• 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 CNSGanglia- 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) Sensation- conscious (perception) or subconscious awareness or subconscious awareness of changes in environmentof 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 outsideGreater 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)

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• 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) Histamine Epinephrine

Amino Acids

Gamma-aminobutyric acid (GABA) Glycine Glutamate

Aspartate

Neuroactive Peptides - partial list!!</FONT< td>

bradykinin beta-endorphin bombesin calcitonin

cholecystokinin enkephalin dynorphin insulin

gastrin substance P neurotensin glucagon

secretin somatostatin motilin vasopressin

oxytocin prolactin thyrotropin angiotensin II

sleep peptides galaninneuropeptide 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