Question for discussion in sectionThe human brain takes years to mature, consumes 30% of thebody’s energy, and has gotten so large that unassistedchildbirth is dangerous.What important function(s) does the brain serve, beyond whatthe spinal cord & brain stem can accomplish?
ReviewOne way to subdivide the brain is according toanatomical features – either macroscopic ones (sulci,gyri) or microscopic ones (appearance of cells & celllayers under microscope)•What’s another way to subdivide the brain?•Which techniques can we use in humans to figure outwhat a brain region does?
Topographic organization in primary motor &somatosensory cortices (Penfield, 1940s-50s)
Primary visual cortexLateral View Medial View W. W. Norton
Retinotopy in Primary Visual Cortex• injected radioactive glucose into bloodstream while monkey viewedimage• “developed” brain like a photograph• Map of retina reproduced in brain! Roger Tootell et al., 1988
Visual processing Two processing streams (pathways):1. “What”: object recognition (ventral stream = occipito-temporal)2. “Where”: spatial localization (dorsal stream = occipito-parietal) (or “How”: how to act w/r to an object) W. W. Norton
Tonotopy in Primary Auditory Cortex
Primary, secondary, and associationcortices Primary cortex Secondary cortex Association cortex W. W. Norton
Frontal cortex: Goal-directed behavior
QuizA. B. C. Which of these lobes would play the biggest role in… •deciding which of two courses to take? •finding your way to the classroom? •remembering facts that you learned in class?
PollWhat does ‘topography’ mean, in the context of thebrain?A) A map of the gyri and sulci of the brainB) The spatial organization of cytoarchitectonic regionsC) The fact that frequencies of sound are representedin a systematic way across primary auditory cortexD) The ordered projection of a sensory surface, like theretina or the skin, or an effector system, like themusculature, to the brain
Poll: Which box represents the sense ofhearing? B A C D Primary cortex Secondary cortex Association cortex W. W. Norton
Next upPrenatal brain development 9 months http://capturedbycarrie.com/
200-300 million sperm deposited – only 1 (if any) will fertilize theegg
That one lucky little spermatozoid
Formation of the embryo
Early stages of embryonic development Inner cell mass will Formation of thereorganize into a disk 3 germ layers
The Ectodermal germ layer will give rise to… • Central Nervous System • Peripheral Nervous System • Sensory epithelium of ear, nose, and eye • Skin (including hair and nails) • Pituitary, mammary and sweat glands • Enamel of teeth• Important gene for ectodermal development: Growth factor BMP4 22
Formation of the neural tube thebrain.mcgill.ca
Week 4: From neural tube to brain andspinal cord
Neural tube defects Humpath.com
Regionalization of the brain Prof. Thomas Jessell, researchchannel.org
From 1 month after fertilization through birth Prof. Thomas Jessell, researchchannel.org
Face development from 5.5 weeks to 8.5weeks• Facial structures fuse during the 7th week• Cleft palate (1 in 500 births) develops from errors during this period
9 weeks• Around the size of a peanut• Head is roughly half the length – bulging forehead reflectsextremely rapid brain growth that has been going on forweeks
11 weeks: major divisions of brain are visible
16 weeks• can tell the sex of the fetus• kicking & some reflexes (breathing movements, grasping, sucking)
20 weeks • sleep/wake cycles • facial expressions (eyebrows, forehead, mouth) • head-down position more frequent
28 weeks • eyelids flutter during REM sleep • reacts to sounds • brain waves similar to newborn • brain and lungs sufficiently developed that – if born now – could potentially survive without medical intervention.
The home stretch: 8th-9th month • Red, wrinkled skin fills out with fat (provides insulation to protect against heat loss) • Gains 1/2 lb. per week • Startle reflex is present; responds to light and sound, lifts its head • 60 percent of adult head size present36
Birth• Considered full-term if born within 10-14 days of calculated delivery date; if born earlier, considered pre-term• The earlier born, the greater the risk (due to underdevelopment)• Correlated with prematurity is low birth weight, which brings its own set of complications and risk • Normal birth weight >3500 grams • LBW <2500 grams • VLBW <2500 grams • ELBW <1000 grams 37
Milestones in prenatal development• Zygote forms after conception• Blastocyst embeds in uterine wall• Germinal stage gives rise to embryonic stage, which lasts about 8 weeks; during this time all organs, systems, etc. form• Fetal stage lasts 7 months (in full term pregnancy) and is period of elaboration and growth• Labor and delivery culmination of all this hard work – generally, 40 weeks post conception Sadler, TW (2010). Medical Embryology, Eleventh 38 38 Edition. Baltimore: Lippincott Williams & Wilkins
When do abortions occur? Percentage of 2008 Reported Abortions by Weeks of Gestation* (CDC)
Who is having abortions?• At current rates, nearly one-third of American women will have an abortion (AGI)• 50% of U.S. women obtaining abortions are younger than 25; women aged 20-24 obtain 33% of all U.S. abortions and teenagers obtain 17% (AGI).• The abortion rate of women with Medicaid coverage is three times as high as that of other women (NAF).