Lecture 4 - The Eukaryotic Cell; The Nervous System Flashcards
(163 cards)
0
Q
Nucleoplasm
A
aqueous soup inside nucleus
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Q
Nucleus
A
- Major feature distinguishing eukaryotic cells from prokaryotic cells
- contains all DNA -> cannot leave nucleus
- Wrapped in a double phospholipid bilayer called the nuclear envelope or membrane
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Nuclear Pores
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- RNA leaves nucleus through them
- Large holes that perforate the nuclear envelope
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Nucleolus
A
- Area within the nucleus where rRNA is transcribed and subunits of ribosome are assembled
- Isn’t separated from nucleus by a membrane
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Q
Endocytosis
A
- Way cells can acquire substances from the extracellular environment
- Types: Phagocytosis, pinocytosis, and receptor mediated endocytosis
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Phagocytosis
A
- cell membrane protrudes outward to envelope and engulf particulate matter
- only a few specialized cells are capable of it
- the binding of proteins on the matter to protein receptors on the phagocytotic cell is the force that makes it happen
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Phagocytosis in Humans
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Antibodies or complement proteins bind to particles & stimulate receptor proteins on macrophages and neutrophils to initiate it
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Phagosome
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What the membrane bound body is called once the particulate matter is engulfed
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Pinocytosis
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- Extracellular fluid is engulfed by small invaginations of the cell membrane
- Performed by most cells in a random fashion
- nonselective
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Receptor-Mediated Endocytosis
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specific uptake of macromolecules such as hormones or nutrients
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Exocytosis
A
opposite of endocytosis
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Eukaryotic Membrane
A
- phospholipid bilayer
- similar to prokaryotes but it invaginates and separates to form individual, membrane-bound organelles and compartments
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Endoplasmic Reticulum
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- Thick maze of membranous walls
- Separates cytosol from the ER lumen or cisternal space
- In many places it is contiguous with the cell membrane and nuclear membrane
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ER Lumen
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- AKA cisternal space
- The extracellular fluid side of the ER
- Contiguous in places with the space between the double bilayer of the nuclear envelope
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Rough ER
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- Synthesizes all proteins not used in cytosol
- AKA granular ER b/c granular appearance
- ER near nucleus that has many ribosomes attached to it on the cytosolic side
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Translation on Rough ER
A
- Propels proteins into the ER lumen as they are created
- The newly synthesized proteins are moved through the lumen toward the golgi.
- Small transport vesicles bud off from the ER and carry the proteins across cytosol to Golgi
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Golgi Apparatus
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- AKA golgi complex
- Series of flattened, membrane bound sacs
- Organizes and concentrates the proteins as they are shuttled, progressively outward from one compartment to the next
- Modifies and packages proteins for use in other parts of the cell and outside the cell
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Cisterna
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compartment of golgi
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How proteins are distinguished in golgi
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based upon signal sequence and carb chains
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Bulk Flow
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Process that packages proteins not possessing a signal sequence into secretory vesicles and are expelled from cell
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How golgi changes proteins
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glycosylation or removing amino acids
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End-Product of Golgi
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vesicle full of proteins
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What happens to vesicle full proteins?
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- expelled from cell as secretory vesicles
- released from golgi to mature into lysosomes
- transported to other parts of cell such as mitochondria or back to ER
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Secretory Vesicles
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- AKA zygomen granules
- may contain enzymes, growth factors, or extracellular matrix components
- release their contents through exocytosis
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Lysosomes
- contain hydrolytic enzymes that digest substances taken in by endocytosis
- came from golgi
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Smooth ER
- site of lipid synthesis including steroids
| - helps to detoxify some drugs
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Cytosol vs. ER Lumen
- cell can be divided into these 2 parts
- in order to reach cytosol, a substance must cross membrane via passive or facilitated diffusion, or active transport
- it can reach the ER lumen via endocytosis without ever transporting across a membrane
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Cytoskeleton
- network of filaments
- determines structure and motility of a cell
- anchors some membrane proteins and other cellular components, move components within cell and moves cell itself
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Two Major Types of Filaments in Cytoskeleton
- microtubules and microfilaments
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Microtubules
- rigid, hollow tubes made from tubulin
- makes spindle apparatus
- makes flagella and cilia
- larger than microfilaments
- have a positive and negative end
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Peroxisomes
- production and break down of hydrogen peroxide
- vesicles in cytosol
- grow by incorporating lipids and proteins from cytosol
- inactivate toxic substances
- regulate oxygen concentration
- play role in synthesis and break down of lipids
- play role in metabolism of nitrogenous bases and carbs
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Microfilaments
- squeeze membrane together in phagocytosis and cytokinesis
- contractile force in microvilli and muscle
- produce contracting force in muscle
- active in cytoplasmic streaming, phagocytosis, and microvilli movement
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Eukaryotic Flagella & Cilia
- specialized structures
- the axoneme of each contains 9 pairs of microtubules forming a circle around 2 lone microtubules -> 9+2 arrangement
- cross bridges connect each of the outer pairs of microtubules to their neighbor
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Axoneme
major portion of flagellum and cilium
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Dynein
protein that makes up cross bridges
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Cross Bridges
- creates a whip action in cilia causing fluid to move laterally
- creates a wiggle action in flagella causing fluid to move directly away from cell (Prok. flagella rotate)
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Centrosome
the major microtubule-organizing center (MTOC) in animal cells
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Centrioles
Function in production of flagella and cilia
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- End of Microtubule
attaches to MTOC in cell
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+ End of Microtubule
grows away from MTOC @ positive end
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Actin
Major component of microfilaments
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Cellular Junctions
- 3 types that connect animal cells
1. tight junctions
2. desmosomes
3. gap junctions
- each performs a different function
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Tight Junctions
- Form watertight seal from cell to cell that can block water, ions, and other molecules from moving around and past cells
- Epithelial tissue in organs like the bladder, intestines, and kidneys
- Also acts as a barrier to protein movement between the apical and basolateral surface of a cell
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Apical Surface
The part of a cell facing the lumen of a cavity
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Basolateral Surface
The opposite side of the apical surface of a cell
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Desmosomes
- Join 2 cells at a single point
- Attach directly to cytoskeleton of each cell
- Don't prevent fluid from circulating around all sides of a cell
- Found in tissues that experience a lot of stress like skin & intestinal epithelium
- Often accompany tight junctions
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Gap Junctions
- Small tunnels connecting cells
- Allow small molecules and ions to move between cells
- In cardiac muscle provide for the spread of the action potential from cell to cell
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Mitochondria
- powerhouse of eukaryotic cell
- where kreb's cycle takes place
- have own circular DNA that replicate independently from the eukaryotic cell
- surrounded by 2 phospholipid bilayers
- Have own ribosomes -> 55-60s in humans
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Endosymbiont Theory
Mitochondria may have evolved from a symbiotic relationship between ancient prokaryotes and eukaryotes
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Mitochondrial DNA
- Contains no histones or nucleosomes
- few dozen to several hundred molecules of DNA in each mitochondria
- genes in it code for mitochondrial RNA that is distinct from the RNA in the rest of the cell
- Most proteins used by mitochondria are coded for by nuclear DNA, not mitochondrial DNA
- Passed maternally
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Inner Membrane of Mitochondria
- Invaginates to form cristae
| - holds the ETC
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Intermembrane Space
between the inner and outer membrane
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Extracellular Matrix
- In some tissues, cells called fibroblasts secrete fibrous proteins such as elastin and collagen that form a molecular network that holds tissue cells in place
- Different tissues from different matrices
- Can be large part of tissue (as in bone) or small part
- Consistency may be liquid or solid
- May provide structural support, help to determine the shape & motility, and affect cell growth
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Three Classes of Molecules That Make up Animal Cell Matrices
1. Glycosaminoglycans & Proteoglycans
2. Structural Proteins
3. Adhesive Proteins
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Basal Lamina
- AKA basement membrane
| - Thin sheet of matrix material that separates epithelial cells from support tissue
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Four Basic Types of Tissue
1. Epithelial
2. Muscle
3. Connective
4. Nervous
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Epithelial Tissue
Separates free body surfaces from their surroundings
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Connective Tissue
- Extensive Matrix
| - Blood, lymph, bone, cartilage, and connective tissue proper making up tendons and ligaments
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Intercellular Communication
- So organism can function as a single unit
- Communication accomplished chemically via 3 types of molecules:
1. neurotransmitters
2. local mediators
3. hormones
- governed by the nervous system, the paracrine system, and the endocrine system
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Major Distinction between Methods of Communication
The distance travelled by the mediator
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Neurotransmitters
Travel over very short intercellular gaps
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Local Mediators
Immediate area around the cell from which they were released
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Hormones
Travel throughout the organism via bloodstream
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Neurotransmitter vs. Hormonal Mediated Communication
- Neuronal communication: rapid, direct & specific
| - Hormonal communication: slower, spread throughout the body, and affect many cells and tissues in many diff ways
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Paracrine System
intermediate communication system
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Nervous System
- Allows for rapid & direct communication between specific parts of the body resulting in changes in muscular contractions or glandular secretions
- Brain, spinal cord, nerves, and neural support cells, and sense organs: eye & ear
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Neuron
- Function unit of nervous system
- Highly specialized cells
- Capable of transmitting an electrical signal from once cell to another via electrical or chemical means
- lost capacity to divide
- relies on glucose for its chemical energy
- uses facilitated transport to move glucose from the blood into its cytosol but is not dependent upon insulin for this transport
- depends heavily on efficiency of aerobic respiration
- Has low stores of glycogen & oxygen and must rely on blood to supply sufficient levels of these nutrients
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Basic Anatomy of Neuron
- Many dendrites, a single cell body, and usually one axon with many small branches
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Dendrites
Receive signal to be transmitted
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Axon Hillock
Receives stimulus from dendrite and if stimulus is great enough, it generates an action potential in all directions, including down the axon
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Axon
Carries the action potential to a synapse, which passes the signal to another cell
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Unipolar
- Sensory only
| - 1 from cell body
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Bipolar
- Retina, inner ear, olfactory area of brain
| - 2 from cell body
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Multipolar
- most neurons of the brain
| - multiple from cell body
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Action Potential
Disturbance in the electric field across the membrane of a neuron
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Resting Potential
Established mainly by an equilibrium between passive diffusion of ions across the membrane and the sodium potassium pump
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The Sodium/Potassium Pump
- Moves 3 sodium ions out of cell while bringing 2 potassium ions into the cell
- This increases the positive charge along the membrane just outside the cell relative to the charge along the membrane on the inside of the cell
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Potential Difference
- The rate at which the sodium potassium pump passively diffuses in/out of cell increases until it reaches equilibrium
- at this point, the inside of the membrane has a negative potential difference (voltage) compared to the outside
- This potential difference = resting potential
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Voltage Gated Sodium Channels
- Integral membrane proteins in the membrane of a neuron
- Proteins change configuration when the voltage across membrane is disturbed
- Configuration change allows sodium ions to flow through the membrane and is a positive feedback mechanism
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Depolarization
Sine the sodium ion concentration moves toward equilibrium, and the potassium ion concentration remains higher inside the cell, the membrane potential actually reverses polarity so that it is positive on the inside and negative on the outside
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Voltage gated Potassium Channels
- Less sensitive to voltage change so they take longer to open
- by the time they open most of the sodium channels are closing
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Repolarization
Potassium ions flow out of cell making the inside more negative
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Hyperpolarization
because the potassium ion channels are so slow to close, for a small period of time, the inside membrane becomes even more negative than the resting potential
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Where does the action potential originate at?
axon hillock
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Steps of Action Potential
1. Membrane is at rest. Sodium Potassium channels are closed
2. Sodium ion channels open and cell depolarizes
3. Potassium ion channels open as sodium ion channels begin to inactivate
4. Sodium ion channels are inactivated. Open potassium ion channels repolarize the membrane
5. Potassium ion channels close and the membrane equilibrates to its resting potential
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All-or-Nothing
- Action potential is all-or-nothing
- The membrane is completely depolarized or no action potential is generated
- The stimulus to the membrane must be greater than the threshold stimulus
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Synapse
- How neural impulses are transmitted from one cell to another chemically or electrically
- Transmission of signal from one cell to another is the slowest part of the process of nervous system cellular communication
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Electrical Synapses
- uncommon
- composed of gap junctions between cells
- cardiac muscle, visceral smooth muscle, and very few neurons in central nervous system contain them
- because don't involve diffusion of chemicals, they transmit signals much faster than chemical synapses and in both directions
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Chemical Synapses
- more common, unidirectional
- small vesicles filled with neurotransmitter rest inside postsynaptic membrane
- membrane near the synapse contains large number of calcium ion voltage gated channels
- when action potential arrives at synapse, the channels are activated, allow calcium ions to flow 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
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Brownian Motion
- How neurotransmitter diffuses across the synaptic cleft
| - random motion of the molecules
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Postsynaptic Membrane
- Contains neurotransmitter receptor proteins
- When neurotransmitter attaches to the receptor proteins, the postsynaptic membrane becomes more permeable to ions
- Ions move across it through proteins called ionophores, completing the transfer of the neural impulse
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Fatigue
When cell is fired too often and is unable to replenish its supply of neurotransmitter vesicles
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What happens if neurotransmitter remains in synaptic cleft?
the postsynaptic cell may be stimulated over and over
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How does the cell deal with this problem?
1. Neurotransmitter may be destroyed by an enzyme in the matrix of the synaptic cleft and its part recycled by the presynaptic cell
2. it may be directly absorbed by the presynaptic cell via active transport
3. neurotransmitter diffuse out of the synaptic cleft
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How many types of neurotransmitters are there?
over 50 types
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Single Synapse
- usually releases only 1 type of neurotransmitter and is designed to either inhibit or excite, not both
- cannot change from inhibitory to excitatory or vice versa
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Second Messenger System
- Receptors may be ion channels themselves or they may act via a second messenger system, activating another molecule inside the cell to make changes
- For prolonged change, such as in memory, the SMS is preferred
- G proteins commonly initiate SMS
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G Proteins
- Attached 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 free
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The Alpha Subunit of the g protein may do what once it breaks free?
1. Activate separate specific ion channels
2. Activate a second messenger (cyclic AMP/GMP)
3. Activate intracellular enzymes
4. Activate gene transcription
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Glial cells or Neuroglia
- Support cells in nervous tissue
- In human brain, glial cells outnumber neurons
- Capable of cellular division
- six types
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Types of Glial Cells
1. Microglia
2. Ependymal Cells
3. Satellite Cells
4. Astrocytes
5. Oligodendrocytes
6. Neurolemmocytes or Schwann Cells
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Microglia
- Arise from white blood cells called monocytes
| - Phagocytize microbes and cellular debris in CNS
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Ependymal Cells
- Epithelial cells that line the space containing the cerebrospinal fluid
- Use cilia to circulate the cerebrospinal fluid
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Satellite Cells
support ganglia
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Ganglia
groups of cell bodies in the PNS
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Astrocytes
Star-shaped neuroglia in the CNS that give physical support to neurons and help maintain the mineral and nutrient balance in the interstitial space
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Oligodendrocytes
Wrap many times around axons in the CNS creating electrically insulating sheaths called myelin
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Myelin
- In the PNS, myelin is produced by schwann cells
| - Increases the rate at which an axon can transmit signals
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White Matter
myelinated axons
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Gray Matter
neuronal cell bodies
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Nodes of Ranvier
- Tiny gaps between myelin
- When an action potential is generated down a myelinated axon, the action potential jumps from one node of ranvier to the next - This is called saltatory conduction
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Functions of Neurons
1. Sensory (Afferent) Neurons
2. Interneurons
3. Motor (Efferent) Neurons
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Sensory Neurons
- Receive signals from a receptor cell that interacts with its environment, and then transfers this signal to other neurons
- 99% of sensory input is discarded by the brain
- located dorsally from the spinal cord
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Interneurons
- Transfer signals from neuron to neuron
| - 90% of neurons in human body
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Motor Neurons
- Carry signals to a muscle or gland called the effector
| - located ventrally (toward the front or abdomen)
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Nerves
- Neuron processes (axons & dendrites) bundled together
| - called tracts in the CNS
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Nervous System
1. CNS
| 2. PNS
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Central Nervous System
- Interneurons and Support tissue
- brain and spinal cord
- function is to integrate nervous signals between sensory and motor neurons
- connected to the peripheral parts of the body by the PNS
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Peripheral Nervous System
- Everything else
- parts of the PNS project into the brain and spinal cord
- handles the sensory and motor functions of the nervous system
- divided into the somatic nervous system and autonomic nervous system
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Somatic Nervous System
- Responds to the external environment
- Contains sensory and motor functions
- its motor neurons innervate only skeletal muscle
- the motor functions of the SNS can be consciously controlled and are considered voluntary
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Somatic Motor Neurons
- The cell bodies are located in ventral horns of the spinal cord
- These neurons synapse directly on their effectors and use acetylcholine for their neurotransmitter
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Somatic Sensory Neurons
The cell bodies are located in the dorsal root ganglion
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Autonomic Nervous System
- Controlled mainly by hypothalamus
- the sensory portion receives signals primarily from the viscera and the motor portion then conducts these signals to smooth muscle, cardiac muscle, and glands
- the function is generally involuntary
- the motor portion is divided into two systems: sympathetic and parasympathetic
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Viscera
the organs inside the ventral body cavity
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Sympathetic and Parasympathetic
Most internal organs are innervated by both with the two systems working antagonistically
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Sympathetic
- "fight or flight" responses
- signals originate in neurons whose cell bodies are found in the spinal cord
- Activates heart and major skeletal muscles, dilates pupils, redirects blood from digestive and excretory systems
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Parasympathetic
- "rest & digest"
- signals originate in neurons whose cell bodies can be found in both the brain and spinal cord
- deactivates what the sympathetic activates, and activates intestines and excretory system
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Ganglion vs. Nucleus
A group of cell bodies located in the CNS is called a nucleus, if located outside the CNS, it is called a ganglion
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Acetylcholine
- Somatic and parasympathetic Nervous system
- The neurotransmitter used by all preganglionic neurons in the autonomic nervous system and by postganglionic neurons in the parasympathetic system
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Epinephrine/Norepinephrine
- Sympathetic Nervous system
- AKA adrenaline and noradrenaline
- the neurotransmitter postganglionic neurons of the sympathetic nervous system uses
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Cholinergic Receptors
- Receptors for acetylcholine
| - two types: nicotinic and muscarinic
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Adrenergic Receptors
Receptors for epinephrine and norepinephrine
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Lower Brain
- Medulla, pons, mesencephalon, hypothalamus, thalamus, cerebellum, and basal ganglia
- Integrates subconscious activities such as the respiratory system, arterial pressure, salivation, emotions, and reaction to pain and pleasure
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Higher Brain
- AKA cortical brain
- cerebrum or cerebral cortex
- incapable of functioning without the lower brain
- acts to store memories and process thoughts
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Sensory Receptors
- Transduce physical stimulus to neural signals
| - 5 Types
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5 Types of Sensory Receptors
1. Mechanoreceptors for touch
2. Thermoreceptors for temp change
3. Nociceptors for pain
4. Electromagnetic Receptors for light
5. Chemoreceptors for taste, smell, and blood chemistry
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Cornea
- Where light first strikes the eye when it reflects off an object in the external environment
- Nonvascular and made largely from collagen
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Anterior Cavity
- From the cornea, light enters the anterior cavity
| - Filled with aqueous humor
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Lens
- From the anterior cavity, light enters the lens
- converging lens
- flattening the eye by relaxing the ciliary muscles makes the lens less powerful, which moves the focal point away from the lens
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Ciliary Muscle
- circles the lens
| - contracts -> opening of circle decreases -> lens becomes more like sphere -> brings focal point closer to lens
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Elasticity of Lens
Declines with age, making it difficult to focus on nearby objects as one gets older
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Retina
- Light is focused through the vitreous humor and onto the retina
- The image on the retina is real and inverted
- Covers the inside of the back of the eye
- Contains light sensitive cells called rods and cones
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Rods and Cones
- named for their shapes
- the tips contain light sensitive photochemicals called pigments that go through a chemical change when one of their electrons is struck by a single photon
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Rhodopsin
- pigment in rod cells
- made of a protein bound to a prosthetic group called retinal which is derived from vitamin A
- don't distinguish colors
- sense all photons with wavelengths in the visible spectrum
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Cones
- Distinguish color
| - 3 types, each with different pigment
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Vitamin A
- precursor to all pigments in rods and cones
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Fovea
- small point on the retina containing mostly cones
| - where vision is most acute
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Iris
- colored portion of eye that creates the opening called the pupil
- Made from circular and radial muscles
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Dark Environment
The sympathetic NS contracts the iris, dilating the pupil and allowing more light to enter the eye
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Bright Environment
The parasympathetic NS contracts the circular muscles of the iris, constricting the pupil and screening out light
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Hyperpolarization of Rod Cell
- Photon isomerizes retinal causing the membrane of the rod cell to become less permeable to sodium ions
- The hyperpolarization is transduced into a neural action potential and the signal is sent to the brain
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3 Parts of the Ear
1. Outer ear
2. Middle Ear
3. Inner Ear
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Auricle/Pinna
- Skin and cartilage flap commonly called the ear
| - directs sound waves into the external auditory canal
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External Auditory Canal
Carries sound wave to the tympanic membrane or eardrum
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Tympanic Membrane
Begins the middle ear
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Middle Ear
- contains 3 small bones: malleus, incus, and stapes
- 3 bones act as a lever system translating the wave to the oval window
- 3 bones change the combination of force and displacement from the inforce to the out force
- the displacement is lessened, which creates an increase in force
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Oval Window
- smaller than the tympanic membrane
| - acts to increase the pressure
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Why is the increase in force necessary?
because the wave is being transferred from the air in the outer ear to a more resistant fluid within the inner ear
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Cochlea
* Detects sound
- the wave in the inner ear moves through the scala vestibuli of the cochlea to the center of the spiral and then spirals back out along the scala tympani to the round window
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Hair Cells of Organ of Corti
- detect movement of vestibular membrane in and out caused by the alternating increase and decrease in pressure as the wave moves through the cochlea
- the movement is detected and transduced into neural signals, which are sent to the brain
- contain specialized microvilli called stereocilia
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Semicircular Canals
- inner ear
- responsible for balance
- detect orientation and movement of the head
- each canal contains fluid and hair cells
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Olfactory
sense of smell, involve chemoreceptors
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Gustatory
- sense of taste, involve chemoreceptors
- All taste combinations are a combination of these 4:
1. bitter
2. sour
3. salty
4. sweet
