RA6 Nervous System and Muscle Flashcards
Divisions of the nervous system
Central nervous system: Brain and spinal cord
Peripheral nervous system:
- Sensory (afferent) vs motor (efferent)
PNS Motor:
- Somatic (voluntary ) vs autonomic (involuntary)
Autonomic nervous system:
- Sympathetic (fight or flight) vs parasympathetic (rest and digest)
- Enteric (digestive system)
Central Nervous System (CNS)
- Consists of?
- Dervied from?
- Brain and spinal cord
- Derived from neural plate
Peripheral Nervous System (PNS)
- Consists of?
- Derived from?
- Nerves and ganglia that lie outside the brain and spinal cord
- Derived from neural crest
PNS:
Somatic vs autonomic nervous system
- Controls what kind of movement?
- Composed of how many neurons?
Somatic:
- Controls voluntary movement of skeletal muscles
- Composed of a single neuron that synapses directly onto the target
Autonomic
- Controls involuntary movement of smooth muscles, cardiac muscles, and glands
- Composed of two neurons in series with a single synpase before synapsing onto the target
ANS: Parasympathetic vs sympathetic nervous system
- Function
- What kind of nerves?
- What kind of neurotransmitters?
Parasymapthetic:
- “Rest and digest”
- Craniosacral nerves
- Cholinergic: acetylcholine
Sympathetic:
- “Fight of flight”
- Thoracolumbar nerves
- Noradrenergic: norepinephrine - except sweat glands (cholinergic: acetylcholine)
Enteric nervous system
- What does it innervate?
- Function?
- Regulated by?
- Innervates the gastrointestinal tract, pancreas, and gall bladder
- Independently controls peristalsis, absorption, and secretion of fluids and enzymes
- Regulated by both sympathetic and parasympathetic systems
Nissl bodies
Rough endoplasmic reticulum in neurons
Dendrites
1. Function?
2. Organelles?
3. Myelinated?
4. Generate what kind of potential?
5. Specialised structures?
- Signal reception
- Typical cytoplasmic elements, RER/SER, ribosomes, Golgi apparatus
- NOT myelinated
- Generate graded potentials
- Form dendritic spines: specialised postsynaptic strutures
Axons
1. Function?
2. Organelles?
3. Myelinated?
4. Generate what kind of potential?
5. Specialised structures?
- Signal conduction
- Few organelles, only has SER
- May be myelinated or unmyelinated
- Generate action potentials
- Form axon terminals: presynaptic sites containing synpatic vesicles
Axon hillock
1. Function?
2. Organelles?
3. Myelinated?
4. Generate what kind of potential?
- Signal integration
- Few organelles
- NOT myelinated
- Subject to graded potentials
Synaptic transmission
- Action potnetial reaches terminal
- Voltage-gated Ca2+ channels open
- Influx of Ca2+ induces vesicle docking (a) and/or formation of pore complex (b)
- Neurotransmitter released into synaptic cleft
- Neurotransmitter binds to receptors/channels on postsynaptic membrane
- Neurotransmitter removed from cleft via degredation (e.g. acetylecholinesterase) or re-uptake (e.g. serotonin)
Anterograde axonal transport
1. Fast or slow?
2. Utilises what motor protein?
3. + or - end directed?
- Can be fast or slow
- Utilises kinesins
- Generally + end directed
Retrograde axonal transport
1. Fast or slow?
2. Utilises what motor protein?
3. + or - end directed?
- Generally fast only
- Utilises dynein
- Generally - end directed
Glial cells
Non-neuronal cells that provide physical and chemical support to neurons and maintain their environment
Types of glial cells
1. PNS: 2 types
2. CNS: 4 types
PNS (nerual crest derived):
1. Schwann cells
2. Satellite cells
CNS (neural plate derived):
1. Oligodendrocytes
2. Astrocytes
3. Microglia
4. Ependymal cells
Schwann cells
1. Location?
2. Derived from?
3. Function?
- Located in the PNS
- Derived from neural crest
- Insulate peripheral axons by forming myelin sheath
- One Schwann cell can ensheath how many axons?
- One Schwann cell can myelinate how many axons?
- One Schwann cell can ensheath (but not myelinate) multiple axons.
- One Schwann cell can only myelinate ONE axon.
Myelination requires vitamin (…)
Myelination requires vitamin B12
Function of myelin sheath
Insulate axons and enable saltatory conduction
Nodes of Ranvier
Axonal regions between adjacent Schwann cells not covered by myelin sheath
Satellite cells
1. Location?
2. Derived from?
3. Function?
- Located in the PNS
- Derived neural crest
- Surround the cells bodies in PNS ganglia and maintain their surrounding envrionment
Oligodendrocytes
1. Location?
2. Derived from?
3. Function?
- Located in the CNS
- Derived from neural plate
- Form myelin sheath around CNS axons
How many axons can one Schwann cell vs one oligodendrocyte myelinate?
- One Schwann cell can myelinate one axon
- One oligodendrocyte can myelinate multiple axons
Astrocytes
1. Location?
2. Derived from?
3. Function?
4. Shape?
- Located in the CNS
- Derived from neural plate
- Respond to injuries (reactive gliosis/astrocytosis - forms glial scar), help to maintain the blood-brain-barrier (contact with endothelial cells induces formation of extensive tight junction between endothelial cells in CNS capillaries; signals to pericytes to maintain vessel integrity)
- Star-shaped
Microglia
1. Location?
2. Derived from?
3. Function?
- Located in the CNS
- Derived from neural plate
- Resident macrophage cells of the CNS; phagocytotic (derived from blood monocytes)
Ependymal cells
1. Location?
2. Derived from?
3. Function?
- Located in the CNS
- Derived from neural plate
- Line the brain ventricles and spinal canal. Ependymal cells of CHOROID PLEXUS secrete cerebrospinal fluid
Gray Matter
1. Location in brain vs spinal cord
2. Contents
- Periphery of brain, inner area of spinal cord
- Contains neuron cell bodies
White matter
1. Location in brain vs spinal cord
2. Contents
- Inner area of brain, periphery of spinal cord
- Contains axons
The meninges that cover the CNS are neural (…) derived
The meninges that cover the CNS are neural crest derived
Epineurium
- Location?
- What kind of tissue?
- What does it contain?
- Surrounds the whole nerve bundle, which contains multiple nerve fascicles
- Dense irregular connective tissue
- Contains blood vessels and adipose tissue
Perineurium
- Location?
- What properties does its cells have?
- Surrounds each individual nerve fascicle
- Contains cells with contractile properties and tight junctions that form a blood-nerve barrier (myoepithelial)
Endoneurium
- Location?
- What kind of tissue?
- Surrounds each axon in a nerve fascicle
- Delicate collagen fibrils
Are injured axons able to regenerate in the PNS vs CNS?
- PNS: axons are able to regenerate
- CNS: axons do not readily regenerate due to inhibition by glial scar (formed from reactive gliosis by astrocytes)
Motor unit
Consists of a motor neuron and all of the muscle fibers it controls
A muscle fibre is usually innervated by how many neurons?
A muscle fibre is usually innervated by a single neuron
Motor end plate
- The part of the muscle cell membrane where the neuron synapses
- AKA neuromuscular junction
Alpha motor neurons (efferent)
- What does it innervate?
- Function?
- Innervate extrafusal muscle fibers
- Generates force for posture and movement
Gamma motor neurons (efferent)
- What does it innervate?
- Function?
- Innervates intrafusal muscle fibers in the muscle spindle
- Controls the length of the muscle spindle
Sensory (afferent) neurons of muscle spindle
- What do they sense?
- What are the activated by?
- Sense changes in and degree of stretch in the muscle spindle
- Activated by stretching of the muscle
Stimulation of the afferent neuron coming from a muscle spindle in a limb muscle leads to:
A. stimulation of a single muscle
B. relaxation of a single muscle
C. contraction of the muscle and relaxation of the antagonistic muscle
D. relaxation of the muscle and contraction of the antagonistic muscle
C. contraction of the muscle and relaxation of the antagonistic muscle
- The afferent neuron senses stretch - stimulation means the muscle is being stretched/overstretched.
- Reflex: afferent neuron senses that muscle is overstretched -> contraction of muscle -> relaxation of opposing muscle.
Sensory (afferent) neuron of Golgi tendon organ
- What do they sense?
- What are the activated by?
- Senses tension (contraction) generated by the muscle
- Activated by contraction of the muscle
Stimulation of the afferent neuron coming from a Golgi tendon organ in a limb muscle leads to:
A. stimulation of a single muscle
B. relaxation of a single muscle
C. contraction of the muscle and relaxation of the antagonistic muscle
D. relaxation of the muscle and contraction of the antagonistic muscle
D. relaxation of the muscle and contraction of the antagonistic muscle
- The afferent neuron senses tension/contraction - stimulation means the muscle is being contracted.
- Reflex: afferent neuron senses that muscle is contracted -> relaxation of muscle -> contraction of opposing muscle.
Striated skeletal muscle fiber
1. Size of cell
2. No. of nuclei
3. Location of nuclei
4. Somatic or autonomic nervous system?
- Large cell
- Multinucleated
- Nuclei on periphery of cell
- Somatic nervous system
Striated cardiac muscle fiber
1. Size of cell
2. No. of nuclei
3. Somatic or autonomic nervous system?
4. Special feature?
- Small
- 1-2 nuclei
- Autonomic nervous system
- Connected by specialised junctions
Smooth muscle cell
1. Size of cell
2. No. of nuclei
3. Location of nuclei
4. Somatic or autonomic nervous system?
- Small
- Single nucleated
- Nucleus in the center of the cell
- Autonomic nervous system
Muscle structure
Sarcomere: Contains actin (thin) and myosin (thick) filaments
Myofibril: Contains many sarcomeres in series
Muscle fiber: Contains many myofibrils
Sarcomere structure
- 3 bands
- 2 lines
- A band (dark band): contains thick myosin and overlapping actin
- I band (light band): contains thin actin only
- H band: contains thick myosin only
- Z line: marks the ends/boundaries of each sarcomere
- M line: middle of the sarcomere, through the middle of the myosin (A band)
During muscle contraction, the (…) band and (…) band are shortened, but the (…) band remains unchanged
During muscle contraction, the I band and H band are shortened, but the A band remains unchanged
Excitation-Contraction (E-C) Coupling
- Action potential passes down the T tubule and opens dihydropyridine receptor (DHP), an L-type Ca2+ channel.
- Sarcoplasmic reticulum (SR) ryanodine receptor opens, releasing Ca2+ into the cytosol.
- Ca2+ binds to troponin, removing blocking action of tropomyosin and exposing the actin to myosin heads.
- Cross bridges form between actin and myosin (uses ATP).
- SR Ca2+-ATPase (SERCA) pumps Ca2+ back into SR.
- Ca2+ removal from troponin restores tropomyosin blocking action.
Maximal velocity of muscle shortening occurs when there is (…) load
Maximal velocity of muscle shortening occurs when there is zero load
Isotonic contraction
- Tension > load
- Muscle shortens
Isometric shortening
- Tension = load
- Muscle does not shorten
Lengthening contraction
- Load > tension
- Muscle slowly lengthens
Creatine phosphate hydrolysis
- Mechanism?
- High/low intensity/endurance?
- Donates phosphate to convert ADP to ATP via enzyme creatine kinase in the first few seconds of muscle activity
- High intensity, low endurance
Anaerobic metabolism
1. Mechanism
2. What does it burn?
3. What does it produce?
- Uses glycolysis
- Burns glucose and muscle glycogen
- Produces ATP and lactic acid
Aerobic metabolism
1. Mechanism
2. What does it burn?
3. What does it produce?
4. High/low intensity/endurance?
- Uses oxidative phosphorylation
- Burns glucose and fatty acids
- Produces ATP, CO2, and water
- Low intensity, high endurance
Muscle fiber types:
Slow-oxidative
vs
Fast-oxidative-glycolytic
vs
Fast-glycolytic
- Aerobic/anaerobic?
- Function
- What type of muscles?
Slow-oxidative:
1. Aerobic
2. Resist fatigue
3. Muscles for posture
Fast-oxidative-glycolytic:
1. Aerobic + anaerobic
2. Resist fatigue
3. Muscles used in walking
Fast-glycolytic
1. Anaerobic
2. Used for outbursts of strong force
3. Muscles used to jump
