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