CH 12: 9-20-13 (BIO 181) Flashcards
(126 cards)
1
Q
the nervous system includes all ___ ____ in the body
A
neural tissue
2
Q
____, ____ ___, ____ receptors, and nerves are all involved in the nervous system
A
brain, spinal cord, sensory receptors
3
Q
nervous system divided into the ___ nervous system, and the ___ nervous system
A
central; peripheral
4
Q
- includes the brain and spinal cord
- processing and coordinating of information
- sensory information (input) from inside and outside body
- motor commands (output) control activites of perpheral organs (skeletal muscles)
- higher functions of brain: learning, memory, emotion and intelligence
A
CNS
5
Q
- includes all neurual issue outside the CNS
- deliver sensory information to the CNS
- carry motor commands to peripheral tissues and systems
- consists of nerves that are bundles of fibes with connective tussues and blood vessels and carry sensory information and motor commands via
- cranial nerves->connect to brain
- spinal nerves -> attach to spinal cord
A
PNS
6
Q
___ and ____ divisions of PNS
A
afferent; efferent
7
Q
- carries sensory information
- contains receptors and effectors
- receptors (source) detect changes or respond to stumuli, consist of neurons and highly specialized cells, complex sensory organs (eyes, ears)
- effectors (target) respond to efferent signals and consist of target cells and organs
A
afferent division (input) of PNS
8
Q
- carries motor commands
- from CNS to PNS muscles and glands
- composed of the somatic and autonomic nervous system
A
efferent division (output) of PNS
9
Q
nervous system in efferent division of PNS that controls skeletal muscle contractions (voluntary and involuntary muscles contractions)
A
somatic nervous system
10
Q
nervous system in efferent division of PNS that
- controls subconscious actions: contractions of smooth muscle and cardiac muscle and glandular secretions
- sympathetic division has a stimulating effect
- parasympathetic division has a relaxing effect
A
autonomic nervous system
11
Q
- the basic functional units of the nervous system
- specialized cells that control and monitor body activities and physiological functions
- sense changing conditions, process sensory input, and direct the body’s responses
- come in all shapes and sizes but all have certain characteristics in common.
A
neurons
12
Q
- Contains nucleus and organelles
- Large nucleus and nucleolus (the brain of neuronal cells)
- Perikaryon (cytoplasm)
- Nuclear Pores (provides a route for the transferring of information)
- Mitochondria (produce energy)
- RER and ribosomes (produce neurotransmitters)
- Cytoskeleton consists of 3 types of filaments that give the cell structural support and enable some degree of motility/contractility
A
cell body (soma)
13
Q
consists of 3 types of filaments that give the cell structural support and enable some degree of motility/contractility
• Together, these filiments keep the organelles suspended in the cytosol.
A
cytoskeleton
14
Q
• _____and_____: resemble the microfilaments and microtubules seen in other cell types
A
Neurofilaments; neurotubules
15
Q
bundles of neurofilaments that provide support for dendrites and axon
A
neurofibrils
16
Q
- Dense areas of RER and ribosomes
* Make neural tissue appear gray (gray matter)
A
nissl bodies
17
Q
- Highly branched projections from the soma
* Function in receiving information from extracellular environment, other cells, or other neurons
A
dendrites
18
Q
- Single long processes extending from the soma
- Functions in sending out (or carrying) information to various targets
- Carries electrical signal (action potential)
- structure is critical to function
A
axon
19
Q
- Contain synaptic terminals, which contain synaptic vessicles that are filled with neurotransmitters
- It is these neurotransmitters that, when released, affect the transmembrane potential of another cell
A
telondenria (collaterals)
20
Q
- Cytoplasm of axon
* Contains neurotubules, neurofibrils, enzymes, organelles
A
axoplasm
21
Q
- Specialized cell membrane of the axon
* Covers the axoplasm
A
axolemma
22
Q
- Thick section of cell body
* Attaches to initial segment
A
axon hillock
23
Q
• Attaches to axon hillock
A
initial segment
24
Q
fine extensions of distal axon
A
telodendria
25
tips of telodendria
synaptic terminals
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area where neuron communicated with another cell
synpse
27
all synapses involve ___ and ___ cells
presynaptic; postsynaptic
28
– Cell that sends message (information)
– Usually a neuron
– Releases chemicals to the postsynaptic cell
presynaptic
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– Cell that receives message (information)
– Can be a neuron or any other type of cell
• The synapse can be anywhere on the receiving cell
postsynaptic
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• Synapse between neuron and muscle
neuromuscular junction
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• Synapse between neuron and gland
neuroglandular junction
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* Is expanded area of axon of presynaptic neuron
| * Contains synaptic vesicles of neurotransmitters
the synaptic knob (terminal buttons)
33
* are chemical messengers
* are released at presynaptic membrane
* affect receptors of postsynaptic membrane
* are broken down by enzymes
* are reassembled at synaptic knob
neurotransmitters
34
Neurons are Classified into____ Types – Based on_____
four; structure
35
* Found in brain and sense organs
* Typically Smaller than other neurons
* All cell processes look alike?……well, not really
* Dendrites and axons are difficult to distinguish
* Function is poorly understood
anazonic neruron
36
* Found in special sensory organs (sight, smell, hearing)
* Are small
* One dendrite, one axon
* Rare?
bipolar neurons
37
* Found in sensory organs of the PNS
* Have very long axons
* Fused dendrites and axon
* Cell body to one side
unipolar neuron
38
* Common in the CNS
* Include all skeletal muscle motor neurons
* Have very long axons
* Multiple dendrites, one axon
multipolar neurons
39
* Afferent neurons of PNS
| * Originate at the periphery and terminate in the CNS
• Sensory neurons
40
* Efferent neurons of PNS
| * Originate in the CNS and terminate at the effector organs (target)
• Motor neurons
41
* Association neurons
| * All located in the CNS
• Interneurons
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* Monitor internal environment (visceral sensory neurons)
* Monitor effects of external environment (somatic sensory neurons)
* Structure of sensory neurons
* Cell bodies are grouped in sensory ganglia
* afferent fibers extend from sensory receptors of the PNS to the CNS
• Functions of Sensory Neurons
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carry instructions from CNS to peripheral effectors (targets)
• Via efferent fibers (axons)
Motor Neurons
44
• includes all somatic motor neurons that innervate skeletal muscles
• Somatic nervous system (SNS):
45
* visceral motor neurons innervate all other peripheral effectors
* e.g., smooth muscle, cardiac muscle, glands, adipose tissue
• Autonomic (visceral) nervous system (ANS):
46
• Motor neurons are grouped into
Ganglia (broad term = cluster of cell bodies)
47
• Neuronal cell bodies that make up the junction between_____ nerves originating from the CNS and autonomic nerves that innervate ___ organs
autonomic; peripheral
48
• Signals from CNS motor neurons to visceral effectors pass synapses at autonomic ganglia and then divide the axons into:
» preganglionic fibers
| » postganglionic fibers
49
• Most interneurons are located in
brain, spinal cord, and autonomic ganglia
50
* Between sensory and motor neurons
| * These comprise over 90% of all neurons
Interneurons
51
* Are responsible for Distribution of sensory information and Coordination of motor activity
* Are involved in higher functions: Memory, planning, learning
Interneurons
52
* Half the volume of the nervous system
* Many types of neuroglia in CNS and PNS
* These are the cells that support and protect neurons
neuroglia
53
* Cell with highly branched processes; contact neuroglia directly
* Form epithelium called ependyma
* Line central canal of spinal cord and ventricles of brain:
* secrete cerebrospinal fluid (CSF)
* have cilia or microvilli that circulate CSF
* monitor CSF
* contain stem cells for repair
Neuroglia in the CNS
| • Ependymal cells
54
* large cell bodies with many processes
* Maintain blood–brain barrier (isolates CNS)
* Repair damaged neural tissue
* Guide neuronal development
* Control interstitial environment
* Absorb and recycle neurotransmitters
• Astrocytes (CNS)
55
• smaller cell bodies with fewer processes
• Processes contact other neuron cell bodies
• Wrap around axons to form myelin sheaths
(a membrane that wraps around the axon, giving it electrical insulation)
• Oligodendrocytes (CNS)
56
* Fewest and smallest of all microglia in the CNS
* Migrate throughout neural tissue
* Clean up cellular debris, waste products, and pathogens
• Microglia (CNS)
57
• Also called amphicytes
• Surround ganglia
• Regulate environment around neuron
– O2, CO2, and nutrient levels
• Satellite cells (PNS)
58
* Also called neurilemmocytes
* Form myelin sheath (neurilemma) around peripheral axons
* One Schwann cell sheaths one segment of axon:
* many Schwann cells sheath entire axon
* Participates in repair after injury
Schwann Cells (PNS)
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* makes nerves appear white
| * Nerves that are not myelinated appear gray
• Myelination
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* internodes: myelinated segments of axon
* nodes
* gaps between internodes
* Extremely important in conduction
• Nodes of Ranvier
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– 1 oligodendrocyte can myelinate
portions of several axons
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– 1 schwann cell can only myelinate
one segment of a single axon
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• myelin ____ myelinated axons
insulates
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myelin _____ speed of electrical signals (action potentials)
increases
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• Neurons perform all _______, information processing, and_____ functions of the nervous system
communication; control
66
preserve physical and biochemical structure of neural tissue and are essential to survival and function of neurons
neuroglia
67
• All plasma (cell) membranes produce____ signals by ion movements
electrical
68
• Transmembrane potential exists due to a difference in _____ and _____ gradients between the inside and outside of cells
chemical; electrical
69
* The transmembrane potential of resting cell
* The “reference point”
* (Typically –70mV)
resting potential
70
* Temporary, localized change in resting potential
| * Caused by stimulus
graded potential
71
* Is an electrical impulse
* Produced by graded potential
* Propagates along surface of axon to synapse
action potential
72
* Releases neurotransmitters at presynaptic membrane
| * Produces graded potentials in postsynaptic membrane
synaptic activity
73
• Response (integration of stimuli) of postsynaptic cell
information processing
74
• Concentration gradient of ions (Na+, K+)
• Selectively permeable through channels
• Maintains charge difference across membrane (resting potential –70 mV)
– Based on chemical and electrical forces
• Three Requirements for Transmembrane Potential
75
* Typical neuron is permeable to potassium and sodium (via leak channels that are always open)
* But, 25 times more permeable to______
potassium
76
• Outside cell
| – Lots of____ and chloride
sodium
77
• Inside cell
| – Lots of ____ and organic anions
potassium
78
* Chemical driving forces are pushing:
* ____ out
* ____in
K+; Na+
79
* Since the membrane is more permeable to K+
| * K+ leaves cell ____ than Na+ enters
faster
80
* As a result, Electrical forces develop that want to push BOTH:
* Na+ ___ cell
* K+ ___ cell
into; into
81
pump maintains this resting potential
sodium/potassium
82
• The sum of chemical and electrical forces acting on a given ion
• Electrochemical Gradient
83
• The transmembrane potential at which there is no net movement of a particular ion across the cell membrane
• Examples
K+ = –90 mV
Na+ = +66 mV
So, the resting membrane potential is closer to the potassium equilibrium potential
• Equilibrium Potential
84
* Transmembrane potential ___ or ___
* In response to temporary changes in membrane permeability
* Resulting from opening or closing specific membrane channels
rises; falls
85
reference point
resting potential
86
more postitive
depolarization
87
more negative
repolarization
88
more negative than the resting potential
hyperpolarization
89
• Membrane permeability to Na+ and K+ determines changes in ____ potential
transmembrane
90
– are always open
| – permeability changes with conditions
passive channels (leak channels)
91
– open and close in response to stimuli
| – at the resting potential, most gated channels are closed
active channels (gated channels)
92
* Open in the presence of specific chemicals (e.g., ACh) at a binding site
* Found on neuron cell body and dendrites
chemically gated channels
93
* Respond to changes in transmembrane potential
* Have activation gates (open upon stimulation) and inactivation gates (close to stop Na+ influx)
* Characteristic of excitable membrane
* Found in neural axons, skeletal muscle, cardiac muscle
voltage-gated channels
94
* Respond to membrane distortion
| * Found in sensory receptors (touch, pressure, vibration)
mechanically gated channels
95
• Transmembrane potential exists across
plasma membrane
96
• Cytosol (ICF) and extracellular fluid (ECF) have different
chemical/ionic balance
97
• The plasma membrane is
selectively permeable
98
• Changes in the Transmembrane potential occur
in response to chemical or physical stimuli
99
* Graded Potentials
| * Action Potentials
two types of transmembrane potentials
100
* Also called local potentials
* Changes in transmembrane potential that cannot spread far from the site of stimulation
* Any stimulus that opens a gated channel produces a graded potential
* determine whether or not an action potential will occur
graded potentials
101
• Opening sodium channel produces graded potential:
– resting membrane exposed to chemical (Na+)
– sodium channel opens
– sodium ions enter the cell
– transmembrane potential rises (becomes more positive)
– depolarization occurs
Graded Potentials: The Resting State
102
* A shift in transmembrane potential toward 0 mV or becomes more positive:
* movement of Na+ through channel
* produces local current
* depolarizes nearby plasma membrane (graded potential)
* change in potential is proportional to stimulus
Graded Potentials: Depolarization
103
a ____ is produced by the spread of sodium ions inside the membrane.
•This results in depolarization of adjacent portions of the plasma membrane – and this continues
local current
104
* The transmembrane potential is most affected at the site of stimulation – and this affect decreases with distance
* The effect spreads passively via local currents
* Whether the membrane depolarizes or hyperpolarizes in response to a given stimulus, depends on the nature of channels that are involved in the membrane itself
* The strength of the response is determined by the strength of the stimulus
graded potentials
105
• When the stimulus is removed, transmembrane potential returns to normal resting potential
repolarization
106
* Here, the stimulus causes the opening of K+ channels
* When K+ channels open, positive ions move OUT of the cell (not in)
* This Increases the negativity of the resting potential
* Opposite effect of opening a sodium channel
* But when stimulus is removed, potential returns to rest
hyperpolarization
107
• The effect of _______ depends on WHERE they happen:
• At cell dendrites or cell bodies:
– trigger specific cell functions
– e.g., exocytosis of glandular secretions
• At motor end plate:
– releases ACh or other neurotransmitters into synaptic cleft
Graded Potentials
108
* Propagated changes in transmembrane potential
* Affect an entire excitable membrane
* Link graded potentials at cell body with motor end plate actions
action potential = nerve impulses
109
• A graded depolarization of axon hillock large enough (10 to 15 mV) to change resting potential
( -70 mV) to threshold level of voltage-gated sodium channels (–60 to –55 mV)
• Initial stimulus must reach threshold!
110
• If a stimulus exceeds threshold amount:
– the action potential is the same
– no matter how large the stimulus
• Action potential is either triggered, or not!
• All-or-none principle
111
Resting State Prior to Action Potential
* Na+ activation gate = closed
* Na+ inactivation gate = open
* K+ gate = closed
112
* Step 1: Depolarization to threshold
* Step 2: Activation of Na+ channels
* Step 3: Inactivation of Na+ channels, activation of K+ channels
* Step 4: Return to normal permeability
Four Steps in the Generation of
| Action Potentials
113
* From beginning of action potential to the return to resting state
* During this time, the membrane will not respond normally to additional stimuli
refectory period
114
* Sodium channels open or inactivated
| * No action potential possible
absolute refractory period
115
* Membrane potential almost normal
| * BUT, Very large stimulus can initiate action potential
• Relative refractory period
116
* The movement of action potentials that have been generated in axon hillock
* This travels along the entire length of the axon
* Consists of a series of repeated actions, NOT passive flow (as we saw in graded potentials)
• Propagation
117
* Continuous propagation: ______ axons
| * Saltatory propagation: ______ axons
unmyelinated; myelinated
118
unmyelinated axon propagation is very ____, repeats in ___ like fashion (tiny steps)
slow; chain
119
* Faster and uses less energy than continuous propagation
* Myelin insulates axon and prevents continuous propagation
* Local current “jumps” from node to node
* Thus, Depolarization occurs only at nodes (rather than along the entire length of the axon in tiny steps)
Saltatory Propagation along Myelinated Axon
120
• Axons behave like electrical cables, so the speed at which action potentials are propagated are determined by
axon diameter and mylenation
121
» Large axon =___ propagation
| » Small axon = ___ propagation
fast; slow
122
» Myelinated axons =____ propagation
| » Unmyelinated axons = ___ propagation
fast; slow
123
• The most important information (vision, balance, motor commands) is carried by
large-diameter, myelinated axons
124
* Are transmitted from presynaptic neuron
* To postsynaptic neuron (or other postsynaptic cell)
* Across a synapse
• Action potentials (nerve impulses)
125
* Direct physical contact between cells
* Are locked together at gap junctions (connexons)
* Allow ions to pass between cells
* Produce continuous local current and action potential propagation
* Are found in areas of brain, eye, ciliary ganglia
• Electrical Synapses
126
* Signal transmitted across a gap by chemical neurotransmitters
* Are found in most synapses between neurons and all synapses between neurons and other cells
* Cells not in direct contact
* Action potential may or may not be propagated to postsynaptic cell, depending on
* Amount of neurotransmitter released
* Sensitivity of postsynaptic cell
• Chemical Synapses
