WEEK 9 Flashcards
What are the 4 components of the CNS?
- The vertebrate nervous systems functions to detect, relay, integrate and respond appropriately to conditions in the outside world. 2. It is composed in the main of glia and neurones, of which glia are the more numerous 3. Glia play a wide variety of roles: structural support and shock absorption 4. Neurones are electrically excitable cells able to convey, integrate and respond to stimuli by changing the resting membrane potential.
What is the generalised structure of nerve cells? Explain the roles of their different functional regions.
Information arrives at the cell body of a neurone via dendrites where it is assimilated and processed. - Dendrites receive information from axons of other cells and convey it towards the cell body. - Processed information is then digitised and transmitted along the axon. At the end of the axon the information is passed to the target (muscle or neurone) via boutons (swellings at the end of the axonal process that make contact with other neurone cells or muscle.) There is a large variation in neuronal phenotype: multipolar (most abundant in CNS), bipolar & pseudounipolar neurons exist
The speed at which the nerve impulse travels along the axon depends what two main factors? Describe how these factors affect the speed.
- The DIAMETER of the axon 2. Whether the axon is MYELINATED or not The larger the diameter of the axon, the lower the resistance is. - Passive movement of charge along the axon is easier with less resistance, therefore larger axons have faster passive charge movement. The more surface area there is on an axon, the higher its capacity to store charge across its membrane. - Capacitance is the amount of charge accumulated the membrane, the ability to maintain a steady state charge across the membrane. - The higher the capacitance the harder it is for charge to cross over the membrane, i.e. to overcome the repellant force of charge accumulated there. - The characteristics of an UNMYELINATED axon are a compromise between these two factors.
Define (i) action potential threshold (ii) absolute refractory period (iii) relative refractory period.
(i) The point at which a depolarising stimulus must reach for an action potential to be generated. (ii) The cell cannot be stimulated to its threshold potential, all Na+ channels closed (inactivation gate). (iii) A stronger stimulus than normal could induce an action potential, some Na+ ready but more K+ channels are open than usual, cell is still hyperpolarised.
What is the role of supporting cells (Schwann cells and oligodendrocytes) in speeding impulse conduction velocity through saltatory conduction?
SCHWANN CELLS - Form the myelin sheath around peripheral axons (PNS). A single Schwann cell forms the myelin around an axon for a single internode of one neurone. OLIGODENDROCYTES - Form the myelin in the CNS (white matter). These cell types have different embryological origins and so produce myelin which has differences in chemical composition. Multiple Sclerosis attacks oligodendrocyte myelin and so the CNS is differentially affected.
What does the voltage dependent Na channel help to do?
Set the refractory period of the action potential
How does an action potential move along an axon?
It’s a combination of passive diffusion currents along the axon and active currents through ion channels
What are the holes in the axons? Why are they there?
The holes are ion channels which are always open. These are essential to set the resting membrane potential of the cell
Define the terms (i) local circuits and (ii) saltatory conduction applied to nerve axons.
(i) LOCAL CIRCUITS (currents) - Voltage gated Na channels open and allow positive Na ions into the axoplasm. These ions set up a more positive potential which, when great enough, causes the next Na channel to open. - As the current leaks across the membrane, the magnitude of the depolarisation is degraded. Larger diameter axons with fewer channels transmit faster than narrow axons or ones with more channels – leaky undersea cable. (ii) SALTATORY (jumping) CONDUCTION - In this situation, the local currents can extend further as the normal leakage is curtailed by the myelin sheath. In this way the conduction of the nerve impulse flows rapidly through the inside of the axon to the node, where it slows and ionic depolarisation (action potential) takes place. Note only a few ions are needed to do this so there is an energy saving. And then the fast conduction along the inside of the axon resumes afresh.
What is the relationship between the sodium pump and action potentials?
The sodium pump is not involved in the action potential itself. - it fine tunes the resting membrane potential, and makes the final potential about 3mV more depolarised than diffusion alone would
In myelinated fibres, where are action potentials produced?
node of Ranvier
What is the code that is used in the CNS?
The action potential frequency
What are the 5 components of illness representation (illness beliefs)? Describe/Explain them.
- IDENTITY = Symptoms experienced by the person as well as person’s label for the disease (pts/drs own diagnosis/label) I have a cold (‘the diagnosis’ = ABSTRACT), with a runny nose and cough (‘the symptoms’ = PERCEPTUAL) 2. CONSEQUENCES = Pts perceptions of the possible effects of the illness on their life. E.g. physical, emotional, financial, social …“My cold will prevent me from going to the pub on Friday night, which will prevent me from seeing my friends” 3. TIMELINE = Pts beliefs about how long illness will last, whether it’s acute, chronic, or cyclical “My cold will be over in a couple of days” 4. CAUSE = Perceived cause of illness, e.g. biological (virus etc), or psychosocial (stress or some health behaviour such as smoking) “My cold was caused by a virus” OR “I got a cold because I was very stressed and run down” 5. CURE/CONTROLLABILITY = Pts beliefs about whether illness can be cured and the extent to which the outcome of their illness is controllable (by themselves or by powerful others) “If I rest and drink lots of fluids, my cold will go away” OR “If I go get medicine from my doctor, my cold will go away”
What are the 3 steps involved in the concept of self-regulation?
- Identification of the goal: e.g. getting to school in time for class in the morning. 2. Selecting a strategy to achieve that goal and implementing: e.g. drive 3. Decide whether the implemented strategies achieved the goal or not . If not, try another strategy. E.g. take the bus
What is health promotion?
The process of enabling people to increase control over, and improve, their health.
What are the 3 major health challenges?
Smoking Obesity Alcohol
What are downstream and upstream influences on health? Explain them both.
DOWNSTREAM INFLUENCES are individual-level determinants or immediate causes such as: - Exposures (e.g. hazardous neighbourhood settings, infectious agents, adverse life events, etc.) - Behaviours (e.g. smoking, diet, exercise, etc.) - Personal strengths or vulnerabilities (e.g. coping styles, resilience, etc.) UPSTREAM INFLUENCES are social determinants or the “causes of the causes” such as: - Population-wide influences (e.g. education, taxation, labour and housing markets, crime and policing) - Most fundamental causes are international political and economic forces, and the forms of social stratification in a given society.
Explain top-down and bottom-up approaches to health promotion.
TOP-DOWN = Priorities set by health promoters who have the power and resources to make decisions and impose ideas of what should be done. BOTTOM-UP = Priorities set by people themselves identifying issues that they perceive as relevant
Describe the 5-tier public health impact pyramid.
On the health impact pyramid as there is an increasing population impact (top to bottom) this is looking upstream. Conversely looking at the bottom to top (increasing individual effort needed) this is looking downstream
What are the 5 approaches to health promotion? Describe them.
- MEDICAL APPROACH: Aim - Free from smoking-related disorders (e.g. lung disease, heart disease, etc.) Activity: Primary prevention - Prevent onset of illness (e.g. encouraging non-smoking) Secondary prevention - Prevent progression of illness (e.g. smoking cessation) Tertiary prevention - Prevent further disability and suffering in those already ill (e.g. patient education, etc.) 2. BEHAVIOUR CHANGE: Aim - Change from smoking to not smoking Activity - Persuasive education - Prevent non-smokers from starting - Persuade smoker to stop 3. EDUCATIONAL APPROACH: Aim - Promote understanding of the effects of smoking on health to inform decision whether to smoke or not (and act on that decision) Activity - Provide information about effects of smoking - Help explore values and attitudes and come to a decision - Help learn how to stop smoking (if they want to) 4. EMPOWERMENT APPROACH: Aim - Smoking only considered if identified as a concern by the “community” Activity - Identify what (if anything) can be done about smoking (cessation or initiation prevention) 5. SOCIETAL CHANGE APPROACH: Aim - Make smoking socially unacceptable or make the healthy option (not smoking) the easy option Activity: Healthy public policy = Smoke-free policy = Increase age of smoking = Increase tax on tobacco products = Limit tobacco advertising and sponsorship
Define the following basic epidemiological terms (i) mortality rate (ii) incidence (iii) prevalence (iv) patterns of outcome occurrence (v) outcomes (vi) exposures.
(i) The no. of deaths in a given area/period, or from a particular cause. Meaningful statistics need: 1. A denominator pop (health board, city, hospital, recruited to a study) 2. Time-frame (person-time, n-year follow up) WITHOUT these death rates are meaningless (ii) Number of new cases in a specific time period. Rate = no.new ppl w.outcome over time period / total no.ppl in group at risk * 100,000 (iii)The proportion of a population found to have a condition. Point = at a specified time. Period = over a specified time period (iv) Sporadic= occasional cases occurring irregularly Endemic= persistent background level of occurrence (low to moderate level) Epidemic = occurrence in excess of the expected level for a given time period Pandemic = epidemic occurring in or spreading over more than one continent. (v) Death, Hospitalisation, First diagnosis with a disease, Recurrence (e.g. cancer), Quality of Life, Surrogates (e.g. blood pressure, lung function etc.) (vi) Non Modifiable = Age, sex, genotype. Modifiable = smoking, weight, diet, alcohol consumption. Interventions = a special kind of exposure. E.g. drug therapy, surgery, lifestyle advice.
How do you calculate and interpret appropriate effect estimates?
Risk = (No. outcomes in group / No. people in a group) x 100 Relative Risk (RR, Risk Ratio) = Risk in exposed / Risk in unexposed Relative Risk Reduction (RRR) = (1-RR) x 100 Absolute Risk Reduction (ARR, Risk Difference) = Risk in unexposed - Risk in exposed. Number needed to treat (NNT) = 1 / Absolute Risk Reduction
Describe and interpret confidence intervals.
Thought of “as a range of possible values” Presented for any statistic/effect measure Values near limits less plausible than those in middle Wider the interval, greater the uncertainty Useful in appraising published research
What is meant by confounding and bias?
CONFOUNDING: True relationship “confused” by a third factor. BIAS: Systematic error = What data are collected, How data are collected, How data are analysed, How data are interpreted, How data are reported Bias leads to wrong conclusions concerning: Effectiveness and Causality
Describe the hierarchy of evidence, and differentiate the various epidemiological study designs (HINT: there’s 4.)
- CROSS SECTIONAL STUDY: Sample a population Estimate the population: Different exposures Different signs/symptoms Different outcomes Use data: To descirbe prevalence/burden To explore associations 2. CASE-CONTROL STUDY: Select cases with an outcome Select controls with the outcome Explore EXPOSURES in cases and controls Identify association 3. COHORT STUDY Select people without an outcome Classify according to an exposure Follow up: Prospective Retrospective Compare RISK of disease in exposed and unexposed. 4. RANDOMISED CONTROLLED TRIAL (RCT) Random allocation: Intervention Control/comparator Compare RISK of outcome in intervention and control groups.
What are the 9 criteria for inferring causality? Describe them.
- STRENGTH (effect size) - A causal link is more likely with strong associations 2. CONSISTENCY (reproducibility) - A causal link is more likely if the association is observed in different studies and different sub-groups 3. SPECIFICITY - A causal link is more likely when a disease is associated with one specific factor 4. TEMPORALITY - A causal link is more likely if exposure to the putative cause has been shown to precede the outcome 5. BIOLOGICAL GRADIENT- A causal link is more likely if different levels of exposure to the putative factor lead to different risk of acquiring the outcome 6. PLAUSIBILITY - A causal link is more likely if a biologically plausible mechanism is likely or demonstrated 7. COHERENCE - A causal link is more likely if the observed association conforms with current knowledge 8. EXPERIMENT - A causal link is very likely if removal or prevention of the putative factor leads to a reduced or non-existent risk of acquiring the outcome 9. ANALOGY - A causal link is more likely if an analogy exists with other diseases, species or settings
What factors affect utilisation of health services? (HINT: there’s 6 factors)
physical, physiological, social, environmental - differences in symptom perception - influence of prior experience, lay referral - individual health beliefs and ideas held (HBM) - cost-benefit evaluation of seeking medical attention - social and emotional factors - quality of relationship with doctor
What 4 factors affect an individuals symptom perception?
- strength of underlying physical sensation 2. tendency to pay attention to internal states 3. degree to which external stimuli competes for attention 4. variety of cognitive, social, emotional processes
The deeper layer, or intrinsic (proper) muscles of the back that keep the vertebral column upright and in extension against gravity. List and describe the superficial group.
Splenius Capitis and Cervicis Ligamentum Nuchae, C and T Spines, to Trans Processes and Skull laterally Together they extend; Alone they rotate and laterally flex
List and describe the intermediate group of intrinsic muscles.
ERECTOR SPINAE 3 columns from lateral to medial From spines and supraspinous ligaments to ribs, trans processes and skull From lateral - medial: Iliocostalis, Longissimus, Spinalis Together – extend; Alone – laterally flex
List and describe the deep group of intrinsic muscles.
Transversospinalis, from trans processes upwards to spines Multiple small muscles in between the spines, in between the trans processes, and from trans processes to ribs Extend, rotate and laterally flex
Discuss the utility of early years’ intervention in prevention. What is a risk factor for future violence?
Inappropriate aggression can develop during the first 24 months following birth:
- Physical aggression is a developmentally appropriate behaviour during early childhood (e.g. play fighting)
- BUT, it needs to be appropriately regulated to ensure the child learns the appropriate alternatives that can be used when necessary.
The early years environment is important for cognitive, language, emotional, and behavioural development. It also lays the foundation for future health.
Child maltreatment is one risk factor for future violence
Describe the process of chemical neurotransmission from filling of presynaptic vesicles to neurotransmitter activation and subsequent signalling by receptors.
Small-molecule transmitters and Peptide transmitters - refer to image attached
Post-synaptic membrane: Embedded in the postsynaptic membrane are membrane spanning proteins called receptors. They all belong to either the G protein-linked receptor group (metabotropic receptors), to to the ligand gated ion channel group (ionotropic receptors). The NT is an agonist, designed to bind to the receptor causing it to activate the post-synaptic membrane channel. NTs have a specific shape and charge, the receptor has a complementary shape and charge. Antagonist blocks activation of these ionic channels often by occupying the binding site.
Receptors are sensitive to NTs and the binding of NTs to receptors causes a change in the conformation of these receptors which in most cases open a pore which allows specifically selected ions to travel through (ionotropic). Metabotropic act by a process of a cascade event which causes an ion channel to open or a process in the nucleus of the cell indirectly.
Ionotropic Receptors: When the ligand binds to its binding site, it induces a conformational change in the receptor such that a pore from the inside to the outside of the cell is formed. The pore is characteristic of the receptor type in both size and charge, which means each receptor can be specific to a single or varied number of ions. The passage of ions into and out of the cell changes the voltage of the cell, either to depolarise (net positive charge) the cell or hyperpolarise (net negative charge) the cell. This can work as an inhibitory pathway if it allows hyperpolarisation as the cell becomes more negative.
Metabotropic Receptors: The NT binds to the receptor changing its binding site ever so slightly on the cytosolic side, allowing the G protein to bind to it. This causes a change in conformation of the G protein which changes a GDP for a GTP (binds another phosphate, increasing in energy, becomes charged) and it also “breaks”, one of the three piece molecule is lost and “floats around”. These changes in conformation allow the G protein to interact with the inactive membrane bound enzyme, activating it such that it can produce its own messengers. These messengers bind to the ion channel activating it and allowing movement of ions in and out of the cell. Upon activating the enzyme the G protein complex loses a phosphate (GTP —> GDP) which again changes its conformation allowing it to rebind to the “lost” piece “floating around the cell”. Now it is ready to interact with the receptor again should it receive a NT.
Define (i) Spatial summation (ii) Temporal summation. (HINT: think of shovel analogy)
(i) When excitatory potentials from many different presynaptic neurons cause the postsynaptic neuron to reach its threshold and fire.
(ii) When a single presynaptic neuron fires many times in succession, causing the postsynaptic neuron to reach its threshold and fire.
As an analogy, spatial summation is like using many shovels to fill up a hole all at once. Temporal summation is like using a single shovel to fill up a hole over time. Both methods work to fill up the whole (the postsynaptic neuron reaches its action potential threshold).
