Administration
Somatic and Special Senses
Communicating with the world around us
The two major groups
Somatic senses
Touch, pressure, temperature and pain
Found in the skin and the deeper tissues
Structurally simple
special senses (sensory)
Smell, taste, hearing, vision, and equilibrium
Found in specialized organs for that sense
Structurally complex
Receptors
Types of receptors
Chemoreceptors
Stimulated by changes in the chemical concentration of substance
Pain receptors
Stimulated by tissue damage
Thermoreceptors
Stimulated by changes in temperature
Mechanoreceptors
Stimulated by changes in pressure and movement
Photoreceptors
Stimulated by light
The sensation
Sensation occurs when the brain interprets the sensory impulses.
Different sections of the brain interpret the signals, dependent on what type of receptor they come from
The cerebral cortex then causes the feeling to seem to come from the area of the stimulated receptor.
This is called projection
This allows us to know what hurts in most cases
Did you adjust?
There is noise all around you, things pressing against you... do you always feel or hear them?
The ability for you mind to ignore unimportant stimuli is called sensory adaptation
Receptors become unresponsive – peripheral adaptation
Inhibition along the CNS leading to the sensory regions of the cerebral cortex - central adaptation
Somatic Sense
Associated with the skin, muscles, joints, and the viscera
Three main types
Touch and pressure
Temperature
Pain
Touch and pressure
Comes from three different types of receptors
They detect mechanical forces that deform or displace tissue
They are:
Free nerve endings – extend between the epithelial cells
Meissner's corpuscles – small oval masses of flattened connective tissue
Abundant in the hairless regions of the body
Respond to light touch
Pacinian corpuscles – large structures in the deeper subcutaneous fissures and muscles tendons and ligaments
Respond toe heavy pressure and deep pressure
Temperature Senses
Depends on two types of free nerve endings in the skin
Warm receptors
Sensitive to temps above 25˚C (77˚F) and are unresponsive with temps more than 45˚C (113˚ F)
Then the pain receptors kick in and you feel a burning sensation
Cold receptors
Sensitive to temps between 10˚C(50˚ F) and 20˚ C (68˚ F)
Below 10˚ C produces a freezing sensation and pain
Pain
Free nerve endings
Spread through the skin and internal tissues
Exception – the brain, it has none
Protect the body
Is stimulated by tissue damage
How this does it is not well understood
Don't adapt well, so pain can be persistent
Visceral Pain
In the vicera, you typically need a widespread stimulation to get a response.
So, a small cut in a region of the intestines = no pain
Intestinal cramping = pain
Visceral pain feel like it is coming from some other part of the body
Called referred pain
Tends to be caused by the sharing of neural pathways that go to the skin as well as the viscera
Pain nerve fibers
Two main types
Acute
Thin and myelinated , fast impulses
Sensation of sharp pain that seldom continues after the stimuli has gone. Easy to pin point location
Typically only from skin
Chronic
Thin and unmyelinated, slow impulses
Dull aching sensation, difficult to pinpoint, continuous
From both skin and deeper tissues
Special Senses
Have large complex sensory organs in the head
Smell – olfactory organs
Taste – taste buds
Hearing – ears
Equilibrium – ears
Sight – eyes
Sense of smell
Olfactory organs
Are located in small patches
Covers the upper nasal cavity, nasal conchea, and portions of the nasal septum
Yellowish brown masses of epithelium
Composed of olfactory receptors
a type of chemoreceptors
Chemicals dissolved in liquids stimulate them
Neurons surrounded by columnar epithelial cells
Have cilia like ending that harbor 400 types of protein receptors
Detects odorant molecules
Smell and taste are closely related
Sense of taste
Taste buds - chemoreceptors
Where are they
Approx 10,000 are located on the tongue
Located on papillae
1,000 are scattered about the roof of the mouth and the walls of the throat.
Composed of
modified epithelial cells called taste cells (gustatory cells)- the receptors
50-150 of these/ taste bud
Taste pore – hole at the top of the spherical shaped bud
Taste hair – protrude from taste cell into the the taste pore
Nerve fibers woven about the cells
Taste sensations
The tastes
4 primary
Sweet, Sour, Salty, Bitter
All taste all of these, but at different levels
Therefore there are areas of concentration of the flavors
Others sometimes recognized
Alkaline, metallic, umami (MSG)
Some taste stimulate other nerves
Chile peppers and ginger – pain receptors
Chile peppers (capsaicin)– warm receptors
Taste is a combination of the different nerves stimulated, texture, temperature, and smell
Sense of hearing
Three zones
Outer ear
Middle ear
Inner ear
Outer ear
Three parts
Auricle (pinna)– outer funnel-like structure
Collects sound waves
External ascoustic meatus (external auditory canal) – s-shaped tube that leads inwards for about 2.5 cm
Tunnels/ directs to the eardrum
Tympanic membrane (eardrum) – semitransparent membrane covered by a thin layer of skin on the outside and a mucous membrane on the inside.
Oval margin and cone-shaped that attaches to the malleus (mallet)
Vibrates when sound waves hit it causing the malleus to move
Middle Ear
AKA Tympanic Caviry
Air filled space in the temporal bone
Contains 3 small bones (auditory ossicles)
Malleus (mallet), Incus(anvil) ,Stapes (stirup)
Attached to the cavity by small ligaments and the oval window (stapes)
Covered by a mucous membrane
The bones transmits the sound waves from the eardrum to the oval window
Also help to amplify the sound waves because the size of the eardrum (larger) and the oval window (smaller)
Middle Ear connection
Auditory tube (Eustachian tube)
Connects the middle ear with the nasopharynx
Helps to regulate the air pressure in the middle ear.
Must be the same as on the outside of the eardrum
If a sudden change happens in external pressure, the adjustment will sound like a pop
Inner ear
Entire region is called the Labyrinth
Divided into two main areas
3 semicircular canals – used in equilbrium
Cochlea – used to hear
Two main parts
Osseous labyrinth – tunnel through the temporal bone
Secrets a fluid called perilymph
Membranous labyrinth – membrane inside of the bone tunnel
Secrets endolymph
Cochlea
The oval window allows sound vibrations into the cochlea. The stapes pulls and pushes on the oval causing the lymphs to move
This movement causes waves through out the cochlea
Has a bony core with the bony shelf that winds about the core in a spiral
The organ of Corti – where the hearing receptors stretches from the apex to the base of the cochlea
Hair like cells detect the changes in the lymph
Two levels of sensitivity
Equilibrium
2 types
Static equilibrium
Sense the head and maintain stability and posture when head and body are still
Dynamic equilibrium
Detects motion and aids in maintaining balance when head and/or body moves or rotates
Static Equilibrium
Organs are located in the vestibule
A bony chamber in between the cochlea and the semicircular canals has two chambers
Utricle and saccule
Macule – structures in the chambers that contain the sensory receptors (hairs) and gelatinous material, and otoliths (CaCO4)
Hairs project into a mass of gelatinous material. When the gelatinous material moves and bends the hairs, the brain is told of the change of position of the head
Dynamic Equilibrium
Organs are in the semicircular canals
Lie at right angles to each other, corresponding to a different anatomical plane
Crista ampullaris
Contains sensory hair cells and supporting cells
Inside a gelatinous mass called cupula
Responds to rapid turns of head or body
Gelatinous material doesn't move, but hair cells do.
Sense of sight
Organs
Eyes – has the visual receptors
Accessory organs to help out
The Accessories
The orbital cavity
Pear shaped cavity in the skull
Has fat, blood vessels, nerves, and connective tissues
Eyelid
4 layers
Skin, Muscle, Connective tissue, conjuntiva
The conjunctive is a mucous membrane that lines the inner surface of the eyelid and the fold to cover the anterior surface of the eyeball, except the center section
Another accessory
Lacrimal apparatus
Lacrimal gland - produces tears
Located in the orbit (eye socket)
Contains lysozyme – an antibacterial agent
Series of ducts-
Lateral and medial ducts empty into the lacrimal sac which then goes to the nasolacrimal duct
Last one
Extrinsic Muscles
6 of them, moves the eyes in specific directions
Superior rectus – upward, towards midline
Inferior rectus- downward, towards midline
Medial rectus- towards midline
Lateral rectus- away from midline
Superior oblique- downwards, away from midline
Inferior oblique – upward, away from midline
The eye
Three layers
Outer layer
Sclera – white of the eye
Optic nerve – attached to the back of eye
Cornea – clear window
Middle layer
Choroid coat -honeycombed, lots of blood vessels, melanocytes to absorb excess light
Ciliary body – extends from choroid coat to the front of the eye, forming an internal ring
Lens – transparent, focus light on retina
Iris – extends form ciliary body to the pupil, muscle
Aqueous humor – liquid from the ciliary body to the cornea
Pupil – hole in the eye that lets light in.
Last layer
Inner layer
Retina – contains the visual receptors
Coats inner surface of the eye, end just behind the ciliary body
Rods- see in greyscale
Cones – see color; three types – red, green , blue
Fovea centralis and Macula Lutea
Macual is the central region of the retina
Fovea – depression in the middle that provides the clearest images
Optic Disc
Where the nerve fibers go in the optic nerve
The blind spot in the eye
Vitreous humor
Jelly like fluid inside the eye
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