Anatomy and Physiology of the Spinal Cord, Nervous Tissue, and Autonomic Nervous System

Spinal Cord and Spinal Nerves

Introduction

• The chapter aims to:
  • Identify and describe the anatomy of the spinal cord and spinal nerves.
  • Discuss the functions of the spinal cord and spinal nerves and how they maintain homeostasis.
  • Understand spinal reflex arcs.

Spinal Cord Anatomy

Protection of the Spinal Cord

• The spinal cord is protected by:
  • Bone (vertebrae).
  • Connective tissue (meninges).
  • Fluid (cerebrospinal fluid).

Meninges

• The meninges consist of three layers:
  1. Dura mater.
  2. Arachnoid mater.
  3. Pia mater.

External Anatomy of the Spinal Cord

• The spinal cord extends from the medulla oblongata at the foramen magnum to the level of L2.

• It terminates at L2, after which it becomes the cauda equina (horse's tail).

• Nerve pairs:

  • Cervical: 8 pairs, nerve number comes from above vertebrae it is named from
  • Thoracic: 12 pairs, nerve number comes from below the vertebrae it is named from
  • Lumbar: 5 pairs, nerve number comes from below the vertebrae it is named from
  • Sacral: 5 pairs, nerve number comes from below the vertebrae it is named from

• C8 is below 7

Sensory and Motor Processing

• The spinal cord's internal anatomy allows organized processing of sensory and motor information.

Spinal Nerves

• Spinal nerves facilitate sensory and motor functions.

Connective Tissue Covering of Spinal Nerves

• Spinal nerves are covered by connective tissue.

Dermatomes

• Dermatomes are skin segments supplied by spinal nerves that carry somatic sensory nerve impulses to the brain.
  • A dermatome is an area of skin that provides sensory input to the brain.
  • A myotome is a group of muscles innervated by a single spinal nerve.
  • These overlap.
  • Used to locate damaged regions of the spinal cord.
  • Can also be used therapeutically (e.g., local anesthetic).

Myotomes

• Myotomes are groups of muscles innervated by a single spinal nerve.

• Cervical:

  • C1-2: Flexion
  • C3: Side bend
  • C4: Scapular elevation
  • C5: Shoulder abduction
  • C6: Elbow flexion, wrist extension
  • C7: Elbow extension, wrist flexion
  • C8-D1: Finger abduction
  • T1-finger abduction
  • C8- Thumb extension

Cervical Plexus

• Supplies skin and muscles of the head, neck, superior shoulders and chest, and diaphragm.

Cervical Plexus Branches

• Superficial (Sensory) Branches:
  • Lesser occipital (C2): Skin of scalp posterior and superior to ear.
  • Great auricular (C2-C3): Skin anterior, inferior, and over ear, and over parotid glands.
  • Transverse cervical (C2-C3): Skin over anterior and lateral aspect of neck.
  • Supraclavicular (C3-C4): Skin over superior portion of chest and shoulder.
• Deep (Largely Motor) Branches:
  • Ansa cervicalis (C1-C3): Infrahyoid and geniohyoid muscles of neck.
  • Phrenic (C3-C5): Diaphragm.
    • C3, 4, 5 keeps the diaphragm alive
  • Segmental branches (C1-C5): Prevertebral muscles of neck, levator scapulae, and scalenus medius muscles.

Brachial Plexus

• Provides almost the entire nerve supply to the shoulders and upper limbs.
• Remembered using the mnemonic: Rugby teams drink cold beer (Root < Trunk < Division < Cord < Branch).
• Key nerves:
  • Musculocutaneous: Supplies the Coracobrachialis, biceps brachii, and brachialis muscles (C5-C7).
  • Axillary: Supplies the Deltoid and teres minor muscles; skin over deltoid and superior posterior aspect of arm (C5, C6).
  • Median: Forearm flexors (except flexor carpi ulnaris and ulnar half of flexor digitorum profundus), lateral palm skin, and lateral 3½ digits (C5-T1).
  • Radial: Triceps brachii, anconeus, forearm extensors, posterior arm and forearm skin, lateral two-thirds of dorsum of hand, and lateral 3½ digits (C5-T1).
  • Ulnar: Flexor carpi ulnaris, ulnar half of flexor digitorum profundus, most hand muscles, skin of medial side of hand, and medial 1½ digits (C8-T1).

Origin, Distribution and Action of nerves

• Dorsal scapular (C5): Levator scapulae, rhomboid major, and rhomboid minor muscles.
• Long thoracic (C5-C7): Serratus anterior muscle. Action: protraction, inserts on medial broder of scapu;a and cause scapular winging injuries with
• Nerve to subclavius (C5-C6): Subclavius muscle.
• Suprascapular (C5-C6): Supraspinatus and infraspinatus muscles.
• Lateral pectoral (C5-C7): Pectoralis major muscle.
• Superior subscapular (C5-C6): Subscapularis muscle.
• Thoracodorsal (C6-C8): Latissimus dorsi muscle.
• Inferior subscapular (C5-C6): Subscapularis and teres major muscles.
• Medial pectoral (C8-T1): Pectoralis major and pectoralis minor muscles.
• Medial cutaneous nerve of arm (C8-T1): Skin of medial and posterior aspects of distal third of arm.
• Medial cutaneous nerve of forearm (C8-T1): Skin of medial and posterior aspects of forearm.

Upper Limb Nerve Injuries

• Brachial Plexus Nerve: Stinger
• Long Thoracic Nerve
• Median Nerve at the Elbow: Pronator Syndrome
• Ulnar Nerve at the Elbow: Cubital Tunnel Syndrome
• Median Nerve at the Wrist: Carpal Tunnel Syndrome

Klumpke’s Palsy

• Klumpke's palsy occurs from damage to the nerves in the brachial plexus, which is a collection of nerves that runs from the spinal cord through the armpit, carrying signals to the hand, arm, and shoulder

Dermatome Assessment

• Subjective: Numbness, tingling, burning
• Objective: Dermatome
  • very lightly go over the different dermatomes bilaterally, note any differences

Myotomes Test

• Myotomes - dance - bilateral
  • L1-2: hip flexion
  • L3: Knee extension
  • L4: Dorsiflexion
  • L5-D1 extension
  • S1: Plantar flexion
  • S2: Knee flexion
• Myotomes-
  • C5- shoulder abduction
  • C6- Elbow flexion/ wrist ext,
  • C7- elbow ext/ wrist flexion
  • C8- D1 ext, DARE (only jodie calls it this) ● Depression, abdution, (ext)rotation, extension (of shoulder)

Dural Tension Test

• Brachial Plexus nerves
  • ULLT(1) - median nerve (branch) - upper limb tension test (Root - C5, 6, 7, 8, T1)
  • ULLTC - 3 - Radial nerve (Branch) - waitors tip (Root - C5, C6, C7, C8, T1)
    • Depression of shoulder, pronation, wrist flexion
  • ULLT D - ulnar nerve (Branch), (owl - abduct shoulder, pronate forearm extend wrist put finger circle over eye)
    • Root: C8, T1
    • Myotomes C8 - D1(Thumb) extension, T1 - Finger abduction

Lumbar Plexus

• Nerves:
  • Iliohypogastric (T12, L1): Muscles of the anterolateral abdominal wall; skin of the inferior abdomen and buttocks.
  • Ilioinguinal (L1): Muscles of the anterolateral abdominal wall; skin of the superior and medial aspect of the thigh, root of penis and scrotum in male, and labia majora and mons pubis in female.
  • Genitofemoral (L1–L2): Cremaster muscle; skin over middle anterior surface of thigh, scrotum in male, and labia majora in female.
  • Lateral femoral cutaneous nerve (L2–L3): Skin over lateral, anterior, and posterior aspects of thigh.
  • Femoral (L2–L4): Flexor muscles of hip joint and extensor muscles of knee joint, skin over anterior and medial aspect of thigh and medial side of leg and foot.
  • Obturator (L2–L4): Adductor muscles of hip joint; skin over medial aspect of thigh.

Sacral Plexus

• Nerves:
  • Superior gluteal (L4–L5 and S1): Gluteus minimus, gluteus medius, and tensor fasciae latae muscles.
  • Inferior gluteal (L5–S2): Gluteus maximus muscle.
  • Nerve to piriformis (S1–S2): Piriformis muscle.
  • Nerve to quadratus femoris and inferior gemellus (L4–L5 and S1): Quadratus femoris and inferior gemellus muscles.
  • Nerve to obturator internus and superior gemellus (L5–S2): Obturator internus and superior gemellus muscles.
  • Perforating cutaneous (S2–S3): Skin over inferior medial aspect of buttocks.
  • Posterior femoral cutaneous nerve (S1–S3): Skin over anal region, inferior lateral aspect of buttocks, superior posterior aspect of thigh, superior part of calf, scrotum in male, and labia majora in female.
  • Pudendal (S2–S4): Muscles of perineum; skin of penis and scrotum in male and clitoris, labia majora, labia minora, and vagina in female.
  • Sciatic (L4–S3): Tibial and common fibular nerves bound together; sends branches to hamstring muscles and adductor magnus.
    • Tibial (L4–S3): Gastrocnemius, plantaris, soleus, popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles.
      • Branches: medial plantar nerve and lateral plantar nerve.
    • Medial plantar: Abductor hallucis, flexor digitorum brevis, and flexor hallucis brevis muscles; skin over medial two-thirds of plantar surface of foot.
    • Lateral plantar: Remaining muscles of foot not supplied by medial plantar nerve; skin over lateral third of plantar surface of foot.
  • Common fibular (L4–S2): Divides into superficial fibular and deep fibular branches.
    • Superficial fibular: Fibularis longus and fibularis brevis muscles; skin over distal third of anterior aspect of leg and dorsum of foot.
    • Deep fibular: Tibialis anterior, extensor hallucis longus, fibularis tertius, and extensor digitorum longus and extensor digitorum brevis muscles; skin on adjacent sides of great and second toes.

Injuries to the Lumbar and Sacral Plexus

• Sciatic nerve: Pain extends from the buttock down the posterior and lateral aspect of the leg and foot.
  • Causes:
    • Herniated disc.
    • Dislocated hip.
    • OA of lumbosacral spine.
    • Pathological shortening of the lateral rotators of the hip (piriformis).
    • Pressure of uterus from pregnancy.
    • Gluteal IM injections.
    • Sitting on a wallet.

Fibular Nerve

• Causes:
  • Fractures of the fibula.
  • Pressure from cast or splint pressure behined fibular head
    Casted below knee joint- can cause pressure on fibular head and irritate fibular nerve
  • Cause “foot drop”.

Dermatomes of the Lower Extremity

• Use:
  • It has low clinical value but it is the only tool we have
• L4-L5 or L5/S1 are major ones
• Describing words
  • Tingling, numbness, parasthesia (No sensation at all)

Myotomes Dance Lower Extremity

• L1/L2- hip flexion
• L3- Knee extension
• L4- dorsiflexion
• L5- D1- big toe extension
• S1- standing plantar flexion
• S2- Knee flexion

Special Tests- neural

• Straight leg raise
  • hip flexion, observe reaction, if pain reproduced, positive test- it puts tension on the sciatic nerve
  • to put more tension dorsiflex foot and cervical flexion- puts tension on the dura
• Slump Test
  • can be used as dura stretching as well

Spinal Cord Physiology

Spinal Cord Physiology

• The spinal cord propagates nerve impulses and integrates information to maintain homeostasis.
• Information travel in the spinal cord:
  • White matter tracts conduct nerve impulses to and from the brain.
  • Gray matter receives and integrates incoming and outgoing information to perform spinal reflexes.

Sensory and Motor Tracts

• Sensory- ascending/ afferent
• Motor- descending/ efferent

Reflexes and Reflex Arcs

• A reflex is a fast, involuntary, unplanned response to a stimulus.
  • Reflexes help maintain homeostasis.
• The gray matter of the spinal cord serves as the integrating center for spinal reflexes.

Reflex Arcs: Vocabulary Terms

• Ipsilateral = same side
• Contralateral = opposite side
• Monosynaptic = one
• Polysynaptic = more than one
• Reciprocal innervation = neural circuit simultaneously contracts one muscle and relaxes its antagonists

Types of Reflexes

• Stretch Reflex: Causes contraction of a muscle that has been stretched.
• Tendon Reflex: Causes relaxation of the muscle attached to the stimulated tendon.
• Flexor (Withdrawal) Reflex: Causes withdrawal of a limb to avoid injury or pain (L3-S2).
• Crossed-Extensor Reflex: Maintains balance during a withdrawal reflex.

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
• C3,4,5 keeps the diaphragm alive
• Extent of paralysis from traumatic injury depends on location
  • A – no function from neck down
  • B – some arm and chest muscle control
  • C – most thigh muscles
  • D – most leg muscles
• Shingles
  • Acute infection of the PNS caused by herpes zoster virus (also causes chickenpox)
  • Causes pain, discoloration of the skin and line of skin blisters
• Spinal cord compression
• Degenerative diseases (Multiple Sclerosis, Amyotropic Lateral Sclerosis)
• Poliomyelitis (Polio)

Nervous Tissue

Introduction

• The purpose of the chapter is to:
  1. Understand how the nervous system helps to keep controlled conditions within limits that maintain health and homeostasis
  2. Learn about different branches of the nervous system
  3. Identify and describe the various types of cells that are found in nervous tissue

Overview of the Nervous System

• The nervous system helps to keep controlled conditions within limits that maintain health and homeostasis

Layout of the Nervous System

• The layout of the nervous system are both the spinal cord and peripheral nerves.

Organization of the Nervous System

• Organization includes:
  • Muscles

Functions of the Nervous System

• Sensory
  • Detect changes through sensory receptors
• Integrative
  • Analyze incoming sensory information, store some aspects, and make decisions regarding appropriate behaviors
• Motor
  • Respond to stimuli via effectors

Histology of Nervous Tissue

• Histology overview includes:
  • Neurons and Nerve
  • Neuroglia

Neurons

• Electrically excitable
• Cellular structures
• Nerve impulse is called an action potential

Structural Classification of Neurons

• Neurons can be classified based on the number of processes extending from the cell body

Functional Classification of Neurons

• Neurons can be classified based on the direction of nerve impulse propagation
  • Sensory/Afferent neurons
    • Conveys information to the CNS
  • Motor/Efferent neurons
    • Conveys action potential from the CNS
  • Interneurons/Association neurons
    • Process sensory information and elicit motor response

Neuroglia

• Not electrically excitable
• Make up about half the volume of the nervous system
• Can multiply and divide
• 6 kinds total (4 in CNS, 2 in PNS)

Myelination of Neurons

• The myelin sheath is produced by Schwann cells (PNS) and oligodendrocytes (CNS) and it surrounds the axons of most neurons

Gray Matter vs. White Matter

• Gray Matter contains:
  • demyelinated Sensory reflexes dermatures motor
  • Als , MS , Polic diseases

Electrical Signals in Neurons

• Excitable cells communicate with each other via Action Potentials or Graded Potentials
• Action Potentials (AP) allow communication over short and long distances whereas Graded Potentials (GP) allow communication over short distances only
  • Production of an AP or a GP depends upon the existence of a resting membrane potential and the existence of certain ion channels

Regeneration & Repair of Nervous Tissue

• Although the nervous system exhibits plasticity, neurons have a limited ability to regenerate themselves
  • Plasticity – the capability to change based on experience
  • Regenerate – the capability to replicate or repair · only amm amonth , will not fix massive injuries

Neurogenesis in the CNS

• In the CNS, there is little or no repair due to:
  • Inhibitory influences from neuroglia, particularly oligodendrocytes
  • Absence of growth-stimulating cues that were present during fetal development
  • Rapid formation of scar tissue

Damage and Repair in the CNS

• In the PNS repair is possible if the cell body is intact, Schwann cells are functional, and scar tissue formation does not occur too rapidly
• Steps involved in the repair process are:
  • Chromatolysis
  • Wallerian degeneration
  • Formation of a regeneration tube
  • cannot get excited or have action Potentials don't need this take away : · our peripheral nerves will heal !

Neural Disorders – Multiple Sclerosis

• Autoimmune disease that causes progressive destruction of myelin sheath
• Cause is unclear; may be genetic and/or environmental
• Symptoms include muscle weakness, abnormal sensations and double vision

Neural Disorders – Depression

• Several types of depression
  1. Major depression
  2. Dysthymia
  3. Bipolar depression (manic-depressive illness)
  4. Seasonal affective disorder (SAD)
• Common feelings are lack of interest in activities, sadness, helpless and possibly suicidal thoughts
• Commonly treated through selective serotonin reuptake inhibitors (SSRIs)

Other Neural Disorders

• Epilepsy
  • Short, recurrent attacks of motor, sensory or psychological function
  • Initiated by abnormal synchronous electrical discharges from the millions of neurons in the brain
• Excitotoxicity
  • Destructions of neurons through prolonged activation of excitatory synaptic transmission
  • Caused by high levels of glutamine in CNS interstitial fluid

The Autonomic Nervous System

Introduction

• The purpose of this chapter is to:
  1. Examine the structure and function of the autonomic nervous system (ANS)
  2. Compare and contrast the somatic and ANS
  3. Examine ANS neurotransmitters
  4. Compare and contrast the sympathetic and parasympathetic nervous systems

Comparison of Somatic and Autonomic Nervous Systems

• The somatic nervous system includes sensory and motor neurons. Sensory neurons are related to touch, pain, temperature, and proprioception (sense of self position), sight, hearing, taste, smell and equilibrium. Motor neurons innervate skeletal muscles.

• The autonomic nervous system receives input from sensory receptors located in organs, blood vessels, muscles and the nervous system.

• The axon of a single, myelinated somatic motor neuron extends from the central nervous system to the skeletal muscle fiber it innervates

• Most autonomic motor pathways consist of two motor neurons in series.

  • A preganglionic neuron has its cell body in the central nervous system and the axon extends to an autonomic ganglion.
  • A postganglionic neuron has its unmyelinated axon extending from the ganglion to the effector

• The autonomic nervous system is divided into two divisions: The sympathetic nervous system is often referred to as the fight-or-flight division because its stimulation leads to increased alertness and metabolism to be ready for an emergency. The parasympathetic nervous system is referred to as the rest-and-digest division as its stimulation slows down most body activity.

Comparison of Somatic and Autonomic Nervous Systems

Anatomy of Autonomic Motor Pathways

• Each division of the autonomic nervous system has two motor neurons: The preganglionic (cell body in the brain or spinal cord) and the postganglionic (cell body and dendrites located in an autonomic ganglion where it synapses with preganglionic axons)
• In the sympathetic division, the cell bodies of preganglionic neurons are in the lateral horns of the gray matter in the 12 thoracic and first 2 or 3 lumbar segments
• In the parasympathetic division, cell bodies of the preganglionic neurons are in the nuclei of four cranial nerves (III, VII, IX and X) in the brain stem and in the lateral gray matter of sacral segments 2–4 of the spinal cord

ANS Neurotransmitters and Receptors

• Based on the neurotransmitter they produce and release, autonomic neurons are considered as either cholinergic or adrenergic
  • Cholinergic neurons release the neurotransmitter acetylcholine.
    • Cholinergic receptors include nicotinic receptors and muscarinic receptors
  • Adrenergic neurons release norepinephrine (noradrenalin)

Sympathetic vs. Parasympathetic

Autonomic Tone

• Autonomic tone is the balance between sympathetic and parasympathetic nervous system activity
• It is regulated by the hypothalamus
• Effects body organs differently
• When sympathetic input increases, parasympathetic input decreases and vice versa

Effects of the ANS

• Heart activity is increased by increasing sympathhetic and decreased by increasing parasympathetic.
• Something happens and you start to cry, there would be an increase in parasympathetic
• Hear your stomach growling- digesting is parasympathetic
• Bear is chasing you- sympathetic increases; for heart racing, respiration is increasing

Integration and Control

• Functions such as heart rate and force of ventricular contraction, blood pressure and blood vessel diameter are controlled by autonomic reflexes that occur when nerve impulses pass through an autonomic reflex arc
• The reflex arc is composed of a receptor, a sensory neuron, an integrating center, motor neurons and an effector

The Nervous System and Homeostasis

• Together with hormones from the endocrine system, nerve impulses provide communication and regulation of most body tissues
• Examples:
  • Sympathetic nerves of the autonomic nervous system (ANS) control contraction of arrector muscles of the hair and secretion of perspiration from sweat glands.
  • Hypothalamus regulates secretion of hormones from anterior and posterior pituitary and ANS regulates secretion of hormones from suprarenal me-dullae and pancreas
  • Pain receptors in bone tissue warn of bone trauma or damage

Disorders

• Autonomic Dysreflexia:
  • Exaggerated response of the sympathetic nervous system occurring in 85% of individuals with spinal cord injury at or above T6.
  • If untreated, can cause seizures, stroke or heart attack.
• Raynaud Phenomenon
  • Occurs due to excessive sympathetic stimulation of smooth muscle in arterioles of digits.
  • Vasoconstriction leads to numbness and ischemia in digits.
  • From spinal cord injury wrongly wired, most of the time sympathetic increases sympathetic nervous system gone worng