ANATOMY &
PHYSIOLOGY
Part 1:
The Nervous System
Three Functions of the Nervous System:
• Sensory Input:
• Gathers stimuli (receives information)
• Integration:
• Processes and
interprets information
• Motor Output:
• Causes a response
to muscles or glands
http://www.google.com/imgres?
Organization of the Nervous System:
Structural Classification:
• Central Nervous System (CNS):
brain & spinal cord
• Peripheral Nervous System (PNS):
spinal & cranial nerves
Functional Classification:
• Sensory Division (a.k.a. Afferent):
nerves carrying info to the CNS
from the body
• Motor Division (a.k.a. Efferent):
nerves carrying info from the CNS
to the muscles or glands
• This includes:
• Somatic Nervous System:
voluntary control (skeletal
muscles)
• Autonomic Nervous System (ANS):
involuntary control (smooth &
cardiac). This includes:
sympathetic & parasympathetic.
Supporting Cells of the Nervous System:
1. Microglial cells: support neurons & carry out
phagocytosis
2. Oligodendrocytes: form myelin within the brain; occur
in rows along nerve fibers
3. Astrocytes: found between neurons & bv’s; support,
regulate [nutrients] & [ions], & form scar tissue
following a CNS injury.
4. Ependymal cells: membrane like structure that covers
parts of the brain (choroid plexuses) & forms inner
linings of brain (ventricles) & spinal cord (central canal).
http://www.colorado.edu/kines/Class/IPHY3430-200/image/gila.jpg
Neurons: Nerve Cells
• Neurons vary in size, shape & function
• Mature neurons do NOT divide
• All neurons have:
• A cell body is the main component of a neuron. It contains cytoplasm, a cell
membrane,
a nucleus, &
organelles.
• The ER of a cell body
is called the
chromatophilic
substance or
nissl bodies
(perform protein
synthesis).
http://www.google.com/imgres?
Neuron Anatomy:
• Dendrites and axons are nerve fibers that attach to
the cell body (most neurons have these).
• Dendrites (usually more than 1 on a cell body) are
the communication means of one neuron to the next.
They receive messages. These are short branched
fibers.
• Axons take impulses away from the cell body. They
are usually one fiber with side branches.
• Large axons have a covering sheath called a myelin
sheath (a membrane of lipoprotein).
• The myelin sheath is composed of Schwann cells
(neuroglial cells).
• The gaps between the myelin sheaths are called
nodes of Ranvier.
• In the CNS, white matter are the fibers that are
myelinated while gray matter are the fibers that are
unmyelinated.
http://www.google.com/imgres?
A neuron:
Terminology:
• Nuclei: clusters of cell
bodies in the CNS
• Nerves: fibers running
through the PNS
• Ganglia: small clusters of • White Matter:
cell bodies in the PNS
myelinated fibers
(outside the CNS)
• Tracts (or nerve tracts):
bundles of nerve fibers
running through the CNS
• Gray Matter:
unmyelinated fibers
Types of Neurons: Structural Classification:
1. Bipolar neurons: 2 nerve fibers,
one at each end (1 axon & 1
dendrite). Found in the nose, eyes,
& ears.
2. Unipolar neurons: 1 nerve fiber
from the cell body that has 2
branches (1 branch acts as a dendrite
& the other branch acts as an axon).
3. Multipolar neurons: many nerve
fibers, 1 axon and many dendrites.
Found in the brain & spinal cord.
http://www.google.com/imgres?
Types of Neurons: Functional Classification:
1. Sensory neurons: carry impulses from peripheral
body parts to brain & spinal cord (from PNS to CNS).
Most are unipolar, some bipolar.
2. Interneurons: carry impulses between neurons.
Multipolar neurons.
3. Motor neurons: carry impulses from the brain &
spinal cord to the effectors (muscles & glands outside
of the NS) to carry out a response. Multipolar.
Nerve Impulses:
• An unmyelinated nerve fiber carries an impulse
slower than a myelinated nerve fiber.
• Nerve impulses range in speed according to their
diameter (thicker=faster). Ex: skeletal muscle
travels ~120 meters/second
• Nerve impulses respond in an all-or-none response.
• More stimuli= more impulses (per second), not
stronger intensity of impulses.
Nerve Impulses:
• A synapse is a junction between 2
communicating neurons. The
neurons are NOT connected.
• A synaptic cleft is the gap between
these 2 neurons.
• A nerve impulse must jump this
gap.
• A neurotransmitter is a chemical
that enables the impulse to jump
the synaptic cleft.
http://www.google.com/imgres?
Neurotransmitters:
• There are 2 types:
• Excitatory (increase membrane permeability) -impulse will likely occur
• Inhibitory (decrease membrane permeability) -impulse will not likely
occur
• There are at least 50 known neurotransmitters,
including these groups:
• Acetylcholine (stimulates skeletal muscles)
• Monoamimes (epinephrine, norepinephrine, dopamine, & serotonin)
• Several amino acids
• Peptides
Reflexes:
• These are rapid, involuntary
responses
• A reflex arc is the simplest
nerve pathway that contains
only a few neurons.
• The withdrawal reflex is a
protective reflex (pulling
your finger away from a hot
pot) b/c it limits tissue
damage. In addition to this
reflex, interneurons also
trigger a response to pain.
• Somatic reflexes include
skeletal muscles (pulling
your hand away from a hot
stove).
• Autonomic reflexes include
smooth and cardiac muscles
as well as glands (pupils
dilating, mouth ‘watering’)
• The knee-jerk reflex is a
nerve pathway involving
only 2 neurons (1 sensory & 1
motor).
Withdrawal Reflex:
http://www.mhhe.com/socscience/intro/ibank/ibank/0022.jpg
This slide show was developed by Dana Halloran,
Cardinal Mooney High School, Sarasota, FL.
Used with her personal permission,
adapted and amended by Rosa Whiting,
Manatee School for the Arts, Palmetto, FL.