Brain
Brain
Overview
18 days after conception
Primitive streak
Outer layer of embryo thickens Ectoderm forms a plate
Edges curl up
Make a neural tube
Neural tube
Cells inside tube become neurons & glial cells Closed tube
Tube with 3 bulges
1. Forebrain
Cerebral cortex Basal ganglia Limbic system Thalamus Hypothalamus
2. Midbrain
Superior colliculi = vision Inferior collicui = hearing Homeostasis & reflexes
3. Hindbrain
Medulla oblongata Cerebellum
Pons
Phases
1st Phase
Symmetrical Division
2 identical founder cells
Radial Glial Cells
Spread out like tree
Neurons climb tree to their proper position
2nd Phase
Asymmetrical Division
About 3 months
Divide into neuron & founder cells End of cortical development
founder cells receive signal (cell death)
Development
Choice 1:
Two fists, crossed arms
NOTES
- Prenatal
- 18 days after conception
- Primitive streak
- Outer layer of embryo thickens
- Ectoderm forms a plate
- Edges curl up
- Make a neural tube
- Cells inside tube become neurons & glial cells
- Closed tube
- Tube with 3 bulges
- Quick Preview
- 1. Forebrain
- Cerebral cortex
- Basal ganglia
- Limbic system
- Thalamus
- Hypothalamus
- 2. Midbrain
- Superior colliculi = vision
- Inferior collicui = hearing
- Homeostasis & reflexes
- 3. Hindbrain
- Medulla oblongata
- Cerebellum
- Pons
- 1. Forebrain
- Phases
- 1st Phase
- Symmetrical Division
- 2 identical founder cells
- Radial Glial Cells
- Spread out like tree
- Neurons climb tree to their proper position
- 2nd Phase
- Asymmetrical Division
- About 3 months
- Divide into neuron & founder cells
- End of cortical development
- founder cells receive signal (cell death)
- Connections
- When neurons reach home
- Connect with each other
- Grow dendrites & axons
- Synapse formation
- Synapse elimination
- 5 Steps of Neurons
- 1. Proliferation
- Production of new cells
- Cells along the ventricles divide to become neurons and glia.
- 2. Migration
- Primitive neurons find their spots
- Chemicals guide cells
- 3. Differentiation
- Neurons get axon & dendrites
- Makes them different
- Axon grow before dendrites
- During migration
- 4. Myelination
- Glia cells produce myelin sheaths
- first in spinal cord
- Then in brain
- Lasts til about 30
- 5. Synaptogenesis
- Continues throughout life
- Forming synapses
- 1. Proliferation
- Age & Neurons
- Neurons go from
- undifferentiated
- differentiated
- dead
- Stem cells
- Nose cells always undifferentiated
- Periodically divide & make new olfactory cells
- Neurons go from
- Pathfinding
- Getting axons to their spots
- Chemical Pathfinding (Weiss, 1924)
- Grafted extra leg to a salamander
- Axons grew, moved in sync with other legs
- Nerves attach to muscles randomly
- Variety of messages are sent
- Each one tuned to a dif. muscle
- Chemical Gradients (Sperry, 1943)
- Severed optic nerve axons
- Rotated them 180°
- Grow back to their original target locations in midbrain
- Axons attracted by some chemicals, repelled by others
- TOPDV protein is 30x more concentrated in dorsal retina than ventral retina axons
- Highest connect to highest
- Lowest concentration axons connect to lowest
- Neural Darwinism
- During development
- Synapses form randomly
- Selection process keeps some and rejects others
- Chemical guidance
- Neurotrophic factors
- Muscles & synapse survival
- produce & release NGF (nerve growth factor)
- Not enough NGF, axons degenerate and cell bodies die
- Neurons automatically die
- don’t make synaptic connection
- Apoptosis = cell death
- Similar to NGF
- Neurotrophin
- promotes survival & activity
- BDNF
- brain-derived neurotrophic factor
- most abundant neurotrophin in cortex
- Neurotrophin
- Make more than enough
- Neurotrophins are also used in adult brains
- More axon & dendrite branching
- Deficiencies of neurotrophins lead to cortical shrinking and brain diseases
- During development
- Developing brain vulnerable
- Toxic chemicals
- Malnutrition
- Infections
- Toxic chemicals
- Teratogens
- Environmental factor
- Interfere with development
- Medication, drug, alcohol or substance
- Disease
- Critical Periods
- Implantation = common blood supply
- Whatever’s in mother’s blood crosses
- 10 to14 days after conception
- 3.5 to 4.5 weeks
- closure of the neural tube
- Central nervous system vulnerable throughout pregnancy
- Implantation = common blood supply
- 3 Major Substances
- Alcohol
- Phenytoin
- Chickenpox
- 1. Fetal alcohol syndrome
- Best known non-genetic cause of mental retardation
- (3 in 1,000)
- Infant brains are especially sensitive to alcohol
- Suppress release of glutamate
- brain’s main excitatory
- neurons receive less excitation and undergo apoptosis
- Alcohol broken down more slowly
- immature liver
- Alcohol levels remain high longer
- Worse when born to alcoholic mothers
- drink more than four to five drinks/day
- No amount of alcohol is safe
- Best known non-genetic cause of mental retardation
- 2. Phenytoin (or Dilantin)
- Anti-convulsive
- used to treat epilepsy (seizure disorder)
- 10% chance of birth defects
- Fetal Hydantoin Syndrome
- If taken in the first trimester
- Anti-convulsive
- 3. Varicella (chickenpox)
- Highly infectious disease
- 95% of Americans have had it
- 90% of pregnant women are immune
- 1 out of 2,000 develop during pregnancy
- A. If in pregnancy (week 1-20)
- 2% chance of defects
- “congenital varicella syndrome“
- Scars
- Malformed and paralyzed limbs
- B. Newborn period
- 5 days before to 2 after birth
- About 25 % newborns become infected
- About 30% of infected babies will die if not treated
- Parental use of:
- Cocaine or cigarettes
- ADHD
- Antidepressant drugs
- Heart problems
- Birth Defects
- 3-5% of newborns
- Leading cause of infant mortality
- Majority have no known cause
- Cortex Differentiation
- Different parts of cortex, different shapes
- Shape and functions depend on input received
- Transplant immature neurons
- Become like neighbors
- Transplant later
- Some new, some old attributes
- Experience fine tunes
- Redesign our brain to fit
- (within limits)
- Enriched environments
- Thicker cortex
- More dendritic branching
- Best enrichment = activity
- Redesign our brain to fit
- Transfer
- Far transfer = do well in one, do well in other tasks
- Near transfer = practice task, do better on that task only
- Train the brain – doesn’t work
- Blind from birth
- Better at discriminating objects by touch
- Increased activation in occipital lobe (vision) doing touch tasks
- Use occipital cortex for Braille; sighted people don’t
- Concept of straight
- Learning to read
- Learn to read as adults
- More gray matter in cortex
- Thicker corpus callosum
- Music Training
- Pro musicians
- Bigger temporal lobe (30%)
- 2x greater response to pure tones (in auditory cortex)
- Violin players
- larger area devoted to left fingers in the postcentral gyrus
- Writer’s Cramp
- Spend all day writing
- Fingers get jerky, clumsy & tired
- Musician’s Cramp
- Practice too much
- Fingers get jerky, clumsy & tired
- Expanded representation of each finger overlaps neighbor
- Pro musicians
- Overruling reflexes
- Antisaccade task
- Object appears in periphery
- Must look in opposite direction
- Top-down processing overruling reflex
- Improves with age unless
- Very young
- hard to look away from attention getter
- ADHD
- Very young
- Antisaccade task
- Age & Neurons
- At 30
- Frontal cortex begins to thin
- Much individual variation
- 60+
- Synapses alter more slowly (learn)
- Hippocampus gradually shrinks
- Compensate by using more brain areas
- At 30
- Blood-Brain Barrier
- (Paul Ehrlich, 1800’s)
- Injected blue dye into animals
- All tissues turned blue EXCEPT brain and spinal cord
- Keeps most chemicals out of brain
- Why need BBB?
- Brain has no immune system
- Neurons can’t replicate-replaced
- No way to fix damage
- Viruses that do enter kill you
- Rabbies
- Neural disorders last whole life
- Chicken pox-shingles
- How it works
- Keeps out harmful chemicals
- Keeps out medications
- Cancer med
- Dopamine for Parkinson’s
- Astrocytes form layer around brain blood vessels
- may be responsible for transporting ions from brain to blood
- Semi-permeable
- Endothelial cells line capillaries
- Small spaces between each
- Some things can move between them
- Loosely joined in body, large gaps
- Tightly joined in brain, blocking most molecules
- Large molecules can’t easily pass thru
- Molecules with a high electrical charge are slowed down
- Protects the brain
- What can cross passively
- Small uncharged molecules
- Oxygen & carbon dioxide
- Molecules dissolve in fats
- capillary walls are fats
- What can cross actively
- An active transport system
- protein-mediated process
- uses energy to pump chemicals
- E.g., burn glucose for energy
- Broken by:
- Hypertension (high blood pressure)
- Development (not fully formed at birth)
- High concentrations of some substances
- Microwaves & radiation
- Inflammation
- Brain injury
- Infections
- Alzheimer’s disease
- endothelial cells shrink
- makes gaps
- harmful chemicals enter
- An active transport system
- Nourishing Neurons
- Almost all need glucose
- Practically only nutrient that crosses blood-brain barrier in adults
- Ketones can also cross but are in short supply.
- If you can’t use glucose
- Korsakoff’s syndrome
- thiamine (vitamin B1) deficiency
- inability to use glucose
- neuron death
- severe memory impairment
- Head Injury
- Open or Closed
- Open head injury (penetrating)
- Object enters brain
- Closed head injury (skull not broke)
- Concussion
- Most common traumatic injury
- Brain gets rattled
- Open head injury (penetrating)
- Causes
- Car, train, airplane accident
- Fall
- Assault
- Sports
- Symptoms
- Can show immediately or develop slowly
- Unequal pupil size
- Headaches
- Obvious
- Object sticking out of head
- Fluid draining from nose-ears
- Clear or bloody
- Coma or unconscious
- Paralysis
- Seizures
- Sort Of Obvious
- Slurred speech
- Blurred vision
- Lack of coordination
- Memory loss
- Stiff neck
- Vomiting more than once; children often vomit once
- Not So Obvious
- Irritability (especially children)
- Mood or personality changes
- Drowsiness
- Confusion
- Loss of hearing, vision, taste or smell
- Low breathing rate
- Memory loss
- Symptoms improve, then get worse
- Get immediate help if
- Loss consciousness, even briefly
- Severe headache or stiff neck
- Vomits more than once
- Behaves abnormally
- Unusually drowsy
- Do
- Call 911
- Make sure breathing
- Assume spinal cord injury
- If normal breathing but unconscious
- Stabilize head and neck
- Hands on both sides of head
- If bleeding
- Press clean cloth on wound
- If soaks through, don’t remove it
- Put another cloth over it
- DO NOT
- Don’t wash deep head wound
- Don’t move or shake
- Don’t remove helmet
- Don’t pick up child
- Don’t drink alcohol (48 hours)
- If skull fracture
- Don’t apply pressure to bleeding site
- Don’t remove debris from wound
- No aspirin
- Aspirin & ibuprofen can increase risk of bleeding
- If vomiting
- Roll the head, neck & body as one unit
- Sleeping
- Wake every 2 to 3 hours, check alertness
- ask simple questions: “What is your name?”
- Open or Closed
