1
Q
What is gametogenesis?
A
The process of gamete formation…sperm and egg
2
Q
What is the process of spermatogenesis?
A
- 1 primary to 2 secondary spermatocytes through Meiosis I
- 2 secondary spermocytes to 4 spermatids through Meiosis II
- 4 spermatids to 4 sperm through Maturation
3
Q
How long does spermatogenesis last?
A
2-3 months
4
Q
What is the process of oogenesis?
A
- Primary oocyte arrested in Prophase I (30,000-40,000 at puberty, last 12-50 years), forms secondary oocyte and polar body
- Both proceed to Metaphase II undergo Meiosis II arrests
- Ootid and three polar bodies are produced
- Ootid matures into ovum and eventually zygote
5
Q
What is the process of fertilization?
A
- Sperm penetration and membrane fusion
- Egg completes meiosis II and goes through changes to prevent the entry of more sperm (polyspermy)
- Fusion of nuclei…now a fertilized egg (zygote)
6
Q
What is cleavage?
A
Mitotic division resulting in smaller cells, but no change in overall size of the embryo
zygote…two-cell…four-cell…morula
7
Q
What is a morula?
A
A solid ball of cells
8
Q
What type of cleavage occurs in eggs with little or no yolk?
A
Holoblastic cleavage: total or entire cleavage
9
Q
What types of eggs have little to no yolk?
A
Invertebrates, amphibians, mammals
10
Q
What type of cleavage occurs in eggs with large amounts of yolk?
A
Meroblastic cleavage: partial cleavage
11
Q
What happens during embryo formation in eggs with large amounts of yolk?
A
Embryo forms thin cap on yolk (reptiles and birds)
12
Q
What is the course of zygote cleavage in the uterus?
A
- Ovary releases secondary oocyte from ovulation
- Fertilization
- Day 1: single cell (zygote)
- Day 2: two cell
- Day 3: 4 cell
- Day 4: 16 cell
- Day 5: blastocyst
- Day 7: embryo starts implantation in the endometrium
13
Q
What is gastrulation?
A
Cell movement and shape change
Causes morula to become a blastocyst
Establishes basic body plan and creates three primary germ layers
14
Q
What is a blastocyst composed of?
A
Trophoblast, blastocoel, and inner cell mass
15
Q
What is a trophoblast?
A
Outler layer of cells develops into part of the placenta
16
Q
What is a blastocoel?
A
Central fluid-filled cavity that also contributes to the placenta
17
Q
What is the inner cell mass?
A
Forms the developing embryo
18
Q
What does the ectoderm become in a fully-formed human?
A
Exterior; epidermis of skin, nervous system
19
Q
What does the mesoderm become in a fully-formed human?
A
Middle; skeleton, muscles, blood vessels, blood, gonads, kidneys
20
Q
What does the endoderm become in a fully-formed human?
A
Inside; lining of digestive tract, liver, pancreas, thymus, thyroid
21
Q
What are the steps of blastocyst development?
A
- Vegetal pole gives rise to the blastopore
- Blastopore gives rise to the archenteron
- Archenteron becomes the digestive tract
22
Q
How is cell movement possible during gastrulation?
A
Through a variety of cell-shape changes
23
Q
What is invagination?
A
Cell sheet dents inward
24
Q
What is involution?
A
Cell sheet rolls inwards
25
What is delamination?
Cell sheet splits into two
26
What is ingression?
Cells break away from cell sheet and migrate as individual cells
27
What is neurulation?
Development of the nervous system in vertebrates
28
What is the role of the notochord?
Stimulates neural plate development
29
What is the role of the neural plate?
Folds together to form a long hollow cylinder (neural tube)
30
What is the role of the neural tube?
Will "pouch out" to become brain and spinal cord (takes about 5 months)
31
What is organogenesis?
Formation of organs in their proper locations
32
Organogenesis occurs by the interaction of what?
Occurs by interaction of cells within and between the three germ layers
33
When does organogenesis occur?
It follows rapidly on the heels of gastrulation
In many animals, it begins before gastrulation is complete
34
What is cell fate determination?
The process by which a cell's ultimate fate becomes fixed
35
What often determines a cell's fate?
Its location in the developing embryo
36
What two things can establish cell fate?
Presence of cytoplasmic determinants
Interactions with neighboring cells (i.e. induction)
37
What is induction?
Cells come in contact with eachother
38
What is primary induction?
Occurs between the three primary germ layers
Happens during differentiation of the central nervous system during neurulation
39
What is secondary induction?
Occurs between tissues that have already been specified to develop along a particular pathway
Happens during development of the lens of the vertebrate eye
40
What is the process of induction relative to the formation of the eye?
1. An extension of the optic stalk grows until it contacts the ectoderm
2. Induces a section of the ectoderm to pinch off and form the lens
3. Other structures of the eye develop from the optic stalk
4. Lens cells reciprocally induce photoreceptor formation in optic cup
41
What is the process of development?
Systematic gene-directed changes throughout an organism's development
42
What are the four subprocesses of development?
Cell division (cleavage), pattern formation, cell differentiation, morphogenesis
43
When does rapid cell division occur?
After fertilization
44
Explain embryo size related to cleavage
The number of cells increases but the size of the cells decrease. So initially, embryo size does not change.
45
What is meant by pattern formation?
Cells direct positional information within the embryo (will affect cell fate)
46
How do organisms determine the basic pattern of the body compartments?
Through positional information
(Positional information then leads to changes in cellular gene activity
and cells ultimately adopt a fate appropriate for their location)
47
How do radially symmetrical cells develop?
They develop two perpendicular axes to define the basic body plan (anterior=posterior axis, dorsal=ventral axis)
48
What is polarity?
The acquisition of axial differences in a developing structure
49
What is meant by cell differentiation?
Cells become particular cell types
(Positional information leads to intrinsic changes in cellular gene activity
and cells ultimately adopt a fate appropriate for their location)
50
What are totipotent cells?
Can become any cell type including placenta
51
Whar are pluripotent cells?
Can become any cell type except placenta
52
What are multipotent cells?
Can become only certain cell types
53
What are unipotent cells?
Can be only one cell type (fully differentiated)
54
What happens when differentiated cells in the body acquire mutations?
Dedifferentiate and become cancerous
55
What is meant by morphogenesis?
The form of the body (organs and anatomical features) take shape; product of changes in cell structure and behavior
56
What are morphogens?
Diffusible signaling molecules that affect developmental fate, secreted from a particular set of cells called organizers, or can be transferred into the embryo from the mother
57
What do morphogens provide?
Positional information; where in the embryo structures will form
58
What does the gradient of morphogen concentration do?
Provides positional cues. Different concentrations affect gene expression differently
59
What does morphogenesis include?
Changes in the number, timing, and orientation of cell divisions, cell growth and differentiation, cell shape, cell migration, and cell death
60
How do cells affect the fate of ther cells?
Requires molecular signals
Receptors and signal transduction pathways
Activation of transcription factors
Example: formation of the vertebrate eye/induction
61
What is apoptosis?
Programmed cell death
62
How are human digits related to apoptosis?
Human embryos begin with webbed fingers; modeling of digits during development occurs as cells undergo apoptosis
63
What is the anterior/posterior axis development in Drosophila based on?
Opposing gradients of two different mRNAs from the mother
Bicoid (anterior) and Nanos (posterior)
64
What is an organizer?
A cluster of cells that release morphogens which convey positional information to other cells
A widespread mechanism for determining relative position and cell fates
65
What happens the closer a cell is to an organizer?
The higher the concentration of the morphogen it experiences
66
What is an example of an organizer?
The notochord: secretes morphogens to stimulate neurulation (formation of the brain and spinal cord)
67
What is Sonic the Hedgehog?
A morphogen discovered in Drosophila, mutation resulted in embryos covered in small pointy projections
Secreted by notochord cells, long-range and can stimulate neural development
Binds to receptors and transmits a signal which alters expression of genes that guide neuron development, also involved in limb development
68
What are homeotic genes?
Genes which regulate the development of anatomical structures in various organisms
69
What happens when there are mutations in homeotic genes?
Appearance of perfectly normal body parts in inappropriate places
70
What are two examples of homeotic gene mutation?
Bithorax gene: when mutated, results in transformation of the thorax resulting in a fly with two complete sets of wings
Atennapedia gene: normally exoressed in posterior segments, specifies development of the leg; when inappropriately expressed in anterior segments, legs grow where antennae usually would
71
What does the nervous system do?
Interprets information about the body, environment, and helps us decide whether and how to respond
72
What is the central nervous system?
Brain and spinal cord, receives and integrates information from the body and directs an appropriate output response
73
What is the peripheral nervous system?
Sensory neurons bring information to the CNS and motor neurons convey information from the CNS to the effector locations (muscles, organs, glands)
74
How are the CNS an PNS related?
Sensory neurons in the PNS conduct information to interneurons in the CNS which produce an appropriate output by motor neurons in the PNS
75
What are the three types of neurons?
Sensory, interneurons, and motor neurons
76
What is the role of sensory neurons?
Located in the PNS, carry information about the body and environment to the CNS
77
What is the role of interneurons?
Located in the CNS, provide a link between the sensory and motor neurons
78
What is the role of motor neurons?
Located in the PNS, carry impulses from CNS to effectors (muscles and glands)
79
What are neurons?
Nerve cells
Their function (nerve impulses) depend on electrical membrane potential of the neuron
80
What are dendrites?
Receive signals (using lots of membrane receptors) from other cells and conduct information toward the cell body
81
What is the cell body?
Has the nucleus and other machinery to maintain the neuron
82
What is the axon?
Conducts signals to other nerve cells or effector organs
83
What is the myelin sheath?
Insulating covering, formed from the cell membrane of Schwann cells, that surrounds an axon with multiple spiral layers
84
What are the Nodes of Ranvier?
Gaps in the myelin sheath of a nerve cell
85
What is the synapse?
Connection of neurons to other cells or neurons
86
What is an exaple of a synapse?
Neuromuscular junction: connection between neurons and muscles
Signal flows from the pre-synaptic membrane through the synaptic cleft to the post-synaptic membrane of the receiving cell
87
What is a nerve?
Bundled axons of many neurons; each neuron may have different properties
88
What is the resting potential of a neuron?
Voltage across membrane in a resting neuron is about -70 mV
89
What is the ion concentration in aqueous solution?
Electrical=ions (in this case, mainly K+ and Na+)
90
What is the ion concentration outside the cell?
[Na+, Cl-]=150 mM, [K+]=5 mM, [proteins]=lower
91
What is the ion concentration inside the cell?
[Na+, Cl-]=15 mM, [K+]=150 mM, [proteins]=higher
92
What do ion channels/pumps do?
Move ions; some K+ diffuses out through open K+ channels
93
What causes imbalances of Na+ and K+?
Active transport by Na/K pumps
Antiporter that exchanges Na+ for K+, pumps 3 Na+ outside and 2 K+ inside, requires ATP (active transport), maintains concentration difference of Na+ K+
Important for maintaining reseting potential
94
What are ion channels?
Action of nerves depends on ions flowing through channels causing change in membrane potential
95
What is a non-gated ion channel?
Always open
96
What is a voltage-gated ion channel?
Respond to voltage differences across the membrane: Na+ and K+ channels
97
What is a chemically gated ion channel?
Membrane channel on dedrites that respond to ligands
98
What gates does a voltage-gated Na+ channel have?
Activation gate: on the extracellular side that allows Na+ ions in
Inactivation gate: on intracellular side that closes and blocks Na+ ions
99
What gates does a voltage-gated K+ channel have?
One gate, an activation gate: on the extracellular side that allows Na+ ions in
100
What do all gates have in common?
All triggered by the threshold voltage and necessary for action potential
101
What is action potential?
The basis of nerve impulses, mediated by the acion of sodium and potassium channels
Rapid electrical depolarization of neuron membranes, and the propogation of that depolarization along the length of the axon to a receiving cell
Triggered when the voltage potential inside the cell reaches -55 mV (threshold voltage)
Avtion potential is only generated if the -55 mV threshold voltage is reached
102
PHASES???
103
Explain the steps of action potential propogation
Resting membrane potential: -70 mV
Stimulus to threshold voltage, threshold voltage to depolarization: -55 mV
Max depolarization voltage leads to repolarization: 50 mV
Repolarization leads to restoration of the resting membrane potential: -70 mV
Direction of action potential propogation: starts at soma
104
What direction does action potential propogation occur?
Down the neuron
Stimulus at the dendrite tip causes depolarization
Sodium ions rush in and cause a new depolarization event in the next section of the neuron
This leads to a chain reaction that propogates from the tip of the dendrite to the end of the axon
105
What two things can increase the speed of conductance?
Insulate axon with myelin: conduction jumps between unmyelinated nodes (found in vertebrates)
Increase diameter: resistance (factors that reduce flow of ions) inversely proportional to diameter; the larger the diameter, the lower resistance and faster conductance; found in invertebrates like giant squid
106
What is saltatory conduction?
An electric ion current carried by depolarization and repolarization of only the unmyelinated sections of the neuron (nodes of Ranvier); much faster than continuous; action potentials are produced at each Node of Ranvier and stimulate an action potential at the next node
107
What is continuous conduction?
Step-by-step depolarization and repolarization of each adjacent segment of the plasma membrane
108
What neurological diseases can be caused by damage to the myelin sheath?
* Multiple sclerosis is an autoimmune disease in which cells of the myelin sheath are attacked
* Causing coordination and walking problems, numbness, and vision problems
* Charcot-Marie-Tooth (CMT) Disease is a group of 25+ genetic disorders that cause nerve damage in the myelin sheath of the PNS
* Causing muscle weakness, loss of sensation and loss of muscle bulk
109
What happens when action potential reaches the end of the axon?
Synapse: connection of neurons to other cells or other neurons
Signal flows from pre-synaptic membrane through the synaptic cleft to the post-synaptic membrane of the receiving cell
110
When an action potential reaches the end of a neuron (the axonal terminal), a chemical signal is released:
* AP causes calcium channels in the terminal end of the axon to open
* Influx of Ca+ causes neurotransmitters to be released
* Neurotransmitters are chemical signals released by neurons into the synaptic cleft
* Usually only one type of neurotransmitter is released by each neuron
* Neurotransmitters binding to receptors on membranes of receving (postsynaptic) cells cause changes in the charge properties of receiving cell
* The neurotransmitter may excite (depolarize and cause to fire) or inhibit (hyperpolarize and inhibit firing) the postsynaptic cell
111
What are inhibitory neurotransmitters?
Make a neuron more negatively charged (hyperpolarized) so less likely to fire an action potential
Dopamine: usually inhibitory; multiple functions, depending upon neurons it acts on (includes those of pleasure/reward system)
Dopamine reuptake is blocked by amphetamines and cocaine, so dopamine has a longer time to remain the synaptic cleft and stimulate neurons involved in pleasure
112
What are excitatory neurotransmitters?
Make a neuron more positively charged (depolarized) so its more likely to reach threshold potential and fire an action potential
Acetylcholine: usually excitatory; used by spinal cord neurons to control skeletal muscles, involved in memory processing in brain neurons
113
What is Channelopathy-Associated Insensitivity to Pain (CIP)?
Involves a mutation in the protein SCN9A that forms part of sodium channel in neurons that respond to pain
Protein is usually 1977 amino acids long but substitution of an A for a C in a codon shortend to 984 amino acids
Produces nonfunctional sodium channel
114
What are the three main muscle types?
Skeletal (striated), cardiac (striated), and smooth (no striations)
115
What are skeletal muscles?
Composed of many bundled fibers: myofibrils are composed on myofilaments
Myofibrils fuse during development to form long multinucleate cells called muscle fiberes
Myofibrils form from myoblasts
Myoblasts lead to myofibrils fusing, which leads to form long multinucleate cells called muscle fibers (myofibers)
116
What is the hierarchical organization of vertebrate skeletal muscle?
Muscle fibers form bundles called fascicles, which are bundled together to form the muscle
117
What is a sarcomere?
A unit of the myofibril that goes from Z line to Z line (striations are Z lines)
The unit of muscle contraction
118
What happens during sarcomere contraction?
H and I bands shrink, Z lines move closer together
119
What is the sliding filament model?
Myosin head interacts with actin by forming a cross-bridge, myosin head ratchets along actin fibers, slides actin relative to myosin
120
What are the molecular events of contraction?
Start with myosin head bound to ATP but not actin:
Myosin hydrolyzes ATP, gives way to ADP+ Pi, ADP remains bound to myosin
Head resets "cocks" under tension
Myosin binds to actin (crossbridge formation)
Myosin head releases ADP, moves in power stroke
Myosin binds to ATP, releasing actin
121
During contraction, what is the effect over the entire muscle?
.5 micrometer shortening per sarcomere
200000 sarcomeres end-to-end x 2.5 micrometers = 500000 micrometers (around 20 in)
200000 x 2 = 400000 micrometers(around 16 in)
Means about 4 inches of contraction, 20% contraction of length
122
What happens in the cross bridge contraction cycle?
Actin slides myosin
Powered by ATP: chemical energy
Converted to mechanical energy
Control step: binding of myosin to actin
Requires other proteins: troponin and tropomyosin
Requires Ca++
123
What are thin myofilaments made of?
Globular protein actin
124
What do regulatory proteins troponin and tropomyosin associate with?
Actin
125
What are thick myofilaments composed of?
Twisted chains of myosin molecules that have globular club-shaped heads
126
What controls troponin shape?
Ca++
127
What alters conformation?
Ca++ biding troponin
128
How does the Ca++ binding troponin process occur?
Troponin binds Ca++
Alters conformation of troponin
Troponin moves tropomyosin
Exposes myosin binding sites on actin
Myosin can bind actin
Power stroke occurs
129
Summarize muscle contraction
Motor neuron converts an electrical action potential into a chemical signal (neurotransmitters)
Neurotransmitter (acetylcholine) is released into synaptic cleft
Acetylcholine receptors are chemically gated Na+ channels located in the muscle cell membrane (depolarizes)
130
What do T (Transverse) Tubules do?
Run deep into muscles and carry action potential to entire muscle
131
What happens during action potential from T-Tubules?
Open Ca++ channels in SR cytoplasm
Ca++ binds troponin, changes shape, moves tropomyosin
Recovery: SR pump removes Ca++
132
What occurs during rigor mortis?
When ATP no longer available, myosin heads become stuck in crossbridge formation
ATP necessary to recharge the myosin head and bring it back to its cocked position so it's ready to make more crossbridges
133
What are slow-twitch fibers?
(oxidative or red muscle): have high ATPase activity and can recycle actin-myosin cross-bridges rapidly
Have lots of myoglobin, an oxygen-binding protein, and have many mitochondria; well-supplied with blood vessels
Have large reserves of glycogen and fat for energy production
Max tension develops slowly, but is highly resistant to fatigue
Muscles with a high proportion of slow-twitch fibers are good for aerobic work (e.g., long-distance running, cycling)
134
What are fast-twitch fibers?
(glycosidic or white muscle): fewer mitochondria and blood vessels, little or no myoglobin
Develop greater max tension faster, but fatigue more quickly
Cannot replenish ATP for prolonged contractions
Good for short-term work that requires maximum strength
Weight lifters and sprinters have leg and arm muscles with high proportions of fast-twitch fibers
135
What muscle fiber type do postural muscles have?
Postural muscles that maintain continuous contractions are mostly slow-twitch fibers
Example: muscles in back and legs that are required for standing and maintaining posture
136
What muscle fiber type do bicept muscles have?
Bicep muscles have higher percentage of fast-twitch fibers
We can use bicep muscles to pick up a heavy object, but not hold that weight for a long period of time
137
What is a twitch?
Contraction of a muscle in response to a stimulus
Measured in terms of tension, or force, it generates
Total force generated: depends on how many muscle fibers are being stimulated and how often
If action potentials are fired rapidly, new twitches are triggered before the myofibrils can return to resting condition
As a result, twitches sum, tension increases and become more sustained
Twitches sum because Ca2+ pumps cannot clear Ca2+ from sarcoplasm before next action potential arrives
Tetanus: max level of contraction. Action potentials are so frequent there is always Ca2+ in the sarcoplasm
Biology 111
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