Chpt 13 Spinal Cord

Landmark that attaches the brain stem to the spinal cord (or vice versa)

Foramen magnum

Groove on posterior side of vertebrae, more narrow (shallow depression)

Posterior median sulcus (PMS)

Deeper groove on anterior side (deep depression)

Anterior median fissure

The gross anatomy ends between what two vertebrae?

L1 and L2

Enlargements are caused by what and involve what?

Gray matter

Involvement with sensory and motor nerves of limbs

Cervical enlargement is nerves in what regions?

Shoulders and upper limbs (more neurons)

Lumbar enlargement involves nerves in what regions?

Pelvis and lower limbs

Thin, conical spinal cord below lumbar enlargement, at end of spinal cord between L1 and L2

Conus medullaris

Thin thread of fibrous tissue at end of conus medullaris, attaches to coccygeal ligament, continuation of innermost membrane (PIA matter)

Filum terminale

Like a horse’s tail, nerve roots extend below conus medullaris

Cauda equina

What structure allows for the passage of the spinal nerves?

Intervertebral foramen

How many spinal cord segments are there?

31

How many spinal nerves are there?

16

Cervical - 8

Thoracic - 4

Lumbar - 10

Sacral - 10

Which nerves are named for inferior vertebra and which are named for superior vertebra?

Cervical - inferior (except C8)

All other nerves - superior

What are the two roots of spinal nerves?

Ventral and dorsal

Which root contains axons of motor neurons?

Ventral

If a spinal nerve is severed what could happen?

A person could lose motor AND sensational function (ventral and dorsal roots)

Which root contains axons of sensory neurons?

Dorsal

What contains cells bodies of sensory neurons?

Dorsal root ganglia

Unipolar neurons are what kind of neurons?

Sensory

Dorsal and ventral roots join to form what?

A spinal nerve

Mixed nerves contain what two fibers?

Afferent (sensory) and efferent (motor) fibers

These specialized membranes isolate spinal cord from surroundings

Spinal meninges

What are the three functions of spinal meninges?

Protecting spinal cord

Carrying blood supply

Continuous cranial meninges

A viral or bacterial infection of the meninges

Meningitis

What are the three meningeal layers?

1. Dura mater (outer layer of spinal cord)

2. Arachnoid mater (middle layer, looks like spider’s web)

3. Pia mater (inner layer)

The subarachnoid space is found where and filled with what?

Between arachnoid mater and pia mater

Contains collagen/elastin fiber network (arachnoid trabeculae)

Filled with cerebrospinal fluid (CSF)

What space contains loose connective and adipose tissue?

Epidural 

What is the space between the arachnoid mater and dura mater?

Subdural

These ligaments extend from pia mater to dura mater to stabilize side-to-side movement

Paired denticulate ligaments

Along surface of spinal pia mater and within subarachnoid space

Blood vessels

This type of matter is superficial and contains myelinated and unmyelinated axons

White matter

What are bundles of axons located in white matter?

Tracts

This type of matter surrounds the central canal, contains neuron cell bodies, neuroglia, unmyelinated axons, and has projections (gray horns)

Gray matter

These are clusters of neuron cell bodies found in gray matter?

Nuclei

What are the three sections of gray horns?

Posterior (somatic and visceral sensory nuclei)

Anterior (somatic motor nuclei)

Lateral (thoracic and lumbar segments, visceral motor nuclei)

These axons cross from one side of the spinal cord to the other before reaching gray matter

Gray commissures

These columns lie between posterior gray horns and posterior median sulcus

Posterior white columns

These columns lie between anterior gray horns and anterior median fissure

Anterior white columns

Area where axons cross from one side of the spinal cord to the other

Anterior white commissure

Area between anterior and posterior columns

Lateral white columns

Every spinal nerve is surrounded by what, supports what, and contains what?

Three connective tissue layers

Supports structures

Contains blood vessels

The outer layer of spinal nerves containing a dense network of collagen fibers

Epineurium

Bundle of axons in PNS

Nerves

The middle layer that divides nerve into fascicles (axon bundles)

Perineurium

The inner layer surrounds individual axons

Endoneurium

This spinal nerve branch goes back to supply meninges to spinal cord

Meningeal

Bilateral region of skin monitored by a specific pair of spinal nerves

Dermatomes

What vertebrae does not have a dermatome?

C1

Segmental distribution for all spinal nerves

Dorsal rami

T2-T12 and remaining intermingle and form 4 nerve plexuses

Ventral rami

Front side, back intercostal + subcostal nerves to innervate intercostal muscles + underlying skin

T2-T12 (NO PLEXUSES)

Innervate upper and lower extremities

Cervical plexus

Brachial plexus

Lumbar plexus

Sacral plexus

Includes ventral rami of spinal nerves C1-C5

Innervates neck, thoracic cavity, and diaphragmatic muscles (C3, C4, C5 keeps the diaphragm alive)

Cervical plexus

What are the two major nerves of the cervical plexus?

Phrenic nerve (controls diaphragm)

Ansa cervicalis (loop-like structure)

Includes ventral rami of spinal nerves C5-T1

Innervates pectoral girdle and upper limbs

Brachial plexus

Trunk distribution of brachial plexus

Superior

Middle

Inferior

Two divisions of trunks

Anterior

Posterior

Three cords of brachial plexus

Lateral

Medial

Posterior

Brachial plexus pneumonic

Real (Roots/ventral rami) Tired (Trunks) Drink (Divisions) Coffee (Cords)

This nerve of the brachial plexus is part of the lateral cord and supplies nerves to the anterior part of the arm

Musculocutaneous nerve

This nerve of the brachial plexus is part of the lateral and medial cords and supplies nerves to the lateral anetior part of the hand (thumb)

Median nerve

This nerve of the brachial plexus is part of the medial cords and supplies nerves to the medial anterior + remaining hand muscles

Ulnar nerve

This nerve of the brachial plexus is part of the posterior cord and supplies nerves to the shoulder region

Axillary nerve

This nerve of the brachial plexus is part of the posterior cords and supplies nerves to the back of the arm and forearm

Radial nerve

This spinal section includes ventral rami of spinal nerves T12-L4

The Lumbar Plexus

Two major nerves of the lumbar plexus

Femoral nerve: anterior compartment of thigh

Obturator nerve: Medial compartment of thigh, adductors

This spinal section includes ventral rami of spinal nerves L4-S4

The Sacral Plexus

Two major nerves at the sacral plexus

Pudendal nerve: supplies pelvic floor

Sciatic nerve: Supplies back of thigh, at the knee the sciatic nerve divides

What are the two branches of the sciatic nerve when it divides?

Fibular nerve: Outside of leg, anterior (superficial), wraps around fibula

Tibial nerve: back of leg

If this is injured, no dorsiflexion (foot drop)

Fibular nerve

Rapid, automatic (reproducible) responses to specific stimuli

Building blocks for neural function

One of these reflexes produces one motor response

Neural reflexes

The wiring of a single reflex

Reflex arc

A reflex arc begins here and is where it can detect the stimulus

Receptor

A reflex arc ends here

Effector

The 5 steps of neural reflexes

1. Receptor

2. Sensory neuron (afferent)

3. Integration center

4. Motor neuron (take response from integration center to target)

5. Effector

Five Classification of Reflexes

1. By early development

2. Motor response

3. Complexity of neural circuit

4. Site of information processing

5. Location of reflex arc components

*May be on same side or different sides

This reflex is genetically determined and classified by development

Innate reflexes

This reflex is learned and classified by development

Acquired reflexes

*Like driving a car

This reflex controls skeletal muscle contractions and includes superficial and stretch reflexes and is classified by response

Somatic reflexes

This reflex controls actions of smooth and cardiac muscles, glands, and adipose tissue and classified by response

Visceral (autonomic) reflexes

This reflex has one synapse and is classified by the complexity of circuit

Monosynaptic

This reflex has multiple synapses (two to several hundred) and classified by complexity of circuit

Polysynaptic

These reflex arcs occur on the same side of the body as the stimulus

Ipsilateral

These reflex arcs occur on the side opposite to the stimulus

Contralateral

This reflex is monosynaptic and controls posture

Stretch reflex

This reflex has the least delay between sensory input and motor output

Stretch reflex (such as patellar reflex)

Completed in 20-40msec

Ipsilateral

What is the receptor for the stretch reflex?

Muscle spindle

-When muscle is stretched, this is triggered

-Sends info to spinal cord

-Muscle contracts

What are the two fibers that make up muscle spindles?

Bundles of small, specialized intrafusal muscle fibers (innervated by sensory + motor neurons)

Surrounded by extrafusal muscle fibers (maintain tone and contract muscle, supplied by alpha motor neurons)

What does the tendon reflex prevent skeletal muscles from?

Developing too much tension

Tearing or breaking tendons

Sensory receptors of the tendon reflex are also what receptors?

Golgi tendon receptors

This reflex inhibits the muscle connected to the tendon, is ipsilateral, and polysynaptic

Tendon reflex

These reflexes move the body away from the stimulus (pain or pressure)

Withdrawal reflexes (or flexor reflex)

-Strength + extent of response depends on intensity and location of stimulus

If you step on a sharp object at the beach or get grabbed from behind, what reflex is activated?

Withdrawal reflexes

These reflexes occur simultaneously, coordinated with the flexor reflex

Crossed extensor reflexes

Ex. Flexor reflex causes leg to pull up, crossed extensor reflex straightens other leg to receive body weight