Lecture 8 & 9 Flashcards
Central Nervous System
brain & spinal cord (acts as the integrating center)
Efferent Nervous System
transmits impulses from the CNS out to the peripheral organs to cause an effect or action. ?
Afferent Nervous System
transmits impulses from peripheral organs to the CNS. ?
Efferent Neurons
a peripheral neuron that carries signals from the CNS to the target cells
Autonomic Neurons
efferent neurons that control smooth muscle, cardiac muscle, many glands, & some adipose tissue
Somatic Motor Neurons
efferent neurons that control skeletal muscles
Parasympathetic
division of the autonomic nervous system that is responsible for day-to-day activities
Sympathetic
division of the autonomic nervous system that is responsible for fight-or-flight response
Tissue Response
The response of living tissues to altered conditions or types of restorative materials, metals or cements. ?
Enteric Nervous System
neurons in the wall of the gastrointestinal tract that are capable of sensing & integrating information & carrying out a response without input from the CNS
Sensory Signal
Sensory signals are converted to electrical signals via depolarization of sensory neuron membranes upon stimulus of the receptor, which causes opening of gated ion channels that cause the membrane potential to reach its threshold. ?
Sensory Receptor
- monitor external conditions
- the sensory receptors of a neural reflex are not protein receptors that bind to signal molecules, like involved in signal transduction
- there are many sensory receptors in the body, each located in the best position to monitor the variable it detected
- those involved in natural reflexes are divided into central receptors & peripheral receptors
Sensory Neurons
a neuron that transmits sensory information to the CNS
Afferent vs Efferent
Afferent Arrives, Efferent Exits.
Afferent neurons are neurons whose axons travel towards (or bringing information to) a central point, while an efferent neuron is a cell that sends an axon (or carries information) away from a central point.
Interneuron
a neuron that is completely contained within the CNS
Pseudounipolar neurons
have a single process called the axon
- during development, the dendrite fused with the axon
Bipolar neurons
have two relatively equal fibers (a single axon & single dendrite) extending off the central cell body
Multipolar CNS interneurons
are highly branched (many dendrites & branched axons) but lack long extensions
a typical multipolar efferent neuron has 5 to 7 dendrites, each branching 4 to 6 times
- a single long axon may branch several times & end at enlarged axon terminals
Dendrite
thin, branched processes that receive & transfer incoming information to an integrating region within the neuron
Cell Body
part of the cell that contains the nucleus & many organelles
Axon Hillock
region of the axon where it joins the cell body
- often contains the trigger zone
Trigger Zone
the region of the axon where graded potentials are integrated & an action potential begins if the signal is above threshold
Node of Ranvier
unmyelinated regions on myelinated axons
Myelin Sheath
form insultating segments along axons
- formed by concentric layers of glial cell membranes compacted together
Synaptic Cleft
the space b/t the pre- & postsynaptic cells
Presynaptic Terminal
neurotransmitters are packaged into synaptic vesicles. When an action potential opens presynaptic voltage-gated Ca2+ channels, the neurotransmitters are released by Ca2+-triggered synaptic vesicle exocytosis into the synaptic cleft, where they activate postsynaptic receptors. ?
Postsynaptic Cell
the cell that receives the signal
Synaptic Vesicles
small secretory vesicles that release neurotransmitter into the synapse
Axon
an extension of a neuron that carries signals to the target cell
Satellite Cells
a nonmyelinating Schwann cell
- trophic factors
- a type of glia in PNS
Schwann Cells
cell that forms myelin around a peripheral neuron axon
- AKA myelinate axons
- a type of glia in PNS
Oligodendrocytes
CNS glial cell that forms myelin around several axons
- myelinate axons
Astrocytes
glial cells in the CNS that contact both neurons & blood vessels
- blood brain barrier, trophic factors, take up excess water & K+, neural stem cells, pass lactate to neurons
Ependymal Cells
CNS glial cell that are specialized cells that create selectively permeable epithelial layer, the ependyma, that separates the fluid compartments of the CNS
- line “ventricles”, make neural stem cells
Microglia
macrophages in the CNS
- “immune cells” of CNS
Ion Channel
- may be specific for one ion or may allow ions of similar size & charge to pass
- other ion channels are Ca2+ channels & Cl- channels
- neurons contain a high density of ion channels
many types of ion channels, classified according to
- ions they carry
- where on the cell they are located
- gating mechanisms
Gating Mechanisms
- Voltage gated ion channel
- Receptor channels
- Phosphorylation gated
- Stretch gated
- Temperature gated
Ionic Movement causes changes in what
electrical signals??
Receptor Channels
(=ligand gated ion channel)
- gate when they bind a ligand (releases neurotransmitter, cGMP…from a presynaptic cell)
- an ion channel that is gonna open/close when it binds to a ligand
Voltage gated channel
- changes in membrane potential open the channel
- “threshold”
- opened & closed by changes in MP
Phosphorylation Gated Channel
- undergoes a small conformational change that can allow some of those channels to open/close
Stretch Activated Gated Channel
- opens & closes when the cell membrane is deformed
Temperature Gated Channel
- cell membrane will open & close depending on changes in specific temps
Graded Potential vs Action Potential (differentiate the two)
Graded Potentials:
- Signals communicated from one neuron to the next are graded potentials: POSTSYNAPTIC POTENTIALS
- Small, “SUBTHRESHOLD” changes in membrane potential
- Can be DEpolarizing or HYPERpolarizing
- PASSIVE (do NOT regenerate)
- Gradually DISSIPATE as they travel through a cell
- Proportional to the SIZE of the stimulus
- Caused by the FLOW OF IONS through a few ion channels
- Can be SUMMED
- Can be LONG-LASTING
Action Potentials:
- Wave of depolarization that ACTIVELY PROPAGATES across neuronal membrane (=REGENERATIVE, NOT PASSIVE)
- ALL or NONE
- FAST! Lasts only a few milliseconds
- Often called a SPIKE, or abbreviated AP
- LARGE AMPLITUDE, about 100 mV (from RMP to peak)
- ALWAYS DEpolarizing
- Requires the membrane be depolarized PAST a THRESHOLD
- There is a REFRACTORY PERIOD
- CANNOT be summed
- In neurons, SITE of AP generation is the AXON HILLOCK
Postsynaptic Potential
- when one neuron stimulates something to happen in a postsynaptic neuron or cell, but the change in MP is gonna be a postsynaptic potential
- a temporary change in the electric polarization of the membrane of a nerve cell (neuron). The result of chemical transmission of a nerve impulse at the synapse (neuronal junction), the postsynaptic potential can lead to the firing of a new impulse. ?
Signal Degradation
Degradation usually refers to reduction in quality of an analog or digital signal. When a signal is being transmitted or received, it undergoes changes which are undesirable. These changes are called degradation. ?
All or none
action potentials are uniform, all-or-none depolarizations that can travel undiminished over long distances
- they either occur as a maximal depolarization (if the stimulus reaches threshold) or do not occur at all (if the stimulus is below threshold)
Summation
is the process of adding things up. In the case of nervous system, it is about adding up the effect of multiple stimuli, that are all individually subthreshold, so that together they are suprathreshold and are able to generate an action potential (a response) ?
Activated State
Molecules must collide with sufficient energy, known as the activation energy, so that chemical bonds can break. Molecules must collide with the proper orientation. A collision that meets these two criteria, and that results in a chemical reaction, is known as a successful collision or an effective collision. ?
Closed State
channels are closed??
Open State
channels are open??
Inactivated State
Closed and inactivated states are ion impermeable. Before an action potential occurs, the axonal membrane is at its normal resting potential, about −70 mV in most human neurons, and Na+ channels are in their deactivated state, blocked on the extracellular side by their activation gates. ?
Absolute vs Relative Refractory
this delay, called the ABSOLUTE refractory period, represents the time required for the Na+ channel gates to reset to their resting position
- b/c of the absolute refractory period, a 2nd action potential CANNOT occur before the 1st has finished
- consequently, action potentials moving from trigger zone to axon terminal cannot overlap & cannot travel backwards
a RELATIVE refractory period follows the absolute refractory period
- during the relative refractory period, some but not all Na+ channel gates have reset to their original positions
- in addition, during the relative refractory period, K+ channels are still open
Rising Phase (of the Action Potential)
the rising phase is due to a sudden temporary increase in the cell’s permeability to Na+
- an action potential begins when a graded potential reaching the trigger zone depolarizes the membrane to threshold (-55mV)
- as the cell depolarizes, voltage-gated Na+ channels open, making the membrane much more permeable to Na+
- Na+ ions then flow into the cell, down their concentration gradient & attracted by the negative membrane potential inside the cell
- the strength of the electrochemical gradient is called the driving force for Na+ movement
Falling Phase (of the Action Potential)
the falling phase corresponds to increase in K+ permeability
- voltage-gated K+ channels, like Na+ channels, open in response to depolarization
- the K+ channel gates are much slower to open, however, & peak K+ permeability occurs later than peak Na+ permeability
- by the time the K+ channels finally open, the membrane potential of the cell has reached +30 mV b/c of Na+ influx through faster-opening Na+ channels
Recovery Phase (of the Action Potential)
This phase is the repolarization phase, whose purpose is to restore the resting membrane potential. Repolarization always leads first to hyperpolarization, a state in which the membrane potential is more negative than the default membrane potential. ?
Fugu Poison
fugu poison, or tetrodotoxin (TTX) comes from pufferfish & several other species of animals
fugu is a very specific antagonist of voltage gated Na+ channels
- high affinity, high specificity
- high efficacy, high potency
prevents entry of Na+ into cells
prevents action potentials in neurons & muscle
lidocaine, benzocaine & other anesthetics also block VG Na+ channels
Antagonist
competing ligands that bind & block receptor activity are called antagonists of the primary ligand
Agonist
a competing ligand that binds & elicits a response is known as an agonist of the primary ligand
Localization of Ion Channels
making the ion channels local???
Demyelination
occurs when myelin, which is the protective coating of nerve cells, experiences damage. When this happens, neurological problems can occur. It can result from various medical conditions, including multiple sclerosis (MS). (demyelination of CNS axons for MS)?
Autoimmune
happens when the body’s natural defense system can’t tell the difference between your own cells and foreign cells, causing the body to mistakenly attack normal cells.
- ex: multiple sclerosis
Genetic vs Environmental
Modern genetics study defines environment as every influence other than genetic—such as air, water, diet, radiation, and exposure to infection—and it subscribes to the overarching assumption that every trait of every organism is the product of some set of interactions between genes and the environment. ?
Acute vs Chronic
Acute conditions are severe and sudden in onset. This could describe anything from a broken bone to an asthma attack. A chronic condition, by contrast is a long-developing syndrome, such as osteoporosis or asthma. ?
Squid Giant Axon
is the very large axon that controls part of the water jet propulsion system in squid. ?
Information Processing Ability
is how individuals perceive, analyze, manipulate, use, and remember information. ?
Hyperkalemia
an increase in blood K+ concentration shifts the RMP of a neuron closer to threshold & causes the cells to fire action potentials in response to smaller graded potentials
Hypokalemia
if blood K+ concentration falls too low - the RMP of the cells hyperpolarizes, moving father from threshold
Salutatory
the apparent leap-frogging of the action potential down myelinated axons
Anaxonic CNS Interneurons
have no apparent axon, but have numerous branched dendrites
