Nervous System pt 3 (LAB)

Eye

• anterior cavity

• posterior cavity

• visual axis and fovea

• blind spot

Eye Muscles

6 muscles

• LR6

• S04

• R3 (parasympathetic but skeletal muscle)

Layers and structures of eyeball

• fibrous

  • outer layer

  • collagen

  • sclera and cornea

• vascular

  • middle layer

  • everything

• nervous/retina

  • retina and photoreceptors

  • visual axis to forea (highest concentration of photoreceptors)

Chambers

• anterior chamber

  • aqueous fluid

  • in front of lens

  • thin

• Posterior chamber

  • vitreous fluid

  • behind lens

  • thick

Important stuff

• choroid coat- pigmentation; causes eyes to glow in animals

• pupillary constrictor- cranial nerve 3

• pupil- hole in vascular layer

  • light hits lens and bends

  • fovea centralis -A tiny depression in the center of the retina, located within the macula lutea. Contains the highest concentration of cone photoreceptors — no rods. Responsible for sharpest visual acuity and color perception.

Rods vs. Cones

🌟 Photoreceptors of the Retina: Rods vs. Cones📌 Overview

• Photoreceptors are specialized neurons in the retina that detect light and convert it into neural signals.

• The two primary types are rods and cones, each designed for distinct visual functions.

🔦 Rods

• Function: Specialized for low-light (scotopic) vision

• Color Sensitivity: None — detect grayscale only

• Visual Detail (Acuity): Low; blurry but sensitive

• Location: Mostly in the peripheral retina

• Number: About 120 million in the human eye

• Adaptation: Slow to adjust between light levels (think stepping into a dark room)

• Extra Insight: Crucial for night vision and motion detection, but easily saturated in bright light

🎨 Cones

• Function: Specialized for bright-light (photopic) and color vision

• Color Sensitivity: Yes — trichromatic system (red, green, blue)

• Visual Detail (Acuity): High; sharp and focused

• Location: Densely packed in the fovea centralis (center of retina)

• Number: About 6 million

• Adaptation: Quick to adjust to brightness

• Extra Insight: Vital for detail-oriented tasks like reading and recognizing faces

Intrinsic Eye Muscles and their response to light

• Bright light=circular muscles contract= small

• dim light= eyes dilate= big

Outer Ear

Outer Ear

• pinna/auricle

• external auditory meatus

• tympanic membrane

Middle Ear

• auditory ossicles

  • malleus, incus, stapes

• oval window

• pharyngotympanic tube

• Tensor tympani

Inner Ear

• semicircular canals

• vestibule

• Nerve 8

• Cochlea

• Round Window

• located in petrous portion of temporal bone

  • vestibulocochlear nerve hole

Static Equilibrium

• vestibule

• utricle and saccule

  • each have hair cells that are filled with otolithic membrane

  • When your head tilts or you experience linear acceleration (like riding an elevator), gravity causes the otolithic membrane to shift.

  • This movement bends the stereocilia on the hair cells, triggering electrical signals

• static equilibrium and linear acceleration of the head

• POSITION

Dynamic Equilibrium

• semicircular ducts

• ampullae

  • When your head rotates, the fluid (endolymph) inside the canals lags behind due to inertia. This causes the cupula to bend, which in turn bends the stereocilia on the hair cells. That bending generates nerve impulses

• rotational acceleration of the head

• MOVEMENT

Hearing

• Cochlea

• organ of corti

  • action potentials

  • Contains hair cells (inner and outer) with stereocilia that detect sound vibrations.

  • When sound waves cause fluid movement in the cochlea, the basilar membrane vibrates, bending the stereocilia.

  • This bending opens ion channels, triggering electrical signals.

  • These signals are sent via the auditory nerve to the brain, where they're interpreted as sound.

Order of how we interpret sound

• Pinna (Auricle): The outer ear collects sound waves and funnels them into the ear canal.

• External Auditory Canal: Channels the sound waves toward the tympanic membrane (eardrum).

• Tympanic Membrane (Eardrum): Vibrates in response to sound waves, converting them into mechanical energy.

• Auditory Ossicles (Middle Ear Bones):

  • Malleus receives vibrations from the eardrum

  • Incus passes them along

  • Stapes pushes against the oval window, amplifying the signal

• Oval Window: Transfers vibrations into the cochlea of the inner ear.

• Cochlear Fluid Movement: Vibrations cause fluid waves inside the vestibular duct, which ripple through the cochlear duct and tympanic duct.

• Basilar Membrane & Hair Cells: Fluid movement causes the basilar membrane to vibrate, bending stereocilia on hair cells in the organ of Corti.

• Neurotransmitter Release: Bending of stereocilia opens ion channels, triggering neurotransmitter release and generating electrical signals.

• Auditory Nerve (Cochlear Branch of CN VIII): Carries the electrical signals to the brainstem, then to the temporal lobe, where sound is interpreted.