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91 Laboratory 7 Brain Anatomy Goals: Describe the organization & function of the three meningeal layers. Explain where cerebrospinal fluid is found in the central nervous system Identify the major structures of the human brain using models. Identify the major structures of the sheep brain by dissection. Identify selected cranial nerves on the human and sheep brains. 1. Coverings of the Brain: The brain and spinal cord are protected by multiple layers of tissue. Most external is the skin, followed by the skull. Underneath the skull are three layers of connective tissue membranes collectively referred to as meninges. The outer most layer is called the dura mater (literally, hard or tough mother). It is a tough, doublelayered membrane. The most superficial layer of the dura mater forms the inner periosteum of the cranial bones. The middle layer, the arachnoid mater (think spider) has a delicate spider weblike appearance and helps to cushion the brain. The innermost layer, the pia mater (literally soft mother), is a thin, waterproof layer that adheres to the outer surface of the brain and spinal cord. Identification: On the sheep brain, identify the three layers of the meninges. Identify & remove the dura and arachnoid maters. 2. Regions of the Brain: The cerebral hemispheres form the largest part of the human brain and are situated above most other brain structures. They are covered with a cortical layer with many bumps and grooves called the cerebrum. The visible part of the cerebrum is the neocortex. Interior to the cortex is the midbrain. Underneath the cerebrum lies the brainstem, resembling handle underneath the main portion of the brain. At the rear of the brain, beneath the cerebrum and behind the brainstem, is the cerebellum,a structure with a much finer bumps than the cerebrum. The same structures are present in other mammals, although the cerebellum is not so large relative to the rest of the brain. During development, the brain develops from three expansions of the embryonic neural tube referred to as the forebrain (also called the proencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon). The forebrain forms the largest region of the human brain form forming the telencephelon or cerebrum, and the diencephalon. The diencephalon becomes the thalamus and hypothalamus controlling movement and autonomic/endocrine function, respectively. The midbrain is the smallest region and is located between the forebrain and hindbrain. The midbrain contains a number

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Page 1: Laboratory7( BrainAnatomy(chavez-smithscience.weebly.com/uploads/9/1/5/0/... · 7.Ventricles:(Thereareaseriesof hollow!spaceswithinthebrain calledventricles.Theventriclesarecontinuouswith

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Laboratory  7  Brain  Anatomy    

Goals:  

• Describe  the  organization  &  function  of  the  three  meningeal  layers.  • Explain  where  cerebrospinal  fluid  is  found  in  the  central  nervous  system  • Identify  the  major  structures  of  the  human  brain  using  models.  • Identify  the  major  structures  of  the  sheep  brain  by  dissection.      • Identify  selected  cranial  nerves  on  the  human  and  sheep  brains.  

1.  Coverings  of  the  Brain:  

The  brain  and  spinal  cord  are  protected  by  multiple  layers  of  tissue.    Most  external  is  the  skin,  followed  by  the  skull.    Underneath  the  skull  are  three  layers  of  connective  tissue  membranes  collectively  referred  to  as  meninges.    The  outer  most  layer  is  called  the  dura  mater  (literally,  hard  or  tough  mother).    It  is  a  tough,  double-­‐layered  membrane.    The  most  superficial  layer  of  the  dura  mater  forms  the  inner  periosteum  of  the  cranial  bones.    The  middle  layer,  the  arachnoid  mater  (think  spider)  has  a  delicate  spider  web-­‐like  appearance  and  helps  to  cushion  the  brain.    The  innermost  layer,  the  pia  mater  (literally  soft  mother),  is  a  thin,  waterproof  layer  that  adheres  to  the  outer  surface  of  the  brain  and  spinal  cord.  

 Identification:    • On  the  sheep  brain,  identify  the  three  layers  of  the  meninges.  • Identify  &  remove  the  dura  and  arachnoid  maters.  

 

2.  Regions  of  the  Brain:  

The  cerebral  hemispheres  form  the  largest  part  of  the  human  brain  and  are  situated  above  most  other  brain  structures.  They  are  covered  with  a  cortical  layer  with  many  bumps  and  grooves  called  the  cerebrum.    The  visible  part  of  the  cerebrum  is  the  neocortex.    Interior  to  the    cortex  is  the  midbrain.    Underneath  the  cerebrum  lies  the  brainstem,  resembling  handle  underneath  the  main  portion  of  the  brain.    At  the  rear  of  the  brain,  beneath  the  cerebrum  and  behind  the  brainstem,  is  the  cerebellum,  a  structure  with  a  much  finer  bumps  than  the  cerebrum.  The  same  structures  are  present  in  other  mammals,  although  the  cerebellum  is  not  so  large  relative  to  the  rest  of  the  brain.    During  development,  the  brain  develops  from  three  expansions  of  the  embryonic  neural  tube  referred  to  as  the  forebrain  (also  called  the  proencephalon),  midbrain  (mesencephalon),  and  hindbrain  (rhombencephalon).    The  forebrain  forms  the  largest  region  of  the  human  brain  form  forming  the  telencephelon  or  cerebrum,  and  the  diencephalon.    The  diencephalon  becomes  the  thalamus  and  hypothalamus  controlling  movement  and  autonomic/endocrine  function,  respectively.    The  midbrain  is  the  smallest  region  and  is  located  between  the  forebrain  and  hindbrain.    The  midbrain  contains  a  number  

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of  nuclei  involved  in  relaying  auditory  and  visual  information  and  in  regulating  voluntary  muscle  movement.    The  hindbrain  is  closest  to  the  spinal  cord  and  forms  the  cerebellum,  pons,  and  medulla  oblongata.      

   

Figure  2.    Developmental  brain  regions  in  the  mammalian  brain.  

 Some  brain  systems  transverse  multiple  brain  regions.    For  example,  voluntary  movement  begins  in  the  neocortex,  but  normal  voluntary  movement  also  requires  input  from  the  cerebellum  and  midbrain  and  signals  are  relayed  in  the  thalamus.        Identification:  • On  the  sheep  brain,  identify  the  telencephalon  (or  cerebrum),  cerebellum,  pons,  and  medulla  oblongata.    

The  diencephalon  and  midbrain  will  not  be  visible.  • On  a  human  brain  model,  identify  all  six  brain  regions.  

 

3.    Surface  anatomy  of  the  brain  –  Cerebral  lobes  

The  cerebrum  is  forms  the  most  superior  portion  of  the  brain  and  is  divided  by  a  prominent  longitudinal  fissure  into  right  and  left  hemispheres.    These  hemispheres  are  further  dived  into  five  cerebral  lobes.    The  four  cerebral  lobes  on  the  surface  of  the  brain  are  named  after  the  skull  bones  under  which  they  lie:  frontal,  parietal,  temporal,  and  occipital.    The  insular  lobe  can  be  found  interior  to  the  lateral  sulcus  separating  the  parietal  and  temporal  lobes.        

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Note  that  the  surface  of  the  cerebral  hemispheres  has  ridges  of  tissue  called  gyri  (singular  gyrus)  separated  by  grooves  called  sulci  (singular  sulcus).    Deeper  sulci  are  referred  to  as  fissures  that  separate  the  cerebrum  into  five  cerebral  lobes.    Forming  the  border  between  the  frontal  and  parietal  lobes,  the  central  sulcus  is  perpendicular  to  the  longitudinal  fissure  on  each  lateral  aspect  of  the  brain.    The  lateral  sulcus  separates  the  temporal  lobe  from  the  parietal  and  frontal  lobes.    The  transverse  fissure  separates  the  neocortex  from  the  cerebellum.    Importantly,  the  precentral  and  postcentral  gyri  are  anterior  and  posterior  to  the  central  sulcus.    The  precentral    gyrus  is  also  known  as  the  primary  motor  cortex.    Neurons  in  this  cortical  region  are  responsible  for  initiating  voluntary  movement.    The  postcentral  gyrus  is  also  known  as  the  primary  somatosensory  cortex  and  the  region  responsible  for  conscious  sensation  from  our  tactile  senses  for  the  body,    

 Connecting  the  right  and  left  cerebral  hemispheres,  and  visible  from  the  dorsal  (superior)  aspect  if  you  gently  pull  apart  the  hemispheres  along  the  longitudinal  fissure  is  the  corpus  collusum.    This  structure  is  comprised  of  white  matter  tracts  that  allow  communication  between  the  two  cortical  hemispheres.    Identification:  • On  the  sheep  brain  and  a  human  brain  model,  identify  gyri,  sulci,  the  4  primary  lobes  of  the  cerebral  

hemispheres  and  the  major  grooves  &  fissures.    

 

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4.Surface  anatomy  of  the  brain  –  Ventral  aspect:  

   From  the  ventral  or  inferior  aspect  of  the  brain,  the  frontal  and  temporal  lobes  are  apparent  as  well  as  the  midbrain,  pons,  medulla  oblongata.        All  twelve  cranial  nerve  are  also  visible  from  the  ventral  view.    The  cranial  nerves  and  their  locations  are  described  in  the  next  laboratory.    The  olfactory  bulbs,  the  neural  tissue  responsible  for  the  sense  of  smell,  are  found  on  the  underside  of  the  frontal  lobes.    These  give  rise  to  the  first  set  of  cranial  nerves,  the  olfactory  nerve.    The  optic  nerves  form  an  ‘X’  at  the  optic  chiasm  and  continues  as  the  optic  tract  until  the  synapsing  in  the  thalamus.    The  rest  of  the  cranial  nerves  can  be  seen  along  the  pons  and  brainstem.    Just    posterior  to  the  optic  chiasm,  you  can  see  the  infundibular  stalk  which  connects  to  the  pituitary  gland  and  the  mammillary  bodies.    Posterior  to  the  hypothalamus  are  two  large  tracts  called  the  cerebral  peduncles  and  this  represents  the  part  of  the  midbrain  viewable  from  this  aspect.        The  medial  gyrus  on  the  temporal  lobe  is  the  parahippocampal  gyrus.    Immediately  deep  to  this  gyrus  is  the  hippocampus,  part  of  the  limbic  system.    

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 5.    Anatomy  of  the  Midsaggital  Section:  

   

The  midsaggital  section  is  a  view  of  the  brain  bisected  along  the  longitudinal  fissure.    From  this  view,  the  frontal,  parietal  and  occipital  lobes  are  seen.    Two  white  matter  tracts  are  readily  apparent:  the  larger  corpus  collosum  which  allows  communication  between  the  hemisphere  and  the  fornix  which  is  the  white  matter  tract  leaving  the  hippocampus.    White  matter  in  the  brain  consists  of  myelinated  axons  as  compared  to  gray  matter  that  consists  of  cells  bodies  and  unmyelinated  neurites.        The  opening  seen  between  the  two  white  matter  structures  is  the  lateral  ventricle.    The  third  ventricle  is  the  space  medial  to  the  hypothalamus  connected  to  the  fourth  ventricle  between  the  cerebellum  and  brainstem  by  the  cerebral  aquaduct.    Immediately  inferior  to  the  fornix  is  a  largish  rounded  area  of  the  thalamus.    Anterior  and  slightly  inferior  is  the  triangularly  shaped  hypothalamus.    The  infidibulum  is  a  stalk  projecting  from  the  anterior  point  of  the  hypothalamus  and  is  attached  to  the  pituaitary.    Immediately  caudal  to  the  hypothalamus  is  the  rounded  mammillary  body.    The  midbrain,  pons,  and  medulla  oblongata  are  seen  as  the  cerebellum  with  the  cerebellar  white  matter  tracts  known  as  the  arbor  vitae.      

 Identification:  • On  the  sheep  brain  and  a  human  brain  model,  identify  as  many  of  the  surface  structures  shown  in  the  

above  illustrations  as  possible.      

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6.    Cerebellum:  

 The  cerebellum  is  located  on  the  caudal  aspect  of  the  brain,  with  the  large  mass  of  the  cerebral  cortex  above  it  and  the  portion  of  the  brainstem  called  the  pons  anterior.    The  cerebellum  is  divided  into  right  and  left  halves  with  the  vermis  (latin  for  worm)  protruding  midline.    The  cerebellum,  responsible  for  fine  control  of  voluntary  movement,  is  composed  of  a  gray  matter  cortex  and  a  white  matter  arbor  vitae.      

7.  Ventricles:  

There  are  a  series  of  hollow  spaces  within  the  brain  called  ventricles.    The  ventricles  are  continuous  with  each  other  as  well  as  the  central  canal  of  the  spinal  cord  through  a  series  of  canals.    The  two  large,  “C-­‐shaped”  lateral  ventricles  encircle  the  two  thalamic  lobes  and  connect  medially  (via  interventricular  foramina)  to  a  centrally  located  third  ventricle.    Arising  from  the  posterior-­‐ventral  wall  of  the  third  ventricle,  the  cerebral  aqueduct  runs  inferior  to  the  corpora  quadrigemina  of  the  midbrain  to  the  fourth  ventricle,  which  lies  inferior  to  the  cerebrum.    The  central  canal  of  the  spinal  cord  begins  at  the  base  of  the  fourth  ventricle.    Cerebrospinal  fluid  (CSF)  is  produced  by  special  vascularized  patches  of  tissue  within  the  ventricles  called  choroid  plexus,  fills  the  ventricles,  ducts,  central  canal.    CSF  flows  from  the  ventricles  to  the  central  canal,  which  is  continuous  with  the  subarachnoid  space  surrounding  the  entire  central  nervous  system.    Once  the  CSF  returns  to  the  head,  it  is  drained  through  specialized  shunts  called  arachoid  villi  and  returned  to  the  circulatory  system.      

                                   

Identification:  • On  the  sheep  brain  and  a  human  brain  model,  identify  the  choroid  plexus,  lateral  ventricles,  third  ventricle,  

cerebral  aqueduct  &  fourth  ventricle.  

 

Figure  7.    Posterior  view  of  the  cerebellum.  

Cerebral Aquaduct

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8.    Sheep  Brain  Dissection  

 Use  the  following  link  for  guidance  on  sheep  brain  dissection:    http://academic.scranton.edu/department/psych/sheep/ieframerow.html    Use  a  digital  camera  or  cell  phone  camera,  take  pictures  of  the  sheep  brain  as  you  dissect  it.    You  should  have  at  least  (but  are  not  limited  to)  one  image  from  each  of  the  different  primary  views  (inferior,  superior,  lateral  &  midsagital  section),      Place  images  into  a  Powerpoint  or  Google  presentation  (ASK  YOUR  INSTRUCTOR  IF  THEY  HAVE  A  PREFERENCE)  and  label  as  many  of  the  following  structures  as  you  can  in  each  image  (you  should  be  able  to  label  all  the  structures  on  the  list  at  least  once):    Cerebrum  Frontal  lobe  Temporal  lobe  Parietal  lobe  Occipital  lobe  Precentral  gyrus  Postcentral  gyrus  Central  sulcus  Lateral  sulcus  Transverse  fissure  Longitudinal  fissure  Corpus  collosum  Fornix  Thalamus    

 Hypothalamus  Lateral  ventricles  Third  ventricle  Cerebral  aquaduct  Fourth  ventricle  Cerebellum  Vermis  Arbor  vitae  Midbrain  Pons  Medulla  Olfactory  bulb  Optic  nerve  Optic  chiasm  Optic  tract

   Attach  the  Word  document  to  the  back  of  your  lab  report  or  share  and  email  the  Google  Doc  to  your  instructor.    ASK  YOUR  INSTRUCTOR  WHICH  THEY  PREFER.      

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Attributions:  

Figure  1.    National  Cancer  Institute  (n.d.).  [Meninges  of  the  CNS].  SEER  Training  Modules,  The  Central  Nervous  System.  Retrieved  July  12,  2012  from  http://training.seer.cancer.gov/anatomy/nervous/organization/cns.htmlu  Figure  2.  Nrets  (2007).  [Encephalon].  and  Looie496(2008).  [Vertebrate-­‐brain-­‐regions].  Wikimedia  Coomons.  Retrieved  August  16,  2012  from  http://commons.wikimedia.org/wiki/File:Encephalon.png,  http://commons.wikimedia.org/wiki/File:Vertebrate-­‐brain-­‐regions.pn.  Figure  3.    Looie496.  (2011).  [Vertebrate  brain  regions].  Wikimedia  Commons.  Retrieved  July  12,  2012  from  http://commons.wikimedia.org/wiki/File:Vertebrate-­‐brain-­‐regions_small.png.  Figure  4.  NEUROtiker.  (2007).  [Brain,  lateral,  medial  and  inferior  views].  Wikimedia  Commons.  Retrieved  July  12,  2012  from  http://commons.wikimedia.org/wiki/File:Gehirn,_lateral_-­‐_Hauptsulci_beschriftet.svg..  Figure  5.    Modified  from  Beal,  J.A.  (2005).  [Human  brain  view  on  traverse  temporal  and  isular  gyri  description].  Wikimedia  Commons.  Retrieved  July  12,  2012  from  http://commons.wikimedia.org/wiki/File:Human_brain_view_on_transverse_temporal_and_insular_gyri_description.JPG.  Figure  6.    Beal,  J.A.  (2006).  [Human  brain  midsagittal  cut  description].  Wikimedia  Commons.  Retrieved  July  12,  2012  from  http://commons.wikimedia.org/wiki/File:Human_brain_midsagittal_cut_description.JPG.  Figure  7.    Figure  8.    Modified  from  Was  a  bee.  (2009).  [Third  ventricle].  Wikimedia  Commons.  Retrieved  July  12,  2012  from  http://commons.wikimedia.org/wiki/File:Third_ventricle.png.LSDB).    

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 Lab  07  Brain         Name                  CNS                 Lab  Section  ____________                            1.    Briefly  define  the  following  terms:              Meninges                                        Hemisphere                                      Lobe                                        Sulcus                                        Fissure                                        Cerebral  Cortex                                      Ventricle  (brain)                                      Choroid  Plexus                              2.    Name  the  adult  brain  structures  that  arise  from  each  of  the  following  embryonic  regions:              Prosencephalon                                      Mesencephalon                                      Rhombencephalon                            3.    Name  the  groove/fissure/sulcus  that  separates  the  following  brain  regions:              Left  &  Right  Cerebral  Hemispheres                                Cerebrum  &  Cerebellum                                    Frontal  &  Parietal  Lobes                                    Parietal  &  Temporal  Lobes                                  Parietal  &  Occipital  Lobes                            

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   4.    Describe  the  position  of  the  insula:                                                                                                5.    Briefly  differentiate  between  “White  Matter”  &  “Grey  Matter”                                                                                                6.    Supply  the  missing  terms  in  the  following  sentences  that  describes  the  LONGEST  possible  route  that  CSF  can  take  from  its  production  till  it  reaches  the  central  canal  of  the  spinal  cord:    CSF  is  produced  by  ______________________________________________in  one  of  the  two      ______________________________________________.    From  there  it  flows  through  a      ______________________________________________  into  the  ___________________________________________.    From      there  it  flows  through  the  ______________________________________________into  the      ______________________________________________,  and  then  into  the  central  canal  of  the  spinal  cord.      7.    You  have  likely  noticed  that  the  Sheep’s  olfactory  bulbs  are  much  larger  (both  their  actual  size  as  well  as  their  size  compared  to  the  overall  size  of  the  brain)  than  the  human’s.    Why  might  this  be  the  case?                                                                                                8.    Attach  your  pictures  of  the  sheep  brain  dissection  or  submit  to  your  instructor  online  (ask  your  instructor  which).