1. IB Biology
Brain Development

2. Neural Development Neural tube formation-
How do organs form from 1 fertilized egg?
After fertilization cells differentiate into 3 tissue layers:
Ectoderm- outermost layer
Brain and nervous system
Endoderm-inner layer
Lining of gut and other organs
Mesoderm-middle layer
Skeleton, muscle system

3. Neural Development, cont.
First organ to form from neural tube brain
Presence of tissue that is developing triggers the development of another tissue
Notochord (mesoderm) ectoderm  neural plate folds in and closes neural tube elongates into brain and spinal cord
Closure of neural tube happens in stages- brain forms before caudal (tail) area closes

4. Neural Devel., cont.
Failure to completely close- spina bifida

5. Activity
In your notebook, create a flow chart illustrating the development of the neural tube. Begin with the cell layers.
Pages

7. Neurogenesis & Migration of Neurons
Neurons of the CNS-
Originate in the neural tube
Neuroblasts: immature neurons, precursor
Neuroblast neuron = neurogenesis
Early neural tube formation-
Neurons- carry messages
Glial Cells- no messages, 90% in brain, give physical and nutritional support

8. Axon Growth Axons grow from CNS to distant areas
Tip of axon has a “growth cone” that directs axons to their destination
In vitro-
Axon avoids unfavorable surfaces, contracts
Axon grows toward favorable surface

9. Axon Growth, cont. Final destination of neuron:
Synaptic connections made with target cells via chemical messages
Some molecules can act as signals to the growth cone
CAM- cell adhesion molecule
Located on cell surface in growth environment of axon
Growth cone has receptor called CAM specific receptor
CAM and CAM receptor recognize each other to produce a chemical signal in neuron activation that causes elongation of neuron.

10. Axon Growth, cont. Some growth cone receptors target cell secretions
Chemotrophic factors
Can be attractive or repellant
Mammalian motor neurons begin in neural tube of CNS, must extend out to target tissue muscles
CAM causes migration to muscle tissue
Longest neurons are motor neurons

11. Axon Growth, cont. Multiple synapses are made initially
Neurons find “best fit” to target cell
When connections don’t work- eliminated
When connections do work- strengthened
Huang- proposed mechanism for this activity:
Mediated by Ig CAM (Immunoglobulin CAM) which has a lock and key mechanism of effect
CAMs form physical but reversible bond
Some connections do not persist, but the strongest ones will

12. Axon Growth, cont.
Some connections do not persist, but the strongest ones will
Neuromuscular junctions have neurons competing for innervation

13. Activity
Create a flow chart illustrating the migration of neurons from the CNS to the PNS.
Pages

14. Neural Pruning
From 2-3 years old, 15,000 synapses are present for each neuron, twice as many as adults
Neural pruning eliminates axons not used.
Remove simpler connections and replace with more complex adult connections
“Use it or lose it”
Makes brain more efficient

15. Neural Pruning, cont. Studies using mice-
Microglia prunes unused synapses
Elimination of weak and re-inforcement of strong synapses key to brain development
Microglia select synapse for removal on basis of inactivity

16. Plasticity of the Nervous System
Brains have the ability to change and adapt as a result of experience
Baby’s brain and adult brains both have plasticity
Evidence of recovery following massive strokes in adults
Plasticity varies with age, environment, heredity

17. Plasticity, cont. Functional and Structural Functional:
Ability to move functions from a damaged area to an undamaged area
Ex: tennis player loses use of arm due to a stroke given the task of cleaning tables. The arm “remembers” how to move during rehab, thus regaining function.

18. Plasticity, cont. Structural: Neuroplasticity
Ex: Taxi drivers with more experience have larger hippocampii (?)
Hippocampus- memory
Neuroplasticity

19. Stroke and Brain Function
Stroke- also called CVA (cerebrovascular accident)- a blood clot or rupture of a blood vessel in the brain.
Brain recovery-
Functional and structural reorganization
Axon sprouting
Post- stroke neurogenesis ( migration of new neurons to the site of injury

20. Stroke, cont. Promotion of recovery
Exercise- primate studies show that the weakness of hand movement due to stroke can be regained with physical therapy (gripping exercises)
Shoulder movement took over hand movement showing evidence of brain reorganization

21. New Technology for Stroke Patients
fMRI- functional MRI maps areas of activity in brain tissue
PET- positron emission tomography
MEG- brain mapping (magnetoenchephalography)
Post- stroke aphasia- loss of speech after stroke can be corrected by technology + physical therapy

22. The Brain
Nerve cells migrate to outer edge of neural tube and cause the walls to thicken
Neural tube becomes the entire central nervous system (CNS- brain and spinal cord)
Anterior endcerebral hemispheres
Posterior endother parts of brain and spinal cord
First to start developing and last to finish

23. Roles of Parts of Brain
Brain- jelly-like mass, 1.4kg, 100 billion neurons, site of memory, learning, personality
Brain regulates:
Unconscious body processes- breathing, heart rate, blood pressure
Balance, muscle coordination, voluntary movement
Speech, emotions, problem solving, thinking, dreaming

24. Roles, cont. Cerebral hemispheres: learning, memory, emotions
Hypothalamus: homeostasis, nervous and endocrine system coordination
Synthesizes hormones stored in posterior pituitary and release factors controlling the anterior pituitary

26. Roles, cont.
Cerebellum- “little brain”- has 2 hemispheres and a highly folded surface
Unconscious functions, movement and balance
Medulla oblongata-automatic and homeostatic activities
Swallowing, digestion, vomiting, breathing, heart activity

28. Roles, cont. Pituitary gland-2 lobes, posterior and anterior
Both controlled by hypothalamus
Both secrete hormones

29. Role of Medulla
Contains a “swallowing center” that coordinates the muscles of the mouth, pharynx, larynx, so that food does not go down the trachea and into the lungs
Controls breathing by monitoring carbon dioxide levels in the blood.
Too much? Breathing rate increases
Cardiovascular center- regulates heart rate

31. Identifying the Role of Different Brain Parts
Brain lesions-
Used to study brain function
Right and left hemispheres
Connected by corpus callosum- thick band of axons
Do not have the same function
Left hemisphere- all forms of communication
Damage causes difficulty speaking or using hand gestures
Deaf people with damage may lose ability to use sign language

32. Identifying Roles, cont.
Right hemisphere-
No communication, but understanding of words
Analysis of all information coming from all senses
Lesions here-
Problems identifying faces
Problems locating objects correctly in a space
Problems identifying melodies

33. Language Areas Broca and Wernicke- 1800s
Left side damage- speech and language problems
Pierre Paul Broca- Broca’s area-
Damage interferes with ability to vocalize words
Carl Wernicke- Wernicke’s area
Damage interferes with ability to put words into sentences

34. Split-Brain Surgery
Patients with severe epilepsy sometimes have their corpus callosum severed- called split-brain surgery.
Input from right visual field perceived by left hemisphere, and vice versa.
Visual information changed in these patients-
Objects flashed for the right eye were correctly identified (Left hemisphere is language)
Objects flashed for the left eye were not identified.

35. Functional MRI Uses radio waves and strong magnetic fields
Sees blood flow in real time
Can determine which sections are active during certain stimulation and how long they remain active.
Used for:
Surgery plan
Treatment for stroke
Placement of radiation therapy
Effects of degenerative disease –Alzheimer’s
Diagnosis of how injured brains work

37. PET
Slower scanner, but can tell how the brain is activated in presence of certain NTs and drugs

39. Autopsy Findings
Determines which brain parts are involved in certain functions
Broca
Autopsied patient with language disorder, found lesion in language center of brain (Broca’s Area)

40. Autonomic Nervous System
Brain and spinal cord- CNS
Everything else- PNS- Peripheral NS
PNS has 2 parts:
Somatic system- sensory info from sensory receptors to CNS muscles(Reflex Arc)
Autonomic system-involuntary- regulates glands, smooth muscle and the heart, located in the medulla

42. Autonomic, cont. Sympathetic NS- response is fight or flight
NT is NA
Exitatory
Increases HR and Stroke Volume
Dilates bronchi and pupil of eye,
Restricts blood flow to the gut
Parasympathetic NS- relaxed, “business as usual”
NT is Ach
Inhibitory
Pupil returns to normal
HR slows, stroke volume reduced
Blood flow back to gut
Systems are antagonistic- both cannot be activated at the same time.

44. The Pupil Reflex Pupil constricts in presence of bright light
Cranial reflex- sensory and motor neurons connect directly to the brain
Controlled by Ach
Can be inhibited by atropine, which blocks Ach temporarily
Pathway- optic nerve receives signals from retinasynapse with bipolar neuronsganglion cells connects with pretectal nucleus of brain stemEdinger-Westphal nucleus (axons run along oculomotor nervesciliary ganglion stimulate circular muscle of iris contracts

46. Brain Death
Brainstem controls heart rate, breathing rate, blood flow to digestive system.
Brain controls body temperature, blood pressure and fluid retention.
All can be maintained artificially without a functioning brain

48. Brain Death, cont. Legal description:
When a physician or physicians has determined that the brain and brainstem have irreversibly lost all neurological function.
Coma- neurological signs can be measured based on responses to external stimuli

49. Brain death, cont. Exams for brain death-
Toxicology- to make sure drug isn’t cause of symptoms
Movement of extremities-no hesitation when dropped
Eye movement-should be fixed
Corneal reflex-must be absent (Q-tip over surface)
Pupil reflex- absent
Gag reflex- absent
Respiration response- absent, cannot breathe without support
Still can have spinal reflexes- go to spine, not brain

50. Brain death, cont.
EEG-(electroencephalogram) check for electrical brain activity
CBF- (cerebral blood flow)- radioactive isotope injected, if it doesn’t make it to the brain, there is no activity
Can maintain patient on ventilator, but not indefinitely