Nervous 3 Flashcards
What re the 2 main functions of the ear and the parts of the ear that undergo these
hearing
○ auditory system: external ear, middle ear and cochlear part of inner ear
balance
○ vestibular system: vestibular part of inner ear
external ear what part of the ear, what consists of and how separated from middle ear
- visible part of ear
- consists of pinna (auricle) and external acoustic meatus
- separated from middle ear by tympanic membrane
Pinna what also called, what part of the ear, what 4 things made of
auricle in external ear • funnel-shaped structure protruding from surface of head • auricular cartilage • auricular muscles (CNVII) • skin • blood vessels
external acoustic meatus what is it, what part of the ear, what made of and the shape
- canal running from narrow part of auricular cartilage to tympanic membrane in external ear
• cartilaginous (auricular and annular cartilages) and osseous parts of wall
• lined with skin containing sebaceous and ceruminous glands
• fine hairs may be present
• curved in dog (vertical and horizontal portions)
tympanic membrane what conissts of and what is on the lateral and medial surface
• thin, complete membrane
• consists of fibrous tissue:
○ firmly attached to osseous tympanic ring (temporal bone)
○ covered laterally by epidermis and medially by mucosa
what are the 3 features of the middle ear
1) tympanic (middle ear) cavity
2) auditory ossicles
Tympanic cavity what filled with, how connected to nasopharynx and inner ear, function
- air-filled cavity in temporal bone
- separated from external acoustic meatus by tympanic membrane
- connected to nasopharynx by auditory tube
- connected to inner ear by vestibular and cochlear windows
- contains auditory ossicles located dorsally
- changes air vibrations (sound waves) into mechanical movement through auditory ossicles
- expanded ventrally within tympanic bulla
Auditory ossicles what are the 3 ossicles, where placed, how moved and function
malleus, incus and stapes:
○ Malleus: - ‘handle’ embedded in medial aspect of tympanic membrane
§ visible through tympanic membrane when viewed with otoscope
○ Incus: - sits between malleus and stapes
○ Stapes: - base sits in vestibular window
• attached to wall of tympanic cavity by ligaments
• can be moved by contraction of m. tensor tympani (attached to malleus) and m. stapedius (attached to stapes)
○ dampens transmission (protective device)
• movement transmitted from tympanic membrane to vestibular window causes movement of fluid in inner ear
inner ear what consist of and within
Bony labyrinth - vestible, semicicular canals, cochlea
Membranous labyrinth - utricle and saccule, semicircular ducts, cochlear duct - contains endolymph and surrounded by perilymph
vestibular system where in the ear, function and how works
• organ responsible for sensing body position
• static and kinetic sensations perceived by hair cells in specialized sensory regions:
○ 40-80 cilia and one kinocilium on apical surface of hair cells
○ movement of cilia towards or away from kinocilium results in depolarization or hyperpolarization of hair cell, and excitation or inhibition of firing of neuron at base of hair cell
Utricle and saccule what are they where found in the ear and main function
inner ear Utricle and saccule • two membranous enlargements • utricle - at base of semicircular canals • saccule: § ventral to utricle § connected to endolymphatic duct (probably involved in absorption of endolymph) • sense static position through maculae:
how does utricle and saccule sense static position through maculae
- monitor position of head with respect to gravity
- kinocilium and cilia of hair cells project into otolithic membrane (gelatinous matrix containing calcium carbonate/protein crystals, i.e.otoliths)
- pull of gravity on otolithic membrane causes shearing force on cilia
- macula in saccule oriented in vertical plane
- macula in utricle oriented in horizontal plane
semicircular ducts where in the ear, how many found, what contain
three in each ear located at right angles to each other - inner ear
• each duct contains enlargement at one end - ampulla:
○ contains sensory region (crista)
• sense dynamic position due to movement of endolymph
• hair cells located on crista, a ridge of cells projecting from wall of ampulla
• cilia of hair cells project into gelatinous material - cupula:
○ cupula readily deflected by movement of endolymph created by rotation or deceleration of head
cochlear part of inner ear what is it, ducts and what communicate with
- Cochlea: - region of temporal bone housing cochlear duct
- spiral canal of cochlea winds around an osseous pyramid (modiolus)
- cochlear duct adherent to walls of spiral canal, subdividing perilymphatic space into two longitudinal canals:
- scala vestibuli (dorsal)
- scala tympani (ventral)
- scala vestibuli communicates with perilymphatic space of vestibule
- scala tympani ends at cochlear window
- scala tympani and scala vestibuli communicate with each other at blind apical end of spiral canal
Basilar membrane where in the ear, what part of, function and how occurs
inner ear
part of cochlear duct adjacent to scala tympani
• transduces sound into nerve impulses
• contains hair cells with tips of cilia embedded in gelatinous tectorial membrane (cochlear hair cells have no kinocilia)
• base of hair cells in contact with nerve endings leading to neurons in spiral ganglion (in modiolus)
what are the 9 steps in the hearing process
vibration of tympanic membrane ⇓ vibration of auditory ossicles ⇓ vibration of stapes against vestibular window ⇓ waves in perilymph of scala vestibuli ⇓ waves in endolymph of cochlear duct ⇓ vibration of basilar membrane ⇓ distortion of hair cell cilia resting against tectorial membrane ⇓ depolarization of hair cells ⇓ impulse in cochlear nerve
List the 3 main nerves involved with the ear
1) vestibulocochlear nerve
2) facial nerve
3) trigeminal nerve
vestibulocochlear nerve what are the 3 ways its involved in the ear
- nerve endings in maculae of utricle and saccule, and in ampullae of semicircular ducts have cell bodies in vestibular ganglion in vestibular branch of CNVIII
- nerve endings in basilar membrane of cochlear duct have cell bodies in spiral ganglion in cochlear branch of CNVIII
- vestibular and cochlear branches unite and travel to brainstem through internal acoustic meatus of temporal bone
Facial nerve what are the 3 ways it is involved with the ear
- enters internal acoustic meatus with CNVIII then travels in facial canal in temporal bone adjacent to inner ear
- gives off a small branch within temporal bone to m. stapedius
- emerges from skull caudal to external acoustic meatus
Trigeminal nerve how is it involved with the ear
branch of mandibular division supplies m. tensor tympani
Within the vestibular system what are the 2 main areas of receptors and receptors within
Crista ampullaris
- Movement of endolymph causes deflection of cilia – increase or decrease in firing of CNVIII
1. Ampulla – dilation within the semicircular duct
2. Cupula – gelationous material
3. Neuroepithelium
Macula (one each in utricculus and saccule)
•Neuroepithelium covered by otolithic membrane
Within the vestibular system what are the 2 main areas, their function and how achieve
- Tell you which way is up and which way your head is moving
1. Cristae ampullaris
• Paired functionally
• Respond to acceleration/changes head position
• Tonic firing from CNVIII each side
2. Maculae
• One oriented vertically one horizontal
• Respond to gravity
• Movement of otoliths relative to hair cells generates firing in CN VIII
Function of Semicircular ducts and canals and how it achieves this, what results
- Remember 3 ducts on each side (left and right ear), each in different plane either x,y or z therefore no matter the direction you move your head always movement of fluid in at least one semicircular canal
- Head turning generates increased activity in CNVIII on side of turn + decreased activity on opposite side (cristae ampullaris)
- Vestibular nuclei compare input from both sides to determine direction of turn
Example:
1. turn of head to R gives ↑↑ input from R CNVIII and ↓↓ input from L CNVIII
2. Vestibular nuclei (within brainstem) compare R and L CN VIII activity and decide R>L - therefore must be turning our head to the right side
3. This results in increased output from R vestibular nuclei - Efferents from vestibular nuclei result in:
1. Change in eye position (nystagmus) towards side of head turn (fast phase)
2. Increase in ipsilateral extensor tone etc on side of head turn (otherwise body may collapse on that side)
Efferents from CNVIII where project to and the 3 areas that are then projected to
- Majority project to vestibular nuclei within the brainstem
- Small number project direct to cerebellum
From vestibular nuclei - spinal cord
- brainstem
- cerebellum
What occurs with the vestibular nuclei projecting to the spinal cord
Lateral and medial vestibulospinal tract
• Interneurons within ventral horn GM (grey matter)
• Facilitatory to ipsilateral extensors + contralateral flexors
• Inhibitory to ipsilateral flexors + contralateral extensors
What occurs with the vestibular nuclei projecting to the brainstem and cerebellum
Brainstem
• Through medial longitudinal fasciculus - nuclei CN III, IV, VI for eyeball movement control
○ Good to look at clinically for issues with midbrain
• Projections to vomiting centre in reticular formation - motion sickness
• Poorly defined projections to thalamus for cerebral awareness
Cerebellum
• Via caudal cerebellar peduncle to flocculonodular lobe + fastigial nucleus
• Coordination movements of eyeballs, head, neck, limbs with rest of body
What are the 3 main places that leads to dysfunction in the vestibular system and what disease corresponds
1) CNVIII/receptors (peripheral vestibular disease)
2) Vestibular nuclei (central vestibular disease)
3) Cerebellum (paradoxical vestibular disease)
What occurs with peripheral and central vestibular disease and what clinical signs
Peripheral vestibular disease: - very common
- Dysfunction of one side leads to loss of tonic firing CN VIII
- Vestibular nuclei interpret as a head tilt to opposite side (loss of input from the other side - R>L if left is gone)
○ Subsequent increase in extensor tone and extraocular signals on side opposite lesion lead to clinical signs
§ Head tilt/circling towards side that is damaged and eyes to the opposite side
- SAME THING WITH CENTRAL VESTIBULAR DISEASE
What occurs with paradoxical vestibular disease and what clinical signs and how know this is occurring
- Normally cerebellar nuclei suppress vestibular nucleus function
- Cerebellar lesions (ipsilateral) - ↓inhibition of one side vestibular nuclei (i.e. disinhibition)
- Comparison of vestibular nuclei activity – ipsilateral side ‘appears’ more active suggesting head is being turned to the side of the lesion
- Vestibular signs appear suggesting vestibular lesion contralateral to side of lesion
○ Get head tilt towards side that is normal and eyes to the side that is damaged - To know this is occurring get cerebellum signs on the side opposite to the head tilt (neuro exam is opposite to the head tilt)
What are the 4 main clinical signs of vestibular disease
1) Head tilt (towards side of lesion)
2) Nystagmus (fast phase of eye away from side of lesion)
3) Circling/rolling/falling to side of lesion
4) Nausea/vomiting
Paradoxical is opposite
Cerebellum what is its function and what side of the body does it control
- Coordinate fine motor control
○ Doesn’t initiate anything - from what we know at the moment - Right side of cerebellum controls ride side of the body
What are the 2 main areas of pathways that come from the cerebellum and list some pathways within
From the spinal cord
- Spinocerebellar tracts
○ Dorsal spinocerebellar
○ Ventral spinocerebellar
○ Spinocuneocerebellar
○ Cranial spinocerebellar
- Transmit unconscious proprioception - Ipsilateral
2. From the motor centres for feedback
1. Pyramidal system (cerebral cortex)
○ Via pontine nuclei
○ Contralateral control
2. Extrapyramidal system - more important in dogs and cats
○ Indirect (via olivary nucleus; contralateral)
○ Direct (from tectum and vestibular nuclei)
○ From hindbrain motor centres
What and how pathways feed into the cerebellar cortex and what leads to
Level of foramen magnum
- Dorsal, and cranial spinocerebellar tract and Spinocuneocerebellar tract come up ipsilateral to cerebellar cortex, ventral spinocerebellar is contralateral (crosses twice)
Brainstem
- Other motor pathways have to feed in via brainstem nuclei (pyramidal and extra-pyramidal pathways)
- From contralateral brainstem goes to cerebellar cortex except vestibular nuclei (ipsilateral)
SAME TIME SEND INFORMATION TO THE CEREBELLUM
- Compared with proprioception information from the spinal cord
- To fine tune the action
Eventually sending signals to skeletal muscle
Feedback circuits or pathways leaving the cerebellum what are the 2 main neurons and their functin
Neuron 1: Purkinje neuron cerebellum
○ Has projections and collects information from all the pathways
Neuron 2: Cerebellar nuclei; projections to:
1. Thalamus (Pyramidal and extrapyramidal feedback)
2. Midbrain motor centres (extrapyramidal feedback)
3. Hindbrain motor centres (extrapyramidal feedback)
○ To readjust the motor programs that go back down into the spinal cord
• There are NO descending spinal pathways efferent from the cerebellum – the cerebellum cannot initiate movement
What are the 3 main regions of the cerebellum and what input/output involved
1) vestibular areas - vestibular input
2) proprioceptive areas - spinocerebellar input
2) feedback areas - from pyramidial and extrapyramidial system feedback
what are the 3 cerebellar functions
1) coordination and regulation of movement - combination of proprioceptive input + copy of information from motor centres of pyramidal/extrapyramidal systems
1. pre-control projections from motor centres (commands issued) compared with feedback pathways
2. Movement regulation – comparison of spinocerebellar input with intended action; feedback pathways alter motor command centre output subsequently
2) Control of Posture
- Similar functioning to coordination/regulation steps
- Addition of special senses (vision, balance)
- Major action over postural muscles (hypaxials/epaxials)
3) Other functions
- Mood/emotion;
What are the 3 areas of dysfunction in the cerebellum and the clinical signs associated
1) Vestibulocerebellum
- Vestibular signs: positional nystagmus, truncal sway, paradoxical vestibular syndrome
2) Spinocerebellum
- Exaggerated postural testing, increase in motor tone (extensors)
3) Pontocerebelum
Intereference with feedback: dysmetria (hypermetria), intention tremors
Conscious and subconscious proprioception where project to and function
Conscious proprioception
- Projects to the contralateral cerebral cortex
- Start off the movement
Subconscious proprioception pathways
- Project to the ipsilateral cerebellar cortex directly so only 2 neuron system
- Ensure the movement is smooth and coordinated by using patterns stored within the brain
where does conscious proprioception travel and what does defect result in
Conscious proprioception primarily travels in the dorsal funiculus = dorsal column which becomes the medial lemniscus in the brainstem
- fasciculus gracilis from caudal to the forelimbs (ie hindlimbs etc)
- fasciculus cuneatus from the forelimbs and neck.
DEFECTS - foot in normal position but abnormal weight bearing -> abnormal posture of the limb
where does subconscious proprioception travel ad what does dysfunction result in
Subconscious proprioception primarily travels in the lateral funiculus
- dorsal and ventral spinocerebellar tracts (still in lateral funiculus) from the caudal body
- cranial spinocerebellar tract from the forelimbs and neck
DEFECTS - abnormal positions of the limb -> such as standing on themselves (may lead to tripping)
