Ascending Neural pathways Flashcards by Kambi Ben-Ejeteh

How are senses split?

Senses are split into conscious and unconscious snesations
Conscious sensations are found in the somatic area
Unconscious is split into proprioception and visceral

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Explain why some areas of the body have a disproportionately large area of representation on the somatic sensory cortex

A Large area of cortex= Areas of higher discrimination = Higher number of discriminatory neurons

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What is the dorsal column-medial lemniscal pathway?

Carries fine touch, vibration, proprioception
Decussates (crosses over) at the medulla
Travels via the medial lemniscus to the thalamus → somatosensory cortex

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Describe the first order neurons in the DCML pathways

enter the dorsal column
ascend to medulla (brainstem) as fasciculus gracilis or cuneatus
synapse with 2nd order neurons in the ipsilateral gracile and cuneate nuclei in the Medulla

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Describe second order neurons in the DCML pathway

Axons form Medial lemniscus
Cross the midline (sensory decussation)
Synapse with 3rd order neurons in the ventral posterolateral (VPL) nucleus of thalamus

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Describe third order neurons in the DCML pathway

travel in internal capsule and project to somatosensory area/cortex (in the post-central gyrus)

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What structures are involved in the relay of sensations from the periphery to the CNS?

Receptors: Meissner and Pacini corpuscles, Ruffini endings and Merkel cell-neurite complexes, neuromuscular spindles, and Golgi tendon organs

Conscious proprioceptive sensation, vibration, discriminative touch, 2-point discrimination

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List the type of information dorsal column medial lemniscus carries?

*Conscious proprioception
*Vibration
*2-point discrimination
*Fine touch (discriminative touch)
*Fine pressure
*Stretch

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List the type of information carried in Anterolateral (spinothalamic) system

*Pain
*Temperature
*Crude touch

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Describe the types of nerve fibres are involved in the dorsal column medial lemniscus

*Large, myelinated fibres
*30-110m/s
*Discriminative mechanoreceptive sensation
*High degree of spatial orientation

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Describe the types of fibres in Anterolateral (spinothalamic) system

*Smaller fibres
*Up to 40m/s
*Broad spectrum of sensory modalities
*Less spatial orientation

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What is nociception?

Nociception is detection of stimuli that can cause tissue injury. Which can lead to pain

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What is Pain associated with nociception is transmitted by?

Unmyelinated type C axons
Finely myelinated Aδ axons

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Describe Unmyelinated type C axons in nociception

Respond to intense heat/cold, mechanical deformation or irritant chemicals
Slow pain
Terminate in reticular formation (spinoreticular tract)
Dull, poorly localized

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Describe Finely myelinated Aδ axons in nociception

Sharp, fast pain
Terminate in NVPL (spinothalamic tract/anterolateral tract) à cortex
Well-localized

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What is pain?

An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage

When is fast (sharp) pain felt?

0.1s after a painful stimulus

What is fast (sharp) pain carried by?

Carried by thinly myelinated A-delta (Aδ) type axons

What are the types of fast pain?

Sharp pain
Stabbing pain
Pricking pain
Acute pain
Electric pain

Where is fast pain felt?

Not felt in most of the deep tissues

Where is slow pain felt?

Begins ~ 1s or more after painful stimulus, increases slowly

What carries slow pain?

Carried by unmyelinated type-C axons

What are the types of slow pain?

Slow burning pain
Aching pain
Throbbing pain
Nauseous pain
Chronic pain

Where is slow pain felt?

Felt both in the skin and deeper tissues, spreads out

What is slow pain associated with?

Usually associated with tissue destruction

What receptors are involved in the anterolateral (spinothalamic) tract?

Nerve endings

What is the mechanism by which pain, temperature and crude touch are detected

Anterolateral (spinothalamic) tract

Describe first order neurons in the anterolateral tract

- enter the spinal cord - ascend or descend 1-2 spinal cord levels and - synapse with 2nd order neurons in the dorsal horn

Describe second order neurons in anterolateral tract

- cross the midline in the anterior white commissure - ascend in the anterior (crude touch) and lateral (pain-temperature) columns, forming a somatotopic organisation - synapse with 3rd order neurons in the ventral posterolateral (VPL) nucleus of thalamus

Describe third order neurons in the anterolateral tract

travel in internal capsule and project to somatosensory area/cortex (in the post-central gyrus)

Where is pain usually referred?

to areas supplied by somatic sensory nerves which enter the same spinal cord segment(s) as the visceral afferents

What is referred pain?

- Noxious stimuli originating in an organ are perceived as pain arising from a superficial part of the body (e.g. skin) - Transmitted by visceral afferent fibers accompanying sympathetic (usually) fibers

What are the probable mechanisms of referred pain?

- Branches of visceral pain fibres synapse with the same 2nd order neurons in spinal cord that receive signals from skin. - When visceral pain receptors are stimulated, pain signals from viscera are conducted through some of the neurons conducting pain signals from skin, so person feels sensations originate in skin

Describe how unconscious proprioceptive senses are carried to the higher centres

spinocerebellar tract: - Essential for smooth, coordinated movements and posture - Very fast conduction is required, therefore largest tract in CNS - Afferent information from muscle Spindles (muscle tension) and Golgi tendon organs (proprioception) terminate in cerebellum, rather than cerebral cortex, hence unconscious ipsilateral - All unconscious propioception detected from one side will be sent to the same side of the brain - Carried by the posterior and anterior spinocerebellar tracts

What are the altered senses of touch

Anesthesia* - Loss of touch sensation Hypoesthesia - reduced sense of touch Hyperesthesia - increased sense of touch Topagnosia - inability to localize touch on the body

What are the altered senses of temperature?

Thermanalgesia- inability to feel painful temperature stimul Thermhypoesthesia- Reduced sensitivity to temperature changes. Thermhyperesthesia- Increased sensitivity to temperature stimuli

What are the altered senses of pain (algesia)?

Analgesia - complete loss of pain sensation Hypoalgesia - reduced pain sensitivity Hyperalgesia - increased pain sensitivity

What is ataxia?

Sensory ataxia is a gait disorder resulting from transmission of from the receptor to the cortex as opposed to a problem in the motor system, usually in the cerebellum (cerebellar ataxia)

Describe what happens in ataxia

- Feet well apart and gaze directed downwards to include the feet when standing unsupported - Severe swaying with the feet together and the eyes closed (the Romberg sign). - Broad based gait, with a stomping action - Loss of kinaesthetic sense (evidenced by finger-to-nose and/or heel-to-knee test) - Impaired vibration and touch - Preserved touch, pain and temperature sensations