6A

• What are stimuli?

  Changes in the environment
• How is a response produced?

  Receptors e.g. cells or proteins on the cell surface detect stimuli, then communicate with effectors e.g. muscles and glands via the nervous and humoural system. These effectors bring about a response.
• What are the three types of neurons?

  Sensory - transmits electrical impulses from receptors to the CNS

  
  

  Motor - transmits electrical impulses from CNS to effectors

  
  

  Relay - transmits electrical impulses between sensory and motor neurons
• What does the human nervous system split into?

  Central nervous system and peripheral nervous system.
• What is the central nervous system?

  Controller of complex commands and decisions.
• What does the central nervous system split into?

  brain and spinal cord
• What is the brain?

  Centre of all conscious awareness.
• What is the spinal chord?

  Connects the brain and PNS and controls reflex actions.
• What is the peripheral nervous system?

  Transmits information between the CNS via neurons.
• What does the peripheral nervous system split into?

  somatic and autonomic
• What is the somatic nervous system?

  Governs muscle movement and transmits information from receptors in sense organs to the CNS, and receives information from the CNS that directs muscles
• What is the autonomic nervous system?

  Governs vital bodily functions e.g. breathing and digestion, and involuntarily transmits information to/from the organs
• What does the autonomic nervous system split into?

  sympathetic and parasympathetic nervous systems
• What is the sympathetic nervous system?

  fight or flight
• What is the parasympathetic nervous system?

  Opposes the sympathetic nervous system, returning the body to its resting state
• What is a reflex?

  when the body responds to a stimulus without making a conscious decision to do so.
• What is a reflex arc?

  The passage of information in a reflex (from receptor to effector).
• Describe the process of a reflex arc.

  Receptors detect stimuli.

  
  

  Sensory neuron carries electrical impulses to the relay neuron.

  
  

  Relay neuron carries impulses to the motor neuron.

  
  

  Motor neuron sends impulses to the effector.

  
  

  The effector provides a response.

  
  

  If there is a relay neuron involved in the reflex arc then it can be over-rided by the brain.
• Give three features of nervous system communication

  localised - neurotransmitters are secreted from neurons directly to target cells.

  
  

  Short-lived - neurotransmitters are quickly removed once they have done their job.

  
  

  Rapid - electrical impulses move quickly which allows animals to have quick reactions.
• What is tropism?

  The response of plants to a directional stimulus, because they can't move, they respond via growth.
• What is positive tropism?

  Growth towards a stimulus
• What is negative tropism?

  growth away from a stimulus
• What is phototropism?

  A growth response to light
• What is gravitropism?

  A growth response to gravity
• What are growth factors?

  Proteins released to stimulate cell division, they speed/slow the growth of plants in certain areas to allow the plant to respond to stimuli.

  
  

  They are produced in growing regions of the plant e.g. tips and leaves, and travel to where growth is needed.
• Give an example of a growth factor?

  Auxin

  
  

  Stimulates growth of shoots by cell elongation, high concentrations inhibits growth in roots.
• What is IAA?

  Indoleacetic acid - a type of auxin that is produced in the shoots and tips of flowering plants.

  
  

  It moves via active transport and diffusion for short distances and via the phloem for longer distances, and the uneven concentration causes plants to grow in response to the tropism.
• What does IAA do in response to photo and gravitropism?

  phototropism - IAA moves to the shaded part so more growth occur there and the plant moves towards the light.

  
  

  Gravitropism - IAA moves to the underside of the shoot so more growth occurs there and the plant moves upwards.
• What are tactic responses?

  When organisms respond to a directional stimulus e.g. wood lice move away from light to survive.
• What are kinetic responses?

  When organisms respond to a non directional stimuli e.g. woodlice move more slowly in humid areas to stay in the condition but move faster in dry areas improving there chances of finding a new condition.
• What are receptors?

  Cells or proteins on cell surface membranes that detect stimuli.
• What are pacinian corpuscles?

  pressure receptors in the skin
• What happens when pacinian corpuscles are stimulated?

  They contain a sensory nerve ending that is wrapped in many layers of connective tissue called lamellae.

  
  

  When the pacinian corpuscle is stimulated the lamellae are deformed and press on the sensory nerve ending.

  
  

  This causes the sensory neurones cell membrane to stretch, deforming the stretch-mediated sodium ion channel which then opens causing sodium ions to diffuse into the cell creating a generator potential.

  
  

  If the generator potential reaches the threshold, an action potential is triggered.
• What are photoreceptors?

  Light receptors in the eye
• How do photoreceptors work?

  light enters the eye through the pupil, with the iris muscles controlling how much.

  
  

  The lens focuses the light rays on the retina which contains photoreceptor cells that detect light.

  
  

  The light hits the photoreceptors and is absorbed by light-sensitive optical pigments.

  
  

  Light bleaches the pigment, causing a chemical change, altering the membrane permeability to sodium ions.

  
  

  A generator potential is created and if the threshold is reached, a nerve impulse is sent along a bipolar neuron.

  
  

  bipolar neurons connect photoreceptors to the optic nerve, which takes impulses to the brain.
• What are the two types of photoreceptors?

  rods and cones
• Where are rods found?

  peripheral parts of the retina
• Where are cones found?

  Packed together in the fovea
• He is information received in rods?

  Black and white
• How is information received in cones?

  In colour as there are three types - red, blue and green sensitive so when they are in different proportions we see different colours.