CHAPTER
NERVOUS
7
TISSUE
III. SAMPLE LECTURE OUTLINE
A. OVERVIEW OF THE NERVOUS TISSUE
1. The nervous and endocrine systems control and integrate all body activities and aid in maintaining
homeostasis.
2. The basic functions of the nervous system are to sense changes (SENSORY), to interpret these changes
(INTEGRATIVE), and to react to changes (MOTOR).
3. The CENTRAL NERVOUS SYSTEM (CNS) consists of the brain and spinal cord.
4. The PERIPHERAL NERVOUS SYSTEM (PNS) includes all nervous tissue outside the central nervous system
5. The nervous system’s activities can be grouped into three basic functions: SENSORY, INTEGRATIVE,
AND MOTOR.
6. The sensory activities involve AFFERENT NEURONS and include all sensory receptors.
7. The motor activities involve EFFERENT NEURONS AND are divided into the somatic nervous system (SNS),
the autonomic nervous system (ANS), and the enteric nervous system (ENS).
8. The SNS consists of sensory neurons that convey information from somatic receptors to the CNS and
motor neurons that conduct impulses from the CNS to skeletal muscles only.
9. The ANS contains sensory neurons that convey information from autonomic sensory receptor to the CNS
and motor neurons that transmit impulses from the CNS to smooth muscle tissue, cardiac muscle tissue,
and glands.
10. The ENS is the “brain of the gut”. Its operation is involuntary. The sensory and motor neurons of the ENS
govern the function of the gastrointestinal tract.
B. HISTOLOGY OF NERVOUS TISSUE
1. Nervous tissue consists of two types of cells: NEURONS and NEUROGLICA.
2. The FUNCTIONAL CELL of the nervous system, the NEURON, consists of three distinct portions. These are the
CELL BODY, DENDTRITES, and the AXON.
3. The CELL BODY contains a nucleus, cytoplasm, and typical organelles.
4. The DENDRITES convey impulses to the cell body. Neurons may have many dendrites.
5. The AXON conducts nerve impulses from the neuron to the cell body of another neuron or an effector organ
of the body such as a muscle or a gland.
6. Axons, especially those outside of the CNS, are often covered with a white phospholipid material called
MYELIN. Non-myelinated neurons lack this material, which functions to increase the speed of impulse
conduction as well as to insulate and maintain the axon. Myelinated axons form WHITE MATTER while
unmyelinated axons, dendrites, and cell bodies form GRAY MATTER.
7. The axons of sensory and motor neurons are arranged into bundles called NERVES outside of the CNS or
FIBER TRACTS within the CNS.
8. NEUROGLIA are specialized cells that support NEURONS, attach neurons to blood vessels, produce the
myelin sheath around axons of the CNS, carry on phagocytosis, and metabolize neurotransmitters. These
cells do not generate or conduct nerve impulses.
9. The NEUROGLIAL CELLS include ASTROCYTES, OLIGODENDROCYTES, MICROGLIA, EPENDYMAL CELLS, SCHWANN
CELLS, and SATELLITE CELLS.
10. REGENERATION, the capability to replicate or repair themselves, is very limited in mammalian neurons.
C. ACTION POTENTIALS AND SYNAPTIC TRANSMISSION
1. The NERVE IMPULSE or ACTION POTENTIAL is the body’s quickest way of controlling and maintaining
homeostasis.
2. The membrane of a resting (non-conducting) neuron is positively charged outside and negatively charged
inside. This is partly due to the permeability properties of the membrane toward sodium and potassium
ions and negatively charged organic phosphate and proteins. This is called the RESTING MEMBRANE
POTENTIAL.
3. When a THRESHOLD STIMULUS is presented to the neuron, the inside of the neuron cell membrane becomes
positively charged and the outside becomes negatively charged.
4. The membrane is said to be DEPOLARIZED, and an ACTION POTENTIAL is produced, which travels from point
to point along the membrane. This traveling action potential is the NERVE IMPULSE.
5. The ABILITY OF A NEURON (OR MUSCLE FIBER) TO RESPOND to a stimulus and convert it into a nerve
impulse is called ELECTRICAL EXCITABILITY.
6. RESTORATION of the resting membrane potential is called REPOLARIZATION.
7. The brief period of time during which the membrane recovers and cannot initiate another action potential is
called the REFRACTORY PERIOD.
8. According to the ALL-OR-NONE PRINCIPLE, if a stimulus is strong enough to cause depolarization to
threshold, the impulse will travel the entire length of the neuron at a constant and maximum strength.
9. Nerve impulse conductions, which leap from Node of Ranvier to Node of Ranvier, are called SALTATORY
CONDUCTION, and are found principally in myelinated fibers.
10. Impulse conduction in unmyelinated axons (and in muscle fibers) is called CONTINUOUS CONDUCTION, and
is significantly slower than saltatory conduction.
11. The speed of impulse conduction is independent of the stimulus strength. Nerve fibers with large
diameters conduct impulses faster than those with smaller diameters; myelinated fibers conduct impulses
faster than unmyelinated fibers; and warm nerve fibers conduct impulses faster than cooler nerve fibers.
D. SYNAPTIC TRANSMISSION
1. NEURONS communicate with other neurons or with effectors by a series of events known as SYNAPTIC
TRANSMISSION.
2. The junction between neurons is called a SYNAPSE.
3. At a chemical synapse, there is only ONE-WAY nerve impulse conduction to a postsynaptic dendrite, cell
body, or axon hillock.
4. At a synapse, the neuron sending the signal is called the PRE-SYNAPTIC NEURON, and the neuron receiving
the message is called the POST-SYNAPTIC NEURON.
5. SYNAPTIC TRANSMISSION is either EXCITATORY or INHIBITORY.
6. An EXCITATORY TRANSMITTER-RECEPTOR INTERACTION is one that can depolarize or lower the postsynaptic
neuron’s membrane potential, so that new impulses can be generated across the synapse.
7. An INHIBITORY TRANSMITTER-RECEPTOR INTERACTION is one that can increase the postsynaptic neuron’s
membrane potential (hyperpolarization), so that new impulses are impeded from being generated across the
synapse.
8. Neurotransmitter is removed from the synaptic cleft by three methods: DIFFUSION, ENZYMATIC DEGRADATION
and RE-UPTAKE.
9. In all instances, the postsynaptic neuron acts as an integrator. It receives signals; integrates them and
responds accordingly.
E. NEUROTRANSMITTERS
1. A neurotransmitter, which causes excitation in a major portion of the central nervous system, is
acetylcholine (ACh).
2. Other important neurotransmitters include glutamate, aspartate, gamma amino butyric acid (GABA), glycine,
norepinephrine, dopamine, serotonin, neuropeptides, and nitric oxide.