5 - Special Sensory (copy)

Where are all of the eye’s visual receptors located?

Retina

How does light enter the eye?

Through clear cornea, then through the clear lens, and the onto the retina (which stimulates photoreceptors)

Can the shape of the lens be adjusted to clear up vision?

Yes, by smooth mms

What do photoreceptors consist of?

Cones (responsible for color vision (RGB), or photopic vision) and rods (responsible for low light and ability to see value - scotopic vison)

Once light hits the retina, what happens?

A chemical reaction is triggers that results in an AP transmitted via the optic nerve to the brain

How are the eyes connected to the optic nerve (CN 2)?

Each eyeball is connected its own optic nerve

What is the optic chiasm?

Where the two optic nerves meet

• 50 % of the axons here cross over to the other side (R vison crosses L and vice versa)

What are optic tracts?

Composed of axons from each eye and are after the optic chiasm on the chain the brain

What is the optic nerve pathway and the three locations the optic tract sends axons to?

• Hypothalamus - used for circadian rhythms and sleep/wake cycles

• Midbrain - form connections with cranial nerves that control extraocular mms

• Primary visual cortex - after synapse in the thalamus

Where does visual processing take place?

In the primary visual cortex 

What happens when the visual info reaches the primary visual cortex?

Axon project to other areas of the brain that allow for interpretation and understanding

What are the main areas the primary visual cortex projects to?

• Visual association cortex - for visual recognition

• Parietal lobe - location object in space and spatial relationships - the “where” pathway

• Temporal lobe - to determine size, shape, color, and texture of what we are seeing - the “what” pathway

Does damage to one optic tract cause some vision loss in the opposite side field of vision?

Yes, b/c there is overlap with the tracts

Hemianopsia 

• Loss of half of the vision on the same side in both eyes

• Common after CVA

Cortical blindness

• The inability to perceive anything visually

• Results when pt has damage to both sides of the visual cortex

What happens when sounds hits the ear drum (tympanic membrane)?

The sound vibrates and transmits vibration into the middle ear

What are the bones located in the middle ear and what do they do?

• Three auditory ossicles

• Transmits vibration caused by sound waves through the middle ear cavity into the inner ear

What are the 2 parts of the inner ear and what do they do?

• Cochlea - for hearing

• Vestibular apparatus - for balance

How does the cochlea work?

• Mvmt of the tectorial membrane pulls on the tips of the hair cells embedded in it, causing them to bend

• This bending causes the release of a neurotransmitter that activates the vestibular cochlear nerve (CN VIII)

What is the vestibular apparatus made up of?

2 parts: 

• Otolithic organs - detect linear movement of the head

  • Utricle - horizonal mvmt

  • Saccule - vertical mvmt

• Semicircular canals

How does stimuli travel from the vestibular apparatus tot he spinal cord?

1.) Hair cells in utricle, saccule and semicircular canals ( all in the vestibular apparatus) depolarize and stimulate the vestibular cochlear nerve (CN XIII)

2.) This signal travels along CN VIII to and synapses with the brainstem vestibular nuclei 

3.) From there, axons project to the motor cortex, cerebellum, and spinal cord

*Vestibular apparatus → CN XIII → brainstem vestibular nuclei → motor cortex, cerebellum, SC

Where does proprioceptive info come from and why it important?

Comes from:

• MM spindles

• GTOs

• Jt receptors

Important b/c they are processed in the brain to improve balance and control mvmt

How does a cochlea implant work?

• Bypasses damaged portions of the ear and directly stimulate the auditory nerve

• This is different than hearing aids which amplify sound for damaged ears

What is osteogenesis imperfecta and how is it related to the auditory system? 

An genetic condition in which bones form poorly and break easily 

• This malformation and breaking of the bones also applies to the auditory ossicles 

What is Meniere’s disease and how is it related to the auditory system?

Condition in which excess endolymph causes swelling inside the vestibular apparatus and cochlea

• Causes debilitating vertigo and hearing loss

How are smells perceived through the olfactory system?

1.) Air flows into the nasal cavity and molecules are dissolved in the mucus and bind to the olfactory cells in the top of the nasal cavity

2.) Axons of each cell synapse in the olfactory bulb

3.) Axons from bulbs are sent through the olfactory tract to the limbic system and primary olfactory cortex (where conscious awareness of odor occurs)

How is taste perceived through the gustation system?

1.) Food molecules are dissolved by saliva and bind too taste receptors (gustatory cells) on the tongue

2.) These cells generate APs that are sent to the brain via CN 7, 9, and 10

3.) Taste is perceived in the gustatory region of the sensory cortex

*Without smell, taste is not as potent