Human Anatomy CH 16 Flashcards
What are the special senses?
- Taste
- Smell
- Sight
- Hearing
- Balance
Define Touch
A large group of general senses
What two types of cells are taste bud cells? BE SPECIFIC
- Gustatory epithelial cells
- Basal epithelial cells
Where are special sensory receptors located?
They are localized and confined to the head region
What are special receptor cells and what do they do?
They are neuronlike epithelial cells or small peripheral neurons. They transfer sensory information to other neurons in an afferent pathway.
What is taste called?
Gustation
What is smell called?
Olfaction
What are receptors that respond to chemical substances called?
Chemoreceptors
How are chemoreceptors able to respond to smell?
Airborne chemicals dissolve in fluids of the nasal mucosa
What are the two types of tongue papillae?
- Fungiform papillae
- Vallate papillae
Where are taste receptors found? BE SPECIFIC
Taste buds, more specifically mostly on the surface of the tongue within tongue papillae
How many cells are in the taste buds?
50-100
How often are taste bud cells replaced?
Every 7-10 days
What are the five basic qualities of taste?
- Sweet
- Sour
- Salty
- Bitter
- Umami
What is umami drawn out by?
It is elicited by glutamate
What extends from the gustatory epithelial cells and where do they extend to?
Long microvilli extends through a taste pore to the surface of the epithelium
Where are taste modalities elicited from?
All areas containing taste buds
What is elicited from areas containing taste buds?
Taste modalities
Where does taste information travel through to reach the cerebral cortex?
Facial (VII), Glossopharyngeal (IX), and Vagus (X) nerves
Out of the 3 taste nerves, which one is NOT one of the primary taste nerves?
Vague Nerve (X)
What does synapse mean?
A junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter
Where do sensory neurons synapse?
Solitary nucleus of the medulla
From the solitary nucleus, where are impulses transmitted to?
The thalamus and ultimately to the gustatory area of the cerebral cortex in the insula
Where are olfactory receptors part of?
Olfactory epithelium
What type of tissue is the olfactory epithelium made of?
Pseudostratified columnar
What are the 3 main cell types of the olfactory epithelium?
- Olfactory sensory neurons
- Supporting epithelial cells
- Olfactory stem cells
Where are cell bodies of olfactory neurons located?
Olfactory epithelium
Describe the cell bodies of olfactory sensory neurons
They have an apical dendrite that projects to the epithelial surface and ends in a knob from which olfactory cilia radiate
What do olfactory cilia do?
Act as receptive structures for smell
What does mucus do?
Captures and dissolves odor molecules
What are the bundles of axons of olfactory sensory neurons called?
Filaments of the olfactory nerve
What do filaments of the olfactory nerves do?
- Penetrate the cribriform plate of the ethmoid bone
- Enter the olfactory bulbs and synapse with mitral cells
What do mitral cells do?
They transmit impulses to the olfactory tract
Where do mitral cells transmit impulses to?
- Limbic System
- Piriform lobe of the cerebral cortex
- Primary olfactory cortex in piriform lobe
What disorder is the absence of the sense of smell?
Anosmia
What is anosmia caused by?
Injury, colds, allergies, or zinc deficiency
What is the distortion of smells or olfactory hallucinations?
Uncinate Fits
What do Uncinate Fits result from?
Irritation of olfactory pathways after brain surgery or head trauma
From what does the olfactory epithelium derive from?
Olfactory placodes
When do taste buds develop?
Upon stimulation by gustatory nerves
What is the dominant sense in humans?
Vision
What’s the percentage of all sensory receptors in the eyes?
70%
What’s the percentage of the cerebral cortex involved in processing visual information?
40%
How much of the eye’s surface is visible?
Anterior one-sixth
Define Eyebrows
Coarse hair on the superciliary arches
What’s another name for eyelids? What are they separated by?
Palpebrae; Separated by the palpebrae fissure
Where do the eyelids meet?
Medial and lateral angles (canthi)
What is the reddish elevation at the medial canthus?
Lacrimal caruncle
What is the connective tissue within the eyelids?
Tarsal plates
What are modified sebaceous glands called?
Tarsal glands
What is transparent mucous membrane called?
Conjunctiva
What are the parts of the conjunctiva called?
- Palpebral conjunctiva
- Bulbar conjunctiva
- Conjunctival sac
What keeps the surface of the eye moist?
Lacrimal apparatus
What produces lacrimal fluid?
Lacrimal gland
Where does the lacrimal fluid drain into?
Empties into the lacrimal sac, then the nasal cavity
How many muscles control the movement of the eye? What are they?
Six muscles;
1. Lateral and medial rectus
2. Superior and inferior rectus
3. Superior and inferior oblique
Where do the 4 rectus muscles originate from?
Annular ring
Where do the extrinsic eye muscles originate and insert into?
Originates in the walls of the orbit and inserts on outer surface of the eyeball
What do the components of the eye do?
- Protect and support the photoreceptors which gather, focus, and process light into precise images
What are the external walls composed of and how many? What are their names?
3 tunics
What are the 4 parts of the fibrous layer?
- Sclera
- Cornea
- Limbus
- Scleral venous sinus
What is the most external layer of the eyeball called?
Fibrous Layer
What is the fibrous layer composed of?
2 regions of connective tissue
Describe the sclera and it’s function
Posterior five-sixths of the tunic that is white and opaque
Function: Provides shape and an anchor for eye muscles
Describe the cornea
Anterior one-sixth of the fibrous tunic
Describe the limbus
Junction between sclera and cornea
What’s the function of the scleral venous sinus?
Allows aqueous humor to drain
What is the middle layer of the eyeball called?
Vascular Layer
What is the vascular layer composed of?
- Choroid
- Ciliary Body
- Iris
What is the vascular, darkly pigmented membrane of the eye?
Choroid
Describe the choroid and it’s function
- Forms the posterior five-sixths of the vascular tunic
- Has a brown color due to melanocytes, which helps absorb light and prevents scattering of light rays within the eye
- Corresponds to the arachnoid and pia maters
What is the thickened ring of tissue, which encircles the lens called? What is it composed of?
Ciliary body, composed of ciliary muscle
What is the posterior surface of the ciliary body called?
Ciliary Processes
What is attached around the entire surface of the lens?
Ciliary Zonule
What is the visible colored part of the eye called? What is it attached to and what is it composed of?
Visible colored part of the eye that is attached to the ciliary body and composed of smooth muscle
What is the pupil? What papillae muscles is it composed of? What is its function?
- Round central opening
- Sphinchter and dilator pupillae muscles
- Acts to vary the size of the pupil
What is the lens natural position? What pulls and causes it to be tense?
- Flat
- Suspensory Ligament
What is the inner layer/deepest tunic called?
Retina
What layers form from the optic cup and compose the retina? What are they made of?
- Pigmented layer made of single layer of melanocytes
- Neural layer made of sheet of nervous tissue
What does the pupillary light reflex do?
Protective response of pupil constriction when a bright light is flashed in the eye
What are the 3 main types of neurons? From one to another, what do they do?
- Light activates photoreceptors cells which signal bipolar cells
- Bipolar cells signal ganglion cells to generate nerve impulses
- Ganglion cells - Axons from the ganglion cells run along internal surface of the retina and converge posteriorly to form the optic nerve
What are the two main types of photoreceptors, their functions, and what they’re considered as?
- Rod Cells - More sensitive to light and allow vision in dim light
- Cone Cells - Operate best in bright light and enable high-acuity, color vision
They are considered neurons
What do the outer segments of the rods and cones do?
They are receptor regions where light-absorbing pigments are present
What to light particles do to visual pigment?
Modify the visual pigment and generate a nerve impulse
Describe photoreceptors and their “survivability”
- Vulnerable to damage by light or heat
- Cannot regenerate if destroyed
- Continuously renew and replace their older segments
What is the junction between the neural and pigmented layer called?
Ora Serrata
Where does the neural layer end? What does the pigmented layer cover?
- Posterior margin of the ciliary body
- Covers ciliary body and posterior surface of the iris
What structures does the posterior part of the eye contain and what do the structures contain/what regions are they known for?
- Macula Lutea - Contains mostly cones
- Fovea Centralis - Contains only cones and is the region of highest visual acuity
- Optic Disc - “Blind Spot”
What supplies blood to the outer third of the retina? What supplies blood to the inner two-thirds of the retina?
- Supplied by capillaries in the choroid
- Supplied by central artery and vein of the retina
What divides the eye?
Lens and ciliary zonules
What is the posterior cavity (segment) filled with? What is the 3 functions of the fluid?
Vitreous humor
1. Transmits light
2. Supports the posterior surface of the lens
3. Helps maintain the intraocular pressure
What does the anterior segment divide? What do the divided parts situate?
- Anterior chamber - Between cornea and iris
- Posterior chamber - Between iris and lens
What is the anterior cavity (segment) filled with? What is the 3 functions/characteristics of the fluid?
Aqueous humor
1. Renewed continuously
2. Formed as a blood filtrate
3. Supplies nutrients to the lens and cornea
Describe the lens
Thick, transparent biconvex disc that is held in place by the ciliary zonules
What covers the anterior surface of the lens?
Lens epithelium
What forms the bulk of the lens? How does this affect the lens as it grows?
Lens fibers
1. Lens fibers are continuously added
2. Lens enlarges throughout life
Where do light rays converge?
On the retina at a single focal point
What are light bending structures called? What are the 3 structures part of it?
Refractory media
1. Lens
2. Cornea
3. Humor
Is the curvature of the lens adjustable? If so, what is it for?
Yes, allows for focusing on nearby objects
What is myopia? How do you fix it?
Nearsightedness; Fixed with concave lenses
What is hyperopia? How do you fix it?
Farsightedness; Fixed with convex lenses
Where does most visual information travel to? What is this destination responsible for?
The cerebral cortex is responsible for conscious ‘seeing’
Where do other pathways travel to?
Nuclei in the midbrain and diencephalon
What allows depth perception?
Partial decussation of axons
Where do optic tracts send axons to? What does it synapse with? Further describe
- Axons are sent to lateral geniculate nucleus of thalamus
- Synapses with thalamic neurons
- Fibers of the optic radiation reach the primary visual cortex
What are two branches axons from the optic tracts travel to?
- Branch to superior colliculi and pretectal nuclei of the midbrain
- Branch to superchiasmatic nucleus
What causes retinopathy of prematurity?
- Blood vessels grow within the eyes of premature infants and have weak walls which causes hemorrhaging and blindness
What is the disorder that’s an contagious infection of the conjunctiva?
Trachoma
By week 4, what protrudes from the diencephalon?
Optic vesicles
What do eyes develop as?
Outpocketings of the brain
Over time, what happens to the ectoderm and what does it form? By week 5, what forms?
- It thickens and forms a lens placode
- Lens vesicle
What is the pathway for blood vessels called?
Optic fissure
What is the receptor organ for hearing and equilibrium?
Ear
What are the 3 regions of the ear? What are their functions?
- Outer ear - Hearing
- Middle ear - Hearing
- Internal ear - Hearing and equilibrium
What is the outer (external) ear composed of? What are their characteristics?
- Auricle (pinna) - Helps direct sounds
- External acoustic meatus - Contains hairs, sebaceous glands, and ceruminous glands
- Tympanic membrane - Forms the boundary between the external and middle ear
What is the middle ear composed of? What are their characteristics?
- Tympanic Cavity - Small air-filled space located within the petrous part of the temporal bone
- Medial wall is penetrated by the oval and round windows
- Pharyngotympanic tube (auditory tube) - links the middle ear and pharynx
- Ear ossicles - smallest bones in the body
- Tensor tympani and stapedius - Two tiny skeletal muscles in the middle ear cavity
What comprises the ear ossicles and what are their characteristics?
- Malleus - Attaches to the eardrums
- Incus - Between the malleus and the stapes
- Stapes - Vibrates against the oval window
What is another name for the internal ear?
Labyrinth
Where is the internal ear located?
Lies within the petrous part of the temporal bone
What is the bony labyrinth and what are its three parts?
A cavity
1. Semicircular canals
2. Vestibule
3. Cochlea
What is the membranous labyrinth, what does it contain, and where is it located?
It is a series of membrane-walled sacs and ducts fit within the bony labyrinth. Filled with endolymph
What does the bony labyrinth contain?
Perilymph and is continuous with cerebrospinal fluid
What is the three parts of the membranous labyrinth?
- Semicircular duct
- Utricle and saccule
- Cochlear duct
What is the spiraling chamber in the bony labyrinth?
Cochlea
What is the pillar of bone that the cochlea coils around?
Modiolus
What is the name of a spiral of bone in the modiolus?
Spiral lamina
Where does the cochlear nerve run through?
Core of modiolus
What contains the receptors for hearing?
Cochlear duct (scala media)
What makes up the roof and floor of the cochlear ducts respectively?
- Vestibular membrane
- Basilar membrane
What does the spiral organ (organ of corti) consist of? What are the functions of what it consists of?
- Supporting cells
- Inner hair cell - Receptors that transmit vibrations of the basilar membrane
- Outer hair cell - Actively tune the cochlea and amplify the signal
*Hair cells are receptor cells
What lies medial to the middle ear?
Vestibule
What is suspended in perilymph and what are they shaped like?
Utricle and saccule, egg-shaped parts of the membranous labyrinth
What do the utricle and saccule house and what is it specifically?
The macula; a spot of sensory equilibrium
What kind of cells does the macula contain and what they synapse with? What is the function of the macula? What is the cells embedded into?
- Receptor (hair) cells and columnar supporting cells. Synapses with vestibular nerve
- Monitors the position of the head when it is still
- Tips are embedded in otolith membrane
What are otoliths?
Crystals of calcium carbonate
What are the 3 ‘structures’ posterior and lateral to the vestibule? On what plane does each one lie?
- Anterior semicircular canal - Lie in vertical plane
- Posterior semicircular canal - Lie in vertical plane
- Lateral semicircular canal - Lie in horizontal plane
What snakes through each semicircular canal?
Semicircular duct
Where is the crista ampullaris housed? Where is that structure located?
Membranous ampulla, located within the bony ampulla
What are the 2 things in the crista ampullaris of semicircular duct and what is their function?
- Cristae that contain receptor cells for rotational acceleration of the head
- Epithelium containing supporting cells and receptor hair cells
What does the ascending auditory pathway do?
Transmits information from cochlear receptors to the cerebral cortex
What are the 4 steps of the auditory pathway?
- Impulses from cochlear nerve to cochlear nuclei in medulla
- Neurons project to superior olivary nuclei
- Axons ascend in lateral lemniscus to inferior colliculus
- Projects to medial geniculate nucleus of thalamus and to the primary auditory cortex
What does the equilibrium pathway do? Where does most of the information go?
- Transmits information on the position and movement of the head
- Most information goes to lower brain centers (reflex centers)
What is another word for carsickness/seasickness? What is the popular theory for its cause?
Motion sickness; a mismatch of sensory inputs
What is the disorder for equilibrium being greatly disturbed? What causes it?
Meniere’s Syndrome; Excessive amounts of endolymph in the membranous labyrinth
What is the disorder in which sound vibrations cannot be conducted to the inner ear? What causes it?
Conduction deafness; ruptured tympanic membrane, otitis media, otosclerosis
What is the disorder that results from damage to any part of the auditory pathway?
Sensorineural deafness
When does embryonic development of the ear begin? What region of each ear forms from what?
- Week 4
- Inner ear - Ectoderm
- Middle ear - First pharyngeal pouches
- Ear ossicles - cartilage
- External ear - Differentiates from first branchial groove
What special senses are sharp in newborns?
Smell and taste
What happens by the fourth decade of life?
Ability to taste and smell declines
What is fully formed by 25 weeks?
Photoreceptors
All newborns are ______
Hyperopic
By month 3 and month 6 respectively, what occurs?
- Month 3 - Image can be focused on the retina
- Month 6 - Depth perception is present
What happens with increased age?
- Lens loses clarity
- Dilator muscles of the iris becomes inefficient
- Visual acuity is dramatically lower in people over 70
What happens in the newborn?
- Responses to sound are reflexive
- Low-pitched and middle-pitched sounds can be heard
What happens in the elderly?
- Hair cells are gradually lost
- Ability to hear high-pitched sounds fade
- Presbycusis occurs
What is presbycusis?
Gradual loss of hearing with age
What kind of fibers make up the cornea?
Dense Regular Connective Tissue
What kind of fibers make up the sclera?
Dense irregular connective tissue
