Neurophysiology Flashcards
What are the functions of the nervous system?
- receive sensory information
- integrate and process information
- decide if a motor reponse will occur
What type of receptor is specialized to detect a particular stimulus modality?
sensory receptor
What are characteristics of receptors?
- all are able to perform transduction
- stimulus intensity encoded by rate and frequency of AP
- stimulus duration encoded by receptor adaptation
- stimulus type encoded by modality
What is receptor adaptation?
decreased sensitivity to continuous stimuli
What receptors do not rapidly adapt (they respond continuously)?
tonic receptors
What receptors rapidly adapt and only respond to new stimuli since they are rapidly changing?
phasic receptors
What are the classifications of receptors by modality?
- thermoreceptors (temperature)
- mechanoreceptors (movement)
- photoreceptors (light)
- chemoreceptors (chemicals)
- baroreceptors (pressure/stretch)
- proprioceptors (position)
- nociceptors (noxious stimuli)
What are the classifcations of receptors by stimulus origin or pathway?
- somatosensory signals
- viscerosensory signals
- special sense signals
Describe somatosensory signals.
originate from peripheral sensory receptors that detect changes in environmental stimuli
Describe viscerosensory signals.
originate from viscera and detect changes in internal stimuli
Describe special sense signals.
originate from special sensory organs localized to the head (vision, hearing, taste, olfaction)
What is pain?
conscious reaction to discomfort and caused by tissue injury or noxious stimulation
What is proprioception?
- the senses of position and movement of our limbs and trunk, the sense of effort, the sense of force, and the sense of heaviness
- receptors involved in proprioception are located in skin, muscles, and joints
The golgi tendon organ detects what?
muscle contraction
The muscle spindle detects what?
muscle stretch
Somatosensory receptors include what modality receptors?
- thermoreceptors
- nociceptors
- mechanoreceptors
- proprioceptors
Once a primary afferent neuron fires, where does the signal go?
- up the nerve fiber of the primary afferent neuron
- the cell body resides in the dorsal root ganglion
- OR the nucleus of the trigeminal nerve for structures of the head
What is a receptive field?
the area of the endings of a primary afferent neuron
Do smaller or larger receptive fields allow more precise stimulus localization?
smaller
What are the functions of the spinal cord?
- conduction (afferent and efferent)
- neural integration
- reflexes
Where can you find gray matter of the spinal cord?
neuronal cell bodies
Where can you find white matter of the spinal cord?
myelinated axons
What houses axons of sensory neurons and cell bodies of interneurons?
dorsal horns
What houses cell bodies of somatic motor neurons?
ventral horns
What houses cell bodies of autonomic motor neurons?
lateral horns
What contains unmyelinated axons connecting left and right gray matter?
gray commissure
What are tracts/fasciculi?
subdivions of each column
What is the conscious somatosensory projection pathway?
- first order neuron (primary afferent) comes from body or head into spinal cord via dorsal root or cranial nerve, respectively
- second order neuron projects from CNS cranially then decussates to contralateral side and ends in thalamus
- third order neuron goes from thalamus to primary somatosensory cortex of cerebrum
Conscious propriocpetion and touch is sensed by?
- fasiculus cuneatus for cranial trunk and thoracic limbs
- fasciculus gracilis for caudal trunk and pelvic limbs
Subconscious proprioception has at least two neuron pathways leading where?
to the ipsilateral cerebellum
What senses subconscious proprioception?
- spinocerebellar tract for caudal trunk and pelvic limbs
- spinocuneocerebellar for cranial trunk and thoracic limbs
What senses nociceptive pathways?
- spinothalamic tract
- spinocervicothalamic tract
Viscerosensory afferents travel via what tract?
spinothalamic tract
Describe referred pain.
- many somatic and visceral sensory neurons send signals via the same ascending tracts within spinal cord
- somatosensory cortex unable to determine true source
Motor control is a two neuron system made up of what?
- upper motor neurons
- lower motor neurons
What controls LMN and intiates voluntary motor?
upper motor neuron
What directly innervates skeletal muscles and intiaites spinal reflexes?
lower motor neuron
Where are lower motor neurons?
cell body in ventral grey horn of the spinal cord or brain stem (“peripheral”)
Where are upper motor neurons?
within the CNS (“central”)
True or false: LMNs can work independently to produce “automatic” or “stereotyped” movement.
True
Conscious motor activity requires what?
a conductor
What area of the cerebrum plans, strategizes, and provides impulse control?
frontal cortex
Plans made by the frontal cortex of the cerebrum are sent where?
to basal nuclei
What are the descending motor tracts of cerebral motor control?
- corticonuclear
- corticopontine
- corticospinal
What is the pyramidal descending tract?
corticospinal
What are the extrapyrimidal descending tracts?
- rubrospinal
- pontine reticulospinal
- medullary reticulospinal
- vestibulospinal
Somatic motor neuron cell bodies of LMNs are found where?
ventral horn
Visceral motor neuron cell bodies of LMNs are found where?
lateral horn
Cranial nerve cell bodies of LMNs (except for I, II, and VIII) are found where?
brainstem
What is a motor unit?
somatic motor neuron and the muscle fibers it innervates
What somatic lower motor neurons innervate extrafusal muscle fibers and are responsible for contraction of extrafusal muscle fibers?
alpha motor neurons
What somatic lower motor neurons innervate the contractile poles of intrafusal muscle fibers of the muscle spindle and are responsible for the contraction of poles of intrafusal fibers that stretch the muscle spindle?
gamma motor neurons
What is a myostatic reflex?
- stretch reflex
- monosynaptic
- antigravity
- includes patellar reflex, biceps reflex, triceps reflex, etc
What structures are responsible for muscle tone and posture?
- femoral nerve
- sciatic nerve
- quadriceps muscles
- hamstring muscles
- hock flexor muscles
- hock extensor muscles
- gravity causing limb flexion
What are polysynaptic reflex arcs?
- multiple synapses within CNS between sensory input and LMN output
- interneurons required
- ipsilateral activation/inhibition of muscle groups
- contralateral activation/inhibition of muscle groups
- intersegmental reflex arc possible
- includes tendon reflex, flexor limb withdrawal, perineal reflex, panniculus reflex, etc
What is a tendon reflex?
- GTO stimulated by vigorous muscle contraction stretching tendon
- stimulate inhibition of alpha motor neuron to agonist muscle
- protective reflex
What is a withdrawal reflex?
- sensory nerve(s) transmits stimulus to spinal cord
- spinal cord interneusons promote activity in ipsilateral flexor LMNs
- spinal cord interneurons inhibit activity in ipsilateral extensor LMNs
What is a crossed extensor reflex?
- normal in standing animal
- interneurons promote activity in contralateral extensor LMNs
- interneurons inhibit activity in contralateral flexor LMNs
Should there be a crossed extensor reflex in a recumbent animal?
NO, this is an indiciation of loss of inhibitory UMN actvity if present in recumbent animal
What is the panniculus reflex?
- spinal nerves T1-L7
- bilateral transmission via interneurons in fasculus proprius
- lateral thoracic nerve (C8-T1) to cutaneous trunci m. bilaterally
What is gaiting?
- central pattern generator-neural circuit
- repetitive, stereotypical behviors like chewing, walking, etc
- typicaly initiated by UMNs but maintained by LMNs and fasciculus proprius
What happens if LMNs are damaged?
the muscles they control do not get stimulated
What are the signs of LMN damage?
- decreased muscle size
- decreased to absent muscle tone
- decreased to absent reflex motor responses
- decreased to absent muscle strength
What happens if UMNs are damaged?
the LMNs and motor units they innervate will not work properly
What are signs of UMN damage?
- decreased muscle strength, paresis or -plegia
- decreased to normal, slow atrophy
- increaed to normal, hypertonia
- increased to normal, hyperreflexia
- can have crossed extension in recumbency
What part of the brain coordinates timing and smooths movements but does not intitiate movement, and helps maintain equilibrium and regulate muscle tone?
cerebellum
What is the rostral cerebral peduncle?
- midbrain
- predominantly efferent neurons
What is the middle cerebral peduncle?
- pons
- only afferent axons from pontine nuclei
What is the caudal cerebral peduncle?
- medulla
- afferent and efferent axons
Describe cerebellar afferent from the spinal cord.
- proprioceptive information and LMNs
- spincerebllar and spinocuneocerebellar pathways
Describe cerebellar afferent from the cerebral cortex.
- motor plan
- corticopontocerebellar pathway
Describe cerebellar afferent from the brainstem.
- extrapyramidal action, eyes, ears
- brainstem UMNs, textum, and vestibular nuclei
What is the spinocerebellum pathway responsible for?
coordinate movement and posture
What is the pontocerebellum pathway responsible for?
coordinated and properly timed skilled movements (limbs)
What is the vestibulocerebellum pathway responsible for?
coordinated balance and eye movement
Describe deep cerebellar nuclei of cerebellar efferents.
- excitatory to nuclei of the pyramidal and extrapyramidal motor systems
- no descending spinal path so unable to initiate movement or directly impact muscle strength
What are signs of dysfunction in spinocerebellar path?
hypermetria and ataxia
What are signs of dysfunction in pontocerebellar path?
intention tremors
What are signs of dysfunction in vestibulocerebellar path?
wide based stance
Describe the vestibular apparatus.
- located in the inner ear
- sets body equilibrium or balance in 3D space and reciprocal eye movement
- houses the receptor organs for detecting head position and movement
What are functions of the vestibular apparatus?
- sense position of head and neck at rest and during motion
- stabilizes position of the head and trunk and coordinates eye movements
- maintains equilibrium and balance during forward movement, head rotation, and tilting of the head or trunk
Where are receptors found for vestibular apparatus?
- found within three semicircular ducts
- and vestibule
What is the first order neuron of the vestibular apparatus?
vestibulocochlear nerve and vestibular ganglion
What is the second order neuron of the vestibular apparatus?
vestibular nuclei in medulla
What are crista ampullaris?
- hair cells embedded in gelatinous cupula
- lag behind endolymph during movement
- stereocilia tip towards kinocilium to induce AP
What are macula saccule and macula utricle?
- hair cells imbedded in gelatinous layer with otoliths
- otoliths weigh down otolith membrane and stimulate hair cells
Macula saccule are in what direction and are responsible for?
- vertical
- static equilibrium
Macula utricle are in what direction and are responsible for?
- horizontal
- linear acceleration
What vestibular nuclei projection is repsonsible for coordination of eye movement with movement of head?
medial longitudinal fasciculus
What is the “direct” vestibulocerebellar pathway?
primary vestibular axons to cerebellar flocculonodular lobe
What is the “indirect” vestibulocerebellar pathway?
vestibular nuclei project to cerebellar flocculonodular lobe
What is the peripheral vestibular subdivision?
- receptors (hair cells)
- vestibular nerve (inner ear structures)
What is the central vestibular subdivision?
- brain stem
- cerebellar vestibular structures
Ataxia can affect which pathways?
- cerebellar
- vestibular
- spinal/proprioceptive
What is a “lesion”?
a localizable region of the nervious system that is dysfunctional or damaged
What comrises the fibrous component of the eye?
- cornea
- sclera
What comprises the vascular (“urea”) component of the eye?
- choroid
- ciliary body
- iris
What comprises the nervous component of the eye?
- retina
The retina has a blind spot known as?
optic disk
Light is refracted as it passes through the cornea and lens, so it is upside down and reversed where?
the retina
True or false: the cornea refracts light more than the lens does.
true
What part of the eye fine tunes the image?
lens
What are the eight layers of the retina?
- pigment cell layer
- photoreceptor layer
- outer nuclear layer
- outer plexiform layer
- inner nuclear layer
- inner plexiform layer
- ganglion cell layer
- optic nerve layer
What does the pigment cell layer of the retina do?
- absorbs light and prevents light scatter between photoreceptors
- convert trans-retinal to cis-retinal needed by photoreceptors
What is the photoreceptor layer of the retina?
outer portion of rods and cones that contain light sensitive pigments
What is the outer nuclear layer of the retina?
cell bodies and nuclei of rods and conces
What is the outer plexiform layer of the retina?
synapses of photoreceptor cell axon terminals with dendrites of retinal interneurons
What is the inner nuclear layer of the retina?
cell bodies of retinal interneurons (bipolar cells, horizontal cells, amacrine cells)
What is the inner plexiform layer of the retina?
synapses of retinal interneuron axon terminals with dendrites of ganglion cells
What is the ganglion cell layer of the retina?
- cell bodies of ganglion cells
- output cells of the retina
What is the optic nerve layer of the retina?
- axons of ganglion cells traversing the inner retina on their way to the optic disk –> optic nerve
What is the tapetum lucidum?
reflective layer in choroid that increases light detection in dark conditions and allows light to pass through and reflect back to stimulate photoreceptors
What are the cells of photoreceptors?
- rod cells
- cone cells
What cells contain rhodopsin for light absorption?
rod cells
What cells contain photopsins or lodopsins?
cone cells
What is phototransduction?
light converted to electrical signal
In the dark, rhodopsin contains what for phototransduction?
cis-retinal
Light abosprtion causes transformation of cis-retinal to what?
trans-retinal
What is the first order neuron of the retinal pathway?
bipolar cell
What is the second order neuron of the retinal pathway?
ganglion cells
Rods work best in what conditions?
dim light/dark conditions
How many photons of light can activate a rod?
one
PLR is a subcortical (midbrain) reflex inducing what?
parasympathetic induced pupil constriction
What does the menace response test?
retina –> optic nerve –> optic chiasm –> optic tract –> visual cortex –> facial nerve nucleus in medulla
What reflex initiates compensating eye movement to keep vision fixed when head turns?
vestibulo-ocular reflex
What reflex involved contraction of neck muscles to turn towards stimulus?
visual startle reflex
What is hearing?
a response to vibrating air molecules
What is equilibrium?
the sense of motion, body orientation, and balance
Where are hearing and equilibrium transduced?
in inner ear –> vestibulocochlear nerve
What are the passageways in petrous temporal bone known as?
bony labyrinth
What are the connective tissue tubes within bony labyrinth known as?
membranous labyrinth
What is the organ of hearing?
cochlea
The membranous labyrinth is filled with what?
endolymph
The membranous labyrinth is floating in what?
perilymph
Perilymph is similar to?
cerebrospinal fluid
Endolymph is similar to?
intracellular fluid, high in K+
What is the dorsal chamber of the inner ear that is filled with perilymph and begins at oval window and spiral to apex?
scala vestibuli
What is the ventral chamber of the inner ear that is filled with perilymph and begins at apex and ends at round window?
scala tympani
What is the triangular middle chamber of the inner ear that is filled with endolymph?
scala media (cochlear duct)
What is conductive deafness?
conditions interfere with transmission of vibration in ear to cause hearing loss
What is sensorineural deafness?
death of hair cells, CN VIII, or any CNS system elements concerned with hearing to cause hearing loss
What is the firt order neuron of the auditory pathway?
cochlear nerve
What are the second order neurons of the auditory pathway?
- drosal nucleus of the trapezoid body (superior olivary nucleus)
- decussate –> DNTB ot lateral lemniscus
What is the acoustic startle reflex?
reflex turning of head and neck in resopnse to stimulation of neck muscle ipsilateral to sound
What are the receptors of olfaction and gustation?
chemoreceptors
What is the olfactory receptor cell in olfaction?
the primary afferent neuron itself
What is the gustatory receptor in gustation?
a specialized epithelial cell that transduces chemical signals and then sends electrical signals to a primary afferent neuron
The right nostril is for what scents?
novel or noxious
The left nostril is for what scents?
familiar
What are the cells for neurogenesis?
basal cells
What is the second order neuron of the olfactory path?
mitral cell
Taste buds are the sensory organs for taste and are found where?
gustatory papillae
Primary afferent axons of first order taste neurons are in what cranial nerves?
- IX
- VII
- X
