Neuro - Part 4 Flashcards
The gustation system is mainly a function of:
- taste buds which contain a taste receptor cell
Taste buds are located in papillae. What are the three types?
- 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
Taste buds are composed of:
- 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
How are taste cells stimulated?
- 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
Taste cells are innervated by _________ neurons that contribute axons to 2 cranial nerves:
Afferent fibers send the message to the:
- bipolar neurons
- CN VII: facial nerve
- CN IX: glossopharyngeal nerve
- cerebral cortex (also projects to the amygdala of the limbic system)
T/F: eyes are an extension of the brain
- true; vision is an integral part of neural function
What is the visual field?
- 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
What is the difference between monocular and binocular vision?
- 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
What are the parts of the eye?
- choroid
- iris
- lens
- retina
- optic nerve (CN II)
What are features of the choroid?
- 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”
T/F: the pigmented structure with muscles that modify the diameter of the pupil is the retina
-false; iris
What are the two muscle types in the iris and their purpose?
- 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
What are features of the lens?
- 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
Behind the lens is a chamber filled with:
- vitreous humor
- gelatinous fluid
- gives spherical shape of the eye
- contains phagocytic cells
What are features of the retina?
- 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
What are features of the optic nerve?
- 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)
What are the two kinds of photoreceptors? What are the two portions of each?
- 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
What are features of rod cells?
- 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
What are features of cone cells?
- 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
What is the difference between polychromatic and dichromatic vision?
- 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
What are the 5 major cell types that make up the retina?
- 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
T/F: the retina is a specialized motor epithelium that contains photoreceptors and other cell types arranged in layers
- false; specialized sensory epithelium
What is the fovea? What are some features?
- 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
Describe activation of photoreceptors by light
- 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
What is visual acuity dependent on?
- 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
What is the pathway of signals from the retina to the cortex?
- 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
What is the sequence of transparent media that causes light to be refracted (direction change)?
- the interface between the air + anterior surface of the cornea
- the interface between the posterior surface of the cornea + aqueous humor
- the interface between the aqueous humor + the anterior surface of the lens
- the interface between the posterior surface of the lens + the vitreous humor
How are the nerve impulses from the cones + rods transmitted?
- 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
What does the auditory system do?
- designed to detect + analyze sounds in the environment
- hearing requires at least 1 ear, localization requires 2
- sounds are pressure waves in the air with given frequencies and amplitudes
- alternating changes in pressure produce the sensation of a sound after striking tympanic membrane
-auditory system perceives:- frequency as pitch
- amplitude as loudness
- alternating changes in pressure produce the sensation of a sound after striking tympanic membrane
What are features of amplitude?
- “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)
What are features of frequency?
- 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
What are the structures involved in hearing?
- external ear
- middle ear
- inner ear
- contains sensory organ in the “organ of corti”
What are features of the external ear?
- 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
What are some features of the middle ear?
- air-filled cavity in the temporal bone
- connected to the nasopharynx by the auditory tube (eustachian tube)
- contains the ossicles
What are the ossicles in the middle ear? What are their functions?
- 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
What are features of the inner ear?
- 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
What are features of the organ of corti?
- 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
Describe the transduction of sound waves
- 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)
The oscillatory pattern of sound wave transduction is called ____________ and is caused by:
- cochlear microphonic potential
- intermittent release of glutamate: intermittent firing of afferent nerves
- mirrors waveform of acoustic stimulus
What are the events involved in hearing?
How are different sounds encoded?
- 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
Information is transmitted from the hair cells to the cochlear nerve via:
- ascending pathways that relay auditory impulses to the cochlear nuclei in the medulla oblongata
- axons ascent the brainstem and reach the thalamus
- the information is processed in the auditory cerebral cortex
What is the location and what are the components of the vestibular system?
- vestibular system is a bacterial receptor system located n the inner ear (membranous labyrinth) and is divided into peripheral and central parts
What are the parts of the membranous labyrinth
- series of fluid filled structures
- 3 semicircular canals (kinetic labyrinth)
- 2 otolith organs (static labyrinth)
- cochlea (audition)
What are the sensory cells of the vestibular system? What are some features? How do they function?
- 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
What are some features of the semicircular canals of the vestibular system? What are features of their hair cells?
- 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
What are some features of the otolith organs of the vestibular system? What are features of their hair cells?
- 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)
What are the functions of the vestibular system?
- 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
T/F: the vestibular system is involved in positioning of the eyes
- true
What are the major clinical signs of peripheral vestibular disease?
- nystagmus
- head tilt
- ataxia
T/F; idiopathic vestibular disease is common in dogs
- false; cats
What are functions of the spinal cord?
- 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
What are the three main functions of the motor system?
- maintain posture + provide a stable platform for movement
- control voluntary movement + locomotion
- controls visceral motor functions (ANS)
What is the difference between upper and lower motor neurons?
What are features of upper motor neurons (UMNs)?
- completely contained in CNS
- cell body in motor nucleus (brainstem) or motor cortex (forebrain)
- axons connect to LMN
- can stimulate or inhibit LMN (LMN innervate muscle)
What is the UMN system divided into?
- 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
What is the UMN system responsible for?
- initiation of voluntary movement
- maintenence of muscle tone for support against gravity
- regulation of posture
What does damage of the UMN system cause?
What are features of lower motor neurons (LMNs)? What does damage result in?
- 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
Compare damage in UMN and LMN
Recall the functional regions of the spinal cord; where do lesions of the spinal cord show their effects?
-lesions in the spinal cord affect limbs caudal or related to the lesion