Chapter 13: The Spinal Cord and Spinal Nerves Flashcards
First layer of protection for the CNS
Skull and vertebral column
Second protective layer of CNS
Meninges
These are three membranes that lie between the bony encasement and the nervous tissue in the brain and spinal cord
Meninges
The third layer of protection for the CNS
a space between two of the meningeal membranes that contains cerebrospinal fluid
This is a buoyant liquid that suspends the central nervous tissue in a weightless environment while surrounding it with shock absorbing, hydraulic cushion
cerebrospinal fluid
The layers of protection for brain and spinal cord
Bones - skull and vertebral column
Meninges - three membranes found between bones and structures
Cerebrospinal fluid - found between two layers of the meninges
Where is spinal cord located in vertebral column?
vertebral canal
What part of the individual vertebrae connect to form the vertebral canal?
The vertebral foramina
What provide protection of the spinal cord?
vertebral canal, vertebral ligaments, meninges, and cerebrospinal fluid
Three meninges, from superficial to deep
- Dura mater
- Arachnoid mater
- Pia mater
The spinal meninges surround the spinal cord and are continuous with…?
the cranial meninges
What part of the vertebral column do spinal cord nerves exit the spinal column?
The intervertebral formina
Where does the three meninges layers stop covering the spinal nerves>
To the point where they exit the spinal column through the intervertebral foramina
Where is fat and connective tissue found that also provides protection to the spinal cord?
The epidural space
Where is the epidural space found?
Between the dura mater and the wall of the vertbral canal
Thick, strong layer composed of dense irregular connective tissue. Forms a sac from the level of the foramen magnum to the second sacral vertebra.
Dura mater
The dura mater of the spinal cord is also continuous with this outer covering of the spinal and cranial nerves
Epineurium
Thin, avascular covering comprised of cells and thin, loosely arranged collagen and elastic fibers. Deep to dura mater and continuous through foramen magnum with the same mater of the brain.
The arachnoid mater
Why is the arachnoid mater called this?
The collagen an delastic fibers are arranged in a spder web like pattern
What is the space between the dura mater and teh arachnoid mater called?
Subdural space
What does the subdural space between the dura mater and arachnoid mater contain?
Interstitial fluid
Inner most meninges, is a thin, transparent connective tissue layer that adheres to the surface of the spinal cord and brain. Consists of thin squamous to cuboidal cells within interlacing budnles of collagen fibers and some fine eleastic fibers.
Pia mater
What is found within the pia mater meninges layer that supplies oxygen and nutrients to the spinal cord?
Blood verssels
What part of the pia mater suspend the spinal cord in the middle of it’s dural sheath?
Triangular shaped membraneous extensions of the pia mater
What are the triangular shaped membraneous extensions that are thickenings of the pia mater that suspend the spinal cord in the middle of its dural sheath called?
Denticulate ligaments
These extensions of the pia mater, project laterally and fuse with the arachnoid mater and inner surface of the dura mater between the anterior and posterior nerve roots on either side
Denticulate ligaments
What is the function of the denticulate ligaments?
Protect the spinal cord against sudden displacement that could result in shock
This is the space found between the arachnoid mater and pia mater and is filled with cerebrospinal fluid
the subarachnoid space
Where is cerebrospinal fluid foudn?
The subarachnoid space
Where does the spinal cord extend from in adults?
The medulla oblongata and the superior border of the second lumbar vertebra
Where is the cervical enlargement found
From C4 to T1
What is found from the 4th cervical vertebra to the first thoracic vertebra?
Cervical enlargement of spinal cord
What arises from the cervical enlargement of the spinal cord?
Nerves to and from the upper limbs
What is the inferior enlargement of the spinal cord called?
Lumbar enlargement
Where does the lumbar enlargement extend from
The 9th to the 12 thoracic vertebra
What arises fromt he lumbar enlargement from from T9 to T12
The nerves to and from the lower limbs
Inferior to the lumbar enlargement of the spinal cord is where the spinal cord terminates as a tapering conical structure called:
Conus medullaris
Where does the conus medullaris terminate?
Between the first and second lumbar vertebra at the intervertebral disc
What arises fromt eh conus medullaris and is an extension of the pia mater that extends inferiorly, fuses with arachnoid mater, and dura mater and anchors the spinal cord to the coccyx?
Filum terminale
How many pairs of spinal nerves are there
31
How many pairs of cervical nerves are there?
8
How many pairs of thoracic nerves?
12
How many pairs of lumbar nerves
5
Sacral nerve pair numbers?
5
Coccygeal nerve pairs?
1
How are each spinal nerve connected to the spinal cord?
Two bundles of axons, called roots, are connected a segment of the spinal cord by even smaller bundles of axons called rootlets
What is the function of rootlets?
Connect larger bundles of axons called roots to a segment of the spinal cord
What are the two roots?
Posterior (dorsal)
Anterior (ventral)
These roots and rootlets only contain sensory axons which carries sensory information to the CNS
The posterior or Dorsal roots
What does the swelling called the posterior root ganglion, that each posterior root has, contain?
The cell bodies of the sensory neuronst
What do the anterior root and rootlets contain axons of?
Motor neurons that carry impulses from CNS to PNS
This structure consists of the roots of the lower spinal cord nerves that branch inferiorly and follow alongside the filum terminale
cauda equina
What does the white matter of the spinal cord contain?
Primarily bundles of myelinated axons of neurons
The wide groove on the anterior side of the white matter of the spinal cord
Anterior median fissure
A narrow furrow on the posterior/dorsal side of the white matter of the spinal cord
Posterior median sulcus
This is shaped like an H and consists of dendrites, cell bodies of neurons, unmyelinated axons, and neuroglia
Spinal cord grey matter
The cross bar of the gray matter H in the spinal cord is called
Gray commissure
What is found in the center of the gray commissure?
a small space called the central canal
What is the central canal?
It extends the entire length of the spinal cord and is filled with cerebrospinal fluid
What is the central canal continuous with at the superior end?
The fourth ventricle in the medulla oblongata
What is found just anterior to the gray commisure that connect the white matter of the right and left sides of the spinal cord?
The white commisure
What do clusters of neuronal cell bodies form in the gray matter of the CNS
Functional groups called nuclei
What do sensory neclei recieve?
sensory information from receptors via motor neurons
What do motor nuclei output?
Output infomation to effector tissues via motor neurons
What is the grey matter on each side of the spinal cord divided into?
Horns
These gray horns contain axons of incoming sensory neurons as well as cell bodies and axons of interneurons
Posterior gray horns
These gray horns contain SOMATIC MOTOR NUCLEI; clusters of cell bodies of somatic neurons that provide nerve impulses for contraction of skeletal muscles
Anterior gray horns
These grey horns are only present in thoracic and upper lumbar segments of the spinal cord
Lateral gray horns
What do lateral gray horns contain?
autonomic motor nuclei
What are clusters of cell bodies of autonomic motor neurons that regulat the acitivty of cardiac muscle, smooth mucles and glands called? This is found in the lateral gray horns of the spinal cord
autonomic motor neuclei
What are the names of the 3 broad regions that the white matter of the spinal cord is divided into
Anterior white column
posterior white column
lateral white column
What does each white column contain?
Tracts - Bundles of axons having a common origin or destination and carrying similar information.
Tracts
Bundles of axons in the CNS`
Nerves
bundles of axons in the PNS
These tracts consist of axons taht conduct nerve impulses toward the brain
Sensory (ascending) tracts
These tracts consist of axons that carry nerve impulses away from the brain
Motor (descending) tracts
Once sensory input triggers input into the posterior nerve root, what are the three possible paths that sensory neuron axons may proceed along
- May extend into white matter and ascend to the brain
- May enter the posterior grey horn and synapse with interneurons whose axons extend to the white matter and then asend to the brain
- May enter posterior grey horn and synapse with interneurons that in turn synapse with somatic motor neurons that are involved in spinal reflex pathways
What is every individual axon wihtin a nerve (myelinated or not) wrapped in?
Endoneurium
This is made up of a mesh of collagen fibers, fibroblasts and macrophages
Endoneurium
What are groups of axons with their endoneurium held together in?
Bundles called fascicles
What is each fascicle wrapped in?
perineurium (middle layer)
What does the perineurium consist of?
It is a thicker layer of connective tissue that contains up to 15 layers of fibroblasts within a network of collagen fibers
What is the third layer, the outer most covering of the entire nerve called?
Epineurium
What does the peineurium consist of?
Fibroblasts and thick collagen fibers
What do extensions of the epineurium fill?
The spaces between fasciles
What fuses with the epineurium as the nerve passes through the intervertebral foramen?
The dura mater
What do spinal nerves divide into after passing through intervertebral foramin?
Branches aka rami
What does the posterior ramus serve?
the deep muscles and skin of the posterior surface of the trunk
Anterior ramus serves
anterior surface of trunk and muscles and structures of upper and lower limbs
What branch of the nerve reenters the vertebral cavity through the intervertebral foramen and supplies that vertebrae, vertebral ligaments, blood vessels and spinal cord?
meningeal branch
What are other branches of the spinal nerve that is a component of the autonomic nervous system
rami communicantes
A network of anterior rami
plexus
The five principle plexussses
Cervical Plexus
Brachial Plexus
Lumbar Plexus
Sacral plexus
coccygeal plexus
Which spinal nerves do not enter a plexus?
T2-12 the intercostal nerves
What does T2 supply?
The intercostal muscles of the second intercostal space, the the skin of the axilla and posteromedial aspect of the arm
What do T3-6 supply?
they extend along the costal grooves of ribs and then tot he intercostal muscles and skin of the anteriror and lateral chest wall
What do T7-T12 supply?
Intercostal and abdominal muscles and overlying skin
What do the posterior rami of the intercostal nerves supply?
The deep back muscles and skin of the posterior aspect of the thoraxW
What is an area of skin that provides sensory input to the cns via one spinal nerve or the trigeminal nerve, called?
a dermatome
What makes up the cervical plexus?
The anterior rami of roots C1-C4, with contributions from C5
What does the cervical plexus supply?
the skin and muscles of the head and neck and superior part of the shoulders and chest
What nerves supply the brachial plexus?
The anterior rami of C5-C8 and T1
What does the brachial plexus supply
Almost the entire nerve supply of the shoulders and upper limbs
What nerves make up the lumbar plexus?
the anterior rami of spinal nerves L1-L4; minimal intermingling
What part of the body does the lumbar plexus supply?
The anterolateral abdominal wall, external genitals and part of lower limbs
What roots make up the sacral plexus?
L4-L5 and S1-S4
What does the sacral plexus (L4-5 and S1-4) supply?
The buttocks,perineum and lower limbs
Two principle function of the spinal cord in maintaining homeostasis
- nerve impulse propogation
- integration of information
What part of the spinal cord is the “highway” for nerve impulse propogation?
The white matter tracts
What is the function of the grey matter in the spinal cord?
To receive and integrate (summate the total EPSPs and IPSPs) information that is incoming and outgoing
What does the name of a white matter tract usually reflect?
It’s position in the white matter and where it beings and ends
Two main routes on each side of the spinal cord that nerve impulses from sensory receptors propogates along up to the brain
The Spinothalamic Tract
Posterior column
The posterior column of the spinal cord is made up of two tracts called:
- Gracile Fasciculus
- Cuneate fasciculus
Where are the gracile fasciculus and the cuneate fasciculus found and what are their functions?
They are 2 tracts in the posterior columns of the spinal cord that sensory impulses propogate up to the brain
What senses do the posterior columns gracile fasciculus and cuneate fasciculus transmit information about?
touch, pressure, vibration, and conscious propioception
Two types of descending pathways in the spinal cord for motor output from brain to skeletal muscle
Indirect
Direct
There are 3 direct motor (pyramidal) pathways that descend down the spinal cord from the cerebral cortex and affect voluntary movements
- lateral corticospinal
- anterior corticospinal
- corticobulbar tracts
There are 5 indirect motor pathways (extrapyramidal) that descend from the brainstem and cause automatic movements
- rubrospinal
- tectospinal
- vestibulospinal
- lateral reticulospinal
- medial reticulospinal
Functions of the indirect motor pathways in the body
Coordinate involuntary body movements with visual stimuli, maintain skeletal muscle tone, sustain contraction of postural muscles, and play a moajor role in equilibrium by regulating muscle tone in response to movement of the head
A fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimuli; can be inborn or learnt
A Reflex
When integration of a relex takes place in the gray spinal cord matter, the reflex is called a:
Spinal reflex
If integration of a reflex occurs in the brain stem, not the spinal cord, the reflex is:
A cranial reflex
What do somatic reflexes consist of?
Contraction of skeletal muscles
Reflexes that are generally not consciously perceived and involve responses of smooth muscle, cardiac muscle, and glands
Autonomic (visceral) reflexes
Eg. Defacating, heart rate, urinating, digestion, etc
What is the pathway followed by nerve impulses that produce a reflex?
A reflex arc (reflex circuit)
What are the five functional components of a relex arc?
- Sensory receptor
- Sensory neuron
- Integrating center
- Motor neuron
- Effector
Distal end of a sensory neuron (dendrite) or an associated sensory structure; responds to a specific stimulus by producing a graded potential
Sensory Receptor
What is a graded potential caused by stimuli affecting a sensory receptor also called?
generator or receptor potential
What happens if a generator/receptor potential reaches threshold for depolarization?
A nerve impulse behin in the sensory neuron
The nerve impulse of a sense travels down the axon of the sensory neuron to its terminal end which is found in the gray matter of the spinal cord or brainstem; at this point relay neurons send info to the brain to allow conscious awareness that the reflex that occured
Step 2 of reflex arc
Step 3 of reflex arc involves the integrating center which is:
One or more area of the gray matter within the CNS
A reflex pathway in which there is only one synapse in the CNS is called:
a monosynaptic reflex
This involves more than two types of neurons and more than one CNS synapse
A polysynaptic reflex arc
Impulses triggere by the integrating center propogate out of the CNS along this type of neuron to the part of the body that will respond
A motor neuron
This is the part of the body that responds to the motor nerve impulse and can be a muscle or a gland
Effector
If the effector of a reflex pathway is a muscle, the relfex is called a
somatic reflex
If the effector of a reflex pathway is a smooth muscle, cardiac muscle, or a gland, the reflex is called a
Autonomic (visceral) reflex
Why are reflexes so useful in examining the health of the nervous system and can even aid in diagnosis of disease?
They are predictable
Four important somatic spinal reflexes:
- Stretch reflex
- Tendon reflex
- the flexor (withdrawal) reflex
- crossed extensor reflex
This somatic spinal reflex causes contraction of a skeletal muscle (the effector) in response to the stretching of the muscle
Stretch reflex
The stretch reflex occurs via what reflex arc?
The monosynaptic reflex arc
Why is the stretch reflex considered a monosynaptic reflex arc?
Because it can be activated with the stimulation of only one single sensory neuron that forms one synapse int he CNS with a single motor neuron
How can stretch reflexes be elicited?
By tapping on tendons attached to muscles at the elbow, wrist, knee and ankle joints
What are sensory receptors in the muscles detect stretch or change in muscle length?
The muscle spindles
When stretched, the muscle spindle generates nerve impulses that propogate along a somatic sensory neuron through the posterior root of the spinal nerve and into the:
Integrating center (spinal cord)
In the integrating center (spinal cord), the sensory neuron makes an excitatory synapse with and thereby activates, a motor neuron in the anterior gray horn and…
If the excitation is strong enough, one or more nerve impulses arises in the motor neuron and travels down the axon through the anterior root and through peripheral nerves tot eh stimulated muscle
What do the axon terminals of the motor neuron form with the skeletal fibers of the stretched muscle?
neuromuscular junction
What is released by nerve impulses at the neuromuscular junction?
Ach - acetylcholine
What does Ach at the in the neuromuscular junction trigger?
One of more muscle action potentials in teh stretched muscle (effector) and causes the muscle to contract to counteract the stretching
What are all monosynpatic reflexes?
Ipsilateral
What makes a reflex an ipsilateral reflex?
The sensory nerve impulse enters the spinal cord on the same side the motor nerve impulses leave the spinal cord
What do smaller diameter motor neurons innervate in the muscle spindles and what do they do?
They innervate specialized muscle fibers in the muscle spindles
Although the stretch reflex pathway is only tweo neurons and one synapse, a polysynaptic arc affects the
antagonistic muscles that operate at the same time
The simultaneous contraction of one muscle and the relaxation of it’s antoganoist
reciprocal innervation
What is the function of reciprocal innervation?
to prevent conflict between opposing muscles
What do the sensory nerve impulses relayeed to the brain do in a stretch reflex?
Sends the brain input about the state of stretch or contraction of skeletal muscles and enables it to coordinate muscular movements as well as provide conscious awareness that the reflex has occured
What does the stretch reflex operate as?
A feedback mechanism to control the muscle length by causing muscle contraction
This type of reflex, in contrast to the stretch reflex, operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons can be torn
Tendon Reflex
The tendon reflex is less sensitive than the stretch reflex but can _____________ if tension is too great
Override
The sensory receptors for the tendon reflex are called this
Tendon (golgi) organs
Where are tendon golgi organs located
they lie within a tendon near its junction with a muscle
Reflex muscle spindles respond to muscle length where as tendon golgi organs respond to
Changes in muscle tension that are caused by passive stretch of muscle contraction
First step of tendon reflex
The tension on the tendon stimulates the tendon golgi organs and depolarizes the neuron
What does the depolarization of a tendon golgi organ cause?
A nerve impulse to arise and travel into the spinal cord along a sensory neuron
What happens within the spinal cord during tendon reflex
The sensory neuron activates an inhibitory interneuron that synapses with a motor neuron
What happens to the motor neuron synapsed with the interneuron
Inhibitory neurotransmitters hyperpolarizes and inhibits the motor neuron which then reduces the number of nerve impulses to the muscle
Final step in tendon reflex
The muscle relaxes
What reflex is responsible for responding to pain (eg stepping on a tack)
flexor reflex or withdrawal reflex
What type of arc pathway is the withdrawal or flexor reflex?
Polysynaptic Reflex arc
What is the main take away about a flexor or withdrawal reflex?
Several segments of the spinal cord are activated by tthe sensory impulse and the motor response is for the muscleS to flex and subsequently withdraw the limb from the danger
When nerve impulses from one sensroy neuron ascend and descend in the spinal cord and activate interneurons in several segments of the spinal cord we have what reflex??
Intersegmental reflex arc
What other reflex is initiated to prevent falls and keep balance when you step on a tack?
crossed extensior reflex
Incoming pain signals cross to he opposite side of the spinal cord through interneurons at different segments of the spinal cord above and below the ppoint of entry thus:
The motor neurons on the oppoosite side that are activated innervate extensor muscles that are activated by the release of acetylcholine to help extend those muscles to compensate for withdrawal of teh muscles on the other side of the body in response to the pain
What type of reflex arc is the crossed extensor reflex?
A contralateral reflex arc
What reflexes are ipsalateral?
Stretch
Tendon
Flexor/Withdrawal
What does it mean that crossed extensor reflexes are contralateral?
Sensory impulses enter on one side of teh spinal cord and motor impulses exit on the opposite side
