Mcat Biology 3

Front 1

What 3 types of molecules allow for communication between cells?

Back 1

(1) neurotransmitters (nervous system)
- rapid, direct, specific
(2) local mediators (paracrine system)
(3) hormones (endocrine system)
- slower, spread throughout body, affect different cells & tissues in different ways

Front 2

paracrine system

Back 2

releases local mediators into interstitial fluid & acts on neighboring cells; includes proteins, amino acid derivations, or fatty acid derivatives (e.g. prostaglandins)

Front 3

prostaglandins

Back 3

- fatty acide derivative local mediators
- affect smooth muscle contraction, platelet aggregation, inflammation & other reactions
- synthesis inhibited by aspirin

Front 4

nervous system

Back 4

- allows for rapid & direct communication b/t specific body parts
- changes in muscular contractions or glandular secretions
- brain, spinal cord, nerves, neural support cells, sense organs (eye, ear)

Front 5

neuron

Back 5

- specialized cell that can transmit electrical signal from one cell to another via electrical or chemical means
- cannot divide
- depends almost entirely on glucose for chemical energy
- not dependent on insulin to transport glucose into cytosol
- consists of dendrites, cell body, axon + branches

Front 6

dendrites

Back 6

receive signal to be transmitted in a neuron

Front 7

axon hillock

Back 7

electrical signal transferred here from cytosol (which is highly conductive); generates action potential in all directions, including down axon

Front 8

axon

Back 8

carries action potential to synapse

Front 9

unipolar neuron

Back 9

sensory only

Front 10

bipolar neuron

Back 10

retina, inner ear, olfactory area of brain

Front 11

multipolar neuron

Back 11

most neurons of the brain

Front 12

action potential

Back 12

disturbance in electric field across membrane of neuron

Front 13

resting potential

Back 13

- equilibrium b/t passive diffusion of ions across membran & Na+/K+ pump
- pump moves 3 Na+ out and 2 K+ in, increasing positive charge along membrane outside cell
- electrochemical gradient of Na+ increases, so force pushing it back into cell increases until rate in = rate out (same for K+)
- at equilibrium, inside of membrane has negative potential difference (voltage) compared to outside

Front 14

voltage-gated sodium channels

Back 14

- integral membrane proteins in neurons that change configuration when membrane voltage is disturbed to allow Na+ to flow through membrane into cell
- positive feedback mechanism as more and more Na+ flows into cell, changing voltage & causing more channels to open

Front 15

depolarization

Back 15

Na+ concentration moves toward equilibrium & K+ concentration remains higher in cell, so membrane reverses polarity to be positive on the inside & negative on the outside

Front 16

voltage-gated potassium channels

Back 16

less sensitive to voltage changes than sodium channels, so don't start to open until sodium channels are closing; allow K+ to flow out of the cell

Front 17

repolarization

Back 17

when K+ flows out of cell through voltage-gated potassium channels, causing the inside of the cell to become more negative again

Front 18

hyperpolarization

Back 18

voltage-gated potassium channels are slow to close, so for a fraction of a second during repolarization, the inside membrane becomes even more negative than the resting potential

Front 19

steps of an action potential

Back 19

1. Membrane is at rest ~ -70mV. Na+ and K+ channels are closed.
2. Na+ channels open and cell depolarizes.
3. K+ channels open as Na+ channels start to inactivate.
4. Na+ channels inactivated & open K+ channels repolarize membrane.
5. K+ channels close & membrane equilibriates to resting potential.

Front 20

accommodation

Back 20

threshold stimulus is reached, but very slowly & an action potential does not occurr

Front 21

absolute refractory period

Back 21

short period of time in which no stimulus will create another action potential

Front 22

relative refractory period

Back 22

time during which only an abnormally large stimulus will create an action potential

Front 23

What is the slowest part of nervous system cellular communication?

Back 23

transmission of signal from one cell to another through a synapse

Front 24

electrical synapses

Back 24

composed of gap junctions b/t cells in cardiac muscle, visceral smooth muscle & a few neurons in CNS; transmit signals much faster than chemical synapses & in both directions; uncommon

Front 25

chemical synapse

Back 25

- more common than electrical synapses
- unidirectional
- vesicles w/ NT lie inside presynaptic membrane
- Ca(2+) voltage-gated channels in membrane are activated by AP arriving at synapse & open, letting Ca(2+) flow into cell, causing NT vesicles to be released into synaptic cleft through exocytosis
- NT diffuse across cleft via Brownian motion
- NT receptor proteins on postsynaptic membrane causes it to become more permeable to ions, which move across it through ionophores (proteins) & complete transfer of neural impulse
- method prevents attenuation of electrical resistance from one cell to the next
- slowest step in the transfer of a nervous signal

Front 26

neural fatigue

Back 26

can occur if a cell is fired too often and cannot replenish its NT vesicle supply

Front 27

How does a cell deal with a neurotransmitter released back into the synaptic cleft?

Back 27

- destroy NT with enzyme in matrix of synaptic cleft & recycle parts in presynaptic cell
- presynaptic cell directly absorbs NT through active transport
- NT may diffuse out of synaptic cleft

Front 28

Can a single synapse be both inhibitory & excitatory?

Back 28

No.

Front 29

Can a single neurotransmitter be both inhibitory & excitatory?

Back 29

Yes. (e.g. acetylcholine - inhibitory on heart, excitatory on visceral smooth muscle of intestine)

Front 30

In what 2 ways might receptors act?

Back 30

(1) ion channel itself (opened when respective NT attaches)
(2) act via second messenger system (preferred for prolonged changes, such as those involved in memory)

Front 31

second messenger system

Back 31

- activates another molecule in the cell to make changes
- often initiated by G-proteins attached to receptor protein along inside of postsynaptic membrane
- when activated by NT, alpha-subunit breaks free & can:
(1) activate separate specific ion channels
(2) activate a second messenger (e.g. cyclic AMP/GMP)
(3) activate intracellular enzymes
(4) activate gene transcription

Front 32

postsynaptic potentials

Back 32

- firing of one or more synapses creates a change in neuron cell potential
- can be excitatory (EPSP) or inhibitory (IPSP)
- usually requires 40-80 synapses firing on same neuron for an EPSP to create an action potential

Front 33

glial cells (neuroglia)

Back 33

- outnumber neurons 10:1
- can divide (fill space during TBI)
- 6 types: microglia, ependymal cells, satellite cells, astrocytes, oligodendrocytes & neurolemmocytes (Schwann cells)

Front 34

microglia

Back 34

type of neuroglia; arise from monocytes & phagocytize microbes & cellular debris in CNS

Front 35

ependymal cells

Back 35

type of neuroglia; epithelial cells that line space containing CS fluid

Front 36

ependymal cells

Back 36

type of neuroglia; use cilia to circulate CS fluid

Front 37

satellite cells

Back 37

type of neuroglia; support ganglia (groups of cell bodies in PNS)

Front 38

astrocytes

Back 38

type of neuroglia; star-shaped neuroglia in CNS that physically support neurons & help maintain mineral/nutrient balance in interstitial space

Front 39

oligodendrocytes

Back 39

type of neuroglia; wrap around axons in CNS to create electrically insulating sheathes of myelin

Front 40

Schwann cells

Back 40

type of neuroglia; produce myelin in PNS

Front 41

myelinated neurons

Back 41

- faster rate of conduction d/t myelin
- appear white (neuronal cell bodies appear gray)
- tiny gaps b/t myelin called "nodes of Ranvier"
- AP "jumps" from node to node in "saltatory conduction"

Front 42

sensory (afferent) neurons

Back 42

receive signals from receptor cell that interacts w/ environment & transfers signal to other neurons (99% of sensory info is discarded by the brain); located dorsally from spinal cord

Front 43

interneurons

Back 43

transfer signals from neuron to neuron (account for 90% of human neurons)

Front 44

motor (efferent) neurons

Back 44

carry signals to muscles or gland called "effector"; located ventrally from spinal cord

Front 45

dorsal

Back 45

toward the back

Front 46

ventral

Back 46

toward the front/abdomen

Front 47

nerves

Back 47

bundles of neuron processes (axons & dendrites) [called "tracts" in CNS)

Front 48

simple reflex arc

Back 48

receptor --> dorsal root ganglion --> sensory neuron --> interneuron --> motor neuron --> effector

Front 49

central nervous system (CNS)

Back 49

- interneurons & support tissue w/in brain & spinal cord
- integrates nervous signals b/t sensory & motor neurons

Front 50

peripheral nervous system (PNS)

Back 50

- connects CNS to peripheral parts of the body
- cranial & spinal nerves project to brain & SC
- sensory & motor functions
- divided into somatic & autonomic nervous systems

Front 51

somatic nervous system

Back 51

- responds to external environment
- sensory & motor functions
- motor neurons only innervate skeletal muscle, cell bodies located in ventral horns of spinal cord, synapse directly on effectors & use acetylcholine as NT [conscious, voluntary control]
- sensory neuron cell bodies located in dorsal root ganglion

Front 52

autonomic nervous system (ANS)

Back 52

- sensory portion receives signals from viscera (organs in central body cavity)
- motor portion conduct visceral signals to smooth muscle, cardiac muscle & glands
- generally involuntary function
- divided into sympathetic & parasympathetic systems (most internal organs have both acting antagonistically)
- pathways mainly controlled by hypothalamus

Front 53

sympathetic ANS

Back 53

"fight or flight"
- increase heart rate & stroke volume
- constricts blood vessels around digestive & excretory systems to increase blood flow around skeletal muscles
- signals originate in neurons w/ cell bodies in SC

Front 54

parasympathetic ANS

Back 54

"rest & digest"
- slows heart rate
- increases digestive & excretory activity
- signals originate in neurons w/ cell bodies in both brain & SC

Front 55

nucleus

Back 55

a group of cell bodies located in the CNS

Front 56

ganglion

Back 56

a group of cell bodies located outside the CNS

Front 57

preganglionic neurons

Back 57

neurons with cell bodies in CNS

Front 58

postganglionic neurons

Back 58

- neurons with cell bodies outside the CNS
- cell bodies of sympathetic are far from effectors in paravertebral ganglion (parallel to SC) or in prevertebral ganglia (in abdomen)
- cell bodies of parasympathetic lie in ganglia inside/near effectors

Front 59

Where is acetylcholine used?

Back 59

- all preganglionic neurons in the ANS
- postganglionic neurons in the parasympathetic ANS
[somatic & parasympathetic nervous systems]

Front 60

Where are epinephrin & norepinephrine used?

Back 60

postganglionic neurons of the sympathetic NS

Front 61

cholinergic receptors

Back 61

- receptors for acetylcholine
- nicotinic (postsynaptic cells of synapse b/t ANS preganglionic & postganglionic neurons; on skeletal muscle membranes at neuromuscular junctions)
- muscarinic (effectors of parasympathetic NS)

Front 62

adrenergic receptors

Back 62

receptors for epinephrine & norepinephrine

Front 63

integrating functions of the spinal cord

Back 63

- walking reflexes
- leg stiffening
- limb withdrawal from pain

Front 64

lower brain parts

Back 64

- medulla
- pons
- mesencephalon
- hypothalamus
- thalamus
- cerebellum
- basal ganglia

Front 65

functions of lower brain

Back 65

- integrates subconscious activities
- respiratory pressure
- arterial pressure
- salivation
- emotions
- reaction to pain & pleasure

Front 66

higher brain parts

Back 66

- cerebrum (cerebral cortex)

Front 67

function of cerebral cortex

Back 67

store memories & process thoughts (cannot function w/out lower brain)

Front 68

What are the 5 types of sensory receptors?

Back 68

(1) mechanoreceptors - touch
(2) thermoreceptors - temperature
(3) nociceptors - pain
(4) electromagnetic receptors - light
(5) chemoreceptors - taste, smell, blood chemistry

Front 69

path of light through the eye

Back 69

cornea
aqueous humor
pupil
lens
vitreous humor
retina
optic nerve

Front 70

cornea

Back 70

- first point on eye to be struck by light
- nonvascular & largely made of collagen
- most bending of light occurs here

Front 71

anterior cavity

Back 71

- light enters here after cornea
- filled with aqueous humor (fluid formed by ciliary processes that leaks out of canal of Schlemm)

Front 72

glaucoma

Back 72

can be caused by blockage of canal of Schlemm and resulting increased ocular pressure

Front 73

lens

Back 73

- light enters here from anterior cavity
- spherical, but tugged by suspensory ligaments which flattent it & are connected to ciliary muscle

Front 74

What happens when the ciliary muscle contracts?

Back 74

opening of circle around lens decreases, allowing lens to become more sphere-like, bringing its focal point closer to the lens

Front 75

What happens when the ciliary muscle relaxes?

Back 75

opening of circle around lens increases, causing lens to flatten, increasing its focal distance

Front 76

vitreous humor

Back 76

gel-like substance that light focuses through onto the retina

Front 77

retina

Back 77

- light focused through vitreous humor onto this
- image on retina is real & inverted
- covers back (distal portion) of eye & contains rods & cones (photoreceptors; light-sensitive)

Front 78

rods

Back 78

- sense all photons with wavelengths in visible spectrums
- CANNOT distinguish colors
- contain pigment rhodopsin (protein bound to retinal prosthetic group derived from vitamin A)
- photon isomerizes retinal causing rod cell membrane to hyperpolarize, which creates action potential

Front 79

cones

Back 79

CAN distinguish colors; 3 types, each with different pigment stimulated by different spectrum of wavelength

Front 80

general characteristics of rods & cones

Back 80

- tips contain pigments (light sensitive photochemicals)
- Vitamin A is precursor to all pigments in these cells

Front 81

fovea

Back 81

small point on retina containing mostly cones; vision is most acute on this point of retina

Front 82

iris

Back 82

- colored portion of eye that creates pupil (opening)
- made of circular and radial muscles
- IN DARK: sympathetic NS contracts iris, dilates pupil & allows more light into eye
- IN BRIGHT: parasympathetic NS contracts iris, constricts pupil & screens out light

Front 83

What are the 3 main parts of the ear?

Back 83

(1) outer ear
(2) middle ear
(3) inner ear

Front 84

auricle (pinna)

Back 84

skin & cartilage flap that directs sound wave into external auditory canal

Front 85

tympannic membrane

Back 85

eardrum; sound carried hear from external auditory canal; begins the middle ear

Front 86

3 small bones of the middle ear

Back 86

(1) malleus
(2) incus
(3) stapes
act as lever system translating wave to oval window (which is smaller than eardrum, creating an increase in pressure)

Front 87

perilymph

Back 87

fluid in inner ear

Front 88

cochlea

Back 88

sound wave moves through this part of the inner ear; alternating increase & decrease in pressure moves vestibular membrane in and out

Front 89

organ of Corti

Back 89

contains hair cells (sterocilia, a specialized type of microvilli) that detect movement of vestibular membrane in & out and transduces that into neural signals sent to brain

Front 90

semicircular canals

Back 90

in inner ear; canal of fluid & hair cells responsible for balance - when body moves, momentum of fluid changes & impacts hair cells, causing body to sense motion; canals oriented at right angles to each other to detect movement in all directions

Front 91

path of sound through the ear

Back 91

pinna
auditory canal
tympanic membrane
ossicles
oval window
cochlea
hair cells
auditory nerve
brain

Front 92

sense of smell

Back 92

olfactory (uses chemoreceptors)

Front 93

sense of taste

Back 93

gustatory (uses chemoreceptors)

Front 94

What are the 4 primary taste sensations?

Back 94

(1) bitter
(2) sour
(3) salty
(4) sweet
[umami?!?!?!]