Introduction to Nerves and the Nervous System

Role of the Nervous System

• Controls the functions of the human body
• Analyzes incoming stimuli
• Integrates internal and external responses

Makeup of the Nervous System

• Central nervous system (CNS)
  • Composed of the brain and spinal cord
• Peripheral nervous system (PNS)
  • Sensory receptors bring information into the CNS
  • Motor nerves carry information away from the CNS
• Autonomic nervous system (ANS)
  • Uses components of the CNS and PNS to regulate automatic or unconscious responses to stimuli

Functions of the Cells That Make Up the Nervous System

• Allow movement
• Allow realization of various sensations
• Provide response to internal and external stimuli
• Stimulate learning, thinking, and emotions

Neuron

 

 

Types of Axons

• Afferent fibers
  • Nerve axons that run from peripheral receptors into the CNS
• Efferent fibers
  • Nerve axons that carry nerve impulses from the CNS to the periphery to stimulate muscles or glands

Action Potential

 

 

Electrolytes Involved in Nerve Cell Action

• Sodium
• Potassium
• Calcium

Movement of Electrolytes With Action

• Rest/repolarization
  • Membrane is impermeable to sodium
  • Membrane is permeable to potassium
• Action/depolarization
  • Sodium goes into the cell
  • Potassium leaves the cell

Formation of Myelin Sheath

 

 

Nerve Synapse

• Presynaptic nerve
• Synaptic cleft
• Postsynaptic effector cell

Neurotransmitters

• Acetylcholine
  • Communicates between nerves and muscles
• Norepinephrine and epinephrine
  • Catecholamines released by nerves in the sympathetic branch of the ANS
• Dopamine
  • Involved in the coordination of impulses and responses
• Gamma-aminobutyric acid (GABA)
  • Inhibits nerve activity and is important in preventing overexcitability or stimulation such as seizure activity
• Serotonin
  • Important in arousal and sleep and in preventing depression and promoting motivation

Central Nervous System

• Made up of brain and spinal cord
• Structures are covered by meninges
• Blood–brain barrier
• Blood supply to the brain

Anatomy of the Brain

 

 

Hindbrain

• Runs from the top of the spinal cord into the midbrain
• Most primitive part of the brain: contains the brain stem
• Controls basic vital functions:
  • Breathing
  • Blood pressure
  • Swallowing
  • RAS

Midbrain

• Contains the thalamus, the hypothalamus, and the limbic system
  • The thalamus sends direct information into the cerebrum to transfer sensations
  • The hypothalamus acts as the major sensor of activity in the body
    • Temperature regulation
    • Water balance
    • Appetite
    • Endocrine function

Limbic System

• Contains high levels of the neurotransmitters:
  • Epinephrine
  • Norepinephrine
  • Serotonin
• Controls expression of emotions

Forebrain

• Made up of 2 cerebral hemispheres joined together by the corpus callosum
• Receives and sends nerve impulses, coordinates speech and communication, and facilitates learning

Spinal Cord

• Made up of 31 pairs of spinal nerves
• Each spinal nerve has 2 components or roots
  • Sensory fiber (dorsal root)
    • Brings information into the CNS from the periphery
  • Motor fiber (ventral root)
    • Causes movement or reaction

Functions of Central Nervous System

• Sensory functions
• Motor functions
• Intellectual and emotional functions

Intellectual and Emotional Function

• Two hemispheres of the brain process information differently
• Right side
  • Artistic
• Left side
  • Analytical
• When learning takes place, an actual change occurs in a neuron
• Some degree of stress facilitates learning
• Increased stress inhibits learning
• The limbic system plays a role in learning
• Emotions associated with memory and the present have an impact on stimulus response