My topic 6

• what is taxes response


  nervous response in which an organisms full body will move towards or away from a stimulus, certain bacteria display chemotaxis in which they move towards a chemical
• what is kinesis response


  nervous response in which an organisms speed of movement and how often they turn increases in response to a stimulus
• example of a hormone in plants


  auxin
• what is tropism


  growth in response to a stimulus
• example of a positive tropism

  plant shoots will grow towards light
• example of a negative tropism

  plant roots will grow away from light
• What does auxin do?

  auxin is responsible for cell elongation, causing shoots to grow up in response to sunlight, whilst inhibiting cell growth in roots
• how does auxin result in plants bending towards light

  auxin will diffuse to the part of the plant shoot which has a lower light intensity and cause the cells there to elongate, making the plant bend towards the light
• What is a pacinian corpuscle?

  pressure receptor consisting of a single sensory neurone wrapped in layers of tissue and gel
• why does the pacinian corpuscle only respond to pressure?

  the neurone inside it has special sodium channels which only open under pressure, so action impulses are only generated when enough pressure is applied
• what is the central nervous system consisted of

  brain and spine
• what consists the peripheral nervous system

  sensory and motor neurones as well as receptors
• how does a stimulus result in a response by the nervous system

  stimulus is detected by receptors, generating an action potential which releases the relay neurone, then it reaches an efector (usually motor neurone) and a response is obtained
• why do organisms need a nervous system

  being able to appropriately respond to a stimulus greatly increases an organisms chance of survival
• what are photoreceptors and where are they found

  receptors which detect light changes (rods and cones) and are found in the retina
• how do rods work

  rods are used in low light intensity conditions, this is because the pigment they contain does not need a low of energy in order to be broken down, however they only produce black and white images
• how do cones work

  there are 3 types of cones that pick up on red, green and blue light wavelengths, cones can produce coloured images however they only work in high light intensity since the pigment they contain needs a lot of energy to be broken down
• what is retinal convergence

  a number of rod cells are connected to a single bipolar cell, this is what allows them to form images in low light intensity, since many cells are connected to 1, less energy (light) is needed in order to generate a high enough action potential
• rods or cones, which one has the highest visual acuity


  cones since 1 cone connects to 1 bipolar cell, allowing the brain to distinguish between light sources and wavelenghts
• how are rods and cones distributed in the retina?

  they are unevenly distributed with cones mostly being found right behind the pupil (fovea) whilst cones are found further away from that area
• owls have a lot of rods in their retina how does this allow them to hunt at night

  high visual sensitivity, several rods are connected to one bipolar cell enough neurotransmitters to reach treshold
• eagles have a lot of cones in their fovea how does this allow them to catch prey


  cones provide high visual acuity since 1 cone is connect to 1 bipolar cell so they send separate impulses to the brain
• how does destruction of myelin sheaths result in slower conduction of impulses

  no saltatory conduction so more depolarization over length of axon
• structure of a motor neurone

  
• 2 advantages of simple reflexes

  do not have to be learned, rapid
• what cells make up the myelin sheath

  Schwann cells, wrapped around themselves
• what is a resting potential


  the difference in electrical charge between the inside and outside of a neuron when it is not conducting an impulse, it has a value -70mv since there more K and Na ions outside of it than inside of it
• how is the resting potential maintained

  there is a higher concentration of potassium ions inside the neuron and a higher concentration of sodium ions outside the neuron, the axon membrane is more permeable to potassium ions so they diffuse into the neuron, whilst sodium ions are actively transported out
• what is an action potential


  when a stimulus makes a neurones voltage increase past a certain point, generating a nervous impulse
• explain depolarization

  some sodium channels open in response to the stimulus and charge slowly starts increasing
• explain why action potential cannot go above the value of +30

  when an action potential reaches +30mv, the voltage gated sodium channels begin closing so no more sodium can move into the axon and the charge starts decreasing
• explain repolarization

  all potassium channels open meaning more potassium is moving out than sodium in and charge starts quickly decreasing
• what is the refractory period/hyper polarization


  neurone overshoots and charge goes below resting potential, the refractory period is the period after this in which the neuron membrane cant be further stimulated
• why is the refractory period important?


  ensures action potentials are unidirectional, ensures action potentials are separate and limits the number of impulses so as to not overwhelm the senses
• saltatory vs continuous conduction

  saltatory conduction is much faster than continuous conduction since the electric impulse jumps between nodes of ranvier. saltatory conduction is cause by the fact that myelin sheaths are made up of lipids which don't allow charges to pass through
• why is the speed of transmission of impulses faster along a myelinated axon than a non-myelinated axon (3 marks)
• what is a node of ranvier

  unmyelinated area between myelin sheaths, only found in myelinated motor neurones
• what is the all or nothing principle


  if a stimulus causes the charge in the neuron to increase past the threshold (-55mv) then an action potential is generated (all) if the threshold is not reached no action potential is generated (nothing)
• what factors affect speed of conductance in axons

  type of conduction- refer to saltatory vs continuous conduction card

  diameter of axon-less ion leakage so faster conductance

  temperature- high temperture leads to a faster conductivity due to ions diffusing faster and enzymes involved in respiration working faster, resulting in more atp being produced so more active transport happens
• how does inhibiting respiration in neurons increase their charge (from -70 to 0mv)