module 10 sensation and perception

PNS

outside of brain and spinal cord

divided into sensory and motor divisions

sensory NS

division of NS that consists of sensory receptors, neurons, and the parts of the brain that receive and assign meaning to information

peripheral ---> central

sensation

due to receptors sending different stimuli into nerve impulses that are conducted into the CNS

perception

integration of sensory information within the brain

sensory divisions

general (somatic) senses and special senses

general (somatic) senses

touch, pain, vibration, pressure, temperature

have similar mechanisms

special senses

vision, smell, hearing, taste

have unique receptors and pathways

transduction

sending signals from receptor to CNS

functional classification of sensory receptors

classified based on their adequate stimulus or modality

only one modality is perceived

thermo, mechano, noci, photo, chemo

thermoreceptors

respond to temperature changes

mechanoreceptors

respond to mechanical or pressure changes by stretching

nocireceptors

aka pain receptors

respond to physical tissue damage

photoreceptors

respond to photons in light

chemoreceptors

respond to chemicals

ex: Ca2+ receptors in parathyroid gland

location of sensory receptors

exteroceptors, interoceptors, proprioceptors

exteroceptors

provide information about the external environment

ex: warm temp in a room

interoceptors

provide information about the internal environment

ex: pressure or chemicals within the body

proprioceptors

provide information about the position of the body in space

located in muscles and joints

loss of proprioception

lack of awareness, balance issues

can be caused by stress or aging

structural classification of sensory receptors

all located on dendritic ends of neurons but vary in structure

free, encapsulated, rods/cones, hair cells

free sensory receptors

embedded in tissue

pain, temperature, smell

encapsulated sensory receptors

enclosed in connective tissue

touch, pressure

rods / cones

receptor cells for sight

rods are outside fovea and cones are inside fovea

hair cells

receptor cells for hearing and equilibrium

sensory unit

a single afferent neuron and all of its receptors on its dendrites

receptive field

the area that can be sensed by a sensory unit

receptor potential

graded potential in a sensory neuron

information is encoded in EPSPs which must reach threshold to fire action potentials in order to reach CNS for perception

stimulus intensity coding

temporal and spatial summation increase the number of action potentials fired, more NTs are sent to CNS, intensity of perception is increased

recruitment

another name for spatial summation

neighboring neurons can be called in to help stronger stimuli reach CNS

sensory adaptation

desensitization to repeated or prolonged stimuli

slow or fast

tonic receptors

slowly adapt to repeated or prolonged stimuli

action potentials slow down over time but do not completely stop

ex: pain receptors

phasic receptors

rapidly adapt to repeated or prolonged stimuli

receptors stop initiating action potentials over time and perception stops

sensory discrimination

receptors and receptor field vary in size and number throughout body

cause varying abilities to pinpoint stimuli

inverse relationship between field size and ability to discriminate between two points throughout body

presynaptic inhibition

presynaptic neuron is blocked from synapsing with a postsynaptic neuron

lateral inhibition

neuron most affected by stimulus blocks the pathways of neighboring neurons

sharpens contrast and allows us to localize sensation

axo-axonic synapse

synapse between two axon terminals

GABA

major inhibitory neurotransmitter

afferent sensory pathways

first order neuron: has receptors in peripheral tissue, synapses on second order neuron

second order neuron: crosses to other side of body, synapses in the thalamus

third order neuron: cell body in thalamus, synapses in somatosensory complex

dorsal column pathway

controls fine touch and proprioception

first order neuron: has receptors in peripheral tissue, moves through spinal cord through two tracts, terminates in medulla, synapses on second order neuron

second order neuron: crosses to other side of body, synapses in the thalamus

third order neuron: cell body in thalamus, synapses in somatosensory complex

fasciculus gracilis

dorsal column lower body tract

fasciculus cuneatus

dorsal column upper body tract

spinothalamic pathway

first order neuron: has receptors in peripheral tissue, moves through spinal cord, terminates in posterior grey horn, synapses on second order neuron

second order neuron: cell body in posterior grey horn, crosses to other side of body, synapses in the thalamus

third order neuron: cell body in thalamus, synapses in somatosensory complex

three layers of the eye

outer fibrous layer, intermediate vascular layer, deep nervous layer

outer fibrous layer

sclera (white) and cornea (clear connective tissue through which light travels)

intermediate vascular layer

iris (color) and choroid (nourishment)

deep nervous layer

retina (contains photoreceptors)

path of light

cornea, aqueous humor (anterior), pupil, lens, vitreous humor (posterior), fovea (highest density of photoreceptors)

myopia

lens is too bulged

focal point is anterior to fovea

nearsightedness

can be fixed with flat or convex glasses

hyperopia

lens is too flat

focal point is posterior to fovea

farsightedness

can be fixed with concave glasses

neurons of the retina

rods/cones, bipolar cells, horizontal/amacrine cells, ganglion cells

bipolar cells

synapse between photoreceptors and ganglion cells

horizontal / amacrine cells

integrate info from multiple photoreceptors on the way to ganglion cells

ganglion cells

dendritic ends synapse with bipolar cells

axons form optic nerve

blind spot

the point in the eye at which no receptor cells are located

eye to brain pathway

lateral and medial retinas ---> thalamus ---> primary visual cortex of the occipital lobe

lateral ganglion axons

stay on same side of brain

temporal (lateral) retina

innermost part of our field of vision

medial ganglion axons

cross over to opposite side of brain through optic chiasma

nasal (medial) retina

outermost part of our field of vision

optic chiasma

close to pituitary gland

tumors may press on crossing fibers, causing us to lose vision from medial retina

external ear

sound wave conduction into head

auricle, external auditory meatus

middle ear

sound waves converted to mechanical vibrations

ossicles, oval window, tympanic cavity, tympanic membrane (eardrum)

inner ear

specialize receptors detect pitch and amplitude

sends info through vestibular cochlear nerve

ear process

stapes vibrates perilymph, fluid displaces basilar membrane, vibrates ciliated receptor cells, stimulates cochlear nerve

pitch

determined by which region of the basilar membrane is displaced when wavelength comes into ear