1. Muscular contractions - NS Flashcards
CNS (recap)
- Brain
-Spinal chord
PNS recap
- all of the other nerves
Different types of PNS
- Sensory division (afferent)
- Motor division (efferent) > Somatic nervous system
What is the somatic Nervous system?
- Part of the peripheral nervous system
- Controls movement of skeletal muscles
Where is the CORTEX in the brain?
Cerebral Cortex is the outer layer that lies on top of your cerebrum
What is the role of the CORTEX?
Key role in memory, thinking, learning, reasoning, problem-solving, emotions, consciousness and functions related to your senses
Different types of homoluculs
a) Motor
b) Sensory
Tracts
Ascending + Descending
Ascending tracts
relay information from the spinal cord to the sensory cortex
Descending tracts
relay information from the motor cortex to the spinal cord
Sensory neurones
Sense touch, stretch, pain etc.
Relay information to spinal cord and brain
Enter spine at the dorsal horn, via dorsal root
Unipolar neurones – cell body is at dorsal root ganglion
Myelinated
Myelinated, what is the advantage?
Neurone is isolated - allows more rapid transmission of neural information along neural fibres
Motor Neurones
Relay nerve impulses from the spine to trigger contraction of skeletal muscle
>Exit spine via ventral root
ONE Alpha motor neurone
Multipolar and myelinated
ONE Alpha motor neurone
Long
ONLY 1 neurones extends from spinal chord and the muscle (different in automatic NS)
What the junction called when the neurone and muscle interact / join?
Neuromuscular junction
How do neurones and muscle interact?
The neurone connects to 1 muscle fibre - NEUROMUSCULAR JUNCTION and communicates
Which neurotransmitter is released at the junction??
Acetylcholine is the neurotransmitter at skeletal muscle NMJs
What type of receptor is Nicotinic Acetylcholine?
Ligangated ion channel
(in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction)
What does the Acetylcholine bind to?
Binds to and activates Nicotinic Acetylcholine Receptor
> Ionotropic
Post synaptic membrane
Motor End Plate (MEP)
At post synaptic membrane if signal is big enough…
trigger effect in muscle (ACTION)
Types of muscle:
- Skeletal (striated)
- Cardiac (straited)
- Smooth
Skeletal (striated) muscle:
Enables movement of limbs and other parts of the skeleton
Connected to bone
- via tendons (origin)
- via tendons (insertion)
Cardiac (striated) muscle:
The pump in the circulation (heart)
Functional syncytium
Intrinsic pacemaker activity
Smooth muscle:
Functional syncytium
Around many hollow internal organs
Striated meaning?
STRIPPED
= Muscle tissue in which the contractile fibrils in the cells are aligned in parallel bundles, so that their different regions form stripes visible in a microscope
Skeletal muscle structure
Muscle cells connected to following muscle cell
Consists lot of cells - many nuclei
Forms fibres and group together = muscles
How are muscle fibres connected?
Sheet of connective tissue
What is the structure of a muscle fibre?
Plasma membrane
Transverse tubule
Myofibril
Terminal cisterna
Tubules
Plasma membrane of muscle fibre
Sarcolemma
Transverse tubule
T-tubule
Terminal cisterna of…
Sarcoplasmic reticulum (smooth reticulum)
Tubules of…
Sarcoplasmic reticulum (smooth reticulum)
Myofibrils
Contractive elements of the mucsle
4 key proteins of myofibril:
1) Myosin
2) Actin
3) Troponin
4) Tropomyosin
Which protein is the thick filament?
Myosin - single thick filament (2 heads - LIKE two golf clubs)
Actin _____ filaments
thin
Troponin + Tropmyosin
Balls that are bound to the filaments
What is troponin’s role?
When Ca2+ bonds to troponin it causes conformational change to tropmyosin which is tightly bound to actin
This unwinds the tropomyosin from the myosin which exposes the myosin binding site which is on the actin = causes CONTRACTION
(allows the myosin to bind to the actin)
How do thick and thin filaments join together in myofibril?
Actin thin filaments are joined/ bridged with Myosin thick filaments (one every other)
Z disk goes parallel to Actin filaments (this is what keeps them together)
What is the H zone
Where there is a gap (NO overlap) between the Actin and Myosin filaments = at rest (this is when there is no contraction)
Therefore thinner
what happens to H zone when there is a contraction?
Overlapping of both filaments; Actin + Myosin are sliding across each other
Will reach point where Actin from either side will reach each other
Cross bridge cycling:
Tight Binding in the Rigor state
Myosin filament BINDS to G-actin molecule
4 steps of cross bridge cycling
1) ATP binds to myosin
2) Myosin hydrolyzes ATP
3) Power stroke
4) Myosin releases ADP
1) ATP binds to myosin
Myosin releases Actin
2) Myosin hydrolyzes ATP
- Energy from ATP rotates the myosin to the coked position
- ADP and Pi remain bound
- Myosin binds weakly to actin
3) Power stroke
- begins when tropomyosinmoves off the binding site.
4) Myosin releases ADP
Myosin releases ADP at the end of the power stroke
WHEN: ADP released - the myosin head tightly bound to actin
The cycle is ready to begin once
more as a new ATP binds to myosin
How does depolarisation lead to contraction?
Excitation-Contraction- Coupling
Excitation-Contraction- Coupling : what does it need?
- Need AP & Calcium
which; AP triggers calcium release
ACTION POTENTIAL
Events at the NMJ:
1) Resting state
2) AP arrival - release od Ach (DEpolarisation of pre-synapse)
3) Depolarisation of MEP - wave of depolarisation passes down fibre
4) Contraction - muscle fibre REpolarises
Depolarisation:
Ca2+i - contraction link
Calcium - Ca2+
intracellular signal for contraction
Summarise of the steps:
1) Action potential in axon
2) Ach release at terminal
3) Muscle contraction
Does skeletal muscle spontaneously contract??
- Skeletal muscle is not spontaneously contractile
- Nerve supply cut – flaccid paralysis
Activity at the neuromuscular junction is acetylcholinergic:
1) ACh formed in the synaptic terminal
2) Generated by ChAT
3) Packaged into vesicles
4) Released into the synaptic cleft
5) Calcium entry causes fusion of synaptic vesicles
6) Ach bind to Nicotinic ACh Receptors
7) Non-Bound = Broken down by Ach- esterase
8) Choline taken up to be reused
Sites of pharmacological interference
Acetylcholine are packed into synaptic vesicles
ACh transferase - Ca2+ into the neurovascular junction and Na+ out into the motor end-plate (in the muscle fibre)
Botox and vesicular
- Botulinum toxic from clostridium botulinum bacteria
inhibitor of vesicular fusion: - Alters proteins required for vesicular fusion with the presynaptic membrane
How does botox work? (P
Stops vesicles from forming
No contraction in skin
