CHAPTER 14 - SPINAL CORD AND NERVES

Descending motor pathways

Descending tracts deliver efferent impulses from the brain to the spinal cord, and are divided into two groups Direct pathways equivalent to the pyramidal tracts Indirect pathways, essentially all others Motor pathways involve two neurons (upper and lower)

The spinal cord

-integrates and processes information -can function with the brain, or function independently of the brain Provides two-way communication to and from the brain Begins at the foramen magnum and end at L1 vertebra, Filum terminale

Peripheral Distribution of Spinal Nerves

-motor impulses leave the spinal cord via the ventral root -sensory information enters the spinal cord via the dorsal root

Cervical plexus

C1-C5 supplies neck and phrenic nerve to the diaphragm consists of cutaneous and muscular branches

Brachial plexus

C5-T1. Branch into superior, middle and inferior trunk. Innervate the upper limb. it's branches innervate deltoid, trees minor, biceps, triceps, skin and muscles of forearm wrist and fingers.

Lumbar tap

CSF fills the subarachnoid space, extend beyond L2. Between L4 and L5 is ideal spot for lumbar tap.

Peripheral nerves

Carry sensory or motor impulses to and from body parts

Gray matter includes

Central canal Consists of somas (cell bodies) surrounding the central canal Consists of glial cells

The expanded area of the spinal cord that supplies nerves to the pectoral girdle and upper limbs is the

Cervical enlargement

Tingling and numbness in the palmar region fo the hand could be caused by

Compression of the median nerve in the carpal tunnel

VENTRAL ROOT

Contain motor nerves (efferent nerves). Transmit impulses away from the spinal cord.

DORSAL ROOT

Contains sensory nerves (afferent nerves). Transmit impulses toward the spinal cord.

The Pia mater

Deepest meningeal layer -Blood vessels are found in this layer -Firmly bound to the brain tissue and the spinal cord tissue.

What prevents side-to-side movements of the spinal cord?

Denticulate ligaments

A sensory region of the skin monitored by the dorsal rami of a single spinal segment is

Dermatome

Spinal nerves from two branches

Dorsal ramus (top branch) - receive sensation from skeletal muscles of the neck and back Ventral ramus- innervates skeletal muscles of the limbs

Segments of the spinal cord

Dorsal root Ventral root

The paired structures that contain cell bodies of sensory neurons and are associated with each segment of the spinal cord are the

Dorsal root ganglia

Dorsal roots

Dorsal roots contain sensory fibers; Somatic Sensory (SS) Visceral Sensory (VS)

The tough, fibrous, outermost covering of the spinal cord is the

Dura mater

Dermatomes are

Each pair of spinal nerves monitor specific surface areas, an area known as dermatome These are clinically important areas, because damage to either a spinal nerve or dorsal nerve ganglia will produce a characteristic loss of sensation in specific area of the skin.

Nerve coverings

Each peripheral nerve has three layers of connective tissue 1. Epineurium 2. Perineurium 3. Endoneurium

The outermost layer of connective tissue that surrounds each spinal nerve is the

Epineurium

In the popliteal region the sciatic nerve divides into _______ and ________

Fibula and tibial

Mr. Y could not bend his knee and had no sense in posterior part of his leg. What nerve is most likely damaged?

Fibular nerve, a branch of sciatic nerve of sacral plexus.

Which nerves are used to move the toes?

Fibular nerve, anterior branch

The ______ is a stand of fibrous tissue that provides longitudinal support as a component of the coccygeal ligament.

Filum terminale

Ascending pathways consist of three neurons

First- order neuron - from receptors Second- order neuron (interneurons) Third- order neuron, to somatosensory cortex

A group of neuron cell bodies outside the gray area (in the PNS is a)

Ganglion

Axons crossing from one side of the spinal cord to the other within the gray matter are found in the

Gray commissures

Sections anatomy of the spinal cord

Gray matter, white matter

sacral plexus

L4-S4, and serves the pelvic structures and the Lower limb, gluteal muscles and posterior cutaneous areas. The major nerve is the sciatic, the longest and thickest nerve of the body. Innervate the hamstrings muscles and most muscles in the leg and foot.

Endoneurium

Layer surrounding a single axon

Perineurium

Layer surrounding fasciae - a fascicle is a bundle of axons

The genitofemoral, femoral and lateral femoral cutaneous nerves are major nerves of the

Lumbar plexus

spinal meninges

Made of three layers Dura mater: Tough, fibrous outermost layer Arachnoid mater: Middle layer Pia mater: Innermost layer

Why is response time in a monosynaptic reflex much faster than response time in polysynaptic reflex?

Polysynaptic: totals several synapses, resulting in a delay Monosynaptic: only 1 synapse so it has a faster response time

Which nerves are used to flex the knee?

Popliteal, fibular and tibial, posterior branch.

the muscle branch

innervates the neck, ear, back of the head, shoulder and rhomboid muscles

Phrenic nerve

is the most important nerve of cervical plexus. The motor and sensory nerve of the diaphragm. Irritation of phrenic nerve can cause spasm of the diaphragm or hiccups

ventral root

motor neron axons

Somatic sensory (SS)

receive impulse from skin, joints, muscle

Visceral sensory (VS)

receive impulses from viscera, such as the heart, kidneys, GI tract.

What is the spinal cord responsible for?

reflexes arc

anterior gray horn

somatic motor nuclei, visceral motor nuclei

Posterior gray horns contain

somatic sensory and visceral nuclei

Spinal nerves

thirty-one pair of mixed nerves- arise from the spinal cord and supply all parts of the body except the head.

The Dura Mater

tough, fibrous outermost layer of the meninges - Stabilizes the spinal cord within the vertebra canal -Cranial and sacral connective tissues stabilize the longitudinal axis of the spinal cord attachments.

Spinal cord regions

The 31 pairs of spinal nerves extend from different regions; Cervical (8) Thoracic (12) Lumbar (5) Sacral (5) Coccygeal (1)

If this nerve is severed the sole of your foot would be numbed. This nerve is the _____

Tibial nerve

Somas

are organized into groups called nuclei Sensory nuclei Motor nuclei

White matter consists of

ascending (sensory) and descending (motor) tracts. Pathways decussate (cross over) via transverse tracts that cross from one side to the other.

four nerve plexuses

cervical, brachial, lumbar, sacral

gray commissure

consists of axons crossing from one side to the other

Spinal nerves are called mixes nerves because

contain both motor and sensory fibers

Features of the spinal cord

45 cm in length Passes through the foramen magnum Extends from the brain to L1

Which nerves innervates Pectoralis muscles?

A branch of lower trunk of the brachial plexus.

Nerves that innervate our upper limb arise from the _________.

Brachial plexus

Nerves that innervate your upper limb arise from ______

Brachial plexus

Rami

Branches of spinal nerves that after passing through intervertebral firemen, they divide into several branches known as rami

White matter includes

-Axons of interneurons (tracts) and form columns -Located outside of the gray matter area

The brain

-Integrates and processes information -Can function independently of the spinal cord

how stretch reflex works

-stretch activates the muscle spindle -sensory neurons synapse directly with motor neurons in the spinal cord -motor neurons cause the stretched muscle to contract

Nerves that only carry information to the CNS are classified as?

Afferent

Which of the following actions would be compromised if a person suffered an injury to lumbar spinal segments L3 and L4?

All of the above

The brachial plexus

All of the above -innervates the shoulder girdle and upper extremities -is formed from the ventral rami of spinal nerves c5-T1 -source of the musculocutaneous, radial, median, and ulnar nerves

Why is it important that a spinal tab be done between the third and fourth lumbar vertebrae?

An adults spinal cord only goes down to L1 or L2. By doing it at L3 and 4, you ensure there is no risk for spinal cord injury

Ganglia

An enlargement in dorsal root, contains the cell bodies of afferent sensory neurons.

Reflex

An immediate involuntary response

The ventral roots of each spinal segment

Both B and C -control peripheral effectors -and contain the axons of somatic motor and visceral motor neurons

Nerve plexuses are...

Interlacing networks of nerves that contains fibers from several spinal nerves Advantage- damage to one nerve may not paralyze the whole limb

filum terminale

Is a slender fibrous tissue anchors the spinal cord to the coccyx. Provide longitudinal support to the spinal cord as component of coccygeal ligament.

If the dorsal root of a spinal cord were damaged what would be affected?

It will not affect other body functions such as sensation which is controlled by the dorsal roots of the spinal nerves. ... If it is damaged, there will be weakness or paralysis in the muscles in the particular area of the body.

Lumbar plexus

L1-L4 Innervates thigh, abdominal wall, and psoas muscle The major nerves are the femoral nerve (innervates quadriceps) and the obturator nerve (innervate adductor muscles)

Pectoralis major muscle is innervated by which nerve?

Medial pectoral nerve, and the lateral pectoral nerve .

If your index finger does not sense anything, the problem is most likely from

Median nerve of brachial plexus

The arachnoid mater

Middle meningeal layer -Cerebrospinal fluid flows within this space.

Stretch reface is an example of..

Monosynaptic reflex- such as patellar reflex

The reflexes that control the most rapid, stereotyped motor responses of the nervous system to stimuli are

Monosynaptic reflexes

Spinal reflexes are

Monosynaptic- Involves a single segment of the spinal cord Polysynaptic- Integrates motor output from several spinal segments

Ventral roots

Motor (efferent) nerves from ventral root - include Visceral motor (VM) fibers Somatic motor (SM) fibers

What is a nerve?

Nerve refers to bundle of axons of neurons in PNS

Epineurium

Outer later- becomes continuous with the dura mater

The middle layer of connective tissue that surrounds each peripheral is the

Perineurium

The major nerve of the cervical plexus that innervates the diaphragm is the

Phrenic nerve

The most important nerve of cervical plexus is the ________ nerve, innervating the diaphragm

Phrenic nerve

Mr. X had no control over his urination and had numbness in his urogenital area. What nerve is most likely damaged?

Pudendal nerve or the lumbar plexus.

What nerve is likely to transmit pain when a person receives an intramuscular injection into the deltoid region of the arm?

Radial nerve

Which nerve control fingers for grabbing a bottle and fro writing.

Radial nerve and a branch of median nerve.

clinical connection

Reflexes are often used for diagnosing disorders of the nervous system and locating injured tissue If a reflex is absent or abnormal, the damage may be somewhere along a particular conduction pathway

This nerve is the longest and thickest nerve of the body

Sciatic

The longest and thickest nerve of the body is the __________

Sciatic nerve

Columns of nerves (funiculi) are either

Sensory tracts (ascending tracts) Motor tracts (descending tracts)

spinal cord protection

Spinal cord is protected by bone, meninges and CSF

the deep crease on the anterior surface of the spinal cord is the

The anterior median fissure

Why are there eight cervical spinal nerves but only seven cervical vertebrae?

The first pair of spinal nerve are located above the atlas. This "extra" pair is the reason there are 8 pair instead of 7

Reflexes arc

The neutral "wiring" of a single relex, begins at a sensory receptor and ends at a peripheral receptor.

What is the role of the meninges in protecting the spinal cord?

The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.

The central nervous system consists of

The spinal cord and the brain

If your little finger is numb and you cannot sense an object what nerve might be affected?

Ulnar nerve

Which of the following structures is referred to as "funny bone" that results in tingling of the forearm when struck?

Ulnar nerve

Sensory and motor innervations of the skin of the lateral and anterior surfaces of the body are provided by the

Ventral ramus

What happens if the fibular nerve is damaged?

You cannot move your toe

Sciatic nerve

branch into tibial and fibular nerves. Innervate flexors of the knee , extensor of ankle, flexors of toe, surface of foot, calcaneal

Somatic motor (SM) fibers

carry motor commands to effectors, such as muscles

Visceral motor (VM) fibers

carry motor commands to internal organs

The gray matter of the spinal cord is dominated by

cell bodies of neurons and glial cells

Spinal Cord Trauma

• Functional losses - Paresthesias: Sensory loss - Paralysis: Loss of motor function, impulses do not reach muscles; there is no voluntary or involuntary control of muscles