Neuro - Part 4 Flashcards
1
Q
The gustation system is mainly a function of:
A
- taste buds which contain a taste receptor cell
2
Q
Taste buds are located in papillae. What are the three types?
A
- fungiform: throughout the dorsal surface of the rostrum 2/3rds of the tongue, especially lateral margins and tip
- vallate: occupy the caudal portion of the tongue
- foliate: dorsal ate real part of the caudal part of the dorsal tongue
3
Q
Taste buds are composed of:
A
- groups of columnar taste receptor cells that are bundled together in clusters
- taste receptors arranged so that their tips form a small taste pore through which microvilli extends
- each taste cell has receptors for only one type of flavor
4
Q
How are taste cells stimulated?
A
- chemical molecules that trigger sense of taste are dissolved by saliva
- they enter the taste bud through the pore
- bind to the receptors located in the membrane of the microvilli
- binding depolarizes the membrane of the taste cells
- mechanism is dependent on the taste molecule that binds to their specific receptors
5
Q
Taste cells are innervated by _________ neurons that contribute axons to 2 cranial nerves:
Afferent fibers send the message to the:
A
- bipolar neurons
- CN VII: facial nerve
- CN IX: glossopharyngeal nerve
- cerebral cortex (also projects to the amygdala of the limbic system)
6
Q
T/F: eyes are an extension of the brain
A
- true; vision is an integral part of neural function
7
Q
What is the visual field?
A
- spatial area seen by ONE eye
- visual fields of each eye do not completely overlap
- extent is dependent on anatomical placement
- animals have a wider peripheral vision than humans
8
Q
What is the difference between monocular and binocular vision?
A
- binocular vision is needed for depth perception, maintained when eyes move as a functional unit as the environment is scanned
-monocular vision does not provide good depth perception
9
Q
What are the parts of the eye?
A
- choroid
- iris
- lens
- retina
- optic nerve (CN II)
10
Q
What are features of the choroid?
A
- consists of loose CT with numerous vasculature and pigmented cels
- nutritive function
- some diurnal animals have melanocytes that absorb light tat passed by photoreceptors without stimulating them
- ** tapetum lucidum - patch of reflective material that enhances dark-adapted vision aka “eye shine”
11
Q
T/F: the pigmented structure with muscles that modify the diameter of the pupil is the retina
A
-false; iris
12
Q
What are the two muscle types in the iris and their purpose?
A
- pupillary dilator muscle
- radially arranged
- opposes action of sphincter
- part of pigmented anterior epithelial cels (myoepithelial cels - smooth muscle)
- contraction results in pupillary dilation (MYDRIASIS)
- dilation reflects genera state of SYMPTHETC tone (pain, fear, anger)
- pupillary sphincter muscle
- circularly arranged near pupillary margin
- contraction results in decreased pupillary size (MIOSIS)
- innervated by PARASYMPATHEIC fibers
- ** size of pupil regulates amount of light entering eye
13
Q
What are features of the lens?
A
- behind iris, supported by suspensory ligaments
- fibers attached to the ciliary body
- muscular structure near base of iris
- help with accommodation of lens
- increase/decrease tension
- makes lens curvature more/less convex
- lens can focus on a near/far object
14
Q
Behind the lens is a chamber filled with:
A
- vitreous humor
- gelatinous fluid
- gives spherical shape of the eye
- contains phagocytic cells
15
Q
What are features of the retina?
A
- where light is transferred into electrical activity of neurons, behind the vitreous humor
- interrupted at a point where axons of the retina ganglion layer leave the eye on their way to the brain
- **optic disc or blind spot
16
Q
What are features of the optic nerve?
A
- CN II
- axons leaving the eye at the optic disc give rise to the optic nerve
- more axons in both optic nerves than in all the dorsal root of the spinal cord
- surface of the retina has blood vessels that that enter at the optic disk and provide nutrition of the retina together with vessels of the choroid
- about 130 million photoreceptor cells in the retina (rods + cones)
17
Q
What are the two kinds of photoreceptors? What are the two portions of each?
A
- rods + cones
- outer segment
- photosensitive region
- in cone cells: composed mainly of membranous indignations
- in rod cells: contains numerous flattened membranous sacs arranged like a stack of coins
- the membrane of these invaginations and sacs contains photopigments (convert a light stimulus to a receptor potential
- inner segment
- metabolic region of the photoreceptor
18
Q
What are features of rod cells?
A
- contain rhodopsin
- photochemical transmitter responsible for perception of SHADES OF GREY
- low threshold of excitability
- easily stimulated by low-intensity light
- 300x more sensitive than cone cells
- essential for night vision
- 95% of photoreceptors present in retina
- vitamin A is important for the formation of rhodopsin - sever vitamin A deficiency can cause night blindness
19
Q
What are features of cone cells?
A
- have colour pigments or cone pigments
- photochemical transmitters responsible for perception of COLOR
- less sensitive to light
- requires relatively high-intensity light in comparison to rhodopsin
20
Q
What is the difference between polychromatic and dichromatic vision?
A
- 3 types of cones in primates (polychromatic)
- each one carries a different type of colour pigment with different pick of absorbencies at different wavelengths
- blue (445 nm), green (535 nm), red (570 nm)
- 2 types of cones in most animals (dichromatic)
- able to detect the blue and yellow portion of the light spectrum (not reds or oranges)
- some birds, lizards, turtles, and fishes have 4 types
- 3 types + UV-sensitive cones
- richer color reception than humans
- ** the visual system must mix and contrast the effect of each cone cell
21
Q
What are the 5 major cell types that make up the retina?
A
- photoreceptor cells: synapse w/ bipolar + horizontal cells
- horizontal cells: transmit signals horizontally from rods + cones to bipolar cells
- bipolar cells: transmit signals vertically from the rods,cones, + horizontal cells to ganglion + amacrine cells
- amacrine cells: transmit signals in 2 directions either directly from bipolar to ganglion cells or horizontally from axons o bipolar cells to dendrites of ganglion cells or to other amacrine cells
- ganglion cells: transmit output from the retina through the optic nerve into the brain
22
Q
T/F: the retina is a specialized motor epithelium that contains photoreceptors and other cell types arranged in layers
A
- false; specialized sensory epithelium
23
Q
What is the fovea? What are some features?
A
- fovea (area centralis): a minute area in the center of the retina that minimizes distortion of light rays cause by the different cells in the retina
- especially capable to acute + detailed vision
- composed almost entirely of cones
- with special long slender bodies that aids their detection in the visual image
- other cells are all displaced allowing light to pass unimpeded to cones
24
Q
Describe activation of photoreceptors by light
A
- photoreceptors and ganglion cells communicate via receptor potentials rather than action potentials
- all the retinal neurons conduct their visual signals by direct flow of electric current: electronic conduction
- the same degree of hyperpolarization in the rod + cone is conducted by direct electric current flow in the cytoplasm all the way to the synaptic body where the neurotransmitter will be released and transmitted to the next cell
- allows graded conduction of signal strength (directly related to the intensity of the illumination)
- all the retinal neurons conduct their visual signals by direct flow of electric current: electronic conduction
- ** signal is not all or one
25
Q
What is visual acuity dependent on?
A
- acuity of visual images reflects several factors:
- population of retinal cells
- ratio of rods to cone photoreceptor cells
- ratio of photoreceptor cells to ganglion cells
- cone cells provide better acuity than rod cells
- hundreds of rods feed signals via bipolar cells to a single ganglion cell to the CNS
- only few one cells feed signals to a single ganglion cell
- more ganglion cells in te area centralis than here are in te peripheral portion of the retina
- area centralis provides the highest acuity in the retina
26
Q
What is the pathway of signals from the retina to the cortex?
A
- the eye catches light reflected by the object + guide its passage until the image is formed
- the iris controls the amount of light that passes through the pupil
- the lens work by converging light rays to a certain oval point on the retina
- the images formed on the retina are REAL, INVERTED, and SMALLER than the object
28
Q
How are the nerve impulses from the cones + rods transmitted?
A
- visual signals are carried by optic nerve fibers that form the optic nerve, optic chasm, and optic tract
- fibers terminate in the THALAMUS for visual perception (lateral geniculate nucleus) or MIDBRAIN for visual reflexes
- ex: body + ocular reflex, pupillary constriction
- the brain processes and reorients the image
30
Q
What are features of amplitude?
A
- “intensity”
- quantified in decibels (dB)
- logarithmic scale
- expresses the energy of sound relative to energy of a standard reference sound = 0 dB (threshold for human hearing)
31
Q
What are features of frequency?
A
- number of pressure oscillation cycles per unit time
- expressed in Hertz (Hz)
- 1 Hz is # cycles per second
- dogs can detect sounds between 30-35,000 Hz
32
Q
What are the structures involved in hearing?
A
- external ear
- middle ear
- inner ear
- contains sensory organ in the “organ of corti”
33
Q
What are features of the external ear?
A
- directs sound waves into ear canal
- 2 parts:
- fleshy part: pinna
- ear canal (L-shaped)
- separated from he middle ear by tympanic membrane or eardrum
34
Q
What are some features of the middle ear?
A
- air-filled cavity in the temporal bone
- connected to the nasopharynx by the auditory tube (eustachian tube)
- contains the ossicles
35
Q
What are the ossicles in the middle ear? What are their functions?
A
- 3 tiny bones:
- malleus: connected to eardrum
- incus: between malleus + stapes
- stapes: connected to oval/round window
- membrane separation between the middle and inner ear
- transfer vibration of the eardrum to the oval window
- avoids significant loss of vibration as the sound wave is transferred from air-filled outer ear to fluid-filled inner ear (sensory receptor location)- decrease amplitude of sound waves protecting sensitive sensory cells
36
Q
What are features of the inner ear?
A
- inner ear (labyrinth) contains the sensory organs for both the auditory system + vestibular system (detects acceleration and static tilt of the head)
- auditory portion of the inner ear complex is called “cochlea”
- spiral shaped
- fluid-filled (perilymph)
- contains organ of corti + hair cell receptors
37
Q
What are features of the organ of corti?
A
- sensory hair cell are mechanoreceptors
- have 50-000 stereocilia in their apical surface
- connected by tip links at the tips - tip links seem to be attached to K channels that open when bending of the stereocilia pulls them apart
- stereocilia do NOT regenerate and cause hearing loss, excessively loud sounds can destroy them via excessive movement
- have 50-000 stereocilia in their apical surface
- tectorial membrane overlies the sensory cells (anchored gel-coated ridge)
- basilar membrane is the floor of the organ of corti (more elastic)
- both the tectorial plate + basilar membrane are important for sound transmission
38
Q
Describe the transduction of sound waves
A
- sound waves are transmitted to the inner ear and cause vibration to the organ of corti
- the base of the hair cell sits on the basilar membrane + cilia are imbedded in the tectoral membrane
- vibration in the organ of corti causes bending of cilia on the hair cells as the psh against the tectonically membrane
- ending produces a change in K+ conductance of the hair cell membrane
- depolarization in one direction (K+ influx, Ca2+ channel opening + release of glutamate neurotransmitter, AP in afferent cochlear nerves)
- hyperpolarization in other direction (Ca2+ efflux, glutamate not released, no AP)
40
Q
What are the events involved in hearing?
A
41
Q
How are different sounds encoded?
A
- different auditory hair cells are activated by different frequencies
- hair cells located at the base of the basilar membrane (inner cells) respond best to high frequencies
- hair cells located at the apex (outer cells) respond best to low frequencies
- the basilar membrane acs as a sound frequency analyzer
- this spatial mapping of frequencies generates a tonotopic map that tells where sounds of different frequency are processed in the brain
43
Q
What is the location and what are the components of the vestibular system?
A
- vestibular system is a bacterial receptor system located n the inner ear (membranous labyrinth) and is divided into peripheral and central parts
44
Q
What are the parts of the membranous labyrinth
A
- series of fluid filled structures
- 3 semicircular canals (kinetic labyrinth)
- 2 otolith organs (static labyrinth)
- cochlea (audition)
45
Q
What are the sensory cells of the vestibular system? What are some features? How do they function?
A
- hair cells
- located in the cupula
- large kinocilium
- tonically active @ resting state
- constant firing when not stimulated
- bend in one direction increased frequency, bend in other decreases frequency
** change in frequency is how the brain determines which side is moving
46
Q
What are some features of the semicircular canals of the vestibular system? What are features of their hair cells?
A
- filled with endolymph, surrounded by perilymph
- main function is to detect rotational/angular acceleration
- hair cells are located in the crista ampullaris of the semicircular canals, covered by a gelatinous mass called the cupula
- during angular acceleration of the head the cupula is displaced, causing excitation or inhibition of hair cells
47
Q
What are some features of the otolith organs of the vestibular system? What are features of their hair cells?
A
- 2 parts: utricle (horizontal) and saccule (vertical)
- detects linear acceleration/deceleration and static tilt of the head
- hair cells located in the macula, otolith mass overlies the vestibular cells
When the head is tires, gravitational forces act on the otolith mass, moving it across the vestibular cells - these cells are either activated or inhibited, alerting change in position (think salt in a box)
48
Q
What are the functions of the vestibular system?
A
- major function is to maintain equilibrium and balance
- function as a sensor of gravity and head acceleration, one of the most important tools in controlling posture
- directly contributes to motor control
- descending motor pathways such as the vestibulospinal tracts receive info to control eye, head, and trunk orientation and to coordinate potential movements
49
Q
T/F: the vestibular system is involved in positioning of the eyes
A
- true
50
Q
What are the major clinical signs of peripheral vestibular disease?
A
- nystagmus
- head tilt
- ataxia
51
Q
T/F; idiopathic vestibular disease is common in dogs
A
- false; cats
52
Q
What are functions of the spinal cord?
A
- sensory system
- receiving and distributing information from the PNS
- relaying afferent/sensory information to the brain centers
- local integration of sensory and motor functions for reflex activity
- both within a limb and between limbs
- relaying efferent/motor information from motor management centers via specific tracts to connect w peripheral neurons
53
Q
What are the three main functions of the motor system?
A
- maintain posture + provide a stable platform for movement
- control voluntary movement + locomotion
- controls visceral motor functions (ANS)
54
Q
What is the difference between upper and lower motor neurons?
A
56
Q
What is the UMN system divided into?
A
- pyramidal neurons
- corticospinal tracts
- mainly in motor area of cerebral cortex
- important for voluntary motor control in primates/humans
- extrapyramidal neurons
- brainstem UMN pathways
- mainly located in brainstem nucleus
- most important or fair and movement in quadrupeds
57
Q
What is the UMN system responsible for?
A
- initiation of voluntary movement
- maintenence of muscle tone for support against gravity
- regulation of posture
58
Q
What does damage of the UMN system cause?
A
59
Q
What are features of lower motor neurons (LMNs)? What does damage result in?
A
- have their cell body in the CNS (brainstem or spinal cord)
- axons project into the PNS via cranial or spinal nerves
- connect with striated or smooth muscle @ neuromuscular junction
- ** when stimulated LMN induce muscle contraction
60
Q
Compare damage in UMN and LMN
A
61
Q
Recall the functional regions of the spinal cord; where do lesions of the spinal cord show their effects?
A
-lesions in the spinal cord affect limbs caudal or related to the lesion
