Bio Exam 4 General Senses

free nerve endings

widespread, especially in epithelia and connective tissues

tactile discs

stratum basale of epidermis

hair receptors

around hair follicle

tactile corpuscles

dermal papillae of fingertips, palms, eyelids, lips, tongue, nipples, and genitals

end bulbs

mucous membranes

bulbous corpuscles

dermis, subcutaneous tissue, and joint capsules

lamellar corpuscle

dermis, joint capsules, periosteum, breasts, genitals, and some viscera

muscle spindles

skeletal muscle near tendon

tendon organs

tendons

epidermis and dermis

sensory receptors location

somatic senses

touch, pressure, vibration, temperature, pain, proprioception (use ascending pathway)

1st-order neuron

dorsal root ganglia, cranial ganglia

2nd-order neuron

spinal cord or brainstem, axons cross over to the opposite side of the CNS

3rd-order neuron

thalamus, conduct impulses to primary sensory cortex of the cerebral hemisphere

dorsal column pathway, spinothalamic tracts, spinocerebellar tracts

3 major ascending pathways

lateral spinothalamic tract

convey pain and temperature

anterior spinothalamic tract

convey crude touch and pressure

Spinocerebellar tracts

transmits subconscious proprioceptive info from trunk and lower limb to the same side of the cerebellum (no crossover)

primary somatosensory cortex

located in the postcentral gyrus; receives somatosensory information from the skin and proprioceptors in skeletal muscles, joints, and tendons – spatial discrimination

somatosensory association cortex

posterior to the postcentral gyrus; integrates sensory inputs to produce an understanding of an object

contralateral side of the body

where does the somatosensory cortex receive signals from

body areas having highest sensitivity

what do large areas in the primary somatosensory cortex represent

specific loss of sensation

what does damage to the sensory homunculus produce

face

what area of the body uses a lot of area on the primary somatosensory cortex

pain

an uncomfortable perception of tissue injury or noxious stimulation

nociceptive pain

Stems from tissue injury such as cuts, burns, and chemical irritation, detected by nociceptors

Comes from receptor level

Can be subdivided into three kinds:

visceral pain

deep somatic pain

superficial somatic pain

neuropathic pain

Stems from injuries to the nerves, spinal cord, meninges, or brain. Examples are: headache, phantom limb pain, fibromyalgia, etc

Comes from beyond receptor level

fast pain

immediate sharp pain one feels from a cut, sting, or burn. Mediated by myelinated A-delta fibers. Can be localized

slow pain

Slow pain has a delayed, burning and aching feel. Mediated by unmyelinated type C fibers. Hard to tell where does it come from.

fibromyalgia

a condition that causes pain all over the body

lateral spinothalamic tract

carries most of the somatic pain signals that ultimately reach the primary somatosensory cortex and produce conscious pain

1^st, 2^nd, and 3^rd order of neurons

spinoreticular tract

carries pain signals to the reticular formation of the brainstem

ultimately reach the hypothalamus and limbic system

Activate visceral, emotional, and behavioral reactions such as nausea, fear, and some reflexes

phantom limb

pain experienced in amputated limb

referred pain

pain felt in uninjured part of the body, but actually originates in another part of the body

endogenous opioids

inhibits pain pathways

CNS modulation of pain

1.First order neuron – release substance p

2.Second order neuron – ascend up the spinothalamic tract

3.3^rd order neuron