Coordination and Response

• A voluntary response is one where you make a conscious decision to carry out a particular action therefore it starts with your brain
• • The human nervous system consists of the:
  • central nervous system (CNS) - the brain and the spinal cord
  • peripheral nervous system (PNS) - all of the nerves in the body
• • Sensory neurones carry impulses from sense organs to the CNS (brain or spinal cord)
• Motor neurones carry impulses from the CNS (brain or spinal cord) to effectors such as muscles, glands etc.
• • Relay neurones are found inside the CNS and connect sensory and motor neurones
• sensory neurones send electrical impulses from the receptor cells in the sense organs to the central nervous system.

  
• relay neurones are present in the cns and transmit impulses from the central nervous system to the motor neurones

  
• motor neurones carry impulses from the central nervous system to the effectors like muscle fibres and glandular cells

  
• • Sensory neurones carry impulses from sense organs to the CNS (brain or spinal cord)

  
• • Sensory neurones are long and have a cell body branching off the middle of the axon
  • Relay neurones are short and have a small cell body at one end with many dendrites branching off it
  • Motor neurones are long and have a large cell body at one end with long dendrites branching off it
• synapse: a junction between two nerve cells, consisting of a gap across which impulses pass by diffusion of a neurotransmitter.
• Neurotransmitter: a chemical substance which is released at the end of a nerve fibre by the arrival of a nerve impulse and, by diffusing across the synapse or junction, effects the transfer of the impulse to another nerve fibre, a muscle fibre, or some other structure.
• • An involuntary (or reflex) response does not involve the brain as the coordinator of the reaction and you are not aware you have completed it until after you have carried it out
  • This is an automatic and rapid response to a stimulus such as touching something sharp or hot
  • As it does not involve the brain, a reflex response is quicker than any other type of nervous response
• what are effectors

  effectors are muscles or glands which respond to the stimulus
• reflex: an action that is performed without conscious thought as a response to a stimulus
• 1. The pin (the stimulus) is detected by a pain/pressure/touch receptor in the skin
  2. Sensory neurone sends electrical impulses to the spinal cord (the coordinator)
  3. Electrical impulse is passed on to relay neurone in the spinal cord 
  4. Relay neurone connects to motor neurone and passes the impulse on
  5. Motor neurone carries impulse to a muscle in the leg (the effector)
  6. The muscle will contract and pull the foot up and away from the sharp object (the response) 
• Electrical impulse travels


  Along the first axon
• Nerve-ending of the presynaptic neurone

  1. Releases chemical messengers called neurotransmitters from vesicles

  2. Vesicles fuse with the presynaptic membrane
• Neurotransmitters

  1. Diffuse across the synaptic gap (or cleft)

  2. Bind with receptor molecules on the membrane of the second neurone (postsynaptic membrane)
• Second neurone

  1. Generates an electrical impulse

  2. Impulse travels down the second axon
• Neurotransmitters

  1. Are destroyed

  2. To prevent continued stimulation of the second neurone

  3. Avoiding repeated impulses being sent
• Synapses


  • Ensure that impulses only travel in one direction
  • Avoiding confusion within the nervous system if impulses were travelling in both directions
• the synapse

  
• Receptor: an organ or cell able to respond to light, heat, or other external stimulus and transmit a signal to a sensory nerve
• Sense organ: A structure that receives sensory information from the external environment.
• • Once the receptor cell in the sense organ has been stimulated, it generates an electrical impulse
  • This is passed on to a sensory neurone which carries the impulse to the central nervous system
• • a response will be decided on and the impulse will be passed to a motor neurone (via a relay neurone)
  • The motor neurone carries the impulse to the effector (muscle or gland)
  • The effector carries out the response
• • The eye is a sense organ containing receptor cells that are sensitive to light (rod cells) and colour (cone cells)
• label the diagram

  
• cornea: the transparent layer refracting light to focus it on the retina.
• iris: a flat, coloured, membrane behind the cornea of the eye, with an adjustable pupil in the centre. it controls how much light enters the pupil
• Lens of the eye- transparent disc that refracts light to focus it on the retina
• Retina- The light-sensitive layer at the back of the eye that contains receptors for light.
• Rods and Cones- photoreceptors that are sensitive to light and color
• optic nerve- carries impulses from the retina to the brain
• pupil- the hole that allows light to enter the eye
• blind spot- At the point where the optic nerve joins the retina, there are no light-sensitive rod and cone cells on that part of the retina. Light falling onto that part of the retina will not result in an image being detected. the brain 'fills in' from surrounding light so we don't see a black hole where no light has fallen
• pupil reflex- reflex action carried out to protect the retina from damage in bright light and protect us from not seeing objects in dim light
• In dim light the pupil dilates (widens) in order to allow as much light into the eye as possible. Radial muscles contract, Circular muscles relax
• In bright light the pupil constricts (narrows) in order to prevent too much light entering the eye and damaging the retina. Radial muscles relax, circular muscles constrict.