IB Biology HL

1. IB Biology HL Option A.1 Neural 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 • https://www.youtube.com/watch?v=lGLexQR9xGs • http://www.dnatube.com/video/12257/The-human-embryonic-brain-development

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 497-498

6. https://www.youtube.com/watch?v=6Ii_v3t9hpU

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 • https://www.youtube.com/watch?v=4P3gj2SHZOw

13. Activity • Create a flow chart illustrating the migration of neurons from the CNS to the PNS. • Pages 499-500

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 • https://www.youtube.com/watch?v=rxPT78F_ZVE

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: • Ex: Taxi drivers with more experience have larger hippocampii (?) • Hippocampus- memory • Neuroplasticity • http://www.dnatube.com/video/1302/Brain-Plasticity

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 • https://www.youtube.com/watch?v=jHxyP-nUhUY

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. • https://www.youtube.com/watch?v=ZMLzP1VCANo

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. • https://www.youtube.com/watch?v=J968Wco1u0s

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

45. http://www.tedmontgomery.com/the_eye/reflex.html

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 https://www.youtube.com/watch?v=Ffqz-vKZO5Q

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