TE 17 Coordination in Humans PDF

TE 17 Coordination in humans e-aristo.hk/r/ bioccfc17.e The human brain is about 2% of your body weight but it uses up ab...

TE 17 Coordination in humans e-aristo.hk/r/ bioccfc17.e The human brain is about 2% of your body weight but it uses up about 20% of the total energy used by your whole body. Links to prior knowledge Chapter preview In the previous chapter, you learned how light is perceived 17.1 Coordination and the nervous system by the eyes and sound by the 17.2 Neurones as the basic units of the nervous system ears. In this chapter, you will look at the ‘behind the 17.3 The central nervous system scenes’ coordinators in your 17.4 Reflex actions and voluntary actions body which collect and 17.5 The endocrine system process information received from receptors and direct 17.6 Comparison between nervous coordination effectors to produce and hormonal coordination appropriate responses.  17 Coordination in humans Dementia It is normal that people become more forgetful as they get older. However, some people will develop more serious problems which affect their ability to cope with daily living. These problems may be the first signs of dementia. Dementia is a progressive disease of the brain. There is decline in cognitive and intellectual functions such as memory, comprehension, the ability to think, as well as language and judgement. Some patients also have emotional and behavioural problems. Alzheimer’s disease is one of the commonest causes of dementia. It is caused by the abnormal build-up of proteins in the brain. This interferes with the ability of the brain cells (neurones) to communicate with one another, and gradually destroys them. Normal Alzheimer's disease normal brain cells proteins and damaged tissue accumulate  The Alzheimer’s disease brain (right) has shrunk—the number of brain cells and their connections progressively reduce. Surf the net Visit the website below to learn more about dementia. e-aristo.hk/r/bioccstn1701.e Think about … 1. Which part of the brain is responsible for memory, comprehension and thinking? 2. How do neurones communicate with one another? (Refer to p.A2 for answers.) Answer dementia 認知障礙症 17- 2 Alzheimer's disease 阿茲海默氏症  TE 17 Coordination in humans 17.1 Coordination and the Learning objective nervous system Be aware of the two main forms of coordination in The human body contains receptors to detect stimuli from the humans Know how the nervous system internal and external environments, and has effectors to produce is organized responses. To produce appropriate responses to stimuli, receptors and effectors need to coordinate. The process of coordination is carried out by two body systems in humans (Figure 17.1): The nervous system is responsible for nervous coordination. The endocrine system is responsible for hormonal coordination. detected bring by coordination systems about stimuli receptors nervous system effectors responses endocrine system Figure 17.1 Coordination between receptors and effectors A general plan of the nervous system The human nervous system can be divided into two parts: the central nervous system (CNS) and the peripheral nervous system (PNS). brain cranial nerves central nervous peripheral nervous system (CNS) system (PNS) spinal cord spinal nerves Figure 17.2 The human nervous system coordination 協調 central nervous system 中樞神經系統 nervous system 神經系統 peripheral nervous system 外圍神經系統 17- 3 endocrine system 內分泌系統  TE 17 Coordination in humans The CNS consists of the brain and the spinal cord. It serves as the processor in nervous coordination. It receives sensory signals in the form of nerve impulses from receptors in different parts of the body, interprets the nerve impulses and initiates responses. The PNS consists of nerves outside the CNS. These nerves are named from where they arise: Cranial nerves arise from the brain. They link the brain with receptors and effectors in the head and the neck. Examples include the optic nerves and auditory nerves. Spinal nerves arise from the spinal cord. They link the spinal cord with receptors and effectors in the rest of the body. Key point The human nervous system can be divided into two parts: the central nervous system (CNS), which consists of the brain and the spinal cord. the peripheral nervous system (PNS), which consists of cranial nerves and spinal nerves. 17.2 Neurones as the basic units Learning objective of the nervous system Distinguish different types of neurones in terms of structure and functions The human nervous system is made up of nerve cells, called Be able to describe the neurones. They are specialized for transmitting nerve impulses. transmission of nerve impulses between neurones A. Structure of a neurone A neurone consists of a cell body and two types of nerve fibres, dendrons and axons (Figure 17.3 on the next page): The cell body contains the nucleus and a variety of organelles. Remember this Dendrons transmit nerve impulses towards the cell body. Nerve fibres are cytoplasmic Branches of dendrons are called dendrites. They receive processes extending from the cell body. Some nerve fibres can be information from a number of neurones. over a metre long. Axons transmit nerve impulses away from the cell body. brain 腦 spinal nerve 脊神經 nerve fibre 神經纖維 dendrite 樹突 17- 4 spinal cord 脊髓 neurone 神經元 dendron 樹突 cranial nerve 腦神經 cell body 細胞體 axon 軸突  17 Coordination in humans Most nerve fibres have a lipid covering called a myelin sheath. Such fibres are said to be myelinated. The myelin sheath has the following functions: To protect the nerve fibres. To insulate the nerve fibres. To speed up the transmission of nerve impulses. x600 cell body nucleus dendron Cell body of a neurone cytoplasm dendrites axon myelin sheath axon myelin sheath x5400 Axon (T.S.) surrounded by a Figure 17.3 Structure of a neurone myelin sheath myelin sheath 髓鞘 17- 5  TE 17 Coordination in humans B. Types of neurones There are three types of neurones (Figure 17.4): sensory neurones, which transmit nerve impulses from receptors to the CNS. A sensory neurone usually has a long dendron and a short axon, with an oval-shaped cell body lying outside the CNS. motor neurones, which transmit nerve impulses from the CNS to effectors. A motor neurone usually has a number of short dendrons and a long axon, with its irregularly shaped cell body lying inside the CNS. interneurones, which link sensory and motor neurones and transmit nerve impulses within the CNS. They are located in the CNS. Their dendrons and axons are short, and their cell bodies have irregular shapes. In the CNS interneurone dendron cell body of cell body axon motor neurone dendron axon axon cell body myelin sheath myelin sheath sensory neurone motor neurone dendron effector (e.g. muscle fibre) receptor (e.g. mechano- receptor in the skin) Key: transmission of nerve impulses Figure 17.4 Different types of neurones sensory neurone 感覺神經元 17- 6 motor neurone 運動神經元 interneurone 中間神經元  TE 17 Coordination in humans C. Structure of a nerve A nerve is made up of bundles of nerve fibres wrapped in tough connective tissue (Figure 17.5). Some nerves consist of nerve fibres of either sensory or motor neurones only. For example, the optic nerve is a cranial nerve consisting of nerve fibres of sensory neurones only. Spinal nerves, however, consist of nerve fibres of both sensory and motor neurones. nerve connective tissue nerve fibre x120 myelin sheath A bundle of nerve fibres (T.S.) blood vessels Figure 17.5 Structure of a nerve Flipped classroom D. Transmission of nerve impulses Synapses e-aristo.hk/r/ Nerve impulses are electrical messages that travel at high speed bioccflip1701.e along a neurone. Neurones link with each other by a junction called a synapse (Figure 17.6 on the next page). There is no physical contact between neurones and they are separated by a tiny gap, called a synaptic cleft. Therefore, nerve impulses cannot travel directly to the next neurone. Test yourself At the end of an axon is a synaptic knob. It is a swollen structure What is the significance of having with numerous mitochondria for energy production and synaptic a large number of mitochondria in vesicles which store chemicals called neurotransmitters. a synaptic knob? Answer (Refer to p.A2 for answers.) When a nerve impulse arrives at the synaptic knob, it stimulates synaptic vesicles to release neurotransmitters into the synaptic Remember this cleft. The neurotransmitters diffuse across the synaptic cleft and The neurone that releases bind to specific receptor sites on the dendron of the next neurone. neurotransmitters is called the The dendron is stimulated to generate a nerve impulse and continue presynaptic neurone. The neurone that receives neurotransmitters is the transmission. called the postsynaptic neurone. synapse 突觸 synaptic vesicle 突觸小泡 presynaptic neurone 突觸前神經元 synaptic cleft 突觸間隙 neurotransmitter 神經遞質 postsynaptic neurone 突觸後神經元 17- 7 synaptic knob 突觸小體  17 Coordination in humans Key: transmission of nerve impulse  A nerve impulse arrives, stimulating the synaptic mitochondrion synaptic mitochondrion knob. vesicle  Neurotransmitters are released from the synaptic vesicle. synaptic knob  Neurotransmitters synaptic vesicle diffuse across the synaptic cleft.  Neurotransmitters synaptic cleft bind to receptor sites on the dendron of the dendron. next neurone  The dendron is stimulated to generate x32,000 a nerve impulse. TEM of a synapse Figure 17.6 Transmission of nerve impulses across a synapse Synapses transmit information from one neurone to another by means of neurotransmitters. They are important for the working of the nervous system in the following ways: Synapses permit transmission of nerve impulses in one direction only, i.e. from the axon of one neurone to the dendron of the next neurone but not vice versa. This is because only synaptic knobs can secrete neurotransmitters and only dendrons possess the receptor sites for binding with neurotransmitters. Through synapses, one neurone can link with many other neurones to form neural networks, so they can communicate with one another. This allows complex coordination between different receptors and effectors. 17- 8  All answers TE 17 Coordination in humans Discovering science Study of synapses The study of synapses demonstrates that scientific development is affected by the technology and the types of equipment available at the time. For some time scientists had suspected that transmission at synapses was chemical, not electrical (by impulses). With the development of electronic microscopes, scientists were able to study the detailed structure of synapses and measure the synaptic gap. The gap was about 20 nm wide, which is simply too wide for an electrical impulse to jump across. Key point 1. A neurone consists of a cell body and nerve fibres (dendrons and axons). 2. Sensory neurones transmit nerve impulses from receptors to the CNS; motor neurones transmit nerve impulses from the CNS to effectors; interneurones link sensory and motor neurones and transmit nerve impulses within the CNS. 3. A nerve is made up of bundles of nerve fibres wrapped in tough connective tissue. 4. A synapse is the junction between two neurones. Transmission of information from one neurone to another is by means of neurotransmitters. Checkpoint The function(s) of synapses is/are to (1) ensure that nerve impulses travel in one direction only. (2) speed up the transmission of nerve impulses. (3) allow a neurone to communicate with many neurones. A. (2) only B. (3) only C. (1) and (3) only D. (1), (2) and (3) Learning objective 17.3 The central nervous system Know how the central nervous system is protected Understand the functions of A. Protection for the central nervous the main parts of the central system nervous system The brain and the spinal cord are made up of many closely packed neurones. They form the central nervous system (CNS), which coordinates all of the body’s activities. If the neurones are damaged, they are repaired slowly, or not repaired at all. 17- 9  TE 17 Coordination in humans The brain and the spinal cord are protected by various structures (Figure 17.7): Bones—The brain is enclosed in the cranium of the skull. The spinal cord is enclosed in the vertebral column. These bony structures offer mechanical protection to the CNS. Remember this Membranes—Both the brain and the spinal cord are covered by A variety of bacteria and viruses three protective membranes called the meninges. can cause inflammation of the meninges, a condition called Cerebrospinal fluid—The cerebrospinal fluid fills the space meningitis. Diagnosis can be done by testing the cerebrospinal fluid. between the inner and middle meninges, as well as the internal If bacteria are the cause, the cavities of the brain and the central canal of the spinal cord. person is treated with antibiotics. This fluid is formed in the cavities in the brain. It acts as a shock absorber and offers mechanical support to the brain and the spinal cord. It also supplies oxygen and nutrients to the neurones and removes wastes from them. cranium cranium brain three meninges brain tissue spinal cord cavity filled with central canal cerebrospinal fluid central canal spinal cord three meninges spinal nerve vertebra of the vertebral column Ventral Dorsal Figure 17.7 Structures protecting the brain and the spinal cord cranium 顱 cerebrospinal fluid 腦脊髓液 meningitis 腦膜炎 17- 10 vertebral column 脊柱 central canal 中央管 meninges 腦膜  TE 17 Coordination in humans B. Main parts of the brain and their functions The human brain consists of the cerebrum, the cerebellum and the medulla oblongata. cerebrum 3D model Human brain e-aristo.hk/r/ biocc3dm1701.e AR cerebellum medulla oblongata Figure 17.8 Human brain (L.S.) 1. Cerebrum The cerebrum is the largest part of the brain, which consists of left and right cerebral hemispheres (Figure 17.9). Each hemisphere is responsible for the opposite side of the body. The two hemispheres are connected by nerve fibres for communication. The thin outer layer of each hemisphere is called the cerebral cortex. It consists of grey matter (Figure 17.10), containing mainly the cell bodies of neurones which appear grey. Although it is less than 5 mm thick, it is highly folded to increase the surface area so that more neurones can be packed into it. Beneath the cerebral cortex is white matter, which consists of myelinated nerve fibres. This region appears white due to the white myelin sheaths. grey matter left cerebral right cerebral white hemisphere hemisphere matter cavities in foldings the brain Figure 17.9 Top view of the brain showing the left and Figure 17.10 Distribution of grey matter and right cerebral hemispheres white matter in the cerebrum cerebrum 大腦 cerebral hemisphere 大腦半球 white matter 白質 cerebellum 小腦 cerebral cortex 大腦皮層 17- 11 medulla oblongata 延髓 grey matter 灰質  TE 17 Coordination in humans The cerebrum is the site of consciousness. It controls voluntary Remember this actions, such as speaking and walking. It is also associated with Voluntary actions are actions that intelligence, reasoning, memory, emotions and personality. are under conscious control (i.e. can be controlled by will). There are three types of functional areas in the cerebral cortex (Figure 17.11): Test yourself The sensory areas receive nerve impulses from sensory A man had a stroke and therefore receptors and interpret them to produce sensations such as is unable to move the right side of his body properly. Which part of vision, hearing, taste, smell, touch and pain. his brain is most likely to be affected? The association areas integrate information from different (Refer to p.A3 for answers.) Answer sensory areas and make decisions in relation to the stored information from the past (i.e. memory). Nerve impulses are generated there and sent to different motor areas to initiate responses. The motor areas generate and send nerve impulses to effectors (e.g. skeletal muscles) to produce voluntary responses. touch, taste, smell limbs, trunk, face, comprehension mouth, tongue vision memory, thinking Key: hearing sensory area association area motor area Figure 17.11 Functional areas of the cerebral cortex voluntary action 隨意動作 motor area 運動區 17- 12 sensory area 感覺區 association area 聯合區  TE 17 Coordination in humans Remember this 2. Cerebellum The cerebellum does not initiate The cerebellum is located at the back of the brain under the movements but is responsible for cerebrum. Like the cerebrum, the outer layer of cerebellum is highly precision and fine control of voluntary movements. Damage to folded and made up of grey matter, and the inner layer is made up the cerebellum may result in jerky of white matter (Figure 17.12). uncoordinated movements. The cerebellum coordinates contractions of skeletal muscles for smooth movements and maintaining body posture and balance. grey matter white matter x5 Figure 17.12 Section through the cerebellum 3. Medulla oblongata The medulla oblongata (also known as the medulla) is located at the base of the brain. The distribution of grey matter and white matter in the medulla oblongata is the reverse of that in the cerebrum and the cerebellum—grey matter is found in the inner layer and white matter in the outer layer. Link it The medulla oblongata controls involuntary actions, which are not Reflex actions are involuntary and under conscious control. These include vital processes such as occur automatically. You will learn more about reflex actions in heart beat and breathing which maintain life. It also serves as the Section 17.6. reflex centre which coordinates many reflex actions in the head, such as sneezing, coughing, saliva secretion and swallowing. Practical 17.1 Examination of a human brain model Your teacher will show you a human brain model. Identify the main parts of the brain.  A human brain model involuntary action 不隨意動作 reflex centre 反射中樞 17- 13 reflex action 反射動作  17 Coordination in humans Key point 1. The brain is protected by the cranium and the spinal cord is protected by the vertebral column. The entire CNS is covered by three meninges. The cerebrospinal fluid fills the space between the inner and middle meninges, the internal cavities of the brain and the central canal of the spinal cord. 2. The brain consists of the cerebrum, the cerebellum and the medulla oblongata. 3. There are three types of functional areas in the cerebral cortex: sensory areas, association areas and motor areas. STSE connections How do scientists study human brains? In the past, the only way to study the functions of different parts of the brain was to examine the behaviours and abilities of people who suffered brain injuries. With the advancement of technology, scientists can now use a number of neuroimaging techniques to study how the brain works. Electroencephalography (EEG) works by attaching electrodes to the scalp to measure electrical signals that characterize brain activities. It is often used to study sleep and sleep disorders.  Attaching electrodes to a baby’s head for EEG Positron-emission tomography (PET) allows scientists to study specific brain regions. It tracks the uptake of radioactively labelled glucose to show metabolic activities of different areas in the brain. Glucose is the energy source for brain cells, and active cells take up more glucose than resting cells.  PET scan of a brain. Red colour indicates higher glucose consumption levels. Functional-magnetic resonance imaging (fMRI) reveals brain activities by detecting changes in blood flow. Areas of the brain with more nervous activities need more blood supply.  fMRI scan of a brain. Red colour indicates more active regions. electroencephalography 腦電圖 17- 14 positron-emission tomography 正電子掃描 functional-magnetic resonance imaging 功能性磁力共振  TE 17 Coordination in humans C. Spinal cord and its functions The spinal cord is a long cylindrical structure running from the medulla oblongata down through the vertebral column. A transverse section through the spinal cord shows that it has two distinct regions (Figure 17.13). The outer region is made up of white matter which consists of nerve fibres. The inner H-shaped region is made up of grey matter which contains the cell bodies of neurones. The central canal runs through the entire length of the spinal cord in the centre of this H-shaped region. It is continuous with the cavities in the brain and is filled with cerebrospinal fluid. Cross section of a vertebra and the spinal cord Dorsal vertebrae dorsal root spinal cord vertebral column spinal nerve ventral root Ventral Dorsal dorsal root grey matter ganglion central canal white matter Ventral Human spinal cord (T.S.) (x12) Figure 17.13 Structure of the spinal cord 17- 15  17 Coordination in humans Arising from the spinal cord are pairs of spinal nerves. Each spinal nerve is connected to the spinal cord by two roots: The dorsal (back) root contains sensory neurones whose cell bodies are located in the dorsal root ganglion. These neurones Remember this transmit nerve impulses from receptors to the spinal cord. The corresponding dorsal and ventral roots join to form a spinal The ventral (front) root contains motor neurones whose cell nerve, which is a mixed nerve bodies are located in the grey matter of the spinal cord. These containing both sensory and neurones transmit nerve impulses from the spinal cord to motor neurones. effectors. grey matter interneurone dorsal root dorsal root ganglion (contains cell bodies of sensory neurones) sensory neurone nerve fibres central canal from receptors to effectors spinal nerve white matter Key : motor neurone ventral root transmission of nerve impulses Figure 17.14 Nervous pathway into and out of the spinal cord The spinal cord has two main functions: To transmit nerve impulses between the brain and other parts of the body. To serve as the reflex centre for reflex actions involving the trunk and the limbs. Key point 1. The spinal cord runs from the medulla oblongata down through the vertebral column. 2. The outer region of the spinal cord is made up of white matter and the inner H-shaped region is made up of grey matter. 3. The spinal cord transmits nerve impulses between the brain and other parts of the body. It also serves as the reflex centre for reflex actions involving the trunk and the limbs. dorsal root 背根 17- 16 dorsal root ganglion 背根節 ventral root 腹根  All answers TE 17 Coordination in humans Checkpoint 1. Toys are often used to develop children’s fine motor skills. Which of the following parts is trained when children play with toys? A. cerebellum B. spinal cord C. pituitary D. medulla oblongata HKDSEE Biology 2015 Paper 1 Section A Q22 2. Which of the following combinations correctly identifies the distribution of grey matter and white matter in the cerebrum and spinal cord? Inner part of the cerebrum Inner part of the spinal cord A. white matter grey matter B. white matter white matter C grey matter grey matter D. grey matter white matter HKDSEE Biology 2018 Paper 1 Section A Q22 17.4 Reflex actions and voluntary Learning objective actions Compare the nature of reflex actions and voluntary actions A. What is a reflex action? A reflex action (also known as a reflex) is a rapid automatic response to a stimulus that allows the body to respond quickly and can protect us from danger. It is stereotyped, meaning that the same stimulus always leads to the same response. Reflex actions are involuntary because they are not under the control of the cerebrum. Most of them are inborn and no prior learning is required. Both the medulla oblongata and the spinal cord serve as reflex centres. Reflex actions that involve the medulla oblongata include sneezing, coughing, saliva secretion, swallowing, etc. Reflex actions that involve the spinal cord are called spinal reflexes. The withdrawal reflex and the knee jerk reflex are examples. withdrawal reflex 退縮反射 knee jerk reflex 膝躍反射 17- 17  TE 17 Coordination in humans Extras: Do you know… Some reflexes in newborn babies Babies are born with a number of reflexes to get them through life. Most of these reflexes disappear during the first six months of life due to a gradual increase in voluntary control over behaviour as the brain develops. Sucking reflex Moro reflex Grasp reflex The baby will automatically suck Sudden movement will make a baby When something is placed in a baby’s anything that touches the roof of its throw out its arms and legs in order to hand, it will grasp tightly and holds on mouth. catch hold of something. very well—enough to support its own weight. B. How does a reflex action work? A reflex action works by means of a reflex arc. This is the nervous pathway along which nerve impulses travel for the reflex action to take place. There are five components of a reflex arc: a receptor, a sensory neurone, an interneurone (may be absent), a motor neurone and an effector.  receptor (e.g. skin)  sensory neurone  interneurone  motor neurone  effector (e.g. muscle) spinal cord Figure 17.15 Components of a reflex arc reflex arc 反射弧 sucking reflex 吸吮反射 17- 18 Moro reflex 莫羅氏反射 grasp reflex 抓握反射  TE 17 Coordination in humans Animation 1. Withdrawal reflex Withdrawal reflex e-aristo.hk/r/ If your hand touches a hot or sharp object accidentally, your hand bioccani1701.e will withdraw automatically. This is called the withdrawal reflex. It protects us from being injured. Figure 17.16 shows the reflex arc of the withdrawal reflex. to the brain from the brain  Nerve impulses are transmitted along the (to cause sensation) spinal cord sensory neurone to the dorsal root spinal cord.  When the hand touches a sharp object, pain receptors in the skin are stimulated and they generate nerve impulses. ventral root  Nerve impulses are transmitted along the interneurone and the motor neurone to the arm muscle. Key : transmission of nerve impulses sensory neurone  The arm muscle contracts to interneurone withdraw the hand. motor neurone nerve fibre of an interneurone in the spinal cord Figure 17.16 Nervous pathway of the withdrawal reflex In this reflex arc, the receptor is linked to the effector by three neurones: a sensory neurone, an interneurone and a motor neurone. The reflex is fast as nerve impulses can usually travel through the reflex arc in less than 0.1 second. Although the cerebrum does not control the reflex, it will receive information from the sensory neurone through another interneurone (not part of the reflex arc). It takes longer for the nerve impulses to travel from the receptor to the cerebrum than to the effector. Therefore, the sensation of pain is felt after the hand has been withdrawn. You can see from figure 17.16 that in the spinal cord, there is an interneurone of another nervous pathway forming a synapse with the motor neurone in the reflex arc. This interneurone transmits nerve impulses from the cerebrum to initiate voluntary movement of the arm. The reflex action can be overcome voluntarily in this way. 17- 19  TE 17 Coordination in humans Animation 2. Knee jerk reflex Knee jerk reflex e-aristo.hk/r/ Sit with your legs crossed and hang one leg loosely on top of the bioccani1702.e other. Tap on your hanging leg just below the knee cap. Your hanging leg will give a little kick automatically. This is called the knee jerk reflex. This reflex helps maintain body posture and balance during walking. Figure 17.17 shows the reflex arc of the knee jerk reflex. to the brain (to cause sensation)  When the tendon  Nerve impulses are just below the knee transmitted along spinal cord cap is tapped, the the sensory neurone dorsal root stretch receptor in to the spinal cord. the upper thigh muscle is stimulated and it generates nerve impulses. ventral root  Nerve impulses are transmitted along the motor neurone to the  The thigh muscle thigh muscle. contracts and the leg kicks forward. Key : transmission of nerve impulses sensory neurone interneurone (not part of the reflex arc) Figure 17.17 Nervous pathway of the knee jerk reflex motor neurone In this reflex arc, the receptor is linked to the effector by only two neurones: a sensory neurone and a motor neurone. We can feel the tapping below the knee cap as nerve impulses are transmitted to the cerebrum by an interneurone of another nervous pathway which forms a synapse with the sensory neurone in the reflex arc. 17- 20  17 Coordination in humans Taking it further Conditioned reflex In the early 1900s, the Russian physiologist Ivan Pavlov (1849–1936) proved that some reflex actions can be acquired through learning and practice. In his experiment, Pavlov rang a bell and at the same time offered a dog some food. After a number of repeats of this procedure, he rang the bell without offering the dog any food. As soon as the bell rang, the dog started to salivate. This response of the dog is called a conditioned reflex. In a conditioned reflex, the response produced (salivation) has no direct connection with the stimulus (ringing a bell). Before conditioning Stimulus: food Response: salivation Stimulus: ringing bell No response (no salivation) During conditioning Stimulus: ringing bell and food Response: salivation After conditioning Stimulus: ringing bell Response: salivation  Ivan Pavlov’s experiment conditioned reflex 條件反射 17- 21  TE 17 Coordination in humans C. What is a voluntary action? A voluntary action is a conscious action that is under the control of the cerebrum. In contrast to reflex actions, voluntary actions do not take place automatically and are not stereotyped. In other words, you can use your ‘will’ to control these actions. Voluntary actions can take place without stimulation of receptors. In such cases, they are caused by nerve impulses generated in the cerebrum. The nervous pathway of a voluntary action is as follows (Figure 17.18):  Receptors detect a stimulus and generate nerve impulses.  The nerve impulses are transmitted along the sensory neurones to the sensory areas of the cerebrum.  The association areas of the cerebrum integrate nerve impulses from different receptors or sensory areas and relate them to past experiences. When a decision is made, nerve impulses are generated and transmitted to the motor areas.  The motor areas of the cerebrum generate and send nerve impulses along motor neurones to effectors.  The effectors produce responses. Key :  transmission of nerve impulses cerebrum sensory neurone interneurone  motor neurone   stimulus receptor spinal cord response effector  Figure 17.18 Nervous pathway of a voluntary action 17- 22  TE 17 Coordination in humans D. Comparison between reflex actions and voluntary actions Table 17.1 compares the differences between reflex actions and voluntary actions. Reflex action Voluntary action Nature Automatic, not under the control of will Voluntary, under the control of will Inborn, no learning is needed Not inborn, learning is needed Stimulus A stimulus detected by a receptor is A stimulus may not be needed, can be needed initiated by the cerebrum Pathway taken by nerve Does not involve the cerebrum, but Involves the cerebrum impulses involves the medulla oblongata or the spinal cord Pattern of responses Stereotyped, the same stimulus always Not stereotyped, responses may vary results in the same response depending on situations Speed of responses Faster Slower Table 17.1 Comparison between reflex actions and voluntary actions Worked example 17.1 The diagram below shows the arrangement of some neurones in a person. 1 X brain Y 2 Z 3 4 spinal cord 5 cont'd 17- 23  TE All answers 17 Coordination in humans (a) Using the numbers in the diagram, write the nervous pathway that would bring about (i) the withdrawal reflex of the arm. (1 mark) (ii) a voluntary action of the arm. (1 mark) (b) The person has some problems in his nervous system after an accident. Although he is able to move his right arm voluntarily, he cannot feel the pain or withdraw his arm when being pricked by a pin. A doctor confirms that his brain is functioning normally. Which part of the nervous pathway is most likely damaged? Explain your answer. (3 marks) Solution (a) (i) 3  4  5.................................................................... (1) Reminder (ii) 1  2  5.................................................................... (1) Voluntary actions may be initiated by the cerebrum directly. (b) Some sensory neurones / receptors are damaged................ (1) No nerve impulse is transmitted from the receptor to the brain Reminder to produce the sensation of pain.......................................... (1) Do not accept sensory areas of the cerebrum as the answer because the Since he can still move his right arm voluntarily, the motor question mentioned that the brain is neurones are still functioning normally................................. (1) functioning normally. Key point 1. A reflex action is a rapid automatic response to a stimulus that allows the body to respond quickly and can protect us from danger. It is involuntary (not under the control of the cerebrum), stereotyped and usually inborn. 2. A reflex arc is the nervous pathway for a reflex action. It consists of a receptor, a sensory neurone, an interneuron (may be absent), a motor neurone and an effector. 3. Voluntary actions are under conscious control of the cerebrum. Checkpoint Which of the following correctly compares reflex actions and voluntary actions? Reflex actions Voluntary actions A. responses may vary responses are always the same B. stimulus is optional stimulus is required C initiated by receptors initiated in the brain D. effectors must be muscles effectors can be muscles or glands HKDSEE Biology 2015 Paper 1 Section A Q23 17- 24  TE 17 Coordination in humans Learning objective 17.5 The endocrine system Understand the nature of hormonal coordination The human endocrine system consists of a number of glands called Use an example to illustrate hormone-mediated response endocrine glands. These glands secrete hormones to coordinate many physiological processes in the body. The coordination brought about by hormones of the endocrine system is called hormonal coordination. A. Endocrine glands and their functions Remember this Endocrine glands are ductless glands and secrete hormones In biology endo- means inside, directly into blood vessels (Figure 17.19). They differ from exocrine exo- means outside. Endocrine glands secrete their product inside glands (e.g. salivary glands, gastric glands and sweat glands), the gland, while exocrine glands which have ducts to carry their secretions. secrete their product through a duct to the outside of the gland. endocrine gland hormone travels throughout the body hormone-secreting cell capillary hormone diffuses into the bloodstream exocrine gland duct secreting cell product secreted Figure 17.19 Structure of an endocrine gland and an exocrine gland endocrine gland 內分泌腺 hormone 激素 17- 25  17 Coordination in humans The diagram below shows the main endocrine glands in the body, Remember this and the table lists the hormones they make and some of their Most hormones are proteins. functions. Some are steroids (e.g. the sex hormones). pituitary gland Link it thyroid gland The pancreas is both an endocrine gland and an exocrine gland. It secretes two hormones involved in adrenal gland the regulation of blood glucose. It is also a gland of the digestive pancreas system, secreting enzymes through the pancreatic duct into the small intestine (see Chapter 7). ovary testis (in female) (in male) Figure 17.20 Main endocrine glands of the human body Endocrine gland Hormone Some functions of the hormone Pituitary gland Growth hormone (GH) Stimulates growth of skeletal muscles and bones Anti-diuretic hormone (ADH) Regulates the water content of the blood (see Chapter 32) Follicle stimulating hormone (FSH) Stimulates egg development and oestrogen secretion in females (see Chapter 35) Luteinising hormone (LH) Stimulates ovulation in females (see Chapter 35) Thyroid gland Thyroxine Regulates the metabolic rate Pancreas Insulin Lowers blood glucose Glucagon Raises blood glucose Adrenal gland Adrenaline Prepares the body for physical activity or emergency Ovaries Oestrogen Stimulates the development of the female (in females) reproductive system and female secondary sexual characteristics Progesterone Regulates the menstrual cycle Testes Testosterone Stimulates the development of the male (in males) reproductive system and male secondary sexual characteristics Table 17.2 Main endocrine glands, the hormones they make and their functions pituitary gland 垂體 growth hormone 生長激素 luteinising hormone 促黃體激素 glucagon 胰高血糖素 progesterone 孕酮 17- 26 thyroid gland 甲狀腺 anti-diuretic hormone 抗利尿激素 thyroxine 甲狀腺素 adrenaline 腎上腺素 testosterone 睾酮 adrenal gland 腎上腺 follicle stimulating hormone 促卵泡激素 insulin 胰島素 oestrogen 雌激素  17 Coordination in humans B. Nature of hormonal coordination In hormonal coordination, responses are mediated by hormones Remember this which serve as chemical messengers travelling throughout the Most organs respond to a number body in the bloodstream. of hormones because they have more than one type of target cells Hormones are very specific and will only act on their target organs. or their cells have more than one type of hormone receptors. The The cells of these organs have specific receptor sites for recognizing shape of the receptor is the hormones and they are called target cells. Binding of hormone complementary to the shape of molecules to the receptor sites stimulates the target cells to produce the hormone molecule. specific responses. Cells other than target cells lack the specific receptor sites and do not respond to the hormone. Link it The regulation of blood glucose is an example of hormonal You will learn more about blood coordination. Figure 17.21 outlines the action of the hormone glucose regulation in Chapter 19. insulin to lower high blood glucose levels to normal.  Carbohydrates from the diet are broken down into glucose, which is then absorbed into the blood. glucose  Cells in the pancreas detect an increase in blood glucose levels and secrete more insulin into the blood. small intestine pancreas blood circulation insulin liver  The blood glucose level  Insulin is transported by blood throughout the body. returns to normal. glucogen  Insulin molecules bind to receptor sites in the cell membrane of liver cells. Liver cells are stimulated to take up more glucose from the blood and convert excess glucose into glycogen. Figure 17.21 Regulation of blood glucose through the action of insulin 17- 27  TE All answers 17 Coordination in humans Hormones are effective in very low concentrations, but they have widespread effects. One hormone may affect a number of target organs situated far away from the gland that produces the hormone. The effects are usually long-lasting. Key point 1. The endocrine system is responsible for hormonal coordination. It consists of endocrine glands which secrete hormones directly into the bloodstream. 2. Hormones are chemical messengers. They are very specific and will only act on target organs. They are effective in very low concentrations, but can have widespread and long-lasting effects. Checkpoint Which of the following statements about a hormone is/are correct? (1) It is transported in the blood. (2) It is secreted by a ductless gland. (3) It acts on one target organ only. A. (1) only B. (3) only C. (1) and (2) only D. (1), (2) and (3) 17.6 Comparison between nervous coordination and Learning objective hormonal coordination Compare nervous coordination and hormonal coordination Both the nervous system and the endocrine system coordinate body activities by transmitting messages to effectors to produce responses. Nevertheless, there are differences between nervous coordination and hormonal coordination (Table 17.3 on the next page). 17- 28  All answers TE 17 Coordination in humans Nervous coordination Hormonal coordination System involved Nervous system Endocrine system, circulatory system Components of the Brain, spinal cord, nerves, neurones Endocrine glands, blood system Nature of message Electrical (nerve impulses) and Chemical (hormones) chemical (neurotransmitters) Route of transmission Along nerve fibres and across synapses Bloodstream Speed of transmission Faster Slower Responses coordinated Voluntary actions, reflex actions and Growth and development, reproduction, other involuntary actions regulation of the internal environment Speed of response Usually faster Usually slower Duration of response Short-term Usually longer-lasting Area affected Localized (restricted to the effectors Widespread (one hormone may affect with nerve supply) several widely separated target organs at the same time) Significance Coping with sudden stimuli or Synchronizing different parts of the emergencies body to bring about overall responses for sustaining long-term survival Table 17.3 Comparison between nervous coordination and hormonal coordination Checkpoint Which of the following comparisons between nervous coordination and hormonal coordination is incorrect? Nervous coordination Hormonal coordination A. Messages are electrochemical Messages are chemical in nature. in nature. B. It is faster in action. It is slower in action. C. It copes with sudden stimuli. It deals with prolonged responses. D. The effect is widespread. The effect is localized. 17- 29  All answers 17 Coordination in humans Article reading Split brain experiment When scientists want to study the functions of a particular biological structure, one approach is to remove it and find out what happens. In the 1960s, Roger Sperry (1913–1994) studied the functions of the corpus callosum, a thick band of nerve fibres that connects the right and left cerebral hemispheres. He performed experiments on patients whose hemispheres had been separated by cutting the corpus callosum to control epilepsy. One experiment was as follows: 1. A patient was blindfolded. 2. A chosen object (e.g. a tennis ball) was placed in the patient’s left hand. No one must name the object to the patient. 3. The patient was asked to put down the object and then to retrieve it from a mixture of objects with the left hand.  Observation 1 The patient could find the tennis ball. blindfold 4. The patient was asked to retrieve the object from a mixture of objects with the right hand.  Observation 2 The patient could not find the tennis ball. 5. The patient was asked to name the chosen object.  Observation 3 The patient could not name the chosen ▲ An experiment to study the effect of object. cutting the corpus callosum in a patient Sperry showed that the two cerebral hemispheres were not communicating after the corpus callosum had been cut. Further studies confirmed that the left and right cerebral hemispheres are specialized in different tasks. For example, the left hemisphere is responsible for language and logical thinking, while the right hemisphere is associated with creativity and artistic ability. Sperry was awarded the Nobel Prize in Physiology or Medicine in 1981. Questions 1. Based on your knowledge of the two cerebral hemispheres, explain how the above experiment demonstrates that the two cerebral hemispheres are not communicating in the split brain patient. (3 marks) 2. Why must no-one name the object to the patient? (1 mark) 3. Why did the patient fail to name the chosen object? (1 mark) corpus callosum 胼胝體 17- 30 epilepsy 腦癇症  17 Coordination in humans e-dictionary Key terms e-aristo.hk/r/ bioccedict.e axon 軸突 p.4 medulla oblongata 延髓 p.11, 13 cell body 細胞體 p.4 motor neurone 運動神經元 p.6 central nervous system 中樞神經系統 p.3, 9 myelin sheath 髓鞘 p.5 cerebellum 小腦 p.11, 13 nerve fibre 神經纖維 p.4 cerebral cortex 大腦皮層 p.11 neurone 神經元 p.4 cerebrospinal fluid 腦脊髓液 p.10 neurotransmitter 神經遞質 p.7 cerebrum 大腦 p.11 peripheral nervous system 外圍神經系統 p.3 dendron 樹突 p.4 reflex action 反射動作 p.13, 17 dorsal root 背根 p.16 reflex arc 反射弧 p.18 dorsal root ganglion 背根節 p.16 sensory neurone 感覺神經元 p.6 endocrine gland 內分泌腺 p.25 spinal cord 脊髓 p.4, 15 grey matter 灰質 p.11 synapse 突觸 p.7 hormone 激素 p.25 ventral root 腹根 p.16 interneurone 中間神經元 p.6 voluntary action 隨意動作 p.12, 22 involuntary action 不隨意動作 p.13 white matter 白質 p.11 Summary Coordination and the nervous system 17.1 1. In humans, coordination is carried out by two body systems: the nervous system and the endocrine system. 2. The human nervous system can be divided into two parts: the central nervous system (CNS), which consists of the brain and the spinal cord. the peripheral nervous system (PNS), which consists of cranial nerves and spinal nerves. 17.2 Neurones as the basic units of the nervous system 3. A neurone consists of a cell body and nerve fibres (dendrons and axons). 4. Neurones are adapted for transmitting nerve impulses: Feature Adaptation A neurone has long nerve fibres To transmit nerve impulses over a long distance A dendron has many branches (called To receive information from other neurones so that dendrites) each neurone can communicate with many others Most nerve fibres are surrounded by a To protect the nerve fibres myelin sheath To insulate the nerve fibres and prevent loss of nerve impulses to the surroundings To speed up the transmission of nerve impulses 17- 31  17 Coordination in humans 5. There are three types of neurones: Type of neurone Transmission of nerve impulses Characteristics Sensory neurone From receptors to the CNS Long dendron; short axon Cell body lying outside the CNS Motor neurone From the CNS to effectors Very short dendrons; long axon (muscles and glands) Cell body lying inside the CNS Interneurone Within the CNS Short dendrons; short axons Cell body lying inside the CNS 6. A nerve is made up of bundles of nerve fibres wrapped in tough connective tissue. 7. A synapse is the junction between two neurones. Transmission of information from one neurone to another is by means of neurotransmitters: Key: transmission of nerve impulses  A nerve impulse arrives, mitochondrion stimulating the synaptic knob.  Neurotransmitters are released from the synaptic vesicle. synaptic knob  Neurotransmitters diffuse synaptic vesicle across the synaptic cleft. synaptic cleft  Neurotransmitters bind to receptor sites on the dendron. dendron of the next neurone  The dendron is stimulated to generate a nerve impulse. 8. Synapses are important in the following ways: They ensure that nerve impulses are passed on in one direction only, i.e. from the axon of one neurone to the dendron of the next neurone. They allow one neurone to communicate with many other neurones to achieve complex coordination. 17- 32  17 Coordination in humans 17.3 The central nervous system 9. The CNS is protected by bones, three meninges and the cerebrospinal fluid. 10. The brain is protected by the cranium and the spinal cord is protected by the vertebral column. 11. The cerebrospinal fluid fills the space between the inner and middle meninges, the internal cavities of the brain and the central canal of the spinal cord. It serves: as a shock absorber. to offer mechanical support to the brain and the spinal cord. to supply oxygen and nutrients to the neurones and remove wastes from them. 12. The brain consists of three main parts: Part of the brain Structural characteristics Functions Cerebrum Highly folded surface Site of consciousness Outer grey matter; inner white matter Controls voluntary actions Cerebellum Highly folded surface Coordinates contractions of skeletal muscles Outer grey matter; inner white matter Maintains body posture and balance Medulla Relatively smooth surface Controls involuntary actions oblongata Outer white matter; inner grey matter Serves as the reflex centre for many reflex actions in the head 13. The cerebral cortex can be divided into three functional areas: The sensory areas receive nerve impulses from sensory receptors and interpre