SL IB Biology Integration of Body Systems PDF

Head to www.savemyexams.com for more awesome resources SL IB Biology Your notes Integration of Body Systems Contents Integration in Living Organisms The Nervous System Reflex Arc & Movement Control Ep...

Head to www.savemyexams.com for more awesome resources SL IB Biology Your notes Integration of Body Systems Contents Integration in Living Organisms The Nervous System Reflex Arc & Movement Control Epinephrine & Melatonin Control Mechanisms Page 1 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Integration in Living Organisms Your notes System Integration Complex living organisms have evolved to make use of living, or body, systems made up of component parts that collectively perform an overall function Coordination of these parts is required in order for the systems to fully integrate and work together for the whole organism Living systems are often made up of billions of cells and so require mechanisms of cell-cell communication within the system and with cells in a separate system in a different part of the organism An example of this, found in both plants and animals, is the use of hormones; these are produced within one body system (the endocrine system) but may have an effect in a different body system (the reproductive system) Page 2 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources System Integration: Cells, Tissues, Organs & Systems Multicellular organisms have developed a hierarchy of organisation that allows for effective Your notes communication and interaction with their environment Specialised cells of the same type group together to form tissues A tissue is a group of cells that work together to perform a particular function. For example: Epithelial cells group together to form epithelial tissue (the function of which, in the small intestine, is to absorb food) Muscle cells (another type of specialised cell) group together to form muscle tissue (the function of which is to contract in order to move parts of the body) Different tissues work together to form organs. For example: The heart is made up of many different tissues (including cardiac muscle tissue, blood vessel tissues and connective tissue, as well as many others) Different organs work together to form organ systems Organ systems work together to carry out the life functions of a complete organism At each hierarchical level there is great efficiency and complexity Example of the hierarchy of organisation diagram Page 3 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Multicellular organisms have many levels of organisation Emergent properties Multicellular organisms are able to undertake functions that unicellular organisms cannot, e.g. move over vast distances and digest large macromolecules This is a result of properties emerging when individual cells organise and interact to produce living organisms Scientists sometimes summarise this with the phrase "The whole is greater than the sum of its parts" , this phrase describes the idea that the individual systems within the organism are more effective when they work together Traditionally, scientists have approached the study of biology from a reductionist perspective, looking at the individual cells, however, due to emergent properties there is an argument that the systems approach should be used For example a cheetah becomes an effective predator by integration of all its body systems Page 4 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Integration of Organs Communication within the bodies of animals is primarily by the nervous system or the endocrine Your notes system Often these two systems are required to work together to maintain body processes such as digestion, maintaining heart rate, blood glucose levels and blood pressure These processes rely on transfer of energy and materials around the body of the organism Transport vessels within the blood system are at times required to move materials around the body to various tissues, for example: Oxygen and glucose are transported to all cells of the body to facilitate respiration Urea, produced by protein metabolism in the liver, is transported in the blood to be excreted by the kidneys Hormones, such as FSH and LH, are transported via the blood from the pituitary gland in the brain to the ovaries during the menstrual cycle The nervous system The human nervous system consists of: Central nervous system (CNS) – the brain and spinal cord Peripheral nervous system (PNS) – all of the nerves in the body It allows us to make sense of our surroundings and respond to them, and to coordinate and regulate body functions Information is sent through the nervous system in the form of electrical impulses – these are electrical signals that pass along nerve cells known as neurones A bundle of neurones is known as a nerve The nerves spread out from the central nervous system to all other regions of the body and importantly, to all of the sense organs More information about the structure of the nervous system can be found here The endocrine system A hormone is a chemical substance produced by an endocrine gland and carried by the blood The endocrine glands that produce hormones in animals are known collectively as the endocrine system A gland is a group of cells that produces and releases one or more substances (a process known as secretion) Glands of the endocrine system diagram Page 5 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Hormones are produced in the glands and travel round the body in the blood Hormones are chemicals which transmit information, via the blood, from one part of the organism to another and that bring about a change They alter the activity of one or more specific target organs Hormones only affect cells with receptors that the hormone can bind to These are either found on the cell surface membrane, or inside cells Receptors have to be complementary to hormones for there to be an effect Effects can be long lived, as long as hormones are bound to the receptors Hormones are used to control functions that do not need instant responses They travel more slowly in the blood compared to a nervous impulse Page 6 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Comparison of the nervous and endocrine systems table Your notes Page 7 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Nervous System Your notes The Brain as Integration Organ The structure of the brain The brain alongside the spinal cord is part of our central nervous system The brain is made of billions of interconnected neurones and is responsible for controlling complex behaviours, both conscious and unconscious Within the brain are different regions that carry out different functions The cerebral cortex: this is the outer layer of the brain which is divided into two hemispheres. It’s highly folded and is responsible for higher-order processes such as intelligence, memory, consciousness and personality The cerebellum: this is underneath the cerebral cortex and is responsible for balance, muscle coordination and movement The brainstem: this relays messages between the cerebral cortex, the cerebellum and the spinal cord. A key part is the medulla which controls unconscious activities such as heart rate and breathing Two important glands of the brain that are integral the endocrine system are The pituitary gland: This gland is responsible for producing many hormones including those involved in controlling the menstrual cycle (FSH and LH) The hypothalamus: This region of the brain is involved in regulating body temperature, it also producing hormones which control the pituitary gland Structures of the brain diagram Page 8 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The brain is made up of several regions The role of the brain The brain coordinates and processes information received Interactions within the brain are responsible for learning and memory The brains requires several receptors in order to receive information (this is input of information) At a conscious level information is received by Photoreceptors located within the retina of the eye for visual information Chemoreceptors found in the tongue for tasting Thermoreceptors located in the skin for detection of temperature changes Mechanoreceptors located in the inner ear which are sensitive to sound vibrations At unconscious level input of information is via Osmoreceptors located in the carotid arteries and hypothalamus which detect the water content of the blood Baroreceptors, also located in the carotid arteries and the aorta, these sense pressure changes of the blood Proprioceptors which are located in muscles and joints and provide information on balance and movement Page 9 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examiner Tip Your notes You are are not required to know complex details of the brain such as the role of slow-acting neurotransmitters. Page 10 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Spinal Cord as Integration Centre The spinal cord is part of the central nervous system (CNS), along with the brain Your notes It is a neural pathway between the body and the brain, yet it can also process information independently from the brain This information is processed at the unconscious level and involves some reflex reactions The spinal cord can be described as an integration centre for unconscious processes Note that information processed at conscious level means that the cerebrum of the brain is also involved The spinal cord is responsible for bringing sensory information to the CNS from the body and enables motor (muscular) information to be sent out There are two types of tissue in the spinal cord White matter contains mainly the axons only of neurones that carry information to and from the brain Grey matter contains the neurones and synapses involved in spinal cord integration processes which create a reflex response Sensory information enters the spinal cord along sensory neurones, this is immediately processed and sent out as motor information along motor neurones; this pathway is called a reflex arc Because the brain is not involved in this pathway this is unconscious control directed by the spinal cord alone Reflex arc diagram Page 11 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The spinal cord of the central nervous system acts as an integration centre for unconscious processes Your notes Page 12 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Input Through Sensory Neurones A neural pathway begins with a receptor Your notes A receptor is a specialised cell that can detect changes in the environment that cause a stimulus Receptor cells are transducers – they convert energy in one form (such as light, heat or sound) into energy in an electrical impulse within a sensory neurone Receptor cells are often found in sense organs (e.g. light receptor cells are found in the eye) Some receptors, such as light receptors in the eye and chemoreceptors in the taste buds, are specialised cells that detect a specific type of stimulus and influence the electrical activity of a sensory neurone Other receptors, such as some kinds of touch receptors, are just the ends of the sensory neurones themselves When receptors cells are stimulated they are depolarised If the stimulus is very weak, the cells are not sufficiently depolarised and the sensory neurone is not activated to send impulses If the stimulus is strong enough, an action potential is initiated in the sensory neurone and the impulse is transmitted to the CNS, specifically the spinal cord and the cerebral hemispheres An example of the sequence of events that results in an action potential in a sensory neurone The surface of the tongue is covered in many small bumps known as papillae The surface of each papilla is covered in many taste buds Each taste bud contains many receptor cells known as chemoreceptors These chemoreceptors are sensitive to chemicals in food and drinks Each chemoreceptor is covered with receptor proteins Different receptor proteins detect different chemicals Chemoreceptors in the taste buds that detect salt (sodium chloride) respond directly to sodium ions If salt is present in the food (dissolved in saliva) being eaten or the liquid being drunk: Sodium ions diffuse through highly selective channel proteins in the cell surface membranes of the microvilli of the chemoreceptor cells This leads to depolarisation of the chemoreceptor cell membrane The increase in positive charge inside the cell is known as the receptor potential If there is sufficient stimulation by sodium ions and sufficient depolarisation of the membrane, the receptor potential becomes large enough to stimulate voltage-gated calcium ion channel proteins to open As a result, calcium ions enter the cytoplasm of the chemoreceptor cell and stimulate exocytosis of vesicles containing neurotransmitter from the basal membrane of the chemoreceptor The neurotransmitter stimulates an action potential in the sensory neurone The sensory neurone then transmits an impulse to the brain Diagram to show the sequence of events initiated by activated chemoreceptors in the taste buds Page 13 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 14 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Sensory neurons convey messages from receptor cells to the CNS Page 15 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Output Through Motor Neurones Once an action potential has been transmitted from a sensory neurone to the CNS Your notes The cerebrum within the brain uses the information to process movements within the body as needed; the part of the cerebrum responsible for this is called the motor cortex The role of motor neurones Motor neurones are used to carry action potentials to muscles to initiate the movement required Motor neurones terminate within a muscle within a neuromuscular junction (also known as motor end plates) There are multiple neuromuscular junctions spread across several muscle fibres within the muscle Neuromuscular junctions work in a very similar way to synapses They are located between the terminal branches of a motor neurone and a muscle cell Transmission across the neuromuscular junction When an impulse travelling along the axon of a motor neurone arrives at the presynaptic membrane, the action potential causes calcium ions to diffuse into the neurone This stimulates vesicles containing the neurotransmitter acetylcholine (ACh) to fuse with the presynaptic membrane The ACh that is released diffuses across the neuromuscular junction and binds to receptor proteins on the sarcolemma (surface membrane of the muscle fibre cell) This stimulates ion channels in the sarcolemma to open, allowing sodium ions to diffuse in Influx of sodium ions depolarises the sarcolemma, generating an action potential that passes down the T-tubules towards the centre of the muscle fibre Action potentials stimulate muscle contraction Action potentials travel down the T-tubules and trigger the opening of voltage-gated calcium ion channel proteins in the membranes of the sarcoplasmic reticulum Calcium ions diffuse out of the sarcoplasmic reticulum (SR) and into the sarcoplasm surrounding the myofibrils Calcium ions bind to troponin molecules, stimulating them to change shape This causes the troponin and tropomyosin proteins to change position on the thin (actin) filaments The myosin-binding sites are exposed to the actin molecules The process of muscle contraction (known as the sliding filament model) can now begin Muscle contraction diagram Page 16 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Action potentials from the motor neurone cross the neuromuscular junction to trigger the events leading to muscle contraction Page 17 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Structure of Nerves Information is sent through the nervous system as nerve impulses – electrical signals that pass along Your notes nerve cells known as neurones Nerves are made up of bundles of sensory neurones or motor neurones These may be myelinated or unmyelinated The different structures of these neurones are considered in more detail here Myelination is covered in more detail here Structure of a Nerve Diagram Page 18 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A nerve is made up of a bundle of individual neurone cells Transverse and Cross Section of Myelinated Neurone Diagram Page 19 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Each Schwann cell wraps its plasma membrane concentrically around the axon to form a segment of myelin sheath about 1mm long Page 20 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Reflex Arc & Movement Control Your notes The Pain Reflex Arc Reflexes Reflex responses are actions of the body that occur without conscious thought Reflexes are automatic and rapid, minimising damage to the body and therefore aiding survival Awareness of a reflex response occurs after it has been carried out; this is because the information takes longer to reach the conscious parts of the brain Examples of reflexes include blinking, coughing, and the pupil and knee reflexes Blinking prevents the outer surface of the eye from drying out as well as protecting it from foreign objects Coughing prevents food from entering the airways and removes mucus from the airways during infection or an allergic reaction The pupil reflex prevents damage to the eye from bright light The knee reflex aids balance when standing upright What is a reflex arc A reflex arc is a pathway along which impulses are transmitted from a receptor to an effector without involving conscious regions of the brain A reflex arc therefore brings about a reflex response Sensory neurones, relay neurones and motor neurones work together in a reflex arc Order of a reflex arc A pain reflex arc is another example of a reflex response The skin has receptors for pressure, touch, and pain The receptor involved is the pain receptor called a nocireceptor The stimulus may be a sharp pin or hot flame which is detected by the nocireceptor in the skin of the hand An afferent (sensory) action potential is sent along a sensory neurone to the CNS An electrical impulse is passed to a relay neurone in the spinal cord Relay neurones are found entirely within grey matter of the spinal cord A relay neurone synapses with a motor neurone A synapse is the junction between neurones; nerve impulses cross synapses by diffusion of a chemical called a neurotransmitter A motor neurone carries an impulse to an effector muscle in the hand When stimulated by the motor neurone the muscle will contract and pull the hand away from the sharp object or heat; this is the reflex response The reflex arc for a spinal reflex is as follows: A Reflex Arc Diagram Page 21 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Spinal reflexes involve relay neurones in the spinal cord as part of a pain reflex Page 22 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Role of the Cerebellum The cerebellum coordinates movement Your notes This includes balance; a highly complex function that requires coordination between multiple parts, including the eyes, semicircular canals in the ears, and many muscles Other movements coordinated by the cerebellum are Posture Walking Hand and finger movements Eye movements Speech The cerebellum does not initiate movement, the motor cortex of the cerebrum is responsible for initiating muscle contractions and therefore movement Once the movement begins the cerebellum receives feedback signals from the area of the body that is moving and different sense organs, it then sends signals to coordinate and control the movement The structure and function of the brain as an organ is covered in more detail here Page 23 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Epinephrine & Melatonin Your notes Melatonin Circadian rhythms Many physiological processes and behavioural patterns occur in regular, daily rhythms in organisms throughout the plant and animal kingdoms Many animal species are only active for a specific part of the 24-hour cycle e.g. nocturnal animals are only active at night Humans are diurnal meaning that we are more awake during daylight hours Humans are adapted to live in a 24-hour cycle and many aspects of our physiology and behaviour, including physical activity, sleep, body temperature, and secretion of hormones, follow specific and regular cycles throughout the 24-hour period These daily cycles are known as circadian rhythms In humans, many circadian rhythms are influenced by the hormone melatonin Melatonin is secreted by the pineal gland, which is located in the brain Melatonin secretion increases in the evening in response to darkness and decreases at dawn in response to light, leading to our diurnal behaviour patterns Melatonin and sleep patterns Although melatonin affects many aspects of human physiology and behaviour, one of the main circadian rhythms it controls is our sleep-wake cycle The pineal gland secretes melatonin into the blood Production is influenced by the detection of light and dark by the retina of the eye Signals are then transmitted to the pineal gland according to the amount of daylight a person is exposed to and varies with changes in day length (this is why the pineal gland is sometimes referred to as both an endocrine clock and an endocrine calendar) Melatonin's target sites are found in many areas of the brain including the hypothalamus and pituitary glands, and also in the cells of the immune system, gonads, kidney, and the cardiovascular system, blood vessels, and intestinal tract Increasing melatonin levels lead to feelings of tiredness and promote sleep Decreasing melatonin levels lead to the body's preparation for waking up and staying awake during the day Experiments have also suggested that Increased melatonin at night contributes to the night-time drop in core body temperature in humans Melatonin receptors in the kidney enable melatonin produced at night to cause the night-time decrease in urine production in humans Melatonin is still released in the absence of light and dark signals, but on a slightly longer cycle than the usual 24 hours Subjects living in the dark with no access to natural daylight still release melatonin on a roughly 24 hour cycle Page 24 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources This suggests that the role of light is to reset the melatonin system every day to keep the circadian rhythm in line with daylight hours Your notes Secretion of melatonin graph The production of melatonin is influenced by the amount of daylight a person is exposed to: melatonin levels peak during Page 25 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Epinephrine During situations that creates stress, fear or excitement, the neurones of the sympathetic nervous Your notes system will stimulate the adrenal medulla (of the adrenal gland) to secrete epinephrine (also called adrenaline) Epinephrine is a hormone that will prepare your body for reacting to a stressful situation This reaction is often called the "fight or flight" response It is the effects of epinephrine that lead to the typical symptoms we experience during stressful situations such as increased heart rate, dry mouth, increased sweating etc The adrenal gland diagram The adrenal glands secrete the hormone epinephrine and prepare the body for vigorous activity Since epinephrine is a hormone, it is transported around the body in the bloodstream It will bind to receptors on its target organs One of the targets of epinephrine is the SAN, leading to an increase in the frequency of excitations This in turn, will increase the heart rate to supply blood to the muscle cells at a faster rate More blood means more oxygen and glucose that reaches the muscle cells, which in turn, increases the rate of aerobic respiration This releases more energy that will be used during the response to the stressful, vigorous or dangerous situation Epinephrine will also stimulate the cardiovascular control centre in the medulla oblongata This increases the impulses travelling along the sympathetic neurones affecting the heart, further speeding up the heart rate Blood vessels to less important organs (such as the digestive system and skin) constrict so that more blood can be diverted to organs that will be involved in the "fight or flight" response Page 26 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Note that blood flow to the brain remains constant, regardless of whether the body is in a state of stress or relaxation The brain is one of the most important organs in the body and needs a constant blood supply Your notes in order to function properly The changes experienced by the body during the "fight or flight" response are controlled by a combination of nervous and hormonal responses Epinephrine is also covered in the course with reference to the second messenger model, this can be found here Page 27 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Control Mechanisms Your notes Control of the Endocrine System A hormone is a chemical messenger produced by an endocrine gland and carried by the blood They are chemicals which transmit information from one part of the organism to another and bring about a change They alter the activity of one or more specific target organs Hormones are used to control functions that do not need instant responses The endocrine glands that produce hormones in animals are known collectively as the endocrine system A gland is a group of cells that produces and releases one or more substances (a process known as secretion) Control of the endocrine system is primarily by the hypothalamus and the pituitary gland The hypothalamus The hypothalamus monitors the blood as it flows through the brain and, in response, releases hormones or stimulates the neighbouring pituitary gland to release hormones The hypothalamus plays an important role in some homeostatic mechanisms Hypothalamus functions include Regulating body temperature The hypothalamus monitors blood temperature and initiates a homeostatic response if this temperature gets too high or too low Osmoregulation Cells in the hypothalamus monitor the water balance of the blood and releases the hormone ADH if the blood becomes too concentrated ADH increases absorption of water in the kidneys Regulating digestive activity The hypothalamus regulates the hormones that control appetite as well as the secretion of digestive enzymes Controlling endocrine functions The hypothalamus causes the pituitary gland to release hormones that control a variety of processes e.g. metabolism, growth and development, puberty, sexual functions, sleep, and mood The pituitary gland The pituitary gland is located below the hypothalamus Its role is to produce a range of hormones Some of these directly influence and regulate processes in the body while some stimulate the release of further hormones from other endocrine glands The pituitary gland is divided into two sections; the anterior pituitary and posterior pituitary The anterior pituitary produces and releases hormones Page 28 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The posterior pituitary stores and releases hormones produced by the hypothalamus e.g. ADH and oxytocin Your notes Page 29 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Feedback Control of Heart Rate There are several circumstances that can cause an individual's heart rate to increase, such as during Your notes exercise The brain is involved in this response of the heart however it does not require any thinking and is under unconscious control There is a specific region of the brain that plays a vital role in controlling the heart rate This cardioregulatory centre in the brain is called the medulla The medulla is found at the base of the brain near the top of the spinal cord The medulla is made up of two distinct parts: The acceleratory centre, which causes the heart to speed up The inhibitory centre, which causes the heart to slow down Both centres are connected to the sinoatrial node (SAN) by nerves These specific nerves are different from the nerves that control conscious activities. They make up the autonomic nervous system The autonomic nervous system is self-controlling Control of heart rate diagram Page 30 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The location of the medulla helps to keep it protected from harm. It has an essential function as a cardioregulatory centre. Increasing heart rate Once the acceleratory centre has been activated impulses are sent along the sympathetic neurones to the SAN Norepinephrine is secreted at the synapse with the SAN Noradrenaline causes the SAN to increase the frequency of the electrical waves that it produces This results in an increased heart rate Decreasing heart rate Once the inhibitory centre has been activated impulses are sent along the parasympathetic neurones to the SAN Acetylcholine is secreted at the synapse with the SAN This neurotransmitter causes the SAN to reduce the frequency of the electrical waves that it produces This reduces the elevated heart rate towards the resting rate Chemoreceptors and baroreceptors Exercise causes several internal conditions to change, creating internal stimuli: Carbon dioxide concentration in the blood increases There is an initial fall in blood pressure caused by the dilation of muscle arterioles These internal stimuli can be detected by chemoreceptors and baroreceptors (pressure) receptors located in the aorta (close to the heart) and in the carotid arteries (they supply the head with Page 31 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources oxygenated blood) Chemoreceptors detect changes in blood pH and oxygen and carbon dioxide levels Baroreceptors monitor changes in blood pressure Your notes Location of the baroreceptors and chemoreceptors Baroreceptors are located on the arch of the aorta and on the enlargement of the carotid arteries called the sinus. Chemoreceptors are located near the baroreceptors but on the outside of the aorta and carotid arteries These receptors release nerve impulses that are sent to the acceleratory and inhibitory centres (coordinators) The frequency of the nerve impulses increases or decreases depending on how stimulated the receptors are: Lower frequency impulses activate the inhibitory centre to slow down the heart rate and stroke volume Page 32 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Higher frequency impulses activate the acceleratory centre to speed up the heart rate and stroke volume Your notes The processes involved in the control of the heart rate. The internal stimuli are detected by chemoreceptors and baroreceptors that send impulses to coordinators (accelerator centre or inhibitory centre). The coordinators send signals to the effector (SAN) which produces a specific response. Page 33 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Feedback Control of Ventilation Rate Ventilation rates in the body are controlled by cells called respiratory centres which are located in the Your notes medulla of the brain At rest, action potentials, produced at random, travel to the diaphragm and intercostal muscles to initiate contraction and therefore ventilation; this occurs at a stable and slow pace During exercise, higher levels of carbon dioxide are produced due to an increase in respiration Waste carbon dioxide produced during respiration diffuses from the tissues into the blood This waste carbon dioxide is transported around the body in different ways In the blood plasma in the form of hydrogen carbonate ions (HCO3-); around 85 % of carbon dioxide is transported in this way Around 5 % of carbon dioxide dissolves directly in the blood plasma Bound to haemoglobin as carbaminohaemoglobin; this accounts for around 10 % of carbon dioxide transport in the blood pH changes in the blood Carbon dioxide released as a waste product from respiring cells diffuses into the cytoplasm of red blood cells Inside red blood cells, carbon dioxide combines with water to form carbonic acid (H2CO3) CO2 + H2O ⇌ H2CO3 Red blood cells contain the enzyme carbonic anhydrase which catalyses the reaction between carbon dioxide and water Without carbonic anhydrase, this reaction proceeds very slowly The plasma contains very little carbonic anhydrase hence H2CO3 forms more slowly in plasma than in the cytoplasm of red blood cells Carbonic acid dissociates readily into hydrogen ions (H+) and hydrogen carbonate ions (HCO3-) H2CO3 ⇌ HCO3– + H+ Hydrogen ions can lower the pH of the blood so their presence is detected by chemoreceptors in the medulla Action potentials are sent at a higher rate to the diaphragm and intercostal muscles of the lungs to increase ventilation rates and the volume of air being moved into and out of the lungs The pH of the blood can then return to normal and respiratory centres will stop sending action potentials to the diaphragm and the intercostal muscles, ventilation rates will return to normal resting rates This is an example of negative feedback Page 34 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Control of Peristalsis in Digestive System Peristalsis is series of muscle contractions in the walls of the oesophagus or small intestine that pass Your notes like a wave along the alimentary canal This wave forces the bolusof food along the alimentary canal These contractions are controlled unconsciously by the autonomic nervous system, specifically the enteric nervous system (ENS) The ENS consists a web of sensory neurones, relay neurones and motor neurones embedded in the tissues of the alimentary canal Peristalsis is controlled by circular and longitudinal muscles which initiate a mechanism called the peristaltic reflex These muscles are smooth muscle (not striated) The bolus of food is detected by stretch receptors (sensory neurones of the ENS) as the alimentary canal becomes distended An action potential is passed to relay neurones of the ENS which synapse with two different motor neurones One motor neurone releases an excitatory neurotransmitter which stimulates Longitudinal muscles to contract behind the bolus to reduce the length of that section the oesophagus or the small intestine This forces the food forwards through the alimentary canal Circular muscles contract to reduce the diameter of the lumen of the oesophagus or small intestine This prevents the food moving backwards towards the mouth A second motor neurone releases an inhibitory neurotransmitter which stimulates smooth muscle ahead of the bolus to relax and open the lumen of the alimentary canal Control of peristalsis diagram Page 35 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The control of peristalsis is initiated by the bolus and is carried out by two different motor neurones Page 36 of 36 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers