Integrative Neuroscience Exam 2- NSC 4354 (Ch. 13-19)

sound

refers to pressure waves generated by vibrating air molecules

physical sound waves

radiate in 3 dimensions, creating concentric spheres of alternating compression and rarefaction

sound wave features

4 major features; waveform, phase, amplitude (usually expressed in logarithmic units known as decibels, dB), and frequency (expressed in cycles per sec or Hertz, Hz)

for a human listener the amplitude and frequency of a sound pressure change at the ear roughly correspond to that listener's experience of

loudness and pitch

auditory system transforms sound waves into ______________, which gets integrated with other sensory information to ____________, especially orienting _____________.

auditory system transforms sound waves into neural activity, which gets integrated with other sensory information to guide behavior, especially orienting responses and communication

external ear and middle ear

collect sound waves and amplify pressure

transmitted to fluid-filled __________ in __________

transmitted to fluid-filled cochlea in inner ear

cochlea breaks down complex sound waves in simple __________

cochlea breaks down complex sound waves in simple sinusoidal components

hair cells encode _______, ________, and _______

hair cells encode frequency, amplitude, and phase

one product of this process is the representation of sound frequency along the length of the ________, referred to as _______, transmitted to _______

one product of this process is the representation of sound frequency along the length of the cochlea, referred to as tonotopy, transmitted to auditory fibers

first stage if central processing is at the cochlear nucleus diverges to specific targets...

1. superior olivary complex

2. inferior colliculus of the midbrain

1. superior olivary complex: first point where the 2 ears interact and the site of initial processing of the cues that allow listeners to localize sound in space

2. inferior colliculus of the midbrain: first point at which auditory information can interact w/ the motor system

the external ear consists of the

pinna, concha and auditory meatus

the external ear gathers energy and focuses it on the

eardrum (tympanic membrane)

inner ear canal (auditory meatus) boosts sound pressure ______, making humans especially sensitive to frequencies around _______ (frequent range of hearing loss)

30- to 100-fold, 3 kHz

important cues for differentiating speech sounds including plosive consonants (ba & pa) are concentrated around _______, therefor hearing loss in this range degrades speech recognition

3 kHz

the major function of the middle ear is to

transform airborne sounds into vibrations that can be detected by cells (hair-cells in inner ear) that sit in body fluid

normally 99.9% of energy is reflected at junction between 2 media

ex. going from low-impedence medium such as air to a higher-impedence medium such as water

middle ear boosts air pressure _____ fold

200

large tympanic membrane funnels sounds onto small ______

oval window

lever action of ______ connects the tympanic membrane to the oval window

ossicles (middle ear bones; malleus, incus, stapes)

conductive hearing loss

damage to the external or middle ear, lowers the efficiency at which sound energy is transferred to the inner ear, can be partially overcome by using a hearing aid

the 2 small muscles, ____________, are activated automatically by loud noises and ________

tensor tympani and stapedius, contract to protect inner ear

the cochlea of the inner ear

transforms waveforms from sound pressure into neuronal signals

normal sounds are complex waveforms (different frequencies) the inner ear

deconstructs complex waveforms into simple tones

oval window and round window

oval window: sound waves enter via ossicles

round window: vibrates opposite to oval window, allows fluid in cochlea to move

the cochlea is bisected by the cochlear partition, a flexible structure that supports the

basilar membrane and tectorial membrane

basilar membrane

A structure that runs the length of the cochlea in the inner ear and holds the auditory receptors, called hair cells.

tectorial membrane

A membrane located above the basilar membrane; serves as a shelf against which the cilia of the auditory hair cells move

there are fluid filled chambers on each side of the cochlear partition called the

scala vestiboli and scala tympani

the chamber that runs within the cochlear membrane

scala media (endolymph)

scala vestiboli and scala tympani's fluids mix known as ______, via the _______

perilymph, helicotrema opening

tonotopy

topographical mapping of frequencies along the basilar membrane, membrane and auditory nerve fibers are tunes to specific frequencies

basal end is ______, responds (vibrates) well to ________

narrow and stiff, high frequency sounds

apical end is _____, responds best to

wide and flexible, low frequency sounds

the organ of coti

transforms pressure waves into action potentials

sits inside the ______, between the ____________

cochlear duct, scala vestibuli and the scala tympabi

the __________ pushes hair cells against the _______ as perilymphatic pressure waves pass

basilar membrane, tectorial membrane

vertical motion of the traveling wave along the _______ induces a ________ between the _________. bends _____ on the ____, causing hyper or depolorization

basilar membrane, shearing motion, basilar membrane and tectorial membrane. stereocilia(hairlike structures that protrude from apical ends of hair cells), hair cells

inner hair cells(3,500) receptors for hearing constitute ________

95% of auditory nerve

outer hair cells(12,000) receive ________ and they ______

efferents from brain, amplify the traveling wave

~15,000 ________ in each ear

hair cells

30-100+ _______ per hair cell

stereocilia, arranged in height and bilaterally symmetrical

_________ connect 2 adjacent stereocilia

tip links--> transform shearing motion into receptor potential --> movement opens and closes channels, can detect movements the size of a gold atom (0.3nm) and respond in tens of microseconds

auditory pathways

auditory nerve enters cochlear nucleus in brainstem --> bilateral projections to the medial and lateral superior olive --> inferior colliculus --> thalamus(MGN) --> primary auditory cortex

________ located in temporal cortex maintains topographical map of ____

auditory cortex, cochlea

the auditory cortex

primary site of most sound processing, including speech, music, and other sound information; point to point projections from medial geniculate thalamus maintain tonotopic map

combination-sensitive neurons, species-specific sounds, speech (wernicke's area)

vestibular system

stabilization of gaze, head orientation, and posture during movement; postural reflexes and eye movements

3 axes of angular acceleration

convert effects of gravity (linear and rotational accelerations of the head) into neural impulses

roll, yaw, pitch

roll: rotation around x axis

yaw: rotation around z axis

pitch: rotation around y axis

labyrinth

works similar as cochlea and is continuous with it, converts effects of gravity (linear and rotational accelerations of the head) into neural impulses

utricle and saccule(ear stone organs)

respond to linear accelerations of the head and static head position relative to ground --> gravity

3 semicircular canals

canals on both sides of the head,specialized to rotational accelerations --> head turning, use vestibular hair cells

vestibular hair cells

work like auditory hair cells, many are open in the absence of stimulations-->vestibular nerves are tonically active, hair cells in the 3 organs (semicircular canals, saccule, utricle) are selective for certain directions

the otolith (ear stone) organs

utricle and saccule, distribution of hair cells and orientation of stereo cilia in utricle and saccule is continuous to encode all possible directions

utricle and saccule

gelatinous layer (otholitic membrane) in which small crystals sit, rub against the hair cells during tilting motion

olfaction

smell; guides search for food or mates, helps avoid predators, influences reproductive and endocrine functions, influences mother-child interactions, warns about danger(chemicals/rotten food) and provides sensual pleasure(flowers and perfume)

classification scheme (j. amoore, 1950s)

perceived quality, molecular structure and inability of some people to smell certain odor(pungent, floral, earthy, musky, peppermint, putrid) however classification has little biological correlate

most consistent distinction is between pleasant and unpleasant

organization of human olfactory system

olfactory receptors-->olfactory bulb-->olfactory bulb targets-->structures

olfactory bulb targets

pyriform cortex-->orbitofrontal cortex

olfactory tubercle-->orbitofronal cortex, thalamus, hypothalamus

amygdala-->orbitofronal cortex, thalamus, hypothalamus

entorhinal cortex--> hippocampal formation

olfactory system

most vertebrates (but not primates) have 2 distinct olfactory systems:

main olfactory system- detects volatile chemicals

accessory olfactory system- detects fluid phase chemicals (pheromones)

olfactory receptor neurons (ORN)

bowmans glands secrete mucus-->mucus protects ORNs; acts as a solvent, replaced every 10 minutes

neurogenesis

bc ORNs are exposed they are protected by mucus and continuously regenerated

Olfatory epithelium

contains stem cells(in the layer of the basal cells) that regenerate olfactory neurons throughout life (every 2-8wks)

odorant receptors

~400 active, coding genes in humans (3-5% of genome), 1200 in mice

ORNs show spatially distinct patterns of expression (i.e. different odors are processed in different locations)

receptor responses

broad response characteristics may reflect the fact that odors represent mixtures of chemical components

ex. the green neuron responds to the individual components of an odor)

receptors project to glomeruli in olfactory bulb

axons of olfactory receptors converge in glomeruli in olfactory bulb

axons that converge share the same odorant receptor gene--> glomeruli are selective for specific odor

axons in the glomeruli converge on the dendrites of mitral cells

mitral cells (receive receptor input) are main projection cells of olfactory bulb

cortical projections from the olfactory bulb

projections from the mitral cells form the olfactory tract, no direct thalamic relay

main target is the pyriform cortex

pyriform cortex

neurons show broad responses and may integrate different odors (function is unclear)

pyriform cortex projects to higher areas including orbitofrontal cortex (reward processing) and amygdala (emotional salience and memory)

the organ of taste

areas of sensitivity on the tongue:

tip of the tongue- sweetness

back of the tongue- bitterness

sides of the tongue- saltiness and sourness

5 primary categories of taste

sour, bitter, sweet, salty, MSG(umami)

distinctions are maintained to the level of cortical processing in insular cortex

taste cells, buds, and papillae

taste cells are clustered in taste buds, taste buds sit in trenches around papillae(small structures found on the upper surface of the tongue)

taste buds

taste receptors containing cells (gustatory cells) found in the oral cavity lining the sides of each papillae

over 10,000 taste buds found on the tongue, soft palate, and the inner surface of the cheek

each of these receptors is specific and can respond to chemicals that dissolve in our saliva

~400 taste buds on human tongue that are regenerated every 2 weeks

5 types of receptors for the 5 categories of taste

Umami: T1R1+T1R3, mGluRs

Salty: ENaC others

Bitter: T2Rs

Sour: intracellular acidification --> ?

Sweet: T1R2 + T1R3, others?

Fat: GPR120, GPR40, CD36, Kch

organization of the human taste system

taste buds in the tongue and larynx--> axons run in cranial nerve VII, cranial nerve IX, and cranial nerve X--> project to nucleus of solitary tract--> projects to thalamus (ventral posterior medial nuc.)--> insult and orbitofrontal cortex

neurons

neurons (<15% of cells in the CNS)

differ in connectivity: principle (or projection) neurons, local-circuit neurons

phenotypes vary regionally: (i.e. different nuclei, different neurons)

developmentally regulated

activity regulated

glia

(Greek: glue)

differ in size and mobility

macroglia(60% of all cells in CNS): astrocytes, oligodendrocytes and schwan cells, epyndemal cells

microglia(15% of all cells in the CNS)

vascular tissue

(~10% of cells in the CNS)

smooth muscle

endothelial cells

connective tissue/basement membranes

types of motor organs

cilia, glands, muscles

glands

endocrine: neuroendocrine cells, pituitary, endocrine organs (adrenals, etc.)

exocrine:

internal- goblet(mucus cells) and digestive(salivary glands, etc.)

external- sweat glands and sebaceous glands

muscles

smooth:

visceral- intestinal, bronchial, vascular

peripheral (iris, etc.)

striated:

cardiac(heart)- atrial and ventricular

skeletal- trunk, limps and digits, head and neck

branches of the ANS

sympathetic NS mediated the "4 F responses"

use energy: increased peripheral motor activity

uses ACh and NE as neurotransmitters

parasympathetic NS

produce energy: increased internal motor activity

uses ACh as neurotransmitter

4 F responses

fight, flight, fright, f*ck

motor neurons are located in

ventral horn

lower MN and interneurons in ventral horn of spinal cord

pathways in the medial part if the spinal cord control posture

pathways in lateral spinal cord control fine movement in extremities

interneurons in the lateral part are strictly local

interneurons in the medial part cover several segments vertically

2 classes of lower motor neurons

a motor neurons and y motor neurons

a motor neurons

innervate the extrafusal, force-producing fibers--> control posture and movement

a single a motor neuron innervates many muscle fibers:

-spreads force evenly across the muscle

-reduces chance that loss of a single a motor neuron results in loss of muscle function

y motor neurons

innervate intrafusal muscle fibers (muscle spindles)--> control tension on the receptors (spindles)

motor unit

1 motorneuron + its muscle fiber targets

a motor neurons/motor unit types

Neuron

Size: large

Threshold: high

Conduction: fastest

Size: medium

Threshold: medium

Conduction: medium

Size: small

threshold: low

conduction: slow

Unit

force: large

fatigue: fast

function: large force(running/jumping)

force: medium

fatigue: intermediate

function: intermediate(walking)

force: small

fatigue: very slow

function: sustained(posture)

3 types(sizes) of a motor neurons

slow (S) (e.g. posture)

fast fatigue-resistant (FR)

fast fatigable (FF) (e.g. running)

muscle spindles (muscle sensors)

group Ia afferents (nuclear bag fibers)--> respond physically to small stretches

group II afferents--> fire tonically to signal degree of sustained stretch; innervate a-motoneuron in spinal cord

y motor neurons

-regulate excitability of muscle spindles

-under sensory and voluntary control (e.g. warm-up stretching or standing on a moving bus, difficult movements, unpredictability)

- coactivate with a-motoneurons so that contraction of the muscle (and loss of tension in muscle spindle) does not lead to stop in firing of group Ia and II fibers

-same principle applies if muscle is relaxed/stretched--> prevents overstimulation of muscle spindles

--> compensates for small changes in load and intrinsic irregularities in the muscle contraction

golgi tendon organ

sensory feedback affects motor control

proprioception: while muscle spindles detect changes in muscle length, mechanoreceptors in tendons predominantly signal changes in muscle tension--> contraction of muscle

provides NEGATIVE FEEDBACK via inhibitory interneurons in spinal cord

bilateral coordination

flexion reflex

painful sensory stimulation leads to flexion reflex:

--> inhibition of extensor

--> activation of flexor on affected side

also accompanied by cross extension reflex

--> opposite activation; serves to maintain posture

interneurons regulate motor control

A) the Ia inhibitory interneuron--> feedforward- inhibition

-mediates reciprocal innervation in stretch reflex circuits

-receives inputs from higher centers(dark red line)

-->allows to coordinate opposing muscles through a single command

pyramidal tract (corticospinal & corticobulbar)

function: initiation of voluntary movement(or intent of movement) via corticospinal pathway

-corticobulbar tract: upper motor neurons of the cranial nerves(muscles of the face, head and neck) terminates on motor neurons within brainstem motor nuclei

-corticospinal tract: controls spinal motor neurons (controls movement of the torso, upper and lower limbs)

pyramidal tract

layer 5 neurons from primary motor cortex and premotor cortex from pyramidal tract

internal capsule(forebrain)

cerebral peduncle(midbrain)

projection thru medullary pyramids(gives names)

in brain stem pyramidal tract innervates:

-cranial nerves V, XII (tongue, pharynx, larynx)

-reticular formation

-red nucleus

Corticobulbar projection (cranial nerves) terminates ONLY in brainstem

Corticospinal projection innervates spinal cord

-pyramidal tract decussation

-->lateral corticospinal tract = 90% cross over

-->ventral(anterior) corticospinal tract = 10%

corticospinal tract

decussation(90%) is the reason why left side of brain controls right side of body and vice versa

lateral corticospinal tract controls distal extremities

-specialized direct connections for hand control

ventral tract controls proximal limbs

premotor cortex

indirect (via primary motor cortex) and direct control of movement

--> 30% of axons in corticospinal tract arise directly from premotor cortex

--> activity is relevant to sensory guidance of movement(e.g. cue predicts movement)

the extrapyramidal tracts

colliculospinal, reticulospinal, vestibulospinal (indirect pathways)

Function: involuntary reflexes and movement, and modulation of movement (i.e. coordination)

Called "extrapyramidal" to distinguish it from the tracts of the motor cortex that reach their targets by traveling thru the "pyramids" of the medulla