biology topic 8 lqc 4 - 9a

• What is a photoreceptor?

  A receptor cell that is sensitive to light
• What are the two forms of photoreceptor in a human and what type of vision do they provide?

  rods: black and white vision

  cones: colour vision
• where are rods and cones located

  retina
• Label the diagram below and draw an arrow to show the direction of light

  
• photochemical pigment present in rod cells

  rhodopsin
• where is rhodopsin located

  within the flattened vesicles of the outer segment of the rod cell
• Describe what happens to a rod cell in the dark:


  1.Na+isactively pumpedout of theinner segmentof the rod cell. This requires thehydrolysis of ATP.

  2.Na+in theouter segmentdiffusesdown its concentration gradient into the inner segment.

  3.Na+ flowsinto theouter segmentthrough opennon-specific cation channels by facilitated diffusiondown its concentration gradient. This influx causes a slight depolarisation of -40mV.

  4. Thisslight depolarisation causes the release of the neurotransmitter glutamatefrom therodcell.Bindingof theglutamateto thebipolarcellhyperpolarisesit andpreventsit fromdepolarising(inhibitory synapse). Thebipolarcell doesnot releaseitsneurotransmittertodepolarisetheganglion neurone.

  
• Describe what happens to a rod cell in the light:


  1. Whenlight(photons)hitsthe rod,rhodopsin(formed of retinal and opsin)absorbsthe light. The retinal (non-protein) converts from itscis form to the transform andbreaksapart from theopsin(protein). This is calledbleaching. The opsinactivatesa series ofmembrane-bound reactionsending in thehydrolysisof acyclic nucleotide molecule. This hydrolysis results in theclosureof the non-specific cation channels in theouter segment.Theinflux of Na+into the rod celldecreases.

  2.Na+ is still pumped outof the inner segment. This results in thehyperpolarisationof the rod cell causing the release ofglutamatetostop.

  3. The lack of glutamate results in thedepolarisationof the bipolar cell. This causes thebipolarcell torelease itsneurotransmitteranddepolarisetheganglionneurone. Anaction potential is generated and impulses are sent along the optic nerve to the brain.

  
• What occurs during dark adaptation?

  The trans retinal converts back to cis retinal.

  
  

  The retinal and opsin recombine to form rhodopsin.

  
  

  This requires ATP. The process can take up to 50 minutes.

  
  

  This enables the eye to transition from a high light setting to a low light setting and restore retinal sensitivity i.e. the eye adapts its definition of what is black.
• State the location of rhodopsin within a rod cell. (1)

  outer segment in vesicles
• what is the cortex divided into

  two cerebral hemispheres
• Identify the 4 main regions (lobes) of the cortex

  motor cortex

  frontal lobe

  temporal lobe

  parietal lobe

  occipital lobe (visual cortex)

  
• function of frontal lobe

  decision making

  reasoning

  planning

  emotions

  forming associations
• function of motor cortex

  neurones connect directly to spinal cord, brain stem & muscles via motor neurones.

  
  

  Stores info about how to carry out movement
• function of parietal lobe

  Orientation,

  movement,

  sensation,

  calculation,

  recognition

  memory
• function of occipital lobe (visual cortex)

  Processes info from eyes -

  vision, colour, shape
• function of temporal lobe

  processes auditory info

  hearing

  sound recognition

  speech

  
  

  also memory
• name the other brain regions

  corpus callosum

  thalamus

  hippocampus

  midbrain

  cerebellum

  medulla oblongata

  pons

  pituitary gland

  hypothalamus

  basal ganglia

  
• corpus callosum function

  White matter composed of axons. Allows connections between the two hemispheres and the other structures.
• medulla oblongata function

  Regulates heart rate (cardiovascular control centre),

  breathing rate (ventilation centre) and blood pressure.
• cerebellum function

  Responsible for balance. Coordinates movement as it is being carried out by receiving inputs from motor cortex, muscles & joints.
• hypothalamus function

  Controls thermoregulation (thermoregulatory centre),

  thirst,

  hunger,

  circadian rhythms and sleep.

  
  

  Acts as an endocrine gland and stimulates the pituitary gland.
• thalamus function

  Routes all incoming sensory information to the correct regions i.e. visual inputs to occipital lobe.
• basal ganglia function

  Selects and initiates stored programmes for movement.
• hippocampus function

  Involved in laying down long-term memory.
• pituitary gland function

  Endocrine gland responsible for secreting hormones controlling growth, blood pressure, energy management, sex organs, thyroid gland, metabolism, pregnancy, childbirth, nursing, water/salt concentration at the kidneys, temperature & pain relief.
• midbrain function

  Relays information to the cerebral hemispheres (auditory information to the temporal lobe and visual information to the occipital lobe).
• pons function

  Relays information from the forebrain to the cerebellum & medulla.

  
  

  Involved in sleep, breathing, respiration, swallowing, bladder control, hearing, taste, eye movement, facial expressions & sensations and posture. Implicated in sleep paralysis, dreams & locked-in syndrome
• MRI stands for

  magnetic resonance imaging
• describe how and mri image is obtained

  A combination of a magnetic field and radio waves cause the nuclei of hydrogen atoms to change their orientation.

  
  

  When the radio waves are switched off some hydrogen nuclei change their orientation which releases energy that can be detected and converted into an image.
• what can MRI scanning be used for

  Identifying issues with soft tissues - tumour location and size, stroke, brain, spinal cord and joint injuries.
• Describe the advantages of MRI

  Uses magnetic field & radio waves, sono harmful X-rays.

  Thin slices of image are created which can be combined to produce a3D image.

  Better resolution than CT.
• Describe the disadvantages of MRI

  Loud noise.

  
  

  Small imaging space - not good for claustrophobic patients, children or those with special learning needs.

  
  

  Can't be used on people with metal implants.
• fmri stands for

  functional magnetic resonance imaging
• describe how an fmri image is obtained

  Increased neural activity results in a greater demand for oxygen and an increased blood flow to that region.

  Oxyhaemoglobin does not absorb fMRI signals (radio waves).

  The more oxyhaemoglobin is delivered, the less the radio waves are absorbed, the more those areas ‘light up’.

  Must compare brain activity whilst doing the task with relaxation
• what can fmri be used for

  Able tostudy the brain in action.

  Studyhuman activitiessuch as memory, emotion, language and consciousness.

  Able to studypsychiatric disorders,epilepsy, Alzheimer’s, tumours, autism, pain, consequences of a stroke.
• advantages of fmri use

  Uses magnetic field & radio waves, sono harmful X-rays.

  Has avery high resolution

  Canidentifywhichareasof the brain are being used for particular tasks andwhich areas are being used together as a network.

  4 images produced per secondso a process can be followed over a short period of time.
• disadvantages of fmri use

  Expensive.

  
  

  Patient/subject must lie completely still - difficult for children and those with special learning needs.

  
  

  Only measures blood flow and not how individual neurones are behaving.
• CT scanning stands for

  Computerised Axial Tomography
• describe how a CT image is obtained

  Narrow beamX-rays fired at different anglesaround the patient.

  The beam isreduced in strength according to the density of the tissue.

  TheX-rays are then detected.

  Slicesof tissue arecreated.