Download The Nervous System

The Nervous
System
Chapter 7
Organization

Objectives:
List the general functions of the nervous
system.
 Explain the structural and functional
classification of the nervous system.
 Define central nervous system and
peripheral nervous system and list the
major parts of each.

What is the nervous system?
The master control and
communication system for the body
 All thoughts, actions, and emotions
 Uses electrical impulses to direct
activity and communicate
 It monitors the entire body…
maintains homeostasis
 Sensory input: gather stimuli from
environment

Homeostasis
1.
2.
3.
Sensory receptors collect and
monitor stimuli (sensory input)
Control center processes and
interprets sensory input and makes
decisions about what to (integration)
Sends a response by activating a
system to take care of business,
usually muscles or glands (motor
output)
The team
Nervous system works with all systems
to regulate functions
 Endocrine system especially, by
releasing hormones into the blood
stream to change things gradually
 Nervous system on the other hand,
makes rapid changes occur

Nerves and more nerves

Two basic subdivisions:
Central nervous system (CNS) which
contains the brain and spinal cord
(command center)
 Peripheral nervous system (PNS) which
contains spinal nerves and cranial nerves
(support center)
 MORE TO COME…

Function

The PNS has two basic functions

Sensory (afferent) division


Sends impulses to the CNS from sensory
receptors
Motor (efferent) division

1.
2.
Sends impulses from the CNS to the effector
organs (muscles and glands)
Somatic nervous system: skeletal muscles
Autonomic nervous system: cardiac muscles
and glands
Nervous Tissue: Structure and
Function

Two types of nervous tissue
Supporting cells: Who and what depend on
which system; PNS or CNS
 Neurons: Basic function and some
difference in structure

CNS: Supporting Cells

Neuroglia “nerve glue”




Astrocytes: barrier between capillaries and
neurons, control chemical environment in brain
Microglia: phagocytes>eat dead brain cells,
bacteria
Ependymal: line cavities of brain and spinal cord,
moves cerebrospinal fluid around
Oligodendrocytes: wrap around nerve endings and
produce myelin sheath (fatty insulation)
PNS: Supporting Cells

Schwann cells:


Form the myelin sheaths around nerve
fibers
Satellite cells:

Protection and cushion
Anatomy of Neurons

These are common to ALL neurons:
Cell body: contains nucleus
 Dendrites: impulses move toward cell body
 Axons:impulses move away from cell body
 Axonal terminals: branches at end of axon
 Neurotransmitters: chemicals released at axon
 Synaptic cleft: tiny gap between neurons
(synapse)
 Myelin: fatty insulation that increases nerve
impulse rates
Let’s DRAW… YEAH!

The Myelin Sheath
Called the neurilemma sometimes “neuron
husk”
 Spaces between myelin are called nodes of
Ranvier, regular spacing
 MULTIPLE SCLEROSIS: a disease in which the
myelin sheaths around the fibers are
destroyed and converted to hard shells, this
short circuits the impulse and muscle control
is effected greatly….AUTOIMMUNE
DISEASE… no cure, but some treatment

Sensory Receptors
Naked nerve endings (pain and
temperature)
 Meissner’s corpuscles (touch)
 Pacinian corpuscle (deep pressure)
 Golgi tendon organ (proprioceptor)
 Muscle spindle (proprioceptor)
*proprioceptor: detect stretch, tension in
skeletal muscles, tendons, joints

Classification of Neurons
Multipolar: all motor neurons
 Bipolar: two processes, an axon and a
dendrite (long in both directions)
 Unipolar: single process that is very
short and divided into proximal and
distal fibers (PNS ganglia neurons)
 See page 202 for a picture…ADD to
notes

Physiology of Neurons

What makes a nerve go?

1.
2.
Stimuli and conductivity… movement of ions
across a membrane
Polarized: resting stage (More sodium
outside)
Depolarization: causes a nerve impulse to
be sent through a neuron (More sodium
inside)

3.
All or none response
Repolarization: neuron becomes polarized
again, back to resting stage (Sodium
moves back inside)
Nerve Impulses
Myelin sheaths cause impulses to travel
faster because they jump from node to
node
 Alcohol, sedatives, and anesthetics all block
nerve impulses by reducing membrane
permeability to sodium ions… no sodium
entry equals no action potential
 Cold temperatures and continuous pressure
mess with impulses because of blood flow,
like sitting on your foot or cold fingers

Reflex Arc
Reflexes are rapid, predictable, and
involuntary responses to stimuli.
 Autonomic reflexes: regulate smooth
muscles, the heart, and glands
 Somatic reflexes: regulate skeletal
muscle (moving hand from hot pan)
 All contain 5 basic things in pathway

Pathway for Arc
1.
2.
3.
4.
5.
Sensory receptor: reacts to stimulus
Afferent neurons: message carrier
CNS integration center: synapse between
afferent and efferent neurons
Efferent neurons: message carrier
Effector organ: muscle or gland that is
stimulated
*Most reflexes only involve the spinal cord and
occur before the brain “notices”
Central Nervous
System
CNS: The control center
Development of CNS
1.
2.
3.
Neural tube: a simple tube that
extends down the dorsal median plane
(center of back)
During the 4th week, brain begins to
form
The tube expands and forms four
chambers called ventricles (regions in
the brain)
Anatomy of Brain
Cerebral Hemispheres
 Diencephalon
 Brain Stem
 Cerebellum

Cerebral Hemispheres





Most superior part, largest region of brain
Folded shaped, wrinkles caused by gyri, sulci,
and fissures
Speech, memory, logical and emotional
response
Consciousness, interpretations of sensation,
and voluntary movements
Main lobes: parietal, occipital, temporal,
frontal
Parietal Lobe
Interprets sensory input from somatic
areas (not special senses like hearing,
smell, taste)
 Recognize and process pain, coldness,
light touch
 Input registered by lips, fingertips and
other areas with lots of sensory
receptors

Occipital and Temporal Lobe
Input from special sense organs are
interpreted here
 Think occipital…eyes…vision
 Think temporal…ears… hearing
 Think temporal…nose…smell

Frontal Lobe
Primary motor area: Deal with
movement of skeletal muscles
 Broca’s area: Deal with speech
development and the ability to speak
 Speech area: located at junction of
temporal, parietal and frontal lobes…
allows us to sound out words

What’s all the Matter?
Gray matter: neurons involved in the cerebral
hemisphere, make up the cerebral cortex
(outermost layer of cerebrum)
 White matter: deeper, under the gray matter



Bundles of nerve fibers
Corpus callosum: connects two hemispheres
Parkinson’s disease
Basal nuclei: regulate voluntary motor activity
by modifying instructs sent to he skeletal
muscle by the primary motor cortex
 Symptoms: trouble initiating movements and
mild/severe hand tremors
 Caused by a lack of dopamine
(neurotransmitter)
 Some drug therapies are proving to benefit
individuals with Parkinson's disease

Diencephalon
Sits on top of brain stem, surrounded
by the cerebral hemispheres
 Major structures: thalamus,
hypothalamus, and the epithalamus

Thalamus
Relay station for sensory impulses
passing upward to the sensory cortex
 Briefly senses pleasant or unpleasant

Hypothalamus
Located under the thalamus (hypo is
under)
 Regulates body temperature, water
balance, and metabolism
 Makes up the limbic system:


Thirst, appetite, pain/pleasure center
Regulates pituitary gland (hormones)
 Regulates reflex areas for smell

Epithalamus
Pineal body (part of endocrine system)
 Choroid plexus: knots of capillaries in
each ventricle that create the
cerebrospinal fluid

Brain Stem
Size of thumb, 3 inches long
 Three structures: midbrain, pons, and
medulla oblongata
 Reticular Activating System (RAS):
consciousness and the awake/sleep
cycle
 Damage to this area may cause
permanent unconsciousness

Midbrain
Small part of brain stem
 Involved in reflex centers for vision and
hearing

Pons
Area that that bridges between the
midbrain and medulla oblongata
 Nerve tracts involved in breating

Medulla Oblongata
Merges into the spinal cord
 Regulates heart rate, blood pressure,
breathing, swallowing, and vomiting

Cerebellum






Outer cortex (layer) made of gray matter
Inner cortex made of white matter
Located at back of head, under cerebrum
Regulates timing of muscle movements
Controls balance and equilibrium
Monitors what is going on and what the brain
wants the body to do
Ataxia
If the cerebellum is damaged by stroke,
blow to the head, tumor or other
means, body movements can become
clumsy and disorganized
 Individuals cannot keep balance, may
appear intoxicated

CNS Protection
Nerve tissue is very soft
 Protected by

Bones (vertebral column, skull)
 Membranes (Meninges)
 Water cushion (cerebrospinal fluid)

Meninges

Three layers that protect the CNS
Dura mater: outer, leathery, dbl layer
 Arachnoid mater: Middle, cobweb
appearance
 Pia mater: inner layer, follows every fold,
covers brain and spinal cord

Meningitis
Inflammation of the Meninges
 Can be bacterial or viral which could
spread throughout nervous system
 Diagnosis can be made by taking a
sample of the cerebrospinal fluid
 Causes brain swelling (encephalitis)

Cerebrospinal Fluid





Watery “broth” that surrounds the brain and
spinal cord
Very similar to blood plasma
Can be sampled by a lumbar tap (spinal tap)
After sampling, patient must stay lying down
or a headache may result because of
decrease fluid pressure
Hydrocephalus: water on the brain…can
cause brain damage due to increased
pressure, can be controlled by shunts that
drain excess fluid into neck vein
Blood Brain Barrier
Brain needs a special constant environment
 Blood changes in consistency and make up
 Capillaries in the brain are only allowed to
pass water, glucose, and essential amino
acids
 Barrier cannot protect against fats,
respiratory gases, blood-borne alcohol,
nicotine, and anesthetics

Brain Dysfunctions

Traumatic Brain Injuries (TBIs)
Concussion
 Contusion
 Cerebral edema


Degenerative Brain Disease (DBDs)
Cerebrovascular accident
 Alzheimer’s disease

Spinal Cord
Approximately 17 inches long
 Provides two-way communication to
and from brain
 Major reflex center
 Protected by vertebral column
 31 pairs of spinal nerves

Explore Spinal Cord injuries:

Look up the following injuries and
summarize your findings:
Spastic paralysis
 Quadriplegic
 Paraplegic

Peripheral Nervous
System
PNS: Spinal Nerves and
Cranial Nerves
Structure of a Nerve
Nerve: Bundle of neuron fibers found
outside the CNS
 Endoneurium: protective covering on a
nerve
 Mixed nerves: have both sensory and
motor fibers, contains all spinal nerves

Cranial Nerves
12 pairs of cranial nerves that serve the head
and neck region
 Only one pair serves the thoracic/abdominal
cavities (Vagus Nerves)
 Olfactory, Optic, Oculomotor, Trochlear,
Abducens, Trigeminal, Facial,
Vestibulocochlear, Glossopharyngeal, Vagus,
Accessory, and Hypoglossal

Spinal Nerves and Plexuses
31 pairs of human spinal nerves that
form the ventral and dorsal roots
 Damage to a spinal nerve effects both
sensation and movement, causing
paralysis in a specific region of the body
 Intercostals nerves: supply the muscle
between the ribs and skin/muscles of
trunk
 Nerve plexuses serve the motor and
sensory nerves of the limbs

Autonomic Nervous System
Subdivision of the PNS
 Controls body functions automatically
 Regulates:

Cardiac muscle (heart tissue)
 Smooth muscle (visera of organs, blood
vessels
 Breathing, pupil dilatation, blood pressure

Hugh player in homeostasis
 Two subdivisions: Sympathetic,
parasympathetic

Sympathetic Division of ANS
“fight or flight” system
 Rapid heart beat, deep breathing, hair
standing on end, dilated pupils,
increased blood flow to the skeletal
muscles
 Adrenal glands are a major player
 Hormones are released for a short time
but have lasting effects, you have to
“come down”

Parasympathetic Division
Does most work while you are sleeping
and not threatened
 “resting and digesting” system
 Works for normal digestion and fecal
removal, conserving body energy

Assignment
List each Cranial Nerve and the function
of the nerve
 On page 229, for each organ or system,
make a table like the one shown,
summarize the points so you can
remember
 Use the WS as your guide
