Transcript lecture fourteen – senses

HUMAN ANATOMY
LECTURE FOURTEEN
SENSES
SENSES
• Means of receiving information about environment and body
• Sensation - conscious awareness of stimuli received by
sensory receptors
• Steps to sensation:
(1) stimuli detected by sensory receptors
(2) action potentials sent to CNS - nerve tracts send action
potentials to cerebral cortex and other areas of brain
(3) cerebral cortex translates action potentials, creating
awareness of stimulus
RESPONSES OF SENSORY RECEPTORS
• Action potential results from interaction of sensory receptors with
stimulus
• Primary receptors - axons conduct action potentials in response
to stimulation of receptor
• Secondary receptors - release of neurotransmitters that bind to
receptors on a neuron causing an action potential
• Accomodation - decreased sensitivity to a continued stimulus
• Proprioceptors - provide information about the precise position
and the rate of movement of various body parts, the weight of an
object being held, and the range of motion of a joint
TYPES OF SENSES
General Receptors:
• Distributed over most of the body
• Primary receptor generates action potential
• May be:
somatic (body) - touch, pressure, temperature,
proprioception, pain
visceral (internal) - pain, pressure
Special Senses:
• Smell, taste, sight, hearing, balance
• Primary receptor produces an action potential by releasing a
neurotransmitter that binds to the secondary receptor that carries
impulse to brain
TYPES OF SENSORY RECEPTORS
Nociceptors - pain
• Detect extreme mechanical, thermal, or chemical (from damaged or
inflamed tissue) stimuli
• All parts of the body except brain
• Free nerve endings with large receptive fields - difficult to detect specific
area
Thermoreceptors - temperature
• Detect changes in temperature
• Free nerve endings in dermis, skeletal muscles, liver, hypothalamus
Chemoreceptors - chemicals
• Smell and taste
• Chemicals attach to receptors on the membrane
Mechanoreceptors - mechanical stimuli
• Compression, bending, stretching of cells, touch, pressure, proprioception,
hearing, balance
• Bending or stretching of plasma membrane on receptor cell stimulates action
potential
eg: Tactile/touch receptors – pressure and light touch
Proprioceptors – stretch of muscles, changes in body position
Baroreceptors – monitor changes in walls of blood vessels, digestive and
urinary tracts
Electromagnetic Receptors - energy wavelengths
• Respond to various wavelengths - electricity, magnetism, light
• Photoreceptors - detect light energy
Sometimes a sensation is a combination of receptors
ie/ wet – no wet receptor = touch, pressure, thermal receptors
SENSORY NERVES IN THE SKIN
Free Nerve Endings
• Simplest, unspecialized,
most common
• Throughout most of body
• Responsible for temperature
sensation, pain, tickle, some
proprioception
TACTILE SENSES
Merkel’s Discs
• Axonal branches with flattened
ends - each associated with a
cell within the basal layer of
epidermis
• Light touch and superficial
pressure
Hair Follicle Receptors
• Very sensitive to light touch
• Respond to bending of hair
• Not localized sensation
Pacinian Corpuscles
• Lamellated corpuscles - single
dendrite surrounded in layers
of corpuscles (like an onion)
• Located in deep dermis or
hypodermis - sense vibration
and deep pressure
• Associated with tendons and
joints - involved with
propreception
Meissner’s Corpuscles
• Located throughout dermal papillae
• Perceive sensations of fine touch and pressure
• Two-point discrimination - ability to detect simultaneous
stimulation at two points on the skin - used to determined texture
(numerous and close on tongue and fingertips)
Ruffini’s End Organ
• Located in reticular dermis
• Sensitive to pressure and
distortion of skin
• Any pulling on dermis
distorts capsular fibers
and stretches dendrites
• Mainly in fingertips
PROPRIOCEPTORS
Muscle Spindle
• Provide information about length of skeletal muscles
• Involved in stretch reflexes when adjusting posture
Golgi Tendon Organ
• Proprioceptors associated with tendons – located between
skeletal muscle and its tendon
• Respond to increased tension on tendon during muscle
contraction
SOMATIC SENSORY CENTER
HOMUNCULUS
• Size of various regions
related to the number of
sensory receptors in that
area of the body
REFERRED PAIN
• Sensation in one region of
body that is not source of
stimulus
• Organ pain usually referred
to the skin
• Both the organ and that
region of the skin input to
the same spinal segment and
converge on the same
ascending neurons
PHANTOM AND CHRONIC PAIN
Phantom Pain
• Occurs in people who have appendage amputated or structure removed (such
as a tooth)
• If sensory pathway is stimulated at any point the action potentials are initiated
and move toward CNS – integration in cerebral cortex results in perception of
pain that is projected to the site of the receptors in the pathway (even if the
receptors are no longer present)
Chronic Pain
• Not a response to immediate direct tissue injury
• Cerebrum and thalamus may malfunction and misinterpret discomfort as pain
• Brain may not properly regulate how much pain stimulation is allowed to
penetrate to the cerebral cortex
ie/ back pain, migraine – associated with frustration, helplessness, depression
SPECIAL SENSES
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Olfaction
Taste
Visual
Hearing and Balance
OLFACTION
Olfaction (smell) occurs when airborne
molecules (odors) enter the nasal
cavity
OLFACTORY NEURONS
• Dendrites found within the
OLFACTORY EPITHELIUM
lining superior part of nasal cavity –
ends in long cilia extending into
surrounding mucus
• Odorants dissolved in mucus attach
to receptors on cilia which initiate
action potential
• Axons pass through cribiform plate
to OLFACTORY BULBS which
extend into OLFACTORY TRACT
and synapse with associated neurons
in OLFACTORY CORTEX of
frontal lobe of brain
OLFACTORY NEURONAL PATHWAYS
Three regions in frontal lobe affect conscious perception of smell:
• Lateral olfactory area - conscious perception of smell
• Medial olfactory area - visceral and emotional reactions to odors
• Intermediate olfactory area - effect modification of incoming information
TASTE/GUSTATION
TASTE BUDS
• Located on PAPILLAE enlargements on tongue
• Consist of TASTE CELLS - each
contain hairlike processes called
TASTE HAIRS that extend into a
TASTE PORE in the epithelium
• Dissolved substances bind to
receptors on hairs and initiate
action potential carried to parietal
lobe of cerebral cortex
Taste sensations from anterior 2/3’s of
tongue carried by facial nerve
(VII), posterior 1/3 carried by
glossopharyngeal nerve (IX), also
vagus nerve (X)
Types of Papillae
Filiform
• Thread-like
• Most numerous, provide friction
• No taste buds
Fungiform
• Mushroom shaped
• Scattered over tongue
• About 5 taste buds on each
Foliate
• Leaf shaped
• In folds of tongue
• Most sensitive
Vallate
• Flat topped
• 100 taste buds on each
Taste Types
Sour
• Most sensitive receptors on lateral surface of tongue
Salty
• Most sensitive receptors on tip of tongue
• Anything with Na+ causes action potential
Bitter
• Most sensitive receptors on posterior of tongue
• Highest sensitivity
Sweet
• Most sensitive receptors on tip of tongue
Water
• Water receptors (mainly on pharynx)
• Processed in hypothalamus to regulate blood volume
Umani
• Pleasant taste ie/ beef broth, chicken broth, parmesan cheese
• Detected by receptors sensitive to amino acids
Taste Facts
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Texture affects perception of taste
Temperature affects taste
Very rapid adaptation, both at level of taste bud and within CNS
Taste influenced by olfaction - sense of taste is reduced when nose is
plugged
• Different tastes have different thresholds with acid and bitter being
tastes to which we are most sensitive (acids will damage mouth and
many poisons are bitter)
• Born with over 10,000 taste buds, number reduces dramatically by age
50
VISION
ACCESSORY STRUCTURES
• Eyebrows - shade, inhibit sweat
• Eyelids (palpebrae) - five layers of tissues
including a dense connective
tissue that maintains shape of lid
- blinking keeps eye lubricated
- protect eye
Palpebral fissure - space between eyelids
Canthi - where eyelids meet, lateral and
medial
Medial canthus - has carnucle with
modified sweat and sebaceous glands
• Eyelashes - double/triple row of
hairs
• Ciliary glands (modified sweat
glands) empty into follicles of
eyelashes
• Meiblomian glands - sebaceous
glands that release sebum (oil)
• Conjunctiva - thin transparent
mucous membrane over inner
surface of eyelid and anterior
surface of eye
- specialized stratified
squamous epithelium
Palprbral conjuctiva - covers
inside eyelids
Ocular (bulbar) conjunctiva covers anterior of eye (except
pupil)
SAGITTAL SECTION OF THE EYE
LACRIMAL APPARATUS
• Lacrimal gland - produce
tears to moisten, lubricate,
wash eye
- tears pass through lacrimal
ducts then into eye
• Lacrimal puncta - two pores
that drain tears
• Lacrimal canaliculi - canals
that tears flow through to the
lacrimal sac
• Nasolacrimal duct - opens
into nasal cavity beneath the
inferior nasal conchae
EXTRINSIC EYE MUSCLES
ANATOMY OF THE EYE
• The eyeball is a hollow, fluid-filled sphere with a large posterior compartment
and a smaller anterior compartment
• The wall of the eye is made up of three layers (tunics):
Fibrous tunic - outer layer including sclera and cornea
Vascular tunic - middle layer including iris, ciliary body, choroid,
Nervous tunic - inner layer including retina
FIBROUS TUNIC
Sclera – white of eye
• firm, white, outer layer continuous with cornea
• maintains roundness of eye
• protects internal structures and provides muscle attachment points
• made up of dense collagenous connective tissue with elastic fibers
Cornea
• transparent area that allows light to enter the eye
• causes light to bend/refract as part of focusing system
• avascular
• connective tissue matrix containing collagen, elastin fibers and
proteoglycans
• collagen fibers are small (so transparent)
• low water content (water would scatter the light)
VASCULAR TUNIC
• Middle layer with many blood
vessels - branch off internal
carotid artery
Iris
• Contains melanin (colored-part)
• Mainly smooth muscle
surrounding the pupil – by
changing size of pupil controls
amount of light entering
- parasympathetic stimulation from
oculomotor nerve causes circular
smooth muscles to contract =
constriction
- sympathetic stimulation causes radial
smooth muscles to contract = dilate
Ciliary Body
• Produces aqueous humor that
fills the anterior chamber
• Ciliary muscles control lens
shape - ciliary processes attach
to suspensory ligaments of
lens
Choroid
• Between sclera and retina
• Contains many blood vessels to
nourish retina
• Contains melanin so appears
black - black absorbs light so it
is not reflected inside the eye
NERVOUS TUNIC
Retina
• Innermost layer of eye wall
• Made up of two layers
(1) Pigmented retina
- outer pigmented layer
- reduces light scattering inside eye
(2) Sensory retina
- inner layer of rod and cone cells that are
sensitive to light
- rods are very sensitive to light and
function in dim light but don’t do color
- cones require more light but do
discriminate color (blue, green, or red)
• rods and cones synapse with neurons that
converge into the optic nerve
OPTHALMIC VIEW OF THE RETINA
Posterior of the eye is examined
with a opthalmoscope
• Macula lutea - only cones
• Fovea centralis - small pit in
center of macula lutea
- area of greatest visual acuity,
cones tightly packed
• Optic disc - white spot
- blood vessels enter eye
- nerve processes from sensory
retina meet and exit eye (optic
nerve)
COMPARTMENTS OF THE EYE
• Two fluid-filled compartments are
separated by the lens
Anterior Compartment
• Filled with aqueous humor - helps
maintain pressure within the eye,
refracts light and provides nutrients to
inner eye
- produced by ciliary process and
returned to venous circulation through
canal of Schlemm that goes around
the eye into veins of sclera
• Anterior chamber - between cornea
and iris
• Posterior chamber - between iris and
lens
Posterior Compartment
• Filled with jelly-like vitreous humor
that maintains intraocular pressure,
holds lens and retina in place
THE LENS
• Transparent, biconvex
• Made of columnar epithelial cells
• Surrounded by a highly elastic,
transparent capsule
• Held by suspensory ligaments
attached to ciliary muscles
• Changes shape as ciliary muscles
contract and relax
- when relaxed lens is flat and
allows for distance vision
- as object moves closer ciliary
muscles contract (parasympathitic
stimulation) and pull ciliary body
toward the lens - reduces tension
on suspensory ligaments and lens
become more spherical shaped
PATHWAY OF LIGHT
light rays strike cornea – refracts and brings rays closer together
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aqueous humor
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pupil
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light rays pass through lens – further refracts rays
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vitreous humor
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focus point at back of retina – rods and cones
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rods and cones send electrical signal along the optic nerve
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occipital cortex of brain interprets vision signals
CLINICAL VISION PROBLEMS
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Conjunctivitis (pink eye) – inflammation of
conjunctiva usually from bacterial infection
Trachoma – greatest single cause of blindness
today, conjunctivitis causing scarring of cornea
Myopia (nearsightedness) – can’t see distant
objects, focal point too near the lens (in front
of retina)
Hyperopia (farsightedness) – can’t see close
objects – focal point past retina
Presybopia – decrease in ability of eye to
accommodate near vision, occurs with age
Astigmatism – defect where cornea or lens
isn’t uniformly curved causing image to be out
of focus
Cataract – clouding of the lens as one ages,
infection, trauma, UV
Retinal detachment – separation of sensory
retina from pigmented retina
THE EAR
• External ear - hearing
- auricle, external auditory meatus and eardrum
(tympanic membrane)
• Middle ear - hearing
- air-filled space containing auditory vesicles
• Inner ear - hearing and balance
- interconnected fluid-filled tunnels and chambers within
the temperal lobe
EXTERNAL EAR
Auricle (pinna)
• fleshy external part
• elastic cartilage covered with
skin
External auditory meatus
• passage leading to eardrum
• lined with hairs and
ceruminous glands (produce
cerumen)
Typmpanic membrane
• separates external from middle
ear
• thin double layered membrane
• vibrates with sound waves
MIDDLE EAR
• Air-filled cavity separated from
internal ear by oval window and
round window
• Contains three auditory ossicles
(bones) that transmit vibrations from
the tympanic membrane to the oval
window
(1) malleus (hammer) - attaches to
tympanic membrane
(2) incus (anvil) - connects malleus
to the stapes
(3) stapes (stirrup) - base rests on
oval window by annular
ligament
• Muscles: tensor tympani inserts on
malleus, stapedius inserts on stapes
INNER EAR
Bony Labyrinth
• Interconnecting tunnels and
chambers continuous with the
temporal bone
• Divided into cochlea, vestibule, and
semicircular canals
Membranous Labyrinth
• Fluid-filled tunnels and chambers
inside the bony labyrinth
Perilymph
• Fluid found between bony and
membranous labyrinths
Endolymph
• Fluid within membranous labyrinth
INNER EAR CONT…
Cochlea
• Large snail shell shaped portion
• Spiral lamina (bone) twists the cochlea into its shape
• Extending from the spiral lamina is a Y-shaped membranous complex which
divides the cochlea into 3 sections
- the base of the Y is the spiral lamina
- one branch is the vestibular membrane
- the other branch is the basilar membrane
- the space above is the scala vestibuli which extends from the oval window
to the apex (helicotrema)
- the space inbetween is the cochlear duct
- the space below is the scala tympani which extends from the helicotrema to
the round window
- the scala vestibuli and tympani are both filled with perilymph fluid
INNER EAR CONT…
Organ of Corti (Spiral Organ)
• Found in cochlear duct
• Contains specialized sensory cells
called hair cells extending from the
basilar membrane
- have 80-100 hairlike microvilli
(stereocilia) on apical surface
- hair tips are embedded within an
acellular gelatinous shelf called the
tectorial membrane - attached
to the spiral lamina, remains
stationary
• Generates sound signals to sensory
neurons through to the cochlear
nerve
INNER EAR CONT…
• Hair cell arranged in rows
- inner hair cells for hearing
- outer hair cells regulate tension
on basilar membrane
• Hair bundle - stereocilia of one
inner hair cell
• Tip link (gating spring) - attaches
to tip of each stereocilium in a hair
bundle to the side of the longer one
- as stereocilia bend the tip links
open the K+ gates to generate
action potential
OPENING OF K+ GATES
HEARING
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3.
4.
Sound waves from auricle and external
auditory canal strike the tympanic
membrane causing it to vibrate
Vibration pushes the three bones of the
middle ear - the foot plate of the stapes
vibrates against the oval window
Vibration of the oval window causes
movement of the perilymph in the scala
vestibuli
Vibration of the perilymph produces
waves in the endolymph – displacing the
basilar membrane
- short waves (high pitch) cause
displacement near the oval window
- long waves (low pitch) cause
displacement near the helicotrema
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Movement of the basilar membrane
is detected in the hair cells of the
Organ of Corti which are attached to
its basilar membrane - as hair
changes shape between basilar
membrane and tectorial membrane
K+ gates are opened and nerve
impuse sent to temporal lobe to be
interpreted
Vibrations of the perilymph in the
scala vestibuli and of the endolymph
in the cochlear duct are transferred
to the perilymph of the scala
tympani
Vibrations in the perilymph of the
scala tympani are transferred to the
round window where they are
dampened
BALANCE AND EQUILIBRIUM
STATIC EQUILIBRIUM
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associated with the vestibule and involved in evaluating the position of the
head relative to gravity, detects linear acceleration and deceleration
Vestibule
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divided into utricle and saccule chambers
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each chamber contains specialized patches of epithelium called maculae
surrounded by endolymph
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the maculae contain hair cells with microvilli (stereocilia) and one cilium
(kinocilium) with their tips embedded in a gelatinous mass weighted down
by otoliths (protein and calcium carbonate particles)
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the gelatinous mass moves in response to gravity which bends the hair cells
and initiates action potentials
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changes in movement cause the otoliths to vary their pressure thus providing
info regarding head position of acceleration
KINETIC EQUILIBRIUM
• associated with the semicircular canals
• evaluates movement of the head in three
dimensional space
Semicircular Canals
• semicircular canals contain endolymph
and are positioned in the transverse,
coronal and sagittal planes
• The base of each expands into an ampulla
• Within each ampulla is specialized
epithelium forming a crista ampullaris
- a ridge of epithelium with a curved
gelatinous mass (cupula)
• Displacement of the endolymph causes
displacement of the cupula causing the
stereocilia to bend and initiate an action
potential to the hair cells