Unit 5.1: Neural control of skeletal muscles Flashcards
What is a voluntary control?
The primary motor cortex initiates movement by sending signal through spinal cord through motor neurons to skeletal muscle. It controls motor neurons on opposite side of body
What is an involuntary control?
They are reflexes : fast, predictable, automatic response to stimuli
Name the components of a reflex
a. receptor detects stimulus (at the beginning of the sensor neurons)
b. afferent sensory neuron (from receptor to CNS)
c. integrating center (brainstem or spinal cord)
d. efferent motor neuron
e. effector -> muscles -> contracts (effect)
- > glands -> secretes
what are somatic reflex
effectors are skeletal muscles - effect is muscle contraction
integrating center is spinal cord
what are withdrawal effect (flexor reflex)
uses more than 1 motor neuron to withdraw hand or foot
what are crosses extensor reflexes
occurs with withdrawal reflex involves contraction of muscles on opposite side of body
How are signals sent through a neuron
along the length of one neuron, uses electrochemical gradient (ions: elements with a charge).
What is the first step of impulse conduction
the resting neuron : resting membrane potential of -70 mV. positive outside, negative inside
what is the second step of impulse conduction
Na+ enter neuron through Na+ channels in neuron membranes triggered by: mechanoreceptors (physical disturbance like touch, pressure, movement), chemoreceptors (respond to specific chemicals/uses ligang-gated channels), photoreceptors (respond to light), electroreceptors (electric charge/voltage-gated channels), thermoreceptors (temperature change), pain receptor (nociceptors)
How is perceived an excess in stimulus?
Pain
What must happen to initiate a signal (impulse)
Membrane potential must reach -55 mV threshold.
No impulse if Na+ enters and potential does not reach threshold
If Na+ enters and potential exceed -55 mV, it will stimulate voltage gated Na+ channels to open
What is the third step of impulse conduction
Depolarization: volatage-gated Na+ channels open, Na+ rush into neuron, membrane potential increases dramatically, membrane potential reaches between 0 and + 30 mV. Na+ channels closes, membranes potential near +30 mV will stimulate K+ channels to open
What is the fourth step of impulse conduction
Repolarization: K+ flow out of the cell, at about -55 mV k+ channels start to close by hyperpolarization will occur (membrane potential less than -70 mV)
What is the fifth step of impulse conduction
restore ion concentration Na+ out K+ in
What are synapses
Junctions between neuron and target cell
What happens globally in a synaptic transmission
neuron releases neurotransmitters and theses chemicals bind to receptors in membrane of target cell
What is the position of the receptors and what is his role
In membrane of post-synaptic cell
1) Bind and respond to specific neurotransmitter
2) sends signal if neurotransmitters present
3) many and ligand-gated ions channel
What are the purpose of voltage-gated Ca++ channels
Open if impulse arrives at end bulb
allow calcium ion to enter
Ca++ initiates movement of vesicles
Describe the steps of synaptic transmission
1) impulse arrives at synaptic end bulb
2) depolarization of pre-synaptic membrane
3) voltage-gated Ca++ channels open- Ca++ enters neuron end bulb
4) Synaptic vesicles move towards neuron cell membranes
5) Exocytosis of neurotransmitters- neurotransmitter release in synaptic cleft
6) neurotransmitters binds to receptor in target membrane, which allows ions to cross membrane
What happens if : Na+ channels open?
Na+ enters –> impulse generated
What happens if : K+ channels open?
K+ exits -> impulse suppressed
What happens if : Cl- channels open?
Cl- enters -> impulse suppressed
how does the synaptic transmission ends?
Termination. Must remove neurotransmitters to end contraction and be ready for the next transmission.
What are the three common termination methods?
a. diffusion: neurotransmitter floats out of synaptic gap
b. degradation: neurotransmitter breakdown by specific enzyme and fragments reabsorbed
c. neurotransmitter re-uptake: neurotransmitter transported back intro pre-synaptic end bulb
What are stretch reflex
receptors are muscle spindles- monitor changes in muscle length, help maintain body positions
What are the three type of somatic reflexes
a. stretch reflex
b. withdrawal reflex
c. crossed extensor reflexes
Is a muscle group considered a organ?
Yes.
What does a muscle contain?
Blood vessels, 1 artery, at least 1 vein, nerves, adipose and connective tissue, bundles of muscle fibers.
What is a fascicle?
bundles of muscle fibers
Describe a cell (fiber) of the fascicle ?
Multinucleate, with glycosomes, myoglobin, many mitochondria, sarcoplasmic reticulum, surrounds myofibrils, stores Ca++
What does a myfibrils contain?
Repeating units of sarcomeres (myofilaments proteins : actin (thin filaments) and myosin (think filaments)
Name the five parts of a sarcomere?
actin attached at one end to Z line myosin (thick filament) = A band I band - area with actin only H zone - area with myosin only M-line area where myosin are connected together
What is the first step in the physiology?
depolarization of sarcolemma: action potential initiated and travels into T-butules
What happens after the depolatization in T-tubules
It stimulates sarcoplasmic reticulum to release Ca++
What is the third step of physiology?
Ca++ binds to troponin (proteins on actin filament) Which make it moves thus opening myosin binding site on actin
Describe the fourth step of physiology?
Movement of filaments (if there is a binding site available on actin)
a. activated myosin binds to actin release Pi
b. ADP released from myosin. Myosin head rotates actin filament movies = contraction
c. ATP binds to myosin detaches from actin
d. ATP hydrolyzed ADP + Pi –> activates myosin
What is the last step of physiology?
Contraction ends when Ca++ ions are pumped back into sarcoplasmic reticulum
