structural classification of the nervous system
DESCRIPTION
Functions of the Nervous System Sensory input – gathering information To monitor changes occurring inside and outside the body Changes = stimuli Integration To process and interpret sensory input and decide if action is needed Motor output A response to integrated stimuli The response activates muscles or glandsTRANSCRIPT
Structural Classification of the Nervous System
Central nervous system (CNS) Brain Spinal cord Peripheral nervous
system (PNS) Nerves outside the brain and spinal cord Functions of
the Nervous System
Sensory input gathering information To monitor changes occurring
inside and outside the body Changes = stimuli Integration To
process and interpret sensory input and decide if action is needed
Motor output A response to integrated stimuli The response
activates muscles or glands Nervous Tissue: Neurons
Neurons = nerve cells Cells specialized to transmit messages Major
regions of neurons Cell body nucleus and metabolic center of the
cell Processes fibers that extend from the cell body Neuron Anatomy
Cell body contains organelles.Neurons lack centrioles and are
incapable of mitosis Nissl substance specialized rough endoplasmic
reticulum.Attached ribosomes.Function to synthesize vital protein
molecules Neurofibrils intermediate cytoskeleton that maintains
cell shape Extensions outside the cell body Dendrites short,
branched receptive surfaces that conduct impulses toward the cell
body Axons long, usually singular and conduct impulses away from
the cell body Axons and Nerve Impulses
Axons end in axonal terminals Axonal terminals contain vesicles
with neurotransmitters Axonal terminals are separated from the next
neuron by a gap Synaptic cleft gap between adjacent neurons Synapse
junction between nerves Nervous Tissue: Support Cells
(Neuroglia)
1. Astrocytes Abundant, star-shaped cells Brace neurons Form
barrierbetween capillariesand neurons Control the
chemicalenvironment ofthe brain Figure 7.3a 2. Microglia 3.
Ependymal cells Spider-like phagocytes
Dispose of debris 3.Ependymal cells Line cavities of thebrain and
spinal cord Circulatecerebrospinalfluid Nervous Tissue: Support
Cells
4.Oligodendrocytes Produce myelin sheath around nerve fibers in the
central nervous system Figure 7.3d Nervous Tissue: Support
Cells
5.Satellite cells Protect neuron cell bodies 6.Schwann cells Form
myelin sheath in the peripheral nervous system Functional
Classification of Neurons
Sensory (afferent) neurons Carry impulses from the sensory
receptors Cutaneous sense organs Proprioceptors detect stretch or
tension Motor (efferent) neurons Carry impulses from the central
nervous system Interneurons (association neurons)
Found in neural pathways in the central nervous system Connect
sensory and motor neurons Structural Classification of
Neurons
Multipolar neurons many extensions from the cell
body.Characteristic of Motor Neurons Figure 7.8a Structural
Classification of Neurons
Bipolar neurons one axon and one dendrite.Found only associated
with special senses.(Olfactory, vision) Figure 7.8b Structural
Classification of Neurons
Unipolar neurons have a short single process leaving the cell
body.Sensory Neurons Figure 7.8c Nerve Impulses The surface of the
nerve cell membrane is polarized due to unequal distribution of
ions on either side of the membrane When nerve cells are at rest
there is a greater concentration of Na+ ions outside the membrane
and a greater concentration of K+ ions inside the membrane. (Rest
Potential) This arrangement of ions gives the outside of the
membrane a positive charge with respect to the inside. A stimulus
causes a change in permeability in a region of the membrane
Na+ ions rush into the cell and K+ ions rush out depolarizing the
region of the membrane This region of depolarization is an Action
Potential An action potential in one region stimulates adjacent
regions to depolarize and the action potential moves away from the
point of stimulus This moving action potential is a Nerve Impulse
The membrane is repolarized in 1/1000 sec. by active transport
Continuation of the Nerve Impulse between Neurons
Impulses are able to cross the synapse to another nerve
Neurotransmitter is released from a nerves axon terminal The
dendrite of the next neuron has receptors that are stimulated by
the neurotransmitter An action potential is started in the dendrite
Reflexes Reflex automatic, unconscious, and involuntary responses
to stimuli Simplest nerve pathways Autonomic Reflexes involve
contractions of smooth muscles Somatic Reflexes involve
contractions of skeletal muscles Help maintain homeostasis by
controlling:body temperature, heart rate, breathing rate, blood
pressure and digestive activities Patellar Reflex (knee-jerk
reflex) Employs only two neurons
Patellar Reflex (knee-jerk reflex)Employs only two neurons.Helps
maintain posture Also swallowing, sneezing, coughing, vomiting are
reflexes Withdrawl Reflex Withdrawl Reflex 1.Receptor sets up a
nerve impulse when something painful is touched 2.Sensory Neuron
carries the impulse to the spinal cord 3.Interneuron conducts the
impulse from the sensory to a motor neuron 4.Motor Neuron conducts
the impulse to the effector 5.Effector responds to stimulation by
muscle contraction