Transcript Option A Cerebral Cortex and Senses

IB Biology
Neurobiology
The Brain and Senses
The Cerebral Cortex
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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
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
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)
Functions of Cerebral Cortex
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
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
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
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
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
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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
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
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
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
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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
Sensory receptors, cont.
• Thermoreceptors- respond to change in
temperature
• Located in skin
• Warmth receptors detect rises in temperature
• Cold receptors respond when temp drops
Receptors, cont.
• Photoreceptors
– Respond to light energy
– Dim light- rods
– Bright light- cones
– All located on the retina
The Eye
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.
• https://www.youtube.com/watch?v=gvozcv8pS3c
• https://www.youtube.com/watch?v=yzyphSTkW2
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The Retina
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
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
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
Contralateral Processing
www.youtube.com/watch?v=7-_8PEDNUy4
Hearing
How Sound is Perceived
• Sound waves are successive vibrations of air
molecules
• Travel to the auditory canal, displace the
tympanic membrane
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
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
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
• https://www.youtube.com/watch?v=ssKoVTWV9
9s
• https://www.youtube.com/watch?v=66rQwocHa
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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
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
https://www.youtube.com/watch?v=GA9gEh1fLs