Transcript NERVOUS SYSTEM - Welcome to the Health Science Program

NERVOUS SYSTEM
Introduction
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Most highly organized system of the body
Fast, complex communication system that
regulates thoughts, emotions, movements,
impressions, reasoning, learning, memory,
choices
Basic Characteristics
Master control system
Master communication system
Regulates, maintains homeostasis
Major Structures and Divisions
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Central nervous system (CNS)
Peripheral nervous system (PNS)
Automatic Nervous System
Functions
Monitors change
(stimuli) sensory input
Integrates
impulses integration
Effects
responses motor output
Histology of Nervous Tissue
Basic Characteristics
Highly cellular
2 types of cells - neurons and supporting cells
(neuroglia)
Neuroglia Characteristics
Dense network of supporting cells for nerve tissue
Over 900 billion
CAN replace themselves
Also known as glia cells (glia = glue)
Supportive scaffolding; insulation; neuron health
and growth (act as “glue” to support, bind, repair,
and protect neurons)
Neurons: Basic Characteristics
Over 100 billion
Highly specialized
Conduct messages in form of nerve impulses
Extreme longevity (>100 years)
High metabolic rate
3 functional components in common: receptive/input
regions, conducting component/trigger zone,
secretory/output component
Three types
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A = afferent (sensory)
C = Connective (associative)
E = Efferent (motor)
Neurons: Characteristics
Excitability: the ability to react to a stimuli,
physical or chemical
Irritability: sensory adaptation, with prolonged
stimulation, irritability is temporarily lost (i.e.
smell)
Conductivity: the ability to transmit an impulse
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Nonmyelinated fibers = 0.5 - 1 meter /sec (1 mph)
Myelinated fibers = 80 - 130 meters/sec (300 mph)
The Hand as a Neuron
A Closer Look:
Parts of a Neuron
nucleus
soma
dendrites
axon
myelin
sheath
terminal
axon
Myelin Sheath
Whitish, fatty (protein lipoid) segmented covering
of axons
Myelinated fibers: conduct nerve impulses rapidly;
electrical insulation
Unmyelinated fibers: conduct impulses slowly
White matter: myelinated sheaths around axons of
the PNS gives the tissue a white color and forms
myelinated nerves (axons = myelinated tracts)
Gray matter: concentrations of cell bodies and
unmyelinated fibers ( in PNS = ganglia; in CNS =
nuclei)
Neurophysiology—Chemical
Events At the Synapse
The Synapse
the dynamic region between an axon terminal
and a receiving neuron
space between a terminal axon and receiving
neuron is called the synaptic cleft
synaptic cleft is where electrochemical
transmission takes place, thus communication
Impulses from one neuron are transmitted across
the synapse to another neuron by a chemical called
a neurotransmitter
Vesicles release
Neurotransmitters
synapse
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Inactivation of
Neurotransmitters
The action of neurotransmitters can be
stopped by four different mechanisms:
1. Diffusion – neurotransmitters drifts away
out of synaptic cleft
2. Enzyme deactivation – specific enzyme
changes structure of neurotransmitter so it
is not recognized by receptor
Inactivation of Neurotransmitters
continued
3. Glia cells – astrocytes remove
neurotransmitters from synaptic cleft
4. Reuptake – whole neurotransmitter
molecule is taken back into axon
terminal that released it
Some of the Better
Known
Neurotransmitters
Acetycholine
Contributes to movement, learning,
memory processes, and REM sleep
Only transmitter between motor
neurons and voluntary muscles
EXCESS: muscle paralysis or
convulsions, sometimes death
DEFICIT: memory impairment
(Alzheimer’s disease)
Dopamine
Used by neurons that control
voluntary movements
Also used by neurons that are
important for learning, attention,
thought & emotion
EXCESS: irrational thought,
delusion, and/or hallucinations
(Schizophrenia)
DEFICIT: tremors, muscular rigidity,
(Parkinson’s disease)
Serotonin
Serotonin plays prominent role in
regulation of mood, sleep,
impulsivity, aggression, and appetite
DEFICIT: related to depression,
aggressive behavior
Norepinephrine
Plays a role in eating, sleep, and
mood
DEFICIT: related to depression
Gamma-Aminobutyric Acid
(GABA)
Appears to have inhibitory effects at
synapses
Contributes to regulation of anxiety
& levels of activity
ABNORMALITY in GABA may cause
epilepsy
Endorphins
Opiate-like substances produced in the
body
Provide relief from pain and produce
feelings of pleasure & well-being
Drugs such as opium, morphine, and
heroin bind with receptors for endorphins
Endorphins may explain “runner’s high”
experienced by long-distance runners
Divisions of the Nervous
System
Central Nervous System –
Brain and the Spinal Cord
Integrates incoming pieces of sensory
information, evaluates the information,
and initiates the outgoing responses
NO potential for regeneration
Brain
Largest structure of the nervous system and one
of the largest organs of the body
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12 billion neurons and neuroglia
The adult human brain weighs between 1300 g and
1400 g (approximately 3 lbs). A newborn human brain
weighs between 350 and 400 g. For comparison:
elephant brain = 6,000 g
chimpanzee brain = 420 g
rhesus monkey brain = 95 g
beagle dog brain = 72 g
cat brain = 30 g
rat brain = 2 g
Brain
Covered by three
layers of membranes
called meninges
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Dura mater
Arachnoid
Pia mater
Structure of the Brain
Cerebrum
Largest mass of brain (83% of brain mass);
uppermost and least protective layer of the brain;
responsible for higher mental functions and
distribution of impulses
Cerebral cortex: outer layer of gray matter; short and long
term memory
Cerebral medulla: white matter, conduction pathways
Divided into right and left hemispheres (left side governs right
side of body, right side governs left side of body)
Two hemispheres connected by the corpus callosum
Each hemisphere has four lobes
Middle regions of the cerebrum are canals, called ventricles
Right vs. Left Hemisphere
Left side
processes:
•Speech
•Analysis
•Time
•Sequence
Right side
processes:
•Creativity
•Patterns
•Spatial
Awareness
•Context
It
Recognizes:
•Letters
•Numbers
•Words
It
Recognizes:
•Faces
•Places
•Objects
Lobes
Frontal: voluntary motor
control, learning,
planning, L = motor, speech
R = non-verbal abilities.
 Parietal: sensory,
distance, size, shape,
cognitive/intellectual
processes
 Occipital: vision, visual
memory
 Temporal: auditory,
olfactory, speech,
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Cerebellum
Located in the lower back of the cranium; below
and posterior to cerebrum
Coordinates muscular movement, posture,
balance, running, walking
Damage produces ataxia (lack of coordination due
to errors in speed, force, direction of movement
Brainstem (damage = coma)
Midbrain: upper part of brainstem
* Controls postural reflexes and walking
* Visual reflexes and auditory control, 3-4
cranial nerves
Pons: (literally means “bridge”) a two-way
conduction pathway that connect the
cerebellum and the cerebrum with the rest of
the brain, mixed gray and white fibers
* Controls inspiration
* Transverse fibers give it a bridge
appearance
* Reflex mediation for 5-8 cranial nerves
Medulla oblongata: the bulb (lowest part before
the foramen magnum) made of white and
gray fibers called reticular formation
* 75% of fibers cross here
* Controls vital functions: respiration center,
cardiac center, and vasomotor center
(constricts or dilates the muscles in the
blood vessel’s walls; thus influences BP
Diencephalon: area between
cerebrum and midbrain
Thalamus: gray matter,
relay station for sensory
incoming and motor
outgoing impulses;
damage - increased
sensitivity to pain, loss of
consciousness
Hypothalamus:
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Regulates autonomic
control
Cardiovascular
control:
dilates/constricts
Temperature control
Controls appetite:
hunger and thirst
Water balance
GI control: peristalsis,
intestinal secretions
Emotional states: fear,
anger, pleasure, pain,
sexual reflexes
Sleep control
Regulates pituitary
secretions
CHO and fat
metabolism
Spinal Cord
Deep grooves: anterior
median fissure (deeper) and
posterior median sulcus
2 bundles of nerve fibers
called roots project from
each side of cord
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Dorsal nerve root: sensory
afferent fibers
Dorsal root ganglion:
sensory cell bodies
Ventral nerve root: motor
efferent fibers
The nerve roots join
together to form a single
mixed nerve called a spinal
nerve
Peripheral nervous system (PNS)
Made of 12 pairs of cranial nerves and 31 pairs of
spinal nerves
Afferent (sensory) division
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Carries impulses toward the CNS
Somatic (skin, skeletal muscles, joints)
Visceral (organs within the ventral cavity)
Connecting (associative) neurons
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Carry impulses from one neuron to another
Efferent (motor) division
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Somatic: carries information from CNS to skeletal
muscles (reflex and voluntary control)
Functions of the Peripheral
Nervous System
Spinal Nerves
31 pairs of mixed nerves
attached to spinal cord by
ventral and dorsal roots
8 cervical 12 thoracic, 5 lumbar
5 sacral, 1 coccygeal
Each nerve forms several
large branches + rami,
which subdivide to four
complex networks called
plexuses (cervical,
brachial, lumbar, sacral)
Dermatome: mapping of
skin surface of nerve
intervention
The Autonomic Nervous
System
Sympathetic system
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The sympathetic nerves are stimulated in
situations that require action like the fight-orflight reaction
Parasympathetic system
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The parasympathetic nervous system
functions in response to normal everyday
situations