Chapter 15 (lectures)

Protects eye

Protects eye

Function of eyelashes

Big blood supply

Why does light touch to the eyelid cause you to blink?

Pupil

Opening in eye that allows light to get through

Conjunctiva

Mucous membrane tat lines eyelids and over whites of eyes

Conjunctivitis

Pink eye. Infection of conjunctiva.

Laccrimal apparatus

where tears come from in eyes. Produces watery component.

1. Lacrimal glands

2. Lacrimal sacs

Two components of lacrimal apparatus

Lacrimal sacs

Tears drain into this sac after flowing down the eyeball and eventually into the nasal cavity.

1. keep eyes moist

2. Wash out irritating substances

3. Response to emotions

Function of tears [3]

Lacrimal glands

Outer corner of the eye, produces and secretes tears

Lacrimal secretions

tears

1. intrinsic eye muscle

2. Extrinsic eye muscle

two types of eye muscle

Intrinsic muscle

Smooth muscle within the eye

1. Iris

2. Ciliary muscle

Two examples of intrinsic muscle in eye

Iris

intrinsic muscle that moves to regulate the size of pupil

Ciliary muscle

Intrinsic muscle that controls the shape of the lense

Extrinsic eye muscles

Skeletal muscles that attach to the outside of the eyeball

1. Oblique (superior, inferior)

2. Rectus (superior, inferior, medial, lateral)

Two groups of extrinsic eye muscles

Cranial nerves

How are extrinsic eye muscles controlled?

Cornea

Covers pupil and iris. Clear. Lets light into the eye.

Retina

Very back of the eye. Where important seeing stuff happens.

Optic nerve.

Main nerve transmits info to CNS. Comes out the back of the eye

1. Millions of photoreceptors

2. Neurons responsible for processing responses to light

3. Glia cells (support)

What does retina contain [3]

1. Lens focuses light on to the focal point of the retina.

2. Lens changes shape depending on how close object is to the eye.

Normal vision: [2]

With age, the lens becomes too elastic and looses its ability to change shape to focus closer images.

Why does vision worsen with age?

Layers of cells in the retina enable light hitting the retina to be transformed into action potentials. referred to as phototransduction.

How are images seen?

AP travels along ganglion cells to optic nerve.

How does action potential travel to optic nerve?

Waves

How does sound travel?

Amplitude and frequency

Quality of sound depends on ..[2]

Amplitude

measurement of intensity of sound. Measured in decibels. Size of sound wave.

Frequency

Depicts pitch of sound. measured in Hz. How many times a wave repeats during a given time.

1. external ear

2. middle ear

3. inner ear

Three divisions of ear structure

External ear

Where sound enters the ear. Lots of elastic cartilage.

Middle ear

Where tympanic membrane of ear (eardrum) is

Inner ear (labrynth)

Where sensors for hearing and balance are located in the brain

inner ear

where is cochlea located?

1. Malleus

2. Incus

3. stapes

Name of three tiny bones on other side of tympanic membrae connected by tiny little joints

Oval window

Opening that leads to cochlea

Basilar membrane

Membrane in the middle of the cochlea that has hair cells attached to it.

It depends on the quality of the sound (pitch), and distinguishes between different sounds. Specific nature of sound combined will have a different affect at different parts of the basilar membrane that are stimulated by specific neurons.

Why do different parts of basilar membrane vibrate for specific sounds?

Impulses from nerve cells in cochlea travel up to nervous system via vestibulocochlear nerve. Signal ends in the primary auditory cortex, allowing to distinguish sound.

How do action potentials get from inner ear to the brain?

1. Sound waves vibrate tympanic membrane

2. Auditory ossicles vibrate (amplified pressure)

3. Pressure waves created by the stapes pushing on the oval window move through fluid

4. Sounds go through cochlear duct, vibrating basilar membrane and deflecting hairs on inner hair cells.

5. Movement of hairs changes membrane permeability, leads to neurotransmitter release

6. Neurotransmitter triggers action potentials to travel along the cochlear nerves.

How do we hear? [6 steps ish]

Balance and equilibrium

Ability to stay upright and resist the pull of gravity.

1. Vision

2. Proprioception

3. Vestibular system

Balance depends on… [3]

1. Semicircular canals (dynamic eq)

2. Vestibules (static eq)

Two parts of vestibular system in inner ear

1. Utricle

2. Saccule

Two components of vestibule

Sensing linear head position (not rotation)

Function of utricle and saccule (vestibule)

Hairs embedded in supporting cells. When head is forward, hair bends forward, action potentials are delivered less frequently. When head is backward, hair bends backward, action potentials are delivered more frequently.

How does vestibule sense head positioning?

Semicircular canals

Structure that detects head rotation in 3 planes due to different orientation of each canal

1. Anterior

2. Posterior

3. Lateral

Three semicircular canals:

Cerebellum, and feeds into special nuclei in the brainstem.

Where does sensory information from inner ear for balance go?

Taste and smell

two primitive chemical senses that determine if things are safe to ingest/be around

Is excited by chemicals that dissolve in fluids coating the nasal membranes

How is smell excited?

Is excited by food chemicals dissolved in saliva

How is taste excited?

Approx. 350 (there are up to 1 trillion odors — meaning receptors respond to one or more odorants)

How many types of smell receptors are there?

1. Air comes in trhoughnose, takes sharp turn to get to olfactory epithelium

2. Substances in air dissolve in fluid on the membrane.

3. Substances excite neurons bybinding to receptors on neurons.

4. Signal is transmitted to olfactory bulb.

5. Ultimate pathway from olfactory bulb out is neurons travelling out via olfactory tract up to the brain.

How does smell happen? [5]

Olfactory epithelium on roof of nasal cavity

Where does smelling happen?

Dissolved substances in the fluid of olfactory epithelium bind to receptors on epithelium and changes membrane potential. triggers action potential.

How do action potentials get generated in neurons that travel to olfactory bulb?

Dissolved chemicals stimulate receptors that use second messenger. Odorant binds to receptors, secondary process gets set up, triggering chain of events. Chain ultimately ends in channels opening on the membrane and ions moving and effect happens— triggering action potential. Olfactory uses a second messenger.

Briefly explain the second messenger concept for dissolved chemicals (smell):

taste buds

Sensory receptors for taste

On tongue. Some on the epiglottis and back.

Where are most taste buds located?

Gustatory epithelial cells

Cells within taste buds that are easily damaged by friction, hot food, etc. and are replaced every 7-10 days

1. Sweet

2. Sour

3. Salty

4. Bitter

5. Umami

   (most substances are a combination of these basic tastes)

5 basic tastes

1. Facial nerve (anterior 2/3)

2. Glossopharyngeal nerve (front 1/3)

3. Vagus nerve (immediately behind tongue)

Three cranial nerves involved in taste

Taste to help ensure body is getting everything it needs.

1. Sweet and salty: satisfies carbs and minerals

2. Sour: rich in vitamin C

3. Umami: guide for protein

How does taste play a role in homeostasis? [3 examples]

1. Sour: warns of spoilage

2. Bitter: warns of spoilage or poisoning

How can taste be used as a protective measure? [2 examples]

80%

How much of taste is actually smell?

1. Thermoreceptors (hot/cold)

2. Mechanoreceptors (texture)

3. Nociceptors (Spicy is painful)

What kinds of receptors in the mouth enhance or distract from taste? [3]