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
- Sensory fiber (dorsal root)
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