IB BIO - 6.5 Nerves, hormones and homeostasis

• 6.5.1 

  • State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that can carry rapid electrical impulses.

• 6.5.1 

  • State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that can carry rapid electrical impulses.

• The nervous system is a complex network responsible for coordinating and regulating bodily functions, sensing and responding to stimuli, and processing information. It consists of two main components: the central nervous system (CNS) and the peripheral nervous system (PNS). Here's an outline of these components and their basic functions:

  • 1. Central Nervous System (CNS):

    •    - The CNS consists of the brain and spinal cord, which are enclosed and protected by the skull and vertebral column, respectively.

    •    - The brain serves as the control center of the nervous system, responsible for processing sensory information, initiating motor responses, regulating homeostasis, and higher cognitive functions such as thinking, memory, and emotion.

    •    - The spinal cord is a long, tubular structure that extends from the brainstem to the lower back. It serves as a pathway for transmitting signals between the brain and the rest of the body and is involved in reflex actions.

  • 2. Peripheral Nervous System (PNS):

    •    - The PNS includes all nerves and ganglia outside of the CNS and connects the CNS to the limbs and organs of the body.

    •    - It is further divided into the somatic nervous system and the autonomic nervous system.

    •    - The somatic nervous system controls voluntary movements and sensory perception, transmitting signals between the CNS and skeletal muscles, skin, and sensory receptors.

    •    - The autonomic nervous system regulates involuntary processes such as heart rate, digestion, and glandular secretion. It is subdivided into the sympathetic and parasympathetic divisions, which often have opposing effects on physiological functions.

  • 3. Neurons:

    •    - Neurons are specialized cells of the nervous system that are capable of generating and transmitting electrical impulses, known as action potentials or nerve impulses.

    •    - They are the basic functional units of the nervous system and are responsible for transmitting information between different parts of the body.

    •    - Neurons consist of three main parts: dendrites, cell body (soma), and axon. Dendrites receive incoming signals, the cell body integrates these signals, and the axon transmits the signal to other neurons, muscles, or glands.

    •    - Neurons communicate with each other and with other cells through junctions called synapses, where neurotransmitters are released to transmit signals across the synaptic gap.

• In summary, the nervous system consists of the CNS and PNS, which work together to regulate bodily functions and respond to external stimuli. Neurons are the specialized cells of the nervous system that transmit electrical impulses, enabling rapid communication and coordination throughout the body.

• 6.5.2 

  • Draw and label a diagram of the structure of a motor neuron.

• 6.5.3 

  • State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons.

• Nerve impulses, also known as action potentials, are electrical signals transmitted by neurons to convey information within the nervous system. These impulses travel along specific pathways and are conducted by different types of neurons. Here's an outline of how nerve impulses are conducted from receptors to the central nervous system (CNS) and then to effectors:

  • 1. Sensory Neurons:

    •    - Sensory neurons, also called afferent neurons, transmit nerve impulses from sensory receptors (such as those in the skin, eyes, ears, and internal organs) to the CNS.

    •    - These neurons have specialized structures, such as dendrites with receptor endings, that detect stimuli and convert them into electrical signals.

    •    - Sensory neurons transmit these signals along their axons to relay neurons or directly to the CNS, where the information is processed.

  • 2. Relay Neurons:

    •    - Relay neurons, also known as interneurons or association neurons, are located within the CNS and act as intermediaries between sensory neurons and motor neurons.

    •    - They receive nerve impulses from sensory neurons and process and integrate this information before transmitting it to other neurons.

    •    - Relay neurons play a crucial role in processing and interpreting sensory information and coordinating responses within the CNS.

  • 3. Motor Neurons:

    •    - Motor neurons, also called efferent neurons, transmit nerve impulses from the CNS to effectors, such as muscles or glands, to produce a response.

    •    - These neurons receive signals from relay neurons or directly from other neurons within the CNS and transmit them to the target tissues or organs.

    •    - Motor neurons have specialized endings called axon terminals that release neurotransmitters, stimulating muscle contraction or glandular secretion.

• In summary, nerve impulses are conducted through the nervous system by sensory neurons, relay neurons, and motor neurons. Sensory neurons transmit signals from sensory receptors to the CNS, relay neurons process and integrate this information within the CNS, and motor neurons transmit signals from the CNS to effectors to produce a response. This coordinated transmission of nerve impulses allows for the detection of stimuli, processing of information, and generation of appropriate responses by the body.

• 6.5.4 

  • Define resting potential and action potential (depolarization and repolarization).

• Resting Potential:

  • Resting potential refers to the electrical charge difference across the membrane of a neuron when it is not transmitting signals. In this state, the inside of the neuron is negatively charged relative to the outside due to an uneven distribution of ions. The resting potential of a neuron is typically around -70 millivolts (mV) and is maintained by the selective permeability of the neuron's membrane to different ions, such as sodium (Na+), potassium (K+), chloride (Cl-), and large negatively charged proteins. The resting potential is essential for the neuron's ability to generate and transmit action potentials.

• Action Potential:

  • An action potential is a rapid and transient change in the membrane potential of a neuron that occurs when it is stimulated above a certain threshold. It involves a sequence of events that lead to the depolarization and repolarization of the neuron's membrane. Here's a brief overview:

  • 1. Depolarization:

    •    - When a neuron is stimulated, channels in the membrane open, allowing sodium ions (Na+) to rush into the cell, depolarizing the membrane. This influx of positive ions causes the inside of the neuron to become less negative (more positive) relative to the outside.

    •    - If the depolarization reaches a threshold level (typically around -55 mV), voltage-gated sodium channels open more fully, leading to a rapid influx of sodium ions and a rapid increase in membrane potential. This rapid depolarization phase is known as the upstroke of the action potential.

  • 2. Repolarization:

    •    - After reaching its peak, the membrane potential begins to repolarize as voltage-gated potassium channels open, allowing potassium ions (K+) to move out of the cell. This outward movement of positive ions restores the negative charge inside the neuron.

    •    - As potassium ions continue to leave the cell, the membrane potential returns to its resting level, or even becomes more negative than resting potential. This phase is known as repolarization and is essential for resetting the neuron's membrane potential to prepare for the next action potential.

• Action potentials are the basis for the transmission of signals along neurons and are crucial for communication within the nervous system. They allow neurons to rapidly and efficiently convey information over long distances, enabling sensory perception, motor control, and cognitive processes.

• 6.5.5 

  • Explain how a nerve impulse passes along a non-myelinated neuron.

• In a non-myelinated neuron, the nerve impulse, also known as an action potential, passes along the axon through a process called continuous conduction. Here's how it occurs:

  • 1. Resting Potential: The neuron begins in a resting state with a negative charge inside relative to the outside. This resting potential is maintained by the unequal distribution of ions across the neuron's membrane, with more sodium ions (Na+) outside and more potassium ions (K+) inside.

  • 2. Depolarization: When a stimulus is received by the neuron, it triggers the opening of voltage-gated sodium channels in the membrane. Sodium ions rush into the neuron, causing a rapid depolarization of the membrane. This depolarization changes the membrane potential from negative to positive, creating an action potential.

  • 3. Propagation: The depolarization at one point of the membrane causes nearby voltage-gated sodium channels to open, initiating depolarization in the adjacent region. This process continues along the length of the axon, with the action potential propagating in a wave-like fashion.

  • 4. Repolarization: After depolarization, potassium channels open, allowing potassium ions to leave the neuron, restoring the negative charge inside. This repolarization phase follows the action potential, ensuring that the membrane potential returns to its resting state.

  • 5. Hyperpolarization: Sometimes, the membrane potential may briefly become more negative than the resting potential during repolarization. This phase is called hyperpolarization and is due to the prolonged opening of potassium channels.

  • 6. Refractory Period: After an action potential, the neuron enters a refractory period during which it is temporarily unable to generate another action potential. This ensures that action potentials propagate in one direction along the axon and prevents the signal from traveling backward.

• In summary, in a non-myelinated neuron, the nerve impulse passes along the axon through continuous conduction. Depolarization at one point of the membrane triggers depolarization in adjacent regions, allowing the action potential to propagate along the axon. Repolarization restores the membrane potential, and a refractory period prevents backward propagation of the signal. This process enables rapid and efficient communication within the nervous system.

• 6.5.6 

  • Explain the principles of synaptic transmission.

• Synaptic transmission is the process by which nerve impulses (action potentials) are transmitted from one neuron to another across a synapse. The synapse is the junction between two neurons, consisting of the presynaptic neuron (sending neuron), the synaptic cleft (the gap between neurons), and the postsynaptic neuron (receiving neuron). Here's an outline of the principles of synaptic transmission:

  • 1. Action Potential Arrival: When an action potential reaches the axon terminal of the presynaptic neuron, it triggers the opening of voltage-gated calcium channels. Calcium ions (Ca2+) rush into the axon terminal from the extracellular fluid.

  • 2. Neurotransmitter Release: The influx of calcium ions stimulates synaptic vesicles, which contain neurotransmitter molecules, to fuse with the presynaptic membrane and release their contents into the synaptic cleft via exocytosis.

  • 3. Neurotransmitter Binding: The neurotransmitter molecules diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane of the postsynaptic neuron. Neurotransmitter binding causes conformational changes in the receptor proteins, leading to the opening or closing of ion channels in the postsynaptic membrane.

  • 4. Postsynaptic Potential Generation: Depending on the type of neurotransmitter and receptor involved, the postsynaptic membrane may become depolarized (excitatory postsynaptic potential, EPSP) or hyperpolarized (inhibitory postsynaptic potential, IPSP). EPSPs make the postsynaptic neuron more likely to generate an action potential, while IPSPs make it less likely.

  • 5. Integration of Signals: The postsynaptic neuron integrates the excitatory and inhibitory signals it receives from multiple synapses. If the net effect is depolarization and reaches the threshold potential, an action potential is generated in the postsynaptic neuron's axon hillock.

  • 6. Termination of Signal: Neurotransmitter action is terminated through reuptake into the presynaptic neuron, enzymatic degradation in the synaptic cleft, or diffusion away from the synapse. This ensures that synaptic transmission is brief and temporally precise.

  • 7. Modulation and Plasticity: Synaptic transmission can be modulated by various factors, including neurotransmitter concentration, receptor properties, and neuromodulators. Synaptic plasticity, such as long-term potentiation (LTP) and long-term depression (LTD), underlies learning and memory processes by altering the strength of synaptic connections over time.

• In summary, synaptic transmission involves the release, binding, and action of neurotransmitters across the synapse to transmit signals between neurons. This process is essential for communication within the nervous system and underlies various physiological and cognitive functions.

• 6.5.7 

  • State that the endocrine system consists of glands that release hormones that are transported in the blood. 

• The endocrine system is a complex network of glands and organs that produce and release chemical messengers called hormones. These hormones are secreted into the bloodstream and travel throughout the body to regulate various physiological processes and maintain homeostasis. Here's an outline of how the endocrine system functions:

  • 1. Glandular Secretion: The endocrine system consists of several glands, including the pituitary gland, thyroid gland, adrenal glands, pancreas, ovaries, testes, and others. Each gland is specialized to produce specific hormones.

  • 2. Hormone Release: Hormones are synthesized and released by endocrine glands in response to various stimuli, such as changes in blood levels of certain substances, nervous system signals, or other hormones. The release of hormones is tightly regulated to maintain balance in the body.

  • 3. Transportation in the Blood: Once released, hormones enter the bloodstream and are transported to target cells or organs throughout the body. The bloodstream serves as a distribution system, allowing hormones to reach their target tissues even if they are located far from the gland that produced them.

  • 4. Target Cell Interaction: Hormones exert their effects by binding to specific receptors on target cells or organs. Each hormone has a unique molecular structure that enables it to interact with specific receptors, triggering cellular responses within the target tissues.

  • 5. Cellular Response: After binding to their receptors, hormones initiate various cellular responses, such as changes in gene expression, alterations in cellular metabolism, or modulation of physiological processes. These responses ultimately lead to the regulation of bodily functions and the maintenance of internal balance (homeostasis).

  • 6. Feedback Mechanisms: The endocrine system is regulated by complex feedback mechanisms that ensure hormonal balance in the body. Negative feedback loops help maintain stable hormone levels by inhibiting further hormone secretion when levels are high and stimulating secretion when levels are low.

  • 7. Integration with the Nervous System: While the endocrine system primarily functions through the release of hormones into the bloodstream, it also interacts closely with the nervous system. Neuroendocrine cells in the brain and other tissues integrate signals from the nervous system and release hormones in response to neural stimuli.

• In summary, the endocrine system consists of glands that release hormones into the bloodstream to regulate physiological processes and maintain homeostasis. Hormones travel throughout the body and interact with specific target cells or organs to initiate cellular responses. This intricate network of communication and regulation ensures coordinated functioning of the body's systems.

• 6.5.8 

  • State that homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance.

• Homeostasis is the process by which organisms maintain a stable internal environment despite external changes. It involves various physiological mechanisms that regulate key parameters within narrow limits to ensure optimal function and survival. Here's an outline of how homeostasis maintains the internal environment for several important factors:

  • 1. Blood pH Regulation:

    •    - Homeostasis maintains blood pH within a narrow range (usually around 7.35 to 7.45) to support proper cellular function.

    •    - Buffers in the blood, such as bicarbonate ions (HCO3-) and proteins, help to minimize changes in pH by neutralizing acids or bases.

    •    - The respiratory system regulates blood pH by adjusting the levels of carbon dioxide (CO2), which can act as an acid when dissolved in water.

  • 2. Carbon Dioxide (CO2) Concentration:

    •    - Homeostasis regulates the concentration of CO2 in the blood to maintain proper acid-base balance and respiratory function.

    •    - The respiratory system controls CO2 levels by adjusting the rate and depth of breathing to eliminate excess CO2 from the body through exhalation.

  • 3. Blood Glucose Concentration:

    •    - Homeostasis ensures that blood glucose levels remain within a narrow range (typically 70 to 100 mg/dL) to provide a steady supply of energy to cells.

    •    - The endocrine system, specifically the pancreas, regulates blood glucose levels through the release of insulin and glucagon hormones, which promote glucose uptake by cells or release glucose into the bloodstream, respectively.

  • 4. Body Temperature:

    •    - Homeostasis maintains body temperature within a narrow range (around 37°C or 98.6°F) to support enzyme function and metabolic processes.

    •    - The thermoregulatory system, including mechanisms such as sweating, vasodilation, and shivering, helps to regulate body temperature in response to changes in environmental temperature or internal heat production.

  • 5. Water Balance:

    •    - Homeostasis regulates water balance to ensure proper hydration and osmotic balance within cells and tissues.

    •    - The kidneys play a key role in maintaining water balance by regulating urine production and excretion based on the body's hydration status and electrolyte levels.

• In summary, homeostasis involves maintaining the internal environment within narrow limits for key parameters such as blood pH, carbon dioxide concentration, blood glucose concentration, body temperature, and water balance. This process requires the coordinated actions of various physiological systems, including the respiratory, endocrine, and thermoregulatory systems, to continuously monitor and adjust these parameters to meet the body's metabolic needs and maintain optimal function.

• 6.5.9 

  • Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms. 

• Homeostasis is the process by which living organisms maintain a stable internal environment despite external fluctuations. It involves the continuous monitoring of various physiological variables and the correction of any deviations from their optimal levels through negative feedback mechanisms.

  • 1. Monitoring Levels of Variables: Homeostasis begins with the constant monitoring of key physiological variables such as body temperature, blood pressure, blood glucose levels, pH balance, and others. Specialized receptors or sensors located throughout the body detect changes in these variables and send signals to control centers.

  • 2. Negative Feedback Mechanisms: When a physiological variable deviates from its set point, negative feedback mechanisms are activated to counteract the deviation and restore the variable to its optimal level. Negative feedback works by reversing the direction of the initial change, thereby maintaining stability within the system.

  • 3. Receptor Detection: Receptors or sensors detect changes in the levels of physiological variables and transmit this information to control centers in the body, such as the brain or specific regulatory organs.

  • 4. Control Center Response: Upon receiving signals from receptors, the control center evaluates the information and initiates an appropriate response to correct the deviation from the set point. This response is typically carried out through the activation of effectors, which are muscles, glands, or organs that produce a physiological change.

  • 5. Effector Action: Effectors implement the corrective action necessary to restore the physiological variable to its optimal level. For example, if body temperature increases above the set point, effectors such as sweat glands are activated to produce sweat, which cools the body and lowers its temperature.

  • 6. Restoration of Homeostasis: As the corrective actions take effect, the physiological variable returns to its set point or within its normal range. Once this occurs, the negative feedback loop is inhibited, and the response ceases. Homeostasis is restored, and the internal environment remains stable.

• In summary, homeostasis involves the continuous monitoring of physiological variables and the implementation of negative feedback mechanisms to correct deviations from their optimal levels. This process ensures the maintenance of a stable internal environment essential for the proper functioning of living organisms.

• 6.5.10 

  • Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering.

• The control of body temperature is crucial for maintaining homeostasis and ensuring the optimal functioning of various physiological processes. The body employs several mechanisms to regulate temperature, including the transfer of heat in the blood and the actions of key organs and systems. Here's an explanation of how body temperature is controlled:

  • 1. Hypothalamus: The hypothalamus, located in the brain, serves as the body's thermostat and plays a central role in temperature regulation. It receives input from temperature receptors throughout the body and initiates responses to maintain the body's set point, typically around 37°C (98.6°F

  • 2. Transfer of Heat in Blood: Blood plays a crucial role in transferring heat throughout the body. When the body temperature rises above the set point, blood vessels near the skin's surface dilate (vasodilation), allowing more blood to flow close to the skin. This facilitates the transfer of heat from the body's core to the skin's surface, where it can be released into the environment through radiation, convection, and conduction.

  • 3. Sweat Glands: Sweat glands are another important component of the body's cooling mechanism. When the body temperature rises, the hypothalamus signals the sweat glands to produce sweat. As sweat evaporates from the skin's surface, it absorbs heat from the body, helping to cool it down.

  • 4. Skin Arterioles: The arterioles (small blood vessels) in the skin play a role in regulating body temperature. During heat loss, these arterioles dilate to increase blood flow to the skin, allowing for efficient heat transfer. Conversely, during heat conservation, these arterioles constrict to reduce blood flow to the skin, minimizing heat loss.

  • 5. Shivering: Shivering is a mechanism by which the body generates heat to maintain its core temperature in cold environments. When the body temperature drops below the set point, the hypothalamus stimulates muscle contractions (shivering), which generate heat as a byproduct of muscle metabolism. This helps to raise the body's temperature back to its set point.

• Overall, the control of body temperature involves a coordinated effort of the hypothalamus, blood vessels, sweat glands, and muscles. Through vasodilation, sweating, and shivering, the body regulates heat production and loss to maintain its core temperature within a narrow range, ensuring optimal physiological function.

• 6.5.11 

  • Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in the pancreatic islets. 

• The control of blood glucose concentration is essential for maintaining energy balance and preventing fluctuations in blood sugar levels, which can have serious health consequences. The process involves the coordinated actions of hormones produced by the pancreas, specifically insulin and glucagon, as well as the α and β cells in the pancreatic islets (islets of Langerhans). Here's an explanation of how blood glucose concentration is regulated:

  • 1. Role of Insulin:

    •    - Insulin is a hormone secreted by β cells in the pancreatic islets in response to elevated blood glucose levels (hyperglycemia).

    •    - When blood glucose levels rise after a meal, insulin is released into the bloodstream. Insulin promotes the uptake of glucose by cells, particularly muscle, liver, and adipose tissue.

    •    - In muscle cells, insulin stimulates the translocation of glucose transporter proteins (GLUT4) to the cell membrane, allowing glucose to enter the cells and be used for energy or stored as glycogen.

    •    - In the liver, insulin promotes glycogen synthesis (glycogenesis) and inhibits glycogen breakdown (glycogenolysis), leading to a decrease in blood glucose levels.

  • 2. Role of Glucagon:

    •    - Glucagon is a hormone secreted by α cells in the pancreatic islets in response to low blood glucose levels (hypoglycemia).

    •    - When blood glucose levels drop, such as between meals or during fasting, glucagon is released into the bloodstream. Glucagon stimulates the liver to break down glycogen (glycogenolysis) into glucose, increasing blood glucose levels.

    •    - Additionally, glucagon promotes gluconeogenesis, a process where the liver synthesizes glucose from non-carbohydrate sources such as amino acids and glycerol.

  • 3. Negative Feedback Loop:

    •    - The actions of insulin and glucagon are part of a negative feedback loop that helps maintain blood glucose homeostasis. When blood glucose levels rise, insulin secretion increases, promoting glucose uptake and storage, which lowers blood glucose levels. Conversely, when blood glucose levels fall, glucagon secretion increases, stimulating glucose production and release from the liver, raising blood glucose levels back to normal.

• In summary, the control of blood glucose concentration involves the reciprocal actions of insulin and glucagon, which are secreted by β and α cells in the pancreatic islets, respectively. These hormones work together to regulate glucose uptake, storage, and production, ensuring that blood glucose levels remain within a narrow range to meet the body's energy needs.

• 6.5.12 

  • Distinguish between type I and type II diabetes.

• Type I and type II diabetes are two distinct forms of diabetes mellitus, a metabolic disorder characterized by high blood glucose levels. Here are the main differences between the two:

  • 1. Etiology:

    •    - Type I Diabetes: Type I diabetes, also known as insulin-dependent diabetes or juvenile-onset diabetes, is an autoimmune condition in which the body's immune system mistakenly attacks and destroys the insulin-producing beta cells in the pancreas. This results in an absolute deficiency of insulin production.

    •    - Type II Diabetes: Type II diabetes, also called non-insulin-dependent diabetes or adult-onset diabetes, is primarily characterized by insulin resistance, where cells become resistant to the effects of insulin, and by progressive loss of insulin secretion by the pancreas. It is often associated with genetic predisposition, lifestyle factors (such as obesity and lack of physical activity), and metabolic syndrome.

  • 2. Age of Onset:

    •    - Type I Diabetes: Type I diabetes typically develops during childhood or adolescence, although it can occur at any age. It accounts for about 5-10% of all diabetes cases.

    •    - Type II Diabetes: Type II diabetes usually develops in adulthood, often after the age of 40, although it is increasingly being diagnosed in children and adolescents due to rising obesity rates. It accounts for the majority of diabetes cases worldwide.

  • 3. Insulin Requirement:

    •    - Type I Diabetes: Individuals with type I diabetes require lifelong insulin therapy to replace the insulin that their bodies cannot produce. Insulin is typically administered via injections or insulin pumps.

    •    - Type II Diabetes: In the early stages of type II diabetes, insulin therapy may not be necessary, as the pancreas still produces insulin. However, as the disease progresses, some individuals with type II diabetes may eventually require insulin therapy, especially if other treatments (such as oral medications or lifestyle modifications) fail to adequately control blood glucose levels.

  • 4. Body Weight and Lifestyle Factors:

    •    - Type I Diabetes: Type I diabetes is not directly associated with obesity or lifestyle factors. It is an autoimmune condition with a strong genetic component.

    •    - Type II Diabetes: Type II diabetes is closely linked to obesity, sedentary lifestyle, unhealthy diet, and other metabolic risk factors. Excess body weight, particularly abdominal obesity, increases the risk of developing insulin resistance and type II diabetes.

  • 5. Treatment Approach:

    •    - Type I Diabetes: Treatment for type I diabetes focuses on insulin replacement therapy, blood glucose monitoring, and lifestyle management (including diet and exercise).

    •    - Type II Diabetes: Treatment for type II diabetes often involves lifestyle modifications (such as diet and exercise), oral medications to improve insulin sensitivity or stimulate insulin secretion, and sometimes insulin therapy if blood glucose levels cannot be adequately controlled with other measures.

• In summary, while both type I and type II diabetes are characterized by high blood glucose levels, they differ in their etiology, age of onset, insulin requirement, association with obesity and lifestyle factors, and treatment approaches. Type I diabetes is an autoimmune condition with an absolute deficiency of insulin, whereas type II diabetes is primarily characterized by insulin resistance and progressive loss of insulin secretion.