Lecture 1-Exam 2 (Special Senses) Flashcards
What does a receptor adaptation refer to?
to a decline in action potential generation when a constant stimulus is applied
Why is receptor adaption necessary?
so that constant environmental stimuli can be partially ignored, preventing a flood of sensory information into the CNS.
What declines over time with a constant stimulus? What does this cause?
The generator potential declines over time with a constant stimulus, causing the frequency of action potentials in the sensory nerve to decrease
When are rapidly adapting (phasic) receptors useful?
useful in situations where the rate of change of a stimulus is important (e.g., the tension of a working muscle).
When are slowly adapting (tonic) receptors useful?
useful where information about a sustained stimulus is important (e.g., application of steady pressure).
Slowly adapting receptors respond to a constant stimulus with what? What about rapidly adapting receptors?
- 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.
- What does the somatosensory system do?
- How many cutanous sensory modalities are there?
- The somatosensory system conveys sensations from the skin and muscle
- there are four cutaneous sensory modalities: touch, vibration, pain, and temperature.
What does the somatosensory sytem include? What is that fxn?
The somatosensory system also includes proprioception, which relates to sensory information from the musculoskeletal system
What is a dermatome?
The area of skin supplied with afferent nerve fibers by a single dorsal root
Where are merkel disks and meissner’s corpuscles located? What do they allow?
Merkel’s disks and Meissner’s corpuscles are both located near the skin surface and have small receptive fields allowing fine discrimination.
What is the difference between merkel’s disks and meissner’s corpuscles?
- 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.
What are ruffini’s endings?
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.
What are pacinian corpuscles?
very rapidly adapting receptors that respond to rapidly changing stimuli, and therefore can sense vibration.
What do Hair follicles have?
have a nerve plexus that transduces displacement of the hair
Explain the main pathways for touch, vibrations, and proprioception
- 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.
What is the main pathway for touch, vibration, proprioception called?
dorsal column-medial lemniscus (DCML)
For the main pathway for touch, vibration, and proprioception, what is the site for decussation?
site of decussation for the dorsal column-medial lemniscus (DCML) tract is at the level of the medulla
What happens when there is a damage below and above medulla in the dorsal column-medial lemniscus (DCML)?
- 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.
How does the main pathway for pain and temperature sensation go?
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
The main pathway for pain and temperature sensation is called what?
Anterolateral (neospinothalamic) tract
What are the NTs in the pain pathway?
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.
What is pain gating?
Pain can sometimes be relieved if nonpainful sensory stimulation is simultaneously applied (e.g., gently rubbing an injured area)
How does pain gating work?
- 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.
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.
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.
The amount of cortex representing a given area reflects what?
the importance of the sensory input.
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.
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.
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.
What are the two cerebral hemispheres fuction?
- 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.
T/F: The branches of the central retinal artery are end arteries that do not anastomose with each other or any other vessel.
True
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.
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
Where does the venous blood and aqueous humor in the anterior chamber drain into?
scleral venous sinus
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.
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
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
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
People with a retinal detachment may complain of what?
flashes of light or specks floating in front of their eye
The edema with papilledema is viewed when?
viewed during ophthalmoscopy as swelling of the optic disc, a condition called papilledema
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).
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
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
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.
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
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
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.
What is open angle and closed angle glaucoma?
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.
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.
What is the accommodation reflex? What is the diffence of distant and near vision?
i - Pupils constrict
ii - Lens thickens
iii - Eyes converge
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
What is the pathway of transduction? (ear)
.
How does the auditory neuron depolarize?
What are the causes of conductive and sensorineural hearing loss?
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.
What is the break out of the PNS and CNS?
Autonomic nervous system consists of what?
- two-neuron efferent pathway: post and preganglionic axon
- releases neurotransmitters at varicosities
- Explain how the ANS has dual innervation of some organs
- What is the difference of craniosacral and thoracolumbar
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).
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
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
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.
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.
Where can ACh be released? Explain
- ACh released by other cells e.g. platelets and macrophages.
- Exogenous poisoning
