Coordination and Control

• The central nervous system consists of the brain and spinal cord, while the peripheral nervous system includes all the nerves outside of the central nervous system.
• Negative feedback occurs when conditions change from the ideal or set point and returns conditions to this point
• Nerves is a bundle of neurones that transmit electrical impulses from one part of the body to another.
• Motor neurons carry signals from the CNS to effectors (muscles or glands) to produce responses.
• Sensory neurons carry information about sensations such as touch, temperature, pain, pressure, taste, smell, hearing, and vision from receptors to the CNS.
• Homeostasis is the maintenance of constant internal environment of the body.
• Sensory neurons carry information about stimuli from receptors to the CNS.
• Mammalian nervous system is divided into two parts: central nervous system (CNS) and peripheral nervous system (PNS)
• The human nervous system allows us to make sense of our surroundings and respond to them, as well as to coordinate and regulate body functions.
• Neurones coordinate the activities of sensory receptors (eg. those in the eye), decision-making centres in the central nervous system, and effectors such as muscles and glands
• The 'flight-or-fight' response controlled by the sympathetic nervous system. The sympathetic nervous system controls the release of adrenaline, a hormone produced by the adrenal glands.
• Adrenaline is released during a fight-or-flight response. (For example, when a zebra sees a lion starting to chase it.)
• Negative feedback mechanisms works in the following way:

  • If the level of something rises, control systems are switched on to reduce it again
  • If the level of something falls, control systems are switched off to raise it again
• The internal conditions within the body need to be kept within set limits, in order to ensure that reactions in the body cells can function. When one of these conditions deviates far away from normal, if not brought back within set limits, the body will not function properly, and the eventual consequence without medical intervention will be death.
• Blood glucose levels are controlled by a negative feedback mechanism involving the production of two hormones – insulin and glucagon.
• Insulin and glucagon are made in the pancreas and are used to control the blood glucose concentration.
• Insulin is produces when blood glucose rises. Insulin stimulates liver cells to take up glucose from the blood and convert the excess glucose into glycogen to be stored. This reduces the glucose concentration into the blood.
• Glucagon is produced when blood glucose falls. Glucagon stimulates liver cells to convert stored glycogen into glucose to be released into the blood. This increases the glucose concentration in the blood.
• Type 1 Diabetes is a condition where the blood glucose levels are not able to be regulated as the insulin-secreting cells in the pancreas are not able to produce insulin.
• Signs of diabetes include:

  • increase blood glucose concentration
  • The presence of glucose in the urine
• Type 1 Diabetes can be treated by regular injections of insulin. This stimulates the liver to convert glucose into glycogen, which reduces the blood glucose level.
• If body temperature increases over 37 degrees Celsius, enzymes will denature and become less effective at catalyzing reactions such as respiration.
• Mammals also have layer of fatty tissue beneath the skin. This act as insulator because fat does not conduct heat well. This help to reduce the amount of heat lost.
• Regulation of temperature is controlled by the brain which contains receptors sensitive to the temperature of the blood, called hypothalamus.
• The skin also has temperature receptors and sends nervous impulses to the brain via sensory neurons.
• The brain responds to this information by sending nerve impulses to effectors in the skin to maintain the temperature within a narrow range of the optimum, 37 degrees Celcius.
• When we are hot, sweat is secreted by sweat glands. This cool skins by evaporation. Heat energy from the body is lost as liquid water in sweat becomes water vapour.
• When we are cold, skeletal muscles contract rapidly and we shiver. THe involuntary muscle contractions need energy from respiration and some of this is released as heat.
• When we are hot, hairs lie flat against the skin, allowing air to freely circulate. This increases heat transfer to environment by radiation.
• When we are cold, erect hairs trap a layer of air around the skin, which acts as an insulator, preventing heat loss by radiation.
• When we are cold, blood flow in capillaries slow down because arterioles leading to the skin capillaries get narrower. This is known as vasoconstriction.

  This reduces the amount of heat loss from blood by radiation as less blood flows through the surface of the skin.
• When we are hot, blood flow in capillaries increases because blood vessels to the skin capillaries get wider. This is known as vasodilation.

  This cools the body as blood (which carries heat around the body) is flowing at a faster rate through the skin surface, and so more heat is lost by radiation.
• A synapse is a junction between two neurones.
• Reflex arc is the pathway of impulse along the neurones. The pathway is:

  stimulus -> receptor -> sensory neurones -> relay neurones -> motor neurones -> effector -> response
• Neurotransmitter molecules are only produced on one side of the synapse (presynaptic membrane) while receptor proteins are only present on the other side (post-synaptic membrane).