more neuro Flashcards
1
Q
Stimulus, receptor, location for Hearing
A
Mechanical, mechanoreceptor, cochlea
2
Q
Stimulus, receptor, location for Balance
A
Mechanical, mechanoreceptor, vestibular system
3
Q
Stimulus, receptor, location for Vision
A
Light, photoreceptor, retina
4
Q
Stimulus, receptor, location for Touch
A
Mechanical, mechanoreceptor, skin
5
Q
Stimulus, receptor, location for temperature
A
Thermal, thermoreceptor, skin
6
Q
Stimulus, receptor, location for pain
A
Mechanical, thermal, chemical
Nociceptor
Skin, internal organs
7
Q
Stimulus, receptor, location for proprioception
A
mechanical, mechanoreceptor,
muscles, tendons, joints
8
Q
Stimulus, receptor, location for olfaction
A
chemical, chemoreceptor, nasal cavity
9
Q
Stimulus, receptor, location for taste
A
chemical, chemoreceptor,
tongue, pharynx, palate, epiglottis
10
Q
What happens after a stimulus has been detected
A
- Sensory receptor activated,
2 Membrane permeability is altered in sensory cell
3 A receptor potential develops in the sensory cell
3a. Neurotransmitter can be released into afferent neuron terminals (that part can be skipped) - An action potential is generated in the afferent neuron terminal
- The action potential propagates to the CNS
- Information is integrated by the CNS
11
Q
Function of inhibitory neurons
A
• Ensures the signal in the most active neuron is propagated e.g. this enables contrast enhancement in the eye
- Help increase contrast
- Send axons laterally
- Inhibitory neurons can inhibit relay neurones to decrease amount of neurotransmitter release
- Achieving lateral inhibition – enables receptor field to be restricted
- Helping with contrast
12
Q
What are the three common steps senses must require?
A
– Require a physical stimulus mechanical, chemical, internally physical
– Must transform the stimulus into nerve impulses
• This occurs in the peripheral nervous system
– Evoke a response to the signal in the form of perception or conscious experience of sensation
• This occurs in the central nervous system
13
Q
What does sensation begin with in the body?
A
Sensation begins with sensory receptors in the periphery
14
Q
What is sensory transduction
A
Sensory receptors enable sensory transduction, the conversion of energy from the environment into electrochemical signals
15
Q
What do many sensory receptors possess?
A
Many sensory receptors possess ion channels and G-protein coupled receptors that are common to many bodily functions
16
Q
How is specificity for sensory modalities achieved?
A
by the structure and position of the sensory receptor
17
Q
Name 9 sensory modalities
A
Vision, smell, hearing, balance, taste, pain, touch, thermal senses, proprioception
18
Q
How can receptors be classified
A
Modality, Origin, Distribution
19
Q
Name origins of different receptors
A
– Exteroceptors: Vision, hearing, touch, cutaneous pain
– Interoceptors: Internal organs, visceral pain, nausea, stretch
– Proprioceptors: Muscles, tendons, joints – position & movement
– Nociceptors: High threshold mechano- & thermoreceptors need a high stimulus
20
Q
What are the two receptor distributions?
A
– General senses (somesthetic): Touch, pressure, stretch, hot, cold, blood pressure/composition
– Special senses: Head, innervated by cranial nerves
21
Q
What is the difference between a graded potential and an action potential?
A
- Graded receptor potentials increase in size in response to increases in stimulus amplitude
- Action potentials are always the same size, but have a threshold for activation
22
Q
Name and explain an receptor which includes a synapse
A
Taste receptors
• Stimulus is chemical e.g. Na in salt
• Membrane depolarises in a graded response
• Voltage gated calcium channels open allowing calcium influx
• Synaptic vesicle fusion triggered, releasing neurotransmitter
• Afferent neuron depolarised
23
Q
Name and explain an receptor with direct neural activation
A
Olfactory receptors
• Stimulus is chemical, an odorant
• Local changes in membrane permeability cause a graded receptor potential within a receptor cilium
• Large enough receptor potentials cause depolarisation in the cell soma, triggering action potentials that travel along the olfactory nerve
24
Q
Sensory receptors convey four types of information
A
- Modality (quality)
- Location
- Intensity
- Timing
25
What is stimulus modality is coded by?
The labelled line code
26
What is modality is determined by?
the type of energy transmitted by the stimulus and the receptors that are specialised to detect that energy
27
Describe the labelled line code
* The receptor is selective for one type of stimulus energy
* The axons of the receptor/associated afferent neuron acts as a modality specific line of communication
* Axons from these neurons make connections with specific areas in the CNS
* Stimulating afferent neurons electrically leads to perception of the associated sensation
28
Where is the labelled line code faulty?
in synaesthesia
29
What gives information about the stimulus?
Spatial arrangement of activated receptors within a sense organ
30
In the somatic system, what is a receptive field?
the region of skin innervated by the terminals of the receptor neuron
31
In the visual system, what is a receptive field
of a photoreceptor is the region of the visual field projected onto that receptor
32
In the auditory system, what does spatial arrangement of receptors enable?
enables frequency discrimination
33
How is intensity of stimulus determined?
Intensity is determined by the response amplitude of the receptor and thus the firing frequency of the afferent neurons
34
What is the sensory threshold?
The lowest stimulus strength that can be detected is known as the
35
What is intensity?
Intensity is the total amount of stimulus energy delivered to the receptor
36
What will an increased neural response lead to?
the perception of a larger stimulus
37
What do weak stimulus intensities activate?
low threshold fibres
38
what do strong stimulus intensities activate?
high threshold fibres
39
What is onset timing determined by?
determined by when the stimulus energy is received by the receptor and causes it to fire
40
What is stimulus duration determined by?
determined by adaptation rates of receptors
41
What are adaption rates of receptors?
Adaptation = In response to continuous stimuli, the firing rate of action potentials decreases
42
Slowly adapting receptors
* Tonic receptors
| * Respond to prolonged stimulation
43
Rapidly adapting receptors
* Phasic receptors
| * Respond at the beginning and end of a stimulus
44
Divergence of Sensory Integration
– allows primary afferent neurons to signal to more than one relay neuron
45
Convergence of Sensory Integration
– ensures that relay neurons have larger receptive fields than primary afferent neurons
46
Inhibitory neurons
• Ensures the signal in the most active neuron is propagated e.g. this enables contrast enhancement in the eye
47
What is Stimulus location is determined by?
the activation of spatially distributed sensory neurons
48
what is Intensity of sensation is determined by?
stimulus amplitude and neuronal firing rate
49
What is light? What does light include?
• Light has:
– a wavelength: distance between peaks or troughs
– a frequency: number of waves per second
– an amplitude: difference between wave peak and trough
50
How does electromagnetic light travel?
Electromagnetic light travels in straight lines, known as rays, until it interacts with atoms and molecules
51
What are the three ways light rays interact:
Reflection, absorption and refraction
52
Example of absorption
pigmented epithelium of retina
53
Example of refraction
bending due to difference in speed of light through different media e.g used by cornea to form images on the retina
54
Function of Pupil
lets light inside the eye
55
Function of Iris
contains muscles which control the amount of light entering the eye
56
Function of Cornea
glassy, transparent covering of the pupil and iris that refracts light
57
Function of Sclera
continuous with cornea, forms the tough, protective wall of the eyeball to give it it’s shape white tough surface, keeps spherical shape
58
Function of Extraocular muscles
move the eyeball, controlled by oculomotor nerve (cranial nerve III)
59
Function of Optic nerve (cranial nerve II)
carries axons from retina to brain
60
What is the Optic disk
origin of blood vessels and optic nerve, cannot sense light why we have a blind spot. no photoreceptors therefore cannot detect light
61
What is the Macula
region of retina for central vision, devoid of large blood vessels to improve vision quality. where light is focused,
62
What is the Fovea
retina is thinnest here and is the area of highest visual acuity. Want most light to be focused, mainly has photoreceptors.
63
Describe the Aqueous humor
a watery fluid that provides nutrients to the cornea and lens, fully replaced ~ every 90 minutes
provides nutrients so no need for blood vessels
64
Describe the Vitreous humor
a viscous fluid, keeps the eyeball spherical and the retina flat to provide clearer images. Never replaced.
65
What is the lens suspended by?
The lens is suspended by zonal fibres (ligaments) which are attached to the ciliary muscle, enabling stretching of the lens
66
Image formation
* Light rays must be focussed onto the retina (ideally the fovea)
* Refraction occurs at the:
* cornea, ~80%
* lens, remaining 20%
67
Degree of refraction is determined by:
* Difference in refractive indices between the two media
| * The angle at which light hits the interface between these two media
68
Refraction by the cornea
Light that hits the cornea directly perpendicular just moves straight through onto the retina.
• Light arrives at the cornea through air, but the cornea is mainly water
• Light travels more slowly through water than air due to higher density = refraction occurs
69
Accommodation by the lens of Distant objects
- almost parallel light rays
| - cornea provides sufficient refraction to focus them on the retina
70
Accommodation by the lens of Closer objects (<7m away)
need additional refraction
- light rays are not parallel
- requires additional refraction to focus them on the retina
- provided by the fattening of the lens
71
What does rounding of lens increase?
increases the refractive power to focus closer objects on the fovea
72
When is the eye emmetropic?
when lens is flat, and we are focussing a distant object
73
What is Hyperopia?
* Farsightedness
* eye is too short
* near objects are focussed behind the retina
* not enough refraction
74
What is Myopia?
* Nearsightedness
* eye is too long
* distant objects are focussed before retina
* too much refraction
75
How is Hyperopia corrected?
Using a convex lens
76
How is Myopia corrected?
Using a concave lens
77
Presbyopia
loss of accommodation with age
78
Accommodation has limits which increase with age
* young children can focus on the end of their nose
* By ~30 years old, the limit is ~10 cm
* By mid 40s, the limit is beyond arms length
79
Pupillary light reflex
• Iris regulates light levels
Pupillary constrictor (smooth circular muscle)
Pupillary dilator (smooth radial muscle)
• Enables us to adjust to changes in light intensity
• Consensual light reflex i.e. occurs in both eyes even if only one is stimulated
80
Pupillary constriction
Parasympathetic stimulation of circular muscle
81
Pupillary dilation
Sympathetic stimulation of radial muscle
82
what do Closer objects require
additional refraction, achieved by accommodation of the lens which is regulated by contraction and relaxation of the ciliary muscles
83
How can Pupil diameter be adjusted?
by contraction of muscles within the iris in response to changes in light levels
84
Laminar organisation of the retina
* Light focussed on the retina must now be converted into neural activity
* Light must pass through ganglion cells and bipolar cells before it reaches the photoreceptors
* Light that passes all the way through the retina is absorbed by the pigmented epithelium
85
Name the Cells of the retina
Ganglion cells, amacrine cells, bipolar cells, horizontal cells, photorecetors
86
Function of Ganglion cells
output from retina
87
Function of Amacrine cells
input from bipolar cells, influence ganglion cells, bipolar cells and other amacrine cells
88
Function of Bipolar cells
connect photoreceptors to ganglion cells
89
Function of Horizontal cells
input from and output to photoreceptors, output to bipolar cells
90
Function of Photoreceptors
sensory transducers, both rods and cones
91
Duplicity theory
– can’t have high sensitivity and high resolution in single receptor
– thus, separate systems for monochrome and colour
92
Rod photoreceptors
– 92 million
• Greater number of disks
• Higher photopigment concentration
• 1000 times more sensitive to light than cones
• Enable vision in low light (scotopic) conditions i.e. at night time
• Low visual acuity/resolution
• More area photopigment can be stored within disks
• Allow us to see outlines in dark
• Take a while to process
93
Cone photoreceptors
```
- 5 million
• Fewer disks
• Used during daylight (photopic) conditions
• Enable colour vision
• High visual acuity/resolution
• Lower sensitivity
• Allows us to see colour due to the photopigments present
• Not good in low light
```
94
Central retina
= low convergence, low sensitivity, high resolution
-Each cone in central retina connected to one bipolar cell to one ganglion cell – receptive field for cone is tiny
95
Peripheral retina
= high convergence, high sensitivity, low resolution-
For rods in peripheral retina; Receptive field of ganglion cell is much bigger – lower resolution, high sensitivity, greater receptor potential – summate and produce action potential
96
Phototransduction
Photoreceptors are hyperpolarised by light
| Resting is more depolarised at -30mv
97
What are open in the dark?
cGMP-gated non-selective cation channels are open in the dark allowing a Na+ influx known as the dark current to depolarises photoreceptors
98
What does light decrease?
cGMP levels, closing the channels and preventing Na+ influx, hyperpolarising photoreceptors
99
Phototransduction- the mechanism
* Rhodopsin is activated by light and undergoes an conformational change
* This stimulates the G-protein, transducin, to become transducin GTP
* The α subunit activates the enzyme phosphodiesterase (PDE)
* PDE reduces cGMP levels, closing Na+ channels
* Signal amplification occurs as this is an enzyme cascade
100
What id Rhodopsin is made out of?
two key components, retinal and opsin.
101
What is Opsin a member of?
the G-protein coupled receptor family.
102
What does Saturation occur in response to?
bright light
* Rods cannot process bright light as they become easily saturated
* cGMP levels are so low that no additional hyperpolarisation can occur
* Cones are not saturated as easily, so are used in bright light
103
What do Retinal ganglion cells respond to?
| What does phototransduction by retinal ganglion cells do?
photons but their properties are not well suited to help image formation
set the circadian clock
104
How do the Responses of retinal ganglion cells to ambient light levels affect us?
- Affect many aspects of our health
- Daily light cycle – entrains circadian rhythms
- Changes in day length and shift work can cause mood alterations and cognitive deficits
- Aberrant light cycles also increase depression, impair - LTP in hippocampus and impair learning
105
Rod photoreceptors are highly sensitive to what? what does this allow?
to light, allowing night vision.
106
What do cone photoreceptors contain? what does this enable?
contain one of three photopigments, enabling colour perception during daylight
107
What does the fovea contain?
a high concentration of cones, with a low convergence on retinal ganglion cells, making this area better for high resolution vision
The fovea contains most of the 5 million cones and very few rods
108
What are photoreceptors?
Membranous disks contain light-sensitive photopigments that absorb light
109
Name the Cone photopigments
three varieties of opsins - S, M and L
| Short, medium, long wavelength
110
Name a Rod photopigment
rhodopsin
111
Name a Retinal ganglion photopigment
melanopsin (found in retinal ganglion cells)
112
The 5 basic tastes
* Salty – vital electrolytes, ionotropic receptors
* Sour – acids, H+, ionotropic receptors
* Sweet – innate fondness, high energy foods, metabotropic receptors
* Bitter – instinctively rejected, often poisons, metabotropic receptors
* Umami – ‘delicious’ in Japanese, savory taste of glutamate, metabotropic receptors -associated with amino acids
113
What are the 5 basic tastes and describe them
* Salty – vital electrolytes, ionotropic receptors
* Sour – acids, H+, ionotropic receptors
* Sweet – innate fondness, high energy foods, metabotropic receptors
* Bitter – instinctively rejected, often poisons, metabotropic receptors
* Umami – ‘delicious’ in Japanese, savoury taste of glutamate, metabotropic receptors -associated with amino acids
114
What do Lingual papillae contain?
Taste buds which are groups of taste cells
115
Name the 4 types of lingual papillae and describe them
Filiform – spiked, no taste buds, sense texture, most abundant
Foliate – ridges
Fungiform – mushrooms, mainly at sides and front
Circumvallate – pimples, large, contain about half of all taste buds
116
What does transduction of different stimuli depend on?
which membranous receptors are expressed
117
Ion channel are receptors for which tastes?
Salty and sour
118
G-proteins coupled receptors are receptors for which tastes?
Sweet: T1R2 bound to T1R3 to detect sweet
Umami: T1R1 bound to T1R3 to detect umami
Bitter: T2Rs
119
Specificity of taste cells vs taste buds vs gustatory afferent fibres
* Taste cells appear to only respond to one type of stimuli
* But taste buds contain taste cells which respond to various stimuli
* Gustatory afferents branch to innervate many different taste cells in different taste buds
120
The olfactory system
Odorants as low as a few parts per trillion can be detected
Human olfactory epithelium = 10 cm2
Dog olfactory epithelium = 170 cm2
Dogs have 100x more receptors/cm2
121
What are olfactory receptor cells and describe them?
Are bipolar chemoreceptive neurons
* Odorants must dissolve in the mucus layer to reach olfactory receptor cells
* Transduction machinery is found within the cilia at the end of the dendrite
* The primary afferent neuron is the axon of the olfactory receptor cell
* The axons are thin, unmyelinated
* Olfactory receptor cells are regularly replaced
122
Odorant receptor proteins (ORs)
* Humans have ~350 odorant receptor proteins
* Olfactory receptor cells only express one odorant receptor
* One odorant receptor can recognise multiple odorants
* It is the unique combination of odorant receptors that recognise an odorant that allows us to distinguish a specific odor
123
Transduction occurs via Golfs, how?
```
• Odorant receptor proteins (ORs) are G-protein coupled receptors (Golfs)
• Every OR uses the same downstream pathway
– Adenylyl cyclase
– cAMP
– Cyclic nucleotide gated ion channels
– Depolarisation
– Ca2+-gated Cl- channels
– Further depolarisation
```
124
Where does transduction occur?
In cilia
125
What do Receptor potentials trigger?
Action potentials
• Large enough receptor potential = threshold for action potential firing reached
• Intense stimulus = large receptor potential = increased action potential firing rate
126
What does amount of action potential firing depend on?
Concentration of odorant
127
Where does each glomerulus of the olfactory bulb receive input from?
- Receives input from only one type of olfactory receptor
| - Each glomerulus will continue to be associated with the same odorant
128
Olfactory Projections- where do second order neurons carry information to?
Second order neurons carry information from glomeruli to various regions of the brain
129
What do the olfactory epithelium contain?
olfactory receptor cells that achieve sensory transduction in their cilia and generate action potentials that propagate along their axons
130
What are Olfactory receptor proteins?
are G-protein coupled receptors that mediate their response using Golf and cAMP
131
What is gustation?
the action or faculty of tasting.
132
What are the taste organs?
primarily tongue, also cheeks, soft palate, pharynx, epiglottis
133
What does the taste pore allow?
• Taste pore allows sensory transduction by microvilli
