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Lecture 18

BGYB30H3 Lecture 18 Notes Endocrinology 1-Nov 10


Department
Biological Sciences
Course Code
BIOD27H3
Professor
Ingrid L.Stefanovic
Lecture
18

Page:
of 2
BGYB30H3 Lecture 18 Notes
-smooth muscle is found in the walls of hollow organs and tubes in blood vessels
-contraction changes shape of organs and moves materials in, out, or around the body
-smooth muscle has low fatigue, low oxygen consumption, less energy required to generate
force
-smooth muscles are small and have a single nucleus in spindle fibres
-neurotransmitters and sex hormones control smooth muscles
-smooth muscles integrate signals and act based on the majority of neurotransmitters
-smooth muscles may hyperpolarize or depolarize depending on the signal
-smooth muscles may depolarize without a graded or action potential or a change in
membrane potential
-in a single unit cell smooth muscle, cells contract as a unit through being connected by gap
junctions, which conducts electrical synapses
-multi-unit smooth muscle involves cells associated with variscosities with no gap junctions,
allowing fine control of contractions
-smooth muscle in the uterus goes from multi-unit to single unit during pregnancy
-smooth muscle has longer actin and myosin filament
-rate of cross bridge cycling is slower in smooth muscle to allow longer contractions
-there is less sarcoplasmic reticulum than skeletal muscles
-caveolae concentrates calcium in the smooth muscle
-smooth muscles lack troponin and sarcomeres
-smooth muscles have oblique bundles that extend diagonally
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-myosin moves slowly and lengthens the contraction period by decreasing the rate of
crossbridge cycling
-myosin light chain kinase regulates contractions
-lack of sarcomere allows myosin to move longer distances with actin sliding over it
- a reflex is the integration of sensory info to control muscles/glands
-input is integrated in the spinal cord or the brain to cause an output
-feedforward allows the body to anticipate stimuli and begin a response prior to the stimulus
-reflexes can be classified by the
x by being viscera or somatic
x number of neurons in the pathway
x learned through conditioning or innate
x originates in the spinal cord or the brain
-autonomic reflexes are sometimes caused by the spinal cord or modulated by descending
tracts from the brain
-spinal reflexes include
x urination
x defecation
-brain stem reflexes include
x Sneezing
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x Salivation
x Vomiting
-higher brain reflexes include
x Blushing
x Goosebumps
x Butterflies in the stomach
-autonomic reflexes are tonically active (continuously stimulated)
-skeletal muscle reflexes respond to muscle and joint movements, muscle tension or muscle
length
-proprioceptors are found in the skeletal muscle, joints, or ligaments
-activation of afferent sensory neurons can cause muscle contraction or relaxation
-relaxation is caused by inhibition of an interneuron in the CNS to inhibit the somatic motor
reflex neuron
-voluntary motor reflex involves the brain while involuntary (knee jerk) involves the spinal cord
-alpha motor neurons result in the contraction of extra fusal muscle fibres
-in monsynaptic motor reflex, there is one synapse at the spinal cord between pre-synaptic
and post-synaptic neuron
-in polysynaptic motor reflex, there are two synapses because of an interneuron
-joint receptors are proprioceptors found in capsules and ligaments around joints that
connect muscles to the bones
-joint receptors respond to mechanical distortion of joints and bones
-joint receptors signal the cerebellum
-muscle spindles are prioproceptors important in responding to muscle stretch
-gamma motor neurons activate intrafusal fibres in the muscle spindles
-intrafusal fibres are parallel to extra fusal fibres and have contractile ends but lack myofibrils
-noncontractile centre of muscle spindle are stimulated by muscle stretch and sensory nerve
endings synapse onto alpha motor neurons in the spinal cord
-sensory neuron is tonically active when attached to intrafusal fibres
-extra fusal fibres maintain a certain level of tension even at rest
-when muscle stretches, muscle spindles increase neuron activation which causes alpha motor
neurons to decrease muscle stretch
-addition of a load causes temporary muscle stretch until alpha motor neurons cause a reflex
contraction
-golgi tendon organs are proprioceptors are found in junctions of tendons
-golgi tendon organs respond to muscle tension during isometric contraction, causing
relaxation reflex to protect the muscle
-stimulation of golgi tendons causes inhibition of alpha motor neurons by activating inhibitory
interneurons to block muscle contraction
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