Unit 2 Study Guide Flashcards
Two anatomic divisions of the nervous system
- central nervous system
- peripheral nervous system
central nervous system
- brain and spinal cord
peripheral nervous system
- includes nerves and ganglia
functional divisions of the peripheral nervous system
- sensory nervous system (afferent)
- motor nervous system (efferent)
- difficult because they sound the SAME
sensory nervous system
- responsible for receiving sensory information from receptors that detect stimuli and transmitting this information to the CNS
divisions of the sensory nervous system
- somatic sensory
- visceral sensory
somatic sensory
- sensory input that is consciously received
- receptors of the five senses and proprioreceptors
visceral sensory
- sensory input that is not consciously perceived
- structures within blood vessels and internal organs
motor nervous system
- initiated and transmits motor input from the CNS to effectors
divisions of the motor nervous system
- somatic motor
- autonomic motor
somatic motor
- initiates and transmits motor output from the CNS to skeletal muscles
autonomic motor
- innervates and regulates cardiac muscle, smooth muscle, and glands without our conscious control
- further divided into sympathetic and parasympathetic
5 characteristics of a neuron
- excitability - responsiveness to a stimulus
- conductivity - ability to propagate an electrical signal. voltage gated channels along membrane open sequentially
- secretion - release neurotransmitter in response to conductive activity. messenger is released from vesicle to influence target cell
- extreme longevity - cell can live throughout person’s lifetime
- amitotic - during fetal development of neurons, mitotic activity is lost in most neurons
SCALE
Cell body of the neuron
- called the soma
- enclosed by a plasma membrane and contains cytoplasm surrounding a nucleus
- serve as neuron’s control center
dendrites
- short, unmyelinated processes that branch off the cell body that receive input and transfer to cell body body for processing
axon
- longer process emanating from the cell body to make contact with other neurons, muscle cells, or gland cells
- attaches to the cell body at the axon hillock
axoplasm
- cytoplasm within the axon
axolemma
- membrane within axon
axon collaterals
side branches which lead to axon terminals with synaptic knobs
structure of a multipolar neuron
- multiple processes extend directly from the cell body
- typically many dendrites and one axon
- most common type of neuron
anterograde transport
- the movement of materials from the cell body to synaptic knobs
- usually newly synthesized materials
retrograde transport
- movement of materials from synaptic knobs to the cell body
- moves used material from axon for breakdown and recycling in soma
fast axonal transport
- movement along microtubules
- power for movement comes from specialized motor proteins that split ATP to supply energy needed
- can be moved in either direction
- anterograde transport of vesicles, organelles, and glycoproteins
- retrograde transport of used vesicles to be broken down and recycled, and potentially harmful agents.
slow axonal transport
- results from flow of axoplasm
- substances only moved from the cell body toward the synaptic knob
- includes enzymes, cytoskeletal components, and new axoplasm for regenerating axons
3 functional classification of neurons
- sensory
- motor
- interneurons
sensory neurons
responsible for conducting sensory input from both somatic and visceral sensory receptors to the CNS
motor neurons
conduct motor output from the CNS to both somatic effectors and visceral effectors
interneurons
- receive stimulation from many other neurons and receive, process, and store information, and “decide” how the body responds to stimuli.
- facilitate communication between sensory and motor neurons
pumps on plasma membrane of neuron
- maintain specific concentration gradients by moving substances against a concentration gradient, a process that requires energy
- plasma membrane contains Na+/K+ pumps (entire neuron) and Ca2+ pumps (transmissive segment)
leak channels on plasma membrane of neuron
- leak channels - always open allowing Na+ to diffuse in and K+ to diffuse out. More K+ leak channels than Na+ leak channels
- Na+ and K+ leak channels located throughout entire neuron plasma membrane.
- important in establishing/maintaining RMP.
chemically-gated channels on plasma membrane of neuron
- normally closed but open in response to binding of neurotransmitter.
- When they open, allow ions to diffuse across the plasma membrane.
voltage-gated channels on plasma membrane of neuron
- normally closed but open in response to changes in electric charge across the plasma membrane
- when they open, allow a specific ion to diffuse across the membrane
- voltage-gated Na+ channels are unique in that they have two gates (an activation gate and an inactivation gate)
four functional segments of the neuron
- receptive
- initial
- conductive
- transmissive
TRIC
receptive segment
- includes both dendrites and the cell body
- chemically gated channels are located here
initial segment
- composed of axon hillock
- contains both voltage gated Na+ and K+ channels
conductive segment
- equivalent to the length of the axon
- contains both voltage gated Na+ and K+ channels
transmissive segment
- includes the synaptic knobs and contains voltage gated Ca2+ channels and Ca2+ pumps
normal resting potential in a neuron
- when neuron at rest, the membrane potential is referred to as RMP
- typically -70 mV
how RMP is maintained and established
- consequence of movement of ions across the plasma membrane through leak channels
- K+ exit the neuron into IF. Leaves inside more negative
- Na+/K+ pumps move 3 Na+ out and 2 K+ into neuron
- help maintain concentration gradient of both Na+ and K+
- concentration gradient allows for diffusion of Na+/K+ as part of neuron’s generation of electrical current
Graded potential
- relatively small, short-lived changes in the RMP that are caused by the movement of small amounts of ion across the plasma membrane
- established in the receptive segments by the opening of chemically gated channels: cation channels, K+ channels, and Cl- channels.
- a graded potential lasts only as long as the channels are open and until the local current ceases.
EPSPs
-postsynaptic potentials that result in the neuron becoming more positive
how EPSPs are generated
- NT crosses synaptic cleft and binds specifically to a receptor that is a chemically gated cation channel, causing it to open
- Na+ and K+ move down concentration gradient, but more Na+ moves into the neuron than K+ moves out
- inside of neuron becomes slightly more positive
- local current of Na+ becomes weaker as it moves along neuron PM
- DEPOLARIZATION
IPSPs
postsynaptic potentials that result in the neuron becoming more negative
how IPSPs are generated
- NT crosses synaptic cleft and binds either to chemically gated K+ channel or Cl- channel
- if binds to K+ channel, channel opens and K+ flows out. If binds to Cl- channel, Cl- flows into neuron
- inside of neuron becomes slightly more negative
- local current of ions becomes weaker as it moves along neuron PM
- HYPERPOLARIZATION
summation
the changes in the membrane potential associated with graded postsynaptic potentials are added in the initial segment
temporal summation
occurs when a SINGLE presynaptic neuron repeatedly releases NT to produce multiple EPSPs in the postsynaptic neuron at the SAME location repeatedly within a very short time
spatial summation
occurs when MULTIPLE presynaptic neurons release NT at VARIOUS locations onto the receptive segment, thus generating EPSPs, IPSPs, or both in the postsynaptic neuron
significance of threshold membrane potential at the initial segment
- the minimal voltage change in membrane potential is the determining factor if an action potential is initiated
- on average, the value for the threshold membrane potential is about -55 mV. Change of +15 from RMP
- When this threshold is reached, the voltage-gated channels are stimulated to open, which will initiate the generation of an action potential that will be propagated along the axon
polarized phase of action potential
- the resting membrane potential
Depolarized phase of action potential
- Na+ flows into region from adjacent areas. Membrane potential becomes more positive.
- voltage-gated Na+ channels triggered to open when sufficient Na+ flows into region to change the membrane potential from -70 mV to -55 mV
- voltage-gated Na+ channels remain open to allow Na+ entry to cause depolarization.
Repolarized phase of action potential
- reaching of threshold value triggers voltage-gated K+ channels to open.
- slow to open and not completely open till about the point depolarization has ended
- voltage-gated K+ channels remain open to allow rapid K+ exit from the axon
- triggers the voltage-gated Na+ channels to change from the inactivation state to the resting state - now can be stimulated again
Hyperpolarized phase of action potential
- the voltage-gated K+ channels typically remain open longer than the time needed to reestablish the RMP.
- the inside of the neuron during this brief time is more negative than the RMP
refractory period
- the brief time period after an action potential has been initiated during which an axon is either incapable of generating another potential or a greater than normal amount of simulation is required to generate another action potential.
absolute refractory period
- the time after an action potential onset when no amount of stimulus, no matter how strong, can initiate a second action potential
- during this time, the voltage-gated Na+ channels are first opened, and then they are closed in the inactivation state (activation gate open, inactivation gate closed)
- generally remain in inactivation state until membrane potential has almost retuned to the RMP through depolarization
- ensures the action potential only moves in one direction
relative refractory period
- occurs immediately after the absolute refractory period
- another AP may now be initiated in an axon only if the stimulation of the PM is greater than the stimulus normally needed to generate an AP.
- at this time, voltage-gated Na+ channels have returned to their resting state, but the neuron is hyperpolarized
continuous conduction
- occurs in unmyelinated axons and involves sequential opening of voltage-gated Na+ channels and voltage-gated K+ channels located within the axon PM along entire length of axon
saltatory conduction
- occurs in myelinated axons
- APs do not occur in regions of the axon that are myelinated
- propagated only at neurofibril nodes which have a relatively large # of both voltage-gated Na+/K+ channels and lack myelin insulation
- ions are relatively free to flow into an out of the axon in these regions when channels are open.
neurofibral node
- initiation of AP
- Na+ into axon (conduction of AP)
- followed by repolarization as voltage-gated K+ channels open, and K+ diffuses out
myelinated regions
- diffusion through axoplasm
- relatively fast
- becomes weaker with distance as experiences resistance
- can’t go through myelin so flows in one direction
next neurofibral node
- arrival of weak Na+ current
- sufficient to cause opening of voltage-gated Na+ channels, new AP generated
Events of the transmissive segment
- release of NT from synaptic vesicles
- before AP arrives, Ca2+ pumps embedded in PM establish Ca2+ gradient by pumping Ca2+ into IF
- nerve signal reaches synaptic knob
- Voltage-gated Ca2+ channels open and Ca2+ enters synaptic knob and binds with proteins associated with synaptic vesicle
- synaptic vesicles fuse with synaptic knob PM and NT is exocytosed
- NT diffuse across synaptic cleft and attaches to receptor on a muscle or to receptors of a neuron or gland
graded potential
- occurs in receptive segment of neuron and are due to opening of CHEMICALLY-GATED channels.
- results in membrane potentials becoming depolarized or hyper polarized
- loses its intensity as it moves along the plasma membrane;
- short lived and travel short distances
THE CONNOR POTENTIAL
action potential
- generated within initial segment and propagated along conductive segment of neuron
- initiated when VOLTAGE-GATED channels open in response to a minimum voltage change
- AP is self-propagating and maintains intensity as it moves along axon to synaptic knob bc of successive opening of voltage-gated channels
THE JL POTENTIAL
synthesis of acetylcholine
- synthesized from acetate and choline and then stored within synaptic vesicles within synaptic knob of neuron.
- released by exocytosis into synaptic cleft in response to arrival of AP in presynaptic neuron
Acetylcholine effect on nicotinic receptor
- directly causes EPSP
acetylcholine effect on muscarinic receptor
- indirectly leads to either EPSP or IPSP
removal of acetylcholine
- some ACh will be immediately digested by acetylcholinesterase, an enzyme that resides in synaptic cleft
- digested into choline and acetate
- choline taken up into the neuron.
neuromodulation
- the release of chemicals from cells that locally regulate or alter the response of neurons to neurotransmitters
facilitation
- occurs where there is a greater response from a postsynaptic neuron because of the release of neurotransmitter in the synaptic cleft
- increase release from presynaptic or less reuptake/breakdown
- or increased number of receptors on postsynaptic neurons
inhibition
- occurs when there is less response from a postsynaptic neuron because of the release of neuromodulators
- results from either a decreased amount of NT in synaptic cleft
- decreased release from presynaptic or greater reuptake/breakdown
- or decreased number of receptors on postsynaptic neurons.
