Chapter 11 Nervous System Flashcards
1
Q
3 main functions of the nervous system
A
sensory input, integration and motor output
2
Q
Sensory input
A
monitoring stimuli/changes inside and outside the body
3
Q
Integration
A
interpretation of sensory input
4
Q
Motor output
A
response to stimuli
5
Q
Organization of the nervous system
A
Central Nervous System (CNS) and Peripheral Nervous System (PNS)
6
Q
What makes up the CNS?
A
*Brain and spinal cord
*integration and command center
7
Q
What makes up the PNS?
A
*Paired spinal and cranial nerves
*spinal nerves: impulses to/from the spinal cord
*cranial nerves: impulses to/from the brain
**carries messages to and from the spinal cord and brain
8
Q
2 functional divisions of the PNS
A
*sensory (afferent) division
*motor (efferent) division
9
Q
Sensory afferent fibers-
A
carry impulses from skin, skeletal muscles, and joints to the brain (CNS)
10
Q
Visceral afferent fibers-
A
transmit impulses from visceral organs to the brain (CNS)
11
Q
Motor (efferent) division-
A
transmits impulses f_rom CNS to effector organs, muscles and glands_
12
Q
Two main parts of the motor division are
A
Somatic Nervous System-Voluntary
Autonomic Nervous System (ANS)-Involuntary
13
Q
Somatic Nervous System is
A
voluntary
14
Q
Autonomic Nervous System is
A
involuntary
15
Q
What does ANS (autonomic Nervous System) regulate?
A
smooth muscle and cardiac muscle
16
Q
What are the divisions of ANS?
A
sympathetic and parasympathetic -one stimulates and the other will inhibit
17
Q
2 principle cell types of the nervous system
A
Neurons and supporting cells
18
Q
Neurons are
A
excitable cells that transmit electrical signals
19
Q
Supporting cells are
A
cells that surround and wrap neurons
20
Q
Other names for supporting cells: neuroglia or glial cells
A
provide a supportive scaffolding for neurons
21
Q
Other names for supporting cells: astrocytes
A
*most abundant, versatile and highly branched glial cells *barrier between neurons and capillaries
22
Q
Other names for supporting cells: microglia
A
small ovoid cells with spiny processes
23
Q
Other names for supporting cells: ependymal cells
A
range in shape from squamous to columnar *line cavities of CNS (brain &spinal cord)
24
Q
Other names for supporting cells: oligodendrocytes
A
*branched cells that wrap CNS nerve fibers *form myelin sheaths
25
Other names for supporting cells: Schwann cells
\*surround fibers of PNS \*form myelin sheaths
26
Other names for supporting cells: satellite cells
surround neuron cell bodies with ganglia, in the PNS
27
What type of division occurs in neurons?
long, lived, amitotic (a simple division of the nucleus with replication of chromosomes)
28
The function of a neurons plasma membrane is
electrical signaling
29
other names for a nerve cell body
Perikaryon or Soma
30
The structure of a nerve cell body
\*contains the nucleus and a nucleolus \*has no centrioles \*has well developed Nissl bodies (rough ER) \*contains an axon hillock
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what are the processes?
axons and dendrites
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Dendrites
\*short branched processes \*receptive \*create enormous surface area for receptions of signal from other neurons \*conduct impulse toward cell body
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Axons-structure
\*slender processes arising from the hillock \*may be short or very long \*long axons are called nerve fibers \*usually there is only one \*rare branches, if present, are called axon collaterals \*larger diameter causes faster conduction
34
Axons-Function
\*generates and transmits action potential
\*carries impulses away from cell body
\*secrete neurotransmitters from the axon terminals
\*movement:
--anterograde: toward axonal terminal
--retrograde: away from axonal terminal
35
Function of myelin sheaths
\*protect the axon
\*electrically insulate fibers from one another
\*increase the speed of nerve impulse transmission
36
Nodes of Ranvier are
gaps in myelin sheath between adjacent Schwann cells
37
Bothe myelinated and unmyelinated fibers are
present in CNS
38
Myelin sheaths are formed bu
oligodendrocytes in the CNS
39
White mater is
dense collections of myelinated fibers
40
White matter is in
regions of the brain and spinal cord that have myelinated fibers
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Gray matter is
mostly soma and unmyelinated fibers
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Gray matter is mostly in
nerve cell body-unmyelinated
43
Structural classifications of neurons
\*multipolar-three or more process (most common)
\*Bipolar-two processes (axon & dendrite)-rare
\*Unipolar-single, short process in PNS ganglia
44
Functional classifications of neurons
\*Sensory (afferent)-transmit impulses toward the CNS
\*Motor (efferent)-carry impulses away from the CNS
\*Interneurons (association neurons)-shuttle signals through CNS pathways-99% of neurons in the body
45
Action potentials, or nerve impulses are
\*Electrical impulses carried along the length of axons
\*Always the same regardless of stimulus
\*the underlying functional feature of the nervous system
46
There is potential on either side of membranes when:
1) the number of ions is different across the membrane
2) the membrane provides a resistance to ion flow
47
Chemically gated channels open with binding of a
specific neurotransmitter
48
Voltage-gated channels open and close in
response to membrane potential
49
what is the resting membrane potential?
\*the potential difference across the membrane of a resting neuron
\*the polarity is more negative on the inside
50
What generates the resting membrane potential?
It is generated by different concentrations of Na+, K+, Cl-, and protein (A-)
51
Ion concentrations
\*differential permeability of the neurilemma to Na+ and K+
\*Operation of the sodium-potassium pump
52
Changes in membrane potential are caused by
Depolarization, repolarization and hyperpolarization
53
Depolarization
the inside of the membrane becomes less negative
54
Repolarization
the membrane returns to its resting membrane potential
55
Hyperpolarization
the inside of the membrane becomes more negative than the resting potential
56
graded potentials are:
- short-lived
- decrease in intensity with distance
- magnitude varies directly with the strength of the stimulus
- sufficiently strong graded potentials can initiate action potentials
57
Action potentials
- a brief reversal of membrane potential
- only generated by muscle cells & neurons
- do not decrease in strength over distance
- an action potential in the axon of a neuron is a nerve impulse
- they are all or none
58
Describe the resting state of an action potential
- Na+ and K+ channels are closed
- leakage accounts for small movements of Na+ and K+
- Each Na+ channel has two voltage-regulated gates
- activation gates closed in the resting state
- inactivation gates-open in the resting state
59
Describe the depolarization phase of an action potential
- Na+ permeability increases; membrane potential reverses
- Na+ (activation) gates are opened; K+ gates are closed
- Threshold-a critical level of depolarization
(-55 to -50 mV)
60
describe the repolarization phase of an action potential
- sodium inactivation gates close
- membrane permeability to Na+ declines to resting levels
- As sodium gates close, voltage-sensitive K+ gates open
- K+ exits the cell and internal negativity of the resting neuron is restored
61
describe the hyperpolarization phase of an action potential
- potassium gates remain open, causing an excessive efflux of K+
- this efflux causes hyperpolarization of the membrane (undershoot)
- the neuron is insensitive to stimulus and depolarization during this time
62
Describe the role of the sodium-potassium pump in relation to an action potentials
- repolarization
1) restores the resting electrical conditions of the neuron
2) Does not restore the resting ionic conditions
- ionic redistribution back to resting conditions is restored by the sodium-potassium pump
63
What are the phases of the action potential?
1-resting state
2-depolarization phase
3-repolarization phase
4-hyperpolarization
64
What is threshold? Describe all or none phenomenon.
- **threshold**-membrane is depolarized by 15-20 mV
- established by the total amount of current flowing through the membrane
- weak (subthreshold) stimuli are not relayed into action potentials
- strong (threshold) stimuli are relayed into action potentials
- **All-or-nothing phenomenon**-action potentials either happen completely or not at all
65
Describe the absolute refractory period
_Time from the opening of the Na+ activation gates until the closing of the inactivation gates_
the absolute refractory period:
- prevents the neuron from generating an action potential (can't respond to another stimulus)
- ensures that each action potential is _separate_
- _enforces one-way transmission_ of nerve impulses
66
Describe the relative refractory period
_The interval following the absolute refractory period when:_
_\*sodium gates are closed_
_\*potassium gates are open_
_\*repolarization is occurring_
- the threshold level is elevated, allowing strong stimuli to increase the frequency of action potential events
- _during the 'after-hyperpolarization' stage-another stimulus could open the Na gates, but only a strong stimulus (Shari)_
67
Rate of **_impulse propagation_** is determined by:
**_axon diameter_**-the larger the diameter, the faster the impulse
**_presence of a myelin sheath_**-myelination dramatically increases impulse speed
68
Describe **_Saltatory Conduction_**
_\*current passes through a myelinated axon **only** at the nodes of Ranvier_
_\*action potentials are triggered only at the nodes and jump from one node to the next_
69
Explain **_multiple sclerosis_**
\***it's an autoimmune disease that mainly affects young adults**
-the immune system _attacks myelin proteins_
_-axons are not damaged_
\*symptoms: visual disturbances, weakness, loss of muscular control and urinary incontinence
\*_nerve fibers are severed and myelin sheaths in the CNS become nonfunctional sclerosis (when sheaths are reduced to hard lesions)_
70
**presynaptic neuron**
conducts impulses _toward the synapse_
71
**Postsynaptic neuron**
transmits impulses _away from the synapse_
72
Describe _two types_ of postsynaptic potentials
\***EPSP**-_excitatory_ postsynaptic potentials
\***IPSP**-_inhibitory_ postsynaptic potentials
73
what is **temporal summation**
presynaptic neurons _transmit impulses in rapid-fire order_
74
what is **spatial summation**
a postsynaptic neuron is _stimulated by a large number of terminals at the same time_
75
**Neurotransmitters**
_\*chemical used for neuronal communication_ with the body and the brain
\*_50 different neurotransmitters have been identified_
_\*classified chemically and functionally_
76
Neurotransmitters and **diseases**
**\*GABA-Gamma(y)-aminobutyric acid**
-_the most prevalent neurotransmitter in the brain_
_-inhibitory_
-**Huntington's**-lack of GABA releasing neurons
\***Acetylcholine**-refer to next card
**_\*Norepinephrine_**-feel good, reuptake blocked by cocaine
\***Dopamine**-feel good, regulation of skeletal movement
-**Parkinson's**-substantia nigra degenerates-decreased dopamine
\***serotonin**-inhibitory, regulates mood, Prozac block reuptake
\***endorphins**-inhibit pain, morphine, heroin mimic
77
Neurotransmitters : **Acetylcholine**
\*_first neurotransmitter identified_, and best understood
_\*released at the neuromuscular junction_
_\*synthesized and enclosed in synaptic vesicles_
_\*degraded by the enzyme acetylcholinesterase (AChE)_
\*released by:
_-all neurons that stimulate skeletal muscle_
-some neurons in the autonomic nervous system
78
**Two classifications of Neurotransmitters**
**excitatory and inhibitory**
\*_excitatory neurotransmitters cause depolarizations_ (e.g., glutamate)
\*_Inhibitory neurotransmitters cause hyper_polarizations (e.g., GABA and glycine)
79
Can neurotransmitters have both effects? Give an example.
\*some neurotransmitters **have both** excitatory and inhibitory effects
\*determined by the receptor type of the postsynaptic neuron
\*example: **acetylcholine**
- Excitatory at neuromuscular junctions with skeletal muscle
- inhibitory in cardiac muscle
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