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Homeostasis Homeostasis describes all of the processes that happen in a cell or organism to maintain (keep) conditions optimal. This is needed to respond to changes in the internal and external environment. Enzyme functioning • Because humans are organisms that live in a changing environment, we must regulate our body’s internal conditions to make sure our enzymes and cells function well. Homeostasis describes all of the processes that happen in a cell or organism to maintain (keep) conditions optimal. This is needed to respond to changes in the internal and external environment. Denaturing • If conditions are not optimal, then our enzymes can denature (change shape). • This reduces their ability to catalyse (speed-up) metabolic reactions (chemical reactions in organisms). What is homeostasis and why is it necessary? • Because humans are organisms that live in a changing environment, it is important to regulate our body’s internal conditions to ensure that our enzymes and cells function well. • If conditions are not optimal, then our enzymes can denature, reducing their ability to catalyse metabolic reactions. • Regulating Internal Conditions • Humans must regulate their body’s internal conditions to make sure that enzymes and cells function well. The conditions that need to be regulated are: • Internal body temperature • Blood sugar levels • Water levels • Carbon dioxide levels • Urea concentration (in Urine) Control Systems Control systems use both nervous and chemical responses. Control systems are made up of three parts: Receptors • Receptor cells detect changes in the environment. Effectors (muscles or glands) • Effectors (muscles or glands) carry out responses to stimuli (events or things) that help to restore optimum levels. Coordination centers • Coordination centres receive and process information arriving from receptor cells. The Human Nervous System The nervous system protects organisms from harm by responding to changes in the environment. It does this by coordinating communication between different parts of organisms. The nervous system is made up of: The brain • The brain is one of the components (parts) of the central nervous system (CNS). • The CNS coordinates the response of effectors. • Effectors are muscles or glands that act in response to a change in the internal or external environment. The Human Nervous System The nervous system protects organisms from harm by responding to changes in the environment. It does this by coordinating communication between different parts of organisms. The nervous system is made up of: The brain • The brain is one of the components (parts) of the central nervous system (CNS). • The CNS coordinates the response of effectors. • Effectors are muscles or glands that act in response to a change in the internal or external environment. The spinal cord • The spinal cord is the other component (part) of the CNS. It is also important in coordinating the response of effectors to changes in the environment. The neurones (nerve cells) • Neurones (nerve cells) carry electrical impulses (signals) between receptors, the central nervous system (CNS) and effectors. Synapse: • At each junction of the reflex arc, there is a synapse. • Synapses are gaps between neurones. Nerve impulses must travel across these gaps: o The electrical impulse reaches the end of the neurone before the synapse. o This triggers the release of chemicals called neurotransmitters. o The neurotransmitters diffuse (move down a concentration gradient) across the synapse. o The neurotransmitters bind to receptors on the next neurone. o The presence of the neurotransmitter causes the production of an electrical impulse in the next neurone. Effectors bring about actions in response to a change in the internal or external environment. Such actions include muscles contracting and glands secreting hormones. Reflex Actions Reflex actions allow us to respond to dangerous situations rapidly and automatically. Reflex actions do not involve conscious thought. The nervous system responds to stimuli (events or things) via a reflex arc. Some examples of reflexes are: Dropping hot objects, Blinking and sneezing. Components of a Reflex Arc The different parts of a reflex arc are: • A stimulus can be any change in the environment to which the body needs to respond. • The stimulus is detected by a receptor. Receptor • Receptors are found all over the body. • They detect the change in the environment and initiate (start) a signaling process within the body. • The signal is picked up by a neurone (nerve cell). Neurones • There are three types of neurone (nerve cell): o The sensory neurone, which carries the signal in the form of an electrical impulse to the central nervous system (CNS). o The relay neurone (in the CNS) relays the electrical impulse from the sensory neurone to the appropriate motor neurone. o The motor neurone is another type of nerve cell that carries the electrical impulse from the CNS to an effector. Effector • An effector is a muscle or gland that brings about an action in response to the change in the internal or external environment. Response • The response can be any action that helps the organism to avoid the harmful situation. • The stimulus is detected by a receptor. • The sensory neurone carries the signal, in the form of an electrical impulse, to the central nervous system (CNS). • The motor neurone carries the electrical impulse from the CNS to an effector. • An effector (a muscle or gland) brings about an action in response to the change in the internal or external environment