The Brain

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The Brain

• BIOL 242

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Extra Parts

• A. Protections and coverings
• meninges

http//www.michigan.gov/images/MDA_CWD_Meninges_61
478_7.jpg
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Meninges - cover and protect CNS

• protect vessels and enclose venous sinuses
• contain CSF
• Pia mater - adjacent to the brain, gentle mother
• thin and transparent, clings to brain, minute
  blood vessels
• subarachnoid space - w/CSF
• meningitis - inflammation of meninges, bacterial
  or viral
• Arachnoid mater - spider's web w/CSF
  subarachnoid collagen and elastic fibers
• also has largest vessels - but provides poor
  protection
• subdural space - arachnoid to dura
• arachnoid villi - knob like projections into
  dura mater
• allows for CSF to be absorbed into venous sinuses
  in dura mater
• Dura mater - thick outer layer, dense irregular
  connective tissue, double layer
• collects venous blood into sinuses and drain it
  into the internal jugular

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Extra Parts

• A. Protections and coverings
• meninges
• B. CerebroSpinal Fluid (CSF)

http//en.wikipedia.org/wiki/Cerebrospinal_fluid
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CSF

• Located in subarachnoid space
• Ventricles w/CSF
• Lateral (2) - in the cerebrum hemispheres
• Third - btw and inferior the R and L thalamus
• Fourth - btw brain stem and cerebellum
• Contents - contains proteins, lactic acid, urea
  - similar to plasma
• cations (Na, K, CA2, MG2) and anions (Cl-,
  and HCO3-)
• glucose - neurons use to make ATP
• more Na and Cl- then plasma, less protein, K,
  and Ca then plasma
• pH important in homeostasis
• Movement
• moved by circulation and respiration and postural
  pressures
• Functions
• mechanical protection - cushion, reduces brain
  weight
• chemical protection - change ions of CSF --gt
  alter PSP's and AP's
• circulation - nutrient and waste products

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CSF

• Produced
• in the choroid plexus
• network of capillary in the walls of the
  ventricles w/ependymal cells
• basically replace every 3-4 hours
• Hydrocephalus - tumor or other structure blocks
  the flow of CSF, accumulates
• babies causes head to enlarge
• because bones not fused and hardened
• adults brain damage - pressure on brain tissue

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Extra Parts

• Blood supply

Circle of Willis - cerebral arterial circle -
base of the brain uses 20 of O2 at rest over 4
min w/o O2 --gt lysosomes ? suicidal Blood Brain
Barrier due to presence of astrocytes
cell membranes overlap capillaries less
leaky tight junctions provides a stable
environment steady chemical environment
shields - toxins selective barrier
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Blood supply - what passes across the blood
brain barrier?

• CO2, fats, fatty acids, O2, ions, hormones
• glucose, essential amino acids, and Fe have own
  carrier molecules
• valium dissolves in lipids
• Alcohol/nicotine
• cocaine is fast
• anesthetics
• heroin is 100 times faster than morphine (less
  lipid soluble)
• insulin endocytosis then exocytosis
• depends upon size, charge, solubility in lipids,
• some snake venom dismantles capillaries

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How to cross the BBB

• Hole in skull catheter
• Mannitol ? carotid
• dehydrates endothelial cells ? openings in caps
• 15 second window
• also allows WBCs (? seizures), NTs , hormones
• Hollow tube implants

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Brain Parts

• Medulla oblongata

Vital centers Cardiac-HR Vasometer-BP in
arterioles Respiration - in out also
hiccuping, vomiting, swallowing, coughing,
sneezing The neurons controlling breathing have
mu (µ) receptors, the receptors to which opiates,
like heroin, bind. This accounts for the
suppressive effect of opiates on breathing.
Destruction of the medulla causes instant death.
Source http//users.rcn.com/jkimball.ma.ultranet
/BiologyPages/C/CNS.html
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Brain Parts

• Pons ( bridge)

http//faculty.ucc.edu/biology-potter/The_Brain/sl
d017.htm
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Pons ( bridge)

• contain nuclei and tracts of white fibers -
  conduction tracts
• Middle cerebellar peduncles - connect R an L
  sides of the brain
• CN - efferent V(mastication), VI(eye mvt), VII
  (taste, salvia and facial expression). VIII
  (vestibular cochlear - balance)
• afferent V, VIII(ear)
• Nuclei of the reticular formation
• Pneumotaxic center inspire to
  exhalerespiratory control,
• w/ medulla ? normal breathing rhythm

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Brain Parts

• Midbrain
• Welllll..

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Vertebrate Central Nervous System (CNS)
Proper development ? functional adult
http//www.brainexplorer.org/glossary/midbrain.sht
ml
thalamus
midbrain
hindbrain
Diseases Parkinsons Disease Tourettes
Syndrome Schizophrenia Attention Deficit
Disorder Addiction behaviour Alzheimers Disease
Roles Motor pathways Reflexes Behaviour Pain Aw
areness
http//www.dkimages.com/discover/previews/768/6406
4.JPG
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Development of the Vertebrate CNS
Spontaneous Synchronous Activity (SSA)
Neuron sub-type specification Axonal outgrowth
and pruning Synaptic initiation and
stabilization Establishment of neuronal
networks Neuronal electrophysiological properties
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Spontaneous Synchronous Activity - Retina
Postnatal ferret retina P5
Shatz, 1996
Ganglion cells (GCL, cells 1-5) and amacrine
cells (cells 6-10) IPL, inner plexiform layer
VL, ventricular layer
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changes in intracellular Ca2reflect electrical
events
Calcium Imaging

Cell loaded with Ca2 indicator dye (fluo4)
Electrical activity raises intracellular Ca2
levels
Free Ca2 binds dye, which then fluoresces
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increased intracellular Ca2 ? increased
fluorescence
Calcium Imaging
Double labeled neurons dextran-identified
neurons (red signal) fluo4 filled neurons as they
fluoresce (green signal)
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Is there spontaneous synchronous activity in the
embryonic mouse midbrain?
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Spontaneous Synchronous Activity (SSA) occurs in
the midbrain over a specific span of
developmental time
Rockhill et al, 2008 in submission
Activity found at E13.5 into rostro-lateral
midbrain. No activity at E14.5.
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Spontaneous Synchronous Activity (SSA) changes
frequency over developmental time
MB midline
MB
MB
43 SSA
80 SSA
Isth
87 SSA
100µm
HB
Frequency of SSA in Midbrain Over Developmental
Time
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Propagation of SSA in the midbrain - a bifurcated
wave
midbrain
isthmus
hindbrain
100 µm
Rockhill et al, 2008 in submission
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mb159b1.xls
Frequency of SSA Midbrain vs Hindbrain
MB midline
MB
MB
Isth
100µm
HB
mb159c1.xls
mb208a1.xls
Time (minutes)
local events
MB
HB
Rockhill et al, 2008 in submission
p 6.2 x10-16 based on paired one-tailed t-test
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Development of the Midbrain
Chick Nakamura 2001
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Development of the Mouse Midbrain Techniques -
Dissection
Stages E10.5 E14.5
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Mammalian Midbrain
http//www.vet.chula.ac.th/physio/lung/midbrain.j
pg
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Midbrain

• Corpora quadrigemini
• Inferior Colliculi - reflex center for head and
  trunk
• Superior Colliculi - reflex center for eye, head,
  neck
• Cerebral Peduncle - ventral portion
• Superior cerebellar peduncles - midbrain to
  cerebellum
• Cerebral Aqueduct - connects the 3rd and 4th
  ventricles
• Substantia Nigra - black (melanin) pigments, deep
  to cerebral Peduncle
• There are about 550,000 cells present
• Up to 80 may die off
• Causes
• Toxins synthetic heroin ? this in a group of 20
  year olds ,San Fran, early 80
• Trauma
• Microbes
• Genetics more prone if exposed to above
• Aging - Everyone gets Parkinsons if they live
  long enough
• Red Nucleus - red due to rich vascular supply and
  Fe
• info from the cerebrum and cerebellum --gt
  commands to maintain muscle tone/posture
• Reticular Formation - some nuclei located here -
  coming up next
• CN - eff IV(superior oblique eye m.), III (eye
  lens and iris)

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Brain Parts

• Reticular Formation w/Reticular Activating System
  - RAS

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• Reticular Formation w/Reticular Activating System
  - RAS
• mainly w/in the midbrain
• In brain stem - medulla, pons, and midbrain
• diffuse network of neurons in what is otherwise
  white matter
• Reticular Activating System - RAS
• maintains consciousness and alertness - filters
  out cont, familiar, weak signals
• RAS cerebral cortex disregard 99 of info input
  
• - otherwise sensory overload
• LSD removes sensory dampeners
• during sleep the RAS is inhibited by centers in
  the hypothalamus
• depressed by alcohol, sleep-inducing drugs, and
  tranquilizers
• depress info travel ways w/anesthesia
• awake from sleeping - sensory signals used to
  awaken

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Limbic system

• fiber tracts gray matter in medial cerebral
  hemisphere and diencephalon
• emotional brain
• hippocampus and amygdala
• emotions and memories - odors "primitive brain"
• VNO ?
• hard to pinpoint exactly how functions

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Brain Parts

• Interbrain

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Brain Parts

• Interbrain - The Diencephalon
• The diencephalon are forebrain structures derived
  from the embryological diencephalic vesicles.
• It is surrounded by cerebral cortex.
• This is conventionally divided into 4 parts
• The epithalamus, which included the pineal gland
  and nearby structures
• The thalamus
• The hypothalamus.

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• The Epithalamus
• This includes the pineal gland and other parts
• Pineal Gland
• It receives light-regulated input
• Retina --gt one or more relays in hypothalamus --gt
  intermediolateral column of spinal cord --gt
  preganglionic sympathetic fibers --gt
  postganglionic neurons of the superior cervical
  ganglion --gt pineal gland
• In fish, amphibians, and many reptiles, it is
  involved in circadian and circannual rhythms.
• The mammalian pineal is an endocrine organ
  involved with reproductive cycles.
• It has, however, no known neural output.
• secretes melatonin sleep-wake cycles, some
  aspects of mood
• sex hormones - release
• It secretes an antigonadotropic hormone called
  melatonin at relatively high rates during
  darkness.
• Therefore, an increase in day lengths leads to
  increased gonadal function.
• By the age of 17, calcareous concretions accrue
  here, making it opaque to x-rays, hence making it
  a useful radiological landmark.

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• The Thalamus
• This is a large, egg-shaped nuclear mass.
• It makes up about 80 of the mass of the
  diencephalon.
• The thalamus is part of a remarkably large number
  of pathways.
• All sensory pathways relay in the thalamus.
• Many anatomical loops comprising cerebellar,
  basal ganglionic, and limbic pathways also
  involve thalamic relays.
• The various systems utilize separate portions of
  the thalamus.
• The thalamus is therefore subdivided into a
  series of nuclei.

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• The Hypothalamus
• This is a small portion of the diencephalon (4
  grams).
• important in the pathways concerned with
  autonomic, endocrine, emotional, and somatic
  functions.
• main visceral control center - vital in overall
  body homeostasis
• hunger, body temp - vessel constriction,
  emotions...
• no Blood brain barrier - several nuclei
  w/receptors
• Functional aspects
• Autonomic control - BP, rate and force of heart
  contractions,
• motility of digestion, resp rate and depth,
• Emotional response and behavior - pain,
  pleasure, fear, rage,
• biological rhythms, drives (sex)
• physical expressions of emotions
• pounding heart, laughing-crying
• Body temp - heat gain - peripheral vessels to
  constrict
• heat loss - dilation of peripheral
  vessels, sweating
• Food intake - hunger center - monitor blood
  glucose levels
• satiety center - no longer hungry
• Water Balance and thirst - ADH, urge to drink
• Sleep/wake cycles - response to
  daylight/darkness cues

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Brain Parts

• Cerebrum
• What can you do with a cerebrum?

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Cerebrum - 83 total brain mass

• corpus callosum - connects 2 hemispheres - bundle
  of nerves white matter
• falx cerebri - dura mater folds
• cerebral cortex - layer of gray matter (3 mm
  thick) - 2/3 of all neurons
• cortex rind or bark
• Functions
• interpret senses
• Vision
• Hearing
• Smell
• Touch
• Pressure
• Pain
• thinking and memory storage
• initiation of motor activity of skeletal muscle
• consciousness

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Cerebrum - 83 total brain mass

• Neocortex - seen when looking at brain
• newest evolutionary
• somatosensory and motor initiation
• 5 lobes frontal, parietal, temporal, occipital,
  and insula
• frontal - motor mvt central sulcus separates
• parietal - sensory
• occipital - vision
• temporal - auditory signals
• insula - (under temporal) olfactory lobe
• Grooves sulci folds - gyri
• Central sulcus - frontal and parietal
• Precentral gyrus - motor
• Postcentral gyrus - touch, pain, temp, pressure
• Lateral sulcus - frontal and temporal
• Parietaloccipital - parietal and occipital
• Transverse Fissure - cerebrum and cerebellum

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Hippocampus et al.

• Hippocampus - folded under neocortex formation
  and recall of memory
• Olfactory lobes - inside insula make up limbic
  system w/hippocampus
• Basal Nuclei - gray matter nuclei or Cerebral
  nuclei - deep w/in cerebrum
• modification and control of muscle mvts,
  cognition, intensity of movement
• similar to cerebellum
• hard to determine exact role
• part of extrapyramidal system - motor system
  that controls
• muscle tone and coordinated learned movement
• Corpus striatum made of several parts
• caudate nucleus where information arrives to
  then be sent on
• lentiform nucleus globus pallidus and putamen
• Globus pallidus - output regions that synapses on
  the thalamus
• Substantia nigra - modifies activity of globus
  pallidus
• pathology - loss of motor control, NCTS def.
  --gtParkinson's
• generate patterns of activity in motor neurons
  --gt complex behavior
• certain programs - preset pattern for a movement
• damage --gt spontaneous, inappropriate motor mvts
• flinging arms or writhing or tremors
• Amygdala - tail of caudate nucleus - actually
  part of the limbic system

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White matter

• myelinated, deep to gray matter, provide
  communication
• Association fibers - connect different areas of
  the same hemisphere
• Commissural fibers - connect areas of one
  hemisphere with another
• enables them to function as a whole
• Corpus callosum Anterior Commissure Posterior
  Commissure
• Projection fibers - connect lower and higher
  areas of the brain (cortex to diencephalon)
• ascending and descending - vertically versus
  others that run horizontally
• internal capsule - between thalamus and some
  basal nuclei
• pathology - damaged often by a stroke

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Brain Parts

• Cerebellum
• Where learned movements are stored.
• Coordination of movements.
• Data are analyzed and a course of action is
  quickly decided.
• Each and every piece of information that leaves
  the cerebellum does so through the Purkinje
  cells.
• Damage to Purkinje cells and nerve cells ? loss
  of coordination and difficulty with speech
• http//images.google.com/imgres?imgurlhttp//www.
  stanford.edu/group/hopes/rltdsci/trinuc/f_f08ioliv
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• Cerebellum - 11 brain mass
• evolutionarily old -
• coordinate and modify skeletal muscle movement
  via brain stem and thalamus
• smoothes and coordinates programs from basal
  ganglia
• predictions future positions of moving body
  parts used by athletes musicians
• No direct connection to cerebrum
• dysfunctions hypotonia - reduced muscle tone
• Ataxia - loss of equilibrium
• dysynergy - breakdown of coordinated movements
• but no inappropriate movements like basal ganglia
  breakdown

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Brain Parts

• Limbic system ( ring)

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• II. Brain
• external Pyramids - ventral side - longitudinal
  ridges
• anterior where the corticospinal tracts located
• motor tracts from cerebrum to spinal cord
• decussion of pyramids - cross to opposite
  sides
• just above where medulla becomes spinal cord
• contralateral control of body - opposite
  sides
• Olives - lateral to pyramids, oval swellings
• contain Inferior Cerebellar Peduncles -
  fiber tracts connecting medulla to cerebellum
• w/nuclei --gt precise, efficient voluntary
  mvts, equilibrium and posture
• relay sensory information from periphery to
  cerebellum
• CN roots - efferent XII, X, IX, XI
  afferent X, VIII, V, IX
• internal Nucleus gracilis and Nucleus cuneatus
  - receive sensory info dorsal side
• dorsal from ascending tracts (fasiculus gracilis
  and cuneatus), relay info to thalamus
• and somatosensory cortex
• Pathologies - polio - affects here - causes
  resp failure if found here
• B.
• D.
• F.