Neurons in brain and spinal cord= Central Nervous System (CNS) Nerves that connect CNS to rest of body= Peripheral Nervous System (PNS)

Types of Neuroglia Microglial cells- support and phagocytosis in CNS Figure 7.3

Oligodendrocytes- form myelin sheaths in brain and spinal cord (CNS)

Astrocytes- between neurons and blood vessels; support, nutrient regulation, form scar tissue (CNS)

Ependymal cells- form epithelial-like membrane that covers parts of brain and forms inner lining that encloses spaces within brain and spinal cord (CNS)

Schwann cells- myelinate PNS

Satellite cells: surround cell bodies of PNS ganglia

Neurons- transmit electrochemical “information” as nerve impulses along nerve fibers

Nerve impulses are carried to Effectors (muscles and glands)

Neuron Structure Cell body- main structure- include Nissl bodies (ER) and neurofibrils Dendrites- receive impulses, one or many Axon- sends impulses, branched, usually only one (arises from axon hillock)

Large axons of peripheral neurons are enclosed in sheaths of neuroglia called Schwann cells –Myelin sheath- contains lipid- protein –Surrounded by membrane called Neurilemma

Nodes of Ranvier- gaps between Schwann cells of myelin sheath

Myelinated cell fibers appear white (white matter) Unmyelinated fibers and cell bodies appear gray (gray matter)

Nuclei- clusters of cell bodies in CNS Ganglia- clusters of cell bodies in PNS Tracts- bundles of nerve fibers running through CNS Nerves- bundles of nerve fibers running through PNS

Path of travel Sensory Neurons---Interneurons---Motor Neurons

Sensation- conscious (perception) or subconscious awareness of changes in environment

Process of sensation begins with receptor (selective)- stimulus produces potential at threshold CNS integrates impulse Three types of receptors: free nerve endings, encapsulated nerve endings, separate cells

Can be grouped on location exteroceptors (external surface of body), interoceptors (internal environment), proprioceptors (muscles, tendons, joints)

Can be grouped by stimulus mechanoreceptors (mechanical stimuli) thermoreceptors (heat) nociceptors (pain) photoreceptors (light) chemoreceptors (chemicals) osmoreceptors (osmotic pressure)

Adaptation to maintained, constant stimulus (can be rapid or slow) A dog (red line) tracks a pheasant (yellow line). As the dog keeps leaving the odour to prevent receptor adaptation, it zigzags.

Figure 7.8

All resting neurons are polarized (different charge outside than inside), –determined by ions, channel pores in membrane K + crosses easily; Na + and Ca ++ with more difficulty Greater Na + concentration outside Greater K + concentration inside

Due to diffusion- resting nerve cell always has a slight surplus of positive charge outside and slight surplus of negative charge inside –This is called resting potential

A threshold potential must be reached to achieve an action potential –Na + permeability suddenly increases, resulting in an inward rush (action potential)

Nerve impulse- when one action potential stimulates adjacent portions of nerve fiber to reach threshold potential and thus action potential –Results in a wave of action potentials moving down a nerve fiber

The firing of a nerve is an “All or None” response (due to threshold potential)

Certain local anesthetics decrease membrane permeability to sodium ions

Synaptic transmission occurs between axon of one neuron (sending signal) and dendrite or cell body of another neuron (receiving signal)

At this gap, Neurotransmitters are released from synaptic vesicles

Certain neurotransmitters increase ion permeability (excitatory) Others decrease permeability (inhibitory)

Small Molecule Neurotransmitter Substances Acetylcholine (ACh)Dopamine (DA)Norepinephrine (NE) Serotonin (5-HT)HistamineEpinephrine Amino Acids Gamma-aminobutyric acid (GABA)GlycineGlutamate Aspartate Neuroactive Peptides - partial list!! bradykininbeta-endorphinbombesincalcitonin cholecystokininenkephalindynorphininsulin gastrinsubstance Pneurotensinglucagon secretinsomatostatinmotilinvasopressin oxytocinprolactinthyrotropinangiotensin II sleep peptidesgalanin neuropeptid e Y thyrotropin- releasing hormone gonadotropnin- releasing hormone growth hormone- releasing hormone luteinizing hormone vasoactive intestinal peptide Soluble Gases Nitric Oxide (NO) Carbon Monoxide

Reflexes: Somatic: stimulate skeletal muscle Autonomic: regulate smooth muscle, heart and glands Figure 7.11