ZOO 2090 Lecture Notes - Lecture 9: Electric Eel, Cranial Nerves, Somite
1 May 2018
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ZOO2090 – Muscles
Exam Examples: *Midterm will cover lectures 1-10
1. C
2. B
3. C
What is a muscle?
• Collection of modified cells that generate force along axis of their fibers
contractile
o Force can be used to produce or restrain movement
• In order to create/stop movement, muscle cells are electrically excitable
responsive to nervous stimulation
• Muscles can generate heat through shivering
o Some muscles are modified to generate electric shocks (electric eel)
or electric fields (electrosensory fish) upon stimulation
Classification:
• By location (somatic and visceral)
• By method of nervous control (voluntary or involuntary)
• By microscopic appearance (skeletal, cardiac or smooth)
Skeletal muscle:
• Associated with the skeleton
• Striated; cylindrical
• No branching; no disks
• Nuclei peripheral
• Voluntary
Cardiac Muscle:
• Muscle of the heart wall
• Striated; cylindrical
• Branched; Intercalated disks
• Nuclei central
• Relatively involuntary
Smooth Muscle:
• Muscles of blood vessels and visceral organs
• Not striated; spindle-shaped
• No branching; no disks
• Nucleus central
• Relatively involuntary
find more resources at oneclass.com
find more resources at oneclass.com
Embryonic Origin
• All muscles originate from mesoderm
Differentiation into segmented somites (epimere), hypomere (surrounds
gut) and mesenchyme
somites are divided further into: *each segment develops from 1 somite
• dermatome (skin)
• myotome (muscle)
• sclerotome (vertebral column)
• somitomeres anterior mesoderm clusters do not become fully segmented
o contain cranial nerves
• muscle homology is often established based on nerve innervation
Fate of Mesoderm Divisions:
1. Somitomeres cranial muscles
2. Myotome (of somites) most postcranial and some cranial muscles
3. Hypomere muscles of gut and heart
4. Mesenchyme some limb and smooth muscles
Actions of Muscles: usually two groups of muscles work opposite to each other
• Flexors/extensors – bend/straighten a limb or part of a limb
• Abductors/adductors – draw a limb away or toward body midline
• Pronators/supinators – turn palm or sole down/up
• Levators/depressors – raise or lower
• Constrictors/dilators – close/open orfices
• Protractors/retractors
• Sphincter
Skeleton-Muscle Relationship:
• Tendon: muscle-bone
• Ligament: bone-bone
• Muscles work together to perform function:
o When biceps are contracted, triceps are relaxed
o When triceps are contracted, biceps are relaxed
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Exam examples: *midterm will cover lectures 1-10: c, b, c. What is a muscle: collection of modified cells that generate force along axis of their fibers. Contractile: force can be used to produce or restrain movement. In order to create/stop movement, muscle cells are electrically excitable. Responsive to nervous stimulation: muscles can generate heat through shivering, some muscles are modified to generate electric shocks (electric eel) or electric fields (electrosensory fish) upon stimulation. Classification: by location (somatic and visceral, by method of nervous control (voluntary or involuntary, by microscopic appearance (skeletal, cardiac or smooth) Skeletal muscle: associated with the skeleton, striated; cylindrical, no branching; no disks, nuclei peripheral, voluntary. Cardiac muscle: muscle of the heart wall, striated; cylindrical, branched; intercalated disks, nuclei central, relatively involuntary. Smooth muscle: muscles of blood vessels and visceral organs, not striated; spindle-shaped, no branching; no disks, nucleus central, relatively involuntary. Embryonic origin: all muscles originate from mesoderm.
