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IMS- Strand 10 > Neural signalling > Flashcards

Neural signalling Flashcards

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1
Q

What do neurons consist of?

A
  • Dendrites
  • Cell body
  • axon
  • synaptic connections allow communication between neurons, facilitating the relay of information
  • Synapses can be chemical or electrical
  • Myelin sheath
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2
Q

What are the 3 functional classifications?

A
  • Sensory neurone
  • Motor neurone
  • Inter- neurone (Relay neurone)
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3
Q

What is the resting membrane potential?

A

-70mv

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4
Q

What determines the resting membrane potential?

A
  • Different conc of ions (Na+ & K+)
    -The relative permeability of the cell membrane to these ions
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5
Q

How does Na+ move?

A

Moves into cell via Na+ leak channels down its electrochemical gradient taking IN positive charge

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6
Q

How does K+ move?

A

moves out of the cell via “K+ leak channels” down its electrochemical gradient taking positive charge OUT (effectively -ve charge in the cell)

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7
Q

What is the Na+/K+ ATPase pump?

A

Is a pump that actively pumps 3Na+ out of the cell in exchange for 2K+ into the cell- maintain the concentration gradients of K+ and Na+ across the membrane

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8
Q

What is action potential generation?

A
  • Brief reversal of membrane potential from -ve to +ve and then back again
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9
Q

First step in AP

A

An action potential begins when the resting membrane is depolarised, so its membrane potential increases and crosses a threshold value- around -55mv

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10
Q

Second step in AP

A

Voltage gated Na+ channels open allowing Na+ ions into the cell (bringing +ve charge into the cell)- results in an increase in membrane potential= DEPOLARISATION to about +30mv

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11
Q

Third step in AP

A

Voltage gated Na+ channels start to inactivate

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12
Q

Fourth step in AP

A

At the same time (as step 3) voltage gated K+ channels open and allow K+ ions to leave the cell (taking +ve charge out of the cell)
Membrane potential starts to decrease= REPOLARISATION
Small overshoot due to excess K+ efflux causes a HYPERPOLARISATION

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13
Q

Fifth step in AP

A

K+ channels close and the Na+ channels are closed (but not inactivated) Na+/K+ ATPase restores the Na+/K+ gradient across the membrane

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14
Q

What are the 3 stages of the voltage gated Na+ channels

A

Closed, open & inactive
Na+ channel has an inactivation gate that blocks Na+ influx shortly after depolarisation and stays in this state until the cell repolarises and the channel enters the closed state again

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15
Q

What is the Absolute Refactory period?

A

period of time during which cell is incapable of repeating an AP in that part of the membrane. Endures AP travels in one direction

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16
Q

Where does AP start?

A

axon hillock and moving down axon

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17
Q

What is the Relative refactory period?

A

A larger stimulus can result in AP in this area of the membrane

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18
Q

What is the all or nothing principle?

A
  • Nerve membrane has to be depolarised beyond threshold for an AP to be generated
  • Increase above threshold> higher AP frequency not larger AP amplitude
  • A neurone either fires or doesn’t, regardless of signal size= all or nothing
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19
Q

5 steps in the propagation of action potential down non- myelinated axons

A

1- Na+ channels locally open in response to a stimulus- generating an AP here
2- Some depolarizing current passively flows down the axon
3- Local depolarisation causes neighbouring Na+ channels to open and generates an AP here
4- Upstream Na+ channels inactivate, while K+ channels open. Membrane potential repolarises and axon is refactory here
5- Process is repeated propagating the AP along the axon

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20
Q

3 steps in the propagation of AP down myelinated axons

A

1- Na+ channels locally open in response to a stimulus- generating an AP here
2- Depolarising current passively flows down the axon
3- Nodes of Ranvier are the only areas where current can pass through the membrane and the only areas where the membrane depolarises
-Myelin sheath prevents flow of ions in regions of the axon it covers
- Impulse travels in jumps= saltatory conduction

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21
Q

What is spatial summation?

A

Signals coming from multiple simultaneous inputs from a number of presynaptic neurones

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22
Q

What is temporal summation?

A

comes from repeated inputs from a presynaptic neurone

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23
Q

What is the most prevalent form of motor neurone disease?

A

ALS- Amyotropic lateral sclerosis

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24
Q

What is MND?

A

-Fatal disease of the nervous system, characterised by progressive voluntary (Striated) muscle weakness and paralysis
-Selective for somatic motoneurones- leaving sensory and autonomic function intact. Mind and memory= unaffected

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25
What is the pathology of MND?
-degradation of upper and lower motoneurones- messages that originate in the motor cortex don't reach the muscles to trigger voluntary contractions - Nerve death= innervating muscles shrink & waste away
26
Cause of MND?
- Exact cause= unknown - Thought to be Glutamate toxicity at the synapse - Excessive levels of the neurotransmitter glutamate in the synapse cause motoneurons to become overexcited= damage and death
27
Why is there a build up of glutamate in MND?
-Due to loss of glutamate transporters (EAAT2) which normally mop up the glutamate in the synapse - Glutamate's toxicity is due to Ca2+ flooding the cell. Prolonged Ca2+ inside the cell causes damage and can activate programmed cell death
28
What is the myelin?
-Insulating layer around nerve axon in the CNS & PNS - Consists of protein and fatty substances. Speeds up the transmission of electrical impulses along axons
29
What is responsible for the myelination of neuronal axons in the CNS?
OLIGODENDROCYTE - cells extend processes that wrap around the axons to form myelin sheath - One oligodendrocyte can myelinate from 3-50 neurons
30
What is the PNS myelin sheath formed by?
formed by schwann cells One schwann cell provides myelination for one axon
31
What is a demyelinating disease?
-condition that results in damage to the myelin sheath- CNS & PNS
32
What happens due to a demyelinating disease?
- Nerve impulses slow/ stop - Deficiency in sensation, movement, cognition or other functions specific to nerves - Axonal degeneration and often cell body degeneration - Usually secondary to inflammation
33
What are the two different classifications of demyelinating diseases?
- Classified based on cause - Demyelinating leukodystrophic diseases - Demyelinating myelinoclastic diseases
34
What are Demyelinating leukodystrophic diseases?
Primary- myelin is abnormal and degenerates= genetics responsible
35
What is demyelinating myelinoclastic diseases?
secondary- healthy myelin is destroyed by a toxic (e.g. alcohol), infectious agents, chemical or autoimmune substance e.g. multiple sclerosis
36
What is Multiple sclerosis?
- Most common demyelinating disease of the CNS- sensory & motoneurones affected - Autoimmune degenerative nerve disorder- immune system attacks the myelin sheath - Results in multiple areas of scarring- impedes nerve signalling
37
Symptoms of MS
-sensory, motor & cognitive problems - Difficulty walking - Blurred vision - Numbness or tingling in different parts of the body - Problems with balance and co-ordination - Problems with thinking, learning and planning
38
Cause of MS
- Exact cause unknown - Possible molecular mimicry - Environmental viruses trigger the autoimmune attack in genetically susceptible individuals via "molecular mimicry - Not considered a hereditary disease; though genetic variations increase risk
39
What is Molecular mimicry?
Defined as the structural similarity between foreign (microbial) & the self molecules of the mammalian host Resulting in the production of autoreactive T and antibody producing B cells which attack the host as well as the foreign body
40
What type of disease is Guillain- barre syndrome?
Demyelinating disease of the PNS
41
What is Gullian Barre syndrome?
Autoimmune disease, often triggered by a preceding viral or bacterial infection - Myelin and Schwann cells around sensory and motoneurones destroyed= conduction block and axonal degeneration - Likely to involve microbial triggered molecular mimicry
42
What are the symptoms of Gulliain Barre syndrome?
- Symmetrical ascending muscle weakness and paraesthsia in arms and legs, loss of sensation, autonomic dysfunction
43
What is the treatment of Guillian Barre syndrome?
-Intravenous immunoglobulins - Plasma exchange
44
What are sensory receptors?
modified nerve endings of sensory neurones
45
What are receptors tuned to detect?
Sensory modalities
46
Mechanoreceptors
- Touch, pressure, vibration, stretch
47
Thermoreceptors
- Hot, cold, temp change
48
Photoreceptors
Light
49
Chemoreceptors
- Chemicals
50
Nociceptors
Pain (usually chemicals)
51
What is sensory transduction?
Sensory stimulus converted to--> Electrical stimulus--> AP generation and propagation along the sensory neurone
52
What is a pacinian corpuscle do?
Convert mechanical pressure to an electrical impulse
53
What does the Pacinian corpuscle do?
- Gel contains Na+ ions - Sensory neurone ending contains stretch mediated Na+ ion channels= open when corpuscle is deformed by pressure - Open= allow Na+ from the gel to flow into the neurone, generating a small depolarisation in sensory neurone ending- receptor potential - Large enough receptor potential= AP fired off along the sensory axon towards CNS
54
Where is the pacinian corpuscle found?
-around the ends of sensory neurones- pressure detectors - Layers of connective tissue with gel in between
55
Steps for the pacinian corpuscle
No pressure - Stretch mediated Na+ channels= too narrow - Na+ ions= outside - RP maintained Pressure - Layers distorted= stretch mediated Na+ channels open - Na+ ions enter axon of Sensory neurone Receptor potential established - Influx of Na+= changes potential of axon= Depolarisation - Enough receptor potential= AP= nerve impulse along axon
56
What are receptor potentials?
- A graded potential - NOT AP - Can summate & give rise to AP in neurone - Depolarising event results from inward current flow - Influx of current brings membrane potential towards threshold= triggers AP
57
What are proprioceptors?
part of PNS
58
What are muscle proprioceptors?
Sensory receptors in muscles 1. The muscle spindle is located within the muscle and stimulated when the muscle is passively stretched 2. When a muscle is passively stretched the spindle is activated and initiates a reflex causing the muscle to contract. Protects muscle being overstretched
59
What is the golgi tendon organ?
1. The golgi tendon organ is located in the tendon and responds to excessive tension (it is stimulated when muscles it is associated with contracts) 2. When stimulated it causes its associated muscle to relax by interrupting its contraction. Prevents the tendon from tearing and muscle damage
60
What is a reflex arc?
A reflex arc is an automatic (involuntary) and rapid response to a stimulus, which minimises any damage to the body from potentially harmful conditions Maintains posture, balance and coordination
61
What are the 5 components of the reflex arc?
Receptor Sensory neuron Interneuron Motor neuron Effector
62
What is the motor neuron?
Carries efferent impulses to the effector (muscle or gland), which produces the response
62
What does the sensory neurone do?
carry input from the receptor (afferent impulses) to a central interneuron, which makes contact with a motor neuron
62
What is the stretch reflex?
- Stretching of muscle activates the spindle resulting in increased discharge of the sensory afferent neurone - This results in increased firing of the motor neurone to muscle thats stretching causing it to contract -No spinal interneurone is involved- i.e. monosynaptic stretch reflex - This contraction usually accompanied by simultaneous reflex inhibition of antagonistic muscle - Effect= dampen the stretch of the muscle- so protecting it - Knee jerk reflex= example
63
What is an example of a stretch reflex?
knee- jerk reflex
64
What is a muscle spindle reflex- maintaining muscle tone?
when the muscle is stretched, the afferent signal from the muscle spindle is relayed to the motor neurone and an efferent signal is sent back to the muscles to cause it to contract (same time inhibiting antagonistic muscle) - muscle always under some degree of stretch, so reflex circuit= usually responsible for muscle tone
65
Golgi tendon reflex
- Excess tension in the tendon caused by the muscle contraction is detected in the golgi tendon organ (GTO) -GTO sends sensory signals along a sensory afferent CNS - This results in a reflex that inhibits muscle from contracting - Accompanied by reciprocal contraction of the antagonistic muscle - Reduces the tension in the tendon= so protecting it
66
Golgi tendon reflex in action
-As the amount of tension generated in the tendon by the bicep increases with each increasing weight- the rate of GTO firing increases - At some point excessive GTO firing occurs, indicates no more force should be generated by the muscle, otherwise the tendon connecting the muscle to the bone might tear - At this point the GTO reflex interrupts the contraction causing muscle to relax

IMS- Strand 10 (3 decks)

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