NERVOUS SYSTEM LECTURE 3: Sensory Systems of the Brain

Funiculus

Big bundle of white matter

Dorsal Funicili

Important for discriminative sensation. 

Info from periphery up spinal cord to brain

Gracile Fasciculus + Cuneate Fasciculus.

Gracile Fasciculus (Dorsal Funicili)

Info related to lower limbs

Info from toe is closest to midline, higher up is further away from midline

Cuneate Fasciculus (Dorsal Funicili)

Info related to torso & upper limbs.

Info from fingers is closer to the midline than shoulders

Lateral Funiculus/Motor Column

Info from brain down spinal cord to activate muscle

Ventral Funiculus

Pain & temperature info from the periphery up the spinal cord to brain

Spinal Cord Grey Matter Principle

Front related to motor type info

Back related to sensory info

Substantia Gelatinosa

Unmyleinated & transparent

Lots of opoid receptors

Proprioception (discriminative sensation)

Where is the body in space physically & what can be felt on the periphery of the body.

Nucleus Proprius

Responsible for proprioception. 

Can integrated info from thousands of neurons into one axon to the brain due to being the same info type.

Allows spinal cord to be smaller

Worse for more precise/fine movements

Intermediate Horn

Autonomic functions, visceral functions (gut movements) & related to posture

Lower Motor Neuron Pool

Where motor neurones that will drive motor activity are localised

Myotatic/Monosynaptic Reflex:

Neurone → dorsal root ganglia → nucleus proprius → lower motor neuron pool and with a single synapse → muscle
Required for quick reflexes & automatic, quick movements like running (rapid flexion & extension)

Reflex

Something happens in the spinal cord & the brain isn’t working on

Thalamus

Constantly receives info from the periphery & decides what is prioritised based on experience. (except olfactory system)

Sends info received  from medial lemniscus → internal capsule → 1° sensory cortex.

Pain > discriminative sensation.

Internal Capsule

White matter

Commisure

Left to right white matter

Spinothalamic Tract (Pain & Temperature Pathway)

Sends pain & temp info from fibres into dorsal root ganglia → SG (synapse) → cross over immediately at the spinal segmental level at ventral anterior white commissure → ventral funiculus → thalamus → representative homcunculus in sensory cortex.

Medial Lemniscal System (Pathway of Discriminative Sensation) [LEG]

Sends discriminative sensation info from fibres into dorsal root ganglia → Cuneate fasciculus→ decussation at internal arcuate fibres → medial lemniscus → pons → midbrain → internal capsule → homcunculus representation in sensory cortex.

Medial Lemniscal System (Pathway of Discriminative Sensation) [ARM]

Same as LEG version but Gracile fasciculus

Medial Lemniscal System (Pathway of Discriminative Sensation) [Nucleus Proprius]

Dorsal root ganglia → nucleus proprius → Gracile/Cuneate Fasciculus

Polysynaptic/Withdrawal Reflex Pathway

Pain & temp info from fibres into dorsal ganglia → SG → lower motor neuron pool → muscle

Polysynaptic/Withdrawal Reflex:

Pulling hand quickly away from hot temp/pain.

Slower due being used less often.

Which Reflex is faster (Monosynaptic vs Polysynaptic Reflex)

Monosynaptic reflex is faster due to a single synapse & heavy myelination compared to polysynaptic reflex

Associative Sensory Loss

Lesion on the left side of the brain/brain stem of the pain & temperature/discriminative sensation pathway would result in right side loss of touch & pressure & pain & temperature.

Dissociative Sensory Loss

Lesion on the left side of the brain/brain stem of the pain & temperature/discriminative sensation pathway would result in left side loss of touch & pressure & right side loss of pain & temperature.

E.g brown-squad syndrome.

Discriminative Pathway (Touch & Pressure)

Myelination: Heavily

Conduction Speed: 50m/s

Function: Discriminative

1st Neuron Terminates at: Cuneate fasciculus, gracile fasciculus, nucleus proprius

Deccusates at: Internal Arcuate Fibres

Non-discriminative Pathway (Pain & Temperature)

Myelination: No

Conduction Speed: 1m/s

Function: Pain & Temperature

1st Neuron Terminates at: SG

Deccusates at: Ventral Anterior White Commisure