CH11 Flashcards
1
Q
3 Functions of the Nervous System
A
**1. Sensory input **
2. Integration
- *3. Motor output
- *
2
Q
• Information gathered by sensory receptors about internal and external changes
A
- Sensory input
3
Q
• Interpretation of sensory input
A
Integration
4
Q
• Activation of effector organs (muscles and glands) produces a response
A
Motor output
5
Q
Divisions of the Nervous System
A
1 Central nervous system (CNS)
• Brain and spinal cord
• Integration and command center
2 Peripheral nervous system (PNS)
• Paired spinal and cranial nerves carry messages to and from the CNS
6
Q
Peripheral Nervous System (PNS)
• Two functional divisions
A
- Sensory (afferent) division
• Somatic afferent fibers—convey impulses from skin, skeletal muscles, and joints
• Visceral afferent fibers—convey impulses from visceral organs - Motor (efferent) division
• Transmits impulses from the CNS to effector organs
7
Q
Motor Division of PNS
has what 2 types of nervous systems
A
- Somatic (voluntary) nervous system
• Conscious control of skeletal muscles
- Autonomic (involuntary) nervous system (ANS)
• Visceral motor nerve fibers
• Regulates smooth muscle, cardiac muscle, and glands
• Two functional subdivisions
• Sympathetic
• Parasympathetic
8
Q
Histology of Nervous Tissue
• Two principal cell types
A
- Neurons—excitable cells that transmit electrical signals
- Neuroglia (glial cells)—supporting cells:
• Astrocytes (CNS)
• Microglia (CNS)
• Ependymal cells (CNS)
• Oligodendrocytes (CNS)
• Satellite cells (PNS)
• Schwann cells (PNS)
MOSSEA
9
Q
This supporting cell has=
• Most abundant, versatile, and highly branched glial cells
• Cling to neurons, synaptic endings, and capillaries
• Support and brace neurons
• Help determine capillary permeability
• Guide migration of young neurons
• Control the chemical environment
• Participate in information processing in the brain
A
Astrocytes
10
Q
* This Supporting cell has=*
• Small, ovoid cells with thorny processes
• Migrate toward injured neurons
• Phagocytize microorganisms and neuronal debris
A
Microglia
11
Q
This Supporting Cell has=
- Range in shape from squamous to columnar
- May be ciliated
- Line the central cavities of the brain and spinal column
- Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities
A
Ependymal Cells
12
Q
_ This Supporting Cell has=_
• Branched cells
• Processes wrap CNS nerve fibers, forming insulating myelin sheaths
A
Oligodendrocytes
13
Q
• Surround neuron cell bodies in the PNS
A
• Satellite cells
14
Q
- Surround peripheral nerve fibers and form myelin sheaths
- Vital to regeneration of damaged peripheral nerve fibers
A
• Schwann cells (neurolemmocytes)
15
Q
Neurons (Nerve Cells)
• Special characteristics:
A
- Long-lived (→ 100 years or more)
- Amitotic—with few exceptions
- High metabolic rate—depends on continuous supply of oxygen and glucose
- Plasma membrane functions in:
- Electrical signaling
- Cell-to-cell interactions during development
16
Q
What is
• Biosynthetic center of a neuron
• Spherical nucleus with nucleolus
• Well-developed Golgi apparatus
• Rough ER called Nissl bodies (chromatophilic substance)
• Network of neurofibrils (neurofilaments)
• Axon hillock—cone-shaped area from which axon arises
• Clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS
A
Cell Body (Perikaryon or Soma)
17
Q
• Rough ER are called what
A
Nissl bodies (chromatophilic substance)
18
Q
• Network of neurofibrils are also know as
A
(neurofilaments)
19
Q
• Axon hillock are
A
cone-shaped area from which axon arises
20
Q
• Clusters of cell bodies are called
A
* nuclei* in the CNS,
ganglia in the PNS
21
Q
Processes
are
A
• Dendrites and axons
22
Q
• Bundles of processes are called
A
• Tracts** in the **CNS
• Nerves in the PNS
23
Q
- Short, tapering, and diffusely branched
- Receptive (input) region of a neuron
- Convey electrical signals toward the cell body as graded potentials
A
Dendrites
24
Q
The Axon
How many axon per cell arising from the axon hillock
A
one
25
The Axon
• Long axons are known as
(nerve fibers)
26
The Axon
• Occasional branches are known as
(axon collaterals)
27
The Axon
• Knoblike axon terminals are known as
(synaptic knobs or boutons)
28
The Axon
• Secretory region of neuron do what
• Release neurotransmitters to excite or inhibit other cells
29
Axons Functions are
## Footnote
* Conducting region of a neuron
* Generates and transmits nerve impulses (action potentials) ***_away from the cell body_***
30
## Footnote
Axons: Function
• Molecules and organelles are moved along axons by motor molecules in two directions:
## Footnote
***_ • Anterograde_***—*_toward axonal terminal_*
• Examples: mitochondria, membrane components, enzymes
***_• Retrograde_***—*_toward the cell body_*
• Examples: organelles to be degraded, signal molecules, viruses, and bacterial toxins
31
• Segmented protein-lipoid sheath around most long or large-diameter axons are what
Myelin Sheath
32
Myelin Sheaths
functions is to:
* Protect and electrically insulate the axon
* Increase speed of nerve impulse transmission
33
• Schwann cells wraps many times around
• Schwann cells wraps many times around ***_the axon
_***
34
• Myelin sheath are
•
• Myelin sheath—_concentric layers of Schwann cell membrane
_
35
peripheral bulge of Schwann cell cytoplasm
are known as
• Neurilemma
36
* Myelin sheath gaps between adjacent Schwann cells
* Sites where axon collaterals can emerge
• Nodes of Ranvier
37
• Thin nerve fibers that are unmyelinated
& One Schwann cell may incompletely enclose 15 or more \_\_\_\_\_\_\_\_\_\_\_\_?
Unmyelinated Axons
## Footnote
38
* Formed by processes of oligodendrocytes, not the whole cells
* Nodes of Ranvier are present
* No neurilemma
* Thinnest fibers are unmyelinated
Myelin Sheaths in the CNS
39
• Dense collections of myelinated fibers
## Footnote
• White matter
## Footnote
40
• Mostly neuron cell bodies and unmyelinated fibers
## Footnote
• Gray matter
## Footnote
41
Structural Classification of Neurons
• Three types:
1. Multipolar—
2. Bipolar—
3. Unipolar (pseudounipolar)—
42
1 axon and several dendrites
• Most abundant
• Motor neurons and interneurons
1. Multipolar—
43
1 axon and 1 dendrite
• Rare, e.g., retinal neurons
Bipolar—
44
—single, short process that has two branches:
• Peripheral process—more distal branch, often associated with a sensory receptor
• Central process—branch entering the CNS
Unipolar (pseudounipolar)—
45
Functional Classification of Neurons
• Three types:
1. Sensory (afferent)
2. Motor (efferent)
3. Interneurons (association neurons)
46
• Transmit impulses from sensory receptors toward the CNS
1. Sensory (afferent)
47
• Carry impulses from the CNS to effectors
2. Motor (efferent)
48
• Shuttle signals through CNS pathways; most are entirely within the CNS
Interneurons (association neurons)
49
* Respond to adequate stimulus by generating an action potential (nerve impulse)
* Impulse is always the same regardless of stimulus
* Neurons are highly irritable
Neuron Function
## Footnote
50
• Energy is required to separate opposite charges across a membrane
* Energy is liberated when the charges move toward one another
* If opposite charges are separated, the system has potential energy
• Opposite charges attract each other
Principles of Electricity
51
measure of potential energy generated by separated charge
• Voltage (V)
52
voltage measured between two points
• Potential difference:
53
the flow of electrical charge (ions) between two points
• Current (I):
54
hindrance to charge flow (provided by the plasma membrane)
• Resistance (R):
55
substance with high electrical resistance
• Insulator:
56
substance with low electrical resistance
• Conductor:
57
• serve as membrane ion channels
•**_ Proteins_**
58
• Two main types of ion channels
1. **_Leakage (nongated) channels_**—always open
2. **_Gated channels_** (three types):
• Chemically gated (ligand-gated) channels—open with binding of a specific neurotransmitter
* Voltage-gated channels—open and close in response to changes in membrane potential
* Mechanically gated channels—open and close in response to physical deformation of receptors
59
Gated Channels
• When gated channels are open:
* Ions diffuse quickly across the membrane along their electrochemical gradients
* Along chemical concentration gradients from higher concentration to lower concentration
* Along electrical gradients toward opposite electrical charge
* Ion flow creates an electrical current and voltage changes across the membrane
60
* Potential difference across the membrane of a resting cell
* Approximately –70 mV in neurons (cytoplasmic side of membrane is negatively charged relative to outside)
Resting Membrane Potential (Vr)
61
Resting Membrane Potential (Vr)
• Generated by:
* Differences in ionic makeup of ICF and ECF
* Differential permeability of the plasma membrane
62
**• Differences in ionic makeup in a**
**Resting Membrane Potential**** **
**• ICF has lower concentration of Na+ and Cl– than ECF**
**• ICF has higher concentration of K+ and negatively charged proteins (A–) than ECF**
63
**• Differential permeability of membrane**
**in a**
**Resting Membrane Potential**
**• Impermeable to A–**
**• Slightly permeable to Na+ (through leakage channels)**
**• 75 times more permeable to K+ (more leakage channels)**
**• Freely permeable to Cl–**
64
**• Negative interior of the cell is due to what?**
* * much greater diffusion of K+ out of the cell than Na+ diffusion into the cell
* *
65
**• Sodium-potassium pump stabilizes the **
**resting membrane potential by maintaining the concentration gradients for Na+ and K+**
66
* *• Membrane potential changes when:
* *
**• Concentrations of ions across the membrane change**
* *• Permeability of membrane to ions changes
* *
67
**• Changes in membrane potential are **
** signals used to receive, integrate and send information**
68
Membrane Potentials That Act as Signals
• Two types of signals
• **_Graded potentials_**
Incoming short-distance signals
• **_Action potentials_**
Long-distance signals of axons
69
Changes in Membrane Potential thats
* A reduction in membrane potential (toward zero)
* Inside of the membrane becomes less negative than the resting potential
* Increases the probability of producing a nerve impulse
• Depolarization
70
Changes in Membrane Potential that has
* An increase in membrane potential (away from zero)
* Inside of the membrane becomes more negative than the resting potential
* Reduces the probability of producing a nerve impulse
• Hyperpolarization
71
** • Occur when a stimulus causes gated ion channels to open
• E.g., receptor potentials, generator potentials, postsynaptic potentials
• Magnitude varies directly (graded) with stimulus strength
• Decrease in magnitude with distance as ions flow and diffuse through leakage channels
• Short-distance signals**
**• Short-lived, localized changes in membrane potential**
**• Depolarizations or hyperpolarizations**
* *• Graded potential spreads as local currents change the membrane potential of adjacent regions
* *
* *Graded Potentials
* *
72
* Brief reversal of membrane potential with a total amplitude of ~100 mV
* Occurs in muscle cells and axons of neurons
* Does not decrease in magnitude over distance
* Principal means of long-distance neural communication
Action Potential (AP)
73
Generation of an Action Potential
* Only leakage channels for Na+ and K+ are open
* All gated Na+ and K+ channels are closed
• Resting state
## Footnote
74
**• Properties of gated channels**
* *• Each Na+ channel has two voltage-sensitive gates
* *
**• _Activation gates_**
Closed at rest; open with depolarization
**_• Inactivation gates_**
Open at rest; block channel once it is open
Opens slowly with depolarization
75
**• Some K+ channels remain open, allowing excessive K+ efflux**
**• This causes after-hyperpolarization of the membrane (undershoot)**
**• Hyperpolarization**
76
* Membrane is depolarized by 15 to 20 mV
* Na+ permeability increases
* Na influx exceeds K+ efflux
* The positive feedback cycle begins
**• At threshold:**
77
**weak local depolarization that does not reach threshold**
**• Subthreshold stimulus—**
78
strong enough to push the membrane potential toward and beyond threshold
• Threshold stimulus—
79
action potentials either happen completely, or not at all
**• AP is an all-or-none phenomenon**
80
Coding for Stimulus Intensity
* All action potentials are alike and are independent of stimulus intensity
* How does the CNS tell the difference between a weak stimulus and a strong one?
**• Strong stimuli can generate action potentials more often than weaker stimuli**
**• The CNS determines stimulus intensity by the frequency of impulses**
81
**
• Larger diameter fibers have less resistance to local current flow and have faster impulse conduction
**
* *• Effect of axon diameter
* *
82
* *• Continuous conduction in unmyelinated axons is slower than saltatory conduction in myelinated axons
* *
• Effects of myelination
83
* Myelin sheaths insulate and prevent leakage of charge
* Saltatory conduction in myelinated axons is about 30 times faster
* Voltage-gated Na+ channels are located at the nodes
* APs appear to jump rapidly from node to node
• Effect of myelination
84
• Nerve fibers are classified according to:
**
• Diameter
• Degree of myelination
• Speed of conduction**
85
• Large diameter, myelinated somatic sensory and motor fibers
## Footnote
**• Group A Nerve fibers**
## Footnote
86
• Intermediate diameter, lightly myelinated ANS fibers
## Footnote
• Group B Nerve fibers
## Footnote
87
Smallest diameter, unmyelinated ANS fibers
## Footnote
• Group C Nerve fibers
## Footnote
88
* A junction that mediates information transfer from one neuron:
* To another neuron, or
* To an effector cell
* *The Synapse
* *
89
conducts _impulses toward_ the synapse
• Presynaptic neuron—
90
transmits _impulses away_ from the synapse
• Postsynaptic neuron—
91
Types of Synapses
—between the axon of one neuron and the dendrite of another
**• Axodendritic **
92
Types of Synapses
• between the axon of one neuron and the soma of another
• Axosomatic
93
Types of Synapses
• Less common types:
* Axoaxonic (axon to axon)
* Dendrodendritic (dendrite to dendrite)
* Dendrosomatic (dendrite to soma)
94
* Less common than chemical synapses
* Neurons are electrically coupled (joined by gap junctions)
* Communication is very rapid, and may be unidirectional or bidirectional
**Electrical Synapses**
95
Electrical Synapses
• Are important in:
**• Embryonic nervous tissue**
**• Some brain regions**
96
• Specialized for the release and reception of neurotransmitters
**Chemical Synapses**
97
Chemical Synapses
• Typically composed of two parts
**• Axon terminal of the presynaptic neuron, which contains synaptic vesicles**
**• Receptor region on the postsynaptic neuron**
98
* Fluid-filled space separating the presynaptic and postsynaptic neurons
* Prevents nerve impulses from directly passing from one neuron to the next
Synaptic Cleft
99
Synaptic Cleft
• Transmission across the synaptic cleft:
**• Is a chemical event (as opposed to an electrical one)**
**• Involves release, diffusion, and binding of neurotransmitters**
**• Ensures unidirectional communication between neurons**
100
• What happens Within a few milliseconds, the neurotransmitter effect is terminated
•
* Degradation by enzymes
* Reuptake by astrocytes or axon terminal
* Diffusion away from the synaptic cleft
101
Postsynaptic Potentials
• Graded potentials
• Strength determined by:
**• Amount of neurotransmitter released**
* *• Time the neurotransmitter is in the area
* *
102
• Types of postsynaptic potentials
**1_. EPSP_—_excitatory_ postsynaptic potentials**
**2. _IPSP_—_inhibitory_ postsynaptic potentials**
103
• One or more presynaptic neurons transmit impulses in rapid-fire order
• Temporal summation
104
• Postsynaptic neuron is stimulated by a large number of terminals at the same time
• Spatial summation
105
* Released at neuromuscular junctions and some ANS neurons
* Synthesized by enzyme choline acetyltransferase
* Degraded by the enzyme acetylcholinesterase (AChE)
* *• Acetylcholine (Ach)
* *
106
Chemical Classes of Neurotransmitters
• Peptides (neuropeptides) include:
• **_Substance P_**
Mediator of pain signals
• **_Endorphins_**
Act as natural opiates; reduce pain perception
**_• Gut-brain peptides_**
Somatostatin and cholecystokinin
107
* Act in both the CNS and PNS
* Produce fast or slow responses
* Induce Ca2+ influx in astrocytes
* Provoke pain sensation
* *• Purines such as ATP:
* *
108
* Synthesized on demand
* Activates the intracellular receptor guanylyl cyclase to cyclic GMP
* Involved in learning and memory
**• Nitric oxide (NO)**
109
is a regulator of cGMP in the brain
**• Carbon monoxide (CO) **
110
* Lipid soluble; synthesized on demand from membrane lipids
* Bind with G protein–coupled receptors in the brain
* Involved in learning and memory
**• Endocannabinoids**
