The Eukaryotic Cell; The Nervous System

Question 1

Nucleus

Answer 1

Eukaryotes have ‘em, prokaryotes don’t. The nucleus contains all of the DNA in an animal cell (except for a tiny amount that’s in the mitochondria). The aqueous ‘soup’ in the nucleus is the nucleoplasm.

Question 2

Nuclear envelope

Answer 2

AKA nuclear membrane; the double phospholipid bilayer that surrounds the nucleus.

Question 3

Nuclear pores

Answer 3

The nuclear envelope is perforated with large holes called nuclear pores. RNA can exit the nucleus through the nuclear pores– DNA can’t. (That’s why transcription MUST take place in the nucleus.)

Question 4

Nucleolus

Answer 4

A structure inside the nucleus where rRNA is transcribed and the subunits of the ribosomes are assembled. The nucleolus is NOT separated from the nucleus by a membrane.

Question 5

Endocytosis

Answer 5

The other way– besides transport across the membrane– that cells can acquire substances from the extracellular environment. Several types: phagocytosis (“to eat”), pinocytosis (“to drink”), and receptor mediated endocytosis.

Question 6

Phagocytosis

Answer 6

1/3 types of endocytosis. The cell membrane protrudes outward to envelope and engulf particulate matter. The impetus for this happening is the binding of proteins on the particulate matter to protein receptors on the phagocytotic cell. For instance, in humans these proteins can be antibodies or complements and the receiving cells can be macrophages or neutrophils.

Once the matter is engulfed, the membrane bound body is called a phagosome.

(Note that only a few specialized cells can perform phagocytosis.)

Question 7

Pinocytosis

Answer 7

1/3 types of endocytosis. Extracellular fluid engulfed by small invaginations of the cell membrane. Performed by most cells randomly, “nonselective”.

Question 8

Receptor mediated endocytosis

Answer 8

1/3 types of endocytosis. Specific uptake of macromolecules like hormones and nutrients. This happens when the ligand binds to a receptor protein on the cell membrane, then is moved to a pit coated with clathrin, a protein that forms a polymer by adding structure to its underside, ultimately invaginating to form a vesicle.

This is different from phagocytosis because receptor mediated endocytosis ABSORBS the ligands, whereas the ligands in phagocytosis are just SIGNALS which initiate phagocytosis of other particles.

Question 9

Exocytosis

Answer 9

The reverse of endocytosis = expulsion of matter. A secretory vesicle brings the particulate matter to the plasma membrane, where it is secreted.

Question 10

Endoplasmic reticulum

Answer 10

In eukaryotic cells. A thick maze of membranous walls which separates the cytosol from the ER lumen/cisternal space. In many places, the ER is continuous with the cell membrane and the nuclear membrane.

The endoplasmic reticulum has two appearances: smooth and rough, which serve different functions.

Question 11

Cytosol

Answer 11

The aqueous solution inside the cell.

Question 12

ER lumen

Answer 12

AKA cisternal space, the “extracellular fluid” side of the ER. Continuous in places with the space between the double bilayer of the nuclear envelope.

Question 13

Rough ER

Answer 13

AKA granular ER. ER near the nucleus has many ribosomes attached to it on the cytosolic side, giving it a granular appearance. TRANSLATION OF ALL PROTEINS NOT USED IN THE CYTOSOL HAPPENS HERE.

Translation on the rough ER propels proteins into the ER lumen as they are created. These proteins are tagged with a signal sequence of amino acids and sometimes have carbohydrate chains added (are “glycosylated”). These newly synthesized proteins are then pushed into the ER lumen toward the Golgi.

Question 14

Golgi apparatus

Answer 14

AKA Golgi complex. The “protein post office”! The Golgi apparatus is a series of flattened, membrane-bound sacs. Small transport vesicles bud off from the ER and carry the proteins across the cytosol to the Golgi.

The Golgi organizes and concentrates the proteins as they are shuttled by transport vesicles progressively outward from one compartment of the Golgi to the next.

The Golgi distinguishes proteins by their signal sequence and carbohydrate chains (which were added in the rough ER, remember?). The Golgi may also glycosylate or remove amino acids from proteins, or form polysaccharides.

If proteins DON’T have a signal sequence, they are packaged into secretory vesicles and expelled from the cell. This is called BULK FLOW.

The end product of the Golgi is a vesicle full of proteins. These proteins may:

1. Be expelled as secretory vesicles
2. Be released to mature into lysosomes
3. Be transported to other parts of the cell

Question 15

Secretory vesicles

Answer 15

AKA zymogen granules. May contain enzymes, growth factors, or extracellular matrix components. Some proteins are also activated here (such as proinsulin, which only becomes insulin after the secretory vesicle buds off the Golgi).

Secretory vesicles release their contents through exocytosis. They also act as the vehicle to supply the cell membrane with its integral proteins and lipids, and as the mechanism for membrane expansion.

Secretory vesicles are constantly released by most cells. Some specialized cells can release them in response to some stimulus.

Question 16

Lysosomes

Answer 16

The “garbage can”!

LYSOSOMES BUD OFF MEMBRANES FROM THE GOLGI.

Lysosomes contain hydrolytic enzymes that function best in acid environments (acid hydrolases such as proteases, lipases, nucleases, and glycosidases), which works because lysosomes have an pH of 5.

1. These enzymes can break down every major macromolecules in the cell. Lysosomes fuse with endocytotic vesicles and digest their contents. Anything not degraded by the lysosomes is ejected by exocytosis.
2. Lysosomes also degrade cytosolic proteins in an endocytotic process.
3. Lysosomes can also rupture and release their contents into the cytosol, killing the cell. This is called autolysis, and is useful in the formation of certain organs and tissues (like destroying the tissue between the digits of a human fetus to form fingers).

Question 17

Smooth ER

Answer 17

AKA agranular ER, because has no ribosomes. Appears tubular. Basically, the site of lipid synthesis including steroids. Also helps to detoxify some drugs.

More specifically, the smooth ER plays several important roles:

1. Contains the enzyme used in the liver, intestinal epithelial cells, and renal tubule epithelial cells. Uses it to hydrolyze glucose 6-phosphate to glucose (an important step in the production of glucose from glycogen).
2. Produces triglycerides and stores them in fat droplets called adipocytes. These are important for energy storage and body temperature regulation.
3. Shares with cytosol the job of cholesterol formation and conversion to steroids.
4. Synthesizes the phospholipids in the cell membrane on the cytosol side, and then flips some to the other side using proteins called “phospholipid translocators”.
5. Oxidizes foreign substances, detoxifying drugs, pesticides, toxins, and pollutants.

Question 18

Peroxisomes

Answer 18

Vesicles in the cytosol which grow by incorporating lipids and proteins from it. PEROXISOMES SELF-REPLICATE (they do not bud off like lysosomes from the Golgi).

Inactivate toxic substances such as alcohol.
Regulate oxygen concentration.
Help synthesize and break down lipids.
Help metabolize nitrogenous bases and carbohydrates.

Question 19

Organelles

Answer 19

Internal compartments in the cell which are separated from the cytosol by membranes.

Question 20

Cytoskeleton

Answer 20

A network of filaments that determines the structure and motility of a cell.

Anchors some membrane proteins and other cellular components, moves components within the cell, and moves the cell itself.

Major types of filaments within the cytoskeleton are microtubules, microfilaments, and intermediate filaments.

Question 21

Microtubules

Answer 21

A type of filament making up the cytoskeleton. Larger than microfilaments.

Rigid, hollow tubes made from tubulin protein, appear as a spiral because of the two types of tubulin (alpha and beta) used in the synthesis. 13 of these filaments lie alongside each other to form the tubes.

Have a (+) and a (-) end. The minus end attaches to a microtubule organizing center (MTOC) in the cell. A microtubule grows away from an MTOC at its (+) end.

Note that the mitotic spindle is made from microtubules. They are also involved in flagella and cilia construction.

Question 22

Microfilaments

Answer 22

A type of filament in the cytoskeleton. Smaller than microtubules.

Made of actin protein.

Squeeze the membrane together in phagocytosis and cytokinesis. Also the contractile force in microvilli and muscle. They are responsible for cytoplasmic streaming (amoeba-like movement).

Question 23

Flagella and cilia

Answer 23

Specialized structures made from microtubules. Contain an axoneme and dynein cross bridges.

Cilia- found only in the fallopian tubes and respiratory tract- have a whip motion, cause fluid to move laterally.

Flagella have a wiggle motion, cause fluid to move away from the cell.

IMPORTANT NOTE. PROKARYOTIC AND EUKARYOTIC FLAGELLA ARE DIFFERENT! Eukaryotic flagella are made from a 9+2 microtubule configuration and undergo a WHIPLIKE motion. Prokaryotic flagella are thin strands of a single protein called flagellin and ROTATE.

Question 24

Axomene

Answer 24

The major portion of each flagellum and cilium.

Contains 9 pairs of microtubules forming a circle around 2 lone microtubules (this arrangement is called 9+2).

Question 25

Dynein

Answer 25

A protein which makes up the cross bridges in flagellum and cilium.

The cross bridges connect each of the outer pairs of microtubules to their neighbor, and also give flagella and cilia their distinctive movements.

Question 26

Centrosome

Answer 26

The major MTOC (microtubule organizing center) in animal cells. Anchors chromosomes to each other in mitosis.

Question 27

Centrioles

Answer 27

Help produce flagella and cilia.

Question 28

Intermediate filaments

Answer 28

Not as dynamic as microtubules or microfilaments. Primary serve to give the cell structural rigidity. One example of keratin, which is found in the epithelial cells and is associated with hair and skin.

Question 29

Tight junctions

Answer 29

1/3 attachments connecting animal cells.

Form a watertight seal from cell to cell that can block water, ions, and other molecules from moving around and past cells. May act as a complete fluid barrier. Also act as a barrier to protein movement around the cell.

Found in the bladder, intestines, kidney, etc., in order to prevent waste materials from seeping around the cells and into the body.

Think of tight junctions as the plastic seal connecting a six-pack of cans (with one caveat: cells may be permeable or impermeable– cans are not.)

Question 30

Desmosomes

Answer 30

1/3 attachments connecting animal cells.

Join two cells at a single point. Attach directly to the cytoskeleton of each cell. (Think of them like spot welds holding cells together.)

Found in tissues that experience a lot of stress, like skin or intestinal epithelium.

Often accompany tight junctions, though they do not prevent fluid from circulating around all sides of a cell.

Question 31

Gap junctions

Answer 31

1/3 attachments connecting animal cells.

Small tunnels connecting cells. Allow small molecules and ions to move between cell.

Found, for instance, in cardiac muscle, where they provide for the spread of the action potential from cell to cell.

Question 32

Mitochondria

Answer 32

Powerhouses of the eukaryotic cell. Krebs cycle takes place here. Formed via endosymbiont theory.

Have their own circular DNA that replicates independently from the eukaryotic cell. This DNA contains no histones or nucleosomes. Most animals have a few dozen to several hundred molecules of circular DNA in each mitochondrion. Mitochondrial DNA is passed maternally, even in organisms whose male gamete contributes to the cytoplasm.

This DNA codes for its own RNA, distinct from the RNA in the rest of cell. Therefore, mitochondria also have their own ribosomes.

Also- interestingly- mitochondria present an exception to the universal genetic code, because some of the codons in mitochondria differ from the codons in the rest of the cell.

Mitochondria are surrounded by 2 phospholipid bilayers (an inner and outer membrane, with an intermembrane space between them). The inner membrane invaginates to form cristae. It is the inner membrane that holds the electron transport chain.

Be able to relate mitochondria to respiration!

Question 33

Extracellular matrix

Answer 33

A molecular network that holds tissue cells in place. “The stuff surrounding the cell, formed by the cell itself.” Differs depending on the tissue.

May provide structural support, help to determine cell shape and motility, and affect cell growht.

Made up of three types of molecules in animal cells:

1. Glycosaminoglycans and proteoglycans, for pliability
2. Structural proteins, for strength (most common is collagen)
3. Adhesive proteins, to adhere together

Question 34

Organization in multicellular eukaryotes

Answer 34

Atom –> Molecule –> Organelle –> Cell –> Tissue –> Organ –> Organ system –> Organism

Question 35

3 intercellular “communicators”

Answer 35

1. Neurotransmitters, which are released by neurons and governed by the nervous system. Travel over very short intercellular gaps. Communication is rapid, direct, and specific.
2. Local mediators, which are governed by the paracrine system (neighbors). Function in the immediate area around the cell from which they were released.
3. Hormones, which are governed by the endocrine system. Travel through the organism via the bloodstream. Communication is slower, spread throughout the body, and affects many cells and tissues in different ways.

Question 36

Interstitial fluid

Answer 36

Fluid between the cells

Question 37

Neuron

Answer 37

Functional unit of the nervous system. A highly specialized cell which transmits an electrical signal from one cell to another, electrically or chemically.

So highly specialized that it does not divide.

Depends on glucose for chemical energy. Depends on facilitated transport to move glucose from blood into cytosol, but IS NOT DEPENDENT on insulin for this transport.

Depends heavily on efficiency of aerobic respiration. Also relies on blood to supply sufficient levels of glycogen and oxygen.

All neurons have a basic anatomy: many dendrites, a single cell body, and usually one axon with many small branches.

Note that neural cells can be unipolar (sensory only), bipolar (in the retina, inner ear, olfactory part of brain), or multipolar (much of the brain)

Question 38

Dendrites

Answer 38

Little fingers at end of cell body which receive signal to be transmitted. Typically, the cytosol of the cell body is conductive, so electrical stimulus creates a disturbance in the electric field that is transferred immediately to the axon hillock.

Question 39

Axon hillock

Answer 39

If a stimulus is great enough, the axon hillock GENERATES AN ACTION POTENTIAL l in all directions, including down the axon to the axon terminal, where it jumps across the synapse.

Question 40

Axon

Answer 40

Carries the action potential to a synapse, which passes the signal to another cell.

Question 41

Action potential

Answer 41

A disturbance in the electric field across the membrane of a neuron.

Occurs at a point on a membrane and propagates along that membrane by depolarizing the section of membrane immediately adjacent to it.

Steps (See fig 4.14):
1. Membrane is at rest. Voltage gated sodium and potassium channels are closed.

2. Voltage gated sodium channels open. Cell depolarizes (more positive inside).
3. Voltage gated potassium channels open as sodium channels begin to inactivate (close).
4. Voltage gated sodium channels are inactivated (closed). Potassium channels are open, this repolarizes the membrane (more negative inside).
5. Voltage gated potassium channel closes. Membrane equilibriates to its resting potential.

Note that the Na+/K+ pump works throughout the action potential.

Question 42

Resting potential

Answer 42

Established by an equilibrium of the Na+/K+ pump. After hyper and depolarization, the membrane is returned to resting potential via passive diffusion.

The Na+/K+ pump moves THREE positively charged SODIUM ions OUT of the cell, while bringing TWO positively charged POTASSIUM ions INto the cell.

This increases the positive charge along the membrane outside the cell (relative to the charge along the membrane inside the cell).

As the gradient of Na+ increases, the force pushing Na+ back into the cell also increases. This is also true of K+ (in the opposite direction, of course). These forces continue until the rate both sodium and potassium are being pumped out = the rate that they are being pumped in = until each (separately) reaches EQUILIBRIUM.

At equilibrium, the inside of the cell is more negative than that outside (remember, three sodiums out/2 potassiums in). THIS POTENTIAL DIFFERENCE IS CALLED THE RESTING POTENTIAL.

Question 43

Voltage gated sodium channel

Answer 43

The membrane of a neuron also contains these integral membrane proteins. They change configuration when the voltage across the membrane is disturbed.

Specifically, they allow Na+ to flow through the membrane for a fraction of a second as they change configuration– this makes the voltage change even further, causing more sodium channels to change configuration, causing more Na+ to flow into the cell (this type of domino effect is POSITIVE FEEDBACK).

As Na+ approaches equilibrium, because K+ is higher inside the cell, the membrane potential reverses polarity so it is positive on the inside and negative on the outside. This is called depolarization.

Question 44

Depolarization

Answer 44

As Na+ approaches equilibrium via the voltage gated sodium channel- because K+ concentration is higher inside the cell- the membrane potential reverses polarity so it is positive on the inside and negative on the outside. This is called depolarization.

Question 45

Voltage gated potassium channels

Answer 45

Also present in the neuronal membrane, but less sensitive than sodium to voltage change, so they take longer to open. By the time they do open, most of the sodium channels are closing. Now K+ flows out of the cell, making the inside more negative in a process called repolarization.

Question 46

Hyperpolarization

Answer 46

The potassium channels are also slow to close. So for a fraction of a second, the inside membrane becomes more negative than the resting potential. This is called hyperpolarization.

Question 47

All-or-nothing

Answer 47

An action potential is all or nothing, the membrane completely depolarizes, or no action potential is generated.

Question 48

Threshold stimulus

Answer 48

In order to create an action potential, the stimulus to the membrane must be greater than the threshold stimulus. Any stimulus greater than the TS creates the same size action potential. If the threshold stimulus is reached too slowly, an action potential may not occur.

Once an action potential has begun, there is a short period of time in which no stimulus will create another action potential.

There is also time during which an abnormally large stimulus will create an action potential.

Question 49

Synapse

Answer 49

Neural impulses are transmitted from one cell to another chemically or electrically via a synapse. Note that the transmission of the signal from one cell to another is the slowest part of this neural communication process, but it still occurs in a fraction of a second.

Most synapses connect dendrites, but some may contact other cell bodies, axons, or other synapses. The firing of one or more of these synapses creates a change in the neuron cell potential that’s either excitatory or inhibitory.

Question 50

Electrical synapses

Answer 50

Rare. Composed of gap junctions between cells. Don’t involve diffusion of chemicals, and thus transmit signals must faster than chemical synapses and in both directions.

Found in cardiac muscle, visceral smooth muscle, and very few neurons in the CNS.

Question 51

Chemical synapses

Answer 51

More common type of synapse. Called a motor end plate when connecting a neuron to a muscle. Unidirectional.

Small vesicles filled with neurotransmitter rest just inside the presynaptic membrane. The membrane near the synapse contains lots and lots of Ca2+ voltage gated channels. When the action potential arrives at a synapse, these channels are activated, allowing Ca2+ to slow into the cell.

The sudden influx of calcium ions causes some of the neurotransmitter vesicles to be released through an exocytotic process into the synaptic cleft.

The neurotransmitter diffuses across the synaptic cleft via Brownian motion.

The post synaptic membrane has neurotransmitter receptor proteins, where the neurotransmitter attaches for only a fraction of a second before being released into the synaptic cleft. Ions move across the postsynaptic membrane through proteins called ionophores, completing the transfer of the neural impulse.

If a cell is fired too often, it will not be able to replenish its supply of neurotransmitter vesicles, and the result is fatigue (the impulse will not be passed to the postsynaptic neuron).

Question 52

Brownian motion

Answer 52

The random motion of molecules The neurotransmitter diffuses across the synaptic cleft via Brownian motion.

Question 53

Neurotransmitter

Answer 53

Over 50 types have been identified; different types are found in different parts of the nervous system. A single synapse usually releases one type of neurotransmitter and is designed either to inhibit or excite, not both. Synapses cannot change back and forth between inhibitory and excitatory.

Some neurotransmitters, though, are capable of inhibition or excitation depending on the postsynaptic receptor. One example is acetylcholine, which has an inhibitory effect in the heart, but an excitatory effect on the smooth muscle of the intestine.

Question 54

Second messenger system

Answer 54

Receptors may be ion channels themselves, or may act via a second messenger system, activating another molecule inside the cell to make changes.

For prolonged changes, like memory, the second messenger system is preferred.

G-proteins commonly initiate second messenger systems. They attach to the receptor protein along the inside of the postsynaptic membrane. When the receptor is stimulated by a neurotransmitter, part of the G-protein, called the alpha-subunit, breaks away, and may:

1. Activate separate ion channels
2. Activate a second messenger like cAMP or cGMP
3. Activate intracellular enzymes
4. Activate gene transcription

Question 55

Myelin

Answer 55

Electrically insulating sheaths for axons that are produced by Schwann cells. Increases the rate at which an axon can transmit signals/increases the speed with which the action potential moves down the axon.

Transmit signals via saltatory conduction.

ONLY VERTEBRATES HAVE MYELINATED AXONS.

Question 56

Schwann cells

Answer 56

In the PNS, myelin is produced by Schwann cells

Question 57

Grey/white matter

Answer 57

To the naked eye, myelinated axons appear white, neuronal cell bodies appear grey.

Question 58

Nodes of Ranvier

Answer 58

Tiny gaps between myelin.

Question 59

Saltatory conduction

Answer 59

When an action potential is generated down a myelinated axon, the action potential jumps from one node of Ranvier to the next as quickly as the disturbance moves through the electric field between them.

Question 60

Sensory neurons

Answer 60

AKA afferent neurons. Receive signals from a receptor cell that interacts with its environment, then transfers this signal to other neurons. Located ventrally.

Note that 99% of sensory input is discarded by the brain.

Question 61

Interneurons

Answer 61

Transfer signals from neuron to neuron. 90% of neurons in human body are interneurons.

Question 62

Motor neurons

Answer 62

AKA efferent neurons. Carry signals to a muscle or gland called the effector. Located dorsally.

Question 63

Nerves

Answer 63

Neuron processes (axons and dendrites) are typically bundled together to form nerves (called tracts in the CNS).

Question 64

CNS

Answer 64

Central nervous system. Interneurons and support tissue, brain and spinal cord. Integrates nervous signals between sensory and motor neurons.

Question 65

PNS

Answer 65

Everything else (including cranial and spinal nerves). Handles sensory and motor function of the nervous system. Can be further divided into the somatic and autonomic nervous system.

Question 66

Somatic nervous system

Answer 66

Designed primarily to respond to the external environment. Contains sensory and motor functions. The cell bodies are located in the “ventral horns” of the spinal cord in the dorsal root ganglion: neurons synapse directly on their effectors and use ACH as their neurotransmitter.

Motor functions can be consciously controlled and are considered voluntary.

Question 67

Autonomic nervous system

Answer 67

The sensory portion receives signals primary from the viscera (organs inside ventral body cavity). Motor portion of ANS conducts these signals to smooth muscle, cardiac muscle, and glands.

Function is generally involuntary. Controlled mainly by the hypothalmus.

Motor portion of ANS is further divided into sympathetic and parasympathetic.

Question 68

Sympathetic ANS

Answer 68

“Fight or flight”.

Originate in neurons whose cell bodies are in spinal cord. These neurons extend out from the spinal cord to synapse with neurons whose cell bodies are located outside the CNS (pre and post ganglionic neurons).

In heart, for instance, increases beat rate and stroke value by constricting blood vessels.

Question 69

Parasympathetic ANS

Answer 69

“Rest and digest”.

Originate in neurons whose cell bodies can be found in both brain and spinal cord. Cell bodies lie in ganglia inside or near their effectors.

Slows heart rate and increases digestive and excretory activity.

Question 70

Acetylcholine

Answer 70

The neurotransmitter used by all preganglionic neurons in ANS and by postganglionic neurons in the parasympathetic system.

Receptors for acetylcholine

Question 71

Epinephrine/Norepinephrine

Answer 71

Also called adrenaline and noradrenaline, the neurotransmitter used by the postganglionic neurons of the sympathetic nervous system.

Question 72

Lower brain

Answer 72

Medulla, hypothalmus, thalamus, cerebellum, etc. Integrates subconscious activities such as respiratory system, arterial pressure, salivation, emotions, and reactions to pain and pleasure.

Question 73

Higher/cortical brain

Answer 73

Cerebrum/cerebral cortex/forebrain. Stores memories and processes thoughts, processes consciousness. Cannot function without the lower brain.

Question 74

Sensory receptors

Answer 74

Mechanoreceptors, thermoreceptors, nociceptors, electromagnetic receptors, chemoreceptors.

Transduce physical stimuli to neural signals.

Question 75

Cornea

Answer 75

Light reflects off an object in the external environment and first strikes the eye on the cornea (first strikes a very thin, protective layer called the corneal epithelium).

Nonvascular, made of collagen.

Clear with a refractive index of 1.4, which means most bending of light actually occurs at interface of air and cornea, and not at lens.

Question 76

Lens

Answer 76

From the anterior cavity, light enters the lens. Would be spherical, but stiff ligaments tug on and flatten it. These ligaments are connected to the ciliary muscle, which circles the lens.

When the ciliary muscle contracts, the opening of the circle decreases, allowing the lens to become more spherical and bringing focal point closer to the lens; when the muscle relaxes, the lens flattens, increasing the focal distance.

The elasticity of the lens declines with age, making it difficult to focus on nearby objects as one gets older.

Question 77

Retina

Answer 77

Covers the back (distal portion) of eye. Contains light sensitive rods and cons.

Question 78

Rods and cones

Answer 78

Rods: light, cones: color. Tips of these cells contain pigments that go through a chemical change when one of their electrons is struck by a photon.

The pigment in rod cells is called rhodopsin; protein bound to a prosthetic group called retinal which is derived from vitamin A. The photon isomerizes retinal, causing the membrane of the rod cell to become less permeable to sodium ions and hyperpolarize. The hyperpolarization is transducted into an action potential and signal is sent to the brain.

Rods sense all photons with wavelengths in the visible spectrum.

There are 3 types of cones, each has a different pigment that is stimulated by a slightly different spectrum of wavelengths.

*Note that vitamin A is a precursor to all the pigments in rods and cones

Question 79

Iris

Answer 79

Colored portion of the eye that creates the opening called the pupil. Made from circular and radial muscles. In the dark, the sympathetic nervous system contracts the iris, dilating the pupil and allowing more light to enter the eye. In the light, the parasympathetic nervous system contracts the circular muscles of the iris, constricting the pupils and screening out light.

Rod cells are depolarized, with Na+ channels open and inactive rhodopsin, in the DARK.

Rod cells are hyperpolarized, with Na+ channels closed and active rhodopsin, in the LIGHT.

Question 80

Parts of the ear

Answer 80

Outer ear, middle ear, inner ear

Question 81

Tympanic membrane

Answer 81

Eardrum. The external auditory canal carries the wave to the TM, which begins the middle ear.

Question 82

Middle ear

Answer 82

COntains three small bones: malleus, incus, stapes. Act as a level system, translating the wave to the oval window. Change the combination of force and displacement from the inforce to the outforce (increases force). Wave gets transferred from air in outer ear to resistant fluid in inner ear.

Question 83

Cochlea/hair cells/organ of Corti

Answer 83

Wave in inner ear moves through the cochlea to the center of the spiral, then spirals back out to the round window. As the wave moves through the cochlea, the alternating increase and decrease in pressure moves the vestibular membrane in and out. This movement is detected by the hair cells of the organ of Corti and transduced into neural signals which are sent to the brain.

Note that hair cells do not contain hair, but a specialized microvilli called stereocilia, which detect movement.

Question 84

Primary taste sensations

Answer 84

Bitter, sour, salty, sweet. All taste sensations are combinations of these four.