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ANSC3104 Nervous system > Neurophysiology > Flashcards

Neurophysiology Flashcards

1
Q

Are solutes equally distributed between interior and exterior of cells?

A

No - there is unequal distribution

This creates concentration gradient as cell membrane is almost impermeable

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2
Q

What ions dominate ECF?

A

Na+ & Cl-

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3
Q

What ions dominate ICF)

A

K+ & A- (anions)

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4
Q

Define membrane potential

A

Separation of ions across a membrane (basis for excitable cell function)

Size of potential depends on amount of separation of opposite charges

Opposite charges are attracted to each other

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5
Q

Define resting membrane potential

A

Neurons at resting membrane potential have constant number of charges separated
Usually ~-70mV

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6
Q

Approximation of resting membrane potential

A

-70mV

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7
Q

Define polarization

A

Having a membrane potential - separation of ions across a membrane

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8
Q

Define depolarisation

A

Decrease in potential

Membrane less negative

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9
Q

Define repolarisation

A

Return to resting potential after depolarisation

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10
Q

Define hyperpolarisation

A

Increase in potential

Membrane more negative

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11
Q

Graded potential

A

Small stimulus –> small number of Na+ channels open –> small influx of Na+

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12
Q

What occurs when Na+ enters cell?

A

depolarisation

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13
Q

Action potential

A

A large stimulus causes membrane to reach threshold
Lots of Na+ channels open
Initially overcorrection: hyperpolarisation

Action potential complete after hyperpolarisation begins

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14
Q

After action potential

A

Na+ - K- pumps restores ions to original concentrations
Pump doesn’t activate after every single AP

  • Huge amounts of each ion in each compartment and only relative few involved in AP
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15
Q

All or nothing rule

A

If the membrane of an excitable tissue is stimulated, it will either respond with a maximal action potential that spreads along the membrane in an undiminished fashion or does not respond at all

All action potentials last for the same amount of time

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16
Q

What determines the strength of AP?

A

The frequency and area (number of nerves) of APs indicates the strength of signal

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17
Q

What is the ‘trigger zone’ of AP?

A

Axon hillock (AP is initiated here)

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18
Q

Can AP only move one way?

A

Yes

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19
Q

Absolute refractory period

A

Membrane area is already undergoing AP
Na+ channels are open & cannot be triggered to re-open until membrane has returned to res23qting potential (inactivation gates)

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20
Q

Relative refractory period

A

New AP can be triggered, by stronger than normal stimulus

When original site has recovered, AP moved too far away to trigger another

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21
Q

How is AP conducted?

A

AP conducted down axon to terminals
AP depolarises adjacent region to threshold, sets off new AP
AP appears to move down the axon (actually triggers identical events down the axon)
Spreads in an undiminished fashion
Signal replicated over long distances

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22
Q

Continguos conduction

A

Occurs on unmyelinated fibres

AP spreads down axon, along every patch of membrane –> requires a lot of energy to return membrane to resting potential

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23
Q

Saltatory conduction

A

Occurs in myelinated fibres
Occurs in long distance signals
Myelin = lipid - stops ions passing through (insulator)

Not continuous - ‘Nodes of Ranvier’
AP travels down axon by jumping from node to node

Quicker and requires less energy than continuous conduction

  • Small sections of axon stimulated, instead of entire axon
  • ~50x faster
  • Larger fibre diamter –> faster signal
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24
Q

What could happen if myelin sheath degrades?

A 
MS 
Signals jump between different pathways 
Only affects motor neurons
Less controlled movements 
e.g. move arm instead of foot
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25
Q

Classic NTRs

A

Small rapid acting

E.g. Acetylcholine, Noradrenalin, dopamine, serotonin, glutamate

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26
Q

Neuropeptides (type of NTR)

A

Larger, slower acting
E.g. insulin, bradykinin, oxytocin

Hormones are a type of neurotransmitter (slow acting)

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27
Q

Synaptic cleft

A

Gap between neurons

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28
Q

Synaptic knob

A

Axon terminals end with a slight swelling

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29
Q

Subsynaptic membrane

A

Membrane of postsynaptic neuron under synaptic knob

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30
Q

Conduction of impulse neuron to neuron junctions

A

Action potential reaches axon terminal of presynaptic neuron

Stimulates opening of voltage Ca+ channels

Calcium enters synaptic knob

Triggers the movement of NTR to the synaptic cleft via exocytosis of vesicles

NTR binds to specific receptors that are part of the chemically gated channels on synaptic membrane of post synaptic neuron

Specific channel opens

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31
Q

Two main types of chemical synapses (postsynaptic potentials)

A 
1. Excitatory 
Small depolarisations (influx of positive ions - closer to threshold) 
2. Inhibitory  
Small hyperpolarisations (influx of negative ions - harder to reach AP)
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32
Q

Excitatory synapses

A

Binding of NTR causes a net increase of positive ions within the cell - triggers a small depolarisation of membrane

Like a graded potential
- One usually not enough to trigger AP

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33
Q

Inhibitory synapses

A

Binding of NTR opens K+ or Cl- channels
K+ goes out or Cl- comes in
And this causes hyperpolarisation of the cell membrane

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34
Q

Grand postsynaptic potential

A

Total summation of Excitatory and inhibitory synapses

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35
Q

Temporal summation

A

Rapid, successive signals from 1 neuron

36
Q

Spatial summation

A

Single signals from 100s of neurons

37
Q

How are NTRs cleaned up from synaptic cleft

A

Enzymatic destruction or re-uptakes

Diffusion only occasionally

38
Q

Where is neuromuscular junction located

A

In the middle of one muscle cell

39
Q

Terminal button

A

Axons terminals end in slight swelling

Neuromuscular junction terminology

40
Q

Motor end plate

A

Membrane of postsynaptic muscle cell under terminal button

Neuromuscular junction terminology

41
Q

What NTR is used in neuromuscular junction?

A

Always acetylcholine

2 Ach molecules bind with nicotinic receptor on motor end plate

42
Q

Muscle cell depolarisation is called…

A

End plate potential
Larger than excitatory postsynaptic potential
- is a graded potential
- causes AP in adjacent membrane

43
Q

In neuromuscular junction Acetylcholine is cleaned up by

A

Acetylcholinesterase

44
Q

Reflexes maintain

A

Posture and balance

45
Q

Lower motor neurons

A

Integrate information & innervate muscles
Synapse at NMJ & only release Acetylcholine
- excitatory postsynaptic potential leads to muscle contraction

46
Q

Reflexes are

A

automated regulatory mechanisms (ANS)

47
Q

Simple somatic reflexes occur at

A

Spinal cord

- usually have protective functions

48
Q

Somatic spinal reflexes

A

Automatic control to maintain posture, control movement

49
Q

Types of spinal reflexes

A

Stretch reflex
Tendon reflex
Withdrawal reflex

50
Q

Stretch reflex

A

Controls the length of skeletal muscles

  • smooths movement
  • maintains posture

Muscle stretch detected by afferent fibres
Send signal that muscle is stretching
Synapse directly to motor neuron in SC (no interneurons)

Motor neuron triggers muscle contraction to prevent overstretch

Local negative feedback

51
Q

Tendon reflexes

A

Inform spinal cord or continual tension

Golgi tendon organs detect stretch - have branched nerve endings interwoven between collagen fibres of the tendon

Muscle fibres contract & pull tendons, changing shape of the entwined Golgi organ

Change in shape increases firing of the sensory fiber
Fibers connected to inhibitory interneurons in spinal cord, which synapse on motor neurons that innervate that muscle

When tendon is greatly stretched it triggers muscle to relax and reduces load

52
Q

Withdrawal reflex

A

Automatically withdraws if touch something painful

Sensory nerve endings in skin

These synapse with interneurons in spinal cord

Stimulate motor neurons innervating the limb

Contracts withdrawal muscles - inhibits antagonistic muscles

53
Q

Pattern generator in spinal cord

A

Controls motor neuron activity
Coordinates left & right, flexor & extensor, fore & hind limb
Also involve thalamic & midbrain input - increase stimulation of these - increase speed of movement

54
Q

What regulates change in gait

A

Midbrain

55
Q

Postural reflexes:

A

Vestibulo-ocular reflex

Vestibular placing reflex

The righting reflex

56
Q

Vestibulo-ocular reflex

A

Stabilises image on the retina during rapid head rotation

Exterior eye muscles move eyeball with & in opposite direction to a movement of the head

Maintains visual field

57
Q

Vestibular placing reflex

A

Shifts centre of gravity to keep the animal stable

Information is received from balance organs (vestibular apparatus) in ears

Coordinates flexion and extension of legs

58
Q

The righting reflex

A

Restores posture when falling

Sensors: balance organs, neck muscle spindles & skin pressure

Head position is adjusted first

Then body position is adjusted (relative to head)

Ear organs detect acceleration of fall & trigger leg extension, ready for landing

59
Q

Upper motor neurons

A

motor neurons from the cortex or brain stem

Project down spinal cord in tracts called pyramids

60
Q

Where do upper & lower neurons synapse?

A

Ventral horn of spinal cord

61
Q

Pyramidal tracts

A

Connect cortex to spinal cord via pyramids in medulla oblongata

No synapse

Activates muscles involved in fine motor skills & initiation of voluntary muscle movement

Most fibres cross over to other side of body in medulla

62
Q

Extrapyramidal tracts

A

Connect cortex to spinal cord

NOT through medulla

Synapse at brain stem nuclei

Activates larger muscle groups - stabilises posture, balance & smooth movements

63
Q

Voluntary movement pathway

A

Primary motor cortex commands muscles to start movements

Cerebellum then gets the plan and minimises difference between intended and actual movements - important in planning and timing of movements (smoothes & coordinates movement)

Basal ganglia and brain stem act together to plan complex movements - creates link between motivation and body movement
(Basal ganglia prepare for movement, inhibit unwanted movement - cerebellum coordinates movement as they are performed)

64
Q

Sympathetic NS preganglionic fibres

A

Myelinated & short

65
Q

Sympathetic NS ganglia located in

A

Sympathetic trunk

66
Q

Sympathetic NS postganglionic fibres

A

Unmyelinated & long

67
Q

Adrenal medulla

A

Large combined sympathetic ganglion & gland

68
Q

Parasympathetic fibres located

A

Cranial & sacral regions

69
Q

Sympathetic fibres located

A

Thoracic & lumbar SC

70
Q

Parasympathetic preganglionic fibres

A

Myelinated & long

71
Q

Parasympathetic postganglionic fibres

A

Short and unmyelinated

72
Q

Parasympathetic Ganglia located

A

Close to target organs

73
Q

In ANS do all preganglionic and parasympathetic postganglionic neurons release Ach

A

Yes

74
Q

What NTR do sympathetic postganglionic neurons release?

A

Noradrenalin

75
Q

Adrenal medulla relases

A

Noradrenalin & adrenalin

Both promote symp NS

76
Q

Cholinergic receptors

A

stimulated by acetylcholine

77
Q

Two types of cholinergic receptors

A

Nicotinic & muscarinic

78
Q

Nicotinic receptors

A

Found on all ANS postganglionic cell bodies

Bind Ach from all preganglionic fibres

Only have excitatory effects E.g. muscle contraction

79
Q

Muscarnic receptors

A

Found on all AND effector cell membranes
Bind with Ach from parasympathetic postganglionic fibres

Excitatory or inhibitory
E.g. contract or relax muscle

80
Q

Adrenergic receptors

A

Stimulated by noradrenalin

81
Q

Types of adrenergic receptors

A

Alpha and Beta receptors

both have subtypes 1 & 2

82
Q

Alpha receptors

A

Alpha 1 - found in most sympathetic tissues that are excited by the sympathetic NS - excitatory response
E.g. Systemic vessels constrict - blood diverted away from GIT spincters that need to stop movement of digesta

Alpha 2- Primarily found in the gut - where action is to inhibit digestive secretions

83
Q

Beta receptors

A

Beta 1 - found primarily in the heart (also kidney) - excitatory response - e.g. heart beats faster

Beta 2- Found in most tissues that are inhibited (relaxed) by sympathetic NS
E.g. Relax GIT muscles to slow movement of digesta or blood vessels in skeletal muscles that need extra blood

Also stimulates insulin release, lipolysis, glycogenolysis - convert stored energy to usable energy

84
Q

Antagonistic control

A

Stimulation vs inhibition

85
Q

Hypothalamic reflexes

A

Homeostasis
Highest level of integration
e.g. thirst & water balance

ANSC3104 Nervous system (3 decks)

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