Exam 1 – Lecture 6: Dr Beasley Neuro-Muscular Flashcards
What does afferent mean?
Towards the central nervous system to control sensory input
What does efferent mean?
Away from the central nervous system to control motor output
What are the parts of a neuron?
Dendrite
Cell body
Axon
What does a dendrite do?
Input
What does an axon do?
Output
What are the 3 types of neurons?
Multipolar
Pseudounipolar
Bipolar
What does a multipolar neuron do?
Motor
What does a pseudounipolar neuron do?
Sensory
What does a bipolar neuron do?
Special sensory (smell and vestibular)
Where is a synapse?
Between axon:dendrite and axon:muscle
What makes up the peripheral nervous system?
Nerves, neuromuscular junction, muscles
What makes up the central nervous system?
Brain and spinal cord
What is a group of neurons called inside the CNS?
Nuclei
What is a group of axons called inside the CNS?
Tracts
What is a group of neurons called outside the CNS?
Ganglia
What is a group of axons called outside of the CNS?
Nerves
What does the brain receive signals from?
Body receptors
What are signals?
Afferent input from various receptors
What signals do exteroceptors do?
Touching
Nociceptors
What signals do proprioceptors do?
Stretching of muscles/joints/tendons
What gets signals from outside the body?
Extroceptors
What are the different exteroceptors?
Mechano-receptor Chemo-receptor Photo-receptor Thermo-receptor Nociceptor
What gets signals from inside the body?
Proprioceptors
What are the different proprioceptors?
Muscles
Tendons
Joints
What allows you to walk without tripping?
Tracts from the spinal cord to proprioceptors in the brain
What are the proprioceptors to cerebellum tracts that impact the forelimbs?
Cuneocerebellar tract
Rostral spinocerebellar
What are the proprioceptors to cerebellum tracts that impact the hindlimbs?
Dorsal spinocerebellar tract
Ventral spinocerebellar tract
What are the proprioceptors to cerebrum tracts that impact the forelimbs?
Fasciculus cuneatus
What are the proprioceptors to cerebrum tracts that impact the hindlimbs?
Fasciculus gracilis
What is proprioception? What does it require when testing exteroceptors?
Testing proprioceptors and mechanoreceptors
Brain input
Does testing proprioceptors with reflexes require brain input?
No
What is an example of normal sciatic hind limb reflexes?
When you hit the muscle bellies causing microstretching and it results in reflexive contraction
What sciatic nerve is associated with the cranial tibial?
Peoneal nerve
What sciatic nerve is associated with the gastroc?
Tibial nerve
What nerve is associated with withdrawal in the stifle and hock?
Sciatic
When testing exteroceptors, does pain sensation require brain input? Does withdrawal?
Yes
No
What is the difference between withdrawal and pain sensation?
Withdrawal is when you are using minimal pain. It is a reflex
Pain sensation requires conscious recognition of the pain
What are the 2 different types of motor systems?
Pyramidal system
Extrapyramidal system
Which motor system do humans use?
Pyramidal
What is the pyramidal system important in?
Higher species (primates) for fine motor control
What is the pyramidal system?
Direct connection of brain to area of spine which controls muscles
What is the extrapyramidal system important in?
Lower species
What is the extrapyramidal system?
Brain to brainstem to area of spine which controls muscles
Not a direct connection
What area of the spine controls muscles?
Ventral horn
How are signals transmitted?
Action potentials
How do we get action potentials?
There must be membrane potential
Why does membrane potential exist?
Because of electrical and concentration difference between the inside and outside of neuronal cell
Does the inside of the cell have more sodium or potassium than the outside?
Potassium
Does the outside of the cell have more sodium or potassium than the inside?
Sodium
What is membrane potential determined by?
Membrane permeability
Diffusion potentials
Na/K pump
Which has a higher permeability, K or Na?
K, 50x
How much more K is inside the cell than outside?
30x
What are cell membranes more permeable to?
Potassium
What is potassium exiting the cell based on?
Concentration gradients
What is sodium entering the cell based on?
Concentration and electrical gradients
What do energy dependent Na/K pumps do?
Expel Na in exchange for K to maintain concentration gradient
How much of the total energy requirements in resting state does the Na/K use?
1/3
When does the pump fire faster?
With increasing intracellular Na concentrations
What does sodium inside the cell determine?
Osmotic balance
If action potential continues for long periods of time, what happens?
Sodium enters the cell faster than it can be pumped out and water increases inside the cell
What does action potential do?
Uses concentration/voltage gradient to propagate a signal down the nerve
What is hyperpolarization?
A safe guard
What happens in action potential-depolarization?
Ligand gated Na channels open and allow Na to enter the cell. Membrane potential changes to a certain voltage and the voltage gate Na channels open allowing an influx of sodium to enter
What happens in action potential-repolarization?
Na channels close after a set amount of time
Na/K ATPase pumps go into overdrive
K channels open allowing K to leave the cell
What does overcompensation of K lead to?
Hyperpolarization
What does hyperpolarization do?
Keeps action potential going in one direction
How does nerve conduction flow?
Cell body, axon, synapse
What does myelin allow for in the myelinated axons?
Keeps from all sodium channels having to be open at once
What is the speed of conduction determined by?
Diameter/internal resistance
Membrane resistance/insulation
Capacity of membrane
What is myotonia?
Occurs when there are abnormalaties of channels
Inability to relax after voluntary muscle contraction (muscles all act at once)
What happens in Cushing’s disease?
There is too much steroid production
How can Cushing’s disease by diagnosed?
Electromyography
What is hyperkalemic periodic paralysis?
Horses, progeny of Impressive
Episodic muscle weakness and trembling
What is hypokalemic myopathy?
Decreased extracellular potassium causes increase in membrane potential
What is a synapse?
A connection between the nerve and muscle cell or nerve and another nerve
What is the synaptic cleft?
The space between the synaptic vesicle and the muscle membrane
What are the different parts of the synapse?
Axon terminal/Bouton
Presynaptic membrane
Synaptic cleft
Postsynaptic membrane
What is the process that occurs within the synapse?
Action potential reaches the bouton
Depolarization opens the voltage-gated Ca channels
Increased intracellular Ca causes exocytosis of synaptic vesicles releasing neurotransmitter into synaptic cleft
Neurotransmitter binds to the receptor on postsynaptic membrane
When the action potential travels down the axon, what happens?
It is opening the Na channels
What is the neurotransmitter inactivated by?
Diffusion
Enzymatic degradation
Reuptake transporter proteins
What drugs can alter the function of the synapse and how?
Prozac-selective serotonin reuptake inhibitors
Cocaine- inhibits dopamine reuptake transporter
How is acetylcholine made?
Choline and acetyl-coenzyme A via choline acetyltransferase
What are the neurons that make acetylcholine called?
Cholinergic neurons
What are the receptors for acetylcholine?
Ionotropic nicotinic (somatic) Metabotroic muscarinic receptors (autonomic)
What does a nicotinic receptor do?
Excitatory synaptic actions, opens Na channels in skeletal muscles
What does curare do?
Blocks nicotinic receptors and used to paralyze
What does alpha-bungarotoxin (snake venom) do?
Binds to nicotinic receptors and blocks the effect of acetylcholine
What does a muscarinic receptor do?
Inhibitor or excitatory of smooth muscles
What are examples of antagonistic muscarinic receptors?
Atropine and scopolamine
What happens in the neuromuscular junction?
Ach is released and the Ach receptors at the top of subneural cleft let Na in
What is the voltage gated Na at the bottom of the subneural cleft triggered by?
Influx of Na from Ach channels
What are the 5 subunits of the Ach receptor?
2 alpha
Beta
Delta
Gamma
How many Ach attach to the 2 alpha subunits of the Ach receptor?
2 (one on each)
What is the most common ion to flow through to the intracellular location?
Na
What does the attachment of Ach to the alpha subunits cause?
An influx of Na triggering action potential
What does botulism toxin do?
Decreases release of Ach from presynaptic membrane
What does botulism toxin cause?
Flaccid paralysis
Muscle weakness
Tongue weakness
GI paralysis
What happens during Myasthenia gravis?
Antibodies are made against Ach receptors and Ach can’t bind
How can myasthenia gravis be treated?
Achesterase inhibitors
What do achesterase inhibitors allow for?
Ach to stay in synaptic cleft longer to find any remaining Ach receptors that haven’t been attacked yet
What is myasthenia gravis a disease of?
Skeletal muscle
What causes tick paralysis?
Dermacentor andersoni and variabilis
Engorged female tick
What happens when the female tick bites an animal?
It inhibits the release of Ach which leads to rapid paralyses and absent reflexes
How can tick paralysis be treated?
Removal of the tick
What is a motor unit?
A single motor neuron innervating a few or many muscle fibers
What does a small motor unit allow for?
Precise control (extraocular muscles)
What does a large motor unit allow for?
Coarse control (quadriceps muscle)
What is the muscle fiber membrane called?
Sarcolemma
What is actin also known as?
Thin filaments
What is actin connected to?
Z disks
What is myosin also known as?
Thick filaments
What does myosin do?
Articulates with the actin filaments
Look at the anatomy of a myofibril
Look at the anatomy of a myofibril
What does the I band contain?
Actin
What does the A band contain?
Myosin and actin
Where is the Z disk located? What does it do?
At the end of actin
Anchors
What is the portion of myofibril between 2 Z disks known as?
Sarcomere
What is the suspended portion in intracellular matrix called?
Sarcoplasm
What does the sarcoplasm contain?
Mitochondria and saroplasmic reticulum
What is myosin made of?
2 heavy chains (MW 200, 000)
4 light chains (MW 20, 000)
Head region
What is the head region of myosin the site of?
ATPase activity
What do the tails of many myosin do?
Bundle together to make the body of the myosin filament
What attaches the actin filament to myosin?
The heads that have an arm stick out to the side for attachment
What makes up actin?
Tropomyosin and troponin
What does tropomyosin do?
Covers active sites
Prevents interaction with myosin
What are the 3 types of troponin?
I, T, and C
What does troponin I do?
Binds actin
What does troponin T do?
Binds tropomyosin
What does troponin C do?
Binds calcium
What happens when calcium is released by the sarcoplasmic reticulum?
Troponin makes tropomyosin stop covering active sites so actin and myosin can bind
What does contraction of muscle result from?
The sliding action of interdigitating actin and myosin filaments
What are transverse tubules?
Invaginations of the sarcolemma filled with extracellular fluid
What do transverse tubules do?
Penetrate the muscle fibers, branch and form networks
Transmit action potentials deep into the muscle fiber
What is the sarcoplasmic reticulum?
Intracellular storage compartment for calcium
What causes the sarcoplasmic reticulum to release calcium?
Action potential in T-tubules cause opening of Ca channels and release of Ca
What is hypocalcemia?
Decreased calcium in blood and interstitial fluid
What does hypocalcemia do?
Lowers threshold for evoking action potential
What is hypercalcemia?
Increased Ca in blood and interstitial fluid
What does hypercalcemia do?
Increases threshold for evoking action potential
Describe type 1 fibers
Slow twitch
High oxidative enzymes
Low glycogen
Aerobic metabolism
Describe type 2 fibers
Fast twitch
Lesser oxidative enzymes
High glycogen
Anaerobic metabolism
Where are type 2M fibers found?
Masticatory muscles
Describe how ATP replenishment can occur via glycogen
Breaks down to pyretic acid and lactic acid, which liberates NRG
Can occur in absence of O2
Get 1-2 per minute
What is needed for ATP replenishment via oxidative metabolism? How long can it take to get ATP?
O2 plus foodstuffs
Hours
What kind of muscle fibers do marathon runners need more of? Sprinters?
Slow twitch
Fast twitch
What is tetanus?
Muscle spasms caused by inhibition of the release of inhibitory neurotransmitters, so only excitatory neurotransmitters are acting
