Nervous System Communication

Kid Concussions In The News

Neurons Nerve cells Parts of neurons Message = nerve impulse 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 Axon Dendrites 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

Interneurons Located within brain & spinal cord Integrate information Axons may not be myelinated

Neuroglia Nerve support cells Provide support, protection, & nutritional stability 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 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

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 acytylcholine

Neuron to Neuron Connections Uses many different neurotransmitters 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 Peripheral 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 Autonomic Voluntary Movements of skeletal muscles Autonomic Involuntary Reflex = automatic response to nerve stimulation 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 Some are abused 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 tolerance

End Chapter 32