5 - MZH - Homeostasis 7 - Neuronal Communication Flashcards

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1
Q

What does the nervous system do?

  • What type of response does it provide?
  • Give 4 examples
A

Provides rapid responses to changes in both the internal and external environment

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2
Q

What does a general nervous pathway look like?

What does each stage do?

A
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3
Q

Define Stimulus, Receptor and Effector

A

Stimulus = Detectable change in the external or internal environment of an organism

Receptor = A cell, or protein on a CSM that detects specific stimuli

Effector = A muscle or gland which carries a body’s response to a stimulus

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4
Q

What are sensory receptors?

What are transducers?

A

Sensory receptor = Specialised cells that respond to stimuli. Most sensory receptors are known as transducers - they convert one form of energy into another.

In this case the transducers are converting energy to electrical impulses/ action potentials.

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5
Q

Give 4 examples of:

Stimulus - Sensory receptor - Energy change involved (what brings abou this every transfer change?)

A

Transducers bring about this transfer of energy

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6
Q

What are Pacinian Corpuscles?

Structure + Function?

A

Pacinian corpuscles = (type of mechanoreceptor) which detects changes in pressure on the skin and joints.

NOTE: NOT constant pressure.

Structure:

  • Each pacinian corpuscle consists of a single nerve fibre of a dendrite of a sensory neurone wrapped around by layers of a membrane called lamellae.
  • Layers of connective tissue are seperated by a jelly/ viscous gel like material.

Function:

  1. Pressure applied to skin deforms the lamaellae which pushes up against the dendrite triggering a generator potential.
  2. Stretch in membrane opens voltage gated Na+ ion channels. Inflow of Na+ ions raises membrane potential - depolarises it.
  3. The more intense the stimuli the larger the generator potential.
    4.
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7
Q

Resting potential = ?

A

Resting potential = -70mV

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8
Q

Structure of a neurone:

Feature: Large cell body

Decription?

A

Contains the nucleus and many of the cell organelles

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9
Q

Structure of a neurone:

Feature: Dendrons

Decription?

A

Short extensions of the cell body which transmit impulses towards the cell body.

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10
Q

Structure of a neurone:

Feature: Dendrites

Decription?

A
  • Each dendron has smaller extensions called dendrites
  • Dendrites are stimulated by other neurones
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11
Q

Structure of a neurone:

Feature: Axon

Decription?

A
  • It’s a single entension of the cell body
  • Can be up to 1m long
  • Always transmits nerve impulses away from cell body
  • Ends in series of synaptic knobs
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12
Q

Structure of a neurone:

Feature: Myelin

Decription?

A
  • In mammals many axons are surrounded by a sheath of fatty material = Myelin sheath
  • Myelin enables the neurones to conduct action potentials rapidly
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13
Q

Structure of a neurone:

Feature: Schwann cell

Decription?

A

Specialised cells which produce myelin

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14
Q

Structure of a neurone:

Feature: Node of Ranvier

Decription?

A
  • Small gaps between the myelin sheath where bare membrane is exposed.
  • Nerve impulses travel along in a series of jumps from one node to the next - Advantage of myelination.
  • This jumping is called Salutatory conduction
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15
Q

Name the different types of neurones (3)

What do they do?

A

Sensory neurone = Carries action potential from a sensory receptor → CNS

Motor neurones = Carries action potentials from the CNS → effector e.g. muscle or gland

Relay neurones = Connects the sensory and motor neurones together

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16
Q

Compare the structure of Sensory and motor neurones:

  • Cell body
  • Dendrites
  • Axon
  • Dendron
  • Myelinated
A
17
Q

Define resting potential and give it’s value

A

Resting potential = Charge difference across a neurone membrane that must be set up before action potentials can be generated

-70mV

18
Q

How is the resting potential generated and maintained?

A

Resting potential = -70mV

There is an imbalance of Na+ and K+ across the membrane. More Na+ on the outside and more K+ inside neurone.

  1. Imbalance of ions is maintaned by a Na+/K+ pump.
  2. Na+/K+ pump uses ATP for active transport to remove Na+ and take up K+.
  3. Ratio of 3Na+ out : 2K+ in
  4. Both ions can diffuse back down their electrochemical gradient through open channel proteins. NOTE: There’s many more K+ channel protein than Na+ channel proteins.
  5. ∴ Many K+ that has been pumped into neurone will leave through their open channel proteins but very few Na+ can return back to neurone once pumped out. This further reinforces the imbalance of ions first established by Na+/K+ pump
19
Q

At what potential difference is the membrane considered to be polarised?

A

Resting potential at -70mV

20
Q

When is a action potential triggered?

A
  • Action potentials begin when a particular stimulus causes the membrane in one part of the neurone to suddenly change its permeability.
  • The depolarisation of the membrane triggers a generated potential and if this generated potential is equal to or exceeds the threshold value then a action potential is triggered.
21
Q

State the 5 steps in the events of an action potential

A
  1. Resting potential
  2. Depolarisation
  3. Repolarisation
  4. Hyperpolarisation
  5. Resting potential

Do it all over again!

22
Q

Describe the sequence of events that occur when an action potential is triggered (+ use figures)

A
  1. Resting potential - Initial membrane potential = -70mV
  2. Depolarisation - A stimulus occus and the voltage gated Na+ channels open. Na+ diffuse into neurone down their electrochemical gradient. Depolarisation causes more channels to open and ∴ results in further depolarisation.
  3. So many Na+ diffuse into of neurone that the inside of neurone becomes positive (+40 mV).
  4. Repolarisation - Na+ channels close and voltage gated K+ channels open. K+ diffuses down it’s electrochemical gradient out of the neurone making the inside of the membrane become more negative.
  5. Hyperpolarisation - So many K+ ions rush out of membrane that the membrane potential falls below the resting potential (undershoot).
  6. Resting potential - Na+/K+ pump restores resting potential by pumping 3Na+ out for every 2K+ in. From hyperpolarisation back to resting potential is called the refactory period.
23
Q

What is the purpose of the refactory period?

A

Period between hyperpolarisation and restoration of resting potential.

Refactory period is split into 2 parts:

  1. Absolute refactory period = Second action potential can’t occur.
  2. Relative refactory period = Second action potetnial can occur with a large enough stimulation.
  • After an action potential, the neurone cell membrane can’t be excited again straight away
  • This is because the ion channels are recovering and they can’t be made open.
  • It also acts as a time delay to ensure that action potentials don’t overlap and are unidirectional i.e. only travel in one direction.
24
Q

What are local currents and their purpose?

A

Local currents allow action potentials to be transmitted as a nerve impulse

25
Q

Describe how the transmission of action potentials occur along a neurone?

A
  1. Action potential at one Node of Ranvier and a resting potetnial at the next node causes a localised circuit of electricity.
  2. This electrical energy opens the voltage-gated Na+ channels at the next node ∴ Na+ rush into axon caused membrane to be depolarised. K+ rush out and a new action potential is generated.
  3. Previous node returns to its resting potential due to Na+/K+ pump.
  4. Action potential continues to travel down the neurone in the same fashion.
26
Q

Give 4 distinct characteristics of action potentials

A
  • They’re only generated if the stimulus triggers a generated potential greater than a certain threshold value
  • Action potentials have a all or nothing law where all action potentials are the same size
  • Strong stimuli cause many action potentials to be generated i.e. increased frequency
  • They always travel in one direction
27
Q

Comparison betwwen myelinated and non-myelinated neurones:

  • What neurones are included in each type
  • Do they have a myelin sheath?
  • Length of axons and dendrons
  • Whether neurones are insulated
  • Transmission speed
  • Type of transmission involved
A
28
Q

Advantages of myelination (2)

Why is speed not as big of a concern in non-myelinated neurones?

A
  • Much faster transmission of action potentials from 2-20ms-1 in non-myelinated neurones to 100-200ms-1 in myelinated neurones
  • Greater speed of transmission ∴ result in a more rapid response as in sensory & motor neurones action potentials may have to travel relatively long distances

Non myelinated nerves tend to be shorter ∴ an increased speed in transmission is not that important

29
Q

State and explain 2 other factors that may affect the speed of conduction of action potentials aside from myelination

A

Temperature - Higher temperatures will increase the rate of diffusion of ions and thus increase the rate of conduction

Diameter - An axon with a larger diameter will transmit action potentials faster but this doesn’t necessarily apply to all animals

30
Q

What is a synapse?

It’s purpose and what type of synapses are involved with action potentials?

Why is it called that?

A

Synapse = The junction between 2 neurones or between a neurone and effector

  • The gap created by the synapse is too wide for electrical impulses to cross ∴ a chemical neurotransmitter is needed.
  • Cholinergic synapses are used for the transmission of electrical impulses. It’s called so as it uses the neurotransmitter Acetylcholine (ACh)
31
Q

Describe the sequence of events that occur during synaptic transmission (8)

A
  1. Action potential arrives at the pre-synaptic bulb
  2. Voltage gated Ca2+ gates in the CSM of the pre-synaptic bulb to open. Ca2+ enter the pre-synaptic bulb.
  3. Vesicles containing the neurotransmitter ACh in the pre-synaptic bulb move to the pre-synaptic membrane and fuse with it releasing ACh into the synaptic cleft by exocytosis.
  4. ACh diffuses across synaptic cleft and attach to ACh receptor molecule present on post-synaptic membrane.
  5. Neurotransmitter/receptor complex triggers the opening of Na+ gated channels on the CSM of the post-synaptic bulb.
  6. If sufficient ions enter the post-synaptic bulb an action potential is generated in the post-synaptic neurone.
  7. ACh bound to receptor proteins on the post-synaptic bulb are hydrolysed. ACh → Choline + Ethanoic acid - enzyme = acetylcholine esterase. Choline and ethanoic acid detach from receptor sites and diffused back to pre-synaptic membrane.
  8. Choline and ethanoic acid molecules enter pre-synaptic bulb and are reformed into ACh (uses ATP) which is stored into vesicles for future use.
32
Q

Explain the all or nothing law with action potentials

A
  • Once the threshold is reached, an action potential will always fire with the same chance in voltage i.e. amplitude doesn’t change.
  • The stronger the stimuli the greater the number of action action potentials fired.

Stronger stimuli = Increased frequency of action potentials (like binary)

33
Q

Synaptic transmission:

Unidirectional (3)

A
  • Transmission at a synapse can only flow in one direction
  • Neurotransmitters are only released from the pre-synaptic membranes
  • Neurotransmitter receptors are only present on the post-synaptic membranes
34
Q

What is the difference between synaptic convergence and synaptic divergence?

A

Synaptic convergence = Many pre-synaptic neurones release neurotransmitters to one post-synaptic neurone.

MANY TO ONE

NOTE: Synaptic convergence allows spatial and temportal summation as well as integration)

Synaptic divergence = One pre-synaptic neurone release neurotransmitters to many post-synaptic neurones.

ONE TO MANY

35
Q

Synaptic transmission:

Summation

A

Weak stimuli leads to not enough neurotransmitter released to reach threshold level ∴ depolarisation of post-synaptic membrane doesn’t occur.

2 Different types of summation:

  1. Spatial summation (down to convergence) - ≥2 presynaptic neurones converge and release their neurotransmitters at the same time onto the same post synaptic neurone.
    • Small amounts of neurotransmitter is released from each presynaptic neurone. They add up to reach the threshold level.
  2. Temporal summation (down to divergence) - ≥2 nerve impulses arrive in qiuck succession from the same presynaptic neurone.
    • Makes action potential more liekly as more neurotransmitter is released into the synaptic cleft
36
Q

Synaptic transmission:

Inhibition

A

MIMIC, BLOCK or INHIBIT (in 2 ways)

  1. MINIC - Chemicals with the same shape as the neurotransmitters. These drugs are called “agonists
    • e.g. Nicotine mimics ACh and binds to certain types of cholinergic receptors in brain.
  2. BLOCK - Chemicals that block receptors so they can’t be activated by neurotransmitters. Fewer receptors (if any) can be activated.
    • e.g. Curare blocks ACh by blocking certain cholinergic receptors at certain neuromuscular junctions, so muscle cells can’t be stimulated ∴ muscle becomes paralysed.
  3. INHIBIT BY PREVENTING HYDROLYSIS THE NEUROTRANSMITTER - Results in more neurotransmitters in the synaptic cleft to bind to receptors. They remain there for longer.
    • e.g. Nerve gases stop ACh from being hydrolysed in the synaptic cleft. This leads to loss of muscle control.
  4. INHIBIT BY RELEASING LESS NEUROTRANSMITTER FROM PRESYNAPTIC NEURONE - So fewer receptors are activated.
    • e.g. Opioids block Ca2+ channels in the presunaptic neurone. Means that fewer vesicles fuse with the presynaptic membrane ∴ less neurotransmitter is released.