Neurons, Synapses, and Signaling - Chapter 48 Flashcards
1
Q
How was the role of electricity in nerves first observed?
A
When Luigi Galvani dissected frog muscle - proposed the theory of animal electricity
2
Q
What was Alessandro Volta’s contributions to discovering how the brain works?
A
Discovered electrical current is generated by contact between different metals
3
Q
How were the structures of single neurons revealed?
A
Camillo Golgi used silver chromate to do so
4
Q
Every cell has voltage across its plasma membrane called a membrane potential
A
5
Q
Define resting potential
A
The resting potential of a neuron is the membrane potential when its not sending signals
6
Q
Define action potential
A
the brief “all or none” signal
7
Q
Where are most of the neurons organelles?
A
its cell body
8
Q
What are dendrites?
A
highly branched extensions that receive signals from other neurons
9
Q
What is the axon?
A
a much larger extension that can transmit action potentials
10
Q
What is the axon hillock?
A
The site of action potential generation - the cone-shaped base of an axon
11
Q
Where is information (in a synapse) transmitted to and from?
A
From a presynaptic cell (neuron) to a postsynaptic cell (neuron, muscle, or gland cell)
12
Q
What is a synapse?
A
a junction between the pre- and postsynaptic element
13
Q
The synaptic terminal of one axon passes information across the synapse as chemical messengers called neurotransmitters OR directly through electrical gap junctions
A
14
Q
Flow of ions (ie current) cause the membrane potential to rise above (depolarization) or below (hyperpolarization) the neuron’s resting membrane potential
A
15
Q
Neurons maintain a certain concentration gradient across their membranes which is different for each ion
A
16
Q
At resting membrane potential, what is K+ doing?
A
Diffusing out, along its concentration gradient
17
Q
At resting membrane potential, what are negative charges (CL-) doing?
A
Building up along the inner membrane creating an opposing electrical force
18
Q
At equilibrium, both electrical and chemical forces are balanced (equilibrium potential)
A
19
Q
What is the typical resting membrane potential for neurons?
A
about -80 to -65 mV
20
Q
Ion pumps generate chemical gradients
A
In a mammalian neuron, the concentration of K+ is highest inside the cell, while the concentration of Na+ is highest outside the cell
- sodium-potassium ATPase uses energy to drive/maintain these K+ and Na+ gradients across the plasma membrane
- these gradients represent chemical potential energy
21
Q
Depolarized definition
A
more positive than resting potential
22
Q
Hyperpolarized definition
A
more negative that resting potential
23
Q
What is the time constant?
A
The time taken for cell voltage to reach approximately 63% of its final value
24
Q
When do membranes become hyperpolarized?
A
When positive ions move out of the cell (or negative ions move into the cell)
25
When do membranes become depolarized?
When positive ions move into the cell (or negative ions move out of the cell)
26
Define graded potentials
changes in polarization where the magnitude of the change varies with the strength of the stimulus
- graded signals cannot be propagated through great distances
27
Define/describe action potentials
a depolarization above a certain threshold results in a massive change in membrane voltage called action potential (AP)
- APs have a constant magnitude, are all-or-none, and may transmit signals over longer distances
28
How/why do APs arise?
because some ion channels are voltage-gated, opening or closing when the membrane potential passes distinct levels
29
Around what value is the resting membrane voltage?
-70mV
30
K+ selective ions are the main (but not only) channels that are open at rest (the voltage-gated ones are closed, but these ones are open)
31
myelin insulates axons in vertebrates, which increases an action potential's speed
myelin sheaths are made by glia - oligodendrocytes in the CNS and Schwann cells in the PNS
32
how does speed of an action potential relate to the axon's diameter
speed increases with diameter
33
saltatory conduction
action potentials are formed only at nodes of Ranvier (gaps in the myelin sheath where voltage-gated Na+ channels are found) - action potentials jump between nodes of Ranvier
34
size of potential varies with stimulus intensity
gentle pressure is low frequency of action potentials per receptor, more pressure creates higher frequency of action potentials per receptor
35
describe the role of glia cells
nourish, support, and regulate neurons; often 10 to 50x more glia that neurons in a given area
36
what do astrocytes do?
induce cells lining capillaries in the CNS to form tight junctions, resulting in a blood-brain barrier (BBB) and restricting entry of most substances into the brain
37
neurons communicate with other cells at chemical and/or electrical synapses
the presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal, the action potential then activates Ca2+ channels, the entry of Ca2+ then triggers the fusion of vesicles, the neurotransmitter then diffuses across the synaptic cleft and is received by the post-synaptic cell
38
a single neurotransmitter may bind specifically to more than a dozen different receptors, causing them to open
39
a neurotransmitter may excite or inhibit postsynaptic cells
- excitatory postsynaptic potentials (EPSPs) are depolarizations that bring the membrane potential toward threshold
- inhibitory postsynaptic potentials are hyperpolarizations that move the membrane further from threshold
40
what does the time constant indicate?
how long the cell takes to charge up its membrane
41
most neurons have many synapses on their dendrites and cell body
42
a single EPSP is usually too small to trigger an action potential in a postsynaptic neuron, but if two EPSPs are produced in rapid succession, an effect called temporal summation occurs
43
spatial summation definition
EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together, which can trigger an action potential (in combination with temporal summation)
44
acetylcholine (ACh) definition/role
a common neurontransmitter in vertebrates and invertebrates involved in muscle stimulation, memory formation, and learning
- vertebrates have acetylcholine receptors that are ligand gated, and some that are metabotropic
45
neuropeptides roles as neurotransmitters
neuropeptides (relatively short chains of animo acids) also function as neurotransmitters, including substances like endorphins, which affect the perception of pain
46
organization of the nervous system
- circuits of neurons and supporting glial cells
- vertebrate brain is regionally specialized
- cerebral cortex controls voluntary movement and cognitive functions
47
opiates role in the nervous system
bind to the same receptors as endorphins and can be used as painkillers
48
the simplest nervous systems
cnidarians have neurons arranged in nerve nets, a series of interconnected nerve cells
49
what does the pons do?
- Raphe nucleus: major source of serotonin in the brain; controls aggression, mood, respiration centres in the medulla oblongata
- locus coerules: major source of norepinephrine in the brain; involved in arousal, alertness, and attention
50
what parts of the brain are included in the metencephalon (back of the hindbrain)
pons, cerebellum
51
role of the cerebellum
motor coordination, learned motor tasks
52
what parts of the brain are included in the myencephalon (bottom of the hindbrain)
medulla oblongata (controls respiration and heart rate)
53
what did Johannes Peter Muller propose?
the law of specific nerve energies: the nature of perception is defined by the pathway over which the sensory information is carried rather than the stimulus itself
54
sensory mechanisms include...
- detectors: convert energy into electrical signals (APs)
- neural circuitry that processes information
55
sensory transduction definition
conversion of stimulus energy into a change in sensory receptor membrane potential - this is called a receptor potential
56
receptor potential and stimulus strength
receptor potentials are graded potentials - their magnitude varies proportionately with stimulus strength
57
graded potentials are converted into action potentials (within the same neuron)
- APs are regenerative and thus enable signals to be transmitted over long distances
- this conversion from graded to "digital" results in the loss of information, however you will be able to transmit the not-lost information long distances
58
sensory adaptation definition
a decrease in responsiveness to the average stimulus statistic
- helps the sensory systems to transmit only novel or new features in the stimulus environment
- we only send signals about changes, not the mean
59
4 types of sensory receptors
mechanoreceptors, chemoreceptors, electromagnetic receptors, and thermoreceptors
60
mechanoreceptors
sense physical deformation caused by forms of mechanical energy
- our responses to pressure, touch, stretch, motion, and sound relies on mechanoreceptors
61
touch receptors are unevenly distributed across our bodies
62
somatosensory afferents convey information from the skin surface to CNS
sensation from most of the body is mediated by 31 pairs of spinal nerves
- cranial nerve V transmits sensation from the head
63
the density of receptors is larger in the hands and head than the rest of the body
64
pain and touch are not carried by the same pathways
65
pain receptors drive a distinct pathway
pain receptors (or nociceptors) detect stimuli that reflect harmful conditions
- respond to excess heat, pressure, or chemicals
66
most invertebrates maintain equilibrium using mechanoreceptors located in organs called statocysts
67
many arthropods sense sounds with body hairs that vibrate, or with localized "ears" consisting of a tympanic membrane stretched over an internal air chamber
68
human hearing system
sound waves in the air cause tympanic membrane to vibrate, three bones in the middle ear amplify and transmit vibrations to the oval window on the cochlea, creating fluid waves, the vibrations create pressure waves in the fluid in the cochlea that travel through the vestibular canal and dissipate when they strike the round window at the end of the tympanic canal
- fluid waves vibrate the basilar membrane
69
each region of the basilar membrane is tuned to a different, particular vibration frequency
this enables the cochlea to distinguish pitch
70
structure and roles of the cochlea
- composed of three large chambers
- the organ of Corti (in the middle chamber) houses hair cells with mechano-sensitive receptors
- when the basilar membrane vibrates, the hair cells bend
71
what happens when the hair cells in your ear move?
bending of the hair cells depolarizes membranes of mechanoreceptors and modulates Ca entry and transmitter release
72
organs in the ear that detect body movement, position, and balance
utricle and saccule contain granules called otoliths that are used to perceive position relative to gravity or linear movement
- three semicircular canals contain fluid and can detect angular movement in any direction
73
fish hear differently from humans
only have a pair of inner ears near the brain - a lateral line system along both sides of their body
74
light detectors all contain photoreceptors: cells that contain light-absorbing pigment molecules
75
the vertebrate visual system
the eye detects color and light which is used for visual and non-visual function
76
humans have photoreceptors in the back of the eye - light has to go through lots of tissue to hit the rods and cones
77
day-night cycle - ambient light determines circadian rhythms
78
rods and their functions
more sensitive, saturate for dusk/night, black and white vision
79
cones and their functions
less sensitive, do not saturate, daylight colour vision
80
light energy is used to isomerize cis-retinal to trans-retinal, activating the photopigment called rhodopsin
81
why are photoreceptor cells depolarized in the dark?
high cyclic GMP keeps cGMP-gated cation channels open - flashes hyperpolarize the membrane (not depolarize)
82
light energy is used to tigger cis-retinal to trans-retinal isomerization - the shift in shape activates the visual pigment rhodopsin (rods) which activates a G protein, closes the cationic channels, and leads to membrane hyperpolarization
83
in light, rods and cones hyperpolarize, shutting off the release of glutamate
84
ON - activated by the onset of light
OFF - activated by darkness
85
distribution of photoreceptors in the human retina
5 million cones
there is a concentration of cones in the fovea - region of about 1.5 mm in diameter
most acute vision limited to foveola
86
sensations from the left visual field of both eyes are transmitted to the right side of the brain - sensations from the right visual field of both eyes are transmitted to the left side of the brain
87
most ganglion cell axons lead to lateral geniculate nuclei - the lateral geniculate nuclei relay information to the primary visual cortex in the cerebrum
88
ventral stream in the temporal lobe - "what pathway"
dorsal stream in the parietal lobe - "how pathway"
89
in humans, perception of colour is based on three types of cones (red, green, or blue)
short (blue) medium (green) long (red) - wavelength
- three distinct opsin proteins
- colour comes from comparison - if you had just blue cones, you'd be colourblind
90
most mammals are colourblind
91
gustation (taste)
dependent on the detection of tastant chemicals
92
olfaction (smell)
dependent on the detection of odorant molecules
93
tastant and odorant molecules are the same, the difference is how it enters the body
94
taste receptors are held in tastebuds
each tastebud houses many taste cells
95
five distinct tastes
sweet, sour, salty, bitter, umami
96
