NERVOUS SYSTEM

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NERVOUS SYSTEM

• CENTRAL PERIPHERAL NERVOUS SYSTEMS

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Structural Divisions of Nervous System

• Central Nervous System (CNS)
• Brain, Spinal Cord
• Peripheral Nervous System (PNS)
• Cranial Nerves
• Spinal Nerves

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CNS Brain

• Four Major Brain Regions
• Cerebrum
• Diencephalon
• Brainstem
• Cerebellum

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CNS Cerebrum

• Cerebrum
• Largest, Superior
• Two Hemispheres
• Separated By Longitudinal Fissure
• Connected by Corpus Callosum (myelinated axons)
• Two Layers Outer Cortex (gray matter)
• Inner White matter

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Cerebrum continued

• Cerebral Cortex
• Neuron Cell Bodies Unmyelinated processes
• Gyri (ridges) Sulci (grooves)
• White Matter (Myelinated axons)
• Nuclei (gray matter imbedded in white)

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Lobes of Cerebrum

• Each Cerebral Hemisphere has 5 Lobes
• Frontal Personality, Judgment, Behavior,
  Voluntary control of skeletal muscle
• Parietal Sensory Input from Skin Organs
• Temporal Hearing, Smell
• Occipital Vision
• Insula Monitors Internal Organs Responsible
  for Aversions

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CNS - Diencephalon

• Diencephalon
• Enclosed by Cerebrum
• Between Cerebrum Brainstem
• Epithalamus
• Thalamus
• Hypothalamus

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Diencephalon Epithalamus

• Superior to Thalamus Third Ventricle
• Contains the Pineal Gland, Produces Hormones
• Includes Choroid Plexus

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Diencephalon Thalamus

• Switchboard for all Sensory Impulses to
  Cerebral Cortex
• Consists of 2 lobes joined by a bridge of gray
  matter Intermediate Mass
• Surrounded by Third Ventricle

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Diencephalon Hypothalamus

• Below Thalamus
• Coordinates Neural Endocrine functions
• Controls Integrates ANS
• Helps regulate body temperature
• Feeding/Thirst

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CNS - Brain Stem

• Between Diencephalon Spinal Cord
• Three parts
• Midbrain
• Colliculi Visual Auditory Nuclei
• Pons Below Midbrain, Fiber Tracts, Joins
  Cerebellum to brainstem
• Medulla Oblongata Below Pons, Cardiovascular
  Resp. Rhythmicity Centers, Joins Brain Spinal
  Cord

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CNS - Cerebellum

• Inferior to Cerebrum, Posterior to Brain Stem
• Joined to brainstem by Pons
• Two hemispheres with convoluted surfaces
• Outer Gray Matter
• Arbor Vitae (Inner, Branching White Matter)
• Provides involuntary coordination of body
  movements

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CNS - Brain Ventricles

• Ventricles
• Cavities within Brain, Filled with CSF
• Continuous with Subarachnoid Space Central
  Canal of Spinal Cord
• Lateral Largest Two, within Cerebral
  Hemispheres
• Third Narrow, Midline, Diencephalon
• Fourth Brain Stem, Continuous with Central
  Canal of Spinal Cord

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Fig. 8.36
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Protection of the CNS

• CNS Protected by
• Bone
• Skull (Brain)
• Vertebrae (Spinal Cord)
• Meninges (C.T. membranes)
• Cerebrospinal Fluid (CSF)
• Blood-Brain barrier (harmful substances in blood)

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CNS Meninges

• Meninges - CT Membranes between Bone CNS
• Dura Mater
• Outer, Tough, Fibrous, Double
• Extends down vertebral cavity, beyond end spinal
  cord
• Dural Sinuses Veins between layers
• Dural Folds Innermost layer extents into
  fissures
• Epidural Space Between walls of vertebral
  cavity Dura of spinal cord

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CNS Meninges

• Arachnoid Mater
• Thin, Spidery, Middle
• Extends past spinal cord
• Subdural Space Between Dura Arachnoid
• Subarachnoid Space Between Arachnoid Pia
  Contains CSF
• Pia Mater
• Innermost, Delicate
• Attached to Surface of Brain Spinal Cord
• Highly Vascular

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CNS - Cerebrospinal Fluid (CSF)

• Secreted by Choroid Plexuses (capillaries
  ependymal cells in ventricles)
• Clear, Similar to Blood Plasma
• Most CSF produced by Lateral Ventricles
• Circulates through Ventricles, Subarachnoid
  Space, Central Canal
• Supports, Absorbs Shocks, Provides Nutrients
• Sample via Spinal Tap (Subarachnoid Space, L-4)

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Spinal Tap
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CNS Spinal Cord

• Protected by Bone, Meninges, CSF
• Vertebral Cavity
• Extends from Medulla Oblongata (Through Foramen
  Magnum) to L2
• 16-18 inches
• Two Enlargements (Limb Control)
• Cervical (Shoulder Arms)
• Lumbar (Pelvis Legs)

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CNS Spinal Cord continued

• Outer White Matter - Bundles Myelinated Axons
• Ascending Tracts or Pathways
• Sensory
• From Sensory Receptors to CNS
• Descending Tracts or Pathways
• Motor
• From CNS to Glands or Muscles

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CNS Spinal Cord continued

• Inner Gray Matter
• Neuron Cell Bodies (somas) unmyelinated
  processes
• Dorsal Ventral Horns project towards outer
  surface
• Dorsal Gray Horn Interneuron Somas
• Ventral Gray Horn Somas of Motor Neurons
• Central Canal through Grey Commissure

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Peripheral Nervous System - PNS

• Consists of
• Peripheral Nerves
• Cranial Nerves
• Spinal Nerves Nerve Plexuses
• Ganglia
• Sensory Receptors
• Carries Sensory Information Motor Commands

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PNS Nerves

• Bundles of Axons
• Sensory, Motor or Mixed
• CT Reinforced
• Endoneurium Surrounds each axon
• Perineurium Around each fascicle (group of
  axons)
• Epineurium Tough, Fibrous C.T. around Nerve

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PNS Cranial Nerves

• Twelve Pairs
• Arise from Cerebrum Brain Stem
• Function
• Sensory
• Motor
• Mixed

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PNS Spinal Nerves

• 31 Pairs
• 8 Cervical
• 12 Thoracic
• 5 Lumbar
• 5 Sacral
• 1 Coccygeal
• All are Mixed both Sensory (Afferent) Motor
  (Efferent)
• Attach to Spinal Cord by Ventral Dorsal Root

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Fig. 8.21
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PNS Nerve Plexuses

• Networks of Spinal
  Nerve Branches
• Cervical
• Brachial
• Lumbar
• Sacral

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Reflex Arcs

• Simple Conduction Pathway
• May not involve brain
• Results in Reflex
• Fast, Predictable
• Automatic motor response
• Five Components
• Receptor
• End of dendrite of sensory neuron
• Responds to specific stimuli
• Sensory Neuron (Receptor to CNS)

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Reflex Arcs continued

• Interneuron
• CNS Gray Matter
• Usually one but may be 0 or gt1
• Transmits, Inhibits, or Reroutes to Motor Neuron
• Motor Neuron (CNS to Effector)
• Effector
• Muscle or Gland responds to motor impulse
• Response is Reflex (e.g. knee jerk, secretion of
  digestive juices, pain withdrawl)

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Types of Reflexes

• Somatic reflexes
• Skeletal muscle
• Involuntary (Autonomic) reflexes
• Smooth muscle
• Heart and blood pressure
• Glandular secretion
• Digestive system regulation

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Autonomic Reflex