Muscle Anatomy Flashcards
Anatomy of Skeletal Muscle
Motor neuron innervates multiple muscle cells
- Muscle cell = myofiber = myocyte = muscle fiber
- Stretch tendon to tendon
- Multinucleated
- Multiple mitochondria
Muscle cell/myocyte can have 100 -1000’s of myofibrils
Myofibrils:
- Long
- Arranged in rows
Anatomy of Smooth Muscle
Appearance:
- Lacks the striations that are seen in cardiac and skeletal
- Still has actin and myosin
Cells:
- Fusiform or spindle
Anatomy of Cardiac Muscle
Appearance:
- Similiar to skeletal muscle
- Composed of sarcomeres (thin & thick filaments)
- Poorly developed T-tubules
- Contractions via sliding filaments
Components of Sarcomere:
Thin filament = Actin
Thick filament = Myosin
Delineated by Z-disc’s
Basic contractile unit
Anatomy and Function of the Muscle Spindle
Intrafusal fibers:
- Part of a stretch receptor or muscle spindle (specialized organ)
Function: sense position and stretch of muscles
- Proprioceptor
Contacted by the axon of 1 SENSORY neuron
Contacted by the axon of 1 MOTOR neuron
Gamma motor neuron
Originates from ventral horn of spinal cord
Intrafusal fibers are in parallel to the extrafusal fibers (force generating fibers)
Compare and Contrast
Muscle Spindles vs. Golgi Tendon Organs
Muscle Spindles:
- Detect changes in length and rate of stretch
Golgi Tendon Organs:
- Measure changes in the force generated via tendon tension
Muscle Properties:
- Contractility
- Actin and Myosin
- Can shorten
- Excitability
- Can be stimulated
- Extensibility
- Can be stretched
- Elasticity
- Can return to original position after being stretched
Myofibrils:
Made up of sarcomeres (repeating units)
Sarcomere:
- Made of 2 myofilaments that interdigitate
- Thick filaments (myosin mostly)
- Thin filaments (Actin)
- Myosin interacts with actin to produce muscle contractions
Myosin & Actin overlap = darker area, looks striped
- Striated muscle
Sarcolemma & Transverse Tubules
- Plasma membrane outside of the sarcolemma (myocyte)
- Allows for communication between outside of fiber and internal parts
Transverse tubules (T-tubules):
- Membrane invaginations into the fiber
- Plasma membrane extends into the muscle fiber
- Extension into the muscle fiber goes deep
- Carry the AP from the surface into the muscle fiber
Sarcoplasmic Reticulum:
- In contact with T-tubules
- Separate strucutre
- Function is for Ca2+ storage
Thick Filaments
- Closer to center of sarcomere
- Myosin
- Top image
Thin Filaments
- Run parallel to the long axis of the sarcomere
- Actin
- Bottom image
Smooth Muscle
Location:
- Organs
- Intestines
- Stomach
- Uterus
- Iris
Involuntary:
- Works on it’s own - no conscious control
Appearance:
- Lacks the striations that are seen in cardiac and skeletal
- Still has actin and myosin
Cells:
- Fusiform or spindle
Functions:
- Motility
- Tension (blood vessels)
Smooth Muscle Synaptic Input:
Synaptic Input from the Autonomic Nervous System:
- Norepinephrine or AcH
- Can be contacted by more than 1 motor neuron
- Excitatory or Inhibitory Input (different from skeletal muscle)
- Receptors spread widely across post-synaptic membrane
- Little specialization of the post synaptic membrane
For ANS: control is regulated by a 2 neuron chain
1 Smooth Muscle Cell can receive more than 1 contact from an axon
- axon approach causes membrane swelling
2 Types of Smooth Muscle
Single-unit
Multi-unit
Single Unit Smooth Muscle
Location:
- GI
- Bladder
- Uterus
- Ureter
- Walls of GI tract
Input:
- Autonomic nervous system
Cells:
- Linked via gap junctions = electrically coupled
- “wave-like” propagation of AP across gap junctions
- Have simaltaneous AP’s
- One motor neuron innervates a single cell which is part of a sheet of cells
Function: coordinated contraction = bladder emptying
Multi Unit Smooth Muscle Cells
Location:
- Iris
- Ciliary muscle of the lens in the eye
- Vas deferens
- Piloerector muscles of the skin
Input:
- Autonomic Nervous System
Contraction:
- Cells are NOT coordinated
- Cells are not coupled together
- Each cell can contract independently of the others
- Can act in a coordinated manner- even if they are not electrically coupled
- Can all by stimulated by multiple neurons to contract at the same time
Each multiunit smooth muscle cell has greater control of function = precision
Cardiac Muscle:
Appearance:
- Similiar to skeletal muscle
- Composed of sarcomeres (thin & thick filaments)
- Poorly developed T-tubules
- Contractions via sliding filaments
Input:
- Autonomic Nervous System
- Chemical synapses to modulate function
Contraction: (Mechanism same as skeletal muscle)
- Use gap junctions
- Pass AP’s to neighboring cells
- Striated muscle cells aren’t coupled to eachother
Function:
- Excitation of cardiac cells translates into tension
Skeletal Muscle Fibers (2 Types)
Extrafusal fibers:
- ONLY innervated by alpha motor neurons
- Responsible for contraction
Intrafusal fibers:
- Part of a stretch receptor or muscle spindle (specialized organ)
- Function: sense position and stretch of muscles
- Proprioceptor
- Contacted by the axon of 1 SENSORY neuron
- Contacted by the axon of 1 MOTOR neuron
- Gamma motor neuron
- Originates from ventral horn of spinal cord
Intrafusal fibers are in parallel to the extrafusal fibers (force generating fibers)
Muscle Spindle = Stretch Receptor
- Corrects changes in muscle length when extrafusal fibers contract (get shorter) or stretch (get longer)
- When extrafusal fibers are stretched = intrafusal fibers are stretched
Sensory afferent neurons (activated)
- detect velocity and length of the muscle change
Activation of sensory neuron = message to spinal cord and to alpha motor neurons which innervate the same muscle
Gamma motor neurons:
- activated during stretch
- ensure that muscle remains sensitive to changes in muscle length even during contraction
Golgi Tendon Organ
- 2nd mechanosensitive proprioceptor
- Measure changes in the force generated via measuring tension in the tendon
- in series with muscle
- Bare nerve endings innervate a collagen matric located between muscle fibers and the tendon
Tension in muscle fibers = squeezes the sensory fibers= AP’s
Protect muscle from tearing
