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Nervous System
Structure
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Brain
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Housed within a protective skull
Contains about 100 billion neurons
Structure
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Cranial nerves
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Emerge from the base of the brain
Twelve pairs (numbered I – XII)
Structure
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Spinal cord
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Connects to the brain
Protected by the bones of the vertebral column
Contains about 100 neurons
Structure
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Spinal nerves
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Emerges from the spinal cord
31 pairs of nerves
 each serves a specific region on
the right or left side of the body
Structures
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Ganglia
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Small masses of nervous tissue
Located outside of the brain and spinal cord
Closely associated with cranial/spinal nerves
Plexus
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Extensive networks of neurons
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Example: enteric plexus
Located in walls of gastrointestinal tract organs
Regulate digestive system
Receptors
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Helps monitor internal or external environment
Ganglia
Plexus
Functions
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Sensory function
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Detects internal stimuli
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Detects external stimuli
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Ex: increase in blood acidity
Ex: raindrop landing on your arm
Afferent or sensory neurons carry sensory information into the
brain/spinal cord
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Af : toward
Ferrent: carried
Functions
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Integrative function
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Processes sensory info and making appropriate responses
Interneurons are neurons that serve this function
Make up the vast majority of neurons in the body
Functions
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Motor function
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Responds to the integration decisions
Carry info out of the brain/spinal cord
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Efferent neurons or motor neurons carry out this function
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ef: away from
ferrent: carried
Effectors: cells and organs innervated by motor neurons
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Ex: muscle fibers, glandular cells
Organization of the Nervous System
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Central Nervous System (CNS)
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Peripheral Nervous System (PNS)
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Somatic Nervous System (SNS)
Autonomic Nervous System (ANS)
Enteric Nervous System (ENS)
Central Nervous System (CNS)
Brain and spinal cord
Incoming sensory information is processed and
correlated.
Thoughts, emotions, memories
Most nerve impulses originate in the CNS
Peripheral Nervous System (PNS)
All nervous tissue outside the CNS
cranial and spinal nerves
ganglia
sensory receptors
PNS
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SNS
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Somat = body
Afferent neurons sends information from the body to the CNS
Efferent neurons from CNS conducts impulses only to skeletal
muscles
Voluntary
ENS
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Enter = intestines
“brain of the guts”
involuntary
PNS : Autonomic Nervous System (ANS)
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Afferent neurons convey info from sensory receptors to
the CNS
Efferent neurons from CNS conduct nerve impulses to
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smooth muscles
Cardiac muscles
Glands
Adipose tissue
Involuntary
Consist of 2 branches
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Sympathetic
Parasympathetic
Branches of the ANS
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Sympathetic Division
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Parasympathetic Division
Nerve impulses stimulates the organ
to increase its activity
Supports body function to conserve
and restore energy
Dominates during physical/emotional
stress
“Rest and digest”
“Fight or flight” response
Neurons
Cell body
Nissl
bodies
Dendrites
Axon
hillock
Nucleus
Node of
Ranvier
Axon
Schwann cells
(neurilemma)
Axon terminals
Neuroglia
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glia = glue
make up half of the volume of the CNS
Multiply and divide in the mature nervous system
Smaller than neurons but 5-50 times more numerous
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Found in the PNS
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Schwann cells
Satellite cells
Found in the CNS
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Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
Astrocytes
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Star shaped
Many processes
Maintains chemical environment,
provide nutrients
Helps form blood-brain barrier
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Prevents passages of many
substances/pathogens from the
blood into the brain.
Oligodendrocytes
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Smaller and fewer processes than
astrocytes
Round or oval cell body
Forms supporting network
Produces myelin sheath
Microglia
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Small cells
Few processes
Protects CNS cells by engulfing
microbes
Clears debris of dead cells
Ependymal cells
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Ciliated epithelial cells
Line ventricles of the brain
Line central canal of the spinal cord
Forms cerebrospinal fluid
Schwann Cells
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Flattened cells
Encircle PNS axons
Produces part of the myelin
sheath
Helps regenerate PNS axons
Satellite cells
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Flattened cells
Around cell bodies of neurons in
the ganglia
Supports neurons of PNS ganglia
Spinal Cord
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Meninges
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Vertebral column
Connective tissue
3 layers
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Dura mater
Arachnoid
Pia mater
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Spinal cord is located in the
vertebral canal
Provides additional protection
to the spinal cord
Internal Anatomy of the Spinal Cord
White matter: propagates sensory impulses from the periphery
to the brain and motor impulses from the brain to the periphery
Gray matter: receives and integrates incoming and outgoing info
Posterior
gray horn
Anterior gray
horn
The Brain
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Principal Parts
 Brain stem
 Cerebellum
 Diencephalon
 cerebrum
Protective Coverings of the Brain
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Cranial bones
Cranial meninges
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Dura mater (outer layer)
Arachnoid ( middle layer)
Pia mater (inner layer)
Blood Flow to the Brain
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Brain represents only 2% of the total body weight
It consumes 20% of the oxygen and glucose used at
rest
A brief slowing of brain blood flow will cause
unconsciousness
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1-2 minutes causes impaired neuronal function
About 4 minutes causes permanent injury
Brain Stem
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Between the spinal cord and
the diencephalon
Consist of
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Medulla oblongata
Pons
midbrain
BS: Medulla Oblongata
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Or the medulla
All sensory and motor tracts that
connect the spinal cord with the
brain is located in the medulla
A hard blow can be cause injury,
paralysis, loss of sensation, or
death.
BS: Pons
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Connects parts of the brain with
one another
Important functions
 Along with the medulla, it
helps regulate breathing
 Eye movement
 Chewing
 Facial expression
 balance, equilibrium
BS: Midbrain
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Important functions
 Helps control eye
movement
 Changes in eye pupil and
shape of lens
 Convey sensations of
touch, proprioception,
pressure, vibration
Cerbellum
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Second largest part of the brain
Main function is to provide smooth
and coordinated complex skeletal
muscle movement.
Regulates posture and balance
“little brain”
Diencephalon
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Composed of
 Thalamus
 Hypothalamus
 Epithalamus
 Subthalamus
D: Thalamus
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Makes up 80% of the
diencephalon
Principal relay station for sensory
impulses form the spine to the
cerebral cortex
Important in awareness and
acquisition of knowledge
(cognition)
D: Hypothalamus
Major regulator of homeostasis
 Controls the ANS
 Regulates rage, aggression, pain,
pleasure
 Regulates eating and drinking
 Satiety center
 Thirst center
 Controls body temperature
 Controls patterns of sleep
Cerebrum
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Forms the majority of the brain
“seat of intelligence”
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Read, write, speak
Calculate, compose music
Memory, imagination
Functional Aspects of the Cerebral Cortex