1. Neurobiology The Brain and Senses
IB Biology
Neurobiology
The Brain and Senses

2. The Cerebral Cortex Develops from front part of neural tube
Largest part of mature brain
2 divisions- right and left hemispheres
Hemispheres covered with thin layer of grey matter (unmyelinated axons)cerebral cortex
Less than 5mm thick, 75% body’s neurons
Reasoning, language, complex thought, visual processing, motor movement , memory, speech

3. Cerebral Cortex, cont.
Human brain larger in proportion to body size than any other animal
3X larger than chimp
2X larger than orca
Correlation between body size and brain size
E:S ratio
E is brain weight
S is body weight

5. Enlargement of Cerebral Cortex
In order for brain to fit into skull proportionate to body, must fold into itself.
More folds, more complexity
More surface area is needed for more complex behaviors
Sulci (sulcus, indentation) and gyri(gyrus, raised bump)

6. Functions of Cerebral Cortex

8. The Visual Cortex, Broca’s, Nucleus Accumbens
Broca’s area- speech and language
Broca’s aphasia- occurs when area is damaged, difficulty in language production
Nucleus accumbens- associated with reward ciruit, responds to dopamine and serotonin
Dopamine-promotes desire, activation is associated with anticipating a reward.
Dopamine synthesized by ventral tegmental area nucleus accumbens via axons
Cocaine and nicotine increase dopamine production
Serotonin- inhibits desire

10. Visual Cortex Receives info from cells in retina of eye
Left hemisphere receives sensory info from right side and vice versa
One of many centers that cooperate to produce vision

11. Sensory Cortex CC made of unmyelinated neurons- grey matter
Hemispheres connected by corpus callosum
Primary somatosensory cortex receives messages about sense of touch
Primary visual cortex-receives info from right and left visual fields

13. Motor Cortex Controls voluntary movement
Right side controls left side of body, and vice versa
Stroke-blocked or ruptured blood vessel, interrupts oxygen flow to the brain cells, causes loss of function
Doctors can tell what part of brain is damaged by what function is lost

15. Brain Metabolism Highly metabolic
Chemical signals sent consume half the energy used by the brain
Brain needs twice the energy of any other body part
Glucose is main energy source
Neurons cannot store it, so it is needed constantly
High quality carbs are best source
Sustained levels of glucose to the brain are necessary for learning

17. Sensory Perception
Comfort food, familiar faces, favorite music, senses linked to memories and emotions
Taste and sound are protective
Sense organs keep the brain aware of surroundings
Brain interprets senses for us

18. Sensory Receptors Mechanoreceptors- detect force and pressure
Arteries- pressure receptors detect change in BP
Lungs- stretch receptors respond to degree of inflation
Proprioceptors in muscles, tendons, joints and ligaments help maintain posture and avoid injury
Inner Ear- pressure receptors manage equilibrium

20. Sensory Receptors, cont.
Chemoreceptors- respond to chemical substances
Taste and smell
In Blood vessels- detect pH changes
Damaged tissue- pain receptors respond to chemicals secreted by damaged tissue
Olfactory receptors- smell
All substances release volatile chemicals into the air
Humans detect 10,000 different odors
Top of nasal passage neurons synapse to brain
Receptors can be stimulated by more than one smell
Olfactory receptors encoded by genes
If your DNA lacks certain genes, you won’t be able to smell certain molecules

21. Sensory receptors, cont.
Thermoreceptors- respond to change in temperature
Located in skin
Warmth receptors detect rises in temperature
Cold receptors respond when temp drops

22. Receptors, cont. Photoreceptors Respond to light energy
Dim light- rods
Bright light- cones
All located on the retina

23. The Eye

24. Visual Pathway
Light enters eye rods and cones of the retinasynapse with bipolar neuronsBP neurons synapse with ganglion cell ( axons of ganglion cells make up the optic nerve) carries nerve impulse to brain interpretation of what is seen.

25. The Retina

27. Rods and Cones Rods- more sensitive to light, work well in dim light
Only 1 type of rod in retina, can absorb all wavelengths of light
Group of rod cells to 1 nerve fiber

28. Rods and Cones, cont.
Less light sensitive, function well in bright light
3 types of cones: red, blue and green
One cone to 1 nerve fiber

29. Red and Green Color Blindness
Dichromatic vision
Defect in red and green cones
Sex-linked trait
More males than females
Have blue and green cones, non-functional red
Have blue and red, non-functional green

31. Contralateral Processing www.youtube.com/watch?v=7-_8PEDNUy4

32. Hearing

33. How Sound is Perceived
Sound waves are successive vibrations of air molecules
Travel to the auditory canal, displace the tympanic membrane

34. Structures in the Middle Ear
Bones of middle ear: malleus, incus, stapes receive vibrations and amplify 20X
Stapes oval windowvibration passes tofluid in cochleafluid causes hair cells (mechanoreceptors) to vibratehair cells release NT to sensory neuron of auditory nerveround window releases pressure so fluid in cochlea can vibrate

35. Sensory hairs of the Cochlea
Hair cells of cochlea have stereocilia that protrude from the hair cells and detect specific wavelengths
Bending of stereocilia create internal change that results in electrical impulse auditory nerve
Short, high frequency waves = high pitched sounds
Long, low frequency waves = low pitched sounds

37. Auditory Processing
Sound is processed in auditory area of cerebral cortex
Hearing varies with individuals and with age
High frequency sounds for long periods can damage hearing, by damaging cochlear hair cells
Hair cells do not regenerate

38. Hair Cells in Semi-Circular Canals
Three semi-circular canals
Filled with fluid and hair cells
Movement of fluid detected by hair cells detect rotational movement of the head
Hair cells are sensory receptorsvestibular nerve
Maintain balance by position of otoliths in vestibular apparatus

39. Cochlear Implants
Convert sound into electrical signals that are sent  brain
External processor worn behind ear
Microphone in Ex Processor picks up sound
Processor digitizes the soundimplant surgically placed in the cochlea
Implant like mini computer translating soundelectrical signals
Auditory nerve brain
Brain interprets sound