Spinal cord notes
Spinal Cord – 42 cm = 17in
Protected by bone, fluid, membranes, adipose tissue
Extends to 1st or 2nd lumbar vertebra starting from the
foramen magnum thru center of VC
Protection
Vert. Column, cerebral spinal fluid, membranes(meninges)
3 Meninges:
superior: dura mater
thick sheath
not attached to VC
separated from VC by epidural space(fat and CT)
Middle: arachnoid
Mat of collagen fibers – spiderwebs
Deep: pia mater
Is attached to spinal cord
Subarachnoid space – filled with CSF
All 3 meninges extend beyond spinal cord
Structure of spinal cord:
A continuous series of 31 segments – to correspond to the 31
pair of spinal nerves
Each segment – pair of spinal nerves via dorsal root ganglia
– cell bodies of SENSORY neuorns
Relay info between SC and peripheral
nerves
Dorsal roots(posterior “PS) – axons of SENSORY neurons
Ventral roots(anterior motor “motor to get ready in the am) axons of MOTOR neurons
Roots exit the Spinal cord via intervertebral foramen
cervical enlargement - supplies sensory and motor nerves to
pectoral girdle and upper limbs
lumbar enlargement – supplies sensory and motor nerves to pelvic
girdle and lower limbs
Tapers to a point at 2nd lumbar vert = conus medullaris
Cauda Equina – spinal nerves that extend beyond
Conus medullaris
Filum terminale – extension of pia mater to coccyx
Cross section of spinal cord
Posterior surface – toward spinous process of vertebra –
notched with the posterior median sulcus – shallow indentation
Anterior surface – toward body of Vertebra – anterior
median fissure – VERY DEEP
Gray matter
Unmyelinated fibers and neuron cell bodies and
neuroglia
Center of cord
Shape of H
Posterior horns = upper arms of H ; sensory nerves
Anterior horns = lower arms of H ; motor nerves
Lateral horn – between posterior and anterior horns
Only on thoracic and 1,2 lumbar vert
Gray commisure – cross bar of H
Central canal in center of GC – CSF
Function of Horns
Anterior gray horns – cell bodies of motor neurons
Fibers of MN extend to sk muscle
Posterior gray horns – terminal end of sensory neuron
Originate in sensory regions of skin, muscle,
organs
Cell bodies(ganglia) just outside of spinal cord
Lateral gray horns – autonomic neurons
White matter:
Myelinated fibers
Surrounds gray matter
Anterior, posterior, lateral columns(funiculi)
Each column represent nerve pathways =nerve tracts
Function of tracts:
Ascending tract – carry sensory info to brain
Descending tract – carry motor info away from brain
Reflex center
Reflex; respond to emergency – rapid
Simplest path for impulse
Fewest # of nerves involved
No thinking involved
Reflex Arc:
Conduction pathway for reflex action
Receptor at end of sensory neuron
Sensory neuron to CNS – Spinal cord only
Association neuron in spinal cord(reflex center)
Routed impulse to motor neuron
Has other connections too
Feel pain AND think how to treat after response
Effectors: motor neuron conduct impulse to
Skeletal muscle to effect the response
Withdrawal reflex
Patellar reflex
both somatic reflexes
B/c effectors are skeletal muscles
Visceral reflexes – affect smooth muscle and cardiac muscle
Heart rate, breathing, vomiting, sneezing,
(show youtube :Babinski reflex)