16.2 Flashcards
What are somatic sensations?
Arise from stimulation of sensory receptors embedded in the skin or subcutaneous layer
Where are somatic sensations found?
In mucous membranes of the mouth, vagina and Anus & in skeletal muscles, tendons and joints
Which areas in the body have the highest density of somatic sensory receptors?
Tip of tongue, lips and fingertips
What are the 4 modalities of somatic sensation?
- Tactile
- Thermal
- Pain
- Proprioceptive
What are tactile sensations?
Include touch, pressure, vibration, itch, tickle
(Touch)
There are 2 types of rapidly adapting touch receptors. What are corpuscles of touch (or Meissner corpuscles)
Touch receptors that are located in the dermal papillae of hairless skin.
Each corpuscle is an egg shaped mass of dendrites enclosed by a capsule of connective tissue.
What are the sensations of corpuscles of touch receptors? Rapid or slow adapting receptors?
Onset of touch and low frequency vibrations
Rapid
Where are corpuscles of touch abundant in the body?
Fingertips, hands, eyelids, tip of tongue, lips, nipples, soles, clitoris, tip of penis
2nd type of touch receptors is hair root plexuses. Where are they found and the structure?
Hairy skin.
Consist of free nerve endings wrapped around hair follicles
Detect movements on the skin that disturb hairs
2 types of slowly adapting touch receptors what are they
Type 1 cutaneous mechanoreceptors (tactile(merkel) discs)
Type II cutaneous mechanoreceptors ;Ruffini corpuscles
What is the structure of tactile (merkel) discs ?
Saucer shaped, flattened free nerve endings that make contact with tactile epithelial cells (merkel cells) on the stratum basale
Plentiful in fingertips, hands, lips, external genitalia?
Type 1 cutaneous mechanoreceptors
Elongated encapsulated receptors located in the dermis, subcutaneous layer and other tissues of the body. Highly sensitive to skin stretching (such as a massage)
Type II cutaneous mechanoreceptors (or Ruffini corpuscles)
A sustained sensation that is felt over a larger area than touch, occurs with deeper deformation of the skin and subcutaneous layer?
Pressure
Which type of receptor consist inure to sensations of pressure?
Type I and II mechanoreceptors
Able to respond to steady pressure stimulus because they are slowly adapting
Where do sensations of vibration result from?
Rapidly repetitive sensory signals from tactile receptors
What are the receptors for vibration?
Lamellated corpuscles and corpuscles of touch
What consists of a nerve ending surrounded by a multilayered connective tissue that resembles a sliced onion?
Lamellated corpuscle (or pacinian corpuscle)
Where are Lamellated corpuscles found?
In the dermis, subq layer and other body tissues
Lamellated corpuscles respond to high or low frequency vibrations?
High
Corpuscles of touch respond to high or low frequency vibrations
Low
What does itch sensation result from?
Stimulation of free nerve endings by certain chemicals, such as bradykinin (a kindin a potent vasodilator), histamine, or antigens in mosquito saliva injected from a bite
Scratching usually alleviates itching by?
Activating a pathway that blocks transmission of the itch signal through the spinal cord
What are free nerve endings that have receptive fields about 1 mm in diameter on the skin surface?
Thermoreceptors
Cold receptors (one of the 2 distinct thermal sensations) are located where? And attached to what fibers?
Located in the stratum basale of the epidermis
Attached to medium diameter myelinated A fibers although a few connect to small diameter unmyelinated C fibers
Where are warm receptors located
In the dermis and are attached to small diameter unmyelinated C fibers
Cold receptors (activated temp between 10 and 35)
Warm receptors (temp between 30 and 45)
What about temps below 10 and above 45? What receptors are stimulated?
Pain receptors
What are nociceptors?
The receptors for pain
Are free nerve endings found in every tissue except the brain
What are the 2 types of pain?
Fast and slow
Fast pain occurs rapidly usually within 0.1 second after stimulus applies. Because of how the nerve impulses propagate along which fibers?
Medium diameter myelinated A fibers
Slow pain begins after a second or more after stimulus and gradually increases in intensity. Impulses for slow pain conduct along which fibers?
Small diameter unmyelinated C fibers
Pain that arises from stimulation of receptors in the skin is called ?
Superficial somatic pain
Stimulation of receptors in skeletal muscles, joints, tendons & fascia causes what type of pain?
Deep somatic pain
Visceral pain?
Results from stimulation of nociceptors of visceral organs
Referred pain?
In instances of visceral pain, the pain is felt in or just deep to the skin that overlies the stimulated organ or in a surface area far from the stimulated organ
What allows us to recognize that parts of our body belong to us and allow us to know where our head and limbs are located and how they move
Proprioceptive sensation (or proprioception)
Kinesthesia
Perception of body movement
Proprioceptors also allow weight discrimination which is?
The ability to assess the weight of an object
3 types of Proprioceptors?
Muscle spindles
Tendon organs
Joint kinesthetic receptors
What are muscle spindles ?
Proprioceptors that monitor changes in the length of skeletal muscles and participate in stretch reflexes
How does a muscle spindle respond to stretching a skeletal muscle not to vigoursly ?
Muscle tone
Brain sets an overall level of muscle tone
Which is the small degree of contraction present while muscle at rest
Each muscle spindle consists of several slowly adapting nerve endings that wrap around 3-10 specialized muscle fibers. What are these called?
Intrafusal fibers
In muscles that produced finely controlled movements (such as fingers or eyes) are muscle spindles plentiful or fewer?
Plentiful
The only skeletal muscle that lacks spindles?
Tiny muscles of ear
What is the main function of muscle spindles?
To measure muscle length - how much a muscle is being stretched
Sudden or prolonged stretching of central areas of the inteafusal muscle stimulates what?
Sensory nerve endings
The resulting nerve impulses propagate into the CNS
Information from muscle spindles arrives quickly at the somatic sensory areas of cerebral cortex which allows conscious perceptions of limb positions and movements
At the same time impulses from muscle spindle pass to cerebellum where input is used to coordinate muscle contractions
Near the middle of intrafusal fibers muscle spindles contain motor neurons called?
Gamma motor neurons
What do these gamma motor neurons do?
Terminate near both ends of the intrafusal fibers and adjust the tension in a muscle spindle to variations in the length of the muscle
Surronding muscle sound also are ordinary skeletal muscle fibers called?
Extrafusal muscle fibers
Supplied by large diameter a fibers called alpha motor neurons
Where are the cell bodies of gamma and alpha motor neurons located?
In the anterior gray horn of the spinal cord (or in the brain stem for muscles in the head)
What are tendon organs?
Slowly adapting receptors located at the junction of a tendon and a muscle
What do tendon organs do when tendon reflexes are initiated?
Protect tendons and their associated muscles from damage due to excessive tension
Each tendon organ consists of?
A thin capsule of connective tissue that encloses a few tendon fascicles (bundles of collagen fibers)
When tension is applied to a muscle, the tendon organs generate nerve impulses that propagate into the CNS providing info about changes in muscle tension. The resulting tendon reflex decrease muscle tension by causing?
Muscle relaxation
Joint kinesthetic receptors present where?
Within and around the articulate capsules of synovial joints
