Nervous System Flashcards
(80 cards)
1
Q
What are the three functions of the nervous system?
A
- detect changes in internal, external environments
- integrates info, make unconscious and conscious decisions
- stimulates muscles and glands to respond
2
Q
What are the two divisions within the nervous system?
A
- central nervous system (CNS) - brain & spinal cord, analyze & coordinates
- peripheral nervous system (PNS) - sensory/afferent division & motor/efferent division
3
Q
What is the job of the sensory division?
A
-receives input from special senses (eyes, ears, nose, mouth), from internal organs (visceral sensory neurons), and from joints and skeletal muscle (somatic sensory neurons)
4
Q
What is the job of the motor division?
A
- sends commands
- 2 parts: autonomic nervous system, somatic motor neurons
5
Q
What is the autonomic nervous system?
A
- mostly involuntary
- sympathetic (fight or flight) to cardiac muscle, smooth muscle, glands
- parasympathetic (rest or digest) to skeletal muscle
6
Q
What is the role of somatic motor neurons?
A
-mostly voluntary
7
Q
What are the special characteristics of neurons?
A
- long-lived - entire lifetime
- amniotic - can’t divide
- high metabolic rate: needs lots of “food”: oxygen, and glucose
8
Q
What are neurons made of?
A
-dendrites, cell body, dendritic spines, axons
9
Q
What is the S&F of dendrites?
A
-dendrites: highly branched processes (stick out) that receive information
10
Q
What is the S&F of dendritic spines?
A
-increase surface area to receive information
11
Q
What is the S&F of the cell body?
A
-cell body: soma: large to produce neurotransmitters, clusters of cells in CNS are called nuclei, clusters of cells in PNS are called ganglia
12
Q
What is the S&F of axons?
A
- length varies
- may be myelinated to increase the speed of impulse transmission
- may have collateral branches = side branches
- synaptic knobs at the end hold vesicles with NT
- axons wrapped in connective tissue
13
Q
What are the types of connective tissue that cover the axons?
A
- endoneurium: covers single axon; has capillaries
- perineurium: covers bundles of axons (nerve fascicles) has arteries and veins
- epineurium: covers bundles of nerve fascicles
14
Q
What are bundles of axons called in the CNS and PNS?
A
CNS: tract
PNS: nerve
15
Q
What are the types of neurons?
A
- multipolar
- bipolar
- unipolar
- anaxonic
16
Q
What are the characteristics of a multipolar neuron?
A
- many dendrites, 1 long axon
- mostly common in CNS, all motor neurons
17
Q
What are the characteristics of a bipolar neuron?
A
- 1 dendrite, 1 axon
- rare, special sense organs
18
Q
What are the characteristics of a unipolar neuron?
A
- dendrites continuous with the axon
- sensory neurons in the PNS
- cell body in dorsal root ganglion
19
Q
What are the characteristics of a anaxonic axon?
A
-can’t distinguish dendrites and axons
20
Q
What is the classification by function for sensory neurons?
A
- mostly unipolar
- carry info from sensory organs/receptors to CNS
- eg. exteroceptors: info from outside: touch, vision, sight
- eg. interoceptors: monitor internal organs
- eg. proprioceptors: monster muscle and joint position
21
Q
What is the classification by function for interneurons?
A
- mostly multipolar and found in CNS but some anaxonic
- between sensory and motor neurons
- integrate info
22
Q
What is the classification by function for motor neurons?
A
- ALL multipolar but the cell bodies are in the CNS
- carry info to muscles and glands
23
Q
What is a characteristic of neuroglia?
A
-smaller than the neurons but also outnumber them 10:1
24
Q
What are the 4 types of neuroglia in the CNS?
A
-astrocytes, microglia, oligodendrocytes, ependymal cells
25
What is the S&F of astrocytes?
- most common, star-shaped
- surround to maintain blood-brain barrier and control transport of the material into the interstitial fluid
- create supportive network for neuron
- recycle NT
- guides neuronal migration in the embryo (growth)
26
What is the S&F of microglia?
- small cells with "thorny" processes
| - defend and remove debris (no WBC in CNS)
27
What is the S&F of oligodendrocytes?
- processes wrap around portions of multiple CNS axons
| - to myelinated/insulate axons to increase the speed of action potential
28
What is the S&F of ependymal cells?
- look like epithelial
- ciliated cells joined to tight junctions
- lines ventricles of the brain, central canal of spinal cord
- produce, monitor, circulate, cerebral spinal fluid (CSF)
29
What are the two types of neuroglia in the PNS?
- schwann cells
| - satellite cells
30
What is the S&F of Schwann cells?
- whole cells wrapped around part of one axon = myeline axon --> AP travels 150x faster
- many Schwann cells needed to myeline 1 axon
- adjacent Schwann cells don't touch (gap= node of Ranvier
- AP is propagated at nodes of Ranvier
- demyelination results in less sensation and control = MS
- Schwann cells also guide axon growth during neuron repair
31
What is the S&F of satellite cells?
- surround cell bodies in ganglia
| - help regulate the environment around the neurons
32
What is the resting potential?
-difference in voltage (+,-) across the membrane when the cell is at rest
33
What generates the resting membrane potential?
- most Na+ in body lies outside cells, most K+ is inside cells - a bit motor negative on the inside of the membrane (-70 mV)
- cells have proteins (large molecules stay inside the cells) with negatively charged amino acids
- cells have leaky K+ channels
34
Why does K+ leak out of cell?
-leaky K+ channels
-K+ diffuses down the electrochemical gradient out of cells
-some K+ is pumped back in via Na+/K+ pump
= overall negative charge left inside the cell (70mV)
35
Where is the location of the graded potential?
-dendrite --> soma --> axon hillock
36
Where is the location that an action potential happens?
-axon hillock --> axon --> synaptic knob
37
What is the location of neurotransmitters?
-synaptic knobs --> synaptic cleft --> dendrites (of another neuron)
38
What are the three types of channels?
1) GP- ligand gated (molecule biding)/mechanically gated (Na/Cl channels)
2) AP- voltage gated Na+/K+ channels
3) NT- voltage gated Ca2+ channels
39
What are the stimulus/triggers of the channels?
1) GP- forced movement (ligand or mechanically gated
2) AP- ion flow, depolarization (increase and charge)
3) NT- depolarization
40
What are the distances that can be travelled?
1) GP-short distance travelled within soma through cytosol
2) AP-long distance travelled (cm) regenerated along the axon
3) NT-short distance across the synaptic cleft
41
What are the events at the dendrites?
- stimulus opens ligand-gated or mechanically-gated ion channels
- ion flow generates graded potentials
42
What stimuli open ligand-gated channels?
- NT
- food (smell molecules)
- chemicals in body (eg. glucose, CO2)
- chemicals released by injured cells
- light (triggers reaction that produce molecules)
43
What stimuli open mechanically-gated channels?
- touch, pressure, vibration
- stretch
- sound
44
When do positive ion flows generate graded potentials?
- if positive ions enter dendrites- increases positive charge in cells = cell depolarizing - makes cell more likely to fire
- if positive ions leaves dendrites -makes cell more negative = hyperpolarization and less likely to fire)
- negative ions enter dendrites
45
What factors change the strength of the graded potential?
- week stimulus: few channels open, few ions flow
| - strong stimulus: many channels open, many ions flow
46
Why can a GP be excitatory?
-Na+ or K+ influx = depolarization = excitatory postsynaptic potential (EPSP)
47
Why can a GP be inhibitory?
-K+ efflux/Cl- influx = hyperpolarization = inhibitory postsynaptic potential (IPSP)
48
What determines if a threshold is reached?
-summation of all the EPSPs and IPSPs
49
What happens if there is a weak stimulus?
-threshold is not reached = no signal passed on
50
What happened in a strong stimulus?
-spacial summation or temporal summation
51
What is spacial summation?
- ions for many synapses add up because many terminals release Its simultaneously
- few AP
52
What is temporal summation?
- high frequency of firing
| - ions from one synapse add up over time because the new NT released before initial amounts degraded
53
What is the axon hillock?
- voltage-gated channels present at axon hillock
- if axon hillock reaches threshold potential, voltage-gated channels open --> AP is generated
- if axon hillock does not reach threshold potential, voltage-gated channels stay closed --> NO AP
54
What does the amount of depolarization have to be in order for an AP to take place?
- -55mV
| - if its -30mV perhaps multiple will fire
55
What are the characteristics of an action potential?
- brief reversal in membrane potential =-70mV
- always the same strength
- only axons and muscle cells have excitable membrane - they have voltage-gated channels therefore can generate an AP
56
What is the first step of an action potential?
- resting membrane potential = -70mV
| - voltage gated Na+, K+ channels @ axon hillock and axon are closed, capable of opening
57
What is the second stop in an AP?
- stimulus triggers graded potential in soma
| - depolarization spreads through soma to voltage-gated Na+ channels at axon hillock
58
What is the third step of an AP?
- when depolarization reaches -55mV, threshold potential reached
- voltage Na+ channels at axon hillock open
- outer gates open fast, inner gate close slowly
59
What is the fourth step of an AP?
- fast depolarization to +30mV
- Na+ rushes down electrochemical gradient
- depolarization opens next set of voltage-gated Na+ channels, AP propagated along axon
60
What is the turning point in an AP?
- step 5
- slow inner gates closed, Na+ channels closed
- no more Na+ enters
- voltage K+ channels open
61
What is repolarization?
- step 6 in AP
| - K+ rushes down the electrochemical gradient
62
What is hyperpolarization?
-step 7 of AP
-K+ gates slow to close
-excess K+ leaves the cell
Na+/K+ will eventually restore ion distribution
63
How is the AP '"all or none"?
- weak stimulus: subthreshold no AP
- strong stimulus: threshold reached AP
- stronger stimulus: threshold reached more often, increased AP but all AP are the same strength
64
What is the refractory period in an AP?
-ensures unidirectional propagation of APq
65
What is the absolute refractory period?
- Na+ gates open or inactivated
- region can't respond to another stimulus
- only Na+ channels further along axon can open
- ensures AP
66
What is the relative refractory period?
- gates have been reset, are ready to open but cell is hyperpolarized
- threshold stimulus won't trigger another AP
- stronger stimulus will reopen Na+ channels, trigger AP
67
What is AP propagation?
1) AP along unmyelinated axons travel by continuous propagation
- voltage gated Na+ channels open along an axon
2) AP along myelinated axons travels by salutary conducting 150x faster
- myeline insulate fibres
- voltage-gated Na+ channels at nodes of Ranvier
- AP generated only at nodes
68
What is the synaptic knob?
- synapse is junction between 2 neurons or between neuron and effector
- converts electrical impulse to chemical signal and back again
69
What are the events at a synapse?
1) voltage-gated Ca2+ channels open
- Ca2+ floods in
2) Ca+ triggers synaptic vesicles to fuse with axonal membrane
- NT released by exocytosis
- Ca2+ removed by mitochondria
3) NT binds to receptors, open ion channels - open Na+ channels
- depolarization = EPSP
- opens K+ or Cl- channels - hyperpolarization =IPSP
4) NT removed from postsynaptic receptor by:
- degration (break down) of enzymes or removed by a transporter
- uptake by neuroglia cell =astrocytes or neuron that released it (presynaptic neuron) for storage (sometimes keeps parts to make something new)
- diffusion
70
What are neurotransmitters (NT)?
- may bind to different types of receptors on different postsynaptic cells
- receptor type determines effect of NT on cell
- NT may be excitatory, inhibitory or both depending on type/location on receptor
71
What is Achetylcholine?
- NT
- excites skeletal muscle, inhibits cardiac muscle
eg. snake venom & curare inhibit binding of Ach to receptor --> flaccid paralysis (NT can't bind to receptor and channels don't open so no AP)
eg. nerve gas prevents Ach removal from synapse --> muscle spasms leading to death (diaphragm is a muscle) (NT builds up channels stay open producing too many AP)
72
What are Monoamines?
NT
- norepinephrine
- dopamine
73
What is norepinephrine?
- excitatory/inhibitory depending on location
- feeling good
- tricyclin antidepressants block NE removal from synapse --> enhance good feelings
74
What is dopamine?
- excitatory/inhibitory
- feeling good skeletal muscle control
- coccaine binds competitively to dopamine
- reuptake transported
- given to Parkinson's patients to control complex movement
- fewer NT, channels stay closed - no AP
- Add NT substitute --> channel opens
75
What is serotonin?
- NT
- inhibitory
- regulates mood, sleep, appetite, nausea
- feeling good
- prozac blocks seretonin uptake --> enhances positive feelings to reduce depression
- LSD blocks seretonin activity --> inhibitory effect reduce excess AP --> hallucinations
76
What affect does prozac have on AP?
- NT builds up and opens more channels
- cells stays hyperpolarized
- decreased firing fear and anxiety centres
77
What affect does LSD have on AP?
- seretonin can't bind therefore channel stays closed
- K+ can't leave but continues to enter through Na+/K+ pump
- (+) charge builds up and cell depolarizes
- excessive EPSP excess AP
78
What are amino acids NTs?
eg. gabba
- inhibitory, opens Cl- channels
- principle inhibitory NT in brain
- alcohol and value --> augment effects
79
What are neuropeptides?
eg. endorphins
- inhibitory
- widely distributed in brain, inhibits pain
- morphine, heroine are structurally similar (bind to receptors and mimic effect)
80
What are neuromodulators?
eg. nitric oxide
- excitatory
- brain, spinal cord induces muscle relaxation
- nitroglycerin released NO --> relaxes smooth muscle of the blood vessels and increases blood flow in the heat, reduces angina
