bio 2 2nd exam review chapter 44

animal phyla without network of nerve cells for gathering information

sponges

includes the brain and the spinal cord
90% glial cells (support)
10% neurons (excitable cells that communicate via electrical and chemical messengers)
**only 2% of brain is neurons**

the brain and spinal cord

glial cells is for support
neurons are excitable cells that can communicate via electrical and chemical messengers

everything outside the CNS
includes the:
-somatic nervous system
(voluntary; controls skeletal muscle)
-autonomic nervous system (involuntary; regulates activity in smooth muscle, cardiac muscle, and glands of the body)

everything outside the PNS
the somatic and the autononmic

-the somatic nervous system ( voluntary; controls skeletal muscle)
-the autonomic nervous system (involuntary; regulates activity in smooth muscle, cardiac muscle, and glands of the body )

produces electrical signals (electrical differences across a neuronal membrane measured as millivolts) that are nerve impulses

plasma membrane of neurons

transmit information from perifery to CNS; sensory neurons
**approaching (CNS): afferent

transmit information from CNS to periphery effectors (muscles and glands)
**exiting (CNS): efferent

**approaching (CNS): afferent
**exiting (CNS): efferent

association neurons
-found only in CNS as complex interconnections between one neuron and another
**complex reflexes, learning, and memory**

found only in the CNS as complex interconnections between one neuron to anther

electrical signal travels from sensory neuron to interneuron in the CNS to motor neuron (no direct brain activity)

functional unit of the nervous system

can produce electrical signals and action potentials where inside of a cell becomes positively charged relative to outside of the cell

made up of:
-dendrites (cytoplasmic portion that recieves incoming information)
-soma (cell body that contains nucleus and most organelles)
-axon (long cellular extension which transmits action potentials/ nerve impulses; axon hillock is closet to the cell body and is responsible for generating action potential)

the "electricochemical gradient" that determines how a charged ion will move through a permeable membrane depends on the combined effects of electrical forces and concentration differences across the membrane

dendrite
soma
axon

dendrite-(cytoplasmic portion that receives incoming information)
soma-(cell body that contains nucleus and most organelles)
axon-(long cellular extension which transmits action potentials/nerve impulses; axon hillock is closest to the cell body and is responsible for generating action potential)

in the axon

support cells and make up 90% of the nervous system

include:
-oligodendrocyte (produce myelin in the CNS)
-Schwann cells (produce myelin in the PNS)
-others include:
-astrocytes (metabolic
support)
-stem cells
-microglia (phagocytic
removal cellular debris)

-oligodendrocyte (produce myelin in CNS)
-Schwann cells (produce myelin in PNS)

myelinated axons in the CNS

dendrites/cell bodies in CNS

white matter- myelinated axons in the CNS
gray matter - dendrites/cell bodies in the CNS

bundled myelinated axons in the PNS

bundled myelinated axons in the PNS

layers of plasma membrane from oligodendrocytes (CNS) and schwann cells (PNS) that form insulation around the axons of neurons thereby reducing a membrane's ion permeability and increasing the speed of action potential
***in an unmyelinated axon conduction velocity is primarily determined by diameter of the axon***

layers of plasma membrane from oligodendrocytes and schwann cells that form insulation around the axons of neurons thereby reducing a membranes ion permeability and increasing the speed of action potential generation

action potential conduction that occurs in myelinated axons where the action potential jump from Node of Ranvier (gap pf exposed axon in the myelin sheath) to Node.

Thus in myelinated axons, action potentials do not propagate continuously as waves, but instead recur at successive nodes, and in effect "hop" along the axon, by which process they travel faster than they would otherwise

action potential conduction that occurs in mylinated axons where the action potential jumps from one node to the other

a potential difference (electrical in nature measured in millivolts) exists across cell's plasma membrane even if the nerves are not producing electrical responses

- factors that influence this are concentration of:
-intracellular anions (e.g., proteins)
-sodium (Na+)
-potassium (K+)
AND the presence of:
-sodium and potassium gated channels
-potassium (K+) leakage channels
-sodium/potassium pump (2 K+ into cell and 3 Na+ out of cell)

- electrochemical forces are acting for sodium ions to move into the cell and potassium ions to move out of the cell (resting membrane is more permeable to potassium than to sodium, so it moves out of cell due to electrochemical gradient);

- when neuron is not being stimulated, inside of the cell is more negative than the outside of the cell primarily because of passive leakage of K+ ions across the membrane and it averages as -70mV (millivolts)

when the neuron is not sending a signal.
separation of potassium ions from intracellular, relatively immobile anions across the membrane of the cell. Because the membrane permeability for potassium is much higher than that for other ions (disregarding voltage-gated channels at this stage), and because of the strong chemical gradient for potassium, potassium ions flow from the cytosol into the extracellular space carrying out positive charge, until their movement is balanced by build-up of negative charge on the inner surface of the membrane. Again, because of the high relative permeability for potassium, the resulting membrane potential is almost always close to the potassium reversal potential. But in order for this process to occur, a concentration gradient of potassium ions must first be set up. This work is done by the ion pumps/transporters and/or exchangers and generally is powered by ATP.

Consider: 3 factors contributing to resting potential:

1. Na+/K+ -ATPase (sodium-potassium pump
-- Transports 3 Na+ out for every 2 K+ moved in

2. Ion specific channels allow passive movement of ions
--K+ channels open more frequently at resting potential
--Membrane more permeable to K+

3. Negatively charged molecules such as proteins more abundant inside cell

open potassium channels

the concentration of K+ ions is higher in the cell, but the diffusion force driving K+ ions out of the cell is balanced by an electrical force keeping K+ from leaving the cell

Protiens: the interior of the neuron contains high concentration of large, negatively charged protiens.

-- Transports 3 Na+ out for every 2 K+ moved in

when neuron is not being stimulated, inside of the cell is more negative than the outside of the cell primarily because of passive leakage of K+ ions across the membrane and it averages as -70mV (millivolts)

determines how a charged ion will move through a permeable membrane depends on the combined effects of electrical forces and concentration differences across the membrane

The rapid inward diffusion of Na+ followed by the outward diffusion of K+ producing a rapid change in the membrane potential towards the positive direction and exceeding threshold

action potentials are regenerated along an axon as one action potential serves as the depolarization stimulus for the next action potential

The rapid inward diffusion of Na+ followed by the outward diffusion of K+ producing a rapid change in the membrane potential towards the positive direction and exceeding threshold

The action potential is then propagated along the length of the axon, ultimately reaching the synaptic terminals. The action potential begins with the opening of voltage-regulated sodium ion channels at one site. The movement of sodium ions into the cell depolarizes adjacent sites, triggering the opening of additional voltage-regulated channels. The result is a chain reaction that spreads across the membrane surface like a line of falling dominoes.

in an excitable cell, the critical value (between -70mV and -55mV) of the membrane potential to which the cell (axon hillock) must depolarized in order to trigger an action potential; this follows the "all-or-none" law

Consider: Positive feedback occurs as the neuron is being depolarized and passes the threshold potential.

Once the neuron has been sufficiently excited above some threshold (typically -55mV), the cell fires, or sends an action potential down its axon to its terminal button.

cell membrane less polarized, less negative relative to surrounding solution, due to increasing the flow of Na+ ions into a neuron at rest

Both opening of the K+ channel gate and closing of the Na+ channel inactivation gate stops the rapid depolarization that occurs as the "upsweep" of membrane potential peaks during the action potential.

Consider: The K+ channel activation gate responds slightly more slowly to depolarization than the Na+ channel activation gate to prevent canceling out each other's effects on membrane potential changes.

period following an action potential during which a neuron cannot be stimulated to generate another action potential
***ensures action potential does not move backward***

period following an action potential during which a neuron cannot be stimulated to generate another action potential

-voltage gated - open close in response to voltage changes
-ligand-gated - open and close in response to ligands or chemicals

ligand gated channels (ionotropic receptor):
located on a different portion of the protein (an allosteric binding site)
voltage gated channels:
Found along the axon and at the synapse, voltage-gated ion channels directionally propagate electrical signals.

a neuron undergoes a change in membrane potential that is proportional to (i.e., varies depending on) the strength of the stimulus given to that neuron
*** important for conveying stimulus intensity in sensory neurons***

graded potential- a neuron undergoes a change in membrane potential that is proportional to (i.e., varies depending on) the strength of the stimulus given to that neuron
neurons that have an important role- important for conveying stimulus intensity in sensory neurons

varies based on axon diameter and/or myelination

functional association (junction) of a neuron with another neuron or effector organ ( muscle or gland)
-can be electrical or chemical
-synaptic cleft is small gap between two successive neurons or between a neuron and an effector

The synapse is a small gap separating neurons.
do:Information from one neuron flows to another neuron across a synapse.

message (ions) travel between cells via gap junction proteins; communication is bi-directional; synapses can be gated; does not utilize neurotransmitters

-makes up most synapses in nervous system
-communication is slower than electrical
-utilizes neurotransmitters
-boundaries are the presynaptic neuron that releases neurotransmitters (chemicals stored in synaptic vesicles which when released via exocytosis must diffuse across the synaptic cleft and by binding to postsynaptic receptors (chemically regulated gates and ligand regulated gates), regenerate the action potential) and the postsynaptic neuron, which contains receptors
-most neurotransmitters are synthesized in cytosol

electrical:An electrical synapse is a mechanical and electrically conductive link between two abutting neuron cells that is formed at a narrow gap between the pre- and postsynaptic cells known as a gap junction. Each gap junction contains numerous gap junction channels which cross the membranes of both cells.when the voltage of one cell changes, ions may move through from one cell to the next, carrying positive charge with them and depolarizing the postsynaptic cell.
chemical:The space between a chemical syapse is much larger than an electrical synapse.
The release of a neurotransmitter is triggered by the arrival of a nerve impulse (or action potential) and occurs through an unusually rapid process of cellular secretion, also known as exocytosis.The arriving action potential produces an influx of calcium ions through voltage-dependent, calcium-selective ion channels. Calcium ions then trigger a biochemical cascade which results in vesicles fusing with the presynaptic-membrane and releasing their contents to the synaptic cleft.

An electrical synapse is faster than a chemical synapse

chemical synapases are far more common.

junction where nerve terminal meets a neuron, muscle cell, or gland and into which neurotransmitters are released

triggered by voltage-gated Calcium channels (these channels open in response to arrival of action potential at the axon terminal, allowing influx of calcium ions that cause fusion of neurotransmitter containing vesicles to membrane and exocytosis of neurotransmitter)-voltage gated channels allow axon and axon terminal function
- neurotransmitter diffuses across cleft to interact with receptors on ligand gated channels, triggering depolarization of post synaptic membrane

calcium ions that cause fusion of neurotransmitter containing vesicles to membrane and exocytosis of neurotransmitter

Neurotransmitter diffuses across the synaptic cleft to bind to the receptor on the muscle or next nerve.

It is then broken down and absorbed back into the nerve.

-Excitatory postsynaptic potential (EPSP):
*Brings membrane closer
to threshold potential
-Inhibitory postsynaptic
potential (IPSP)
*Takes membrane farther
from threshold potential
(hyperpolarization)

refers to the summing of excitatory (EPSP) or inhibitory (IPSP) influences in a postsynaptic neuron

-Action potentials are generated in the neuron -stimulation of the entry of Ca2+ into the neuron
-release of acetylcholine into the synapse
-muscle fiber membrane is depolarized

diffusion out of cleft
-degradation by enzymes (such as acetylcholinesterase)
-active reuptake across the presynaptic membrane (after which they can be reused)
-binding to the receptor (concentration of neurotransmitter primarily determines binding)

After the message has been sent, the neurotransmitter is released from the receptor back into the synapse where one of two things occurs: either another chemical agent, an enzyme, goes to work on the neurotransmitter and dissolves it, or the neuron re-absorbs it for later use.

released by cholinergic synapse in somatic motor neurons

found in PNS & CNS
**most abundant neurotransmitter in PNS and is always an excitatory neurotransmitter

excess degraded by acetylcholinesterase into acetate and choline (which is transported back into the axon terminal to be resynthesized into active neurotransmitter)

by blocking dopamine reuptake from synapses causing disruption of neural signaling and producing profound changes in mood and behavior

B. The neuron will exhibit a slow hyperpolarization even before the stimulus is applied.

E. along myelinated axons.

A. gap junctions

D. The neuron would become hyperpolarized.

E. presynaptic membrane.