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Neurons transmit nerve impulses between parts of the nervous system. ... The central nervous system (CNS) is made up of the spinal cord and the brain. ...

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chapter 12

Chapter 12

Nervous System

outline
Outline
  • Nervous Tissue
  • The Nerve Impulse
    • Action Potential
  • Central Nervous System
    • The Spinal Cord
    • The Brain
  • Peripheral Nervous System
    • Nerves and Ganglia
  • Drug Abuse
  • Degenerative Nervous System Diseases
nervous tissue
Nervous Tissue
  • Nervous Tissue contains two types of cells.
    • Neurons transmit nerve impulses between parts of the nervous system.
    • Neuroglia support and nourish neurons.
neuron structure
Neuron Structure
  • Neurons are classified according to function.
    • Sensory neurons take impulses from a sensory receptor to the CNS.
    • Interneurons receive input from sensory neurons, and other neurons, and then communicate with motor neurons.
    • Motor neurons take nerve impulse away from the CNS to an effector that carries out responses to environmental change.
neuron structure5
Neuron Structure
  • Neurons contain three basic parts.
    • Cell body contains nucleus and other organelles.
    • Dendrites receive signals from sensory receptors or other neurons.
    • Axon conducts nerve impulses.
myelin sheath
Myelin Sheath
  • Some axons are covered by a protective myelin sheath.
    • Formed by Schwann cells containing myelin in plasma membranes.
    • Nodes of Ranvier are gaps on the axon with no myelin sheath.
the nerve impulse
The Nerve Impulse
  • The nervous system uses the nerve impulse to convey information.
    • Resting potential is the voltage level when an axon is not conducting an impulse.
  • Sodium-potassium pump causes greater concentration of Na+ outside the axon, and greater concentration of K+ inside the axon.
    • Unequal ion distribution causes inside of axon to be negative relative to the outside.
action potential
Action Potential
  • An action potential is a rapid change in polarity across an axomembrane as the nerve impulse occurs.
    • All-or-none once threshold is reached.
      • Sodium gates open, allowing Na+ to move inside the axon.
      • Potassium gates open, allowing K+ to move outside the axon.
transmission across a synapse
Transmission across a Synapse
  • Transmission across a synaptic cleft is carried out by neurotransmitters stored in synaptic vesicles.
    • Depending on the neurotransmitter and the receptor, the response of the postsynaptic neuron can be towards excitation or inhibition.
      • Integration is the summing of signals received by a postsynaptic neuron.
the central nervous system
The Central Nervous System
  • The central nervous system (CNS) is made up of the spinal cord and the brain.
    • Both are wrapped in protective membranes, meninges, with spaces between meninges filled with cerebrospinal fluid.
  • CNS is composed of two types of nervous tissue.
    • Gray matter – Short, nonmyelinated fibers.
    • White matter - Myelinated axons.
the spinal cord
The Spinal Cord
  • The spinal cord extends from the base of the brain through the foramen magnum into the vertebral canal.
functions of the spinal cord
Functions of the Spinal Cord
  • The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord, and is a center for reflex actions.
the brain
The Brain
  • The Cerebrum.
    • The cerebrum, telencephalon, is the largest portion of the human brain.
      • Communicates with, and coordinates activities of, other parts of the brain.
      • Divided into left and right cerebral hemispheres.
        • Divided by longitudinal fissure.
the brain20
The Brain
  • Gray matter of cerebrum consists of cerebral cortex and basal nuclei.
    • Cerebral cortex is a highly convoluted outer layer that covers the cerebral hemispheres.
    • Basal nuclei are masses located deep within white matter.
  • White matter consists of long myelinated axons organized into tracts.
the brain22
The Brain
  • Diencephalon is made up of hypothalamus and thalamus, and circles the third ventricle.
  • Cerebellum is separated from the brain stem by the fourth ventricle.
  • The brain stem contains the midbrain, pons, and medulla oblongata.
    • Reticular formation is a complex network of nuclei and fibers extending the length of the brain stem.
the limbic system
The Limbic System
  • Limbic system is a complex network of tracts and nuclei.
    • Blends primitive emotions and higher mental functions into a united whole.
    • Composed of hippocampus and amygdala.
higher mental functions
Higher Mental Functions
  • Memory is the ability to hold a thought in mind or to recall events from the past.
    • Short-term versus long-term.
    • Skill memory.
  • Learning takes place when we retain and utilize past memories.
  • Language and speech depends on motor centers in the occipital and temporal lobes.
language and speech28
Language and Speech
  • Left and right brain have different functions.
    • Left Hemisphere:
      • Verbal, Logical, Analytical, Rational.
    • Right Hemisphere:
      • Nonverbal, Intuitive, Creative.
peripheral nervous system
Peripheral Nervous System
  • Composed of nerves and ganglia.
      • Cranial nerves take impulses to and from the brain.
      • Spinal nerves take impulses to and from the spinal cord.
somatic system
Somatic System
  • Somatic system includes nerves that take sensory information from external sensory receptors to the CNS and motor commands away from the CNS to the skeletal muscles.
    • Reflexes are automatic responses to a stimulus.
autonomic system
Autonomic System
  • Autonomic system regulates the activity of cardiac and smooth muscles and glands.
    • Sympathetic division brings about fight or flight responses.
    • Parasympathetic division brings about relaxed responses.
drug abuse
Drug Abuse
  • Drugs that affect the nervous system have two general effects.
    • Impact limbic system.
    • Promote or decrease action of a particular neurotransmitter.
  • Drug abuse is apparent when a person takes a drug at a dose level and under circumstances that increase the potential for a harmful effect.
drug abuse36
Drug Abuse
  • Alcohol.
  • Nicotine.
    • Causes neurons to release dopamine.
      • Excess dopamine has reinforcing effect that leads to dependence.
  • Cocaine.
    • Prevents synaptic uptake of dopamine.
      • Continued use causes body to produce less dopamine.
drug abuse37
Drug Abuse
  • Heroin.
    • Binds to receptors meant for endorphins.
      • Continued use causes body to produce fewer endorphins.
  • Marijuana.
    • Binds to receptor for anandamide.
      • Brain impairment?
homeostasis
Homeostasis
  • Governance of internal organs and the regulation of blood and tissue fluid usually takes place below the level of consciousness.
    • Heart Rate.
    • Breathing Rate.
degenerative nervous system diseases
Degenerative Nervous System Diseases
  • Alzheimer disease.
    • Presence of abnormal neurons.
      • Plaques.
      • Neurofibrillary tangles.
  • Parkinson disease.
    • Overactive basal nuclei due to the degeneration of dopamine-releasing neurons in the brain.
review
Review
  • Nervous Tissue
  • The Nerve Impulse
    • Action Potential
  • Central Nervous System
    • The Spinal Cord
    • The Brain
  • Peripheral Nervous System
    • Nerves and Ganglia
  • Drug Abuse
  • Degenerative Nervous System Diseases