Introduction to:
The Nervous System

Highly organized  Contains:
network of billions
 Brain
on neurons and
 Cranial Nerves
even more
 Spinal Cord
neuroglia
 Spinal Nerves
 Ganglia
 Enteric Plexus
 Sensory Receptors
Parts of the Nervous System:
Brain
Enclosed by skull
 Contains 100 billion neurons

Parts of the Nervous System:
Cranial Nerves
12 pair
 Labeled I-XII
 Emerge from base of brain

Parts of the Nervous System:
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

Parts of the Nervous System:
Spinal Cord
Connects to the brain
 Encircled by bones of the vertebral
column
 Contains approx. 100 million neurons

Parts of the Nervous System:
Spinal Nerves
Emerge from the spinal cord
 31 pairs
 Serve specific regions on each side of
the body

Spinal nerve diagram:
http://vitalfrequency.com/blogs/2010/03/09/
pain-free-drug-free/spinal-nerves-2/

Parts of the Nervous System:
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

Parts of the Nervous System:
Enteric Plexus
Extensive network of neurons
 Found in the walls of organs in the
gastrointestinal (GI) tract
 helps regulate the digestive system

Parts of the Nervous 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
Functions of the Nervous System
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


contain short axons contact nearby neurons in
the brain and spinal cord
Comprise vast major of neurons in the body
Functions of the Nervous System
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 originate
in the CNS


Peripheral Nervous System
Consists of: cranial nerves, spinal
nerves, ganglia and sensory receptors
 3 divisions

 Somatic Nervous System
 Autonomic Nervous System
 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

Autonomic Nervous System (ANS)

2 Divisions of the ANS
 Sympathetic Division
○ Helps support exercise and emergency actions of
“fight or flight” response
 Parasympathetic Division
○ Takes care of “rest and digest” activities

*The 2 divisions usually have opposing
actions
 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 within the GI tract and the
stretching of its walls
 Motor neurons govern

 contractions of GI tract smooth muscle
 secretions of GI tract organs (stomach acid
secretions)
 activity of GI tract endocrine cells