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Medicine Year 2 > HNN Topic 17 - General Neurology > Flashcards

HNN Topic 17 - General Neurology Flashcards

1
Q

List the sequence of events which occur when an action potential is fired

A
  1. Membrane potential reaches threshold value - fires action potential (depolarisation)
  2. Repolarisation
  3. Hyperpolarisation
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2
Q

What is the effect of an excitatory postsynaptic potential?

A

Brings the postsynaptic membrane potential closer to threshold (depolarisation), therefore increasing the probability of the postsynaptic cell producing an action potential

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3
Q

Where are the parasympathetic preganglionic neurons located?

A
  • Brainstem - leave with 4 cranial nerves
  • Sacral spinal cord, leave in spinal nerves S2-4
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4
Q

Which ions are most important in determining the resting membrane potential?

A

Sodium, potassium and chlorine

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5
Q

What causes multiple sclerosis?

A
  • Autoimmune, antibodies attack myelin
  • Discrete lesions affecting myelin of many CNS axons
  • Formation of scars (‘sclerosis’) delays/blocks AP - seen as ‘plaques’ in white matter of brain, spinal cord
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6
Q

How does Myasthenia Gravis disrupts cholinergic synaptic transmission?

A
  • Interferes with cholinergic signalling at the neuromuscular junction
  • Inflammatory disease, antibodies bind to ACh receptors in postsynaptic membrane at motor end plate
  • Severe muscle weakness particularly affects eyelids, eyes, face, throat and limb muscles
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7
Q

What is the effect of an inhibitory postsynaptic potential?

A

Moves the postsynaptic membrane potential further away from threshold (hyper-polarisation), therefore reducing the probability of the postsynaptic cell producing an action potential

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8
Q

What is the role of glial cells?

A

Support neurons

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9
Q

Define divergence and convergence in the nervous system

A

Methods of spread of information in the nervous system

  • Divergence - one neuron, signal spreads to many targets
  • Convergence - many signals affect one neuron
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10
Q

What is the cause of Guillain-Barre syndrome?

A

Inflammatory disease - inflammatory cells destroy myelin sheath

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11
Q

Where are the sympathetic preganglionic neurons located?

A

Thoracic and upper lumbar spinal cord, leave in spinal nerves T1-L3

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12
Q

Explain the clinical relevance of voltage-gated sodium channels?

A
  • Local anaesthetics - Lidocaine (NaV antagonist)
  • Pain treatment - target NaV on nociceptive terminals
  • Epilepsy - NaV antagonist
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13
Q

Describe the normal resting membrane potential of cells

A
  • More positive ions outside, more negative ions inside
  • Measured in relation to outside, RMP is negative
  • Typically -60mV to -70mV
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14
Q

How can cerebral function be investigated?

A
  1. Electroencephalography (EEG) - record electrical activity of brain, investigate cognitive response to stimulus
  2. Positron emission tomography (PET) - measures blood flow via small dose of radiation in the bloodstream, locate brain activity while performing a task
  3. Functional magnetic resonance imaging (fMRI) - measures blood flow
  4. Transcranial magnetic stimulation (TMS) - uses electromagne to stimulate brain activity, causing depolarisation or interrupted firing, interrupts brain activity while performing a task
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15
Q

Describe the sequence of events which occurs in firing an action potential in terms of movement of ions

A
  1. Sodium channels (voltage gated) open, sodium ion influx, depolarisation
  2. Rapid inactivation of voltage gated sodium channels, repolarisation
  3. Slow opening voltage-gated potassium channels open, hyperpolarisation
  4. Sodium-potassium pump rebalances potassium and sodium ions
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16
Q

What causes depolarisation and repolarisation of membranes?

A
  • Depolarisation - increased permeability of membrane to sodium ions
  • Repolarisation (+ hyperpolarisation) - increased permeability to potassium ions
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17
Q

How is an action potential propagated along an axon?

A
  • Opening of NaV during AP depolarises axon on either side, reaches threshold, opening of NaV, trigger zone = axon hillock
  • Wave depolarisation travels one way along axon
  • Destination of current depends on axon diameter + number of open pores in membrane
    • Follows path of least resistance - widest diameter and most pores
18
Q

What are the clinical signs of Guillain-Barre syndrome?

A

Progressive motor weakness, motor and sensory loss (face, limbs, trunk, diaphragm)

19
Q

List the types of glial cells in the PNS

A
  • Satellite cells
  • Schwann cells - myelination
20
Q

What is usually the first symptom of an entrapment neuropathy?

A

Paraesthesia - tingling

21
Q

Define pre- and post-ganglionic neurons of the ANS

A
  • Preganglionic - cell body in CNS, axon enters PNS
  • Postganglionic - cell body in PNS, axon supplies target organ
  • Ganglion - synpase of pre- and post-, collection of neurons which causes a swelling, where postganglionic cell body is located
22
Q

List the types of glial cells in the CNS

A
  • Ependymal - ventricles
  • Oligodendrocytes - myelination
  • Astrocytes
  • Microglia - neuropathic pain
23
Q

List disorders associated with defective myelination

A
  1. Multiple sclerosis
  2. Guillain-Barre syndrome
24
Q

What is the effect of hyperpolarisation of the membrane following the firing of an action potential?

A

Inhibition of new action potential for a few seconds

25
Q

Describe the innervation of the limbs

A
  • Nerve fibres travelling to/from limbs leave spinal cord as spinal nerves - 2 per segment
  • Pass through plexuses - brachial and lumbosacral, emerge as peripheral nerves
26
Q

List the types of neurotransmitters

A
  1. Cholinergic - acetyl choline
  2. Biogenic amines - catecholamines (noradrenaline, dopamine), serotonin
  3. Amina acids - excitatory (glutamine), inhibitory (gamma-aminobutyric acid) - GABA
  4. Neuropeptides - endogenous opiods
  5. Miscellaneous - gases (nitric oxide), pruines (adenosine, ATP)
27
Q

What is the function of the autonomic nervous system?

A

Regulates eyes, GI tract and glands, heart and BVs, lungs, reproductive and urinary systems, skin

28
Q

Explain the patterns of sensory loss which can occur

A
  1. Dermatomal - in the distribution of a spinal nerve e.g. slipped disc compressing L5, muscles supplied by spinal nerve also potentially affected
  2. Peripheral nerve injury - sensory changes in area supplied by nerve e.g. median nerve in carpal tunnel syndrome - entrapment neuropathy
  3. Longest fibres affected = stocking-glove distribution e.g. metabolic disorders such at Vitamin B12 deficiency
29
Q

Describe the clinical presentation of multiple sclerosis

A
  • Partial vision loss, blurred vision, double vision
  • Sensory changes e.g. numbness
  • Motor symptoms e.g. weakness, partial paralysis, ataxia
  • Fatigue
  • Pattern of symptoms can’t be explained by one focal lesion - widespread CNS white matter lesions
30
Q

What is the function of neurons?

A

Functional unit of nervous system:

  • Excitable
  • Conduct action potentials
  • Release neurotransmitters

Different classes of neurons with specialised structures have different functions, all neurons have input, conductile region and an output (secretory)

31
Q

Where are the sympathetic and parasympathetic ganglia located?

A
  • Sympathetic - sympathetic chain next to vertebral column
  • Parasympathetic - walls of viscera which they innervate e.g. heart wall
32
Q

Define action potential

A
  • Brief but dramatic change in membrane potential
  • If membrane potential reaches threshold value, fires action potential
33
Q

What produces the myelin sheath?

A

Oligodendrocytes in CNS, Schwann cells in PNS

34
Q

Define the equilibrium potential

A

Membrane potential when number of ions entering cell = number of ions leaving cell (no net gain/loss)

Calculated using Nernot equation

35
Q

How does Botulism disrupt cholinergic synpatic transmission?

A
  • Distrupts cholinergic signalling at the neuromuscular junction
  • Clostridium bacteria produce botulinum toxin (contaminated food), disrupts exocyotsis preventing ACh release
  • Skeletal muscle weakness, paralysis of diaphragm (respiratory failure)
36
Q

How do ions move across membranes?

A
  • Ion channels - voltage-gated, ligand-gated (neurotransmitter, drug etc.)
  • Ion pump - active transport, requires ATP
37
Q

How is resting membrane potential measured?

A

Using electrophysiology - intracellular and extracellular electrodes

38
Q

List the parts of neurons

A
  • Dendrites - input
  • Cell body (soma)
    • Nucleus
  • Axon hillock
  • Axon - transmission
    • Node of Ranvier
    • Myelin
  • Synapse
    • Pre- and post-synaptic terminals
39
Q

Describe the sequence of events which occurs during synaptic transmission

A
  1. AP enters presynaptic terminal
  2. Calcium entry through voltage-gated calcium channel
  3. Docking of synaptic vesicled containing neurotransmitters
  4. Neurotransmitters released (exocytosis)
  5. Neurotransmitter binds to and activates receptors on post-synaptic membrane, ions (sodium/chlorine) enter cell
  6. Depolarisation (excitation) or hyperpolarisation (inhibition)
40
Q

Describe summation of post-synaptic potentials

A
  • When combined, potentials can depolarise the membrane to reach firing threshold
    • Temporal summation - increased frequency of firing
    • Spatial summation - firing at multiple sites
41
Q

What is the function of the nodes of Ranvier?

A

Gaps in myelin - allows for saltatory conduction (action potential jumps from node to node), faster transmission

Medicine Year 2 (41 decks)

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