SENSORY TRANSMISSION - 38

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What is Sensation?: The ability to perceive information about the external environment
What are the 4 classifications of sensation?: 1. SUPERFICIAL OR CUTANEOUS: touch pressure, thermal, pain

2. DEEP: muscle, tendon and joint sensibility
a. kinesthetic sense - change in spatial positions of limbs are perceived
b. deep pressure
c. deep pain

3. VISCERAL SENSATION: hunger, thirst, sexual sensations, nausea, visceral pain

4. SPECIAL SENSES

*NOTE: The first three classifications are somatic
What are the 5 characteristics of sensation?: 1. QUALITY: subjective diff. btw individual sensation e.g cold, warm, hot, touch, pain

2. INTENSITY: strength, amplitude

3. LOCUS: site, localization

4. DISCRIMINATION OR JUDGMENT: comparison e.g size, shape, texture, position, spatial relationship

5. AFFECT: response, perception - subjective e.g pleasant, unpleasant
Why is the somatosensory system importiant?: It is responsible for detecting all stimuli that contact the body.
What are roles of the somatosensory system?: 1. Mediates the sensation of touch and temperature that are produced by innocuous stimuli contacting the skin

2. Mediates the sensation of pain that are produced by injury or disease

3. Responds to skeletal movements and mediates the kinesthetic sensations that signal limb position.
What are needed to perform sensory transmission in the C.N.S?: RECEPTORS : Specialized sensory elements for particular type of sensory information e.g., touch, temperature, pressure, pain.
What are the 4 diff types of receptors?: 1. Mechanoreceptors- sensitive to touch, pressure etc. May be:
a.) Corpuscles-encapsulated within fibrous capsules; Pacinians, Messner, Ruffini
b.) Other: Merkelâ€™s disc, hair follicles
c.) Adaptation- some rapid (phasic); Some slow (tonic)

2. Thermoreceptors- sensitive to cooling below normal body temperature (cold receptors)
Warming- above normal body temperature (warm receptors)

3. Nociceptors- sensitive to tissue damage

4. Proprioception- senses joint position, muscle length, muscle tension

a.) Muscle spindles- encodes muscle length
b.) Golgi tendon- muscle tension
c.) Joint capsules- angle of joint
What are PERIPHERAL NERVE FIBERS?: --Convey somatic information to the CNS which includes all of the general somatic afferents that innervate the skin, muscles and joints.

--They also supply the meninges, surfaces of nasal and oral cavities and thoracic and abdominal viscera and project to specific nuclei in brainstem and spinal cord that project to brain
What are the two major subdivisions of the somatic sensory system and their major components?: 1. Subsytem for detection of mechanical stimuli (e.g., light touch, pressure, vibration. They have:
a.) subcutaneous and cutaneous receptors
b.) muscles, joint receptors
c.) deep receptors (proprioceptors)

2. Subsystem for detection of pain, temperature, etc.
What are the functions two major subdivisions of the somatic sensory system and their major components?: They give animals the ability to identify :
1. Shapes and texture of objects

2. Monitor environmental (external and internal)forces acting on the body.

3. Detect potentially harmful or nociceptive information
What are 2 places that central afferent terminals from receptors synapse on?: 1. Interneurons at different levels in the spinal cord
2. Neurons of ascending pathways that relay information to the cerebral cortex.
What are the two major ascending pathways for transmission of sensory info?: 1. The Dorsal Column Medial Lemniscal System (DCMLS)

2. Anterolateral system
Describe the The Dorsal Column Medial Lemniscal System (DCMLS)as it relates to: 1. Origin 2. Sensation 3. Course: The system conveys tactile and kinesthetic information and mediate the rapid and accurate transmission of signals from structures where they originate from to the thalamus and cortex

1. Origin: Mechanoreceptor: skin, muscle, joints, viscera

2. Sensation:
-fine touch
-proprioception
-vibration

3. Course:
-The receptors go to dorsal root fibers then to dorsal column, and ascend to the medulla.

- At the medulla, they synapse in gracile and cuneate nuclei of the medulla in an ipsilateral manner.
Where are some of the signals of the DCMLS processed? and where do they project?: They are processed at:
1. dorsal column nuclei
2. thalamic nuclei

They project to the cortex into conscious perception.
What are the First order relay neurons in DCMLS?: They are located in the dorsal root ganglion at all levels and they make connections with the second order neurons in the Gracile and Cuneate nuclei (lower medulla).
Where are the two locations of second order relay neurons in DCMLS?: 1. gracile nuclei of the caudal medulla.
2. cuneate nuclei of the caudal medulla.
Where do the second order relay neurons in DCMLS cross and ascend to?: They cross the midline and ascend in the medial lemniscus (note: decussation) to synapse in the Ventral Posterior lateral (VPL) nucleus of the Thalamus.
Where is the location of third order relay neurons in DCMLS?: Ventral Posterior lateral (VPL) nucleus of the Thalamus.
Where do the third order relay neurons in DCMLS project to?: Primary Somatic Sensory Cortex (I & II)
What is stereognosis? It is a special feature of what?: It is spatial identification of objects and this is a special feature of the perception of mechanical skin stimuli conveyed by the DCMLS
Movements such as those of tactile exploration of the environment are guided with the aid of what?: feedback signals from the skin, joints and muscles.
What happens to individuals with dorsalcolumn lesions?: They experience impaired ability to identify objects by touch or to recognize in the absence of visual inspection, figures or letters written onto the skin.
What are 4 reasons why the DCMLS is important?: 1. It is a route for rapid, accurate transmission of signals from the periphery to the thalamus and cortex of mechanical stimulation of skin and position of joints.

2. It is important for some info processed in conscious sphere (touch sensibility and deep sensibility)

3. Important for localization acuity and spatial identification of objects (stereognosis)

4. Important for exploration of environment by touch (with aid from feedback from skin)
4 characteristics of synaptic transmission into medial leminiscus relay neurons or DCMLS?: 1. Preservation of receptor specificity; afferents of the same type of receptor usually converge on a given central relay neuron.

2. Hi-fidelity synaptic transmission; a single impulse in presynaptic fiber may cause postsynaptic discharge

3. Localization acuity

4. Somatotopic organization : orderly spatial represntation of peripheral reception in relay nucleus.
Why is the Posterior horn important?: Plays significant role in coding intensity and quality of somatosensory sensations (pain I, VI, V) (some VI, VII) thermal and tissue damaging stimulation
What is the location of axons of the anterolateral system?: anterior part of lateral funiculus
What type of info does the Anterolateral system receive?: nociceptive information and non-noxious information
What is Enkephalin?: A powerful neurotransmitter that inhibits reponsiveness of neurons in anterolateral system
1. Where are enkephalic neurons located? 2. Where do enkephalic neurons send their axons to?: 1. substantia gelatinosa (Lamina II)

2. They send axons to
a. Lamina I
b. Lissauers tract
What does Substantia Gelatinosa (SG) receive from the brainstem (raphe)? What do this things do?: 1.
a.serotonergic projections

b.noradrenergic projections

2. They activate SG to release Enkephalin and thus inhibits anterolateral system (Gating Concept)
What is Spinothalamic Tract. (STT)?: The STT is the classical spinal pathway for the perception of pain and temperature. It also mediates crude touch and pressure.
In general, the STT is concerned with what?: the transmission of poorly localized and â€œcrude sensations.â€
1. Some of the fibers of the anterolateral system end where? 2. Others project where?: 1. end in the specific relay nuclei of the thalamus

2. others project to the midline and intralaminar, nonspecific projection nuclei.
Differentiate btw the DCMLS?: 1. The STT is phylogenetically older than the DCMLS.

2. It is less precisely organized topographically.

3. its cells of origin are activated by a broader range of dorsal root afferents
What dorsal root afferents activate the cells of origin of STT?: A-delta and C-fibers.
There is a major input from the anterolateral system into where?: Mesencephalic reticular formation.
Thus, sensory input activates the reticular activating system
What is the role of the reticular activating system?: It maintains the cortex in the awake and alert state
Cutaneous receptors are capable of what?: transducing a number of different stimuli which in turn lead to the production of different sensations.
What are sensory modalities?: They are different sensations produced by diff stimuli transduced by Cutaneous receptors .
4 examples of sensory modalities are?: 1. touch-pressure
2. temperature
3. kinesthesia
4. pain.
What is lamination?: They are tumors located laterally that compress the first STT caudal and lumbar area and result in loss of pain and temp.
What results from intraspinal tumors?: loss of sensation in higher segments.
Compare myleination, conduction velocity, and fiber diameter of: 1. Dorsal Lemniscal System 2. Anterolateral Spinothalamic System: 1. DCMLS has mostly large myelinated fibers, conduction velocity btw 30-110m sec, and fiber diameter btw 5 â€“ 18 um.

2. Anterolateral System
has Smaller myelinated fibers, diameter impulse traffic btw 10-60 m/sec, and fiber diameter of 4mm.
Compare spatial orientation of: 1. Dorsal Lemniscal System 2. Anterolateral Spinothalamic System: 1. DCMLS has a High degree spatial orientation:
a) fine gradation of intensity
b) high degree of localization

2. Anterolateral System
has a Small degree spatial orient
Compare how info is carried by: 1. Dorsal Lemniscal System 2. Anterolateral Spinothalamic System: 1. DLS carries info rapidly.
2. AS does not need to carry info rapidly.
Compare fine graduations of intensity btw: 1. Dorsal Lemniscal System 2. Anterolateral Spinothalamic System: 1. DLS carries sensations detecting fine graduations of intensity.

2. AS lacks fine graduations of intensity
Compare localization of sensation btw: 1. Dorsal Lemniscal System 2. Anterolateral Spinothalamic System: 1. DLS has sensations that are discretely localized.

2. AS has sensations that are less exact localized
Compare type of sensory transmission btw: 1. Dorsal Lemniscal System 2. Anterolateral Spinothalamic System: 1. DLS only transmits mechanoreceptive transmissions. (Pressure sensations that note fine degrees of judgment of pressure intensity!) and it signals movement on skin.

2. AS transmits a Broad spectrum of sensory modalities (e.g., pain, warmth, cold, crude touch, tickle, itch)
How is touch information transmitted?: both spinothalamic and dorsal column-medial lemniscal pathways
What must occur before tactile sensation is totally abolished?: Disruption of both spinothalamic and dorsal column-medial lemniscal pathways and this would require relatively large lesions.
What 2 things happens to touch info if the dorsal columns are destroyed?: 1. Vibratory sensation is lost and the touch threshold is elevated.

2. localization of touch sensation becomes impaired along with a decrease in the number of touch sensitive spots (areas) in the skin.
What happens after spinothalamic tract (STT) disruption?: 1. There is a decrease in touch sensitive areas and an increase in touch threshold

2. the touch deficit is less severe and touch localization remains essentially normal.
Light touch is detected by ?: Receptors in the skin found close to a hair follicle so even if the skin is not touched directly, movement of the hair maybe detected.
What happens when there is light movement of a hair?: This triggers a generator potential in mechanically-gated sodium channels in a neuron located next to the hair follicle.
What do generator potentials in hair follicle cause?: They cause an opening of opens voltage- gated sodium channels and it reaches threshold, triggers an action potential in the neuron.
Compare information carried in: 1. STT 2. dorsal column-medial lemniscal system: 1. Information carried in STT is concerned with poorly localized gross tactile sensation.

2. Information carried in the dorsal column-medial lemniscal system is concerned with detailed localization, spatial form and temporal pattern of tactile stimuli.
Are touch receptors distributed evenly over the body?: No, the fingertips and tongue may have as many as 100 per cm2, the back of the hand fewer than 10 per cm2.
What is the two-point discrimination test used for?: -It is used to determine the minimum separation of the points that produces two separate touch sensations.

- This is is far better on the fingertips than on, say, the small of the back.
What is receptive field size used for?: It determines the ability to discern closely spaced stimuli.
Where are touch receptors located?: On most of the body surface.
It is sparce in the trunk but it is rich in the lips and finger tips.
What are the 2 types of mechanical stimuli?: 1. Slowly adapting: respond to mainted touch. Have AB, and C.

2. Rapidly adapting: respond to onset and termination. Have AB, A$.
Give 2 examples of structures that are slowly adapting?: 1. Merkel
2. Ruffini
Give 2 examples of structures that are rapidly adapting?: 1. Meissner
2. Pacini
Describe stereognosis?: Recognition of 3-dimensional objects by palpation e.g keys in pocket. It is not a true perception but it uses a complex of several modalities.
What is Thermoreception?: The subjective difference in the temperature sense between â€œwarmâ€ and â€œcoldâ€
What are the 2 populations of receptors involved in temperature sensation?: 1. cold receptors: naked nerve endings of either thin myelinated fibers

2. warm receptors: unmyelinated fibers
Distinguish btw cold receptors and warm receptors regarding their response peak?: 1. Cold receptors have a broad response with peak at about 30º C

2. warm receptors show response peak at about 43 º C

---Both sets of receptors are sensitive only to thermal stimulation.
Temperature affects all biophysical processes like?: excitation of nerves, so the sensitivity of all sensory units is, to a degree, influenced by the prevailing temperature.
What is unique about some sensory receptors?: They respond to temperature changes with a sensitivity that far exceeds the temperature dependence of other cellular processes.
The response of the temperature receptor is dependent on what?: The temperature gradient.

-This is because human observer can detect temperature changes more accurately than he/she can estimate a prevailing (steady state) temperature.
where are thermoreceptors located and why is this important?: thermoreceptors are located sub-epithelially, so it is the temperature of the subcutaneous tissues that determines the responses
Cool metal objects feel colder than a cork of the same temperature because?: the metal conducts heat away from the skin more rapidly, cooling the subcutaneous tissue to a greater degree.
What type of adaptations are thermoreceptors?: They are slowly adapting
What does â€œcomfortâ€ zone mean in terms of thermoreception?: It is a zone of thermal neutrality where there is a temperature range within which complete adaptation occurs
What happens above or below the â€œcomfortâ€ zone?: permanent sensations of heat or cold are produced even when the skin temperature is kept constant for a long period of time (example â€“ feeling that oneâ€™s feet are cold for hours).
1. What happens below a skin temperature of 20oC and above 40oC? 2. What happens btw this range?: 1.there is no adaptation
2. there is adaptation, so that the sensation produced by temperature change gradually fades to one of thermal neutrality.
What happens at a temp above 45 degrees?: Tissue damage begins to occur and sensation then becomes nociceptive.

*NOTE: There are 5-10x more cold spots than warm.
Position sense is mediated by?: muscle and joint afferent fibers
The 2 kinds of position sense are?: 1.) kinesthesia (joint movement)

2.) static limb position.
What was dicovered by experiments about the knee joint afferents?: They are not sensitive to joint angle over the midrange where static position sense is well developed.
What happens when there is anesthesia of the joint capsule?: The subjects have good static limb position and this is why individuals with artificial joints can have good static limb position sense.
How is Proprioceptive (position sense) information transmitted?: In the dorsolateral fasciculus
Where does Proprioceptive (position sense) information pass to consciousness?: In the anterolateral columns of the spinal cord.
How do joint afferents differ from muscle spindle receptors?: muscle spindle receptors have complex properties that are controlled by efferent signals from the CNS.
Joint afferents play a role in?: signaling the extremes of limb position and pressure changes within the joint capsule.
How does position sense gives input to the cerebellum?: via the med. leminiscus to thalamus to cortex
What is ataxia?: this is a disease of position sense, where there is an inability to coordinate voluntary muscular movements.
What is kinesthesia?: Conscious recognition of orientation of diff body parts to each other even during movement.
Kinesthesia is due to what?: Due to extensive sensory endings in joint capsules and ligaments
The sensation(s) evoked by impulses generated in a receptor depends upon what?: the specific part of the sensory cortex that is ultimately activated e.g if a sensory nerve from a pacinian corpuscle is stimulated by pressure on the elbo or by a tumor in the brachial plexus, the sensation experienced at the cortex is pressure.
What does the law of projection illustrate?: It shows that stimulation at any point along the sensory pathway to the cortex produces a conscious sensation that is projected to the location of the receptor
What happens when a cortical receiving area for impulses from the left hand is stimulated?: the patient reports sensation in his left hand and not in his head.
What is phantom limb pain?: It is when amputees sometimes complain of pain and proprioceptive sensations in the absent limb
Phantom limb pain is due to what?: due in part to pressure on the stump of the amputated limb, which initiates impulse in nerve fibers which previously came from sense organs in the amputated limb, and the sensations evoked are projected to where the receptors used to be.
What are repetitive sensations?: 1. It is when DCMLS can follow repetitive stimuli up to 400Hz

2. Vibrations up to 700Hz are detected
What is: 1. Homoculus 2. PET 3. MRI 4. SSI 5. SSII: 1. Homonculus = Mapping less than or equal to fine electrodes

2. PET = Position Emission Tomography

3. MRI = Magnetic Resonance Imaging

4. SSI = in the thalamus, it is postcentral gyrus, brodeman 1,2,3

5. SSII = Wall of Sylvian Fissure

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