Module 5 Flashcards
What part of a neurone transmits away from its cell body?
The axon
What are the main (structural) differences between motor and sensory neurones?
Motor neurones have no dendron, only dendrites, and sensory neurones have their cell bodies in the ‘middle’ of the cell, with axons and dendrons and roughly equal length
What does a Schwann cell do?
It lays down up to twenty phospholipid bilayers around some neurones, forming a ‘myelin sheath’
What are the gaps called between the sheaves of myelinated neurones?
Nodes of Ranvier
What do sensory receptors do?
Act as a transducer - they each convert one specific type of stimulus into a nerve impulse
Name the four broad types of sensory receptor?
Mechanoreceptor
Chemoreceptor
Thermoreceptor
Photoreceptor
Describe and explain the role of the Pacinian Corpuscle and how it works
The Pacinian Corpuscle is a mechanoreceptor abundant in the skin, fingers and feet, which detects pressure. When pressure is applied to the receptor, it stretches the stretch-mediated sodium ion channels in the membrane, causing sodium ions to flood into the dendron and fire an action potential
What is the approximate potential difference across a resting potential, and how is it maintained?
About -70mV. The sodium-potassium ion pump pumps 3 sodium out for every 2 potassium it pumps in. Almost all of the voltage-gated sodium ion channels are closed but most potassium ion channels are open - making an overall charge gradient across the axon. The neurone is ‘polarised’
Describe the events of an action potential
Stimulus triggers voltage-gated sodium ion channels to open - causing sodium ions to flood in. If the ‘threshold’ is exceeded, this influx causes other ion channels to open and more ions to flood in (positive feedback loop, at about +40mV the membrane, is considered depolarised
How is the membrane of a neurone repolarised?
The membrane becomes more permeable to potassium ions and hence, they diffuse out of the membrane down their electrochemical gradient, reducing the charge in the axon until ‘hyperpolarisation’ occurs (axon < -70mV) causing the potassium channels to close and allows the resting potential to be restored
How does the mechanism of action potential propagation ensure a unidirectional impulse?
The action potential propagates a ‘wave of depolarisation’ through the neurone, followed by its repolarization (known as the refractory period) stopping the impulse being conducted backwards. Think of it like a Mexican wave!
What is saltatory conduction?
When depolarization occurs only across the nodes of Ranvier, creating ‘local circuits’ to more efficiently transmit the impulse (It effectively ‘jumps’ the myelin sections)
Which 3 factors have the highest influence on an axon’s speed?
Presence of myelin sheath, Diameter and temperature
What is the strength of an impulse related to?
It’s frequency of impulse, NOT it’s speed or anything
What is the neurotransmitter released from cholinergic synapses, and what is the basic nature of the neurotransmitter?
AcetylCholine (ACh), excitatory (depolarises the membrane)
Name an Inhibitory neurotransmitter
GABA, inhibitory (hyperpolarizes the membrane)
What happens when an action potential reaches a typical synapse?
The action potential’s ‘wave of depolarisation’ causes voltage-gated calcium ion channels on the presynaptic knob to open, allowing calcium ions to flood in. The influx of calcium ions causes the vesicles in the presynaptic knob to fuse to the presynaptic membrane and release the neurotransmitter (say, ACh) by exocytosis, to diffuse over the synaptic cleft
What happens at the post-synaptic membrane when a neurotransmitter has been released?
The neurotransmitter (probably ACh) will attach to sodium ion channels on the postsynaptic membrane and cause them to open, thus allowing sodium ions to flood in and propagate the action potential
What happens to ACh after it has propagated the action potential?
It is hydrolysed by Acetylcholinesterase, which returns acetate and choline to the presynaptic knob to be regenerated
What are the two forms of neuronal summation?
Spatial and temporal
Describe briefly the main organisation of the mammaliam nervous system
CNS and PNS. From PNS leads Autonomic (subconscious) and Somatic. From Autonomic leads Sympathetic Motor (flight or flight) and Parasympathetic Motor (relax/slowing)
What are the features of somatic neurones?
Heavily myelinated
ACh transmitter
What are the features of autonomic sympathetic neurones?
Lightly myelinated preganglionic neurones
Unmyelinated postganglionic neurones
NA transmitter
What are the features of autonomic parasympathetic neurones?
Lightly myelinated preganglionic neurones
Unmyelinated postganglionic neurones
ACh transmitter
What does the cerebellum control?
Muscle movement and posture
What does the medulla oblongata control?
Contains regulatory centres and coordinates reflexes
What does the hypothalamus do?
Autonomic control hub, regulating sleep, hunger, aggression, blood composition, and temperature and also produces some hormones
What does the pituitary gland do?
Anterior: controls hormones like FSH etc.
Posterior: releases ADH
Describe the features of skeletal muscle
Voluntary, striated and regularly arranged. They contract quickly for short periods of time and are multinucleate
Describe the features of cardiac muscle
Involuntary, specially striated and branched (for simultaneous contraction) of an intermediate speed. Muscle is uninucleate and myogenic
Describe the features of smooth muscle
Involuntary, non-striated with no regular arrangement. Contract slowly, but for long periods of time. Also uninucleate
Describe the gross structure of muscle tissue
Bunches of myofibrils surrounded by a sarcoplasmic reticulum (containing the nuclei), encased by a sarcolemma, infoldings in the sarcolemma are called t-tubules
Describe the structure of myofibrils
A ‘lattice’ of Actin (thinner filament) and Myosin (thicker filament)
What is a sarcomere?
Functional unit of the muscle, one sarcomere is defined as the distance between two Z-bands
What is the sliding filament model/theory?
Myosin filaments pull Actin inwards towards the centre of the sarcomere. The sarcomere is shortened and the H-zone becomes narrower
When a muscle contracts, what happens to the length of the dark and light bands?
The light band gets narrower but the dark band remains the same length
Describe the mechanism of muscular contraction
When an impulse reaches an NMJ, the depolarization travels deep into the sarcolemma (down t-tubules) and opens calcium ion channels in the sarcoplasmic reticulum. The calcium ions bind to troponin pulling tropomyosin out of the way of the actin-myosin binding site. Once attached, the myosin head flexes and pulls the filament along, and releasing ADP. This lets ATP bind to the head of the myosin and pulls it off. The myosin head can re-attach further up and repeat. Think of it like the oars of rowing!
What is aerobic respiration used for?
Long periods of low-intensity exercise using ATP from oxidative phosphorylation
What is anaerobic respiration used for?
Short periods of high-intensity exercise using ATP from glycolysis, producing lactic acid from pyruvate
What are creatine phosphate reserves used for?
Instants of vigorously intense exercise using creatine phosphate to immediately reform ATP
What does the endocrine system do?
Secrete (hormones) from glands
What are the properties of steroid hormones?
Lipid Soluble
Bind to steroid receptors inside cells
Can facilitate or inhibit transcription
What are the properties of non-steroid hormones?
Hydrophilic (lipid insoluble)
Bind to cell-surface receptors, triggering a cascade reaction (with 2” messengers)
What does the adrenal cortex do and what is its relative position?
It is superior to the kidneys, and the cortex is the outer region of the adrenal gland. It produces essential hormones like cortisol and aldosterone. It also makes glucocorticoids (control metabolism), mineralocorticoids (control blood concentrations), and androgens (sex and puberty hormones)
What does the adrenal cortex do and what is its relative position?
The medulla is the inner region of the adrenal gland. It produces ‘non-essential’ hormones such as adrenaline and noradrenaline
What is the exocrine role of the pancreas?
Produces juices containing amylases, proteases and lipases etc. which are secreted into ducts leading to the duodenum
What is the endocrine role of the pancreas?
Produce and release Insulin and Glucagon directly into the blood, from the beta and alpha cells of the islets of Langerhans respectively
What are the cells of the pancreas called that aren’t in the islets of Langerhans, and what do they do?
Pancreatic acini, they secrete digestive enzymes
Define glycogenolysis
Breaking down stored glycogen into glucose
Define gluconeogenesis
Producing glucose from non-carbohydrate sources such as lipids
Define glycogenesis
Producing glycogen from glucose
How do beta cells detect that blood glucose concentration is too high, and release insulin?
When glucose is abundant, it is loaded into the beta cells, where its mitochondria produce ATP. The ATP closes potassium ion channels and depolarises the membrane, causing calcium ion channels to open. Calcium floods in and causes the vesicles to fuse with the plasma membrane and secrete insulin by exocytosis
Which cells in the body have glucagon receptors?
Liver cells and fat cells
What is type-1 diabetes mellitus?
When the patient is unable to produce insulin. It can be regulated by insulin injections
What is type-2 diabetes mellitus?
When the patient produces very little insulin or their glycoprotein receptors do not respond to it. It can be acquired through excessive carbohydrate intake and usually develops in later life. It can sometimes be regulated by dietary care.
What does the amygdala do when it encounters a ‘fight or flight’ scenario?
Secretes AdrenoCorticoThrophic Hormone (ACTH) to signal other tissues to prepare accordingly
What secondary messenger does adrenaline use?
cyclic AdenosineMonoPhosphate (cAMP)
How does adrenaline activate its secondary messenger (cAMP)?
When it binds to cell surface receptors, it activates adenylyl cyclase, which turns AMP into cAMP, communicating with protein kinases. This process is called a cascade reaction
Which two nerves transmit impulses from the medulla oblongata to regulate heart rate?
Accelerator nerve and Vagus nerve
What do baroreceptors do?
Detect changes in blood pressure
What do chemoreceptors do (regarding heart rate)?
Detect changes in blood composition, such as carbon dioxide concentration
Give mechanisms of thermoregulation in ectotherms
Behavioural
- basking, shivering, seeking shade
Physiological
- dark coloured skin, regulate heart rate
Give mechanisms of thermoregulation in endotherms
Vasodilation and vasoconstriction - shunt vessels Sweating Hair contraction (erector pili)
Define excretion
Specifically the removal of waste products from the body, i.e. urine, faeces etc. but NOT sweat or mucus
In the liver, hepatocytes line _______, where blood that has mixed from the hepatic portal vein and hepatic artery flows past toward the hepatic vein. Hepatocytes secrete bile into _________, where it drains to the gall bladder
sinusoids
canaliculi
What happens in the Orthinine cycle?
Ammonia from the deamination of excess amino acids combine with intermediates (Orthinine and Citruline), to form urea, which is less toxic and doesn’t affect pH
The liver is also the site of most detoxification, name two enzymes important in detoxification …Hint: hydrogen peroxide and ethanol are the toxins being referred to!
Catalase
Alcohol dehydrogenase
How does the filtrate from the renal pelvis get to the bladder?
Through the ureter
What is the part of the nephron called that houses the glomerulus?
The Bowman’s capsule / renal capsule
With regard to the histology of the nephron, why does ultrafiltration occur (in the glomerulus)?
The afferent arteriole to the glomerulus is quite wide relative to the efferent arteriole, and so a pressure is built up - this forces fluid through the basement membrane
What special cells are found in the renal capsule?
Podocytes, which have extensions called pedicels, that wrap around the capillaries in the glomerulus
What does hypotonic mean?
Less concentrated than the blood
What happens in the proximal convoluted tubule (PCT)?
About 85% of the sodium ions, chloride ions and water are reabsorbed (sodium by active transport), the epithelial cells have microvilli and many mitochondria
What happens from the descending limb loop of Henle onwards, during reabsorption?
The descending limb of the loop of Henle receives a concentrated solution because water moved back into the vasa recta when in the PCT. After the ‘hairpin bend’ ions are pumped out of the ascending limb of the loop of Henle (into the tissue fluid) to form a dilute solution again (hypotonic to blood), excess water is then drawn out of the DCT and CD into the vasa recta by osmosis (mediated by ADH)
Where is ADH produced, and secreted?
The ADH is produced in the Hypothalamus and secreted from the posterior pituitary gland, once stimulated by osmoreceptors in the hypothalamus
What effect does ADH have on the DCT and CD?
ADH increases the permeability of the DCT and CD to water, via a cAMP 2” messenger
Describe the mechanism of ADH action
ADH causes vesicles in the collecting duct to fuse with the side of the membrane in contact with the medulla tissue fluid. These vesicles contain aquaporins, which provides a route for water to move out of the cell by osmosis
How does a urine stick pregnancy test work?
Mobile MonoClonal Antibodies (MCAs) with a dye attached bind to any human Chorionic Gonadotrophin (hCG) found in the urine, and move up the test stick. The complex binds to immobile hCG-MCA at the test line to form a coloured band. Excess MCAs move further up the test stick to bind to the immobile strip and produce a second coloured band, in order to show that the test has worked regardless of outcome
What is the difference between haemodialysis and peritoneal dialysis?
Peritoneal dialysis occurs in the peritoneum (a body cavity) and the fluid is inserted through a catheter
What does auxin do?
Cell elongation, prevent abscission and maintain apical dominance
What does gibberellin do?
Cause stem elongation (extend internodes), trigger pollen fertilisation
What does ethene do (in its role as a plant hormone)?
Cause fruit ripening and promotes leaf abscission in deciduous trees
What does abscisic acid (ABA) do?
Maintains seed dormancy, stimulates the ‘cold weather responses’ and regulates stomatal closure
What evidence is there to support the role of gibberellins in activating seed germination?
Seeds with gibberellin removed don’t germinate
Gibberellin inhibitors stop germination
What evidence is there to show that auxins are responsible for apical dominance?
Removing the apical shoot promotes lateral growth because the auxin has gone too
What is photoperiodism, and how does it relate to abscission?
A plant’s sensitivity to a lack of light, from photosynthetic pigments, called Phytochromes. An increase in a dark period triggers abscission - by increasing ethene production in the ethene sensitive abscission zones - ethene activates digestive enzymes that ‘cut’ the petiole from the stem.
What mainly controls stomatal opening and closure?
ABA, but changing the turgor in guard cells
What plant defences are there against herbivory?
Thorns, spikes, tannins, alkaloids, and pheromones (for ‘social’ behaviour, like signalling to initiate callose production in other plants)
Give examples of commercial hormone use
- Climacteric fruits have their ripening controlled by ethene
- Rooting powders help propagate cuttings (especially from micropropagation)
- Synthetic auxins disrupt broad-leaved dicots, making growth unsustainable and killing weeds
Explain the process of ATP production by chemiosmosis
High energy electrons pass through electron transport chain (ETC) and carry protons across the membrane forming a proton gradient, the only way they can move back down is through hydrophilic membrane channels linked to ATP synthase
What is a photosystem?
Primary pigment in the reaction centre (usually chlorophyll a) surrounded by accessory pigments to form an antennae complex
Is any NADP reduced in cyclic phosphorylation?
No, the electron required re-enters PS1
What happens in photolysis?
The incident light from the sun breaks water into two protons, two electrons, and an oxygen atom - the electrons enter the electron-deficient PS2
Describe the processes of the Calvin cycle, and where it occurs
The Calvin cycle is part of the light-independent stage of photosynthesis and occurs in the stroma. Ribulose bisphosphate (RuBP) is fixed by RuBisCo to form an unstable intermediate that breaks into 2 glycerate-3-phosphate molecules (GP). The 2 GP are reduced by ATP and reduced NADP to form 2 triose phosphate molecules (TP). 10 out of 12 TP is regenerated into RuBP and the other 2 out of 12 becomes lipids and amino acids
State some factors that can affect the rate of photosynthesis
Light intensity, carbon dioxide availability and temperature
What (in order) are the four stages of glycolysis, and where does it occur?
In the cytoplasm…
1) Phosphorylation (2 ATP in)
2) Lysis
3) Phosphorylation
4) Dehydrogenation and ATP formation (4 ATP out and 2 reduced NADP out)
What happens during oxidative decarboxylation (the Link Reaction) and where does it occur?
In the mitochondrial matrix…
Pyruvate is converted to an acetyl group (forming reduced NAD and carbon dioxide) and the acetyl group binds with coenzyme A (CoA) to make acetyl CoA
What happens in the Krebs cycle and where does it occur?
In the mitochondrial matrix…
Acetyl CoA enters the cycle and binds to (4C) oxaloacetate making (6C) citric acid and releasing CoA. The citric acid is decarboxylated to a variety of intermediates (5C then 4C) releasing carbon dioxide and reducing NAD as it does so until oxaloacetate is regenerated. In total; 3 NAD are reduced, one FAD is reduced to FADH2 and one ATP is reformed from ADP
What happens in oxidative phosphorylation, and where does it occur?
In the mitochondrial matrix…
Reduced NAD molecules donate electrons to the electron transport chain, and at the end of the chain oxygen accepts the protons from the NAD in question to reform water
What are the similarities and differences between lactate and alcohol fermentation?
Both use reduced NAD to convert pyruvate into lactate or ethanol respectively, but alcohol fermentation goes via an intermediate (ethanal) releasing carbon dioxide as it does so.
How is respiratory quotient (RQ) calculated?
Carbon dioxide produced divided by oxygen consumed
Which two reactions occur during photophosphorylation?
ATP is synthesised and NADP is reduced
Name two properties of DCPIP that make it useful for investigating the effect of light on photosynthesis?
DCPIP is a blue solution that decolourises when it accepts a proton (and electron)
DCPIP will decolourise faster in ‘redder’ light wavelengths because of this
How is ATP synthesises by chemiosmosis?
Hydrogen ions diffuse through the intermembrane space of the mitochondria into the matrix through ATPsynthase
What can a respirometer be used for?
Measure the rate of oxygen uptake
Measure the difference between oxygen uptake and carbon dioxide production
