pns quiz

sensation

receptors convert (transduce) various stimuli into nerve impulses sent to the CNS

what does the sensory division of the nervous system include

sensory recptors

neurons

brain regions that receive and interpret incoming information

perception 

the brain processes and assigns meaning to those sensory signals 

what are special senses

vision

hearing

smelling (olfaction)

taste (gustation)

equilibrium (balance)

somatic senses

touch

temperature

pain

itch

proprioception

what do special senses rely on

specialized organs like the yes and ears for precise information 

what do somatic senses rely on

widespread receptors throughout the body to monitor general sensations like touch and pain

why are special senses special

highly specialized sensory organs

dedicated regions of the brain for processing

more complex neural pathways for interpreting the stimuli

somatic stimuli 

muscle length, muscle tension, proprioception 

visceral stimuli

blood pressure

Gi tract distension

lung inhalation

pH of cerebrospinal fluid

pH and oxygen content of blood

types of sensory transduction

functional, location, structure

types of stimulus receptors 

thermoreceptors

mechanoreceptors

nociceptors

photoreceptors

chemoreceptors

thermoreceptors

detect temperature changes (hot v cold)

mechanoreceptors

detect mechanical forces

(touch, pressure, vibration, STRETCH in muscles and organs)

example of mechanoreceptors 

muscle spindles monitor muscle stretch for posture and balance

nociceptors

detect pain

tissue damage or potentially harmful stimuli

photoreceptors

detect light

where are photoreceptors found

in the retina of the eye

rods

for low-light and peripheral vision 

cones

for color and sharp detail

chemoreceptors

detect chemical changes (o2, pH, molecules, taste)

what does each receptor respond best to

one specific type of stimulus; its adequate stimulus

what happens when a sensory neuron is stimulated

only ONE sensory modality will be perceived (only one type of receptor will be received)

sensory receptors: location classification

exteroceptors

interoceptors

proprioceptors

exteroceptors are located where

near the body surface

exteroceptors

detect external stimuli

examples of exteroceptors

touch, temp, vision, hearing, smell

interoceptors located where

in internal organs and blood vessels

interoceptors 

monitor internal environemts

most sensations are subconscious 

examples of interoceptors

blood pressure

GI stretch

proprioceptors located where

muscles, tendons, joints, and inner ear

proprioceptors 

provide awareness of body position and movement 

example of proprioceptors

muscle stretch receptors

loss of proprioception does what

leads to poor balance and coordiantion

may rely more on vision to move safely 

possible causes of proprioception

aging

stress/fatigue

injury or disease

aging - proprioception

reduced receptors sensitivity and slower neural processing

stress/fatigue - proprioception 

can temporarily impair body awareness 

injury or disease - proprioception

damage to nerves, joints, or inner ear (neuropathy)

sensory receptors: structural types

free nerve endings

encapsulated receptors

rods and cones

hair cells

free nerve endings - structural types

pain

temperature

some smell detection 

encapsulated receptors - structural types

touch 

pressure 

encapsulated receptors are protected by what

connective tissue capsules for finer sensing

rods & cones - structural types

vision

retina photoreceptors that sense light and color

hair cells - structural types

hearing

equillibrium

vibrate or bend to detect sound and balance

sensory unit

a neuron and all of its receptors

receptive field

the area or region that can be sensed by a sensory unit

receptor potential 

a type of graded (synaptic) potential 

amplitude correlates with stimulus intensity 

problems with receptor potential (l)

graded potential are local, but long-distance transmission requires action potentials

recruitment

stronger stimuli “call in” additional afferent neurons 

a more intense stimulus activates more sensory receptors, increasing the total number of signals sent to the CNS

spatial summation

problem with recruitment

graded potentials fade over distance, so they must be covered to action potentials to reliably travel along the neuron to the brain or spinal cord

step 1 of stimulus intensity 

receptor potential strength and duration vary with the stimulus

step 2 of stimulus intensity

receptor potential is integrated at the trigger zone

step 3 of stimulus intensity

frequency of action potentials is proportional to stimulus intensity. Duration of a series of action potentials is proportional to stimulus duration

step 4 of stimulus intensity 

neurotransmitter release varies with the pattern of action potentials arriving at the axon terminal 

tonic receptors

slowly adapting

continue to respond throughout the stimulus

example of tonic receptors

pain receptors keep signaling while the injury persist

phasic receptors

rapidly adapting

respond only at the beginning of a stimulus

example of phasic receptors

you feel your shirt when your first put it on, then stop noticing it

desensitization

decreased response to repeated or prolonged stimuli

example of desensitization

becoming less aware of a strong smell after being in the room for a while

receptor fields - sensory discrimination

unevenly distributed throughout the body

sensory discrimination 

the ability to detect and distinguish separate stimuli on the skin

high discrimination

small, densely packed receptor fields

high discrimination ex.

fingertips → can tell two points apart

low discrimination

large, sparse receptor fields

low discrimination ex.

back → two points may feel like one

receptor density

determines how precisely a stimulus can be located

where are rods and cones located

retina (w)

cones

high density in the fovea (center of retina) → sharp, detailed vision, for color

rods →

peak density in the peripheral retina → motion detection and low-light vision

sensory implication - rods & cones

areas w/ high receptor density → better spatial resolution

areas w/ low receptor density → poorer localization

overlap of receptive fields

receptive fields of neighboring sensory neurons partially overlap

what happens in overlapping regions

stimulus activates multiple neurons

functional significance

improves accuracy of stimulus localization 

what does functional significance help with

the nervous system determine exact location by comparing input from multiple neurons

lateral inhibition

mechanism where activated neurons inhibit neighboring neurons

what does lateral inhibitions help with 

telling your brain exactly where the touch or signal is

function of lateral inhibition

sharpens contrast in the pattern of action potentials sent to the cns

allows finer resolution of stimulus location

example of lateral inhibition

helps the brain precisely localize touch or visual stimuli 

step 1 of stimulus lateral inhibition

primary neuron response is proportional to stimulus strength

step 2 of stimulus lateral inhibition

pathway closest to the stimulus inhibits neighbors 

step 3 of stimulus lateral inhibition

inhibition of lateral neurons enhances perception of stimulus

presynaptic inhibition

inhibitor of a neurons neurotransmitter release at its axon terminal

mechanism of presynaptic inhibition 

occurs at an axon-axonic synapse (2 neurons synapsing onto another axon)

function 1 of presynaptic inhibition

reduces or modulates the signal sent to the postsynaptic neuron

function 2 of presynaptic inhibition

helps fine-tune neural communication

sensory pathways have how many neurons chain

3

step 1 of presynaptic inhibition

action potential arrives

step 2 of presynaptic inhibition

less calcium enter

step 3 of presynaptic inhibition

less neurotransmitter released

step 4 of presynaptic inhibition

reduced effect on postsynaptic membrane

1st order neuron where

spinal cord (right side)

what are the two parts of the 1st order neuron

fasiculus gracilis - lower body

fasiculus cuneatus - upper body

first order neuron

from peripheral tissues → spinal cord → medulla

very first messenger that tells the nervous system “something just happened)

second-order neuron

cross over (decussates)

brain processes signals from the opposite side of the body

synapses in the thalamus

where does the 2nd order neuron originate from

medulla (right side)

where does the 2nd order neuron desucatte or synapse to

thalamus (left side)

third-order neuron

cell body in thalamus

synapses in the somatosensory cortex

perception

third-order neuron thalamus

filters and directs the sensory signals

where does the 3rd order neuron originate from 

thalamus