The Nervous System
(NS)
Introduction
• 1. Distinguishing between the two major types
of cells that make up the NS
i. Neuron
ii. Neurolgia
• 2. Name and describe the two major groups of
NS organs.
i. Central Nervous System (CNS)
ii. Peripheral Nervous System (PNS)
Introduction Continued:
• The nervous system is the major controlling,
regulatory, and communicating system of the
body. It is the center for all mental activity. It
works closely with the endocrine system, and
aids in maintaining homeostasis.
Functions of the NS
• Sensory function- Sensory receptors detect changes called stimuli
that occur inside and outside the body. They monitor outside
things, such as temperature, light, and sound. Inside the body they
monitor pressure, pH, carbon dioxide concentration, and levels of
electrolytes. All of this gathered information is called sensory input
• Integration-sensory input is converted into electrical signals called
nervous impulses, which are sent to the brain for processing. They
are brought together to create sensations, produce thoughts, or
add to memory.
•
• Motor function- The NS can respond by signals to the muscles once
sensory and integration has taken place. The signals will cause the
muscles to contract, or to the glands, causing them to produce
secretions. Muscles and glands are called effectors because they
cause an effect in response to directions from the NS.
Types of Cells
I. The Neuron (nerve cell)
The Neuron (nerve cell)
• The neuron conducts nerve impulses.
• They are highly specialized and amitotic.
• Amitotic =If they are destroyed they can not
be replaced. They do not go through mitotic
division.
Types of Neurons
Structure of the Neuron
• Each neuron has a cell body (soma)
• One or more dendrites, and a single axon
• Dendrites and axons are cytoplasmic
extensions, or processes, that project
from the cell body.
• They are sometimes referred to as fibers.
Dendrites and Axon
• The number of dendrites vary; however, they
are referred to as afferent because they
transmit impulses to the nerve cell. The axon
transmits impulses away from the cell body so
it is referred to as an efferent process.
Axons
• Axons are covered by a myelin sheath giving it
a white appearance (white matter) found in
the brain and spinal cord CNS.
• The gray matter is composed of cell bodies
and appears gray (no myelin sheath).
• Narrow gaps between schwann cells called
nodes of Ranvier
• Another axon covering is the neurilemma, it is
a membranous sheath on nerves of the PNS.
Cell Body
• The area within the neuron that contains all
the components of a typical eukaryotic cell.
• Genetic material (DNA) is stored here.
Ganglia-(sing. Ganglion) sm. Collection
of nerve cell bodies outside the CNS.
The Neuroglia Cells
• These cells do not conduct nerve impulses.
• They support, protect, and nourish the
neuron.
• They are more numerous than the neuron.
• They can go through mitotic division.
Neuroglia
Types of Neuroglia CellsMicroglial cells
1. Microglial cells- scattered throughout the CNS
Function: Support neurons
Phagocytize bacterial cells
Removes cellular debris
Forms scars in damaged areas
Types of Neuroglia CellsOligodendrocytes
2. Oligodendrocytes- align along the nerve fibers
Function: Provide insulating layers of myelin
(Myelin sheath) in CNS
Types of Neuroglia CellsAstrocytes
3. Astrocytes- Most commonly found between
nerves and blood vessels.
Functions: Provide structural support
Join parts by their cellular
processes
Regulate concentrations of
nutrients & ions within the
tissues
Form scar tissue in CNS
Creates “Blood-Brain Barrier.”
Types of Neuroglia CellsEpendymal cells
4. Ependymal cells- epithelial-like membrane that
covers specialized brain parts (choroid plexuses)
Function: Forms inner linings that enclose
spaces in the brain and central canal
of the spinal cord.
Ependymal cells
• Nerve impulse:
Nerve Impulse
• Functional characteristics of neurons are
excitability and contractility. Excitability is the
ability to react to stimuli. Conductivity is the
ability to transmit a nerve impulse from one
point to another.
• The resting membrane is the cell membrane
of a non-conducting, or resting neuron. The
membrane is impermeable to the passive
diffusion of Na+ (sodium)and K+ (potassium).
Events Leading to a Nerve Impulse
•
•
•
•
•
•
Neuron membrane maintains a resting potential
Threshold stimulus is received
Na+ channel in trigger zone of neuron open
Na+ diffuses inward, depolarizes membrane
K+ channel in membrane opens
K+ ions diffuse outward, re-polarizing the
membrane
• The action potential causes local bioelectric
current
• A wave of action potential travels the length of
the axon.
Cell Membrane Potential
There are 2 major components the
PNS and CNS
CNS & PNS
• Central NS- brain and spinal cord
•
•
• Peripheral NS- Cranial nerves (12 pairs, Spinal nerves (31 pairs) and
the Autonomic nerves (parasympathetic and sympathetic)
•
• Sympathetic nerves stimulate the body in times of stress and crisis.
They increase heart rate and forcefulness, dilate (relax airways so
more oxygen can enter. Increase bp, stimulate adrenal glands to
secrete epinephrine (adrenaline) , and inhibit intestinal contractions
slowing digestion.
•
• Parasympathetic nerves normally act to as a balance to the
sympathetic nerves. They slow down heart rate, contract pupils of
the eye, lower bp, stimulate peristalsis to clear rectum, and
increase quantity of saliva.
• Called fight or flight responses.
•
Plexus
• A plexus is a network of nerves in the PNS.
Chemical Messengers
• Neurotransmitters: chemical messenger
released at the end of nerve cells. It either
stimulates or inhibits other cells. It can be
another nerve cell, gland or muscle cell.
Neurotransmitters
The Meninges
• Meninges: 3 layers of connective tissue
membranes that surround the brain and
spinal cord.
Spinal Cord
Function of the Spinal Nerves
The Brain
This three-pound organ is the seat of intelligence, interpreter of the senses,
initiator of body movement, and controller of behavior
Cerebellum
• The hindbrain includes the upper part of the
spinal cord, the brain stem, and a wrinkled ball of
tissue called the cerebellum
Function: The hindbrain controls the
body’s vital functions such as
respiration and heart rate. The
cerebellum coordinates movement
and is involved in learned rote
movements.
Cerebrum
• The forebrain is the largest and most highly
developed part of the human brain: it consists
primarily of the cerebrum
two halves (hemispheres)
mirror images of each other
Midbrain
• Uppermost part of the brainstem –midbrain
Function: Controls some reflex actions
and is part of the circuit involved
in the control of eye movements
and other voluntary movements
Neurological Disorders
• Neurological Disorders
When the brain is healthy it functions quickly and
automatically. But when problems occur, the results can be
devastating. Some 50 million people in this country—one in
five—suffer from damage to the nervous system. The National
Institute of Neurological Disorders and Stroke (NINDS)
supports research on more than 600 neurological diseases.
Some of the major types of disorders include: neurogenetic
diseases (such as Huntington’s disease and muscular
dystrophy), developmental disorders (such as cerebral palsy),
degenerative diseases of adult life (such as Parkinson’s
disease and Alzheimer’s disease), metabolic diseases (such as
Gaucher’s disease), cerebrovascular diseases (such as stroke
and vascular dementia), trauma (such as spinal cord and head
injury), convulsive disorders (such as epilepsy), infectious
diseases (such as AIDS dementia), and brain tumors.
References:
• NINDShttp://www.ninds.nih.gov/disorders/brain_ba
sics/know_your_brain.htm
• Hole’s Essentials of Anatomy and Physiology
11th ed.
• http://www.youtube.com/watch?v=0p_HHHO
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• http://www.youtube.com/watch?v=4M82Ww
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