Nervous System

• Nervous System


  Allows animals to respond to changes in their internal and external environment
• Nervous System


  • Irritability - responds to changes
  • Reception of stimulus
  • Conduction of a signal
  • Response by an effector
• Functions of the Nervous System

  • Sensory - detects changes in internal and external environment
  • Integrative - brings sensory information together and makes decisions
  • Motor - responds to stimuli by initiating muscular contraction or glandular secretion
• Types of Nervous Systems in Animals

  • Nerve net (cnidarians, echinoderms)
  • Linear/Bilateral/Ladderlike (flatworms)
  • Centralized (annelids, arthropods, vertebrates)
• Nerve net


  • Simplest nervous system organization
  • Network of nerve cells (protoneurons) connected to receptors in epidermis
  • Single impulse travels in all directions producing a generalized response or contraction
• Ring-like nervous system


  • Consists of a ring around the esophagus with five nerves radiating outward
  • No brain
• Linear/Bilateral/Ladderlike nervous system


  • Distinct ganglia ("brain") connected to two main nerve trunks/cords running posteriorly and laterally
• Centralized nervous system


  • Two ventral nerve cords, with pair of ganglia, afferent and efferent neurons in each body segment
• Vertebrate nervous system


  • Embryonically with single, hollow, dorsal nerve cord
  • Exhibit cephalization with anteriorly located brain connected to spinal cord and nerves
• Neuron


  Nerve cell, the functional unit of the nervous system
• Parts of a neuron

  • Cell body (soma, perikaryon)
  • Dendrites - highly branched, carry nerve signals toward cell body
  • Axon - long fiber, typically carries signals away from cell body
• Functional classification of neurons

  • Sensory/Afferent - receive stimuli and transmit impulses to CNS
  • Motor/Efferent - transmit impulses from CNS to muscles and glands
  • Interneurons/Association - connect afferent and efferent neurons
• Structural classification of neurons

  • Unipolar
  • Bipolar
  • Multipolar
• Neuroglia


  Non-neuronal cells that support and protect neurons but do not conduct impulses
• Types of neuroglia


  • Astrocytes
  • Oligodendrocytes
  • Microglia
  • Ependymal cells
  • Schwann cells
• Resting membrane potential


  The membrane of a nerve cell is selectively permeable to K+ which tends to diffuse outward, making the outer membrane more positively charged and the inner negatively charged (-70 mV)
• Action potential


  A rapid depolarization of a nerve membrane, with the outside becoming highly negative compared to the inside, associated with increased permeability to Na+ ions
• Synapse


  Functional junction between two neurons or between a neuron and an effector organ
• Types of synapses


  • Electrical - action potential travels across a narrow gap junction
  • Chemical - involve neurotransmitters to transmit impulses
• Neurons in a chemical synapse


  • Presynaptic - conducting impulses toward the synapse
  • Postsynaptic - carrying impulses away
• Central Nervous System (CNS)


  Acts as the "main switchboard" controlling and coordinating the entire nervous system, consisting of the brain and spinal cord
• Peripheral Nervous System (PNS)


  Carries messages between the CNS and the rest of the body, consisting of cranial and spinal nerves
• Subdivisions of the PNS

  • Somatic Nervous System - conveys information from receptors to CNS and from CNS to skeletal muscles
  • Autonomic Nervous System - conveys information from visceral receptors to CNS and from CNS to smooth muscles, cardiac muscles, and glands
• Branches of the Autonomic Nervous System

  • Sympathetic - responds to increased activity and emergencies, utilizes body energy
  • Parasympathetic - opposes sympathetic actions, active when body is at rest, involved in restoration and conservation of energy
• Reflex arc


  Simple neural pathway linking a receptor and an effector
• Parts of a reflex arc

  • Receptor
  • Afferent/sensory neuron
  • CNS
  • Efferent/motor neuron
  • Effector
• Reflex


  Rapid, predictable and involuntary responses to stimuli
• Types of reflexes


  • Somatic - stimulate skeletal muscles
  • Autonomic - regulate smooth muscles, cardiac muscles, and glands
• Brain


  • Largest organ of the body, covered and protected by the skull, covered by the meninges (dura mater, arachnoid, pia mater)
  • Three principal divisions: Forebrain, Midbrain, Hindbrain
• Development of the brain from primary brain vesicles

  • Forebrain (Telencephalon, Diencephalon)
  • Midbrain (Mesencephalon)
  • Hindbrain (Metencephalon, Myelencephalon)
• Cerebrum


  Largest part of the brain, divided into right and left hemispheres
• Brain


  One of the largest organs of the body
• Brain


  • Covered and protected by skull
  • Covered by the meninges: pia mater, arachnoid, and dura mater
• Dura mater


  The outermost layer of the meninges; a double-layered membrane
• Arachnoid mater


  The middle layer of the meninges
• Pia mater


  The innermost layer of the meninges, the most delicate
• Principal divisions of the brain

  • Forebrain
  • Midbrain
  • Hindbrain
• Telencephalon


  Part of the forebrain that develops into the cerebrum
• Diencephalon


  Part of the forebrain that develops into the thalamus and hypothalamus
• Mesencephalon


  The midbrain