Nervous system and hormones

• The hormonal system is slow, long lasting, and its method of transformation is chemicals in the blood stream. The nervous system is fast, short lasting, and its method of transformation is electrical impulses via neurones
• Anything that we respond to is called a stimulus, e.g. light, sound, pain
• The conjunctiva is a thin transparent protective outer covering
• the cornea is the transparent front part of the eye that allows light to enter the eye; causes some refraction
• The pupil is the space in the eye through which light passes
• The retina is the inner coat of the eye where light-sensitive cells are found.
• Aqueous and vitreous humours helps maintain the shape of the eyes and keeps the retina against the wall of the eye.
• The lens refracts light
• The optic nerve contains neurones carrying information to the brain
• The muscles f the iris can contract band relax to change the size of the pupil. It contains two types of muscle, theradial and circulare muscles
• Raduial muscles are like spokes of a wheel moving from the edge of the pupil tko the iris
• Circular muscles form rings within the iris around the pupil
• In dim light:

  Circular muscles relax

  Radial muscles contract

  Size of pupil increases

  When the pupil enlarges(dilates), sufficient light falls on the retina to produce an image.
• In bright light:

  Circular muscles contract

  Radial muscles relax

  Size of pupil increases

  When the pupil get smaller (contracts) the amount of light entering the eye is reduced. his protects the sensitive cells in the retina from damage
• The lens is thin when you are focusing on an object far away in the distance, the lens is thick when you are focusing on an object close to you.
• The process of changing the thickness of the lens is called accomodation.
• Nerve cells are called neurons. They link receptors, e.g. eye, ear, and effectors(muscles) to the coordinators (brain and spinal cord)
• Neurones are specially adapted to carry electrical messages called nerve impulses. These adaption are:

  1. They have long branched ends(dendrites) that allow them to transmit impulses over a greater area to make more connections with other neurons
  2. The axon is a long extension of the cytoplasm which can be up to one metre in length to transmit information from the CNS to the extremities of the body by one cell
  3. The axons are coated by a fatty layer known as the insulin sheath. It acts as an insulator and helps speed up transmission speed#
• There are 3 types of neurones:

  Sensory : conducts nerve impulses from the receptor to the central nervous system

  Association/Relay: can connect a sensory neuron directly with a motor neuron directly with a motor neuron in a reflex arc

  Motor neurones: conducts nerve impulse from the central nervous system to an effevtor
• Sensory neurones receives impulses from a receptor and passes it to the central nervous system

  Relay neurones receive impulses from sensory neurones and pass the impulses to motor neurones

  Motor neurones receive impulses from the central nervous system and pass it on to the effector (usually a muscle or a gland)
• There v are small gaps between neurones known as synapses. Electrical impulses move across these gaps to using chemicals. Synapses allow many connections to be made.

  Synapses can be can be affected by drugs or alcohol, which slow down synapses or even stop them. For an impulse to pass across a synapse the end of a neurone produces a chemical transmitter (neurotransmitter). This diffuses across the synapse to the next neurone. If the concentration is high enough an impulse will be triggered in the next neurone
• Actions that we have to think about(conscious control) are called voluntary actions e.g. putting your hand up to answer a question
• Actions that we do NOT have to think about are called reflex actions e.g. blinking. These actions are rapid
• Reflex actions occur very rapidly because there atre only 3 neurones involved. they do not involve concious control
• Homeostasis is how the body keeps conditions inside it the same. It is the maintenance of a constant internal environment
• the pancreas detects blood glucose level, produces insulin in response to increased blood glucose, and releases insulin into the blood stream.
• The cells of the liver and muscle are important in lowering the blood glucose concentration - Insulin causes the cells of the muscle and liver to absorb more glucose from the blood, insulin increases the respiration rate of the liver and muscle cells, lowering blood glucose concentration, and glucose is converted to glycogen, which is stored in the livers and muscles.
• The roles of the kidney are filtration, reabsorbtion, and osmoregulation.
• The hypothalamus in the brain constantly monitors the concentration of blood in the brain, if there is too little water, it causes the hormone ADH to be released from the pituary gland.
• When shoots are exposed to v light coming from one direction,, they grow towards the light

  this is called phototropism - a growth response towards the light

  the growth response is controlled by a hormone called auxin and it's distribution in the shoot changes when exposed to unidirectional light