Lecture 1-Exam 2 (Special Senses) Flashcards
1
Q
What does a receptor adaptation refer to?
A
to a decline in action potential generation when a constant stimulus is applied
2
Q
Why is receptor adaption necessary?
A
so that constant environmental stimuli can be partially ignored, preventing a flood of sensory information into the CNS.
3
Q
What declines over time with a constant stimulus? What does this cause?
A
The generator potential declines over time with a constant stimulus, causing the frequency of action potentials in the sensory nerve to decrease
4
Q
When are rapidly adapting (phasic) receptors useful?
A
useful in situations where the rate of change of a stimulus is important (e.g., the tension of a working muscle).
5
Q
When are slowly adapting (tonic) receptors useful?
A
useful where information about a sustained stimulus is important (e.g., application of steady pressure).
6
Q
A
7
Q
Slowly adapting receptors respond to a constant stimulus with what? What about rapidly adapting receptors?
A
- Slowly adapting receptors respond to a constant stimulus with a gradual decline in the generator potential and the action potential frequency
- Rapidly adapting receptors have a generator potential and an action potential frequency that declines rapidly in response to a constant stimulus.
8
Q
- What does the somatosensory system do?
- How many cutanous sensory modalities are there?
A
- The somatosensory system conveys sensations from the skin and muscle
- there are four cutaneous sensory modalities: touch, vibration, pain, and temperature.
9
Q
What does the somatosensory sytem include? What is that fxn?
A
The somatosensory system also includes proprioception, which relates to sensory information from the musculoskeletal system
10
Q
What is a dermatome?
A
The area of skin supplied with afferent nerve fibers by a single dorsal root
11
Q
Where are merkel disks and meissner’s corpuscles located? What do they allow?
A
Merkel’s disks and Meissner’s corpuscles are both located near the skin surface and have small receptive fields allowing fine discrimination.
12
Q
What is the difference between merkel’s disks and meissner’s corpuscles?
A
- Merkel’s disks are slowly adapting and sense steady pressure.
- Meissner’s corpuscles are more rapidly adapting and sense more rapid changes in skin contacts.
13
Q
What are ruffini’s endings?
A
contribute to the sensation of touch but have large receptive fields and are slowly adapting, making them useful for sensing local stretching of the skin rather than fine discriminative touch.
14
Q
What are pacinian corpuscles?
A
very rapidly adapting receptors that respond to rapidly changing stimuli, and therefore can sense vibration.
15
Q
What do Hair follicles have?
A
have a nerve plexus that transduces displacement of the hair
16
Q
Explain the main pathways for touch, vibrations, and proprioception
A
- The first-order neuron is the somatosensory receptor neuron. The afferent fiber is in the peripheral spinal nerve, the cell body is in the dorsal root ganglion, and the axon ascends the dorsal column white matter of the spinal cord to the brainstem.
- The second-order neuron is located in the dorsal column nuclei of the caudal medulla. The axon crosses to the opposite side and ascends through the brainstem to the thalamus in a tract called the medial lemniscus.
- The third-order neuron is located in the thalamus and ascends to the primary somatosensory cortex (post central gyrus) via the white matter of the internal capsule.
17
Q
What is the main pathway for touch, vibration, proprioception called?
A
dorsal column-medial lemniscus (DCML)
18
Q
For the main pathway for touch, vibration, and proprioception, what is the site for decussation?
A
site of decussation for the dorsal column-medial lemniscus (DCML) tract is at the level of the medulla
19
Q
What happens when there is a damage below and above medulla in the dorsal column-medial lemniscus (DCML)?
A
- Below the level of the medulla will result in an ipsilateral loss of sensation.
- Above the medulla will result in a contralateral loss of sensation.
20
Q
How does the main pathway for pain and temperature sensation go?
A
The tract crosses immediately in the spinal cord then goes up as the anterolateral system. When it tract hits the midbrain, the tract turns into the spinothalamic tract. Tract goes to the thalamus then into the primary somatic sensory cortex
21
Q
The main pathway for pain and temperature sensation is called what?
A
Anterolateral (neospinothalamic) tract
22
Q
What are the NTs in the pain pathway?
A
Glutamate or Substance P is released by the first-order neuron in the afferent pain pathway
* glutamate, which depolarizes the cell, and substance p, which promotes inflammation and pain.
23
Q
What is pain gating?
A
Pain can sometimes be relieved if nonpainful sensory stimulation is simultaneously applied (e.g., gently rubbing an injured area)
24
Q
How does pain gating work?
A
- Touch fibers entering the same dorsal root as the pain fiber send a collateral branch that synapses on inhibitory interneurons within the spinal gray matter.
- The inhibitory interneurons release opioids (enkephalins) to inhibit transmission in the pain pathway between the first- and second-order neurons.
25
What does the convergence projection theory explain?
* referred pain on the basis that afferent fibers from the viscera converge with somatic pain afferents on the spinal cord
* the CNS misinterprets the source of pain by projecting the visceral signal onto the somatic map.
26
What are the two descending pathways? What does this do?
Two descending pathways can also stimulate the **enkephalinergic interneurons** to inhibit pain transmission:
* a **serotonergic pathway** from the raphe nucleus of the medulla
* a **norepinephrinergic pathway** from the locus ceruleus of the pons.
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The amount of cortex representing a given area reflects what?
the importance of the sensory input.
28
What does a two-point discrimination test measures?
measures the minimum distance between two points of contact that can be perceived as two distinct stimuli.
29
Where is the greatest spatial resolution is found? Lowest?
found on the fingertips and lips, and the lowest spatial resolution is found on the skin of the calf and lower back.
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The high two-point discrimination of the fingertips is due to what?
high density of Merkel’s disks and Meissner’s corpuscles, the large number of neurons in the sensory pathway, and the large representation of these areas in the somatosensory cortex.
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What are the two cerebral hemispheres fuction?
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* The inner aspect of the optic part of the retina is supplied by what?
* Outer, light-sensitive aspect is nourished by what?
* The inner aspect of the optic part of the retina is supplied by the **central retinal artery**
* Outer, light-sensitive aspect is nourished by the **capillary lamina of the choroid.**
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T/F: The branches of the central retinal artery are end arteries that do not anastomose with each other or any other vessel.
True
36
What structures of the eye are both muscular and vascular?
The ciliary body is both muscular and vascular, as is the iris, the latter including two muscles: the sphincter pupillae and dilator pupillae.
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What does the iris separate?
The iris separates the anterior and posterior chambers of the anterior segment of the eyeball as it bounds the pupil
38
Where does the venous blood and aqueous humor in the anterior chamber drain into?
scleral venous sinus
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How does the Dilation and constriction of pupil work?
In dim light, sympathetic fibers stimulate dilation of the pupil. In bright light, parasympathetic fibers stimulate constriction of the pupil.
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When are the layers of the retina separated and by what? When do they fuse?
* The layers of the developing retina are separated in the embryo by an intraretinal space
* During the early fetal period, the embryonic layers fuse, obliterating this space
41
When the retina layers fuse, what becomes firmly fixed and not firm?
the pigment cell layer becomes firmly fixed to the choroid, its attachment to the neural layer is not firm
* normal order: Retina, pigment layer then choroid
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What does a detached retina usually results from?
from seepage of fluid between the neural and pigmented layers of the retina, perhaps days or even weeks after trauma to the eye
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People with a retinal detachment may complain of what?
flashes of light or specks floating in front of their eye
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The edema with papilledema is viewed when?
viewed during ophthalmoscopy as swelling of the optic disc, a condition called papilledema
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What is increased in papilledema? What does this cause?
An increase in CSF pressure slows venous return from the retina, causing edema of the retina (fluid accumulation).
46
What happens to the lens are people age?
* As people age, their lenses become harder and more flattened. These changes gradually reduce the focusing power of the lenses, a condition known as presbyopia
* Some people also develop cataracts, cloudiness of the lens
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What is myopia and hyperopia? What type of lens help?
**Myopia**: light is focused in front of the retina due to having a long eyeball (near sightedness)
* Concave lens causes divergence of light before it enters the long eyeball
**Hyperopia**: Light is focused behind the retina due to having a short eyeball (far sightnedness)
* Convex lens causes convergence of light before it enters the short eyeball
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How is the astigmatism caused? How is it fixed?
* Astigmatism is caused by incorrect curvature of the eye in one plane. Two different focal distances are produced, depending on the plane on which light enters the eye.
* Eyeglasses with a cylindrical lens are needed to correct the refraction error of astigmatism.
49
Outflow of aqueous humor through the scleral venous sinus into the blood circulation must occur at what rate?
at the same rate at which the aqueous is produced
50
If the outflow decreases significantly because the outflow pathway is blocked, what happens? What is this caused?
intraocular pressure (IOP) builds up in the anterior and posterior chambers of the eye, a condition called **glaucoma**
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What can happens in glaucoma?
Blindness can result from compression of the inner layer of the eyeball (retina) and the retinal arteries if aqueous humor production is not reduced to maintain normal IOP.
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What is open angle and closed angle glaucoma?
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What is accommodation? What is presbyopia?
* **Accommodation** is the ability to change optical power to maintain focus as the distance to an object varies.
* **Presbyopia**: reduced ability to accommodate near or distant objects due to a decrease in the elasticity of the lens, which occurs with increasing age.
54
The accommodation-convergence reflex occurs when focusing on a near object and has three components:
i. **Convergence** of the eyes to maintain a single image.
ii. **Constriction** of the pupils by contraction of circular muscle in the iris, to prevent excess light scattering that would blur the image.
iii. **Contraction** of ciliary muscles to increase refractory power of the lens to focus the object.
55
The accommodation-convergence reflex is mediated via what?
parasympathetic nerves to the eye (CN 3)
56
The eye converges light to a focal point on the retina by what?
a convex lens
57
During fixation, the center of the image falls on what?
the fovea
58
For distant vision, the lenses are what?
are flattened, and rays from a distant object are brought to a sharp focus.
59
For near vision, the lens curvature are what?
curvature increases with accommodation, and rays from a nearby object are focused
60
What is the accommodation reflex? What is the diffence of distant and near vision?
i - Pupils constrict
ii - Lens thickens
iii - Eyes converge
61
* What are rods?
* What are cones?
* **Rods** are monochromatic (single color) receptors, which are highly sensitive to light and **allow objects to be seen in low-intensity light.**
* **Cones** function best under high light intensity conditions and allow **color vision.** There are three types, with overlapping sensitivity to light of different wavelength (i.e., blue, green, and red cones)
62
What does the fovea only have? The high visual acuity at the fovea is due to?
* The fovea only contains **cone cells**
* High visual acuity at the fovea occurs because most cone cells in the fovea synapse with a single bipolar cell, which in turn synapses with a single ganglion cell to produce very small receptive fields.
63
Where is the visual acuity lower? Why?
Visual acuity is much lower at the periphery of the eye because there is a high proportion of rod cells, and many rods converge on each ganglion cell.
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Where is the high resolution? What is this area poor in?
central vision has a high resolution but is poor in dim light, whereas peripheral vision has low resolution but allows vision in low light
65
What is color blindness?
* A common condition in which there is a range of possible defects in color vision.
* Most commonly, a single type of cone receptor is missing. X-linked recessive mutations are a common cause of defective color vision, resulting in a higher proportion of males than females with this condition
66
What is phototransduction? What happens in light and darkness?
is the cascade of chemical and electrical events through which light energy is converted into a receptor potential.
Dark:
* Rhodopsin is inactive
* Na+ channels are open
* Cell is depolarized
* High rate of glutamate is being released from rod cell
* Bipolar cell is inhibited so no activity on ganglion cell
Light:
* Rhodopsin is active
* Na+ channels are closed
* Cell is hyperpolarized
* No glutamate is being released by rod cell
*Bipolar cell is no longer inhibited
* Bipolar cell releases NTs and activated the optic nerve fiber
67
What happens in light adaptation (walk out into sunlight)
* Pupil constriction reduces light intensity
* Color vision and acuity below normal for 5 to 10 minutes
* Time needed for pigment bleaching to adjust retinal sensitivity to high light intensity
* Rods quickly bleach and become nonfunctional; cones take over
68
What happens in dark adaption (turn lights off)?
* Dilation of pupils occurs
* In the dark, rhodopsin of rods is regenerated
* In 1 to 2 minutes, night (scotopic) vision begins to function
* After 20 to 30 minutes, amount of regenerated rhodopsin is sufficient for eyes to reach maximum sensitivity
69
Why do we need vitamin A in our body? What does vitamin A deficiency cause?
* Vitamin A has many important functions in the body, including maintenance of healthy epithelia and vision.
* Vitamin A deficiency results in night blindness (rod cell dysfunction), xerophthalmia (dry eyes that are prone to ulceration and infection), and follicular hyperkeratosis (rough elevations of skin around hair follicles resembling goose bumps).
70
The main visual pathway conveys signals from the retina to the primary visual cortex as follows:
i. Axons from retinal ganglion cells enter the **optic nerve** in each eye.
ii. The optic nerves meet at the optic chiasm, where **some axons cross** the midline.
iii. An optic tract leads from each side of the optic chiasm to the **lateral geniculate** body of the thalamus, where retinal ganglion cells synapse.
iv. Second-order sensory neurons follow a course to the **primary visual cortex** via the optic radiation.
71
Images from each half of the visual field are processed by what?
contralateral side of the visual cortex (e.g., the left visual cortex is concerned with information from the right half of the visual field).
72
How does the nasal and temporal half cross in the pathway?
Axons from the nasal half of each retina must cross the midline at the optic chiasm, whereas axons from the temporal half of each retina remain on the ipsilateral side
* For example, light from the right half of the visual field projects onto the nasal half of the right retina and will cross at the optic chiasm before continuing on to the left visual cortex, whereas the light that projects on the temporal half of the left retina will not cross at the optic chiasm and will continue on to the left visual cortex.
73
What is the pathway of transduction? (ear)
.
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Internal surface of the TM is inn by what?
CN 9
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What is otitis media?
An earache and a bulging red tympanic membrane may indicate pus or fluid in the middle ear, a sign of otitis media Infection of the middle ear is often secondary to upper respiratory infections. (dt the eustachian tube)
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Where is scala vestibuli and tympani in the pathway?
* Scala vestibuli: upward path from vestibule to helicotrema
* Scala tympani: downward path from helicotrma to round window
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The structures of the middle and inner ear are encased in what?
temporal bone of the skull
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What does the external and middle portions of the ear do?
transmit airborne sound waves to the fluid-filled inner ear, amplifying sound waves in the process.
85
What are two ways a person can be deaf?
Deafness can be characterized as either conductive or sensorineural hearing loss.
* **Conductive hearing loss** can be caused by a defect in any of the sound-conducting structures (e.g., auricle, external auditory canal, tympanic membrane, or the middle ear).
* **Sensorineural hearing loss** can be a result of a lesion of the inner ear or CN VIII (vestibulocochlear nerve).
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How does the auditory neuron depolarize?
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lesions of CN VIII may cause what?
tinnitus (ringing or buzzing of the ears), vertigo (dizziness, loss of balance), and impairment or loss of hearing.
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Central lesion of vestibulocochlear nerve may involve what?
May involve cochlear or vestibular divisions of CN VIII.
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What are the causes of conductive and sensorineural hearing loss?
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What are the structurs we need to know in the vestibular system?
* two endolymph-filled chambers within the labyrinth, the **utricle and the saccule**
* hair cells located in a sensory epithelium called the **macula**.
* tips of hair cell stereocilia project into a gelatinous cap, which is covered in small calcium carbonate crystals called **otoliths**.
* movement of the head displaces otoliths and bends the stereocilia, resulting in development of a **receptor potential** in the same way as that described for auditory hair cells.
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How do you get a receptor potential in the vestibular system?
movement of the head displaces otoliths and bends the stereocilia, resulting in development of a receptor potential in the same way as that described for auditory hair cells.
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What are the two types of information that the otolith organs transduce? How?
1. **Tilting of the head (static angle)** changes the angle
between the otolith organs and the direction of the force of gravity. Different degrees of tension are placed on hair cell stereocilia, depending on their orientation. All possible angles are represented because the macula of each utricle is oriented horizontally and the macula of each saccule is oriented vertically.
2. **Linear acceleration (e.g., starting and stopping when riding in a vehicle)** also displaces the otoliths and excites hair cells in the maculae. (Note: When traveling at a constant velocity, there is no acceleration, resulting in the sensation of being perfectly still.)
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The semicircular canals:
* Detects what?
* Arranged how?
* Where are the hair cells location?
* Movement of the cupula causes what?
* Detects the angular acceleration produced by rotation of the head
* 3 SC canals arranged at right angles of each otehr
* The hair cells of wach canal are located in a swelling called the ampulla; the cilia of the hair cells project into agelatinous mass called the cupula
* Movements of the cupula cause generation of receptor potentials in the hair cells. The presence of three semicircular canals provides information about all possible orientations
94
* Rotation of the head produces what?
* When the head begins to rotate, there is what?
* Rotation of the head produces angular acceleration forces.
* When the head begins to rotate, there is a lag in the movement of the endolymph, causing the cupula to be deflected
95
What does the superior, horizontal and posterior canal sense?
* The superior canal senses rotation front to back (e.g.,nodding the head for “yes”).
* The horizontal canal senses rotation left to right (e.g.,shaking the head for “no”).
* The posterior canal senses rotation in the plane from the left to the right shoulder.
96
The position of the semicircular canals on one side of the head is the mirror image of those on the other side. **In this arrangement, any rotation will cause what?**
stimulation on one side and inhibition on the other side, thereby augmenting the vestibular stimulus to the brain.
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The deviation of nasal septum can be the result of what?
result of a birth injury, but more often, the deviation results during adolescence and adulthood from trauma (e.g., during a fist fight).
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What can happen if the nasal deviation is so severe?
the deviation is so severe that the nasal septum is in contact with the lateral wall of the nasal cavity and often obstructs breathing or exacerbate snoring
101
* Epistaxis (nosebleed) is relatively common because why?
* What is the blood supply of the anterior and posterior epistaxis?
of the rich blood supply to the nasal mucosa
* Ant: Kiesselbach plexus
* Post:Woodruff plexus of the sphenopalatine artery
102
What is the break out of the PNS and CNS?
103
ANS controls involuntary functions. ANS functions categorized in three areas:
* Maintenance of **homeostasis** in response to the normal fluctuations of controlled variables (e.g., the negative feedback regulation of blood pressure).
* Integration of the **stress response** - including the response to exercise and the classic “fight or flight” response.
* Integration of **visceral function** (e.g., coordination of organs in the digestive system after the ingestion of food).
104
The functions of the ANS are integrated with what? Why?
integrated with the endocrine system because the hypothalamus controls both efferent ANS activity and the secretion of hormones by the pituitary gland.
105
What are the divisons of the ANS?
sympathetic, parasympathetic, and enteric nervous system
106
Autonomic nervous system consists of what?
* two-neuron efferent pathway: post and preganglionic axon
* releases neurotransmitters at varicosities
107
What does the sympathetic system contain to act like the relay impulse?
* Sympathetic ganglia chain
108
What does the somatic motor system utilizes?
a one-neuron pathway and releases neurotransmitters from localized nerve endings
109
* Explain how the ANS has dual innervation of some organs
* What is the difference of craniosacral and thoracolumbar
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111
What are the paravertebral and prevertebral ganglia?
Para:
* superior cervical ganglion
* Middle cervical ganglion
* Inferior cervical ganglion
Pre:
* Celiac ganglion (solar plexus)
* Superior mesenteric ganglion
* Inferior mesenteric ganglion
112
Where is tonic activity?
in some smooth muscles eg blood vessels
113
What is unique about the adeneral medualla and sweat glands?
Adeneral medulla: SNS and no postganglion
Sweat glands: SNS but cholinergic inn
114
How was the penile inn?
Both PNS and SNS
* PNS: point
* SNS: shoot
| Work together
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What do many autonomic postganglionic fibers contain ?
**cotransmitters** along with acetylcholine and norepinephrine including ATP, adenosine, neuropeptide Y, vasoactive intestinal peptide, calcitonin gene-related peptide, and substance P.
118
How does the synthesis and degradation of acetylcholine (ACh) and norepinephrine (NE) work?
Acetylcholine is synthesized from choline and acetyl CoA, transported into vesicles, released in a calcium-dependent manner, and degraded in the synaptic cleft by acetylcholinesterase.
* It can interact with muscarinic or nicotinic receptors (shown in the figure on the same membrane but generally located on different postsynaptic cells).
Tyramine is the precursor for all catecholamines. It is converted to dopamine in the cytosol, which is then transported into vesicles. Once there, it can be converted to NE if the enzyme dopamine-β-hydroxylase is present. Norepinephrine is released in a calcium-dependent manner. It is removed via uptake by the norepinephrine transporter, or it can diffuse away, be taken up by other cell types, and degraded by catechol-O-methyltransferase (not shown). In the cytosol, it can be recycled into the vesicle or degraded by monoamine oxidase.
* After release, NE can interact with α or β adrenergic receptors (shown in the figure on the same membrane but generally located on different postsynaptic cells).
119
What differ from the rest of the SNS?
Adrenal medulla and sweat gland inn
* Adrenal medulla with chromaffin cells only has preganglionic sympathic axons
* For sweat glands, the mediator is acetylcholine instead of noradrenaline
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Some autonomic fibers contain neither acetylcholine nor norepinephrine but instead UNDERGO what? What is an example?
Nonadrenergic noncholinergic (NANC) parasympathetic nervous system (PSNS) mediation of penile erection. Release of nitric oxide from NANC PSNS postganglionic fibers acts in the corpus cavernosum to produce smooth muscle relaxation allowing engorgement from increased blood flow and subsequent erection. Phosphodiesterase type 5 (PDE5) converts cGMP to 5'-GMP. This can be inhibited with selective PDE5 inhibitors such as sildenafil.
| NO FOR EXAMPLE
126
What can modulate functioning of the ANS?
* Presynaptic inhibition can modulate functioning of the ANS
* an increase in the activity of one system can directly decrease the activity of the other system
127
What are two types of dual innervation?
* **Antagonistic** effect: oppose each other
* **Cooperative** effects: two divisions act on different effectors to produce a unified overall effect
128
However, both divisions do not normally innervate an organ equally. Explain
* Parasypmathetic exerts more influence on digestive organs
* Sympathetic has greater effect on ventricular muscle of heart
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What are antagonistic effects?
“oppose each other”
Same effector cells, opposite effect e.g.
* Heart rate decreases (parasympathetic)
* Heart rate increases (sympathetic)
Different effector cells, opposite effect e.g.
* Pupillary dilator muscle (sympathetic) dilates pupil
* Constrictor pupillae (parasympathetic) constricts pupil
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What are cooperative effects?
when two divisions act on different effectors to produce a unified effect e.g.
* During sex, the parasympathetic division stimulates arousal, while the sympathetic division stimulates orgasm - “Point & Shoot”
131
What is an example of antagonistic autonomic integration? Explain
Eye receiving input from the PSNS and SNS
* opioids relieving inhibition on parasympathetic fibers innervating the iris thus producing release of ACh, activation of muscarinic receptors, and contraction of circular muscles. PINPOINTS
* amphetamine and cocaine increase the activation of adrenergic receptors in the iris resulting in contraction of radial muscles and pupillary dilation.
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How does the autnomoic fibers exert tonic control of blood vessels?
Vasculature receives input only from the SNS, which contributes to the maintenance of appropriate blood pressure.
133
Where can ACh be released? Explain
* ACh released by other cells e.g. platelets and macrophages.
* Exogenous poisoning
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* SNS is providing appropriate blood supply to what?
* NE acts how?
* SNS is providing appropriate blood supply to skeletal muscle (e.g. “fight-or-flight” response).
* NE acts locally in the area in which it was released from the postganglionic fiber, but EPI circulates throughout the periphery as a peripheral hormone.
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What is the Net effect of systemic epinephrine?
increase in blood pressure because β2 vasodilation in skeletal muscle is masked by much greater α1 vasoconstriction.
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What happens if the a1 receptors are blocked in epinephrine?
decrease in blood pressure (“epinephrine reversal”)
* Epinephrine reversal: The fall in blood pressure produced by epinephrine when given following blockage of α-adrenergic receptors by an appropriate drug such as phenoxybenzamine
