Ch 13- Spinal Cord
Meninges- surround brain & sc
-protection & nutrients
1. Dura mater – hard mother, outer
SUBdural/Epidural space - space
between dura mater and arachnoid
mater
-used to deliver anesthetic
2. Arachnoid mater – spider mother,
thin, spiderwebby
Subarachnoid space - this is the
largest of the spaces between maters
and this one is full of
CerebroSpinalFluid (CSF) which
bathes the spinal cord.
-used for spinal taps (meningitis, MS,
cancers)
3. Pia mater – delicate mother,
attached directly to brain & s.c.,
extensions that anchor the cord come
off the pia matter and are known as
"denticulate ligaments"
Spinal Anesthesia- pg 422
http://www.youtube.com/watc
h?v=S3r6oJ1rEio
Meningitis
• Infection of meningeal membranes by bacteria/virus
• Infection causes inflammation = disruption to circulation of CSF =
damage/death of neurons
• Vaccinations can be given to prevent some forms of meningitis
• Can be diagnosed by spinal tap
• Highest risk group are children under 5, followed by individuals 1625
• Newest outbreak cause by steroid injections contaminated by a
fungus
Spinal Cord regions
1. It is the link between the brain
and the PNS.
2. pathway for sensory and motor
impulses
• (31 pairs) cervical spinal nerves
have an extra set, C8. All the others
correspond to the number of
vertebra in that particular spine.
1. Cervical- 8 pairs
2. Thoracic- 12 pairs
3. Lumbar- 5 pairs
4. Sacral- 5 pairs
•
5. Coccygeal- 1 pair
Anatomical landmarks to know
1. 2 longitudinal depressions
a. Posterior Median Sulcus - PMS
b. Anterior Median Fissure - AMF
2. 2 enlargements of the spinal cord
a. Cervical enlargement (biggest) pectoral girdle – C4-C8
b. Lumbar enlargement - supplies
and innervates lower limbs
3. Conus Medullaris - L1 - tapering end
of the spinal cord proper
4. Cauda Equina - L1 to sacrum "Horse Tail" this is made up of bundles
of nerves/axons
5. Filum Terminale - one terminal fiber
which anchors the spinal cord to the end
of the sacrum, comes off the cauda
equina.
Internal Anatomy
Grey matter - made up of unmyelinated axons, cell bodies of
neurons, & neuroglia
a. Dorsal Root - posterior - sensory nerves
b. Dorsal Root Ganglion (contains sensory nerve
cell bodies)
c. Ventral Root - anterior - motor neurons
"AMPS" anterior/motor and posterior/sensory
*Spinal nerves start where the dorsal root ganglia and ventral
root fuse or come together and join to become a mixed
nerve/exit the spine at the intervertebral foramen.
1. Anterior Gray Horn:
cell bodies of somatic motor neurons (anterior motor)
2. Posterior Gray Horn:
cell bodies of somatic sensory neurons and visceral sensory neurons
(posterior sensory)
3. Lateral Gray Horns
cell bodies of autonomic nervous neurons
4. "grey & white commisures"
- this is where nerve impulses cross over
- remember that the right side of the brain deals with the left side of the
body, etc. impulses cross over contralaterally at some point in the spine.
- Central Canal in middle- contains cerebrospinal fluid
White Matter- Columns/Funiculi
-has myelinated & unmyelinated
1. Anterior (efferent)ascending and descending
motor
2. Lateral (efferent)ascending and descending
motor
3. Posterior (afferent)ascending sensory to brain
Fascicle/Tracts-axons in
each column which share
functional & structural
characteristics
AMPS
Anatomy of Spinal Nerves
• 3 layers of CT
• Epineurium
• Outermost layer
• Consists of dense network
of collagen fibers
• Perineurium
• Middle layer
• Divide nerve into series of
compartments which
contain bundles of axons
(fascicles)
• Endoneurium
• Innermost layer
• Surround individual axons
Distribution of Spinal Nerves
• Spinal Nerves:
• Consist of dorsal root + ventral root
• Branch to form pathways to destination
• Includes motor and sensory nerves
Dermatomes:
a. each pair of spinal nerves controls a region
of body surface sensation - the exception to
this is C1, which does not.
b. from dorsal and ventral rami fibers
c. damage to the spinal nerve results in loss of
sensation to a region of skin
d. this is a helpful diagnostic tool, sometimes
pain is referred from one nerve to a
corresponding region of skin.
Peripheral Neuropathies
• Regional loss of sensory or
motor function
• Due to trauma or compression
• Example: if your foot “falls
asleep”
Shingles
• Caused by varicella-zoster virus
(chickenpox)
• After chickenpox, virus hides in
neurons of spinal cord
• Later in life, attacks neurons in
dorsal roots of nerves = painful
rash/blisters
• Distribution of rash corresponds
to dermatome nerves affected
Plexus- “braid” of nerves
-a group of spinal nerves that do a
specific job
-Nerves do not go directly to the
body structure they supply
-from anterior rami
-cervical, brachial, lumbar and
sacral
*Note: the Thoracic nerves are
NOT A PLEXUS.
1. Cervical plexus
C1-C4 – head, neck, upper shoulders & chest
Phrenic nerve- C3- C5 -diaphragm
2. Brachial Plexus
C5-T1 -upper limbs and pectoral girdle.
5 major terminal branches:
Axillary- armpit, shoulder
Median- down the middle of the arm & hand
Musculocutaneous – flexors of the arm
Radial - along the radial bone, thumb, fingers 2-3
Ulnar - along ulna, little finger
3. Thoracic nerves (Intercostals)
• T2-T12 remember, these are not a plexus, because
they directly innervate each rib space
Intercostal nerves - along each rib
4. Lumbar Plexus
L1-L4- abs, external genitals, lower limbs
Femoral Nerve -anterior thigh/leg, medial leg & foot
Obturator nerve – adductors of leg
Genitofemoral- middle thigh and genitals
Ilioinguinal- genitals
Iliohypogastric- abs & butt
5. Sacral Plexus
• L4-S4- butt, perineum, lower limbs
Sciatic nerve-posterior to femur, largest & longest
nerve in the body, most of legs & even feet
-2 divisions fibular/peroneal divison & tibial
division
Gluteal- butt
Neuronal pools
• Interneurons (CNS)
organized into
function groups
• May stimulate or
depress parts of the
brain/spinal cord
• Five different ways
organization takes
place
Divergence
• Spread of info from one neuron/pool to several neurons/pools
• Occurs when sensory neurons bring info to CNS
• Allows for message to reach multiple places at the same time
Convergence
• Several neurons synapse on single post-synaptic neuron
• Allow for control of same motor neurons both consciously and
subconsciously
Serial processing
• Information relayed from one neuron to another in stepwise fashion
• Occurs when sensory info is relayed from one part of the brain to another
Parallel processing
• Several neurons/pools process same info simultaneously
• Divergence must take place first
• Allows for responses to occur simultaneously
Reverberation
• Branches of axons extend back toward source of impulse to trigger further
stimulation
• Positive feedback loop
• Help maintain consciousness, muscular coordination and normal breathing
1. Arrival of stimulus activates receptor
2. Sensory Neurons are activated and produce AP
3. Information processing in CNS
AP = release of neurotransmitters which allow postsynaptic cell (interneuron or motor neuron) to
process information
4. Activation of motor neuron releases
neurotransmitters
5. Release of neurotransmitters leads to response by
effector
Classification of Reflexes
1. Development
• Innate reflexes
• Genetically determined
• Include chewing, suckling, tracking object with eyes, blinking when eyelash
touched
• Acquired reflexes
• Learned motor patterns enhanced by repetition
• Driving, walking, skiing
2. Response
• Somatic reflexes
• Involuntary control of skeletal muscle contractions
• Include superficial and stretch reflexes
• Provide rapid response that can be modified later by voluntary commands
• Visceral (automatic) reflexes: Controls actions of smooth/cardiac
muscles, glands, adipose tissue
Classification of Reflexes
3. Complexity
• Monosynaptic: one synapse, little delay between stimulus and
response
• Polysynaptic: multiple synapses, longer delay between stimulus and
response
4. Processing site
• Spinal reflexes: Processing occurs in the spinal cord
• Cranial reflexes: Processing occurs in the brain
Spinal Reflexes
The Stretch Reflex
• Most common monosynaptic reflex
• Example: patellar reflex
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Physician taps on patellar tendon
Receptors in quadriceps are stretched
Distortion of receptors stimulates sensory neurons
This leads to reflex contraction of stretched muscle = kick
Slow response can indicate defect with nerve conduction
Patellar reflex helps with balance and walking, contracts muscle automatically when
weight is put on feet during standing/walking
Spinal Reflexes
Withdrawal Reflex
• Type of polysynaptic reflex
• Example: flexor reflex
• Affects muscles of a limb
• Occurs when you grab a hot pan
• Grabbing hot pan stimulates pain receptors
• Sensory neurons activate interneurons in spinal cord
• Stimulate motor neurons in anterior gray horns
• Result=contraction of flexor muscles that yanks hand away from stove
• Inhibitory signals used to relax extensor muscles
Babinski Reflex
• Babinski sign (positive Babinski reflex)
• Occurs in absence of descending inhibition
• Normal in infants/pathological in adults
• If seen in adults = sign of damage to nerve paths connecting the spinal cord
and brain
• Plantar reflex (negative Babinski reflex): Stroking lateral sole of
foot produces curling of the toes