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
The nervous system
› Is the primary coordinating and controlling
system of the body
› Uses electrochemical impulses to fulfill its
functions

General functions include
1. Detect internal and external changes
2. Analysis of information
3. Organization of information
4. Initiation of appropriate action

Anatomical divisions
› Central nervous system (CNS)
 Brain and spinal cord
 Body’s neural control center
› Peripheral nervous system (PNS)
 Located outside the nervous system
 Consists of nerves and sensory receptors
 Receptors
 Effectors
 Functional
divisions
› Sensory division
 Carries impulses from sensory receptors
to the CNS
› Motor division
 Carry impulses from CNS to effectors
 Motor division has two divisions
 Somatic nervous system
 Voluntary control of skeletal muscle
 Autonomic nervous system
 Involuntary control of cardiac muscle,
smooth muscle, and glands

Neurons
› Specialized to transmit neural impulses
› Structural and functional units of nervous system
› Though they vary in size and shape, neurons
have many common features

Structure of a neuron
› Cell body
 Possesses the
nucleus and
organelles
› Dendrites
 Numerous, short,
highly branched
 Extend from cell
body
 Primary sites for
receiving impulses
 Carry impulses
toward cell body
and axon
› Axon
 Long, thin process
 Ends in axon
terminals with
synaptic knobs
 Carry impulses away
from cell body or
dendrites
 Some have a
myelin sheath
 Insulates axons
 Increases speed of
impulse
transmission
 Nodes of Ranvier
 Functional
classification of neurons
› Sensory (afferent) neurons
 Carry impulses from peripheral body
parts to the CNS
 Detect homeostatic changes directly or
via sensory receptors
 Ganglia in the PNS house sensory
neuron cell bodies
 Functional
classification of neurons
› Interneurons
 Located entirely in CNS and associate
with other neurons
 Process and interpret impulses from
CNS
 Activate motor neurons
 Functional
classification of neurons
› Motor (efferent) neurons
 Carry impulses from CNS to effectors to
produce an action
 Cell bodies and dendrites are in CNS
 Axon is located in nerves of PNS

Neuroglia
› Support and protect neurons
› More numerous then neurons
› Schwann cells (PNS cells)
 Form myelin sheath by wrapping plasma membrane
around axon
 Forms a neurolemma as outer layer of myelin sheath
 Schwann cell nucleus and cytoplasm
 Essential for axon regeneration
› Oligodendrocytes (CNS cells)
 Form myelin sheath around CNS axons
 Do not form neurolemma
 Axon regeneration is not possible
› Astrocytes (CNS cells)
 Bind neurons to blood vessels
 Regulate exchange of materials between
blood and neurons
 Provide structural support
 Stimulate neuronal growth
 Influence synaptic transmission
› Microglial cells (CNS cells)
 Engulf and digest cellular debris and
bacteria
› Ependymal cells (CNS cells)
 Line cavities in brain and spinal cord

Neurons have two unique functional
characteristics
› Irritability
 Ability to respond to a stimulus by forming an
impulse
› Conductivity
 Ability to transmit an impulse along a neuron to
another cell

Resting potential
› Membrane is polarized due to an unequal
distribution of electrical charges on each side
of the plasma membrane
› Excess of positively charged ions outside
 Na+ outside
› Excess of negatively charge ions on the
inside of the neuron membrane
 K+, PO4-3, and SO4-2 inside

Impulse Formation
› Neurons have an all-or-none response
› Threshold stimulus is needed to activate a
neuron
› All impulses are alike
› When activated by a
stimulus
 Na+ permeability
increases
 Na+ diffuse into the
neuron
 Causes positive and
negative ions to be
equally abundant on both
sides of the membrane
 Membrane is
depolarized: this is the
nerve impulse or action
potential

Repolarization
› After depolarization,
K+ diffuses outward to
reestablish the resting
potential
› Na+ is then pumped
out and K+ is pumped
in to reestablished
resting-state ion
distribution

Impulse Conduction
› Depolarization at one point triggers
depolarization in adjacent portions, etc.
› Forms a wave of depolarization sweeping
along the neuron
› More rapid in myelinated neurons than
unmyelinated neurons
 Impulses only form in membrane exposed at
nodes of Ranvier
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
Synaptic Transmission
› Synapse
 Junction of an axon with another neuron or an
effector cell
› Synapse structure
 Synaptic knob of presynaptic neuron
 Postsynaptic structure (neuron or effector)
 Synaptic cleft
› Steps of synaptic transmission
 Arrival of an impulse causes synaptic
knob to release a neurotransmitter into
the synaptic cleft
 Neurotransmitters bind to receptors on
postsynaptic neuron’s plasma
membrane
 A response is triggered in the
postsynaptic neuron
 Stimulates impulse formation
 Inhibits impulse formation
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operating systems, some animations
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viewed in Presentation Mode (Slide
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in the “Normal” or “Slide Sorter” views.
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› Signal transmission across a
synapse is only in one direction
 Only the synaptic knob can release
neurotransmitters
› Neurotransmitters are quickly
removed
 Prevents continuous stimulation of
postsynaptic neuron or effector
 “Resets” the synapse
 Neurotransmitters
› Enable communication between
neurons and neurons with other cells
› One neuron releases only 1 or 2
types of neurotransmitters
› Two basic types of neurotransmitters
 Excitatory neurotransmitters
 Inhibitory neurotransmitters
› Excitatory neurotransmitters
 Cause impulse formation in postsynaptic
neuron and activate other cells
 Examples: acetylcholine, norepinephrine
› Inhibitory neurotransmitters
 Inhibit the formation of impulses in
postsynaptic cells and function of other
target cells
 Examples: dopamine, endorphins

Bones
› Cranial bones
› Vertebrae

Meninges: three fibrous membranes
› Pia mater
 Thin, innermost layer
 Adheres to CNS structure surfaces
 Contain blood vessels to nourish brain and spinal cord
› Arachnoid mater




Middle layer
Thin, web-like, avascular
Does not penetrate smaller depressions like the pia
Subarachnoid space
 Filled with cerebrospinal fluid
› Dura mater
 Tough, outermost layer
 Attached to cranial bones
 Forms protective tube in vertebral canal
 Epidural space
Contains about 100 billion neurons
 Four major components: cerebrum, cerebellum,
diencephalon, brain stem

Largest portion of the brain
 Performs higher brain functions

› Sensations
› Voluntary actions
› Reasoning
› Planning
› Problem solving

Structure
› Left and right cerebral hemispheres
 Separated by longitudinal fissure
 Connected by corpus callosum
› Surface shows numerous gyri (folds) with sulci (shallow
grooves) between them
› Cerebral cortex
 Outer surface of gray matter
 Neuronal cell bodies and unmyelinated fibers
› White matter lies beneath the cortex
 Myelinated fibers that transmit impulses
 Between hemispheres
 Between cerebral cortex and lower brain areas
 Several gray matter masses are deep in the
white matter
› Cerebral hemisphere is divided into 4 lobes





Frontal lobe- conscious muscle movement, higher mental functions
Parietal lobe- sensation
Temporal lobe- hearing and smell
Occipital lobe- vision
Insula- taste

Functions
› Interpretation of sensory impulses
› Controlling voluntary motor responses
› Intellectual processes
› Will
› Personality traits
› Three type of functional areas
 Sensory areas
 Motor areas
 Association areas
› Sensory areas
 Receive impulses from sensory
receptors
 Interprets impulses as sensations
 Sensory areas receive information from
opposite sides of the body
 Due to cross over of ascending sensory fibers
› Motor areas
 Located in frontal lobe




Primary motor area- controls skeletal muscles
Premotor area- planning, learning, and judging
Broca’s area- speech
Frontal eye field area- voluntary eye movements
 Left side of the cerebrum controls
skeletal muscles on the right side of the
body
 Due to cross over of descending motor fibers
› Association areas
 Interrelate sensory inputs and motor
inputs
 Role in interrelationships of sensations,
memory, will, and coordination of motor
responses
 General interpretative areainterpretation of complex sensory
experiences and thought processes.

Hemisphere Specialization
› Each hemisphere performs basic functions
 Receiving sensory output
 Initiating voluntary motor output
› Some functions are only performed by one
hemisphere
 Left hemisphere
 Analytical and verbal skills
 Right hemisphere
 Musical, artistic, spatial awareness, imagination,
and insight
Lies between the brain stem and midbrain
 Consists of two major areas

› Thalamus
› Hypothalamus

Thalamus
› Receives all incoming sensory impulses
(except smell) before relaying them to the
cerebral cortex
› Provides a general, nonspecific awareness of
sensations
 Interpretation is carried out by the cerebral
cortex

Hypothalamus
› Communicates with thalamus, cerebrum, and
other brain regions
› Major control center for autonomic nervous
system
› Connecting link between brain and endocrine
system
 Controls the pituitary gland
› Primary function is maintain
homeostasis by regulating
 Body temperature
 Mineral and water balance
 Appetite and digestive processes
 Heart rate and blood pressure
 Sleep and wakefulness
 Emotions of fear and rage
 Secretion of hormones by pituitary gland

Complex of deep nuclei of cerebrum
› Associated with the thalamus and diencephalon

Involved in:
› Memory
› Emotions
› Emotional behaviors

Malfunctions can result in mood disorders
Stalk-like portion connecting higher brain
centers with the spinal cord
 Contains nuclei surrounded by white
matter
 Consists of

› Midbrain
› Pons
› Medulla oblongata

Midbrain
› Maintains consciousness
› Reflex center for visual and auditory stimuli
 Controls head, eye, and body movements

Pons
› Between midbrain and medulla oblongata
› Aids in controlling the rate and depth of
breathing

Medulla oblongata
› Most inferior portion of the brain that connects
to the spinal cord
› Contains the respiratory control center
 Regulate depth and rate of breathing
 Reflexes like coughing and breathing
› Contains the cardiac control center
 Regulate rate of heart contractions
› Contains the vasomotor center
 Regulates blood pressure and blood flow

Controls and coordinates the interaction of
skeletal muscles

Controls posture, balance, and muscle
coordination

Damage results in loss of equilibrium,
muscle coordination, and muscle tone

Brain contains four interconnecting
ventricles
› Cavities lined by ependymal cells

Filled with cerebrospinal fluid
› Produced by choroid plexuses in the ventricles

Flow of cerebrospinal fluid
› Lateral ventricles to third ventricle to fourth ventricle to
central canal or subarachnoid space
› Cerebrospinal fluid is reabsorbed in dural sinus within
dura mater
 Secretion and absorption of CSF is at equal rates to keep
a constant hydrostatic pressure
Descends from medulla oblongata through
foramen magnum
 Passes through vertebral canal to level of
2nd lumbar vertebra

› Only spinal nerves occupy lower levels of
vertebral canal

Functions
› Transmit impulses to and from brain
 Ascending (sensory) tracts
 Descending (motor) tracts
› Reflex center for spinal reflexes

Consists of cranial and spinal nerves that
connect to parts of the body

Nerves are neuronal processes bundled
together by connective tissue

There are three types of nerves
› Motor nerves
› Sensory nerves
› Mixed nerves

Nerves can contain fibers from both
somatic and autonomic nervous systems

Cranial Nerves
› Twelve pairs of nerves
› Arise from brain and connect with structures
of head and neck
› Most are mixed nerves, though some are
primarily sensory or primary motor

Spinal Nerves
› 31 pairs
› Pair one emerges between atlas and occipital bone
› Remainder emerge through intervertebral foramina

Nerves are identified by the spinal region
from which they branch and are
numbered in sequence
› 8 pairs of cervical nerves
› 12 pairs of thoracic nerves
› 5 pairs of lumbar nerves
› 5 pairs of sacral nerves
› 1 pair of coccygeal nerves

Spinal cord
terminates at L2
› Descending from
this point are
proximal portions of
spinal nerves
› Cauda equina

Spinal nerves form from two roots from the spinal
cord
› Ventral root
 Motor axons
› Dorsal root
 Sensory axons
 Dorsal root ganglion

Spinal Plexuses
› Spinal nerves divide into parts after emerging
from the vertebral column
 Anterior branch
 Posterior branch
 Visceral branch
› A plexus is a made of merged anterior
branches from several nerves
 Gives rise to nerves that supply specific body
parts
› Cervical plexus
 Formed by first four cervical nerves
 Nerves from it service muscles and skin of
neck, head, and shoulders
› Brachial plexus
 Formed by last four cervical nerves and first
thoracic nerve
 Nerves from it service skin and muscles of arms
and shoulders
› Lumbar plexus
 Formed by last thoracic nerve and first four
lumbar nerves
 Nerves from it supply skin and muscles of lower
trunk, genitalia, and part of thighs
› Sacral plexus
 Last two lumbar nerves and first four sacral
nerves
 Nerves from it service skin and muscles of
buttocks and legs

Reflexes
› Rapid, involuntary, and predictable responses
to internal and external stimuli
› Maintain homeostasis and increase chances
for survival
› Reflex pathways are called reflex arcs
› Two types of reflexes
 Autonomic reflexes
 Act on smooth muscle, cardiac muscle, and
glands
 Maintain homeostasis and body functions at
unconscious level
 Somatic reflexes
 Act on skeletal muscle
 Conscious awareness of these reflexes exists

Consists of parts of central and peripheral
nervous systems

Functions involuntarily without conscious
control
 Purpose
is to maintain homeostasis
in response to changes in internal
conditions
› Effects cardiac muscle, smooth muscle,
and glands
› Uses involuntary reflexes
› ANS is subdivided into
 Sympathetic division
 “Fight or flight”
 Prepares body for stress, energy-expending, and
emergencies
 Parasympathetic Division
 “Rest and digest”
 Active during relaxation and digestion
 Autonomic
Neurotransmitters
› Divisions differ in the neurotransmitters
used at synapses
 All preganglionic neurons use acetylcholine
 Parasympathetic postganglionic use
acetylcholine
 Sympathetic postganglionic use
norepinephrine
 Disorders
are characterized as
› Inflammatory disorders
› Non-inflammatory disorders

Meningitis
› Bacterial, fungal, or viral infection of the
meninges
› If the brain is involved, it is called encephalitis

Neuritis
› Inflammation of nerve or nerves
› Caused by infection, compression, or trauma
› Severe to moderate pain

Sciatica
› Neuritis involving the sciatic nerve
› Pain can be severe with radiating pain down
thigh and leg

Shingles
› Caused by reactivation of the chickenpox
virus that has been dormant in the nerve root
› Painful blisters form at sensory nerve endings

Alzheimer’s disease
› Characterized by progressive loss of memory,
disorientation, and mood swings
› Exhibit loss of cholinergic neurons in brain
› Also have reduced ability to secrete
acetylcholine
Neurons waste away or die, and can no
longer send messages to muscles.
 This eventually leads to muscle weakening,
twitching, and an inability to move the arms,
legs, and body.
 The condition slowly gets worse. When the
muscles in the chest area stop working, it
becomes hard or impossible to breathe.


Cerebral palsy
› Partial paralysis and possible mental
retardation
› Caused by prenatal brain damage, German
measles, delivery brain trauma

Cerebrovascular accidents
› Strokes
› Disorders of brain blood vessels
› Caused by blood clots, aneurysms, or
hemorrhage
› Cause severe brain damage

Comas
› Patient is unconscious and cannot be
aroused
› Alteration of reticular formation function may
be a cause

Concussion
› Caused by severe jarring of brain due to blow
to the head
› Can be accompanied by unconsciousness,
amnesia, and confusion

Dyslexia
› Person reverses letters or syllables in words
or words within sentences
› Due to malfunctioning language center

Epilepsy
› Can be hereditary or triggered by injuries,
infections, or tumors
› Two types of epilepsy
 Grand mal epilepsy
 Convulsive seizures
 Petit mal epilepsy
 Momentary loss of reality without convulsion or
unconsciousness

Fainting
› Loss of consciousness due to sudden
reduction in brain blood supply
› Physical or psychological causes

Headaches
› Various causes
 Most due to dilation of blood vessels within the
meninges
 Some are caused by tension in head and neck
muscles
› Migraine headaches
 Visual or digestive side effects
 Causes include stress, allergies, or fatigue
› Sinus headaches
 Cause may be inflammation that increases
pressure within the sinuses

Mental illnesses
› Neuroses
 Mild maladjustments to life situations
 Produce anxiety and interfere with normal
behavior
› Psychoses
 Severe mental disorders
 Cause delusions, hallucinations, or withdrawal
from reality

Multiple sclerosis
› Progressive degeneration of myelin sheath
around CNS processes
› Also have development of scleroses
› Effect is a short-circuiting of neural pathways,
which impairs motor function

Neuralgia
› Pain arising from a nerve regardless of cause
of pain

Paralysis
› Permanent loss of motor control over body
parts
› Common cause is injury to CNS

Parkinson’s disease
› Insufficient dopamine production by basal
nuclei in cerebrum
› Causes tremors and impairs skeletal muscle
contraction