Nervous System
Functions of the Nervous System
• Sensory Input
– Monitors changes
(stimuli) inside and
outside the body
• Integration
– Processes and interprets
sensory input to decide
what should be done
• Motor Output
– Supplies response by
activating muscles or
glands
Nervous System Divisions
• Central Nervous System (CNS)
– Includes the Brain and Spinal Cord
• Peripheral Nervous System (PNS)
– Includes Spinal nerves & Cranial nerves
Further Breakdown of PNS
• Sensory (afferent) Division
– Sends impulses to the CNS from sensory
receptors in body
– Somatic sensory fibers: messages from skin,
muscles and joints
– Visceral sensory fibers: messages from
internal organs
• Motor (efferent) Division
– Carries impulses from CNS to effector organs
(muscles and glands) to cause a response
SAME
Sensory = Afferent
(comes first, body  brain)
Motor = Efferent
(comes second, brain  body)
Further Breakdown of Motor Division
• Somatic System
– Voluntary control of skeletal muscles
• Autonomic System
– Involuntary body responses, such as smooth
& cardiac muscles, and glands
Nervous Tissue
• Made up of two types of cells
– Supporting Cells: these structures do not
directly transmit any signals, but they help the
neurons to function properly; aka “glia”
– Neurons: actually pass signals
Supporting Cells
• Neuroglia: supporting cells (glia) lumped
together (term is commonly used to
reference all types of supporting cells)
Neuron
Cell Body
Neuroglia
Cells
Types of Supporting Cells in CNS
• Astrocytes
– Form barrier between capillaries and neurons
– Help control chemical environment in brain
– “To Make Mice Smarter, Add A Few
Astrocytes!”
–
Scroll to bottom of website to see how astrocytes communicate
• Microglia
– Dispose of debris, such as dead brain cells
and bacteria (immune system)
Astrocytes can release
gliotransmitters (like glutamate) by
exocytosis to send signals to
neighboring neurons.
Each astrocyte has its own
territory (they don't overlap),
and each may interact with
several neurons and
hundreds to thousands of
synapses to properly
integrate information.
"End-feet" connect to blood vessels in
the brain. By signaling blood vessels to
expand or narrow, astrocytes regulate
local blood flow to provide oxygen and
nutrients to neurons in need.
Neurons
Astrocytes
Types of Supporting Cells in CNS
• Ependymal
– Lines cavity of brain & spinal cord
– Circulate cerebrospinal fluid
• Oligodendrocytes
– Wrap around nerve fibers, forming myelin
sheaths
Types of Supporting Cells in PNS
• Schwann cells: form myelin sheaths in
PNS
• Satellite Cells: protective, cushioning cells
in PNS
Neuron
Cell Body
Neuroglia
Cells
Parts Of A Neuron
• Cell Body: metabolic
center, contains rough
ER (Nissl substance)
and neurofibrils
(maintain shape)
• Dendrites: convey
incoming messages
toward cell body
Parts Of A Neuron
• Axons: conduct
outgoing messages
away from cell body (has
only one originating at
axon hillock)
• Axon Terminal:
branching at end of axon
which contain
neurotransmitters
Parts Of A Neuron
• Synaptic Cleft
(Synapse): gaps
between neurons
• Myelin Sheath:
protects and insulates
nerve fibers (axon),
increases rate of nerve
impulses; made of
proteins and lipids
Parts Of A Neuron
• Schwann cells: cells
forming myelin sheath in
PNS
– CNS =
oligodendrocytes
• Nodes of Ranvier:
gaps between Schwann
cells on axon
Did you know Einstein’s brain was
STOLEN? Here the story here.
FYI: Multiple Sclerosis
• Myelin sheaths around the fibers are
destroyed, and converted into hardened
sheaths called scleroses
• Person loses ability to control muscles
Neuron Classification
• Functional
– Sensory (afferent): carry impulses from
sensory receptors to CNS
– Motor (efferent): carry impulses from CNS to
body
– Association (interneurons): connect motor and
sensory neurons in neural pathways of CNS
Neuron Classification
• Structural
– Multipolar: several
extensions from cell body
(common for motor neuron)
– Bipolar: one axon and one
dendrite from cell body
(common for interneurons)
– Unipolar: single process
from cell body, process
divides (common for
sensory neuron)
Central Nervous System
http://www.youtube.com/watch?v=snO68aJT
OpM
Central Nervous System
…also called the
CEREBRUM
Brain Characteristics
• Gyri: elevated ridges of
tissue (gyrus is
singular)
• Sulci: shallow grooves
separating gyri (sulcus
is singular)
• Fissures: deep
grooves separating
large regions of brain
• Lobes: separations of
hemispheres of brain
Senses & Controls of Brain - Cerebrum
• White matter: collections
of myelinated nerve
fibers, usually found in
deeper brain matter;
carries the impulses
(axons)
• Gray matter: collections
of UNmyelinated nerve
fibers and cell bodies;
usually found in the outer
areas; contains the
neuron cell bodies
Cerebrum
• The cerebrum is
divided into right and
left hemispheres by
the longitudinal
fissure
• Controls
consciousness
• Senses and motor
control occurs here!
• Each hemisphere
divided into 4 lobes
Funny thing about the brain…
• The somatic sensory area (cortex)
– Where your senses are picked up & processed
– Upside down
• Signals from body parts toward the head are picked
up at the base of the area, while signals from lower
(inferior) body parts are picked up at the top of the
area
– Crossed pathways
• Left side of the sensory area receives impulses from
the right side of the body, and vice versa
Funny thing about the brain…
• The primary motor area (cortex)
– Responsible for sending out signals for
movement
– Also upside down with crossed pathways
Senses & Controls of Brain - Cerebrum
• Occipital Lobe:
contains visual sense
• Temporal Lobe:
contains smell &
auditory senses
– Also includes the
hippocampus, which is
responsible for longterm memory
(including forming new
memories about
events) and spatial
navigation
Senses & Controls of Brain - Cerebrum
Frontal Lobe…
• Broca’s area: ability to
speak (vocalize),
usually more
developed in left
hemisphere Language
Comprehension
• Language
comprehension area:
word meanings
Broca’s Area
Senses & Controls of Brain - Cerebrum
• Speech Area (aka
Wernicke’s Area)
– located at the
junction of the
temporal, parietal,
and occipital lobes
– Allows one to
context spoken
words (use them
correctly)
– Usually more
developed in left
hemisphere
Speech Area
Senses & Controls of Brain - Cerebrum
• The Corpus Callosum
is a very large nerve
fiber tract (bundle)
that connects the
cerebral hemispheres
& allows them to
communicate
Cerebellum
• Provides timing for
skeletal muscle
activity
• Controls balance and
equilibrium
• Are you clumsy?
Uncoordinated?
Blame your
cerebellum!
Sections of Diencephalon
• Thalamus
– Relay station for
sensory impulses up
to correct part of
sensory cortex
– Like an e-mail
server… sends the
message to the right
place!
Sections of Diencephalon
• Hypothalamus
– Helps regulate body
temp, water balance,
and metabolism
(homeostasis)
– Involved with
emotions; contains
thirst, appetite, sex,
pain, fear, rage,
affection, and
pleasure centers
Sections of Diencephalon
– Regulates the
pituitary gland
(attached)
– Mammillary body
(smell recognition)
and optic chiasma
(optic nerves
crossing) attached
ANATOMY HUMOR…
The hypothalamus is one of the
most important parts of the brain,
involved in many kinds of
motivation, among other functions.
The hypothalamus controls the
“Four F’s”: fighting, fleeing, feeding,
and mating.
-Unknown psychology professor in
neuropsychology course
Sections of Diencephalon
• Epithalamus
– Pineal body: assists in
biological clock
(daily/seasonal/life
cycles) by releasing
melatonin
– Choroid plexus: forms
cerebrospinal fluid
(there is also another
one in the brainstem)
Sections of Brainstem
• Midbrain
– Conveys ascending
and descending
impulses
• Pons
– Conveys ascending
and descending
impulses
– Helps to regulate
breathing
Sections of Brainstem
• Medulla Oblongata
– Conveys ascending and
descending impulses
– Regulates autonomic
activities such as heart
rate, blood pressure,
breathing, swallowing,
vomiting, defecation,
sneezing, coughing… the
list goes on
• As soon as it passes out of
the skull (through the
foramen magnum), the
brainstem is then known as
the spinal cord
Meninges of the CNS
• Dura Mater: thick, outermost
• Arachnoid: spiderweb-like
• Pia Mater: innermost,
clings to brain
Cerebrospinal Fluid
• A watery broth that circulates and protects the
brain & spinal cord from trauma
• Formed by choroid plexuses, circulated by
ependymal cells
• A very weak salt solution with low amounts of
protein (200 mL total; 135-150 mL around the
brain)
• Any change in composition (levels of protein,
presence of blood, glucose levels) may be a
sign of meningitis, tumors, infection, or
something else
• Tested through a spinal tap
• Ventricles
– Set of structures
(openings)
containing CSF in
the brain
– Drains into the
central canal of the
spinal cord
Central Nervous System
• Brain
• Spinal Cord
– Extends from medulla
oblongata (at foramen
magnum) to the T12 vertebrae
(last thoracic vertebrae)
– Below T12 is the cauda equina
(a collection of spinal nerves)
Spinal Cord – 3 Basic Parts
• Inner gray matter
columns
– Mostly cell bodies
• Outer white
matter columns
– Conduction tracts
– Composes most
of spinal cord
• Central canal
filled with CSF
Peripheral Nervous System
• Composed of Nerves: bundles of nerve
fibers
• Neuron fibers surrounded by connective
tissue (work similar to muscle fibers!)
• Two Types of Peripheral Nerves:
Spinal & Cranial Nerves
Nerves
• Endoneurium
surrounds each fiber
• Groups of fibers are
bound into fascicles
by perineurium
• Fascicles are bound
together by
epineurium
Spinal Nerves
• Spinal Nerves
– 31 originating from
spinal cord
– Named for segments
• Cervical – 8 (not 7)
• Thoracic – 12
• Lumbar – 5
• Sacral – 5
• Coccygeal – 1 (not
4)
• Spinal nerves continue on
to form the rest of the
nerves in your body!
Nerves
• Endoneurium
surrounds each fiber
• Groups of fibers are
bound into fascicles
by perineurium
• Fascicles are bound
together by
epineurium
Nerves
• Cranial Nerves
– 12 originating from
brainstem
• Olfactory – smell
• Optic – vision
• Oculomotor – eye lens
shape, pupil size
(moving eyeball)
• Trochlear – follow
moving objects with eye
Nerves
• Trigeminal – skin senses from face, chewing
muscles
• Abducens – roll eye laterally
• Facial – facial expression muscles, lacrimal
(tear) and salivary (spit) glands, taste
• Vestibulocochlear – sense of balance, hearing
• Glossopharyngeal – swallowing and saliva
production
Nerves
• Vagus – sense & motor of pharynx & larynx
• Accessory – activate sternocleidomastoid and
trapezius muscles (turn neck, shrug
shoulders)
• Hypoglossal – control tongue movements
Transmitting Impulses
• Nerve impulses have a domino effect
• Each neuron receives an impulse and
must pass it on to the next neuron
– Dendrites pick up the impulse
– Shuttled through the axon
– Transmitted to next neuron at axon terminal
Sending The Signal
Impulse through a neuron…
• Polarized: the neuron at rest
– More sodium ions outside the cell, less
potassium ions on the inside (in comparison to
the # of Na ions on outside)
– Sodium/Potassium pumps keep it this way
– Because the abundance of sodium ions outside
the cell is way higher than the abundance of
potassium ions on the inside, we would say that
there is a partially positive charge on the
outside of the cell, and a partially negative
charge on the inside of the cell
– This balance of charges is called the Resting
Potential
Through a neuron…
• Depolarization: A stimulus comes along,
and Na+ moves into the membrane
– The stimulus (neurotransmitter) opens
sodium channels, allowing Na+ to rush in
– The neuron continues to open channels
all along membrane
Through a neuron…
• Action Potential: The depolarization
wave continues to move down the
membrane
– Once this process is started, it continues
to move all the way down the membrane
• Once you “pop”, you can’t stop!
Through a neuron…
• Repolarization: K+ ions move outside,
and Na+ ions stay inside the membrane
– Potassium channels on inside of membrane
open to allow K+ to move out
Through a neuron…
• Refractory period: Everything gets put back to
normal… K+ returns to inside, Na+ returns to
outside
– All thanks to Na+/K+ pump
– Can’t respond to another stimulus during this
period
• The cell is then returned to the polarized
state until another impulse comes along
• Remember: the process takes less time if it has
a myelin sheath around the neuron processes!
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter14/animation__the_nerve_impulse.
html
Between neurons…
• Remember that action potential that was
created? Well, eventually, it reaches the
end of the axon (axon terminals)
• When it does, it goes through steps to
pass the signal on to the next neuron…
Between neurons
• Calcium gates in axon
terminals open, allowing
Ca+2 in
• Due to Ca+2 entering the
axon terminal, a specific
neurotransmitter gets
released
• Neurotransmitter diffuses
across synapse
• Neurotransmitter binds with
specific receptors on the
next neuron
Returning to normal
• The neurotransmitter can do one of two things…
– If received by another neuron, it will open Na+
gates on the next neuron, beginning a new
action potential on the new neuron
– If received by some body part, it will stimulate
some sort of change (muscles, glands, etc.)
• After neurotransmitter does its job, the receptor
releases it back into synapse, and finds its way
back to the neuron so it can be re-released
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/
chapter14/animation__chemical_synapse_
_quiz_2_.html
• There are approximately 20 known
neurotransmitters
Types of neurotransmitters
• Acetylcholine (ACh) – voluntary movement of
muscles
• Norepinephrine – wakefulness or arousal
• Dopamine – motivation, pleasure, associated
with addiction and love
• Serotonin – memory, emotions, temperature
regulation
• Histamine – wakefulness
• Endorphins – natural pain killer
** Many neurotransmitters also have hormonal
effects.
Nervous System Conditions
Meningitis
• Inflammation of the meninges
• Can then spread to actual nervous tissue
of CNS, and inflame the brain
(encephalitis)
Hydrocephalus
• CSF accumulates (most commonly)
because of an obstruction
• “Water on the Brain”
Myelitis
• Swelling of the spinal cord
• Disrupts CNS functions linking the brain
and limbs
Multiple Sclerosis
• Myelin sheaths around the fibers are
destroyed, and converted into hardened
sheaths called scleroses
• Person loses ability to control muscles
• Victims experience muscle weakness,
abnormal muscle spasms, and difficulties
in movement, coordination, & balance
Cerebrovascular Accident
• Commonly called a stroke
• The result of a ruptured blood vessel
supplying a region of the brain
• Brain tissue supplied with oxygen from
that blood source dies
• Loss of some functions or death may
result
Alzheimer’s Disease
• Progressive
degenerative brain
disease
• Structural changes in the
brain include abnormal
protein deposits, twisted
fibers within neurons,
and atrophy of the brain
• Victims experience
memory loss, irritability,
confusion, and
hallucinations
Parkinson’s Disease
• Loss of dopamine-secreting cells
• Causes other transmission problems,
which leads to symptoms
• Victims experience tremors, rigidity, and
gait issues (posture and walking)
Traumatic Brain Injury (TBI)
• Concussion
– Slight or mild brain injury
– Bleeding & tearing of nerve fibers happened
– Recovery likely with possible memory loss
• Contusion
– A more severe TBI
– Nervous tissue destruction occurs
– Nervous tissue does not regenerate
Traumatic Brain Injury (TBI)
• TBI can often result in either temporary or
permanent amnesia
– Anterograde amnesia: new events are not
transferred to the permanent as long-term
memory
– Retrograde amnesia: inability to recall
memories of the past