Spinal Cord and Nerves

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• Spinal Cord and Nerves

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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

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Divisions of the Nervous System

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

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Review of Nervous Cells

• Neuron
• Cell body
• Dendrite
• Axon
• Myelin Sheath
• Neuroglia
• Interneuron
• Reflex Arc
• Synapse

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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

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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

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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)

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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

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Spinal Cord Segments
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Meninges of Spinal Cord

• Dura mater (superficial)
• Spinal dural sheath
• Does not attach to bone
• Epidural space
• Fat and veins
• Between dura mater and vertebra
• Subdural space
• Between dura mater and arachnoid

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Meninges of Spinal Cord

• Arachnoid mater (middle)
• Impermeable layer barrier
• Raised off pia mater by rootlets
• Subarachnoid space
• Between arachnoid and pia mater
• Contains CSF
• Pia mater (deep)
• Highly vascular
• Adheres to brain/spinal cord tissue

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Regions of Spinal Cord

• Cervical
• Thoracic
• Lumbar
• Sacral
• Coccygeal
• Cervical Lumbar enlargements
• Cauda equina
• Conus medullaris
• Filum terminale

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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

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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 - swelling in dorsal root
  that these interneurons pass through
• 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

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White Matter

• Surrounds gray matter
• Composed of myelinated and unmyelinated axons
• Divided into white columns (funiculi)
• Posterior funiculus
• Anterior funiculus
• Lateral funiculus
• Allow for communication between
• Parts of the spinal cord
• Spinal cord and brain

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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
• control precise, skilled movement writing,
  maintain balance, create movement
• Commissural
• Cross from one side of cord to the other

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Spinal Nerves (31 Pairs)

• Part of the PNS (Somatic)
• Lie in intervertebral foramina
• Send lateral branches to body
• Named according to their point of issue from the
  vertebral column
• 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

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Spinal Nerves

• Each spinal nerve connected to spinal cord via
  dorsal (sensory) and ventral (motor) root
• Spinal nerves branch into dorsal ramus and
  ventral ramus
• Ventral ramus
• Connects to rami communicates, which then lead to
  sympathetic chain ganglia
• Supply anterior and lateral regions of the neck,
  trunk, and limbs
• Dorsal ramus
• Supply the dorsum of the neck and trunk (back)

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The Big Picture

• Just lateral to intervertebral foramen, each
  spinal nerve then splits in 2
• Dorsal Rami
• Ventral Rami
• Contain BOTH Sensory and Motor fibers!!

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Autonomic Nervous System

• Visceral Motor Function
• Not easily controlled by will
• Get nervous and sweat
• Innervate smooth muscle, cardiac muscle, glands
• Regulate visceral function
• Heart rate, blood pressure, digestion, urination
• Has 2 divisions
• Parasympathetic
• Sympathetic

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ANS

• Parasympathetic
• Enables body to unwind and calm down
• Most active when body at rest
• Routine maintenance functions
• Craniosacral division
• Fibers emerge from brain and sacral spinal cord

• Sympathetic
• fight or flight
• Mobilizes the body during extreme situations
• Becomes active when extra metabolic effort needed
• Thoracolumbar division
• Fibers arise from thoracic and lumbar parts of
  spinal cord

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Somatic Nervous System

• Innervates skeletal muscle
• Neurons runs from CNS directly to muscle
• Consists of single neuron plus skeletal muscle
  cells
• Voluntary control
• Running, moving limbs, typing on a computer!