Spinal Cord and Nerves lecture presentation

Spinal Cord and Nerves
The Nervous System

• Coordinates the activity of muscles, organs, senses, and actions
• Made up of nervous tissue
• Has 3 main functions:
• 1. Receives sensory Input
• 2. Integration
• 3. Dictates motor output

Structural Divisions of the
Nervous System

• Central Nervous System (CNS)
• Brain and spinal cord
• Interprets incoming sensory signals
• Dictates motor responses
• Peripheral Nervous System (PNS)
• Nerves
• Cranial nerves and spinal nerves
• Nerve plexuses
• Enteric system
• Communication between regions of body and CNS

Review of Nervous Tissue

• Features of Nervous Tissue
• Neuron
• Cell body
• Dendrite
• Axon
• Myelin Sheath
• Surrounds thicker axons
• Forms insulating layer
• Prevents leakage of electrical current
• Speeds up the impulse conduction

Review of Nervous Tissue

• Neuroglia
• Reflex Arc
• Interneurons
• Rapid, automatic motor response
• Synapse
• Action potential

Organization of a Nerve

• Endoneurium
• Surrounds each axon (nerve fiber)
• Myelinated and Unmyelinated axons
• Motor and Sensory nerve fibers
• Loose CT
• Perineurium
• Bundles axons into fascicles
• CT
• Epineurium
• Bundles fascicles into a nerve
• Fibrous CT
• CT layers contain blood vessels

Types of Nerve Signals/Fibers

• Sensory (afferent)
• Picked up by sensory receptors thru body
• Carried by nerve fibers of PNS into CNS
• Motor (efferent)
• Carried away from the CNS by nerve fibers into PNS
• Innervate muscles and glands
• Causes these organs to contract or secrete
• Remember: SAME

Sensory and Motor Signals/Fibers

• Somatic sensory
• Body senses
• touch, pressure, temperature, vibration of body, muscles stretching, balance
• Visceral sensory
• Organ senses
• Stretch, pain, temperature in organs
• (eg) nausea, hunger, cramps
• Somatic motor
• Body movement
• Voluntary contraction of skeletal muscles
• Visceral motor
• Organ movement
• Contraction of smooth muscle, glands
• = Autonomic Nervous System (involuntary)

CNS – Spinal Cord

• Runs through vertebral canal of the vertebral column
• Protected by bone, meninges, and cerebrospinal fluid
• Spinal cord made of a core of gray matter surrounded by white matter
• 31 pairs of spinal nerves branch off spinal cord through intervertebral foramen
• Functions in many ways:
• Involved in sensory and motor innervation of body inferior to the head (through spinal nerves)
• Provides a 2-way conduction pathway for signals between body and brain
• Major center for reflexes

Meninges of Spinal Cord

• Membranes surrounding the spinal cord
• 3 Layers of connective tissue
• Functions
• Protect spinal cord
• Contains cerebrospinal fluid (CSF)
• Protect blood vessels serving spinal cord

Meninges of Spinal Cord 

• Dura mater (superficial)
• Spinal dural sheath
• Does not attach to bone
• Merges w/epineurium of spinal roots & nerves
• Epidural space
• Loose CT, fat and veins
• Between dura mater and vertebra
• Not present around brain
• Subdural space
• Between dura mater and arachnoid

Meninges of Spinal Cord 

• Arachnoid mater (middle)
• Impermeable layer = barrier
• Raised off pia mater by rootlets
• Subarachnoid space
• Between arachnoid and pia mater
• Contains cerebrospinal fluid
• Contains large blood vessels
• *Runs to level of S2
• Pia mater (deep)
• Highly vascular
• Adheres to brain/spinal cord tissue
• Creates denticulate ligaments

Regions of Spinal Cord

• Cervical
• Thoracic
• Lumbar
• Sacral
• Coccygeal
• Cervical + Lumbosacral enlargements
• Cauda equina
• Conus medullaris
• Filum terminale
• CT & pia mater
• Attaches to coccyx

Gray Matter

• Consists of neuron cell bodies, unmyelinated axons, dendrites, and neuroglia
• Shaped like an “H”
• Gray commissure (crossbar)
• Central canal
• Posterior horns
• Anterior horns

Gray Matter

• Posterior horns
• Consist of interneurons that transmit in from outside spinal cord into it
• Dorsal root contain sensory fibers
• Somatic Sensory (SS)
• Visceral Sensory (VS)
• Dorsal root ganglia –clusters of cell bodies outside of CNS
• Anterior horns
• Cell bodies of motor neurons send info out of spinal cord to muscles and glands
• Ventral Root contains Motor Fibers
• Visceral Motor
• Somatic Motor

White Matter

• Surrounds gray matter
• Composed of myelinated and unmyelinated axons
• Divided into white columns (funiculi) that create tracts
• Tracts = bundles of axons traveling to similar destination
• Posterior funiculus
• Anterior funiculus
• Lateral funiculus
• Allow for communication between
• Parts of the spinal cord
• Spinal cord and brain

White Matter

• 3 types of nerve fibers:
• Ascending
• Carry sensory info from sensory neurons of body to brain
• touch, pressure, pain, temperature
• Descending
• Carry motor instructions from brain to spinal cord
• Contraction of muscles and secretion of glands
• controlling precise, skilled movement  (e.g. writing, maintain balance, create movement)
• Commissural
• Cross from one side of cord to the other

Spinal Nerves (31 Pairs)

• Part of the PNS
• Lie in intervertebral foramina
• Send lateral branches to body
• Named according to their point of attachment to spinal cord segment
• 8 pairs of cervical spinal nerves; C1-C8
• 12 pairs of thoracic spinal nerves; T1-T12
• 5 pairs of lumbar spinal nerves; L1-L5
• 5 pairs of sacral spinal nerves; S1-S5
• 1 pair of coccygeal spinal nerves; C01

Spinal Nerves

• Each spinal nerve connects to spinal cord via posterior root (sensory) and anterior root (motor)
• Each spinal nerve branches into a posterior ramus and an anterior ramus
• Anterior rami
• Supply anterior and lateral regions of the neck, trunk, and limbs
• Posterior rami
• Supply the dorsum of the neck and trunk (back)

Recurrent Meningeal Nerves
Recurrent meningeal nerves branch from spinal nerves to supply intervertebral discs, dura mater, ligaments and blood vessels.
They access the vertebral canal via intervertebral foramina.
The Big Picture

• Just lateral to the intervertebral foramen, each spinal nerve then splits in 2
• Dorsal Ramus
• Ventral Ramus

• RAMI contain BOTH Sensory and Motor fibers!!

• Remember: Roots have sensory OR motor fibers, not both

Dermatomes

• Area of skin innervated by cutaneous branches of single spinal nerve
• Clinical application for testing neurological function

Autonomic Nervous System

• Visceral Motor Function
• Not controlled voluntarily
• e.g. get nervous and sweat
• Innervates smooth muscle, cardiac muscle, glands
• Regulates visceral function
• Heart rate, blood pressure, digestion, urination
• Has 2 divisions:
• Parasympathetic
• Sympathetic

Autonomic Nervous System

• Sympathetic
• “fight or flight”
• Mobilizes the body during extreme situations
• Becomes active when extra metabolic effort needed
• Most release norepinephrine
• Axons branch widely
• Thoracolumbar division
• Fibers arise from thoracic and lumbar parts of spinal cord

• Parasympathetic
• “rest and digest”
• Enables body to unwind and calm down
• Most active when body at rest, normal activities
• Routine maintenance functions
• Most release acetylcholine
• Axons branch less
• Craniosacral division
• Fibers arise from brain and sacral spinal cord

Sympathetic Innervation

• Comes from thoracolumbar regions (T1-L2)
• Travels through anterior root and rami
• Communicates with the sympathetic trunk          (via a connection called a ramus communicans)
• Back to anterior rami (via another ramus communicans) to spinal nerve to reach target structures
• Can operate at same level of spinal cord (T1-L2) or above a different level

Parasympathetic Innvervation

• Parasympathetic innervation comes from cranio-sacral region of central nervous system
• Cranial nerves III, VII and IX provide parasympathetic innervation to structures of head and neck
• CN X (Vagus) provides parasympathetic innervation below neck to organs of thoracic & abdominal cavities
• Spinal nerves S2-S4 provide parasympathetic innervation to inferior abdominal organs, pelvic organs and tissue of perineum
•  Nerve fibers exit spinal cord through anterior roots and then anterior rami into plexuses to serve organs

Nervous System Overview

• Sensory information (visceral and somatic) travels along sensory nerves to the posterior root into the spinal cord
• The information is then processed by brain or a response is determined within the spinal cord (e.g. in a reflex arc)
• Motor information (visceral and somatic) goes out of the spinal cord through the anterior root along motor nerves to the body to make muscles contract or glands secrete

Sympathetic Innervation at Same Level of Spinal Cord

• Sympathetic fibers providing innervation through spinal nerves at same level of spinal cord (T1-L2)
• Sympathetic fibers runs through anterior root into anterior ramus
• It then connects to a white ramus communicans, which leads to the sympathetic chain ganglia and sympathetic trunk
• Fibers then pass through the gray ramus communicans back out the anterior ramus into a spinal nerve to body

Sympathetic Innervation at Different Level of Spinal Cord
Only from level T1-L2, so

• Fibers may travel out anterior root and anterior ramus
• Through white ramus communicans up or down sympathetic trunk to different level of cord
• Then through gray ramus communicans out anterior root along spinal nerve to the body