NSCI Exam 2

What structures make up the PNS

Cranial nerves, somatic nervous system, spinal nerves (dorsal and ventral roots), and the autonomic nervous system

What structures make up the CNS

Cerebral lobes, cerebrum, cerebellum, brainstem, spinal cord, thalamus, ventricles, and the glymphatic system

Afferent

Carries information toward the CNS

Incoming sensory info via dorsal root

Efferent

Caries information away from CNS

Exiting motor info into muscles via the ventral root

Function of Cranial Nerve I (Olfactory)

Smell

Function of Cranial Nerve II (Optic)

Vision

Function of Cranial Nerve X (Vagus)

Information from internal organs (viscera)

Function of Cranial Nerve IX (Glossopharyngeal)

Taste and other mouth sensations

Function of Cranial Nerve VIII (Vestibulocochlear)

Inner ear functions: hearing and balance

Superior/Dorsal

Refers to the top

Function of Cranial Nerve VII (Facial)

Taste on the tongue and soft palate sensations

Function of Cranial Nerve V (Trigeminal)

Sensations from face, sinuses, and teeth

Somatic nervous system

Consious and subconscious control over skeletal muscles, skin, and joints

Cell bodies in the CNS, axons in the PNS

Autonomic nervous system (visceral PNS)

Involuntary/vegetative control of viscera (internal organs, smooth muscle, blood vessels, glands, blood pressure, and oxygen levels)

Dorsal root

Sensory, afferent information coming from body into the spinal cord

Cell bodies reside in the dorsal root ganglia outside the cord

Ventral root

Motor, efferent information going from the spinal cord to muscles, releasing ACh to trigger voluntary movement

Sympathetic nervous system

Fight or flight response

Release norepinephrine, releases airways for more O2, accelerates heart rate, stimulates glucose release, inhibits digestion, and triggers norepinephrine from adrenal glands

Parasympathetic nervous system

Rest and digest

Uses ACh exclusively, slows heart rate, stimulates digestion, contracts airways, and stimulates salivation

Frontal lobe

Primary motor cortex, language, executive function, attention, memory, and impulsivity

Temporal

Primary auditory cortex, learning and memory

Parietal

Primary somasensory cortex and visual processing

Occipital

Primary visual cortex and visual processing

Insular

Gustatory cortex (sense of taste)

Cerebellum

Dense motor center for coordination and movement

Brainstem

Divided into midbrain, pons, and medulla

Midbrain

Conduit for information passing from the spinal cord to forebrain and vice versa

Tectum/colliculi for vision/hearing, tegmentum/substarate nigra)

Pons

Switchboard connecting cortex to cerebellum

Medulla

Sensory/motor functions, touch, taste, tongue

Thalamus

Acts as the primary relay and processing center for brain

Ventricles

Fluid-filled cavities containing cerebral spinal fluid (CSF)

Cerebral spinal fluid (CSF)

Provides chemical balance, shock absorption, and nutrients

Flows from lateral ventricles to 3rd ventricles to cerebral aqueduct to 4th ventricle to subarachnoid space

Gymphatic system

A waste clearance network using CSF during sleep to flush out harmful metabolic byproducts and proteins

Flow is unidirectional from arteries (clean CSF during sleep) to veins (dirty CSF)

Astrocytes facilitate this using aquaporin water channels

Midsaggital

Cut along rostral-caudal axis dividing left and right hemispheres

Horizontal

Divides top and bottom of brain

Coronal

Separates the front (anterior) from the back/brainstem (posterior)

Inferior/Ventral

Refers to the bottom

Medial

From the middle

Lateral

From the side

How do humans and rodent brains differ structurally in scaling?

Rodent scale neuron size rapidly as the brain grows, whereas humans have an evolutionary advantage of packing an exceptionally high amount of neurons into the cerebral cortex without excessive neuron enlargement

CT (Computed Tomography)

Measures X-ray absorption to map tissue density (gray vs. white matter, ventricles)

Inexpensive and fast

Valuable for detecting skull fractures, brain swelling, tumors

Lower resolution than MRI

Uses radiation

MRI

Uses strong magnetic fields and hydrogen protein alignment to create highly detailed structural maps of soft tissue without X-radiation

fMRI

Detects changes in brain metabolism and blood oxygenation (BOLD signal) in active brain areas

Non-invasive

High spatial resolution

PET scan

Uses injected radioactive chemicals to track metabolic activity or receptor density

Ex: comparing dopamine D2 receptors in addiction

DTI (Diffusion Tensor Imaging)

An MRI technique measuring the diffusion of water molecules to map white matter tracts

Ex: detecting microstructural differences in autism or white matter injury

Concussion (mild TBI)

A transient disturbance of brain function caused by biomechanical accelerateion/deceleration forces

Typically showing no gross structure damage on standard CT/MRI

Three layers of the Meninges from outermost to innermost

Dura mater (tough outer bag)

Arachnoid membrane (middle, separated by subarachnoid CSF space)

Pia mater (thin inner membrane adhering to the brain)

How does a subdural hematoma form

Ruptured blood vessels passing through the dura mater cause blood to pool in subdural space, compressing the CNS and disrupting brain function

Sweet

Sugars (fructose, sucrose) and artificial sweeteners

Bitter

Ions (K+, Mg2+), quinine, caffeine (evolutionary toxin warning)

Sour

Acids/hydrogen ions (H+/lower pH)

Salty

Sodium ions (Na+)

Umami

Amino acids (savory)

Three types of papillae containing taste buds

Foliate (sides)

Vallate (middle back)

Fugiform (all over tongue)

What is the structure of a taste bud

A cluster of 50-150 taste receptor cells with microvilli extending into a taste pore to interact with dissolved chemicals

Taste cells have a short lifespan (~2 weeks) and constantly regenerate

Salty transduction

Na+ ions flow down their concentration gradient directly through amiloride-sensitive sodium channels into the taste cell, causing depolarization

Sour transduction

H+ ions enter through protein channels, block special potassium (K+) channels, cause depolarization, and trigger serotonin release

What receptor family do Sweet, Bitter, and Umami tastes share?

G-protein coupled receptors (GPCRs) from the T1R and TR2 families

Sweet taste receptors

T1R2+T1R3

Umami taste receptors

T1R1+T1R3

Bitter taste receptor

TR2

Gustatory pathway from tongue to cortex

Taste receptor cell to gustatory afferent axon to gustatory nucleus (brainstem) to VPM nucleus of thalamus to primary gustatory cortex (insular cortex)

Population coding in taste perception

While individual taste cells/axons are broadly tuned or have biases, the brain distinguishes complex flavors through the combined response pattern of many broadly tuned neurons

What did Bulbotomoy (disconnecting olfactory bulbs) prove about taste and smell?

Eliminating olfactory inputs severely reduced concentration-dependent liking for sweet/fatty foods, but did not alter instinctive avoidance of bitter toxins, showing olfaction drives ingestive motivation rather than basic taste regulation

Cribiform plate in olfaction

A thin sheet of bone through which olfactory receptor cell axons pass to reach the olfactory bulb

Injury to this plate causes anosmia (loss of smell)

Olfactory trandusction

1. Odorants bind GPCR receptors to proteins on cilia

2. Activates Golf protein, which activates adenylyl cyclase, which increases cAMP

3. cAMP ions cyclic nucleotide-gated cation channels (Na+ and Ca2+ influx)

4. High internal Cl- causes CL- to flow out of the cell, causing massive depolarization and firing action potentials

How does COVID-19 cause anosmia?

SARS-CoV-2 infects and damages surrounding support cells (which express ACE2/TMPRSS2) in the olfactory epithelium, rather than infecting olfactory neurons directly

Glomerulus in the olfactory bulb

A spherical convergence point where ~25,000 primary olfactory axons expressing the exact same odorant receptor genes synapse onto second-order neurons, creating an orderly spatial map of odor information

Each receives input from only one kind of olfactory receptor cell

What is unique about the Olfactory pathway compared to all other senses

Olfactory information projects directly from the olfactory bulb to the cortex (temporal/oribitofrontal cortex) without stopping at the thalamus

Olfactory epithelium

Contains the olfactory nerve, cribriform plate, basal cells, olfactory receptor cells and their cilia, supporting cells, and odorants

Olfactory nerve

Consists of axons originating from olfactory receptor cells that carry afferent odor information

These combined axons constitute the olfactory nerve

Penetrate through the cribriform plate, heading toward the olfactory bone

Basal cells in olfactory epithelium

Act as the source for new receptor cells, serving as a rare example of neurogenesis in the body

Olfactory receptor cells

Responsible for odorant transduction

Cilia

Contain specific odorant receptors that bind to chemical odors

Supporting cells

Glia-like cells

Mucus layer

Mucopolysaccharides, antibodies, enzymes, odorant binding proteins designed to concentrate odors

Odarants

Activate the transduction processes in neurons

Why are humans weak smellers compared to other animals

Humans have a relatively small surface area of the olfactory epithelium

Olfactory pathway1

Olfactory receptor cell to olfactory bulb to olfactory cortex in the temporal lobe (no thalamus)

Olfactory pathway 2

Olfactory receptor cell to olfactory bulb to olfactory tubercle to thalamus to orbitofrontal cortex

Olfactory bulb

Action potentials from receptor cells enter, where they form synapses in the glomeruli (~200 glomeruli total, each containing ~25,000 primary axons)

Describe the “inside-out” cellular arranagement of the retina

Light must pass through transparent ganglion and bipolar cell layers before reaching photoreceptors at the very back of the retina

What is the path of light and information flow through the Retina

Light passes through transparent ganglion and bipolar cells to reach photoreceptors at the back

Temporal coding

Depends on the timing of spikes, which might encode the quality of odors

Evident in spatial odor maps because they sometimes change shape during the presentation of a single odor

What do receptor cells express regarding olfactory proteins

A single olfactory receptor protein is expressed (a color code)

This raises the question: How do we smell a single small if receptor cells are so broadly tuned in population coding?

What three factors answer how the brain processes smells given broadly tuned receptor cells

1. Each odor is represented by the activity of a large population of neurons

2. The neurons responsive to particular odors may be organized into spatial maps

3. The timing of action potentials may be an essential code for particular odors

What kind of spatial patterns do specific odors generate

They generate complex but reproducible spatial patterns

However, it remains unknown whether these neural maps are actually used by the brain to distinguish among chemicals

What are the only light-senstive cells in the retina

Rod and cone receptors

Which retinal cells serve as the sole output source of the retina

Ganglion cells

Which retinal neurons fire action potentials

With the exception of amacrine cells, ganglion cells are the only retinal neurons that do

All other cells depolarize with a rate of neurotransmitter release proportional to their membrane potential

What is the direct path that visual information takes through the retina

Photoreceptors to bipolar cells to ganglion cells

Horizontal cells

Receive input from photoreceptors and project to other photoreceptors and bipolar cells

Amacrine cells

Recieve input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells

What are the four main structural regions shared by rods and cones

Outer segment, inner segment, cell body, and synaptic terminal

They use photopigments in their disk membranes to convert electromagnetic radiation into neural cells

Rods

Detect light using the photopigment rhodopsin

Highly sensitive even in low light; does most of the work at night

~100 million located outside of the fovea (in the periphery)

Larger receptive field size and lower visual acuity, but slower response time

Cones

Detect light using three different opsins (detecting short, medium, or long wavelengths), enabling color vision

Low sensitivity (requires strong stimulation), do most of the work in the daytime

~4 million total; heavily concentrated in and near fovea

Small receptive field size and high visual acuity in the fovea (larger outside it) and a relatively rapid response time

Duplex retina

A retina that combines two complimentary systems in one eye: the scotopic (dark/rods) and the photopic (light/cones) system (with mesospic handling intermediate light levels)

Why is visual acuity greatest at the fovea

Only cones are present, and other cellular layers/blood vessels are pushed out of the way, allowing direct light input that does not pass through other cells

Central vision has greater detail in photopic conditions, but our central vision is blind in scotopic conditions due to the lack of rods

Is light hyperpolarizing or depolarizing to photoreceptors

Hyperpolarizing

Steps of phototransduction in rods and cones

1. Light bleaches rhodopsin, changing retinal from inactive to active conformation

2. G protein becomes active, which activates phosphodiesterase (PDE)

3. PDE reduces cGMP levels

4. Reduced cGMP levels cause cGMP-gated Na+ channels to close

5. Less Na+ influx leads to hyperpolarization (creating a receptor potential, not an action potential)

Cones require higher-energy opsins

Receptive field

The area of the retina or visual space where applying a stimulus (like light) changes the neuron’s firing rate