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Physiology 209 > Sensory > Flashcards

Sensory Flashcards

1
Q

What is the CNS made up of?

A

The brain and spinal cord

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2
Q

What afferents?

A

Neurons that deliver information to the CNS(sensory input)

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3
Q

Where are the cell bodies and axons of afferents located?

A

Cells bodies: Outside of CNS
Axons: Stick into the CNS in the brain or spinal cord

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4
Q

What are the spinal nerve afferents responsible for?

A

Where somatosensation (touch, temperature and pain) enter the spinal cord

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5
Q

What are the cranial nerve afferents responsible for?

A

Carry information about visual, olfactory, somatic into the brain

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6
Q

How many cranial nerves and how many go into the brainstem?

A

12 cranial nerves
10 out of 12 go into the brainstem

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7
Q

What is visceral input?

A

Somatosensation from within your body

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8
Q

What are efferents?

A

Neurons that send outputs out of the CNS (motor outputs)

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9
Q

Where are the cell bodies of efferent?

A

In the CNS and their Axons are outside of the CNS

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10
Q

T/F: cranial nerves and spinal nerves have efferents?

A

True

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11
Q

What somatic efferents?

A

Motor neurons with their cell bodies in the CNS and axons innervating the skeletal muscles to make you move

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12
Q

What are autonomic efferents?

A

Innvervate things other than skeletal muscle such as smooth muscle, interneurons and cardiac muscle

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13
Q

What are gyrus?

A

Wirnkles in the cerebral cortex responsible for out smartness

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14
Q

What are sulcus?

A

The cracks in between the gyrus

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15
Q

What is the central sulcus?

A

Separates the gyrus responsible for primary somatosensory processing from the gyrus responsible for primary motor cortex

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16
Q

What is grey matter?

A

Location of the cell bodies for the neurons in the cerebral cortex

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17
Q

What is white matter?

A

Axons travelling from different areas of the brain

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18
Q

What is the basal nuclei/ganglia?

A

A bunch of cell bodies together inside the cerebral cortex

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19
Q

What do cervical nerves innervate?

A

-Neck, shoulders, arms and hands

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20
Q

What do Thoracic nerves innervate?

A

-Shoulders, chest, upper abdominal wall

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21
Q

What do the lumbar nerves innervate?

A

-Lower abdominal wall, hips, legs

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22
Q

What do the sacral nerve innervate?

A

-Genital and lower digestive tract

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23
Q

How many spinal nerves?

A

31

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24
Q

What is the butterfly shape of the spinal cord?

A

THe grey matter

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25
Q

What is the central canal and where is it located?

A

In the middle of the gray matter of the spinal cord and it is a canal for CSF

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26
Q

Ventral horn vs Dorsal horn

A

Ventral horn: Area of the grey matter closest to the stomach
Dorsal horn: Area of the grey matter closest to the back

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27
Q

What does the dorsal root carry?

A

Sensory afferent (inputs) into the spinal cord

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28
Q

What does the ventral root carry?

A

Motor efferent axons (output)

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29
Q

Where are the cell bodies of the seonsory afferents located?

A

Dorsal root ganglion

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30
Q

Where are the cell bodies of the motor efferents located?

A

Ventral horn

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31
Q

What would happen if you damage the dorsal root?

A

Somatosensory input would be affected bu motor output would be fine

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32
Q

What two nerves don’t go into the brainstem?

A
  1. Olfactory nerve
  2. Optic Nerve
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33
Q

What is brain edema?

A

Brain bleeding`

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34
Q

How does a brain bleed affect pupillary response?

A

When your brain bleeds there is increase intercranial pressure which compresses the brain stem and cranial nerves that regulate the pupillary response. Now you pupil will no longer dilate when light is flashed into it

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35
Q

What are the three layers of the embryonic disk?

A
  1. Ectoderm
  2. Mesoderm
  3. Endoderm
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36
Q

What occurs during week 3 and 4 of embryonic development?

A

The ectoderm folds up into a neural groove and then becomes the neural tube

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37
Q

Where do the cells of the CNS come from in development?

A

Ectoderm

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38
Q

Where do the cells that become the organs and muscles come from during development?

A

Mesoderm

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39
Q

Where does the digestive system come from during development?

A

Endoderm

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40
Q

What does the neural tube become?

A

THe CNS and part of the PNS

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41
Q

Neural crest cells become?

A

Part of the PNS

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42
Q

What is the dura, where does it come from and what does it become?

A

Cells from the mesoderm become the dura which is the covering/liniing of the CNS

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43
Q

What occurs during week 4 of embryonic development?

A

The neural tube forms vesicles with a cavity in the middle that later become parts of the brain (forebrain, midbrain and Hindbrain)
The neural tube also form a part with no vesicles that becomes the spinal cord

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44
Q

What is the cavitiy used for in the neural tube?

A

Becomes the ventricles of the brain and central canal of the spinal cord

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45
Q

What produces CSF?

A

The ventricles

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46
Q

What are the four ventricles?

A
  1. Lateral ventricles
  2. Third ventricle
  3. Fourth ventricle
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47
Q

What are the largest types of ventricles?

A

Lateral ventricles
There is one in each hemisphere of the brain

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48
Q

Which ventricles produce the most CSF?

A

The lateral ventricles

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49
Q

Do all ventricles produce CSF?

A

Yes

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50
Q

What is the choroid plexus?

A

Lines the inside of all of the ventricls and is repsonsible for oozing out CSF(produces CSF) produces 500mL per day

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51
Q

How much CSF is in the brain?

A

150mL

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52
Q

What are the functions of the CSF?

A
  1. Supports and cushions the CNS (the brain floats in CNS)
  2. Provides nourishment to the brain (contains glucose)
  3. Removes metabolic waste through absorption at the arachnoid villi
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53
Q

How is CSF removed from the brain?

A

Absorption by the arachnoid villi

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54
Q

Composition of the CSF?

A

-Sterile, colourless fluid that contains glucose

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55
Q

How does the CSF flow throughout the brain?

A

Passively flows throughout the brain and ventricles and requires no energy

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56
Q

What is the Foramen of Monro?

A

COnnects the two lateral ventricles to the third ventricle

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57
Q

What is the cerebral aqueduct?

A

Connects the third ventricle to the fourth ventricle

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58
Q

What is the role of the subarachnoid space?

A

THe CSF created by the chroid plexus passively moves around the subarachnoid space until it gets to the very top(midline). Where the arachnoid villi are located

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59
Q

Where does the subarachnoid space come from in development?

A

The dura

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60
Q

What is the role of the arachnoid villi?

A

Found at the midline of the brain, the acrachnoid villi take CSF out of the subarachnoid space and empty it into the venous blood supply

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61
Q

How hoes the CSF enter the subarachnoid space?

A

Via 3 foramens and 2 lateral and magendie

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62
Q

What happens if the CSF is not taken up by the arachnoid villi?

A

If the ventricle cannot empty CSF, yet it continues to produce it this will cause pressure on the brain

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63
Q

Communicating hyrocephalus vs noncommunicating?

A

Hydrocephalus - Water on the brain
Communication - blockage outside of the ventricles
Noncommunicating - blockage between ventricles

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64
Q

What are meninges?

A

Membranes that cover the CNS(brain and spinal cord)

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65
Q

What are the three meninges?

A

1.Dura
2. Arachnoid membrane
3. Pia matter

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66
Q

What helps produce the subarachnoid space?

A
  1. Arachnoid membrane
  2. Trabeculae( legs)
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67
Q

What is the pia matter?

A

Thin membrane that attaches to the brain below it

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68
Q

What is the dural venous sinus?

A

Dura open and creates a cavity at the midline of the head. Arachnoid villi line the dural sinus and take up CSF from the subarachnoid space and empty it into the dural sinus which goes to the venous blood supply

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69
Q

Where does CSF return to the blood?

A

At the dural sinus

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70
Q

Only substrate metabolized by the brain?

A

Glucose

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71
Q

Do neurons keep a back up supply of glycogen in the brain ?

A

No

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72
Q

Does the brain reuqire insulin to uptake glucose?

A

No

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73
Q

The brain needs a constant supply of…

A

Glucose and oxygen

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74
Q

What happens if there is a lack of blood supply to the brain?

A

Few seconds: Loss of conciousness
Few minutes: stroke which leads to neuronal death

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75
Q

Is glucose transported into neurons?

A

No, it diffuses in

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76
Q

Describe blood flow to brain?

A

Aorta diverges into the common carotid artery which then diverges into the external carotid (supplies blood to outside of the skull) and the internal carotid(supplies bloos to the base of the brain).

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77
Q

What is the basilar artery?

A

Where the two vertebral arteries come together

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78
Q

What is the circle of Willis?

A

Where the basilar artery and the two internal carotid arteries come together and form a loop and then they branch off to different parts of the brain

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79
Q

How is the cricle of willis a safety factor?

A

If an internal carotid artery or vertebral artery is blocked blood is still able to flow to the other side of the brain due to the loop

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80
Q

What is between the endothelial cells of the capillaries in the brain and what do they do?

A

There are tight junctions between endothelial cellsthat prevent anything from leaving/entering the blood from the ECF of the brain.

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81
Q

What can pass through the blood-brain barrier?

A

Lipid soluble substance
- things such as O2, CO2, H2O, alcohol, caffeine, nicotine, heroine

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82
Q

Can ions cross the blood brain barrier?

A

Barely

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83
Q

How does glucose cross the blood-brain barrier?

A

Active transport brings glucose into the ECF of the brain from the blood

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84
Q

What are astrocytes ?

A

Cells that maintain the blood-brain barrier(induce tight junctions)
-Non neuronal cells of the CNS(glial)

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85
Q

Role of astrocytes?

A
  1. Induce tight junctions by putting their foot processes on capillaries
  2. Provide structural support for the brain
  3. Take up extra neurotransmitters/ions to keep everything regulated
  4. Phagocyte debris
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86
Q

Sensation vs Perception?

A

Sensation: Awarness of sensory information(im aware something is hurting)
Perception:Understanding of a sensation’s meaning (My finger hurts because I bumped it)

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87
Q

T/F: We percieve the energy of a seonsory stimulus?

A

False, we do not percieve the photons striking out retina

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88
Q

T/F: We perveice the neural activity that is produced by a sensory stimulation

A

True

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89
Q

What is the law of specific nerve energies and give an example?

A

Does not matter how you activate the receptor on an afferent, what your brain perceives is what it is designed to detect
ex. When you rub your eeyes in the dark you may see some light becaus eyou are putting pressure on the retina

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90
Q

What is the law of projection?

A

Regardless of where in the brain you stimulate a sensory pathway, the sensation is always felt at the sensory receptors location
Ex. Phantom limb pain, axons carry the somatosensory information regrow in the wrong spots and then are activated for the worng reasons

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91
Q

What is the labeled line code?

A

Every afferent that arrives in the CNS carrying sensory information is labeled both on the modality and location

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92
Q

What is modality?

A

Class of stimulus (ex. pain, auditory, visual)

93
Q

T/F: THe brain knows the modality and location of every sensory afferent?

A

True

94
Q

What is an adequate stimulus?

A

In order for the membrane receptor channels to open the stimulus must match what the membrane is designed to transduce. If it is not a match channels will not open
- Ex. Somatosensory receptors in the finger are designed to detect deforamtions of the skin

95
Q

What happens to sensory receptors when they are activated?

A
  1. Stimulus energy
  2. Receptor Membrane is depolarized by opening/closing ion channels
  3. Transduction
  4. Ion channel activation
  5. Afferent
96
Q

How is a weak stimulus encoded by the afferent?

A
  1. Lower magnitude of receptor potential
  2. Frequency of action potentials decreases
  3. Less neurostransmitter is released
97
Q

How is a strong stimulus encoded by the afferent?

A
  1. Bigger magnitude of receptor potential
  2. Frequency of action potentials increases
  3. Lots of neurotransmitter released
98
Q

How is a subthreshold stimulus encoded by the afferent?

A

-Produces a receptor potential that is not strong enough to produce an action potential
- No neurostransmitter is released

99
Q

What is adaptation?

A

Change in the frquency of action potentials, even though the stimulus is constant

100
Q

What are non-adapting afferents?

A

Continuously discharges action potentials due to an ongoing stimulus
-Not coomon
-Encodes stimulus energy just as it is

101
Q

What are slowly adapting afferents?

A

-Starts as a strong action potential than as time goes on the action potentials occur less frequently
-Moderate stimulus changes

102
Q

What is a rapidly adapting stimulus?

A

-Fires rapidly when a stimulus is presented, then falls silent in the prescence of the stimulus

103
Q

What is a receptive field?

A

Region in space that activates a sensory receptor or neuron

104
Q

What happens when there is is a deformation in the middle of the RF vs the outskirts of the RF?

A

Middle of the RF will produce more action potentials
Outsides of the receptive field will produce less action potentials
This explains the graded response of the RF

105
Q

What happens if an action potential occurs outside of the Receptive Field ?

A

No action potentials will be fired by that receptor

106
Q

What is a population code how is it produced?

A

Receptive Fields overlap. When a stimulus is presented it will mainly activate one afferent but it will also activate other afferents around it slightly less(less action potentials) because it will be at the edge of its RF

107
Q

How does the brain utilize the population code?

A

The brain knows where every receptive field is located. The brain uses the population code to determine which afferents are active and which receptive fields were activated in the middle vs edge to determine the precise location of the stimulus

108
Q

Define acuity?

A

Ability to differentiate one stimulus from another

109
Q

How do receptive fields relate to acuity?

A

Small RF = High Acuity
Large RF = Low acuity

110
Q

What is lateral inhibition?

A

When afferents adjacent to eachother try to inhibit each other

111
Q

How does lateral inhibition occur ?

A

The main receptive field afferent (B) has inhibitory interneurons that inhibit the 2nd order neurons of the afferents nearby (reducing their activity)

112
Q

What is the goal of lateral inhibition?

A

“sharpen” the population code, makes it easier for the brain to distiguish where the stimulus is

113
Q

How is lateral inhibition a bottom up mechanism?

A

Way of making sense of the stimuli starting with the receptors and working its way up to the brain(happens automatically)

114
Q

Does lateral inhibition inhibit first order neurons?

A

No, only second order neurons are inhibited , the first order will still fire more action potentials when the stimulus is at the edge of their RF

115
Q

How is sensory information shaped?

A

By both bottom-up(lateral inhibition) and top-down mechanisms(descending pathways)

116
Q

What are the modalities of somatosensory information?

A

-Touch
-Pain
-Proprioception
-Thermal

117
Q

Receptors classes for somatosensory information?

A
  1. Chemoreceptors
  2. Mechanoreceptors(touch)
  3. Thermoreceptors(thermal)
  4. Nociceptors(pain)
118
Q

What are the two types of touch mechanoreceptors in the deep layers?

A

Pacinian corpuscle
Ruffini endings

119
Q

Where are the pacinian corpuscle and ruffini endings found?

A

In the deep layers of the skin

120
Q

Pacinian Corpuscle Vs Ruffini Endings

A

Pacinian Corpuscle: Rapidly Adapting. Detects vibrations
Ruffini endings: Slowly adapting afferents. Signal how the body is bending/stretching (tells you the shape of an object you are touching)

121
Q

What is proprioception?

A

Sense of body awareness (the state of your body)

122
Q

How are mechanoreceptors activated?

A

Stretching the cytoskeletal strands

123
Q

Describe the transduction mechanism of somatosensory receptors?

A
  1. Deformation of the skin results in deformation of the cell membrane of an afferent
  2. Afferents have cytoskeletal strands that attach to ion channels, when the cell membrane deforms it causes sytoskeletal strands to pull on the ion channels and open them
  3. Open ion channels causes a receptor potential. If it is big enough it will produce an action potential sent to the brain/CNS
124
Q

What kind of ion channels are found in the afferents cell membrane?

A

Mechanically-gated(this is why they open due to cytoskeletal strands pulling)

125
Q

What are the two types of mechanoreceptors of touch in the superficial layers?

A
  1. Meissner’s corpuscle
  2. Merkel disk
126
Q

What is the role of specialized end organs on mechanoreceptors?

A

Only allow selective mechanical information to activate the nerve terminal

127
Q

Describe the Meissner’s Corpuscle?

A

-Superficial layers
- Rapidly adapting
- Signal light stroking and fluttering

128
Q

Describe the Merkel disk?

A
  • Superficial layers
  • Slowly Adapting
  • Sensitive to pressure and texture
129
Q

What are the two types of thermoreceptors?

A
  1. Cold Afferents
  2. Warm Afferents
130
Q

Sense of temperature is mediated by….

A

Free nerve endings
Afferents that don’t have specialized end organs wrapped around them

131
Q

T/F : Free nerve endings of the thermoreceptors are located near the surface of the skin?

A

True
-This allows them to ge the most accurate reading of temperature

132
Q

T/F: Free nerve endings have ion channels?

A

True, they open/close depending on temperature

133
Q

Describe the cold afferents?

A

-Ion channels open between 0 and 35 degrees
-Also activated by menthol (Vick’s)

134
Q

Describe the warm afferents?

A

-Ion channels open between 30 and 50 degrees
-Also activated by capsaicin and ethanol

135
Q

What are the pain receptors?

A

Nociceptors

136
Q

Are pain receptors free nerve endings or do they have specialized ned organs?

A

They are free nerve endings with ion channels that open in response to intense mechanical deformation, excessive temperature or chemicals

137
Q

What does it mean when pain afferents are highly modulated?

A

Either enhanced or surpressed

138
Q

Where are nociceptors located?

A

Close to the surface of the skin

139
Q

What are visceral pain receptors?

A

Receptors inside you (stomach hurts, internal inflammation)

140
Q

Describe what happens when you poke your finger?

A
  1. Nociceptors activate
  2. Nociceptors prodcue action potentials
  3. These action potential go to the spinal cord and release substance P
  4. Substance P activates second order neurons that go to the brain
  5. Brain then registers the the poke in the thumb hurt
141
Q

What is enhancement in terms of nociceptors?

A

A process by which the nociceptors become more sensitive to stimuli after having been previously activated

142
Q

Give an example of nociceptor enhancement?

A

After you poked your finger, the next morning when you pick up an object with that finjet you will experience pain because the nociceptor became more sensotive

143
Q

How does enhancement of nociceptors work ?

A

When the afferents were first activated they not only sent axons to the spinal cord but they also sent them to the surrounding tissue of the site of injury.
They released substance P on mast cells which causes the release of histamine which increases sensitivity of the nociceptors. They also release substance P which causes the blood vessels to dilate and the skin at the site of injury to be swollen and red. Mechanical swelling also causes nociceptors to be more sensitive

144
Q

What is hyperalgesia?

A

-Bottom up mechanism
-When a stimulus activates nociceptors that the stimulus normally would not.
-Occurs at previous sites of injury
Body is telling you to not use it till it is healed

145
Q

Describe the touch and proprioception pathway

A
  1. Activation of the receptor
  2. Afferent of the receptor then goes from the finger into the spinal nerve and then into the dorsal root ganglion
  3. Afferent then enters the spinal cord and goes up through the dorsal columns(white matter)
  4. Afferent then crosses the midline in the medula and synapses onto second order neurons
  5. They then synapse onto the thalamus which then goes to the somatosensory cortex
146
Q

What does the dorsal column carry in terms of touch and proprioception?

A

Ipsilateral touch and proprioception

147
Q

Ipsilateral vs Contralateral

A

Ipsilateral : same side
Contralateral: opposite side

148
Q

What does the somatosensory coretx recieve?

A

Contralateral touch and proprioception

149
Q

If a patient has no sense of touch on the left side of the body from chest down, where could there be a lesion.

A

Thoracic damage to the dorsal columns

150
Q

Describe the temperature and pain pathway?

A
  1. Afferent enters through the dorsal root
  2. Afferent synapses onto 2nd order neuron in the grey matter of the spinal cord and crosses the midline in the spinal cord
  3. Afferent axons then go up a white matter track in the anterolateral column
  4. Then synapses onto the thalamus which goes to the somatosensory cortex
151
Q

Anterolateral columns carry what?

A

Contralateral temperature and pain

152
Q

How does a lesion at the anterolateral column affect the body?

A

Temperature and pain from the segment with the lesion and down will be lost on the contrlateral side

153
Q

What would happen if you cut a dorsal root?

A

Loss of temperature, pain, touch and proprioception at the level of the cut on the ipsilateral side

154
Q

What regions of the body have higher acuity ?

A

Lips, face, fingers

155
Q

Why do certain regions of the body have higher acuity?

A

These regions of the body have more neurons in the somatosensory cortrx that represent these parts of the body

156
Q

Where is the somatosensory cortex located?

A

Behind the central sulcus

157
Q

What would a lesion to the somatosensory cortex do ?

A

Loss of temperature, touch , proprioception and pain to the contralateral side

158
Q

When is label line code not true?

A

For referred pain

159
Q

What is referred pain caused by ?

A

Nociceptive afferents from the surface of the skin share the same 2nd order neurons as the nociceptors that are visceral

160
Q

What is referred pain ?

A

When the brain puts the location of the pain of the skin rather than the visceral organ
ex. Heart attack = pain in right arm

161
Q

What are descending pathways?

A

Originate in the brainstem and come down the spinal cord
Inhibit the neural transmission of substance P at the 2nd order neurons that are recieving pain information

162
Q

What is analgesia?

A

Top-down mechanism
-Under your control
The reduction in pain

163
Q

Describe a situation where descending pathways occur?

A

If you get injured during a race but don’t realize till after the race due to adrenaline

164
Q

What are opiate receptors and how are they involved in the descending pathways?

A

Descending pathways of the brain release opiate neurostransmitters that bind to the opiate receptor and stop the release of substance P. Now you will feel no pain

165
Q

T/F: Opiate receptors are sites for drugs such as morphine?

A

True, morphine is used to reduce pain

166
Q

What is the stimulus energy for the visual system?

A

Light

167
Q

What are the recepotrs for the visual system?

A

Photoreceptors

168
Q

What controls the pupil?

A

Iris

169
Q

What is the retinal pigment epithelium?

A

Lines behind the retina and helps with transduction

170
Q

What is the Fovea Centralis?

A

-Point of highest visual acuity (smallest RF)
-Center of vision
-This is where you do all of your detailed looking and reading
-Photorecptors are only cones

171
Q

What is the optic disk?

A

-Blind spot
- Where the optic nerve leaves
-No photoreceptors

172
Q

What opens/closes ion channels in the eyes?

A

Photons

173
Q

What is the retina?

A

-Lines back of eye
-Contains the photoreceptors where transduction occurs
-Contains neurons that start processing the visual information before it is sent out via the optic nerve

174
Q

Role of the cornea and lens?

A

Focus light on the retina

175
Q

T/F: refraction occurs at the cornea and lens?

A

True, photons light bends due to the cornea and lens

176
Q

T/F: Cornea refracts light more than the lens?

A

True

177
Q

What does it mean when something is in focus?

A

All of the different light rays are projected to a single point at the retina

178
Q

Projection on the retina is upsidedown ?

A

Lnes inverts the image

179
Q

What happens to the lens when an object is further away from you?

A

Lens becomes thinner to change refraction

180
Q

What happens to the lens when an object is really close to you?

A

Lens becomes rounder so that there is more refraction of light

181
Q

T/F: Lenses accomodate for changes in object location

A

True

182
Q

What happens if an object is close to the eye but the lens does not become rounder?

A

Object will be out of focus

183
Q

What is a myopic eye?

A

Nearsightedness
-When you can see objects up close just fine but at a distance there is too much refraction and the focus is in front of your retina

184
Q

What is a hyperopic eye?

A

Farsightedness
-Can see things at a distance but objects thar are up close are focuse behind the retina

185
Q

What is astigmatism?

A

The lens or cornea are not spherical

186
Q

What is presbyopia?

A

When the lens gets stiff and is unable to accomodate for near vision as you get older

187
Q

What is cataract?

A

Changes in the lens colour, it becomes opaque which blocks photons from the retina

188
Q

What are the two types of photoreceptors?

A
  1. Cones
  2. Rods
189
Q

Where are the photoreceptors found?

A

Lining the back of the retina
Right next to the retinal pigment epithelium since they undergo a biochemical reaction

190
Q

How does light travel through the eye?

A

Photons travel through the cornea then the lens and then through the vitreous humor and then to the retina

191
Q

What must photons go through before reaching the retina?

A

Must go through the neurons in the retina. The Bipolar, Horizontal and Amacrine neurons are transparent but help process the photons

192
Q

What is convergence?

A

THe idea that the optic nerve has one million axons but there are 100 million photoreceptors. The ganglion cells (axons of the optic nerve) recieve information from many photoreceptors and put it together

193
Q

Describe convergence in the fovea?

A

Since the fovea has higher acuity there are only 1-2 cones driving a ganglion cell

194
Q

Describe convergence in the periphery(outside of the fovea)?

A

Since there is less acuity, there are lots of rods driving one single ganglion cell

195
Q

Why is the fovea the clearest image?

A

All of the cells that distort the image normally are pushed out of the way at the fovea, this creates the little notch and creates the clearest image because photons do not need to pass by all of those cells

196
Q

What are opsin molecules?

A

The proteins that capture photons

197
Q

T/F: Photons cause ion channels to close?

A

True

198
Q

What is phototransduction?

A

Process by which light is converted into electrical energy so that it can be understood by the nervous system

199
Q

Explain phototransduction?

A
  1. Photon is absorbed by chromophore which causes a conformational change and the chromophore to dettach
  2. This then triggers a G-protein cascade which converts cGMP to GMP
  3. As cGMP concentrations fall the sodium ion channels start closing
  4. This results in the hyperpolarization of the photoreceptor and stops the release of neurotransmitters
200
Q

When to photoreceptors release neurtransmitters?

A

In the dark when the cGMP activates the sodium ion channels and the membrane is depolarized

201
Q

Where are opsin molecules foundd?

A

In both rods and cones (photoreceptors)

202
Q

Rod properties?

A
  1. High sensitivity to photons (used as night vision)
  2. Have more rhodopsin to capture as much light as possible at night
  3. High amplification (one photon may close many Na+ channels)
  4. Slow response time
  5. More sensitive to scattered light
203
Q

Cone properties?

A
  1. Low sensitivity to photons(used as day visions)
  2. Less opsin because photons are numerous during the day
  3. Lower amplification
  4. Faster response time
  5. Most sensitive to direct axial rays
204
Q

Describe the rod system?

A

-Low acuity: not present in the central fovea, highly convergent
-Achromatic: one type of opsin molecule(don’t see colour at night)

205
Q

Describe the cone system?

A

-High acuity: concentrated in the central fovea. less convergent
-Chromatic: three types of opsin molecules (colour perception)

206
Q

Describe Dark Adaptation

A
  1. Start with bright lights where the rods are inactivated and the cones are activated
  2. IF you turn the light off you will have temporary blindness until the rods “reactivate”(opsin reattaches to chromophores) and take over
207
Q

Why are rod inactive in bright lights?

A

Due to all of the photons which have broken down the opsin molecules in the rods (no more opsin attached to chromophore)

208
Q

Why are cones inactive in the dark?

A

Not enough photons present

209
Q

Describe Light Adaptation

A
  1. Start in the dark where rods are active and cones are inactive
  2. Turn on the lights this results in temporary blindness until the rods “inactivate” and the cones take over
    The rods are initially saturated (all activated) when the lights turn on which is why it is incredibly bright.
210
Q

Why are the rods near the retinal pigment epithelium?

A

When light breaks the chromophore from the opsin in rods, they have to go into the retinal epithelium is that they can be put back together

211
Q

What determines the intensity of light ?

A

Depends on what is next to the image(contrast)

212
Q

What is the role of the ganglion cells in contrast?

A

Compare the middle of the Receptive field to the surrounding and signal the relative difference of light (contrast) across their receptive fields

213
Q

Patterns retinal ganglion cells like best with excitatory centre?

A
  1. Bright center dark surround (fires a lot of action potentials)
  2. Dark center bright surround(stops firing action potentials)
  3. Uniforma light(center and surround cancel out, doesnt do anything when stimulus comes on)
214
Q

Patterns retinal ganglion cells like best with inhibitory centers?

A
  1. Bright center dark surround(stop firing action potentials)
  2. Dark center bright surround(fires a lot of action potentials)
  3. Uniform(center and surround cancel out, doesnt do anything when stimulus comes on)
215
Q

Where does colour perception come from?

A

Cones

216
Q

What determines the chromatic sensitivity of the photoreceptor?

A

The opsin molecule

217
Q

T/F: Retinal ganglion cells don’t only compare brightness between center and surrround but they also compare colour

A

True

218
Q

Where is colour transmitted?

A

In the fovea because that is where the cones are

219
Q

What are the two types of colour comparisons?

A
  1. Red-Green
  2. Blue-Yellow
220
Q

Why is colourblindness common in males?

A

Opsin molecules are found on the X chromosome, since females have two X’s they are less likely to be colour blind

221
Q

What is colourblindness?

A

Missing an opsin molecule (only have two/one cones)

222
Q

What is the optic chiasm?

A

Where both optic nerves come together (fibers that cross come from the nasal side of the retina)

223
Q

What is the optic tract carrying?

A

Visual information from the contralateral visual fields

224
Q

What is optic nerve carrying?

A

Information from one eye but with both visual fields

225
Q

What does the left and right visual cortex recieve?

A

Left visual cortex recieves info about the right visual field
Left visual cortex recieves info about left visual field

226
Q

What is the primary visual cortex?

A

-Region of small RFs
-These RFs are sensitive to edges, the edges get put together to form a more complex strcuture

227
Q

Two pathways after the primary visual cortex ?

A
  1. Parietal visual stream
  2. Temporal visual stream
228
Q

What is the parietal visual stream?

A

-The “where” pathway
-RFs are larger
-Brain uses this pathway to determine where things are located and whether or not they are moving
-Get mixed up with touch

229
Q

What is the temporal visual stream?

A

-The “what” pathway
-RFs are larger (the entire image)
-Respond to complex features such as faces, hands and landmarks

Physiology 209 (9 decks)

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