Peripheral nervous system

sensation

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

Perception

the brain processes and assigns meaning to those sensory signals

special senses

vision, hearing, taste, smell, equilibrium

somatic sensory 

touch, temp, pain, itch, proprioception

Somatic stimuli (subconscious processing)

Muscle, proprioception

Visceral Stimuli

Equilbrium (blood pressure), breathing, pH

Thermoreceptors

detects temperature changes

mechanoreceptors

detects mechanical forces (touch, pressure, vibration, stretch)

Nociceptors

detects pain

Photoreceptors

detects light, rods for low-light and peripheral, cones for color and sharp detail

chemoreceptors

detects chemical changes

exteroceptors

external

interoceptors

internal

proprioceptors

body position

loss of proprioception

aging, stress, injury

free nerve ending

pain, temp, smell

encapsulated

touch, pressure

Rods and cones

sight

hair cells

hearing, equilibrium

sensory unit

a neuron and all its receptors

receptive field

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

receptor potential

a type of graded potential, amplitude correlates, with stimulus intensity 

receptor potential problem

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

Recruitment

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

Tonic Receptor 

slowly adapting, aware of it for a long time, 

phasic receptor 

rapidly adapting

desensitization

decreased response to repeated or prolonged stimuli

receptor field

unevenly disturbed throughout the body

sensory discrimination

the ability to detect and distinguish separate stimuli on the skin

High discrimination

small, densely packed receptor fields, can tell two points apart

low discrimination

large, sparse receptor fields, two points may feel like one

receptor capacity

determines how precisely a stimulus can be located

cones

high density of fovea, sharp detailed vision

rods

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

overlap of receptor fields

stimulus in overlapping region activates multiple neurons

functional importance of overlap

helps nervous system determine exact location

lateral inhibition

activated neurons inhibit neighboring neurons, finer resolution of stimulus location

presynaptic inhibition mechanism

one axon synapse onto another axon

presynaptic inhibition function

reduce or modulates the signal sent to the postsynaptic neuron, fine-tune

sensory pathways (first-order)

peripheral tissue to CNS, enters the spinal cord or brainstem

sensory pathways (second-order)

decussation occurs, synapse at the thalamus

sensory pathways (third-order)

cell body in thalamus, filters and directs the sensory signals, synapse in the somatosensory cortex

Dorsal Column pathway

fine touch & proprioception

lower body

fasciculus gracilis

upper body

fasciculus cunteatus 

dorsal column pathway (second-order)

decussates in the medulla, terminates in the thalamus

dorsal column pathway (third-order)

cell body in the thalamus, synapse in the somatosensory cortex

spinothalamic pathway

pain and temperature

spinothalamic pathway first order neuron

peripheral tissue to dorsal grey horn of spinal cord

spinothalamic (second order neuron)

decussates in spinal cord, terminates in the thalamus

spinothalamic pathway (third-order neuron)

cell body in thalamus, synapses in the somatosensory cortex

sclera (outer)

white, protective layer

cornea (outer)

transparent, refracts light

iris (intermediate)

controls pupil size

choroid (intermediate)

provides blood supply to retina

retina

contains photoreceptors

myopia

nearsightedness, elongation of eyeball

hyperopia

far-sightedness, short eyeball

bipolar cells

transmits signal from photoreceptors to ganglion cells

lateral ganglion cell axons

stay on same side

medial ganglion cell axons

crosses over at optic chiasm

thalamus

ganglion cell synapses to primary visual cortex

external ear

conducts sound waves to the middle ear

middle ear

converts sound waves into mechanical vibrations

ossicles 

malleus, incus, stapes

inner ear

detect pitch and amplitude, cochlea and vestibular apparatus