Ch 16 Final

Production and movement of lacrimal fluid

1. A lacrimal gland, located within the super-lateral depression of each orbit, continuously produces lacrimal fluid that drains through short ducts to the eye surface 2. Blinking (15 to 20 times per minute)"washes" the lacrimal fluid over the eyes. Gradually, the lacrimal fluid is transferred to the lacrimal caruncle at the medial surface of the eye 3. Fluid drains into the lacrimal puncta, which are two small openings on the superior and inferior side of the lacrimal caruncle (appears as a "hole") 4. Each punctum has a lacrimal canaliculus (small canal) that drains lacrimal fluid into a rounded lacrimal sac 5. The fluid drains from the lacrimal sac into a nasolacrimal duct. The duct drains lacrimal fluid into the nasal cavity, where it mixes with mucus and then moves into the pharynx (throat) and is swallowed. Excess production of lacrimal fluid produces tears

What two features are critical to allow sensory receptors to function as transducers

1. Sensory receptors, like neurons and muscle cells, establish and maintain a RMP across their plasma membrane 2. Sensory receptors contain modality gated channels within their plasma membranes.

When we feel discomfort in our internal organs, it often occurs because

1. a tissue has been deprived of oxygen (eg heart attack) 2. the smooth muscle int he wall of the organ has been stretched so much that we are uncomfortable 3. the tissue has suffered trauma and damaged cells have released chemicals that stimulate specific nociceptors

Five groups of sensory receptors, based upon their modality of stimulus

Chemoreceptors - detect chemicals, either molecules or ions, dissolved in food. Taste buds are chemoreceptors. Thermoreceptors - present in the both the skin and hypothalamus. Components of reflexes that regulate and maintain body temperature Photoreceptors - located in the eye, detect change in light intensity, color and movement Mechanoreceptors - respond to distortion of the plasma membrane that occurs due to touch, pressure vibration and stretch. Include baroreceptors, proprioceptors, tactile receptors and other specialized cells such as the hair cells in the cochlea of the ear that move in response to sound waves. Nociceptors - Respond to painful stimulus. Informs the brain of injury or other damage so that an appropriate response may be made. Somatic nociceptors detect chemical, heat or mechanical damage to the body surface, joints or skeletal muscles. Visceral nociceptors detect internal body damage within the viscera

Fibrous tunic

Composed of posterior sclera and anterior cornea Most of it (posterior five-sixths) is the tough sclera - composed of dense irregular CT containing numerous blood vessels and nerves.

Taste buds

Cylindrical sensory receptor organs containing cells that have the appearance of an onion. Composed of three distinct cell types Gustatory cells/receptors - detect tastants Supporting cells - sultan the gustatory cells Basal cells - function as neural stem cells to continually replace the relatively short-lived gustatory cells

Gustatory pathways

Dendritic endings of primary neurons are associated with gustatory cells, with each neuron contacting several gustatory cells. Primarily components of the facial nerve (CN VII), which innervated taste buds from the anterior two-thirds of the tongue and the glossopharyngeal nerve (CN IX), which innervates taste buds from the posterior one-third of the tongue Axons within these nerves project to the medulla oblongata (nucleus solitaires) to synapse with secondary neurons. The secondary neurons project to the thalamus and axons of tertiary neurons project to the primary gustatory cortex in the insula of the cerebrum

Encapsulated tactile receptors

Dendritic endings of sensory neurons that are wrapped either bye connective tissue or by CT and specialized glial cells called neurolemmocytes (Schwann cells). Encapsulated tactile receptors include end bulbs, lamellate corpuscles, bulbous corpuscles and tactile corpuscles

General sense receptors

Distributed throughout the body and simple in structure. Subdivided into two categories based upon their location - Somatic sensory and visceral sensory Somatic sensory receptors - tactile receptors housed within both the skin and mucous membranes. Monitor several types of stimuli (object texture, pressure, stretch, vibration, temperature and pain). Also within joints, muscles, and tendons and conclude joint receptors, muscle spindles and Golgi tendon organs. Detect stretch and pressure relative to position and movement of the skeleton and skeletal muscles.

Sensory receptors can also be classified based upon where the stimulus originates. What are the classificaitons?

Exteroceptors - detect stimuli from the external environment. Include somatic sensory receptors of the skin and mucous membranes, as well as the receptors of the special senses. Respond to a stimulus outside of the body. Interoceptors - Detect stimuli from within our internal environment Include the visceral sensory receptors within the wall of internal organs and blood vessels. Keep our CNS informed about the changes that are occurring within our bodies Proprioceptors - Detect body and limb movements and include only the somatic sensory receptors within joints, muscles and tendons

End bulbs

Krause bulbs Dendritic endings of sensory neurons ensheathed in CT. Located both in dermis of the skin and in the mucous membranes of the oral and nasal cavity, vagina and anal canal. Tonic receptors that detect light pressure stimuli and low frequency vibration

Special senses

Located only within the head and are specialized, complex sense organs. Olfaction (smell), gustation (taste), vision (sight), hearing (audition), and equilibrium (head position and acceleration)

Sensory receptor distribution

May be classified based upon their distribution in the body - General or Special senses

Choroid

Most extensive and posterior region of the vascular tunic Composed of areolar CT that houses both an extensive network of capillaries and melanocytes Two primary functions are associated with the choroid Its vast network of blood vessels supplies oxygen and nutrients to the retina (inner adjacent layer of eye that contains photoreceptors) and melanin produced by its melanocytes absorbs extraneous light to print it from scattering within the eye

Detecting smells

Most inhales air does not pass across the olfactory epithelium in normal, relaxed breathing to detect smells, we must sniff repeatedly or breathe deeply which causes the inhaled air to mix and swirl into the mucus layer covering the olfactory receptor cells Within the mucus, soluble proteins called odorant-binding proteins display an affinity for a variety of odorants

Referred pain locations

Pain associated with a heart attack (MI) may be referred to the skin innervated by T1-T5 spinal nerves, which lie along the pectoral region and medial side of the arm. Some people who are experiencing heart problems may perceive pain along the medial side of the left upper limb where the T1 spinal nerve innervates Kidney and ureter pain may be referred along the T10-L2 spinal nerves, which typically overlie the inferior abdominal wall in the groin and loin regions Visceral pain can be referred along the sympathetic or parasympathetic nerve pathways. Referred pain fro the urinary bladder often can follow the parasympathetic pathways (via the splanchnic nerves - S2-S4). May be referred to the medial buttocks region.

Accomodation

Process of making the lens more spherical to view close-up objects Controlled by autonomic motor neurons of the parasympathetic division that extend within the oculomotor nerve (CN III)

Our tongue detects just five basic taste sensations:

Sweet - produced by organic compounds such as sugar Salt - produced by metal ions, such as sodium and potassium Sour - associated with acids in the ingested material, such as hydrogen ions in vinegar Bitter - produced primarily by alkaloids, such as quinine, unsweetened chocolate, nicotine and caffeine Umami - "delicious flavor." Related to amino acids, such as glutamate and aspartate to produce a meaty flavor

What is adaptation

The decrease in sensitivity to a continuous stimulus Difference in adaptation is used to categorize sensory receptors as either tonic or phasic receptors

Ciliary muscle

a ring of smooth muscle. Extending from the ciliary muscle to the lens are suspensory ligaments, which anchor the lens Relaxation and contraction of the ciliary muscles change the tension on the suspensory ligaments, thereby altering the shape of the lens

Stimulation of olfactory receptor cells

activates G proteins within these cells Activated G proteins stimulate adenylate cyclase enzymes, which convert ATP to cAMP cAMP stimulates the opening of cation channels that allow the inflow of both Na+ and Ca2+ Net inflor oof positive ions results in generation of local receptor potentials within the olfactory hairs of the olfactory receptor cells Local potentials initiate an action potential that is propagated along the axon of olfactory receptor cells, causing the release of neurotransmitter from the terminal ends of the axon This results in stimulation of different patterns of ~200 glomeruli

Tactile corpuscles

aka Meissner corpuscles receptors formed from highly intertwined dendritic endings of sensory neurons enclosed by modified neurolemmocytes, which are then covered with dense irregular CT. Housed within the dermal papillae (projections of the dermis), especially in the lips, palms, eyelids, nipples and genitals. Phasic receptors for discriminative touch to distinguish texture and shape of an object and for detecting light touch

Lamellated corpuscles

aka Pacinian corpuscles Large, leaf-shaped tactile receptors composed of several dendritic endings ensheathed with an inner core of neurolemmocytes and outer concentric layers of CT. Phasic receptors found deep within the reticular layer of the dermis of the skin; in the hypodermic of the palms of the hands, soles of the feet, breasts and external genitalia; and in thew alls of some organs. Function in coarse touch and sensing continuous deep-pressure and high-frequency vibration stimuli

Limbus

aka corneal scleral junction where the cornea merges with the sclera at its outer edge The corneal epithelium forming the external portion of the cornea is continuous with the ocular conjunctiva that covers the sclera

Retina

aka internal or neural tunic Composed of two layers: an outer pigmented layer and an inner neural layer Pigmented layer is immediately internal to the choroid and attached to it. Two primary functions are associated with the pigmented layer: it provides vitamin A for the photoreceptor (light-detecting) cells of the neural layer and absorbs extraneous light to prevent it from scattering within the eye (a function it shares with the choroid) Inner neural layer (neural retina) houses all of the photoreceptor cells and their associated neurons - responsible for vision by absorbing light rays and converting them into nerve signals that are transmitted to the brain

Tactile discs

aka merkel discs flattened dendritic endings of sensory neurons that extend to tactile cells (merkel cells), which are specialized epithelium located in the stratum basale of the epidermis. These discs function as tonic receptors for light touch. Only specialized tactile receptor cells; the remaining tactile receptors are simply the dendritic endings of sensory neurons

Eyelids

aka palpebrae form the protective covering over the surface of the eye. Formed primarily by a fibrous core (tarsal plate), the orbiculares oculi muscle, an d thin covering of skin Muscle associated only with the upper eyelid is the levator palpebral superioris muscle, which pulls the upper eyelid to "open the eye"

Sphincter pupillae muscle

aka pupillary constrictor arranged in a pattern that resembles concentric circles around the pupil This muscle contracts (pupil becomes smaller) when stimulated by visceral motor neurons of the parasympathetic division of the ANS that are within he oculomotor nerve (CN III)

Dilator pupillae muscle

aka pupillary dilator organized in a radial pattern extending peripherally through the iris. This muscle contracts (and the pupil becomes larger) when stimulated by neurons of the sympathetic division of the ANS

Vascular tunic

aka uvea houses an extensive array of blood vessels, lymph vessels and the intrinsic muscles of the eye Composed of three distinct regions (from posterior to anterior): choroid, ciliary body, and the iris

Vitreous Humor

aka vitreous body transparent, gelatinous fluid that completely fills the posterior cavity. Permanent fluid that is produced during embryonic development and helps to both maintain eye shape and support the retina to keep it flush against the back of the eye

Nutrients and oxygen are supplied to the internal epithelium of the cornea by

aqueous humor within the anterior cavity of the eye, whereas the surface corneal epithelium receives its oxygen and nutrients from lacrimal fluid

Internal to olfactory epithelium

areolar CT layer called the lamina propria Housed within the collagen fibers and ground substance of this layer are mucin secreting olfactory glands (Bowman glands) and many blood vessels and nerves Secretions from both supporting cells and olfactory glands form the mucus that covers the exposed surface of the olfactory epithelium

Suspensory ligaments

attach to the lens capsule at its periphery, where they transmit tension that enables the lens to change shape. Relative tension in the suspensory ligaments is altered by relaxation and contraction of theciliary muscles in the ciliary body. When we view objects greater than 20 feet away, the ciliary muscles relax, the ciliary body moves away from the lens, and so the tension of the suspensory ligaments increases Constant tension causes the lens to flatten Flattened shape of the lens is the resting position of the lens

Olfactory tracts

axon bundles of the mitral and tufted cells project posteriorly along the inferior frontal lobe surface directly to the primary olfactory cortex int he temporal lobe and selected different regions of the brain, including the hypothalamus and amygdala Olfactory pathways do NOT project to the thalamus and therefore do not undergo any thalamic processing prior to reaching the cerebrum

Why does an initially strong smell seem to dissipate as your olfactory receptor cells quickly adapt?

because once there captors are stimulated, changes to the ion channels alter the flow of ions. This results in interfering with the subsequent general of local receptor potentials within olfactory receptor cells

Olfactory receptor cells

bipolar neurons that have undergone extensive differentiation and modification Serve as the primary neuron in the sensory pathway for smell Olfactory receptor cells have both a single dendrite and an unmyelinated axon Projecting from the dendrites are numerous thin, nonmotile cilia called olfactory hairs that extend into the layer of mucus.

How are olfactory receptor cells stimulated?

by contact of odorant-binding proteins with olfactory cell receptors

Only nerve signals that reach the _____ of the brain result in our conscious awareness

cerebral cortex

Sensory information from olfactory pathways reaches different regions of the brain, including

cerebral cortex, which allows us to consciously perceive and identify the smell hypothalamus, which controls visceral reactions to smell (such as salivation, sneezing or gagging) amygdala, which is a center for recognition of odors and often associating those odors to a particular emotion

What are sensory receptors

components of the nervous system that that provide us with information about our external and internal environments

What is the most common non traumatic eye complaint seen by physicians

conjunctivitis

Interior of the eye

consists of two fluid-filled (posterior and anterior) cavities that are separated by the lens - a transparent, biconvex structure enclosed in a fibrous capsule

Ciliary processes

contain capillaries that secrete aqueous humor

Olfactory hairs

contain chemoreceptors within their plasma membrane that detect one specific odorant molecule ~400 types of scent receptors Depending upon which olfactory receptor cells are stimulated, different smells will be perceived Axons of olfactory receptor cells form bundles (fascicles) of the olfactory nerves (CN I) These fascicles project through foramina (holes) in the cribriform plate of the ethmoid bone to enter an olfactory bulb

Optic disc

contains no photoreceptors axons of the ganglion cells extend from the back of the eye as the optic nerve Commonly called the blind spot because it lacks photoreceptor cells and no image forms there

Peripheral retina

contains primarily rods and functions most effectively in low light

Cornea

convex, transparent structure that forms the anterior one-sixth of the fibrous tunic its convex shape refracts (bends) light rays coming into the eye Composed of an inner simple squamous epithelium, a middle layer of collagen fibers, and an outer stratified squamous epithelium called the corneal epithelium Contains no blood vessels

Orbital fat

cushions the posterior and lateral sides of the eye, providing support and protection and facilitating oxygen and nutrient delivery by the blood through is associated blood vessels

Tonic receptors

demonstrate limited adaptation In response to a constant stimulus, tonic receptors continuously generate nerve signals and only slowly decrease the number relayed to the CNS

Unencapsulated tactile receptors

dendritic endings of sensory neurons with no protective covering. 3 types: Free nerve endings, Root hair plexuses, and tactile discs

Accessory structures of the eye are located

either attached to the eye or around the eye. Include: extrinsic eye muscles, eyebrows, eyelids, eyelashes, conjunctiva and lacrimal glands

Papillae of the tongue

epithelial and CT elevations on the dorsal surface of the tongue. Four types: Filiform - short and spiked; distributed on the anterior two-thirds of the tongue surface. Do not house taste buds and have no role in gustation. Bristlelike structure serves in detecting texture and food manipulation Fungiform - clocklike projections primarily located on the tip and sides of the tongue. Contains a few taste buds. Foliate - not well developed on human tongue. Extend as ridges on the posterior lateral sides of the tongue and house only a few taste buds during infancy and early childhood Vallate - aka circumvallate. Least numerous (10 to 12) yet are the largest papillae on the tongue. Arranged in an inverted V shape on the posterior dorsal surface of the tongue. Each one is surrounded by a deep, narrow depression. Most taste buds are housed within the walls of these papillae along the side facing the depression

Phasic receptors

exhibit rapid adaptation to a constant stimulus. Generate nerve signals only in response to a new (or changing) stimulus and quickly decrease the number of nerve signals relayed to the CNS

Sclera provides for

eye shape, protects the eye's delicate internal components and serves as an attachment site for extrinsic eye muscles. Posteriorly, the sclera is continuous with the optic nerve sheath, which is an extension of dura mater that surrounds the optic nerve

Ganglion cells

form the innermost layer in the neural layer and are adjacent to the posterior cavity Axons of the ganglionic cells extend into and through the optic disc to form the optic nerve. Incoming light must pass through the ganglion cells and bipolar cells before reaching the photoreceptor cells. Electrical signals (initiated by transduction of light by photoreceptor cells) are then relayed to bipolar cells and then to ganglion cells

Other cells that function in transmission of light stimuli

horizontal cells - sandwiched between the photoreceptor and bipolar cells in a thin web Regulate and integrate the electrical signals sent from the photoreceptor cells to the outer cell layers

Bipolar cells

immediately internal the photoreceptor cells. Bipolar cells are located between photoreceptor cells and ganglion cells Dendrites of the bipolar cells synapse with dendrites of ganglion cells

Anterior cavity

in front of the lens, contains a circulating fluid called aqueous humor Subdivided into two chambers by the iris (colored part of the eye) - anterior chamber (between the iris and cornea) and posterior chamber (between the iris and lens)

Ora serrata

jagged margin between the photosensitive posterior region of the retina and the nonpohotosensitive anterior region of the retina. Nonphotosensitive portion continues anteriorly to cover the ciliary body and the posterior aspect of the iris

Free nerve endings

least complex and reside closest to surface of skin, usually in the papillary layer of the dermis. Some branches extend into deepest epidermal strata and terminate between epithelial cells. Also located in mucous membranes. Primarily detect temperature and pain stimuli, but some also detect light touch and pressure. Can be either tonic (adapt slowly) or phasic (adapts quickly)

Posterior cavity

lies behind the blends, contains a permanent fluid called vitreous humor

Depolarization of a receptor taste cell generates

local receptor potentials that initiate nerve signals that cause the release of neurotransmitter at its basal side. The neurotransmitter stimulates a primary neuron, which is within the facial or glossopharyngeal nerves that relay nerve signals to the brain

Ciliary body

located immediately anterior to the choroid and is composed of both a ciliary muscle and ciliary process

Visceral sensory receptors

located in the walls of the viscera and blood vessels. Detect stretch in the smooth muscle within the walls of internal organs, chemical changes in the contents within their lumen (CO2 levels in blood), temperature and pain

What is the leading cause of blindness in developed countries?

macular degeneration associated with diabetes, an ocular infection, hypertension or trauma to the eye

Sensory information first reaches the

medulla oblongata (specifically, the nucleus solitaires) to trigger reflexes that increase salivation and release of stomach secretions in anticipation of the arrival of food. A gag or vomiting reflex may also occur in response to a nauseating substance. Sensory information is then relayed via secondary sensory neurons to the thalamus and then via tertiary sensory neurons tot he primary gustatory cortex for the conscious perception of taste. This requires integration taste sensations with those of temperature, texture and smell

A sensory receptor must be able to provide the CNS with what characteristics regarding a stimulus

modality (form of a stimulus) - provided by a given type of sensory receptor relaying sensory input along designated sensory neurons to specific regions of the CNS location intensity - A greater or more intense stimulus results in both the most sensitive sensory receptors initiating nerve signals more frequently and the less sensitive sensory receptors (which are not typically active) initiating nerve signals duration - all sensory receptors become less sensitive to a constant stimulus and initiate a progressive decrease in nerve signals

Sensory receptors may also be classified according to the stimulus they respond to, which is called

modality of stimulus, aka stimulating agent Some sensory receptors respond only to temperature changes, whereas others respond to chemical changes.

Iris

most anterior region of the vascular tunic is the iris - which is the colored portion of the eye Composed of two layers of smooth muscle fibers, melanocytes, and an array of vascular and nervous structures. In the center of the iris is an opening called the pupil, which allows light to enter the eye to reach the retina. The iris controls pupil size (diameter), and thus the amount of light entering the ey using its two smooth muscle layers

Tactile receptors

most numerous type of sensory receptor mechanoreceptors located in the skin and mucous membranes Dendritic endings that compose sensory receptors are either unencapsulated or encapsulated

Conjunctiva contains

numerous goblet cells, which secrete mucin to lubricate and moisten the eye Contains many blood vessels, which supply oxygen and nutrients to the avascular sclera, as well as abundant nerve endings that detect foreign objects as they contact the eye Does NOT cover the surface of the cornea (transparent cent of the anterior eye), so no blood vessels interfere with passage of light into eye

Referred pain

occurs when sensory nerve signals from certain viscera are perceived as originating not from the organ, but from somatic sensory receptors within the skin and skeletal muscle Numerous somatic sensory neurons and visceral sensory neurons conduct nerve signals on the same ascending tracts within the spinal cord - as a result, the somatosensory cortex in the brain is unable to accurately determine the actual source of the stimulus, and so the stimulus may be localized incorrectly

What cells produce action potentials in the retina?

only amacrin and ganglion cells other cells generate graded potentials

Photoreceptor cells

outermost layer of cells in the neural layer contain pigment molecules that react to light energy Two types of photoreceptor cells are rods (rod-shaped outer portion and function in dim light) and cones (outer portion and function in high-intensity light and in color vision)

Space between the open eyelids

palpebral fissure

Amacrine cells

positions between the bipolar and ganglion cells and help process and integrate electrical signals between bipolar and ganglion cells electrical signals are either action potentials or graded potentials

Lacrimal apparatus

produces, collects and drains lacrimal fluid Contains water, sodium ions, antibodies and an antibacterial enzyme called lysozyme Lubricates the anterior surface of the eye to reduce friction from eyelid movement; continuously cleanses and moistens the eye surface; helps prevent bacterial infection; and provides oxygen and nutrients to the corneal epithelium

What three criteria are used to categorize sensory receptors

receptor distribution stimulus origin modality of stimulus

Gustatory cells

regenerated every 7 to 9 days by basal cells within the taste bud and decrease with age, beginning at about age 50 Specialized neuroepithelial cells Dendritic ending of each gustatory cell is formed by a slender gustatory microvillus, sometimes called a taste hair. Many extend through an opening in the taste bud, called the taste pore, to the surface of the tongue. This is the receptive portion of the cell. Within the oral cavity, saliva keeps the environment moist; the tastants in our food dissolve in the saliva, and then they are able to contact and stimulate gustatory cells

Olfactory receptor cells are one of the few neuronal types that are

replaced regenerated every 40 to 60 days by basal cells within the olfactory epithelium. Decreases with age, and the olfactory receptor cells that remain lose their sensitivity to odors.

Macula lutea

rounded, yellowish region just lateral to the optic disc Within the macula luted is a depressed pit called the fovea centralis (contains the highest proportion of cones and almost no rods). Fovea centralis is the area of sharpest vision because of its high concentration of cones

Tarsal glands

sebaceous glands located within the tarsal plates of the eyelid. Release an oily secretion at the edge Contribute to the gritty, particulate material often noticed around the eyelids after waking

Olfactory epithelium

sensory receptor organ for smell lines the superior region of the nasal cavity, covering both the inferior surface of the cribriform plate and superior nasal conchae of the ethmoid bone Composed of three distinct cell types Olfactory receptor cells (olfactory neurons) - detect odors Supporting cells (sustentacular cels) - sustain the olfactory receptor cells Basal cells - function as neural stem cells to continually replace olfactory receptor cells

Root hair plexuses

specialized dendritic endings of sensory neurons that form a weblike sheath around hair follicles in the reticular (deeper) layer of the dermis. Any movement or displacement of the hair changes the arrangement of these dendritic endings, initiating nerve signals. Phasic receptors that adapt quickly. Conscious awareness subsides immediately until root hair plexuses are restimulated (putting on and taking off a shirt)

Conjunctiva

specialized stratified columnar epithelium that forms a continuous, transparent lining over the anterior surface of the sclera ("white") of the eye (ocular conjunctiva) and the internal surface of the eyelid (palpebral conjunctiva) The junction of the ocular conjunctiva and palpebral conjunctiva is called the conjunctival fornix (prevents a contact from moving behind the eye)

The tastants in our find bind to

specific receptor plasma membrane proteins of gustatory cells The initial binding of a specific tasting molecule to its receptor causes depolarization of that specific receptor cell, but the manner in which cell depolarization occurs varies. Sweet, bitter and umami stimuli (which are tastant molecules) bind to receptors on the taste bud surface, which activate a G protein. The G protein activation causes the formation of a secondary messenger, which results in cell depolarization. In contrast, salt and sour stimuli (tastant ions) do not use a G protein and depolarize the cell directly

Lens

strong yet deformable transparent structure Composed of precisely arranged layers of cells that have lost their organelles and are filled completely by a protein called crystallin, which are enclosed by a dense, fibrous elastic capsule. Focuses incoming light onto the retina and its shape determines the degree of light refraction

tastant

taste-producing molecules and ions of what we eat and drink Gustatory cells are chemoreceptors located within tase buds on the tongue and soft palate Tongue and soft palate also house mechanoreceptors and thermoreceptors to provide us with information about the texture and temperature of our food

Olfactory bulbs

terminal ends of olfactory tracts located inferior to the frontal lobes of the brain Axons of olfactory nerves synapse with both mitral cells and tufted cells (which are secondary neurons) within the olfactory bulbs Resulting spherical structures are called olfactory glomeruli

Pupillary reflex

the ability of the iris to change the size of the pupil in response to varying amounts of light When stimulated by bright light, the reflex involves the relaying of sensory input from the photoreceptors of the eye to the brain, which initiates nerve signals along the parasympathetic division fibers of the oculomotor nerve to stimulate the sphincter pupillae muscle to contract, which decreases pupil diameter

What is a receptive field

the area within which the dendritic endings of a single sensory neuron are distributed. Small receptive field provides us with the ability to identify the stimulus location more specifically

The eyelids are joined at

the medial and lateral palpebral commissures, or canthi At the medial commissure is a small, reddish body called the lacrimal caruncle

Three regions that have rods and cones in the retina

the optic disc macula lutea peripheral retina

Cells of the neural layer

three distinct layers of neurons form the neural layer: photoreceptor cells, bipolar cells and ganglion cells

The wall of the eye is formed by

three principal tunics (layers): fibrous tunic (external), vascular tunic (middle), and the retina (inner)

Sensory receptor (aka transducer) general function

to respond to a stimulus and initiate sensory input to the CNS Involves converting stimulus energy into an electrical signal. Original energy form detected is specific to the type of sensory receptor Energy is always transducer to electrical energy and sent along a sensory neuron

Bloodshot eyes occur with

vasodilation of the scleral blood vessels, which become visible through the transparent conjunctiva

Odorants

volatile molecules that must be dissolved in the mucus in our nasal cavity to be detected by chemoreceptors

When is the pupillary reflex tested

when brain trauma is suspected e.g. from a car accident or drug overdose