Spinal Cord/Nerves Flashcards
The spinal cord begins as a continuation of _____ (the most inferior portion of the brain stem) extending from the foramen magnum of the ____ bone to its termination as the ____ between L1 - L2
the medulla oblongata
occipital
conus medullaris
Three meninges, from outer to inner:
Dura Mater (only 1 layer, unlike brain dura mater)
Arachnoid mater
Pia Mater
The spinal meninges surround the spinal cord, and are continuous with the cranial meninges, which encircle the brain
Forms a sac from the level of the foramen magnum to the second sacral vertebra
Dura mater
____ between the dura mater and the wall of the vertebral canal contains a cushion of fat and connective tissue further cushioning the spinal cord
Epidural space
Between the dura mater and the arachnoid mater is the thin ____ space, which contains interstitial fluid
subdural
Contains blood vessels that supply oxygen and nutrients to the spinal cord
Pia mater
thin transparent connective tissue layer that adheres to the surface of the spinal cord and brain
Pia mater
Between the arachnoid mater and the pia mater is a space filled with cerebrospinal fluid called the ____
subarachnoid space
Membranous, thickened extensions of the pia mater that project laterally and fuse with arachnoid mater and inner surface of dura mater
Denticulate ligaments
Suspend the spinal cord within its dural sheath, protecting it against sudden displacement
Denticulate ligaments
Delicate strands of tissue emanating from the arachnoid mater
Arachnoid trabeculae
slide 9
Span the subarachnoid space, connecting the arachnoid and the pia
Arachnoid trabeculae
slide 9
In adults the spinal cord extends from the medulla oblongata to the superior border of the ___ lumbar vertebra
second
The ___ enlargement and ___ enlargement accommodate nerves to and from the upper and lower limbs, respectively
cervical
lumbar
Inferior to the lumbar enlargement the spinal cord tapers to a conical-shaped portion termed the ___, which in adults ends at the level of the IV disc between vertebrae L1 & L2
conus medullaris
The ___ is an extension of the pia mater that arises from the conus medullaris to anchor the spinal cord to the coccyx
filum terminale
Nerves that arise from the inferior part of the spinal cord do not immediately leave the vertebral column, but rather continue in the vertebral canal in fine strands collectively termed the ___
cauda equina
___ are the paths of communication between the spinal cord and the nerves innervating specific regions of the body
Spinal nerves
Two bundles of axons connect each spinal nerve to a segment of the cord. Each bundle is called a root, which in turn is composed of smaller bundles of axons called ___
rootlets
The roots are posterior (or dorsal) root and anterior (or ventral) root
Each posterior root has a swelling, the posterior (dorsal) root ganglion, which contains the cell bodies of ___ neurons
sensory
The ___ root and rootlets contain axons of motor neurons, which conduct nerve impulses from the CNS to effectors (muscles and glands)
anterior (ventral)
The gray matter of the spinal cord is shaped like the letter H, or a butterfly, and is surrounded by white matter. The gray ___ forms the crossbar of the H.
commissure
Anterior horns contain cell bodies of somatic ___ neurons and ___ nuclei that provide nerve impulses for the contraction of skeletal muscles.
motor
___ gray horns contain somatic and autonomic sensory nuclei. The gray commissure connects gray matter of the right and left sides.
Posterior
The central canal extends the length of the spinal cord, and is continuous with the ____ in the medulla oblongata of the brain
fourth ventricle
Anterior to the gray commissure is the anterior (ventral) ___ commissure, which connects the white matter of the right and left sides of the spinal cord
white
Lateral gray horns contain cell bodies of ____ motor neurons that regulate activity of smooth muscle, cardiac muscle, and glands.
autonomic
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Lateral gray horns are present only in the thoracic and upper lumbar, (T1 – L2 or T1 – L3) and sacral (S2 – S4) segments of the spinal cord.
___ matter receives and integrates incoming and outgoing information
Gray
Bundles of myelinated axons, called ___, have a common origin or destination, and carry similar information up or down the spinal cord
tracts
Sensory tracts comprise axons that conduct nerve impulses toward the brain
(ascending)
Motor tracts carry nerve impulses down the spinal cord
(descending)
___ matter tracts ascend to or descend from the brain. Gray matter processes information input and output
White
There are __ pairs of spinal nerves
31
Spinal nerves are named and numbered according to the region and level of the ____ from which they emerge
vertebral column
The first cervical pair emerges between the
occipital bone and the atlas
All other spinal nerves emerge through ____ between adjoining vertebrae
intervertebral foramina
Most spinal nerves exit inferior to the vertebra of the same number, the exception being cervical nerves due to the fact that C1 exits superior to the __ (which is the first cervical vertebra)
atlas
Spinal nerves do not necessarily exit the spinal cord in the same plane as their corresponding vertebrae
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Illustrated: spinal nerve L1 exits the vertebral column inferior to L1 vertebra, but it exits the spinal cord on a plane between T11 & T12 vertebrae
The dorsal and ventral nerve roots unite at their points of exit from the vertebral canal to form a ___
spinal nerve
The dorsal and ventral nerve roots unite at their points of exit from the vertebral canal to form a ___
spinal nerve
Spinal nerves technically comprise only that brief interval between union of the dorsal and ventral roots, and subsequent division into dorsal and ventral rami
After the spinal nerve exits the intervertebral foramen, each spinal nerve divides almost immediately into a dorsal primary ___ and a ventral primary ___,
ramus
Each nerve divides into several branches just after passing through its ___
intervertebral foramen
___ are the terminal branches of spinal nerves
Rami
The ____ ramus innervates deep muscles and skin of the dorsal surface of the trunk
posterior (dorsal)
The ____ ramus serves muscles and structures of the upper and lower limbs and the skin of the lateral and ventral surfaces of the trunk
anterior (ventral)
The _____ of each spinal nerve reenters the vertebral canal to supply the vertebrae and associated structures
meningeal branch
Other branches form the ____ and contribute to the trunk ganglia of the autonomic nervous system
rami communicantes
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Except for most thoracic nerves, the ANTERIOR RAMI of spinal nerves do not go directly to the body structures they supply. Rather, they form networks on both the left and right sides of the body by joining with other axons from anterior rami of adjacent nerves, called a ____
plexus
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
Principal plexuses
Also, a smaller coccygeal plexus
(no thoracic plexus)
Anterior rami of spinal nerves T2 – T12 are called ___ nerves. Another name for them is thoracic nerves
intercostal
Intercostal nerves/thoracic nerves connect directly to the structures they supply, which are:
intercostal muscles
abdominal muscles
skin overlying the muscles
The ___ rami of the intercostal nerves supply the deep back muscles and skin of the posterior aspect of the thorax
posterior
Plexuses are formed from the ___ rami of spinal nerves
anterior
They are paired (left and right)
Plexuses have subunits of varying numbers, depending on the complexity of the plexus
They contain both motor and sensory neurons
Trunks are formed by union of roots (fortunately this is only in the brachial plexus), e.g.,
Superior trunk
Middle trunk
Inferior trunk
Divisions are the consequence of branching of trunks
Anterior division
Posterior division
The ____ supplies the skin and muscles of the head, neck, superior portion of the shoulders and chest, and the diaphragm
cervical plexus
The ____ arise from the cervical plexuses and supply motor fibers to the diaphragm
phrenic nerves
Complete severing of the spinal cord above the origin of the phrenic nerves (C3, C4, and C5) causes respiratory arrest. Breathing stops because the phrenic nerves no longer send impulses to the diaphragm.
The _____ supplies the shoulders and upper limbs
brachial plexus
The ____ arises from the brachial plexus and supplies muscles on the posterior aspect o the arm/forearms
radial nerve
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The ____ supplies the anterolateral abdominal wall, external genitals, and part of the lower limbs
lumbar plexus
The ____ supplies the buttocks, perineum, and lower limbs
sacral plexus
lumbar plexus
supplies the anterolateral abdominal wall, external genitals, and part of the lower limbs
sacral plexus
supplies the buttocks, perineum, and lower limbs
sciatic nerve is the largest nerve in the body. It is actually two nerves bound by a common sheath of connective tissue, arising from the ____ plexus
sacral
Various branches of the sciatic nerve supply muscles of the leg, foot, and toes
Sciatic supplies muscles of?
Leg, foot, toes
Injury to the sciatic nerve results in sciatica, pain that may extend from the buttock down the posterior and lateral aspect of the leg and into the foot
Injury may be due to herniated disc, dislocated hip, osteoarthritis, pressure from the uterus during pregnancy, or an improperly administered gluteal intramuscular injection
Sensations that arise in the skin , and include tactile sensations (touch, pressure, vibration, tickling), thermal sensations (warmth, coolness), and pain?
Cutaneous sensation
Maps of the afferent nerves that convey cutaneous sensations toward the CNS are of two types:
Dermatomes
Peripheral nerve fields (cutaneous nerves)
The area of the skin that provides sensory input to the CNS via one pair of spinal nerves
Dermatomes
The skin is supplied by somatic sensory neurons that carry nerve impulses from the skin into the spinal cord and brain stem
Each spinal nerve contains sensory neurons that serve a specific segment of the body
Dermatomes
The area of the skin that provides sensory input to the CNS via one pair of spinal nerves or cranial nerve V is called a ___ (cranial nerve V is the trigeminal; it serves most of the skin of the face and the scalp)
dermatome
Knowing which spinal cord segments supply each dermatome makes it possible to locate damaged regions of the spinal cord
Nerves supplying a specific dermatome may be damaged if the sensation is not perceived when the skin in a particular region is stimulated
Adjacent dermatomes typically overlap, except at the ____, which is the line of junction of dermatomes supplied from discontinuous spinal levels
axial line
spinal cord has two principal functions in the maintenance of homeostasis
Nerve impulse propagation
Information integration (processing)
___ receives and integrates incoming and outgoing information
(spinal cord)
Gray matter
___ tracts carry sensory impulses toward the brain, and motor impulses from the brain toward effectors
(spinal cord)
White matter
Name of a tract indicates . . .
Its position in the white matter
Where it begins and ends
By extension, the direction of information flow
Example: lateral corticospinal tract
A lateral white column
Begins in the cortex (of the brain
Ends in the spinal cord
Since flow is away from the brain, it is a motor (descending) tract
ability to feel exactly what part of the body is touched
Discriminative touch
ability to distinguish the touching of two different points on the skin which are close together
Two-point discrimination
Sensory systems provide input to the CNS regarding the environment. ___ in several areas of the brain and spinal cord integrate the input
Interneurons
The ___ has a major role in controlling precise, voluntary muscular movements
cerebral cortex
Motor output to skeletal muscles travels down the spinal cord in two types of descending pathways
Direct
Indirect
These nerve impulses originate in the cerebral cortex
They cause precise, voluntary movement of skeletal muscles
Direct pathways
Direct pathways include:
Lateral CORTICOspinal
Anterior CORTICOspinal tract
CORTICObulbar tract
These impulses originate in the brain stem or other parts of the brain that govern automatic movements
Indirect pathways
They help coordinate body movements with visual stimuli, maintain skeletal muscle tone and contraction of postural muscles, regulate muscle tone in response to movements of the head
Indirect pathways
Indirect pathways include:
Rubrospinal tract
Tectospinal tract
Vestibulospinal tract
Lateral reticulospinal tract
Medial reticulospinal
a fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus
reflex, may be Innate (inborn) or Learned
when integration takes place in spinal cord gray matter
type of reflex
spinal reflex
when integration occurs in brain stem
type of reflex
cranial reflex
___ reflexes involve contraction of skeletal muscles
Somatic
Visceral reflexes . . .
Involve contraction of smooth muscle, cardiac muscle, and glands
Are not usually consciously perceived
Are not easy to initiate by clinical processes
Are also termed autonomic reflexes, since they are mediated by the autonomic nervous system
The pathway followed by nerve impulses that produce a reflex is termed a ____ (or reflex circuit)
reflex arc
___ comprise very specific pathways as they propagate into, through, and out of the central nervous system
___ are of diagnostic value due to the property of having specific pathways
Reflex arcs
A reflex arc includes the following five functional components:
Sensory receptor Sensory neuron Integrating center Motor neuron Effector
Sensory receptor Sensory neuron Integrating center Motor neuron Effector
components of a reflex arc
The dendrite or sensory structure of the sensory neuron responds to a specific stimulus by producing a graded potential called a generator (or receptor) potential. If the potential reaches threshold, it will trigger one or more nerve impulses in the sensory neuron
reflex arc step 1,2
The gray matter within the central nervous system is the integrating center. The simplest reflex consists of the integrating center comprising just one synapse between sensory neuron and motor neuron, called a monosynaptic reflex arc. Most reflex arcs are polysynaptic, involving more than two types of neurons and more than one CNS synapse
step 3
Reflex arcs
The integrating center sends impulses out of the CNS along a motor neuron to the part of the body that will respond
step 4
Reflex arcs
The effector is the part of the body that responds, generally a muscle or gland. The responsive action of the effector is called a reflex. If the effector is skeletal muscle, the reflex is a somatic reflex. If the effector is smooth muscle, cardiac muscle, or a gland, the reflex is an autonomic reflex (or visceral reflex)
step 5
Reflex arcs
If the effector is skeletal muscle, the reflex is a ___ reflex. If the effector is smooth muscle, cardiac muscle, or a gland, the reflex is an autonomic reflex (or___)
somatic
visceral reflex
operates as a feedback mechanism to control muscle length by causing muscle contraction
Prevents injury from over-stretching, because muscle contracts when it is stretched
Stretch Reflex
Monosynaptic, ipsilateral reflex arc
Stretch Reflex
muscle spindle (stretch receptors) in the muscle signals stretch of muscle
motor neuron activated & muscle contracts
Events of stretch reflex
___ sets muscle spindle sensitivity as it sets muscle tone (degree of muscle contraction at rest)
(for stretch reflex)
Brain
Reciprocal innervation (polysynaptic- interneuron): ___ muscles relax as part of reflex
antagonistic
operates as a feedback mechanism to control muscle tension by causing muscle relaxation when muscle force becomes too extreme
Tendon Reflex
Tendon vs. Reflex
Causing muscle relaxation or contraction slide 78
Polysynaptic, ipsilateral reflex
Golgi tendon organs (tension receptors) are in tendon, at the musculotendonous junction of skeletal muscles
Tendon Reflex
activated by stretching of tendon
inhibitory neuron is stimulated (polysynaptic)
motor neuron is hyperpolarized and muscle relaxes
Tendon Reflex
Both tendon & muscle are protected
Reciprocal innervation (polysynaptic)
Tendon Reflex
ipsilateral and is a protective withdrawal reflex that moves a limb to avoid pain (also known as nociceptive withdrawal reflex (NWR))
flexor (withdrawal) reflex
This reflex results in contraction of flexor muscles to move a limb to avoid injury or pain
flexor (withdrawal) reflex
contralateral, helps to maintain balance during the flexor reflex
crossed extensor 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
crossed extensor reflex
This reflex results from the gentle stroking of the lateral outer margin of the sole
Plantar flexion reflex
Babinski sign
Autonomic reflexes are not practical diagnostic tools since it is difficult to stimulate most visceral receptors because they are deep inside the body (one exception being the
pupillary light reflex—pupils of both eyes decrease in diameter when either is exposed to light)
Damage or disease anywhere along a ____ can cause the reflex to be absent or abnormal
reflex arc
___ reflexes suggest central nervous system disease
Hyperactive
Decreased reflexes are found in
Damage to relevant spinal segments
Diseases of muscles
Diseases of the
neuromuscular junction
Loss of sensation
