Nervous Tissue Ch 11

Organization of the Nervous System

Anatomical Divisions of the Nervous System Enteric Nervous System gut Central Nervous System (CNS) brain spinal cord Peripheral Nervous System (PNS) cranial nerves (12 pr) spinal nerves (31 pr)

CNS PNS

Enteric Nervous System Myenteric plexus Submucosal plexus

Function of the Nervous System sensory input motor input sensory receptor effector Function of the Nervous System integration

Neuroglia of CNS Astrocytes Ependymal Cells Regulate extracellular brain fluid composition Promote tight junctions to form blood-brain barrier Ependymal Cells Line brain ventricles and spinal cord central canal Help form choroid plexuses that secrete CSF

Neuroglia of CNS Microglia Oligodendrocytes Specialized macrophages Form myelin sheaths if surround axon

Neuroglia of PNS Schwann cells Satellite cells Wrap around portion of only one axon to form myelin sheath Satellite cells Surround neuron cell bodies in ganglia, provide support and nutrients

Typical Neuron Dendrites convey incoming messages to the cell body

Myelin Sheath Speed: small, unmyelinated fibers = 0.5 - 2.0 m/sec large, myelinated fibers = up to 120 m/sec

Myelin Sheath

Types of Neurons bipolar unipolar multipolar eye, ear, & olfactory Dorsal root ganglion cells multipolar most abundant type in CNS

Neuron Interaction & Integration Interaction Between Neurons

Resting Potential of an Axon Negative charge (-70 mV) Na+ more concentrated in the ECF K+ more concentrated in the ICF

Resting Potential of an Axon

Depolarization of the Axon Membrane

Action Potential

Propagation of an Action Potential

Propagation of an Action Potential

Propagation of an Action Potential

Refractory Period

Saltatory Conduction

Synapses Ca2+ Presynaptic neuron Postsynaptic membrane Synaptic vesicles containing neurotransmitters

EPSP & IPSP

Synapses

Neurotransmitters Acetylcholine- slows heart rate; PNS Glutamate- most prevalent neurotransmitter in the brain Aspartate- in CNS GABA- inhibitory neurotransmitter Glycine- inhibitory neurotransmitter Norepinephrine- awakening from deep sleep Epinephrine- increase heart rate Dopamine- movement of skeletal muscles Seratonin- sensory perception, temp regulation, mood, sleep Nitric oxide- may play a role in memory and learning Enkephalin- inhibit pain impulses by suppressing release of substance P Substance P- enhances perception of pain tyrosine

Neurotransmitters

Types of Circuits in Neuronal Pools

Neuronal Circuits Converging circuit same source Pacinian corpuscles- pressure different sources control of respiration Diverging Circuit permits broad distribution of a specific input types A.  amplification B.  divergence into multiple tracts

Neuronal Circuits Parallel after-charge circuit several neurons process same information at one time each chain has a different number of synapses, but eventually they all reconverge on a single output output neuron may go on firing for some time after input has ceased important in withdrawal reflexes longer-lasting output from small period of pain 

Neuronal Circuits Reverberating Circuit axons extend back toward the sources of an impulse and further stimulate the presynaptic neuron helps maintain consciousness, muscular coordination, normal breathing, short term memory... 

Neuron to Neuron Transmission synapses Afferent (sensory) Integration center Interaction Between Neurons Efferent (motor)

Disorders of the Nervous System Multiple Sclerosis Autoimmune disease Destruction of myelin sheath Scar tissue may form Interaction Between Neurons

Disorders of the Nervous System Epilepsy Rapid synchronous firing of neurons Seizure Treatments: Drugs Implants Brain surgery Interaction Between Neurons

INQUIRY What voltage is the threshold potential? Describe depolarization, repolarization and hyperpolarization. Which ion causes the neurotransmitters to be released across the synapse? Name 2 instances that you can stimulate a neuron to depolarize. What disease is characterized by myelin sheath degeneration? Can all parts of the CNS regenerate if damaged?