exam 2

DRAW IT (L9): The 3-part and 5-part developing brain

3-PART: PROSENCEPHALON (forebrain), MESENCEPHALON (midbrain), RHOMBENCEPHALON (hindbrain). 5-PART: prosencephalon splits into TELENCEPHALON + DIENCEPHALON; rhombencephalon splits into METENCEPHALON + MYELENCEPHALON; the MESENCEPHALON does NOT subdivide. Label what comes from each: telencephalon = cortex/basal ganglia/limbic; diencephalon = thalamus/hypothalamus/pineal/pituitary; mesencephalon = tectum + tegmentum; metencephalon = pons + cerebellum; myelencephalon = medulla.

DRAW IT (L9): Directional terms on an animal

Draw a four-legged animal and label: DORSAL (back/top), VENTRAL (belly/bottom), ROSTRAL (toward the nose), CAUDAL (toward the tail), MEDIAL (toward midline), LATERAL (toward the side), PROXIMAL (closer to the trunk), DISTAL (farther away). Then explain why DORSAL does not equal POSTERIOR in a human: standing upright bends the axis at the neck, so dorsal means the BACK for the body but the TOP for the head.

DRAW IT (L9): Spinal cord cross-section

Label: GRAY matter as the central butterfly/H (cell bodies); WHITE matter surrounding it (myelinated axons); DORSAL HORN receiving SENSORY input; VENTRAL HORN sending MOTOR output; DORSAL ROOT and VENTRAL ROOT; and the DORSAL ROOT GANGLION on the dorsal root holding sensory cell bodies. TEST HACK: find the ganglia on any diagram and you instantly know which side is dorsal.

DRAW IT (L9): The nervous system division tree

CNS = brain + spinal cord. PNS = everything else, splitting into SOMATIC (sensory in / voluntary motor out) and AUTONOMIC (involuntary), and the autonomic splits again into SYMPATHETIC (fight or flight) and PARASYMPATHETIC (rest and digest). Past exam asked directly: the two main parts of the PNS are SOMATIC and AUTONOMIC.

L10 - EXAM Q: Explain the roles of cerebrospinal fluid and the meninges

CSF cushions the brain, removes waste and toxins, and fills the ventricles and central canal (the leftover hollow of the neural tube). The MENINGES are the three membranes encasing the brain and spinal cord that hold the CSF in place. Together they protect the brain both physically and chemically.

L10 - EXAM Q: Compare and contrast spinal nerves and cranial nerves

SPINAL NERVES: 31 pairs, serve the BODY, connect to the spinal cord, and are ALL MIXED (sensory in and motor out). CRANIAL NERVES: 12 pairs, serve the HEAD, connect to the BRAINSTEM, and VARY - some purely sensory, some purely motor, some mixed.

L10 - EXAM Q: List the structures of the midbrain

TECTUM ('roof'): superior colliculus (VISION) and inferior colliculus (AUDITION). TEGMENTUM ('floor'): reticular formation, periaqueductal gray (pain), substantia nigra (movement), and red nucleus.

L10 - EXAM Q: Name the areas of the diencephalon

HYPOTHALAMUS at the bottom (motivational systems, and the pituitary hangs off it), THALAMUS in the middle (sensory relay), PINEAL gland on top. The PITUITARY is pea-sized and part of the endocrine system.

EXAM Q (L11): What are the core principles of neurodevelopment / what develops first?

The four stages in order: PROLIFERATION, MIGRATION, DIFFERENTIATION, APOPTOSIS. In the textbook's wording: cell division, then cell migration, then axon growth, then dendrite growth. Related exam facts: INTERNEURONS develop BEFORE projection neurons and connect LOCALLY; differentiation does NOT happen before proliferation; and an adult has FEWER neurons than at birth, not more, because of apoptosis.

EXAM Q (L11): Explain neural proliferation

The generation of new neurons by cell division in the ventricular zone of the neural tube. PLURIPOTENT (stem) cells are unspecialized and can become many cell types; PROGENITOR cells are more specialized and restricted to one lineage - a neural progenitor makes neural cell types but not muscle or cardiac. The brain deliberately OVERPRODUCES neurons at this stage, which is what makes apoptosis necessary later.

EXAM Q (L11): Explain the basic principles of neural migration

Newly born neurons travel from where they were generated to their final positions. RADIAL GLIA - a fifth glial type that exists ONLY in early development - provide the scaffolding neurons climb along, and they line the interior of the NEURAL TUBE. CELL-ADHESION MOLECULES (CAMs) are membrane proteins attracted to specific proteins on other cells that guide migration. Developing axons also use SUBSTRATES, GRADIENTS, CHEMICAL CUES, and GROWTH CONES to reach targets - a past exam keyed this as all of them.

EXAM Q (L11): Main principles of neural differentiation, and Sperry's contribution

DIFFERENTIATION = specialization; cells become different from those around them, growing axons and dendrites and forming synapses. SPERRY'S CHEMOAFFINITY HYPOTHESIS: growing axons find their targets by following specific CHEMICAL identity tags, so connections form by MATCHING, not by chance. His evidence: he cut the optic nerve and ROTATED the eye 180 degrees, and each axon RETURNED TO THE AREA WHERE IT HAD ORIGINALLY BEEN - producing systematically inverted vision. This is exactly why the visual system became the model system for development.

EXAM Q (L11): Why does cell death matter in neurodevelopment?

Apoptosis is construction, not damage. The brain overproduces neurons, then eliminates the ones that FAIL TO MAKE USEFUL CONNECTIONS - neurons that do not get enough trophic support (like NGF) die off. This sculpts accurate circuitry. NEURAL DARWINISM is the name for this idea: cells that have not made meaningful connections get destroyed. Exam wording: 'if an axon does not make the appropriate connections by a certain age, IT DIES.'

L12 - EXAM Q: How is the fovea specialized?

Three specializations for high spatial resolution: (1) the overlying cell layers are pushed aside so light has a clear path to the photoreceptors; (2) photoreceptors are packed densely so receptive fields are tiny and you can discriminate nearby points of light; (3) it is ALL CONES, no rods at all in the center.

L12 - EXAM Q: What is lateral inhibition?

When a photoreceptor is hit by light it excites its own vertical pathway AND inhibits its neighbors'. HORIZONTAL cells do this just below the photoreceptors; AMACRINE cells do it deeper at the bipolar/ganglion level. Net result: the lit column's ganglion cell fires and the neighbors go silent. Purpose: sharp EDGE and CONTRAST detection.

L12 - EXAM Q: What is opponent process theory? (and how to draw it)

Rather than sending every cone's raw output to the brain, a downstream cell SUMS two OPPOSING inputs and makes a judgment call - sending the difference is more efficient. RED vs GREEN: L cone and M cone both feed one opponent cell, then a ganglion cell, then CN II. BLUE vs YELLOW: there is NO yellow cone, so yellow must be BUILT from L + M summed together and compared against the S cone.

L12 - EXAM Q: Cut ONE optic nerve vs. ONE optic tract

Cut one optic NERVE (before the chiasm): completely blind in THAT ONE EYE; both visual worlds still reach both hemispheres via the other eye. Cut one optic TRACT (after the chiasm): you lose the OPPOSITE half of the visual world in BOTH eyes. Both eyes still work - they just cannot send anything from that half of space.

L13 - EXAM Q: How is the LGN organized?

Three dimensions at once: (1) RETINOTOPICALLY side to side, with far more tissue devoted to the fovea than the periphery (cortical magnification); (2) BY CELL TYPE in six layers - MAGNOCELLULAR in layers 1-2, PARVOCELLULAR in layers 3-6, koniocellular in between; (3) BY EYE OF ORIGIN, with layers alternating contralateral and ipsilateral input.

L13 - EXAM Q: Describe simple and complex cells

Both are feature detectors in visual cortex, found by HUBEL AND WIESEL. A SIMPLE CELL fires to a line at a particular ORIENTATION in a specific PLACE in the visual field - both conditions required. A COMPLEX CELL requires those two PLUS the line must be MOVING in a particular direction.

L13 - DRAW IT: How a simple cell is activated

One simple cell is wired to exactly FOUR ganglion cells in a row and no others. A PINK bar in the wrong orientation activates only 1 of the 4 - one tiny EPSP, below threshold, no action potential. A GREEN bar in the right orientation activates all 4, the EPSPs SUMMATE past threshold, and the cell fires. It is spatial and temporal summation applied to vision.

L13 - DRAW IT: How a complex cell detects direction

Four simple cells (S1-S4) converge on one complex cell. A bar moving left to right hits them in sequence, staggered in time, which would not summate. The fix: the body tunes each axon's CONDUCTION SPEED - via axon LENGTH, CALIBER, and MYELINATION - so all four arrive SIMULTANEOUSLY. Run the bar backwards and the signals arrive maximally out of phase and the cell stays silent. Direction selectivity is a TIMING trick.

L13 - EXAM Q: Impact of experience during development on adult vision

There is a CRITICAL PERIOD. Kittens raised in goggles with vertical slits over one eye and horizontal over the other grew up with cortical cells for ONLY that orientation - the cells for the other orientation did not exist. Adults over 20 with severe UNCORRECTED astigmatism still could not see the missed orientations even after being given perfectly correcting lenses. The retina works; the cortex never developed.

L14 - EXAM Q: How can we measure auditory input?

FREQUENCY in HERTZ (cycles per second), perceived as PITCH - how squeezed together the peaks are. AMPLITUDE in DECIBELS, perceived as LOUDNESS - how TALL the wave is. Every sound has both.

L14 - EXAM Q: How does sound get amplified within the ear?

The OSSICLES amplify two ways. (1) AREA RATIO: the tympanic membrane is much larger than the oval window, and focusing energy from a big surface onto a small one amplifies it - like a hammer driving a nail. (2) LEVER EFFECT: the three bones are arranged so one kicks out the next and the last strikes sideways, amplifying about 200x.

L14 - DRAW IT: Outer, middle, and inner ear

OUTER: (1) pinna, (2) external auditory meatus, (3) tympanic membrane. MIDDLE: (4) ossicles - malleus, incus, stapes - with the Eustachian tubes running down toward the throat. INNER: (5) oval window, (6) cochlea. Six numbered steps in order.

L14 - EXAM Q: Trace sound from the environment to the hair cells

Pinna funnels sound into the external auditory meatus, vibrating the tympanic membrane at the incoming frequency. The ossicles conduct and amplify; the stapes strikes the oval window. The basilar membrane vibrates at that frequency, carrying the organ of Corti with it, while the tectorial membrane above wobbles at a different rate - shearing the cilia. TIP LINKS pull open ion channels, sodium in and potassium out, the hair cell depolarizes, and the signal leaves via the 8th cranial nerve.

L14 - EXAM Q: The 3 theories of frequency coding

FREQUENCY THEORY: an individual cell fires at the exact same frequency as the sound; capped at about 200 cycles/sec by the refractory period, so it only explains low frequencies. VOLLEY THEORY: a POPULATION does it by committee, each cell firing on a different oscillation so the summed output matches the input; roughly 180-600 Hz; this is the CROSS-FIBER principle found in every sensory system. PLACE THEORY: different LOCATIONS along the organ of Corti code different frequencies; covers up to 20,000 Hz.

L15 - EXAM Q: What happens in the cochlear nucleus?

(1) It is TONOTOPIC - each cell has a BEST FREQUENCY, mapped in a cat study by playing tones low to high; highest frequencies map to the middle, lowest toward the side, with INTENSITY on the other axis, and the organization is preserved all the way to cortex. (2) It is the LAST place damage can deafen one ear, because fibers cross the midline past this point.

L15 - EXAM Q: Trace information from the brainstem to the cortex

Cochlea, 8th CN, cochlear nucleus, brainstem auditory nuclei (superior olivary nucleus and trapezoid body), INFERIOR COLLICULUS in the midbrain, MEDIAL GENICULATE NUCLEUS in the thalamus, primary auditory cortex at BRODMANN AREA 41, then secondary and tertiary association cortex. The inferior colliculus is OBLIGATORY, and the thalamus is ALWAYS the last relay before cortex.

L15 - EXAM Q: Name several ways we localize sound

(1) TIME CONCEPT - interaural time difference; brainstem cells fire only if one ear reports first and the other second; works only at ONSET. (2) PHASE DIFFERENCE - one ear at a trough while the other is at a peak, compared continuously; works up to about 1,500 Hz. (3) LOUDNESS - your head casts a SOUND SHADOW so the near ear hears it louder; works up to about 3-4 kHz, best for sustained sounds. Then you ORIENT until both ears match.

L15 - EXAM Q: Compare and contrast the visual and auditory pathways

VISION BRANCHES - the retina can go to the superior colliculus OR the LGN (plus the SCN and others), so it has PARALLEL pathways. AUDITION IS STEP BY STEP with NO parallel pathways. Vision: LATERAL geniculate, area 17, RETINOTOPIC, superior colliculus optional. Audition: MEDIAL geniculate, area 41, TONOTOPIC, inferior colliculus OBLIGATORY. (Careful - this is the one your notes had backwards.)

L15 - DRAW IT: The semicircular canals and otolith organs

SEMICIRCULAR CANALS: three per ear (ANTERIOR, POSTERIOR, LATERAL), one per plane (X, Y, Z). Glued into the tissue of your head so they move with you, but the GEL inside SLOSHES and bends the hair cells sticking up into it - the martini-glasses-on-a-waiter's-tray image. They are BIDIRECTIONAL ANGULAR ACCELEROMETERS: am I moving, and how fast. OTOLITH ORGANS: the UTRICLE (X plane) and SACCULE (Y plane), two per ear. Their hair cells are topped by CALCIUM CARBONATE crystals the body makes itself, which load weight onto the cells; whether the cells are SMUSHED or RELEASED tells you your ORIENTATION RELATIVE TO GRAVITY. Both use the SAME transduction as hearing: deflect, trapdoors open, SODIUM INFLUX, one direction depolarizes and the other hyperpolarizes. One-line split: CANALS = am I moving? OTOLITHS = which way is down?

TRAP: Superior vs. inferior colliculus

SUPERIOR colliculus = VISION (lets you foveate/orient toward what you see; an OPTIONAL branch off the retina). INFERIOR colliculus = AUDITION (an OBLIGATORY stop on the way to the thalamus). Both sit in the TECTUM of the midbrain.

TRAP: Lateral vs. medial geniculate nucleus

LATERAL geniculate = VISION. MEDIAL geniculate = AUDITION. Both are nuclei of the THALAMUS, and in both systems the thalamus is the last relay before cortex.

TRAP: Brodmann 17 vs. 41

Area 17 = primary VISUAL cortex (V1), reached via the optic radiation. Area 41 = primary AUDITORY cortex. Area 18 is secondary visual.

TRAP: Retinotopic vs. tonotopic

RETINOTOPIC = an orderly map of SPACE, in the visual system. TONOTOPIC = an orderly map of FREQUENCY, in the auditory system. Both are preserved from the periphery all the way up to cortex. (Ionotropic and metabotropic are RECEPTOR types, not maps - a common distractor.)

TRAP: Which structures transduce, and from what to what

PHOTORECEPTORS transduce LIGHT energy into neural energy. HAIR CELLS transduce mechanical VIBRATION into neural energy - in the cochlea for hearing and in the vestibular organs for movement and gravity. Transduction always means converting one form of energy into another.

TRAP: Which cranial nerves carry the senses in this unit

CN II (OPTIC) carries vision out of the eye. CN VIII (VESTIBULOCOCHLEAR) carries BOTH hearing and balance. Do not confuse CN VIII with CN X (vagus), which handles the gut.

TRAP: Nerve vs. tract

Fibers OUTSIDE the CNS travel in NERVES; fibers INSIDE the CNS travel in TRACTS. That is the ONLY thing that changes at the optic chiasm - same axons, same information, new label. Parallel pair: a cluster of cell bodies is a GANGLION outside the CNS and a NUCLEUS inside it.

TRAP: Sperry shows up in three places

Lecture 11 (chemoaffinity hypothesis, rotating the frog's eye), Lecture 12-13 (why the visual system became THE model system for development), and Lecture 10 (split-brain and lateralization work). If a question mentions Sperry, check which of the three it means.

TRAP: Summation shows up in three places

Spatial and temporal summation explain (1) how a SIMPLE CELL fires only when all four ganglion cells hit it at once, (2) how a COMPLEX CELL detects direction by tuning conduction speeds so signals arrive simultaneously, and (3) how brainstem cells compute INTERAURAL TIME DIFFERENCE for sound localization. Same principle, three systems.

TRAP: Critical periods and plasticity across lectures

L11: enriched environments change brain structure; Merzenich's owl monkey shows adult cortical reorganization after amputation. L13: the kitten goggle study and the human astigmatism study show a CRITICAL PERIOD in vision. Textbook 6.3: deaf individuals' auditory cortex responds to sign language. All the same theme - experience wires the brain.

CONFLICT ALERT: Does light DEPOLARIZE or HYPERPOLARIZE rods?

THE TEXTBOOK SAYS HYPERPOLARIZE - and 'according to the text' questions will use that. In the DARK, rods sit DEPOLARIZED at about -40 mV, held there by sodium flowing in through channels kept open by cGMP. LIGHT lowers cGMP, the sodium channels CLOSE, and the rod HYPERPOLARIZES with reduced transmitter release. The key point the text makes: what matters is that light is DETECTED, not whether detection happens by depolarization or hyperpolarization.

CONFLICT ALERT: What defines a COMPLEX cell?

LECTURE version: orientation + specific location + MOVING in a particular direction. TEXTBOOK version: complex cells respond to bar-shaped stimuli but are LESS SELECTIVE ABOUT THE LOCATION of the bar in the visual field. If a question says 'according to the text,' use the location-selectivity framing. Both agree simple cells need a specific orientation AND a specific location.

CONFLICT ALERT: How many opponent pairs?

The LECTURE gave TWO: red vs. green, blue vs. yellow. HERING'S original theory in the TEXTBOOK gives THREE: green vs. red, blue vs. yellow, AND BLACK vs. WHITE. If the question says 'according to the text,' include black/white.

CONFLICT ALERT: Cone peak sensitivities

TEXTBOOK numbers: 420 nm (blue-violet), 560 nm (yellow-green), 630 nm (orange-red). The lecture used looser figures (violet ~400, blue ~470, yellow ~600). Use the textbook's three numbers for 'according to the text' items.

CONFLICT ALERT: What do magno and parvo carry?

LECTURE: magno = movement, parvo = fine detail AND color. TEXTBOOK: magnocellular layers are the VENTRAL layers with LARGER cells and provide the 'WHERE' (position); parvocellular layers are DORSAL with smaller cells and provide the 'WHAT' (identifying detail); the KONIOCELLULAR layer is interspersed below each and handles COLOR. Past exams have asked this as 'parvocellular is to ___ as magnocellular is to ___' with the answer DETAIL, MOVEMENT.

REVIEW SESSION Q: Which is NOT part of the parasympathetic nervous system? (heart rate decrease / bladder contraction / pupil dilation / increased salivation)

PUPIL DILATION. That is SYMPATHETIC - fight or flight, you dilate to take in more of the scene. Parasympathetic is rest and digest: heart rate DOWN, bladder contraction, salivation UP, pupils CONSTRICT.

REVIEW SESSION Q: Which is NOT derived from the prosencephalon? (hypothalamus / primary visual cortex / pituitary gland / pons)

THE PONS. Prosencephalon = FOREBRAIN, which splits into telencephalon (cerebral cortex, including V1) and diencephalon (hypothalamus, thalamus, and the pituitary hanging off the hypothalamus). The pons comes from the METencephalon, out of the rhombencephalon (hindbrain).

REVIEW SESSION Q: What cell type is concentrated in the fovea?

CONES. The very center of the fovea is all cones and zero rods. Rods are concentrated in the periphery.

REVIEW SESSION Q: What unit measures the frequency of a sound?

HERTZ. Frequency = Hertz = cycles per second = perceived as PITCH. Decibels measure amplitude/loudness; nanometers measure light wavelength.

PAST EXAM REPEAT: Which is NOT directly innervated by retinal ganglion cells?

THE VISUAL CORTEX. Retinal ganglion cells DO directly innervate the suprachiasmatic nucleus, the lateral geniculate nucleus, and the superior colliculus. The visual cortex is reached only INDIRECTLY, via the LGN and the optic radiations. This exact question appeared on BOTH the 2018 and 2019 exams - treat it as near-certain.

PAST EXAM: Cells that synapse DIRECTLY with photoreceptors

BIPOLAR cells and HORIZONTAL cells. NOT amacrine cells (they sit deeper, at the bipolar/ganglion junction) and NOT ganglion cells (one layer further down).

PAST EXAM: Which ganglion cell type is in or near the fovea?

PARVOCELLULAR. Magnocellular cells are concentrated in the periphery. Koniocellular is a real third type (color) but is not the foveal answer.

PAST EXAM: The developmental sequence, exam wording

CELL DIVISION, then CELL MIGRATION, then AXON GROWTH, then DENDRITE GROWTH. This is the same sequence as proliferation-migration-differentiation, just phrased in the textbook's terms. Watch for a version where the first stage listed is not proliferation at all - then the answer is 'none of these.'

PAST EXAM: Sperry's rotated eye, exact result

When Sperry cut a newt's optic nerve and rotated the eye 180 degrees, each axon RETURNED TO THE AREA WHERE IT HAD ORIGINALLY BEEN. Not random, not split, not the opposite part of the target - back to its original target, which is why the animal's vision was systematically inverted. That is the evidence for the CHEMOAFFINITY hypothesis.

PAST EXAM: Neural Darwinism

The idea that cells which have NOT made meaningful connections get DESTROYED. Related exam wording: 'if an axon does not make the appropriate connections by a certain age, IT DIES' - which is why all neurons in a healthy adult brain have appropriate connections.

PAST EXAM: Interneurons vs. projection neurons

Interneurons develop BEFORE projection neurons and make connections LOCALLY.

PAST EXAM: Do we have more neurons as adults than at birth?

NO - FALSE. The brain OVERPRODUCES neurons and then eliminates them through apoptosis, so an adult has FEWER, not twice as many.

PAST EXAM: Which neural tube sections subdivide?

The PROSENCEPHALON (into telencephalon + diencephalon) and the RHOMBENCEPHALON (into metencephalon + myelencephalon). The MESENCEPHALON does NOT subdivide. Related: which structure has RADIAL GLIA lining the interior? The NEURAL TUBE.