BIOL 207 Lecture Notes - Lecture 21: Somatic Nervous System, Intercalated Disc, Gap Junction
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Muscle tissue
• prefix for muscle is myo (muscle) and sarco (flesh)
• innervation - what is muscle connecting to?/what it is connecting to, as well as supplied by
nerves
• 40% of body is muscle
3 categories of muscle
• voluntary/striated/somatic/skeletal - voluntary because if you want to move it you can, you
have voluntary control over it. striated because these muscles have a lot of stripes, and they look like
striations. called somatic because they make up the body. skeletal because all these muscles connect to
the skeleton.
• these are all voluntary and under control of the SNS (somatic nervous system). this is also called
you olutay N“. stiated usles ae elogated, hih ake the uiue. they a’t oe o thei
own and have to be innervated. they are most active and most energy requiring tissue in body. muscles,
especially striated, are the most energy requiring tissue in the body. striated muscle is innervated by
SNS. every single striated muscle cell is individually innervated, so theres no way a voluntary muscle will
contact unless innervated.
• involuntary/smooth/visceral - this muscle is involuntary. the ANS (autonomic nervous system)
controls all involuntary movements/activities. line the walls of hollow organs (blood vessels, GI (gastro
intestinal) tract, other viscera). smooth muscle is innervated by ANS. smooth (and cardiac - below),
aye o ill e ieated that ill set thigs i otio.
• the striated will not contract unless the nerve contracts.
• gap junctions allow ions to float freely from one cell to another by the passageway. basically a
porthole that allows smooth movement of ions from one to another.
• nexus is the gap junction for smooth muscle
• cardiac muscle
• also involuntary, innervated by ANS. forms 98% of heart. not all cardiac muscle cells are
individuals innervated. impulses can be transported to special places such as the pacemaker.
intercalated disc is the gap junction that allows impulses to move from one cardiac cell to another, even
though they are not innervated. (its the gap junction for cardiac muscle)
• audtorhythmicity - these cells (smooth and cardiac) can randomly contract and relax
(involuntary - but no nervous connection)
• amitotic - incapable of dividing.
Nervous system/tissue
2 types of cell that form nervous tissue
• neuroglia/glial - protect, support, and insulate neurons. outnumber neurons between 5-10 to 1
ratio.
• neurons (as well as striated muscle cells) are amitotic, meaning they are incapable of dividing.
• Neuron - are capable of (a) picking up stimuli (b) converting the stimuli to nerve impulses and (c)
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