Somatic Sensations 1 Flashcards by Matt Brittain

Components of the central and peripheral nervous systems that receive sensory information from the external and internal environment:

Somatic Senses

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Specific functions making it possible for humans to experience and interact with the enviornment

Special Senses

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Special senses:

Grouped in localized areas
Concentrated in specific locations in the head
Complex neural pathways (Vision, Hearing/Balance, Smell, Taste)

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Somatic senses:

Widely distributed
Scattered throughout the body
Simple structures (relatively) (Tactile, Thermal, Pain, Proprioceptive, Visceral, “Deep”)

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Somatic Senses - Mechanoreception:

Tactile &Position

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Somatic Senses - Thermoreception:

Hot & Cold

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Somatic Senses - Nociception:

Pain from tissue damage

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Somatic Senses - Exteroreception:

Surface of the body

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Somatic Senses - Proprioception:

Position of the body

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Somatic Senses - Visceral:

Internal organ sensations

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Somatic Senses - Deep:

Tissues, muscle, bone, tendons

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6 Types of Tactile receptors:

Free nerve endings
Meissner’s corpuscle
Merkel’s Discs
Hair end-organ
Ruffini’s endings
Pacinian Corpscle

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What Receptor is associated with - Touch, & Pressure detection (Only receptor found in cornea of the eye)

Free Nerve Endings

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What Receptor is associated with - Touch and vibration, is very sensitive, quickly adapts to sensation, is a long encapsulated nerve ending (Large myelinated fibers type AB) Location: non-hairy skin, fingertips, fingernails, lips.

Meissner’s Corpuscle

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What Receptor is associated with - “expanded Tip” Iggo dome receptor, Touch localization and texture sensation, determination of continual touch, Strong initial adaptation followed by weak adaptation of stimulus continues, Location: Fingertips, Hairy-parts of the skin, Steady-state signals

Merkel’s Discs

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What Receptor is associated with - Protruding epithelium with a collection of Merkel discs creating a “dome”, “Receptor Organ”, Extremely sensitive receptor!, One large myelinated cell (type AB)

Merkel’s Discs - Iggo Dome Receptor

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What Receptor is associated with - Interweaving base of hair roots, Touch receptors, Detects movement of the object on the skin and initial contact with the body.

Hair End- Organ

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What Receptor is associated with - Deep in the skin layers & internal tissues, Also found in joint capsules (joint rotation), multi branched, encapsulated, slow adaptation (signals continuous states of stimulation), Touch & pressure receptors.

Ruffini’s Endings

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What Receptor is associated with - lay beneath the skin & deep into tissues, rapid local compression stimulation, adapt to the compression very QUICK! detects rapid changes & tissue vibration, single myelinated nerve

Pacinian Corpuscles

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More critical Receptors:

Transmit signals via Type AB nerve fibers, 30-70m/sec, Precision of location, minute intensity changes, or acute changes in sensation. Meissner’s, Iggo Dome, Hair, Pacinian & Ruffini’s

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Not-so critical Receptors:

Transmits signals via Type A delta fibers, 5-30m/sec, Pressure, poorly localized touch & tickle (some FNEs transmit via C fibers, 2m/sec, mainly tickle)

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What types of tactile receptors are involve in detection of vibrations?

All tactile receptors, but each detects different frequencies

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What tactile receptor detects high frequency vibrations in the 300-800 cycles/se range, has rapid response to deformation, Type AB nerve fiber transmission

Pacinian

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What tactile receptor detects slow frequency vibrations in the 2-80 cycles/sec range (slow response to deformation compared to Pacinian)

Meissner’s

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Sensory information from our specialized receptors enter the spinal cord through ________ roots of the spinal nerves.

Dorsal

Name the pathway: Stimulus travels through the dorsal roots up to the medulla of the brain in the dorsal columns of the cord. After signals synapse and cross to the opposite side of the cord (decussate), signal continues upward through the brain stem to the thalamus by way of the medial lemniscus.

Dorsal Column-Medial Lemniscal System

Name the pathway: Stimulus travels through the dorsal roots and immediately after entering the spinal cord from the dorsal roots, synapse occurs in dorsal horns gray matter in the spinal cord. Signal crosses over to opposite side of the cord and ascends through the anterior and lateral white lower brain stem to the thalamus.

Anterolateral System (Spinothalamic pathway) (Ventrolateral system) all the same thing..

Name the pathway: Large nerve fibers from mechanoreceptors divide into the medial and lateral branches of the spinal root. (medial branch turns medially into the dorsal root column immediately) (Lateral branch enters dorsal horn gray matter then divides and synapses with other local neurons which can illicit cord reflexes and other tracts)

Dorsal Column Medial Lemniscal System

Dorsal Column Medial Lemniscal System - 1st order neuron:

Enters dorsal columns passing uninterrupted (ipsilateral) to the dorsal medulla where they synapse in the dorsal column nuclei.

Dorsal Column Medial Lemniscal System - 2nd order neuron:

(in the medulla they) immediately decussates to the opposite (contralateral) side of the brain stem and continues upward as the medial lemniscus (hence the name) to the thalamus

Dorsal Column Medial Lemniscal System - 3rd order neuron:

From the thalamus, the medial lemniscal fibers terminate in the sensory Mecca: Ventrobasal Complex (aka the Ventral Posterior Lateral Nucleus (VPL) and the 3rd order neurons branch to their specified regions of the postcentral gyrus of the cerebral cortex (somatosensory area 1). These fibers also project to the lateral parietal coretex (somatic sensory area 2).

Name the pathway: Large Myelinated Nerve Fibers

Dorsal Column Medial Lemniscal System

Name the pathway: 30-110ms

Dorsal Column Medial Lemniscal System

Name the pathway: High degree of spatial orientation, Transmits localization sensations & fine gradations (sensations that might need your attention quickly!) (Fine touch, pressure, 2-point discrimination, Vibration, Proprioception/Kinesthesia) THINK DISCRETE!

Dorsal Column Medial Lemniscal System

Name the pathway: Small, Myelinated Nerve Fibers

Anterolateral System

Name the pathway: 2-40m/s

Anterolateral System

Name the pathway: Less degree of spatial orientation, Transmits broad sensory modalities (Pain, Temperature (Warm & Cold), Crude tactile, ticket, itch, Sexual Sensations) THINK CRUDE!

Anterolateral System

LOWER parts of the body travel LESS LATERALLY (more medial in the cord):

DCML tract to the ventrobasal complex

The more ________ the sensory fibers /spinal nerves are in the body, the more _________ these fibers travel within the DCML tract to the ventrobasal complex (VPL)

Proximal, Laterally

Because these fibers decussate in the medulla, the left side of the body is represented in the ______ side of the thalamus & the right side of the body is represented in the ______ side of the thalamus.

Right, Left

The DCML is comprised of what two dorsal columns?

The gracile fascicles (gracile tract) and the Cuneate fascicles (cuneate tract)

The Anterolateral System is comprised of what two tracts?

Lateral spinothalamic tract, Anterior spinothalamic tract

What is Brodmann's Area?

50 distinct areas based on histological differences

What is Broca's area responsible for?

Language production

What is Wernicke's Area responsible for?

Language comprehension

What is the Frontal Lobe responsible for?

Reasoning, planning, speech, voluntary movement

What is the Parietal Lobe responsible for?

Movement, orientation, recognition, perception

What is the Temporal Lobe responsible for?

Auditory perception, memory, speech

What is the Occipital Lobe responsible for?

Visual processes

In the Cerebral Cortex there is a Large central fissure (Central Sulcus) what area is located Anterior to the Fissure?

Motor Cortex (muscle contraction and body movements)

In the Cerebral Cortex there is a Large central fissure (Central Sulcus) what area is located Posterior to the Fissure?

Somatosensory Cortex

True or false: A major part of the motor cortex activity is in response to the somatosensory cortex which keeps the motor cortex informed at each instant about the positions and motions of the different parts of the body.

True

Distinct and separate spatial orientation of the different parts of the body is found in Somatosensory Area 1 (SSA 1) and Somatosensory Area 2 (SSA 2). Which is more complex and extensive?

SSA1

Signals from Somatosensory Area ___ are required for functioning of Somatosensory Area ___.

1, 2

With removal of Somatosensory Area ___ there is no apparent effect on. the neuronal response in Somatosensory Area ___

2, 1

Horizontal Layers of the Somatosensory Cortex - Layer 1:

Superficial, nonspecific signals from lower brain

Horizontal Layers of the Somatosensory Cortex - Layer 5:

Deep into the brain (sends signals to brain structures to control excitability levels), Larger and project more distal into the brain (basal ganglia, brain stems, and spinal cord controlling signal transmission)

Horizontal Layers of the Somatosensory Cortex - Layer 2:

nonspecific signals from lower brain, sends signals to opposite sides of the brain via corpus callosum

Horizontal Layers of the Somatosensory Cortex - Layer 3:

Sends signals to opposite sides of the brain via corpus callosum

Horizontal Layers of the Somatosensory Cortex - Layer 4:

Sensory signals from the body enter in the 4th layer

Horizontal Layers of the Somatosensory Cortex - Layer 6:

Sends signals to brain structures to control excitability levels. Sends signals from the cortex to the thalamus; large in number

Horizontal Layers of the Somatosensory Cortex - Columns extend:

All the way through the 6 Horizontal Layers

Horizontal Layers of the Somatosensory Cortex - Within horizontal layer _______ (where the sensory signals from the thalamus (from the body) enter), the neurons work almost completely separately where in the other columns interact with one another to analyze sensory signal information

Layer 4

Horizontal Layers of the Somatosensory Cortex - What columns respond to muscle, tendon, and joint stretch receptors which spread sensory signals anteriorly so It can interact with the motor cortex (influential in activating muscle contraction)

The columns closest to the post-central gyrus

The process of sensory interpretation becomes more complex and refined the more ______ we move from the post- central gyrus.

Posterior

Functions of Somatosensory area 1 include:

Discrete localization. Different sensation in different parts of the body. Judge critical degrees of pressure, weights, textures, and shapes. Pain and temperature quality and intensity are preserved when the SSA1 is excised but localization of the pain and temperature is poorly interpreted without SSA1.

Functions of Somatosensory area 2 include:

Brodman's 5 and 7. Parietal Cortex. Important in deciphering meanings of sensory information. Combines info from multiple points in SSA 1 to interpret meaning. Receives sensory info from (SSA1, Ventrobasal nuclei of the thalamus, visual cortex, auditory cortex). Amorphosynthesis: removing/damage to the somatosensory association area on the left side of the brain (unable to recognize objects or feel forms on the right side (opposite) of the body), Damage on right, means sensory deficits on left side of body)

What is Divergence:

To separate, dividing, parting

What occurs at each synaptic stage in the DCML pathway?

Divergence

Two point discrimination on fingertip:

1 to 2 millimeters

Two point discrimination on back:

30-70 millimeters

What tract transmits two point discrimination?

DCML

Lateral inhibition:

Excited sensory pathways spread inhibitory signals to adjacent neurons

Inhibitory transmitters:

Serotonin, GABA, Dopamine