Chapter 12: Nervous Tissues Flashcards
1
Q
How does the spinal cord connect to the brain?
A
The foramen magnum of the occipital bone.
2
Q
What is the PNS?
A
All nervous tissue outside of the CNS including cranial nerves, spinal nerves and sensory receptors.
3
Q
Somatic and autonomic nervous systems are part of which division of the nervous system?
A
PNS; motor
4
Q
What is the somatic nervous system?
A
Conveys output from CNS to skeletal muscles for voluntary movement.
5
Q
What is the autonomic nervous system?
A
Conveys output from CNS to smooth muscle, cardiac muscle, and glands for involuntary movement.
6
Q
Which nervous system controls fight or flight?
A
Sympathetic.
7
Q
Which nervous system controls rest and digest?
A
Parasympathetic.
8
Q
Sympathetic, parasympathetic and enteric nervous systems are part of which division?
A
Autonomic.
9
Q
What does the enteric nervous system do?
A
Regulate activity of smooth muscle and glands of GI tract.
10
Q
Nerve.
A
Bundle of axons and associated tissue and blood vessels in the PNS.
11
Q
Tract.
A
Bundle of axons in the CNS that interconnect neurons in the spinal cord and brain.
12
Q
How many pairs of cranial nerves and spinal nerves are in the human body?
A
Cranial: 12. Spinal: 31.
13
Q
What are the 3 basic functions of the nervous system?
A
Sensory, integrative and motor.
14
Q
Stimulus.
A
Any change in the environment strong enough to elicit an AP.
15
Q
How does a nerve impulse travel?
A
Rapidly and at a constant strength.
16
Q
What are the components of a neuronal cell body?
A
Nucleus, cytoplasm, cellular organelles, cytoskeleton, neurofibrils, microtubules.
17
Q
Neurofibrils.
A
Bundles of intermediate filaments that provide cell shape and support.
18
Q
Microtubules.
A
Assist in moving materials between cell body and axon.
19
Q
Ganglion.
A
Collection of neuronal cell bodies in the PNS.
20
Q
Nucleus.
A
Collection of neuronal cell bodies in the CNS.
21
Q
Lipofuscin.
A
Pigment found as clumps of granules in the cytoplasm of aging neurons. Is not harmful for the neuron.
22
Q
What are the components of neuronal dendrites?
A
They are short and highly branched processes that receive input. The PM contains receptors sites for NTs, and the cytoplasm contains organelles.
23
Q
Describe the neuronal axon.
A
Long and thin process that propagates nerve impulses.
24
Q
Initial segment.
A
The part of the axon closest to the axon hillock.
25
Trigger zone.
Where the nerve impulses arise and is the junction between the axon hillock and initial segment.
26
Axoplasm.
The cytoplasm surrounded by plasma membrane (which is also called axolemma).
27
Axon collaterals.
Side branches off of the axon.
28
Axon hillock.
Where the axon joins the cell body of the neuron.
29
Does protein synthesis occur in the axon?
No, because there is no RER.
30
Slow axonal transport.
Moves materials 1-5mm a day to convey axoplasm in one direction only (from cell body to axon terminal).
31
Fast axonal transport.
Moves materials 200-400mm a day and uses proteins to transport along microtubule surfaces in two directions.
32
Anterograde.
Forward. Cell body to axon terminals.
33
Retrograde.
Backward. Axon terminals to cell body.
34
Retrograde.
Backward. Axon terminals to cell body.
35
How are neurons structurally classified?
Based on their number of processes.
36
Multipolar neuron.
Many dendrites and a single axon. Most commonly found in CNS.
37
Bipolar neuron.
One main dendrite and a single axon. Found in retina, inner ear and olfactory area of brain.
38
Unipolar neuron.
Many dendrites and a single axon are fused together to form a continuous process that emerges from the cell body. The trigger zone is at the junction of the dendrites and axon.
39
Why is the unipolar neuron also called the pseudounipolar neuron?
They begin in embryo as bipolar neurons.
40
How are neurons functionally classified?
Based on the direction in which the impulse is conveyed.
41
Sensory neuron.
Contains sensory receptors at dendrites or is located right after a sensory receptor. Forms APs activated by stimuli. Most are unipolar.
42
Motor neuron.
Convey APs away from the CNS. Most are unipolar.
43
Interneuron.
Usually located in CNS between sensory and motor neurons. Most are multipolar.
44
Neuroglia.
Smaller than neurons, makes up half the volume of the CNS, cannot generate or propagate APs, and can multiply and divide in the mature nervous system.
45
What is the function of neuroglia?
They multiply to fill in spaces formerly occupied by neurons.
46
Glioma.
Highly malignant brain tumour derived from glia.
47
What are the 6 types of neuroglia and where are they located?
Astrocytes (CNS), oligodendrocytes (CNS), microglia (CNS), ependymal cells (CNS), Schwann cells (PNS), satellite cells (PNS).
48
What characteristics can neuroglia of the CNS be classified by?
Size, cytoplasmic processes, and intracellular organization.
49
Astrocytes.
Large star-shaped neuroglia with many processes that make contact with capillaries, neurons and pia mater.
50
Protoplasmic astrocytes.
Neuroglia in gray matter with short branching processes.
51
Fibrous astrocytes.
Neuroglia in white matter with many long unbranched processes.
52
What are the functions of astrocytes?
1) They contain microfilaments which give them strength and allow them to support neurons. 2) Processes of astrocytes wrapped around capillaries isolate neurons of the CNS from harmful substances in the blood by secreting chemicals. 3) In embryo, astrocytes secrete chemicals that regulate growth, migration and interconnection of neurons in the brain. 4) They maintain appropriate chemical environment for the generation of nerve impulses. 5) They play a role in learning and memory by influencing the formation of neural synapses.
53
Oligodendrocytes.
Resemble astrocytes, but are smaller and have fewer processes. Processes form the myelin sheath.
54
Microglia.
Small neuroglia with slender processes that give off spineline projections. Function as phagocytes.
55
Ependymal cells.
Cuboidal and columnar-shaped neuroglia arranged in a single layer. Line ventricles of the brain and central canal of spinal cord. Produce CSF and form the blood-CSF barrier.
56
Schwann cells.
Neuroglia that encircle PNS axons, form myelin sheath, and has a role in axon regeneration.
57
Satellite cells.
Flat neuroglia that surround PNS cell bodies, provide structural support, and regulate the exchanges of materials between cell bodies and interstitial fluid.
58
Which neuroglia completely surround axons and cell bodies?
Neuroglia of the PNS.
59
Myelin sheath.
Layers of lipids and proteins that cover axons.
60
Which neuroglial cells are involved in myelin sheath formation?
Schwann cells (PNS) and oligodendrocytes (CNS).
61
What is the role of a Schwann cell in myelin sheath formation in the PNS?
Schwann cells begin to form myelin sheaths around axons during fetal development by spirally many times around axons.
62
What is the outermost layer of PNS myelin sheath made of?
Schwann cell cytoplasm (neurolemma) and nucleus.
63
What is the innermost layer of PNS myelin sheath made of?
100 layers of Schwann cell membrane.
64
What is the role of an oligodendrocyte in myelin sheath formation of the CNS?
Oligodendrocytes myelinate parts of several axons by spiralling many times. CNS myelin sheaths do not have a neurolemma, oligodendrocyte cell body or nucleus.
65
Why are an infant's responses to stimuli slow and uncoordinated?
Myelination is still in progress.
66
What are the components of white matter?
Myelinated axons.
67
What are the components of gray matter?
Unmyelinated axons, neuronal cell bodies, dendrites, axon terminals, neuroglia.
68
Why does gray matter appear gray?
Due to unmyelinated axons and gray colour of Nissl bodies.
69
Are blood vessels present in both white and gray matter?
Yes.
70
Graded potentials.
Short distance communication. A small deviation from the resting membrane potential that makes the membrane either more or less polarized.
71
Hyperpolarizing graded potential.
Makes the membrane more polarized, and more negative.
72
Depolarizing graded potential.
Makes the membrane less polarized, and less negative.
73
When and where does a graded potential occur?
When: a stimulus causes mechanically-gated or ligand-gated channels to open or close. Where: dendrites and cell body of a neuron, and in sensory receptors.
74
Decremental conduction.
Graded potentials die out as they spread along the membrane, which is not the case for action potentials.
75
Summation.
A graded potential can become stronger and last longer by summating with other graded potentials.
76
Are refractory periods present in graded potentials?
No.
77
Receptor potentials.
Graded potentials that occur in sensory receptors.
78
Postsynaptic potentials.
Graded potentials that occur in dendrites or cell bodies.
79
Action potentials.
Long distance communication. Decreases and reverses the resting membrane potential and then restores it.
80
Depolarizing phase.
Negative membrane potential becomes less negative, reaches zero, and then becomes positive due to Na+ channels opening to allow Na+ ions to flow inwards. (-70 mV --> -55 mV --> +33 mV).
81
Repolarizing phase.
Membrane potential is restored to resting by Na+ channels closing and K+ channels opening to allow K+ ions to flow outwards. (+33 mV --> -70 mV).
82
After hyperpolarization phase.
Membrane potential becomes more negative than resting since K+ channels remain open, and then the membrane potential returns to rest once K+ channels close. (-70 mV --> -90 mV --> -70 mV).
83
Vg Na+ channel.
At rest, inactivation gate is open, and activation gate is closed. At threshold, both gates open.
84
Vg K+ channel.
Does not have an inactivated state so it alternates between open and closed.
85
Threshold for action potential.
-55 mV
86
Subthreshold stimulus.
Weak depolarization that cannot bring the membrane potential to threshold.
87
Suprathreshold stimulus.
Strong depolarization that can generate multiple action potentials.
88
Refractory period.
Period of time after an AP begins where an excitable cell cannot generate another AP in response to a normal threshold stimulus because inactivated Na+ channels cannot reopen before returning to resting.
89
Absolute refractory period.
Period of time where even a very strong stimulus cannot initiate a second AP.
90
How long is the absolute refractory period in large diameter axons, and in small diameter axons?
Large: 0.4 msec. Small: 4 msec.
91
Relative refractory period.
Period of time where a second AP can be initiated only by a large stimulus and when K+ channels are still open after Na+ channels have returned to resting.
92
Describe the steps of an electrical potential when picking up a pen.
You touch the pen --> a graded potential develops in a sensory receptor in the skin --> triggers axon of sensory neuron to form an AP --> travels along axon to CNS --> causes release of NTs at a synapse with an interneuron --> NTs stimulate interneuron to form a graded potential in it dendrites and cell body --> axon of interneuron forms a nerve AP --> travels along axon --> causes NT release at next synapse with another interneuron --> perception occurs once interneurons in cerebral cortex are activated --> you feel the pen in your hand.
93
Describe the steps of an electrical potential when writing a letter.
Stimulus in brain causes a graded potential to form in the dendrites and cell body of an UMN --> causes a nerve AP in axon of UMN --> NT release --> generates a graded potential in a LMN --> causes a nerve AP in the LMN --> NT release at NMJ --> NTs stimulate skeletal muscle fibres that control finger movements to form muscle APs --> muscle fibres contract.
94
What does the production of graded potentials and action potentials depend on?
The existence of a resting membrane potential and the presence of specific ion channels.
95
Leak channel.
Gate randomly opens and closes.
96
Ligand-gated channel.
Gate opens and closes in response to ligand binding. Located in dendrites of sensory neurons, and dendrites and cell bodies of interneurons and motor neurons.
97
Mechanically-gated channel.
Gate opens and closes in response to mechanical stimulation (vibration, touch, pressure, stretching).
98
Voltage-gated channel.
Gate opens and closes in response to membrane potential changes.
99
Resting membrane potential.
Buildup of negative ions inside the cell, and buildup of positive ions outside the cell.
100
How does the resting membrane potential arise?
1) Unequal distribution of ions in the cytosol and ECF. Cytosol is rich in K+, and the ECF is rich in Na+ and Cl-. More K+ leave the cell than Na+ enter the cell because of K+ leak channels. 2) Inability of most anions to leave the cell because they are attached to nondiffusible molecules. 3) Electrogenic nature of Na+/K+ ATPases, since they pump out 3 Na+ as fast as it leaks in and also brings in 2 K+.
101
How does an action potential propagate by positive feedback?
It regenerates over and over at adjacent regions of the membrane from the trigger zone to the axon terminals.
102
Continuous conduction.
Step-by-step depolarization and repolarization of each adjacent segment of the PM. Occurs in unmyelinated axons and muscle fibres.
103
Saltatory conduction.
Special mode of propagation that occurs along myelinated axons due to the uneven distribution of Vg channels. There are lots of Vg channels at the nodes of Ranvier, but not along the myelinated axon, so the impulse jumps from node to node, resulting in faster conduction. As the current passes through the nodes, each node repolarizes after it depolarizes.
104
Under what conditions would an AP propagate more rapidly.
Along myelinated axons, large diameter axons, and warmed axons.
105
A-fibres.
Large diameter axons, myelinated, brief refractory period, fast. Respond to touch, pressure, joint position, temperature, pain, skeletal muscle impulses.
106
B-fibres.
Myelinated, long refractory period, conduct sensory impulses from viscera to CNS. Respond to autonomic motor neurons.
107
C-fibres.
Small diameter axons, unmyelinated, longest absolute refractory period. Respond to pain, touch, pressure, temperature. Simulate the heart, smooth muscle and glands through autonomic ganglia.
108
Electrical synapse.
AP conducts directly between PMs of adjacent neurons through gap junctions.
109
Where are gap junctions located?
Visceral smooth muscle, cardiac muscle, brain, and developing embryo.
110
What are the advantages of gap junctions?
Faster communication and synchronization.
111
Chemical synapse.
PMs of a presynaptic and postsynaptic neuron do not make contact, so they are separated by a synaptic cleft.
112
Why are chemical synapses slower than electrical synapses?
Synaptic delay of 0.5 msec in chemical synapses.
113
What happens at a chemical synapse?
Nerve impulse travels to synaptic end bulb of presynaptic neuron --> depolarizing phase opens Ca2+ channels which allows Ca2+ ions to flow inward --> triggers exocytosis of synaptic vesicles --> NTs are released into synaptic cleft --> binds to receptors on postsynaptic cell --> channels open to allow ions to flow across PM --> change in membrane potential (depolarization or hyperpolarization) --> AP is triggered in axon of postsynaptic neuron if a depolarizing potential reaches threshold.
114
Excitatory postsynaptic potential.
Depolarization. Brings membrane closer to threshold, making cell more excitable. Results if the total excitatory effects are greater than the total inhibitory effects, but less than threshold.
115
Inhibitory postsynaptic potential.
Hyperpolarization. Brings membrane farther from threshold. Results if total inhibitory effects are greater than excitatory effects.
116
Ionotropic receptor.
Contains NT binding site and ion channel in one protein.
117
Metabotropic receptor.
Contains NT binding site that is coupled to a separate ion channel by a G-protein.
118
What happens when excitatory NTs bind to inotropic receptors that contain cation channels?
EPSP --> Na+, K+, Ca2+
119
What happens when inhibitory NTs bind to inotropic receptors that contain anion channels?
IPSP --> Cl-
120
What happens when inhibitory NTs bind to metabotropic receptors linked to K+ channels?
IPSP --> K+
121
What is the role of the G-protein in metabotropic receptors?
When a NT binds, the G-protein either directly opens or closes the ion channel, or the G-protein activates a second messenger to work indirectly.
122
How can NTs be removed from the synapse?
Diffusion, enzymatic degradation, reuptake, uptake.
123
Spatial summation.
Summation of postsynaptic potentials in response to stimuli that occur at different locations in the membrane, but at the same time.
124
Temporal summation.
Summation of postsynaptic potentials in response to stimuli that occur at the same location in the membrane, but at different times.
125
Acetylcholine.
Small molecule NT released by PNS and CNS neurons. Excitatory at NMJ. Inhibitory for heart rate. Inactivated by AChE.
126
Amino acids.
Small molecule NTs. Glutamate and aspartate are excitatory. GABA and glycine are inhibitory.
127
Biogenic amines.
Small molecule NTs that bind to metabotropic receptors. NE, EP, DA, 5HT.
128
Norepinephrine.
NT, hormone and catecholamine released by adrenal medulla. Synthesized from tyrosine. Inactivated via reuptake or COMT/MAO. Involved in regulating arousal, dreams, and mood.
129
Epinephrine.
NT, hormone and catecholamine released by adrenal medulla. Synthesized from tyrosine. Inactivated via reuptake or COMT/MAO.
130
Dopamine.
NT and catecholamine synthesized from tyrosine. Inactivated via reuptake or COMT/MAO. Involved in regulating emotional responses, addictive behaviours, pleasurable experiences, and skeletal muscle tone.
131
Serotonin.
NT involved in regulating sensory perception, temperature, mood, appetite and sleep.
132
ATP and purines.
Small molecule NTs that are excitatory in CNS and PNS. Sympathetic neurons release ATP and NE together. Parasympathetic neurons release ATP and ACh together.
133
Nitric oxide.
Small molecule NT that is excitatory and secreted in CNS, adrenal glands and nerves to penis. Not synthesized in advance so it is rapidly formed from arginine by nitric oxide synthase when needed. Highly reactive, lipid soluble, associated with memory and learning, and activates cGMP.
134
Carbon monoxide.
Small molecule NT that is anti-inflammatory, excitatory and secreted in the brain in response to neuromuscular and neuroglandular functions. Involved in blood vessel dilation, memory, olfaction, vision, thermoregulation and insulin release.
135
Neuropeptides.
NTs consisting of 3-40 amino acids linked by peptide bonds. Bind to metabotropic receptors to have excitatory and inhibitory effects. Formed in neuronal cell bodies, packaged in vesicles and transported to axon terminals for exocytosis.
136
Opioid peptides.
Enkephalins, endorphins and dynorphins. Natural painkillers. Memory, learning, pleasure, euphoria, temperature control, hormone regulation, sexual drive, reproduction, depression and SCZ.
137
Substance P.
Enhances pain perception and counters the effects of nerve damaged chemicals. Enkephalin and endorphin suppress substance P release.
138
Neural circuit.
A functional group of neurons that processes a specific type of information.
139
Simple series circuit.
Presynaptic neuron stimulates a single postsynaptic neuron to stimulate another and so on...etc.
140
Divergence.
A single presynaptic neuron synapses with several postsynaptic neurons.
141
Diverging circuit.
A nerve impulse from a single presynaptic neuron causes the stimulating of increasing numbers of cells along the circuit.
142
Convergence.
Several presynaptic neurons synapse with a single postsynaptic neuron.
143
Converging circuit.
A postsynaptic neuron receives nerve impulses from several different sources.
144
Reverberating circuit.
The incoming impulse stimulates the first neuron which stimulates the second, and so on...etc. Branches from later neurons synapse with earlier ones to send impulses back through the circuit again and again. Inhibitory neurons may turn off this circuit after a period of time.
145
Which activities are controlled through a reverberating circuit?
Breathing, coordinated muscle movements, waking up, short-term memory.
146
Parallel after discharge circuit.
A single presynaptic cell stimulates a group of neurons, each of which synapses with a common postsynaptic cell. A different number of synapses between the first and last neuron imposes varying synaptic delays so that the last neuron exhibits multiple EPSPs and IPSPs. If the input is excitatory, the postsynaptic neuron can send out a stream of impulses in quick succession.
147
In the PNS, axons and dendrites that are associated with a neurolemma may undergo repair if:
Cell body is intact, Schwann cells are functional, and scar tissue formation does not occur too rapidly.
148
Chromatolysis.
When the Nissl bodies of a neuronal process break into fine granular masses 24-48 hours after injury.
149
Wallerian degeneration.
Degeneration of distal part of axon and myelin sheath.
150
Regeneration tube.
Formed by Schwann cells. Guides growth of a new axon from the proximal area across the injured area into the distal area.
151
Neurogenesis.
Birth of new neurons from undifferentiated stem cells.
152
Epidermal growth factor.
Stimulates cells to proliferate into neurons and astrocytes.
153
Hippocampus.
Region of neurogenesis in the adult brain.
154
Why is there no neurogenesis in other regions of the adult brain?
Inhibitory influence of neuroglia and absence of growth-stimulating cues.
