Nerves and Hormones

Nerves and Hormones

1. The Nervous System

   • The nervous system enables humans to react to their surroundings and coordinate their behaviour
   • Cells called receptors detect stimuli (changes in the environment)
     • Receptors in the eye are sensitive to light
     • Receptors in the ear sensitive to sound
     • Receptors in the ears are sensitive to changes in position and enable us to keep our balance
     • Receptors in the nose and on the tongue are sensitive to chemicals and enable us to taste and to smell
     • Receptors in the skin are sensitive to touch ,pressure and pain
   • Light receptors, like most animal cells, have a nucleus, cytoplasm and cell membrane
   • Information from receptors passes along cells (neurones) in nerves to the brain
     • The brain coordinates a response
   • Reflex actions are automatic and rapid because they do not involve the brain
     • The information passes along the sensory neurone to the central nervous system where chemical is released at the synapse to the relay neurone, then from the relay-motor synapse (in a similar fashion) to the effector
       • The effector is either a muscle or a gland which contracts or secretes chemical substances, respectively

2. Control in the Human Body

   • Internal conditions which are controlled
     • Water content
       • Water leaves the body via the lungs when we breathe out and via the skin as we sweat to cool us down,and excess water is lost via the kidneys in the urine
     • The Ion content
       • Ions are lost via the skin when we sweat and excess water is lost via the kidneys in the urine
     • Temperature
       • To maintain the temperature at which enzymes work best
     • Blood sugar levels
       • to provide the cells with a constant supply of energy
   • Many processes within the body are coordinated by chemical substances called hormones
     • Hormones are secreted by glands and are usually transported to their target organs by the bloodstream
     • Hormones regulate the functions of many organs and cells
       • Several hormones are involved in the menstrual cycle of a woman
         • Follicle Stimulating Hormone is secreted by the pituitary gland and causes eggs to mature in the ovaries, as well as, stimulating the ovaries to produce hormones including oestrogen
           • Lutenising Hormone stimulates the release of eggs from the ovary
             • Oestrogen is secreted by the ovaries and inhibits the further production of FSH
       • Controlling Fertility
         • Oral contraceptives contain hormones (e.g. oestrogen, progesterone) inhibit the production of FSH so that no eggs mature
           • Too much oestrogen can cause significant side effects
           • Progesterone only pills lead to fewer side effects
         • Giving FSH and LH to a woman with low FSH production stimulates eggs to mature, e.g. IVF
           • Once the eggs mature, they are collected and fertilised by the father's sperm
             • The fertilised eggs develop into embryos and one or two are inserted into the mother's womb

3. Control in Plants

   • Plants are sensitive to light moisture and gravity
     • Their shoots grow towards light and against the force of gravity
     • Their roots grow towards moisture and in the direction of the force of gravity
   • Plants produce hormones to coordinate and control growth, Auxins controls phototropism and gravitropism
     • Auxins are produced from the tip of a plant and affect the growth of plant cells and spread in greater mass on the shaded side of the plant
       • Because the shaded side of the plant has more auxins it grows more and consequently, the plant tip bends towards the sunlight
   • Plant growth in hormones are used in agriculture and horticulture as weed killers and as rooting hormones