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Biol 2401 Anatomy and Physiology I notes - Nervous System: Senses Ch 10
General pathway:
stimulus --------------------------------------------------------------------------------> response
receptor cells ----> afferent sensory ----> interneurons ----> efferent motor ----> effectors
neurons
neurons
(muscles,
glands)
I------peripheral N.S. ---------------- -I ---central N.S. ----I --peripheral N.S.--I
Fig 9.7
Sensory receptors
- receptor cells + accessory structures that surround cells
- simplest are dendrites of sensory cells with no surrounding structure
- usually a receptor cell is sensitive to one kind of stimulation, specialized to detect one type
environmental change, although some are also sensitive to extreme stimulation
- all receptor cells relay information to brain or spinal cord as an action potential
- sensation is interpreted by region of brain that receives the action potential,
- perception is interpretation of stimulus by brain region
- projection is sensation associated with the body region from which the stimulus originated
- receptor cells can become less sensitive to stimulation after repeated stimulation
(sensory adaptation)
-sensory adaptation can be at the receptor (peripheral) or in the CNS pathways (central)
- receptor cells can be classified by the energy that stimulates, or environmental change that
stimulates them:
- chemoreceptors - molecules of different shape and concentration of chemicals
- thermoreceptors - temperature difference (some sensitive to hot, others to cool)
- mechanoreceptors - mechanical strain (stretching, flexing, pressure, etc.)
- photoreceptors - light energy
- nociceptors - pain, any strong stimulus that would damage cells
*Explain “phantom limb” pain. How can a hand “feel” if it is not there?
*Explain what projection and sensory adaptation are.
*List five types of receptors and describe the energy that stimulates each.
General and special senses
-general senses, or somatic senses, are typically widely scattered through body, mostly skin and
deeper tissues (although they may be more concentrated in certain places) and they either
have no accessory structure or a simple structure
- special senses are located in a specific region and have a complex enclosing accessory
structure (organ)
*Describe two differences between general somatic senses and special senses.
General senses:
Fig 10.1
touch and pressure (also called tactile or cutaneous senses)
- several varieties that provide fine and crude touch and fine and deep pressure
with combinations giving information about size, shape, texture, movement
- range in complexity from free nerve ending to multilayer capsule accessory
structure, all types of mechanoreceptors :
- free nerve endings in or near epithelial tissues - very sensitive to touch
- root hair plexus - free nerve endings associated with hair follicle - very sensitive
to touch which moves the hair
- Meissner’s (tactile) corpuscles - enclosed in connective tissue capsule, just below
epidermis in hairless areas of skin such as lips, finger tips, nipples, external
genitalia, palms of hands and soles of feet - fine touch and pressure
- Pacinian (lamellated) corpuscles - enclosed in multilayered connective tissue capsule, in
deeper skin and tendons, sensitive to deep pressure and high pressure vibrations
- baroreceptors - mechanoreceptors that detect pressure (and thus volume) changes in
certain visceral organs (blood vessels, digestive tract, respiratory tract, urinary bladder)
temperature - thermoreceptors - free nerve ending of sensory neuron, some sensitive to
cold (“cold receptors”) and others sensitive to warm (“warm receptors”)
- they adapt quickly and are much more effective at detecting change
pain - nociceptors - most located in somatic organs (skin, joints, muscles, bones),
fewer in visceral organs, none in the brain and spinal cord
- somatic pain localized, frequently trigger somatic reflex (flexor withdrawal
reflex for example) and protect body by stimulating a response to remove stimulus
- visceral pain often perceived as originating in more superficial area (referred
pain)
Fig. 10.2, 10.3
- nociceptors adapt slowly, although the sensations decrease within the CNS due to
certain chemicals (enkephhalins and endorphins)
- acute pain fibers (localized and short acting) and chronic pain fibers (more generalized
area and long acting)
proprioception - mechanoreceptors that give information about body position and
movement, adapt very slowly or not at all
- linked with sense of equilibrium (a special sense coming up soon) to produce a
sense of body position within environment in relation to gravity
- muscle spindles give stretch (length) of muscles
- tendon organs give stress on tendons
- joint kinesthetic receptors give angular position of joints
*Give four examples of general senses.
*List several types of mechanoreceptors involved in touch and pressure sensations and tell where
each is located, its accessory structure and its sensitivity.
*Describe the sense of proprioception - give the receptors involved, where they are located and
what this sense tells us.
*Why do we usually sense stimulation of visceral pain receptors as pain originating in the
more superficial body regions (skin and muscles)? What is this called?
Special Senses:
Smell (olfaction)
10.4
- olfactory organs in superior nasal cavity just beneath ethmoid bone
- composed of chemoreceptors called olfactory receptor cells, supporting cells and
olfactory glands:
10.4
- olfactory glands produce mucus to clean, protect sensory cells and to
produce fluid to dissolve chemicals
- 5 cm2 area per nasal cavity, about 6 million receptor cells per nasal cavity
- olfactory receptor cells have cilia that extend into mucus layer, have protein
receptors that will bind with different shape molecules, one type receptor per cell
- an odorant molecule may fit into several type receptors (about 400 type
receptors but detect 1000s of odors via different receptor combinations)
- receptors adapt slowly, but pathways are blocked to cause rapid adaptation;
one odor does not affect another odor
Taste (gustatory)
- chemoreceptors located in taste buds on the tongue and other surfaces of the mouth and
throat
10. 5
- chemoreceptors called gustatory (taste) cells are bundled in connective tissue
capsules (organs) called taste buds (about 10,000)
- each gustatory cell has extensions called taste hairs that extend from capsule into
saliva, which covers surface of tongue
- taste hairs have protein receptors that bind with particular shaped molecules
dissolved in the saliva, which cause an action potential; one type receptor per cell
- sensations are interpreted as primary taste - sweet, salty, sour, bitter and umami
- all receptors scattered around mouth but concentrated in certain areas
- receptors adapt slowly, but pathways are blocked to cause rapid adaptation
- taste perception involves information from gustatory cells, olfactory cells and
tactile receptors
Equilibrium and hearing
Ear divided into three regions:
10.6, 10.8
- outer ear: pinna (auricle), external auditory canal (external acoustic meatus)
- together these structures collect and direct sound waves (air pressure)
into tympanic membrane (tympanum)
- middle ear (tympanic cavity) in temporal bone:
- auditory ossicles (malleus, incus, stapes) - conduct and amplify
vibrations from tympanic membrane to oval window
10.7
- auditory tube (Eustachian tube) connects to throat to equalize pressure
- mastoid sinuses (air cells in mastoid process) muffle internal vibrations
- oval and round windows, flexible membranes between middle and inner
- tensor tympani muscle and stapedius muscle prevent excessive vibrations
- inner ear: the bony (osseous) labyrinth is a series of channels and chambers in the
temporal bone, filled with perilymph.
- three parts of inner ear are the vestibule, semicircular canal and cochlea
- the membranous labyrinth is a series of fibrous tubes and chambers in
the bony labyrinth filled with endolymph
*Make a detailed drawing of the ear and label all of the structures listed above.
Hearing - in cochlea.
10.9
- the bony labyrinth is divided into 2 ducts, the upper vestibular duct
and the lower tympanic duct, both filled with perilymph.
- between these is the membranous labyrinth, the cochlear duct, with endolymph
- hair cells, a type of mechanoreceptor, and associated structures in the cochlear
duct form the organ of Corti, also called the spiral organ - the sensory
organ of hearing which extend the length of the cochlear duct
- the spiral organ is composed of hair cells attached at their base to the basilar
membrane and their cilia (“hairs”) projecting up under the tectorial membrane
- when the basilar membrane vibrates it pushes the hair cells up into the tectorial
membrane, causing them to be stimulated, stimulating sensory nerves
- the frequency of the vibration (pitch) is determined by the area along the spiral
organ that is stimulated and the intensity (volume) is determined by the
number of hair cells stimulated. Perception occurs in the auditory cortex.
*Follow a sound vibration from the outside to where it ends - list all of the structures.
*Describe the organ of Corti and tell how vibrations are converted to nerve impulses.
*Explain how pitch and volume are determined in the organ of Corti.
Equilibrium – in vestibule and semicircular canals, based on type mechanoreceptor called hair
cells (as in sense of hearing)
- static equilibrium (posture and position in relation to gravity)
10.11
- static equilibrium from 2 expanded areas in the vestibule, the saccule and utricle
- macula are hair cells with cilia in gelatinous mass with otoliths (dense crystals)
- when the head is tilted or accelerates the gelatinous mass moves.
- when hair cells are flexed nerve cells are stimulated. Do not adapt.
- dynamic equilibrium (rotational movement of head)
10.12, 10.13
- dynamic equilibrium from 3 semicircular canals, each in a different plane
- each canals has an enlarged area called the ampulla, with hair cells.
- cilia of hair cells are embedded in a gelatinous block called the cupula.
- hair cells and cupula form crista ampullaris, the organ of dynamic equilibrium
- when the endolymph in a semicircular moves it moves the cupula, deforming the
hair cells, causing nerve impulse
- each semicircular canal gives different plane of movement. Adapt quickly.
*What is the difference between static and dynamic equilibrium?
*Describe the organs of static and dynamic equilibrium - tell what they are made of and where
they are located.
*What type receptor cells are involved in equilibrium and hearing? Describe their structure.
*How is the sense of equilibrium related to the sense of proprioception?
*What is the difference between the bony labyrinth and the membranous labyrinth?
*What is the difference between perilymph and endolymph? Where is each located?
*What are otoliths and why are they important?
Vision (sight)
- complex structure around photoreceptors (eye capsule) with accessory structures
- accessory structures protect, clean and move the eye capsule
10.14
- eyelids (palpebrae) with eyelashes - cover and protect exposed eye
- conjunctiva - epithelium that covers exposed eye to corneal epithelium
- lacrimal glands - produce tears to lubricate, clean and nourish exposed
surface and to fight bacterial infections
10.15
- lacrimal canals and ducts -drain tears from surface of eye into nasal
cavity
- extrinsic eye muscles - six muscles that move eye capsule up, down, left,
right and rotate eye left and right
10.16
- orbital fat - cushions and insulates eye capsule
- eye capsule
10.17
- fibrous layer is outer layer, made of dense fibrous connective tissue;
forms structure of eye
- sclera is opaque capsule (“white” of the eye), posterior 90%
- cornea is transparent anterior bulge - lacks blood vessels, light
enters and, because it is curved, it helps focus light
- vascular layer is middle layer, highly vascularized
- choroid - dark colored posterior layer that absorbs stray light,
contains many capillary beds to nourish surrounding tissue
- ciliary body
10.18
- ciliary processes secrete aqueous humor
- ciliary muscles help change shape of lens to focus light
- suspensory ligaments attach lens to ciliary body 10.19
- iris is anterior portion anterior to lens - light enters through 10.20
- pupil is opening in iris that regulates the
amount of light entering the eye.
- two smooth muscle layers, circular and radial muscles, in
iris contract to constrict or dilate pupil, respectively Fig 10.20
*List three intrinsic eye muscles and tell where each is located and what each does.
- neural layer, or retina, is layer containing photoreceptors and numerous
neurons; ends just posterior to ciliary body
10.21
- pigmented layer to absorb stray light
- photoreceptors, rods and cones, respond to light
- bipolar cells synapse with rods and cones, ganglion cells synapse
with bipolar cells - together they integrate action potentials
from rods and cones and carry information to brain (optic nerve)
- optic disc, or blind spot, is area where optic nerve exits eye
- macula lutea contains only cones, and in center, the fovea, the
cones are the most dense - this is the area of sharpest vision
(visual acuity)
10.23
- lens layers of transparent cells in elastic capsule
10.19
- avascular to allow it to be transparent ( cataracts - opaque lens)
- supported by suspensory ligament to ciliary body
- lens can change shape to focus light rays on to retina at fovea 10.24
*Describe the process of focusing, or accommodation. Tell what the focal point and focal
distance are and how these are related to the shape of the lens and the fovea.
*List two structures in the eye that are used to focus, or refract, light rays. Which of these
can change shape and which cannot?
*Describe how the lens change shape when the ciliary muscles contract.
- the spaces within the eye capsule
10.17
- posterior cavity is between lens and retina
-filled with vitreous humor, or vitreous body, which is thick
gelatinous material which is not replaced and gives shape
to capsule and holds retina in place
- anterior cavity is between lens and cornea, divided into 2 chambers
- posterior chamber is between lens and iris
- anterior chamber is between iris and cornea
- aqueous humor is produced by ciliary processes, flows over lens
and through pupil, and is absorbed into blood vein at
junction of iris and cornea.
- aqueous humor is constantly replaced, nourishes the lens and
cornea which lack blood vessels
- glaucoma is caused by excess aqueous humor, increased pressure
- retina organization and physiology
10.25
- rods (125 million) are sensitive to low light but not color - respond to all
visible light wave lengths; respond more slowly
- most around edge of retina, none in macula lutea
- more integration with bipolar cells, therefore more sensitive
- cones (7 million) are less sensitive and respond to different wave lengths
of light; gives color vision (blue, green and red)
- fast but require higher light intensity
- mostly in macula lutea and more concentrated in fovea
- less integration with bipolar cells, therefore sharper image
- rods and cones have segments that contain visual pigments (rhodopsin)
- made of retinal and opsin - different opsins in different photoreceptors
(1 for rods, 3 for cones to absorb different wave lengths (colors)
- retinal absorbs photon of light -> changes shape -> activates opsin which
triggers a series of chemical reactions -> increases release
of neurotransmitter which is excitatory to bipolar cells
- this process breaks retinal and opsin - “bleaching”
- energy (ATP) required to reassemble rhodopsin
*Give five examples of special senses.