10-15a Spinal Cord Anatomy I Flashcards
Where does the spinal begin and cord end?
foramen magnum
extends until L2
What are the cervical and lumbar enlargements on the SC due to?
more n. here where we have extremeties
Where do nerves emerging from each spinal segment go next?
leave at different levels
If someone fractures their T12 vertebra and the spinal segments there are L2/L3, where is the injury? What other spinal segments are affected?
L2/L3
all the ones below it
How many pairs of spinal nerves are there?
31
What is grey matter?
What is it divided into?
a group of cells/neurons dorsal horn (sensory neurons/connects to dorsal root) ventral horn (motor neurons/anterior horn cells)
Which grey matter horn is afferent?
dorsal horn
Which grey matter horn is efferent?
ventral/anterior horn
What other features are visible in the transversely orientated spinal segment?
white matter tracts, central canal
What varies the grey matter to white matter ratios on different leveled spinal segments?
cervical and lumbar levels: large ventral/anterior horns (cervical and lumbar enlargements = extremities)
thoracic spine: smaller anterior horns (lateral horns: SNS)
What are the white matter tracts bundled into? What comprises them?
three funiculi:
posterior funiculus:
lateral funiculus
anterior funiculus
no cell bodies: primarily axons that are either going from SC towards CNS or from CNS to SC
What are the columns/layers of cells of the grey matter called?
Rexed’s laminae
What is the gradient along Rexed’s laminae
dorsal: n. that receive sensory input (ex. lamina 1 and 2 pain fibers, 3 and 4 mechanoreceptor)
middle: integration b/w sensory input and motor output (5 and 6)
ventral: anterior horn cells/motor n. (9 and 10: anterior horn cells/somatic n.)
Where do the dorsal and ventral nerve roots join? Sensory or motor?
spinal root/spinal nerve
mixed
What does the dorsal ramus supply?
mixed n. of the muscles and skin of the back
what does the ventral ramus supply?
mixed n. that forms a part of the plexi (brachial and lumbosacral plexus that supplies UE and LE) and visceral organs
Where is the brachial plexus?
C5-T1
Where is the lumbar plexus?
L1-L4
Where is the sacral plexus?
L5-S4
What are axons surrounded by?
Schwann cells
What is the outermost CT layer of the spinal n?
epineurium
What are the different divisions of the brachial plexus?
five roots (ventral rami) three trunks six divisions three cords five branches
What is are the axons and * coated by?
endoneurium
What are bundles of axons grouped into?
fasicle
What are each bundle of axons coated by?
perineurium
What are the bundles of axons coated by?
epineurium
What is the path of the sensory component to a peripheral spinal nerve to the SC?
dorsal root < sensory axons and cell bodies in DRG < spinal nerve < dorsal or ventral ramus < sensory n. receptors (free nerve endings of sensory n.)
are the dorsal/ventral roots mixed?
no
What can the functional anatomy be categorized into?
sensory and motor organization
Where are the cell bodies for sensory axons
DRG
what composes the sensory org?
peripheral sensory organs
affarent/sensory axons whose cell bodies are in DRG, which goes into the SC > synapses at level of SC or it goes up to CNS
what composes the motor org?
n. in anterior horn (anterior horn cells) > exit through ventral root > pass through plexus > supplies m. fibers
what is the sensory component of the peripheral n?
receptor > sensory afferent n. > DRG no synapse here bipolar neuron: one axon goes to peripheral receptor and the other goes to CNS
What are the three pathways once the sensory afferent n. reaches spinal cord?
- relays info at the level it enters and innervates that n. center
- goes up to the somatosensory cortex
- synapses to other segments of the SC
Where do the spinal motor n. sit?
anterior horn cells
What are the characteristics of the anterior horn cells?
- Final common motor output
- Three types: Alpha, Beta and Gamma
- Axons of AHC are myelinated
- Organized in columns in the anterior grey matter of the spinal cord
what is a motor unit?
the neuron and all the m. fibers it innervates
All muscles in motor unit contract together when neuron fires : ALL OR NONE LAW
how do we grade forces?
motor units are critical parts of the mechanism
to create more motor force, what do we recruit
more motor units
what is the all or none law?
If I activate a motor unit, it will lead to contraction of all the m. fibers it innervates
myotomes
Muscles served by a single spinal nerve root emerging from a spinal segment
can have multiple motor units
What does Spinal Nerve C5 innervate?
deltoid
what are dermatomes?
Area of the skin innervated by a single nerve root
What is a scerotome?
Connective tissue structures innervated by a specific spinal nerve
what are sensory receptors? What is the specificity of receptors?
Specialized organs that transform a specific type of stimulus energy in to electric signals
The process by which stimulus energy is converted into an electrical signal: stimulus transduction
Sensory receptors are responsive to a single type of stimulus energy
What are exteroceptors?
peripheral sensory receptors sensitive to stimuli arising from outside body
What are interoceptors?
visceroreceptors, from internal viscera
What are proprioceptors?
monitor degree of stretch in skeletal m., tendons, joints, and ligaments
Where are exteroceptros located? What are the types located there?
skin
epidermis/derms
hypodermis
Merkel’s discs: epidermis (light touch)
Meissner’s corpuscles: dermis (light pressure)
Ruffini’s corpuscle: dermis (deep pressure)
free nerve endings: no special receptor, (pain and temperature)
Where are proprioceptors present?
skeletal m., joints, tendons, ligaments
sense degree of stretch of m., therefore info on body movement
to cerebrum, cerebellum, and spinal reflex arcs
m. spindles
golgi tendon organs
joint kinesthetic receptors
What are the grades of receptive fields for the exteroceptors?
area of the skin it receives input from
sharply mediated or diffused
Which two exteroceptors are sharply mediated?
meissner corpuscles
merkels discs
Which two exteroceptors are diffused?
pacinian corpuscle
ruffini’s corpuscle
Which exteroceptors are rapidly adapting (phasic)
Meissner’s corpuscle
pacinian corpuscle
Which exteroceptors are slowly adapting (tonic)?
Merkel’s discs
ruffini’s corpuscle
What are m. spindles sensitive to?
length of change of m. length
What do golgi tendon organs respond to?
tension
What do joint kinesthetic receptors respond to?
position of the joint in space
How are muscle spindles arranged?
in parallel to skeletal m. fibers
What are extrafusal muscle fibers?
skeletal m. spindles
What are the fibers within extrafusal m. fibers? What do they detect?
intrafusal m. fibers
length of the m. and change of length
Where are golgi tendon organs located? What is it in series with? What does it detect?
in the tendon
in series with extrafusal m. fibers
any tension on the fibers detected
what are the two types of intrafusal m. fibers? Where are they positioned?
nuclear bag fibers
nuclear chain fibers
positioned in parallel with the extrafusal m. fibers
what are the two functions of intrafusal m. fibers? Which one is their main function?
centrally sensory organs (detects change in m. length) with a small motor component
What are the two parts of intrafusal m. fibers?
central receptor part
lateral contractile part
What two things does the central sensory intrafusal m. fiber detect?
static length of the m.
rate of change of length
Which fibers in the intrafusal m. fiber detect static length?
nuclear chain fibers
static nuclear bag fibers
length only
Which intrafusal m. fibers detect dynamic change of m. length?
dynamic nuclear bag fibers
both m. length and its rate of change
What do group Ia sensory afferents do?
carry inputs from dynamic and static nuclear bag and nuclear chain fibers; provide information about both length and velocity
What do group II sensory afferents do? What fibers do they not innervate
inputs from static nuclear bag and nuclear chain fibers; provide information about length alone.
dynamic nuclear bag fibers
What is the golgi tendon organ? location? function?
located in the tendon
nerve endings that weave into the collagen of tendon and senses tension
high threshold for stimulation
functions to prevent m. and soft tissue injury
how does transduction work?
Conversion of a stimulus (such as light, or sound, or the position of the body) into an electrical signal in the nervous system
What is an example of transduction?
stimulus from environment deforms lamillae of receptors > changes mechanical input of axons > mechanically gated ion channels open > changes membrane conductance > Na depolarizes and causes EPSP for AP
how are different types of sensory info detected?
different receptors and different axon types with different diameters and conduction velocity
what is the receptor type for proprioception? What are the characteristic of the axon it detects upon?
muscle spindles
(proprioception needs to be quick for action and is conducted quickly)
therefore: large diameter, myelinated axons
what is the receptor type for pain, temperature, and itch? What are the characteristic of the axon it detects upon?
free nerve endings
lightly myelinated/unmyelinated
small axon diameter
slow conduction velocity
once inside the spinal cord, where do the afferent sensory axons go next?
DRG > synapses at level of spinal segment > brain stem and ascends to other levels of spinal cord
Where in the brain is sensory input received?
somatosensory cortex (in parietal lobe)
what is the function of the thalami?
regulation of all input going towards cortex
what are the two major ascending pathways that carry info to the contralateral somatosensory cortex?
Dorsal Column Medial Leminiscal System (DCML)
Anterolateral System (ALS)
carry info from R foot to L cortex etc.
What info travels via the DCML? Where are they located in the SC?
tactile (light touch), proprioception, and vibration
dorsal column/posterior portion of SC
What info travels via ALS?
pain, itch, and temperature
What are the similarities b/w ALS and DCML? Where are the first order n.? Where are the Third order n?
- Project input to contralateral thalamus and somatosensory cortex
- Three main neurons: 1st, 2nd and 3rd order neurons
a) First order neuron: in the DRG b) Third order neuron: in thalamus (ventral posteriolateral nucleus (VPL nucleus) of thalamus)
Where is the first order n?
DRG
Where is the third order n?
VPL nucleus of thalamus
What is the pathway for afferent sensory first order n. in DCML?
one end of 1st order n. receives input from mechanoreceptors and some from proprioceptors
other end of axon enters the SC via DRG and does not synapse at dorsal columns and travels to medulla oblongata (dorsal funiculus)
What is the pathway for afferent sensory second-order n in DCML?
lies in the n. cuneatus or n. gracilis of medulla> cross and ascend to thalamus
What is the pathway for afferent sensory third order n in DCML?
lies in the thalamus and reaches primary somatosensory cortex
what is the somatotopic organization of the dorsal columns in the DCML? Which are part of gracilis fasciculus and which are part of cuneatus fasciculus?
medial to lateral
leg, lower trunk, upper trunk, arm, neck, occiput
gracilis fasciculus: LE and lower trunk
cuneatus fasciculus: UE and neck
For the Anterolateral system where does the first order n. begin and synapse?
DRG enters SC and synapses on the second order n. in the dorsal horn
For the Anterolateral system where does the second order n. begin and synapse?
begins in dorsal horn and crosses to other side and ascends in anterolateral funiculus to the thalamus
For the Anterolateral system where does the third order n. begin and synapse?
begins in the Thalamus and goes to primary somatosensory cortex
What is the somatotopic organization of the Anterolateral system?
Lateral to medial:
leg, trunk, arm, and neck
