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KIN 267 > Chapter 12 > Flashcards

Chapter 12 Flashcards

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1
Q

Everything done in NS involves (3) fundamental steps

A

1) sensory function detects internal & external stimuii
2) interpretation is made (analysis)
3) motor response occurs (reaction)

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2
Q

Divisions of the Nervous System (2)

A

CNS → brain & spinal cord

PNS → all nervous tissue outside CNS (includes nerves, ganglia, enteric plexuses & sensory receptors)

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3
Q

Most signals that __ muscles to ___ and __ to ___ originate in CNS

A

stimulate muscles to contract and glands to secrete originate in CNS

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4
Q

PNS is further divided into (3) ?

A

1) somatic sensory system (SNS)
2) autonomic nervous system (ANS)
3) enteric nervous system (ENS)

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5
Q 
**SNS** 
consists of (3)?
A

1) somatic sensory (afferent) neurons
2) Somatic motor (efferent) neurons
3) Interneurons

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6
Q

SNS

1) somatic sensory (afferent) neurons

A

convey info from sensory receptors in head, body wall & limbs toward CNS

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7
Q

SNS

2) Somatic motor (efferent) neurons

A

conduct impulses from CNS to skeletal muscle under voluntary control in periphery

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8
Q

SNS

3) Interneurons

A

any neurons that conduct impulses between afferent and efferent neurons within the CNS

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9
Q

PNS → 2) ANS

consists of? (2)

A

1) Sensory Neurons
2) Motor Neurons

  • sympathetic division
    • parasympathetic division
      *
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10
Q

ANS → sensory neurons

A

convey info from :

autonomic sensory receptors mostly in visceral organs (stomach/lungs) → CNS

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11
Q

ANS → motor neurons

A

under involuntary control

conduct nerve impulses from CNS → smooth muscle, cardiac muscle & glands

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12
Q

ANS → motor neurons

  • (2) branches
A

Sympathetic division

Parasympathetic division

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13
Q

Neurons

  1. gather info where?
  2. process info where?
  3. transmit info where?
A

1) gather info at dendrites
2) process info in dendritic tree & cell body
3) transmit info down axon to axon terminals

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14
Q

Synapse

A

site of communication between two neurons OR between a neuron & another effector cell

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15
Q

Synaptic Cleft

A

gap between pre & postsynaptic cells

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16
Q

Synaptic end bulbs & other varicosities on axon terminals of presynaptic neurons contain many?

A

tiny membrane-enclosed sacs (synaptic vesicles) that store packets of neurotransmitter chemicals.

→ many neurons even contain 2 or 3 types of neurotransmitters, each with different effects on postsynaptic cell

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17
Q

Like muscle fibers, neurons are electrically excitable

  • communicate with each other using (2) types of electrical signals
A

1) Graded Potential
2) Action Potential

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18
Q

1) Graded Potential

A

used for short-distance communication only

only in dendrites & cell bodies

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19
Q

2) Action Potential

A

allow long-distance communication within body

at axon hillock

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20
Q

Producing electrical signals in neurons depends on ?

A

existance of resting membrane potential (RMP)

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21
Q

How is a cell’s RMP created?

A

created using ion gradients & variety of ion channels that open/close in response to specific stimuli

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22
Q

Prevalence of Ion Channels in Body

A

present in plasma membrane of all body cells but especially prominant part of NS

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23
Q

Steps of touching a pen → to CNS

A

touch → GP in sensory receptor of skin → triggers axon to form AP → along axon into CNS

→ causes release of neurotransmitters at synapse with interneuron → stimulates interneuron to form GP in dendrites & cell body (process repeats as interneurons in higher parts of brain [thalamus/cerebral cortex] are activated)

→ perception occurs when interneurons in cerebral cortex are activated

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24
Q

Steps of using a pen →

A

stimulus in brain → GP in dendrites/cell body of upper motor neuron → causes AP in axon → neurotransmitter release →GP in lower motor neuron → AP → neurotransmitter release at NMJ → stimulate muscle fibers → AP → contraction

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25
When Ion channels are **open,** this allows..?
specific ions to move across plasma membrane down their **electrochemical gradient**
26
**Electrochemical Gradient**
*concentration (chemical) difference plus an electrical difference* **Chemical (concentration)** part → ions move from areas of [high] to [low] **Electrical** aspect → **cations** move toward **negatively-charged area** & **anions** move towards **positively-charged area**
27
Active channels open in response to?
stimulus (they are "gated")
28
(3) types of **active, gated channels**
1) ligand-gated 2) voltage-gated 3) mechanically-gated
29
Ligand-gated Channels
respond to a **neurotransmitter** or **hormone** and are **mainly concentrated at synapse**
30
Voltage-gated Channels
respond to **changes in transmembrane electrical potential** & mainly located along **neuronal axon**
31
Mechanically-gated Channels
respond to **mechanical deformation** (applying pressure to receptor due to **vibration, touch, stretch)**
32
Leakage channels
gated but NOT active - open & close randomly
33
RMP exists because of?
small buildup of **negative ions in cytosol** inside membrane & **positive ions** in ECF on surface → occurs very close to membrane, cytosol elsewhere is electrically neutral
34
Why is **RMP** slightly negative?
leakage channels favor gradient where more K+ leaks out than Na+ leaks in (more K+ channels than Na+ channels) - also **large negatively charged proteins** that always remain in cytosol
35
What would eventually destroy RMP if left unchecked?
small **inward** leakage of **Na+**
36
What offsets inward Na+ leak & outward K+ leak?
**NA+/K+ ATPases (sodium-potassium pump)** - pumps out Na+ as fast as it leaks in
37
**Polarized** cell
A cell that exhibits an RMP
38
Cell is "primed"
Cell in **polarized** state (exhibiting an RMP) → **ready to produce an AP**
39
To produce an AP, what needs to happen first?
Graded potential must first be produced in order to **depolarize cell to threshold**
40
- A graded potential occurs whenever ...?
**ion flow** in mechanically/ligand-gated channels produce **current** that is **localized** ## Footnote * - it **spreads to adjacent regions** for short distance & then dies out within few millimeters of its point of origin.*
41
(2) types of **Graded Potentials**
1) **Depolarizing** graded potential 2) **Hyperpolarizing** graded potential
42
1) **Depolarizing** graded potential
From RMP, stimulus that causes cell to be **less negatively charged** than ECF
43
2) **Hyperpolarizing** graded potential
stimulus that causes cell to be **more negatively charged**
44
Graded potentials have dif names depending on (2)
type of stimulus where they occur
45
Graded Potentials occur mainly in? (2)
**dendrites & cell body** do NOT travel down axon
46
(2) main phases of AP
1) depolarizing 2) repolarizing
47
AP steps
GP → **_depolarization_** of neuron from **-70mV to threshold (-55mV)** → Na+ channels **open** → Na+ inflow → inside becomes more positive **_repolarization_ →** Na+ channels inactivating, K+ channels **open → ** K+ outflow **_after-hyperpolarizing phase_** → K+ channels still open, membrane potential becomes even **more negative (-90mV)** As K+ channels close, MP returns to resting level **(-70mV)**
48
Absolute refractory period
period of time during which **cell can’t generate another AP,** no matter how strong stimulus is ## Footnote coincides with ***period of Na+ channel activation & inactivation*** (inactivated Na+ channels must 1st return to resting state.) This places an upper limit of **10–1000 nerve impulses/second**, depending on neuron
49
Relative refractory period
period of time during which **2nd AP can be initiated,** but only by **larger-than-normal stimulus** - *coincides with when voltage-gated K+ channels are still open after inactivated Na+ channels have returned to resting state.*
50
Do graded potentials exhibit refractory periods?
NO ## Footnote *In contrast to action potentials, graded potentials **do not** exhibit refractory period*
51
Propagation of AP down length of axon begins at?
**trigger zone** near **axon hillock** by passive spread
52
**Propagation of AP** down length of axon **begins at trigger zone near axon hillock** by **passive spread**, the **current** proceeds by (2)
1) continuous conduction 2) saltatory conduction
53
1) continuous conduction
slower, in **unmyelinated axons**
54
2) saltatory conduction
much faster process in **myelinated axons** AP jumps from one node to next
55
In addition to **nodes of Ranvier** that allow saltatory conduction, **speed of an AP** is also affected by? (3)
1) axon **diameter** 2) amount of **myelination** 3) **temperature**
56
(2) factors that play role in **determining perception of stimulus** or **extent of response**
1) **Frequency** of AP 2) **# of neurons recruited (activated)**
57
**(3) Fiber Types** of Neuronal Axons
1) **A** fibers 2) **B** fibers 3) **C** fibers
58
1) A fibers
large, fast (12-130 m/sec) → *(290 mph)* myelinated neurons carry **touch & pressure sensations** many motor neurons are this type
59
2) B fibers
medium size & speed (15 m/sec) → *34 mph* comprise **myelinated visceral sensory**
60
3) C fibers
smallest & slowest (2 m/sec) comprise **unmyelinated sensory & autonomic motor neurons**
61
Signal transmission at the synapse is ..
**one-way transfer** from presynaptic neuron to postsynaptic neuron
62
When AP reaches end bulb of axon terminals...
voltage-gated Ca2+ channels open → Ca2+ flows inward from ECF → triggering release of neurotransmitter → crosses synaptic cleft & binds to ligand-gated receptors on post-s membrane
63
Conversion of signal from pre to post-synaptic neuron
**presynaptic** neuron converts **electrical** signal (**nerve impulse**) into **chemical** signal (released **neurotransmitter**) **postsynaptic** neuron recieves this chemical signal → generates **electrical** signal (**postsynaptic potential)**
64
Synaptic Delay
time required for these processes at chemical synapse (conversion of electrical signal → chemical → electrical) about **0.5 msec**
65
Neurotransmitter effects can be modified by in many ways (4)
1) **synthesis** → stimulated/blocked 2) **release** → blocked/enhanced 3) **removal** → stimulated/blocked 4) **receptor site** → blocked/activated
66
Agonist
any chemical that **enhances or stimulates** the effects at a given receptor
67
Antagonist
any chemical that **blocks or diminishes** the effects at a given receptor
68
A neurotransmitter causes either an ...(2)
**excitatory** or an **inhibitory** graded potential
69
Excitatory postsynaptic potential (EPSP)
- causes **depolarization** of postsynaptic cell, bringing it closer to threshold ## Footnote * - Although single EPSP normally does not initiate a nerve impulse, postsynaptic cell does become more excitable.*
70
**Inhibitory** postsynaptic potential (IPSP)
- **hyperpolarizes** postsynaptic cell taking it farther from threshold.
71
Spatial Summation
summation of postsynaptic potentials in response to stimuli that occur at **different locations** in the membrane of a postsynaptic cell **at the same time** ## Footnote *involves input from dif neurons stimulating post-s neuron in dif parts of membrane at same time*
72
Temporal Summation
summation of postsynaptic potentials in response to stimuli that occur **at same locations** in the membrane of a postsynaptic cell but **at different times**
73
Whether or not postsynaptic cell reaching threshold depends on ?
**net effect after summation** of all **postsynaptic potentials**.
74
If neurotransmitter could linger in synaptic cleft, it would influence ?
postsynaptic neuron/muscle fiber/gland cell indefinitely Therefore, **removal of neurotransmitter** is essential for normal function
75
Removal of neurotransmitters is accomplished by ? (3)
1) Diffusion 2) Enzymatic Degredation 3) Re-uptake by cells
76
1) Diffusion
Some of the released neurotransmitter molecules diffuse away from synaptic cleft. Once a neurotransmitter molecule is out of reach of its receptors, it can no longer exert an effect.
77
2) Enzymatic Degredation
Certain neurotransmitters are **inactivated** through enzymatic degradation. ## Footnote *For example, the enzyme acetylcholinesterase breaks down acetylcholine in the synaptic cleft.*
78
3) Re-uptake by cells
Many neurotransmitters are actively transported back into neuron that released them (**reuptake**). Others are transported into neighboring neuroglia (**uptake**). * The neurons that release norepinephrine, for example, rapidly take up norepinephrine & recycle it into new synaptic vesicles. * * →membrane proteins that accomplish such uptake are called **neurotransmitter transporters.***
79
Integration
process by post-synaptic neuron that combines all excitatory & inhibitory inputs & responds accordingly ## Footnote *→occurs over & over as interneurons are activated in **higher parts of the brain** (such as the t**halamus & cerebral cortex**).*
80
Neuronal Circuit
many neurons organized into complex networks
81
Types of Circuits (4)
1) Diverging 2) Converging 3) Reverbrating 4) Parallel after-discharge
82
**1) Diverging**
small # of neurons in brain stimulate much larger # of neurons in spinal cord.
83
2) Converging
opposite of diverging circuit **large** # of neurons stimulate **smaller** # of neurons in spinal cord
84
3) Reverbrating - *used in?*
impulses sengt back through circuit time & time again *used in **breathing, coordinated muscular activies, waking up & short-term memory***
85
4) Parallel after-discharge ## Footnote *used in?*
involve single presynaptic cell that **stimulates group of neurons,** which then synapse with **common postsynaptic cell** ## Footnote *– used in precise activities such as mathematical calculations*
86

KIN 267 (12 decks)

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