Transcript Nervous System

Regulation of Body Processes
• Responses to both internal and external
stimuli must be regulated and coordinated
• These responses are controlled by the
body’s nervous and endocrine systems
• Nervous System:
– sends electrochemical signals using neurons
• Endocrine System:
– sends chemical signals by using hormones
secreted by glands.
Mechanisms of Nervous Regulation
• Receptors:
– sensory organs with
specialized structures that
are sensitive to changes or
“stimuli”
– When stimulated, receptors
cause impulses to be
carried both electrically and
chemically between nerve
cells.
– Sensory Organs Include:
• eyes, nose, skin, taste buds, ears
– Stimuli They Respond to:
• Physical forces
– Ex: heat, cold, pressure, light
• Chemical changes
– inside and outside organism
• Effectors: specialized structures that
respond to commands of nervous system
– gland (increases or decreases secretion)
– muscle (contracts)
Nerve Cells (Neurons)
• Carry electrochemical
messages or impulses from
receptor to effector
– Stimulus occurs
– Receptor senses stimulus
– Impulses sent along nerve
pathway
– Effector responds
• Nerve = many neurons
bundled together
Types of Neurons
• Sensory Neurons
– Carry impulses from receptors to spinal cord and brain
• Motor Neurons
– Carry impulses from brain and spinal cord to effectors (muscles)
• Interneurons
– Relay impulses between neurons, (found in brain and spinal cord)
Basic Neuron Structure
• Cell Body:
– contains nucleus and cell organelles
– Carries out metabolic activities and controls growth
• Dendrites:
– short highly branched fibers
– receive impulses
• Axon:
– long thin fiber that extends away from cell body
– Carries impulses from dendrites to terminal branches
• Schwann Cells:
– Surround axons of many vertebrates
– Produce myelin which forms an insulating covering
around axon
– Gaps between cells are called Nodes of Ranvier
• Terminal Branches:
– Branches at end of axon
– End in “synaptic knobs” that
contain neurotransmitters
– They lie very close to
dendrites of other neurons
– Chemical communication of
a nerve impulse happens
between neurons here
• Synapse:
– small gap between synaptic
knob of one neuron and
dendrite of another
How does Signal Travel Along a
Neuron?
Sending a Nerve Impulse
• Electrical Signal Travels:
– At rest: nerve membrane is “polarized”
• Outside is +, inside is –
– During Impulse:
• Switch in polarity travels along the nerve cell
• Myelination of axon helps to insulate the
signal and it conducts faster
• Signal can jump quickly between Nodes of
Ranvier
Sending a Nerve Impulse
• Chemical Communication
Occurs Between Neurons:
– Happens at the synapse
• Tiny gap between synaptic knob
of one neuron and dendrite of
another
– Electrical impulse triggers
release of neurotransmitter
molecules from vesicles into
the synapse
• Ex: acetylcholine, seratonin
• These molecules bind
to specific receptor
proteins in the
membrane of the
adjoining neuron
• That neuron will now
“fire” and send signal
along itself
• Impulses travel in one
direction across a
synapse
•
•
Synapse and Neurotransmitters:
http://www.youtube.com/watch?v=p5zFgT4ao
fA&safe=active
• Note:
• Each neurotransmitter
will only bind to a
specific receptor that
it will “fit”
– Certain drugs mimic
the effects of
neurotransmitters by
binding to these
receptor molecules
• Stopping a Signal:
– After a signal is sent enzymes at the synapse
break down the neurotransmitters in the
synapse or they are reabsorbed back into
vesicles.
Electrical, Chemical, Electrical
Chemical…
Neuron Firing Animation:
http://www.youtube.com/watch?v=90cj4NX
87Yk&safe=active
The Neuromuscular Junction
• Synaptic point of contact
between motor neurons and
muscle cells
• Motor neurons end in “motor
end plates” that release the
neurotransmitter acetylcholine
• These molecules bind with
receptors in membrane of
muscle cells causing them to
contract.
Drugs and the Synapse
• Certain poisons and drugs
can effect activity of
neurotransmitters
– Ex: nerve gas, botulin toxin
(botox), insecticides, venom
• Can cause muscular paralysis
and even death
• Stimulants: speed up nervous response
– Caffeine, amphetamines, cocaine
• Depressants: slow down nervous system
– alcohol, marijuana, barbiturates
• LSD: (hallucinogenic)
– blocks enzyme that removes neurotransmitter serotonin from synapse.
– It remains in gap and keeps neurons firing.
The Human Nervous System
• Divided into the:
• Central Nervous System:
– Brain
– Spinal Cord
• Peripheral Nervous System
– Somatic: controls skeletal muscles (voluntary)
– Autonomic: controls smooth muscles (involuntary)
Central Nervous System
• Brain and Spinal Cord
• Receive impulses from
sense receptors
• Interprets information
• Sends impulses for
responses to muscles
and glands
The Brain
• Large mass of neurons
located in the cranial cavity.
• Covered and protected by
tough membranes called
meninges.
• Cerebrospinal fluid
surrounds brain and
cushions against shock
• One of the most active
organs of the body, major
user of glucose!
• Concussion: when brain is severely shaken
• Meningitis: membranes that surround the
brain and spinal cord get infected
Parts of the Brain
• Cerebrum
–
–
–
–
Center for voluntary activity
Interprets sensory impulses
Initiates some motor activities
Responsible for memory,
thinking and reasoning
• Cerebellum
– Coordinates motor activities
– Aids in maintaining balance
• Medulla
– Controls involuntary activities
such as breathing, heartbeat,
blood pressure and peristalsis
(is part of the brain stem)
– Most “primitive” part of brain
Know the Three Parts of the Brain
and What They Do!
Hemispheres of the Brain
Each hemisphere controls the
opposite side of the body.
Brain Size and Intelligence
Spinal Cord
• Protected by vertebrae of
spinal column and rings of
cartilage
• Surrounded by meninges
and cerebrospinal fluid
• Coordinates activities
between the brain and
peripheral nervous system
• The center for reflex action
http://www.youtube.com/watch?v=38zEmPuWd-o&safe=active
Getting
a Spinal
Tap
Peripheral Nervous System
• All neurons and nerve
fibers outside of brain
and spinal cord.
• Somatic System
• Connects brain and spinal cord to skeletal
muscles, skin and sensory organs
• Responsible for voluntary movement
• Under conscious control
– Ex: moving arms, legs, watching TV, listening to music
• Autonomic System
• Relays information to and
from internal organs
• Involuntary movement
• Not under conscious control
Ex:
– Rate of heart beat, breathing,
peristalsis in digestive tract
Turning Responses On and Off
• Sympathetic Nervous System
– Generally speeds up autonomic processes
– Responsible for “fight or flight” response
• Ex: Urinary Muscles contract, pupils contract,
saliva secreted
• Parasympathetic Nervous System
– Generally slows things down
• Ex: Urinary Muscles relax, pupils dilate, saliva
stopped
Somatic vs. Autonomic
Muscle
Organ
Reflexes
• Involuntary response to a
stimulus
– Part of somatic nervous system
• Simple pathway:
– Receptor - spinal cord - effector
• Many normal body functions
controlled this way
– Ex: Blinking, sneezing, coughing
Pupil size in response to light:
http://www.youtube.com/watch?v=Yj5-cJgVX3c&safe=active
• Why do doctors
check reflexes?
– If you do not have a
response to a reflex,
something is wrong
with your nervous
system.
– Ex: Pupils “fixed and
dilated”
http://www.youtube.com/watch?v=GgQq79YxuUg&safe=active
• Reflec Arc
• Pathway nerve impulses
travel in a reflex
• Simplest have only one
sensory neuron and one
motor neuron
– Ex: knee jerk response
http://www.youtube.com/watch
?v=nKPEWao2Wg&safe=active
Reflex Arc
• Most reflexes involve 3
or more neurons
– Ex:
• hand pulling back from
burn or pain (withdrawal
reflex)
• Sensory Neuron
• Interneuron (in spinal
cord)
• Motor Neuron
Reflexes in Babies
http://www.youtube.com/watch?v=lA6EkByW8wk&safe=active
Disorders of the Nervous System
• Polio: viral infection that affects motor function and can
cause paralysis
• Stroke: a burst blood vessel in the brain, causing cerebral
hemorrhage. Can cause brain damage, paralysis, death
• Cerebral Palsy: birth disorder, causes problems with
motor function
• Multiple Sclerosis: myelin coating around neurons
degenerates affecting motor function.
• Meningitis: inflammation of membranes surrounding
brain or spinal cord.
Adaptations for Nervous Regulation
• Protists
–
–
–
–
–
No true nervous system
Can respond to certain stimuli
Can tell food from nonfood, strong light, harmful chemicals
Can respond to irritants in environment
Paramecium have neurofibrils that connect cilia on
membrane and coordinate their beating
Hydra
• Has a nerve net
– Nerve cells form a network
between two cells layers of body
– Impulses travel in all directions
• Coordinates movement of
tentacles to bring in food
• Whole body tend to respond
to a stimulus at once
•
•
Time Lapse Video of Hydra Moving
http://www.youtube.com/watch?v=UI531GMRTM&safe=active
Earthworm
• Central Nervous System:
– “brain” connected to pair of ventral nerve cords with ganglia
in each segment
• Peripheral Nervous System:
– Sensory receptors in skin for light, vibrations, chemicals
– Motor neurons from nerve cord to muscles and glands
Grasshopper
• Dorsal “Brain” made of
fused ganglia
• Ventral nerve cord with
series of fused ganglia
• Peripheral nerves
branch from ganglia to
muscles, sensory
organs
• Complex sensory
organs include
tympana, eyes,
antennae
• Crash Course: The Nervous System
• http://www.youtube.com/watch?v=x4PPZC
LnVkA&safe=active