Download 6-1 Nervous System

Nervous System
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Nervous System
master control system
master communicating center

nerve tissue develops from embryonic
ectoderm
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Role of the Nervous System
monitors changes
- (sensory function)
 processes and interprets information
- (integrative)
 elicits responses
- (motor)

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Nervous System Organization
anatomical organization
- central nervous system (CNS)
- peripheral nervous system (PNS)
 functional organization
- sensory
- integrative
- motor

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Central Nervous System (CNS)
brain
- cerebrum
- diencephalon four principal parts
- brain stem
- cerebellum
 spinal cord
- continuation of brain stem
- continues from base of skull to
the 1st lumbar vertebra

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diencephalon
cerebrum
pituitary
gland
brain midbrain
stem pons
medulla
oblongat
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cerebellum
spinal cord
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Peripheral Nervous System (PNS)
cranial nerves
- 12 pairs
- emerge from the brain
 spinal nerves
- 31 pairs
- emerge from the spinal cord

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Functional Organization
sensory
- gathers information that occurs within
internal and external environment
 integrative
- analyzes sensory information
- decides necessary responses
 motor
- carries instructions (nerve impulses) to
muscles and glands (effectors)

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Basic Types of Functional
Neurons
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Sensory Neurons

afferent neurons
- carry information from various body
parts to the brain or spinal cord (input)
Motor Neurons

efferent neurons
- carry instructions from the CNS to
muscles and glands (output)
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Interneurons or Connecting
Neurons
analyze information
 determine appropriate response
 located in the CNS

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Peripheral Nervous System
(subdivisions)
somatic nervous system (soma = body)
- voluntary
- sensations are consciously perceived
 autonomic nervous system (auto = self)
- involuntary and automatic
- sensations are usually not consciously
perceived

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Somatic Nervous System
(SNS)
sensory neurons
- carry impulses to the CNS from
receptors for general and special senses
(touch, pressure, vibration, temperature,
pain, proprioception, smell, taste,
vision,hearing and equilibrium)
 motor neurons
- carry impulses away from CNS only to
skeletal muscles

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Autonomic Nervous System
(ANS)
sensory neurons
- carry impulses to the CNS from
visceral receptors (internal organs)
 motor neurons
- carry impulses from CNS to smooth
muscle, cardiac muscle, and glands

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Motor Division of Autonomic
Nervous System
Two principal divisions work together,
i.e., impulses of one division activate an
organ, while impulses from the other
division inhibit the organ
 sympathetic
 parasympathetic
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Sympathetic

prepares the body for energyexpending, stressful, or emergency
situations
Parasympathetic
active under normal ordinary, restful
conditions
 counterbalances effects of sympathetic
division
 restores body to resting state

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Protection and Coverings of
the Brain
bones of cranium
 cerebrospinal fluid
 connective tissue membranes called
meninges
 vertebral column

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Cranium
frontal
 sphenoid
 ethmoid
 occipital
 parietal
 temporal

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Cerebrospinal Fluid
(CSF)
formed by filtration and secretion from
networks of capillaries
- choroid plexuses
located in the (4) ventricles of the brain
form blood-brain barrier
 clear, colorless liquid
 contains glucose, proteins, lactic acid, urea,
cations, anions, and lymphocytes

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Cerebrospinal Fluid
(cont.)
acts as shock-absorbing medium
 protects brain from banging against
inner walls of cranium
 is a medium for exchange of nutrients
and waste products between blood and
nervous tissue

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Cerebrospinal Fluid
(cont.)
significant changes in composition can
indicate disease conditions
- meningitis
- tumors
- multiple sclerosis
 if drainage of CSF is obstructed,
excessive pressure on the brain will
cause hydrocephalus

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Blood-Brain Barrier
permits certain substances to enter the fluid
but prohibits others
 protects the brain from harmful substances
 formed by tightly adherent cell connections

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Meninges
protective membranes
 delicate
 envelop brain and spinal cord
 Three connective tissue membranes:
- dura mater
- arachnoid
- pia mater

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Dura Mater
outermost layer
 leathery
 next to bony inner surface of cranium
 separated from arachnoid by subdural
space which is fluid filled

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Arachnoid
middle layer
 looks like a cobweb
 Two components:
- layer next to the subdural space
- system of supporting fibers (trabeculae)
forming web-like structure between
arachnoid and pia mater

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Arachnoid
(cont.)
in some areas, arachnoid material
perforates dura mater forming protrusions
called arachnoid villa
 Functions:
- reabsorption of CSF into blood

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Pia Mater
innermost
 thin layer of loose connective tissue
 transparent
 contains many blood vessels
 between pia mater and nerve tissue is a
thin layer of neuroglial processes firmly
attached to pia mater

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Meningitis
inflammation of meninges
 serious threat to brain
 bacterial and viral meningitis can spread
to nervous tissue of CNS

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Regions of the Brain
cerebrum (cerebral hemisphere )
 diencephalon
 brain stem
 cerebellum

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Cerebrum
(cerebral hemisphere)
largest, obscures most of brain stem
 looks like mushroom cap
 made up of 2 deeply grooved hemispheres
- left and right
 Surface is covered by:
- grooves - fissures or sulci
- ridges - gyri or convolutions which serve
as landmarks

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Cerebrum
(con’t)
 concerned with higher brain functions
 Contains centers for:
- interpreting sensory impulses
- initiating voluntary muscular movements
 stores information of memory
 utilizes information in reasoning
processes
 functions in determining a person’s
intelligence and personality
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Left Hemisphere

More important for:
- right-hand control
- spoken and written language
- numerical and scientific skills
- reasoning
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Right Hemisphere

More important for:
- left-hand control
- musical and artistic awareness
- space and pattern perception
- insight and imagination
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Lobes
each hemisphere is subdivided into 4
lobes
 named for cranial bone that covers
them
 more precisely defined by surface
landmarks, i.e., sulci and fissures

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Lobes
(cont.)
parietal lobe
 occipital lobe
 temporal lobe
 frontal lobe

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White Matter
underlying the cortex
 whitish appearance is due to fatty
component of myelin
 consists of myelinated axons extending
in three principal directions
- association fibers
- commissural fibers
- projection fibers

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Association Fibers

connect and transmit impulses between
gyri in the same hemispheres
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Commissural Fibers

transmit impulses from the gyri in one
cerebral hemisphere to corresponding
gyri in the opposite hemisphere
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Three Important
Commissural Fibers
corpus callosum (corpus = mass or body)
- great commissure of the brain between
the cerebral hemispheres
 anterior commissure
 posterior commissure

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Projection Fibers
form descending and ascending tracts
 tracts transmit impulses from cerebrum
and other parts of brain to spinal cord
 tracts transmit impulses from spinal
cord to brain

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Gray Matter
made primarily of densely packed neuron
cell bodies
 basal ganglia
- paired masses of gray matter
- found in cerebral hemispheres
 cerebral cortex
- layer of gray matter approx. 3 mm thick
- has 6 distinct layers
- divided into 3 areas based on function

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Cerebral Hemisphere

outer layer of gray matter is cerebral
cortex
- made up of lobes composed of
dendrites and cell body neurons
- interior is composed of white matter
(nerve fibers arranged in bundles called
tracts)
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Functions of Cerebral Cortex

divided into three main areas based on
function
- sensory area
- motor area
- association area
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Sensory Areas

Function in interpreting impulses,
located in several lobes of cerebrum
- general sensory area
- primary visual area
- primary auditory area
- primary gustatory area
- primary olfactory area
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Sensory Areas
primary
gustatory
primary
auditory
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sensory
primary
visual
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General Sensory Area
Receives impulses from:
- the skin
- muscles
- internal organs
 localizes precisely where sensations
originate
 located on the postcentral gryus on the
occipital lobe

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Primary Visual Area
receives input from the eyes
 Interprets:
- shape
- color
- movement
 located on the occipital lobes

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Primary Auditory Area
(cont.)
receives input from internal ear
(cochlea)
 Interprets:
- pitch
- rhythm
 located on the temporal lobes

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Primary Gustatory Area
receives input from taste buds
 Interprets:
- sensations related to taste
(sweet, sour, salty, bitter)
 located at base of postcentral gryus on
parietal lobes

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Primary Olfactory Area
receives input from olfactory bulbs
 Interprets:
- sensations related to smell
 located on temporal lobes

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Motor Areas
All located on frontal lobes, control
actions of specific muscles or groups of
muscles
- primary motor area
- motor speech area
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Motor Areas
primary motor
motor speech
(Broca’s)
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Primary Motor Area
controls muscles in specific parts of
body
 located on precentral gyrus of frontal
lobe
 The translation of thoughts into speech
involves the motor speech area

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Motor Speech Area (Broca’s Area)
Coordinates complex muscular
actions of the:
- mouth
- tongue
- larynx
 located at junction of temporal, parietal,
and occipital lobes in only one cerebral
hemisphere (usually left)

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Association Areas

Concerned with:
- personality
- intelligence
- emotions
- reasoning
- problem solving
- creativity judgment
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Association Areas
(cont.)
somatosensory association area
 visual association area
 auditory associations area (Wernick’s
area)
 gnostic area
 premotor area
 frontal eye field

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Association Areas
promotor
somatosensory
gnostic
visual
frontal
eye field
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Somatosensory Association Area
integrates and interprets sensations
 Determines:
- shape and texture of an object
- orientation of one object to another as they
are felt
- sense relation of one body part to another
 stores memories, so present sensations can
be compared to previous experiences

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Visual Association Area
relates present to past visual experiences
by recognizing and evaluating what is
seen
 located in occipital lobe

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Auditory Associations Area
(Wernick’s area)
interprets meaning of speech
 determines type of sound
- speech, music, and noise
 also interprets meaning of speech by
translating words into thoughts
 located inferior to primary auditory area
in temporal lobe

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Gnostic Area
(gnosis = knowledge)

(NOS-tik)
integrates sensory interpretations from
the association areas and impulses
from other areas so that a common
thought can be formed
- sends signals to other parts of the
brain to cause appropriate response
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Premotor Area
anterior to primary motor area
 neurons from this area communicate
with primary motor cortex, sensory
associations areas in the parietal lobe,
the basal ganglia, and the thalamus
 concerned with learned motor activities
of complex and sequential nature such
as writing or playing the piano

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Frontal Eye Field
in frontal cortex
 controls voluntary scanning movements
of the eyes such as searching for a
word on a page of text or dictionary

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Diencephalon
consists primarily of the thalamus and
the hypothalamus
 sits on top of brain stem

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Thalamus
oval structure
 consists of paired masses of gray matter (1
inch long) organized into nuclei
 form lateral walls of third ventricle
 right and left halves are joined by bridge of
gray matter called intermediate mass
 principal relay station
 allows crude recognition of sensations; pain,
temperature, or pressure

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Hypothalamus
under thalamus
 single most important region of brain for
maintaining homeostasis
 Regulates:
- temperature, hunger, thirst, smell, fear,
rage, sexual behavior, endocrine
rhythms, and posterior and anterior
pituitary secretions

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Brain Stem
Three parts:
- midbrain
- pons
- medulla oblongata
 three inches long

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Midbrain
mesencephalon
(meso = middle, enkephalos = brain)
 extends from pons to diencephalon
 about one inch
 involved with visual and auditory stimuli

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Pons
(pons = bridge)
directly above medulla
 anterior to cerebellum
 about one inch long
 consists of white matter with regions of
gray matter (nuclei) scattered throughout
 bridge connecting spinal cord with brain
via transverse and longitudinal fibers
 helps to control respiration

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Medulla Oblongata
merges with spinal cord
 contains all ascending and descending
tracts that connect spinal cord and
various parts of brain
 contains centers that control heart rate,
blood pressure, breathing, swallowing
and vomiting

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Cerebellum
looks like a cauliflower
 located behind the pons and below
occipital lobes of cerebrum
 controls subconscious skeletal muscle
contractions required for smooth,
coordinated movements and equilibrium
“automatic pilot”
 second largest part of brain

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Spinal Cord
continuation of brain stem
 extends from large opening in base of
cranium (foramen magnum) down to
upper region of the lower back (1st lumbar
vertebra)
 cylindrically shaped
 approximately 17 inches long
 1 inch in diameter

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Spinal Cord
(cont.)
Surrounded and protected by:
- meninges
- cerebrospinal fluid
- a layer of fatty tissue
- the vertebra
 no possibility of spinal cord injury below
L4; ideal site for removal of cerebral
spinal fluid

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