Neurobiology The Brain and Senses IB Biology Neurobiology The Brain and Senses

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

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 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 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=yzyphSTkW2U

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=ssKoVTWV99s https://www.youtube.com/watch?v=66rQwocHahI

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