I.
Nervous System – Neurology – study of
A. Functions – control center
1. sensory – senses change within the body and
outside environment
2. integrate or interpret – interprets change
3. response – motor function - initiates action in
the form of muscular contraction or glandular
secretions
B. Organization – 2 principal divisions
1. Divisions a. Central nervous system – CNS – brain and
spinal cord – control center for entire nervous
system
- sensory info is integrated and correlated,
thoughts and emotions are generated and
muscles are stimulated to contract and glands
to secrete
b. Peripheral nervous system – PNS – nerves
from brain cranial and spinal cord – spinal
carry inward from receptors and outward
from CNS
1.SNS – somatic nervous system – sensory
neurons from cutaneous and sensory
receptors in head, body wall, and
extremities to CNS and motor neurons
from CNS to skeletal muscles only voluntary
2. ANS –autonomic nervous system –
contains sensory neurons that convey
homeostatic info from receptors to viscera
of CNS and motor neurons from CNS to
smooth muscle, cardiac muscle and
glands – involuntary
- sympathetic – neurons involve
expediture of energy
 speeds heart beat
- parasympathetic – neurons – restore
and conserve body energy
 slows heart beat
C. Histology –
1. Cell types – only 2
a. Neuroglia – glial cells – 6 types (exhibit 9.1)
- support and protect neurons
- smaller than neurons and out number
them by 5-10 times
- common source of tumors (gliomas) –
 40-45% of all brain tumors
b. Neurons – conduct impulses from one part
of body to another
(fig 8.2 pg 217)
- cell body – well defined nucleus and
nucleolus surrounded by cytoplasm
along with another organelles – no
mitotic apparatus in adults
- dendrites – short, thick highly
branched extensions of cytoplasm
o (neuron usually has several)
o receive impulses and conduct
toward cell body
- axon – single long thin extension that
sends impulses to another neuron or
tissue
o vary from 1mm – 1meter
o has side branches called synaptic
terminals or knobs that secrete
neurotransmitters
- myelin – multi layered lipid and protein
covering of axons (called myelin sheath)
- electrically insulates the axon and
increases the speed of conduction
- some are unmyelinated – no sheaths
- 2 types of neuroglea produce myelin
sheaths – page 218
- neurolemmocytes (schwann cells) form
sheaths around axons during fetal
development and 1st term of life – PNS
only ** can regenerate
- Oligodendrocytes myelinated axons of
the CNS cannot regrow ( no
neurolemma)
 Myelin increases from birth to
maturity and greatly increases the
speed of impulse conduction
 since it is still in progress during
infancy, the infant has slow reflexes
and lack coordination
 MS (pg 224) and Tay-Sachs disease
2. Grouping of neural tissue –
a. Nerve fiber- any process projecting from
the cell body
 axon or dendrite
b. nerve – group of many fibers in PNS
 Sciatic nerve of thigh
 Most nerves have motor and sensory
fibers
c. ganglia – group of cell bodies (neurons) and
synapses in the PNS
d. tract – bundle of fibers in the CNS
 May run long distances up and down
the spinal cord or connect parts of the
brain
 Ascending tract carries impulses
upward
 Descending tracts carry impulses
downward
e. white matter – groups of myelinated axons
from many neurons
 looks white
f. gray matter – neuron cell bodies &
dendrites or or unmyelinated axons
(bundles)
 found covering outer surface of the
brain and in the deeper regions called
nuclei (similar to ganglion but has
unmyelinated dendrites) ex. Horns of
spinal cord
3. Classification of neuronsa. structural –based on # of processes
extending from cell body
- multipolar – several dendrites – 1 axon
most neurons in the brain and spinal
cord are like this
- bipolar – 1 dendrite and 1 axon
found in retina of eye, inner ear and
nose
- unipolar – have only 1 process that
divides into a central branch which
functions as axon and a peripheral
branch - dendrite
- originate as bipolar but fuse during
development
- found in the dorsal root ganglia
(sensory) of spinal nerves
b. functional- based on the direction in which
they transmit nerve impulses
- sensory (afferent) – transmit form
receptors in skin, sensory organs
muscles, joints, and viscera to the brain
and spinal cord
- motor (efferent) – convey impulses
from brain and spinal cord to effectors
which may be muscles or glands
- association (interneurons) – carry
impulses from sensory neurons to
motor neurons and are located in the
brain and spinal cord only – makes up
most neurons of humans
II. Functions –
A. Nerve Impulses – like tiny electrical currents that
pass along neurons – these result from ion
movement in and out of plasma membranes of
neurons
1. Ion Channels – highly selective with respect to
which ions pass through – some are always open
but most are not
 ion passage is controlled by protein
molecules (gate) that open and close in
response to a change in voltage of the
plasma membrane or differences in ion
concentration on either side of the
membrane
 others open and close in response to
chemicals (hormones, neurotransmitters)
2. Membrane potentials – in a resting neuron
there is a difference in electrical charges on the
outside and inside of the plasma membrane. One
cause is the varying numbers of K+ and Na+ on
either side. More K+ in and 15x more Na+ out. The
other factor is the presence of large charged ions
trapped inside (phosphates and proteins)
pg 220 membrane potentials
3. Excitability – ability of nerve cells to respond to
stimulus and convert into nerve impulses
- stimulus - anything capable of reducing
resting membrane potential

*depolarization – loss and reversal of
polarization due to rapid openings of
Na+channels
 *repolarization – recovery of resting
membrane potential due to slower opening
of K+ channels and crossing of Na+ (*takes
1/1000 of a second)
(see fig 8.6 pg 221)
- action potential – rapid change in
membrane potential (read pp. 220-221)
4. All or none principle – any stimulus strong
enough to initiate a nerve impulse is called
threshold
- if stimuli is strong enough to generate a nerve
action potential, the impulse travels along the
entire neuron at maximum strength
- EX. gun powder trail
5. Continuous and salutatory conduction
- step by step depolarization of each adjacent area
of an axon or a dendrite is called continuous
conduction (unmyelinated)
- salutatory conduction – in myelinated fibers the
myelin insulates so ion movement is inhibited
- thus nerve impulse jump from node to node
much faster (see figure 8.8b pg 223)
6. Speed of nerve impulse –determined by
temperature , diameter of fiber and presence of
myelin
- warm faster – ice slows pain
- large fibers - faster
- myelinated faster
B. Conduction across synapsis – neuromuscular and
neuroglandular junction
- across synapse – most diseases of brain and
psychistric disorders involve disruption of
synaptic communication
1. pre-synaptic neuron
2. post-synapic neuron (pg 224 fig 8.9)
- neurotransmitters are made by neurons from
amino acids
- when an impulse arrives at synaptic bulb of the
pre-synaptic neuron , depolarization occurs, and
calcium channels open – liberates(sets free)
neurotransmitters
- this causes excitatory transmission – creates
impulse – or inhibitory transmission which
prevents impulse only one way – post synaptic
neuron is an integrator – responds 3 ways
1. facilitation – if excitatory
(depolarization) is greater than
inhibitory effect but less than
threshold a subsequent stimuli can
generate an impulse – building up
effect
2. If excitatory is greater than
inhibitory and threshold, one or
more impulses will be generated
3. If inhibitory is greater than
excitatory then no impulse will be
generated
C. Altering conduction across synapsis
- disease, drugs, and pressure can alter conduction
- myasthenia gravis – antibodies attack of
acetylcholine receptors on skeletal muscle
- alkalosis – increase of Ph above 7.45 and
increases excitability of neurons causes light
headiness, numbness, tingling, spasms,
convulsions
- acidosis – decreases in Ph below 7.35, depression,
weakness and coma
D. Regeneration
- limited ability
- around 6 months old – they lose ability to
respond
- PNS – some myelinated axons and dendrites
(neurolemmas present)
- CNS – oligodendrocytes – no regeneration