The Nervous System
-Highly organized network of billions of neurons and even more neuroglia
Contains:
Parts of the Nervous System:
-Brain
- Enclosed by skull
- Contains 100 billion neurons
- Cranial Nerves
- 12 pair
- Labeled I-XII
- Emerge from base of brain
-Nerve
- Bundle of hundreds to thousands of axons plus connective tissue and blood vessels
- Lie outside of the brain and spinal cord
- Each has defined path and serves specific region of the body
-Spinal Cord
- Connects to the brain
- Encircled by bones of the vertebral column
- Contains approx. 100 million neurons
-Spinal Nerves
- Emerge from the spinal cord
- 31 pairs
- Serve specific regions on each side of the body
-Ganglia
- Small masses of nervous tissue located outside of the brain and spinal cord
- Contain cell bodies of neurons
- Closely associated with cranial and spinal nerves
-Enteric Plexus
- Extensive network of neurons
- Found in the walls of organ in the gastrointestinal (GI) tract
- helps regulate the digestive system
-Sensory Receptors
- Dendrites of sensory neurons
or
- separate specialized cells that monitor change in internal and external environment
Functions of the Nervous System
1. Sensory Function
- Sensory receptors detect different types of internal and external stimuli
- Sensory Neurons (Afferent Neurons) carry sensory info. TO the spinal cord and brain through cranial and
spinal nerves
2. Integrative function
- Information processed by analyzing and storing information and making decisions for appropriate
responses
- Perception – conscious awareness of sensory stimuli
- Interneurons – participate in integration
o contain short axons contact nearby neurons in the brain and spinal cord
o Comprise vast major of neurons in the body
3. Motor Function:
- Response to stimulus through use of motor neurons (Efferent Neurons)
- Motor Neurons carry information FROM the brain toward the spinal cord to muscles and glands through
cranial and spinal nerves
- Causes muscle contraction and gland secretions
Organization of the Nervous System
-
Central Nervous System
Peripheral Nervous System
 Somatic Nervous System
 Autonomic Nervous System
 Sympathetic Division
 Parasympathetic Division
 Enteric Nervous System
Central Nervous System (CNS)
- Consists of: Brain and Spinal Cord
- Integrates and correlates different kinds of sensory information
- Source of thoughts, emotions, and memories
- Most nerve impulses that stimulate muscle contraction and gland secretion orginiate in the CNS
Peripheral Nervous System
- Consists of: cranial nerves, spinal nerves, ganglia and sensory receptors
- 3 divisions
o Somatic Nervous System
o Autonomic Nervous System
o Enteric Nervous System
Somatic Nervous System (SNS)
Voluntary
- Consists of sensory neurons that convey info from receptors in the head, body wall and limbs and
receptors for special senses (vision, hearing, taste, smell) TO the CNS
- Consists of motor neurons that conduct impulses FROM the CNS to skeletal muscles
Autonomic Nervous System (ANS)
- Involuntary
- Consists of sensory neurons which convey information from receptors in organ (i.e. stomach, lungs) TO the
CNS
- Consists of motor neurons that conduct impulses FROM CNS to smooth muscle, cardiac muscle, glands
- 2 Divisions of the ANS
o Sympathetic Division
 Helps support exercise and emergency actions of “fight or flight” response
o Parasympathetic Division
o Takes care of “rest and digest” activities
- *The 2 divisions usually have opposing actions
o Ex: Sympathetic neurons speed the heartbeat and parasympathetic neurons slow it down
Enteric Nervous System (ENS)
- Involuntary
- “the brain of the gut”
- Sensory neurons monitor chemical changes wtihin the GI tract and the stretching of its walls
- Motor neurons govern
o contractions of GI tract smooth muscle
o secretions of GI tract organs (stomach acid secrections)
o activity of GI tract endocrine cells