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ANSC3104 Nervous system > Neurophysiology > Flashcards

Neurophysiology Flashcards

(85 cards)

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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
Classic NTRs
Small rapid acting | E.g. Acetylcholine, Noradrenalin, dopamine, serotonin, glutamate
26
Neuropeptides (type of NTR)
Larger, slower acting E.g. insulin, bradykinin, oxytocin Hormones are a type of neurotransmitter (slow acting)
27
Synaptic cleft
Gap between neurons
28
Synaptic knob
Axon terminals end with a slight swelling
29
Subsynaptic membrane
Membrane of postsynaptic neuron under synaptic knob
30
Conduction of impulse neuron to neuron junctions
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
31
Two main types of chemical synapses (postsynaptic potentials)
``` 1. Excitatory Small depolarisations (influx of positive ions - closer to threshold) ``` ``` 2. Inhibitory Small hyperpolarisations (influx of negative ions - harder to reach AP) ```
32
Excitatory synapses
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
33
Inhibitory synapses
Binding of NTR opens K+ or Cl- channels K+ goes out or Cl- comes in And this causes hyperpolarisation of the cell membrane
34
Grand postsynaptic potential
Total summation of Excitatory and inhibitory synapses
35
Temporal summation
Rapid, successive signals from 1 neuron
36
Spatial summation
Single signals from 100s of neurons
37
How are NTRs cleaned up from synaptic cleft
Enzymatic destruction or re-uptakes Diffusion only occasionally
38
Where is neuromuscular junction located
In the middle of one muscle cell
39
Terminal button
Axons terminals end in slight swelling Neuromuscular junction terminology
40
Motor end plate
Membrane of postsynaptic muscle cell under terminal button Neuromuscular junction terminology
41
What NTR is used in neuromuscular junction?
Always acetylcholine 2 Ach molecules bind with nicotinic receptor on motor end plate
42
Muscle cell depolarisation is called...
End plate potential Larger than excitatory postsynaptic potential - is a graded potential - causes AP in adjacent membrane
43
In neuromuscular junction Acetylcholine is cleaned up by
Acetylcholinesterase
44
Reflexes maintain
Posture and balance
45
Lower motor neurons
Integrate information & innervate muscles Synapse at NMJ & only release Acetylcholine - excitatory postsynaptic potential leads to muscle contraction
46
Reflexes are
automated regulatory mechanisms (ANS)
47
Simple somatic reflexes occur at
Spinal cord | - usually have protective functions
48
Somatic spinal reflexes
Automatic control to maintain posture, control movement
49
Types of spinal reflexes
Stretch reflex Tendon reflex Withdrawal reflex
50
Stretch reflex
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
Tendon reflexes
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
Withdrawal reflex
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
Pattern generator in spinal cord
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
What regulates change in gait
Midbrain
55
Postural reflexes:
Vestibulo-ocular reflex Vestibular placing reflex The righting reflex
56
Vestibulo-ocular reflex
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
Vestibular placing reflex
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
The righting reflex
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
Upper motor neurons
motor neurons from the cortex or brain stem Project down spinal cord in tracts called pyramids
60
Where do upper & lower neurons synapse?
Ventral horn of spinal cord
61
Pyramidal tracts
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
Extrapyramidal tracts
Connect cortex to spinal cord NOT through medulla Synapse at brain stem nuclei Activates larger muscle groups - stabilises posture, balance & smooth movements
63
Voluntary movement pathway
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
Sympathetic NS preganglionic fibres
Myelinated & short
65
Sympathetic NS ganglia located in
Sympathetic trunk
66
Sympathetic NS postganglionic fibres
Unmyelinated & long
67
Adrenal medulla
Large combined sympathetic ganglion & gland
68
Parasympathetic fibres located
Cranial & sacral regions
69
Sympathetic fibres located
Thoracic & lumbar SC
70
Parasympathetic preganglionic fibres
Myelinated & long
71
Parasympathetic postganglionic fibres
Short and unmyelinated
72
Parasympathetic Ganglia located
Close to target organs
73
In ANS do all preganglionic and parasympathetic postganglionic neurons release Ach
Yes
74
What NTR do sympathetic postganglionic neurons release?
Noradrenalin
75
Adrenal medulla relases
Noradrenalin & adrenalin Both promote symp NS
76
Cholinergic receptors
stimulated by acetylcholine
77
Two types of cholinergic receptors
Nicotinic & muscarinic
78
Nicotinic receptors
Found on all ANS postganglionic cell bodies Bind Ach from all preganglionic fibres Only have excitatory effects E.g. muscle contraction
79
Muscarnic receptors
Found on all AND effector cell membranes Bind with Ach from parasympathetic postganglionic fibres Excitatory or inhibitory E.g. contract or relax muscle
80
Adrenergic receptors
Stimulated by noradrenalin
81
Types of adrenergic receptors
Alpha and Beta receptors | both have subtypes 1 & 2
82
Alpha receptors
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
Beta receptors
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
Antagonistic control
Stimulation vs inhibition
85
Hypothalamic reflexes
Homeostasis Highest level of integration e.g. thirst & water balance

ANSC3104 Nervous system (3 decks)

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