Sensory Receptors and the PNS

what does incoming sensory influence determine

activity and output of our CNS

how does sensory information get into our system?

sensory stimulus is picked up by a sensory receptor

sensory receptor def

specialized cell that detects specific kinds of stimuli

what do sensory receptors produce

an electric response

what are sensory receptors NOT 

neurons or glia 

two main locations of sensory receptors

• at body’s surface to detect external stimuli

• within the body to monitor internal organ functions 

common way to classify sensory receptors

by adequate stimulus

adequate stimulus

the type of stimulus to which a given sensory receptor is most sensitive 

5 types of adequate stimuli

• chemoreceptors

• photoreceptors

• thermoreceptors

• mechanoreceptors 

• nociceptors

what do chemoreceptors respond to

chemicals

what do photorecepotrs respond to

light

what do thermoreceptors respond to 

temperature 

what do mecahnoreceptors respond to 

physical deformation 

what do nociceptors respond to

pain

3 general parts of all receptors

1. receptive area

2. area rich in mitochondria

3. synaptic area 

what happens in the synaptic area 

where a receptor’s message is passed toward or into CNS 

what must receptors do in order for the mesage to be passed to the brain 

must transduce a physical stimulus into an electrical signal (called a receptor potential) 

receptor potential 

a graded, local, electrical response of a sensory receptor 

how does transduction occur

by the opening and closing of ion channels

what causes electrical signals

shift inions across a sensory receptor cell membrane

what do neurotransmitters cause in synaptic membranes 

cause opening or closing of ion channels in postsynaptic membranes 

what does adequate stimuli cause in sensory receptors 

opening or closing of ion channels 

all sensory receptors produce _______ potentials, but some do not produce ____________ potentials 

receptor, generator 

what are receptor potentials

focally produced inputs to a sensory receptor cell that spread electronically

two results of receptor potential 

• NT release into the next cell

• receptor cells can propagate an electrical signal in the form of an action potential 

what is a receptor potential called when it propogates an action potential 

generator potential 

2 main divisions of sensory system 

1. somatosensory 

2. special sensory 

somatosensory system 

sensations experienced by the skin and subcutaneous tissue 

3 divisions of somatosensory system

1. tactile

2. proprioception

3. pain and temp 

special sensory deef

sensations experienced by the special senosry strcutures

5 main special sensory structures

• vision 

• hearing 

• smell 

• taste

• balance 

5 general processes of somatosensation

1. sensory stimuli is 

2. picked up by a specialized sensory receptor where stimulus is transduced into an electrical impusle

3. receptor potential and sometimes also an action potential

4. information travles toward the CNS via the peripheral process of a pseudounipolar sensory neuron whose cell body is in the dorsal root ganglion 

5. central prcess of pseudounipolar sensory neuron then transmits information to other parts of the CNS via various pathways and synapses

different cutaneous receptors

1. pacinian copuscle

2. meissner corpuscle

3. ruffini ending

4. endings around hairs 

5. merkel endings

6. free nerve ending 

cutaneous receptor distribution

not evenly distributed throughout our body

what does a higher density of cutaneous receptors mean 

leads to better tactile discrimination 

how does one measure tactile discrimination

2 point discrimination: minimum distance needed to detect 2 closely spaced points as separate

better tactile discrimination =

better 2-point discriination value

receptive fields def 

particular locations on our bodies where application of an adequate stimulus causes a receptor to respond

mapping of receptive field

can be spatially mapped in CNS

areas with better tactile discrimination have better 

cortical representation 

types of nociceptors 

some are modality specific while some are polymodal 

why is pain useful

warns of danger or damage

axon reflex

in response to tissue damage, nociceptor fibers can send APs toward the CNS and back toward sensory endings to cause release of neurotransmitters to heal the wound 

congenital insensitivity to pain 

children born without the ability to perceive pain 

anhidrosis

inability to sweat

hyperalgesia/sensitization

enhancement of the sensoation of pain

hyperalgesia results from 

results from tissue damage and the release of many chemicals that activate nociceptors or activate their thresholds 

phantom limb pain 

the experience of pain emerging from an amputated limb 

neuralgia

severe persistent pain in the distribution of a cranialor spinal nerve 

muscle spindles def

sensory receptors that detect stretch in striated muscles 

what are muscle spindles attached to and why 

ordinary muscle fibers so they stretch when the muscle stretches 

communication of muscle spindles 

send signals to our CNS and allow us to detect both length of muscle and rate of length change 

what do muscle spindles contribute to

proprioception

proprioception def

knowing where our body is in space wito9ut seeing it (aka position sense) 

what do golgi tendon organs (GTOs) sense

detect muscle tension

where are GTOs located

junnctions between muscles and tendons

what do GTOs detect and monitor

muscle tension as a result of muscle contraction

joint recepotrs

joints have free nerve endings as well as receptors similair to GTOs 

what do we call sensory receptors in joints

joint receptors

what do joint receptors detect

joint position (proprioception) ad movement (kinesthesia)

what detects proprioception 

joint receptors and muscle spindles 

3 types of sensory receptors in viscera 

1. mechanoreceptors

2. chemoreceptors

3. nociceptors 

mechanoreceptors in viscera

stimulated by pressure

chemoreceptors in viscera

stimulated by changes in blood gases or pH

nociceptors in viscera

stimulated by distentsion, damage, and disease

peripheral nerves are surrounded by 3 components 

1. epineurium

2. perineurium

3. endoneurium 

epineurium 

dense, loose connective layer enclosing each peripheral nerve; continuous with dura mater

perineurium

lies within epineurium, sheath of connective tissue continuous with arachnoid enclosing each bundle of nerve fibers

endoneurium

loose, delicate connective tissue layer within the perineurium in which individual nerve fibers are enclosed