Ch 13: Spinal Cord & Nerves, Somatic Reflexes PART ONE
Fasciculus
A ___ is a tract of nerve fibers a column of the spinal cord.
Fasciculus
A ___ is a tract of nerve fibers within a column of the spinal cord
Gray Matter
A layer of tissue in the CNS that contains neurons cell bodies, dendrites, and synapses. Has a relatively dull color because it contains little myelin. Acts as the site of synaptic contact between neurons, and therefore is the site of all neural integration in the spinal cord.
Anterior Median Fissure
A longitudinal groove on the ventral surface of the spinal cord.
Subarachnoid Space
A space in the meninges beneath the arachnoid membrane and above the pia mater that contains the cerebrospinal fluid.
Lateral Horn
Additional horn of the spinal cord grey matter from T2 to L1. Contains the neurons of the sympathetic nervous system, which sends their axons out of the cord by way of the anterior root along the somatic efferent fibers.
ALS
Also known as Lou Gehrig disease, marked by the degeneration of motor neurons and atrophy of the muscles, as well as sclerosis (scarring) of the lateral regions of the spinal cord. Most cases occur when astrocytes fail to reabsorb the neurotransmitter glutamate from tissue fluid, create neurotoxic levels. Symptoms include muscular weakness, difficulty in speaking and swallowing, and impaired use of the hands.
Spinothalamic tract
Ascending Spain's tract that forms the anterolateral system with other smaller tracts. Passes up the anterior and lateral columns of the spinal cord. Carries sensory signals for pain, temperature, pressure, tickle, itch, and light or crude touch. First order neurons end up in the posterior horn of the spinal cord near the point of entry. They synapse with second-order neurons, which decussate and form the contralateral spinothalamic tract which leads to the thalamus. Third order continue from the thalamus to the cerebral cortex.
Spinoreticular tract
Ascending tract that travels up the anterolateral system with the spinothalamic tract. Carries pain signals from tissue injury.. first order enters the posterior horn and immediately synapse with second order fibers, which decussate and end in a loosely organized core of grey matter (retinacular formation) in the medulla and pins. Third order neurons continue from the pins to the thalamus, and fourth order neurons complete the path to the cerebral cortex.
Posterior & Anterior Spinocerebellar Tracts
Ascending tracts that travels through the lateral column and carry proprioceptive signals from the limbs and trunk to the cerebellum at the rear of the brain. First order neurons originate in the muscles and tendons and the end of the posterior horn. Second order send their fibers up the tracts to end in the cerebellum. Posterior tract: travels ipsilaterally. Anterior tract: decussate and the cross back over to the ipsilateral side of the cerebellum. Both tracts provide the cerebellum with feedback needed to coordinate muscle actions.
Conduction
Because it contains ascending and descending nerve tracts, a function of the spinal cord is the ___ of nerve signals between the CNS and the periphery of the body.
Decussation
Because the nerve tracts of the spinal cord undergo ___, the right side of the brain communicates with the left side of the body (and vice versa).
Tracts
Bundles of axons that carry signals from one level of the CNS to the others. Located within the white matter of the spinal cord.
Columns/Funiculi
Bundles of axons within the white matter of the spinal cord that provide avenues of communication between different levels of the CNS. Includes a posterior (dorsal), lateral, and anterior (ventral) column on each side. Each one consists of subdivisions called tracts/fascículi.
Gray Matter
Central core of the spinal cord that looks like a butterfly or H-shaped (in cross sections). Consists of two posterior (dorsal) horns, which extend to the posterolateral surfaces of the cord; and two thicker anterior (ventral) horns, which extend toward the anterolatersl surfaces. In the middle is the central canal, which is collapsed in most of the adult spinal cord, but remains open in some places (and in young children) lined with ependymal cells and filled with CSF. An additional lateral horn is visible on each side from T2 to L1.
Spinal cord regions
Cervical, thoracic, lumbar, sacral regions. Named for the level of the vertebral column that the spinal nerves emerge from, not for if they contain the spinal cord itself.
Spinal cord functions
Conduction, neural integration, locomotion, reflexes.
Spinal cord
Cylinder of nervous tissue that arises from the brain stem at the formen magnum of the skull. Passes through the vertebral canal as far as L1. Averages 45cm long and 1.8 cm in adults.
Tectospinal tract
Descending tract that originates in the midbrain section called the Tectum and crosses contralaterally. Descends through the brainstem ti the upper spinal cord on that side, going as far as the neck. Involved in reflex turning of the head, especially in response to sights and sounds.
Lateral corticospinal tract
Descending tract wherein most corticospinal fibers decussate in the lower medulla and form on the contralateral side of the spinal cord.
Lateral & medial vestibulospinal tracts
Descending tracts that begin in the brainstem vestibular nuclei, which receives signals for balance from the inner ear. Lateral tract passes down the anterior column of the spinal cord and facilitates neurons that control extensor muscles of the limbs, like stiffening and straightening. The medial tract splits into ipsilateral and contralateral fibers that descend through the anterior column on both side ps of the cord and terminate in the neck - plays a role in the control of head position.
Lateral & medial reticulospinal tracts
Descending tracts that originate in the reticular formation of the brainstem. Control the muscles I'd the upper and lower limbs, especially to maintains balance and posture. Also contain the descending analgesic pathways that reduce transmission of pain signals to the brain.
Polimyelitis
Disease caused by the poliovirus, which destroys motor neurons in the brainstem and the anterior horn of the spinal cord. Symptoms include muscle pain, weakness, and a loss of some reflexes, followed by paralysis, muscular atrophy, and respiratory arrest. Spreads by fecal contamination of water.
Denticulate Ligaments
Extensions of the pia mater that extend through the arachnoid to the dura in regular increments. Function to anchor the cord and limit side-to-side movement.
Terminal Filum
Fibrous strand-like structure that anchors the bottom of the spinal cord to the vertebral column.
Spinal cord
Gives rise to 31 spinal nerves, exhibits longitudinal grooves on the anterior and posterior sides - the anterior median fissure and the posterior median sulcus.
For the level of vertebral column from which it's spinal nerves arise
How are the spinal regions named?
Three
How many neurons are typically found in an ascending pathway between the receptors and the brain?
31 pairs
How many pairs of spinal nerves are there (in adults)?
L1
In adults, the spinal cord ends at which vertebrae?
Third-order neuron
In ascending spinal retracts, neuron that carries sensory information from the first and second-order neurons the rest of the way to the cerebral cortex.
Second-order neuron
In ascending spinal tracts, these neurons continue as far as a "gateway" called the thalamus at the upper end of the brain stem.
First-Order Neuron
In ascending tracts, this neurons detects the stimulus and transmits a signal to the spinal cord or brain stem.
Central Canal
In the spinal cord, the ______ canal is lined with ependymal cells and contains cerebrospinal fluid.
Superficial
In the spinal cord, where is the white matter in relation to the grey matter?
Amyotrophic Lateral Sclerosis (ALS)
In which disease does sclerosis of the lateral spinal cord occur, with destruction of motor neurons?
Three neurons
It takes ___ neurons for a somatic sensation nerve signal to complete the sensory pathway.
Coccygeal Ligament
Ligament that attaches the spinal cord and meninges to the vertebral column at Co1. Made up of the terminal filum fused to the dura mater.
Gracile Fasciculus
Major ascending tract that carries signals from the midthoracic and lower parts of the body. Below T6, it composes the entire posterior column. At T6, joins with the cuneare fasciculus. Consists of fist-order nerve fibers from that travel up the ipsilateral side of the spinal cord and terminate in the gracile nucleus in the medulla oblongata of the brainstem. Carry signals for vibration, visceral pain, deep and discriminative touch, and proprioceptikn from lower limbs and lower trunk.
Cuneate fasciculus
Major ascending tract that joins the gracile fasciculus at T6. Occupies the lateral portion of the posterior column and forces the gracile fasciculus medially. Carries the same type of sensory signals, originating from T6 and up (upper limbs and chest). Fibers end in the cuneate nucleus on the ipsilateral side of the medulla oblongata. Second order fibers decussate and turn into the medial lemniscus, third-order fibers go from the thalamus to the cerebral cortex. Because it decussates, the signals carried by the gracile ANS cuneate fasciculi go to the contralateral side.
Upper motor neuron
Neuron of the descending spinal tracts that begins with a soma in the cerebral cortex or brainstem, and has an axon that terminates on a lower motor neuron in the brainstem or spinal cord.
Neural Integration
Pools is spinal neurons receive input from multiple sources, integrate the information, and execute an appropriate output. For example, the spinal cord can integrate the stretch sensation from a full bladder with the cerebral input concerning the appropriate time and place to urinate and execute control of the bladder accordingly.
Locomotion
Repetitive, coordinated contraction of several muscle groups in the limbs. Motor neurons in the brain initiate this movement and determine speed, distance, and direction.
Medullary Cone
Section of the spinal cord inferior to the lumbar enlargement where the cord tapers to a point.
Lumbar enlargement
Section of the spinal cord that is slightly thicker. Gives rise to the nerves of the pelvic region and lower limbs. Located in the lumbosacral region of the spinal cord.
Cervical enlargement
Section of the spinal cord that is slightly thicker. Gives rise to the nerves of the upper limbs, located in the cervical region.
Spinal Tracts
Sections of the spinal cord which direct sensory information and motor impulses. All nerve fibers in a particular section have similar origins, destinations, and functions.
Lumbar Cistern
Subarachnoid space located inferior to the medullary cone that is occupied by the cauda equina and cerebrospinal fluid (CSF)
Lower motor neurons
The ___ motor neurons of the descending pathway innervate skeletal muscle
Anterior Horns
The ___ of the spinal cord contain the cell bodies of outgoing somatic motor neurons
Meninges
The _____ are a series of fibrous connective tissue membranes covering the central nervous system.
Motor Neurons
The anterior horns of the spinal cord contain somas of somatic ___ neurons
Cerebrospinal fluid
The central canal of the spinal cord contains _____ fluid
Decussation
The crossing of nerve fibers from the right side of the CNS to the left (or vice versa), especially in the spinal cord, medulla oblongata, and optic chiasma. As a result, the right left side of the brain receives info from the right side of the body and sends motor commands to that side (and vice versa). A stroke that damages the motor centers of the right side of the brain causes paralysis of the left limbs.
Pia Mater
The deepest layer of the meninges, a delicate and transparent membrane that is composed by 1-2 layers of squamous and cuboidal cells and delicate collagenous and elastic fibers. Closely follows the contours of the spinal cord.
Anterior corticospinal tract
The descending corticospinal tract that does not decussate, and instead is formed by ipsilateral fibers. These decussate lower in the cord, so they control contralateral muscles. This tract gets smaller as it descends and give off nerve fibers, and usually Dias appears by the midthoracic level.
Dorsal Horns
The horns of the spinal cord gray matter. Extend towards the posterolateral surfaces of the spinal cord. Receives sensory nerve fibers from spinal nerves, which synapse with networks of interneurons within the horn.
Gray commissure
The left and right sides of the gray matter in the spinal cord are connected by _____
Posterior median sulcus
The longitudinal groove located on the dorsal surface of the spinal cord.
Arachnoid Mater
The middle layer of the meninges, made of 5-6 layers of squamous and cuboidal cells adhering to the inside of the dura, with a looser layer of cells and collagenous and elastic CT spanning the gap to the pia mater.
Dura Mater
The most superficial layer of the spinal meninges, forms a loose fitting sheath (dura sheath) around the spinal cord. Tough and rubbery, made of multiple layers of dense irregular connective tissue.
Upper motor neurons
The neurons of the descending pathway that have their somas in the cerebral cortex or brainstem.
Proprioception
The non visual sense of the position and movements of the body.
Two neurons
The number of descending pathway is _____
Terminal Filum
The pia mater that continues past the medullary cone as a fibrous strand within the lumbar cistern. Exits the cistern at S2 and fuses with the dura mater to form the coccygeal ligament to anchor the cord to the vertebral column.
Brainstem
The source for many spinal nerves. A vertical stalk that supports the large cerebellum it the rear end of the head. The site wherein spinal tracts begin and end.
Subarachnoid Space
The space between the arachnoid mater and the pia mater is called what?
Epidural Space
The space between the dura sheath and the vertebral column that contains blood vessels, adipose tissue, and loose CT. Common anesthesia site to block pain signals during childbirth or surgery.
Conduction
The spinal cord contains bundles of nerve fibers that conduct information up and down the cord, connecting different levels of the trunk with each other and the brain. This enables sensory information to reach the brain, motor bombards to reach effectors, and input received at one level of the cord to affect output from another level.
Ventral Horns
The two thicker horns of the spinal cord gray matter. Extend towards the anterolateral surfaces of the spinal cord. Contains the large neurosomas of motor neurons whose axons lead out of the skeletal muscles.
Regions of the spinal cord
Thoracic, lumbar, cervical, sacral
Meninges
Three fibrous membranes between the central nervous system and the surrounding bone. Contains the dura mater, arachnoid mater, pia mater. Act to separate soft tissue of the CNS from surrounding bones of the vertebrae and skull.
Medial lemniscus
Tract of nerve fibers that lead from the medulla to the thalamus. Made up of Second order fibers of the gracile and cuneate systems that decussate.
Ascending Spinal Tract
Tract of the spinal cord that carries sensory information up the spinal cord.
Descending Spinal Tract
Tract of the spinal cord that conducts motor neurons down the cord.
Corticospinal Tracts
Tracts of the descending spinal tracts that carry signals from the cerebral cortex for precise, finely coordinated limb movements. The fibers of this system form ridges called pyramids on the anterior Surface of the medulla oblongata, so these are called pyramidal tracts.
Posteriori, lateral, and anterior
What are the three pairs of funiculi in the spinal cord?
A tract of nerve fibers within a funiculus
What is a fasciculus in the spinal cord?
Dura mater
What is the dura sheath around the spinal cord made of?
Arachnoid Mater
What is the middle layer of the meninges called?
Dura mater, arachnoid mater, pia mater
What is the order of the meninges, from superficial to deep?
Bundles of myelinated and unmyelinated axons found superficial to grey matter
What is the white matter of the spinal cord?
Ipsilateral
When a tract does not decussate, and its origin and destination are on the same side of the body.
Contralateral
When the origin and destination of a spinal tract decussate, and are therefore on opposite sides of the body.
Gray Matter
Where are the neuron cell bodies, dendrites, and synapses found in the CNS?
At the formen magnum
Where does the spinal cord arise from the medulla oblongata?
Superficial to the gray matter
Where is the white matter in the spinal cord?
Anterior
Which horns of the spinal cord contain the cell bodies of outgoing somatic motor neurons?
Pia Mater
Which meninx is closely associated with the contours of the spinal cord?
Arachnoid Mater
Which meninx is located deep to the dura mater?
Ventral, dorsal, and lateral horns
Which spinal cord areas are composed of grey matter?
Ipsilateral
Which tract will have its origin and destination on the same side of the body?
Poliomyelitis
Which viral disease results in the destruction of motor neurons?
White Matter
White myelinated nervous tissue located deep to the cortex of the cerebrum and cerebellum, and superficial to the gray matter of the spinal cord. Composed of bundles of axons (tracts) that carry signals from one level of the CNS to the others.
Sensory information
Within the spinal cord, an ascending tract will carry ___ information you to the brain
Sensory Tracts
Within the spinal cord, which tracts carry information up to the brain?
Descending Tracts
Within the spinal cord, which tracts carry motor signals down from the brain?
Causa Equina
a bundle of spinal roots located caudal to the end of the spinal cord (from L2 to S5). Inner ages the pelvic organs and lower limbs.
Central pattern generators
groups of neurons that coordinate repetitive sequences of contractions for walking. Produce the sequence of outputs to the extensor and flexor muscles that cause alternating movements in the legs.
Reflexes
specific patterns of motor response that are triggered by specific patterns of sensory stimulation. Play vital roles in posture, motor coordination, and protective responses to pain or injury.