Chapter 9

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Chapter 9
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Applied Learning Outcomes

• Use the terminology associated with the nervous
  system
• Learn about the following
• Nerve structure
• Types of nerve pathways
• Nervous system components
• Central nervous system structure and function
• Peripheral nervous system structure and function
• Understand the aging and pathology of the nervous
  system

Chapter 9 Structure of the Nervous System
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Overview
Nervous system composed of neurons and
neuroglia. Bundled into two major components
Central Nervous System (CNS) Major division of
the nervous system composed of the brain and
spinal cord works as a controlling network for
the entire body Peripheral Nervous System (PNS)
The part of the nervous system made up of neurons
and neuroglia outside of the brain and spinal
cord provides motor and sensory communication
between the CNS and the body
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Overview
Chapter 9 Structure of the Nervous System
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Nerve Structure
A typical nerve is covered by a continuous
protective sheet of connective tissue called the
epineurium. Within that are neurofascicles
surrounded by a covering called the perineurium.
Chapter 9 Structure of the Nervous System
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Nerve Structure
Nerve is defined as an enclosed bundle of
neurons and associated neuroglia
running to various structures throughout the
body. Nerves primarily constitute the PNS. Nerve
tracts are found in the brain and spinal cord
(CNS) Nerve tracts are neurons bunched together
in pathways that are
not indistinct bundles. Afferent nerves carry
sensory information from the body to
brain. Efferent nerves carry information from
the CNS to muscles
and glands
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Nerve Structure
Nerve is covered by epineurium-it forms a
protective sheath around the nerve and is an
entryway for blood vessels that assist the
nerve. Within the epineurium are numerous
Neurofascicles a tight bundle of axons and
associated neuroglia It generally contains a
mix of myelinated and unmylinated
axons. Each neurofascicle is covered by the
perineurium. Each neuron and its associated
neuroglia within a neurofascicle are surrounded
by an endoneurium.
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Nerve Structure

• Ganglia are collections of nerve cell bodies
  covered by the
• epineurium.
• They are an accumulation of nerve cell bodies
• located outside the CNS.
• Ganglia of the PNS are
• Composed of unipolar neurons
• Are usually associated with sensory function

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Nervous System Components
Central Nervous System (CNS) Composed of the
Brain and Spinal Cord Three layers of tissues
separate the brain and spinal cord from their
bony covering. These three layers called meninges
are made of the dura mater arachnoid mater
pia mater
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The Meninges

• Dura mater
• Outmost layer
• Pressed tightly against the interior of the
  cranium and
• the vertebral column
• Acts as a barrier against trauma to the CNS
• Prevents CNS from rubbing against skull or
  vertebral
• column

• Arachnoid mater
• Located below the dura mater
• Like a spider web
• Cushions the CNS from rapid movements and blunt
  hits
• to the skull and vertebral column.
• Under it is subarachnoid space-a cavity filled
  with cerebro-
• spinal fluid and blood vessels.

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The Meninges

• Pia mater
• Directly makes contact with the brain and spinal
  cord
• Adheres to brain and spinal cord
• Carries blood vessels to CNS
• Forms sheaths over nerves passing through the
  outer
• meninges layers
• Assists with the production of cerebrospinal
  fluid
• Associated with pia mater is the choroid
  plexus--it is a mass
• of blood vessels and glial cells (ependymal
  cells) that secrete
• cerebrospinal fluid

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The Central Nervous System
The central nervous system is composed of the
brain and the spinal cord. Afferent peripheral
nerves act as trunks that feed sensory
information to the brain through their entry into
the spinal cord.
Chapter 9 Structure of the Nervous System
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Central Nervous System

• The Brain
• Three Major parts
• Forebrain, Midbrain, and Hindbrain
• Forebrain composed of the cerebrum and
  diencephalon
• responsible for emotions, memory,
• motor movement, and thought.
• Cerebrum is divided into the left and right
  cerebral hemispheres
• Cerebrum is separated by midsagittal crease
  called longitudinal
• cerebral fissure.
• Left Hemisphere are specialized for language and
  speech
• Right Hemisphere said to be the site of more
  creative side.
• Corpus callosum band of white matter that
  connects the left
• and right brain.

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Cerebrum

• The hemispheres are divided into four lobes
• Frontal lobe- processes intellectual information
  that helps
• with organization of thoughts.
• also posterior region has voluntary control
  over
• skeletal muscles.
• Parietal lobe- involved with emotions and sensory
  
• interpretation.-interprets sensory info from the
• lips, skin, and tongue.

• Temporal lobe- organizes and stores memories of
• sounds and vision.
• Occipital lobe- interprets vision and assists
  with eye
• function.
• Insula is a small region near the temporal lobe
  that plays
• And important role in processing memories.

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Forebrain

• Diencephalon contains the thalamus and
  hypothalamus.
• Ventricles are also found in the forebrain.
• Consists of four connected cavities that contain
• cerebrospinal fluid
• They are associated with the choroid plexus and
• continue into the spinal cord
• They protect the brain from trauma by acting as a
  
• cushion when head is hit or violently moved.

Hydrocephalus is a disease in children where they
produce too Much cerebrospinal fluid.
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Midbrain
Small strip of neurons that connects cerebrum to
the hindbrain Possesses the auditory and visual
reflex areas Controls the ability of the eyes to
adjust to changes in light Intensity or sound.
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Hindbrain

• Pons first part of the hindbrain. It is
  connected to midbrain
• Organizes and transmits sensory information
  received
• from the body.

• Medulla oblongata lies just below the pons
• Regulates involuntary body functions such as
  blood pressure,
• breathing, heart rate, and swallowing.

• Cerebellum lies posterior to the pons
• Plays a role in balance, posture, and
  coordination of body
• movement

Brain Stem refers to the midbrain and hindbrain
by many people
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Spinal Cord
Is a cylinder of nervous tissue enclosed in the
spinal canal of the Vertebral column. Meninges
covers its surface Central canal contains
cerebral spinal fluid is continuous with
ventricles of the brain Surface of spinal cord is
covered with white matter. Ascending tract found
along the dorsal portion of the spinal cord
They carries sensory information up to the
brain. Descending tract run along the ventral and
lateral portions of the spinal cord. They
carry motor information directly to the PNS
and our effectors.
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The Peripheral Nervous System
The peripheral nervous system is composed of
somatic nerves, autonomic nerves, and ganglia. It
is divided into the sympathetic and
parasympathetic nervous systems.
Chapter 9 Structure of the Nervous System
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Peripheral Nervous System

• PNS
• composed of nerves that branch out from the brain
  and
• spinal cord
• not covered with meninges
• do not have a cavity containing cerebrospinal
  fluid
• Divided into the
• Somatic nervous branch
• Autonomic nervous branch

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Peripheral Nervous System

• Two nervous branches
• Somatic nerves
• Enable the voluntary control of body movements
• through their communication with skeletal
  muscles.
• Composed of
• afferent neurons which collect sensory
• information
• efferent neurons which relay commands
• for muscle action.

• Autonomic nervous system
• Controls involuntary body functions
• Its primary purpose is to maintain a stable
  internal
• environment for the body.

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12 Cranial Nerves
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Spinal Nerves
Nerves that originate from the spinal cord and
pass out of The vertebral column. Spinal nerves
carry motor and sensory information for reflex
control and two way communication to the
brain. Each spinal nerve exits the spinal cord
from two short, lateral Branches. The sensory
branch called the dorsal root. The motor branch
is called the ventral root.
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Autonomic Nervous System

• Uses the cranial and spinal nerves to carry out a
  wide array of tasks.
• It performs these tasks by sending out regulatory
  information from
• the brain.
• This information controls the glands, cardiac
  muscle, and
• smooth muscles necessary for maintaining
  homeostasis.
• It does not require conscious thought
• It is integrated with the endocrine system to
• assist body with digestion, sexual functions,
  and
• stress responses.
• Autonomic Nervous System has two regions
• Parasympathetic nerve division
• Sympathetic nerve division

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Autonomic Nervous System
Parasympathetic nerve division emerges from the
cranial nerves and the sacral spinal
nerves. Sympathetic nerve division arises from
the thoracic and lumbar spinal cord. These two
components typically counteract each others
actions to fine tune the bodys responses to
internal changes and environmental stimuli.
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Autonomic Nervous System
Sometimes called the fight or flight and rest to
digest system. Sympathetic system prepares the
body to react to stress. Parasympathetic system
promotes relaxation and digestion.
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Human Senses

• GustationChemoreceptors on the tongue sense
  taste
• OlfactionChemoreceptors in the nose sense smell
• VisionPhotoreceptors in the retina of the eye
  sense light
• HearingNeurons in the cochlea sense sound
  vibrations
• EquilibriumNeurons in the semicircular canals
  and vestibule of the ear sense position
• Taction or TactilitySensory receptors in the
  skin perceive touch

Chapter 9 Structure of the Nervous System
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Human Senses
The human head contains a concentration of
sensory structures.
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Human Senses
Sense of smell -- olfaction Sense of taste--
gustation Sense of vision-- photoreceptors Sense
of hearing-- audition Sense of
balance--equilibrium Both smell and taste rely
on chemoreceptors to detect chemicals dissolved
in the air or water. Vision uses photoreceptors
to convert light into a neural signal. Hearing
uses a series of receptors that are sensitive to
different types of sounds and vibrations.
Equilibrium uses a combination of receptors to
detect the bodys position as it Is moving and
standing still.
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Taste
Taste buds are distributed throughout the upper
surface of the tongue. Saliva is to ensure wet
environment for taste to occur. Taste is detected
by chemoreceptors. Five taste sensations bitter,
salt, sour, sweet, and umani Umani the taste that
occurs when food ingredient monosodium Glutamate
(MSG) dissolves in mouth. Umani receptors are
distributed throughout the tongue. Thought to
stimulate appetite.
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Smell
Olfaction serves two purposes detect
potentially harmful or valuable chemicals in the
air an important supplement to
taste. Chemoreceptors for smell are within the
olfactory bulb These are located in upper region
of nasal cavity Olfactory bulb is an extension of
olfactory nerve.
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Vision
Eyes are specialized organs used to see objects
and perceive movement. Eyelids and eyelashes are
used to protect eyes. Conjunctiva-thin
transparent layer that tightly covers anterior
surface of the eye Lacrimal gland-
produces tears that lubricate and protect eye
from infection Lacrimal duct-tube that connects
with nasal cavity, tears usually drain off
surface of the eye Retina-inside layer
located at back of eye, contains
photoreceptors Sclera-tough outermost layer of
the eye, white in color Cornea-clear covering at
the front surface of the eye
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Parts of the Eye
Extrinsic muscles- the six muscles that move the
eye Choroid- layer of blood vessels lining the
inner surface of the
sclera Ciliary body-a ring of muscles and
connective tissue attached
to the lens, adjusts lens of the
eye Lens-transparent structure inside the eye
that focuses the light rays for clear
vision Iris-colored part of the eye, ring of
muscles that adjusts the
pupil Pupil-opening in the eye that lets the
light enter
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Parts of the Eye
Aqueous humor-a clear watery fluid in the
anterior chamber of the eyeball, helps
maintain shape of cornea for properly
focused vision Vitreous humor-gel-like fluid that
fills the cavity behind the eye lens,
maintains the spherical shape of the
eye Cones-a photoreceptor sensitive to bright
light and color. Rods-a photoreceptor sensitive
to dim light. Fovea-central point at back of the
eye that contains only the densest
concentration of cones.
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Diagram of the eye
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The Ear
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The Ear
Human Ear converts sounds and body orientations
into neuron Signals for the brain The ear is
composed of three regions external ear middle
ear inner ear The external ear is composed of
the auricle or pinna-fleshy part of the ear
that catches sound waves and funnels them
into the ear canal external auditory meatus or
auditory canal- ear canal
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The Ear
The Middle ear tympanic membrane or
eardrum-vibrates in response to sounds
transmitted by the auditory canal. ossicles are
the three ear bones that the eardrum vibrates
against. These vibrations are transmitted to the
inner ear. Three ossicles are the malleus
-hammer incus- anvil stapes-stirrup Eustachia
n tube connects the middle ear to the
throat. It prevents damage to the middle ear by
adapting to changes in air pressure.
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The Ear
The Inner ear is housed in a cavity in the
temporal bone it is composed of the
cochlea-is a coiled, fluid filled organ that
converts vibrations into neuron impulses
that are sent to the brain. semicircular
canals-are fluid filled chambers that
respond to body position. The vibrations are
transferred from the stapes to part of the
cochlea called the oval window. Organ of Corti
is the part of the inner ear that contains
the neurons that respond to different
sounds. Sound waves then vibrate again the round
window of the cochlea. This permits pressure from
sound waves to be released so they dont echo.
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The Ear
The Inner Ear continued Semicircular canals-
respond to body position Changes in the
direction of flow stimulates neurons, which the
brain interprets as movement. Three canals
superior canal detects forward and backward
motion lateral canal detects
forward and side to side motion posterior
canal also detects side to side
motion Vestibule-is the base of the
semicircular canals detects body
position.
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Wellness and Illness over the Life Span

• Most brain aging is due to loss of myelinization
  and decreased blood flow.
• Most people show a decrease in complex brain
  functions as they age.
• Aging is accompanied by some neuron loss in the
  brain.

Chapter 9 Structure of the Nervous System
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Pathology of the Nervous System
Common categories are trauma cerebrovascular
and neurovascular diseases nervous system
tumors developmental disorders metabolic and
toxic diseases CNS infections neurogenerative
diseases
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Trauma categorized by its location
Peripheral neuropathy It causes numbness, pain,
tingling, or weakness in the PNS. Traumatic
neuropathies of the CNS Whiplash-nerve damage in
the neck caused by an abrupt, forced movement of
the head. Shaken baby syndrome is severe
injuries that result when a young
child is violently shaken.
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Cerebrovascular and neurovascular diseases are
blood vessel disorders that impair the nervous
system function Aneurysms-bulges in blood
vessels caused by stretching and thinning of
the vessels. Ateriovenous malformations is an
unusual tangling of blood vessels in the CNS
or PNS that disrupt blood flow occur after
birth but may not cause problems until
adulthood. Ischemic attacks a condition caused
by insufficient flood flow to a body part.
(Stroke) Transient ischemic attack (mini
stroke) caused by temporary loss of blood
flow
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Nervous system tumors
Abnormal growths that develop from neuroglia
(glioma) cells of the meninges
(meningioma) Immune cells in the nervous system
(lymphoma) Neurons (neuroblastoma and neuroma)
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Developmental disorders of the nervous system
Caused by some factor that interferes with the
DNAs ability to form Or carry out normal
functions of a body component. Can produce four
characteristic problems with nerve
function athetosis causes slow, involuntary
movements of the hands and
feet. repetitive, involuntary twisting
movements chorea causes muscular twitching of
the arms, legs, and face. short, irregular,
nonrepetitive muscle contractions palsy causes
paralysis of a muscle or group of muscles.
muscle paralysis caused by nerve loss tremor
causes uncontrollable, rhythmic shaking
movements
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Metabolic or toxic nervous system diseases
Caused by poisons that impede the functions of
neuroglia or neurons. Large amounts of calcium
sodium, and potassium affect the action
potential of the neurons. Many types of metals
interfere with the metabolism of nervous system
cells. Bacterial, fungal, and protistan
infections of the nervous system damage cells
due to the toxins they produce.
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Aging of the Nervous System
Nerve cell mass of the brain and spinal cord
decreases after the Age of 40. The average person
loses 5 to 10 of his or her brains
weight between ages 20 and 90 years. Decreased
blood flow may account for brain shrinkage and
weight loss. People in older age groups have
diminished and slower memory capabilities. PNS
degeneration also occurs. This causes a reduction
or loss of reflexes. This produces a problem in
balance and mobility. Sensory loss is also seen
with age. It is most likely due to degradation Of
the sensory structure. Hearing loss affects men
more than women in the age range of 70-79. Vision
loss occurs equally in each gender.
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Summary

• The human nervous system is formed of two
  components that work together to coordinate body
  functions the central and peripheral nervous
  systems.
• Information from the environment is transmitted
  to the CNS by nerves of the PNS.
• Sensory information is used by the brain to
  formulate a response. Responses of the brain are
  channeled to the body via the somatic or
  autonomic nervous system.
• Nervous system structure is subject to damage
  resulting from a variety of diseases.

Chapter 9 Structure of the Nervous System