Unit 6: The Peripheral Nervous System (Afferent Division- special senses) Flashcards
1
Q
What is the name of information coming to the CNS for internal viscera called, as it is usually subconscious?
A
Visceral Afferent
2
Q
What is an sensory afferent?
A
When sensory information is sent to receptors and afferent information reaches a CONSCIOUS level, known as sensory afferent.
3
Q
What are Somatic Sensations?
A
Body sense (arising from the body) Include somesthetic sensation from the skin, and proprioception from the muscles and joints, as well as the inner ear.
4
Q
What is Perception?
A
- Our conscious interpretation of the external world as created by the brain from a pattern of nerve impulses delivered to from sensory receptors.
- does not duplicate reality
5
Q
What are Special Senses?
A
-Vision, hearing, taste and smell
6
Q
What is a stimulus?
A
A change detectable by the body- energy forms, modalities such as heat, light and sounds.
7
Q
Where do receptors lie?
A
Afferent neurons have receptors at their peripheral ends that pick up stimuli.
8
Q
What are Nociceptors?
A
- Pain receptors
- Sensitive to pressure/ tissue damage
9
Q
How is pain sensed?
A
Stimulation of receptors on afferent fibres generate action potentials changing the membrane permeability. There is an inward flux of Na+ into the cell, causing depolarization in the cell.
–>If there is a separate receptor, this is called the receptor potential. If the receptor is on an afferent neuron, its called a generator potential.
10
Q
How are Photoreceptors activated?
A
Hyperpolarization (increasingly neg)
11
Q
How is a receptor potential produced?
A
This means the receptor is separate from the afferent neurons.
-The receptor potential activates a chemical messenger that crosses the gap to the afferent neuron and binds a special protein receptor, chemically opening Na+ channels in the afferent neurons.
12
Q
How is a generator potential produced?
A
-The generator potential is generated as current flows from the receptor directly to the afferent neuron, opening Ca2+ channels and causing an action potential if it reaches threshold.
13
Q
What is intensity of the stimulus reflective of?
A
-Magnitude of the threshold potential= greater frequency of actions potentials= greater intensity.
14
Q
Explain Adaptation of receptors…
A
-Receptors can diminish the extent of their depolarization despite large action potentials.
15
Q
What is the difference between Tonic and Phase receptors?
A
Tonic receptors react slowly or not at all
Phasic receptors are rapidly changing receptors.
16
Q
What is the off response?
A
When a stimulus is removed from a receptor, the receptor typically responds with a slight depolarization.
17
Q
What is the Pacinian Corpuscle?
A
A rapid adapting skin detector that detects changes in pressure and vibrations.
*contains both mechanical (detection of pressure stimulus) and electrochemical (decrease in the influx of Na+ into the cell) mechanisms.
18
Q
What is Habituation?
A
-A modification of the synaptic effectiveness in the CNS; causes a decrease in stimuli intensity effectiveness.
19
Q
Once an action potential gets to the spinal cord, where is it’s final destination?
A
2 ways:
- Can become apart of a reflex arc
- May be relayed to different parts of the brain for further processing, or they may become conscious thought.
20
Q
What are the pathways that integrate information of conscious somatic sensations?
A
Somatosensory pathways
-Pathways consist of labelled lines, which integrate information more efficiently.
21
Q
What is the Receptor Field?
A
- The small region of skin the receptor responds to stimulus for.
- The smaller the area, the greater the acuity and discrimination.
22
Q
What is Lateral Inhibition?
A
The most strongly activated signal pathways originating from the center of the receptor inhibits less excited pathways of surrounding areas
23
Q
What are the three categories of Nociceptors?
A
Mechanical, Thermal and Polymodal Nociceptors (respond equally to all forms of pain)
24
Q
True or False: Nociceptors adapt to stimuli.
A
False.
25
What increases Nociceptor sensitivity?
Prostaglandins
26
What is the Fast Pain Pathway?
Signals detected from mechanical/ thermal nociceptors are transmitted over small, myelinated A- delta fibres at 30m/ sec.
27
What is the Slow Pain Pathway?
Impulses from Polymodal nociceptors are carried by small, unmyelinated C fibres at 12m/ sec.
-->The following slow, dull, aching, poorly localized pain occurs due to this pathway, and is generally activated by chemicals such as bradykinin.
28
What activates afferent C fibres ?
Capsaicin
| Can be used to treat pain. (killing receptors)
29
Higher Processing of Pain Stimulus
-Primary afferent pain fibres synapse with specific second order interneurons in the dorsal horn of the spinal cord. When the stimulus is detected, action potentials relay the release neurotransmitters Substance P and Glutamate through afferent nerve fibres.
30
What is Substance P's main function?
-Activates ascending pathways that transmit nociceptor signals to higher levels for further processing.
31
What is Glutamate's main function?
- Excitatory neurotransmitter
| - Binds AMPA receptors that cause action potentials in the dorsal horn, where the signal is taken for higher processing.
32
What is the Analgenic System?
-Stops pain by blocking the release of substance P from afferent pain fibre terminals.
33
What type of receptor is the analgenic system dependent on?
Opiate receptors
34
What gland produces tears?
Lacrimal Gland
35
What are the three layers of the eye?
The outer layer is the cornea/ sclera, middle is the choroid layer, and the inner layer is the retina.
36
What is the Sclera?
-Outer "white part of the eye"
37
What is the Cornea?
An outer transparent layer that allows for the passage of light rays into the eye.
38
What is the Choroid?
- The middle layer of the eye which contains an abundance of blood vessel's that nourish the eye.
* Highly pigmented.
39
What is the Retina?
-An outer pigmented layer and inner nervous tissue layer.
40
What is the difference between Rods & Cones?
- Rods are responsible for low-levels of light, where as cones are photoreceptors for color vision.
* Both convert light into nerve impulses.
41
What separates the two fluid filled cavities of the eye?
-An elliptical lens
42
What is the large, posterior fluid filled cavity called?
- Vitreous Humor
- ->Jelly-like fluid
* Important in maintaining spherical eyeball shape.
43
What is the smaller, anterior fluid filled cavity called?
- Aqueous Humor
* Located between the cornea and the lens.
- Clear, watery fluid which carries nutrients to the cornea and lens, which lack blood vessels.
44
What layer and specialized part of the eye is responsible for producing the Aqueous Humor?
-->The choroid layer; the ciliary body.
45
What is Glaucoma?
- Occurs when the Aqueous Humor does not drain as quickly as it forms, causing pressure on the eye.
* *Can cause retinal/ optic nerve damage & blindness.
46
What is the Iris?
-A thin, pigmented smooth muscle that forms a visible band within the aqueous humor (eye color).
47
What is the round opening in the center of the Iris that allows for the interior passage of light?
The Pupil
48
What is the role of Circular (Constrictor) Muscles of the eye?
- In the presence of light, circular muscles of the eye causing the formation of a smaller ring.
* So less light enters.
- ->Parasympathetic Stimulation
49
What is the role of Radical (Dialator) Muscles of the eye?
- In the absence of light, these dialator muscles expand so the ring gets larger.
* Emphasizes the drawing in of light.
- ->Sympathetic Stimulation
50
What is the range of visible light for humans?
400-700 nm
51
Short Wavelengths are what color on the spectrum?
Blue
52
Long Wavelengths are what color on the spectrum?
Red
53
Where do light rays focus themselves in the eye?
The Focal Point
54
What is the name of the process that slows down light rays as it moves through an area of greater density?
Refraction
55
What way does a convex ray bend light?
Outward
56
What way does a concave ray bend light?
Inward
57
What is Astigmatism?
The curvature of the cornea is uneven, so light rays that enter are unevenly reflected.
58
What 2 structures of the eye are responsible for the refraction of light rays?
-The cornea and the lens
59
What is Accommodation?
-The ability to adjust the strength of a lens.
60
What is the function of the Ciliary Muscle?
* Apart of the choroid layer.
- A circular ring of smooth muscle attached to the lens by suspensory ligaments.
- ->The strength of the lens is dependent on it's shape, regulated by the Ciliary Muscle.
61
What is Presbyopia?
-With loss of elasticity, the lens can no longer assume the spherical shape required for near vision.
62
What is the name of a condition where the Ciliary Muscle fibres become opaque?
A Cataract
63
What is Myopia?
A far light source is focused IN FRONT of the retina, causing blurriness.
*Nearsightedness
64
What is Hypertopia?
Near objects are focused behind the retina, causing blurriness.
* Farsightedness
- Can be fixed with LASIC eye surgery.
65
What are the 3 layers of the Retina?
1 ) Rods & Cones
2) Middle layer of bipolar cells
3) Inner layer of ganglion cells
* Axons of the ganglion cells form at the optic nerve, where impulses are sent to the CNS.
66
What is the name of the part of the retina where the optic nerve leaves and blood vessel's pass?
The Optic Disc
67
Why is the blind spot at the optic nerve?
There are no rods or cones!
68
Where is the fovea, and what is it's function?
- ->The center of the retina.
* ganglion/ bipolar layers of the fovea move out of the way of light rays so they can strike photoreceptors immediately.
* ONLY cones are found in the fovea.
69
TRUE OR FALSE:
| Light must pass through all ganglion/ bipolar layers before striking photoreceptors, besides the fovea.
True!
70
What is the Macula Lutea (also known as the fovea) ?
- Part of the retina that is highly enriched with cones and fairly high acuity.
- ->Mascular degeneration is a loss in photoreceptors in the Mascular Lutea in association with aging.
71
How do photoreceptors generate action potentials?
-->Photopigment molecules undergo chemical alterations when activated by light (in photoreceptors). This leads to a generation of action potentials, which transmit information to the brain regarding visual processing.
72
What are the 2 components of Photopigments?
1. Opsin (protein of the disc membrane)
| 2. Retinene (vitamin A derivative)
73
What are the 4 types of Photopigments (1 rod 3 cones) ?
Rod: Rhodopsin (absorbs all visible wavelengths)
Cones: Red, green and blue cones (all three respond to different wavelengths)
74
What is Phototransduction?
The process of converting light stimuli into electrical signals.
- ->On exposure of light, the conc. of cGMP is reduced.
- ->Retinene change shape, which activates the photopigment. Rods & cones contain a G protein called transductin, which activates phosphodiesterase, and it's phoshodiesterase which breaks down cGMP.
* *Causes Na+ channels to close, causing hyperpolarization of the photoreceptors.
75
What is dark adaptation?
-Going from light to dark in a short time span, and waiting for the darkness to gradually fade out.
76
True of False: The breakdown of photopigments after the exposure of sunlight DECREASES sensitivity of photoreceptors.
True.
77
What is Light Adaptation?
Enough rhodopsin is broken down to "burn out" rods, so they can no longer respond to light.
78
What causes night blindness?
A deficiency of Vitamin A
79
How is color vision established?
Color vision is dependent on the ratios of stimulation of all 3 cones.
*Cones absorb light at some wavelengths and give off the opposing colors.
80
What is Color Blindness?
When an individual lacks a particular cone type
81
What's the main function of on-center and off-center ganglion cells?
To emphasize difference in relative brightness of the receptive field.
82
What are On-center ganglion cells?
Increase the rate of firing when light is most intense in the center hole.
83
What are Off- center ganglion cells?
Increase the rate of firing when the periphery (dough of donuts) is most intensely illuminated.
84
Where do they optic nerve's meet after they exit each retina?
The Optic Chiasm
* Fibres of the medial half cross over, but fibres of the lateral half remain on the same side.
- ->Reorganized bundles leave the Optic Chaism, known as Optic Tracts.
85
What information do the Optic Tracts carry?
- Optic tracts carry information for the medial half of one eye, and the lateral half of the other eye.
* This allows for visual information of the same sides of the visual field to be processed.
86
What is the first stop for information in the visual pathway from the Optic Tracts?
- The Lateral Geniculate Nucleus in the Thalamus.
| * Separates information from the eyes and relays it via Optic Radiations!
87
Where do Optic Radiations relay visual input?
To different zones of the cortex
88
What is the Binocular Field of Vision, and why is important in depth perception?
- ->Overlapping area seen by both eyes.
| - The brain uses slight disparity in the information received from the 2 eyes to estimate distance.
89
Where is visual information processed first?
-->The Primary Visual Cortex, and then sent to higher- level visual areas fro complex processing.
90
What does the Ear consist of ?
- An external, middle and inner component.
- ->The external and middle ear transmit sound waves to the fluid filled inner ear, that converts these sound waves into sound energy.
91
What are the components of the Inner Ear?
-The Cochlea and the Vestibular Apparatus
92
How is Pitch (or Tone) determined?
Frequency of vibration
93
How is Intensity determined? (loudness)
Amplitude of sound
| *measured in dB's
94
What is the name of the fainest sound that can be heard, used to compare the dB logarithmic scale?
The Hearing Threshold.
95
What is Timbre (quality) dependent on?
-Depends on it's overtones, which are additional frequencies superimposed on the fundamental pitch.
96
What constitutes the External Ear?
- The Pinna, which funnels the sound down the ear canal. The ear canal is lined with fine hairs and modified sweat glands that produce cerumen (ear wax) to trap foreign molecules. The sound travels through the canal to the Tympanic Membrane, where it vibrates from sound waves.
* The eardrum is exposed to atmospheric pressure via the Eustachian (auditory) Tube, which connects the middle ear to the pharynx.
97
What are the 3 bones of the middle ear, and what is their function?
The ossicles - the malleus, incus and stapes
| *The ossicles transfer the vibratory movements of the tympanic membrane to the fluid of the inner ear.
98
What is the function of the Cochlea, and what are it's 3 divisions?
- The upper compartment: scala vestibuli - perilymph
- The middle compartment: scala media -fluid is called endolymph
- The lower compartment: scala tympani -perilymph
99
What is Helicotrema?
Fluid beyond the cochlear duct where upper and lower fluids are continuous.
100
What is the round window?
-Seals the scala tympani from the middle ear.
101
What does the vestibular membrane seperate ?
-The scala media and the scala tympani
102
What membrane forms the floor of the cochlear duct, sepearting it from the scala tympani?
Basilar Membrane
103
What key component is housed in the basilar membrane?
The Organ of Corti
* Contains hair cells for sound
- Hair cells contain stereocilia, which generate neural signals when their surfaces are mechanically deformed, causing depolarization and spiking action potentials.
- Hair cells contact the tectorial membrane
104
How do the inner hair cells communicate their deformation?
-Via a chemical synapse with the terminals of afferent nerve fibres, making up the auditory nerve. (cochlear nerve)
105
What is Electromotility?
Hair cells rapidly change length in response to changes in membrane potential.
- ->Lengthen on hyperpolarization
- ->Shrink on depolarization
106
Sound Transduction Process:
Sound waves --> Vibration of Tympanic Membrane -> Vibration of Ossicles --> Vibration of Oval Window --> Fluid movement in cochlea --> Vibration of Basilar Membrane, which houses the Organ of Corti --> Deformation of inner hairs --> Graded Potentials of receptor cells --> Changed in rate of action potentials generated in auditory nerve --> Propagation of action potentials in Auditory Cortex.
107
What is Pitch Discrimination ?
-The ability to distinguish between various frequencies of incoming sound waves.
108
What is Loudness Discrimination?
Depends on the amplitude of vibration.
| -Greater Basilar membrane movement = Louder sound.
109
Where and what is the Primary Auditory Cortex?
-Located in the Temporal Lobe- linked to specific regions of the Basilar Membrane.
110
What is the difference between Conductive Deafness & Sensorineural Deafness ?
Conductive deafness occurs when the sound waves are not adequately conducted through the external and middle ear to set the fluids in motion.
Senorineural deafness occurs when sound waves are transmitted to the inner ear, but aren't transmitted into nerve signals
111
What is Neural Presbycusis?
-A degenerative, age-related process where hair cells "wear out".
112
What is the Vestibular Apparatus?
- Besides the cochlea, the second specialized portion of the inner ear.
- ->Provides information essential for the sense of EQUILIBRIUM - AND COORDINATING HEAD/ POSTURE BALANCE.
- Contains 3 semicircular canals that detect rotational or angular acceleration of the head.
- ->Receptive hair cells are stimulated by the motion on the Ampulla, which sit in a gelatious layer, the Capulla.
113
What are the components of vestibular hair cells?
- One cilium, the kinicillium, 20-50 microvilli, and the stereocilia which are arranged in rows of increasing height.
- When stereocilia bend to kinicillium, it depolarizes.
- When stereocilia being away from kinicillium, it hyperpolarizes the cell.
114
What are the molecular bridges that link stereocilia?
-Tip links
115
What nerve do these vestibular hair cells form with afferent neurons?
The Vestibular nerve, which joins with the Auditory nerve to form the Vestibulocochlear nerve.
116
What is the role of Otilith Organs?
- Provide information about the position of the head relative to gravity, and also detect changes in the rate of linear motion.
- ->Saccule and Utricles, which are situated between the semicircular canals and cochlea, are tiny crystals or calcium carbonate which give the hair cells more inertia.
117
How is taste sensed?
Binding of a tastant causes receptor cells to depolarize, which initiates action potentials within the afferent neuron and receptor.
-These signals are sent to the brain stem and thalamus, and then to the Cortical Gustatory Area.
118
What are the 5 primary tastes?
-sour, sweet, savory (umami), bitter and salty
119
How is Sour sensed and interpreted as an action potential?
Na+ ions enter the cell, and cause a direct entry of sodium ions, causing depolarization.
120
How is Sour sensed and interpreted as an action potential?
H+ ions block K+ channels. This forces K+ out of the cell, causing depolarization.
121
How is Sweet sensed and interpreted as an action potential?
Binding of glucose activates a G protein, which activates cAMP pathway's in a taste cell. This results in phosphorylation and blockage of K+, leading to depolarization.
122
How is Bitter sensed and interpreted as an action potential?
The G protein in taste- gustducin- initates a signalling pathway, leading to depolarization.
123
How is Umami sensed and interpreted as an action potential?
Triggered by amino acids, especially glutamate.
| -->Glutamate binds G- protein, and activates the second passenger system leading to depolarization.
124
What are the three types of cells found in Olfactory Mucosa?
- Olfactory receptors- respond to stimuli
- Supporting cells- produce mucus
- Basal cells- Precursors for new olfactory cells
* Axons of Olfactory receptors form the Olfactory nerve.
125
What mechanisms include molecules being smelled?
Cilia bind Odourants
- Binding of an odourant to the olfactory receptor activates G-protein, which initiates the cAMP cascade. Leads to the opening of Na+ and depolarization- thus action potentials in the afferent fibre.
- -> The Olfactory bulb synapses with these afferent nerve fibres carrying the signal.
126
Characteristics of the Olfactory Bulb?
- Lined with glomeruli, which receive these relayed signals from the olfactory receptors. Glomeruli can only respond to one discrete odourant.
- ->Glomeruli send signals to mitral cells.
127
Where do Glomeruli send signals?
Mitral cells
128
What are the two pathways for relaying info from the Mitral cells?
1. The Primary Olfactory Cortex
| 2. The Thalamus
129
How is Odour discriminated against?
- Based on different patterns of glomeruli activated by various scents.
- ->Allows the cortex to differentiate over 10,000 scents.
130
What is the Vomeronasal Organ of animals (VNO)?
- Detects pheromones, which are non-volatile chemical signals passed subconsciously from one another.
* Governs emotional/ sociosexual behavior.
