NSC 4354 FINAL EXAM REVIEW

what is included in the sensory systems?

1) Sensory receptor cells- receive stimuli from external/internal environment

2) Neural pathways (afferent)- conduct sensory information from receptors to brain/spinal cord

3) Brain- processes information

5 qualities of information to encode:

- modality

- intensity

- duration

- location

- salience

5 factors that influence success/failure:

- fatigue

- adaptation

- sensitization

- overlap/redundancy

- damage/overload

receptive field

area of skin innervated by branches of the somatic afferent fiber

large receptive field

areas where receptor density is low; covers wide area on skin

small receptive fields

areas where receptor density is high; covers small area on skin

two point threshold

the minimum interstimulus distance required to perceive two simultaneously applied stimuli as distinct

somatosensation: TOUCH

- stimuli = fine touch, pressure, vibration, stretch

- receptor = mechanoreceptor

Meissner corpuscle

- sensory function: motion detection, grip control

- effective stimuli: skin motion

- location: most superficial, dermal papillae

- slow adapting afferents -> spatial attributes (size and shape)

- small receptive fields

Merkel cell-neurite complex

- sensory function: shape, texture

- effective stimuli: edges, points, corners, curvature

- location: borders between dermis and epidermis

- rapidly adapting afferents -> changes in stimulation

- small receptive fields

Ruffini corpuscle

- sensory function: tangential force, hand shape, motion, direction

- effective stimuli: skin stretch

- location: dermis

- slow adapting afferents -> spatial attributes (size and shape)

- large receptive fields

Pacinian corpuscle

- sensory function: perception of distant events through transmitted vibrations; tool use

- effective stimuli: vibration

- location: dermis and deeper tissues

- rapidly adapting afferents -> changes in stimulation

- large receptive fields

what receptors can detect touch?

Merkel, Meissner, Pacinian, and Ruffini cells

what afferent axon type does touch have?

- Aβ

- myelinated

what is the pathway for unipolar neurons?

sensory neuron = 1st order neuron

cell body in dorsal root ganglion (DRG)

enters dorsal horn of spinal cord

dermatomes

area of skin innervated by afferent nerve fibers from single dorsal root of spinal nerve

dorsal column - medial lemniscus pathway (neurons + axons)

1st order neuron enters dorsal horn of spinal cord

1st order axons from upper limbs = fasciculus cuneatus (cuneate tract) -cervical spinal cord-

1st order axons from lower limbs = fasciculus gracilis (gracile tract) -lumbar spinal cord-

dorsal column - medial lemniscus pathway

1st order neuron travels ipsilaterally to medulla -> synapses w/ 2nd order neurons @ gracile and cuneate nucleus

2nd order neuron decussates in the medulla @ medial lemniscus

2nd order neuron synapses in contralateral thalamus (ventral posterior lateral complex; VPL)

3rd order neurons travel through the internal capsule and synapse on the primary somatosensory cortex

homunculus

distortion due to amount of information and density of receptors

dorsal trigeminothalamic tract (DTTTr)

1st order neuron = trigeminal nerve (5)

1st order neuron synapses in principal nucleus of trigeminal complex

decussates immediately

2nd order neuron synapses in contralateral thalamus (VPM)

somatosensation: PROPRIOCEPTION

- stimuli = information about the position of the body parts in space (internal)

- receptor = proprioceptor

mechanoreceptors

large muscles for coarse movements have few spindles, while extraocular muscles (eye movements) and muscles in neck and hand have many spindles -> require precise control

what receptors detects proprioception?

muscle spindle

what afferent axon type does proprioception have?

Aα, Ia, II

group II afferents

- found in intrafusal muscle fiber

- respond to static limb position (sustained stretch)

muscle spindle = muscle length

group Ia afferents

- found in intrafusal muscle fiber

- largest myelinated sensory axons

- respond to changes in muscle length (stretch)

- respond to velocity and direction of movement

muscle spindle = muscle length

group Ib afferents

- found in golgi tendon organ

- respond to muscle tension

golgi tendon organ = muscle tension

somatosensation: NOCICEPTION

- stimuli = temperature and/or pain

- receptor = nociceptor

what receptors detects nociception (pain, temperature, itch)?

free nerve endings

what afferent axon type does nociception have?

Aδ, C

types of nociception

first pain

- sharp initial pain

- due to activation of Aδ fibers

second pain

- delayed, diffuse, longer-lasting pain

- due to activation of C fibers

anterolateral system

aka spinothalamic tract

- 1st order neuron synapses @ the ipsilateral dorsal form

- 2nd order neurons begin

-> Aδ fibers synapse @ lamina 1 + 5

-> C fibers synapses @ lamina 2

- anterior white commissure (connection)

referred pain

pain perceived at a location other than the site of the actual stimulus.

convergent inputs from various tissues at the same segment of the spinal cord.

anterolateral system pathway

1st order neuron synapses in dorsal horn

2nd order neuron synapses in thalamus (VPL)

3rd order neuron synapses in the primary somatosensory cortex

ventral trigeminothalamic tract

1st order neuron enters pons -> descends -> synapses in trigeminal complex (medulla)

2nd order neuron synapses in thalamus (VPM)

3rd order neuron synapses in the primary somatosensory cortex

nucleus of spinal tract

midbrain to C2

emmetropia

normal vision

myopia

nearsightedness

hyperopia

farsightedness

organs of the eye

aqueous humor in anterior chamber

ciliary muscle (ciliary body = muscle + process)

choroid

- uveal layer

->choroid: capillaries + melanin

->ciliary body

->iris (colored portion of the eye)

--> 2 muscles -> constrict/dilate pupil

retina (converts light stimulus to neural impulses)

pupil

posterior chamber

accommodation

dynamic changes in the refractive power in the lens

(the eye accommodates for close vision by tightening the ciliary muscles, allowing the pliable crystalline lens to become more rounded)

visual system

stimulus: light

receptor: photoreceptor

phototransduction

conversion of light into electrical signals

photoreceptors

rods and cones are distinguished by:

- shape (gives them their name)

- sensitivity to light

- photopigment they use

- distribution across the retina

- pattern of synaptic connection

scotopic vision

rod-mediated vision, which predominates in dim light.

photopic vision

cone-mediated vision, which predominates when lighting is good

luminance

light intensity

wavelengths

the different energies represented in the electromagnetic spectrum

Ishihara test

test for color blindness

color blindness

trichromacy = normal trichromatic color vision

anomalous trichromacy

- most common form of color blindness

- 8% of males (and much fewer women) are "color blind"

- "faulty" trichromatic vision

- red/green or blue/yellow

protanopia - loss of long (red) wavelength perception

deuteranopia - loss of medium (green) wavelength perception (most common form of anomalous trichromatism)

BOTH PROTANOPES AND DEUTERANOPES HAVE DIFFICULTY TO DISTINGUISH RED AND GREEN (RED-GREEN BLINDNESS)

tritanopia - extremely rare, deficiency in short wavelengths = blue-yellow blindness

genetics of color blindess

inherited failure to make one or more of the cone pigments, or from changes in the sensitivity of the pigment(s).

genes for red (L) and green (M) pigments are very similar and they lie adjacent to each on the X-chromosome (explains high prevalence of red-green blindness)

macular degeneration

loss of vision in the center of the visual field (the macula) b/c of damage to the retina.

- difficulty to read/recognize faces

- peripheral vision remains

"dry" form (90% of all cases), debris between the retina and the choroid -> disappearance of the retinal pigment epithelium and loss of photoreceptors.

"wet" form (more severe), blood vessels grow from the choroid, and the retina can also become detached.

treated w/ laser coagulation and medication to stop the growth of blood vessels.

retina

horizontal and amacrine cells enable interactions between photoreceptors and bipolar cells -> maintain contrast over different light intensities (luminance)

xanthophyll

yellow pigment

scotoma

blind spot

dorsal stream

where pathway

parvocellular layers

ventral stream

what pathway

magnocellular layers

lateral geniculate nucleus: MAGNOCELLULAR

- large receptive fields

- faster conduction velocity

- cannot transmit color information

- insensitive to differences in wavelength of light

- respond to presentation of visual stimuli

- high temporal resolution

- damage -> reduces ability to perceive rapidly changing stimuli (location, speed, direction of a rapidly moving object)

lateral geniculate nucleus: PARVOCELLULAR

- small receptive fields

- slower conduction velocity

- transmits color information

- sensitive to differences in wavelength of light

- high spatial resolution (shape/size/color)

- damage -> impairs visual acuity and color perception

pupillary light reflex

afferent nerve: optic nerve (CN II)

efferent nerve: oculomotor nerve (CN III)

effect: miosis of ipsilateral eye; consensual response in contralateral eye

sound

pressure waves generated by vibrating air molecules

sound waves propagate in three dimensions

frequency

(cycles per second, Hertz, Hz) -> pitch

humans hear frequency range between 20 Hz to 20 KHz

external ear

pinna

concha

e. auditory meatus

function of the external ear

to gather sound and focus it on the eardrum (tympanic membrane)

middle ear

3 ossicles:

- malleus

- incus

- stapes

function of the middle ear

to amplify sound onto the oval window

eardrum

boosts sound pressure 30-100-fold

ossicles

malleus, incus, stapes

lever action of 3 ossicles increases air pressure onto oval window

muscles in the eye

contract in response to loud sounds -> stiffens movement of ossicles

stapedius muscle: smallest skeletal muscle connected to stapes

tensor tympani muscle: connected malleus

inner ear

cochlea

function of the inner ear

converts sound waves to neural impulses analyzes frequency

hair cells

arranged in height and bilaterally symmetrical

the shear on the hair cells pulls on the tip links to open non-selective cation channels (permeable to K+ and Ca2+), leading to hair cell depolarization.

depolarization opens voltage-dependent calcium channels at the synaptic basal pole of the cell.

- triggers vesicle exocytosis and glutamate release

- induces action potentials in auditory nerves

organ of corti

INNER HAIR CELLS (3,500)

- receptors for hearing constitute 95% of auditory nerve

OUTER HAIR CELLS (12.000)

- receive efferents from brain -> amplify the traveling wave

sound induced vibration

the basilar me mbrane pushes the hair cells against the tectorial membrane as perilymphatic pressure waves pass.

vertical motion of the traveling wave long the basilar membrane induces a shearing motion between the basilar membrane and the tectorial membrane -> bends stereocilia on the hair cells, causing hyper- or depolarization

tonotopy

topographical mapping of frequencies along the basilar membrane.

the membrane and auditory nerve fibers are tuned to specific frequencies.

basal end is narrow and stiff -->

responds (vibrates) well to high frequency sounds

apical end is wide and flexible -->

responds best to low frequency sounds

coincidence detectors

interaural time differences (ITD)

- below 1.6 kHz

interaural intensity/level differences (ILD)

- above 1.6 kHz

midbrain auditory center

auditory space map

sound duration

frequency of sound

mid-pons

coincidence detection

conductive hearing loss

disturbance in sound conduction from outer and/or middle ear to inner ear

loss/reduction in sensitive to air conducted sound

- e.g. ear wax, damage to tympanic membrane and/or ossicles, fluid in middle ear

nerve/sensorineural deafness

damage to auditory nerve and/or hair cells

loss/reduction in sensitive to both air conducted and bone conducted sound

- e.g. repeated exposure to loud noise, drugs, presbycusis, viral

central deafness

relatively rare due to bilaterality of auditory pathways

difficult to detect and treat

weber test

tuning fork placed on top of head equidistant from both ears

tests both ear simultaneously

normal- sound heard equally on both sides

conduction deafness- affected ear will hear louder

sensorineural deafness- normal ear will hear louder

rinne test

tuning fork placed on mastoid process

-> sound no longer heard

-> place in front of ear

-> sound no longer heard

tests one ear at a time

normal- sound heard in front of ear (AC > BC)

conduction deafness- do not hear sound in front of ear (BC > AC)

sensorineural deafness- not tested

functions of the vestibular system

perception of self-motion

head position

spatial orientation relative to gravity

motor functions

stabilize gaze, head, posture

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

components of the vestibular system

the vestibular apparatus/labyrinth

- 2 otolith organs (utricle and saccule)

- 3 semicircular canals

3 parts of the semicircular canals

anterior, lateral, and posterior canals

where are the semicircular canals located?

- on the other side of the vestibule from the cochlea

- in the labyrinth

what are the 3 organs in the labyrinth?

semicircular canals, saccule, utricle

motion in the labyrinth is due to?

otolith: linear acceleration of head & static head position relative to gravity

semicircular canals: rotational acceleration of head

hair cells in the 3 organs are...

selective for certain directions

depolarization in hair cells leads to...

Ca2+ influx

hyperpolarization in hair cells leads to...

less Ca2+ influx

perilymph

fluid within the labyrinth of the inner ear; allows us to detect which direction

- depolarization lead to Ca2+ influx

- hyperpolarization lead to less Ca2+ influx

- low K+

endolymph

fluid within the labyrinth of the inner ear

- normal extracellular conditions

- high K+

- mechanically-gated K+ channels open

otoconia

tiny calcium carbonate stones in the ear that provide inertial mass for the otolith organs, enabling them to sense gravity and linear acceleration

- sits on top of otolithic membrane

stereocilia of hair cells

fiber bundle

- arranged in height order

- embedded in otolithic membrane (gelatinous material)

cochlea is to ______________ as otolith is to _________.

- organ of Corti

- macula

utricular macula

orientation: horizontal

senses: horizontal movement (head tilt F/B, linear acceleration)

- longest cilia face each other