Neuro380 Exam 2

papillae

multicellular groupings of taste cells and supporting structures

types of papillae

25% fungiform
50% circumvallate

25% foliate

+filiform (doesn’t contain tastebuds; moves food)

two cell types of taste buds

• basal epithelial cells

• gustatory epithelial cells

  • extend microvili through taste pore

connections of taste buds

• innervated by cranial nerves VII, IX, X

• nucleus of medulla oblongota

• thalamus + gustatory cortex of insula

• internal signal amplifiation (GABA, ATP, 5HT)

main functions of vestibular system

maintaining balance and posture, stabilizing gaze, spatial orientation

3 parts of the inner ear

semicircular canals, vestibule, cochlea

utricle and saccule function

equilibrium sensations: horizontally (utricle) and vertically (saccule)

semicircular canals + head movement

stereocilia (hair cells) embedded in membrane are spatially tuned mechanoreceptors- fire when bending toward kinocilia

Rotational VOR

• very old

• head turns, nods, tilts

• semicircular canals

• full field image stabilization

• established 3 neuron pathway

Translational VOR

• relatively new

• linear head acceleration: otolith organs

• gaze stabilization

• unknown neural pathway

rVOR pathway

• afferent fiber

• central VNC neuron

• eye muscle neuron

• ipsiafferent excitement, contraafferent inhibition

• ipsi-VNC excitement

• contralateral VNC projection

• back to ipsi-neural activation

Nystagamus

• rapid involuntary eye movements

• VOR generates slow phases - eye drifts away slowly bc of defect in gaze holding

• at the edge, quick phase (saccale) jerks the eye back

olfactory organs

• contain olfactory receptor cells

• 2 layers: olfactory epithelium + lamina propria

lamina propria

aveolar tissue, blood vessels, nerves, w glands to absorb water and form mucus

supporting cells

basal stem cells constantly produce new receptor cells for replacement

molecular basis of smell

1. odorants bind to GPCRs, activate adenine cyclase (converts ATP > cAMP)

2. cAMP opens sodium channels in plasma membrane, starts depolzrization

3. if enough depolarization; AP is triggered, info > CNS

neural pathway of smell

1. odorants bind to GPCRs and stimulate sensory neurons in olfactory organs

2. bundled axons leave olfactory epithlium- penetrating the cribiform plate of the ethmoid bone

3. 1st synapse in olfactory bulb

4. axons leaving bulb follow olfactory tract to cortex, hypothalamus, limbic system

Neural representation through labeled line code

shows what fires together, which receptors activate together such as taste and smell

taste map

not distinct but slight preference; bitter in back to avoid posion (gag reflex)

Three cranial nerves in taste pathway

VII, IX, X

Taste pathway

Cranial nerves > nucleus of solitary tract > VPM of thalamus > insular and frontal taste cortices > hypothalamus + amygdala

Merkel cell

sense edges, points, corners, curves, shapes + textures. found on tip of epidermal sweat ridges

Meissner corpuscle

sense motion detection, grip control, found in dermal papillae

Pacinian corpuscle

senses vibration, located in dermis and deeper

Ruffini corpuscles

sense skin stretch, tangential force, motion detection. located in dermis

pseudo-unipolar neuron

a type of a neuron with a single axon that branches into two pathways (mechanoreceptors and thermoreceptors)

pain/thermoreceptor fibers + connections

A omega and C fibers, Lamina 1 + 2 of dorsal horn

fine touch/proprioception fibers + connections

A alpha and A beta fibers, Lamina 3-6

proprioceptors fibers + connections

lamina 7 + 9

touch pathway

dorsal column (lower/upper body, fine touch) and anterolateral system (head + face, pain + thermoreception)

touch neural pathway

thalamus > SI

VPL recives info from body, VPM from face

SI area 1+3b

cutaneous stimulation

SI area 3a

propricoception

SI area 2

cutaneous stimulation and proprioception

damage to area 3b

generalized defecit

damage to area 1

texture recognition deficit

damage to area 2

shape and size recogntion deficit

thermoreceptors v nocireceptor response

thermoreceptors do not vary with intensity of stimulus; nocireceptors do, and require threshold

1st pain

brief, sharp, localized. carried by A-delta fibers to the VPL and SI, SII. sensory-discrimination

2nd pain

dull, longer-lasting, less well localized, carried by C fibers to complex neural pathways. involved with motivation

Type A fibers

myelinated, carry fast responses, quickly reach SI. Laminae 1, 5

Type C fibers

unmyelinated, general activation of reticular form + thalamus, less localized. Laminae 1, 3

Parallel pain pathways

nociceptive receptors cross over, mechanoreceptors same side

Referred pain

few nociceptors for internal organs, pain is referred to other parts of body

Gate theory of pain

in dorsal horn ‘gate’ decides which pain signals go to brain. A-delta and C fibers inhibit inhibitory interneurons and pen gate; A-beta fibers stimulate neurons and close gate (why rubbing is helpful)

Phantom limb pain

neuroplastic changes in SI, premotor and primary motor cortex contralateral to amputation. maladaptive changes in CNS

head direction cells

map to dorsal thalamus, subculum

sense direction of head

cells have preferred direction

place cells

map to hippocampus

activate in specific familiar place, forming cognitive map

grid cells

map to entorhinal cortex, self position and direction

border cells

entorhinal cortex; sense environemental boundaries

theories of magnetoreception

• photoreceptor based

• trigemenal nerve based

• Lagena associated

photoreceptor based magnetoreception

light dependent, birds ‘see’ magnetic pathway/percieve it as visual patterns through differently oriented light sensitive molecules in retina.

evidence:
- wavelength dependent orientation abilities
- lesion of cluster N makes birds unoriented
- visual pathway links structures

trigemanal nerve theory

pigeons need intact trigemenal nerve for navigation

magnetetic field changes activate the trigmenal complex

lagena associates theory

lagena (in the inner ear) senses magnetic field
evidence:

lagena has iron

the vestibular system is activated by a magnetic field w rotaional markers

weak + weak

super additivity

mid + mid

additivity

strong + strong

subadditivity

head and gaze shift controlled by

superior colliculus

audiovisual integration in SC

combines cortical and thalamic inputs (anterior extosylvian sulcus) and somatosensory IV

upper motor neurons control

signals down spinal cord to command movement (CNS)

lower motor neurons control

skeletal muscles

corticospinal tract

• projects to lower motor neurons in spinal cord

• conscious control of skeletal muscles

corticobulbar tract

• projects to control centers in brainstem

• skeletal muscles for eye, jaw, face, neck

brain regions that maintain posture

• reticular formation

• vesitbular nuclei

• bilateral axial muscle LMNs

McGurk Effect

• seeing lip movement for one sound and hearing another leads to misperception (combination/fusion of sounds or new sound)

• demonstrates brain’s inability to differenientate seperate sensory infromation when all senses work together