Nervous System Flashcards
somesthetic receptor / somatosensory
a sensory end organ concerned with reception of stimuli producing one of the generalized sensations (such as temperature, pressure, position, or movement)
sensory information goes to _____ horn
posterior / dorsal
motor signal leaves from _____ horn
anterior / ventral
the journey of sensory information to brain
sensory information travels from receptors → sensory neurons (1st order neuron - from receptor to dorsal horn) → spinal cord or brainstem (2nd order neuron - to contralateral thalamus) → thalamus (3rd order neuron - from thalamus to sensory cortex) → sensory cortex
sensation
signals transmitted by receptors to brain in form of light, sound, tactile, thermal, pain, etc
perception
how sensory information is organized, interpreted and consciously experienced
unconscious processing (sensation) occurs at ____ level
subcortical
perception (conscious) occurs at the _____ level
cortical
meissner’s corpuscles
mechanoreceptors present in highly sensitive areas like fingertips, palms, soles, tongues, lips, and genital skin
- small receptive fields to allow two-point discrimination
- respond to low frequency stimuli (flutter)
pacinian corpuscles
- rapidly adapting mechanoreceptors for pressure and vibration
- get used to the sense and stop sending signals to perceive (ex - clothes on skin)
hair follicle receptors
rapidly adapting mechanoreceptors that respond to movement across surface of skin
merkel’s disks
slow adapting mechanoreceptors that respond to pressure and touch
ruffini’s corpuscles
slow adapting mechanoreceptors that respond to stretch found in dermis and joints
thermal receptors
free nerve endings that respond to temperature changes; divided in cold and warm slow adapting receptors (specific ones for each temp category)
nociceptors
- free nerve endings found in skin, muscle, joints, periosteum and visceral organs capsules
- respond to noxious chemicals, mechanical stimuli (stretch) and temperature
Muscle Spindles (in muscles) & Golgi Tendon (in tendons)
proprioception (awareness of your body and its position in space) and coordination of motor activity
Sensory Receptive Fields
region of skin that elicits a response in a somatic sensory neuron; vary in diameter (1-2 mm on fingertips [high precision], 5-10 mm on palms, larger in abd and back [lower precision] and may overlap)
Transduction of Sensory Signals
- stimuli will generate a graded potential in receptors that if strong enough (summation to threshold) will elicit an AP in a sensory neuron axon
- APs travel to thalamus that will send each sensation modality to specific area of sensory cortex
- cortex has the task of assembling all the information - modality (what), magnitude (how strong), duration (when), location (where) and deciding if it is important (nociceptors get priority!)
ascending (afferent) tracts - anterior column
ventral spinothalamic tract (pressure and crude touch)
ascending (afferent) tracts - lateral column
lateral spinothalamic tract (pain and temperature); ventral and dorsal spinocerebellar tracts
ascending (afferent) tracts - posterior column
fasciculus cuneatus and gracillis (vibration, proprioception, two-point discrimination/fine touch)
descending (efferent) tracts - anterior column
ventral corticospinal (pyramidal) tract (voluntary movements, reflexes)
descending (efferent) tracts - lateral column
lateral corticospinal (pyramidal) tract (voluntary movements, reflexes)
thalamus
- integration and relay of motor and sensory functions except olfactory
- awareness of nociceptive stimuli (non-discriminative form)
- controls subjective response to sensation
- activation and arousal with reticular formation
- modification of affective component of behavior with limbic system
- — limbic system: includes hippocampus, amygdala -> emotion, behavior and long term memory
reticular formation
functions:
- conscious awareness and behavioral responses to stimuli
- maintains wakefulness
- muscle tone and posture
- respiratory centers (rhythm, depth, pattern)
- blood pressure and cardiac output
- blood distribution to organs
wernicke’s area
comprehension of written and spoken language
broca’s area
production of language
Somatic Sensory Cortex / Postcentral Gyrus
receives information from thalamus (skin sensation, proprioception, stereognosis [perception of depth or 3D]); integrates information with visual and auditory signals
Sensory Association Area
complex sensory information processing (spatial relationships, body image, two-point discrimination, graphesthesia [ability to recognize symbols when they’re traced on skin])
pain fibers
- group A fibers = transmit sharp, shooting intense pain
- group C fibers = transmit steady, slow, constant pain
pain
- free nerve endings detect damage to tissues (ischemia - low blood flow, mechanical - pressure or stretch, thermal damage, muscle spasm)
- visceral pain is produced by distension, spasm, contraction, torsion, ischemia, chemical irritation or inflammation of viscera
- has associated autonomic manifestations and is often referred to parts of body that share a spinal segment with injured viscus (internal organ)
ascending pain pathways
- spino-thalamic-somatosensory cortex = mediates sensation of pain
- spino-thalamic-frontal cortex/anterior cingulate gyrus = subjective psychological and physiological effects of pain
descending pain pathways
- modulation by fibers from periaqueductal grey matter, nucleus raphe and reticular formation to doral horn (descend in dorsolateral funiculus)
- neurotransmitters = adrenaline, GABA, serotonin, endorphins (opoids)
