Year 9 Oxford Textbook CH3 - PDF

3 How does your body CHAPTER respond to change? 33.1 Receptors detect stimuli 3.2 Nerve cells are called neurons The nervous system 3.3 controls...

3 How does your body CHAPTER respond to change? 33.1 Receptors detect stimuli 3.2 Nerve cells are called neurons The nervous system 3.3 controls reflexes 3.4 The central nervous CONTROL ssystem controls our body Things can go wrong with AND 33.55 the nervous system REGULATION The endocrine system causes 3.6 long-lasting effects What if? Exploring your senses What you need: 3.7 Homeostasis regulates through negative feedback Blindfolds What to do: 1 With a partner, explore how the Science as a human endeavour: 3.8 Hormo Hormones are used in sport senses of touch, hearing and smell can be used to navigate around a room without the use of sight. 2 Ensure all small or potentially Science as a human hazardous obstacles are removed 3.9 endeavour: Pathogens from around the room. Decide with your partner the path that the cause disease blindfolded student is required to take around the room. 3 Take turns being blindfolded and navigating the room, with your Th immune system protects The 3.10 ou our body in an organised way partner walking with you to ensure your safe navigation and providing assistance if needed. What if? Things can go wrong with the 3.11 immune system » What if you wore earmuffs as well as the blindfold? » What if you blocked your nose? » What if you were barefoot? Licensed to Daniel Beek, from Werribee Secondary College ege until 2027-12-31. 2027-12-31 3.1 Receptors detect stimuli In this topic, you will learn Your body has receptors that detect changes (stimuli) in the environment. The five main types of external receptors detect light, sound, chemicals in the air that: and in your mouth, and touch. Your body responds to changes in its Video 3.1 How taste works environment. Receptors detect these changes and pass the information to other parts of the body. A stimulus is any information that your Interactive 3.1 body receives that might cause it to respond. The human ear Responding to change Within our bodies, we regularly respond to changes without being aware of a stimulus stimulus and response. What makes any information that the you aware that you’re hungry or body receives that causes thirsty? Something in your body is it to respond communicating with your brain to receptor tell you to find food or water. A similar a structure that detects process occurs when you feel tired or have a a stimulus or change in headache. What is the source of these stimuli? the normal functioning Other examples of stimuli are less obvious. of the body We are surrounded by bacteria, viruses and fungi. Although many of them are too small to see, our bodies are constantly monitoring their numbers and fighting off harmful micro-organisms. Figure 2 We often respond to hot weather by Your body is an amazing combination of drinking more. cells, tissues, organs and systems, all working together. Each plays a part in detecting stimuli and passing on the information to other parts The sense organs of the body. The structures that receive stimuli Our body can detect five main signals: light are called receptors. (sight), sound (hearing), chemicals in the air Figure 1 The human (smell) and in our mouth (taste), and touch. papillomavirus (seen These are external senses because they tell us here under a microscope) stimulates an immune about the world outside our body. The sense response in the organs – the eyes, ears, tongue, nose and skin human body. – are highly specialised to receive stimuli from the environment. Sight Sight tells us more about the world than any other sense. The pupils change size to control how much light enters the eye. The different types of photoreceptor cells at the back of the eye transform the light into nerve signals for the brain. It is not only your eyes that allow you to 48 OXFORD SCIENCE 9 VICTORIAN CURRICULUM OXFORD UNIVERSITY PRESS Lice Li cen ns sed d to Da ani niel el Bee eek ek, fro rom W Weerr rrib beee eSSecondary College until 2027-12-31.  3.1: Testing your senses CHALLENGE Go to page 176. The lens focuses incoming light. Photoreceptor cells in the retina change light into nerve signals. The cornea bends incoming light. Nerve impulses travel through the optic nerve to the brain. The iris controls the amount of Figure 3 A crocodile’s eye has an elliptical (oval- light entering the shaped) pupil, which helps to protect its sensitive eye. retina from the bright light of day. Figure 4 Photoreceptors in the human eye transform light into nerve signals. see, but also your brain! The information from your eyes is transferred to your brain, which then tells you what you are seeing. Hearing The strumming of a guitar causes the particles in the air to vibrate. This in turn Figure 5 The large ears of some bats help them use causes your eardrum to vibrate. The vibrations sound waves to locate are transferred along the bones of the middle their prey. ear – the smallest bones in your body – and converted into nerve impulses. The brain then interprets the information, telling you what you are hearing. Nerve impulses travel through the auditory nerve to the brain. Sounds enter the ear through the ear canal. Eardrum The cochlea contains fluid that moves due Vibrations passing through to vibrations coming from the middle ear. the middle ear are changed to This motion becomes an electrical signal nerve impulses. that is passed to nerve cells. Figure 6 The human ear transfers vibrations to the middle ear. These vibrations become nerve impulses. OXFORD UNIVERSITY PRESS CHAPTER 3 CONTROL AND REGUL ATION 49 Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31.  Taste Smell Your tongue is covered in thousands of tiny Like taste, our perception of smell depends taste buds. You can see this in a mirror. on chemical receptors. The receptors in our Taste buds contain special receptor cells that nostrils detect chemicals in the air and then react to chemicals in foods. These chemical send messages to the brain, which interprets receptors can recognise basic kinds of taste the messages and tells us what we are smelling. molecules, such as sweet, salty, sour, bitter and Smell is closely linked to taste. If this seems umami (savoury). When you eat or drink, the strange, think about the last time you had a information from the taste receptor cells is sent bad cold and a blocked nose. Did it affect your to your brain through nerves. It is the mix of ability to taste? A lot of what people think is chemical molecules that your brain detects as taste is actually smell. the flavours you are tasting. Non-taster tongue Supertaster tongue Figure 7 A dog uses its tongue for many things, including taste and temperature control. Panting moves cool air over the tongue and lungs, allowing moisture to evaporate and thus cooling the body. Papillae Figure 8 The tongue is covered in bumps, called papillae, which contain tastebuds that enable us to taste. A supertaster has many more papillae than average, and a non-taster has fewer. Mucus provided by nasal sinuses helps to Smell receptors above nasal cavity trap bacteria and stimulate olfactory bulb, which small particles. sends messages to brain. Air moves through nasal cavity to back of throat. Air travels to Figure 9 Elephants use Air enters nose trachea and their trunks for a wide through nostrils. into lungs. range of smelling tasks, such as sensing danger. Figure 10 Smell receptors in human nostrils detect chemicals and send messages to the brain. 50 OXFORD SCIENCE 9 VICTORIAN CURRICULUM OXFORD UNIVERSITY PRESS Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31. Touch While the other four senses are in specific locations, touch is felt all over the body, through the skin. The inner layer of skin, called the dermis, contains many nerve endings that can detect heat, cold, pressure and pain. Information is collected by the different receptors and sent to the brain for processing Figure 11 The skin of a and reaction. human fingertip has about 100 touch receptors. Hair Sweat pore Epidermis Papillae Capillaries near Dermis surface of skin Subcutaneous fat layer Sweat gland Hair root Blood vessels Figure 12 A cross-section of human skin 3.1 Check your learning Remember and understand 6 ‘A person has more than five senses.’ 1 Define the term ‘stimulus’. Evaluate this statement by: 2 Stimuli can be changes in our immediate environment describing the five senses that are being referred to or changes within our bodies. Describe two examples describing what happens to your balance when you of each. spin around quickly (sense of balance) 3 Identify the five major sense organs. describing how your body reacts when you are sick (sensing bacteria) Apply and analyse deciding whether the statement is correct. 4 Describe two situations in which each sense organ would need to respond. 5 Compare (similarities and differences between) the way you detect smell and the way you detect taste. OXFORD UNIVERSITY PRESS CHAPTER 3 CONTROL AND REGUL ATION 51 Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31. 3.2 Nerve cells are called neurons In this topic, you Neurons are cells in our body that enable messages to be passed quickly. will learn A change is detected by the receptor and an electrical message is passed along the that: neuron to the synaptic terminal. Chemical neurotransmitters pass the message across the gap to the next neuron. The myelin sheath protects parts of the neuron and increases the speed of messages being sent. Dendrites are nerve endings that branch Nerves out of the cell body. These highly sensitive, thin neuron The basic unit of the nervous system is the branches receive information from the synaptic a nerve cell nerve cell, or neuron. Scientists believe that terminal of other neurons, allowing nerve cell body we may have up to 100 billion neurons in our impulses to be transmitted. the main part of a cell bodies, connected in paths called nerves. that contains the nucleus/ Neurons have many highly specialised genetic material features. Each neuron has a large cell body that axon connects to a long thin axon (Figure 1). An the part of a neuron (nerve axon carries nerve impulses away from the cell cell) that carries an electrical message away from the cell body. The axons connecting your spinal cord to body to the synapse your foot can be up to 1 m long. 1 Electrical myelin sheath At the end of the axon are small bulbs, called impulse passes a fatty layer that covers the synaptic terminals. Each synaptic terminal along neuron axon of a nerve cell releases information into the synapse (Figure 2). dendrite The next neuron receives these messages from 2 Neurotransmitters the part of a neuron (nerve the synapse via its dendrites. stimulated cell) that receives a message Nerves work just like electrical wires and and sends it to the cell body require insulation in the same way. The axons are covered by a fatty layer called the myelin sheath. The myelin sheath helps to speed up a nerve impulse along an axon by controlling its path. People with multiple sclerosis have damaged myelin sheaths. This means that the Neurotransmitters nerve impulse is disrupted, blocked or unable cross the synapse to move along the length of the axon. A person with multiple sclerosis can therefore have difficulties with movement. Cell body (soma) Myelin sheath Nucleus Direction of impulse Axon Dendrites Synaptic terminal Figure 2 Electrical messages are converted to (axon terminal) chemical messages (neurotransmitters), which Figure 1 A typical neuron cross the gap in the synapse. 52 OXFORD SCIENCE 9 VICTORIAN CURRICULUM OXFORD UNIVERSITY PRESS Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31.  3.2: Pipe cleaner neurons CHALLENGE Go to page 177. Dendrites bring information Interneuron Axon terminal to the cell body and axons take Axon information away from the cell Neurilemma body. Information from one Myelin sheath neuron flows to another neuron across a synapse. The synapse is a small gap separating neurons. When the message reaches the Cell body Schwann end of the axon, chemicals called Dendrites cell nucleus Node of Ranvier neurotransmitters are released from the synaptic terminal and Sensory Neuron Schwann travel across the gap in the synapse cell nucleus Cell body to the dendrite of the next neuron. In this way, electrical messages are passed around the body. Neurilemma There are three specialised Myelin sheath Sense types of neuron, all with Axon organ different jobs. Dendrites > Sensory neurons (or afferent Node of Ranvier neurons) are sensitive to various stimuli, collecting Motor Neuron information from either the Cell body body’s internal environment Myelin sheath Node of Ranvier or the outside world. Sensory Neurilemma neurons send the information they have collected to the Effector central nervous system for processing. Axon > Interneurons (or connector Schwann cell nucleus neurons) link sensory and Dendrites Skeletal muscle motor neurons, as well as other interneurons. Figure 3 In these examples of an interneuron, a sensory neuron Interneurons are the most and a motor neuron, you can see how they are structured synapse common neuron in your differently to send and receive different messages. a small gap between central nervous system two neurons that (brain and spinal cord). > Motor neurons (or efferent neurons) carry messages must be crossed by They only make connections from the central nervous system to muscle cells neurotransmitters with other neurons. throughout the body, which then carry out the response. neurotransmitter a chemical messenger that crosses the synapse 3.2 Check your learning between the axon of one neuron and the dendrite of Remember and understand 4 Describe the role of the myelin sheath. another neuron 1 With a partner, create a way to remember Apply and analyse sensory neuron the difference between sensory neurons, 5 Use a diagram to explain the problem a nerve cell that carries a motor neurons and interneurons. Be creative! message from a receptor to that may result from damage to the myelin Share your memory trick with the class. the central nervous system sheath. 2 Describe the features of a neuron that enable interneuron 6 Compare (the similarities and differences it to pass messages on to other neurons. a nerve cell that links sensory between) sensory neurons and motor and motor neurons; also 3 Describe where you will find sensory neurons. known as a connector neuron neurons that detect: 7 Contrast (the differences between) motor neuron a smell b taste sensory neurons and interneurons. a nerve cell that carries a c sound d touch message from the central e light. nervous system to a muscle cell OXFORD UNIVERSITY PRESS CHAPTER 3 CONTROL AND REGUL ATION 53 Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31. 3.3 The nervous system controls reflexes In this topic, you Receptors in the nervous system detect a stimulus and pass it on to control centres. will learn The control centres initiate a message to the effectors, which causes a response. that: Reflexes are special pathways that allow a response to occur before the brain has time to think. Video 3.3 Stimulus–response model Reflexes Microscope skills Stimuli can be in many different forms. A If you have ever accidentally touched something stimulus may be pressure or heat on the very hot, you will remember how quickly you skin, a puff of air or strong light in your snatched your hand away. In fact, it would have eye. The stimulus is detected by receptors been so quick that you didn’t even have time to and the message gets sent to the spinal cord think about it – it was automatic. reflex and the brain via sensory neurons. The A reflex, or reflex action, is an involuntary an involuntary movement spinal cord and brain are the control centre and nearly instantaneous movement in response in response to a stimulus of the nervous system. Interneurons in this to a stimulus. control centre pass the message on to other During a reflex action, the sensory neuron interneurons as your brain thinks about carries the message from the receptor to the how you should respond to the stimulus. spinal cord. The interneuron then sends two Stimulus Eventually, you make a decision and the messages at the same time: one to the brain and motor neurons pass the message on to the the other to the muscles via the motor neuron. muscles. In this case, the muscles are This means the muscle is moving at the same called the effectors, as they are the cells time as the brain gets the message (e.g. that Receptor that cause the body to respond. This simple the object is hot). This makes reflexes even pathway is called the stimulus–response faster than usual responses. Most reflexes help Via sensory model (Figure 1). us in survival situations. Can you think of the neuron advantages of these reflexes? Control centre Sensory neuron Interneuron Motor neuron Effector Sensory Spinal cord Via motor neuron receptors Response Figure 1 The stimulus– response model Figure 2 A reflex action ensures that your hand pulls away from the flame very quickly, even before you feel the pain. 54 OXFORD SCIENCE 9 VICTORIAN CURRICULUM OXFORD UNIVERSITY PRESS Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31.  3.3B: How fast is the nervous 3.3A: Testing reflexes system? CHALLENGE Go to page 177. CHALLENGE Go to page 178. )LJXUH*UDVSUHмH[. When an )LJXUH6QHH]LQJUHмH[. When )LJXUH6WDUWOHUHмH[. When a object is placed on a baby’s palm, their small particles land on receptors in the newborn baby is startled, they will fling fingers curl over and grasp it. back of your nose, the muscles in your their arms out wide and grab anything diaphragm force air out rapidly. they touch. )LJXUH3ODQWDUUHмH[. When a )LJXUH3DWHOODU NQHHMHUN UHмH[. blunt object (such as the blunt end of When a small section below the a pencil) is moved along the underside kneecap (the tendon that connects the of the foot, the toes usually curl muscle to the bone) is stimulated with a downwards. quick, firm tap, the foot will kick out. 3.3 Check your learning Figure 8 Quick reflexes! Remember and understand 4 Explain the advantage of a baby having 1 Define the following terms. the startle reflex. a stimulus 5 If a person has a damaged upper spinal cord, they may not be able to feel their b receptor toes. Analyse whether this will affect c effector their knee-jerk reflex (by describing how d response a person ‘feels’ their toes, describing 2 Describe the stimulus–response model the role of the spinal cord in a knee-jerk of regulation. reflex and determining whether damage Apply and analyse to the upper spinal cord will affect the messaging in a knee-jerk reflex). 3 Explain why the brain is not involved in a reflex action. OXFORD UNIVERSITY PRESS CHAPTER 3 CONTROL AND REGUL ATION 55 Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31. 3.4 The central nervous system controls our body In this topic, you > Humans are constantly receiving stimuli from their environment through the will learn peripheral nervous system. that: > Neurons use electrical messages that are passed along to neurons in the brain and spinal cord that make up your central nervous system. Video 3.4 The core of the nervous system Central nervous system Cerebrum central nervous system The central nervous system is the control Cerebellum the brain and spinal cord centre of the body. All incoming messages Brain stem from your environment and your responses Spinal cord to them are processed through your central nervous system. The two main parts of the central nervous system are the brain and the spinal cord. Thoracic nerves Brain The brain is the processing centre of the body and is mainly concerned with your Lumbar nerves survival. It is a soft, heavy organ surrounded by a tough skull. The Sacral nerves interneurons in the brain gather information about what is going on inside and outside the body. It then compares the information to events that have occurred previously, before making decisions about things such as internal changes and movements. The brain is also home to your memories, personality and thought processes. Lobes of the brain The cerebrum, or outer section of the brain, is divided into four lobes or sections. These lobes have specific functions. > The frontal lobe is at the front of the brain. Its functions include emotions, reasoning, movement and problem-solving. > The parietal lobe manages the perception of senses, including taste, pain, pressure, temperature and touch. > The temporal lobe is in the region near your ears. It deals with the recognition of sounds and smells. > The occipital lobe is at the back of the brain. Figure 1 The nervous system of the body is made up of the central nervous system and the peripheral nervous system. It is responsible for the various aspects of vision. 56 OXFORD SCIENCE 9 VICTORIAN CURRICULUM OXFORD UNIVERSITY PRESS Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31.  3.4: Sheep brain dissection SKILLS LAB Go to page 179. Figure 2 The The thalamus processes and cerebrum (the carries messages for sensory large pink area) information, such as information Parietal lobe is divided into sent from the ears, nose, eyes and four lobes, each skin, to the cortex. with a specific function. The cerebellum is important in the Frontal lobe Cerebrum fine control of Peripheral nervous system movement, balance and coordination. The peripheral nervous system is a large system made up of all the nerves outside the central nervous system. The peripheral nervous system carries information to and from the central nervous system to the rest of the body, such as the limbs and organs. The peripheral nervous system is divided into two parts. Occipital lobe > The somatic nervous system controls voluntary skeletal muscle movements, such as waving or reaching out to take an object. > The autonomic nervous system controls The brain stem sits mostly inside the involuntary actions, which happen without brain. At its base it becomes the spinal our conscious control. This includes cord. The brain stem is made up of heartbeat, digestion, respiration, salivation The medulla is the bottom three major parts – the medulla, the part of the brain stem and pons and the midbrain. The pons and perspiration. The autonomic nervous controls automatic assists in some automatic functions, system maintains your body’s internal such as breathing, and also controls functions, such as environment (homeostasis). sleep and arousal. The midbrain respiration (breathing) and The autonomic nervous system also has digestive system activities. contains areas that receive and two parts: the sympathetic division and the process sensory information, such as parasympathetic division. These two divisions movement and vision. often have opposite effects. For example, the Figure 3 Structure of the human brain. The fourth lobe of the cerebrum, the parasympathetic division slows down the heart temporal lobe (not shown here), is near the ears. rate, whereas the sympathetic division speeds up the heart rate. The systems work together to maintain a balance in the body. peripheral nervous 3.4 Check your learning system all the neurons (nerve cells) Remember and understand 4 Describe how the peripheral nervous that function outside the 1 Identify the two parts of the body that system and the central nervous system brain and spinal cord make up the central nervous system. work together. Use an example to somatic nervous system illustrate your answer. the part of the nervous system 2 Describe the role or function of the 5 Explain why, if you slipped and hit the that controls the muscles peripheral nervous system. attached to the skeletal system back of your head, everything might go Apply and analyse black. autonomic nervous system 3 Draw a scientific diagram of the brain the part of the nervous 6 Contrast (the differences between) system that controls that shows the four lobes. In each of the the somatic nervous system and the involuntary actions such lobes: autonomic nervous system. as heartbeat, breathing a write the functions that are carried out 7 Describe the possible effect on and digestion in that lobe behaviour that would occur if a b draw something to remind you of the person had damage to the frontal lobe functions carried out in that lobe. of their brain. OXFORD UNIVERSITY PRESS CHAPTER 3 CONTROL AND REGUL ATION 57 Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31.  3.5 Things can go wrong with the nervous system In this topic, you A slipped disc can press on the nerves in the spinal cord. will learn When the myelin sheath is damaged in multiple sclerosis, the movement of the that: body can be affected. Motor neurone disease affects messages being passed to the muscles. Alzheimer’s disease is caused by progressive damage to neuron functioning. The nervous system plays a very important role called a disc, which is filled with a thick fluid, in coordinating and regulating your body. Things or gel, and allows the vertebrae to move. If a that can go wrong with the nervous system include disc becomes weak and puts pressure on the the spinal cord being damaged (paraplegia), nerves entering or leaving the spinal cord, this things pressing on the nerves in the spinal cord will cause pain or numbness along the nerve. (slipped disc), the myelin sheath in neurons being Treatment usually involves pain relief, along damaged (multiple sclerosis), the motor neurons with exercises that strengthen the muscles in failing (motor neurone disease) and damage to the the back. Occasionally, surgery is required to neurons in the brain (Alzheimer’s disease). remove the damaged part of the disc. Spinal damage Multiple sclerosis Spinal injury is a major type of injury in The myelin sheath plays a very important role Australia, especially in young men. These in ensuring the electrical message passes along injuries commonly result from motor vehicle the axon of a neuron. If the myelin sheath is accidents, everyday falls and sports. damaged, the electric signal can be lost, like a When the spinal cord is damaged, the broken wire in an electric circuit. Your immune messages from the neurons below the level of system usually fights and kills bacteria and viral injury can no longer travel to the brain. This infections. In multiple sclerosis, the immune Ruptured means the individual cannot receive messages system mistakenly recognises myelin sheath discs from the sensors in this part of the body. It also cells as dangerous, and attacks and destroys means the messages from the brain cannot reach them. This means messages to and from the past the injury. How much of the body is able to senses (including the eyes, skin and bladder) Spinal nerve move after a spinal injury depends on where the and the muscles become lost. Muscles can injury is in the spinal cord. If it is high up, most become weak, and the sufferer can feel dizzy or Ruptured disc pressing on of the body is ‘cut off’ from the brain; if it is tired, or have difficulty seeing properly. Most spinal nerve lower down, then the upper body and arms may commonly, the symptoms appear for a short Lumbar be able to work as they normally would. time, before disappearing completely, and then vertebrae People with severe damage to the upper returning later on. This is called a relapsing– Normal part of the spinal cord have quadriplegia – they remitting cycle. healthy are unable to use their arms or legs. If the disc injury is very high, they may even have trouble Motor neurone disease breathing on their own. People with severe Figure 1 The vertebrae in your In motor neurone disease (also known as damage below the arms have paraplegia – they spine are separated from each amyotrophic lateral sclerosis, ALS), the other by fluid-filled discs. are still able to use their arms but not their legs. neurons that send messages to the muscles Rupturing of a disc can put become weak and eventually lose function. As pressure on the spinal nerves. Slipped disc the muscles grow weaker, they can cramp and Top: X-ray of spine, showing two ruptured discs. Bottom: Your backbone consists of 26 bones, or become stiff. This usually starts in the muscles A ruptured disc presses on the vertebrae, that surround the nerves of your in the legs and arms, before progressing to the spinal nerve, causing pain. spinal cord. Between each vertebra is a sac face and chest. This can affect the person’s 58 OXFORD SCIENCE 9 VICTORIAN CURRICULUM OXFORD UNIVERSITY PRESS Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31.  Dendrites ability to talk and, eventually, to breathe. Neurons in the brain are also affected by this Neuron disease. Scientists do not know what causes the Cell body motor neurons to lose function. Research in this area is continuing. Nucleus Alzheimer’s disease Myelin sheath Alzheimer’s disease is caused by progressive damage to the neurons in the brain. This Synapses gradually affects memory, and the ability Figure 3 AFL legend Neale to reason or plan and carry out everyday Daniher was diagnosed with Nucleus activities. Problems with short-term memory motor neurone disease (MND) Axon mean that the sufferer cannot remember in 2013. Daniher’s diagnosis what happened a few hours ago, or what they has increased awareness and Myelin fundraising for MND. are meant to be doing that day. The disease also has wider impacts. Sufferers can forget Normal nerve where they are and how to get home. This makes life very confusing for them and they Damaged myelin can become upset very easily. Symptoms can vary from day to day, depending on tiredness or stress. The cause of Alzheimer’s disease is not known. Research suggests that plaques develop around neurons in the Damaged nerve brain, making it hard for them to transmit messages. Chemical changes in the neurons Figure 2 The myelin sheath surrounds the axon and helps electrical messages to move along the nerve. may be caused by genetic, environmental and In multiple sclerosis, damage to the myelin sheath health factors. prevents the nerves from passing on messages. a Cerebral b Extreme shrinkage cortex of cerebral cortex Severely enlarged ventricles Extreme shrinkage Figure 4 Damage to the neurons Hippocampus Entorhinal of hippocampus in Alzheimer’s disease can cause cortex the brain to shrink. a Normal brain Cross-section of Cross-section of b Brain of a person with Alzheimer’s normal brain Alzheimer’s brain disease 3.5 Check your learning Remember and understand 5 Identify another name for motor neurone 1 Identify the name of the individual bones disease. Describe the role motor neurons that make up the spine. usually play in a healthy nervous system. 2 Contrast quadriplegia and paraplegia. Apply and analyse 3 Describe the role of a disc in the spinal 6 Think about where you were and what column. you were doing one hour ago. Describe 4 Explain why the destruction of the how you would be affected if you could myelin sheath causes symptoms in not remember this. multiple sclerosis. OXFORD UNIVERSITY PRESS CHAPTER 3 CONTROL AND REGUL ATION 59 Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31. 3.6 The endocrine system causes long-lasting effects In this topic, you The endocrine system uses chemical messengers called hormones to maintain will learn control and to regulate growth. that: Hormones travel through the bloodstream to receptors or target cells. The effects of hormones often last longer than the effects of the nervous system. The endocrine system is a collection of Video 3.6 glands that secrete (release) hormones. Fight, flight or freeze? The endocrine system The hormones are secreted directly into the If you are ever in a dangerous or frightening bloodstream and then travel around the body situation, you may experience a ‘fight, flight or endocrine system through the blood. Some cells in the body freeze’ response. You break out in a cold sweat, a collection of glands that have receptors that match the hormone, like your heart beats wildly, everything around you make and release hormones a lock to a key. These cells are called target seems to slow down and your senses bombard hormone cells. It only takes one hormone ‘key’ to cause you with information. a chemical messenger a change in the target cell ‘lock’. Most of these symptoms are triggered by that travels through blood the release of the hormone adrenalin (also The glands and organs of the endocrine vessels to target cells called epinephrine). Adrenalin is constantly system are spread throughout the body (see target cell Table 1 and Figure 1). produced by the adrenal glands in small doses. a cell that has a receptor that matches a specific hormone Table 1 Some organs and hormones of the endocrine system Organ Hormone Target tissue Main effects Hypothalamus Wide range of Pituitary gland Sends messages from nervous system to the neurohormones pituitary gland to control functions such as body temperature, hunger, thirst and sleep patterns Ovaries Progesterone Uterus Thickens wall of uterus to prepare for pregnancy Oestrogen Body cells Development of female sexual characteristics; aspects of pregnancy and foetal development Testes Testosterone Male reproductive Development and control of male sexual system, body cells characteristics; production of sperm Pancreas Insulin Liver, most cells Lowers blood glucose level Glucagon Liver Raises blood glucose level Pituitary gland Thyroid-stimulating Thyroid Changes the rate of thyroxine release from the hormone thyroid Antidiuretic Kidneys Reduces the amount of water reabsorbed hormone from the kidneys Pituitary growth Bones, muscles Stimulates muscle growth; controls the size of hormone bones Thyroid gland Thyroxine Body cells Affects rate of metabolism, and physical and mental development Parathyroid Parathyroid Blood Regulates the amount of calcium in the blood glands hormone Adrenal glands Adrenalin Body cells Increases body metabolism in ‘fight or flight’ response Pineal gland Melatonin Skin cells Involved in daily biological rhythms 60 OXFORD SCIENCE 9 VICTORIAN CURRICULUM OXFORD UNIVERSITY PRESS Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31.  3.6: Glands and organs of the endocrine system CHALLENGE Go to page 180. The adrenal glands are located above the kidneys. The usual function of this hormone Pineal gland is to stimulate the heart rate and enlarge blood Pituitary gland Hypothalamus vessels. However, when you are in danger, adrenalin takes on another role. It floods your Thyroid gland system, causing an increase in the strength and rate of the heartbeat, raising your blood Thymus pressure and speeding up the conversion of glycogen into glucose, which provides energy to the muscles. In this way, adrenalin prepares Adrenal gland Pancreas your body for the extra effort required should Kidney you need to defend yourself (fight), run away (flight) or hide (freeze). Panic attacks Sometimes the ‘fight, flight or freeze’ response can be triggered without any obvious reason. This means adrenalin can flood the body, causing the heart to pound, breathing to become fast and shallow, and a flood of sensory information to stimulate the brain. When this Ovaries Testes occurs, lights appear brighter, sounds are louder FEMALE MALE and smells stronger. These sensory messages can become jumbled as the brain struggles to make sense of all the information. This combination of endocrine and nervous system responses is called a panic attack. These symptoms are not life threatening and will eventually disappear. Support from friends and family can help. Figure 1 The human endocrine end system Figure 2 Adrenalin is re responsible for the 'fight, flight or freeze' response respons in mammals and can help them to survive. 3.6 Check your learning Remember and understand Apply and analyse 1 Id Identify if the h name off theh system ini your 5 C Compare ((the h similarities i and body that is responsible for hormones. differences between) a hormonal response 2 Describe what is meant by the phrase and a nervous response. Describe one ‘fight, flight or freeze’ and how it relates advantage for each system. to hormones. 6 Explain why telling someone to ‘calm 3 Describe the symptoms of a panic attack. down’ during a panic attack will not stop 4 Explain why the endocrine system is their symptoms. (HINT: Are they able to referred to as a communications system. control their hormones?) OXFORD UNIVERSITY PRESS CHAPTER 3 CONTROL AND REGUL ATION 61 Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31. 3.7 Homeostasis regulates through negative feedback In this topic, you The body needs to detect and correct changes in its levels of nutrients, water and will learn temperature to stay healthy. that: The process of regulating the internal conditions of the body is called homeostasis. Negative feedback occurs when the body responds in a way that removes the initial stimulus. Scientists have not yet discovered another planet that humans could inhabit. Humans can Homeostasis only survive in very specific environments. Our To maintain homeostasis, your body uses a bodies have particular requirements, including mechanism that is similar to a thermostat in a the right amount of food and water, oxygen and heater. When temperature receptors on your carbon dioxide. If you were lost in a desert or skin and in the hypothalamus of your brain in freezing temperatures, your body would try detect cooling down (stimulus), a message gets to maintain a temperature of about 37°C at all sent to a variety of effectors around your body. times, to keep all cells working efficiently. This Effectors are glands or muscles that cause a ‘business as usual’ approach of responding change in the way your body functions. This to stimuli to maintain a stable state is called may include muscles to make you shiver (to homeostasis homeostasis. warm up) or blood vessels to redirect the flow the process by which the of warm blood to the important organs in your body detects and responds body (heart, liver and brain). to stimuli to ensure a stable If the temperature receptors detect that internal state is maintained you are too hot (stimulus), then the effectors include your sweat glands and blood vessels. Figure 1 Homeostasis is your body’s ability to regulate and maintain a stable condition (balance) inside your body, regardless of changes to the Figure 2 When your body is stimulated by heat, external environment. homeostasis ensures you cool down by sweating. 62 OXFORD SCIENCE 9 VICTORIAN CURRICULUM OXFORD UNIVERSITY PRESS Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31.  3.7: Experiencing homeostasis EXPERIMENT Go to page 180. Your body responds by sending more blood, which is carrying heat, to your skin, where Pineal gland sweat is evaporating, carrying away the heat Pituitary gland Hypothalamus and cooling you down. This a negative feedback mechanism – the effectors respond Thyroid gland and, as a result, remove the stimulus. If you are too hot, then your body tries to cool you down. Thymus If you are too cold, then your body works to warm you up. Adrenal gland Pancreas Hormones at work Kidney The rate of hormone production and secretion is often regulated by a negative feedback mechanism. If a stimulus is received that indicates something in the body is happening ‘too much’, Figure 4 The pancreas is the endocrine organ responsible for the the body has receptors to detect it. The body regulation of blood glucose levels. responds by producing a hormone to remove the then receptors in the pancreas detect it. They negative feedback stimulus and return the body to normal. then release a hormone called insulin into the mechanism a regulatory loop in which Blood glucose blood. Insulin travels throughout the body the stimulus causes a to insulin receptors on the target muscle and As you eat, food gets broken down into smaller response that acts in the liver cells. These cells then act as effectors opposite direction to nutrients. All carbohydrates get broken down and remove glucose from the blood. This whatever is being regulated into simple sugars, including glucose. These causes the blood glucose to decrease, removing glucose molecules travel through your blood the original stimulus. This is an example of and provide energy for cellular respiration (the negative feedback. reaction of glucose with oxygen to produce If blood glucose levels are too low, your carbon dioxide, water and ATP). Too much body will use negative feedback to restore levels glucose in the blood is not healthy, because to a homeostatic state. Low glucose levels are it causes water to be lost from cells through detected by receptors in the pancreas (stimulus). osmosis. Your body tries to control the amount This time, the hormone glucagon is released into of glucose in your blood. If the concentration the blood. Receptors for glucagon are also found of glucose in your blood is too high (stimulus), on the effector cells in the liver and muscles. Glucagon binding to the receptors causes the Pancreas receptors muscle and liver cells to release stored glucose respond and release insulin into the blood (response), increasing the amount of blood glucose once again. Glucose increases Liver changes glucose to glycogen Blood sugar level Healthy glucose level Glucose decreases Liver releases its glycogen store as glucose 1 hour 2 hours Pancreas receptors Time after eating respond Figure 5 After you eat, your blood glucose levels and release glucagon increase. The body’s response is to release insulin, Figure 3 The pancreas and the liver work together which causes the muscle and liver effectors to to maintain healthy glucose levels in the body. remove the glucose and restore homeostasis. OXFORD UNIVERSITY PRESS CHAPTER 3 CONTROL AND REGUL ATION 63 Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31. Figure 6 Water controls around your body until it reaches target effector the chemical reactions Water regulation cells in your kidney. The ADH binds to the that occur in cells. You may have noticed that when you drink lot of receptors on the effector cells, causing them water, you need to visit the bathroom in the next to reabsorb extra water from your urine. This hour. Your body uses homeostasis to control the makes your urine more concentrated or darker balance of water in your body. Water is needed in colour. The extra water that was reabsorbed to control all the chemical reactions that occur in goes back into the blood, keeping the blood the cells. If there is too much or too little water, volume high. This is a form of negative these chemical reactions will be affected and the feedback, as the response (reabsorbing water cells can become damaged. from the urine and returning it to the blood) The water balance in your body is tightly results in a decrease of the stimulus (improving controlled by the hypothalamus in your brain. water levels in the blood). If it has been a hot day, or you have been doing Drinking a lot of water causes the blood physical exercise and sweating, then your body volume to increase. This is also detected by may have lost a lot of water. Receptors in the receptors in the hypothalamus. This time hypothalamus of the brain detect changes in the message to the pituitary gland is ‘STOP fluid levels in your blood and send a message to producing ADH’. The lack of ADH is detected the pituitary gland at the base of your brain. by the effector cells in the kidney, and they stop The pituitary gland releases a chemical reabsorbing water from the urine. This means messenger called antidiuretic hormone (ADH) the urine has more water in it, and it becomes into your blood. This hormone travels all very clear and diluted. Water content Water content of the blood of the blood LOW HIGH Too much salt Too much or sweating water drunk Water content Brain Brain of the blood normal produces produces more less ADH ADH High volume of water Low volume of water reabsorbed by kidney reabsorbed by kidney Urine output Urine output LOW HIGH (small volume of (large volume of concentrated urine) diluted urine) Figure 7 Water regulation in the human body 64 OXFORD SCIENCE 9 VICTORIAN CURRICULUM OXFORD UNIVERSITY PRESS Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31.  making you feel Oxygen and carbon dioxide puffed. The message homeostasis also goes to the heart Have you ever wondered why you become to make it beat faster. puffed when running a race? Oxygen and This makes the blood carbon dioxide in the blood are under strict move faster, carrying homeostatic control. You need the oxygen for the carbon dioxide to cellular respiration in a cell. Carbon dioxide is the lungs where it can the waste product of this reaction. be removed by breathing out. These two responses act Sprinting during a race causes the muscle as negative feedback, removing cells in your legs to use a lot of glucose and the stimulus of high levels of carbon oxygen and to produce a lot of carbon dioxide. dioxide in the blood. Figure 8 After a race, you The muscle cells release the carbon dioxide Meditation often involves sitting or lying may be puffed. into the blood, where it forms carbonic acid. This is not good for your body. The acid down and relaxing. This means the level of content of the blood is measured by receptors cellular respiration in muscles is low. Little in the medulla in the brain stem. If the level oxygen is used and little carbon dioxide is is too high from excess carbon dioxide, a produced. As a result, the levels of carbon message is sent through the nervous system dioxide in the blood decrease. The receptors to the muscles that control your breathing. in the medulla once again detect the change This causes the diaphragm to move faster, from the homeostatic state and signal the increasing the rate of your breathing and heart to slow its beat and the lungs to slow their breathing. 3.7 Check your learning Remember and understand Evaluate and create 1 Define the term ‘homeostasis’. 7 In type 1 diabetes, cells in the pancreas 2 Describe how your body responds to are unable to produce insulin. Predict cold weather. what effect this would have on blood 3 Describe how your blood sugar level glucose levels. Research how people with changes when you eat. type 1 diabetes ensure that their blood 4 Describe how your body responds to low glucose levels remain at the homeostatic blood sugar levels. level. 8 Describe how and why your body Apply and analyse responds to the following: 5 Identify the stimulus, location a drinking a bottle of water of receptors, effectors and response to b swimming 15 m under water high body temperature. c swimming in the ocean on a cold day. 6 If a negative feedback loop reduces the effect of a hormone, describe what a positive feedback loop should do. Figure 9 When you meditate, the carbon dioxide levels in your body decrease. OXFORD UNIVERSITY PRESS CHAPTER 3 CONTROL AND REGUL ATION 65 Liice censsed ed to Da Dani niiel Beek, eek, ee k fro om We Werr rrrriib bee ee Se ec con onda darry y Colle ege until 2027-12-31. //SCIENCE AS A HUMAN ENDEAVOUR// 3.8 Hormones are used in sport Erythropoietin is a hormone normally produced by the erythropoietin is produced by the kidneys. The erythropoietin travels through the blood kidneys to increase the number of red blood cells in the to receptors in the bone marrow. The effector body. Athletes can use this version of a negative feedback bone marrow cells then produce more red mechanism naturally or artificially to increase their blood cells to replace those lost. Exercising at a high altitude stimulates the performance on the sporting field. body to react as though there are not enough Many athletes and sporting clubs spend red blood cells to carry oxygen to the muscles. months training high in the mountains to help Erythropoietin is produced, causing the bone their performance in competitions. The air marrow to make extra red blood cells. It takes in the mountains is much thinner. Although about three weeks for the extra cells to become it is still 21 per cent oxygen, it is harder for a noticeable. When the athlete returns to sea level person to fill their lungs as the particles in the to compete, the red blood cells remain active air are spread out further. As a result, when a for up to a month. This means the athlete’s person first arrives at high altitude, their body blood is more efficient at carrying oxygen struggles to get enough oxygen. This can make to muscles, making the athlete less likely to the person feel tired, as they are unable to burn become fatigued (tired). Training at a high the glucose in aerobic cellular respiration. altitude uses the negative feedback mechanism to the athlete’s advantage. Negative feedback Some athletes bypass high-altitude training and inject erythropoietin directly into their in action blood. This is called blood doping. However, The body normally produces just enough red the amounts of hormone introduced into the blood cells to carry oxygen around the body. blood are not controlled. This can cause an When red blood cells die, a hormone called over-production of red blood cells, which strains the heart. The athlete is at risk of a heart attack or a stroke. Figure 2 Erythropoietin increases the production Figure 1 Training at a high altitude can increase an athlete’s performance. of red blood cells. 66 OXFORD SCIENCE 9 VICTORIAN CURRICULUM OXFORD UNIVERSITY PRESS Licensed to Daniel Beek, from Werribee Secondary College until 2027-12-31. Drug testing Medical uses of Erythropoietin was first synthesised in the erythropoietin laboratory in the 1990s. Unfortunately, it was Erythropoietin is produced in the kidneys. Any 10 years before drug testing could distinguish disease that affects kidney function will also the artificial hormone from naturally affect the production of erythropoietin. As a occurring erythropoietin. In 2002, at the result, a person with kidney disease will also Winter Olympic Games in Salt Lake City, have low levels of red blood cells. This is called United States, the first athlete was identified anaemia. Symptoms of anaemia are a pale as having a version of erythropoietin in their appearance and feeling tired when exercising. urine and blood. Regular injections of erythropoietin will increase the production of red blood cells and improve the person’s health. Figure 3 In 2013, Lance Armstrong admitted to Figure 4 Anaemia can make you feel tired when exercising. injecting erythropoietin to help him win world cycling events. 3.8 Develop your abilities Evaluating the ethics in sports should be allowed and which should be Sport competition prides itself on fairness banned. In each situation, justify your for all competitors. There are many ways decision (by describing how the athlete would to improve an athlete’s chances of winning be advantaged, describing the potential a competition, including training, special dangers to the athlete, describing whether diets, shaving body hair and wearing special all athletes would have equal access, and clothing that reduces air resistance. Some deciding whether the situation could be athletes undergo surgery to improve their described as cheating). ability to compete. This can include a golfer