Nervous System Flashcards
(313 cards)
1
Q
A feature of generator potentials that distinguished them from action potentials
A
Graded in amplitude
2
Q
Region of most central neurons that has the lowest threshold for initiation of Na+-dependent action potentials
A
Proximal segment of the axon
3
Q
When is axonal transport considered orthograde?
A
When the direction of transport is from the soma to the axon terminal.
4
Q
Access from the blood to CSF is limited by tight junctions between:
A
Endothelial cells and choroid epithelial cells
5
Q
Cerebrospinal Fluid (CSF)
A
- Flows from ventricles out into the sub arachnoid space
- Flows into the blood through the arachnoid villi
- Mechanically and chemically buffers the brain
- Originates in the choroid plexus
6
Q
Reflex
A
Subconscious, predictable responses to specific sensory stimuli
7
Q
Reflex arc
A
Neural pathway or “wiring” of the reflexes
8
Q
Main components of the reflex arc (monosynaptic)
A
1) receptors (pressure, pain, chemical)
2) Afferent (sensory) neurons
3) Efferent (motor) neurons
4) Effectors (muscles, organs or glands)
5) Synapses
9
Q
Purpose of receptors in reflex arc
A
To receive stimuli
10
Q
Purpose of afferent/sensory neurons in reflex arc
A
carry the stimulus information into the integration center (CNS)
11
Q
Purpose of efferent/motor neurons in reflex arc
A
Carry information out of the target muscle, organ, or gland
12
Q
Purpose of effectors in reflex arc
A
Execute actions
13
Q
Purpose of synapses in reflex arc
A
one synapse with the motor (efferent) neuron or multiple with interneurons
14
Q
Main components of polysynaptic reflex arc
A
1) receptors (pressure, pain, chemical)
2) Afferent (sensory) neurons
3) Interneurons (CNS)
4) Efferent (motor) neurons
5) Effectors (muscles, organs or glands)
6) Synapses
15
Q
Purpose of interneurons polysynaptic reflex arc
A
Process information, directs motor output
16
Q
Are interneurons needed in a reflex arc?
A
No. Monosynaptic arcs don’t have any.
17
Q
Explain the patellar reflex.
A
1) Hammer hits patellar tendon (right below kneecap).
2) Stretch receptor on afferent/sensory neuron activated
3) Signal transmitted down axon to cell body and then dorsal root ganglion through spinal cord
4) Sensory neuron activates efferent (motor) neuron on extensor muscle. Also activated interneuron in spinal cord, which then activates motor neuron on flexor muscle.
5) Motor neurons signal transmits out of spinal cord and back to flexor and extensor muscles.
6) Flexor muscle contracts white extensor extends, causing reflex reaction.
18
Q
Example of a monosynaptic reflex
A
Muscle stretch/patellar reflex
19
Q
Example of a polysynaptic reflex
A
Withdrawal reflex
20
Q
Somatic reflexes
A
Stimulate skeletal muscles
21
Q
Autonomic reflexes
A
Regulate smooth muscle, glands
22
Q
Structure of a neuron
A
1) Dendritic branches
2) Dendrites
3) Cell body: Mitochondria, ER, Golgi, Nucleus
4) Axon Hillock
5) Axon
6) Telodendria
7) Synaptic terminals
23
Q
5 Classifications of Neurons
A
1) Anaxonic: no axon
2) Unipolar: one structure extend from soma (cell body)
3) Bipolar: one axon + one dendrite
4) Multipolar: One axon + multiple dendrites (CNS)
5) Pseudounipolar: One extension that divides into two (PNS)
24
Q
Structure of a synapse
A
1) Presynaptic: neurotransmitter vesicles
2) Synaptic cleft: space between neuron and receiving structure
3) Postsynaptic: ligand-gated receptors for NT, ion channels for depolarization
25
Types of Neuroglia
1) Ependymal cells
2) Oligodendrocytes
3) Astrocytes
4) Microglia
5) Satellite cells
6) Schwann cells
26
Neuroglia in central nervous system
1) Ependymal cells
2) Oligodendrocytes
3) Astrocytes
4) Microglia
27
Neuroglia in peripheral nervous system
1) Satellite cells
| 2) Schwann cells
28
Ependymal cells
- CNS
- Assist in producing, circulating, and monitoring of CSF
- Columnar, ciliated cells lining the ventricles (brain) and central canal (spinal cord)
29
Oligodendrocytes
- CNS
- Myelination: faster APs and better conductance
- Degradation, immune surveillance, and antigen transfer to microglia
30
Astrocytes
- CNS
- Structure/Scaffold
- Regulate ion, nutrient, and dissolved gas concentrations
- Neuroprotection to neuron
- Clear the synapsis: absorb and recycle
- Homeostasis
- Glial fibrillary acid protein (GFAP)
- End feet (cover blood vessels, BBB)
- Maintain BBB
- Form scar tissue after injury
31
Microglia
- CNS
- Immune response: protection from pathogens
- Neurotransmission to neuron
- Macrophage-like
- Scavenging cells
- Remove cell debris, wastes, and pathogens by phagocytosis
32
Satellite Cells
- PNS
- Surround neuron cell bodies in ganglia
- Regulate O2, CO2, nutrient, and NT levels around neurons in ganglia
33
Schwann cells
- PNS
- Myelination of peripheral axons
- single wrap = unmyelinated
- multiple-wrap = myelinated
- Participate in repair process after injury
34
How is the nervous system organized?
Central Nervous System: Brain & spinal cord
- input from afferent division of PNS
- output to efferent division of PNS
Peripheral nervous system: afferent/efferent
- afferent: sensory & visceral stimuli
- efferent: somatic & autonomic NS
- Somatic: motor neurons --> skeletal
- Autonomic: Sym, para, & enteric
- Sympathetic & parasympathetic
- Smooth muscle
- Cardiac muscle
- Exocrine glands
- Some endocrine glands
- Enteric: stimuli in digestive tract
- Affects digestive organs only
35
Bundles of neurons
CNS: nuclei
PNS: ganglia
36
Describe the withdrawal reflex (polysynaptic reflex)
PNS:
1) Painful stimulus at receptor
2) Signal travels down sensory neuron axon
CNS:
3) synapse with interneurons 1 and 2 (excitatory)
4) Interneuron 1 excites motor neuron 1 while 2 inhibits motor neuron 2
5) Interneurons synapse with motor neurons 1 (excitatory) & 2 (inhibitory) respectively
PNS:
6) Signals travel down motor neuron 1 & 2's axons
7) Motor neuron 1 connects to flexor muscle (contract) while motor neuron 2 connects to extensor muscle (no contraction)
37
Why are interneurons needed?
They are mostly inhibitory neurons connecting different brain regions, including sensory and motor neurons. Forms circuits with nearby neurons to analyze small pieces of info and connect circuits of neurons in different (or distant) regions.
In reflex, inhibits opposite muscle group to facilitate action of activate group. Without this, actual response would be diminished, jerk would be less vigorous, withdrawal slow and milder.
38
How does neuron morphology relate to its function?
Provide evidence of the role of that particular type of neuron.
39
How does unipolar neuronal structure relate to function?
Structure: Only one process extends from the cell body.
Function: Less common in vertebrates. One example is dorsal cochlear nucleus.
40
How does pseudo-unipolar neuronal structure relate to function?
Structure: one extension from cell body, and axon split into two branches
Function: signal can bypass cell body and propagate rapidly. One example is sensory neurons, with one branch to PNS and the other to CNS.
41
How does multipolar neuronal structure relate to function?
Structure: Single axon, many dendrites
Function: the higher the need for processing higher information inputs, the higher the number of dendrites. Examples include motor neurons, cone cells, and Purkinje cells.
42
How does the high specialization of neurons affect their functioning?
Require high metabolic resources, virtually all from aerobic glucose metabolism, therefore requiring large amounts of oxygen and thus blood flow. Any alteration in blood flow can lead to neuronal cell death.
Postmitotic terminally differentiated so neurogenesis ends during adulthood.
43
White matter
highly myelinated - axons
44
Gray matter
Myelin + cell bodies
45
Two major methods to send electrical information
Active & passive
46
Use of action potentials
For active transfer of information
47
Use of local graded potentials
For passive transfer of information
48
Active spread of information
An AP propagates to a synapse on the dendrite of a neuron where a local synaptic potential is generated in the dendrite.
AP later generated at axon hillock travels in the axon from the motor neuron to the neuromuscular synapse with a muscle fiber.
AP generated at muscle fiber propagates to the ends of the muscle fiber initiating contraction.
49
Passive spread of information
Local potentials generated by AP passively flows to the cell body and axon hillock.
Local EPP (end plate potential) generated by neuromuscular synapse in the muscle fiber flows across synapse.
50
Action potentials ____ propagate along nerve and muscle membrane
Actively
51
APs send ___ information
electrical
52
Information is coded in the ___ and ___ of the action potentials
frequency; spacing
53
APs typically propagate ____ change in size or shape as a pulse of voltage changes
Without
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The distance an AP can travel is only limited by the ___
Length of the axon or muscle fiber
55
APs require ___ to propagate
voltage dependent Na+ and K+ channels
56
The amplitude of graded potentials ___ with increasing distance from the site of current injection
Decreases
57
What are the conductors in living organisms?
The intracellular and extracellular electrolyte solutions
58
How is current carried in living organisms?
By the movement of 150 mM of positive ion and 150 mM of negative ions
59
Does a cell membrane have low or high resistance?
High resistance
60
Why do cell membranes have the level of resistance that they do?
Have high resistance because it greatly impedes the movement of ions across it
61
What changes the resistance of cell membrane?
Ion channel proteins
62
How do ion channels affect resistance of cell membranes?
Decrease resistance by opening their pores
63
Time constant
Tau (c)
The time for current to inc to 63% of steady state level or to decay to 37% of steady state level
Typical range: 1-20 ms
64
Length constant
lambda (c)
The distance at which the voltage falls to 37% of its highest value
Typical range: 0.1-5 mm
65
When is lambda (length constant) smallest?
Small diameter axons and muscle fibers
66
What two factors can increase lambda?
Increasing diameter and myelination
67
How does myelination increase lambda?
By decreasing membrane capacitance and increasing membrane resistance
68
Cable properties
The passive properties of axons and muscle fibers
69
When is repetitive discharge of excitable cells important?
1) Neurons that integrate local potentials and translate them into frequency of AP discharge
2) Some cells are driven to threshold by inputs from other cells
3) some cells have intrinsic pacemaker activity, including many neurons and the heart
70
What determines AP firing properties?
Ion channels!
Also: cell geometry and pattern of ion channel disrtibution
71
How is the membrane depolarized?
Influx of Na+ and Ca2+ --> more positive
72
How is the membrane hyper polarized?
Efflux of K+ --> more negative
73
How is depolarization achieved?
1) Activating depolarizing channels (Na, low voltage activate Ca, nonselective cation)
2) Turning off some of the depolarizing K+ channels (some turn off with time, others with depolarization)
74
Does repetitive AP activity require both hyper polarizing and depolarizing currents?
Yes
75
Compound AP
Extracellular AP produced by stimulating and recording from whole nerve. Grows as stimulation voltage is increase and more nerve fibers are recruited. Graded in size and at most a few mV.
76
Synapse
Junction between:
- neuron-neuron
- neuron-muscle
Where the axon of one neuron (presynaptic) terminates on the (postsynaptic):
- dendrite
- axon
- cell body of another neuron
- cell body of a muscle cell
77
Classification of synapses
- Chemical
- Electrical
- Conjoint (chemical + electrical)
78
Differences between chemical and electrical synapses
Chemical | Electrical
--------------------------------------------------
Use NTs | Gap junctions
1-way transmission | transmission both ways
More common | More rare
Synaptic cleft | Gap junction
0.5 ms delay | 0.2 ms delay
Signal amplification | Same signal
Signal inversion. | Same signal
79
What is a neurotransmitter?
1) chemical must be found within presynaptic neuron
2) When presynaptic neuron is stimulated, it must release the chemical
3) when the chemical is applied exogenously, it must act on a post-synaptic neuron and case a biological effect
4) after a chemical is released, it must be inactivated
80
Synaptic transmission process
1) . AP arrives at axon terminal
2) Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal
3) Ca2+ entry causes NT-containing synaptic vesicles to release their contents by exocytosis
4) NT diffuses across the synaptic cleft and binds to ligand-gated ion channels on the postsynaptic membrane
5) Binding of NT opens ligand-gated ion channels, resulting in graded potentials
6) Reuptake by presynaptic neuron, enzymatic degradation, and diffusion reduce NT levels, terminating the signal.
81
Acetylcholine
Derived from: Choline
| Synthesized in: presynaptic cytosol
82
Dopamine
Derived from: Tyrosine
| Synthesized in: Presynaptic cytosol
83
Norepinephrine (noradrenaline) and Epinephrine (adrenaline)
Derived from: Tyrosine
Synthesized in:
- NE: dopamine containing vesicles
- epi: NE containined vesicles
84
Serotonin
Derived from: Tryptophane
| Synthesized in: presynaptic cytosol & cells in GI
85
Histamine
Derived from: histidine
| Synthesized in: presynaptic cytosol, mast cells, basophils/eosinophils
86
Glutamate-Glutamine Cycle
1) Glutamate release in synaptic cleft
2) Uptake into glia cell
3) Conversion of glutamate to glutamine via glutamine synthetase
4) Transfer glutamine to presynaptic terminal
5) Glutamine to glutamate via glutaminase
6) Package glutamate into vesicles
87
GABA
Derived from: Glutamate
| Synthesized in: Presynaptic cytosol
88
Synaptic vesicle types
Small clear core and large dense core
89
Small clear core
Contain small molecule NTs like ACh, Glue, GABA, and biogenic amines
90
Large dense core
Contain serotonin, peptides, and biogenic amines
91
Fusion of vesicles to presynaptic membrane
1) Dimer on presynaptic membrane binds with VAMP on vesicle membrane result in SNARE complex
2) Binding brings presynaptic membrane closer to vesicle membrane
3) Ca2+ facilitates binding of SNARE complex to synaptotagmin on vesicle membrane
4) Bindings fuses vesicle membrane with presynaptic membrane, allow exocytosis of NT in vesicle
92
Types of postsynaptic receptors
Inotropic and metabotropic
93
Ionotropic receptors
1) primary transmitter attached to receptor
| 2) Gate is opened, allowing influx of ions
94
Metabotropic receptors
1) primary transmitter attached to primary receptor
2) Release of internal second messenger
3) second messenger binds to secondary receptor
4) Gate is opened, allowing influx of ions
95
How do receptor types differ in terms of response times?
Inotropic are rapid (5-10 ms) while metabotropic are slower (20-50 ms)
96
Where can each receptor type be found?
Ionotropic on postsynaptic only. Metabotropic can be both pre and post synaptic (pre regulates NT transmission)
97
Which NT is degraded in cleft??
Acetylcholine only by acetylcholinesterase
98
How are all NTs (except ACh) removed from cleft?
By transporters
```
GABA - GAT
Glutamate - GluT
Serotonin - SerT
Dopamine - DAT
Norepinephrine - NET
```
99
How does each structure on a neuron relate to function?
1) Dendrites, soma, and axon hillock: get input from many presynaptic endings
2) Soma and axon hillock: integrate input and "decide" to fire APs
3) Axon: Conducts APs to the synaptic ending
4) Synaptic ending: contacts other neurons and excites/inhibits
100
What is the importance of convergence?
Allows summation and integration of information from multiple sources
101
What is the importance of divergence?
Provides amplification: one input signal can reach a large number of targets
102
Excitatory chemical synapses
The NT depolarizes the posynaptic cell, inc the probability for an AP.
If reversal potential for the channel is more positive than the threshold, the synapse is excitatory.
103
Inhibitory chemical synapses
If reversal potential for channel is more negative than the threshold --> synapse is inhibitory
104
What determines if a chemical synapse is excitatory or inhibitory?
Postsynaptic neuron firing AP is:
Easier --> excitatory
Harder --> inhibitory
105
Trigger zone
Location where APs are initiated.
Highest density of Na channels --> lowest threshold --> AP will initiate here
106
What is the impact of synapse location?
Synapses closer to the trigger zone have a large impact on probability of the neuron to fire an AP
107
Spatial summation
Occurs when multiple terminals at diff location on one neuron are activated simultaneously --> postsynaptic potentials spread passively (cable properties) and "add up"
108
Temporal summation
Occurs when one terminal is activated at rapid succession
109
Why is axonal transport necessary?
1) Proteins synthesized in cell body but axons and nerve endings need continuous supply
2) Neuropeptides processed during transport
3) Signal molecules and growth factors travel to targets across neuron
4) Needed for repair after injury
110
Types of transport
1) Orthograde: away from cell body; fast and slow
2) Fast: carries vesicles and organelles
3) slow: carries enzymes and cytoskeleton components
4) Retrograde: toward cell body; fast
111
Fast orthograde transport mechanism
Vesicles and organelles move along microtubules powered by Kinesin using ATP
112
Retrograde transport mechanism
Organelles and vesicles separately move along microtubules powered by Dynein using ATP
113
Retrograde transport - general
- Carries growth factors from terminals to cell body
- May carry info about state of terminals
- Transports viruses such as herpes, polio, chickenpox, and rabies
- Transports toxins like tetanus
114
Blood brain barrier
Limits passage of molecules into the brain. Can override by injecting straight into CSF or increasing oil/water partition coefficient (hydrophobic is better).
Endothelial cells of BBB are fused tightly together to form tight junctions to nothing can get through. Surrounded by astrocytic end feet.
115
Generator potential
- Depends on stimulation
- Changes in sensory cell's resting potentials
- Graded in amplitude
- Produced by ion channels or GPCR
- Adapt with varying speed (Fast vs slow)
116
Why is the generator potential graded?
So the response to a stronger second stimulus is larger
117
What does a generator potential generate?
A sufficient depolarization in excitable cells can reach threshold and GENERATE APs (even a little after the stimulus once firing begins)
118
Why do generator potentials adapt?
Stronger stimulus produce larger responses (graded), but as a strong stimulus persists, the response diminished in time.
119
What is the mechanism of the generator potential?
1) A change in ion channel conductance, often by opening channels that allow entry of Na or Ca
2) Channels may be directly activated by mechanical force, temp change, or another stimulus
3) In other cases, the stimulus is sensed by a GPCR and a cascade of second messengers changes channel conductance
4) A stronger stimulus opens more channels, so the response is larger.
120
Generator potentials at synapses
Cause more NT to be released a more positive voltages and less a more negative voltages
121
Neurons
- Highly specialized, excitable cells
| - Morphologic diversity
122
Glia
Supporting cells
1) Schwann (neurolemmacytes): myelin producing - PNS
2) Oligodendrocytes: myelin producing - CNS
3) Astrocytes: nutritional support
4) Microglia: macrophages (immune support)
123
Central Nervous system (CNS)
- Brain and spinal cord
| - Collection of nerve cell bodies = nucleus
124
Peripheral Nervous System (PNS)
- Peripheral nerves
| - Collection of nerve cell bodies = ganglia
125
Sensory (afferent) function of NS
- General - Touch
| - Special sense - sight, sound, taste, smell
126
Motor (efferent) function of NS
- Voluntary (somatic): skeletal muscle
| - Involuntary (autonomic): smooth & cardiac
127
Involuntary (autonomic) NS
- Parasympathetic: craniosacral - fight or flight
| - sympathetic: thoracolumbar - feed or fornicate
128
Integrative function of NS
Interneurons within the CNS
129
Types of Synapses
1) Axosomatic or axodendritic: terminal to dendrite, no invagination of dendrite
2) Axodendritic: terminal to dendrite, invagination of dendrite to terminal
3) Axoaxonic: terminal to terminal
130
Presynaptic inhibition
Inhibit excitatory neuron directly (on terminal)
131
Postsynaptic inhibition
Inhibit excitatory neuron indirection (not on terminal, elsewhere on postsynaptic)
132
Most common communication method with neurons?
Chemical synapse
133
Saltatory conduction
Signal jumps along axon between nodes, increasing speed and better signal recognition/strength (bc it doesn't degrade)
134
The role of myelin
- Increase neural transmission along axon via saltatory conduction
- Provides some limited protect but other methods provide more
- No nutrition
135
Organization of nerves
Smallest --> largest
| Endo --> Peri --> Epi
136
Endoneurium
Smallest; surrounds individual nerves/schwann cells
137
Perineurium
Middle; surrounds fascicles, holds fibers together
138
Epineurium
Largest; surrounds peripheral nerves, holds fascicles together
139
Meninges
CNS
| Dura, arachnoid, and pia mater
140
Dura mater
CNS
| Dense, fibre-elastic connective tissue
141
Arachnoid mater
CNS
| Fibrous connective tissue, subarachnoid space
142
Pia mater
CNS
| Collagen, elastin, and few fibroblasts
143
Order of meninges
Dura (outer) --> arachnoid --> pia (inner)
144
Choroid plexus
- Modified ependymal cells
| - Highly vascular: produces CSF
145
Autonomic Sympathetic mechanism
1. preganglionic cell bodies: thoracolumbar (T1-L2/L3)
2. Preganglionic fibers: shorts, ACh release
3. Postganglionic cell bodies: sympathetic chain ganglia
4. Postgangionlic fibers: long, NE release
5. Target
146
Autonomic parasympathetic mechanism
1. preganglionic cell bodies: craniosacral (III, VII, IX, X; S2-4)
2. Preganglionic fibers: long, ACh release
3. Postganglionic cell bodies: ganglia close to target
4. Postgangionlic fibers: short, ACh release
5. Target
147
Ganglia
Peripheral collections of neuronal cell bodies
1) Autonomic ganglia
2) Sensory ganglia
3) satellite cells
148
Autonomic ganglia
a. sympathetic chain ganglia: on thoracic vertebral bodies
| b. parasympathetic ganglia: on the walls of the organs
149
Sensory ganglia
Pseudounipolar neurons
a. cranial ganglia (V, VII, IX, & X)
b. Doral root (spinal) ganglia (spinal nerves)
150
CNS Matter
Gray matter
| white matter
151
Gray matter
a. nerve cell bodies (nuclei)
b. dendrites & axons
c. glia
152
White matter
a. nerve fibers (axons) - myelinated
| b. glia
153
Matter organization in brain
White in, gray out
154
Matter organization in spinal cords
gray in, white out
155
Subdivision of CNS
1. Cerebral cortex
2. Cerebellar cortex
3. Spinal cords
156
Cerebral cortex
a. 6 histological layers
| b. integration of afferent & efferent info
157
Cerebellar cortex
a. 3 histological layers: molecular, purkinje, and granula
| b. coordinates balance and muscle tone
158
Spinal cord organization
a. central gray matter
b. peripheral white matter
c. reflexes and basic integration
159
Spinal cord central organization
1. dorsal horn: sensory (afferent)
2. lateral horn: autonomic
3. ventral horn: motor (efferent)
160
Dorsal horn
Sensory (afferent)
161
Lateral horn
Autonomic
162
Ventral horn
Motor (efferent)
163
Major NT used in ANS
Acetylcholine
164
When is ACh not used in ANS?
Postganglionic sympathetic uses NE
165
In spinal cord, gray matter is ____ while white matter is ____.
Internal; external
166
In cortex and cerebellum, gray matter is ____ while white matter is ____.
external, internal
167
Steps in Neurodevelopment
1. Formation of neural plate (notochord)
2. Formation of Neural tube
3. Cell proliferation
4. Cell migration
5. Axon/dendrite outgrowth
6. Cell death
7. Synapse formation
8. Synapse elimination
9. Myelination
10. Critical periods
168
Neural plate
Develops by Day 18 = notochord plate
169
Neural tube
Closed at 3 weeks; starts closing in middle and goes cranial/caudal
170
What happens if neural tube fails to close cranially/rostrally?
Anencephaly
171
What happens if neural tube fails to close caudally?
Spinal bifida
172
Division of neural tube cells
Start S-phase in pial (outer) surface and move towards ventricle (inner) surface by M-phase. Move back to pial after division.
173
Neural tube has progenitors of the neurons and glia in the ____ and ____.
Brain, spinal cord
174
Ventral-derived interneurons become ____
GABAergic cells
175
Cortical-dervived pyramid neurons become ___
Glutamatergic cells
176
Is transmitter choice due to inheritance or environment?
Inheritance but environment can overrule.
177
Development of axons
Grow at tips (filopodium, then growth cone) followed by intercalar growth (axon)
178
Semaphorin 3A mechanism
1. Acts on apical dendrite, causing it to grow towards pial surface
2. Axons repel it so grow away, towards ventricular zone
179
Why to neurons reach the target they do?
Molecular gradients!
If molecules repel each other, cell bodies in high concentration area of one molecule will extend their axon towards area with lower concentration of repelling molecule.
180
Can neurotransmitter receptors move after innervation?
Yes, usually scatter but will reorganize at innervation
181
What happens with polyneuronal innervation?
If more than one neuron innervates a muscle fiber, it will lead to lots of competition between each neuron on each fiber. Cells will figure out which neuron will stay on the cell so that only on nerve per fiber (no competition).
182
How does re-innervation happen?
1. Partial de-nervation: cell loses a neuron
2. Sprouting: Schwann cells move and bring axon
3. Re-innervation: via a different pathway than original
183
Pruning
During maturation, some connections will be pruned. Some general wiring happens early but will be readjusted and specified via pruning.
184
Occular dominance
Separation of projections of left and right eyes to primary visual cortex --> creates patterns on cortex
185
Critical period
Period during which synapses in the cortex are plastic and change with neuronal activity.
186
What is the purpose of cortical folding?
Brings related regions closer together
187
4 Basic properties of sensory systems
- Modality
- Location
- Intensity
- Duration
188
Meissner's corpuscle
- Modality: respond to movement, deep touch
- Location: 2nd smallest, tight
- Intensity: constantly changing stimuli
- Duration: short
- Adaptation: rapid
189
Merkel cells
- Modality: sustained light touch (braille)
- Location: smallest field size
- Intensity: sustained touch
- Duration: long
- Adaptation: slow
190
Pacinian corpuscle
- Modality: vibrations/light touch
- Location: targeted but dispersed wide
- Intensity: constantly changing stimuli
- Duration: short
- Adaptation: rapid
191
Ruffini endings
- Modality: skin stretch
- Location: wide range, nonspecific
- Intensity: sustained touch
- Duration: long
- Adaptation: slow
192
Touch is signaled primarily by those with ____ axons
Larger
193
What type of axon is used in touch?
A-beta
194
Two point discrimination
With smaller receptive fields, 2 tips can be discriminated better. Measure of receptive field size and acuity.
195
Receptive fields of cells are sharpened by ____, mediated by inhibitory interneurons
Lateral inhibition
196
Lateral inhibition
Receptive fields of touch afferents are entirely excitatory, but second order neurons have opponent center-surround organization.
197
Homunculus
Contralateral body surface maps onto the primary somatosensory cortex. Fixed by adulthood but can change via plasticity following injury.
198
Nociception
Acute perception of a potentially damaging stimulus
199
Inflammatory pain
Pathologic chronic pain associated with tissue damage and infiltration of immune cells
200
Neuropathic pain
Pathologic chronic pain that may occur after nerve fibers are injured
201
Analgesia
Lack of or reduced pain
202
Hyperalgesia
Exaggerated response to a noxious stimulus
203
Allodynia
Sensation of pain in response to a normal innocuous stimulus (ex: touch)
204
Causalgia
Spontaneous burning pain that occurs long after seemingly trivial injuries
205
Pain, itch, and temperature are signaled by the ____ axons
Smallest --> slowest
206
Which axon type signals pain?
A-delta and C
207
Which axon type signals temperature?
A-delta and C
208
Which axon type signals itch?
C
209
What is the mechanism for pain?
1. A-delta fibers convey "1st pain", releasing glutamate in spinal cord
2. C fibers convey "2nd pain", releasing glutamate, substance P, and CGRP in spinal cord
210
How are nociceptors activated?
By chemical mediators released after tissue damage.
Ex: prostaglandin, histamine (immune)
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Basics of inflammatory pain
1. Prostaglandin produced after skin cell damage
2. Prostaglanding bind to blood vessels and dilate (widen)
3. Neutrophils in blood released from vessels
4. Neutrophils release inflammatory mediators
5. Bind to nerve endings and activate
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What is the function of aspirin?
Block prostaglandin production, breaking inflammatory pain pathway
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Why is long term potential and depression important?
1. underlies learning and memory
2. Used in Alzheimer's treatment
3. Might be involved in Alzheimer's itself
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Mechanism of long term potentiation
1. Presynaptic neuron has glutamate (excitatory)
2. Post synaptic has AMPA and NMDA receptors
3. AMPA receptors open but NMDA can't bc Mg2+ blocks the channel
4. Increasing presynaptic stimulation pushes Mg2+ off and opens NMDA channels, allowing more Ca2+ in
5. Leads to a larger EPSP
6. Larger influx of Ca2+ activate kinases
7. Increase strength and number of AMPA receptors
8. Continue to increase potentiation of EPSP and therefore LTP
215
Can LTP be transferred to neighboring synapses?
Yes --> coincident imputes at a neighboring synapse can trigger LTP at that one
216
What determines LTP vs LTD?
Frequency of impulses!
Rate of impulses affects size of EPSP due to summation --> affects # of NMDA receptors unblocked --> determines depolarization --> affects amount of CA2+ entry
217
What is LTD?
Similar to LTP, but:
- Low freq --> lower Ca2+ (only NMDA open, no AMPA)
- Low Ca2+ --> activate phosphatase instead of kinase
- Oppositve effect from LTP
218
Declarative memory
Episodic: facts, events, places
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Nondeclarative memory
- Procedural: playing an instrument
- Conditioning: Pavlov
- Priming: patterns
- Nociception: pain
220
How is LTP related to learning?
1. Learning related to hippocampus.
2. Hippocampus has dendritic spines.
3. Dendritic spines grow via LTP in a dish!
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Factors that enhance consolidation
1. NTs: ACh and NE
2. Stress (mixed effects)
3. Attention
4. Relevance
5. Repetition
6. Sleep
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Visual system
1. Photoreceptors on retina
2. Optic nerve
3. Optic chiasm (split)
4. Optic tract
5. Lateral geniculate nucleus (LGN)
6. Optic radiation
7. Striate cortext
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Receptive field mapping
If on-center field:
- light in center --> on
- light in periphery --> off
Lateral inhibition!
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Layered structure of retina
1. Light comes in
2. Pigment epithelium
3. Photoreceptors: rods and cones
4. Horizontal and bipolar cells
5. Amacrine cells
6. Ganglion cells to optic nerve
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Distribution of photoreceptors on retina
Cones in the center, rods surround
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Proteins used by photoreceptors for color
Cone opsin (short, medium, and long) and rod rhodopsin
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Mechanism of bipolar cells
1. Cones release glutamate
2. Hyperpolarize on-bipolar cells
3. depolarize off-bipolar cells
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Why is the surround of a receptive field antagonistic?
Horizontal cells feed back on surrounding photoreceptors and suppress their responses
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Ventral/dorsal divergence from primary visual cortex
```
Ventral = what
dorsal = where
```
230
Crista ampularis of semi-circular canals in ear
fluid movement moves hair cells, which depolarize. Signal travels via tight junctions
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Otolith organs of ears
Vestibular sense!
Utricle: forward acceleration (horizontal)
Sacculus: gravitational acceleration (vertical)
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Organ of cord in ears
Hearing via inner hair cells
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Hair cell mechanism
1. Hair cells pushed in one direction stretched trp link between channels on cells
2. Depolarize one (open Na/Ca channels)
3. Link bounces back
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Traveling waves along basilar membrane
As freq of sound decreases, peaks are further from stapes
235
What is the relationship between taste and olfaction?
Combination with olfaction leads to sense of taste
236
What mechanism do odorant receptor neurons use?
GPCR (metabotropic)
1. Odorant to cilia on outer olfactory epithelium
2. Olfactory receptor cells to olfactory bulb
3. Bundles of olfactory receptor cells to bulb = cranial nerve 1
4. Glomeruli of olfactory bulb connect to mitral cells and tufted relay neurons
5. Go to olfactory cortex
237
What mechanism do NSAIDs use to reduce pain?
Block prostaglandin synthesis
238
A key molecular event to increase postsynaptic responsiveness to glutamate during hippocampal LTP?
Phosphorylation of AMPA receptors to increase their conductance
239
What can enhance both LTP and is used to improve memory in Alzheimer's disease?
Inhibition of acetylcholinesterase to increase acetylcholine levels
240
Simtulation of the center of the receptive field of an "on" center retinal ganglion cell with light results in ___
The cell firing rapidly
241
When the hair bundle is deflected towards the tallest steocilium, __ enter the cell via selective channels near the tips of the stereo cilia and the hair cell ____
k+ ; depolarizes
242
During development, axon growth is controlled by:
- growth stimulating molecules on cell surface and intracellular matrix (laminin)
- growth inhibiting molecules on cell surface and in extracellular matrix (ephori's)
- diffusible molecules that attract axons (entrain)
- diffusible molecules that repel axons (semaphorin)
243
Mechanism of vestibular system
1. Rotation of head moves endolymph (liquid) inside semicircular canal that corresponds with the plane of movement (L-R, up down, shake).
2. Endolymph moves to ampulla with hair cells with stereocilia at top that move to release NT to brain
244
Mechanism for taste
1. Taste buds on tongue have multiple taste cels with microvilli (taste hairs)
2. Microvilli come in contact with taste chemicals and depolarize
3. Send signals to thalamus and then gustatory cortex
4. Encode for sweet, salty, bitter, savory/umami, sour
245
How long does the spinal cord extend along the vertebrae?
Extends to L1/L2 level
246
Number of spinal nerves
31 pairs
247
Order of spinal nerves
1. 8 cervical
2. 12 thoracic
3. 5 lumbar
4. 5 sacral
5. 1 coccygeal
248
What is the impact of an injury higher on the spinal cord compared to lower?
Higher injuries lead to greater deficit
249
Conus Medullaris
End of spinal tail
250
Cauda Equina
End of spinal nerves
251
Spinal cord meninges
1. Epidural space: created by loose attachment of dura mater
2. Dura mater
3. Subdural space
4. Arachnoid mater
5. Subarachnoid space: CSF
6. Pia mater: denticulate ligaments - support spinal cord
252
Gray matter of spinal cord
1. Anterior (ventral) horn
2. Lateral horn: Intermediolateral cell column
3. Posterior (dorsal) horn
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Anterior (ventral) horn
Gray Matter
1. Somatic motor - skeletal muscle
2. Cervical enlargement (C5-T1)
3. Lumbosacral enlargement (L1-S3)
4. Anterior (ventral) rootlets
254
Specific motor distribution of anterior horn
Somatotopic homunculus: Proximal areas of horn regulate proximal muscles of limbs, vice versa with distal
255
Lateral horn (intermediolateral cell column)
Gray matter
1. T1-L2 (preganglionic sympathetic) & S2-S4 (pregangionlic parasympathetic)
2. Autonomic (visceral motor - smooth muscle)
256
Posterior (dorsal) horn
Gray matter
Sensory
1. Nucleus gracilis (lower extremity) - in medulla
2. Nucleus cuneatus (upper extremity) - in medulla
3. Nucleus dorsalis (of Clark)
4. Posterior (dorsal) rootlets - posterior (dorsal) root
5. Posterior (dorsal) root ganglion (sensory cell bodies)
257
White Matter of spinal cord
1. Ascending tracts (sensory)
| 2. Descending tracts
258
Ascending tracts of white matter in spinal cord
1. Posterior (dorsal) column sensory pathways
| 2. Lateral column sensory pathways
259
Posterior (dorsal) column sensory pathways (ascending - white matter)
General sensation
1. Fasciculus cuneatus (upper extremity)
2. Fasciculus gracilis (lower extremity)
260
Lateral column sensory pathways (ascending - white matter)
1. Spinothalamic tract: pain and temperature
| 2. Spinocerebellar tracts: spine to cerebellum --> position in space
261
Fasciculus cuneatus
- ascend via here (lateral) if above T6
- Upper extremity general sensation
- Synapse in nucleus cuneatus
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Fasciculus gracilis
- ascend via here (medial) if below T6
- Lower extremity general sensation
- Synapse in nucleus gracilis
263
Spinothalamic tract
Pain and temperature
264
Spinocerebellar tract
Spine to cerebellum --> position in space
265
Descending tracts of white matter in spinal cord
1. Lateral column motor pathways
| 2. Anterior (ventral) column pathways
266
Lateral column motor pathways (descending - white matter)
1. Rubrospinal tract: don't use
| 2. Corticospinal tract: voluntary movement (skeletal)
267
Rubrospinal tract
Don't use
268
Corticospinal tract
Voluntary movement skeletal)
269
Anterior (ventral) column pathways (descending - white matter)
1. vestibulospinal tract: balance
2. Reticulospinal tract: varied
3. Tectospinal tract: visual
4. Anterior corticospinal: trunk musculature
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Vestibulospinal tract
- White matter
- descending
- anterior ventral column pathways
- Act on spinal cord neurons for proper control of head and neck musculature in balance and posture.
271
Reticulospinal tract
- White matter
- descending
- anterior ventral column pathways
- Coordinated postural movements
- Descending autonomic and pain modulation information
272
Tectospinal tract
- White matter
- descending
- anterior ventral column pathways
- Visual spatial orientation
- Act on contralateral motor neurons in upper spinal cord mediating head and neck musculature allowing for proper head and neck postural reflexes based on visual information.
273
Anterior corticospinal
- White matter
- descending
- anterior ventral column pathways
- Bilaterally innervate alpha motor neurons that control trunk musculature, where coordination b/t the muscles on both sides of the body is important.
274
Central canal in Spinal Cord
Contains CSF
275
The spinal cord is shorter than the vertebral column and ends at the ____.
1st/2nd lumbar vertebra
276
In the spinal cord gray matter, the anterior horn has ____ neurons, the lateral horn has ____ neurons, and the posterior horn has ____ neurons.
Motor - Skeletal
Autonomic
Sensory
277
Function of posterior (dorsal) columns
1. Fine touch - Meissner corpuscles
2. Vibration sensation/deep touch - Pacinian corpuscles
3. Proprioception - muscle spindles, Golgi tendon organs (ear)
4. Stereognosis - recognize an object by touch without visual cues
278
Pathway of posterior (dorsal) columns and medial lemniscus
1. Myelinated, rapid conducting axons enter via posterior (dorsal) root ganglion/posterior (dorsal) root neurons (first order neurons)
2. Ascend in posterior (dorsal columns (no synapse)
3. In the caudal medulla
4. 2nd order neurons cross over in medulla oblongata
5. Ascend in contralateral medial lemniscus
6. Synapse in thalamus (VPL)
7. 3rd order neurons ascend through internal campus to cerebral cortex (post central gyrus)
279
Dermatomes
Show cervical levels and connection to body --> creates patterns important for clinical practice
280
Function of spinothalamic tract
1. Pain - free, unmyelinated nerve endings in skin
| 2. Temperature - free, unmyelinated nerve endings in skin
281
Pathway of spinothalamic tract
1. Enter via posterior (dorsal) root ganglion / posterior (dorsal) root (1st order neurons)
2. Synapse in posterior (dorsal) horn)
3. 2nd order neurons cross over at the spinal cord level of entry (anterior white commissure)
4. Ascend in contralateral spinothalamic tract (anterolateral tract)
5. Synapse in thalamus (VPL)
6. 3rd order neurons ascend through internal capsule to cerebral cortex (post central gyrus)
282
Lesions of posterior (dorsal) columns
1. ipsilateral deficit in spinal cord lesion
| 2. Contralateral deficit in brain stem/cortical lesion
283
Lesions of spinothalamic tract
1. Contralateral deficit in spinal cord lesion
| 2. ipsilateral deficit in brain stem/cortical lesion
284
Function of corticospinal tract
Voluntary motor (skeletal muscle)
285
Pathway of corticospinal tract (descending - motor)
1. Arise in cerebral cortex (precentral gyrus or premotor cortex)
2. Descend through internal capsule, cerebral peduncle in midbrain
3. Cross over in caudal medulla (pyramidal decussation) becoming the lateral corticospinal tract
4. Descend through spinal cord (contralateral side)
5. Synapse in anterior (ventral) horn on anterior (ventral) horn cells or on interneurons
6. Lower motor neurons pass through anterior (ventral) root to spinal nerve to supply skeletal muscles
286
Ascending (sensory) white matter tracts are found in the ____ & ____ columns.
Lateral, posterior
287
Pain & temperature sensation travels by a different pathway than general sensation. Which pathway decussates in spinal cord?
Pain & temperature only
288
The descending motor pathway (corticospinal tract) decussates in the _____.
Brain stem (medulla oblongata)
289
Define two-point discrimination.
Way to determine discrimination b/t 2 points
290
What receptors are activated in the 2-point discrimination test?
Merkel cells: smallest receptive field
291
Does the measurement on the 2-point discrimination differ between the fingertip and the arm or other locations?
Yes, much smaller on finder than arm or elsewhere
292
Why do you think the measurements may differ in 2-point discrimination between finder and other areas?
Finger has smaller receptive fields
293
Which skin areas have a higher density of receptors?
Finger has highest density of receptors, followed by palm, forearm, etc.
294
Explain the concept of receptive field.
Region that stimulated will change nerve's response --> can be positive or negative response
295
What are the implications of having different sensitivities in different skin areas/
Areas with higher sensitivity are more important for survival evolutionarily (ex: fingers)
296
What is the pathway followed for info form sensory receptors in the skin to get to the brain?
- 1st order neurons: primary sensory afferent - cell body in dorsal root ganglia.
- 2nd order neurons: Interneurons that connect to 1st and cross over in medulla
- 3rd order neurons: thalamus to somatosensory cortex
297
Which two sensory systems are involved in rubber hand illusion?
Somatosensation and vision
298
The pathway that mediates reflexes involve what types of neurons?
Sensory and motor
299
Characterization of the ionic changes in an axon that produce an AP
1. Influx of sodium
| 2. Outflux of potassium
300
What would be impaired if tyrosine hydroxylase is decreased?
Dopamine and noradrenaline
301
In temporal summation, a ________ of Aps in the presynaptic neuron elicits postsynaptic potentials that add together.
high frequency
302
What is the mechanism by which acetylcholine is inactivated in the synaptic cleft?
Enzymatic breakdown
303
_____ provide the main cytoskeletal "track"s for axonal transportation.
Microtubules
304
What mechanism would work to design a drug that penetrates the CNS?
Adjunctive administration of vasoactive substances that can permeate tight junctions between endothelial cells.
305
____ afferents have small receptive fields and produce sustained responses.
Merkel
306
The first order neurons of somatosensory pathways typically have bodies in the _______.
Dorsal root ganglia
307
The ability of synapses to strengthen or weaken over time in response to increases or decreases in their activity.
Synaptic plasticity
308
Types of axons
- A alpha
- A beta
- A delta
- C
309
Properties of A alpha axons
Diameter: 13-20
Speed: 80-120
Receptors: Proprioceptors/skeletal muscle
310
Properties of A beta axons
Diameter: 6-12
Speed: 35-75
Receptors: Mechanoreceptors (touch)
311
Properties of A delta axons
Diameter: 1-5
Speed: 5-30
Receptors: Pain/temp
312
Properties of C axons
*Not myelinated!
Diameter: 0.2-1.5
Speed: 0.5-2
Receptors: Pain/temp/itch
313
Diameter/speed of axons
Alpha > beta > delta > C
