• 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)
• 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