Powerpoint 8 – Sensory Physiology Part 2

1. Anatomy of Eara. Three parts

i. External (outer) ear1. Formed of cartilage2. Auricle, ear canal, surface of ear drum

ii. Middle ear1. Contains…s

a. Ear drum tympanic membraneb. Three bones ossicles

i. Malleus (hammer)1. Attached to tympanic membrane by long process (handle)

ii. Incus (anvil)1. Connects malleus and stapes

iii. Stapes (stirrup)1. Smallest bone in body2. Transfer vibrations of incus to oval window

c. Eustachian tubeiii. Inner ear

1. Two partsa. Cochlea for hearing

i. Contains organ of Cortib. 3 Semi-circular canals for balance and body equilibrium

2. Cochleaa. Structure of organ of Corti

i. Stapes connected to oval windowii. Behind this we have cochlea and three semicircular canals.

iii. Inside cochlea, we have organ or Corti which has three parts. 1. Scala vestibule

a. Fluid is perilymph (high sodium)2. Scala media

a. Fluid is endolymph (high potassium)b. At base we have basilar membranec. Hair cells on top of basilar membraned. Tectorial membrane on top of hair cells

3. Scala tympani a. Fluid is perilymph (high sodium)

b. How we heari. The sound wave travels through auditory tube, through ear, and is converted into pressure

wave in the fluid which exists in organ of Corti. ii. The sound waves vibrate tympanic membrane. By this vibration, we have movement of the

three ossicles in middle ear. iii. Last ossicle is stapes which is connected to oval window. By movement of stapus, it pushes

back the oval window. Behind oval window we have perilymph in Scala vestibule.

iv. Pushing oval window leads to circulation of perilymph in Scala vestibule and it reaches Scala tympani and reaches round window.

v. Because of perilymph fluid circulation in Scala vestibule and Scala tympani, we have vibration of basilar membrane located at base of hair cells.

vi. This causes the hair cells to move in Scala media. 1. Bending of hair cells in one direction against tectorial membrane increases

potassium outflow from hair cells hyperpolarization and no signal2. Bending of hair cells all in other directions against tectorial membrane decreases

potassium outflow (remains in hair cell) which leads to depolarization of hair cell and opening of calcium channels.

a. Calcium enters into hair cell leads to exocytosis of vesicle full of stimulatory neurotransmitters

b. This release stimulates afferent fiber of cochlear nerve. i. Cochlear nerve takes information about sound to stations in brain. ii. Last station for auditory is located in Temporal lobe of brain Area

41 and 42 called Primary Auditory area. vii. Oscillation of hair cells causes intermittent firing of cochlear nerve

c. Encoding of Soundi. Different frequencies activate hair cells on different locations of basilar membrane (flipped

Xylophone)1. Base of basilar membrane – near oval and round windows

a. Narrow and stiffb. Responds to high frequencies

2. Apex of basilar membrane – away from windowsa. Wide and compliantb. Responds to low frequencies

3. Auditory pathway a. Signal from cochlea to brain.b. Stations in pathway

i. Afferent nerve (cochlear nerve) from hair cells to medullar oblongata1. Two nuclei dorsal and ventral nuclei of cochlear nerve

ii. Next is ponsiii. Next is midbrain

1. We have superior and inferior colliculusiv. Next is thalamus

1. We have medial geniculate nucleusv. Then to temporal lobe of brain area 41 and 42

c. Flow in pathwayi. 1st group of neurons travel to spiral ganglion to synapse with 2nd groupii. 2nd group of have some neurons travel to contralateral side of station

iii. 3rd group passes through pons and this group of fibers is called lateral lemniscus and synapse with 4th group in inferior colliculus in midbrain

iv. 5th group synapses with 6th group in nuclei of thalamus called Medial Geniculate nucleusv. 6th group travel to area 41 and 42 in temporal lobe

d. Infection of middle eari. Any bacterial infection in middle leads to bacterial meningitis because it is close to brain and

meningeal layer. ii. No treatment

e. Otitis mediai. Inflammation of middle earii. Usually buildup of fluid causes ear ache

iii. Leads to meningitis usually by Streptococcusf. Signa and symptoms of meningitis

i. Headacheii. Speech disorder mental confusion

iii. Sever condition: comaiv. Muscle weaknessv. Pain in muscles, back, neck

vi. Nausea or vomitingg. Auditory disorders

i. From any modification or damage to cochlear nerve, organ of Corti, or auditory pathway that travels to different stations in brain

ii. Could be from head traumaiii. Bacterial infectioniv. Viral infectionv. Congenital problem

vi. Tumor

4. Vestibular systema. Two parts

i. Formed from 3 semicircular canals detect angular acceleration (turning head left and right)

1. Structurea. Anterior (superior) canalb. Posterior (inferior) canalc. Lateral (horizontal) canald. Dilated part at base of each canal ampulla

2. Each canal forms two layersa. Bone layer – outside and external, contains perilymphb. Membranous layer – membrane layer inside, contains endolymph

ii. Utricle and saccule detect linear acceleration (falling down)1. Ampulla, utricle and saccule contain hair cells which are covered by gelatinous

substance called cupula. 2. Small cilia called stereocilia3. Large cilia called kinocilium4. At the top of cupula, we have heavy membrane called Statoconia

5. Detecting Angular Acceleration with 3 Semicircular canalsa. Angular acceleration is detected by semicircular canalsb. Inside canals we have hair cells, at base of hair cells are afferent fiber for vestibular system. At top

of hair cells, we have cupula. Inside canal we have endolymph. c. The endolymph goes toward opposite direction that you turn your head. d. Endolymph comes around and pushes cupula in opposite direction as well.e. When adaptation to new position is achieved, we have stimulation of hair cells, depolarization of

hair cells, and stimulation of nerve which takes information to the CNS. f. When adaptation is achieved, cupula comes back to resting position and endolymph goes back to

original position (back in direction the head turned). g. This pushes cupula in same direction as head turn. h. In this way, semicircular canals and hair cells and nerve control angular acceleration and maintain

equilibrium.

6. Detecting Linear Acceleration with Utricle and Sacculea. Step 1: When a person suddenly falls, we have a change in hair cells in utricle and saccule.b. Step 2: Structure of hair cell, big cilia is called kinocilium and small parts are called stereocilia. c. We have jelly like substance called cupula above hair cells and statoconia above the cupula. d. Statoconia is heavier than jelly substance in hair cell (cupula). In equilibrium position statoconia

falls back and stereocilia move toward kinocilium which leads to depolarization. Depolarization of hair cells stimulated vestibular nerve which takes the signal to the CNS and different stations that exist in CNS.

e. The efferent fibers take the information from CNS to statoconia and different part of body such as upper and lower limbs. In this condition, statoconia comes back to resting phase and that person maintains equilibrium. The upper and lower limbs also receive signal from spinal cord and they help

control the body equilibrium.

7. Vestibular pathwaya. Stations

i. Between medulla oblongata and pons 4 vestibular nuclei ii. In lower part of cerebellum flocculo-nodular lobe

iii. Midbrain Red nucleus b. Pathway (control body movement and equiliubrium)

i. Depolarization of hair cells in semicircular canals, utricle, and sacculeii. Then nerve fibers…

iii. (1st pathway) Fibers travel to vestibular nucleus and then to spinal cord Vestibulo spinal tract

1. Functiona. Facilitates extensor muscleb. Inhibits flexor muscle of upper and lower limb.

iv. (2nd pathway) Fibers travel to vestibular nuclei, then to reticular nuclei, then efferent of reticular nucleus to spinal cord Reticular spinal tract

1. Functiona. Controls gamma and alpha motor neurons which innervate skeletal muscle

v. (3rd pathway) Fibers travel to vestibular nuclei and then to flocculo-nodular lobe (lower lobe of cerebellum)

1. Functiona. Controls body movement

vi. (4th pathway) Fibers travel to vestibular nuclei, then to three nuclei for three cranial nerves which are nerve 3, 4, and 6. This tract is Medial longitudinal fasciculus

1. Functiona. Innervate extraocular muscles (eyes move because of this tract in same

direction that you turn your head)vii. (5th pathway) Travel to vestibular nuclei, travel to red nucleus in midbrain, then efferent

fiber travel back to spinal cord Rubro spinal tract1. Function

a. Facilitates flexor muscles in upper and lower limbsb. Inhibits extensor muscle in upper and lower limb.

c. Pathological conditionsi. Nystagmus abnormal eye movement

1. Could by pathological, physiological, or congenital2. Could be due to extra ocular muscle disorders which are innervated by cranial

nerves 3, 4, and 6. 3. Could be physiological, after spinning around, body should adjust direction of eyes.

ii. Vertigo – dizziness1. Could be due to hypertension or hypotension2. Increased or decreased blood cholesterol3. Could be physiological such as pregnancy – normal due to hormonal change4. Any trauma or damage to vestibular system semicircular canals, Utricle, or

Saccule5. Damage or head trauma in vestibular pathways can lead to dizziness. 6. Tumor or head trauma, infection, intercranial hemorrhage can cause dizziness

8. Clinical questiona. 25 year old female has severe headache, vomiting, nausea, nosebleed, vertigo, vision problem,

sleep disorder, sweating. Which receptor is involved in this case? i. Alpha 1ii. Alpha 2

iii. Beta 1iv. Beta 2 v. Answer: These are signs and symptoms for hypertension. Alpha 1 is correct answer

because is controls sweat glands (increases), increase blood pressure (vasoconstriction), vomiting, sweating, headache are general signs for hypertension.

b. 6 year old had head trauma. Post trauma he had vertigo, some vision problem, and he was not able to have normal extension of upper limb and lower limb. He also had some eye movement disorder. Which part of brain could be damaged in this head trauma?

i. Vestibular spinal tract and medial longitudinal fasciculusii. Red nucleus and reticular nucleus

iii. Vestibular spinal tract and reticular spinal tract

iv. Answer: Vestibular spinal tract and medial longitudinal fasciculus are damaged. Medial longitudinal moves eye

c. 55 year old male has palpitation – irregular heart rate, headache, vomiting, and sometimes feels pain in retrosternal area, which is called angina pectoris, and pain in left arm.

i. Which receptor is involvedii. Answer: Beta I

d. 25 year old female had car accident. Few months later, she realizes she cannot see well with her left eye and cannot see well left and right temporal fields. What part/parts of optic tract could be damaged in this case?

i. Answer is left optic nerve and optic chiasm. e. Cholinergic receptor…

i. Nicotinic in neuromuscular junction, adrenal medulla, and postganglionicii. Muscarinic is in heart

f. Receptor for adrenaline

i. Alpha 1 – ii. Alpha 2 -

iii. Beta 1 - iv. Beta 2 – relaxation of diaphragm