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Nervous System Communication
Kid Concussions
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Neurons
• Nerve cells
• Parts of neurons
– Cell body
– Long extensions (fibers=dendrites or axons)
• Message = nerve impulse
Animal Nervous Systems
• Sponges – no nervous system
• Other animals all have neurons in systems
Nerve Net
• In all cnidarians
• Interconnected
nerve cells
• No brain
Ringlike Nervous System
• In echinoderms
• Ring with 5 radiating nerves
Ladderlike Nervous System
• In many Platyhelminthes
• Some have distinct brain (ganglia)
Annelid Nervous System
• Segmental ganglia
– Ganglia = aggregations of nervous tissue
• Ventral nerve cord & brain
Arthropod
Mollusks(depends
level of activity) some have
giant fibers
Vertebrate Nervous System
• Central nervous system
– Brain & spinal cord
• Peripheral nervous system
– Nerves to & from CNS
Nerve Cells
(Neurons)
• Cell body
– Contains nucleus and organelles
– Produces substances necessary for cell to live &
function
• Axon (conducts or passes on impulse)
– Long cell extension
– May have myelin covering
• Dendrites (receive impulse)
– Usually short cell extensions
– No myelin covering
– most neurons have multiple dendrites
Sensory Neurons
• Receive information from sense organ receptors
• Transmit to the central nervous system
• Cell bodies of sensory neurons lie near the CNS
Motor Neurons
• Transmit commands away from CNS to effector (muscle or
gland)
• Each neuron has one long axon
• Cell bodies on most motor neurons lie in or near CNS
Interneurons
• Located within brain & spinal cord
• Integrate information
• Axons may or may not be myelinated
• usually axons are shorter than those in PNS
Neuroglia
• Nerve support cells
• Provide support, protection, & nutritional
stability
• Schwann cells (special neuroglial cells)
– Found around axons
– Produce myelin sheath
• Oligodendrocytes – produce myelin
sheath around some CNS axons
Myelin Sheath
• Insulates axon
• Nodes of Ranvier-allows impulse to move
at a greater speed along axon
• Uninsulated areas- no myelin sheath
Nerve Impulses
• Electrical signals transmitted along
membranes of nerves
Resting Potential
• Neuron is electrically charged at rest
• Outside is positively charged
• Inside is negatively charged
Sodium-Potassium Pump
• Proteins embedded within cell membrane
• Moves sodium to the outside
• Moves potassium to the inside
• Maintains resting potential
• Requires energy (ATP)
Action Potential
• Nerve impulse is started by a stimulus
• Stimuli cause movements of ions through
membrane
• Threshold potential
– Sufficient stimulation to depolarize membrane
• Action potential
– Rapid reversal of membrane electric potential
Nerve Transmission
• Action potential at one point depolarizes next area
• Depolarization moves in self-propagating wave
Saltatory Conduction
• Nerve impulse jumps & moves faster
along myelinated axon
Synapse
• Area where nerve communicates
• Transfers message
– Another neuron
– An effector
Synaptic Cleft
• Neurons do not touch other neurons or
effector cells
• Nerve impulse must cross gap (electrical
signal is changed to a chemical signal)
Neurotransmitters
• Organic molecules (> 60 different chemicals)
• Transfer message across synaptic cleft
• Attach to receptors on target cell
Neuromuscular Junctions
• Synapse between neuron & skeletal muscle
• Neurotransmitter is aceytylcholine
Neuron to Neuron Connections
• Uses many different neurotransmitters
(such as dopamine, norepinephrine, serotonin)
• Some cause different effects
– Excitatory synapse – continuation of impulse
– Inhibitory synapse – reduce ability to depolarize
Integration of Nerve Impulses
• Summed impulses determine if
postsynaptic neuron will depolarize
Human Nervous System
• Central nervous system
– Brain
– Spinal cord
• Peripheral nervous system
– Brings messages to & from CNS
– Somatic nervous system – voluntary
– Autonomic nervous system - involuntary
Central Nervous System
• Integrates sensory & motor impulses
Spinal Cord
• Connects peripheral nervous system with brain
• Receives information via spinal nerves
• Includes reflex arcs
CNS Protection - Meninges
• Layers of membranes
– Dura mater
– Arachnoid
– Pia mater
Peripheral Nervous System
• Sensory & motor impulses
• Cranial nerves communicate directly with brain,
some are strictly sensory or motor, some are mixed.
Spinal Nerves
•
•
•
•
Sensory & motor nerve fibers
31 pairs and all are mixed nerves
Travel directly to spinal cord
Nerves are bundled to form mixed nerves
Motor Neuron Systems
• Somatic nervous system, part of PNS
– Voluntary
– Movements of skeletal muscles
– requires a single motor neuron
– Reflex = automatic response to nerve
stimulation
• Autonomic nervous system, part of PNS
– Involuntary motor pathways
– requires two motor neurons
Divisions of the Autonomic
Nervous System
• Parasympathetic
– Acetylcholine is the neurotransmitter
– Prevails during periods of inactivity
– Housekeeping
• Sympathetic
–
–
–
–
Norepinephrine is the neurotransmitter
“fight or flight”
Responds to stress
Prepares body for action
• Parasympathetic & sympathetic together help
to maintain homeostasis
Psychoactive Drugs
• Affect action of neurotransmitters
In specific parts of the brain
• Some are abused
Drug Addiction
• Chronic use (or abuse) of psychoactive drugs
• Person becomes physically dependant
• Drug use tends to increase due to drug
tolerance
End Chapter 32