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36 Cards in this Set

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Somatic sensation
enables our body to feel, to ache, to chill and to know what its parts are doing
The somatic sensory system is different from other sensory systems in two ways
1. receptors are distributed all over the body
2. Responds to different kinds of stimuli: 4 senses: touch, pain, body position, & temperature
Proprioception
the sense of body position
The two types of skin
hairy and glabrous
Inner and outer layer of skin
dermis and epidermis
Skin is important because
1. a protective function
2. prevents evaporation of body fluids into dry environment
3. provides direct contact with the world
Mechanoreceptors are sensitive to what
physical distortions such as stretching or bending
Mechanorectors do what
monitor contact with skin
At the heart of each mechanoreceptor is
unmeyelinated axon branches with mechanosensitive ion channels
The gating of mechanosensitive ion channels depends on
stretching or changes in tension
Name some mechanoreceptors
1. Pacinian corpuscle
2. Ruffini's ending
3. Merkel's disk
4. Meissners corpuscle
Rapidly adapting
Tend to respond quickly at first but then stop firing even though the stimlulus continues
ex: Meissner and Pacinian corpuscles
Primary afferent axons
Axons bringing information from the somatic sensory receptors to the spinal cord or brain stem
The primary afferent nerves enter the spinal cord where, and their cell bodies lie where
1. dorsal root
2. dorsal root ganglion
What group has the most unmeyelinated axons
Group C or IV
How many spinal segments are there and what are the names of the four groups
30, cervical, thoracic, lumbar and sacral
Dermatome
The area of skin innervated by the right and left dorsal roots of a single spinal segment
The organization of the dermatone is best revealed when
one bends over to stand on both hands and feet
Spinal grey matter is divided into
1. dorsal horn
2. intermediate zone
3. ventral horn
Second-order sensory neurons
The neurons that recieve sensory input from primary afferent neurons
Dorsal coloumn-medial leminiscal pathway
Pathway serving touch
Ipsilateral
touch information from the left side of the body is represented in the activity of cells in the left dorsal coloumn nuclei
Dorsal coloumn nuclei
The axons of the dorsal coloumn terminate here
The dorsal coloumns carry information about
tactile sensation (limb position) toward the brain
Medial lemniscus
The axons of the dorsal column nuclei ascend within this white matter tract
The route of the axon synapse in the dorsal cloumn-medial lemniscal pathway
Large dorsal root axons through dorsal coloumn through dorsal coloumn nuclei in medial lemniscus rises throug the medulla. Its axons synapse upon neurons of VP of the thalamas. Thalamic neurons of the VP nucleus then project to specific regions of the primary somatosensory cortex (S1)
Trigeminal nerves (cranial nerve V)
Somatic sensation of the face is supplied here
Brodmann's area 3b is the primary somatic sensory cortex because
1. it recieves dense inputs from the VP nucleus of the thalamus
2. its neurons are very responsive to somatosensory stimuli (but not to other sensory stimuli)
3. lesions here impair somatic sensation
4. electrically stimulated, it evokes sensory experiences
Somatotopy
The mapping of the body's surface sensations onto a structure in the brain
Nociceptors
The free, branching, unmeyelinated nerve endings that signal that body tissue is being damaged
Nociception
The sensory process the provides the signals that trigger pain
Substance P
A peptide synthesized by the nociceptors themselves
Information about touch ascends which way, while information about pain ascends
ipsilaterally, contralaterally
The rate of a chemical reaction depends on
Temperature
Thermoreceptors
Neurons due to specific membrane mechanisms are exquisitely sensitive to temperature. Contribute to perception of temperature
The sensitivity of a sensory neuron to a change in temperature depends on
The type of ion channels the neuron expresses