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Nervous and Endocrine Aims: Must be able to compare and contrast the nervous and endocrine systems. Should be able to outline how nervous and endocrine systems work together. Could be able to explain examples of nervous and endocrine control in homeostasis. Comparison of Nervous and Endocrine Feature Nervous System Endocrine System Speed of Response Faster Slower Length of Action Shorter Longer Area of Action Can be Smaller Larger Transmission of Message Electrical Impulse and Neurotransmitter (Chemical Messenger) Hormones (Chemical Messenger) Structures Involved CNS and/ or PNS path Neurons (sensory, motor, inter) Neurotransmitters Neurohormones Blood vessels Blood Glands Blood vessels Blood Hormones (steroid, polypeptide based) Second messengers Nerves and Hormones Together Homeostatic responses usually involve BOTH the nervous system and the endocrine system. Some neurotransmitter substances stimulate neurons, muscles or glands others released by different neurons inhibit neurons, muscles or glands. The nervous system may stimulate glands to correct a change that disturbs homeostasis. As the response of the gland takes effect and the balance is restored, further action by the nervous system inhibits the gland. Blood Pressure Blood pressure is controlled by a negative feedback mechanism. If the blood pressure falls - Detected by pressure receptors in the muscle in the walls of blood vessels. The signal passes to the brain which responds by sending electrical signals to the heart and blood vessels. Nerves also produce neurohormones and stimulate the production of hormones that act on smooth muscle in blood vessels. The heart rate increases as a result of neuron and hormone signals. Core Body Temperature To maintain a stable core temperature, heat gain must balance heat loss. In humans, this balance results in a core temperature of about 37°C. Drop in temperature = Heat-sensing neurons in the skin transmit information to hypothalamus. The brain is alerted to a potential drop in temperature of the cells of the body. Messages sent out via neurons to ensure that changes occur in the body to balance the loss of heat. continued… Nerve impulses constrict blood vessels in the skin. – This reduces the surface area of the vessels across which heat can be lost by radiation. The hypothalamus sends messages to the skeletal muscles to contract = shivering. Continuous muscle contractions produce significant amounts of heat. The heat produced by metabolic processes within the body of a person contributes to the maintenance of a stable body temperature of the person. Blood Pressure Maintenance of blood pressure is also associated with water balance: As water varies, blood pressure varies: An increase in water brings about an increase in blood pressure. An decrease in water brings about a decrease in blood pressure. Kidneys are the major organ that control water balance in vertebrates. Blood Pressure Significant compounds: – Antidiuretic hormone (ADH) Vasopressin – Renin Vasopressin: – Produced by neurosecretory cells in the hypothalamus. – Very little present in blood if water is sufficient. – If blood water concentration drops, osomoreceptors in hypothalamus detect this and vasopressin is released… Blood Pressure 1. Vasopressin flows through the axons of the neurosecretory cells to the posterior pituitary where it is released into the bloodstream. 2. It is then transported to the kidneys - It increases the permeability of distal tubules and collecting ducts to water 3. The amount of water reabsorbed increases and blood water concentration returns to normal. Activity Complete flow diagrams for the control of Body Temperature, and blood water levels. Biozone pages p82/3