Chapter 13 - The Spinal Cord and Spinal Nerves Flashcards
What are the Functions of the Spinal Cord?
1- Process reflexes
2- Integrate EPSP and IPSP
3- Conduct sensory impulses to the brain and motor impulses to effectors
What is the Protection of the Spinal Cord?
Spinal Cord is protected by:
1- Bone (vertebrae)
2- Connective Tissue (meninges)
3- Fluid (CSF)
What are Meninges?
The meninges are composed of 3 layers (same for brain):
1- Dura Mater
2- Arachnoid Mater
3- Pia Mater
Epidural space - between Dura and bone
Subdural space - between Dura and Arachnoid
Subarachnoid space - between Arachnoid and Pia, where CSF is
What is the External Anatomy of the Spinal Cord?
The spinal cord begins as an extension of the Medulla Oblongata at the level of the Foramen Magnum
Terminates at the level of L2
What is the Internal Anatomy of the Spinal Cord?
Spinal Nerve (plus Nerve Impulses trajectories)
Anterior Root of Spinal Nerve (plus Axons of Motor Neurons)
Posterior Root of Spinal Nerve
Posterior Root Ganglion (plus Axon of Sensory Neuron)
Anterior Rootlets
Posterior Rootlets
Lateral White Column
Anterior White Column
Posterior White Column
Anterior Gray Horn (plus Cell Body of Somatic Motor Neuron)
Posterior Gray Horn (plus Cell Body of Interneuron)
Lateral Gray Horn (plus Cell Body of Autonomic Motor Neuron)
Anterior Median Fissure
Posterior Median Sulcus
Anterior White Commissure
Gray Commissure
Central Canal
What is Sensory and Motor Processing?
The internal anatomy of the spinal cord allows sensory and motor information to be processed in an organized way:
SOMATIC NERVOUS SYSTEM:
First, Sensory receptors (ex: in skin) send nerve impulses
Second, Nerve impulses travel along sensory neuron to posterior root ganglion
Then one of the following happens:
1- Nerve impulses go to Brain through Sensory (Ascending) Tract
Then back through Motor (Descending) Tract to Somatic Motor Neuron in the Spinal Cord
Then to Effectors (Skeletal Muscles) through Anterior Root of Spinal Nerve
2- Nerve impulses go to Interneuron in Spinal cord
Then go to Brain through Sensory (ascending) Tract
Then back through Motor (Descending) Tract to Somatic Motor Neuron in the Spinal Cord
Then to Effectors (Skeletal Muscles) through Anterior Root of Spinal Nerve
3- Nerve impulses go to Interneuron in Spinal Cord
Then go to Somatic Motor Neuron in the Spinal Cord
Then to Effectors (Skeletal Muscles) through Anterior Root of Spinal Nerve
AUTONOMIC NERVOUS SYSTEM:
Autonomic Motor Neuron in Spinal Cord sends nerve impulses
Nerve impulses go through Anterior Root of Spinal Nerve
Nerve impulses go to another Autonomic Motor Neuron to Effectors (Cardiac Muscle, Smooth Muscles, and Glands
What are the Characteristics of Cervical Segment of the Spinal Cord?
Relatively large diameter
Relatively large amounts of White Matter - oval
In upper Cervical segments (C1-C4):
Posterior Gray Horn is large
Anterior Gray Horn is relatively small
In lower Cervical segments (C5 and below)
Posterior Gray Horns are enlarged
Anterior Gray Horns are well developed
What are the Characteristics of Thoracic Segment of the Spinal Cord?
Small diameter due to relative small amounts of Gray Matter
(Except 1st Thoracic segment)
Anterior and Posterior Gray Horns are relatively small
Small Lateral Gray Horn is present
What are the Characteristics of Lumbar Segment of the Spinal Cord?
Nearly circular
Very large Anterior and Posterior Gray Horns
Small Lateral Gray Horn is present in upper segments
Relatively less White Matter than Cervical segment
What are the Characteristics of Sacral Segment of the Spinal Cord?
Relatively small
Relatively large amounts of Gray Matter
Relatively small amounts of White Matter
Anterior and Posterior Gray Horns are large and thick
What are the Characteristics of Coccygeal Segment of the Spinal Cord?
Resembles lower Sacral spinal segments but much smaller
What are Spinal Nerves?
Part of PNS
Spinal Nerves connect CNS to sensory receptors, muscles, and glands
31 Pairs of Spinal Nerves
Anterior and Posterior Roots attach a spinal nerve to a segment of the spinal cord
What is the Structure of Spinal Nerves?
Epineurium: covers spinal nerve
Fascicles and blood vessels inside spinal nerve
Perineurium: covers each Fascicle
Many Axons inside Fascicle
Endoneurium: covers each Axon
Many Axons covered by Myelin Sheath
What are Branches of a Spinal Nerve?
Shortly after passing through its intervertebral foramen, a spinal nerve divides into several branches known as Rami
Rami: branches of a spinal nerve
ex:
Anterior Ramus
Posterior Ramus
Meningeal Branch
Rami Communicantes
What is Dermatome?
Certain segments of the skin are supplied by spinal nerves that carry somatic sensory nerve impulses to the brain
What is Cervical Plexus?
Cervical Plexus: C1-C5
Supplies the skin and muscles of the:
Head
Neck
Superior portion of shoulders and chest
Diaphragm
What are the Superficial (Sensory) Branches of Cervical Plexus Nerves?
Lesser Occipital nerve
Great Auricular nerve
Transverse Cervical nerve
Supraclavicular nerve
What is Lesser Occipital Nerve?
Origin:
C2
Distribution:
Skin of scalp posterior and superior to ear
What is Great Auricular Nerve?
Origin:
C2-C3
Distribution:
Skin anterior, inferior, and over ear
Over Parotid glands
What is Transverse Cervical Nerve?
Origin:
C2-C3
Distribution:
Skin over anterior and lateral aspect of neck
What is Supraclavicular Nerve?
Origin:
C3-C4
Distribution:
Skin over superior portion of chest and shoulder
What are the Deep (Largely Motor) Branches of Cervical Plexus Nerves?
Superior Root of Ansa Cervicalis nerve
Inferior Root of Ansa Cervicalis nerve
Phrenic nerve
Segmental Branches nerve
What is Superior Root of Ansa Cervicalis Nerve?
Origin:
C1
Distribution:
Infrahyoid and Geniohyoid muscles of neck
What is Segmental Branches Nerve?
Origin:
C1-C5
Distribution:
Prevertebral (deep) muscles of neck
Levator Scapulae
Middle Scalene muscles
What is Inferior Root of Ansa Cervicalis Nerve?
Origin:
C2-C3
Distribution:
Infrahyoid muscle of neck
What is Phrenic Nerve?
Origin:
C3-C5
Distribution:
Diaphragm
What is Brachial Plexus?
Brachial Plexus: C4- T2
Provides almost the entire nerve supply to the shoulders and upper limbs
Subunits of the Brachial Plexus: (Risk Takers Don’t Cautiously Behave)
1- Roots
2- Trunks (Superior, Middle, Inferior)
3- Divisions (Anterior and Posterior)
4- Cords (Medial, Posterior, Lateral)
5- Branches
What are the Nerves of the Brachial Plexus?
Dorsal Scapular nerve
Long Thoracic nerve
Nerve to Subclavius
Suprascapular nerve
Musculocutaneous nerve
Lateral Pectoral nerve
Upper Subscapular nerve
Thoracodorsal nerve
Lower Subscapular nerve
Axillary nerve
Median nerve
Radial nerve
Medial Pectoral nerve
Medial Cutaneous nerve of arm
Medial Cutaneous nerve of forearm
Ulnar nerve
What is Dorsal Scapular Nerve?
Origin:
C5
Distribution:
Levator Scapulae
Rhomboid Major
Rhomboid Minor
What is Long Thoracic Nerve?
Origin:
C5-C7
Distribution:
Serratus Anterior
(If affected, leads to winged scapula)
What is Nerve to Subclavius?
Origin:
C5-C6
Distribution:
Subclavius muscle
What is Suprascapular Nerve?
Origin:
C5-C6
Distribution:
Supraspinatus
Infraspinatus
What is Musculocutaneous Nerve?
Origin:
C5-C7
Distribution:
Coracobrachialis
Biceps Brachii
brachialis
What is Lateral Pectoral Nerve?
Origin:
C5-C7
Distribution:
Pectoralis Major
What is Upper Subscapular Nerve?
Origin:
C5-C6
Distribution:
Subscapularis
What is Thoracodorsal Nerve?
Origin:
C6-C8
Distribution:
Latissimus Dorsi
What is Lower Subscapular Nerve?
Origin:
C5-C6
Distribution:
Subscapularis
Teres Major
What is Axillary Nerve?
Origin:
C5-C6
Distribution:
Deltoid
Teres Minor
Skin over Deltoid and superior aspect of arm
What is Median Nerve?
Origin:
C5-T1
Distribution:
Flexors of forearm, except Flexor Carpi Ulnaris
Ulnar half of Flexor Digitorum Profundus
Some muscles of hand (lateral palm)
Skin of lateral 2/3 of palm of hand and fingers
What is Radial Nerve?
Origin:
C5-T1
Distribution:
Triceps Brachii
Anconeus
Extensor muscles of forearm
Skin of posterior arm and forearm, lateral 2/3 of dorsum of hand, and fingers over proximal and middle phalanges
What is Medial Pectoral Nerve?
Origin:
C8-T1
Distribution:
Pectoralis Major
Pectoralis Minor
What is Medial Cutaneous Nerve of Arm?
Origin:
C8-T1
Distribution:
Skin of medial and posterior aspects of distal third of arm
What is Medial Cutaneous Nerve of Forearm?
Origin:
C8-T1
Distribution:
Skin of medial and posterior aspects of forearm
What is Ulnar Nerve?
Origin:
C8-T1
Distribution:
Flexor Carpi Ulnaris
Ulnar half of Flexor Digitorum Profundus
Most muscles of hand
Skin of medial side of hand, little finger, and medial half of ring finger
What is Lumbar Plexus Nerves?
Lumbar Plexus: T12-L5
Roots, Anterior Divisions, Posterior Divisions
Iliohypogastric nerve
Ilioinguinal nerve
Genitofemoral nerve
Lateral Cutaneous Nerve of Thigh
Femoral nerve
Obturator nerve
What is Iliohypogastric Nerve?
Origin:
L1
Distribution:
Muscles of anterolateral abdominal wall
Skin of inferior abdomen and buttock
What is Ilioinguinal Nerve?
Origin:
L1
Distribution:
Muscles of anterolateral abdominal wall
Skin of superior and medial aspects of thigh, root of penis, and scrotum in male, and Labia Majora and Mons Pubis in female
What is Genitofemoral Nerve?
Origin:
L1-L2
Distribution:
Cremaster
Skin over middle anterior surface of thigh, scrotum in make, and Labia Majora in female
What is Lateral Cutaneous Nerve of Thigh?
Origin:
L2-L3
Distribution:
Skin over lateral, anterior, and posterior aspects of thigh
What is Femoral Nerve?
Origin:
L2-L4
Distribution:
Largest nerve arising from Lumbar Plexus
Distributed to flexor muscles of hip joint
Extensor muscles of knee joint
Skin over anterior and medial aspects of thigh and medial side of leg and foot
What is Obturator Nerve?
Origin:
L2-L4
Distribution:
Adductor muscles of hip joint
Skin over medial aspect of thigh
What is Sacral Plexus Nerves?
Sacral Plexus: L4-S5
Roots, Anterior Division, Posterior Division
Superior Gluteal nerve
Inferior Gluteal nerve
Nerve to Quadratus Femoris and Inferior Gemellus
Nerve to Obturator Internus and Superior Gemellus
Perforating Cutaneous nerve
Posterior Cutaneous Nerve of Thigh
Pudendal nerve
Sciatic nerve
Tibial nerve
Medial Plantar nerve
Lateral Plantar nerve
Common Fibular nerve
Superficial Fibular nerve
Deep Fibular nerve
What is Superior Gluteal Nerve?
Origin:
L4-L5
S1
Distribution:
Gluteus Minimus
Gluteus Medius
Tensor Fasciae Latae
What is Inferior Gluteal Nerve?
Origin:
L5-S2
Distribution:
Gluteus Maximus
What is Nerve to Piriformis?
Origin:
S1-S2
Distribution:
Piriformis
What is Nerve to Quadratus Femoris and Inferior Gemellus?
Origin:
L4-L5
S1
Distribution:
Quadratus Femoris
Inferior Gemellus
What is Nerve to Obturator Internus and Superior Gemellus?
Origin:
L5-S2
Distribution:
Obturator Internus
Superior Gemellus
What is Perforating Cutaneous Nerve?
Origin:
S2-S3
Distribution:
Skin over inferior medial aspect of lower leg
What is Posterior Cutaneous Nerve of Thigh?
Origin:
S1-S3
Distribution:
Skin over anal region, inferior lateral aspect of buttock, superior posterior aspect of thigh, superior part of calf, scrotum in male, Labia Majora in female
What is Pudendal Nerve?
Origin:
S2-S4
Distribution:
Muscles of Perineum
Skin of penis and scrotum in male and Clitoris, Labia majora, Labia Minora and Vagina in female
What is Sciatic Nerve?
Origin:
L4-S3
Distribution:
2 Nerves - Tibial Nerve and Common Fibular Nerve
Bound together by common sheath of connective tissue
Splits into 2 divisions usually at knee
As Sciatic Nerve descends through thigh, it sends branches to Hamstring muscles and Adductor Magnus
What is Tibial Nerve?
Origin:
L4-S3
Distribution:
Gastrocnemius
Plantaris
Soleus
Popliteus
Tibialis Posterior
Flexor Digitorum Longus
Flexor Hallucis Longus
Branches of Tibial Nerve in foot are Medial and Lateral Plantar Nerve
What is Medial Plantar Nerve?
Origin:
L4-S3
Distribution:
Abductor Hallucis
Flexor Digitorum Brevis
Flexor Hallucis Brevis
Skin over medial 2/3 of plantar surface of foot
What is Lateral Plantar Nerve?
Origin:
L4-S3
Distribution:
Remaining muscles of foot not supplied by Medial Plantar Nerve
Skin over lateral 1/3 of plantar surface of foot
What is Common Fibular Nerve?
Origin:
L4-S2
Distribution:
Divides into Superficial Fibular Nerve and Deep Fibular Nerve
What is Superficial Fibular Nerve?
Origin:
L4-S2
Distribution:
Fibularis Longus
Fibularis Brevis
Skin over distal 1/3 of anterior aspect of leg and dorsum of foot
What is Deep Fibular Nerve?
Origin:
L4-S2
Distribution:
Tibialis Anterior
Extensor Hallucis Longus
Fibularis Tertius
Extensor Digitorum Longus
Extensor Digitorum Brevis
Skin on adjacent sides of great and second toes
What is Spinal Cord Physiology?
In order to maintain homeostasis, the spinal cord must propagate nerve impulses and integrate information
White Matter Tracts conduct nerve impulses to and from the Brain
Gray Matter receives and integrates incoming and outgoing information to perform spinal reflexes
Where are Sensory Tracts?
Sensory Tracts:
1- Posterior Column:
Gracile Fasciculus (medial)
Cuneate Fasciculus (lateral)
2- Posterior Spinocerebellar Tract
Anterior Spinocerebellar Tract
3- Lateral Spinothalamic Tract
Anterior Spinothalamic Tract
Where are Motor Tracts?
1- Lateral Corticospinal Tract
Anterior Corticospinal Tract
2- Rubrospinal Tract
3- Lateral Reticulospinal Tract
Medial Reticulospinal Tract
4- Vestibulospinal Tract
5- Tectospinal Tract
What is Reflexes and Reflex Arcs?
A reflex is a fast, involuntary, unplanned response to a particular stimulus
Reflexes help maintain homeostasis
The Gray Matter of the Spinal Cord serves as the integrating center for spinal reflexes
Reflex Arc:
Sensory Receptor
Sensory Neuron
Spinal Cord
Motor Nerve
Effector
What are Reflex Arcs Terms?
Ipsilateral (same side)
Contralateral (opposite side)
Monosynaptic
Polysynaptic
Reciprocal Innervation (avoidance of commotion/confusion)
Hemiplegia: 1/2 paralysis
Monoplegia: 1 limb paralysis
Paraplegia: Lower half Paralysis
Quadriplegia: 4 limb paralysis
-Plegia: Complete death
-Paresis: Weakness
What is Stretch Reflex?
Causes contraction of a muscle that has been stretched
1- Stretching stimulates sensory receptor (muscle spindle)
2- Sensory neuron excited
3- Within integrating center (spinal cord), sensory neuron activates motor neuron and inhibits motor neuron to antagonistic muscles
4- Motor neuron excited
5- Effector (same muscle) contracts and relieves the stretching
What is Tendon Reflex?
Causes relaxation of the muscle attached to the stimulated tendon
1- Increase tension stimulates sensory receptor (tendon organ)
2- Sensory neuron excited
3- Within integrating center (spinal cord) sensory neuron activates inhibitory interneuron, motor neuron to antagonistic muscles is excited, antagonistic muscle contracts
4- Motor neuron inhibited
5- Effector (muscle attached to same tendon) relaxes and relieves excess tension
What is Flexor (Withdrawal) Reflex?
Causes withdrawal of a limb to avoid injury or pain
1- Step on tack stimulates sensory receptor (dendrites of pain-sensitive neuron)
2- Sensory neuron excited
3- Within integrating center (spinal cord) sensory neuron activates interneurons in several spinal cord segments
4- Motor neuron excited
5- Effectors (flexor muscles) contract and withdraw leg
What is Crossed-Extensor Reflex?
Maintains balance during a withdrawal reflex
1- Step on a tack stimulates sensory receptor (dendrites of pain-sensitive neuron) in right foot
2- Sensory neuron excited
3- Within integrating center (spinal cord) sensory neuron activates several interneurons
4- Motor neurons excited
5- Effector (extensor muscles) contract and extend left leg
What are some Spinal Cord and Spinal Nerves Disorders?
Traumatic injuries:
Monoplegia
Paraplegia
Hemiplegia
Quadriplegia
Damage that results from traumatic injuries depends on :
Degree of spinal cord section
Or
Degree of compression of the segments involved
Spinal Cord compression
Degenerative disease
Shingles:
1st Time chicken pox, goes to dorsal roots of spine and wait until body is weaker, then acts when immune system is weak
Poliomyelitis:
GI virus, goes to spinal cord
