majory relay station
the spinal cord extends from...
formen magnum to second lumbar vertebra
regions of spinal cord
cervical, thoracic, lumbar, sacral, coccygeal
How many spinal nerves does the spinal cord give rise to/
31 mixed nerves
supplies upper limbs
supplies lower limbs
what runs thru the vertebral canal?
connective tissue membranes of the spinal cord are...
dura mater, arachnoid mater, pia mater
outermost layer, continuous with epineurium of spinal nerves
thin and wispy
- bound tightly to surface
- -forms filum terminale (anchors spinal cord to coccyx)
- -forms denticulate ligaments that attach the spinal cord to dura
what are the spaces in the spinal cord?
epidural space, subdural space, subarachnoid space
- external to dura
- -anesthestics injected here
- between pia and arachnoid
- -filled with CSF
neuron cell bodies, dendrites, axons,... divided into horns
- myelinated axons
- -divided into 3 columns and into sensory or motor tracts
somatic sensory (SS)
axons of somatic sensory neurons
visceral sensory VS
neurons of nisceral sensory neur.
Visceral motor VM
cell bodies of visceral motor neurons
Somatic motor SM
cell bodies of somatic motor neurons
white matter in spinal cord is divided into 3 columns/funiculi and have 3 differ types of fibers
- funiculi: posterior, lateral, anterior
- -fibers: ascending, descending, trans.
fiibers of the white matter runs in 3 directions
- ascending fibers - compose of sensory tracts
- descneding fibers - compose motor tracts
- commissural (transverse) fibrs: connect opposite sides of cord
generalizations about white matter fiber tract
- pathways decussate
- -consist of chain of 2 or 3 neurons
- exhibit somatotopy (precise spatial relationships)
- pathways all paired (one on ea. side of spinal cord)
descending pathways divides into two groups
- -pyramidal (corticospinal) tract
- -indirect pathways, essentially all others
motor pathwyas involve two neurons
UMN & LMN (anterior horn motor neuron/final common pathway)
pyramidal tracts originate
precentral gyrus of brain
pyramidal neuron is what kind of neuron?
upper motor neuron
UMG synapses where?
- in anterior horn with LMN
- -some decussate in pyramids - lateral corticospinal tracts
- -others at other levels of sc - anterior corticospinal tracts
- (anterior horn motor neurons)
- -exits spinal cord via anterior root
- -activates skeletal muscles
Pyramidal tracts regualtes ...
fast and fine (skilled) movements
corticospinal tracts... pathways...
- location of UMN cell body in cerebral cortex
- -decussate of UMN axon in pyramids or at level of exit of LMN
- -synapse of UMN and LMN occurs in anterior horn of sc
- -LMN axon exits via anterior root
extrapyramidal motor tracts includes
all motor pathways not part of pyramidal system
extrapyramidal motor tracts; UMN originates
- in nuclei deep in cerebrum (not in cerebral cortex)
- -doesnt pass thru pyramids
LMN in extrapyramidal motor tracts...
is an anterior hor motor neuron
extrapyramidal motor tracts, this system includes..
rubrospinal, vestibulospinal, reticulospinal, tectospinal tracts
extrapyramidal motor tracts regulates...
- axial muscles that maintain balance and posture
- -muscles controling coarse movements of proximal portions of limbs
- -head, neck, and eye movement
pathway of extrapyramidal tract
- -UMN cell body location
- -UMN axon decussates in pons
- -synapse between UMN and LMN occurs in anterior horn of sc
- -LMN exits via ventral root
- -LMN axon stimulates skeletal muscle
reticulospinal tracts originates at...
reticular formation of brain; maintain balance
rubrospinal tracts originates
in 'red nucleus' or midbrain; control flexor muscles
tectospinal tracts originate
in superior colliculi and mediate head and eye movements towards visual targets (flashlight)
- central processes of 1st order neurons branch diffusely as enter spinal cord and medulla
- -some braches take part in spinal cord reflexes
- -others synapses with 2nd order neurons in cord and medullary nuclei
3 ascending pathways
- nonspecific and specific ascending pathways send impulses to sensory cortex
- responsbile for discriminative touch and conscious proprioception
- -spinocerebellar tracts send impulses to cerebellumm do nto contribute to sensory preception
nonspecific ascending pathway includes which tracts?
lateral and anterior spinothalamic tracts
nonspecific ascending pathway; the lateral spinotha. tract transmits
impulses concerned with pain and temp; to opposite side of brain
nonspecific ascending pathway; the anterior spinotha. tract transmits...
impulses concerned with crude touch and pressure to opposite side of brain
nonspecific ascending pathway; 1st neuron:
nonspecific ascending pathway; 2nd neurons:
interneurons of dorsal horn; synapse with 3rd order neuron in thalamus
nonspecific ascending pathway; 3rd neuron:
carry impulse from thalamus to postcentral gyrus
dorsal column tract
- aka Medial lemniscal pathway
- -fibers run only dorsal column
- -transmit impulses from receptors in skin and joints
- -detect discriminative touch and proprioception
- 1st order neuron: sensory neuron; synapses with 2nd order neuron in nucleus gracilis and nucleus cuneatus of medulla
- 2nd ord. neur.: interneuron decussate and ascend to thalamus where it synapses with 3rd ord neur.
- 3rd ord.(thalamicneurons): transmits impulses to somatosensory cortex (postcentral gyrus)
- transmit info about trunk and lower limb mucles and tendons to cerebellum
- -no conscous sensation
damage to ventral root
- flaccid paralysis (limp and unresponsive)
- -skeletal mucles cant move iether voluntarily/involuntarily
Only UMN of primary motor cortex damaged
- spastic paralysis (muscles affected by persistent spasms and exaggerated tendon reflexes)
- -muscles remain healthy longer but movements no longer subject voluntary control
- -muscles norm. become permanently shortened
transection at any levels results in ...
- total motor and sensory loss in body regions inferior to site of damage
- -in cervical region, all four limbs affected (quadriplegia)
- -between T1 and L1, only lower limbs affected (paraplegia)
- transient period of functional loss that follows injury
- -results in immediate depression of all reflex activity caudal to lesion
- -bowel and bladder reflexes stop, bp falls, and all muscles below injury are paralyzed and insensitive
- -neural function usually returns within few hours following injury
- -if not returned within 48hrs, paralysis is permanent
Amyotrophic Lateral sclerosis (Lou gehrig's disease)
- progressive destruction of anterior horn motor neurons and fibers of hte pyramidal tracts
- -lose ability to speak, swallow, breathe
- -death within 5 yrs
- -cause unknown (90%); others have high glutamate levels
- virus destorys anterior horn motor neurons
- -victims die from paralysis of respiratory muscles
- -enters body in feces-contaiminated water
primary sensory function of dorsal column
- brings ifno from sensory receptors in periphery all way to primary somatic sensory cortex
- -via SC, brainstem, and thalamus
- -3 neuron circuit - sites of synaptic contact
- from dorsal column; bipolar neurons receive info from peripheral sensory receptors and bring to SC and BS, where info 1st processed
- -synapse at relay nucleus in medulla
- [axons] of these neurons from DC nucleus decussate at medulla and cont as medial lemnicus --> thalamus
- -thalamic neurons send axons to internal capsule, then synapse at primary somatic sensory cortex
corticospinal tract serves...
- primary motor function; brings info from primary motor cortex to skeletal muscle in periphery (activates muscle contraction)
- -only ONE synapse
- 1° motor cortical
- neuron (pre-central gyrus of the frontal lobe)
- à internal capsule à ventral surface of midbrain à pyramids on ventral surface of medulla.
- These axons decussate
- at caudal medulla and travel in the lateral column of the SC à synapse at motor neurons in the ventral horn à these axons travel to the spinal nerve (through ventral
- nerve roots) à to synapse at the
intermediatte zone of gray matter
integration of sensory and motor functions (inter-neurons, reflexes), which serve direct spinal reflexes
white matter: nerve tracts are...
dorsal column contains...
lateral column contains...
- -contains dorsal column
- -contains...motor descending axons