Clinical Anatomy of Sensory Systems Flashcards by Aoife Aoibhinn O Connor

What is the Spinal Cord

Part of the central nervous system

Consists of Tightly packed nerves extending from the brainstem of the brain

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Function of the Spinal Cord

Relays motor and sensory info from brain to periphery

Provides seperate neuronal circuits for reflexes

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Name two enlargements/ swellings on spinal cord

Cervical
Lumbrosacral

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Cervical Enlargement

Located between spinal nerves c5-t1

Innervates the upper limbs

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Lumbrosacral Enlargement

Located between L1 to S3

Innervates the lower limbs

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External Structure of Spinal Cord

33 Vertebrae
Arranged in 5 regions
- Cervical
- Thoracic
-Lumbar
- Sacral
- Coccygeal

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Internal Structure of Spinal Cord

grey matter and white matter

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Grey Matter

Rich in cell bodies
Shape of butterfly with 4 wings (HORNS)

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White Matter

Column surrounding grey matter
Contains axons

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Fissures/ Sulci on Spinal Cord

Anterior Median Fissure
Posterior Median Sulcus
Posterolateral Sulcus

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Spinal Cord Entry

Sensory nerve fibres enter the spinal cord via the Posterior (Dorsal) Root

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Spinal Cord Exit

Motor and Preganglionic autonomic fibres exit via anterior (ventral) root

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Anterior/ Ventral Ramus

innervates most of the skeletal muscles

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Posterior/ Dorsal Ramus

Innervate intrinsic back muscles

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Somatosensory System

network of neural structures in brain and body that produce perception of
- touch
-temp
-body position
-pain

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Sensory Receptors in Skin

Thermoreceptor- temp
Mechanoreceptors- pressure and surface texture
Nociceptors- pain

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Sensory Receptors in Muscle and Joints

provide info about muscle length and tension, joint angles

Nociceptors

activated by noxious stimuli
-thermal
-mechanical
-chemical

Difference in Speed in nerve cell conduction

A delta fiber- big diameter and thick myelin sheath

C-fiber- small diameter and thin myelin sheath

What is a two- point discrimination scale

measures the minimal interstimulus distance required to perceive two simultaneously applied stimuli as distinct

Describe how the two-point discrimination test is completed

stimulus to the fingertips can be persceived at 2mm

Stimulus on the forearm might not be perceived until 40mm

> > mechanoreceptors of the fingtertips are more numerous than the hand

What are the two main somatosensory pathways of the Central Nervous System

1) Posterior/ Dorsal Medial Leminiscus (fine touch, vibration, prooprioception)

2) Spinothalamic Pathway (pain and temp)

General Third Order Neuron Pathway

1st Order- sensory neurons from the peripheries deliver info to SC, neuronal cell body in DRG

2nd Order- cell body in SC or Brainstem, send impulses to the thalamus, these axons decussate at midline

3rd Order- located in thalamus, send impulses to somatosensory cortex

Function of Posterior Column-Medial Lemniscus Pathway

convey sensory info
- fine touch
-vibration
pressure
two point discrimination
proprioception from skin and joints

Discuss the Posterior Column-Medial Lemniscus Pathway

1st Order)- sensory neurons from the peripheries to medulla oblongata (brain stem) Two possible paths - Cuneate or Gracile Cuneate Tract: signals from upper limb travel to the facilicus cuneatus and synapse with the cuneate nucleus in the medulla oblongata Gracle Tract: signals from lower lim travel in the facilicus gracilis and synapse with the gracile nucleus in the Medulla Oblongata 2nd Order) begins in the cuneate or gracile nucleus in M.O, within M.O fibres decussate and travel to the thalamus in the contralateral medial leminiscus 3rd Order) transmit sensory signals from the vetroposterior nucleus of the thalamus to the primary sensory cortex

Clinical Relevance of the Posterior Column-Medial Leminiscus Pathway

Damage at the level below the crossing results in a loss of vibration and joint sense on the same side of the body as the lesion Damage above crossing point results in damage on the opposite side of the body to the lesion

What is the function of the Spinothalamic Tract

Convey sensory info regarding - crude touch -pain -temperature

Name the two adjacent pathways of the Spinothalamic Tract

Anterior Spinothalamic Tract (crude touch and pressure) Lateral Spinothalamic Tract (pain and temperature)

Discuss the Spinothalamic Pathway

1st Order) arise from sensory receptors in periphery, enter the SC and synapse at the tip of the dorsal horn (Substantia Gelatinosa) 2nd Order) carry info from Substansia Gelanintosa to the thalamus after synapsing with 1st order these fibres decussate WITHIN SC and then form two distinct tracts - anterior and lateral 3rd Order) carry sensory info from thalamus to the primary sensory cortex

Clinical Relevance of the Spinothalamic Tract

Lesions here will result in loss of pain, temp, crude touch and temperature sensation

Difference between the spinothalamic and dorsal column medial leminiscus pathway

Spinothalamic decussates within SC, medial.... decussates at the level of the medulla oblongata

What is Brown Sequard Syndrom

Hemisection-damage to one half of the brain

What are the causes of Brown Sequard Syndrome

Trauma Spinal Cord Tumor Obstruction of a blood vessel MS

What tracts does Hemisection impact

corticospinal (motor) Spinothalamic (sensory) Medial Column Dorsal Leminiscus (sensory)

What are the symptoms of Brown Sequard Syndrome

loss of different factors at each level of the pathways - corticospinal (spastic paralysis) - spinothalamic (vibration, fine touch, proprioception) - medial dorsal ( crude touch, temp and pain sensation)

Where is the primary Somatosensory Cortex located

ridge of cortex called the postcentral gyrus, found in the parietal lobe, posterior to the central sulcus

What brodmanns areas does the primary somatosensory cortex consist of

Brodmanns areas 3a, 3b, 1 and 2

What is the function of the Primary Somatosensory Cortex

responsible for processing sensations from the body, final destination of the sensory pathways

Function of Brodmann areas

3a- responds to infr from proprioceptors 3b- processing touch 1- sensing texture of objects 2- perceiving size and shape

What does Homonculus mean

regions with high receptor density are depicted to have more cortical space

What does dermatome mean

area of skin supplied by sensory neurons that arise from spinal nerve ganglion