chapter 13: spinal cord and spinal nerves Flashcards
what are the functions of the spinal cord and spinal nerves
- spinal reflexes
- integration (summation) of inhibitory and excitatory nerves. (Excitatory inputs bring a neuron closer to threshold, while inhibitory inputs bring the neuron farther from threshold)
- highway for upward and downward travel of sensory and motor information
what protects the spinal cord
protected by the vertebral column, the meninges (3 layers) and cerebrospinal fluid (CSF)
what are the layers of the meninges from superficial to deep
epidural space, dura mater, subdural space, arachnoid mater, pia mater, subarachnoid space
explain dura matter
thick, strong layer of dense irregular CT> continuous with the epineurium (the outermost layer of dense irregular connective tissue surrounding a peripheral nerve)
where is the epidural space found
is the space between the dura mater and the vertebrae- contains fat
where is the subdural space found? what does it contain?
between dura mater and arachnoid mater. contains interstitial fluid
explain arachnoid mater
middle space that is avascular, thin layer of loose CT
pia mater
the thin layer of loose CT that adheres to the spinal cord. Contains blood vessels that bring oxygen and nutrients to the spinal cord
where do you find the subarachnoid space
between the arachnoid mater and the pia mater. contains cerebrospinal fluid
What cells produce CSF?
a) Neurons
b) Satellite cells
c) Ependymal cells
d) Blood cells
e) Astrocytes
c) ependymal cells
The space between the middle layer of the
meninges and the deepest layer of the meninges is
a) Epiarachnoid space
b) Subdural space
c) Subarachnoid space
d) Epipia space
e) Subpia space
c) subarachnoid space
where can you find CSF? when would you remove it and what is that called? Where is it performed and why there?
it circulates through brain ventricles and subarachnoid space of the brain and spinal cord (also central canal)
removal of cerebrospinal fluid from the subarachnoid space is called a spinal tap. done to diagnose infections such as meningitis
performed between L3-L4 or L4-L5 because the spinal cord isn’t there
epidural vs spinal tap
*Epidural injections can be performed anywhere along the
vertebral column; spinal tap injections are in the lumbar
section.
*Easier to achieve segmental (local) analgesia/anesthesia
with epidural; effects of spinal tap are less localized
*Drug is injected through catheter placed with epidural
injection, and more drug can be released if needed
*Generally higher doses are needed for epidural injections,
and onset of analgesia is slower with epidural injections
Where is an epidural injection performed?
a) In the dura mater
b) In the epidural space
c) Between the pia mater and the arachnoid mater
d) Between the arachnoid mater and the dura mater
e) b and d
b) In the epidural space
describe the spinal cord and its 2 sections
- Flattened cylinder
- 42-45 cm long &
2 cm diameter - In adult ends at L2
Cervical enlargement: spinal nerves to and
from upper limbs
Lumbar enlargement: spinal nerves to and
from lower limbs
what is the caude equina
the roots of the lowest spinal nerves. called “horse’s tail”
what is the conus medularis
it’s the cone shaped end of the spinal cord
what is filum terminale
extension of pia mater that fuses with arachnoid and dura mater. It anchors spinal cord to coccyx
how does the spinal cord communicate with specific regions in the body
31 pairs of spinal nerves
Why is a spinal tap performed bellow L3?
a) Because the epidural space is not present above L3
b) To have better access to lumbar nerves
c) To make sure not to damage cervical nerves
d) To make sure not to damage the spinal cord
e) a and d
D)
Which segment contains more spinal nerves
than vertebrae?
a) Cervical
b) thoracic
c) Lumbar
d) Coccygeal
a) cervical
describe the gray matter in the spinal cord
shaped like a butterfly; connects neuron cell bodies, neuroglia, umyelinated axons and dendrites
In the gray matter of the spinal cord and brain, clusters of neuronal cell bodies form functional groups called nuclei. Sensory nuclei receive input from receptors via sensory neurons, and motor nuclei provide output to effector tissues via motor neurons. The gray matter on each side of the spinal cord is subdivided into regions called horns (
describe the gray commissure
forms the crossbar of the H / crosses the midline
describe the central canal of the spinal cord
runs the whole length of the spinal cord and contains cerebrospinal fluid
describe the dorsal / posterior gray horn
contain axons of incoming sensory neurons as well as cell bodies and axons of interneurons. Recall that cell bodies of sensory neurons are located in the spinal ganglion of a spinal nerve.
describe the lateral gray horn
The lateral gray horns contain autonomic motor nuclei, which are clusters of cell bodies of autonomic motor neurons that regulate the activity of cardiac muscle, smooth muscle, and glands.
describe the anterior/ ventral grey horns
somatic motor nuclei to skeletal mucle
nuclei vs sensory nuclei vs motor nuclei
Nuclei = clusters of cell bodies in the grey matter
* Sensory nuclei – receive input from sensory neurons
* Motor nuclei – provide output to tissues via motor neurons
describe white matter in the spinal cord
surrounds the gray matter; contains mostly myelinated axons
ascending tracts vs descending tracts
The white matter surrounds the grey matter
◦ Divided into columns that contain tracts (bundles
of axons in the CNS)
◦ Each tract contains axons having a common origin
or destination, carrying similar information
◦ Ascending tracts carry sensory information up to
the brain
◦ Descending tracts carry motor information down
from the brain
what are the two main functions of the spinal cord
The spinal cord has two main (non-reflex) functions:
◦ The grey matter receives and integrates incoming and outgoing information
◦ The white matter tracts are highways for nerve impulse conduction to and
from the brain
◦ Sensory (ascending) tracts conduct nerve impulses toward the brain
◦ Motor (descending) tracts conduct impulses down the cord
how are tracts named
named for where the neurons begi and end. The cortico-spinal tract begins in the cortex and ends in the spinal cord. is also a motor tract
True or False? The lumbar enlargement
extends from L1 to L4 and contains nerves
that travel to and from the lower limbs.
a) This is a true statement
b) False. It is called the thoracic enlargement.
c) False. The lumbar enlargement extends from T9-T12.
d) False. The lumbar enlargement innervates the back, not the
lower limbs.
e) C and D
c) false.
where do spinal nerves form from?
posterior (dorsal) and anterior (ventral) roots
what are anterior roots composed of?
axons of outgoing motor neurons
what are posterior root ganglia made of?
cell bodies and sensory neurons
what are posterior roots made of?
axons of incoming sensory neurons
what are mixed spinal nerves?
when the posterior and anterior roots merge to form a mixed spinal nerve
A mixed nerve is composed of
a) Sensory neurons
b) Afferent neurons
c) Efferent neurons
d) Motor neurons
e) All the above
e) all of the above
what are rami
Almost immediately after
exiting the intervertebral
foramen, spinal nerves divide
into several branches or rami
what are the 4 different spinal nerves that branch into branches
- Posterior (dorsal) rami supply skin & muscles of posterior trunk (back)
- Anterior (ventral) rami form plexus supply anterior trunk & limbs
- Meningeal branches re-enter and supply meninges, vertebrae & blood vessels
- Rami communicantes is another branch that supplies the ANS
what is special about anterior rami
Anterior rami do not go directly to the part
they supply instead they join to form nerve
networks or plexuses (“braid” or “network”). ADVATANGE OF THIS IS THAT IF ONE IS DAMAGE IT CAN GO THROUGH ANOTHER PATHWAY
Found in neck, arm, lower back, and sacral
regions
Emerging from each plexus are nerves
named for regions they innervate
what is the cervical plexus and what is an important nerve within it.
spinal nerves C1 to C5
Supplies parts of head, neck &
shoulders
The phrenic nerve which supplies the diaphragm
damage above C3 can cause respiratory arrest
what is the brachial plexus
involves C5 to T1 (cervical enlargement from C4 -T1)
supplies shoulder and upper limbs
what is special about intercostal nerves
there is no thoracic plexus because these nerves don’t need to be specialized
anterior rami of spinal nerves (t2-T12) do not enter a plexus but instead directly innervate intercostal spaces
THESE ARE CALLED INTERCOSTAL NERVES
which ones are the lumbar plexus
involves roots from spinal nerves (t12-L4)
supplies abdominal wall, external genitals and anterior/medial thigh
sacral plexus
involves spinal nerves L4-S4
T12-L2 vertebrae
anterior to the sacrum; supplies buttocks, perineum and lower limbs
coccygeal plexus
involves spinal nerves S4-Co1
supplies small area of skin in coccygeal region
Which spinal nerves go directly to the tissues
they supply rather than forming a plexus?
a) C1 through C4
b) T2 through T12
c) L1 through L5
d) S1 through S5
b
what happens when you damage C1-C3
no function maintained from neck down; ventilator needed for breather electric wheelchair with breath, head, or shoulder controlled device required
damage C4-C5
diaphram function maintained. can breathe
damage C6-C7
some arm and chest muscles functions maintained, which allows feeding, sone dressing; wheelchair required
damage T1-T3
intact arm function
damage T4-T9
control of trunk above umbilicus
damage T10-L1
most thigh muscles ok, which allows walking with long leg braces
L1-L2 damage
most leg muscles ok, which allows walking with short leg braces
When a spinal nerve enters the
spinal cord, it is then called…
a) Whiter matter
b) Gray matter
c) Column
d) Tract
d
what are dematomes
◦ All spinal nerves except C1 innervate specific,
constant segments of the skin; the skin segments are
called dermatomes
◦ Note: Skin on face supplied by CN V (trigeminal)
what is a reflex and what are the different kinds
like where they take place and what system are used
A reflex is a fast, predictable, automatic response to changes in the environment
that helps maintain homeostasis
◦ Reflexes may be
◦ spinal (integration takes place in spinal cord)
◦ cranial (integration takes place in brain)
◦ somatic (involves contraction of skeletal muscles)
◦ autonomic (involves contraction of visceral smooth muscles)
monosynaptic vs polysynaptic reflex
NTEGRATING CENTER. If the
sensory neuron synapses
directly onto the motor neuron,
it’s a monosynaptic reflex. If an
interneuron is involved, it’s a
polysynaptic reflex.
ipsilateral vs contralateral reflex
MOTOR NEURON. If the motor
neuron affects organs on the same
side as the sensory neuron, it’s an
ipsilateral reflex. If the motor
neuron crosses to the other side of
the body, it’s a contralateral reflex
somatic reflex vs autonomic reflex
EFFECTOR. If the effector is a
skeletal muscle, it’s a somatic
reflex. If the effector is
smooth muscle or a gland,
it’s an autonomic reflex.
what are teh 4 important somatic spinal reflexes
- The stretch reflex
- The tendon reflex
- The flexor (withdrawal) reflex
- The crossed extensor reflex
what is the stretch reflex
It operates as a feedback mechanism to control muscle
length by causing muscle contraction
◦ Prevents injury from over-stretching by causing muscle to
contract (shorten) when it is stretched
what are the events of stretch reflex
Events of stretch reflex
◦ Muscle spindle signals stretch of muscle
◦ Motor neuron activated and muscle contracts
◦ Brain sets muscle spindle sensitivity as it sets muscle
tone (degree of muscle contraction at rest)
example is patellar reflex
In the STRETCH reflex
a) The sensory neuron sends the sensory information directly to the
brain
b) The sensory neuron synapses directly with the motor neuron
c) The activated motor neuron causes the antagonist muscle to
contract
d) The stimulus involves stretching of sensory neurons
b
what is the tendon reflex
It operates as a feedback mechanism to control muscle tension by causing
muscle relaxation when muscle force becomes too extreme.
Golgi tendon organs lie within tendons
◦ Activated by stretching of tendon
◦ Inhibitory neuron is stimulated (polysynaptic)
◦ Motor neuron is hyperpolarized, and muscle relaxes
Both tendon and muscle are protected
Reciprocal innervation (also polysynaptic)
◦ Causes contraction of antagonistic muscle group
n the TENDON reflex
a) The stimulus involves stretching of muscle fibers
b) The sensory neuron brings information directly to the other side
of the spinal cord
c) The activated motor neuron innervates the antagonistic muscle
d) No motor neuron gets inhibited
e) C and D
C)
what is the flexor reflex
the flexor (withdrawal) reflex is a protective withdrawal reflex that moves a
limb to avoid pain
This reflex results in contraction of flexor
what is the crossed extensor reflex
he crossed extensor reflex helps to maintain balance during the flexor reflex.
This is a balance-maintaining reflex that causes a synchronized extension of the
joints of one limb and flexion of the joints in the opposite limb
In the FLEXOR reflex
a) The stimulus involves pain
b) The sensory neuron brings information directly to the brain
c) Motor neurons in several spinal cord segments get activated
d) a and c
e) a and b
d)
In the CROSSED EXTENSOR reflex
a) The sensory neuron synapses directly with motor neurons in
several segments of the spinal cord
b) The sensory neuron brings information directly to the other side
of the spinal cord
c) Motor neurons are activated on the opposite side of the spinal
cord
d) No motor neuron gets inhibited
C
why do we check a patient’s reflex. give an example
to help detect disorder or injuries
E.g., Plantar flexion reflex → stroke the lateral margin
of the sole
◦ Normal response is curling under the toes
◦ Abnormal response (or normal response of children
under 18 months) is called Babinski sign
◦ Upward fanning of toes due to incomplete
myelination
If a patient does not initiate a spinal reflex in
response to a stimulus this could mean
damage to all the following, EXCEPT:
a) The sensory neuron
b) The motor neuron
c) The spinal cord
d) The brain
e) The effector (e.g. muscle)
d) the brain
