coordination & response

• Co-ordination


  The way all the organs and systems of the body are made to work efficiently together
• Nervous and endocrine systems

  • Play a vital role in coordination
  • Endocrine system brings about coordination by use of hormones
  • Nervous system does so through nerve impulses or electric impulses
• Nerve impulse


  An electrical signal that passes along nerve cells called neurones

  
• Irritability or sensitivity


  The ability to detect and respond appropriately to changes in the environment
• Components of the human nervous system

  • Central nervous system (CNS)
  • Peripheral nervous system (PNS)

  
• Central nervous system (CNS)


  • Made up of the brain and the spinal cord
  • Brain is enclosed in the skull or cranium
  • Spinal cord is protected by the vertebral column

  
• Peripheral nervous system (PNS)


  • Made up of nerves that innervate all other parts of the body
  • Nerves that connect other body parts to the brain are cranial nerves
  • Nerves that connect body parts to the spinal cord are spinal nerves
  • Nerves are organized in bundles called nerve fibres

  
• Neurone


  A specialized cell that transmits information in the form of electric impulses from one part of the body to another
• Structure of a neurone

  • Cell body surrounded by cytoplasm enclosed by a membrane
  • Cell body gives rise to an extension called an Axon
  • Myelin insulates the nerve fibres to allow faster transmission of impulses
• Types of neurones


  • Sensory neurones
  • Motor neurones
  • Relay neurones

  
• Sensory neurones


  • Carry impulses from sense organs (receptors) to the central nervous system
  • Cell bodies are not terminally located but are axillary

  
• Motor neurones


  • Carry impulses from the central nervous system to effectors
  • Cell bodies are terminally located

  
• Relay neurones


  • Form a link between sensory neurones and motor neurones
  • Located in the central nervous system
  • Multipolar to provide many alternative paths for impulses
  • Lack myelin sheath

  
• Reflex arc


  The path taken by an impulse during a reflex action
• Reflex action


  1. Automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands)

  2. Rapid involuntary response to stimulus
• Synapse


  A junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter

  
• Synaptic transmission


  Impulse arrives at synaptic bulb -> Vesicles containing neurotransmitter move to presynaptic membrane -> Neurotransmitter released into synaptic gap -> Neurotransmitter binds to receptors on postsynaptic membrane -> Impulse triggered in postsynaptic neurone -> Neurotransmitter broken down by enzyme

  
• Excitatory drugs


  Increase the activity of the nervous system by stimulating the release of neurotransmitters

  
• Inhibitory drugs


  Reduce the effects of neurotransmitters by acting on presynaptic neurones or blocking receptors

  
• Sense organ


  Groups of sensory cells responding to specific stimuli
• Stimulus


  A change in the environment that causes a change in the behavior of an organism
• Receptor


  Structures that detect stimuli
• Sense organs and their stimuli

  • Eye - Light
  • Ear - Sound
  • Skin - Touch, temperature, pressure
  • Tongue - Taste
  • Nose - Smell
• Transduction


  The conversion of one form of energy to another, e.g. light energy to electrical energy in nerves
• Pupil/Iris reflex


  1. In bright light: Circular muscles contract, radial muscles relax, pupil constricts

  2. In dim light: Radial muscles contract, circular muscles relax, pupil dilates

  
• Accommodation


  The ability of the eye to adjust its structures to bring to focus images of either far or near objects
• Accommodation of a close (nearby) object

  Ciliary muscles contract, suspensory ligaments slacken, lens becomes short and thick, light rays more refracted
• Accommodation of a distant (far) object

  Ciliary muscles relax, suspensory ligaments become taut, lens becomes long and thin, light rays less refracted
• Accommodation of a Close (Nearby) Object

  1. Rays from close objects are divergent

  2. Ciliary muscle contract to form a smaller circle

  3. Suspensory ligaments become slacken (relax their pull on the lens)

  4. The lens becomes short and thick

  5. The light rays are more refracted, thereby focusing the image on the retina

  
• Accommodation of a Distant (Far) Object

  1. Ciliary muscles relax

  2. Suspensory ligaments become taut (contract their pull on the lens), making the lens long and thin

  3. Light rays are less refracted, thereby focusing the image on the retina
• Retina


  At the back of the eye, when light falls on receptor cells they send electrical impulses along the optical nerve to the brain which builds up an image

  
• Retina


  • Receptor cells are packed most closely together in the fovea, which is where light is focused when looking straight at an object
  • There are no receptor cells where the optical nerve leaves the retina, this is the blind spot
  • The choroid absorbs all the light after it has been through the retina

  
• Receptor cells in the retina

  • Rod cells
  • Cone cells
• Rod cells


  Sensitive to dim light but do not respond to colour
• Cone cells


  Able to distinguish between different colours of light, but only function in bright light
• The fovea in the centre of the retina contains cones and no rods, giving a detailed colour image
• The rest of the retina contains rods and few cones, giving peripheral vision that is not as detailed
• The position of the fovea is in the centre of the retina on the same horizontal level as the blind spot, with the fovea in the right eye to the right of the blind spot

  
• Hormones


  Chemical substances produced by a gland and carried by the blood, which alter the activity of one or more specific target organs
• Hormones play vital roles in regulating growth and development, controlling proper cell functions and controlling animal behavior especially during breeding