Protective structures:
Vertebral column and the meninges (3) (protective CT layer) provide protect the spinal cord and provide physical stability.
1) dura mater - superficial, continuous with brain dura mater, epineurium (outer layer of cranial/spinal nerve)
SUBDURAL SPACE
2) arachnoid mater - spiderweb arrangement
SUBARACHNOID SPACE
3) pia mater - deep, adheres to surface of CNS, denticulate ligament suspend spinal cord in middle of its dural sheath
External anatomy of spinal cord
(2) enlargements
1) conus medullaris
2) filum terminale
cervical & lumbar enlargement
inferior to lumbar enlargement, spinal cord terminates at tapering conus medullaris
extension of pia mater extending inferiorly & fuses to arachnoid & dura mater - filum terminale anchors spinal cord to coccyx
External anatomy of Spinal cord
Posterior (dorsal) root & anterior(ventral) root
Posterior (dorsal root) ganglion
cauda equina
roots = 2 bundles of axons that connect each spinal nerve to segment of cord by rootlets
posterior (dorsal) root - only sensory axons, has swelling that contains sensory neuron cell bodies (posterior ganglion)
anterior (ventral) root - only motor axons
cauda equina - roots of lumbar, sacral & coccygeal regions that run alongside filum terminale like wisps of hair
Internal Anatomy of Spinal Cord
1) anterior median fissure
2) posterior median sulcuss
3) gray & white commissures
4) central canal
5) anterior, posterior & lateral gray horns
6) anterior, posterior & lateral white columns
1) wide groove on anterior side
2) narrow furrow on posterior side
3) gray- forms crossbar of H, white- connects white matter of left & right sides
4) space in center of gray commissure filled with CSF
5) gray matter subdivided into horns
6) white matter divided into columns - contains bundles of axons with common destination (tracts) - sensory = ascending, motor = descending
White Matter
Gray Matter
White - bundles of myelinated axons
Gray - neuronal cell bodies & dendrites, unmyelinated axons & neuroglia
Nuclei
functional clusters of neuronal cell bodies in gray matter
Spinal Nerve - 31 pairs; mixed nervs
Cervical (8)
Thoracic (12)
Lumbar (5)
Sacral (5)
Coccygeal (1)
Connective tissue covering of spinal nervs (3)
define: fiber, fascicle & nerve
1) endoneurium - wraps individual axons within nerve
2) perineurium - wraps fascicles
3) epineurium - wraps around entire nerve
fiber - single axon within endoneurium
fascicle - bundle of fibers within perineurium
nerve - bundle of fascicles with epineurium
Rami of Spinal Nerves
spinal nerve branches
Rami of Spinal Nerves (2)
posterior (dorsal) ramus - serve deep muscles & posterior skin of trunk
anterior (ventral) ramus - muscles/structures of limbs & skin of lateral & anterior trunk
All anterior rami form plexuses except?
T1-T11
Cervical Plexus
formed by anterior rami of C1-C5
superficial & deep branches
phrenic nerve - important (diaphragm)
Brachial plexus
formed by anterior rami of C5-C8 & T1
supplies shoulders & upper limbs
Brachial Plexus:
roots (unite)→ __..?
roots (unite)→ trunk (superior/middle/inferior) → divisions (anterior/posterior)→ cord (lateral/medial/posterior)→ nerves
Important nerves that arise from brachial plexus (5)
axillary
musculocutaneous
radial
median
ulnar
Lumbar Plexus
formed by anterior rami of L1-L4
supplies anterolateral abdominal wall, external genitals, and part of lower limbs.
Femoral & Obturator Nerves
Sacral Plexus
anterior rami of L4-L5 and S1-S4
supplies butt, perineum & lower limbs
gives rise to large nerve in body - SCIATIC nerve
Coccygeal Plexus
Formed by anterior rami of S4-S5 and coccygeal nerves.
supplies small area of skin in coccygeal region
Dermatome
the area of the skin that provides sensory input to CNS via 1 pair of spinal nerves or trigeminal nerve
Sensory and Motor Tracts
White matter tracts & gray matter
White Matter Tracts - highways for nerve impulse propogation
Gray matter - recieves & integrates incoming & outgoing info
Reflex
fast, involuntary. unplanned response to a stimulus
Reflex Arc
pathway followed by nerve impulses that produce a reflex
A reflex arc includes (5)?
1) sensory receptor - responds to stimulus
2) sensory neuron - nerve impulse propogates to axon terminals in gray matter -> relay neurons to brain
3) integrating center
4) motor neuron
6) effector
The Stretch Reflex
feedback mechanism to control muscle LENGTH
Causes contraction of skeletal muscle in response to stretching of muscle.
monosynaptic
ipsilateral - same side
ex) knee jerk: stretching → activation of muscle spindles → sensory neuron →spinal cord →motor neuron → muscle contraction
Tendon Reflex
feedback mechanism to control muscle tension by causing relaxation
polysynaptic
sensory receptor = golgi tendon organs
tension applied to tendon → tendon organ stimulated →nerve impulse →spinal cord →motor neuron → muscle relaxation to relieve tension
Flexor (withdrawal) Reflex
Stepping on a tack (stimulus) → nerve impulse → activation of interneuron → activation of motor neuron →muscle contraction →withdrawal of the leg.
polysynaptic
ipsilateral
Crossed Extensor Reflex
polysynaptic
contralateral
Contraction of muscles that extend joints in opposite limb in response to a painful stimulus.
Stepping on a tack (stimulus) → nerve impulse→activation of several
interneurons → motor neurons → muscle contraction→ flexion of leg stepping on a tack & extension on opposite side.
for maintaining balance
