Nervous System

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Nervous System

• One of 2 controlling and communicating systems of
  the body (other is the endocrine system)
• -Sensory input - Integration - Motor output

-The two principal cell types of the nervous
system are

• Neurons
• hundreds of thousands of neurons extend axons and
  make synapses all over the body with other
  neurons, muscles and glands

• communicate through action potentials
• allows for short response times to changes in
  homeostasis (excitable cells)

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• Neuroglia
• guide developing neurons to make synapses
• provide a supportive scaffolding for developed
  neurons ( a supportive cell)

Organization of the Nervous System

• Central nervous system (CNS) -BRAIN and SPINAL C.
• consists of the brain located within the skull
  and the spinal cord located within the vertebral
  foramen
• large masses of neurons

• integration and command center of the body
• covered by meninges and surrounded by
  cerebrospinal fluid

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• Peripheral nervous system (PNS)
• consists of neurons that bridge the gap between
  the CNS that extend to other locations in the body

• propagate APs to and away from the CNS

• the neurons are organized into nerves (bundle of
  axons) and ganglions (group of cell bodies
  outside the CNS)
• - carries messages to and from the spinal
  cord

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Anatomical Organization of the Nervous System
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Nerves

• Nerve
• cordlike organ of the PNS consisting of axons
  enclosed by connective tissue

Connective tissue coverings include

• Endoneurium
• loose connective tissue that surrounds each
  individual axon

• Perineurium
• coarse connective tissue that bundles axons into
  fascicles

• Epineurium
• tough fibrous connective tissue around a nerve

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Structure of a Nerve
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Functional Organization of the Nervous System
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Functions of the Nervous System
-Transmit sensory information

• propagate APs to the CNS following a stimulus
  which has changed a variable from its set point
• from eyes, skin, blood vessels, ears, digestive
  tract, joints, muscles, lungs

• Integration
• interpretation of sensory information by the CNS
• type, location and magnitude of stimulus

• Transmit motor information
• propagate APs from the CNS to various effector
  organs throughout the body
• provides a way to respond to stimuli

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Neuron Types of the Nervous System

• Sensory (afferent)
• associated with sensory receptors
• propagate APs via the PNS toward the CNS

• Interneurons
• integrate information within the CNS
• receive APs from sensory neurons and initiate APs
  in motor neurons (shuttle signals thru CNS)

• Motor (efferent)
• propagate APs via the PNS away from the CNS to
  effectors

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Basic Function of the Nervous System
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Sensory Receptors

• Structures specialized to respond to stimuli
• nerve endings (dendrites of neurons)
• sense organs

• nerve endings combined with other tissue types to
  enhance detection of a stimuli
• example taste buds

• Mechanoreceptors
• respond to touch, pressure, stretch and itch

• Thermoreceptors
• respond to changes in temperature

• Photoreceptors
• respond to light

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• Chemoreceptors
• respond to chemicals

• Nociceptors
• respond to pain

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Neural Integration of the CNS

• Qualitative information (salty, pain or
  temperature) depends upon which neurons are
  propagating APs
• Quantitative (strength) information depend on
• the number of neurons that are firing APs
• the frequency of APs fired per neuron

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Myelination of Neurons of the Nervous System
-Some neurons in the CNS are myelinated, while
most are unmyelinated
-All of the neurons in the PNS are myelinated

• Areas of the CNS that are made of myelinated
  neurons are called white matter
• represent the locations of long sensory and motor
  neurons

• Areas of the CNS that are made of unmyelinated
  neurons are called gray matter

-represent the locations of short
interneurons which make many synapses for
integration to process sensory information and
initiate motor information
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Reflexes
-A rapid, predictable motor response to a stimulus

• Reflexes can be
• simple
• involve peripheral nerves and the spinal cord
• spinal reflexes (Inborn intrinsic innate)

• learned (acquired)
• involve peripheral nerves and the brain

• Following a stimulus, the sensory and motor
  information of a reflex follows a pathway called
  a reflex arc

• in many spinal reflexes, the effector is nearby
  the location of the stimulus

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-May involve only peripheral nerves and spinal
nerves-May involve Higher brain centers as
well-That is, the brain may be informed later
(after the reflex has occurred)
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Reflex Arc

• There are five components of a reflex arc

• Receptor
• respond to stimulus

• Sensory neuron
• transmits the afferent impulse to the CNS

• Integration (control) center
• region within the CNS where synapses (processing
  of sensory info) occur (brain or s.cord)

• Motor neuron
• sends efferent information to an effector

• Effector
• muscle fiber or gland that responds to the
  efferent impulse
• the activity of the effector depends upon the
  magnitude of the stimulus

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-Reflexes are to limit damage i.e. to protect
quickly
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Meninges and CSF
-The meninges are 3 connective tissue membranes
that lie external to the brain and the spinal cord

• dura mater
• arachnoid mater
• pia mater

• cover and protect the CNS
• hold cerebrospinal fluid (CSF)
• prevents harmful substances from entering CSF

• The CSF is the extracellular fluid of the cells
  of the nervous system

• surrounds and fills the spaces within the spinal
  cord and the brain

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• prevents the brain from crushing under its own
  weight
• protects the CNS from trauma

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Meninges-
- connective tissue surrounding spinal cord and
brain (continuous with each other)
1. Dura Mater - most superficial
- dense irregular connective tissue
2. Arachnoid - middle layer
-avascular (no blood vessels)
- spider web arrangement of delicate collagen
fibers and some elastic
3. Pia Mater - thin transparent connective tissue
that adheres to surface of brain or spinal cord
- interlacing bundles of collagen and fine
elastic fibers
- contains many blood vessels to supply oxygen
and nutrients
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Meninges
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Brain
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Cerebrum
- largest portion of the brain, about 2/3
-upper most portion and divided into 2 hemispheres
Cerebral cortex
-Outermost portion of cerebrum
-human cerebral cortex is more developed than in
any other animal

• 4 lobes
• frontal, parietal, temporal and occipital
• location of interneurons for perception of all
  senses
• Site of memory, emotion, learning
• site of initiation of voluntary skeletal muscle
  contraction

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• -superficial is called gray matter
• 40 of brain mass
• -enables sensaton, communcation. Memory,
  understanding
• Hemispheres are contralateral i.e. left side of
  brain controls left side of face but right side
  of body

• -no functional area acts alone i.e. behavior
  involves entire cortex

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The Cerebellum
-Located dorsal to the pons and medulla
-Protrudes under the occipital lobes of the
cerebrum
-Makes up 11 of the brains mass

• Modifies the motor information leaving the motor
  cortex

• provides precise timing and appropriate patterns
  of skeletal muscle contraction to maintain
  balance and coordination

Cerebellar activity occurs subconsciously Responsi
ble for balance and coordination
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Brain Stem
-Comprised of the pons and the medulla oblongata
-Clusters of neurons (brain centers) in regions
of the pons and medulla control the basic life
functions

• heart rate
• controlled by the cardioacceleratory and
  cardioinhibitory centers in the medulla

• blood pressure
• controlled by the cardioacceleratory,
  cardioinhibitory, and vasomotor centers in the
  medulla

• breathing rate
• controlled by the inspiratory and expiratory
  centers in the medulla and pons, respectively

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• Control of effectors occurs through the Autonomic
  Nervous System
• Provides pathways between higher and lower brain
  centers

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Brain
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Hypothalamus and Pituitary

• Hypothalamus and Pituitary (Master glands) (caps
  Brain stem)
• 2 glands located inferior to the thalamus

• Secrete hormones which regulate a large number of
  metabolic processes

• metabolic rate
• sex hormone levels in the blood
• growth
• water balance
• blood nutrient levels

-The hypothalamus secretes hormones which in
turn cause the pituitary to secrete hormones,
thus the hypothalamus controls the function of
the pituitary
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Hypothalmus regulates blood pressure, heart rate,
force of heart rate, rate of breathingPerception
of pleasure, maintains body temperatureFeelings
of hunger and regulates sleep
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Spinal Cord

• The spinal cord is attached to the brain and
  extends to the lumbar region of the vertebral
  column

• Functions include
• integration of basic stimuli presented to the
  body below the neck through simple reflexes
• withdrawal reflex in response to pain

-sending sensory and motor information to and
from the brain
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31 pairs of spinal nerves.There are enlargements
in the cervical and lumbar regions where nerves
of limbs emerge.Cauda equina is a collection of
nerve roots at the inferior end of the vertebral
column
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Spinal Cord Anatomy

• Dorsal (posterior) horns (left and right)
• sensory information enter the cord on the dorsal
  aspect where they synapse with interneurons or
  motor neurons

-extend into dorsal roots and ganglia

• Ventral (anterior) horns (left and right)
• motor information exits the cord on the ventral
  aspect where they control effectors (muscle or
  glands)

-extend into motor roots
-Dorsal and ventral roots merge together to form
spinal nerves
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Spinal Cord Anatomy
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Peripheral Nervous System (nerves
outside of the CNS)

• The PNS consists of 12 pairs (left and right) of
  cranial nerves originate from the brain and 31
  pairs (left and right) of nerves are attached to
  the spinal cord

• Sensory (afferent)
• all axons carry impulses from sensory receptors
  via the PNS to the CNS

• Motor (efferent)
• all axons carry impulses via the PNS from CNS

• Mixed
• a mixture of sensory and motor neurons that carry
  impulses via the PNS to and from CNS
• most common type of nerve in the body

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Sensory Division of the PNS

• Sensory division
• made of afferent neurons
• Somatic (body)

• sensory neurons send APs from skin, skeletal
  muscles, and joints

• visceral sensory neurons send APs from organs
  within the abdominal and thoracic cavaties

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Motor Division of the PNS

• Motor division
• made of efferent neurons
• control the action of effectors

• somatic motor neurons send APs to voluntary
  skeletal muscle

• visceral motor neurons send APs to involuntary
  cardiac muscle, smooth muscle and glands
• a.k.a. the Autonomic Nervous System (ANS)
• 2 antagonistic (opposing) divisions

• Sympathetic
• Parasympathetic
• the two divisions control the same effectors
  (with few exceptions) but create opposite
  responses in the effectors

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Autonomic Nervous System
-Visceral motor neurons of the PNS control the
activity of involuntary effectors such as cardiac
muscle, smooth muscle and glandular secretion
affecting

• heart rate
• breathing rate
• sweating
• digestion
• blood pressure

-Action potentials in these motor neurons are
initiated in the medulla oblongata and the pons

• these motor neurons exit the brain by
• descending tracts of the spinal cord
• exit spinal cord via spinal nerves
• cranial nerves

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Efferent Pathways of the ANS
-Efferent pathways of the ANS consist of a
two-neuron chain between the brain or spinal cord
and the effector
-synapses between the neurons occur at
ganglions
-The preganglionic begins in the CNS and
extends along a nerve to the ganglion

• The postganglionic neuron extends from the
  ganglion to an effector organ

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Organization of the Sympathetic Division
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Organization of the Parasympathetic Division
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Function of the Sympathetic Division
-The sympathetic division is called the fight or
flight system (mobilizes body in extreme
situations)
-activated when the body needs to expend
energy

• Involves E activities
• exercise, excitement, emergency, and embarrassment

• Promotes necessary changes during these
  activities
• increases heart rate, blood pressure, respiration
  rate, blood flow to skeletal muscles, glucose
  metabolism

-decreases the activity of and blood flow to
the digestive system organs
-Its activity is illustrated by a person who is
threatened
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-the individuals heart rate increases and the
breathing becomes deep-skin is cold and
sweaty-pupils dilate
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Function of the Parasympathetic Division

• The parasympathetic nervous system is called the
  rest and digest system
• activated when the body needs to conserve energy

• Involves the D activities
• digestion, defecation, and diuresis (urination)

• Promotes necessary changes during these
  activities
• decreases heart rate, blood pressure, respiration
  rate, blood flow to skeletal muscles, glucose
  metabolism

• increases the activity of and blood flow to the
  digestive system organs

Its activity is illustrated in a person who
relaxes after eating a meal
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-Therefore maintenance activities-gastrointestina
l activity is high-skin is warm and pupils
constricted
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-most visceral organs are innervated by both
sympathetic and parasympathetic
nerves-Therefore, dynamic antagonisms that
precisely control visceral activitye.g.
sympathetic increases heart rate, respiration,
and inhibits digestion while the parasympathetic
decreases heart and respiratory rates and allows
for digestive system to be rid of wastes
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Neurotransmitters of Sympathetic and
Parasympathetic Divisions

• The way the 2 divisions of the ANS can create
  opposite responses in the effectors that they
  control is by the release of different
  neurotransmitters onto the cells of the effectors

• All preganglionic neurons (sympathetic and
  parasympathetic) exocytose acetylcholine (ACh)
  onto postganglionic cells
• creating an AP in the postganglionic cell

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• Sympathetic postganglionic cells release
  norepinephrine (NE) onto the effector
• Parasympathetic postganglionic fibers release ACh
  onto effector

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Efferent Sympathetic vs. Parasympathetic
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Effects of Neurotransmitters of the Autonomic
Nervous System

• The cells of each organ controlled by the ANS
  have membrane receptors to BOTH ACh and NE
• organs are dually controlled

-The response of the organ is determined by the
identity of the neurotransmitter released

• the binding of ACh to its receptor will cause the
  effector to respond in one way

-the binding of NE to its receptor will
cause the effector to respond in the opposite way
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• The effect of ACh and NE on an effector can be
  either stimulatory or inhibitory (effector
  specific)

-NE increases heart rate, ACh decreases
heart rate

• NE decreases the secretion of saliva, ACh
  increases the secretion of saliva

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Dual Control by the Sympathetic and
Parasympathetic Systems
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Brain
Left Brain-
-Logic Details Facts Words
Present/past Math/Science Knowing Reality
Right Brain-
- Feeling Big Picture Imagination
Symbols Future Philosophy/Religion
Spatial perception Risk Fantasy
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Brain Dysfunctions
Traumatic Brain Injuries
-Damage is caused not only at the site of a blow,
but also by the effect of Ricocheting brain
hitting the opposite side of the skull
1. Concussion
- slight brain injury
- maybe dizzy seeing stars or loss of
consciousness, briefly
Levels of injury
G-1 less than 15 min
G-2 greater than 15 min
G-3 loss of consciousness
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Recovery (from sport)
G-1 1 week G-2 2 weeks G-3 1
month
2. Contusion
- marked tissue damage
- if cerebral cortex is injured the individual
may remain conscious
- but severe brain stem contusions always result
in a coma lasting hours to a Lifetime
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3. Inter Cranial Hemorrhage
- bleeding from ruptured vessels or cerebral
edema (swelling of the brain due to inflammatory
response to injury)
- individuals who are initially alert and lucid
may begin to deteriortae neurologically later
Signs of a serious impact
- headache that gets worse

• Confusion
• Disorientation
• Slurred speech
• Sleepiness
• Droopy eye
• amnesia

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4. Cerebrovascular accident (strokes)
-3rd leading cause of death in the US
- blood circulating to the brain area is blocked
(clot or ruptured blood vessel) - vital tissues
dies
- brain area affected determined by observing
patients symptoms
5. Cerebral Palsy
-One cause temporary lack of oxygen at birth
- neuromuscular disability gt voluntary muscles
are poorly controlled because of brain damage
- 50 of patients have seizures
-some have mental retardation
- some have vision or hearing problems
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Tracking down the problems
1. Test reflexes - test of brain and spinal cord
2. Electroencephalography (EEG)
-electrodes placed on scalp to measure brain
activity (impulses or brain waves)
- patterns vary depending on activity e.g.
sleeping, coma
- lack of waves means brain death
3. CT Scan - 3D image from x-rays and the use if
intravenously administered contrast dyes (high
radiation)
4. MRI - Magnetic Resonance Imaging
-better image than a CT Scan
- uses a magnetic field therefore no radiation
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5. PET - Positron Emission Tomography
-3D image
-uses gamma rays from a radioisotope that has a
short half life
- may be used in conjunction with a CT Scan