M5, C13 Neuronal Communication Flashcards Preview

A-Level Biology - OCR A > M5, C13 Neuronal Communication > Flashcards

Flashcards in M5, C13 Neuronal Communication Deck (64)
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1
Q

Give an example of a stimulus in the internal environment and external environment

A

interenal - water potential, ion levels, temperature, blood glucose levels, cell pH

external - temperature, light intensity, humidity, new or sudden sound

2
Q

Describe the nervous system

A
  • transmission is very rapid
  • response is localised
  • effect is temporary and reversible
  • response is short-lived
  • transmission is by neurones
  • response is rapid
  • nerve impulses travel to specific parts of the body
  • communication is by nerve impulses
3
Q

define:

a) sensory neurones
b) relay neurones
c) motor neurones

A

sensory neurones - transmit impulses from receptor cells to the central nervous system

relay neurones - transmit impulses between neurones

motor neurones - transmit impulses from the CNS to an effector cell

4
Q

give two types of effector cells

A

muscle

gland

5
Q

what is the basic steps impulses go through

A

receptor - sensory neurone - relay neurone - motor neurone - effector

6
Q

what are the 4 main parts of a neurone and describe each part

A

cell body - contains nucleus, mitochondria and ER, produces neurotransmitters

dendron - carries impulses towards cell body

dendrite - smaller branches of the dendrons

axon - carries impulses away from cell body

7
Q

define receptors

A

specialised cells that can detect changes in the body’s internal and external environment

8
Q

define generator potential

A

start of the nerve impulse

receptors convert the energy of the stimulus into the generator potential

9
Q

define transducers

give some examples

A

receptors which convert energy of the stimulus into a nerve impulse

  • photoreceptors (light energy)
  • thermoreceptors (thermal energy)
  • mechanoreceptors (kinetic energy)
  • chemoreceptors (chemical energy)
10
Q

define pacinian corpuscle

A

specific sensory receptors that detect mechanical pressure

11
Q

how does the pacinian corpuscle detect mechanical pressure? (5 steps)

A

1) There are sodium ion channels in the plasma membrane of the sensory neurones, which in its normal state are too narrow to allow sodium ions through. The pacinian corpuscle has a resting potential.
2) When pressure is applied to the Pacinian corpuscle, the shape changes - the membrane stetches.
3) The sodium ion channels widen so sodium ions can now diffuse into the sensory neurone.
4) The potential of the membrane changes - becomes depolarised. Results in generator potential.
5) A nerve impulse is created which passes along the sensory neurone.

12
Q

How is the resting potential established and maintained in neurones

A
  • sodium-potassium pump where 3 sodium ions are pumped out for every 2 potassium ions that are pumped in
  • there are sodium ion channels and potassium ion channels. more sodium ion channels are closed, whereas many potassium ion channels are open, allowing more potassium ions to diffuse out than sodium ions diffusing in

This results in a more negative inside of the cell as ore positively charged ions are outside the cell. This creates the resting potential of -65mV. Said to be polarised.

13
Q

Why is a neurone active even though it is said to be resting

A

the sodium-potassium pump involves active transport so requires ATP
3 sodium ions are actively pumped out and 2 potassium ions are actively pumped in

14
Q

how is an action potential generated

A

1) neuron has a resting potential - most Na ion gated channels are closed / some potassium ion channels are open
2) the energy of the stimulus triggers some sodium voltage-gated channels to open. Diffusion of Na ions into neuron increases. the inside is less negative
3) Once the threshold potential is met, more sodium ion channels open due to the increase of positive charge.
4) the inside now becomes more positive to +40mV so the voltage-gated sodium ion channels close and voltage-gated potassium ion channels open. this means the membrane is more permeable to potassium ions
5) Potassium ions diffuse out resulting in the inside becoming more negative than the outside
6) the neuron eventually becomes more negative than the resting potential (hyperpolarisation). the voltage-gated potassium ion channels now close. the sodium-potassium pump now has a large effect when pumping sodium ions out and K ions in. the neuron returns to resting potential

15
Q

define localised circuit

A

diffusion of sodium ions sidewards

16
Q

how is the action potential transmitted along the cell

A
  • The stimulus causes the first section of the cell to carry out an action potential
  • When the threshold potential is met, there is an influx of sodium ions into that section of the cell
  • There is a higher concentration of sodium ions in that section of the cell compared to the rest so localised circuits form
  • This creates a threshold potential in that section of the cell so an action potential follows - starting with the opening of voltage-gated sodium ion channels causing depolarisation
  • The section of the cell before has to return to resting potential before another impulse is sent
17
Q

what is the refractory period during the action potential

A
  • delay between one action potential and another
  • prevents action potential travelling backwards
  • caused by the time taken to restore resting potential
18
Q

what is the structure of myelinated neurones

A

Have Schwann cells wrapped around their axons and dendrons.

The Schwann cells have a fatty substance called myelin in their membrane.

19
Q

what are the gaps called between myelinated neurones

A

nodes of Ranvier

20
Q

what is saltatory conduction

A

the neurone’s cytoplasm conducts enough electrical charge to depolarise to the next node, so the impulse ‘jumps’ from node to node
happens in myelinated neurones at the nodes of Ranvier

21
Q

what increases the speed of conduction of action potentials

A

myelination
axon diameter (bigger diameter means less resistance)
temperature (diffusion increases with a higher temp until around 40 degrees where the proteins will denature)

22
Q

what is the all-or-nothing principle

A

the action potential is created when the threshold potential is met
no matter how large the stimulus the size of the action potential will be the same
when the stimulus is large it just creates more frequent action potentials, increasing the number of impulses sent

23
Q

How are impulses transmitted across a synapse

A
  • An action potential arrives at the end of the presynaptic neurone. This causes calcium ion channels to open and calcium ions enter the synaptic knob
  • The influx of calcium ions cause synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft
  • Acetylcholine diffuses across the cleft and binds with receptors on the postsynaptic membrane. This causes sodium ion channels to open and sodium ions diffuse into the neurone
  • This cause a new action potential to occur in the postsynaptic neurone
24
Q

define synapse

A

the junction between two neurones

25
Q

what is the actual gap called between 2 neurones

A

synaptic cleft

26
Q

define neurotransmitter

A

a chemical that diffuses from one neurone to the next

27
Q

what are the 2 types of neurotransmitter

A

Excitatory - result in depolarisation of the postsynaptic membrane = action potential

Inhibitory - result in hyperpolarisation of the postsynaptic membrane - no action potential

28
Q

give an example of a excitatory neurotransmitter and a inhibitory neurotransmitter

A

excitatory - acetylcholine

inhibitory - GABA

29
Q

what is acetylcholinesterase

A
  • an enzyme located on the postsynaptic membrane
  • it hydrolyses acetylcholine into choline and ethanoic acid
  • these diffuse back across the cleft and enter the presynaptic neurone
  • ATP is used to recombine the 2 chemicals into acetylcholine and repackaged into vesilces
30
Q

how could drugs affect synapses

A
  • could be similar to the shape of the neurotransmitter so the channels would open when they aren’t meant to
  • could block receptors on postsynaptic membrane
  • could inhibit acetylcholinesterase
  • could block calcium ion channels
31
Q

what are the roles of synapses

A
  • ensure impulses travel in one direction (receptors are only present on postsynaptic membrane
  • can allow an impulse from one neurone to be transmitted to a number of neurones (a single stimulus creates a number of simultaneous responses)
  • a number of neurones may feed into the same synapse (many stimuli produce a single result)
32
Q

define summation

A

when the amount of neurotransmitter builds up sufficiently to reach the threshold which triggers an action potential

33
Q

define spatial summation

A

when a number of presynaptic neurones connect to one postsynaptic neurone
each releases neurotransmitter which builds up to a high enough level in the synapse to trigger an action potential in the single postsynaptic neurone

34
Q

define temporal summation

A

when a single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period
this builds up in the synapse until the quantity is sufficient to trigger an action potential

35
Q

what are the 2 main branches of the nervous system

A

CNS - brain and spinal cord

PNS (peripheral nervous system) - neurones that carry impulses to and from the CNS

36
Q

what 2 parts is the peripheral nervous system divided into

A

Somatic - motor neurones carry impulses from CNS to skeletal muscles under CONSCIOUS control

Autonomic - motor neurones carry impulses from CNS to cardiac muscle, smooth gut muscle and glands under UNCONSCIOUS control

37
Q

what 2 systems is the autonomic peripheral nervous system divided into
what are the neurotransmitters involved

A

Sympathetic - gets body ready for action “fight or flight”. the neurones secreted is noradrenalin

Parasympathetic - calms body down “rest and digest”. neurones secreted are acetylcholine

38
Q

what are the steps for the knee-jerk reflex

A

1) leg tapped below kneecap
2) stretches patellar tendon (stimulus)
3) initiates reflex arc that causes extensor muscle on top of thigh to contract
4) at the same time, relay neurone inhibits motor neurone of flexor muscle causing it to relax
5) so the extensor muscle is contracting and flexor hamstring muscle relaxing causing the leg to kick

39
Q

what happens during the blinking reflex

why do both eyes close as a result

A

1) cornea of eye irritated by foreign body
2) triggers impulse along a sensory neurone
3) impulse passes through a relay neurone in the lower brain stem
4) impulses sent along branches of the motor neurone to initiate a motor response to close eyelids
5) both eyes are closed because this is a consensual response

40
Q

in the brain, what does the cerebrum do? where is it located

A

the biggest part all over the top of the brain. split into 2 hemispheres

it controls voluntary actions like learning, memory, personality and conscious thought

41
Q

in the brain what does the pituitary gland do? where is it located?

A

stores and releases hormones that regulate many body functions

it’s quite central

42
Q

in the brain what does the hypothalamus do? where is it located?

A

regulatory centre for temperature and water potential

central

43
Q

in the brain what does the medula oblongata do? where is it located?

A

used in automatic control eg. breathing and heart rate

top of spinal cord, bottom of brain

44
Q

in the brain what does the cerebellum do? where is it located?

A

controls unconscious functions such as posture, balance and non-voluntary movement

back of brain

45
Q

Define spinal cord

A

Column of nervous tissues running up the back

Surrounded by spine for protection

46
Q

Why are reflex actions important for the survival of organisms

A

Avoid body being harmed and reduce severity of damage
The brain can deal with complex responses involuntary which reduces time
Reflexes are present at birth so provide immediate protection
The reflex arc is short so means it’s extremely fast

47
Q

for involuntary muscles, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope

A

structure: non-striated, smooth, spindle cell shaped, one nucleus per cell
slow speed of contraction and slow to fatigue
autonomic nervous system
examples: organ walls, blood vessels, iris, uterus
appearance: unstriped, uninucleated

48
Q

for skeletal/voluntary muscles, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope

A

structure: lots of nuclei, long, striated
speed of contraction: rapid and quick to fatigue
nervous system: somatic
examples: bulk of body muscle tissue
appearance: stripy, multinucleated

49
Q

for cardiac muscle, describe the cell structure, speed of contraction & fatigue, nervous system that controls it, examples and appearance under microscope

A

structure: branched, uninucleated, discs between cells, some striations
speed of contraction and fatigue: intermediate speed and never fatigues
nervous system: autonomic
examples: found only in the heart
appearance: some striations, uninucleated

50
Q

name the features of a cell in skeletal muscle

A
sarcolemma (cell-surface membrane)
sarcoplasm (cytoplasm)
mitochondria
myofibrils (cause contraction)
nucleus (many nuclei per cell)
sarcoplasmic reticulum (endoplasmic reticulum)
T tubules (a fold of the sarcolemma)
51
Q

describe the structure and function of muscle fibres in skeletal muscles

A

Muscle fibres are enclosed in a plasma membrane called sarcolemma
They contain a number of nuclei and are much longer than normal cells
They make the muscle stronger
Have lots of mitochondria to provide ATP for muscle contraction
Has a modified version of ER called sarcoplasmic reticulum which extends the muscle fibre and contains calcium ions

52
Q

what are myofibrils

what proteins are they made of

A

myofibrils are long, cylindrical organelles made of protein and specialised for contraction. they are lined up in parallel in the skeletal muscle

actin - thinner filament, 2 strands twisted around each other

myosin - thicker filament, consists of long, rod-shaped fibres

53
Q

in myofibrils, describe the different bands that can be seen

A

Because of the way the myofilaments are arranged, the myofibril appears to have dark and light bands, giving the muscles a striated appearance.
The dark bands consist of thick filaments (myosin) and some thin filaments (actin).
At the centre of the dark band is the H-zone, where only thick filaments are present.
The light bands, are the regions containing thin filaments only (actin), and are found between the dark bands.
There is a Z-line found at the centre of each light band where the sarcomere distance between each adjacent Z-line

54
Q

what is the sliding filament model

A

where myosin and actin filaments slide over one another to make the sarcomeres contract
the myofilaments themselves don’t contract

the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract

55
Q

In the sliding filament model, what happens to each of the bands of the myofibrils during contraction

A

The light bands become narrower
The Z lines move closer together, shortening the sarcomere
The H zone becomes narrower
Dark band remains same width

56
Q

What is the structure of myosin (thick bands)

A

They have globular heads that are hinged which allows them to move back and forwards

On the head is a binding site for each of actin and ATP

The tails are aligned together to form the myosin filament

57
Q

What is the structure of actin filaments (thin bands)

A

2 strands of actin wrapped around each other
a long strand of tropomyosin wrapped around the actin
attached to the tropomyosin are heads called troponin

58
Q

When a muscle is in resting state what has happened to the actin-myosin sites

A

They are blocked by tropomyosin
This means the myosin heads can’t bind to the actin
So the filaments can’t slide past each other
The muscle can’t contract

59
Q

describe what is happening when a muscle is stimulated to contract
(from the neuromuscular junction to muscle contraction)

A

1) An action potential arrives at a motor neurone
2) A neurotransmitter diffuses across the cleft and binds to the receptors on the sarcolemma
3) A wave of depolarisation spreads around the sarcolemma down the T-tubules to the sarcoplasmic reticulum
4) Causes sarcoplasmic reticulum to released stored calcium ions into the sarcoplasm
5) The influx of calcium ions triggers muslce contraction. They diffuse into the myofibril
6) Calcium ions bind to the troponin causing it to change shape
7) This pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament
8) This allows the myosin to bind to the binding site
9) An actin-myosin cross-bridge is formed
10) With the addition of ATP, the myosin head which is attached to the actin moves to the side in a rowing action

60
Q

What happens when a muscle stops being stimulated to contract

A

1) Calcium ions leave their binding sites on the troponin
2) the ions are moved by active transport back into the sarcoplasmic reticulum
3) Troponin molecules return to its original shape so the tropomyosin block the actin-myosin binding site again
4) Actin filaments slide back to their relaxed position which lengthens the sarcomere

61
Q

How is ATP used in muscle contraction

A

ATP is broken down by ATPase into ADP which releases energy.
This energy is used to move the myosin head which is moved along the actin filament to cause muscle contraction.
The energy is also used to remove the myosin head and position it in another place on the actin.

62
Q

what are the differences between a synapse and a neuromuscular junction (NJ)

A

-synapse is from a neurone to a neurone
NJ is from motor neurone to muscle

-synapse creates new action potential
NJ makes muscle contraction

-the neurone before the junction on the synapse is round and is called the synaptic knob
the neurone before the junction on the NJ is flat called the motor-end plate

63
Q

what are the similarities between a synapse and a neuromuscular junction (NJ)

A
  • both involve neurotransmitters that have been released by exocytosis
  • both have complementary receptors for that neurotransmitters
64
Q

where does the ATP supply come from for the neuromuscular junction

A
  • aerobic respiration
  • anaerobic respiration
  • creatine phosphate (the phosphate from this can be added to ADP to make an ATP molecule)