NERVOUS SYSTEM

• Nervous System - Master control and communication system of the body
• Nervous System Functions

  • Provides for higher mental function and emotional expression
  • Regulates and maintains homeostasis
  • Regulates the activities of muscles and glands
• Nervous Tissue

  • Made up of closely packed cells that are separated by very little amount of intercellular substance.
  • Organized to comprise the Nervous System.
• Purpose of Nervous System

  • Carry sensory information from the sensory organs to the brain.
  • Process that sensory information in the brain to produce perceptions, memories, decisions, and plans.
  • Carry motor information from the brain to the skeletal muscles in order to exert an influence on the individual’s surroundings.
• Classification of Nervous System

  • Structural Classification
  • Functional Classification
• Structural Classification of Nervous System

  • Central Nervous System - Brain and Spinal cord
  • Act as the integrating and command centers of the nervous system.
• Structural Classification of Nervous System

  • Peripheral Nervous System - Spinal Nerves and Cranial Nerves
  • Nerves serve as communication lines.
• Sensory Division or Afferent Division - consists of nerves that convey impulses to the central nervous system from sensory receptors located in various parts of the body.
• Sensory Division or Afferent Division

  • Somatic sensory fibers – fibers delivering impulses from the skin, skeletal muscle, and joints
  • Visceral sensory fibers – transmit impulses from visceral organs
• Functional Classification: Motor Division

  Motor division or Efferent division - carries impulses from the CNS to effector organs, the muscles and glands.
• Two Subdivisions of Motor Division

  • Somatic Nervous System – allows us to consciously, or voluntarily, control our skeletal muscles.
• Two Subdivisions of Motor Division

  • Autonomic Nervous System - regulates events that are automatic, or involuntary, such as the activity of smooth muscle, cardiac muscle, and glands.
  • Sympathetic Nervous System
  • Parasympathetic Nervous System
• Nervous Tissue: Structure and Function

  Supporting Cells

  • lumped together as Neuroglia in the CNS
  • Support, insulate, and protect the delicate neurons
• Nervous Tissue: Structure and Function

  Supporting Cells - Different types of Neuroglia

  • Astrocytes
  • Microglia
  • Ependymal
  • oligodendrocytes
  • schwann cells
  • satellite cells
• Nervous Tissue: Structure and Function

  Neurons – aka NERVE CELLS

  • highly specialized to transmit messages (nerve impulses) from one part of the body to another.
• Supporting Cells: Types of Neuroglia (CNS)

  • Astrocytes – abundant star-shaped cells that account for nearly half of neural tissue. Form a living barrier between capillaries and neurons.
• Supporting Cells: Types of Neuroglia (CNS)

  • Microglia – spiderlike phagocytes that monitor the health of nearby neurons and dispose of debris
• Supporting Cells: Types of Neuroglia (CNS)

  • Ependymal cells – line the central cavities of the brain and the spinal cord. The beating of their cilia helps to circulate the cerebrospinal fluid that fills those cavities and forms a protective watery cushion around the CNS.
• Supporting Cells: Types of Neuroglia (CNS)

  • Oligodendrocytes – wrap their flat extensions (processes) tightly around the nerve fibers, producing fatty insulating coverings called myelin sheaths
• Supporting Cells: Types of Neuroglia (PNS)

  • Schwann Cells - form the myelin sheaths around nerve fibers in the PNS.
• Supporting Cells: Types of Neuroglia (PNS)

  Satellite Cells - act as protective, cushioning cells for peripheral neuron cell bodies.
• Neurons - building blocks of the nervous system
• Neurons (Nerve Cells)

  Processes of:

  • Dendrites - Plasma membrane contain specialized receptors that react to the release of neurotransmitters.
  • Axons - Plasma membrane is specialized to transmit electrochemical signals called action potentials.
• Parts of Neurons

  • Cell Body - the metabolic center of the neuron.
  • Nissl bodies – rough ER
  • Neurofibrils – intermediate filaments that maintain cell shape
• Parts of Neurons

  • Processes/Fibers
  • Dendrites – convey incoming electrical signals toward the cell body
  • Axons – generate nerve impulses and conduct them away from the cell body. It arises from a conelike region of the cell body called the axon hillock.
• Parts of Neurons

  • Axon terminals – contains hundreds of tiny vesicles or membranous sacs that contain chemicals called neurotransmitters
• Parts of Neurons

  • Synaptic cleft – tiny gap that separate each axon terminal from the next neuron.
  • This functional junction is called a synapse.
• Parts of Neurons

  • Myelin Sheaths – whitish, fatty material with a waxy appearance that covers the long nerve fibers. It protects and insulates fibers and increased the transmission rate of nerve impulses.
• Neuron Terminology -

  • Clusters of neuron cell bodies and collections of nerve fibers are named differently in the CNS and in the PNS.
  • Clusters of neuron Cell Bodies
  • CNS – Nuclei
  • PNS - Ganglia
  • Bundles of Nerve Fibers/ Neuron Processes
  • CNS - tracts
  • PNS - nerves
• White matter - consists of dense collections of myelinated fibers
• Functional Classification of Neurons

  • Sensory Neurons
  • Motor Neurons
  • Interneurons
• Sensory Neurons

  • Aka known as Afferent Neurons
  • The cell bodies of sensory neurons are always found in a ganglion outside the CNS.
• Sensory Neurons

  • Neurons that carry impulses from sensory receptors to the CNS
  • Sensory neurons keep us informed about what is happening both inside and outside the body
• Types of Sensory Receptors

  • Pain and temperature receptors - Naked/Free/Bare nerve endings
  • Touch receptors - Meissner’s corpuscles
  • Deep pressure receptors – Pacinian/Lamellar corpuscles
  • Proprioceptor – detects the amount of stretch or tension in the skeletal muscles, their tendons and joints
• Motor Neurons

  • Aka Efferent Neurons
  • The cell bodies of motor neurons are usually located in the CNS.
  • Motor (efferent) neurons transmit impulses from the CNS to effectors in the body periphery.
• Interneurons

  • Aka Association Neurons
  • Their cell bodies reside in the CNS.
  • They connect the motor and sensory neurons in neural pathways
• Structural Classification of Neuron

  • Multipolar Neuron – the most common type, with several processes.
  • Bipolar Neuron – With two processes (one axon and one dendrite); Found only in some special sense organs
• Structural Classification of Neuron

  • Unipolar Neuron – with single process emerging from the cell body
  • Divided into proximal (central) and distal (peripheral) processes
  • Only the small branches at the end of peripheral process are dendrites
  • The remainder of the peripheral and central process function as axon
• Functional Properties of Neurons

  • Irritability – ability to respond to a stimulus and convert it into a nerve impulse
  • Conductivity – ability to transmit the impulse to other neurons, muscles or glands
• Reflexes - are rapid, predictable, and involuntary responses to stimuli

  • Somatic reflexes – reflexes that stimulate the skeletal muscles
  • Autonomic reflexes – regulate the activity of the smooth muscles, the heart, and glands