Spinal Cord + Tracts

• Sensory = Ascending (SC to brain)

  • Spinothalamic
  • DCML
  • 3 neuron pathway: sensory afferent, SC tract, thalamus to cortex
• Motor = Descending (brain to SC)

  • Pyramidal (corticospinal + corticobulbar)
  • Extrapyramidal (involuntary control)
  • 2 neuron pathway: UMN to LMN
• 3 Neuron Sensory System

  1. Sensory afferent from dorsal root ganglion
  2. Decussates, synapses in thalamus
  3. Ends in somatosensory cortex
• 2 Sensory Pathways:

  1. DCML = discriminatory touch + pressure + proprioception
  2. Spinothalamic = pain + temperature
• Sensory pathways ascend from body to brain
• Spinothalamic Tracts

  • Pain and temperature
  • From free nerve endings in skin and muscles 
  • Comes in through the back of the spinal cord and synapses immediately
  • Synapse 1: Spinal Cord
  • Fibers cross @midline and ascend contralaterally to stimulus
  • Synapse 2: Thalamus
• DCML – Spinocerebellar (dorsal)

  • Proprioception
  • Info from spindles and tendon organs goes to cerebellum
  • Spinocerebellar pathway branches from here
  • Information on position of axial skeleton 
  • To thalamus, then cortex
  • Ascent is ipsilateral, the decussates at the medulla into the thalamus
• DCML

  • Touch and pressure
  • Fibers ascend ipsilaterally to stimulus in dorsal column
  • Synapse 1: Medulla
  • Nucleus Gracilis: (legs, below T6)
  • Nucleus Cuneatus (arms, above T6)
  • Synapse in the medulla with the 2nd order neuron, that's when it decussates and become medial lemniscus and then goes up to thalamus, then synapses from a 3rd neuron to go out to the somatosensory cortex
  • Fibers become “medial lemniscus” on their way to thalamus and decussate
• Thalamus to somatosensory cortex
• Thalamus: sensory integration – relay nuclei

  • Post-central gyrus
  • Motor: balance basal ganglia + cerebellum
  • Sensations: 
  • vision/hearing
  • Touch, pressure, proprioception
  • Temperature and pain
  • Cortical Input: determine which info is sent to cortex
• The DCML is in the posterior column of the spinal cord, where the gracile fasciculus and cuneate fasciculus is
• 1st Order Sensory Afferents/Nerves

  1. Joints
  2. Muscles
  3. Skin
• 1st Order Sensory Afferents/Nerves

  1. Joints
  2. Muscles
  3. Skin
• Qualitative Sensations: temperature and nociception
• Quantitative Sensations: touch and pressure and proprioception
• 5 Sensory Modalities

  1. Touch 
  2. Pressure
  3. Proprioception: where your body is in space
  4. Temperature
  5. Nociception/Pain
• SENSORY PATHWAYS

  1. Effector Organ
  2. 1st order: neuron Sensory Afferent Neuron
  3. Spinal Cord
  4. 2nd order neuron: Ascending Tracts
  5. Brainstem
  6. Brain
  7. 3rd order neuron: to somatosensory cortex
• 2 neuron system:

  1. UMN
  2. LMN (spinal/cranial nerve)
• Corticobulbar = head and neck
• Corticospinal Tract = body
• Pyramidal = voluntary control

  • Corticospinal & Corticobulbar
• Motor pathways descend from brain to body after receiving input from the basal ganglia + cerebellum
• Motor pathways descend from brain to body after receiving input from the basal ganglia + cerebellum
• Facial Nerve - CN VII

  • If we took out the facial nerve, everything would be knocked out
  • UMN impaired = stroke
  • LMN impaired = Bell’s Palsy
  • Nerve that heads to the forehead has bilateral innervation
  • Contralateral innervation to cheeks: so that means if we were to knock out the left side of the cortex, the cheeks would only be impaired while the forehead is spared because it has bilateral innervation
• Implication of Pyramidal Tract Lesions

  • Stroke
  • Left-sided muscle weakness
  • Trouble lifting left arm → LATERAL CORTICOSPINAL TRACT
  • If there is an impairment on the left side of the body, the tract has to start on the right side of the brain
  • Facial muscle drooping but could move left eyebrow
  • CN VII is an exception (facial nerve)
  • If we take out the bilateral piece then we have only contralateral innervation and in this case it will cause a stroke
• Lower Motor Neurons = Spinal/Cranial Nerves

  • Motor Information: SC to Muscles
• Corticobulbar Tracts

  • Approximately 15%
  • UMN
  • Bilateral innervation to head/neck (innervates both left and right side)
  • Exceptions: CN VII (facial) and CN XII (hypoglossal)
  • Only contralateral innervation
  • Synapse Location: motor nuclei of cranial nerves (nuclei have 2 sources of information)
  • III, IV, V, VI, VII, IX, X, XI, XII
• Internal Capsule: white matter tract that exists between the thalamus and the lentiform nucleus
• Corticospinal Tracts 

  • Approximately 85%
  • UMN
  • Send out info via a LMN
  • Divisions: 
  • Lateral (most of fibres)
  • Decussates over the midline: fibers decussate @medulla
  • Limb and trunk muscles 
  • Anterior/Ventral (only in thoracic)
  • Ipsilateral so it does not decussate: fibres decussate @spinal cord
  • Trunk muscles
  • Synapse Location: ventral/anterior horn of SC

  Contralateral innervation to body
• Pyramidal Tracts (UMN)

  • Origin: pre-central gyrus/primary motor cortex
  • Somatotopic organization
• Descending Pathways

  • Motor Information
  • Brain to body/spinal cord
  • 2 neuron system: UMN to LMN
  • Pyramidal System: initiate voluntary movement
  • Corticospinal: Body
  • Corticobulbar: Head and Neck
• Corticospinal Tract

  • Sends info from brain to body
• Cerebellar Peduncles (input/output)

  • Sits at the level of the pons (brainstem) and is connected via 3 peduncles
  • Peduncles are highways
  • Superior peduncle = output
  • Middle and Inferior peduncle = input (vision, vestibular, proprioception
• Cerebellum

  • Modulates motor plan based on sensory (vestibular, visual and proprioceptive) inputs
  • Tells you where your body is in space and takes in your surroundings
• Basal Ganglia consists of striatum: thalamus, caudate, putamen, globus pallidus

  • The putamen and globus pallidus from the lentiform nucleus
• Basal Ganglia consists of striatum: thalamus, caudate, putamen, globus pallidus

  • The putamen and globus pallidus from the lentiform nucleus
• Motor System

  • Basal Ganglia
  • Cerebellum
  • Corticospinal Tract
• MOTOR PATHWAYS

  1. Brain
  2. Brainstem
  3. UMN
  4. Spinal Cord
  5. LMN
  6. Muscle
• Parts of the Motor descending tracts

  • Lateral corticospinal tract
  • Anterior corticospinal tract
• Parts of the Sensory ascending tracts

  • Posterior column: gracile fasciculus and cuneate fasciculus
  • Lateral spinothalamic tract
  • Anterior spinothalamic tract