BIO120 UNIT 5

sensation

conscious awareness of stimulus

perception

interpretation and conscious awareness of sensory input

somatosensory receptor stimuli

specialized sensory nerves that respond to various stimuli, including vision, hearing, taste, and smell

• located in skin and internal organs

mechanoreceptors

pressure, stretch, and vibration stimulus

• ex. merkel disks

nociceptors

painful stimuli

• ex. free nerve endings

thermoreceptors

temperature changes

• ex. free nerve endings

photoreceptors

light stimulus

• ex. rods and cones in retina

chemoreceptors

chemical (smell, taste) stimuli

• ex. olfactory and gustatory cells

primary neuron

somatic sensory receptor (PNS) to spinal cord (CNS)

secondary neuron

spinal cord to thalamus

tertiary neuron

thalamus to primary somatosensory cortex

anterolateral spinothalamic

function: pain, temp, crude touch

decussation: spinal cord

destination: primary somatosensory cortex

dorsal column medial lemniscus (DCML)

function: fine touch, pressure, vibration

decussation: medulla oblongata

destination: primary somatosensory cortex

spinocerebellar

function: proprioception to cerebellum (unconscious)

decussation: none (ipsilateral)

destination: cerebellum

trigeminothalamic

function: sensory input from face

decussation: brainstem

destination: primary somatosensory cortex

upper nerve neurons

nerve cells within the brain and spinal cord that initiate and modulate movement

• primary motor cortex to spinal cord

lower motor neuron

the final common pathway for motor signals from the central nervous system to muscles

• spinal cord to skeletal muscle

corticospinal

function: voluntary control of limb (lateral) and axial (anterior) muscles

decussation: lateral in medulla and anterior in spinal cord

medullary route: pyramidal

corticobulbar

function: voluntary facial muscle control

decussation: brainstem (midbrain, pons, and medulla)

medullary route: pyramidal

rubrospinal

function: semi-voluntary hand and finger movement

decussation: midbrain (red nucleus)

medullary route: extrapyramidal

tectospinal

function: visual reflexes

decussation: midbrain

medullary route: extrapyramidal

vestibulospinal

function: balance and posture

decussation: none (ipsilateral)

medullary route: extrapyramidal

reticulospinal

function: muscle tone and posture

decussation: none (ipsilateral)

medullary route: extrapyramidal

parietal lobe

touch

insular lobe

taste

temporal lobe

smell

occipital lobe

vision

temporal lobe

hearing

primary motor cortex (frontal lobe)

initiates voluntary movement

primary somatosensory cortex (parietal lobe)

perception of touch, pain, and temperature

premotor cortex (frontal lobe)

plans movement

broca’s area (frontal lobe)

speech production

wernicke’s area (temporal lobe)

language comprehension

arcuate fasciculus (temporal lobe)

connects broca’s and wernicke’s areas

cranial nerve 1

olfactory (smell)

smell and taste receptors

chemoreceptors

key smell cells

basal cells: stem cells

supporting cells: structural

gland cells: produce mucus

olfactory cell activation

Odorant binds receptor → G-protein → Adenylate cyclase → cAMP → Na⁺ channels open

cranial nerves 7, 9, 10

taste

where taste buds are found

foliate, fungiform, vallate papillae (not filiform)

taste cell activation

Tastant binds receptor → G-protein → Adenylate cyclase → cAMP → Na⁺ channels open

eye accessory structures

palpebra(eyelid): protects, moistens

cornea

the clear, dome-shaped front part of the eye that acts as a protective window, allowing light to enter and helping to focus it on the retina

• most anterior, refracts light

lens

a clear, curved structure at the front of the eye behind the pupil, focuses light rays that enter the eye through the pupil

retina

contains photoreceptor cells (rods and cones), which are responsible for detecting light and color

sclera

the white outer layer of the eyeball, providing structure and protection

iris

the colored part of the eye that surrounds the pupil

• controls pupil size

aqueous humor (anterior)

clear, watery fluid that fills the anterior and posterior chambers of the eye

vitreous humor (posterior)

a gel-like substance that fills the space between the lens and the retina in the human eye

photoreceptor cones

specialized cells in the retina responsible for color vision and detail perception in bright light

photoreceptor rods

a type of photoreceptor cell in the retina of the eye, specialized for vision in low light conditions

• Low light, black/white, contain rhodopsin (11-cis retinal + opsin)

rod cell activation

Light strikes rhodopsin → 11-cis retinal → all-trans retinal → G-protein → phosphodiesterase → cAMP → AMP → Na⁺ channels close

outer ear

auricle

middle ear

ossicles (malleus, incus, stapes)

inner ear

cochlea (hearing), semicircular canals (balance)

cochlear hair cell activation

Tympanic membrane → Malleus → Incus → Stapes → Oval window → Cochlear hair cells

semicircular canal hair cell activation

Head movement → Semicircular canal hair cells →  Vestibular nerve → Thalamus →