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Nervous System Communication
Kid Concussions
In The News
• Nerve cells
• Parts of neurons
– Cell body
– Long extensions
• 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
Annelid Nervous System
• Segmental ganglia
– Ganglia = aggregations of nervous tissue
• Ventral nerve cord & brain
Vertebrate Nervous System
• Central nervous system
– Brain & spinal cord
• Peripheral nervous system
– Nerves to & from CNS
Nerve Cells
• Cell body
– Contains nucleus
– Organelles necessary for cell
• Axon
– Long cell extension
– May have myelin covering
• Dendrites
– Cell extensions
– No myelin covering
Sensory Neurons
• Receive information
• Transmit to the central nervous system
Motor Neurons
• Transmit commands away from CNS
• To muscles & glands
• Located within brain & spinal cord
• Integrate information
• Axons may not be myelinated
• Nerve support cells
• Provide support, protection, & nutritional
• Schwann cells
– Found around axons
– Produce myelin sheath
Myelin Sheath
• Insulates axon
• Nodes of Ranvier
– Uncovered areas
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
Action Potential
• Nerve impulse is started by a stimulus
• Stimuli cause movements of ions through
• 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
• 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
• 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 acytylcholine
Neuron to Neuron Connections
• Uses many different neurotransmitters
• Some cause different effects
– Excitatory synapse – continuation of impulse
– Inhibitory synapse – reduce ability to
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
Spinal Nerves
• Sensory & motor nerve fibers
• Travel directly to spinal cord
• Nerves are bundled to form mixed nerves
Motor Neuron Systems
• Somatic
– Voluntary
– Movements of skeletal muscles
• Autonomic
– Involuntary
– Reflex = automatic response to nerve
– Involuntary motor pathways
Divisions of the Autonomic
Nervous System
• Parasympathetic
– Prevails during periods of inactivity
– Housekeeping
• Sympathetic
– “fight or flight”
– Responds to stress
– Prepares body for action
• Parasympathetic & sympathetic
together help to maintain homeostasis
Psychoactive Drugs
• Affect action of nervous system
– Neurotransmitters
– 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
End Chapter 32