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THE NERVOUS SYSTEM
Anatomy & Physiology Unit 7
What is the Nervous System?


Master controlling and communicating system of the
body
Communicates by electrical impulses that cause
rapid and specific responses
Functions of the Nervous System

Monitors changes occurring both inside and outside
the body
 Vocab:
 Changes
= stimuli
 Gathered information = sensory input
Functions of the Nervous System

Processes and interprets the sensory input and
makes decisions about what should be done at each
moment
 Vocab:
 This
process is called integration
Functions of the Nervous System

Effects a response by activating muscles or glands
via motor output
Nervous System Function Example

You are driving…
 Sensory
input: you see a red light
 Integration: nervous system processes this information
 Red
 Motor
light means stop
Output: muscles of right leg and foot receive
nerve impulse
 Response: foot goes for the brake pedal (muscles)
Structural Classification

Central Nervous System (CNS)
 Brain
and spinal cord
 Acts as the integrating and command center
 Interprets incoming sensory information and issues
instructions based on past experience and current
conditions
Structural Classification

Peripheral Nervous System (PNS)
 Nerves
that extend from the brain and
spinal cord
 Spinal nerves
 Carry
information to and from the spinal
cord
 Cranial
 Carry
 Link
nerves
impulses to and from the brain
sensory receptors to the CNS
 Link the CNS to glands and muscles
Functional Classification


Only covers the PNS
Sensory/Afferent Division
 Nerve
fibers that carry impulses to the CNS
 Somatic
Sensory Fibers: deliver impulses from the skin,
skeletal muscles, and joints
 Visceral Sensory Fibers: transmit impulses from the visceral
organs
Functional Classification

Motor/Efferent Division
 Carries
impulses from the CNS to muscles/glands
 Activate muscles and glands
 Muscles or glands are called the effectors
Put these in the correct order

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Afferent neuron
Effector
Efferent neuron
Integration center
Receptor
correct order ANSWER

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Receptor
Afferent neuron
Integration center
Efferent neuron
Effector
Subdivisions of the Motor Division

Somatic Nervous System
 Conscious/Voluntary
 Skeletal
muscle control
muscles
 Involuntary reflexes can also be activated by this
division
Subdivisions of the Motor Division

Autonomic Nervous System
 Regulates
automatic/involuntary events
 Smooth muscle, cardiac muscle, glands
 Two Parts
 Sympathetic
– fight or flight
 Parasympathetic – rest and digest
Interneurons


Connect sensory and motor neurons
Also called Association Neuron
Nerve Cell
Neurons in adults do not undergo mitosis.
Ganglia

Small collection of nerve cell bodies found in a few
locations outside the CNS
 Ganglia
(plural)
 Ganglion (singular)
Physiology: Nerve Impulses


http://www.youtube.com/watch?v=7EyhsOewnH4
https://www.youtube.com/watch?v=U0NpTdge3aw
Physiology of Nerve Impulses

Resting Neuron
 Plasma
membrane is polarized
 There are fewer positive ions on the inside than the
outside
 K+ ions inside
 Na+ ions outside
 While inside remains negative relative to outside, the
neuron is inactive
Physiology of Nerve Impulses

How are neurons excited?
 Light
 Sound
 Pressure
 Neurotransmitters

released by other neurons*
The action potential is essential for nerve impulses
to fire.
Physiology of Nerve Impulses

Response to Stimuli
 Permeability
of membrane change briefly
 “gated” sodium ion channels open if the enough stimulus
is present
 Inward rush of sodium ions
 Depolarization: changes the polarity of the neuron
 Inside
more positive
 Outside less positive
 Called: Graded Potential
Physiology of Nerve Impulses

Response to Stimuli
 If
the stimulus is strong enough, depolarization activates
the neuron to initiate an action potential (nerve impulse)
 Nerve impulse = all-or-none response
 Membrane permeability changes again
 Impermeable
to sodium ions
 Permeable to potassium ions
 Outflow of positive ions
 Repolarization: restores the resting state
Physiology of Nerve Impulses

Response to Stimuli
 Initial
concentrations of sodium and potassium ions
restored by the sodium-potassium pump

Immediately after the action potential is
propagated (highest point), potassium diffuses out
of the cell.
Physiology of Nerve Impulses
Physiology of Nerve Impulses
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
The previous description was for unmyelinated
axons
Myelinated Axons
 Conduct
impulses faster
 Impulse “jumps” from node to node
What Happens When the Impulse
Reaches the Axon Terminal?

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Vesicles containing neurotransmitters fuse with the
membrane and release their contents into the
synapse
Neurotransmitters bind to receptors on the
membrane on the next neurons
Neurotransmitter binding is brief
 Reuptake
by axon terminal
 Enzymatic breakdown
Axon Terminal
Recap of Action Potential
1.
2.
3.
4.
Sodium channels open and sodium ions diffuse
inward.
The membrane becomes depolarized.
Potassium channels open and potassium ions
diffuse outward while sodium is actively
transported out of the cell.
The membrane becomes repolarized.
Reflexes


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Rapid, predictable, and involuntary responses to
stimuli
Once a reflex begins, it always goes in the same
direction
Reflex arches:
 Neural
pathways for reflexes
 Involve the CNS and PNS
Somatic Reflexes


Reflexes that stimulate skeletal muscles
Why you pull your hand away from a hot object
Autonomic Reflexes

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Regulate the activity of smooth muscles, the heart,
and gland
Examples:
 Sweating
 Pupil
dilation
 Secretion of saliva
5 Elements of a Reflex
PUT THESE IN ORDER
 Sensory receptor
 Effector organ
 Sensory neuron
 Motor neuron
 Integration center
5 Elements of a Reflex ANSWER
PUT THESE IN ORDER
 Sensory receptor
 Sensory neuron
 Integration center
 Motor neuron
 Effector organ
Brain
Parts of the Brain
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Cerebrum
Brain stem
Diencephalon – p239, thalamus, hypothalamus
Cerebellum
Parts of the Brain Stem

Brain Stem
 Midbrain
– motor control
 Pons - hearing, equilibrium, and taste
 Medulla oblongata – heart rate, breathing, swallowing
Lobes of the Cerebrum
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Parietal lobe – sensory information
Temporal lobe – long term memory
Occipital lobe - vision
Frontal lobe – voluntary movement
Others parts to know

Hypothalamus
 Regulates

body temperature
Corpus Callosum
 It
connects the left and right cerebral hemispheres and
facilitates interhemispheric communication.

Basal Ganglia
 Helps
regulate motor activities
Meninges

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are the three membranes that envelop the brain
and spinal cord.
In mammals, the meninges are the dura mater, the
arachnoid mater, and the pia mater.
Cerebrospinal fluid is located in the subarachnoid
space between the arachnoid mater and the pia
mater. The primary function of the meninges is to
protect the central nervous system.
Brain Dysfunctions

Traumatic Brain Injuries
 Concussion
 Slight
brain injury
 No permanent brain damage
 Brain
Contusion
 Tissue
destruction
 Can cause a coma
 Intracranial
 Bleeding
 Cerebral
 Swelling
hemorrhage*
from ruptured blood vessels
Edema*
of the brain
Brain Dysfunctions

Cerebrovascular Accident (CVA); Stroke
 3rd
leading cause of death in the U.S.
 Occur when blood circulation to the brain is blocked
 Blood
 Vital
clot or ruptured blood vessel (bleeding)
brain tissue dies
 Fewer than 1/3 of those who survive a CVA are alive 3
years later
Parkinson’s and Huntington’s disease
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Parkinson's disease is characterized by gradual loss
of the ability to initiate movement. Tremors also
Huntington's disease is characterized by an inability
to prevent parts of the body from moving
unintentionally.
Both caused by degeneration of basal ganglia.
Parkinson's Disease Video
Multiple Sclerosis
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Autoimmune disease that destroys the myelin sheath
of neurons
http://www.nationalmssociety.org/What-is-MS
Alzheimer’s Disease
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Progressive degeneration that results in dementia
(mental deterioration)
Effects cognition and memory
Alzheimer's brain comparision
Spinal Cord
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Approximately 17 inches long
White continuation of the brain stem
Conduction pathway to and from the brain
Major reflex center
Enclosed in the vertebral column
Extends from the foramen magnum to the 1st or 2nd
lumbar vertebra
Spinal Cord


Cushioned and protected by meninges
Meningeal sac continues beyond L3
 Ideal
spot for CSF removal
Spinal Cord
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31 pairs of spinal nerves arise from the spinal cord
Spinal cord is about the size of a thumb, thicker in
cervical and lumbar regions
Cervical – 7 vertebrae but 8 nerves
Thoracic - 12
Lumbar - 5
Sacral - 5
Coccygeal - 1
There is no possibility of damaging the spinal cord below the 3rd lumbar vertebra.
Gray Matter of the Spinal Cord and
Spinal Roots
Shaped like a butterfly
 Surrounds the central canal of the cord, which
contains CSF
 Unmyelinated, considered
gray(dk pink here)

White Matter of the Spinal Cord and
Spinal Roots

Composed of myelinated fiber tracts (white)(light
pink here due to dye)
Peripheral Nervous System

Nerve:
A
bundle of neuron fibers found outside the CNS
 Endoneurium
 Delicate
connective tissue sheath surrounding each fiber
 Perineurium
 Coarser
connective tissue wrapping groups of fibers
 Fascicles
 Fiber
bundles
 Epineurium
 Tough
fibrous sheath, binds fascicles together
Autonomic Nervous System
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Motor subdivision of the PNS that controls body
activities automatically
Homeostasis depends largely on this system
Autonomic Nervous System
Sympathetic
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Fight or flight system
Activity is evident
when we are
excited/stressed
Pounding heart, rapid
breathing, dilated
pupils
Parasympathetic
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Resting and digesting
Activity is evident
when we are
resting/not threatened
Promoting digestion,
decreases demands on
cardiovascular system
Developmental Aspects of the Nervous
System
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
Formed during first month of embryonic
development
Any maternal infection in early pregnancy can have
extremely harmful effects
 Lack
of Oxygen
 Smoking
decreases oxygen in the blood, can lead to neuron
death
 Radiation
and Drugs
 Damaging
 Maternal
 Causes
to nervous system during fetal development
Measles
deafness and other CNS damage
Developmental Aspects of the Nervous
System
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Cerebral Palsy
 Temporary
lack of oxygen during delivery
 Voluntary muscles are poorly controlled and spastic
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Anencephaly
A
failure of the cerebrum to develop
 Child cannot hear, see, or process sensory inputs

Spina Bifida
 Vertebrae
form incompletely
 Various levels of severity, affects lower limbs most
Developmental Aspects of the Nervous
System

Hypothalamus: one of the last areas of the CNS to
mature
 Contains
centers for regulating body temperature
 Premature babies usually have problems controlling
their loss of body heat
Developmental Aspects of the Nervous
System
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Brain reaches maximum weight in young adulthood
Neurons are damaged and die over the next 60
years
An unlimited number of neural pathways are always
available and ready to be developed
Alcoholics, boxers, etc. accelerate the shrinking of
the brain before aging has an affect