Physiology and pharmacology Flashcards
Which part of a neurone RECEIVES INPUTS from other neurones and which part CONVEYS OUTPUTS to other neurones?
Dendrites receive inputs
Axons carry outputs
Where is the site of initiation of the “all or none potential”?
Axon hillock
What type of neurones are peripheral neurones?
Unipolar
What type of neurones are dorsal root ganglion neurones?
Pseudounipolar
What type of neurones are retinal neurones?
Bipolar
What type of neurones are LMN?
Multipolar
What is the resting membrane potential of a neurone?
-70mV
The distance over which current spreads depends upon which two factors of a neurone?
Membrane resistance
Axial resistance of the axoplasm
What cell type surrounds axons in the CNS vs in the PNS?
Schwann cells in the PNS
Oligodendrocytes in the CNS
What term is used to describe how one action potential jumps from one node of ranvier to the next?
Saltatory conduction
What is the main excitatory neurotransmitter?
Glutamate
What is the main inhibitory neurotransmitter?
GABA
What is meant by spatial vs temporal summation?
Spatial summation - Many inputs converge on a neurone to determine its output
Temporal summation - A single input determines output
Merkel cell neurite complexes are sensory receptors of glabrous skin, what is their classification?
SA1
Slow adapting type 1
(type 1 = small receptive field)
Meissner corpuscles are sensory receptors of glabrous skin, what is their classification?
FA1
Fast adapting type 1
(type 1 = small receptive field)
Pacinian corpuscles are sensory receptors of glabrous skin, what is their classification?
FA2
Fast adapting type 2
(type 2 - large receptive field)
Drugs which are agonists vs antagonists of NA channels have what effects on neurotransmission?
Agonists of Na channels open the channel causing sodium influx and excitation
Antagonists of Na channels close the channels causing inhibition
Drugs which are agonists vs antagonists of K channels have what effects on neurotransmission?
Agonists of K channels cause K outflow form the cell causing inhibition
Antagonists of K channels retain K in the cell causing excitation
What is the difference between inotropic and metabotropic receptors?
Inotropic receptors form an ion channel pore. Metabotropic receptors are indirectly linked with ion channels on the plasma membrane through signal transduction mechanisms (often G proteins)
Inotropic receptors - rapid gating of ion channels
Metabotropic receptors - slower gating of ion channels
What is meant by ‘quanta’?
The amount of neurotransmitter release from a single vesicle
What is meant by ‘lateral inhibition’?
When one neurone is active, it inhibits the activity of its neighbours via inhibitory interneurons (this sharpens stimulus perception)
What is ‘neglect syndrome’?
Damage to one side of the brain results in the patient believeing the contralateral side of the world doesn’t exist and may even disclaim the existence of that side of their body
E.g - Usually due to damage to the right parietal cortex - patient doesn’t recognise the left side of their body
What terms are used to describe muscles which work together and muscles which oppose eachother?
Muscles which work together = synergists
Muscles which oppose eachother = antagonists
Axons of LMNs exit the spinal cord via which roots?
Ventral roots
they then join with dorsal roots to form a mixed spinal nerve
Motorneurones innervating the distal and proximal musculature are mainly found in which segments of the spinal cord?
Cervical and lumbar-sacral segments
An a-MN and al the skeletal muscle fibres which innervate it are collectively known as what?
A motor unit
smallest functional component of the motor system
The collection of a-MNs that innervate a single muscle is known as what?
A motor neurone pool
Describe the properties of slow-oxidative (type 1) muscle fibres?
Slow contraction and relaxation
Fatigue resistant
Red fibres/ dark meat (due to high myoglobin content)
Describe the properties of fast (type 2a and 2b) muscle fibres?
Fast contraction and relaxation
Fatigue resistant
“Red meat”
Fast contraction and relaxation
NOT fatigue resistant
“White meat”
Poor vascularisation
What is the “Henneman size principle”?
Smaller a-MNs have a lower threshold than larger
Small motor units are more easily activated and trained, so motor units are recruited from smallest to largest.
What is the function of golgi tendon organs?
Located at the junction between muscle and tendon these monitor changes in muscle tension and regulate tension to protect muscles from overload.
Where are free nerve endings found and what is their role?
Connective tissue
Nociceptive function
Where are golgi-type endings found and what is their role?
Ligaments
Protective role
Where are paciniform endings found and what is their role?
Found in periosteum
Acceleration detectors
Where are ruffini endings found and what is their role?
Found in the joint capsule
Static position and speed of movements
What are the three mechanisms for amplification of sound in the middle ear?
Area ratio of the eardrum to the stapes footplate
Lever action of the ossicles
Buckling of the eardrum
The 2 different types of hair cells within the ear are separated by what structure?
Rods of corti
Which type of hair cell are the main source of afferent signal in the VIII nerve?
Inner hair cells
Which type of hair cell controls stiffness and amplifies membrane vibration?
Outer hair cells
Which type of movements do the semicircular canals vs the saccule and utricle detect?
Semicircular canals
- sense head rotation
Saccule and utricle (otolith organs)
- sense translational movement and gravity
Describe the following;
Vestibulo-ocular reflex
Vestibulo-colic reflex
Vestibulo-spinal reflex
Vestibulo-ocular reflex - eyes stay still while head moves
Vestibulo-colic reflex - head stays still while body moves
Vestibulo-spinal reflex - adjustments of posture for rapid changes in position
Describe the differences between rods and cones in the eye
RODS Seeing in dim light - achromatic Peripheral retina High convergence, low density High sensitivity, low acuity
CONES Seeing in normal light - chromatic Central retina Low convergence, high density Low sensitivity, high acuity
What is the striate cortex responsible for?
It is the primary sensory cortical area for vision in the brain
*Damage to this area causes scotomas (blind regions in the field of vision)
What is meant by reciprocal inhibition?
Muscles on one side of a joint relax to accommodate contraction on the other side of the joint
(extensor contract, flexors relax and vice versa)
What is the myotatic reflex?
The stretch reflex!
Muscle contraction in response to stretching within the muscle
(e.g contraction of an extensor will stretch an antagonistic flexor)
What is meant by hyperalgesia and allodynia?
Hyperalgesia - increased perception of painful stimuli
Allodynia - perception of pain even when the stimulus is non noxious
Describe the difference between Aδ-fibres and C-fibres, the two subtypes of nociceptors
Aδ-fibres
- Thinly myelinated
- Mediate first/ fast pain
- Respond to mechanical stimuli and very high termperatures
C-fibres
- Unmyelinated
- Mediate second/ slow pain
- Polymodal - respond to mechanical, thermal and chemical stimuli
What is viscerosomatic pain
Pain caused by inflammatory exudate from an organ coming into contact with the body wall (e.g ruptured appendix)
What are the steps on the WHO analgesic ladder?
1 - NSAID/ paracetamol (aspirin, diclofenac etc)
2- Weak opioid (codeine, tramadol etc)
3- Strong opioid (e.g morphine, oxycodone etc)
What is the difference between opiates and opioids?
Opiates = substances extracted from opium Opioids = agents acting on opioid receptors
Describe the gate control theory
Non-painful input closes the gates to painful input therefore suppressing pain sensation
What regions of the brain are involved in pain perception?
Cortex
Amygdala
Thalamus
Hypothalamus
What 3 brainstem regions are involved in the regulation of pain?
Periaqueductal grey (PAG)
Nucleus raphe magnus (NRM)
Locus coeruleus (LC)
List some of the major adverse effects of opioids
Apnoea Orthostatic hypotension Constipation Confusion Hallucinations
PO admission of morphine is best for chronic pain. Which forms of the drug are used for immediate vs sustained release?
Oramorph = for immediate release
MST continus = for sustained release
What is the side effect to be aware of with codeine?
Constipation
When is fentanyl used?
IV for maintenance analgesia (only given by an anaesthetist)
Transdermal or buccal delivery for chronic pain
When is pethidine used?
Used for acute pain - particularly for labour
Pethidine shouldn’t be used in conjunction with which drug class?
Pethidine shouldn’t be used in conjunction with MAO inhibitors (used to treat depression) as it may cause convulsions and hyperthermia
When is buprenophine used?
In chronic pain states with patient controlled injection systems
Which patients should avoid tramadol?
Epileptic patients
What is important about the half life of methadone?
It has a long plasma half life (>24 hours) so is useful in treating patients with chronic pain/ terminal cancer and heroin withdrawal
When is naloxone used?
To reverse the effects of opioid toxicity
What is important about the half-life of naloxone?
It has a very short half life, meaning each individual dose needs to be titrated and the patient closely monitored
*NB naltrexone is similar to naloxone but can be given PO and has a much longer half life
What effect can naloxone have in opioid addicts?
Naloxone can trigger an acute withdrawal response in opioid addicts and patients who require high dose opioid analgesia regularly
What is the mechanism of action of NSAIDs?
Inhibit COX enzymes which inhibits the synthesis and accumulation of prostaglandins
What are some of the side effects of NSAIDs to be aware of?
Peptic ulcers
Nephrotoxicity
Why is paracetamol not considered an NSAID?
It has no anti-inflammatory activity and only acts centrally
List some conditions which are examples of causes of neuropathic pain
Trigeminal neuralgia
Diabetic neuropathy
Post-herpetic neuralgia
Phantom limb pain
What drug class do gabapentin and pregabalin come under?
Anti-epileptics
They reduce the expression of some channels on damaged sensory neurones
- they are therefore useful in conditions like shingles
What drug class does amitriptyline come under?
Tricyclic antidepressant
What is the first line treatment for trigeminal neuralgia?
Carbamezepine
Why is metoclopromide for GI issues contraindicated in patients with parkinson’s? What medication can be used instead?
It is a dopamine receptor antagonist so can exacerbate symptoms
Domperidone can be used instead as it doesn’t cross the BBB
Why is haloperidol contraindicated in patients with parkinson’s disease? What medication can be used instead to manage psychosis?
Haloperidol is contraindicated in Parkinson’s because it causes EPSE.
Psychosis should instead be managed with quetiapine.
What drug is used to treat Parkinson’s? What are it’s main side effects?
Levodopa
Main side effects; dyskinesia and drug resistance
