PNB Quiz Prep - PNS Sensation

What is the sensory division of the nervous system?

includes sensory receptors, neurons, and brain regions that receive and interpret incoming information

What is sensation?

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

What is perception?

the brain processes and assigns meaning to those sensory signals

What are special senses?

vision, hearing, gustation (taste), olfaction (smell), equilibrium (balance)

What are somatic senses?

touch, temperature, pain, itch, proprioception

What do special senses rely on?

specialized organs like the eyes and ear for precise information

What do somatic senses rely on?

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

What makes senses “special”

more complex neural pathways for interpreting the stimuli 

What is somatic stimuli?

muscle length, muscle tension, proprioception

What is subconscious processing?

somatic and visceral stimuli

What is visceral stimuli?

blood pressure, GI tract distension, blood glucose concentration, internal body temperature, osmolarity of body fluids, lung inflation, pH of cerebrospinal fluid and oxygen content of blood

What are receptors classified by?

the type of stimulus they detect 

What are the kinds of functional sensory receptors?

thermoreceptors, mechanoreceptors, nociceptors, photoreceptors, chemoreceptors

What are thermoreceptors?

detect temperature changes (hot vs. cold)

What are mechanoreceptors?

detect mechanical forces (touch, pressure, vibration, stretch in muscles and organs)

What are nociceptors?

detect pain (tissue damage or potentially harmful stimuli) 

What are photoreceptors?

detect light (found in the retina of the eye)

What are chemoreceptors?

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

What does each sensory receptor respond best to?

one specific type of stimulus (its adequate stimulus)

What occurs no matter how a sensory neuron is activated?

the brain interprets the signal as one sensory modality

What are location sensory receptors?

exteroceptors, interoceptors, proprioceptors

Where are exteroceptors located?

near the body surface 

What are exteroceptors?

detect external stimuli (touch, temp, vision, hearing, smell)

Where are interoceptors located?

internal organs and blood vessels

What are interoceptors?

monitor internal environment, most sensation are subconscious (blood pressure, GI stretch)

Where are proprioceptors located?

muscles, tendons, joints, and inner ear 

What are proprioceptors?

provide awareness of body position and movement (muscle stretch receptors)

What does loss of proprioception lead to?

poor balance and coordination, may rely on vision to move safely

What are possible causes of loss of proprioception?

aging, stress/fatigue, injury or disease

How can aging result in loss of proprioception?

reduced receptor sensitivity and slower neural processing 

How can stress/fatigue result in loss of proprioception?

can temporarily impair body awareness

What injury or disease can result in loss of proprioception?

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

What are structural sensory receptors?

free nerve endings, encapsulated receptors, rods and cones, hair cells

What are structural free nerve ending sensory receptors?

pain, temperature, some smell detection 

What are structural encapsulated sensory receptors?

touch, pressure

What are encapsulated receptors protected by?

connective tissue capsules for finer sensing

What are structural rods and cones sensory receptors?

vision, retina photoreceptors that sense light and color

What are structural hair cell sensory receptors?

hearing, equilibrium (vibrate or bend to detect sound and balance) 

What is a sensory unit?

a nueron and all of its receptors

What is a receptive field?

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

What is a receptor potential?

amplitude correlated with stimulus intensity

What category does a receptor potential fall under?

graded (synaptic) potential 

What is the problem with receptor potential?

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

What is recruitment?

stronger stimuli “call in” additional afferent (sensory) neurons

What does a more intense stimulus activate?

more sensory receptors, increasing the total number of signals sent to the CNS

What is the problem regarding graded signals?

fade over distance, must be converted to action potentials to reliably travel along the neuron to the brain or spinal cord 

What are tonic receptors?

slowly adapting, continue to respond thorughout a stimulus

What is an example of tonic receptors?

pain receptors keep signaling while the injury persists

What are phasic receptors?

rapidly adapting, respond only at the beginning of a stimulus

What is an example of phasic receptors?

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

What is desensitization?

decreased response to repeated or prolonged stimuli

What is an example of desensitization?

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

What are receptive fields?

unevenly distributed throughout the body

What is sensory discrimination?

the ability to detect and distinguish separate stimuli on the skin 

What is high discrimination?

small, densely packed receptor fields, can tell two points apart (ex. fingertips)

What is low discrimination?

large, sparse receptor fields, two points may feel like one (ex. back)

What is receptor density?

determines how precisely a stimulus can be located

Where are rods and cones found?

in the retina

What are cones?

high density in the fovea (center of the retina), provide sharp and detailed vision, and color

What are rods?

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

What is sensory implication?

areas with low or high receptor density

What are areas with high receptor density?

better spatial resolution 

What are areas with low receptor density?

poorer localization

What is overlap of receptive fields?

receptive fields of neighboring sensory neurons partially overlap

What does stimulus in overlapping region activate?

multiple neurons

What is functional significance?

improves accuracy of stimulus localization 

How does functional significance help the nervous system?

determines exact location by comparing input from multiple neurons

What is lateral inhibition?

mechanism where activated neurons inhibit neighboring neurons

How does lateral inhibition help the brain?

better tell exactly where the touch or signal is

What is the function of lateral inhibition?

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

What is presynaptic inhibition?

inhibition of a neuron’s neurotransmitter release at its axon terminal

What is the mechanism of presynaptic inhibition?

occurs at an axo-axonic synapse (axon synapses onto another axon)

What is the function of presynaptic inhibition?

reduces or modulates the signal sent to the postsyanptic neuron

What does presynaptic inhibition help fine-tune?

neural communication 

What are first-order neurons?

from peripheral tissue to CNS, usually entering the spinal cord or brainstem

What is the first-order neuron considered?

very first messenger that tells the nervous sytem “something just happened”

What are second-order neurons?

crosses over (decussates), brain processes signals from the opposite side of the body

Where are the synapses in second-order neurons?

in the thalamus 

What are third-order neurons?

cell body in thalamus, synapses in the somatosensory cortex

How does the thalamus relate to third-order neurons?

filters and directs the sensory signals

What are the three sensory pathway neurons?

first order, second order, third order neurons

What is the dorsal column associated with?

fine touch and proprioception 

What is the first-order neuron in the dorsal column pathway?

from peripheral tissue to spinal cord to medulla

What is the lower body of the first-order neuron in the dorsal column?

fasciculus gracilis

What is the upper body of the first-order neuron of the dorsal column?

fasciculus cuneatus

What are second-order neurons of the dorsal column pathway?

decussates (crosses over) in medulla 

Where do second-order neurons of the dorsal column pathway terminate?

in the thalamus

What are third-order neurons in the dorsal column pathway?

cell body in thalamus (signal filtering)

What do third-order neurons in the dorsal column pathway synapse?

in the somatosensory cortex

What does the spinothalamic pathway associate with?

pain and temperature

What are first-order neurons in the spinothalamic pathway?

from peripheral tissue to posterior gray horn of spinal cord

What are second-order neurons of the spinothalamic pathway?

decussates (crosses over) in spinal cord

Where do second-order neurons in the spinothalamic pathway terminate?

in the thalamus 

What are the three layers of the eye?

outer fibrous layer, intermediate vascular layer (uvea), deep nervous layer

What are parts of the outer fibrous layer?

sclera & cornea

What is the sclera?

white, protective layer

What is the cornea?

transparent, refracts light and helps focus it onto the retina

What are parts of the intermediate vascular layer (uvea)?

iris and choroid

What is the iris?

colored part of the eye; adjusts the size of the pupil to regulate how much light enters

What is the choroid?

vascular layer between the sclera and retina; supplies oxygen and nutrient to the retina