nervous tissue Flashcards
1
Q
deals with normal functioning and disorders of the nervous system
A
Neurology
2
Q
is a physician who diagnoses and treats disorders of the nervous system.
A
Neurologist
3
Q
Mass of only 2 kg (4.5 lb), about 3% of the total body weight, the ____________is one of the smallest and yet the most complex of the 11 body systems.
A
nervous system
4
Q
Structures of the Nervous System
A
• Brain
• Spinal Cord
• Nerves(Cranial and Spinal)
• Ganglia
• Enteric Plexuses
• Sensory receptors
5
Q
neurons enclosed within skull
A
Brain
6
Q
connects to brain and enclosed
within spinal cavity
A
Spinal cord
7
Q
bundles of many axons of neurons
A
Nerves
8
Q
(12 pairs) emerge from brain
A
Cranial nerves
9
Q
(31 pairs) emerge from spinal cord
A
Spinal nerves
10
Q
groups of neuron cell bodies located outside of brain and spinal cord
A
Ganglia
11
Q
networks in digestive tract
A
Enteric plexuses
12
Q
monitor changes in internal or external environments
A
Sensory receptors
13
Q
Functions of the Nervous System
A
• Sensory (Input)
• Integration (Process)
• Motor Activity (Output)
14
Q
• receptors and sensory nerves
A
Sensory (input)
15
Q
• Carry information into brain and spinal cord
A
Sensory (input)
16
Q
information processing
A
Integration (process)
17
Q
awareness of sensory input
A
Perception
18
Q
Analyzing and storing information to help lead to appropriate responses
A
Integration (process)
19
Q
efferent nerves
A
Motor activity (output)
20
Q
Signals to muscles and glands (effectors)
A
Motor activity (output)
21
Q
Organization of the Nervous System
A
• Central Nervous System (CNS)
• Peripheral Nervous System (PNS)
22
Q
Brain (100 billion neurons) and spinal cord (100 million neurons)
A
Central Nervous System (CNS)
23
Q
source of thoughts, emotions, and memories
A
Central Nervous System (CNS)
24
Q
signals that stimulate muscles to contract and glands to secrete
A
Central Nervous System (CNS)
25
All nervous system structures outside of the CNS
Peripheral Nervous System (PNS)
26
include nerves, ganglia, enteric plexuses, and sensory receptors
Peripheral Nervous System (PNS)
27
Central nervous system (CNS) structures:
• Brain
• Spinal cord
28
Peripheral nervous system (PNS) structures:
• Cranial nerves and branches
• Spinal nerves and branches
• Ganglia
• Sensory receptors
29
Divisions of Peripheral nervous system (PNS)
• Somatic (SNS)
• Autonomic (ANS) nervous systems
• Enteric nervous system (ENS)
30
Sensory neurons from head, body wall, limbs, special sense organs
Somatic (SNS)
31
Motor neurons to skeletal muscle: voluntary
Somatic (SNS)
32
Sensory neurons from viscera
Autonomic (ANS) nervous systems
33
Motor neurons to viscera (cardiac muscle, smooth muscle, glands): involuntary
Autonomic (ANS) nervous systems
34
“fight-or-flight” or “fight-fright-flight”
• Sympathetic (ANS)
35
“rest-and-digest”
Parasympathetic (ANS)
36
“brain of the gut”
Enteric nervous system (ENS)
37
govern contraction of GI tract smooth muscle to propel food, secretions of the GI tract organs such as acid from the stomach, and activity of GI tract endocrine cells, which secrete hormones (involuntary)
Enteric nervous system (ENS)
38
Skeletal muscle
SNS
39
Smooth muscle,
Cardiac muscle,
Glands
ANS
40
Smooth muscle,
Glands,
Endocrine cells of GI tract
ENS
41
HISTOLOGY OF NERVOUS TISSUE
Two cell types:
• Neurons
• Neuroglia cells
42
Can respond to stimuli and convert stimuli to electrical signals (nerve impulses or action potentials) that travel along neurons
Neurons
43
support, nourish and protect neurons
Neuroglia cells
44
critical for homeostasis of interstitial fluid around neurons
Neuroglia
45
continue to divide throughout an individual’s lifetime
Neuroglia
46
Parts of a Neuron
• Cell body (perikaryon or soma)
• Dendrites
• Axon
47
nucleus, cytoplasm with typical organelles
Cell body (perikaryon or soma)
48
highly branched structures that carry impulses to the cell body
Dendrites
49
receiving or input portions of a neuron
Dendrites
50
conducts away from cell body toward another
neuron, muscle or gland
Axon
51
Emerges at cone-shaped axon hillock
Axon
52
contain synaptic vesicles that can release neurotransmitters
Axon terminals
53
Structural Classes of Neuron
• Multipolar
• Bipolar
• Unipolar
54
Have several or many dendrites and one axon
Multipolar
55
Most common type in brain and spinal cord
Multipolar
56
Have one dendrite and one axon
Bipolar
57
Example: in retina of eye and inner ear
Bipolar
58
Have fused dendrite and axon
Unipolar
59
Sensory neurons of spinal nerves
Unipolar
60
Sensory receptors
dendrites of unipolar neurons
61
Functional Classes of Neuron
• Sensory (afferent)
• Motor (efferent)
• Interneurons (association neurons)
62
sensory neuron forms an action potential in its axon and the action potential is conveyed into the CNS through cranial or spinal nerves. (unipolar)
Sensory (afferent)
63
convey action potentials away from the CNS to effectors (muscles and glands) in the periphery (PNS) through cranial or spinal nerves. (multipolar)
Motor (efferent)
64
integrate (process) incoming sensory information from sensory neurons and then elicit a motor response by activating the appropriate motor neurons. (multipolar)
Interneurons (association neurons)
65
Cells smaller but much more numerous than neurons
Neuroglia
66
Can multiply and divide and fill in brain areas
Neuroglia
67
brain tumors derived from neuroglia
Gliomas
68
Do not conduct nerve impulses
Do support, nourish and protect neurons
Neuroglia
69
Neuroglia of the CNS (4 types)
• Astrocytes
• Oligodendrocytes
• Microglia
• Ependymal cells
70
(star shaped): help form blood brain barrier
• regulate the growth, migration of neurons in the brain & play a role in learning and memory
Astrocytes
71
have many short branching processes and are found in gray matter.
Protoplasmic astrocytes
72
have many long unbranched processes and are located mainly in white matter.
Fibrous astrocytes
73
produce myelin in CNS
Oligodendrocytes
74
• protect CNS cells from disease
• function as phagocytes.
Microglia
75
form CSF in ventricles
Ependymal cells
76
produce myelin around PNS neurons; help to regenerate PNS axons
Schwann
77
support neurons in PNS ganglia
Satellite cells
78
• Axons covered with a myelin sheath
• Many layers of lipid and protein: insulates neurons
• Increases speed of nerve conduction
• Appears white (in white matter)
Myelination
79
gaps in the myelin
Nodes of Ranvier
80
are important for rapid signal conduction
Nodes
81
Some diseases destroy myelin
• Multiple sclerosis
• Tay-Sachs
82
Collections of Nervous Tissue
• Clusters of neuron cell bodies
• Bundles of axons
83
cluster of cell bodies in PNS
Ganglion
84
Bundles of axons
• Nerve
• Tract
85
cluster of cell bodies in PNS
Ganglion
86
cluster of cell bodies in CNS
Nucleus
87
bundle of axons in PNS
Nerve
88
bundle to axons in CNS
Tract
89
primarily myelinated axons
White matter
90
cell bodies, dendrites, unmyelinated axons, axon terminals, neuroglia
Gray matter
91
white matter (tracts) surround centrally located gray matter “H” of “butterfly”
Spinal cord
92
gray matter in thin cortex surrounds white matter (tracts)
Brain
93
Axons and dendrite in the PNS can be repaired if cell body is intact and Schwann cells functional. These form a regeneration tube and grow axons or dendrites if scar tissue does not fill the tube
Regeneration of PNS neurons
94
• Very limited even if cell body is intact
• Inhibited by neuroglia and by lack of fetal growth- stimulators
Regeneration of CNS neurons
95
nerve impulses
Action potentials
96
a charge difference across cell membrane (polarization)
membrane potential
97
allow ions to move by diffusion from high to low concentration
Ion channels
98
four types of ion channels
• leak channels,
• ligand-gated channels,
• mechanically gated channels,
• voltage-gated channels
99
allow ions to leak through membrane; there are more for K+ than for Na+
Leakage channels
100
opens and closes in response to the binding of a ligand (chemical) stimulus.
Ligand-gated channel
101
opens or closes in response to mechanical stimulation in the form of vibration (such as sound waves), touch, pressure, or tissue stretching.
Mechanically gated channel
102
opens in response to a change in membrane potential (voltage). Participate in the generation and conduction of action potentials in the axons of all types of neurons.
voltage-gated channel
103
Resting Membrane Potential
• Typically –70 mV
• Inside of membrane more negative than outside
104
Inside (more negative) because cytosol has:
• Many negative ions (too large to leak out):
amino acids (in cellular proteins) and
phosphates (as in ATP)
• K+ that easily leaks out through many K+ channels
Outside (more positive) because interstitial fluid has:
• Few negative ions
• Na+ that does not leak out of cell: few Na+ channels
• Membrane “pumps” that quickly pump out Na+ that does leak (diffuse) into cell
Caused by presence of ions
105
RMP three major factors
(1) unequal distribution of ions in the ECF and cytosol,
(2) inability of most anions to leave the cell
(3) the electrogenic nature of the Na/K ATPases.
106
a sequence of rapidly occurring events that decrease and reverse the membrane potential and then eventually restore it to the resting state.
Action Potential (impulse)
107
An initial event (stimulus) is required
• Triggers resting membrane to become more
permeable to Na+
• Causes enough Na+ to enter cell so that cell membrane reaches threshold (~ –55 mv)
• If so, the following events occur: action potential which spreads along neuron or muscle fiber
Action Potential (impulse)
108
Na+ channels open à as more Na+ enters cell, membrane potential rises and becomes positive
(-70-> -55 -> 0 + 30 mv)
Depolarizing phase
109
K+ channels openàas more K+ leave cell, membrane potential is returned to resting value
(+ 30 -> 0 -> -70 mv)
Repolarizing phase
110
May overshoot
hyperpolarizing phase
111
Typically depolarization and repolarization take place in about _____________
1 millisecond (1/1000 sec)
112
• Levels of ions back to normal by action of Na+/K+
pump
• Refractory period (brief): even with adequate stimulus, cell cannot be activated
Recovery
113
If a stimulus is strong enough to cause depolarization to threshold level, the impulse will travel the entire length of the neuron at a constant and maximum strength.
All-or-none principle
114
Each section triggers the next locally as even more
Na+ channels are opened (like row of dominos)
Nerve impulse conduction (propagation)
115
Types of conduction
• Continuous conduction
• Saltatory conduction
116
In unmyelinated fibers; slower form of conduction
Continuous conduction
117
In myelinated fibers; faster as impulses “leap” between nodes of Ranvier
Saltatory conduction
118
Factors that increase rate of conduction
Myelin,
large diameter and
warm nerve fibers
119
(neuron-neuron)
Synapse
120
(neuron-muscle fiber)
Neuromuscular junction
121
(neuron-gland)
Neuroglandular junction
122
Triggered by action potential
nerve impulse
123
Sending neuron
presynaptic neuron
124
Space between neurons:
synaptic cleft
125
Receiving neuron
postsynaptic neuron
126
NT serves as ____________ (stimulus) of ion channels
chemical trigger
127
Only ______________ release NT
presynaptic cells
128
Only ____________ have receptors for NT binding
postsynaptic cells
129
Finally, NT must be removed from the cleft. Three possible mechanisms
• Diffusion out of cleft
• Destruction by enzymes (such as ACh-ase) in cleft
• Transport back (recycling) into presynaptic cell
130
Neurotransmitters
• Biogenic Amines
• Acetylcholine (ACh)
• Neuropeptides
• Amino acids
• Nitric oxide (NO)
131
common in PNS
Acetylcholine (ACh)
132
on skeletal muscles
Stimulatory
133
on cardiac muscle
Inhibitory
134
Glutamate, aspartate, gamma aminobutyric acid
(GABA), glycine
Amino acids
135
Norepinephrine (NE), dopamine (DA), serotonin
Biogenic Amines
136
such as endorphins
Neuropeptides
137
major inhibitory NT of brain
GABA
