Module 5

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Section 1 - The nervous system

Animals increase their chances of survival by changing to their environment, this is a stimuli

Receptors (e.g. cells) detect stimuli, and are very specific

Effectors are cells that respond to stimuli and bring change, e.g. muscle cells

Homeostasis includes control systems that maintain your internal environment

Negative feedback - mechanism to keep things at normal temperature

Positive feedback - amplifies change from a normal level e.g. platelets are released to form a blood clot, they are constantly released till the clot forms

3 main type of nerve: sensory, relay and motor neurones

Sensory receptors act as transducers, converting a stimulus into electrical energy

Example: Pacinian corpuscle (mechanoreceptors) is a nerve ending surrounded by lamellae. When stimulated, the lamellae are deformed, causes deformation of sodium ion channels. Sodium is released, creating a generator potential.

At rest, the outside is positively charged compared to the inside, and so the membrane is polarised.

The resting potential is -70VmV, which is maintained by sodium potassium pumps and potassium ion channels

SALTY BANANA - 3 Na ions pumped out to every 2 K ions pumped in

Depolarisation of a neurone

Stimulus - excites the neurone, causing sodium ion channels to open. Na ions diffuse into the neurone, making the inside of the neurone less negative

Depolarisation - if the potential difference reaches the threshold , Na voltage gated channels open

Repolarisation - at around 30mV, Na channels close and K channels open, so K ions diffuse out of the of the neurone down their concentration gradient

Hyperpolarisation - K ion channels don't shut quick enough so there is an 'overshoot'

Resting potential - ion channels are reset

Refractory period - Before the neuron can respond again it has to reset to salty banana

Action potentials move along neurons as a wave of depolarisation - as sodium ions diffuse sideways and cause sodium ion channels to open

Bigger stimulus = more frequent impulses

All or nothing, if the threshold isn't met then the action potential won't fire

Neurons with a myelin sheath (electrical insulator made of Schwann cells) respond faster to action potentials as between the cells are gaps of bare membrane - nodes of Ranvier.

Depolarisation only happens at the nodes, the cytoplasm conducts enough electrical energy to depolarise the next node, so the impulse jumps - this is saltatory conduction

Synapses are junctions between two neurons, they work by:

Action potential arrives at the presynaptic knob

Stimulates voltage-gated calcium channels to open, the Ca ions move the synaptic vesicles to move to the presynaptic membrane and fuse. Neurotransmitter is released by exocytosis

Neurotransmitter diffuses across the synaptic cleft and binds to the receptors at the postsynaptic membrane

This causes Na ion channels to open, causing depolarisation of the postsynaptic membrane.

Neurotransmitter is removed so the response doesn't keep happen

Synapses cause convergence (many to one) and divergence (one to many), and also spatial summation (adding together of many stimuli to cause a single response) and temporal summation (where 2 or more nerve impulses arrive at the nerve in succession - action potential more likely)

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Section 2 - The Hormonal system:

Made up of endocrine glands and hormones - chemical messengers

Stimulus - Receptors - Hormone - Effector - Response

Hormones are first messengers, they carry the message from the endocrine gland to the receptor on the target cell and bind to the target cell

Inside the cell, a signalling molecule is made - which is a secondary messenger - and causes a chain reaction to occur in the cell

E.g. Adrenaline is the first messenger, which binds to the muscle cell. This activates the enzyme adenylyl cyclase, which produces cAMP - a secondary messenger that activates a cascade of reactions

The adrenal gland has 2 parts: the outer cortex and the inner medulla

Medulla: Secretes catecholamine hormones (adrenaline). These increase heart rate, break down glycogen into glucose and divert blood to produce more energy

Cortex: Secretes steroid hormones (cortisol). These stimulate the break down of fats and proteins to glucose for energy, increases blood volume, and suppresses the immune system as a response to stress

The pancreas has an area of endocrine tissue that is called the Islets of Langerhans. They're made of two types of cells:

Alpha cells: secrete glucagon

Beta cells: secrete insuline

Control of blood glucose:

Insulin lowers blood levels, it binds to receptors on liver and muscle cells and increases the permeability of cell membranes to glucose. It also causes glycogenesis (conversion of glucose to glycogen) and increases the rate of respiration in cells

Glucagon raises blood glucose concentration by binding to receptors on liver cells, gluconeogenesis and glycogenolysis.

Diabetes:

Type 1: Auto-immune disease where the body attacks the beta cells in the Islets of Langerhans - no insulin production. Blood glucose levels get very high and don't come back down, so a lot of glucose is excreted in urine

Treating Type 1: insulin injections/pump, islet cell transplantation (risk of rejection), keeping healthy and active

Type 2: Beta cells not producing enough insulin/the cells don't respond well to insulin. Linked to poor diet and lifestyle.

Treating Type 2: Lifestyle change, medication, insulin therapy

Insulin is made from genetically modified bacteria, as it is cheaper, faster, ethically and produces human insulin which is more effective

Stem cells: being grown into beta cells, and implanted in the pancreas so they could produce their own insulin

Homeostasis - control of body temperature:

Ectotherms - reptiles and fish - control their body temp with changes of behaviour, as their internal body temp is dependent on the external temperature. They have variable metabolic rates and activity levels depend on how warm they are

Endotherms - mammals - control their own body temperature and have a high metabolic rate which generates a lot of heat

Mammals mechanisms of changing body temperature:

Sweating - water evaporating uses energy, cooling the skin

Hairs lying flat/up - erector pili muscles control how much air is insulated around the skin

Vasodilation/Vasoconstriction - arterioles near the skin surface dilate or contract to control the volume of blood going to the skin and heat lost by radiation

Hormones - adrenaline and thyroxine increase metabolism which produces heat

Shivering - muscles contracting in spasm produces heat and increases respiration

Hypothalamus controls body temperature , as it receives info from internal thermoreceptors (in the brain) and external thermorecpetors (on the skin)

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Section 3 - Excretion:

Excretion - removal of metabolism waste products from the body

The liver:

Functions of the liver:

Deamination of amino acids - removal of the amine group from amino acids, forming ammonia and organic acids. Organic acids can be used for respiration to give ATP or be converted to carbohydrates. Ammonia + carbon dioxide occurs in the ornithine cycle.

Breaks down alcohol into ethanal, into acetic acid. Excess alcohol causes cirrhosis of the liver (scar tissue blocks blood flow).

Breaks down paracetamol, and excess insulin.

Stores glycogen

Structure of the liver:

Hepatic artery supplies the liver with oxygenated blood, the hepatic vein takes deoxygenated blood away.

Hepatic portal vein brings blood from the duodenum (small intestine), which is full of products of digestion. Any harmful products are broken down.

Bile duct takes bile (emulisfies fat) to the gall bladder to be stored.

Liver is made up of lobules, which are made of hepatocytes

Each lobule has a central vein, and branches of hepatic artery, vein, and hepatic portal vein

Hepatic portal vein and hepatic artery are attached to the central vein by sinusoids

Kupffer cells remove bacteria and break down old red blood cells

Bile duct is connected to the central vein by the canaliculi

The kidney:

Main function is to excrete waste products, and regulate water potential

Structure:

Blood enters via the renal artery, through the afferent arteriole, to the glomerulus, through the proximal convoluted tubule, to the loop of henle, back out the distal convoluted tubule and out the collecting duct

Ultrafiltration:

In the glomerulus, blood goes three layers to get into the bowman's capsule (capillary membrane, basement membrane, podocytes).

Selective reabsorption:

Takes place in the PCT, loop of Henle and DCT.

The walls of the PCT have microvilli that have a large surface area for reabsorption. Useful solutes like glucose, AAs, vitamins and salts are reabsorbed due to active transport and facilitated diffusion

Controlling water potential:

Near the top of the ascending limb, Na and Cl ions are actively pumped into the medulla, lowering the water potential in the medulla.

The lower water potential means water diffuses out of the descending limb by osmosis. This water is then reabsorbed back into the blood

Near the bottom of the ascending limb, Na and Cl ions diffuse out as they are in such high concentration

Water potential is controlled by the anti-diuretic hormone, they are released when you're dehydrated. Osmoreceptors in the hypothalamus detect this. the posterior pituitary gland releases more ADH which makes the collecting duct and DCT more permeable, so more water is reabsorbed back into the blood.

Kidney failure:

Can be detected by measuring the glomerular filtration rate

Caused by kidney infections, that mean swelling of the kidneys stops filtering at the bowman's capsule or reabsorption

High blood pressure damages the glomeruli, large molecules can get into urine

Causes many problems: urea is toxic in the body, fluid accumulates and parts of the body swell, blood may become to acidic, long term kidney failure leads to anaemia

Renal dialysis:

Using a machine to filter blood, by passing it by a partially permeable membrane with dialysis fluid on the other side. It takes 3 to 5 hours, you feel ill between sessions, expensive, less risky that surgery

Kidney transplant:

Cheaper, convenient, major op, may be on immune system suppression drugs

Detecting chemicals:

Pregnancy tests:

Stick with an application area that contains antibodies for hCG bound to coloured beads. When any urine is applied with hCG in, it will bond to the antibodies and move up the strip. The test strip has antibodies attached to it also, if the strip turns blue, the hCG has bound to the strip with the coloured beads

Steroids:

Gas chromatography/mass spectrometry is used to see if there are steroids in the urine of an athletes

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Section 4 - Neuronal Communication:

Sensory Receptors

Specialised tissues that detect change in the environment. They usually convert one type of energy into electrical energy (transducer), and then this message is relayed through the body.

There are many parts of the body that detect changes. For example:

Rods and cones in the back of the eye detect change in light intensity - cause iris to constrict

Thermoreceptors detect changes in temperature in skin and hypothalamus - causes constriction of arterioles in skin, shivering

Chemical receptors in the tongue, change chemical energy to electrical, sent to pleasure centres in the brain

Pacinian corpuscle is a pressure sensor in the skin - when pressure is applied onto the rings, they change shape and put pressure on the sensory nerve fibre.

Sensory neurone

Long dendron

Short axon

Relay neurone

Many dendrites

Very short axon

Motor neurone

Long axon

Myelinated neurones

Schwann cells create myelin sheath around the axon

Gaps in the sheath are called Node of Ranvier

Advantages - can carry signals a lot further and faster than non-myelinated neurones due to saltatory conduction.

Nerve impulse generation and transition

Generation of an impulse - a few sodium ions move into the cell , as the voltage-gated channels are opened by the action at the synapse, cell becomes depolarised

If the threshold is reached, a positive feedback loop is triggered, more sodium channels open and the cell becomes more depolarised

Refractory period - cell starts to repolarise and potassium ions diffuse out of the cell down the concentration gradient - may overshoot (hyperpolarisation)

Synapses

Presynaptic knob:

Stores neurotransmitter, has lots of mitochondria, large amounts of SER, has acetylcholine in vesicles ready to diffuse across synaptic cleft

Postsynaptic membrane

Have specialised sodium channels that acetylcholine can bind to

How it works:

Action potential arrives at the synaptic knob, causing calcium ions to diffuse into the cell and move vesicles containing a neurotransmitter to the presynaptic membrane.

Here they fuse, and are released by exocytosis into the synaptic cleft where they diffuse across to the postsynaptic membrane and bind to the receptor sites.

Excitatory postsynaptic potential is created, and when they combine they could meet threshold levels and cause another action potential

Acetylcholine esterase breaks down acetylcholine into ethanoic acid and choline - which diffuse back into the synaptic knob and recombine using energy from ATP.

Action potentials

All or nothing response

Doesn't vary in size or intensity

Convergence (many presynapses to one postsynapse) and divergence (one presynapse to many postsynapses)

Only the presynaptic knob contains the neurotransmitter

Filters out low level stimuli, as action potential in next neurone unlikely to fire

Summation - low levels may be amplified from a persistant stimuli

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Section 5 - Plant and Animal Responses:

Plant responses

Types of chemical defences

Tannins - make the leaf taste unpleasant, can be toxic to microorganisms

Alkaloids - bitter tasting chemicals (e.g. caffeine)

Pheromones - released from one plant and effects another

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Section 6 - Photosynthesis:

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Section 7 - Respiration:

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