Unit 2: Nerve Impulses & Neural Communication Flashcards
1
Q
two divisions of the nervous system
A
1) central nervous system (CNS)
2) peripheral nervous system (PNS)
2
Q
role of central nervous system
A
- consists of the spinal cord and the brain
- receives and processes information from internal and external environment
- integrates this information to illicit appropriate responses in the body to maintain homeostasis
3
Q
role of peripheral nervous system
A
- includes all neural tissue outside the CNS
- provides communication between the CNS and the rest of the body
- has two divisions: afferent and efferent neurons
4
Q
role of afferent neurons
A
transmits sensory and visceral information from organs and sends it to the CNS
5
Q
role of efferent neurons
A
transmit information from the CNS to the organs in the PNS
6
Q
what are neurons?
A
cells that rapidly send and receive electrical signals
7
Q
branches of the efferent division
A
- somatic nervous system = consist of motor neurons to help with movement
- autonomic nervous system = regulate function of internal organs
8
Q
role of somatic nervous system (SNS)
A
- voluntary control of muscles
- innervate skeletal muscles (i.e leg)
9
Q
role of autonomic nervous system (ANS)
A
- regulates involuntary visceral processes like heart rate, blood pressure, respiration, digestion
- innervate all other peripheral effectors (smooth muscle, cardiac muscle, glands, adipose tissue)
10
Q
divisions of autonomic nervous system
A
1) parasympathetic = “rest and digest”
2) sympathetic = “fight or flight”
11
Q
types of cells in the nervous system
A
1) neurons = excitable cells
2) glial cells = support cells
12
Q
3 main parts of a neuron
A
1) cell body (soma) = contains the nucleus and most organelles
2) dendrites = receive incoming signals at synapses
3) axon = sends outgoing information
13
Q
structure of a cell body
A
- contains a nucleus and other organelles
- essential to the well-being of the neuron
- the position varies in different type of neurons
14
Q
structure of a dendrite
A
- thin, branched processes with smaller branches off them
- increase the surface area of the neuron
- allow communication with multiple other neurons
15
Q
structure of an axon
A
- originates from an axon hillock of cell body
- varies in length
- transmit electrical signals (action potentials) from cell body to axon terminal
16
Q
axon hillock
A
- where an axon originates
- where action potentials are initiated
17
Q
axon terminal
A
- the region where neurotransmitters are released from after signal reaches it
- makes a synaptic contact with another cell
- contains mitochondria
18
Q
what is an action potential?
A
- when a change in a membrane potential occurs, and the inside of the cell is positive compared to the outside
- allows information to be transmitted over long distances in axons
19
Q
what is a synapse?
A
the site of communication between two neurons or between a neuron and an effector organ
–> axon terminal meets target cell
20
Q
2 types of transportation in neurons
A
- anterograde transport = cell body to axon terminal
- retrograde transport = axon terminal to cell body
21
Q
what is axonal transport?
A
- two types: (1) slow axonal transport and (2) fast axonal transport
- a mechanism for moving products between cell body and the axonal terminal of neurons
- slow axonal transport is used for small soluble molecules in cytosol
- fast axonal transport is used for movement of vesicles using microtubule tracks
22
Q
two ways to classify neurons
A
1) structural classification
2) functional classification
23
Q
structural classification of neurons
A
- based on the number of processes (axons and dendrites) that project from the cell body
- 4 classes: multipolar, bipolar, pseudounipolar, anaxonic
24
Q
functional classification of neurons
A
- based on the direction of the information
- 3 classes: afferent, interneurons, efferent
25
structural characteristics of multipolar neurons
- many processes
- highly branched (5-7 dendrites) + 1 axon
- lack long extensions
- must abundant neuron
26
structural characteristics of bipolar neurons
- 2 approximately equal projections from cell body
- single axon + single dendrite that branch off the cell body
27
structural characteristics of pseudounipolar neurons
- cell body is attached to a single axon
- the dendrites are fused to the axon and appear as a single projection
- most abundant afferent neuron
28
structural characteristics of anaxonic neurons
- lacks an axon
- has numerous dendrites projecting from it
- functions has an interneuron in the CNS
29
what are interneurons and their role?
- intermediate neurons between sensory (afferent) and motor (efferent) neurons
- enables communication between sensory or motor neurons and the central nervous system
- has very complex branching (are anaxonic)
30
types of sensory (afferent) neurons
1) interoceptors
2) exteroceptors
3) proprioceptors
31
role of interoceptors
- monitor internal systems (digestive, respiratory, reproductive etc.)
- internal senses (taste, pain etc)
32
role of exteroreceptors
- monitor exernal environment
- external senses (touch, temperature, pressure etc.)
- distance senses (sight, smell, hearing)
33
role of proprioceptors
- relay information where our limbs are to allow for coordinated movements
- monitor position and movement of skeletal muscles and joints
34
role of glial cells
- provide strucural integrity to thte nervous system ("the glue")
- preserve physical + biochemical structure for neurons to carry out function
- essential for survival and function of neurons
35
5 types of glial cells
- ependymal
- microglia
- astrocytes
- oligodendrocytes
- schwann cells
36
characteristics and role of ependymal cells
- highly branched processes that have cilia or micro cilia
- form the epithelium called ependyma
- they line the spinal cord and ventricles of the brain and contribute to the production of cerebrospinal fluid (CSF)
37
characteristics and role of microglia
- have many fine-branched processes ("thorny") that monitor and protect neurons
- transform into phagocytic macrophages to internalize and destroy neuronal debris, waste products, pathogens in brain
38
characteristics and role of astrocytes
- large star-shaped cells with many projections
- participate in the blood-brain barrier to regulate what neurons are exposed to from the blood stream
- provides physical support (act as bars)
- highly metabolically active and provide substrates for ATP production
- repair damaged neural tissue
- control interstitial environment
39
characteristics and role of oligodendrocytes
- small cell bodies with few processes
- projections contact several axons of other neurons
- act to insulate axons by wrapping their cell processes tightly around them = form myelin sheath
40
characteristics and role of schwann cells
- insulate axons by forming myelin sheath
- many individual cells (not just one large piece)
- leave tiny unmyelinated gaps between cells called "nodes of Ranvier"
41
what is the blood brain barrier?
- is at the cellular level
- projections from astrocytes protect capillaries from allowing substances from entering
42
importance of myelin sheath
- rolled up plasma membrane surrounding axons
- form an insulating layer that prevents leakage of electrical current
- helps increase speed and efficiency of action potentials in an axon
43
internodes
myelinated segments of axons
44
nodes of ranvier
- gaps between internodes
- where axons may branch
- unmyelinated
45
two factors influencing membrane potential
1) uneven distribition of ions across cell membrane (more potassium leak channels than sodium leak channels)
2) different membrane permeability to those ions (K+ > Na+)
46
three requirements for establishing membrane potential
1) ICF and ECF must differ significantly in ionic concentration
--> ECF = more Na+
--> ICF = more K+
2) selectively permeable through channels
--> more permeable to K+ because there is more leak channels
3) the cells passive and active transport ensure an unequal distribution of charges across its membrane
47
how does membrane potential develop?
- the plasma membrane is more permeable to K+ than Na+
- K+ in the ICF wants to flow out (high to low), and does so faster than Na+ from the ECF flows in
- the outward movement of K+ exceeds the inward movement of Na+ which causes the cell to become more negative (because +ve charge leaves)
- the difference in charge across the membrane results in the membrane potential
48
what is resting membrane potential?
- is -70mV (inside relative to outside)
- occurs when K+ outflow slows down and Na+ inward flow speeds up, and eventually causes the membrane potential to stabilize
- this happens because an electrical force is created when the membrane potential becomes negative inside the cell, and attracts the Na+ positive ions (located in ECF) into the cell faster than K+ move out due to concentration gradient
- eventually, the movement of sodium into the cell is equal and opposite to the movement of potassium out of the cell, and reaches a steady state
49
what does resting membrane potential depend on?
1) ratio of concentrations of K+ and Na+ on either side of the membrane (concentration gradients)
2) specific membrane permeability to each ion through the membrane
50
passive forces acting across the membrane
- chemical gradients = concentration gradients of Na+ and K+
- electrical gradients = separate charges of +ve and -ive ions resulting in potential difference across the membrane
51
what is equilibrium potential?
the transmembrane potential when there is no net movement of an ion across the cell membrane
52
active forces acting across the cell membrane
- sodium/potassium ATPase (pump)
--> active transport using ATP helps ensure the resting potential is maintained
--> the goal is to maintain a steep gradient for Na+ and K+
--> balances passive forces of diffusion
--> moves 3 Na+ out and 2 K+ in
53
what is a graded potential?
- small electrical impulses that helps communicate over short distances
- a result of small changes in membrane potential that occur when ion channels open or close in response to a stimulus
- magnitude depends on strength of stimulus (not all or nothing)
54
definitions to describe the changes in membrane potential
hyperpolarization = K+ channels open and potassium moves out of the cell, making the membrane potential more negative
depolarization = Na+ channels open and sodium moves into the cell, making the membrane potential more positive
55
what is hyperpolarization?
when the membrane becomes more polarized, and changes to a more negative value than -70mV
56
depolarization
when the membrane becomes less polarized and changes to change to a less negative or to a positive potential
57
repolarization
occurs when the membrane potential returns to the resting membrane potential following a depolarization
58
2 ways cells communicate
- graded potentials
- action potentials
59
graded vs action potentials
graded = small electrical signals that act over short ranges because they diminish in size with distance
action = large signals capable of traveling long distances without decreasing in size.
60
what is a subthreshold graded potential?
- a graded potential starts above the threshold (T) at its initiation point but decreases in strength as it travels through the cell body
- at the trigger zone, it is below threshold and doesn't produce an action potential
61
what is a suprathreshold graded potential?
- a stronger stimulus on the cell body creates a graded potential above the threshold (T) by the time it reaches its initiation point
- an action potential results
62
what is the significance of graded potentials?
- they determine whether a cell will generate an action potential
- graded potentials generate action potentials if they depolarize a neuron to the threshold (a value of membrane potential that must be met or exceeded if an action potential is to be generated)
63
3 stages of an action potential
1) rapid depolarization
- the membrane potential changes from -70mV to +30mV due to sudden permeability to sodium into the cell
2) repolarization
- membrane potential returns from +30mV back to resting levels (-)70mV
- the sodium permeability decreases rapidly and potassium permeability increases
3) after-hyperpolarization
- potassium permeability remains elevated for a brief time after the membrane potential reaches the resting membrane potential
- during this time, the membrane potential becomes even more negative
64
what does propogation of action potential mean?
the movement of an action potential along the entire length of an axon
65
propagation of an action potential
1) an initial stimulus (could be heat, pressure etc.) that triggers the nerve impulse.
2) if the initial stimulus is strong enough, a graded depolarization of axon hillock occurs which is large enough to change resting potential from -70mV to -55mV. this causes the cell to meet a critical level (-55mV) which opens gated sodium ion channels.
3) the sodium ions rush into the cell and causes an increase in the membrane potential (more positive)
4.) the change in charge (the electrical current) travels down the axon which connects the graded potential with the synaptic axon terminal, where it can communicate with the next nerve cell.
5.) causes the nerve cell to be "excited" and prepared to pass the message
66
types of gates in Na+ channels
1) activation gate: opening of sodium channel during the depolarization phase of an action potential
2) inactivation gate: closing of sodium channels during the repolarization phase of an action potential.
67
how do voltage gated Na+ channels work?
- at resting membrane potential (-70mV), the activation gate closes the channel
- the activation gate opens by a depolarizing stimulus arriving at the channel
- when the gate opens, Na+ enters the cell and causes depolarization (+30mV)
- the inactivation gate closes and prevents further entry of Na+ into the cell.
- Potassium channels open and K+ leaves the cell causing repolarization, and the the activation and inactivation gate reset to their original position
68
how do voltage-gated K+ channels work?
- at resting membrane potential (-70mV), the K+ channels are closed. they remain closed until depolarization occurs due to the influx of Na+ ions into the cell.
- as the membrane potential becomes more positive during depolarization, voltage-gated K+ channels open and allow K+ ions to move out of the cell.
- the outward flow of K+ ions repolarizes the membrane, bringing it back to a negative potential and restore it to resting potential
- once the membrane potential returns to rest, the voltage-gated K+ channels close and prevents further outward flow of potassium ions
69
all-or-none action potential principle
if a stimulus exceeds threshold amount...
--> the action potential is the same regardless of how large the stimulus from graded potential is
--> the strength of graded potential initiating AP has no influence on amplitude of AP
--> if the membrane is not depolarized to threshold, no action potential occurs
*the key is that an action potential is either triggered or not*
70
what is the absolute refractory period?
- occurs during the depolarization + repolarization phase of an action potential
- ensures that a a second action potential cannot be generated in response to a second stimulus
- it is caused by the voltage gated sodium channels being inactivated
71
what is relative refractory period?
- occurs during the hyper-polarization phase of an action potential
- a second action potential could be initiated, but requires a large stimulus than before
- occurs when potassium channels open and there is outward diffusion of K+
72
two methods of propagating an action potential
1) continuous propagation: in unmyelinated axons
2) saltatory propagation: in myelinated axons
73
what is continuous propagation?
- after an action potential fires, the Na+ influx causes depolarization (+) of an adjacent region of the axon = a new action potential to occur
- the process repeats along the axon and the action potential amplitude is the same
74
steps to continuous propogation of an action potential
1) a graded potential above threshold reaches the trigger zone
2) voltage gated Na+ channels open and they enter the axon
3) the positive charge flows into adjacent sections of the axon via local current flow
4) local current flow from the active region causes new section of the membrane to depolarize (become more positive)
5) the refractory period prevents backward conduction. K+ leaves the cytoplasm of the cell an repolarizes the membrane (more negative)
this process continues over and over again until the action potential is produced at the axon terminal
75
what factors affect action potential speed?
- diameter of the axon (larger = faster)
- resistance to ion leakage (leak resistant = faster)
- myelination (limit contact with ECF, less chance of leakage)
76
what is saltatory propagation?
- action potentials occur at node of Ranvier (has voltage gated channels) and leap to adjacent nodes until reaching the axon terminal.
- works similarly to continuous propagation
--> this is due to myelin sheath preventing Na+ and K+ from going in/out of the cell due to high resistance
77
what is faster: saltatory or continuous propogation
saltatory propagation is faster
--> thick myelinated axons is better than thin, unmyelinated axon
78
presynaptic cell
a neuron that sends a message
79
postsynaptic cell
a cell that receives a message
80
synaptic cleft
a small gaps that separates the presynaptic membrane and the postsynaptic membrane
81
what is an electrical synapse?
- when an electrical signal is passed directly from the cytoplasm of one cell to the cytoplasm of another via gap junctions
- can occur between neurons or neurons and glial cells
- can be excitatory (increase activity) or inhibitory (decrease activity)
82
how does an electrical synapses take place?
- the cells are physically connected by a gap junction (often bidirectional)
- when an electrical signal occurs in one cell, it can be passed to the other via ions rapidly passing between cells
83
what is chemical synapses?
- a signal is transmitted across a gap by chemical neurotransmitters
- the cells are not in direct contact
- most neurons use chemical synapses
84
how does chemical synapses work?
- a neuron secretes a neurotransmitter into the ECF in response to an action potential arriving at its axon terminal
- the neurotransmitter binds to receptors on the plasma membrane of a second cell
- this triggers an electrical signal that may/may not initiate an action potential in the second cell
85
what does chemical synapses depend on?
- type and amount of neurotransmitter released
- the sensitivity of the post-synaptic cell (receiving the signal)
86
what are the steps to chemical synapses occurring?
1) an action potential arrives at the end of the axon terminal
2) voltage gated Ca2+ channels open and move into the presynaptic cell
3) the influx of Ca2+ signals the synaptic vesicles to move to the presynaptic membrane and fuse (exocytosis)
4) once the vesicle fuses, they release their contents (the neurotransmitter)
5) the neurotransmitters diffuses across the cleft and bind to the receptors on the post-synaptic neuron membrane
5) a response is generated
87
what do neurotransmitters do after being released for chemical synapses?
- after being released the neurotransmitter cannot remain in the synaptic cleft
- so enzymes degrade them and terminate the signal
- some neurotransmitters are actively transported back into the presynaptic cell (usually are broken down and recycled)
88
types of signal transduction at chemical synapses
1) fast response = ionotropic receptor
2) slow response = metabotropic receptor (direct coupling or linked with a second messenger)
89
what is a ionotropic receptor?
- a ligand-gated channel
- allows for a fast response/ signal transduction in chemical synapses
90
how does an ionotropic channel work?
-a neurotransmitter binds to the channel in the synaptic clef and allows specific ions to permiate the plasma membrane
- causes a change in electrical properties of the post-synaptic neuron
91
what is a metobotropic receptor?
- a protein linked receptor
- using a coupling mechanism with an ion channel
- slower response/signal transduction in chemical synapses
92
how does a metobotropic receptor work?
- a neurotransmitter binds to the receptor which activates a G protein
--> in direct coupling, the G protein opens or closes an ion channel
--> in a second messenger system, the G protein activates or inhibits an enzyme that produces a second messenger, which either opens or closes the ion channel
93
5 major classes of neurotransmitters
- acetylcholine
- biogenic amines
- amino acids
- purines
- neuropeptides
94
what is acetylcholine?
- a neurotransmitter that is is released from neurons in both CNS and PNS
- synthesized in the cytosol of axon terminals (acetyl CoA + Choline)
95
what is cholinergic synapses?
- is any synapse that releases ACh (acetylcoholine)
- these synapses can be found in skeletal muscles, CNS, PNS, ANS
96
types of acetylcholine receptors
1) nicotinic cholinergic receptors
2) muscarinic cholinergic receptors
97
what is a nicotinic ACh receptor?
- requires a ligand-gated channel (ionotropic)
- an excitatory postsynaptic potential (EPSP)
98
what is an muscarinic ACh receptor?
- requires a G protein operated channel (metabotropic)
- an inhibitory post synaptic potential (IPSP)
99
what is acetylcholinesterase (AChE)?
- an enzyme that breaks down acetylcholine (ACh) into acetate and choline
- choline can be reabsorbed into presynaptic terminal to be resynthesizes into ACh for further release at different time
100
steps to synthesis and recycling of acetylcholine
- acetylcholine (ACh) is made from choline and Acetyl CoA
- in the synaptic clef, ACh is rapidly broken down by the enzyme acetylcholinesterase
- choline is transported back to the axon terminal via cotransport with Na+
- recycled choline is used to make more ACh
101
what are biogenic amines?
- neurotransmitters derived from amino acids
- there are 3 catacholamines = dopamine, norepinephrine, epinephrine
- and then serotonin and histamine
102
where are biogenic amines released?
dopamine, serotonin, histamine = CNS
epinephrine = adrenal medulla in CNS
norepinephrine = PNS
103
what are amino acid neurotransmitters?
- the main inhibitory and excitatory messengers in the nervous system (CNS)
--> excitatory = aspartate, glutamate
--> inhibitory = glycine, GABA
104
what do excitatory and inhibitory synapse depend on?
- type of neurotransmitter
- type of receptor
105
excitatory synapse vs inhibitory synpase
excitatory = brings membrane potential closer to AP threshold
inhibitory = takes membrane potential away from AP threshold
106
what is summation?
- the additive effects of graded potentials (IPSP and EPSP) to see if it reaches threshold (-55mV) to produce an action potential
107
two types of summation
1) temporal = one presynaptic neuron releases a neurotransmitter many times over a period which may exceed the threshold value of post synaptic neuron
2) spatial = multiple presynaptic neurons together release enough neurotransmitter to exceed threshold of postsynaptic neuron
108
what is frequency coding? what does this mean?
- as the intensity of a stimulus increase, the frequency/rate of action potential increases
--> more action potentials result in moire neurotransmitter being released = greater IPSP or EPSP in next neuron
109
what is neural integration?
one simple rule
--> an action potential is triggered if the membrane potential at the axon hillock is depolarized (more positive) to threshold
--> if the potential is below threshold, no action potential will occur
110
what is the role of the axon hillock in neural integration?
serves as the decision-making site for a neuron
--> receives signals and determines if it will reach threshold, and if an action potential will occur
