KIN 101 Midterm 2 Flashcards
CNS
CNS: Central Nervous System
- Consists of
○ Brain
○ Spinal cord
PNS
PNS: Peripheral Nervous System
- Consists of
○ Sensory division (afferents)
○ Efferent division (motor neurons)
PNS (Efferent division - Parasympathetic)
Parasympathetic: Rest
Controls: Cardiac muscle, smooth muscle,
exocrine glands/cells, some endocrine
glands/cells, some adipose tissue
Triggers tissue responses
PNS (Efferent division - Sympathetic)
Sympathetic: “Fight or Flight”
Controls: Cardiac muscle, smooth muscle,
exocrine glands/cells, some endocrine
glands/cells, some adipose tissue
Triggers tissue responses
Enteric Nervous System:
Enteric Nervous System:
network of neurons in the walls of the digestive
tract that controls gastrointestinal behavior
(Controlled by the autonomic nervous system but
is also able to function autonomously)
Neurons/Glial cells (two types of cells in the nervous system)
Nervous system is made up of two cells
- Neurons: the basic signaling units of the
nervous system
○ Neurons carry electrical signals
○ Known as functional units
- Glial cells/glia/neuroglia: support cells.
Nerves
Nerves: axons bundled with connective tissue
- There are sensory, motor and mixed nerves.
Neuron Classes (Myelinated Somatic)
Myelinated with a central nucleus
For somatic senses
Pseudounipolar:
Have a single process called the
axon, during development the
dendrite is fused with the axon
Neuron Classes (Unmyelinated Somatic)
Unmyelinated with a central nucleus
For vision and smell
Bipolar:
Have two relatively equal fibers
extending off the central cells of the
body
Neuron Classes (Interneurons)
- Have one central nucleus and dendrites branch out
in all directions
□ Anaxonic:
Interneurons have no apparent
axon
□ Multipolar:
Interneurons are highly branched but
lack long extensions
Neuron Classes (Motor neurons)
- Regular (to me) neurons
□ Multipolar:- Efferent neurons have 5 to 7 dendrites that
each branch 4 to 6 times. - A single long axon may branch several times
and end at enlarged axon terminals
- Efferent neurons have 5 to 7 dendrites that
Axon hillock (Neuron Anatomy)
Axon hillock: where axon begins and where action potential is produced
Dendrites (Neuron Anatomy)
Dendrites: input signal
Cell body (Neuron Anatomy)
Cell body: the control center and is the site for integration of electrical signals and protein synthesis
- (where summation occurs)
Presynaptic axon terminal (Neuron Anatomy)
Presynaptic axon terminal: output signal
Axonal transport (Definition)
Axonal transport: the process of moving proteins synthesized by the cell body in vesicles down the axon.
Axonal transport (Fast axonal transport)
Fast axonal transport:
- Moves organelles at a rate of up to 400 mm/day
- Fast is protein mediated
- Anterograde transport: from cell body to axon
terminal
- Retrograde transport: from axon terminal to cell
body
Axonal transport (Slow axonal transport)
Slow axonal transport:
- Moves material by axoplasmic (cytoplasmic)
flow at a rate of 0.2-2.5 mm/day
Establishing synapses (Growth cones)
Growth cones: allow developing neurons to find their targets.
- Growth factors, molecules in the extracellular
matrix, membrane proteins all help growth
cones work to help the neuron grow
Establishing synapses (Neurotrophic factors)
Neurotrophic factors: allow developing neurons to survive.
Establishing synapses (Are synapses fixed?)
Synapses are also not fixed to one place for life as they can be rearranged
- Synapse formation must be followed by
electrical and chemical activity, or the synapse
will disappear
- Neuroplasticity: Variations in activity can cause
the rearrangement of synaptic connections, this
occurs through life.
Glial Cells (glue)
Glial cells (glue): are said to be the unsung hero’s of the nervous system. They are also supportive
○ They outnumber neurons by 10-50 to 1
Glial cells (PNS - Satellite Cells)
Satellite cells (PNS): are non myelinating Schwann
cells that form capsules around
nerve cell bodies that are
located in the ganglia
Ganglion
Ganglion: collection of nerve cell bodies outside of the
CNS
Glial cells (CNS - Ependymal cells)
○ Ependymal cells
§ Create barriers between compartments
§ Form the ependyma which separates parts of
the nervous system
§ Are a source of neural stem cells
Glial cells (CNS - Astrocytes)
○ Astrocytes (CNS):
§ Take up K+, water and neurotransmitters
§ Secrete neurotrophic factors
§ Help form the blood and brain barrier
§ Provide substrates for ATP production
§ Source of neural stem cells
Glial cells (CNS - Microglia)
○ Microglia (modified immune cells)
§ Act as scavengers
Glial cells (CNS - Oligodendrocytes)
○ Oligodendrocytes
§ Form myelin sheaths (form one long one)
Glial cells (PNS - Schwann cells)
○ Schwann cells
§ Form myelin sheaths (multiple along the axon)
§ Secrete neurotrophic factors
§ Wrapping motion on the axon (nucleus within)
Steps of Repair of an Axon (step 1-3)
- If the cell body dies the cell dies
- In the axon, Axoplasm leaks out triggering
events to seal the damaged end - Schwann cells release chemical signals alerting
of tissue damage
- In the axon, Axoplasm leaks out triggering
Steps of Repair of an Axon (step 4-6)
- In the distal axon the myelin sheath unravels and the
axon degenerates
○ The debris from this is removed by
microglia and phagocytes in about one month - These axons in the PNS can regenerate and re-
establish synaptic connections
(this is unlikely in the CNS) - Schwann cells secrete neurotrophic factors to keep
the body alive and encourage axon regeneration, the
axon then behaves again like a growth cone and
navigates its way back together
Steps of Repair of an Axon (step 7)
- Sometimes loss is permanent and the pathway
is destroyed
○ If this is a motor neuron it may result in
permanent paralysis
○ If this occurs in a sensory neuron there is
a loss of sensation from the innervated area
RMP
RMP: the resting membrane potential and this causes
selectively permeable ion channels which
permit specific ions through
Nernst Equation
Nernst equation: predicts the membrane potential of a
typical cell if the membrane were
permeable only to one ion
(The number represents the equilibrium potential)
(Permeability does not matter in this equation)
Equilibrium potentials (Sodium/Potassium)
Equilibrium potential for Na+ is +60mV (most outside)
Equilibrium potential for K+ is -90mV (mostly inside)
Goldman-Hodgkin-Katz Equation
- Takes into account permeability of an ion channel
- Is negative at rest
- Is positive when action potential occurs
Ion concentrations (In action potential)
- Resting state = large potassium within (-70mV)
- Depolarization = sodium enters within (-55mV)
- Repolarization = Na+ leaves K+ enters (-70mV)
- Hyperpolarization = Too much K+ enters (-90mV)
Gated Channels (Mechanically gated channels)
- Mechanically gated
○ Respond to physical force such as pressure or
stretch
Gated Channels (Chemically gated channels)
- Chemically gated channels (most in nervous system)
○ Respond to a variety of neurotransmitters and
neuromodulators or intracellular signals
Gated Channels (Voltage-gated Channels)
- Voltage-gated channels (most in nervous system)
○ Respond to changes in the cells membrane
potential.
Electrical signals (Graded potentials)
- Graded potentials: (work off summation)
○ Variable strength signals that travel over short
distances in the dendrites and cell body and
lose strength (aptitude) over time
- use voltage and chemically gated channels
- can be excitatory or inhibitory
- the results of are what cause action potential
- if they are more negative K+ leaves (inhibitory)
- if they are more positive Na+ enter (excitatory)
Electrical signals (action potentials)
- Action potentials (essentially what happens in the
axon hillock)
○ Brief large depolarizations that travel for long
distances (such as brain too toe) without losing
strength
○ Regenerate as they travel down the axon
- only use voltage gated channels
Graded potential (Two types - Subthreshold)
- Subthreshold graded potentials
○ A graded potential starts above the threshold at
its initiation point but decreases in strength as it
goes along. At the trigger zone it is below
threshold and therefore does not initiate an
action potential
Graded potential (Two types - Suprathreshold)
- Suprathreshold graded potentials
○ A stronger stimulus at the same point on the
cell body creates a graded potential that is still
above the threshold so by the time it reaches
the trigger zone it triggers the action potential
Axonal Na+ channels
Activation gates (the plate)
- Open rapidly
- Initiate the action potential
Inactivation gates (the ball)
- Close more slowly
- This terminates the action potential
- Causes the absolute refractory period
- Prevents action potentials from travelling
backwards
Refractory periods (Absolute - happens first)
Absolute refractory period: (Make hard to produce)
starts at the point the threshold is reached and
lasts until hyperpolarization reaches its low
Refractory periods (Relative - happens second)
Relative refractory period: (Don’t fire during)
starts when hyperpolarization begins to head back
towards resting membrane potential
Soma
Soma: main body of the cell
Factors to Conduction Speed (Two factors)
Two factors that influence conduction velocity
- Axon diameter
○ The larger the diameter of the axon the faster it will move
- The resistance of the membrane to ion leakage
○ The less leakage the faster it travels
(Speed is also influenced by myelin sheathes by increasing resistance - reduces ion leakage)
Saltatory Conduction
Saltatory conduction: when action potentials only occur at the nodes of Ranvier as they jump past large patches of membrane
Neurocrines (Two types)
Neurocrines
- Neurotransmitters and neuromodulators act as
paracrine with their target cells located close to
the neuron that secretes them
- Neurohormones are secreted into the blood and
distributed throughout the body
Neurocrine receptors (Two types - Ionotropic)
- Ionotropic receptors: open when a ligand
(neurocrine) binds to them (ligand gated-
chemical gated) then ions move across the
membrane. This mediates rapid responses
Neurocrine receptors (Two types - Metabolic)
- Metabotropic receptors: signal is transduced
through a G protein coupled second messenger
system. (these responses are slower)
Neurocrines cause
Responses possible:
- Excitatory post-synaptic potential (ECSP)
depolarization
- Inhibitory post-synaptic potential (IPSP)
hyperpolarization
- Other intracellular events like protein synthesis
can also occur.
Common Neurotransmitters
- Acetylcholine (ACh): neurons that secrete ACh and
receptors that bind ACh are cholinergic. - Glutamate: the main excitatory neurotransmitter of
the CNS they depolarize their target cells usually by
opening ion channels that allow the flow of positive
ion in - Gamma-aminobutyric acid: works by opening
chloride ions
Reserve pool
Neurotransmitters stored in vesicles that are farther from the synaptic cleft
Neurotransmitter release (What causes it?)
Ca2+ ions, action potentials.
Neurotransmitter termination (What removes them?)
blood vessels, glial cells
Acetylcholine (what happens to it after?)
- Acetophenone is synthesized in the presynaptic
vesicle - Once it reaches the post synaptic vesicle it becomes
acetylcholinesterase
Divergent pathway
Divergent pathway: one presynaptic neuron branches to affect a larger amount of postsynaptic neurons
- One response leads to multiple others that go
further
Convergent pathway
Convergent pathway: one presynaptic neuron branches to affect a larger amount of postsynaptic neurons
- Multiple signals can amplify the affects and
bring a neuron to threshold that otherwise
wouldn’t fire
Synaptic responses (Speed)
Fast synaptic responses:
ionotropic channels = ligand binds to receptor
and things flow
Slow synaptic potentials:
metabotropic channels = use Gproteins
Summation
When one or more signals add together
Summation occurs
- When the first one doesn’t have time to decay
- When they reach each other close enough in
time
- Called integration
- Temporal summation (adding together in time)
- Spatial summation (adding together from
different spaces)
Inhibitions (Two places they occur)
Global inhibition: the inhibition is happening at the top of the cell body
- Affects all targets
- No effects occur
- Nonselective
Presynaptic inhibition: when it occurs only at the presynaptic cleft
- Only on one terminal
- Effects still occur
- Selective
Long term potentiation
Long term potentiation: can be strengthened
- Glutamate is key in this
- Glutamate binds to
○ NMBA receptors (unique in that there is a
magnesium ion imbedded in its receptor)
When the magnesium leaves calcium can
then go in
○ AMPA receptors (allow in sodium in which
pushes out the magnesium making a new
receptor available)
Grey Matter
Made up of:
- Interneurons
- Unmyelinated nerve bodies
- Dendrites
- Axons
- Terminals
White matter
Made up of:
- Myelinated axons
- Very few cell bodies
- bundles of axon connecting regions called tracts
(Similar to nerves in PNS)
Cranium
Cranium: protects the brain
Meninges
Meninges:
- Dura mater
- Arachnoid membrane
- Pia Matter
Vertebral column
Vertebral Column: where the spinal cord runs through
Cerebrospinal fluid (CSF)
Cerebrospinal fluid (CSF):
- Surrounds the brain
- Produced by the Choroid Plexus in walls of the
ventricles
- Is constantly produced and replaced by the
arachnoid membrane 3 times a day
- Provides a means for wastes to be excreted
The BBB
The BBB:
- A functional barrier between the interstitial fluid and
the blood with highly selective permeability
- Promoted by Astrocytes
- Supply the brain with the oxygen and glucose it
needs to survive
- Can remove toxins from the brain
Transcutaneous Spinal Cord Stimulation:
Transcutaneous Spinal Cord Stimulation:
- Placing stimulants on cervical spinal nerves
- Placing stimulants on lumbar spinal nerves
- This allows us to move the patients arms and legs
Spinal cord
Spinal cord:
- Used for communication between the brain and rest
of body
- 4 regions
- Cervical spinal nerves
- Thoracic spinal nerves
- Lumbar spinal nerves
- Sacral spinal nerves
Spinal cord (2 Roots)
Dorsal root: sensory information into the spinal cord.
Ventral root: where information exits to stimulate muscles and glands.
Spinal cord (3 Horns)
(All in the grey matter)
- Dorsal horns: Visceral and somatic sensory nuclei
- Lateral horns: Autonomic motor nuclei
- Ventral horns: Somatic motor nuclei
Spinal cord (The white matter)
- Ascending tracts: take sensory info to the brain
- Descending tracts: Carry motor signals from the
brain - Propriospinal tracts: stay within the cord
Corpus collosum
Connects the left and right hemispheres
Cranial nerves
Cranial nerves: carry sensory and motor information from the head and neck
Midbrain, pons, medulla
Midbrain: Eye movement
Pons: Relay between Cerebrum and cerebellum
- Coordination of breathing
Medulla oblongata: Controls involuntary functions
Cerebellum
Cerebellum (little brain): coordinates muscle
movement and balance
- Intakes sensory feedbacks and can tell whether the
right movement is being made
Diencephalon
Diencephalon (between brain): Between the brain
stem and the cerebrum.
Consists of:
- Thalamus: Integration center in relaying information
sensory and motor
- Hypothalamus: Control homeostasis for behavioral
drives (like hunger, thirst) and
influences autonomic endocrine
function
The Two Endocrine Glands
Pituitary and Pineal gland
3 Regions of grey matter
- Cerebral cortex: the thin outer layer of cells in
distinct layers- Limbic system: the link between cognition and
emotions
○ Amygdala and Cingulate Gyrus:
§ Emotion and regulation
○ Hippocampus:
§ Learning and memory - Basal Ganglia (inner brain): control of
movement
- Limbic system: the link between cognition and
3 Systems of Control
Sensory system: monitors internal and external environments, initiates reflex responses
Cognitive system: initiates voluntary responses
Behavioral state system: governs sleep-wake cycles and other intrinsic behaviors
Four lobes (Frontal)
- Frontal lobe: coordinates information from other
association areas, controls some
behaviors
○ Skeletal muscle movement
§ Motor association
§ Primary motor cortex
○ Prefrontal association area
Four lobes (Parental lobe)
- Parietal lobe: sensory information from skin,
musculoskeletal system, viscera, taste
buds
○ Primary somatic sensory cortex
○ Sensory association area
Four lobes (Occipital lobe)
- Occipital lobe: vision
○ Visual association area
○ Visual cortex
Four lobes (Temporal lobe)
- Temporal lobe
○ Smell: Olfactory cortex
○ Hearing: auditory cortex and auditory
association area.
Gustatory cortex/Insula
Gustatory cortex: senses and interprets taste
Insula: the deep cortical region that lies beneath the
lateral sulcus
3 Governing systems of the CNS (Skeletal muscle movement)
- Coordinates skeletal movement via the somatic motor division (voluntary movements are coordinated by the primary motor cortex and motor association areas
3 Governing systems of the CNS (Neuroendocrine signals)
- Sends neuroendocrine signals via the blood coordinated by neurons located primarily in the hypothalamus and adrenal medulla
3 Governing systems of the CNS (Visceral responses)
- Sends visceral responses through the actions of smooth and cardiac muscle or endocrine and exocrine glands governed by the autonomic division of the nervous system
(they are still primarily from the hypothalamus and medulla)
What can Motor output be modulated by?
(Motor output can be modulated by the behavioral state system. Diffuse neuromodulatory systems project to large areas of the brain and regulate function by influencing attention, motivation, wakefulness, memory, motor control, mood, and metabolic homeostasis)
Wernicke’s Area
Wernicke’s area: understanding language
- Receptive aphasia (unable to understand
sensory input)
Broca’s Area
Broca’s area: produces speech
- Expressive aphasia (unable to understand
complicated sentences with multiple elements,
difficulty speaking words or writing normally)
Somatic motor pathway (process involved)
- Somatic motor pathway
§ CNS -> Ach to nicotinic receptor.
Autonomic motor pathway (Parasympathetic - Process involved)
○ Parasympathetic pathway
§ CNS -> ACh to Nicotinic receptor (in ganglion) ->
ACh to muscarinic receptor -> autonomic targets
Autonomic motor pathway (Sympathetic - process involved)
○ Sympathetic Pathways
§ CNS -> ACh to nicotinic receptor (in ganglion) ->
norepinephrine to alpha receptor and beta receptor
-> autonomic targets
Autonomic motor pathway (Adrenal Sympathetic Pathway - Process involved)
○ Adrenal sympathetic pathway
§ CNS -> (into adrenal cortex and into adrenal
medulla) ACh -> epinephrine (exits adrenal cortex)
-> (enters blood vessel and exits when at target) ->
Epinephrine binds to beta 1 and beta 2 receptor
-> autonomic targets
Homeostasis (In regards to the autonomic branches)
Homeostasis: the dynamic balance between the autonomic branches
Ways motor output can be expressed
Motor output can be expressed by
- Autonomic responses
- Endocrine responses
- Behavioral responses
Where are integrated homeostatic control centers found?
Input signals are integrated in homeostatic control centers that are found in
- Hypothalamus
- Pons
- Medulla
Where does sensory input come from?
Sensory input comes from receptors in
- Hypothalamus
- Viscera
- Somatic receptors (muscles, joints, skin)
What do autonomic control centers regulate?
Autonomic control centers regulate
- Water balance
- Temp
- Hunger
- Respiration
- Cardiac
- Vomiting
- Swallowing
Antagonistic control
Governs most organs in the autonomic division
- Most internal organs feature this (one
excitatory, one inhibitory branch)
- Some have exceptions and are dual
antagonistically controlled
○ Sweat glands and smooth muscle on blood
vessels
§ Only sympathetic innervation; tonic control
○ Cooperative control
§ Work on different tissues to achieve a
common goal
Two Efferent Ganglions (Postganglionic)
Postganglionic neuron
- Cell body located in the ganglion
- Projects from ganglion to target
- Synapses with target
Two Efferent Ganglions (Preganglionic)
Preganglionic neuron:
- Cell body located in the CNS
- Projects to an autonomic ganglion outside of
the CNS
- Synapses with a postganglionic neuron
The neuroeffector junction
The neuroeffector junction: the synapse between postganglionic autonomic neurons and the target cell
How are sympathetic and Parasympathetic different (Release signals)
- Sympathetic: releases Norepinephrine
- Parasympathetic: releases ACh
- (some exceptions to both apply)
How are sympathetic and Parasympathetic different (neurons)
Sympathetic neurons:
- In the middle of the spinal cord
- Ganglia are close to spinal cord
Parasympathetic neurons:
- On the top and bottom of spinal cord
- Ganglia are close to tissue
(This means there are short preganglionic and long postganglionic neurons in the sympathetic system and long preganglionic and short postganglionic neurons in the parasympathetic system)
Varicosity
Varicosity: a series of swollen areas at the distal ends of the postganglionic axon that
- Contain vesicles filled with neurotransmitter
- Site of neurotransmitter release and synthesis
- (they are not usually located next to receptors
but release to defuse to receptors)
Adrenal medulla (Charactaristics)
Adrenal medulla: a modified sympathetic ganglion and
- Is a specialized neuroendocrine tissue
- Part of the sympathetic nervous system
- Primary neurohormone released is epinephrine
- Has multiple and distant targets
(adrenal cortex and adrenal medulla fuse together during development)
Somatic motor pathways (Charactaristics)
A somatic motor pathway consists of one neuron and:
- It originates in the ventral horn of the spinal
cord
○ (NEVER DOES A MOTOR NEURON
PROJECT FROM THE BRAIN TO MUSCLE)
- Myelinated, long and always excitatory
- Powerful synapses that are always a 1:1
relationship between motor neuron discharge
and muscle fiber discharge
- Axon branches close to target and each
terminal innervates a single skeletal muscle
fiber (target)
Neuromuscular junction (NMJ)
Neuromuscular junction (NMJ)
- Synapse between somatic neuron and skeletal
muscle fiber
- ACh binds to nicotinic ACh receptor
The neuromuscular junction (NMJ) consists of:
- Axon terminals
- Motor end plates on the muscle membrane
- Schwann cell sheaths
Motor unit
Motor unit: A somatic neuron and all the muscle fibers it innervates
Neuromuscular junction (NMJ) (Anatomy)
- The nicotinic cholinergic receptor binds two ACh
molecules - This opens a nonspecific monovalent cation
channel - The channel allows Na+ and K+ to pass through
- This depolarizes the cell
(Botox paralyzes your neuromuscular junction which in turn removes wrinkles but keeps the neuromuscular junction inactive.)
Motor unit recording (electromyography)
Motor unit recording (electromyography):
- Inserting wire electrodes into the muscle to
control somatic nerve activity during a
contraction because of the 1:1 relationship
between motor neuron and the muscle fiber
discharge.
- From this we can learn about what is going on
in the spinal cord
Skeletal muscle (Charactaristics)
- Skeletal muscle:
○ Fibers are large multinucleate cells that appear
striped or striated under the microscope
○ Attached to and moves bones via the
somatic system
Types of muscle forces
Types of muscle forces
- Flexion
○ Moves bones closer together (arm curls)
- Extension
○ Moves bones further from each other
(push up)
Origin
Origin: closest to the trunk or more stationary bone or
joint
Insertion
Insertion: more distal or more mobile attachment of a
joint
Antagonistic muscle groups
Antagonistic muscle groups: move muscle bones in opposite directions
Skeletal muscles (Composition)
Skeletal muscles are composed of:
- Muscle fibers
○ Long and cylindrical
○ Fused together with many nuclei
- Satellite cells (stem cells)
○ Differentiate into muscle for growth or repair
- Fibers bundled into fascicles
○ Surrounded by connective tissue sheath
- Connective tissue surrounds the entire muscle
○ Continuous connective tissue sheath
○ Holds muscle to bone with tendons
Muscle fascicle
Muscle fascicle: a group of muscle fibers
Sarcolemma
Sarcolemma: muscle membrane fibers that carries action potentials along fibers
T-tubules
T-tubules: carry action potentials deep into muscle fibers
Sarcoplasmic reticulum
Sarcoplasmic reticulum: collects and stores Ca2+
Muscle cells (amount of nucleus)
Muscle cells have multiple nucleus that that contain many myofibrils.
General terms = Muscle equivalents
Cell membrane = sarcolemma
Cytoplasm = sarcoplasm
Modified endoplasmic reticulum = Sarcoplasmic
reticulum
General terms = Muscle equivalents
Cell membrane = sarcolemma
Cytoplasm = sarcoplasm
Modified endoplasmic reticulum = Sarcoplasmic
reticulum
Sarcomere
Sarcomere: the basic contractile unit of muscle and has a straightened pattern of light and dark bands
A-band (myosin)
A-band (myosin): dark bands along the whole length of a thick filament
- Essentially the myosin (filament that travels up
the actin)
(A-band does not change in width nor do filaments)
M-line
M-line: connection between adjacent thick filaments
- The farthest point into an actin tube
I-band
I-band (actin only): light colored bands show the region occupied by thin filaments
- Region that exists only when myosin filaments
aren’t fully within the actin
H-zone (no actin)
H-zone(no actin): central part of A-band, gap between thin filaments
- Region that only exists when Myosin filaments
aren’t fully within actin (distance between two
actin ends)
Z-disks
Z-disks: attachment sites for thin filaments
- area from one center of an actin to another
(Z-disks get closer together and H-zone and I-band narrow as filaments overlap)
Myosin crossbridge
Myosin crossbridge: branches of the A-band that that pull up into the Z-disks
Myosin filaments
Myosin filaments: A-bands
Thick filaments
Thick filaments: made up of about 250 myosin molecules
Hinge region
Hinge region: joins the myosin heads and myosin tail
Myosin head
Myosin head: has one actin binding site and one ATP binding site
Tropomyosin
Tropomyosin: wraps around actin filaments and in resting skeletal muscle and prevents actin and myosin from generating force
Troponin
Troponin: has a binding site for Ca++ and controls positioning tropomyosin and thus the binding between actin and myosin
G-actin molecule
G-actin molecule: has one myosin binding site
- Multiple of these form together to create F-actin
molecules
- Two F-filaments twisted together form the thin
filament
Titan
Titan: spans the distance from one Z-disk to the
neighboring M-line.
- Provide elasticity and stabilizes myosin
Nebulin
Nebulin: lie along the thin filaments, attaches to a Z-
disk but doesn’t extend to the M-line
Muscle tension
Muscle tension: force created by muscle
Load
Load: weight or load opposing contraction
- Contraction: creation of tension in muscle
- Relaxation: release of tension
Steps of muscle contraction
- Events occur at the neuromuscular junction
that send action potentials- Muscle action potentials trigger calcium
release - Calcium release initiates the contraction-
relaxation cycle - The filaments then slide and contraction is
produced - Muscle twitch or full muscle contraction occurs
- Muscle action potentials trigger calcium
Contraction
Contraction: calcium release causes filaments to slide and thus sarcomeres shorten
Relaxation
Relaxation: calcium transported back into SR, then filaments uncouple, sarcomeres then lengthen
What stages in action potentials does muscle action occur?
Contraction is when depolarization occurs
Relaxation is when the refractory period takes place
Steps in muscle movement (1-3)
- Cytosolic calcium levels rise
- Calcium binds to troponin
- The binding of troponin and Ca2+ pulls the
tropomyosin away from the actin and myosin
binding site to expose it
Steps in muscle movement (3-8)
- Myosin binds to the action and creates a “power
stroke” - ATP binds to myosin to release from the actin
- The myosin hydrolases ATP into ADP and Pi
- The leaving of the Pi allows the head to make
another power stroke - After the stroke ADP leaves allowing for ATP to
rebind to the myosin
3 Uses of ATP within muscle contraction
3 Uses of ATP within muscle contraction:
- Energize the cross bridges: hydrolysis of ATP by myosin provides energy for producing force
- Unbind: the cross bridge from actin: frees cross-bridge for another cycle (without ATP the bridge stays locked this can be identified by rigor mortis)
○ When we die
- Provide energy for active Ca2+ transport from cytosol into the sarcoplasmic reticulum (this ends contraction)
Contraction of muscle initiation
- Acetylcholine is released from somatic motor
neuron - Acetylcholine initiates an action potential in the
muscle fiber - The muscle action potential triggers calcium
release from he sarcoplasmic reticulum - Calcium combines with troponin to initiate
contraction
Where does calcium go back into durring relaxation?
Calcium gets pumped back into the sarcoplasmic reticulum
when is ATP required? (Muscle contraction/relax)
Muscles require a steady supply of ATP
- Durring contraction for the cross bridge
movement and release
- Durring relaxation to pump Calcium back into
the sarcoplasmic reticulum
- After contractions to restore and maintain the
balance of Na and K
How many twitches can be produced by readily available ATP?
There is only enough “free” ATP to produce 8 twitches of the muscle
Two types of fatigue (Peripheral)
Peripheral fatigue: includes the neuromuscular junction and muscle
- Extended submaximal exercise leads to
depletion of glycogen stores
- Short duration maximal exertion leads to
increased levels of physical activity
- Maximal exercise leads to ion imbalances
Two types of fatigue (Central)
Central fatigue: happen in the CNS and can be things such as motivation
