Fig 12-2 Organization of Nervous System
A. Central Nervous System (CNS)
- brain and spinal cord
- integrating and command center of the
nervous system
B. Peripheral Nervous System (PNS)
- part of nervous system that extends from the
brain and spinal cord
1. cranial nerves : carry signals to and from the brain
2. spinal nerves: carry signals to and from the spinal
cord
Somatic vs Autonomic – are categorized based on the efferent pathway
Somatic
Autonomic (“self governing”)
-Voluntary
-Involuntary
-Carry impulse to skeletal muscles
and skin
-Carry impulses to viseral organs
smooth, cardiac muscle and
glands
Sympathetic – “fight, fright & flight”
division. It prepares the body to cope
with danger or excitement (arise from
the thoracic and lumbar region)
Parasympathetic – “resting & digesting”
division. It over-sees digestion, elimination
and glandular function (arise from brain and
sacral region)
“fight or flight”
“rest and repair”
1) Sensory neurons - or afferent neurons transmit impulses
toward the CNS from sensory receptors in the PNS.
(Sensory input/function)
2) Interneurons - or association neurons connect motor and
sensory neurons and are confined to the CNS. The processing
and interpreting of the sensory input to make decisions about
what should be done at the moment.
(Integrative function)
3) Motor neurons - or efferent neurons, carry impulses away
from the CNS to the effector organs, muscles or glands.
Most are multipolar.
(Motor output/function)
*Let’s say you are driving a car and you happen
to come upon a red light (sensory input), your
nervous system integrates this info (red light means
“
“ and your foot goes for the brake
(motor output).
Nervous Tissue - made up of 2 main cells
1. Neurons / nerve cells: basic structural units of
the nervous system and are specialized to
react to physical and chemical changes in the
environment. They conduct nerve impulses
2. Neuroglial cells / supporting cells: nonexcitable cells that surround and wrap
neurons (exp: Schwann cells)
Glial cells - supporting cells of the CNS and PNS.
They fill spaces, support neurons, provide
structure, produce myelin, and carry on
phagocytosis. Glia means “glue”
Types of Glial Cells
1. Astrocytes - “star cells” are the most abundant.
They are found between nervous tissue and blood vessels.
Their function is to provide support, hold parts together,
and regulate nutrients and ion concentrations. (BBB)
*Responsible for scar tissue
2. Oligodendrocytes - they are arranged in rows along
nerve fibers and wrap their cell processes around the axons
of nerve fibers within the brain and spinal cord, producing
myelin sheaths.
http://www.myelin.org/
3. Microglia - are phagocytes of the CNS. They
engulf invading microorganisms and injured
or dead neurons. (smallest and least abundant)
4. Ependymal - form a simple epithelium that lines the
central cavity of the spinal cord and brain. Function in
producing and circulating fluid. (covers the ventricles
of the brain and the central canal of the spinal cord)
5. Schwann cells – found in the PNS, they provide
support for nerve fibers and sometimes form myelin
around them (neurilemma).
*Could be a possible treatment for nerve damage or even spinal cord injury.
Text : p348 Fig 12-4
Cell body - consists of a nucleus, nucleolus, cytoplasm, and various
organelles.
Neurofibrils - fine threads that extend into nerve fibers (cytoskeleton).
Dendrites - nerve fibers that branch like the limb of a tree, function as
receptive sites and conduct electrical signals toward the cell
body.
Nissel Bodies - lg clusters of RER and free ribosomes. They renew
the membranes of the cell and the protein part of the cytosol
which is needed for nerve transmission.
Axon - arises from the cone shaped region of the cell body called
the axon hillock and then tapers to form a slender process
that conducts nerve impulses away from the cell body.
Schwann cells - tightly wrapped layers of cell membrane composed
of a lipoprotein called myelin forming the myelin sheath
around nerves found in the PNS. Neurilemma sheath
surrounds the myelin sheath.
Nodes of Ranvier - gaps in the myelin sheath between adjacent
Schwann cells inc rate of impulse.
*tract – bundles of nerve fibers running through the CNS
*nerves- bundles of nerve fibers running through the PNS
*white matter – myelinated nerve fibers
*gray matter – unmyelinated nerve fibers
P349 Fig 12-6
1) Multipolar neurons - more than 2 processes or
nerve fibers
2) Bipolar neurons - have 2 processes that extend
from opposite sides of the cell body (ear, smell
region of nose, retina of eye)
3) Unipolar neurons - have a short, single process
that emerges from the cell body and divides like
a “T” into 2 long branches
Bipolar
Multipolar
Unipolar
*Cell membrane surface is polarized/electrical due
to a difference in ion concentrations. This is important in
the conduction of muscle and nerve impulses.
Nerve cell at rest or not conducting impulses has a
[Na+] outside the cell membrane and a
[K+] inside the cell membrane
Na+ Na+ Na+
K+ K+
Polarized
Membrane Potential
A. Resting Potential - in a resting nerve cell, the
potential difference or difference in
electrical chg between 2 regions (-70mV).
p354 Fig 12-12, p355 Fig 12-13
+ + + + + + + + + + (+)
(Polarized)
++++++
(-)
++++++
++++++++++
*Net effect = more (+) chgd ions outside the membrane making
the inside more (-) compared to the outside (Resting/Polarized/
Inactive neuron).
Potential Changes
1. Depolarized - resting potential decreases, meaning as Na ions
enter the cell, the inside of the cell membrane becomes more
positive than the outside (+30mV); therefore, making the outside more
negative. Once the threshold potential is reached the action
potential/nerve impulse is propagated.
Depolarized
- - - +++++
++++++++
++++++++
- - - +++++
Na+ diffuse inward
and membrane loses
its electrical chg
2. Repolarization - K+ ion channels open and allow K+ ions to
diffuse outward making the cell membrane chgd again
(Na+ & K+ pump) fully restores membrane potential
p356 Table 12-1, Fig 12-15
++++++++++
- - - - - - - - - - - - - - - - - - ++++++++++
http://trc.ucdavis.edu/biosci10v/bis10v/week10/06potential.html
action potential - the sequence of depolarizing and repolarizing
*All-or-none response…..if threshold is reached the chg is
irreversible.http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html
Read conduction of action potential on pg357
Impulse Conduction - myelinated nerve fibers
conduct impulses at a faster rate then
unmyelinated nerve fibers b/c of the greater
diameter and the nodes….jumping vs walking,
the myelin also inc the surface area and conducts
better.
http://www.brainviews.com/abFiles/AniSalt.htm
Synapse - the junction between the axon of one
neuron and the dendrite of another neuron or
an axon and an effector organ.
Presynaptic terminal / neuron - end of the axon
postsynaptic membrane / neuron - the dendrite or the
effector cell
synaptic cleft - the space separating the presynaptic and
postsynaptic neurons, or the gap in a synapse
synaptic transmission - the process of an impulse crossing the gap at a synapse.
* Axons have several rounded structures called synaptic
knobs that contain numerous membraneous sacs called
synaptic vesicles that release neurotransmitters or
molecules that transmit signals across a synapse.
Fig 12-20 p359, Fig 12-21 p360
Chemical substances that transmit signals/messages across a synapse
A. Stimulatory - acetylcholine and norepinephrine
cause increased postsynaptic membrane
permeability to sodium ions.
B. Inhibitory - dopamine, serotonin, and the amino
acids GABA and glycine cause a decrease
in membrane permeability to sodium ions.
Reflexes - rapid, automatic motor responses to
stimuli.
Reflex Arc - reflexes that are mediated by chains
of neurons.
1. Sensory receptor - the site where the stimulus acts
(dendritic ending of a sensory neuron)
2. Afferent or sensory neuron - transmits a impulse
from the receptor into the CNS.
3. Association / Interneuron - neurons located between
sensory and motor neurons
4. Motor Neuron - conducts impulse from CNS to an
effector neuron
5. Effector - the muscle or gland that responds
to the efferent impulses by contracting or
secreting. Fig 14-15 p430
http://www.brainviews.com/abFiles/AniSalt.htm
A. Meninges - a group of 3 membranes that cover
the brain and spinal cord.
1. Dura mater - outermost layer, it extends
inward between lobes of the brain.
2. Arachnoid mater - a thin, weblike membrane
that lacks blood vessels and is located
between the dura and pia maters.
3. Pia mater - very thin and contains many
nerves as well as blood vessels.
p376 Fig 13-2
Spinal cord - nerve column that extends from the
brain into the vertebral canal and consists of 31
segments each giving rise to a pair of spinal nerves.
Functions:
•Conduct nerve impulses
•Serve as a center for spinal reflexes
The anterior median fissure and the posterior
median sulcus divide the spinal cord into right
and left halves…….Fig 13.6 p381
1. Gray matter - butterfly structure or “H” in center, it has
posterior and anterior lateral horns.
2. White matter - surrounds the gray matter and is divided
into 3 regions the anterior, lateral, and posterior funiculi
which contain nerve tracts
3. Central canal - narrow canal that contains the cerebrospinal
fluid.
Nerve Tracts
a) ascending tracts – conduct sensory impulses from body to the
brain
b) descending tracts – conduct motor impulses from brain to
muscles and glands.
Posterior median sulcus
Posterior funiculus
Lateral funiculus
Anterior
Median fissure
Anterior funiculus
Spinal Reflexes – reflex arc passes through the spinal cord … pg 218 Fig 9.23
3 Major parts
-Cerebrum
-Cerebellum
-Brain Stem
I. Cerebrum - largest, contains nerve centers associated
with sensory and motor functions
-cerebral hemispheres - 2 lg masses on either side
-corpus callosum - connects the 2 hemispheres
-convolutions or gyri - twisted ridges in the cerebrum
-sulci - shallow groove
furrows
-fissure- deep groove
Happy Valentines Day!!!!
http://www.medtropolis.com/VBody.asp
*Lobes are named after the skull bones
they lie under.
1) frontal lobe
2) parietal lobe
(p391 Fig 13-13)
3) temporal lobe
*Read about these!!
4) occipital lobe
5) insula - buried deep within the lateral fissue
p392 Fig 13-14, 13-15
-cerebral cortex - superficial gray matter that covers the
cerebrum “conscious mind”
-cerebral white matter - mass of white matter beneath the
cerebral cortex.
-basal/cerebral nuclei - several masses of gray matter
deep in the white matter.
Functions of Cerebrum
1. Interprets sensory impulses
2. Stores info and memory and uses it to reason
3. Determines a persons intelligence / personality
p393 13-16
Read over this section!!
1. Motor Areas - (frontal lobes) motor area of the right
hemisphere controls muscles on the left side,
concentration, drawing, problem solving, eye
control, speech, concentration etc.
Broca’s area - motor speech area, coordinates
muscular actions of the mouth, tongue,
and larynx
Frontal Eye field - controls voluntary movements of
the eyes and eyelids
2. Sensory Areas
- skin sensations…...along center sulcus of parietal lobe
- visual …..posterior end of occipital lobe
- auditory area……..temporal lobes
- sense of taste ……..base of central sulci
- sense of smell …….deep in cerebrum
* like motor fibers, sensory fibers originate in a hemisphere
that controls the opposite side of the body
3. Association Areas - analyze and interpret experiences, memory,
reasoning, verbalizing, judgement and emotional feeling.
Ventricles - central cavities filled with cerebrospinal fluid and are
continuous with each other and the central canal of the
spinal cord
a) lateral ventricle - (1st & 2nd ventricles) lie in the
cerebral hemispheres
b) third ventricle - in the middle of the brain, beneath
the corpus callosum, communicate
with the lateral ventricles
c) fourth ventricle - in the brainstem just in front of
the cerebellum connects to 3rd vent
Cerebrospinal Fluid - clear liquid that surrounds the brain
and spinal cord. Helps protect and
maintain a stable ionic concentration.
I) Diencephalon - “inter-brain” between cerebral
hemispheres and above midbrain
thalmus - “gateway” to the cerebral cortex.
Receives all sensory impulses (except smell)
and sends to the cortex for interpretation.
…..it makes us aware of pain, touch, and temp
p386 Fig 13-9
Hypothalmus - below the thalmus; main visceral control
center of the body.
Functions :
1. Regulates heart rate and blood pressure
2. Regulates body temp
3. Regulates thirst, hunger, weight and electrolyte balance
4. Control of endocrine system: controls secretions of
hormones from the pituitary gland and in turn regulates
functions of visceral organs
Functions Continued…….
5. Regulation of sleep and wakefulness, circadian rhythms
6. Controls movements and glandular secretions of the stomach
and intestines
7. Center for emotional response, pleasure, fear, rage etc.
Limbic system - involved in emotional experience and
expression…. “emotional brain”
- connects cerebrum to the spinal cord.
The parts of it include the midbrain,
pons, and medulla oblongata
I. Midbrain - located between diencephalon and pons…
consists of gray matter that serve as reflex centers
II. Pons - the bulging region on underside of the brain
stem wedged between the midbrain and the medulla
oblongata….relays impulses to help control our
breathing movements.
III. Medulla Oblongata - extends from the pons to the
foramen magnum of the skull…contains
a central gray matter like the spinal cord
p384 Fig 13-8
Most Important Visceral centers in the Medulla
1. Cardiac center - adjusts the force and rate of the heart beat
2. Vasomotor center - regulates blood pressure
vasoconstriction - constricts arteries causing blood
pressure to rise
vasodilation - dialates arteries reducing blood pressure
3. Respiratory center - basic pattern and rate of breathing
4. Additional centers regulate vomiting, hiccuping, swallowing, coughing and sneezing.
Reticular formation - nerve fibers within brain stem that function
in arousing the cerebrum
*Responds to sensory impulses by activating a state
of wakefulness and with decreased activity results sleep.
Cerebellum - located dorsal to the pons and medulla.
It smooths and coordinates body movements that
are ordered by other brain regions that help maintain posture and equilibrium (voluntary muscle
movements).
*consists of 2 cerebellar hemispheres connected by the
worm-like vermis.