chapter 4 and 5?

the senses of touch, temp body position and pain

• receptors in the skin, muscles, joints, and viscera (internal organs of the body especially of the thorax and abdomen, as the heart, lungs, kidneys, intestines etc...
• relates to structures derived from a series of mesodermal somites, including skeletal muscles

a segmental block like mass of mesoderm (middle layer of skin) on either side of notochord, gives rise to muscles, vertebral and skin

• middle of three primary germ layers
• midline strip of cells sandwiched between the endoderm and ectoderm

primitive, solid, skeletal structure derived from specialized mesodermal cells that is retained in intervertebral disk as nucleus pulposus and lies ventral to neural tube

• 1. thermoreceptors-receptors sensitive to temp, respond to change in temp and are located in the skin
•    -hot and cold receptors are separate and are not distributed evenly across the skin (approx 1 mm wide)
• 2. nociceptors-(nocere means to hurt) receptors which respond to tissue damage (pain receptors)
•     -serve as body's warning system

both are free afferetn nerve endings, take info from skin surface to brain

• mechanoreceptors -respond to mechanical pressure or deformation of the receptor and adjacent tissues
• photoreceptors- respond to light directed on the retina of the eye
• chemorecepotors-respond to taste and smell

viscera

• initial pain is fast and sharp
• secondary pain is achy and slow and runs along the nerve

• in the dorsal root ganglia of neurons
• these are clusters that lie outside of the spinal cord

1st in line to receive info from the periphery and transmit it to the second order neurons

an axon process dividing into two branches, one extending into the periphery, and another central branch that extends into the spinal cord (2 axons)

• 1. terminal of the peripheral branch transduces stimulus energy from a sensory receptor
• 2.  the signal is transmitted as an action potential along the peripheral bran and its continuation in the central branch
• 3.  primary afferent fiber: both branches together (peripheral and central), terminates on a sensory neuron in the dorsal horn on the spinal column (second order neuron)

• a-delta fibers
• c fibers

• 1. conduction velocity of the action potential (along the fiber to the nervous system)
• 2. aspects of the stimulation that must occur to evoke a response (ex-intensity, (strength), duration (length), and quality (clarity)
• 3. characteristic responses of the nociceptor to natural stimuli (ex-slow v fast adaptation)

• lightly myelinated 
• important because we need to speed up the info

• by low threshold meaning that it doesn't take much to activate, superficial receptors
• associated with pain that has a sharp, pricking quality and can be localized on the body surface and diminishes quickly
• fast pain, initial pain, first pain

• unmylinated
• stimulated by high-threshold receptors
• convey diffuse, persisting pain that we perceive as:
• aching, throbbing, burning pain that is poorly localized 
• called slow pain, delayed or second pain
• found to be intolerable relative to the initial stabbing pain conducted by a-delta fibers, which can often preceed slow pain

a delta fibers

c fibers

• this is where you are hit by a hard ball and then fell the pain afterwards
• c fibers