Neuro: Final Prep

Vision and Sensory Receptors

• Sensations on the skin are detected by cutaneous receptors.
• Receptors occur rapidly after stimuli, in approximately 0.1 seconds, and are not felt in deeper tissues
• The saccule (vertical) is more sensitive when going up or down in an elevator.

Visual Pathway:

• The visual pathway consists of the cornea, aqueous humor (anterior chamber), pupil (hole in iris), lens, vitreous body, photoreceptors( rods and cons), bipolar cells, ganglion cells, optic nerve CN II, optic chiasm, optic tract, Thalamus (LGN), optic radiation, and visual cortex
• The primary/ 1st order neuron is the bipolar cells of the retina, that transmit signals from rods/cones to ganglion cells.
• The secondary/2nd order neuron is the optic nerve/optic tract, which transmits signals from the retina to the LGN of the thalamus after passing the optic chiasm.
• The tertiary/3rd order neuron is the optic radiation, which transmits signals from the LGN of the thalamus to the primary visual cortex (Area 17) of the occipital lobe.
• Damage to the lateral spinothalamic pathway may result in a loss of pain sensation.

Ear Anatomy

• Outer ear structures include the auricle (pinna) (helix, lobule), tragus, external auditory canal, and ceruminous glands.
• Middle ear structures include auditory ossicles (malleus, incus, stapes), tensor tympani and stapedius muscles, and the auditory/eustachian tube, as well as the oval and round windows.
• Inner ear structures include the bony labyrinth (perilymph), consisting of the semicircular canals (3), vestibule,and cochlea; and the membranous labyrinth (endolymph), consisting of the utricle and saccule, semicircular ducts (3), ampulla, and cochlear duct.
• The eardrum is also called the tympanic membrane.
• The inner ear contributes to both equilibrium and hearing.
• The auditory tube is also called the eustachian tube.
• Otitis media (ear infection) can be caused by strep travelling up the auditory/eustachian tube.
• Swallowing and yawning opens the eustachian/auditory tube, which allows air to enter or leave the middle ear, equalizing the pressure.
• Otitis media is a middle ear infection (FALSE).

Vision Conditions

• Myopia is nearsightedness.
• If the right eye has a detached retina on the outer lower portion, they cannot see the upper left.
• Astigmatism is an irregular curvature of the lens
• Emmetropia is normal vision.
• Presbyopia is the gradual loss of the eyes' ability to focus on nearby objects, as the lens gets thicker + less elastic with age.
• Conditions associated with aging include:
• Presbyopia (eyes): Loss of accommodation due to the lens getting thicker + less elastic with age.
• Cataracts (eyes): Loss of transparency of the lens, and can lead to blindness.
• Presbycusis (ears): Hearing loss due to damage/loss of hair cells in the organ of Corti.
• Tinnitus (ears): Ringing in ears.
• The rubrospinal tract is not a pyramidal pathway; it is extrapyramidal.
• Stages of sleep include NREM and REM.

Memory and Neural Pathways

• Consolidation of memory from short-term to long-term requires chemical, physical, and anatomical changes:
• Short-term memory involves electrical and chemical events.
• Long-term memory involves anatomical and biochemical changes at synapses.
• Second-order neurons go from the CNS to the thalamus (FALSE; they do not go from the PNS to the CNS).
• The tensor tympani is innervated by the trigeminal nerve (CN V).
• Taste in the anterior tongue is detected by the facial nerve (CN VII).
• Taste in the epiglottis is detected by the vagus nerve (CN X).
• The olfactory nerve is CN I.
• The vestibular nuclei (associated with hearing) sends commands to CN 3, 4, 6, 11; the vestibulospinal tract, and the VPN of the thalamus, but NOT CN 1.
• The central fovea has the highest visual acuity.
• The function of aqueous humor is to nourish the cornea and lens, and is NOT associated with floaters
• Constriction of circular muscles in the retina are innervated by parasympathetic fibers (CN 3 - oculomotor).
• Parts of the brainstem include the medulla, pons, and midbrain.
• The RAS is part of the reticular formation
• The RAS controls sleep and wakefulness.
• Pitch and frequency are measured in Hertz.
• Volume is measured in decibels.
• Any sensation one is aware of goes to the cerebral cortex.
• Mitral cells release glutamate.
• Serotonin is made from the amino acid tryptophan.
• Sensation is the conscious and unconscious awareness of external or internal stimuli.
• Perception is the conscious awareness and interpretation of a sensation.
• Somatic sensory modalities include tactile sensations (touch, pressure, vibration, tickle, itch), thermal sensations (warm and cold), pain sensations, and proprioceptive sensations.
• Visceral senses contain info about internal organs.
• Only first-order neurons have sensory receptors.

Stimuli and Adaptation

• Stimuli that can be detected include chemoreceptors, nociceptors, and mechanoreceptors.
• Adaptation is the tendency for the generator or receptor potential to decrease in amplitude during a maintained constant stimulus.

Equilibrium

• Static equilibrium structures include the vestibular apparatus (utricle (horizontal) + saccule (vertical)) AND the macula (hair cells, supporting cells, otolithic membrane, otoliths, stereocilia, kinocilium).

• Dynamic equilibrium structures include the 3 semicircular ducts, the semicircular canals (anterior (side tilt), posterior (yes), lateral (no)); the ampulla and cupula AND utricle + saccule ONLY with linear movt

• The utricle and saccule have a small thickened region called the macula, which is associated with static equilibrium.

• Endolymph within the ampulla lags during rotational acceleration, and is associated with dynamic equilibrium.

• Semicircular ducts contain a swollen area called the ampulla, which is associated with dynamic equilibrium.

• Plasticity is the capability for change with learning.

• A cataract is a loss of transparency of the lens.

Rods and Cones

• Rods:

• Are for dim light.

• See scales of grey as well as shapes and movement.

• Have poor acuity.

• Have highly convergent circuits.

• Are not in the fovea, which is the location of greatest acuity.

• Have good night vision.

• Contain high levels of photopigment.

• Only need 1 photon of light to be activated.

• Cannot see color.

• Cones:

• Only can see color.

• Have good acuity.

• Have circuits that are not highly convergent.

• Have a high concentration in the fovea.

• Have poor night vision.

• Contain a lower amount of photopigment.

• Require roughly ~100 photons of light for activation.

• There are types of cones; each best absorbs either red, green, or blue light.

• CN involved with taste: CN 7, 9, 10.

• CN II is the optic nerve.

• Aqueous humor is found in both the posterior and anterior chambers of the eye.

• Aqueous humor is replaced every 90 minutes, but vitreous humor is not.

• The iris sits between the cornea and lens.

• The choroid provides the retina with nutrients.

• The ciliary body/ciliary process creates aqueous humour.

• Hyperacusis is not an age-related pathology (inc sensitivity to hearing due to paralysis of stapedius).

• Semicircular canals do not have 4 rings; they have 3.

Eyelids and Inner Ear

• Functions of eyelids/palpebrae include shading the eyes during sleep, protecting the eyes from debris, and spreading tears.
• The auditory/eustachian tube balances the pressure in the middle ear and is not on both sides of the outer and middle ear.
• Chemicals that have an odor and stimulate the olfactory hairs are called odorants.
• Exteroceptors should not include proprioception (receives external stimuli and are located near surface of the body like hearing, vision, smell, taste, touch, pressure, pain, vibration, and temperature).
• An increase in frequency leads to an increase in pitch.
• The middle ear is an air-filled cavity.
• The auricle is also called the pinna

Matching: Ear + Eye Structures

• Palpebrae: Upper and lower eyelids. They shade the eyes during sleep and spread lubricating secretions over eyeballs.
• Lacrimal Apparatus: Produces and drains tears.
• Eyebrows: Arches above the eyeballs to protect them from foreign objects, perspiration, and direct rays of the sun.
• Extrinsic Eye muscles: Move the eyeball medially, laterally, superiorly, or inferiorly.
• Tarsal Plate: A thick fold of CT that gives form and support to eyeballs.
• Tarsal or Meibomian Glands: Modified sebaceous glands, and their secretion helps keep eyelids from adhering to one another.
• Eyelashes: Project from the border of each eyelid to help protect eyeballs from foreign objects and perspiration .
• Conjunctiva: A thin, protective mucous membrane that lines the inner aspect of the eyelids and passes from the eyelids onto the surface of the eyeball, covering the sclera.
• Iris: Colored portion of the eyeball. Regulates the amount of light entering the posterior part of the eyeball.
• Retina: Innermost layers of eyeball. It is the beginning of the visual pathway and contains rods and cones.
• Ciliary muscles: A circular band of smooth muscle that alters the shape of the lens for near or far vision.
• Aqueous humor: Watery fluid in the anterior cavity that helps nourish the lens and cornea and maintains the shape of the eyeball.
• Pupil: The hole in the center of the iris.
• Sclera: The white of the eye. It provides shape to the eyeball, makes it more rigid, and protects its inner parts.
• Fibrous Tunic: Avascular superficial layer of the eyeball that includes the cornea and sclera.
• Vascular Tunic: The middle vascularized layer of eyeball that includes the Choroid, Ciliary body and the Irish.
• Ear Anatomy
• Tympanic Membrane (Eardrum): Partition between the external auditory canal and middle ear.
• Vestibule: Oval central portion of the bony labyrinth; contains utricle and saccule.
• Macula: Receptor for static equilibrium, also contributes to some aspects of dynamic equilibrium, and consists of hair cells and supporting cells.
• Spiral Organ: Contains hair cells which are the receptors for hearing.
• Auditory Ossicles: Ear bones including the malleus, incus, and stapes.
• Auditory/Eustachian Tube: A pressure equalization tube that connects middle ear to nasopharynx
• Cochlea: Contains the spiral organ.
• *Endolymph:
• Fluid found within the membranous labyrinth. Pressure waves in this fluid cause vibration of the basilar membrane.
• Vestibular Apparatus: Receptor organs for equilibrium and includes the saccule, utricle, and semicircular canals
• Ampulla: Swollen enlargement in semicircular canals and contains structures involved in dynamic equilibrium.
• Round Window: An opening between the middle ear and internal ear, and is enclosed by a membrane called the secondary tympanic membrane.
• Auricle:
• A flap of elastic cartilage covered by skin that captures sound waves. It is also known as the pinna.
• Perilymph: Fluid found inside the bony labyrinth; bulging of the oval window causes pressure waves in this fluid.
• Oval Window: Opening between the middle and inner ear and receives the base of the stapes.
• Nociceptors: Receptors that respond to stimuli resulting from physical or chemical damage to tissues.
• Encapsulated Nerve Endings: Dendrites enclosed in CT capsule

Sensory Receptors (Matching)

• Meissner Corpuscles/Type 1 Cutaneous Mechanoreceptors: Receptors for touch, located in the dermal papillae of glabrous skin (aka hairless skin). They are abundant in fingertips, hands, eyelids, tip of the tongue, lips, nipples, soles, and clitoris. These detect touch and lower-frequency vibration.

• Merkel Discs/Type II Cutaneous Mechanoreceptors: receptors also known as Ruffini corpuscles. Located deep in the dermis and ligs and tendons and detects touch and pressure. The have higher-frequency vibrations or make contact with merkle cells of stratum and basale of epidermis to detect touch and pressure

• Mm Spindles: measures mm length and either sudden or prolong stretch central areas of intrafusal mm fibers stimulates sensory nerve endings

• GTO: Protects tendons + associated muscles from damage due to excessive tension.

• Jt Kinesthetic Receptors: Present within and around articular capsules of synovial jts. Free nerve endings and Type 2 (Ruffini) are within jts, while lamellated (Pacinian) are CT outside. These receptors detect jt position and movement.

• Cold Receptors: More cold receptors vs. warm. These receptors are superficial vs. warm receptors because they are in the stratum basale of epidermis and attached to small-diameter myelinated A fibers .

• Warm Receptors: Located in the dermis and attached to small-diameter unmyelinated C fibers.

Types of Receptors (MT Matching)

• Proprioceptors: Receptors located in muscles, tendons, joints, and the inner ear.
• Interoceptors: Receptors located in blood vessels, visceral organs, muscles, and the nervous system.
• Thermoreceptors: Receptors that detect temperature changes.
• Photoreceptors: Receptors that detect light that strikes the retina of the eye.
• Exteroceptors: Receptors located at or near the external surface of the body.
• Free Nerve Endings: Bare dendrites associated with pain, thermal sensation, tickle, itch, and some touch sensations.
• Proprioceptors: Receptors that provide information about body position, muscle tension, and the position and activity of joints.
• Osmoreceptors: Receptors that sense osmotic pressures of body fluids.
• Chemoreceptors: Receptors that detect chemicals in the mouth, nose, and body fluids.
• Mechanoreceptors: Receptors that detect mechanical pressure or stretching.

Somatic Sensory and Motor Pathways

• Located in the precentral gyrus, this is the major control region of the cerebral cortex for the initiation of voluntary movements and also known as the primary motor area

• Direct pathways conveying impulses from the cerebral cortex to the spinal cord that result in precise, voluntary movement as knowns as the pyramidal pathways

• Contains motor neurons that control skilled movements of the hands and feet and also known as the lateral corticospinal tract

• Tracts include the rubrospinal, tectospinal, vestibulospinal, and lateral + medial reticulospinal and this is known and the extrapyramidal pathways

• Contain neurons that help initiate and terminate movements, can suppress unwanted movements, and influence muscle tone and this is the basil ganglia

• Carries impulses for pain, temperature, tickle, and itch and also known as the Anterolateral / Spinothalamic Pathway

• Major routes relaying proprioceptive input to the cerebellum, critical for posture, balance, and coordination of skilled movements of the Spinocerebellar Tracts

• Composed of axons of first-order neurons, includes the gracile and cuneate fasciculus and also known as the posterior column

• Contains motor neurons that coordinate movements of the axial skeleton known as the anterior corticospinal tract

• Contains axons that convey impulses for precise, voluntary movements of the eyes, tongue, neck, chewing, facial expression, and speech which is the corticobulbar tracts

• Conveys sensations of touch, conscious proprioception, pressure, and vibration to the cerebral cortex and is the PCML Pathway

• Carries impulses for most somatic sensations from the face, nasal cavity, and oral cavity and is the trigeminothalamic pathway