Nervous system Flashcards
1
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Central nervous system
A
(CNS), brain and spinal cord, surrounded by skull and vertebral column
2
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Peripheral nervous system
A
PNS, cranial and spinal nerves
3
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Autonomic nervous system
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ANS, gut motility
4
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Structures of brain
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Cerebrum for learning, memory, hearing, other senses,
Cerebellum for balance and coordination
Brain stem to control breathing
5
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Meninges
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protects CNS. consist of 3 layers: dura mater, arachnoid, pia mater
6
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leptomeninges
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arachnoid and pia mater
7
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subarachnoid space
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space between the arachnoid and pia mater
8
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cerebrospinal fluid
A
CSF, circulates within the subarachnoid space, similar to inter and extra cellular fluid, helps slow brain movement to protect it, Maintains chemical stability of the CNS and maintains electrical properties
9
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Which layers of meninges are simple squamous epithelium?
A
arachnoid and pia mater
10
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hydrocephalus
A
CSF production is maintained but can not be gotten rid of it
11
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meningitis
A
inflammation due to bacteria, virus, mycotic, causes cervical pain and secondary infection to the CNS
12
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meningioma
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slow growing tumor, 40% of all canine primary brain tumors, frequent in dogs older than 10
13
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meningeal encephalitis
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inflammation of meninges and brain
14
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White and grey matter in cerebrum
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white is on the inside and grey is on the outside
15
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White and grey matter in spinal cord
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grey matter on the inside and white matter on the outside
16
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Gray matter cells
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neurons and neuroglia
17
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white matter cells
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neuroglia
18
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Neurons
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found in grey mater, stop dividing 3-4 months after birth
Excitable cells: generate action potential, release neurotransmitters
19
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Morphology of neuron
A
cell body (soma, perikaryon): nucleus/ nucleolus, cytoplasm is nissl substance with RER and ribosomes that stain
Dendrites: inputs
Axon: target/ action potential
Dendrites and axons not viewed with nissl stain
20
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variation in neurons
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size and shape, dendritic organization, axon length, nucleus size
21
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structure and functions of neurons
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Multipolar is sensory and motor, bipolar is sensory for eyes and ears, unipolar is sensory
22
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dorsal vs ventral root
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ventral root controls motor innervation while dorsal root controls sensory innervation
Note: dorsal root could be target of sensory neuron
23
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CNS neuroglia
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ependymal cell, astrocyte, oligodendrocyte, microglia (in macrophages)
24
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neuroglia in PNS
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Schwann cell
25
neuroglia
over 90% of cells that make up the central nervous tissue
Small cells and only nuclei can be seen with routine stains
Continue to divide throughout life
26
Purpose of ependymal and astrocytes
provide optimal extracellular environment for neurons
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ependymal cells
lining central canal and ventricles in brain
Apical surface with cilia and assist the CSF circulation
Form choroid plexus, modified ependymal cells have microvilli to increase surface area to produce CSF and absorb to modify CSF
28
Choroid epithelium
forms blood-CSF barrier, really tight junctions, ependymal cells with microvilli
Selects what gets into the CSF
Connective tissue and fenestrated capillaries
Blood is filtered through capillary endothelium and choroid epithelium. Capillary has initial selection then choroid has final say
29
CSF circulation
in ventricles and subarachnoid space
| production in ventricles, reabsorbed in specialized area of subarachnoid space to go into venous system
30
Astrocytes
most abundant neuroglia of CNS (50%), looks like a star, most common cells in brain,
numerous cell processes
Respond to injury of CNS, proliferating to form scar tissue,
Maintain optimal CNS environment
31
Functions of astrocytes
1. Induct and maintain capillary endothelium as the blood-brain barrier
2. Help transport glucose to neurons
3. STore glycogen- energy reserves
4. Promote neuronal survival by secreting growth factors (nerve growth factor, NGF)
5. Prevent glutamate neurotoxicity by converting glutamate to glutamine (which neuron converts back to glutamate)
32
capillary endothelium
regulates exchange of solutes between the blood and CNS tissue
structural basis of blood-brain barrier
Can be modified by end feet of astrocytes with different receptors
33
capillary tight junction
formed when astrocytes release glial cell line-derived neurotrophic factor (GDNF)
34
Methods of blood brain barrier
regulates the exchange of solutes between the blood and CNS tissue
Diffusion of water, gases, and lipophilic substances
transporter with GLUT1 glucose transporter
carrier mediated transport of amino acids
Water can diffuse but water soluble substances need transported
35
Which amino acids are used to produce neurotransmitters?
Tyrosine and tryptophan, (catecholamine and serotonin respectively)
36
Which neurotransmitters are transported out of the CNS?
Glycine and GABA (inhibitory neurotransmitters)
37
glucose transport to neurons
either through diffusion through extracellular space or through the astrocyte
38
Glutamate
neurotransmitter in CNS
released from terminal end of axons
Neurotoxic at high concentration
39
What neuroglia respond to tissue damage and remove debris by phagocytosis?
microglia
40
Microglia
20% of CNS glia, once activated they proliferate and assume a phagocytic role
Constantly migrating through CNS looking for damaged cells or foreign matter that will activate it
Will release factors to recruit more microglia
small nucleus
41
Neuroglia responsible for myelination
oligodendrocytes in CNS, Schwann cells in PNS
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Myelin sheath
plasma membrane of neuroglia concentrically wrapped around an axon in a spiral fashion, effectively insulating axons from extracellular fluid
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node of Ranvier
space between the Schwann cell shere axon is exposed
44
Formation of myelination
1. Cell processes elongate and encircle the axon
2. One process starts wrapping the plasma membrane around the axon
3. Exclusion of cytoplasm from encircling cell process, forming the myelin sheath
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unmyelinated axons
Oligodendrocytes do not support at all
| Schwann cells support axons, but no myelination. Space around axons is open to extracellular space.
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Endoeurium
surrounding nerve fiber: axon + Schwann cells
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Perineurium
surrounding fascicle/ bundle of nerve fibers
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Epineurium
surrounding nerve/ bundle of fascicles
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Schwannoma
neurilemmoma, neurofibroma, can get very big
~27% of canine nervous system tumor
brachial plexus is common area for schwannoma
(schwann cell= neurilemmocyte)
50
sensory receptors definition
receptors that detect changes in thermal, mechanical, or chemical stimuli applied to the surface or interior of the body and generate nerve impulses to be transmitted to the CNS for processing
(receptors do not "feel" pain but transmit signal to CNS for pain to be felt)
51
somatic sensory receptors
skin, muscles, tendon, bone,
| Retina, organ of Corti, carotid body, carotid sinus
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Visceral sensory
viscera, taste buds, olfactory cells
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sensory neuron of PNS
body in dorsal root ganglion
| central projection goes to spinal cord, peripheral projection goes to sensory receptors in body
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termal end of primary sensory neurons
1. forms free nerve endings
2. Innervates specialized cells
3. Encapsulated by cells or connective tissue
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modality of free nerve endings
one of pain (nociceptor), temp (thermoreceptor), or touch (mechanorecptor)
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modality of hair follicle terminal
touch (mechanorecptor)
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Merkel's corpuscle
touch and pressure (mechanoreceptor)
| Merkel cell + axon terminal
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Meissner's corpuscle
touch and vibration <100Hz (mechanoreceptor)
Merkel's cell in integument releases substances that effect neuron
dermis/ epidermal junction
Encapsulated by cells
only in thick skin because they are located in dermal papillae
59
Pacinian corpuscle
skin, vitration >100Hz and pressure (mechanoreceptor)
| encapsulated by many layers of cells
60
Golgi-tendon organ
musculoskeletal, muscle tension (mechanoreceptor) and proprioception (proprioceptor)
collagen fibers, sensory fibers and connective tissue capsule
Too much tension of muscle causes Golgi tendon organ to prevent further contraction to prevent injury
61
muscle spindle
musculoskeletal, proprioception (proprioceptor)
intrafusal muscle fibers, sensory fibers and connective tissue capsules
located in perimysium
62
intrafusal muscle fibers
arranged similar to skeletal muscle but with addition of stretch receptors
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sensory receptors
1. Sensory receptors are terminal end of sensory axons
2. sensory modality is receptor specific
3. Sensory neurons carry signals to the CNS
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Resting membrane potential
RMP, potential difference across the membrane
-65 mV= net charge on the inside of the plasma membrane compared to the outside. Inside is more negative
Reflects uneven distribution of ions across the plasmamembrane by the electrochemical gradients
65
What are the key players crucial for maintaining RMP?
potassium and sodium ions, large negatively charged in cell
66
What creates uneven ion distribution?
1. Na K pump (ATPase)
2. Intracellular anions (too large to exit cell)
3. Selective membrane permeability to ions:
nongated/leak K and Cl channels
Few leak/nongated channels for sodium,
sodium channels are closed when cell is at rest, difficult for sodium to enter cell
67
Resting membrane potential is basis for which other membrane pontials
All the potentials associated with neuronal functions:
| Receptor, action, and graded
68
depolarization
decrease the potential difference across the plasma membrane, going to more positive, approaching 0 mV
69
Overshoot
potential difference rises above 0 mV
70
Repolarization
Return of the membrane potential to its normal RMP
71
Hyperpolarization
increase the potential difference across the membrane, going to more negative, away from RMP
72
receptor potential
depolarizing membrane potential generated by sensory receptor, 1st step for CNS recognition of sensory stimulus
sensory receptor requires generation of receptor potential to function
stimulus-specific Na channels open and sodium influx
Magnitude of receptor potential depends on stimulus intensity
73
A test of proprioception involves which sensory receptor?
muscle spindle
74
Signal transduction of sensory receptors
conversion of sensory stimulus to electrical signals (receptor potential)
1. Opens stimulus-specific sodium channels
2. Generates receptor potential
3. Receptor potential proportional to stimulus intensity
Once sodium channel is open, sodium moves inside and resting potential decreases or becomes more positive
75
T/F? Magnitude of the receptor potential reflects stimulus intensity to sensory receptors
True
76
Action potential
brief reversal in electrical potential across the plasma membrane
Generated when receptor potential is greater than threshold potential (-55 mV). Activates voltage gated sodium and potassium channels
All or none response
77
voltage-gated sodium channels
undergoes resting, activated and inactivated states during action potential cycle
Channels close almost immediately after opening
78
Which state does sodium cross membrane through voltage-gated sodium channel?
activated state
79
de-inactivation
inactivated sodium channels must be de-inactivated to resting state before they can open again
80
hyperpolarization
because potassium has left the cell
81
phases of action potential
```
Rising phase (depolarization and overshoot)
Falling phase (re and hyperpolarization)
```
82
Hyperkalemia leads to de or hyperpolarization?
depolarization
83
hypokalemia leads to de or hyperpolarization?
hyperpolarization
84
Does hyper or hypo kalemia make it easier to generate action potentials?
Hyperkalemia
| Resting membrane potential changes bout threshold potential does not.
85
Blocking these channels prevents propagation of action potentials
Voltage gated sodium channels
| voltage gated potassium channels
86
What substances block voltage gated sodium channels?
lidocaine and tetrodotoxin of puffer fish
87
What substance blocks voltage gated K channels?
Noxiustoxin from Mexican scorpion
88
absolute refractory period
period during which voltage-gated sodium channels are inactivated state and action potential cannot be generated
89
relative refractory period
stronger than normal stimulus needed to elicit action potential
90
Why are voltage gated sodium and potassium channels important?
They define the behavior of action potential
Postsynaptic neurons rely on incoming frequency of action potential for interpretation of stimulus intensity applied to sensory receptor (or any other presynaptic neurons)
91
What is the consequence of refractory periods?
no overlap of action potentials
92
What properties of the action potential are impacted by the 3 stage of voltage gated channels?
Amplitude, duration of each cycle and propagation speed of the action potential
93
How are action potentials like toilets?
All or none: it either reaches the threshold and goes or doesn't
Action potentials travel toward the terminal end of axon at full speed
Refractory periods prevent new generation of action potential until the end of each cycle
94
propagation of action potentials
once action potential is generated, it propagates to the other end of an axon
Conduction speed of action potentials reflects axon diameter and size and myelination
95
myelination
enhances conduction speed of axons
96
signal transmission efficiency
STE= Rm/ Rin (membrane resistance divided by longitudinal resistance)
97
For current to travel faster without significant decrement, a cable must have a _____ membrane resistance and a ____ longitudinal resistance.
High, low
| Electrical current must be fed continuously
98
flow of electrical current
electrical current must be fed continuously
99
nonmyelinated axons
voltage gated Na and K channels all along axons
action potential triggers local depolarizing electrical current
Local current spreads along an axon, activating adjacent voltage-gated sodium and potassium channels and generates an action potential
action potentials run all the way to the terminal end of axons
100
myelinated axons
myelin sheath insulates an axon, increasing STE, enabling local current to reach far longer distance
Voltage-gated sodium and potassium channels are at the nodes of Ranvier (not located throughout the membrane)
Action potential generates local currents that is strong enough to generate a new action potential. This continues all along the axon to the terminal end.
Allows local current to travel longer distance
Propagation involves the generation of a 'new' action potential at each node of Ranvier, resulting in saltatory conduction
101
saltatory conduction
action potential jumps from node to node
102
Is propagation of the action potential decremental or nondecremental.
Nondecremental
103
If axon diameter is larger, how is conduction speed impacted?
Less Rin and conduction speed is faster.
| Larger the myelinated axon, longer the internode, and faster the conduction speed.
104
myelination increases the conduction speed by _____
increasing Rm
105
letter system for axon diameters
A is larger than B is larger than C
106
numerical system for axon diameter
sensory fibers, I is larger than II is larger than III is larger than IV
107
loss of myelin increases or decreases the signal transmission efficiency (rm/rin)?
decrease, and action potentials can't reach the node of Ranvier
voltage gated Na and K channels often reappear along the demelinated areas of axons, but such actions diminishes with repeated demyelination episodes.
108
diseases causing demyelination
multiple sclerosis in human
| degenerative myelopathy
109
degenerative myelopathy
similar to human amyotrophic lateral sclerosis (Lou Gehrig's disease)
Progressive muscle weakness and incoordination
Complete paralysis and muscle atrophy
110
synapse
a structure that enables a neuron to pass an electrical signal to another neuron
Terminal branches of axons make synapses with many other neurons
specific area between presynaptic neuron and postsynaptic neuron
111
Location of synapses
Axosomatic (perikaryon)
Axodendritic (dendrite)
Axoaxonic (axon)
112
presynaptic structues
synaptic vesicles with neurotransmitter
| Presynaptic membrane
113
synaptic cleft
between presynaptic and postsynaptic membrane
114
postsynaptic structures
postsynaptic membrane with neurotransmitter receptors
115
Synaptic events
1. action potentials
2. Membrane depolarization opens voltage-gated Ca channels
3. Neurotransmitter release
4. Neurotransmitters and receptors
5. Changes postsynaptic membrane potential
116
Excitatory neurotransmitters
aceytcholine (CNS, PNS)
| Glutamate (CNS)
117
Excitatory synapse
release excitatory neurotransmitter that depolarize postsynaptic membrane
118
excitatory neuron
makes excitatory synapses
119
inhibitory neurotransmitters
Glycine (CNS)
| GABA (Gamma aminobutyric acid
120
inhibitory synapse
release inhibitory neurotransmitters that hyper polarizes postsynaptic membrane
121
inhibitory neuron
makes inhibitory synapses
122
changes in membrane potential for excitatory synapse
1. Excitatory neurotransmitters and receptors
2. Receptors open ligand-gated ion channels for Na
3. Na influx
4. Generation of graded potential excitatory postsynaptic membrane potential (EPSP)
5. Amplitude of EPSP depends on amount of neurotransmitter released, frequency of action potentials, and stimulus intensity
reflects depolarization
123
Changes in membrane potential for inhibitory synapse
1. inhibitory neurotransmitters and receptors
2. Receptors open ligand-gated ion channels for CL
3. Chloride influs
4. Generates graded inhibitory postsynaptic membrane potential (IPSP)
5. Amplitude of IPSP depends on neurotransmitter released, frequency of action potentials, and stimulus intensity
reflects hyperpolarization
124
Graded potentials (EPSP, IPSP) at dendrites and soma
1. travel to the axon hillock for summation of graded potential
2. Generate action potentials when the sum of graded potential is greater than threshold voltage
125
temporal summation
summate multiple signals arriving at a single synaptic site
126
spatial summation
summate multiple separate signals arriving at different synaptic sites simultaneously
127
graded potentials generating action potential
summated graded potential at the axon hillock (NOT dendrites) goes over the threshold to create action potential
voltage-gated Na and K channels at the axon hillock
128
strychnine toxicity
Prevents release of GABA and glycine, presynaptic deficit of inhibitory synapses
Spasm of muscles every 10-30 minutes after exposure
Death from asphyxiation
129
Tetanus
Tetanus toxin stays bound to inhibitory neurons for over 3 weeks
Prevents release of GABA and glycine from inhibitory neurons
Clinical signs reflect over-activity of skeletal muscles
130
motor unit
a motor neuron and all of the muscle fibers it innervates
131
motor endplate
numerous nerve endings
132
How is movement precision controlled?
The number of fibers the motor neuron innervates is dependent on how precise the movement needs to be
133
Neuromuscular junction
motor end plate and junctional fold of sarcolemma
| Acetylcholine transmitter with AChR Receptor
134
Transmission at neuromuscular junction
1. Membrane depolarization by action potentials opens voltage-gated Ca channels
2. Synaptic vesicles release acetylcholine by exocytosis
3. ACh opens ligand gated ion channels for Na (receptor of ACh), Na influx and depolarization of sarcolemma
4. Voltage gated Na and K channels open when membrane voltage is greater than threshold voltage
5. Action potentials of sarcolemma that leads to muscle contraction
135
Tic paralysis
Presynaptic deficit of neuromuscular junction
Neurotoxin secreted by female wood tick interferes with release of ACh by interfering with neurosynaptic tunnel
Generalized muscle weakness/ paralysis with recovery 1-3 days after removal of ticks
136
Myasthenia gravis
postsynaptic defics of neuromuscular junction
Autoimmune disease
Antibody blocks, alters or destroys acetylcholine receptor, resulting in progressive loss of the receptor and muscle strength
Typically seen as exercise induced motor weakness that improves following rest.
Sensory is functional but motor is not
137
nissl substance
stains RER and ribosomes
138
Where is the nucleus of a Schwann cell located?
the outside of the cell, but can't differentiate with a normal stain
139
Dura mater
thickest and strongest connective tissue sheath
| Composed of collagen fibers, elastic fibers, fibroblasts, nerves, lymph vessels, and blood vessels.
140
What are arachnoid and pia mater made of?
fibroblasts and collagen fibers
