Somatosensory System Flashcards
Somatosensation = ?
Somatosensory System
Somatosensation:
- The sensory information from skin and musculoskeletal systems
- Information in the somatosensory system proceeds from the receptor through a series of neurons to the brain.
Ascending pathways
Information ascends via (?) in the (?) to various regions of the brain.
Somatosensory System
Ascending Pathways:
(a) Receptors in the periphery encode the mechanical, chemical and thermal information.
(b) Receptors are stretched, compressed, deformed, or exposed to thermal, chemical agents
- Ion channels to open, encoding information into ionic currents.
(c) Action potential conducted from the peripheral axons, to the dorsal root ganglion, then into the SC.
(d) Information ascends via axons in the white matter to various regions of the brain.
Sensory Receptors
- Located where = ?
- Four types = ?
Somatosensory System
Sensory Receptors:
(a) Located at the distal end of peripheral neurons.
(b) Each type of receptors are specialized, and respond to a specific type of stimulus of adequate intensity.
(c) Classified as follows:
- Mechanoreceptors: Respond to mechanical deformation.
- Chemoreceptors: Respond to chemicals released by cells.
- Thermoreceptors: Respond to heat / cold.
- Nociceptors: Sensitive to stimuli that damage or threaten to damage tissue.
- Sensation of pain
Receptive Fields = ?
Somatosensory System
Receptive Fields:
(a) Area of skin innervated by a single afferent neuron
- Receptive field for that neuron.
(b) Small distally and larger proximally
- Greater density of receptors distally than proximally
(c) Two closely applied stimuli on fingertip
- Small receptive field + greater density of receptors distally = distinguish between two closely applied stimuli
Peripheral neurons
Cell bodies are located outside the spinal cord in _ (?) _ , or outside the brain in the _ (?) _.
Somatosensory System
Peripheral Neurons:
(a) Cell bodies are located outside the spinal cord in dorsal root ganglia or outside the brain in the cranial nerve ganglia.
(b) Distal / peripheral axons
- Messages from receptor to cell body
(c) Proximal / central axons
- Cell body to spinal cord or brainstem
Peripheral SENSORY Neurons
Are classified according to _ (?) _ .
Somatosensory System
Peripheral SENSORY Neurons:
(a) Also called afferents; are classified according to axon diameter:
- Ia
- Ib
- II
- Aβ
- Aδ
- C
(b) Larger diameter axon transmit information faster than small diameter axons.
Somatic Sensory afferents that link receptors to the Central nervous system
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Somatosensory System
Different diameter axons
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Somatosensory System
Pathways to brain
Somatosensory pathway are named according to = ?
Somatosensory System
Pathways to Brain:
(-) Somatosensory pathway are named according for the origin and termination of tract that contains the second order neuron in series (spinothalamic).
Pathways to the Brain
Three types of pathways to bring sensory information to brain = ?
Somatosensory System
Pathways to the Brain:
(a) Three types of pathways to bring sensory information to brain
(1) Conscious Relay Pathways:
- Brings information about location and type of stimulation to cerebral cortex.
- Provide accurate details about the stimulus & location, somatotopically organized.
- Discriminative, information allows us to make fine distinctions about stimuli.
(2) Divergent pathways:
- Transmit information to many locations in the brainstem and cerebrum.
- Sensory information is used at conscious and unconscious levels, not somatotopically organized.
(3) Unconscious relay pathways:
- Unconscious proprioceptive information and other movement related information to the cerebellum.
- Role in automatic adjustments of our movements and posture.
Describe the three order neuron system.
Somatosensory System
Three Order Neuron System: Information from the peripheral sensory endings is conducted through the nervous system by a series of neurons,
(a) Simplest form, consist of three neurons
- First order neuron - has cell body in posterior root ganglion.
- Fibers enter the spinal cord to synapse with second order neuron.
- Axons decussate and ascend to higher level of nervous system, where it synapse with 3rd order neuron - usually in the thalamus
(b) Projection fibers pass to the cerebral cortex.
_ ? _ Pathway = Brings information about location and type of stimulation to the cerebral cortex.
Somatosensory System
Conscious Relay Pathways:
- Brings information about location and type of stimulation to cerebral cortex.
- Provide accurate details about the stimulus and location, somatotopically organized.
_ ? _ Pathways
- Transmits sensory information, used at conscious & unconscious levels, and is NOT somatotopically organized, to locations in the brainstem and cerebrum.
Somatosensory System
Divergent pathways:
- Transmit information to many locations in the brainstem and cerebrum.
- Sensory information is used at conscious and unconscious levels, not somatotopically organized.
_ ? _ Pathway = Plays a role in automatic adjustments of our movements and posture, as well as, sends unconscious proprioceptive & movement related information to the cerebellum.
Somatosensory System
Unconscious relay pathways:
- Unconscious proprioceptive information & other movement related information to the cerebellum.
- Role in automatic adjustments of our movements & posture.
- A = ? order neuron
- B = ? order neuron
- C = ? order neuron
Somatosensory System
- A = Third order neuron
- B = Second order neuron
- C = First order neuron
- Dorsal Column/ Medial Lemniscus System (DCML), senses what = ?
- Anterolateral tracts / Spinothalamic tract, senses what = ?
Somatosensory System
Conscious Relay Pathways to Cerebral Cortex: Pathway to consciousness travel upward in the spinal cord via two routes.
(a) Dorsal Column/ Medial Lemniscus System (DCML):
- Discriminative touch
- Conscious proprioception
(b) Anterolateral tracts / Spinothalamic tract:
- Discriminative pain
- Temperature
- Crude touch
Three types of sensations = ?
Somatosensory System
Types of Sensations:
(I) Deep:
- Joint position sense (proprioception)
- Movement awareness (kinesthesia)
- Vibration
(II) Superficial:
- Pain
- Temperature
- Light touch
- Pressure
(III) Combined Cortical:
- Two point discrimination
- Barognosis = Ability to perceive and evaluate the weight of objects, or to differentiate objects of different weights, by holding or lifting them.
- Graphesthesia = Ability to recognize symbols when they’re traced on the skin.
- Tactile localization
- Texture recognition
- Stereognosis = Ability to identify the shape and form of a three-dimensional object, and therefore its identity, with tactile manipulation of that object in the absence of visual and auditory stimuli.
Types of Sensations
Deep sensations = ?
Somatosensory System
Types of Sensations:
(I) Deep:
- Joint position sense (proprioception)
- Movement awareness (kinesthesia)
- Vibration
Types of Sensations
Superficial sensations = ?
Somatosensory System
Types of Sensations:
(II) Superficial:
- Pain
- Temperature
- Light touch
- Pressure
Types of Sensations
Combined Cortical sensations = ?
Somatosensory System
Types of Sensations:
(III) Combined Cortical:
- Two point discrimination
- Barognosis
- Graphesthesia
- Tactile localization
- Texture recognition
- Stereognosis
Dorsal Column Sensations = ?
Somatosensory System
Dorsal Column Sensations:
- Discriminative touch
- Proprioception
- Vibration
- Two-point discrimination
- Barognosis
(-) The ability to perceive and evaluate the weight of objects, or to differentiate objects of different weights, by holding or lifting them. Accuracy requires an intact and healthy peripheral and central nervous system.
(-) The ability to recognize symbols when they’re traced on the skin.
- Texture recognition
- Stereognosis
(-) The ability to identify the shape and form of a three-dimensional object, and therefore its identity, with tactile manipulation of that object in the absence of visual and auditory stimuli.
- Integration of touch and proprioceptive information in cerebral cortex allows identification of an object by touch and pressure information.
- Fasciculus gracilis (medial), axons from = ?
- Fasciculus cuneatus (lateral), axons from = ?
Somatosensory System
- Fasciculus gracilis (medial): Axons from lower limb and lower trunk.
- Fasciculus cuneatus (lateral): Axons from upper limb, upper trunk, neck.
Size of the area of primary sensory cortex devoted to specific part of the body is represented by the = ?
Somatosensory System
Somatotopic Arrangement of Information
- Size of the area of primary sensory cortex devoted to specific part of the body is represented by the homunculus.
Somatotopic Arrangement of Information
- Area 1= ?
- Area 2 = ?
- Area 3a = ?
- Area 3b = ?
Somatosensory System
- Area 1= Texture
- Area 2 = Size and shape
- Area 3a = Proprioception
- Area 3b = Touch
Secondary somatosensory cortex analyzes information from = ?
Somatosensory System
Secondary somatosensory cortex:
- Analyzes information from primary sensory cortex and thalmus.
- Provide stereognosis by comparing somatosensation from current object with memories of other objects.
Lesion = “x” / Effects = “y”
- Cerebrum, Midprain, Pons, Upper Medula = ?
disc. touch & con. proprioception
Somatosensory System
- Lesion in cerebrum, midprain, pons, upper medula = Contralateral loss on distriminative touch, and conscious proprioceptive information.
Lesion = “x” / Effects = “y”
- Lower Medula = ?
Somatosensory System
- Lower Medula Lesion = Ipsilateral loss on distriminative touch, and conscious proprioceptive information.
DCML: Lesion = “x” / Effects = “y”
- Spinal Region = ?
Somatosensory System
- Spinal Region Lesion = Ipsilateral loss on distriminative touch, and conscious proprioceptive information.
Lesion = “x” / Effects = “y”
- Peripheral Region = ?
Somatosensory System
- Peripheral Region Lesion = Ipsilateral loss on distriminative touch, and conscious proprioceptive information
Anterolateral Column Pathways
Contain axons that transmit information about = ?
Somatosensory System
Anterolateral Column Pathways:
- Contain axons that transmit information about
- Pain (free nerve endings/ nociceptors)
- Temperature
- Crude touch
Anterolateral Column Pathways
Four different Anterolateral pathways = ?
Somatosensory System
Anterolateral Column Pathways:
- Different anterolateral pathways:
(1) Spinothalamic: conscious relay pathway
- Anterior = Carries information about crude touch
- Lateral = Carries information about pain and temperature
(2) Spinolimbic
(3) Spinoreticular
(4) Spinomesencephalic
Spinothalamic Pathway:
3 order neuron, conscious relay pathway
- Primary neurons brings information = ?
- Axons of secondary neurons cross the midline and project from the = ?
- Tertiary neurons project from the = ?
Somatosensory System
Spinothalamic Pathway:
3 order neuron, conscious relay pathway
- Primary neurons brings information into the dorsal horn of the spinal cord.
- Axons of secondary neurons cross the midline and project from the spinal cord to the thalamus.
- Tertiary neurons project from the thalamus to the cerebral cortex.
Spinothalamic pathway
- Lateral spinothalamic pathway = ?
- Anterior spinothalamic pathway= ?
What senses
Somatosensory System
- Lateral spinothalamic pathway = pain, temperature
- Anterior spinothalamic pathway = crude touch
Lateral Nociceptive System:
- Lesion in Thalamus results in = ?
Somatosensory System
Sharp Localized Pain / Lateral Nociceptive System:
- Also known as lateral pain system - because tracts terminate in the lateral thalamus.
- Thalamus lesion = inability to localize the pain stimuli despite feeling the emotional aspect of pain.
Absence of pain in response to a stimuli that normally would be painful = ?
Somatosensory System
Analgesia: Absence of pain in response to a stimuli that normally would be painful.
Compare/Contrast:
- Dorsal Column/Medial Lemniscus = ?
- Spinothalamic Systems = ?
Somatosensory System
Dorsal Column / Medial Lemniscus:
- Discriminative touch, conscious proprioception
- Midline crossing at medulla
- Axons of 1st-order neuron ascends ipsilateral
Spinothalamic Systems:
- Pain, crude touch, temperature
- Midline crossing at spinal cord
- Axons of 2nd-order neuron ascends contra laterally
Fast vs. Slow Pain
- Fast Pain, fiber = ?
- Slow Pain, fiber = ?
Somatosensory System
Fast vs. Slow Pain = Pain can be separated into early perception of sharp pain (fast pain) and a later sensation that is described as having a duller bright quality (slow pain)
(a) Fast pain:
- Initial and immediate sharp sensation that indicates location of lesion.
- Aδ fibers
(b) Slow pain:
- Following sharp pain
- Dull throbbing, burning ache, not well localized
- C fibers, unmyelinated
Divergent Pathways / Medial Nociceptive System
- Does NOT use = ?
Somatosensory System
Medial pain system:
- Many responses to nociception are carried by medial pain systems.
- Affective, motivation, arousal, withdrawal and autonomic responses.
- Uses several pathways, NOT a three order neuron pathway.
- Variable number of projection neurons that synapse in different locations in the CNS.
- NOT somatotopically organized: cannot be accurately localized.
Divergent Pathways / Medial Nociceptive System:
Medial pain system reaches the midbrain, reticular formation, limbic areas via three tracts = ?
Somatosensory System
Medial pain system reaches the midbrain, reticular formation, limbic areas via three tracts:
- Spinomesencephalic
- Spinoreticular
- Spinolimbic
Spinomesencephalic Tract:
Carries nociceptive information to two areas in the midbrain = ?
Somatosensory System
Spinomesencephalic Tract:
Carries nociceptive information to two areas in the midbrain:
(1) Periaqueductal gray (PAG): Periaqueductal gray is part of the descending pain control system.
- Involved in turning the eyes & head toward the source of noxious input, and in activating descending tracts that control pain
(2) Superior Colliculus
Spinoreticular Tract
- These ascending neurons synapse in the = ?
- Modulates = ?
Somatosensory System
Spinoreticular Tract:
- These ascending neurons synapse in the reticular formation.
- Reticular formation: A neural network in the brainstem that includes the reticular nuclei and their connections.
- Modulates arousal, attention, and sleep - waking cycles.
- Severe pain needs attention and interferes with sleep.
Spinolimbic Tract
Axons of the spinolimbic tract transmit _ ? _ information.
Somatosensory System
Spinolimbic Tract:
- Axons of the spinolimbic tract transmit slow pain information to the medial and intralaminar nuclei in the thalamus.
- Axons project to anterior cingulate cortex, insula, amygdala.
- Interferes with thinking, behavior and social activities.
Spinolimbic Tract
- Spinolimbic tract axons project to = ?
- Inteferes with = ?
Somatosensory System
Spinolimbic Tract:
- Axons of the spinolimbic tract transmit slow pain information to the medial and intralaminar nuclei in the thalamus.
- Axons project to anterior cingulate cortex, insula, amygdala.
- Interferes with thinking, behavior and social activities.
Unconscious Relay Tracts to Cerebellum
Information from proprioception is transmitted to cerebellum via four spinocerebellar tracts, they are = ?
Somatosensory System
Unconscious Relay Tracts to Cerebellum:
- Information from proprioception is transmitted to cerebellum via spinocerebellar tracts:
(1) Posterior spinocerebellar pathway =
- Transmits information from legs and lower half of the body)
(2) Cuneocerebellar pathway =
- Arm and upper half of the body
(3) Anterior spinocerebellar pathway =
- Thoracolumbar spinal cord
(4) Rostrospinocerebellar pathway =
- Cervical cord
Notes:
- Information is not consciously perceived
- Information is used for unconscious adjustment to movements and posture
Unconscious Relay Tracts to Cerebellum
True or False:
- Information is not consciously perceived.
- Information is used for unconscious adjustment to movements and posture.
Somatosensory System
- TRUE, Information is not consciously perceived
- TRUE, Information is used for unconscious adjustment to movements and posture
Lesion = “x” / Effects = “y”
Lateral Nociceptive System:
- Cerebrum, Midbrain, Upper Pons = ?
Somatosensory System
Lateral Nociceptive System - Lesion in:
- Cerebrum, Midbrain, Upper Pons = Entirely Contralateral loss
Lesion = “x” / Effects = “y”
Lateral Nociceptive System:
- Lower Pons, Medulla = ?
Somatosensory System
Lateral Nociceptive System - Lesion in:
- Lower Pons, Medulla =
- Crossed analgesia, involving contralateral body and ipsilateral face, occures when trigeminal and spinothalamic acons are interrupted.
- Contralateral loss from the face IF the trigeminal lemniscus axons are interrupted.
Lesion = “x” / Effects = “y”
Lateral Nociceptive System:
- Spinal Region = ?
Somatosensory System
Lateral Nociceptive System - Lesion in:
- Spinal Region = Loss of pain & temperature sensation from contralateral body, one or two levels below lesion.
Lesion = “x” / Effects = “y”
Lateral Nociceptive System:
- Peripheral Region = ?
Somatosensory System
Lateral Nociceptive System - Lesion in:
- Peripheral Region = Ipsilateral loss
Explain this picture
Somatosensory System
Receptive Fields:
(-) Picture:
(A)
- The caliper points touching the skin would be percieved as one point, because both points are within the receptive field of a single neuron.
(B)
- The caliper points would be perceived as two points, because the points are contacting the receptive fields of two neurons.
(-) Notes:
- Area of skin innervated by a single afferent neuron- receptive field for that neuron.
- Small distally and larger proximally.
- Greater density of receptors distally than proximally.
- Two closely applied stimuli on fingertip.
- Small receptive field+ greater density of receptors distally = distinguish between two closely applied stimuli.
