Ch 7 Flashcards
1
Q
CNS
A
brain + spinal cord
2
Q
PNS
A
cranial/spinal nerves
3
Q
neurons
A
- -> conduct impulses but generally cannot divide 9but CAN repair)
- respond to chemical/physical stimuli (ex. pain/pressure/heat)
- conduct electrochemical impulses (ex. an action potential)
- release chemical regulators (at synapse)
- enable perception of sensory stimuli, learning, memory, and control of muscles/glands
4
Q
glial cells (neuroglia)
A
support the neurons, can NOT conduct impulses, but CAN divide
5
Q
Neuron Structure
A
- cell body
- dendrites
- axon
6
Q
Cell body
A
contains the nucleus/other organelles
cluster in groups = nuclei/ganglia
7
Q
nuclei
A
cell body in CNS
8
Q
ganglia
A
cell body in PNS
9
Q
dendrites
A
receive impulses and conducts a graded impulses toward the cell body
-shorter than axon
10
Q
axon
A
conducts action potentials away from the cell body
11
Q
axon hillock
A
where action potential is generated –> then propagated down the axon
12
Q
Axonal Transport
A
an active process (needs energy) needed tome organelles and proteins from the cell body –> axon terminals
- fast component moves vesicles (neurotransmitters)
- slow components move microfilaments, microtubules, and proteins (a.k.a. cytoskeleton)
- -> anterograde/retrograde transport
13
Q
anterograde transport
A
cell body –> dendrites/axon
14
Q
retrograde transport
A
dendrites/axon –> cell body
15
Q
Functional classification of neurons
A
- -> based on direction impulses are conducted
1. sensory
2. motor
16
Q
sensory neurons
A
conduct impulses from sensory receptors to CNS
17
Q
motor neurons
A
conduct impulses from CNS to target organs
-not just voluntary: somatic (ex. skeletal muscle) vs. autonomic (ex. HR)
18
Q
Categories of motor neurons
A
- Somatic
- Autonomic
- sympathetic
- parasympathetic
19
Q
somatic motor neurons
A
responsible for reflexes and VOLUNTARY control of skeletal muscles
20
Q
autonomic motor neurons
A
innervate INVOLUNTARY targets such as smooth muscles, cardiac muscle, and glands
- sympathetic: emergency situations/”fight or flight”
- parasympathetic: normal functions/”rest and digest”
21
Q
Nerves
A
bundles of axons located outside the CNS
- most composed of sensory + motor neurons (“mixed nerves”)
- some have sensory only
22
Q
tract
A
bundle of axons in CNS
23
Q
Types of neuroglia in PNS
A
- Schwann Cells
2. Satellite Cells
24
Q
Types of neuroglia in CNS
A
- Oligodendrocytes
- Microglia
- Astrocytes
- Ependymal Cells
25
Schwann Cells
PNS neuroganglia
| form myelin sheaths around peripheral axons
26
Satellite Cells
PNS neuroganglia
support cell bodies within the ganglia of PNS
-ex. secreting growth factors
27
Oligodendrocytes
CNS neuroganglia
form myelin sheaths around the axons of CNS neurons
-analogous to schwann cells
28
Microglia
CNS neuroganglia
| migrate around CNS tissue and phagocytize foreign and degenerated material
29
Astrocytes
CNS neuroganglia
regulate the external environment of the neurons
-regulate tight junctions to regulate material movement in endothelial cells --> create BBB
30
Ependymal Cells
CNS neuroganglia
| line the ventricles and secrete cerebrospinal fluid
31
BBB
- capillaries in the brain do not have pores between adjacent cells but are joined by tight junctions
- substances can only be moved by very selective processes of diffusion through endothelial cells, active transport, and bulk transport
- movement is transcellular, not paracellular
- astrocytes: support cell bodies/regulate formation of BBB
32
Resting Membrane Potential
neurons have a resting potential of -70mV
- established by large negative molecules inside the cell
- Na+/K+ pumps
- permeability of the membrane to positively charged, inorganic ions
--> at rest there is a high concentration of K+ inside the cell and Na+ on the outside
33
Depolarization
occurs when positive ions enter the cell (usually Na+)
- -> membrane potential moves towards 0/more positive
- EXCITATORY
34
Hyperpolarization
occurs when positive ions leave the cell (usually K+)
| -INHIBITORY
35
Ion Gating
Two types of channels
1. K+ leakage channels: not gated (always open), increases permeability to K
2. Voltage-gated K+ channel: open when a particular membrane potential is reached, closed at resting potential
-Na+ voltage-gated channels are closed at rest, the membrane is less permeable to Na+ at rest
36
Voltage Gated K+ Channel
- -> these channels open if the membrane potential depolarizes to -55mV (a.k.a. threshold)
1. Channels open --> sodium rushes in due to electrochemical gradient
2. Membrane potential increases toward Na+ equilibrium potential
3. Channels deactivated at +30mV
4. Voltage-Gated K+ Channels open and K+ rushes out of cell following electrochemical gradient
5. This makes the cell depolarize back toward K+ equilibrium potential
37
Action Potentials
1. At threshold membrane potential (-55mV), voltage-gated Na+ channels open and Na+ rushes in
2. As cell depolarizes, more Na+ channels are open, and the cell becomes more and more permeable to Na+
- POSITIVE feedback loop
- causes an overshoot of membrane potential --> reaches +30mV
3. At +30mV, Na+ channels close and K+ channels open
- results in repolarization of membrane potential
- NEGATIVE feedback loop
38
All-or-None
-threshold is reached --> action potential occurs
- size of stimulus will NOT:
1. affect size of action potential (will always reach +30mV - may recruit more neurons)
2. affect action potential duration, but will make them happen more frequently
39
Refractory Period
action potentials can only increase in freq to a certain point
- there is a refractory period after action potential when neuron can NOT become excited again (for milliseconds)
- absolute vs. refractory periods
- each action potential remains a separate, all-or-none event
40
Absolute Refractory Period
occurs during the action potentials
| -Na+ channels are inactive (not just closed)
41
Relative Refractory Period
- K+ channels are still open (still in hyper polarization phase)
- only a very strong stimulus can overcome this
42
Conduction of Nerve Impulses
- action potential occurs at neuron membrane
- voltage gated Na channels open as a wave down the axon
- axon potential at one location serves as depolarization stimulus for next region of axon
43
Conduction: Unmyelinated
* chaotic/unorganized
- axon potentials produced down entire length of axon
- slow conduction rate b/c so many action potentials are generated
- amplitude of each action potential is the same (conducted w/o reduction)
44
Conduction: Myelinated
* much more organized
- myelin = insulation
- Nodes of Ranvier allow Na and K to cross membrane every 1-2mm
- -> Na ion channels concentrated at the nodes
- action potentials "leap" from node to node
- --> called "saltatory conduction"
45
What is the resting potential in a myelinated neuron?
-70mV
46
What is axon potential conduction speed increased by?
1. diameter: reduces resistance to spread of charges via cable properties
2. Myelination b/c of saltatory conduction
- -> thin unmyelinated= 1 m/sec
- -> thick myelinated= 100 m/sec
47
Synapse
- ->the functional connection between a neuron and the cell it's signaling
* electrical or chemical
1. in CNS, second cell = another neuron
2. in PNS, second cell= muscle/gland (neuromuscular junction)
48
Electrical Synapses
- can occur in mostly in smooth/cardiac muscle, between neurons of brain or glial cells
- cells joined by gap junctions
- stimulation causes phosphorylation or dephosporylation of connexion proteins to open or close the channels
49
Chemical Synapses
- most involve the release of a neurotransmitter from axon terminal
- synaptic cleft: very small, released neurotransmitter can readily diffuse across this space
50
Release of a Neurotransmitter
Neurotransmitter is enclosed in synaptic vesicles in the axon terminal
1. when action potential reaches the end of the axon --> voltage gated Ca channels open
2. Ca stimulates the fusing of synaptic vesicles to the plasma membrane and exocytosis of neurotransmitter
51
Actions of Neurotransmitter
Neurotransmitter diffuses across the synapse, where it binds to a specific receptor protein.
1. neurotransmitter is referred to as the ligand
2. results in opening of chemically regulated ion channels (a.k.a. ligand-gated ion channels)
52
Acetylcholine (ACh)
Neurotransmitter: directly opens ion channels when it binds to a receptor
- Excitatory in some areas of CNS, in some autonomic motor neurons, and in all somatic motor neurons
- Inhibitory in some autonomic neurons
53
Nicotinic ACh Receptors
- can be stimulated by nicotine
| - found on motor end plate of skeletal muscle cells, in autonomic ganglia, and in some parts of the CNS
54
Muscarinic ACh Receptors
- can be stimulated by muscarine (from poisonous mushrooms)
| - found in CNS and plasma membrane of smooth/cardiac muscles and glands innervated by autonomic motor neurons
55
Agonists
drugs that can stimulate a receptor
56
Antagonists
drugs that inhibit a receptor (ex. beta-blockers)
57
Acetylcholinesterase (AChE)
- enxyme that inactivates AChE activity shortly after it binds to the receptor
- hydrolyzes ACh into acetate and choline, which are taken back into the presynaptic cell of reuse (recycles to rebuild ACh)
58
Monoamines
Regulatory molecules derived from AAs
1. Catecholamines: derived from tyrosine (ex. dopamine, norepinephrine, and epinephrine)
2. Serotonin: derived from L-tryptophan
3. Histamine: derived from histidine
59
Monoamine Action/Inactivation
- made from presynaptic axon, released via exocytosis, diffuse across synapse, and bind to specific receptors
- quickly taken back into the presynaptic cell (reuptake) and degraded by monoamine oxidase (MAO)
