The Somatic Senses

Sensory reception of the five senses

Receptors Five types of receptors

Chemoreceptor – changes in chemical concentrations

Pain – tissue damage Temperature (thermoreceptors)- changes in

temp Mechanoreceptors – changes in pressure and

movement Photoreceptors – changes in light energy

Sensation – what is it?When you touch an objects actually, are

they really hot or cold?

What is happening when you touch hot water or step outside when it is very “cold” out?

Sensation is.. The feeling when the brain interprets

sensory impulses. What you feel when you touch something

“hot” or “cold” is the energy transfer into or out of your body.

Projection is … When the cerebral cortex causes the

feeling to seem to come from the stimulated receptors. This is at the same time the sensation forms.

Basically the brain projects the sensation back to its apparent source.

This allows to pinpoint the region of stimulation. The eyes seem to see; the ears seem to hear.

Sensory adaptation… When sensory receptors are continuously

stimulated As receptors adapt, the impulses

decrease, and continue to decrease, and the reception may even stop

Change in strength of the stimulus will trigger impulses again

Touch and Pressure - Mechanoreceptors: Three kinds of receptors: sensory

nerve fibers (free end), Meissener’s Corpuscles, Pacinian corpuscles

These receptors perceive sensations such as pressure, vibrations, and texture.

Touch and Pressure - Mechanoreceptors: Those found in the very top layers of the

dermis and epidermis and are generally found in non-hairy skin such as the palms, lips, tongue, soles of feet, fingertips, eyelids, and the face.

Those located deeper in the dermis and along joints, tendons, and muscles feel sensations such as vibrations

traveling down bones and tendons, rotational movement of limbs, and the stretching of skin. This greatly aids your ability to do physical activities such as walking and playing ball.

Temperature Senses Two types of free nerve

endings: warm and cold Warm Receptors

Most sensitive at temps above 77oF

Unresponsive at temps above 113oF

This will stimulate pain receptors, produces burning sensation

Cold receptors Most sensitive between 50-68oF Temps below 50oF stimulate pain

receptors, produces freezing sensation

Temperature Senses Cold receptors are found in greater density than

heat receptors. The highest concentration of thermoreceptors can be found in the face and ears (hence why your nose and ears always get colder faster than the rest of your body on a chilly winter day).

Pain receptors Free nerve endings Widely distributed throughout the body,

except in the nervous tissue and brain Adapt poorly, if at all Once stimulated, may continue to send

impulses to the CNS = persistent pain Pain is poorly understood

Pain Pain elicited during a muscle cramp stems

from sustained contraction that squeezes capillaries and interrupts blood flow.

Deficiency in oxygen-rich blood may trigger pain sensations

Referred pain Pain that is coming from some part of the

body other than the part being stimulated Pain from the heart may be felt from the left

shoulder or upper left limb. Generally comes from visceral pain = deep

within the body/ visceral tissue

Special Senses = smell, taste, sight, hearing /equilibrium,

Sense Organ

Smell Olfactory organs

Taste Taste buds

Hearing/ equilbrium Ears

Sight eyes

Smell Olfactory receptor cells =

bipolar Stimulated fibers synapse

with neurons in olfactory bulb

Impulses from the olfactory bulb travel along olfactory tracts to the limbic system

Major interpretation sites are found in the temporal lobes and parts of the frontal lobe.

Olfactory Stimulation Uncertain how this stimulation begins Smells are interpreted as a code

For example, if there are 10 receptors, parsley may stimulate receptors 3, 4, & 8 and chocolate might stimulate 1,5, & 10

Olfactory organs are located high in the nasal cavity May need to force air in during inhale to get a

faint smell Undergo sensory adaptation rapidly

Taste

Each taste bud has a group of taste cells Each bud has 50-150 cells replaced every three days

Entire structure is within the taste pore

Tiny projections are called taste hairs

Taste Salivary glands dissolve chemicals in order for

the tongue to taste 4-7 taste sensations

Sweet Sour Salty Bitter Metallic Alkaline Umami – detects MSG

Taste Each taste cell can detect two sensations,

although one sensation may dominate over the other

Taste cells undergo sensory adaptation rapidly

Impulses move from taste cells through facial, glossopharyngeal and vagus nerves to medulla oblongata They then move to the thalamus to the parietal

lobe

Hearing The ear has an external, middle and inner

part External ear has two parts – auricle and the

external auditory meatus Both direct sound waves toward the middle ear

Middle ear – includes tympanic cavity, eardrum, and auditory ossicles (three small bones)

Eardrum moves back and forth in response to vibrations of the sound wave

These vibrations are transferred to the auditory ossicles, which then stimulate the hearing receptors

Hearing The ear has an external, middle and inner

part Inner Ear – comprised of two labyrinths which

include semicircular canals and the cochlea Sound waves move through this area exciting

hair cells (nerve cells) Sound frequency stimulates only certain cells Cells do not have dendrites or axons, but act

very much like a neuron Impulses are interpreted in the temporal lobe

of the brain

Sight