Nervous System (III)

Sensory Receptors

collects information from the environment, and relay it to the CNS on sensory neurons

General Senses

• Receptors that are widely distributed throughout the body

• Skin, various organs and joints

Special Senses

• Specialized receptors confined to structures in the head

• Eyes, ears, nose and mouth

Sensation

A feeling that occurs when the brain becomes aware of sensory information

Perception

The way the brain interprets the sensory information

Chemoreceptors

Respond to changes in chemical concentrations (smell, taste, oxygen concentration)

Pain Receptors (nociceptors)

Respond to tissue damage (mechanical, electrical, thermal energy)

Thermoreceptors

Respond to moderate changes in temperature

Mechanoreceptors

Respond to mechanical forces that distort receptor (touch, tension, blood pressure, stretch)

Photoreceptors

Respond to light (eyes)

Exteroceptive Senses

Senses associated with body surface, such as touch, pressure, temperature, and pain

Interoceptive (visceroceptive) senses

Sense associated with changes in the viscera, such as blood pressure stretching blood vessels.

Proprioceptive Senses

Senses associated with changes in muscles, tendons, and joins, as when changing position or exercising

Smell

olfactory organs in nasal cavity

Taste

taste buds in oral cavity

Hearing and Equilibrium

inner ears

Sight

eyes

chemoreceptors

What type of receptors cells are Olfactory receptors?

chemicals dissolved in liquids

What do olfactory receptors respond too?

75-80%

How much sense of taste does sense of smell provide?

olfactory nerves → olfactory bulbs → olfactory tracts → limbic system (for emotions) and olfactory cortex (for interpretation)

Pathway

Gustation

the sense of taste

taste buds

• organs of taste

• located on papillae of tongue, roof of mouth, linings of cheeks and wall of pharynx

• about 10,0000 taste buds, each with 50-150 taste cells

Taste Receptors

• Chemoreceptors

Taste cells

modified epithelial cells that function as receptors

• cells are replaced every 3 days

taste hairs

microvilli that protrude from taste cells through pores of taste buds; sensitive parts of taste cells

Sweet, Sour, Salty, Bitter, Umami

5 primary taste sensations

Sweet

stimulated by carbohydrates

Sour

stimulated by acids (H+)

Salty

stimulated by salts (Na+ or K+)

Bitter

stimulated by many organic compounds, Mg and Ca salts

Umami

Stimulated by some amino acids, MSG

cranial nerves → medulla oblongata → thalamus → gustatory cortex in the insula

Taste Pathway

Ear

Organ of hearing

Outer/external ear, middle ear, inner/internal ear

3 sections of the ear

Auricle (Pinna)

• Funnel - shaped

• Collects sounds waves

External Acoustic Meatus

• Lined with ceremonious glands

• Carries sound to tympanic membrane

Tympanic Membrane (Eardrum)

Vibrates in response to sound waves

Tympanic cavity

Air filled space in temporal bone

Auditory ossicles

• 3 tiny bones

• Vibrate in response to tympanic membrane vibrations; amplify force

• Malleus, incus, and stapes

• Hammer, anvil, and stirrup

Oval Window

• Opening in wall of tympanic cavity

• Stapes vibrates against it to move fluid in inner ear

Auditory (eustachian) tube

• Connects middle ear to throat

• helps maintain equal pressure on both sides of tympanic membrane

• Usually closed by valve like flaps in throat

Cochlea, Semicircular canals, vestibule

3 parts of labyrinths

Cochlea

Functions in hearing

Semicircular canals

Functions in dynamic equilibrium

Vestibule

Functions in static equilibrium

Oval window

• Opening in the wall of the tympanic cavity, through which the stapes transfers vibrations to the fluid of the inner ear; these vibrations stimulate hearing receptors

Round Window

• Window in the wall of the inner ear facing the tympanic cavity, through which excess vibrations dissipate into the tympanic cavity

Cochlear branch of vestibulocochlear nerve → medulla oblongata → midbrain → thalamus → auditory cortex in temporal lobe of cerebrum

Auditory Pathways

the eye

Where are visual receptors usually found?

Upper and lower eyelids, eyelashes, lacrimal apparatus, extrinsic eye muscles

Accessory organ for sense of sight

Upper and lower eyelids

palpebrae, protection

eyelashes

protection

lacrimal apparatus

tear production

extrinsic eye muscles

eye movement

eyelids

palpebrae

skin, muscle, connective tissue, conjuctiva

composed of 4 layers

Orbicularis Oculi

Muscle closes eyelid

Levator palpebrae superioris

muscle opens eyelid

tarsal glands

secrete oil onto eyelashes

conjuctiva

mucous membrane lines eyelid and covers portion of eyeball

lacrimal gland

• in orbit, lateral to eye

• secretes tears

canaliculi

• 2 ducts that collect tears

lacrimal sac

• collects tears from canaliculi

• lies in groove in lacrimal bone

nasolacrimal duct

• collects from lacrimal sac

• empties tears into nasal cavity

lysozyme

• antibacterial component of tears

outer (fibrous) tunic, middle (vascular) tunic, inner (nervous) tunic

What are the three layers of the eye wall?

Outer (fibrous) tunic:

Cornea + Sclera

Cornea

• Anterior sixth

• Transparent

• Helps focus light rays

• Transmits and refracts light

Sclera

• Posterior five sixths

• White, opaque

• Protects eye, attaches muscles

• Pierced by optic nerve and blood vessels

Middle (vascular) tunic

choroid coat + ciliary body + iris

choroid coat

• posterior five - sixths

• provides blood supply

Ciliary Body

• Forms rings to hold lens

• Changes lens shape for focusing

Iris

• Pigmented

• Controls light entering eye

pupil

is window or opening in center or iris

retina

what the inner tunic consists of

vitreous humor

thick gel that holds retina flat against choroid coat, and helps maintain the eye’s shape