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PHCY320 - Neurology Exam Latest Update
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PHCY320 - Neurology ExamLatest Update
Briefly describe the length, location and function of a motor neuron, sensory neuron and
interneuron - Answer Motor neuron (efferent)
- message from brain or spinal cord to muscles, organs
- short dendrites, long axons
- dendrites and cell body in the spinal cord, axon outside the spinal cord
- conduct impulse to an effector (muscle or gland)
Sensory neuron (afferent)
- message from receptors to brain or spinal cord
- long dendrites, short axon
- cell body and dendrite outside of the spinal cord; cell body in a dorsal root ganglion
- conduct impulse to the spinal cord
Interneuron
- message fro sensory neuron to motor neuron
- short dendrites, short or long axon
- entirely within the spinal cord or CNS
- connect sensory neuron with appropriate motor neuron
Discuss some conventional and non-conventional neurotransmitters - Answer
Conventional
* Small molecules
- amino acids: glutamate, glycine, GABA
- biogenic amines: dopamine, NA, A, serotonin, histamine
- purines: ATP, adenosine
- acetylcholine
,* Neuropeptides
- enkephalin, endorphins, substance P, neuropeptide Y
Non-conventional
- endocannabinoids
* Gasotransmitters
- carbon monoxide, nitric oxide
Glutamate is main excitatory NT in CNS
GABA is main inhibitory NT (brain)
Glycine is main inhibitory NT (spinal cord)
Acetylcholine and dopamine effects depend on which of its receptors are present on
postsynaptic cell
Discuss the drugs affecting dopaminergic neurons - Answer Synthesis
- L-DOPA facilitates synthesis of DA by acting as a precursor (agonist)
Storage
- reserpine blocks DA uptake into vessicles (antagonist)
Action
- selegeline prolongs action of DA by blocking degredation (MAO-B inhibitor) (agonist)
Release
- amphetamine increases release of DA (agonist)
Reuptake
- cocaine and amphetamine blockd DA reuptake (agonist)
Discuss the drugs affecting serotonergic neurons - Answer Synthesis
- alpha-methyltyrosine inhibits synthesis of 5-HT (antagonist)
Release
- fenfluramine facilitates the release of 5-HT (agonist)
Reuptake
- fluoxetine blocks reuptake of 5-HT (agonist)
,Describe the neurotransmitters that regulate sleep/wakefulness - Answer Regulation of
sleep/wakefulness is complex
Cortical arousal regulated by:
- NA (locus coeruleus)
- cholinergic pathway (brainstem)
- histamine (tuberomamillary nucleus)
- serotonin (raphe nucleus)
- orexins/hypocretins (peptide neurotransmitters) promote wakefulness
Sleep induced by: GABA, melatonin and galanin
Drugs potentiating GABA(A) transmission
1. Hypnotic (sleep inducing properties)*
2. Sedative (moderating excitement and calming)*
3. Anxiolytic (anxiety-relieving)
Explain the mechanisms of action, and give examples of drugs that produce hypnotic
effects - Answer GABA effects
- (gamma)-aminobutyric acid, major inhibitory neurotransmitter
- decrease neuronal excitability
- activation = decreased neuronal excitation, decrease CNS function
Benzodiazepine receptor agonists (e.g. triazolam, temazepam, diazepam, flurazepam,
lorazepam)
- dose related hypnotic effects
- facilitate onset and duration of sleep
- alter NREM:REM
* Healthy = respiratory change c.f. natural sleep
- pulmonary/respiratory disease: respiratory and CV depression
* Differing rate of onset, duration, rebound insomnia
* Pharmacodynamics - positive allosteric modulator of GABA(A) R
- GABA(A) R abundant in CNS
, - 'tonic' inhibition
- [Cl-](intracellular) < [Cl-](extracellular)
- hyperpolarisation
- excitation less likely
* Pharmacokinetics - differing mg potency, when dosed appropriately have similar
efficacy
* Choice: PK and situational
- potency: hydrophobicity
- plasma protein binding (decreased [drug](free)), appears less potency in vivo
- duration - diazepam (rapid onset, long acting) vs. midazolam (rapid onset, short acting)
> short half-life means generally awake once worn off
- metabolised by CYP3A4 (CYP2C19)
> inhibitors = ketoconazole, macrolides
> inducers = rifampicin, omeprazole, nifedipine
> caution: impaired hepatic function
* Caution: increased potency with low albumin (e.g. haemodilution, liver dysfunction)
Dark side of benzos
- problems as short term and long-term therapy
* SEs related to sedation, muscle relaxation
- drowsiness (driving, machinery operation)
- ataxia, muscle weakness (falls in elderly), respiratory depression
- greatest risk, least benefit in elderly
* Abuse and dependence
- addictive
- withdrawl symptoms after 4-6 weeks continuous use
- abuse potential - rapid onset, high potency, brief duration
* Problems on withdrawal
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