Spinal Cord and PNS Flashcards
Spinal Cord Functions
Convey sensory information from periphery to brain
Convey motor information from brain to periphery
Reflexes
Modify ascending and descending information
Where does the spinal cord end?
At L1-L2 intervertebral space
Filum Terminale
Connective tissue that connects end of cord to coccyx
Cauda Equina
L2-S5 nerve roots
Why are there cervical and lumbar enlargements?
Because of plexuses - lots of alpha-motor neurons so the area swells up
Where are cell bodies of sensory neurons located?
Dorsal root ganglion
What leaves the ventral horn?
Motor neurons
What leaves the dorsal horn?
Sensory neurons
Dorsal Horn (Sensory)
Contains endings of sensory neurons, interneurons and cell bodies of tract cells
Lateral Horn
ONLY AT T1-L2 SPINAL SEGMENTS
Contains cell bodies of preganglionic sympathetic neurons
Ventral Horn (Motor)
Contains cell bodies of lower motor neurons, alpha-motor and gamma-motor neurons
Alpha-motor Neurons
Primary
Travel to muscles
Gamma-motor Neurons
Secondary
Travel to spindle fibers (protect quick stretch of muscles and maintain appropriate length)
Dorsal Column
Contains sensory tracts and medial lemniscus pathway
Lateral Column
Contains sensory and motor tracts
Anterior Column
Contains motor tracts
Involved with muscle regulation
Dorsal Column
Divided in fasciculus gracilis and cuneatus
Fasciculus Gracilis
Receives information from LE
Fasciculus Cuneatus
Receives information from UE
How to tell if you are looking at a cervical cross-section?
Indentation between cuneatus and gracilis
Posterior Intermediate Sulcus
Separates different sections of dorsal column
Anterior White Commissure
Connecting left and right spinal cord
Muscle fibers are characterized into what group?
Medial
Pain and temperature fibers are characterized into what group?
Lateral, in dorsal horn
Large Myelinated Axon Classification
Efferent - A-alpha
Afferent - Ia, Ib, II
Medium Myelinated Axon Classification
Efferent - A-gamma
Small Myelinated Axon Classification
Efferent - B (smaller diameter)
Afferent - A-beta (larger diameter)
Unmyelinated Axon Classification
Efferent - C
Afferent - C (pain, temperature, visceral receptors)
Lesion in Spinal Region
Results in myotomal and/or dermatomal distribution
Lesion in Periphery
Results in peripheral nerve distribution
Periphery Lesion Symptoms
Paresis/paralysis Sensory loss Abnormal sensations Muscle atrophy Reduced/absent DTR
Upper Motor Neuron
Neurons with axons that descend from cerebral cortex or brain stem and end on LMN
Neurons within CNS
UMN Example - Corticospinal Pathway
Starts in motor cortex, crosses in medulla and innervates LMN at respective spinal level
Lower Motor Neuron
Cell body in brain stem or ventral horn of spinal cord
Axone leaves CNS and synapses in periphery on muscle
Starts in CNS but ends in PNS
UMN Clinical Signs
Paresis
Spasticity
Hypertonia
Hyperreflexia
UMN Diseases
Stroke SCI Parkinson's TBI MS
LMN Clinical Signs
Loss of reflexes
Atrophy
Flaccid paralysis
Fibrillation/fasciculations
LMN Diseases
Polio
Peripheral Nerve Injury
Guillan Barre
Rexed’s Laminae
10 regions of spinal gray matter
Reflex
Involuntary, stereotyped response to sensory input
Involves sensory input and motor output
Reflex Examples
Stretch reflex via spindle
Autogenic inhibition via GTO
Reflex Arc
Quick stretch stimulates Ia afferent in spindle
Ia afferent synapses in spinal cord with alpha-motor neurons
No interneuron involvement
Reflex Arc Modulation
Afferent input synapses with interneuron
Also under influence of UMN
Lose descending control (leads to hyperreflexia)
Dorsal Column Function
Conscious touch
Proprioception
Spinothalamic Function
Conscious pain
Temperature
Spinoreticular Function
Alerting
Arousal
Spinocerebellar Function
Unconscious proprioception
Dorsal Column Neuron Orders from Body
1st: DRG
2nd: Nucleus cuneatus/gracilis
3rd: VPL nucleus of thalamus
Dorsal Column Neuron Orders from Face
1st: Trigeminal ganglion
2nd: Main sensory nucleus of trigeminal nerve
3rd: VPM nucleus of thalamus
Dorsal Column Pathway
Enters spinal cord Ascends dorsal column Synapses in medulla Crosses over and ascends in medial lemniscus to contralateral thalamus Synapses in thalamus Ascend to cortex
Spinothalamic Column Neuron Orders from Body
1st: DRG
2nd: Dorsal horn of spinal cord
3rd: VPL nucleus of thalamus
Spinothalamic Column Neuron orders from Face
1st: Trigeminal ganglion
2nd: Spinal nucleus of trigeminal nerve
3rd: VPM nucleus of thalamus
Spinothalamic Pathway
Enters spinal cord Synapses in dorsal horn Crosses to contralateral spinal cord Ascends in spinothalamic tract Synapses in thalamus Ascends to cortex
Corticospinal Function
Voluntary movement
Fine motor control
Rubrospinal Function
Gross motor movements
Reticulospinal and Vestibulospinal Function
Trunk movements
Postural control
Tectospinal Function
Reflexive movement of head
Corticospinal Tract Pathway
Cell body in motor cortex
Crosses in medullary pyramid
Descends in lateral column
Synapses with alpha-motor neuron
Rubrospinal Tract
Cell body in red nucleus
Crosses immediately
Synapses with alpha-motor neuron
