Membrane becomes less negative/depolarised →+30mV
    →Action potential is generated
    *size of action potential is fixed at +30mV
    *the higher the strength/intensity of the stimulus, the higher the frequency of action potentials
    *also-the more neurones are depolarised
31
Q

Describe what happens during repolarisation (+30mV->-70mV)

A
  1. Voltage gated Na+ channels close
  2. Voltage gated K+ channels open
    *K+ move out of cell
    *inside becomes more negative/repolarised->-70mV
32
Q

What is a voltage-gated channel protein:

A

A channel protein through a cell membrane that opens or closes in response to-changes in electrical potential across the membrane

33
Q

Describe what happens during hyper-polarisation/refractory period (less than -70mV)

A
  1. Voltage-gated Na+ channels remain closed
  2. Voltage-gated K+ channels close
    *but slight delay so excess K+ ions have moved out of axon
    When membrane is hyperpolarized=refractory period
    *Membrane is insensitive to any depolarisation
    *No action potential can be generated

→Function=ensure one way transmission
*due to the refractory period, action potentials are discrete events/do not merge into one another

→Function:Length of refractory period limits maximum frequency of action potentials
E.g. longer refractory period=lower maximum frequency

34
Q

Describe the return to resting potential (-70mV) after hyperpolarisation/refractory period

A

*Na+/K+ pump acts again

→Membrane can be depolarised again

→Action potential can be generated again

35
Q

Describe how action potentials are transmitted along a non-myelinated axon?

A
  • depolarisation spreads to next region due to movement of positive ions to negative regions

→A “local circuit” is set up

→This causes voltage -gated Na+ channels to open in the next region

→Causing next action potential

36
Q

How are action potentials are transmitted along a myelinated axon?

A

With the myelin sheath, there is an increased speed of conduction.

Myelin insulates axon

→does not allow movement of ions

→Lengthens local circuits
*Passage of ions only at nodes of Ranvier

→Action potential/depolarization only at nodes of ranvier

→Local circuit is set up between nodes

→Action potential “jumps” from node to node

→This is called saltatory conduction

37
Q

Explain saltatory conduction

A

Saltatory conduction is the faster transmission because myelin sheath insulates axons
Local circuit is set up between nodes
Action potential jumps from node to node

38
Q

What is threshold potential (-50mV)

A

*minimum potential needed for action potential to be generated

→only depolarisation that reaches threshold produces an action potential

*If depolarisation <-50mV, action potential is not generated
→only local depolarisation occurs

*Only if depolarisation >=-50mV action potential is generated
→Size of action potential is fixed at +30mV
→All or nothing law

39
Q

What are the roles of synapses

A
  1. Ensure one way transmission.
  2. Allow interconnection of nerve pathways.
  3. Involved in memory and learning.
  4. Filter out low level stimuli.
40
Q

Describe how the synapses ensure one way transmission

A

Synapse ensures one way transmission as the receptors and neurotransmitter vesicles are only on pre-synaptic neuron.

41
Q

Describe how the synapses allow interconnection of nerve pathways

A

The synapse allow the interconnection of nerve pathways because nerve impulses can diverge/integrate and allow wider range of behaviour/action in response to a stimulus.

42
Q

Describe how the synapses are involved in memory and learning

A

Synapses are involved in memory and learning due to new synapses being formed

43
Q

Describe how synapses filter out low level stimuli

A

Weaker stimulus cause release of low quantities of neurotransmitters
No impulse generated in post synaptic neuron ➡️brain
Prevent brain from being overloaded with sensory information

44
Q

In normal conditions where is the concentration of K+ and Na+ in the axon higher?

A

Na+ concentration higher outside of axon and lower inside of axon
K+ concentration lower outside axon and higher inside axon.

45
Q

Describe the cholinergic synapse

A

Neurotransmitter = acetylcholine (ACh)
1. Action potential reaches presynaptic membrane
2. Voltage-gated Ca2+ channels open
→Presynaptic membrane becomes more permeable to Ca2+
→Ca2+ ions enter pre-synaptic neuron
3. Vesicles containing ACh move towards and fuse with presynaptic membrane
→Exocytosis occurs
→ACh released into synaptic cleft
4. ACh diffuse across synaptic cleft
5.ACh binds with receptor proteins on post synaptic membrane
6. Receptor proteins change shape and Na+ channels open
→Na+ enter post synaptic neuron
* Postsynaptic neurone depolarized
* Action potential is generated
*As long as ACh binds with receptors, Na+ channels will stay open
→Continuous transmission of action potential
→Can cause synaptic fatigue/paralysis
7. ACh breakdown by acetylcholinesterase at synaptic cleft
ACh →acetate and choline
ACh is recycled (ATP needed)
*Depolarisation stops in post synaptic membrane
→Stop continuous action potential

46
Q

Describe the striated muscles

A

Striated=striped under microscope
Attached to bones by tendons
Many Long, cylindrical muscle fibres
→Multinucleated
→Each muscle fibre is made up of myofibrils

47
Q

Muscle fibre

A

Muscle fibres have=
*Plasma membrane = sarcolemma
→Sarcolemma infoldings= transverse system tubules ( T-tubules)
→ Can conduct action potentials

*Cytoplasm=sarcoplasm
→ Many parallel myofibrils
→ Fibres are Multinucleated
→ Many mitochondria

*Specialised ER=sarcoplasmic reticulum
→ have protein pumps
→ have lots of Ca2+

48
Q

What are the two type of myofilaments:

A

*Thick filaments = made of myosin
→Fibrous protein with globular protein head
→ Attached to M line

*Thin filaments=made of actin
→Chain of globular protein molecules
→Has binding sites for myosin
→ Troponin and tropomysin is attached to actin
→ Attached to Z line

49
Q

What is a sarcomere

A

Sacromere is the repeating unit of myofibril
It is the interdigitation of thick and thin filaments and gives striated appearance.

50
Q

Describe the structure of the sarcomere

A

*Myosin attached to the M line
*Actin attached to the Z line

*Sarcomere = between 2 Z lines
*Describe between the Z line decreases during muscle contraction

*I band = light band
*Only thin filaments
*Shortens during muscle contraction

H band = light band at centre of dark band
*Only thick filaments
*Shortens during muscle contraction

A band= dark band
*Overlap of thick and thin filaments
* Stays the same during muscle contraction

51
Q

What is a neuromuscular Junction?

A

A synapses between a motor neuron and a muscle

52
Q

Give an overview of muscle contraction

A

Muscle contraction begins at neuromuscular junction
→Cholinergic synapse between a motor neuron and a muscle fibre
*Terminal knobs of motor neurone = motor end plate
* Neurotransmitter = acetylcholine (Ach)

53
Q

What is the name of the four steps that must occur for a muscle contraction

A
  1. Cholinergic synapse of neuromuscular junction
  2. Depolarisation and Ca2+ channels open
  3. Troponin and tropomyosin
  4. Sliding Filament model
54
Q

Describe the role of Cholinergic synapse of neuromuscular junction

A

*Action arrives at the pre-synaptic membrane
* gated calcium ion channels open
* Calcium ions enter presynaptic knob

  • vesicles containing ACh fuse with pre-synaptic membrane
    *ACh released by exocytosis into synaptic cleft
  • ACh diffusers across synaptic left

*ACh bind to receptors on sacrolemma (muscle cell membrane)
*Na+ channels open
*Na+ ions enter sarcoplasm of muscle cell
*Sacrolemma depolarised

55
Q

Describe the role of depolarisation and calcium ions in muscle contraction

A
  1. Depolarisation and Ca2+
    *Depolarisation spread via T-tubules →sacroplasmic reticulum (ER)
    *Sacroplasmic reticulum depolarised

*Voltage gated Ca2+ channels open
*Ca2+ diffuse out from sacroplasmic reticulum →sarcoplasm
*Ca2+ initiates muscle contraction

56
Q

Describe the role of troponin and tropomyosin in muscle contraction

A

When muscle is relaxed:
* Troponin = attached to tropomyosin
* Tropomyosin = blocks myosin-binding sites on actin

When muscle contracts:
*Ca2+ in sarcoplasm bind to Troponin
→Troponin changes shape and moves tropomyosin
→ Exposes myosin-binding site on actin
→ Allows myosin head to attach and form cross-bridge almost with actin

57
Q

Describe the role of the sliding filament model in muscle contraction

A

1) Myosin head with ADP and Pi form cross-bridges with actin
→Pi is released

2) Myosin head tilts and pull actin
→ Power stroke moves actin towards M line
→ Myofibril/sacromere shortens
→ ADP released from myosin head

3) ATP binds to myosin head
→ATPase hydrolyses ATP into ADP and Pi
→ Myosin head lets go of actin
→ Myosin moved back to original position

4) Process repeated at site further along actin molecule
Sarcomere shortens during muscle contraction
* H band shortens
* I band shortens
*A band remains the same

58
Q

What happens when action potential stimulation stops during muscle contraction?

A

Action potential stimulation stops
Calcium ions is actively pumped into sacroplasmic reticulum
→ calcium ions do not bind troponin on actin filament
→ tropomyosin moves to block myosin-binding sites on actin filament

→Filaments slide back to original position
→ Muscle relaxes

59
Q

What are the sources of ATP for muscle contraction?

A

Muscles use a lot of ATP and only a small amount of ATP is present in muscle

More ATP is synthesis by
1. Aerobic respiration in mitochondria.
2.Lactate pathway in sarcoplasm

  1. Creatine phosphate in sacroplasm
    * immediate source of energy once ATP is used up

Creatine phosphate + ADP ⇌ Creatine + ATP

Creatine → blood plasma →ultrafiltration @ kidney → urine

*Reversible when the demand of ATP reduced
*If not, Creatine converted to creatinine and excreted in urine

A level biology-CIE (14 decks)

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