Ch.10 Somatic and Special Senses


10.1 -Introduction
Somatic Senses
Somatic Senses are the the components of the central and peripheral nervous systems that receive and interpret sensory information from organs in the joints, ligaments, muscles, and skin. This system processes information about the length, degree of stretch, tension, and contraction of muscles; pain; temperature; pressure; and joint position.

Special Senses



Special senses consist of the eyes, ears, nose, throat and skin. Each of these organs have specialized functions that make if possible for humans to experience and interact with the environment.

-vision (the eye)
-hearing and balance (ears)
-sound (nose)
-taste (the tongue)

Sensory Receptors function to detect changes in the environment and stimulate neurons to send nerve impulses to the brain
Thalia Martin-Williams

10.2 Receptors and Sensations

Sensory Receptors are categorized into 5 types according to their sensitivities:

  1. Chemoreceptors: Stimulated by changes in the chemical concentration of substances
  2. Painreceptors: Stimulated by tissue damage
  3. Thermoreceptors: Stimulated by changes in temperature
  4. Mechanoreceptors: Stimulated by changes in pressure or movement
  5. Photoreceptors: Stimulated by light energy

Sensations:

  • A sensation is a feeling that occurs when the brain interprets sensory impulses
  • The nerve impulses that travel away from the receptors into the central nervous system are similar, because of this the resulting sensation depends on what part of the brain recieves the impulse.
  • The cerebral cortex causes the sensation to seem to come from the stimulated receptors. This is called Projection, because the brain projects the sensation to its apparent source. This allows a person to pinpoint the region of stimulation.

Sensory Adaptation:

Sensory Adaptation is the ability to ignore unimportant stimuli. This is important because the brain needs a way to prioritize the sensory input it recieves or it would be overwhelmed with unimportant information. Sensory Adapation may involve receptors becoming unresponsive (peripheral adaptation) or inhibition along the central nervous system pathways leading to the sensory regions of the cerebral cortex.


10.3 Somatic Senses

Somatic senses are associated with receptors in the skin, muscles, joints, and viscera(organs within the body).

Touch and Pressure senses

external image Image492.gif
touch and pressure can be sensed from three types of receptors.
they are the free nerve endings, the Meissner's corpuscles, and the Pacinian corpuscles.

  • free nerve endings - receptors that sense touch and pressure. They are common in the epithelial tissues.

Meissner's corpuscles - receptors that sense light touch. They are common in hairless portions of the skin, such as the lips, fingertips, and palms.

Pacinian corpuscles - receptors that sense heavy pressure. They are common in the deeper subcutaneous tissues(beneath the dermis), muscle tendons, and joint ligaments.



- Temperature Senses:

Temperature can be sensed from two types of receptors.
  • Warm receptors sense temperatures from 25- 45°C. Pain receptors can be stimulated if temperature rises abouve 45°C and cause a burning sensation.
  • Cold receptors sense temperature between 10 - 20°C. Pain receptors are stimulated when temperatue falls below 10°C and cause a freezing sensation.
These receptors adapt rapidly to the environment.

Sense of Pain:

Pain receptors are free nerve endings that are stimulated by tissu damage.
  • They are spread in the skin and internal tissues. Except, the brain's nervous tissue lacks pain receptors.
  • They adapt poorly, thus causing persistant pain.
  • It is thought that injuries promote a build up of certain chemicals that stimulate pain receptors.
  • Dificiency of oxygen rich blood cans trigger pain receptors as well.
Visceral Pain
  • pain receptors are the only receptors that cause sensation in the viscera.
  • external image Image493.gif





  • visceral pain may feel as if it is coming from some other part of the body than where it is actually stimulated, known as referred pain.
  • for example, pain originating from the hear may be referred to the left upper limb.
  • Visceral pain may be referred because the sensory impulses from the skin and viscera travel on the same nerve pathway



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Pain Nerve Fibers:

  • Two main types of nerve fibers conduct impulses away from receptors.
    They are the acute pain fibers and chronic pain fibers.
  • Acute pain fibers conduct nerve impulses rapidly, and produce sharp pain.
  • Chronic pain fibers conduct nerve impulses more slowly and produce dull pain and feel from deeper tissue.
  • pain impulses originating from the head travel on the sensory fibers of cranial nerves.
  • impulses that do not originate from the brain travel on the sensory fibers of spinal nerves and processed in the gray matter, then transmitted to the brain.
  • Once in the brain, the impulses settle in the reticular formation then conducted to the cerebral cortex.

Regulation of Pain Impulses:
  • Pain awareness arises when pain impulses reaches the thalamus
  • The cerebral cortex determines pain intensity and locates its source
  • thalamus.jpg
  • Movement of pain impulses are regulated by gray matter in the midbrain, pons, and medulla oblangata
  • These areas of brain have special neurons that stimulate the release of certain biochemicals that can inhibit pain signals.
  • These biochemicals are pain-relieving neuropeptides. Examples include enkephalins and endorphins.
  • Enkephalins supress acute and chronic pain impulses.
  • The monoamine serotonin can stimulate neurons to release more enkephalins.
  • Endorphins also work to supress pain. They are produced in the pituatary gland and hypothalamus.


10.4 Special Senses

external image 41785_304764990556_4478759_n.jpg

Special Senses are those whose sensory receptors are within large, complex sensory organs in the head. They are:
    • Smell --------------------> Olfactory Organs
    • Taste---------------------> Taste Buds
    • Hearing-------------------> Taste Buds
    • Equilibrium----------------> Ears
    • Sight---------------------> Eyes

10.5 Sense of Smell
The olfactory organs cover the upper nose, mainly the superior nasal conchae and part of the nasal septum. These tiny organs are about the size of a postage stamp and contain olfactory receptors. These receptors are chemoreceptors. This means that chemicals that are dissolved in a liquid stimulate them. That is why the functions of taste and smell work closely together. The olfactory receptor cells are surrounded by columnar epithelial cells and at the edges of these cells are cilia. The chemicals that stimulate the receptors are called odorant molecules and they bind to the receptors in different patterns, creating an impulse. This impulse travels to the olfactory bulb, where the impulse is analyzed. Then, the bulb sends another impulse through the olfactory tract into the limbic system, where the main area for interpreting these impulses are.

10.6 Sense of Taste

Taste Buds are the special organs of taste

external image taste+buds.jpg
The four primary taste sensations are:
1. Sweet
2. Bitter
3. Sour
4. Salty

Video on the sense of taste:
http://www.youtube.com/watch?v=FSHGucgnvLU

Each taste bud includes modified epithelial cells, taste cells, that function as receptors.Each bud has about 50 to 150 receptors cells, which are replaced about every 3 days. There are also epithelial supporting cells. The bud itself has a spherical shape with an opening called the taste pore. It has tiny projections called taste hairs protruding from the outer ends of the taste hair extending to the taste pore.Interwoven and wrapped around the
external image Taste%20Bud_2.jpg
taste cells are a network of nervefibers.Stimulation of a receptor cell triggers and impulse on a nearby nerve fiber, and the impulse then travels into the brain. There is a watery fluid that the salivary glands provide and before a particular chemical can be tasted it has to be desolved in the fluid. Food molecules bind to receptors and the pattern generates a sensory impulse on nearby nerve fibers and then is interpreted as a particular taste sensation.



10.7 Sense of Hearingexternal image Fig33.gifThe ear, the organ of hearing, is divided into the puter, middler, and inner ear parts. The ear also functions in equilibrium.Outer (External) Ear:The outer ear consists of the auricle, external acoustic meatus, and the eardrum.Sound wavea are collected by the auricle and directed into the external acoustic meatus. Sound waves that pass through the external acoustic meatus change the pressure on the eardrum. The eardrum vibrates in response to the waves.  Middle Ear:The middle ear consists of three small bones called the auditory ossicles. They include the malleus, the incus, and the stapes. These bones form a bridge between the eardrum and inner ear. When the eardrum vibrates, the malleus vibrates, then causes the incus and then the stapes to vibrate. The stapes is connected to the oval window which leads the vibration into the inner ear. Auditory Tube:Also known as the eustachian tube, conects the middle ear to the throat. The tube maintains equal air pressure on both sides of the eardrum. Inner (Internal) Ear 10.8 Sense of Equilibrium

There are two types of equilibrium in our bodies: Static and Dynamic equilibrium.


Static Equilibrium- The gravity receptors that respond to linear acceleration of the head are the maculae of the utricle and saccule. These two areas both contain maculae. The maculaes are filled with hair cells that act as sensory receptors. When the head is bent forward, backward, or from side to side, these hairs are stimulated. They stimulate the nerve fibers associated with them, then the impulse travels into the CNS and tell the brain the new position of the brain. The brain then sends impulses to the muscles that tell them to contract or relax to maintain balance. (Kevin 1)
Dynamic Equilibrium- Interprets balance when the head isn't moving, but the body is. There are three semicircular canals and within each of these is a crista ampullaris. In these structures are hair cells that are stimulated by rapid movements of the head or body. This stimulation sends impulses to the brain, specifically the cerebellum, where the impulses are interpreted. Then the brain acts by sending impulses to the muscles that tell them to contract or relax in order to maintain balance. (Kevin 1 and 2)

10.9 Sense of Sight


Sources

Kevin

1. http://www.britannica.com/EBchecked/topic/175622/human-ear/65064/Detection-of-linear-acceleration-static-equilibrium

2.http://apbrwww5.apsu.edu/thompsonj/Anatomy%20&%20Physiology/2010/2010%20Exam%20Reviews/Exam%204%20Review/CH%2015%20Inner%20Ear-Static-Dynamic-Equilibrium.htm

3.http://www.obstructednose.com/nasal_anatomy.html













Addie Saldana P-3 table 1

Chapter 10 Section 2 : Receptors & Sensations


*Sensory receptors are broken up into 5 different types according to their sensitivity.

Chemoreceptors : stimulated by changes in the chemical concentrations of substances.
Pain receptors : stimulated by tissue damage
Thermoreceptors : stimulated by the changes in temperature
Mechanoreceptors : stimulated by changes in pressure or movement
Photoreceptors : stimulated by light energy

*Sensations :
Sensation : also known as a perception, is a feeling that occurs when the brain interprets sensory impulses.
- the sensation depends on which region of the brain recieves the impulse.
Projection : the process by which the brain causes a sensation to seem to come from the region of the body being stimulted.
- allows a person to pinpoint the region of stimulation.
- the cerebral cortex causes this feeling to seem to come from the stimulated responces.

*Sensory Adaptation :
So the brain doesn't get over whelmed with the sensory input it recieves it has learned to use Sensory Adaptation,
giving the brain the ability to ignore the unimportant stimuli.
-Sensory Adapation may involve receptors becoming unresponsive (peripheral adaptation) or inhibition along the central nervous
system pathways leading to the sensory regions of the cerebral cortex.


Chapter 10 Section 4 : Special Sences

- Special Sences are those whose sensory recpetors are within large, complex sensory organs in the head.


  • Smell ----------> Olfactory organs
  • Taste ---------->Taste Buds
  • Hearing -------------> Ears
* Equalibrium --------> Ears
*Sight ----------> Eyes
Chapter 10 Section 6 : Sence of Taste
- taste buds : special organs of taste
*Taste Receptors:
-Each taste bud includes modified epithelial cells, taste cells, which function as receptors.

nrn1365-f2.jpg
nrn1365-f2.jpg
-Each bud has about 50 to 150 receptors cells, which are replaced about every 3 days.There are also epithelial supporting cells. The bud itself has a spherical shape with an opening called the taste pore. It has tiny projections called taste hairs protruding from the outer ends of the taste hair extending to the taste pore.

- the taste hairs are believed to be the sensitive parts of the receptor cells
-Interwoven and wrapped around the taste cells are a network of nerve fibers. Stimulation of a receptor cell triggers an impulse on a nearby nerve fiber, then impulse travels into the brain.
-There is a watery fluid that the salivary glands provide and before a particular chemical can be tasted it has to be desolved in the fluid. Food molecules bind to receptors and the pattern generates a sensory impulse on nearby nerve fibers and then is interpreted as a particular taste sensation.

*Taste Sensations :
- Each part of the tounge taste different things.
tongue_taste_zones.jpg
tongue_taste_zones.jpg





Chapter 10 Section 8 : Sense of Equilibrium

- The sence of equilibrium is really two sences, static and dynamic equilibrium, that come from different sensory organs.
- Static equilibrium : the sense of position of the head, maintaining the stability and posture when the head and body or still.
- Dynamic Equilibrium: detects sudden movement or rotation of the head and body to aid in maintaining balance.

*Static Equilibrium :

- the organs of static equilibrium are located with in the vestibule: a bony chamber between the semicircular canals and the cochlea.
- The membranous labyrinth inside the vestibule consists of two expanded chambers : utricle and a saccule.
- each of these chambers has a tiny structure called a macula. Macula contain many hair cells which serve as sensory receptors. The nerve impulses travel into the CNS on the vestibular branch of the vestibulocochlear nerve. These impulses inform the brain of the head's new position. The brain responds by sending motor impulses to skeletal mucles, which contract or relax to maintain balance.

* Dynamic Equilibrium :

- The organs of dynamic equilibrium are the three semicircular canals within the labyrinth.
- The detect motion of the head and aid in balancing the head and body during sudden movement
- Suspended in the perilymph of the osseous portion of each semicircular canal is a membranous canal that ends in swelling called ampulla, which contains the sensory organs of the semicircular canals. Each of those organs, called crista ampullaris which contain many sensory hair cells and supporting cells.
- Rapid turns of he head or body stimulate the hair cells of the crista ampullaris. At the same timethe semicircula canals move with the hed or body, but the fluid inside the membraneous canals staying stationary. This bends the culpula in one or more of the canals in a direction opposite thast of the head or body moveent, and the hairs embedded in it also bend. The stimulated hair cells signal their associated nerve fibers, sending impulses to the brain.
-the cerebellum helps interpret the impulses from the semicirular canals. The analysis allows the brain to predict the consequences of rapid body movements, and by modifying signals to appropirete skeletal musclesm the cerebellum can maintain balance.