The somatosensory homunculus proportions reflect what?
the number of specialized sensory receptors within that part of the body
The somatosensory homunculus proportions constant?
No. Can be modified with learning, for example learn to read Braille & will have larger area representing fingertips
The motor homunculus proportions reflect what?
the number of motor units within that part of the body
Where do Somatic sensory pathways relay information?
from somatic sensory receptors to: Primary somatosensory area (cerebral cortex) Cerebellum
What is the Neuronal order ?
Pathways to the cerebral cortex: First-order neurons Second-order neurons Third-order neurons
First-order neurons conduct impulses _________.
from somatic receptors to the CNS
Characteristics fo second-order neurons
impulses from the brain stem and spinal cord to the thalamus decussate in either the brain stem or the spinal cord.
Characteristics of Third-order neurons
from the thalamus to the primary somatosensory area of the cortex
Somatic sensory pathway - conscious
Posterior column-medial lemniscus pathway or Anterolateral (spinothalamic) pathways Decussate first, second, and third order neurons to the cerebral cortex
Somatic sensory pathway - non-conscious proprioception
Posterior spinocerebellar tract Anterior spinocerebellar tract NO decussation only first and second order Neurons to the Cerebellum
Somatic sensory impulses from the trunk and lower limbs
follow first order neurons located where?",Fasciculus gracilis
Somatic sensory impulses from the neck
upper limbs, and upper chest follow first order neurons located where?",Fasciculus cuneatus
First-order neurons in the Posterior column-medial lemniscus pathway terminate where?
correspondingly-named nucleus in the medulla: Gracile nucleus Cuneate nucleus
Somatic sensory impulses from the trunk and lower limbs
follow what Path?","First order neuron through Fasciculus gracilis to Gracile Nucleus Second order neuron Decussate then Through Medial Lemniscus to V.P. nucleus in Thalamus third-order neuron To Primary Somatosensory Area of Cerebral Cortex
Somatic sensory impulses from the neck
upper limbs, and upper chest follow what Path?","First order neuron through Fasciculus cuneatus to Cuneate Nucleus Second order neuron Decussate then Through Medial Lemniscus to V.P. nucleus in Thalamus third-order neuron To Primary Somatosensory Area of
Which Sensations follow the posterior column-medial lemniscus pathway
Fine touch Stereognosis Graphesthesia Proprioception Vibratory
Spinothalamic (anterolateral) pathway Carries nerve impulses for
Pain, thermal, tickle, and itch sensations Some impulses for crude, poorly localized touch and pressure Vibration
carries sensory impulses for pain and temperature Follow what pathway?
The lateral spinothalamic tract
The lateral spinothalamic tract (Pathway)
First-Order neuron to posterior grey horn Second-Order neuron Decussate then through Laterial Spinothalamic Tract to V.P. nuceous of thalamus third-order neuron To Primary Somatosensory Area of Cerebral Cortex
carries sensory impulses for tickle
itch, crude touch, pressure, and vibration Follow what pathway?",The anterior spinothalamic tract (Pathway)
The anterior spinothalamic tract (Pathway)
First-Order neuron to posterior grey horn Second-Order neuron Decussate then through Anterior Spinothalamic Tract to V.P. nuceous of thalamus third-order neuron To Primary Somatosensory Area of Cerebral Cortex
Trigeminothalamic pathway
First-order neuron to Pons or madulla Second-order neurons decussate then to VPN of thalamus Third-order to Primary Somatosensory Area of Cerebral Cortex
Summary of Principles for Dorsal column-medial lemniscus
Encapsulated receptors (Pacinian/Meissner corpuscles) Touch and position (proprioception) All axons myelinated
Summary of Principles Anterolateral (Spinothalamic)
Free nerve endings Temperature and pain Many axons unmyelinated
Summary of Principles Trigeminothalamic
Encapsulated receptors and free nerve endings Virtually all sensations for face
What are the proprioceptive tracts to the cerebellum
Anterior spinocerebellar tract Posterior spinocerebellar tract
The anterior spinocerebellar tract is mostly concerned with what information?
proprioceptive information from the lower limbs and with the control of posture
The posterior spinocerebellar tract is mostly concerned with what information?
Impulses from the upper part of the body
Characteristics of First order neurons in cerebellar pathways
(sensory neurons) cell bodies in the posterior root ganglia Synapse w/ second-order neurons in the posterior gray horn
Characteristics of Second-order neurons in cerebellar pathways
(association neurons) cell bodies in the posterior gray horns of the spinal cord Terminate in the cerebellum
Cerebellar vs Cerebral problems
Cerebellar problems = ipsilateral Cerebral problems = contralateral
Syphilis
STD leads to tabes dorsalis a late sign of the neurological damage from syphilis bacterium
tabes dorsalis
damage caused by the syphilis bacterium demyelination and deterioration of the posterior portions of the spinal cord inc. gracilis and cuneatus and posterior roots Leads to poor muscle coordination and unstable gait Bacterial invasion of the sensory (dor
2 divisions of Somatic motor pathways
Pyramidal tracts Everything else
Upper vs. lower motor neurons
Upper: originate in the brain Lower: output from the CNS to skeletal muscle fibers
What are the Pyramidal tracts?
The lateral and anterior corticospinal tracts (left & right) major motor pathways concerned with voluntary movement, especially precise or skilled movements
Flaccid Paralysis
Neuron: Lower motor Ipsolateral Both voluntary&reflex absent little/no tone
Spastic Paralysis
Upper motor Contralateral increased Muscle tone is exaggerated Reflexes
Direct motor pathways
AKA pyramidal pathways vs. Indirect motor pathways, AKA multineuronal pathways","to lower motor neurons via axons that extend directly from the cerebral cortex to lower motor neurons from motor centers in the brain stem
Three tracts contain axons of upper motor neurons
Lateral corticospinal tracts Anterior corticospinal tracts Corticobulbar tracts
Lateral corticospinal tract
Neuron origin: primary motor area of the cerebral cortex Decussation: medulla Motor neurons innervate: muscles in distal parts of the limbs responsible for precise, skilled movements
Anterior corticospinal tract
Neurons origin: primary motor area of the cerebral cortex Decussation: spinal cord Motor neurons innervate: muscles of neck trunk and proximal parts of the limbs
Corticobulbar tract
Neurons origin: in the primary motor area of the cerebral cortex May or may not decussate Axons terminate in motor nuclei of nine pairs of cranial nerves (all except I, II, and VIII) Lower motor neurons of the cranial nerves control: precise, voluntary m
what are the 5 Indirect motor pathways?
Rubrospinal Tectospinal Vestibulospinal Lateral reticulospinal Medial reticulospinal