Lecture 8 + Assignment 7

Question 1

Vestibular labyrinth contains 5 things

Answer 1

Two otolith organs
- utricle and saccule
= detect head tilt and linear acceleration

Three semicircular canals
- superior, posterior, horizontal
= detect head rotation

Question 2

Otolith organ orientations

Answer 2

utricle
= horizontal hair cells
- face towards striola

saccule
= vertical hair cells
- face away from striola

Question 3

Otolith organ components

Answer 3

otoconia chalk pieces (cal. carbo. CaCO3)
= 1-5 micron diameter

otolithic jelly membrane

hair cells

supporting cells

Question 4

Otolith organ tilt / lin. acceleration detection

Answer 4

otoconia add mass+inertia to the otolithic membrane

makes jelly lag behind

Question 5

Adaptation of hair cells in otolith organs

Answer 5

Transduction:
Head tilt
- more tip link tension
- opens K/Ca channels
- depolarization

adaptation:
- more Ca inside stereocilium
- tip link motor slips
- closes K/Ca channels

Question 6

3 planes of rotation

Answer 6

Yaw
= rotation around z-axis

Pitch
= rotation around y-axis

Roll
= rotation around x-axis
forward and back

Question 7

Semicircular canal organization

Answer 7

are orthogonal to one another (90 degrees)

roughly in the three planes

each detect rotation in their own plane

Question 8

Semicircular canal components

Answer 8

Ampulla: bulge in the bony canal

Cupula: gelatinous substance in which stereocilia are embedded

Crista: epithelial cell layer in which the hair cell bodies are embedded

Question 9

Semicircular canal detecting acceleration

Answer 9

• cupula displaced in the opposite direction of movement
• due to endolymph inertia

Question 10

Rotation stimulus graph

Answer 10

transduction (up)

quickly adapts back to the baseline (no more acceleration)

off response (down)
- bumps into cupula from other side when you stop
hair cells hyperpolarize
= firing rate below baseline

Question 11

Vestibulo-ocular reflex circuitry

Answer 11

• scarpa’s ganglion / cranial nerve 8 comes into the medulla
• synapses onto neurons in vestibular nucleus
• decussates in rostral medulla
• synapses onto abducens nucleus
• connects to 2 neurons
• one goes out through 6th cranial nerve
  = releases acetyl choline into muscle (lateral rectus of opposite eye)
• causes contraction
• other decussates and ascends into the midbrain
• release glutamate onto oculomotor nucleus
• onto 3rd cranial nerve
• signals to release acetyl choline onto medial rectus
• causes turn to opposite side
• both eyes rotate in the opposite direction of head movement
• inhibitory relaxes the antagonist

Question 12

Do peripheral nerves decussate

Answer 12

no

anything that leaves central does not decussate

Question 13

3 nerves involved in VOR

Answer 13

CN 3 - oculomotor nerve
- motor
- eye movements
- pupil constriction
- upper eyelid muscle

CN 6 - abducens nerve
- abducens or lateral eye movements

CN 8 - vestibulocochlear (auditory) nerve
- hearing, balance

Question 14

VOR during left rotation

Answer 14

activates:
1. the hair cells on the left horizontal semicircular canal
2. the left vestibular nucleus
3. the right abducens nucleus -> right lateral rectus muscle
4. the left abducens nucleus -> left lateral rectus muscle

= rightward eye rotation

Question 15

Oscillopsia

Answer 15

• bilateral loss of VOR
• causes thinks to look like they’re shaking + vision blurring
• can be due to some antibiotics
  ex. hair cells destroyed by ototoxic medications such as streptomycin

Question 16

Benign paroxysmal positional vertigo (BPPV)

Answer 16

• dislodged otoconia enter posterior semicircular canal
• causes dizziness in certain head positions
• can be helped by Epley Maneuver which tries to return them to correct spot

Question 17

Positional alcohol nystagmus

Answer 17

• alcohol enters cupula
• makes it lighter than endolymph = buoyant
• causes it to deflect in certain head positions

Question 18

Primary motor and premotor cortex

Answer 18

premotor
- in front
- brod. area 6
- lesion here causes apraxia = inability to PLAN and execute complex voluntary motor tasks
- much larger in humans than other animals

primary motor
- further back
- brod. area 4
- correlates to animal size

Question 19

Motor homunculus

Answer 19

looks like somatosensory homunculus

1. corticospinal tract
   - top
   - upper and lower extremities
   - axons go all the way down to the spinal cord
   - cortical efferent
   - commands muscle movements
2. corticobulbar tract
   - face
   - goes to brain stem motor neurons

cortex layer 5

Question 20

Corticospinal and corticobulbar tracts

Answer 20

do this

Question 21

LCST and VCST

Answer 21

LCST
- 90% of the CST axons
- decussates in the medulla
- terminates contralaterally in the lateral part of the ventral horn
DISTAL muscles

VCST
- 10% of CST axons
- does not decussate in the medulla
- terminates bilaterally (mainly contralaterally) in the medial ventral horn
AXIAL/PROXIMAL muscles

Question 22

Lateral corticospinal tract topography

Answer 22

on the sides of the butterfly

SLTC CTLS

Question 23

Directional tuning of a M1 neuron

Answer 23

primary motor complex

• respond preferentially to a certain angle of movement
• can do a population vector to see resulting vector
• ones that fire more have more influence

Question 24

Dr. Apostolos Georgeopolous

Answer 24

• Came up with idea of population vector for the motor cortex
• M1 neurons basically vote on what to movement to cause

Question 25

Motor neuron pool

Answer 25

- group of alpha motor neurons in the ventral horn of the spinal cord that all go to one muscle - can span multiple spinal segments

Question 26

Motor unit

Answer 26

- alpha (lower) motor neuron connects to multiple muscle fibers and causes contraction - larger muscles = more fibers innervated by a single alpha motor neuron - gives more control and dexterity, more graded movement ex. leg muscles = 1000 innervated by 1 fingers = 10 extraocular = 3

Question 27

Neuromuscular junction

Answer 27

- synapse between an alpha motor neuron and a muscle fiber - axon releases acetyl choline into a cleft, binds to receptors - muscle AP causes contraction = movement instead of reuptake, acetylcholine degraded by acetylcholinesterase enzyme each vesicle = 10 000 ACh molecules AChE = degrades 5000 molecules/second

Question 28

Amyotropic lateral sclerosis

Answer 28

- Lou Gehrig's disease - death of lower and upper motor neurons - flaccid paralysis (loss of muscle tone) - muscles atrophy

Question 29

Duchenne muscular dystrophy

Answer 29

- death of skeletal muscles - x-linked recessive genetic mutation in gene for dystrophin protein dystrophin - helps hold muscle cells together, part of the cytoskeleton

Question 30

Myasthenia Gravis

Answer 30

- autoimmune destruction of skeletal muscle ACh receptors = lack of communication - alpha motor neurons and muscle NOT damaged - normal life expectancy with treatment ex. inject acetylcholinesterase inhibitor = keeps ACh in cleft

Question 31

Multi-electrode extracellular recording + Dr. Andrew Schwartz

Answer 31

Record from multiple electrodes at the same time - Very close together on an array Done by Dr. Andrew Schwartz - Recordings in monkeys, looked at M1 and resulting arm movement - M1 population vector just precedes arm movement bc command must travel down - Could use M1 (brain) to move a robotic arm Used for human paralysis

Question 32

Inertia

Answer 32

an objects resistance to changing speed due to otoconia or endolymph

Question 33

Shear force direction

Answer 33

- opposite direction of acceleration

Question 34

Muscle spindle

Answer 34

- set of small thin muscle fibers - inside main extrafusal fibers, parallel to them - 1a afferent axon weaves between them when the muscle is stretched - 1a mech gated ion channels open due to deformation - signals lengthening

Question 35

Golgi tendon organ

Answer 35

- not in parallel to the muscle instead in series with it - full of collagen fibers and 1b afferent axon weaving between them when the muscle is stretched - collagen fibers stretch - 1b mech gated ion channels open - collagen hard to stretch = signals tension

Question 36

Gamma motor neuron

Answer 36

- innervates the intrafusal muscle fibers (alpha innervates extrafusal) - when muscle contracted and short, slack muscle spindle - gamma tightens it up again - resets it to detect changes again makes 1a fire again

Question 37

Knee-jerk / myotatic stretch reflex

Answer 37

* Tap tendon pulls knee down, stretches quadriceps muscle, makes leg kick out * Stretch causes contraction * Muscles have sensors * Upon stretch, mech gated ion channels in muscle spindle cause 1a axons to fire APs * Enters dorsal horn, release glutamate onto alpha lower motor neuron = returns to muscle + releases ACh = muscle contraction Spinal inhibitory interneuron releases GABA onto flexor alpha motor that innervates antagonist muscle ex. Head tilting, stretch causes contraction to keep posture Spring in step be stretch causes contraction again = efficient

Question 38

Autogenic inhibition reflex

Answer 38

- so you don't hit yourself in the face when lifting a drink Golgi tendon organ: defects tension in the muscle=APs in 1B axon (btwn tendon/ muscles Dorsal spinal cord -> ventral horn -> synapse onto inhibitory interneuron -> back to same muscle REDUCES CONTRACTION ALSO - 1B excites excitatory purple interneuron = activates triceps muscle to oppose movement

Question 39

Flexion-crossed extension reflex

Answer 39

Step on something painful = Adelta or C axon signal * Goes to STT AND dorsal horn excitatory interneurons to either excite or inhibit - same interneurons decussate Realises pain - flexor muscle makes painful foot pull up and relaxes the antagonist muscle Other side - opposite * hamstring relaxed, extensor muscles activated so quad straightens * you don't fall over when you put all your weight on one foot Polysynaptic reflex (multiple synapses) Polysynaptic excitation of right flexor and left extensor Polysynaptic inhibition of right extensor and left flexor