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an unpleasant sensory and emotional experience associated with actual or potential tissue damage



reception of signals in the CNS evoked by activation of specialized sensory receptors that provide information about tissue damage


Aside from the thalamus cerebral cortex, fibers from the lateral spinothalamic tract also travel where?

amygdala, hypothalamus, periaqueductal gray, superior colliculus, and reticular formation


Acute Pain

an essential biological signal of the potential for or the extent of injury; lasts or is expected to last a short time.


Chronic Pain

arbitrarily defined as pain persisting > 1 month beyond the resolution of an acute tissue injury or pain persisting or recurring for > 3 months

*Chronic pain has no adaptive biological role


What are the components of nociception?

transduction (detection of tissue damage by specialized receptors) > transmission (nociceptive information travels from the site of damage along the peripheral nerve) > nociceptive information travels up the spinal cord > modulation (of this information by multiple sites in the brain)


Chemical Nociception

algogenic (pain producing) chemicals are released in the region of nerve endings capable of detecting noxious stimuli; occurs in the PRESCENCE of actual tissue damage


Mechanical Nociception

pain arising from stretching of collagen fibers and thus squeezing nerve endings between them; occurs in the ABSENCE of actual tissue damage, but when tissue is excessively strained


Mechanical nociception is enhanced by:

algogenic chemical sensitization and pre-stressing collagen fibers


A-delta fibers vs. C-fibers

A-delta: lightly myelinated; responsible for initial pain (sharp/prickling or stinging type of pain)
C: unmyelinated; responsible for long-lasting pain (dull aching type of pain)


Lamina I receives:

C-fibers and A-delta fibers; 2nd order neurons project to thalamus


Lamina II receives:

C-fibers and A-delta fibers; synapse on interneurons and dendrites from neurons in Lamina V


Lamina V receives:

A-delta fibers only; 2nd order neurons project to brainstem and thalamus


Ectopic Foci

myelin damaged; increased production of mechanosensitive and chemosensitive ion channels in demyelinated area; results in abnormal sensitivity to mechanical and chemical stimuli


Ephaptic Transmission

crosstalk between nerves (in demyelinated areas); action potential from one neuron may indue an action potential in another neuron


Central Sensitization

excessive responsiveness to peripheral input causing alteration in central function; cellular changes may include: increased spontaneous activity, increased responsiveness to afferent inputs, prolonged after-discharge in response to repeated stimulation, and expansion of receptive field


Size Principle

slow-twitch muscle fibers are recruited first because they require a smaller threshold, these fibers generate less tension and require less energy expenditure; fast fatigue-resistant fibers are recruited next, followed by fast-fatigable fibers


Muscle Spindles

primary endings are velocity sensitive; secondary endings are not velocity sensitive, more important for holding something steady in space


Golgi Tendon Organ

located at the musculotendinous junction; sensitive to changes in tension and involved with proprioception and adjusting muscle tension


What do all normal movements require?

1) the convergence of information from the peripheral sensors in the spinal cord
2) spinal connections
3) descending pathways onto the cell body and dendrite of the motor neurons, as well as descending control of the interneurons


Phasic Stretch Reflex

(DTR, myotatic reflex); Ia afferents and alpha-motor neurons are involved; monosynaptic reflex that DOES NOT involve interneurons


Tonic Stretch Reflex

slow, sustained stretch applied to the central muscle spindle facilitates contraction of the muscle; Ia & II afferents and gamma-motor neurons are involed


Reciprocal Inhibition

activation of Ia afferents; contraction of homonymous and synergistic muscle groups, and inhibition of antagonistic muscle groups due to activation of Ia inhibitory interneurons; used extensively during voluntary movements


Golgi Tendon Organ Reflex

autogenic inhibition; Ib afferents excite antagonistic motor neurons and Ib interneurons inhibit homonymous and synergistic motor neurons; also referred to as reverse myotatic reflex


Flexor Withdrawal Reflexes

requires the integration of multiple spinal levels and multiple muscle groups; activates flexor muscles


Cross Extension and Flexor Withdrawal Reflexes

requires the integration of multiple spinal levels and multiple muscle groups bilaterally, activates flexors on ipsilateral side and extensors on contralateral side


Upper Motor Neurons that control reflexes

- corticospinal tract: lateral and anterior
- reticulospinal tract: interacts with spinal interneurons
- vestibulospinal tract: excitatory to extensor muscles and inhibitory to flexors
- tectospinal tract: involved with reflexes and head movement


Amyotrophic Lateral Sclerosis (ALS)

a disease that destroys only somatic motor neurons and can involve UMN and brainstem, as well as spinal cord LMNs; results in both UMN and LMN sings; astrocytes fail to remove glutamate resulting in excitoxicity


Myasthenia Gravis

an autoimmune disorder that destroys Ach nicotinic receptors on muscle cells, affecting the NMJ activity and causing decreased reflexes


Muscular Dystrophy

myopathy; muscle fibers degenerate resulting in motor units with fewer muscle fibers than normal and a decreased ability to produce force during contraction; decreased reflexes