martin chapter 4 Flashcards
spinal somatic sensory system
conveys info from the body (limbs, neck, trunk..) to the brain
trigeminal somatic sensory system
conveys info from the face, scalp, head to the brain
what is proprioreception?
our sense of limb position and limb movement
each somatic sensation (modality) has multiple?
submodalities
what is a dorsal root ganglion?
cluster of neuronal cell bodies located in the dorsal root of a spinal nerve, just outside the spinal cord
dorsal root ganglion neurons are which type of neurons?
pseudounipolar neurons
the cell bodies of dorsal root ganglion neurons are in?
the dorsal root ganglia
dorsal root ganglion neurons are pseudo unipolar. a single axon arises from the cell body and it branches in?
one axonal branch is directed towards the periphery (where it innervates the skin or other tissues)
one axonal branch is directed towards the CNS, to synapse with CNS neurons
the peripheral or central axon branches of dorsal root ganglion neurons are called?
primary (afferent) sensory fibers
the receptive portion of the dorsal root ganglion neuron is?
the peripheral axon terminal
the receptive field of the neuron corresponds to?
the area of the skin where stimulation activate the neuron
where are mechanoreceptors located?
at the terminal end of the peripheral axon branch of a dorsal root ganglion neuron
which types of channels are present in the membrane of mechanoreceptors?
stretch activated channels
rapidly adapting receptors
receptors that respond quickly to the onset of the stimulus or when the stimulus changes (such as the end of the stimulus)
slowly adapting receptors
respond for the duration of the stimulus
rapidly adapting receptors (2)
Meissner corpuscles and pacinian corpuscles
slowly adapting receptors (2)
Merkel’s receptor and Ruffini corpuscles
5 major types of encapsulated sensory receptors that mediate mechanosensation
-Meissner corpuscles
-Pacinian corpuscles
-Merkel’s receptor
-Ruffini corpuscles
-hair receptors
location of Merkel’s receptor and Meissner corpuscles
at the epidermis-dermis border
small receptive field
high spacial resolution
(High spatial resolution means you can feel the difference between two separate points of pressure, even if they are very close together)
receptors important in fine tactile discrimination
location of Ruffini and pacinian corpuscles
in the dermis
Ruffini corpuscles are sensitive to skin stretch and are important in discriminating the shape of grasped objects
pacinian are the most sensitive, can respond to slight skin displacments.
each peripheral axon of each dorsal root ganglion neuron has multiple branches, so….
multiple terminal ends->multiple mechanoreceptors
where is the muscle spindle positioned?
within the muscle belly
what does the muscle spindle contain?
intrafusal fibers (tiny muscle fibers) that detect changes in muscle length.
intrafusal fibers are controlled by the CNS
muscle spindle provides info to the brain about?
limb proprioception
the ability to know the position of our limbs in space without seeing them
Golgi tendon receptor, where is it? is sensitive to what?
it is within the collagen fibers of tendons
it is sensitive to the force generated by the contracting muscle
it may have a role on the individual perception of the effort it takes to perform a specific motor action
Does the Merkel cell accomplish mechanosensory transduction?
yes. it forms a synapse-like apposition with the axon terminal of the sensory fiber
mechanosensory transduction is performed by the merkel cell, which synaptically activates the sensory fiber
morphology of nociceptors, pruritic receptors, thermoreceptors
bare nerve endings
Each spinal cord segment is associated with a specific somite during development. As a consequence, each spinal cord segment innervates what?
each spinal cord segment innervates the muscle and skin of the body parts deriving from its associated somite
what is a dermatome?
The area of the skin innervated by the axons of a single dorsal root. Dermatomes overlap->if damage occurs to a single dorsal root no anesthetic area is observed (usually damage to a single dorsal root causes radicular pain to the dermatome associated with that dorsal root).
the dorsal horn of the grey matter of the spinal cord mediates?
sensory functions
the ventral horn of the grey matter of the spinal cord mediates?
motor functions
what is the Lissauer’s tract?
a region in the spinal cord made of unmyelinated and thinly myelinated fibers for pain and temperature.
which branch of the axon of a dorsal root ganglion neuron is the main one for perception?
ascending branch
each dorsal column transmits info from….to….?
from the ipsilateral side of the body to the ipsilateral medulla
where in the dorsal column axons coming from the lower limbs ascend?
in the most medial portion of the dorsal column, termed the gracile fascicle
where in the dorsal column axons coming from the lower trunk ascend?
within the gracile fascicle, lateral to those coming from the lower limbs
where in the dorsal column axons coming from the upper trunk, upper limbs, neck and occiput ascend?
within the cuneate fascicle
at which thoracic segment does the cuneate fascicle begins?
at the level of the 6th thoracic segment
what separates the gracile and the cuneate fascicles?
the dorsal intermediate septum
the dorsal columns at the two halves of the spinal cord are separated by?
the dorsal median septum
where do dorsal column axons synapse?
in dorsal column nuclei
->the first major relay in the ascending pathway for touch and limb position senses.
where do axons of the gracile fascicle synapse?
into the gracile nucleus
located close to the midline
where do axons of the cuneate fascicle synapse?
in the cuneate nucleus
what does the somatotopic organization ensure?
that adjacent structures in the periphery are represented at adjacent sites in the CNS.
in the Dorsal Column-Medial Lemniscus Pathway, what are the second order neurons?
neurons in the gracile and cuneate nucleus
name of axons of second order neurons
internal arcuate fibers
where do internal arcuate fibers decussate?
in the caudal medulla (they cross the midline)
which one between gracile and cunate fibers decussate more ventrally?
gracile fibers decussate more ventrally
internal arcuate fibers decussate and converge to form?
the medial lemniscus
axons in the medial lemnisucs ascend to synapse where?
in the thalamus
the ventral posterior nucleus in the thalamus has a lateral and medial division
ventral posterior lateral nucleus and ventral medial lateral nucleus
neurons receiving inputs from leg and arms are located in which division of the ventral posterior nucleus?
in the lateral division of the nucleus
neurons receiving inputs from the face are located in which division of the ventral posterior nucleus?
medial division
where do axon in the ventral posterior nucleus ascend?
to the primary somatic sensory cortex in the posterior limb of the internal capsule
mechanoreceptive informations are processed in 3 main cortical areas
primary somatic sensory cortex
secondary somatic sensory cortex
posterior parietal cortex
where is the primary somatic sensory cortex located?
in the post central gyrus of the parietal lobe
what is the sensory homunculus?
The sensory homunculus is a visual representation of the human body mapped onto the primary somatosensory cortex
in which layer of the cerebral cortex does the thalamus primarily project?
layer IV (and the adjoining portion of layer III)
neurons within a cortical column in the primary sensory cortex receive informations from?
the same peripheral location on the body and from the same class of mechanoreceptors
how many layers does the cortex comprise in the post central gyrus?
6
in the postcentral gyrus neurons whose cell bodies are located in layer II and III project to?
other cortical areas
in the postcentral gyrus neurons whose cell bodies are located in layer V project?
to subcortical regions
in the postcentral gyrus neurons whose cell bodies are located in layer VI project?
to the thalamus
what do neurons in layer IV of the postcentral gyrus do?
receive infos from the thalamus and transmit infos to other cortical layers
the primary somatic sensory cortex consists of 4 cytoarchitectonic divisions (brodmann’s areas)
1,2,3a,3b
association areas
-regions of the cerebral cortex that integrate and process information from multiple sensory and motor areas.
-are involved in higher order functions
