A&P2—Chapter 13: Spinal Cord

What covers the neurilemma?

Basal lamina (this enwraps the neurilemma of a single nerve fiber)

Spinal Cord Functions

*Conduction of afferent and efferent signals *Coordination of locomotion (neural integration and pattern generation-input from multiple sources, integrated, and executed output) *Reflexes

What is a plexus?

A branching network of axons from anterior rami

What is a fascicle?

A bundle of a bunch of single nerve fibers (these exist in most nerves)

What is a sensory nerve?

A nerve composed only of afferent fibers. These are rare! Include olfactory and optic nerves.

What is a motor nerve?

A nerve that carries only efferent fibers.

What is a mixed nerve?

A nerve that consists of both afferent and efferent fibers, therefore conducting signals in two directions. Most of our nerves are mixed nerves.

The part of the spinal cord supplied by each pair of spinal nerves is called...

A segment

What covers the fascicles within a nerve?

A sheath called the perineurium (composed of layers of overlapping, squamous epithelium-like cells)

What is the dorsal root ganglion?

A short distance away from the spinal cord (barely even out of it), the posterior root swells into a dorsal root ganglion. It contains the somas of sensory neurons.

What covers the basal lamina of a single nerve fiber?

A thin sheath of loose connective tissue called the endoneurium

What type of info enters via the posterior (dorsal) horn of the spinal cord?

Sensory

What do ascending tracts carry?

Sensory information up the cord

Describe the arachnoid mater. What lies between this and the pia mater?

Simple squamous epithelium adhering to the inside of the dura. It looks like a cobweb because of the large number of fibers spanning the gap between the arachnoid and the pia mater and the denticulate ligaments that extend from the pia through the arachnoid, anchoring the cord. The subarachnoid space lies between the arachnoid membrane and the pia mater and is filled with CSF.

What type of info is carried to the anterior (ventral) horn of the spinal cord?

Somatic motor neurons (skeletal muscles)

Describe poliomyelitis

Viral infection, which destroys motor neurons in the brainstem and ventral horn of the spinal cord. S/S include muscle atrophy, pain, weakness, loss of some reflexes, and respiratory arrest.

Describe Rabies

Virus contracted from animal bite. Spreads via somatic nerve fibers to the CNS then to autonomic nerve fibers. Leads to seizures, coma, and death.

At what level does the spinal cord typically terminate? What happens to it after this?

~L1; The tapered tip is called the medullary cone. After this, the bundle of nerve roots that drop down from the lumbar enlargement to S5 is called the cauda equina (it innervates the pelvic organs and lower limbs)

How many pairs of spinal nerves are there?

31 (8 cervical, C1 being between the skull and the atlas; 12 thoracic; 5 lumbar; 5 sacral; and 1 coccygeal)

4 properties of reflexes

1. Require stimulation 2. Quick 3. Involuntary 4. Stereotyped (occur in essentially the same way every time)

Describe the five steps of a general somatic reflex arc.

1. Somatic receptors stimulated in the skin, muscle, or tendon 2. Afferent nerve fibers are stimulated and send a signal to the spinal cord's dorsal (posterior) horn 3. Interneurons integrate the signal in the gray matter of the cord or brainstem 4. Efferent nerve fibers are stimulated, carrying a motor impulse to a skeletal muscle 5. Effectors-skeletal muscle receives information and contracts

What are the 6 steps of the flexor/crossed extension reflex?

1. Stepping on glass stimulates pain receptors in right foot 2. Sensory neuron activates multiple interneurons 3. Ipsilateral motor neurons to flexor excited. 4. Ipsilateral flexor contracts. 5. Contralateral motor neurons to the extensor are excited. 6. Contralateral extensor contracts.

Describe the 7 steps of the tendon reflex using the knee-jerk reflex as an example. (Seen in figure 13.21)

1. Tap on patellar ligament excites nerve endings of muscle in quadriceps femoris. 2. Stretch signals travel to spinal cord via afferent fiber and dorsal root. 3. Primary afferent neuron stimulates a motor neuron in the spinal cord. 4. Efferent signals stimulate quads to contract, producing the knee jerk. 5. At the same time, a branch of the afferent nerve fiber stimulates inhibitory motor neuron in spinal cord. 6. That neuron inhibits the motor neuron that supplies hamstring muscles. 7. Hamstring contraction is inhibited so that they don't antagonize the quads.

How are ascending sensory signals sent up the spinal cord to the brain?

1st order neuron: Detects a stimulus and transmits the signal to the spinal cord 2nd order neuron: Spinal cord to the thalamus ("gateway" at the upper end of the brainstem) 3rd order neuron: Carries the signal the rest of the way to the sensory integration centers of the cerebral cortex

How many pairs of spinal nerves exit the spinal cord?

31

A. What is the function of the vestibulospinal tract? B. Where is it?

A. Balance and posture; Control of head position B. Anterior

A. What is the function of the reticulospinal tract? B. Where is it?

A. Balance and posture; Regulation of awareness of pain B. Anterior and lateral

A. What are the functions (ie: what travels up) the dorsal (posterior ascending) column? B. Where is it?

A. Deep touch, visceral pain, vibration, sensations of limb and trunk position and movement B. Posterior spinal cord (duh, dorsal)

A. What is the function of the corticospinal tract? B. Where is it?

A. Fine control of limbs B. Lateral and anterior (see fig. 13.4)

A. What is the function of the spinocerebellar tract? B. Where is it?

A. Proprioception (feedback from the muscles) B. Lateral spinal cord

A. What is the function of the spinoreticular tract? B. Where is it?

A. Sensation of pain from tissue injury B. Lateral and anterior (mostly anterior) *This is mostly just an FYI. This tract is not listed as need to know by Dr. Cone.

A. What are the functions of the spinothalamic tract? B. Where is it?

A. Sensations of light touch, tickle, itch, temperature, pressure, and pain B. Lateral and anterior (mostly anterior) spinal cord

Describe paresthesia

Abnormal sensations of prickling, burning, numbness, or tingling. From nerve trauma or other peripheral nerve disorder.

Describe Guillan-Barre syndrome

Acute demyelinating nerve disorder usually triggered by a virus. S/S-Muscle weakness, elevated heart rate, unstable blood pressure, SOB, and sometimes death from respiratory paralysis.

Name the nerves of the Coccygeal Plexus.

Anterior rami of S4, S5, and the Coccygeal nerve (tiny plexus).

Describe peripheral neuropathy

Any loss of sensory or motor function due to nerve disorders

Name and describe the nerves found in the Cervical Plexus.

C1-C5 including: Lesser occipital-Sensory innervation of the upper ear, and the skin behind the ear and back of the neck Great auricular-Sensory innervation of most of the ear, some of the face Transverse cervical-Sensory innervation of front and side neck and below chin **Ansa cervicalis-Mixed; Hyoid bones Supraclavicular-Sensory innervation of the lower front and side of the neck, shoulder, and chest **Phrenic-Mixed; Diaphragm

Name and describe the nerves found in the Brachial Plexus.

C5-T1 including (all mixed nerves): Musculocutaneous-Sensory innervation of anterolateral forearm and elbow joint; Muscular innervation of Brachialis, biceps, and coracobrachialis Axillary-Sensory innervation of lateral shoulder, arm, and shoulder joint; Motor innervation of deltoid and teres minor Radial-Sensory innervation of posterior arm; Posterior and lateral forearm and wrist; Joints of elbow, wrist, and hand....Motor innervation of extensor muscles of posterior arm and forearm Median-Sensory innervation of lateral 2/3 of hand; tips of digits I-IV; Joints of hand....Motor innervation of Forearm flexors, thenar group and lumbricals I-II of hand Ulnar-Sensory innervation of palmar and medial hand and digits III-V; Joints of elbow and hand....Motor innervation of some forearm flexors; adductor pollicis; hypothenar group; interosseous muscles; lumbricals III-IV

Where are the two spinal cord enlargements? Why are they larger?

Cervical enlargement in the inferior cervical region and the lumbar enlargement. The cervical enlargement gives rise to nerves of the upper limbs while the lumbar enlargement gives rise to nerves of the pelvic region and lower limbs.

Name the plexuses

Cervical plexus Brachial plexus Lumbar plexus Sacral plexus Coccygeal plexus (tiny)

What are the four regions of the spinal cord?

Cervical, Thoracic, Lumbar, Sacral

Name the major descending (motor) tracts.

Corticospinal Reticulospinal Vestibulospinal Tectospinal (don't need to know this one)

Describe ALS

Degeneration of motor neurons and atrophy of the muscles; Sclerosis (scarring) of the lateral regions of the spinal cord. Occur when astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue so it accumulates to nearly toxic levels. S/S include proximal muscle weakness, hand dysfunction, difficulty speaking/swallowing, etc. Sensory and intellectual functions are intact!

What are the names of the ascending (ie: sensory) tracts?

Dorsal column (which is made up of the gracile fasciculus and cuneate fasciculus) Spinothalamic Spinoreticular Spinocerebellar

Describe gray matter.

Dull color. Unmyelinated axons and cell bodies. Site of synaptic contact between neurons (and consequently the site of all neural integration in the spinal cord).

Name the meninges from most superficial to deepest.

Dura mater, arachnoid mater, pia mater (right next to spinal cord)

What two nerves of the sacral plexus make up the sciatic nerve?

Fibular and Tibial nerves

Describe neuralgia

General term for nerve pain, often caused by pressure on spinal nerves from herniated intervertebral discs or other causes.

Describe spinal meningitis

Inflammation of the spinal meninges due to viral, bacterial, or other infection

What does the posterior (dorsal) ramus do?

Innervates the muscles and joints in the spine and skin of the back

What significant thing does a spinal nerve do as it nears its attachment to the spinal cord?

It branches into a posterior (dorsal) root and anterior (ventral) root.

What does the meningeal branch do?

It reenters the vertebral canal and innervates the meninges, vertebrae, and spinal ligaments with sensory and motor fibers.

Be sure to...

Know the following tables (all are listed in Dr. Cone's Chapter 13 notes): ***Figure 13.1 (Gross spinal anatomy) ***Figure 13.2 (Cross-sectional) *Table 13.1, function only *Figure 13.4, 13.5, and 13.6 *Figure 13.10 Also might want to check out: Figure 13.5 Figure 13.6 Figure 13.13a for a view of the sympathetic chain ganglion (covered in a diff chapter) Figure 13.21 Figure 13.22 I covered most of this stuff here but some of it can only really be looked at visually.

Name and describe the nerves found in the Lumbar Plexus.

L1-L4 including: Iliohypogastric (mixed)-Sensory innervation of lower anterior abdominal and posterolateral gluteal regions; Motor innervation of internal and external abdominal oblique & transverse ab muscles Ilioinguinal (mixed)-Sensory innervation of upper medial thigh; Male scrotum and root of penis; Female labia majora....Motor innervation of internal abdominal oblique Genitofemoral (mixed)-Sensory innervation of middle anterior thigh; male scrotum; female labia majora....Motor innervation of male cremaster muscle Lateral femoral cutaneous (sensory)-Sensory innervation of anterior and upper lateral thigh **Femoral (mixed)-Sensory innervation of anterior thigh....Motor innervation of iliacus, pectineus, quad femoris, and sartorius **Obtutrator (mixed)-Sensory innervation of Medial thigh, hip and knee joints....Motor innervation of obturator externus, medial thigh muscles

Name the nerves found in the Sacral Plexus.

L4, L5, and S1-S5 including: Superior gluteal (Mixed)-Motor innervation of gluteus minimus, medius, and tensor fasciae latae Inferior Gluteal (Mixed)-Motor innervation of gluteus maximus Posterior cutaneous (Sensory)-Sensory innervation of gluteal region, perineum, posterior and medial thigh, popliteal fossa, and upper posterior leg **Tibial (Mixed)-Sensory innervation of posterior leg; plantar skin; knee and foot joints....Motor innervation of hamstring muscles; most intrinsic foot muscles **Fibular (mixed)-Sensory innervation of anterior distal third of leg; dorsum of foot; knee joint; toes I-II....Motor innervation of biceps femoris, anterior and lateral muscles of leg; extensor digitorum brevis of foot Pudendal (Mixed)-Sensory innervation of skin of penis and scrotum; clitoris; labia majora and minor and lower vagina....Motor innervation of muscles of perineum

What do descending tracts carry?

Motor impulses down (ie: Secrete, Contract)

What does the anterior (ventral) ramus do?

Much larger! Innervates the anterior and lateral skin and muscles of the trunk and limbs.

What does the lateral horn contain?

Neurons of the sympathetic nervous system (their axons are sent out of the anterior root along with somatic efferent fibers) *Note that the lateral horn of the gray matter is only visible from T2 to L1.

What are the three layers of meninges of the spinal cord?

Pia mater, arachnoid mater, and dura mater (also called the dural sheath)

Name two major diseases discussed that involve destruction of motor neurons

Poliomyelitis and amyotrophic lateral sclerosis (ALS)

Describe what happens in spina bifida.

Related to a lack of folic acid.One or more vertebrae fail to completely enclose the spinal cord. In serious cases (spina bifida cystica), a sac protrudes from the spine, and may contain dura mater, CSF, parts of the spinal cord, and nerve roots.

Where in the spinal cord is white matter found? Describe the anatomy of the white matter.

Surrounds the gray matter. It is bundles of axons that go up and down the cord, providing trackways of communication up and down the CNS. These bundles are called columns/funiculi. There is a posterior (dorsal), lateral, and anterior (ventral) column and each of these are further divided into subdivisions called tracts/fasciculi.

What is the crossed extension reflex?

The contraction of extensor muscles in the limb opposite from the one that is withdrawn (for instance when you step on a piece of glass). This prevents you from falling over and helps you maintain balance. It is paired with the flexor reflex, which is the quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus.

Describe the anatomy of the core (butterfly part).

The core consists of two dorsal (posterior) horns and two ventral (anterior) horns. Right and left sides of the core are connected by a gray commissure. The central canal is in the middle of the commisure-usually collapsed in adults, in kids it is filled with CSF.

Describe the dural sheath.

The dura mater forms a loose-fitting sleeve around the spinal cord called the dural sheath. It is tough, collagenous membrane.

What covers the entire nerve?

The epineurium covers a bunch of fascicles, creating a nerve *All this can be viewed on pg 489, Figure 13.8

Where in the spinal cord is gray matter found?

The middle butterfly core part of the spinal cord is gray matter.

What happens after the spinal nerves emerge from the intervertebral foramen?

The nerve divides into an anterior ramus, a posterior ramus, and a small meningeal branch. **Note: As the spinal nerve approaches the spinal cord, it branches into anterior and posterior roots and then enters the gray matter, as we saw earlier. As the spinal nerve exists the vertebral column, it splits into anterior and posterior rami. So basically it's only conjoined for a little bit. If that doesn't make sense, check out Figure 13.11 on pg 492.

Describe the pia mater.

The pia mater a delicate membrane next to the spinal cord.

What is the tendon reflex?

The reflexive contraction of a muscle when its tendon is tapped. It's a type of stretch reflex. This is the type of reflex you think of most often (the knee-jerk reflex).

What is the neurilemma?

The sheath of Schwann cells around a nerve fiber, myelinating it

What is a dermatome?

The specific area of skin innervated by a spinal nerve. (C1 doesn't innervate the skin). See Figure 13.9 on pg 500

What is the thecal sac? Why are epidurals and spinal taps done here?

The thecal sac is the dura matter sleeve over the cauda equina. Between the sheath and the vertebral bones there is an area called the epidural space occupied by blood vessels, adipose tissue, and loose connective tissue. Epidurals are given here to block pain in the lower half of the body without damaging the spinal cord (which ends above the thecal sac/cauda equina).

Just a friendly reminder...

To study the crap out of page 481, figure 13.2!

Describe the descending motor pathway.

Upper motor neuron: travels from cerebral cortex to VENTRAL horn of the spinal cord Lower motor neuron: travels from VENTRAL horn to neuromuscular junction or gland

What is the stretch reflex?

When a muscle is suddenly stretched it "fights back" by contracting, increasing tone, and feeling stiffer than unstretched muscle. Stretch reflexes are important to maintain equilibrium and posture.

What is decussation?

When a tract crosses over from the left side of the body to the right or vice versa. (This happens with some tracts but not all). This can be clinically significant because the left side of the brain can receive sensory info from the right side of the body and send motor commands to the right side. Therefore, a stroke that damages the right side of the brain can cause left side paralysis. (and vice versa)

Describe white matter.

White in color. Made of myelinated bundles of axons (tracts).

A picture of the descending pathway can be seen on pg 487, figure 13.6

Yay!

An ascending pathway diagram can be seen on pg 485 (figure 13.5) and a diagram of the locations of the tracts is on pg 484 (figure 13.4)

Yep!