Control of heart rate in mammals C/W 18/10/2016 Describe homeostasis as the maintenance of a state of dynamic equilibrium through the response of the body to internal and external stimuli. Explain how the autonomic nervous system controls the heart rate in a variety of ways Engage – In your exercise book, complete the Venn diagram to describe the difference between Rod and Cone cells.

Cones Rods High sensitivity, can detect a single photon 109 cells per eye Night vision Poor sensitivity, need bright light 106 cells per eye Each cone connected to one bipolar cell Good visual acuity 1 type – used for monochromatic vision 3 types (red, green and blue) colour vision Found only in fovea Many rods usually connected to one bipolar cell Poor visual acuity Throughout retina 18/10/2016

Cones Rods 109 cells per eye 106 cells per eye High sensitivity, can detect a single photon Each cone connected to one bipolar cell Good visual acuity Night vision 3 types (red, green and blue) colour vision 1 type – used for monochromatic vision Found only in fovea Many rods usually connected to one bipolar cell Poor visual acuity Poor sensitivity, need bright light Throughout retina 18/10/2016

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From Topic 4 What are the units for each of these? Heart is controlled by impulses initiated in the sinoatrial node (SAN) and then spreads through the atrioventricular node (AVN) and the bundle of His to give a regular, coordinated heartbeat. When your body demands more glucose and oxygen, the heart can respond by increasing the number of beats and the volume of blood pumped at each heartbeat. Cardiac output = cardiac volume x heart rate What are the units for each of these? 18/10/2016

Nervous control of the heart Autonomic (involuntary) nervous system Cardiac control centre is in the medulla oblongata Chemical, stretch and pressure receptors in the lining of blood vessels send nerve impulses to the cardiac control centre. Sympathetic – noradrenaline stimulates SAN. In contrast parasympathetic nerve release acetylcholine, inhibiting the SAN and slowing the heart down. 18/10/2016

The Nervous System Nervous System Peripheral Nervous System The nervous system contains a network of specialized cells called neurons that coordinate actions and transmit signals between different parts of the body. In most animals the nervous system consists of two parts: Peripheral Nervous System Consists of sensory and motor neurons and all of the nerves connecting them to each other and to the Central Nervous System. Central Nervous System Contains the brain and the spinal cord. Autonomic Nervous System Involuntary Input from internal receptors. Output to internal organs, blood vessels and glands. Somatic Nervous System Voluntary. Input from sense organs. Output to muscles, skin and joints. Sympathetic Nervous System ‘Fight or flight’ responses e.g. speeds up heart rate Parasympathetic Nervous System Relaxing responses e.g. slows down heart rate

Parasympathetic and sympathetic nervous systems Inhibits effectors Controls actions under resting conditions Slows down activity Conserves energy Sympathetic Stimulates effectors Controls conditions under stress or activity Speeds us up (fight or flight)

Slows heart

Slows heart Parasympathetic

Inhibits urination

Inhibits urination Sympathetic

Dilates bronchi

Dilates bronchi Sympathetic

Constricts pupil

Constricts pupil Parasympathetic

Promotes ejaculation

Promotes ejaculation Sympathetic

Stimulates glucose release

Stimulates glucose release Sympathetic

Constricts bronchi

Constricts bronchi Parasympathetic

The role of baroreceptors Baroreceptors found in the sinuses of the carotid arteries in the neck and on the aorta are important in the feedback control of the heart rate during exercise. When exercise starts blood vessels dilate in response to adrenaline which is released in response to anticipation of exercise and blood pressure falls a little. This reduces stretch on the baroreceptors and they almost stop responding. This causes signals to be sent via the control centre along the sympathetic nerve to stimulate the heart rate and increase blood pressure by vasoconstriction. What are baroreceptors and where are they found? What happens when exercise starts? How is blood pressure increased? 18/10/2016

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The role of chemoreceptors in the aorta The walls of the aorta and carotid arteries contain chemoreceptors as well as baroreceptors. Sensitive to carbon dioxide levels in blood, high CO2 pH of blood goes down Chemoreceptors in aorta and carotid arteries send signal to control centre in medulla This increases the impulses travelling down the sympathetic nerve to the heart. Heart rate increases, increased blood flow to the lungs and more carbon dioxide removed. Blood pH increases and heart rate can return to normal. SYNOPTIC LINK BOHR SHIFT 18/10/2016

How is Carbon Dioxide Transported in the Blood TOPIC 4 LINK How is Carbon Dioxide Transported in the Blood Carbon dioxide is transported from the tissues to the lungs in one of three ways: Some is bound to haemoglobin to form HbCO2 A very small fraction gets dissolved in the blood plasma (CO2 dissolves poorly in water) The majority (~85%) diffuses into the erythrocyte and is converted into carbonic acid

Explain the role of the Bohr shift in the supply of oxygen to respiring tissues Take 5 minutes to explain to your partner what happens during the Bohr shift.

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Hormonal control of the heart When stressed, sympathetic nerve stimulates the adrenal medulla to release the hormone adrenaline. Carried in blood and binds to receptors at SAN. Stimulates cardiac centre in the brain, increasing the impulses in the sympathetic neurones supplying the heart, and it also has a direct effect on the SAN, increasing the heart rate, supplying you with extra oxygen and glucose. 18/10/2016

Bring the 3 specimen papers with you next lesson Bring the 3 specimen papers with you next lesson. All 3 should be completed. 18/10/2016

The Human Eye Sensitive to light 400 – 700nm. Other species sensitive to different wavelengths of light Demo dissection or students complete 18/10/2016

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The role of the retina The retina contains over a hundred million light- sensitive cells (photoreceptors) Rods and cones Rods – Greyscale vision only, low light intensities or at night. Very sensitive to light. Spread evenly, except at retina where there are none. Several synapse with same sensory neurone. Cones – Tightly packed together in the fovea. Around 6 million. Bright light and colour. Each cone usually has its own sensory neurone. 18/10/2016

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How do rods and cones work? Rhodopsin is the visual pigment – made from vitamin A. Photon of light causes Rhodopsin to break up into opsin and retinal. We call this bleaching. When rhodopsin is bleached it triggers a cascade reaction that causes sodium ion channels to close. Interior becomes more negative than usual. This is hyperpolarisation is known as the generator potential and depends on the amount of light hitting the rod. If stimulus is large enough, NTs are released into the synapse with bipolar cell. This causes an action potential in the sensory neurone. All sensory neurones leave the eye at the same point to form the optic nerve leading to the brain. 18/10/2016

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Exam Questions 18/10/2016

Synapses Wherever two neurones meet they are linked by a synapse. Every cell in the central nervous system is covered with synaptic knobs from other cells. A synapse is effectively a gap between two cells. The arrival of an impulse at the synaptic knob increases the permeability of the presynaptic membrane to Calcium ions as calcium ion channels open up. This causes synaptic vesicles, which contain a transmitter substance or neurotransmitter, to move to the presynaptic membrane. The vesicles then fuse with the membrane and release the neurotransmitter molecules into the synaptic cleft. These molecules diffuse across the gap and attach to specific protein receptor sites on the sodium channels of the post-synaptic membrane. This causes sodium channels to open. Sodium ions then flood into the post-synaptic neuron causing a change in the potential difference across the membrane and an excitatory post-synaptic potential (EPSP). 18/10/2016