1. Skeletal (striated) 2. Cardiac (straited) 3. Smooth

1. Muscular contractions - NS Flashcards by Casi Jones

CNS (recap)

Brain
-Spinal chord

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PNS recap

all of the other nerves

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Different types of PNS

Sensory division (afferent)
Motor division (efferent) > Somatic nervous system

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What is the somatic Nervous system?

Part of the peripheral nervous system
Controls movement of skeletal muscles

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Where is the CORTEX in the brain?

Cerebral Cortex is the outer layer that lies on top of your cerebrum

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What is the role of the CORTEX?

Key role in memory, thinking, learning, reasoning, problem-solving, emotions, consciousness and functions related to your senses

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Different types of homoluculs

a) Motor
b) Sensory

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Tracts

Ascending + Descending

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Ascending tracts

relay information from the spinal cord to the sensory cortex

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Descending tracts

relay information from the motor cortex to the spinal cord

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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

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Myelinated, what is the advantage?

Neurone is isolated - allows more rapid transmission of neural information along neural fibres

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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

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ONE Alpha motor neurone

Long

ONLY 1 neurones extends from spinal chord and the muscle (different in automatic NS)

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What the junction called when the neurone and muscle interact / join?

Neuromuscular junction

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How do neurones and muscle interact?

The neurone connects to 1 muscle fibre - NEUROMUSCULAR JUNCTION and communicates

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Which neurotransmitter is released at the junction??

Acetylcholine is the neurotransmitter at skeletal muscle NMJs

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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)

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What does the Acetylcholine bind to?

Binds to and activates Nicotinic Acetylcholine Receptor
> Ionotropic

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Post synaptic membrane

Motor End Plate (MEP)

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At post synaptic membrane if signal is big enough…

trigger effect in muscle (ACTION)

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Types of muscle:

Skeletal (striated)
Cardiac (straited)
Smooth

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Skeletal (striated) muscle:

Enables movement of limbs and other parts of the skeleton

Connected to bone
- via tendons (origin)
- via tendons (insertion)

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Cardiac (striated) muscle:

The pump in the circulation (heart)

Functional syncytium

Intrinsic pacemaker activity

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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?

1. 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