Chapter 13: The Spinal Cord & Spinal Nerves

What are the 3 functions of the spinal cord?

1. Processes reflexes

2. Integrates EPSPs & IPSPs

3. Conducts sensory impulses to the brain & motor impulses to effectors

what is the cauda equina?

roots of the lower spinal nerves

What is the spinal cord protected by?

• bone (vertebrae)

• connective tissue (meninges)

• fluid (cerebrospinal fluid)

What are the meninges?

3 connective tissue membranes covering the spinal cord and brain:

1. Dura mater (outermost; tough)

2. Arachnoid mater (middle; cobweb-like)

3. Pia mater (innermost; thin)

What is the name for a group of interconnected nerves that facilitate communication?

plexus

what are the plexuses of the spinal cord?

1. cervical plexus (C1-C5)

2. brachial plexus (C5-T1)

3. lumbar plexus (L1-L4)

4. sacral plexus (L4-S4)

Where does the spinal cord begin and terminate (end)?

begins: medulla oblongata

terminates: L2

How many spinal bones and spinal nerves of each section are there?

Bones:

• 7 cervical

• 12 thoracic

• 5 lumbar

• 5 sacrum

• 1 coccygeal

Nerves:

• 8 cervical

• 12 thoracic

• 5 lumbar

• 5 sacrum

• 1 coccygeal

what is the filum terminale?

(“Strand terminal”) an extension of the pia mater that extends inferiorly and blends with the arachnoid and dura to anchor the spinal cord to the coccyx

what is the conus medullaris?

tapered terminal end of the spinal cord

what is the first cervical vertebrae?

atlas

what is the second cervical vertebrae?

axis

What are the 2 enlargements of the spinal cord and what do each of them handle?

1. cervical enlargement (C4-T1) → sensory input & motor outpute to the UPPER extremities

1. lumbar enlargement (T9-T12) → motor output & sensory input TO & FROM the LEGS

Where is white and gray matter in the spinal cord VS. the brain?

spinal cord:

• white matter → OUTSIDE

• gray matter → INSIDE

brain:

• white matter → INSIDE

• gray matter → OUTSIDE

Distinguish the cervical segment of a spinal cord

Distinguish the thoracic segment of a spinal cord

Distinguish the Lumbar segment of the spinal cord

Distinguish the Sacral and Coccygeal segments of the spinal cord

What is the function of spinal nerves and how many pairs are there?

• function: connect the CNS to sensory receptors, muscles, & glands and are part of the PNS

• 31 pairs (62 total)

Describe how spinal nerves are connected to the spinal cord

• roots (2 bundles of axons) connect each spinal nerve to a seegment of the cord by even smaller bundles of axons called ROOTLETS

Contrast posterior (dorsal) and anterior (ventral) roots/rootlets

posterior (dorsal):

• contains only SENSORY axons

• conducts nerve impulses from sensory receptors in skin, muscles, & organs to CNS

• has GANGLION; contains cell bodies of sensory neurons

anterior (ventral):

• contain only MOTOR axons

• conducts nerve impulses from the CNS to effectors

what is a lumbar puncture?

needle inserted into subarachnoid space for the purpose of withdrawing CSF (for diagnosis or to reduce pressure or to introduce a drug or contrast agent)

• CSF often collected for meningitis or other CNS diseases

what does the gray matter of the spinal cord consist of ?

• dendrites

• cell bodies of neurons

• unmyelianted axons

• neuroglia

Internal spinal cord anatomy: Locate/describe the anterior median fissure

wide groove on anterior (ventral) side

Locate/describe the posterior median sulcus

narrow furrow on the posterior (dorsal) side

locate/describe the gray commissure

froms crossbar of the H

locate/describe the central canal

• small space in the center of the gray commissure

• extends the entire length of the spinal cord

• filled with CSF

locate/describe the anterior white commisure

• anterior to the gray commissure

• connects the white matter of the right and lefct sides of the spinal cord

locate/describe the posterior gray horns

• contain axons of incoming sensory neurons & cell bodies & axons of interneurons

locate/describe the anterior gray horns

• contain soma\tic motor nuclei — provide nerve impulses for contraction of skeletal muscles

locate/describe the lateral gray horns

• between posterior/anterior gray horns

• only present in thoracic & upper lumbar & mid-sacral segments

• contain autonomic motor nuclei — regulate cardiac muscle, smooth muscle, & gland activity

locate and describe funiculi

3 broad areas of white matter; contains bundles of acons (tracts

1. anterior white funiculi

2. posterior white funiculi

3. lateral white funiculi

Contrast tracts & nerves

• tracts → bundles of axons in CNS

  • sensory tracts: ascend to brain

  • motor tracts: descend from brain

• nerves → bundles of axons in PNS

Trace the processing of sensory/motor output by the spinal cord.

1. sensory receptors detect a sensory stimulus

2. sensory neurons convey sensory input along axons from sensory receptors → spinal nerves → posterior root. Then proceeds along 3 possible paths (3, 4, or 5)

3. SENSORY (ASCENDING) TRACT: axons of sensory neurons may enter the posterior gray horn then extend into white matter then ascend to brain

4. SENSORY (ASCENDING) TRACT: axons of sensory neurons may enter the posterior gray horn and synapse with interneurons whose axons extend into the white matter then ascend to the brain

5. MOTOR (DESCENDING TRACT): axons of sensory neurons may enter the posterior gray horn and synapse with interneurons that synapse with somatic motor neurons which are involved in spinal reflex pathways

6. Motor output from the spinal cord to skeletal muscles involves somatic motor neurons of the anterior gray horn.

7. when activated, somatic motor neurons convey motor output in the form of nerve impulses along their axons, which sequentially pass through the anterior gray horn and anterior root to enter the spinal nerve. from the spinal nerve, axons of somatic motor neurons extend to skeletal muscles of the body

8. motor output from the spinal cord to cardiac & smooth muscle, & glands involves autonomic motor neurons of the lateral gray horn. when activated, autonomic motor neurons convey motor output along their axons, which then pass through the lateral gray horn, anterior gray horn,, ande anterior root to enter the spinal nerve

9. from the spinal nerve, axons of autonomic neurons from the spinal cord synapse with another group of autonomic motor neurons located in the PNS. the axons of the 2nd group in turn synapse with with cardiac muscle, smooth muscle, & glands.

____ wrap each axon which are arranged in bundles called ___ surrounded by a ___, with the entire nerve sheathed by a CT ____

1. endoneurium

2. fascicles

3. perineurium

4. epineurium

When the spinal nerves exit the CNS into the PNS, they almost immediately split into 3 major branches:

1. anterior ramus → serves the muscles & structures of the upper and lower limbs and the skin of the lateral and anterior surfaces of the trunk (form the cervical, brachial, etc. plexuses)

2. posterior ramus → serves deep muscles & skin of posterior surface of trunk

3. rami communicantes

what is a dermatome

cutaneous area of skin that provides sensory input to the CNS via the posterior roots of one pair of spinal nerves or via the trigeminal (V) nerve

Describe the cervical plexus and its major nerve

• C1-C5

• supplies the skin and muscles of the head, neck, superior portion of the shoulders & chest, & diaphragm

• contains phrenic nerve (origin: C3-C5) — causes contraction diaphragm

Describe the brachial plexus and its major nerves

• C5-T1

• provides almost entire nerve supply to shouldeers & upper limbs

• major nerves

  • long thoracic; origin C5-C7

    • serratus anterior muscle

  • median; origin C5-T1

    • lesion = carpal tunnel syndrome

    • digits

  • radial; origin C5-T1

    • digits

  • ulnar; origin C8-T1

    • digits

    • “funny bone”

What is Erb’s palsy?

paralysis of the arm that most often occurs as an infant’s head & neck are pulled toward the side at the same time as the shoulders pass through the birth canal

Describe the lumbar plexus and its major nerves

• L1-L4

• supplies antrolateral abdominal wall, external gentials, part of lower limbs

• major nerves:

  • femoral (L2-L4): largest lumbar plexus nerve, distributed to flexor muscles of hip joint & extensor muscles of knee, skin over anteior & medial aspect of thight, & medial side of leg & foot

  • obturator (L2-L4): adductor muscles of hip joint, skin over medial aspect of thigh

Describe the sacral plexus & it's major nerve

• L4-S4

• supplies buttocks, perineum, lower legs

• major nerve:

  • sciatic nerve (L4-S3): 2 NERVES — tibial & common fibular bound tgt by sheath of CT (Splits into 2 at knee). sends branches to hamstrings and adductor magnus

How does info travel in the spinal cord?

1. WHITE matter tracts conduct nerve impulses to and from the brain

2. GRAY matter receives & integrates incoming/outgoing info to perform spinal reflexes

what is the origin and destination of the spinothalamic tract? which kind of tract is it?

origin: spine

destination: thalamus

therefore: sensory ascending tract

What is a reflex?

fast, involuntary, unplanned response to a stimulus

• maintains homeostasis

• gray matter of spinal cord = integrating center for spinal reflexes

List and breifly explain the 5 components of a reflex arc

1. Sensory Receptor → resp. to stimulus

1. Sensory Neuron → axon conduscts impulses

2. Integrating Center → 1+ regions within CNs that relay impulses from sens. to motor neurons

3. Motor Neuron → axon conducts impulses from integrating center to effector

4. Effector → muscle or gland that responds to motor impulses

List and differentiate the 6 types of reflex arcs

• ipsilateral → sensory neuron ENTERING & motor neuron EXITING on the SAME SIDE of the integrating center

• contralateral → sensory neuron entering ONE side & motor neuron exiting on the OTHER

• monosynaptic → single synapse between sensory and motor neuron

• polysynaptic → 1+ association neurons relaying messages to other association/motor neurons

• intersegmental → signal of a single sensory neuron activates several motor neurons via the association neurons in several segments of the spinal cord

• reciprocal innervation → neural circuit simultaneously contracts one muscle & relaxes its antagonists

Explain what a stretch reflex is

causes contraction & relief of a muscle that has been stretched

• stimulates receptors in muscle spindle of the agonist (stretched muscle)

• monosynaptic & ipsilateral

1. stretching stims sensory receptor (muscle spindle)

2. sensory neuron excited

3. integrating center: sensory neuron activates motor neuron

4. motor neuron excited

5. effector: same muscle contracts and relieves the stretching

Explain what a tendon reflex is

causes relaxation of the muscle attached to the stimulated tendon

• polysynaptic & ipsilateral

• prevents injury due to excess muscle tension or over-contraction

1. increased tension stimulates sensory receptor (tendon organ)

2. sensory neuron excited

3. integrating center: neuron activates inhibitory neuron

4. motor neuron inhibited

5. agonist muscle reflazes and relieves excess tension, antagonist muscles contract

Explain what a Flexor (withdrawal) reflex is

causes withdrawal of a limb to avoid injury or pain (i.e pulling hand away from stove)

• polysynaptic, ipsilateral, & intersegmental

1. stepping on tack stims sensory receptor (dendrites of pain-sensitive neuron)

2. sensory neuron excited

3. integrating center: sensory neuron activates interneurons in several spinal cord segments

4. motor neurons excited

5. effectors: flexor muscles contract & withdraw leg

Explain what a crossed-extensor reflex is

maintains balance during a withdrawal reflex

• polysynaptic, contralateral, intersegmental

flexor muscles contract/withdraw right leg

1. stepping on tack stims sensory receptor

2. sensory neuron excited

3. integrating center: spinal cord; sensory neuron activates several interneurons

4. motor neuron excited

5. effectors: extensor muscles contract and extend left leg

Describe the patellar reflex

• leg extends in response to stretch of the patellar tendon

• can be blocked by damage in corticospinal tracts from diabetes, neurosyphilis, or damage to the lumbar region

describe the achilles reflex

• causes contraction of the calf when a force is applied to the achilles tendon

• absent after damage to the lower cord or lumbosacral plexus

describe the babinski/plantar flexion reflex

• normal in adults if they flex (curl) big toe when sole of foot stimulated (negative babinski)

• if extend/point up → damage to corticospinal tract (positive babinski) (normal in infants

Indicate the extent of paralysis from traumatic injury for each sement of the spinal cord

Cervical → no function from the neck down

Thoracic → some arm and chest muscle control

Lumbar → most thigh muscles

Sacral → most leg muscles

What does “transection” of the spinal cord mean?

ascending and descending tracts are partially or completely severed

• at base of skull → death by asphyxiation

• upper cervical area → quadriplegia (paralysis of four limbs)

• between cord enlargements results in some form of paraplegia (paralysis of both lower limbs)

List the 4 major spinal disorders

1. spinal cord compression

2. degenerative diseases

3. shingles

4. poliomyelitis

What is spinal cord compression

the spinal cord may be compressed by bone, blood (hematomas), pus (abscesses), tumors (Cancerous or not), or a ruptured or herniated disk

What are degenerative diseases?

• mulitple sclerosis → deymyelination of olgidendroglia

• amyotropic lateral sclerosis (ALS) → progressive nervous system disease that affects nerve cells in the brain and spinal cord, causing loss of muscle control

What is shingles?

• acute infection of the PNS caused by herpes zoster virus (also causes chicken pox)

• causes pain, discoloration of the skin and line of skin blisters

• never crossses mid-line; only on one side of the body

What is poliomyelitis (Polio)

• caused by the poliovirus

• virus spreads from person to person & can infect a person’s spinal cord, causing paralysis