Nervous 4 & Sensory 1

dorsal root ganglia

sensory, always unipolar; a cluster of sensory neuron cell bodies located in the dorsal root of a spinal nerve, just outside the spinal cord

terminal ganglia

regulate homeostatic functions

receive autonomic signals from CNS (not somatic, not voluntary)

there are ___ pairs of spinal nerves

31

sensory spinal nerves connect on___

the dorsal side

motor branches of spinal nerves connect on___

the ventral side

nerve plexus

networks of nerves arising from different spinal nerves that are reorganized to form systemic nerves

functions: redundancy (in injury reduce impacts of function loss), developmental patterns (arise for more complex structures)

cervical plexus

formed from nerves C1–C4, mostly innervates posterior neck and head

ex: phrenic nerve innervates diaphragm

brachial plexus

formed from nerves C5-T1

ex: radial, ulnar, median nerves innervate the arm

lumbar plexus

formed from nerves T12 & L1–L5, innervate hips and anterior legs

ex: femoral → saphenous nerve innervates anterior lower leg

sacral plexus

formed from nerves L4–L5 & S1–S4

ex: tibial nerve + fibular nerve = sciatic nerve

sciatica

pain resulting from compression/irritation of sciatic/tibial/fibular nerves

T2-T11 spinal nerves are not plexi, but are systemic nerves and innervate___

skin and muscles around ribs

sensation

activation of sensory receptor cells by stimuli, detection of stimuli at the cellular level

perception

central processing of sensation into a meaningful pattern, detection of stimuli at the conscious level

transduction

translation of a stimulus into an electrical signal in a sensory receptor cell

influenced by: type of stimulus, structure of the sensory receptor cell, position of the sensory receptor cell relative to stimulus, function of the sensory receptor cell

chemical stimuli

ions/macromolecules interact with transmembrane receptor proteins

e.g., smell, taste

physical stimuli

physical changes that cause changes in cell potential

e.g., balance, hearing, pain, temperature, touch

electromagnetic stimuli

electromagnetic radiation that cause changes in cell potential

only vision in humans, many varieties in other animals

receptor cells (sensory neurons)

cells that detect stimuli by transducing stimuli from internal or external environment into electrical signals

categorized by structure, position relative to stimulus, function

receptor cells structure→free dendrites

less precise, more versatile

e.g., pain, temperature

receptor cells structure→encapsulated dendrites

greater specificity and spatial resolution

e.g., complex touch (vibration, texture)

receptor cell structure→specialized

neither encapsulated or free dendrites, may be hard to recognize as neuron

receptor cells function→chemoreceptor

chemical stimuli

receptor cells function→osmoreceptor

solute concentration of bodily fluids

receptor cells function→nociceptor

chemicals associated with tissue damage, results in pain signals

receptor cells function→mechanoreceptor

physical stimuli (pressure, vibration)

receptor cells function→thermoreceptor

temperature

sensory modality

how sensory information is encoded

type of stimulus + type of receptor cell + neural/cortical processing pathway

general sensory modalities

receptor cells are distributed throughout the body

ex: itch, pain, pressure, temperature, vibration

specialized sensory modalities

receptor cells are localized to specialized organs/structure

ex: balance, hearing, scent, taste, vision

chemical sensory modalities

olfaction (smell), gustation (taste)

physical sensory modalities

audition (hearing), somatosensation (touch)

electromagnetic sensory modalities

vision

three layers of eye

fibrous tunic (sclera, cornea), vascular tunic (choroid, iris), neural tunic (retina)

fibrous tunic

sclera, cornea; protection

vascular tunic

choroid – provides blood supply

ciliary body – ciliary muscle (bends lens) + epithelium (secretes aqueous humor)

iris – muscle for controlling size of pupil

neural tunic

retina – nervous tissue with photoreceptors

anterior cavity of eye

contains aqueous humor

nutrient/waste transport for avascular tissues (lens, cornea)

pressure regulation

posterior cavity of eye

contains vitreous humor

maintain shape

stabilizes retina

normal vision

light is focused directly on the retina

nearsightedness

visual image is focused in front of retina (distant objects blurry)

farsightedness

visual image is focused behind the retina (close objects blurry)

cone photoreceptor

light color

rod photoreceptor

light intensity

opsin

transmembrane proteins with retinal molecule

photoisomerization

change in physical structure of opsin due to transduction of visual signal→opsins no longer detect light

cellular processes continually reverting opsins to original structure so they can detect it again

transduction of visual signal

photons strike retinal molecule → opsin triggers chemical signal for light/vision→ opsin no longer light receptive → cellular processes revert opsin back to light recepting original structure