Chapter 16 Nervous System: Senses

Root hair plexus

In reticular layer of the dermis. Detect movement of the hair. Phasic

How we see

1. Light is refracted then focused on the retina 2. Light rays are transduce to nerve signals 3. These nerve signals are transmitted to the brain

Photo transduction with rods steps

1. Rhodopsin (opsin + cis-retinal) absorbs light rays 2. Upon exposure to light the retinal straightens out and reconfigures into a form called trans-retinal 3. Trans - retinal dissociates from the Opsin and photo transduction occurs. This dissociation of the rhodopsin into its two components is a process termed a bleaching reaction because the rhodopsin goes from a bluish - purple color to colorless. Bleaching reduces rhodopsin amounts in rods and temporarily affects our ability to see in dim light conditions. 4. Trans-retinal is re-converted to cis - retinal within the pigmented layer of the retina using ATP. 5. Cis-retinal associates with opsin to re-form rhodopsin.

Conjunctiva

A specialize stratified columnar epithelium termed the conjunctiva, 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 an palpebral conjunctiva is called the conjunctival fornix (this prevents contact lens from moving behind the eye) 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 Scalera as well as abundant nerve endings that the detect foreign objects as they contact the eye. Conjunctiva does not cover the surface of the cornea so no blood vessels interfere with passage of light into the eye

Refraction of light

Ability to see clearly requires refraction (or bending) of light rays so that they hit on the retina specifically at the fovea centralis. Light rays are refracted when they pass between two media of different densities and these media meet at a curved surface. The re-fraction of light rays is greater when there is a large difference in the refractive index between adjacent media, such as between air and water and with increasing curvature of the media surface. Both the cornea and lens play significant role in refraction of light for vision. The cornea because of the relatively large refraction of light that occurs as light passes from air into the cornea and the lens because of its ability to change shape

Photopigments

Are the specific molecules that absorb light and that are embedded within the plasma membrane of the outer segment of both rods and cones. Composed of a protein called an opsin and a light absorbing molecules called a retinal( or retineme) which is formed from vitamin A

Sour tastes

Associated with acids in the ingested material such as hydrogen ions in vinegar

External ear

Auricle (pinna): visible portion of the external ear is a skin covered elastic cartilage. Serves both to protect the entry into the ear and to direct sound waves into the bony tube called the External acoustic meatus. External acoustic meatus: narrow external opening prevents large objects from entering and damaging the Tympanic membrane. Fine hairs help guard the opening. Deep within the Canal, ceruminous glands produce a wax like secretion called Cerumen, which combines with dead sloughed skin cells to form earwax. Tympanic membrane (eardrum) : composed of fibrous connective tissue sandwiched between two epithelial sheets. Vibrates when sound waves hit it, and it's vibrations provide the means for transmission of sound wave energy from the external ear to the middle ear. Pain associated with trauma to the Tympanic membrane is relayed to the brain along sensory neurons within both the Vagus and trigeminal nerves.

2. Optic nerve

Axons of retinal ganglion cells form optic nerves and exit the eye

Fungiform

Block like projections primarily located on the tip insides of the tongue. Each contains only a few taste buds

Pupillary Constriction

Bright light causes sphincter pupillae contracts (parasympathetic)

Explain referred pains significance in diagnosis

Cardiac problems are often a source of referred pain because the heart receives its sympathetic innervation from the T1 - T5 segments of the spinal cord. Pain associated with myocardial in fraction (heart attack) maybe referred to the skin innervated by the T1 - T5 spinal nerves which lie along the pectoral region in the medial side of the arm. 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

Modality of stimulus

Chemo receptors: check chemicals (molecules or ions) dissolved in fluid. Ex: taste receptors, receptors and blood vessels that monitored hydrogen ions Thermo receptors, photo receptors, Mecahnorecptors: detect physical D formation of the plasma membrane due to touch, pressure, vibration and stretch ex: barorecptors, proprioceptors, tactile receptors, and other specialized cells such as the hair cells in the cochlea of the ear that move in response to soundwaves. Barorecptors: stimulated by changes in stretch or diss tension within the wall of body structures. In blood vessels Nociceptors: detect painful stimuli

Photo transduction in cones

Cis-retinal transforms to trans - retinal and a bleaching reaction occurs but a more intense light is required. The regeneration of photopsin occurs more quickly than the regeneration of rhodopsin.

Structures for hearing

Cochlea and spiral organ

The bony labyrinth is structurally and functionally partitioned into three distinct regions

Cochlea: houses a membranous labyrinth structure called the cochlear duct (or Scala media) Vestibule: contains two saclike membranous labyrinth structures the utricle and the saccule Semicircular Canal's: each contain a membranous labyrinth structure called the semicircular duct

Iris

Colored portion of the eye. Composed of two layers of smooth muscle fibers, melanocytes and an array of vascular and nervous structures. Iris controls pupil size or diameter and thus the amount of light entering the eye using its too smooth muscle layers.

Cillairy Body

Composed of both ciliary muscles and ciliary processes. Ciliary muscles - are bands of smooth muscle. Extending from the ciliary muscle to the capsule surrounding the lens are suspensory ligament's, which anchor the lens. Ciliary processes- contain capillaries that secrete aqueous humor

outer segment

Composed of hundreds of disks that are flattened membranous sacs constantly being replaced

Choroid

Composed of loose connective tissue that house is both an extensive network of capillaries and melanocytes. It's vast network of blood vessels supplies oxygen and nutrients to the retina, and melanin produced by its melanocytes absorbs extraneous light to prevent it from scattering within the eye.

Lens

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. The lens focuses incoming light onto the retina, and it shape determines the degree of light refraction. 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 on the suspensory ligament's increases, this constant tension causes the lens to flatten. When we wish to view objects closer than 20 feet Ciliary muscles contract the ciliary body moves closer to the lens and the tension on the suspensory ligaments decreases this causes the lens to become more spherical or curved.

Fibrous tunic (external)

Composed of the posterior sclera and the anterior cornea. Most of this tunic is the tough Scalera, a part of the outer layer that is called the white of the eye. It is composed of dense regular connective tissue containing numerous blood vessels and nerves. The Scalera provides for eyes shape, protects the eyes delicate internal components, and serves as attachment site for extrinsic eye muscles. Cornea - it's convex shape refracts (bends) light rays coming into the eye. The cornea is composed of an inner simple Squamous epithelium, a middle layer of collagen fibers, and an outer stratified squamous epithelium called the corneal epithelium. Cornea contains no blood vessels. Nutrients and oxygen are supplied to the internal epithelium of the cornea by aqueous humor within the anterior cavity of the eye, where as the surface corneal epithelium receives its oxygen and nutrients from the lacrimal fluid.

Retina (inner layer)

Composed of two layers and outer pigmented layer and an inner neural layer

Macula lutea

Contains a depressed pit called the fovea centralis which contains the highest proportion of cones and almost no rods. This pit is the area of sharpest vision

Inner segment

Contains the organelles for the cell such as mitochondria. synaptic terminal's on the other side of the cell body house synaptic vesicles with glutamate newer transmitter

Photo transduction

Converting light energy into an electrical signal. Rods and cones are the specific cells that engage. Photo receptor cells are composed of an outer segment, and intersegmental, cell body, and synaptic terminal's

Proprioceptors

Detect stimuli within joints, skeletal muscles, and tendons that since body or limb movement ex: joint receptors, muscle spindles,golgi tendon organs

Interoceptors

Detect stimuli within the body ex: receptors within walls of viscera and blood vessels

Stimulus origin

Exteroceptors: detect stimuli in the external environment ex: receptors within skin or mucous membranes or 5 senses

Accessory structures of the eye

Extrinsic I muscles, eyebrows, eyelid, eyelashes, conjunctiva, and lacrimal glands

Myopia(nearsightedness)

Eyeball is too long so far objects are blurry. Concave corrective lenses

Hyperopia(farsightedness)

Eyeball is too short so near objects are blurry. Convex corrective lens

Eyelids (palpebrae)

Formed primarily by a fibrous core the tarsal plate, the orbicularis oculi muscle ( which closes the eyelid), and a thin covering of skin. Muscle associated only with the upper eyelid is the levitator palepebrae superioris muscle, which pulls the upper eyelid to open the eye

Eyebrows

Function in both nonverbal communication associated with facial expressions and prevent sweat from dripping into the eyes

Sensory receptor distribution

General senses: distributed throughout the body; structurally simple -somatic sensory receptors(somatosensory): located in skin and mucus membranes ex: tactile (touch) receptors Located in joints, muscles, and tendons ex: joint receptors, muscle spindles, Golgi tendon organs. These detect stretch and pressure relative to position and movement of the skeleton and skeletal muscles. -visceral sensory receptors: located within walls of viscera and blood vessels ex: stretch receptors and stomach wall, chemo receptors in blood vessels Special senses: located only in the head; structurally complex sense organs ex: receptors for smell, taste, vision, hearing and equilibrium

Dark adaptations

Going quickly from bright light to darkness. Occurs because initially our cones become nonfunctional in the low light because they require a more intense stimulus, but our rods are still bleached from the bright light conditions from outside

Neural layer

Houses all photo receptor cells and their associated neurons responsible for absorbing light rays and converting them into nerve signals that are transmitted to the brain.

Vascular Tunic middle layer (uvea)

Houses an extensive array of blood vessels, lymph vessels and the intrinsic muscles of the eye. Composed of three regions: the choroid, the Ciliary body, and Iris.

Tactile disc

In stratum basale epidermis. Detects light touch. Tonic

Umami stimuli

Is a Japanese word meaning the delicious flavor. It is a taste related to amino acid's, such as glutamate and aspartame, to produce a meaty flavor

Pigmented layer

Is immediately internal to the choroid and attached to it. It provides vitamin a for the photo receptor cells of the Neural layer and absorbs extraneous light to prevent it from scattering within the eye

Modality

Is provided by a given type of sensory receptor relaying sensory input along designated sensory neurons to specific regions of the CNS

Olfaction

Is the sense of smell, whereby volatile molecules called odorants must be dissolved in the mucus and are nasal cavity to be detected by chemo receptors. Compared to many other animals our olfactory ability is much less sensitive and not as highly developed

6. Pretectal nucleus of the midbrain

Limited number of optic track axons project to the pretectal nucleus of the midbrain. Function as the control centers in both the pupillary reflex to regulate the amount of light that enters the eye and the accommodation reflex for focusing the lens

gustatory receptors

Located in taste buds, detect tastants in our food. Regenerated every 7 to 9 days by basal cells within the taste bud.

Pupillary dilation

Low light causes dilator pupillae contract (sympathetic innervation)

Explain the characteristic of a stimulus that sensory receptors provide to the CNS

Modality, location, intensity, and duration

Emmetropia

Normal vision

Foliate

Not well developed on the human tongue. They extend as ridges on the posterior lateral sides of the tongue and house only if you taste buds during infancy and early childhood

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.

Papillae of the Tongue

On the dorsal surface of the tongue are epithelial and connective tissue elevations called papillae which are of four types: Filiform, fungiform, vallate, and foliate

Define a sensation

Only nerve signals that reach the cerebral cortex of the brain results in our conscious awareness. A stimulus that we are consciously aware of is called a sensation.

3. Optic Chiasm

Optic nerve axons from the medial region of the retina cross at the optic chiasm; The axons from the lateral region of the retina remain uncrossed

1. Retina

Photo receptors and neurons in the retina process the stimulus from incoming light

Structures of the eye

Posterior cavity - lies behind the lens, contains a permanent fluid called vitreous humor. Anterior cavity- in front of the lens, contains the circulating fluid called aqueous humor The wall of the eye is formed by three principal tunics the fibrous, vascular and retina.

Eyelashes

Prevent particulate matter from entering the eye

Salt tastes

Produced by metal ions such as sodium and potassium

Sweet tastes

Produced by organic compounds such as sugar or other molecules

Bitter taste

Produced primarily by alkaloid such as quinine, unsweetened chocolate, nicotine, and caffeine

Lacrimal apparatus

Produces, collects, and drains lacrimal fluid. Lacrimal fluid contains water, sodium ions, anti-bodies, and anti-bacterial enzyme called lysozyme. This fluid lubricates The anterior surface of the eye to reduce friction from the eyelid movement, continuously cleanses and moistens the eye surface, helps prevent bacterial infection, and provides oxygen and nutrients to the corneal epithelium

Spiral organ (organ of corti)

Protected within the membranous cochlear duct is the spiral Organ which is the sensory structure for hearing. Cochlear duct contains endolymph. The spiral organ is a thick sensory epithelium consisting of both hair cells and supporting cells that rest on the basilar membrane. Two categories of hair cells rest on the basilar membrane including a single roll of inner hair cells which function as a sensory receptors for hearing and three rows of outer hair cells which alter the response of the spiral organ to sound

8. Primary visual cortex of occipital lobe

Receives processed information from the thalamus

Identify and describe the three criteria used to classify receptors

Receptor distributions, stimulus origin, modality of stimulus

Rods and cones

Rods are longer and narrower than cones. Rods located in peripheral retina. Rods activated by dim light. Cones in the fovea centralis. Activated by high intensity light

Describe the general function of sensory receptors as transducers

Sensory receptors convert or transduce stimulus energy to electrical energy Two features are critical to allow sensory receptors to function as transducers: 1. Sense receptors like neurons and muscle cells establish and maintain the resting membrane potential's across their plasma membrane. 2. Sensory receptors contain modality gated channel that opens in response to a stimulus at the plaza membrane.

Describe the general structure of a receptor

Sensory receptors range in complexity from the relatively simple, bare terminal endings of a single sensory neuron to specialized, complex structures called sense organs. All receptors are functionally connected to the CNS by sensory neurons relaying information to the brain and spinal cord

Filiform

Short and spiked, they are distributed on the anterior two thirds of the tongue surface. These papillae do not house taste buds and thus have no role in Gustation. There bristle like structures serves as a mechanical function, they assist in detecting texture and manipulating food

7. Superior colliculus of midbrain

Some optic track axons project to the superior colliculus of midbrain. Coordinate the reflexive movements of the extrinsic Eye muscles

End bulb

Structure: Terminal endings of sensory neurons ensheathed in connective tissue. In the dermis, mucous membranes of oral cavity, nasal cavity, vagina and anal canal. The text light pressure and low frequency vibration. Tonic

Tactile corpuscle

Structure: highly intertwined terminal endings of sensory neurons enclosed by modified nureloemmocytes and dense irregular connective tissue. In dermal papillae, especially in lips, palms, eyelids, nipples, genitals. Discriminative touch for distinguishing texture and shape of an object; light touch. Phasic

Lamellated corpuscle

Structure: terminal endings of sensory neurons ensheathed with an inner core of neurolemmocytes and outer concentric layers of connective tissue. In the reticular layer of the dermis; hypodermis of the palms of the hands, soles of the feet, breasts and external Genitalia; and walls of some organs. It functions in coarse touch detects continuous deep pressure and high frequency vibration. Phasic

Bulbous corpuscle

Structure: terminal endings of sensory neurons within connective tissue. In dermis and subcutaneous layer. Detects continuous deep pressure and skin distortion. Tonic

Glands associated with the eyelids and eyelashes

Tarsal glands - are sebaceous glands located with the tarsal plates of the eyelid, release and oily secretion at the edge of the eyelid. Both a sebaceous gland and modified sweat gland are located at the base of each eyelash. These glands contribute to the gritty, particulate material often noticed around the eyelids after waking

Gustatory pathways

Taste sensations are transmitted by the facial nerves (CN VII) from the anterior two thirds of the tongue and by the glossopharyngeal nerves (CN IX) from the posterior one third of the tongue. These taste sensations are transmitted to the nucleus solitarius of the medulla oblongata before being transmitted to the thalamus and finally entering the gustatory cortex of the cerebrum.

Encapsulated tactile receptors

Terminal endings of sensory neuron's that are wrapped either by connective tissue or by connective tissue and specialized Gilal cells called neurolemmocytes. Include end bulbs, lamellated corpuscles, bulbous corpuscles and tactile corpuscles.

Compare and contrast unencapsulated and encapsulated tactile receptors

Textile receptors of the most numerous type of sensory receptor. Unencapsulated Tactile receptors: simply terminal endings of sensory neurons with no protective covering. 1. Free nerve ending: closest to skin surface usually in the papillary layer of the dermis; and in mucous membranes. The text temperature, pain, some detect like touch and pressure. Canbe phasic or tonic

Duration

The CNS is able to determine the duration of stimulus because all sensory receptors become less sensitive to a constant stimulus and initiate a progressive decrease in nerve signals. This decrease in sensitivity to a continuous stimulus is called adaptation.

Intensity

The CNS is able to interpret the relative intensity of the stimulus because of the change in number of nerve signals that are arriving along a designated nerve

Explain the significance of a receptive field

The area that the terminal endings of a single sensory neuron is distributed is called its receptive field. The size of the receptive field will determine the ability of the CNS to identify the exact location of the stimulus. A small receptive field provides us with the ability to identify the stimulus location more specifically. A large receptive field allows us to determine only the general region of the stimulus

Inner ear

The inner ear is located within the Petrous part of the Temporel bone, where there are spaces or cavities called the bony labyrinth. Within the bony labyrinth are membranous fluid filled tube's and sacs called the membranous labyrinth. Receptors for both hearing and equilibrium are within the membranous labyrinth. The space between the outer walls of the bony labyrinth and the membranous labyrinth is fluid with a fluid called perilymph that is similar in composition to interstitial fluid. The perilymph suspense, supports, and protects the membranous labyrinth from the wall of the bony labyrinth. The space within the membranous labyrinth contains a fluid called endolymph which is similar in composition to intracellular fluid with relatively high levels of potassium.

Vallate (circumvallate)

The least numerous about 10 to 12 yet are the largest papillae on the tongue. Most of our taste buds are housed within the walls of these papillae along the side facing the depression

5. Lateral geniculate nucleus of Thalamus

The majority of the optic track axons project to the lateral geniculate nucleus of Thalamus

Components of the retina

The optic disc, macula lutea and peripheral retina.

4. Optic tract

The optic tract contains axons from both eyes, and these axons will project to either the Thalamus or the midbrain.

Describe the olfactory pathways that relays sensory input to the brain

The pair of olfactory bulbs are the terminal ends of olfactory tracks located inferior to the frontal lobe's of the brain. Axons of olfactory nerve synapse with both mitral cells and tufted cells within the olfactory bulbs. The resulting spherical structures are called olfactory glomeruli. The convergence of signals within the glomerulis facilitates our ability to detect faint odor's. Axon bundles of the mitral and tufted cells form the paired olfactory tracts the project posteriorly along the inferior frontal lobe surface directly to the primary olfactory cortex in the temporal lobe and select a 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 make processing prior to reaching the cerebrum.

Photopsin

The photo pigment and cones. Three different types: blue cones - detect wavelengths of light at about 120 nm Green cones - maximally absorb light at 531 nm Red cones - best detect light at 558 nm

Rhodopsin

The photo pigment in rods. Involved in the transduction of dim light and is most sensitive to light at 500 -nm wavelength

Light adaptation

The process by which your eyes adjust from low light to bright like conditions, such as when you wake up at night and turn on the bright light in the bathroom. Even though your pupils constrict to reduce the amount of light entering your eyes, you are temporarily blinded as the rods become in active in the cones, which initially were overstimulated, gradually adjust to the brighter light

Accommodation

The process of making the lens more spherical to view close of objects. Controlled by by Visceral motor neurons of the parasympathetic division that extend within the oculomotor nerve (CN III)

Olfactory epithelium

The sensory receptor organ for smell Composed of three distinct cell types: 1. Olfactory receptor cells which detect odors. 2. Supporting cells: that sustain the olfactory receptor cells. 3. Basal cells: which function as a neural stem cells to continually replace olfactory receptor cells.

Location

The specific location of a stimulus is able to be determined by the CNS because sensory information is relayed either from different regions of a sensory receptor or from different locations within the body along designated sensory neurons within a given nerve that reaches specific regions of the CNS. The specific location of receptors of the skin relays sensory input to designated regions of the postcentral gyrus of the parietal lobe for interpretation.

Visual pathway from the photo receptors to the brain

The visual pathways begin at the retina where the photo receptor cells transduce light stimuli to an electrical signal. The bipolar cells are the primary neurons and the ganglion cells are the secondary neurons

Ear structure

Three distinct regions: external, middle and inner

Sensory receptors are either tonic receptors or phasic receptors

Tonic receptors: demonstrate limited adaptation. In response to a constant stimulus, tonic receptors continuously generate nerve signals and only slowly decrease the number relate to the CNS. example: receptors within the inner ear that determine head position, and proprioceptors in the joints and muscles that provide information of where your body is in space. All pain receptors are tonic receptors. Phasic receptors: exhibit rapid adaptation to a constant stimulus. Phasic receptors generate nerve signals only in response to a new or changing stimulus and quickly decrease the number of nerve signals relate to the CNS. Examples include the deep pressure receptors that since the increased pressure when we first sit down in a chair.

Vitreous humor

Transparent gelatinous fluid fills the posterior cavity. Produced during embryonic development and both helps to maintain eye shape and support the retina to keep flush against the back of the eye

Middle ear

Tympanic cavity: Air filled. To membrane covered openings the oval window and round window Auditory tube (pharyngotympanic tube or Eustachian tube): serves as a passageway that extends from the middle ear into the nasopharynx. This tube is normally closed. Air movement through this tube occurs as a result of chewing, yawning, and swallowing, which equalize pressure on either side of the Tympanic membrane allowing the Tympanic membrane to vibrate freely. The Tym panic cavity, auditory tube, and nasopharynx are lined with continuous mucous membrane Auditory ossicles: the malleus (hammer), the incus(anvil) and stapes (stirrup) MIS. Responsible for amplifying sound waves from the Tympanic membrane to the oval window. When sound waves strike the Tym panic membrane the three middle ear ossicles vibrator long the Tympanic membrane causing the footplate of the states to move in and out of the oval window. The movement of this ossicle initiates pressure waves in the fluid within the closed compartment of the inner ear. The tensor Tympani (attached to malleus) and the stapedius restrict ossicle movement when loud sounds occur included when we are speaking, and thus protect the sensitive sensory receptors within the inner ear.

Aqueous humor

Watery fluid that circulates within the anterior cavity. Continuously produced by the Cililary processes. The circulation of aqueous humor provides nutrients and oxygen to both the avascular cornea (specifically its inner epithelium) and lens.

Peripheral retina

Which contains primarily rods and functions most effectively in low light

Cochlea

Wraps approximately 2.5 times around a spongy bone axis called the modiolus giving the cochlea snail shaped appearance. The roof of the cochlear duct is formed by the vestibular membrane and the floors form by the basilar membrane, both filled with perilymph

Optic disc

Contains no photo receptors. Called the blind spot

Pitch

Dependent upon frequency of the vibrating object.

Soundwave pathways through the ear

Sound waves enter the external ear and vibrate the tympanic membrane to move the ossicles of the middle ear, which ultimately causes movement of a specific region of the spiral organ within the inner ear

Sound

The perception of pressure waves that are established by vibrating a object. These waves move through any medium, including air, liquid, or solid. Two properties of sound we perceive are pitch and loudness.

Frequency

The rate of back and forth motion of the vibrating object and is measured in cycles per second and expressed in Hertz(Hz). The spiral organ of the human ear can perceive sounds with frequencies that range from 20Hz to 20,000Hz, but we are most sensitive to sounds with frequencies b