CHAPTER 12
Nervous system
 3 main parts: brain, spinal cord, nerves
 Function: To detect changes in the internal and
external environment, evaluate the information and
possibly respond by initiating changes in muscles or
glands.
 Endocrine system works very closely with nervous
system.
 Nervous system: immediate responses
 Endocrine: slower uses hormones.
Divisions
 Central Nervous System (CNS)= Brain and spinal cord
 Peripheral Nervous System (PNS)= nerves outside of
SC
 Afferent division- incoming sensory information.
Toward the SC
 Efferent division- outgoing pathways. Motor neurons.
Divisions cont…
 Somatic Nervous
System:
 12 pairs of cranial nerves
 31 pairs of spinal nerves
 Bundles of neuron axons
bound together by
connective tissue. Cell
bodies are in the spinal
column.
 Relay to skeletal muscle
 Reflexes
Autonomic Nervous System
 Carries impulses from the CNS to
internal organs. Involuntary responses
 -Sympathetic Nervous System: Stress
fight or flight.
 -Parasympathetic Nervous System:
Rest and repair functions (digestion)
Cells in the nervous system
 30 billion cells in the NS with over 100 trillion
connections that are electrical in nature and generate a
great deal of heat. Heat loss is primarily through
head.
 Neuron-basic unit of the nervous system
 Many support cells as well.
Glial- satellite cells of the nervous
system 4 types
 1. Microglial
 2. fibrous astroglial
 3. protoplasmic
astroglial
 4. oligodendroglial
 Also known as
ASTROCYTES
Support Cells
 Microglial- small. Immune function. Act like white
blood cells in the CNS. Fight bacteria, breakdown
worn out organelles.
 Epedemal Cells – surround spinal cord and make
cerebrospinal fluid. This bathes the brain and spinal
cord.
 Fibrous Astroglia- white matter.
 Protoplasmic Astroglia-white matter.
 Both work to form the blood brain barrier.
Blood Brain Barrier
 You do not get the same free exchange of nutrients and
gases through the capillaries into nervous tissue of the
brain. Astroglia form a protoplasmic foot that guards
the capillary to prevent material from coming
through.
 Astroglia- forms scar tissue in the brain
4. Oligodendroglia
 Creates the myelin that surrounds the axon by
wrapping several times around the axon.
 Myelin insulates the nerve and speeds nerve
transmission.
Schwann Cells
 Found in the peripheral nervous system (PNS) and
have the same function as oligodenrdriocytes.
 Gaps between these cells create NODES OF RANVIER.
These gaps are important for proper nerve conduction
as an impulse jumps from node to node.
 Schwann Cells form the NEURILEMMA
 Forms WHITE MATTER or myelinated fibers
Neuron.
 Cell body = soma
 Dendrites= several ways into cell body
 Axon = 3-4 inches in length.
Dendrite
Myelin sheath
Axon
Axon endings
Cell body
Nucleus
Structural classification of neurons
 Classified by their number of extensions from the cell
body.
 Multipolar- most neurons of brain and spinal cord.
Have one axon but several dendrites
 Bipolar-One axon and one highly branched dendrite.
Only found in the retina of the eye inner ear, and in the
olfactory pathway (nose).
 Unipolar-single extending process from the cell body.
Branches to form one way into the CNS, the second
toward the PNS. Always sensory conducting
information to the CNS.
3 types of neurons:
 Sensory- impulses from
spine to brain
(AFFERENT NERVES)
 Motor- carry response
brain to organ or
muscle that was
stimulated to respond.
(EFFERENT NERVES)
 Interneurons- within
the spinal cord
Nerves and Tracts
 Nerves are bundles of peripheral nerves that are held
together by several layers of connective tissues.
Surrounding each nerve fiver is an delicate layer of
fibrous connective tissue: Endoneurium, perineurium,
epineurium (sound familiar?)
Repair of Nerve Fibers
 1. Injury or cut nerve
 2. Distal portion of axon degenerates
 3. Remaining neurolemma forms a tunnel from
effector to nerve body.
 4. Axons sprout on form within the tunnel.
 5. Neruon’s connection is re-established
 Can grow from 3-5mm per day.
 Page 352 Figure 12-10
Electrical Function of a Neuron
 Volt= difference in electrical potential.
 Energy flows from the point of higher voltage to an
area of low voltage.
 Depolarization occurs when a stimulus hits the nerve
and Na++ flows into the axon in a wave pattern. As the
stimulus travels it is called an ACTION POTENTIAL.
 Na++ is High outside the cell (4:1)
 K++ is High inside the cell (30:1)
 Na++ flows into the area of lower potential and is
pumped out by Active transport (requiring ATP) after
the impulse passes. This is called REPOLARIZATION
 The difference between the inside and outside of the
cell is called the RESTING POTENTIAL.
 High K+ concentration in tissue increases the resting
potential making it harder to stimulate. If K+
concentration gets too high you can go into cardiac
arrest.
 Neurons are high energy users.
Threshold
 Threshold is the minimum amount of stimulus
required to produce a response. (elicit an action
potential)
 All or none law- If you stimulate a nerve below the
threshold you will get NO response.
 At threshold you get a maximum response.
 The strength of a stimulus or action potential remains
constant from the time it is generated until it is
complete. The impulse does not weaken in transit.
Refractory period.
 For a few milliseconds after a threshold potential has
been reached the nerve will not respond to a stimuli
no matter how strong. This is called the refractory
period.
Neurotransmitters- how nerves
communicate
 More than 30 kinds of transmitters
 Classified by function and structure
 Acetylcholine
 Various locations. Excitatory in muscles, inhibitory in
the heart.
 Amines
 From amino acids. In brain, learning, emotions, motor
control
 Amino Acid
 Most common NTs in the Central Nervous System
 In PNS- stored in synaptic vesicles
 Neuropeptides
 Co- transmitter used to regulate the effects of other NTs
when they are released.
 Neurotransmitters released through the blood stream
are called HORMONES.
SYNAPSE
CNS
 Brain Anatomy:
 Brain: control system of entire nervous system. 3 main
Cerebrum
parts.
Skull
Cerebellum
Medulla
oblongata
Anatomy of the brain
Motor area
Cerebrum
Sensory area
Speech area
Language area
Vision area
Taste area
Intellect,
learning, and
personality
General
interpretation
area
Hearing
area
Balance
area
Brain stem
Cerebellum
Cerebrum
 2 hemispheres connected by bundles of
nerves
 Conscious activity
Lobes of the brain
 Parietal lobe
 Sensory association areas- impulses from skin such as
pain and temp. Estimates distances
 Frontal lobe
 Motor cortex, controls skeletal muscles
 Broca’s speech area- forming words
 Personality
 Temporal lobe
 Auditory, memory and speech
 Occipital lobe
 vision
Cerebellum
 Back of your brain
 Balance
 Posture
 Coordination
Brain stem: 3 main parts
Medulla oblongataInvoluntary activitybreathing and heart
rate
Pons-Connect
various parts of the
brain together
Midbrain- similar
function to the Pons
Midbrain
Cerebellum
Pons
Medulla
oblongata