spinal cord + spinal nerves (theory) Flashcards
proof of spinal cord-brain independent functioning
- the brain can still function if one is quadriplegic
- one can still have reflexes even if the brain is injured
spinal cord and brain interactions
- both can integrate and process information
- both can function with each other
- both can also function independently of each other
spinal cord general features
- 45 cm in length (18 in)
- passes through the foramen magnum
- ends between L1 and L2
- has enlargements
spinal cord regions
- cervical
- thoracic
- lumbar
- sacral
- coccygeal
spinal taps and spinal cord ending
the spinal cord ends between L1 and L2 of the lumbar region, spinal taps are done below L2 to prevent spinal injury because the meninges of the spinal cord continues past L2 and still contains some CSF
enlargements
bulges or collections of nerves coming off the the spinal cord
ex… cervical and lumbosacral enlargements
spinal cord anchoring
- crista gali
- filum terminale
the crista gali anchors the spinal cord (cephalically) and the filum terminale anchors it caudally
cauda equina
means “horse tail”
subarachnoid space
between the arachnoid and pia matters of the brain and spinal cord
CSF is present in this space in the spinal cord
filum terminale
this anchors the spinal cord caudally
the filum terminale eventually becomes a component of the coccygeal ligament
crista gali
the spinal cord dura matter is continuous with brain’s dura matter
the crista gali anchors the brain’s dura matter which by extension anchors the spinal cord
31 spinal segments consist of…
- dorsal root (horn)
- dorsal root ganglia
- ventral root (horn)
- spinal nerve
dorsal horn of grey matter
where all sensory information from the PNS enters the spinal cord
dorsal root ganglia
large bulbous part of the nerve that precedes the dorsal root and dorsal horn of the grey matter
differentiating the anterior spinal segment from the posterior
- dorsal horns (pointy)
- anterior median fissure
- posterior median sulcus
- dorsal root ganglia
- spinous process are posterior
spinal nerves (2x)
- sensory nerves (afferent)
- motor nerves (efferent)
spinal meninges
the spinal meninges is a membrane surrounding the spine that offers protection, stability and shock absorption
- pia
- arachnoid
- dura
denticulate ligaments
anchors the spinal cord from the sides
it anchors the pia to arachnoid and the dura
dura matter
tough fibrous material, outermost layer of the spinal meninges
provides crista gali and filum terminale anchoring of the spinal cord
arachnoid
middle layer, with spider like network
pia
delicate inner most layer of the spinal meninges
blood vessels are found in this layer
spinal cord blood supply
the sulci hides the blood vessels which are covered up by the pia matter
grey matter contents
- central canal
- cell bodies (somas)
- glial cells (neuroglia)
white matter contents
- axons
- organization into ascending and descending columns
grey matter organization
- dorsal grey horns
- lateral grey horns
- ventral grey horns
- gray commissure
dorsal grey horn
receives sensory input from the visceral organs and the muscles (somatic)
lateral grey horn
sends motor commands to the visceral organs (visceral motor nuclei)
ventral grey horn
sends motor commands to the muscles (somatic motor nuclei)
grey commissure
contralateral crossover point of axons
funiculi
columns of nerves
white matter organization
- funiculi
- posterior white column
- anterior white column
- lateral white column
- descending and ascending tracts
posterior white column sensations (4x)
- proprioception
- fine touch (meissners)
- pressure (pacinian)
- vibration (pacinian)
spinothalamic sensations
- crude touch
- pain
- temp
ascending tract (sensory)
spinothalamic tract
descending tract (motor)
corticospinal tract
peripheral nerve organization
- epineurium
- perineurium
- endoneurium
much like skeletal muscle, fascicles are bundles of axons
epineurium
outermost layer of the peripheral nerve and is continuous with the dura matter
perineurium
surrounds a fascicle
endoneurium
surrounds a single axons
spinal nerve merge
all 31 pairs of spinal nerves merge from the ventral and dorsal roots
spinal nerve organization
- dorsal ramus
- ventral ramus
- white ramus
- grey ramus
dorsal and ventral rami
the spinal nerves branch off into the dorsal and ventral rami
the dorsal ramus contains postganglionic fibers that innervate smooth muscle and glands
the dorsal ramus also contains fibers from the ventral horn that innervate the skeletal muscles of the neck and back
the ventral rami contains postganglionic fibers that innervate smooth muscle and glands
the ventral rami also contains fibers that from the ventral horn that innervate the skeletal muscles of the limbs
rami communicantes
grey and white rami
spinal nerves coming from T1 to L2 have two additional branches on top of the dorsal and ventral rami
both branches converge onto the sympathetic ganglion before becoming the sympathetic nerve
grey = postganglionic
white = preganglionic
postganglionic innervates smooth muscle, glands and visceral organs of the thoracic cavity
preganglionic innervates abdominopelvic viscera
dorsal and ventral rami
(sensory reception)
the dorsal and ventral rami can also receive sensory input from the somatic and visceral tissue, these lead back to the dorsal grey horn
dorsal ramus = interoceptors, exteroceptors, proprioceptors of the back
ventral ramus = exteroceptors, proprioceptors, interoceptors of the limbs
dermatomes
sensory branches of the skin (spinal nerve) which are important for clinical uses
ex… if a patient has lost sensation in their calf, then it is likely a problem with S2 of the cutaneous branch of the spinal nerve
four nerve plexuses
- cervical
- brachial
- lumbar
- sacral
there is no thoracic or coccygeal plexus
plexus = a bundle of branching nerves coming our of the spinal cord
cervical plexus
ranges from C1-C5
nerves to note:
1. phrenic nerve = supplies the diaphragm and extends from the neck to the diaphragm (long)
the phrenic nerve is especially marked in neck surgeries to avoid loss of patient breathing if nicked
brachial plexus
ranges from C5-T1
the brachial plexus overlaps with the cervical plexus
nerves to note:
1. medial
2. ulnar
3. radial
all three nerves supply the hand
lumbar plexus
ranges from T12-L4
the lumbar plexus overlaps with the sacral plexus and can be called the lumbosacral plexus
major nerves:
1. obturator
2. femoral
3. lateral femoral cutaneous
sacral plexus
ranges from L4-S4
major nerves:
1. sciatic nerve = largest nerve of the leg, it supplies the back of the thigh to the back of the lower leg
reflex
definition: an immediate involuntary motor response
reflex arc pathway
- sensory receptor stimulated
- sensory info related to the CNS
- CNS processes information
- CNS activates a motor neuron
- response on the effector
reflex classification
reflexes are classified based on…
- development
- site where info is processed
- nature of the resulting motor response
- neural circuit complexity
developmental reflexes
- innate
- acquired
ex… the babinski reflex is innate
site where info is processed reflexes
- spinal
- cranial
nature of the motor response reflex
- somatic
- visceral
- autonomic
circuit complexity
- monosynaptic
- polysynaptic (interneurons)
polysynaptic reflex example (landing on a nail)
stretch reflex example (monosynaptic)
patellar ligament stretch example
- tap the patellar ligament
- muscle stretches
- intrafusal muscle spindle receptors fire
- sends to the CNS via the dorsal ramus
- no interneuron
- extrafusal muscle fibers fire
- quads contract
