Neuromuscular System - Detalles

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Part of sarcomere. Dark. Stacked set of filaments along with the portions of the thin filaments that overlap on both ends of the thick filaments.

A band

Is released when action potential reaches axon terminal. Ach completes the connection. Opens channels between neuron and muscle, permitting exchange of Na+ and K+.

Acetylcholine (Ach)

Protein, thin filament. ≈3000 per myofibril. One end inserted into Z-disk, opposite end between myosin filaments.

Actin

-55 mV threshold. The change in electrical potential associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.. Inside the cell isn’t necessarily negatively charged, just less positive than the outside.. Negativity comes from high K+ concentration. Positive charge comes from high Na+ concentration. Large diameter conducts nerve impulse faster.

Action Potential (AP)

Sensory information transmitted to CNS (sensory input, e.g. smelling food(

Afferent division

Part of antagonistic muscle pair. Contracts as partner relaxes. Action swapped to reverse the movement.

Agonistic muscle

Automatic nervous system. Supplies the interrenal organs and blood vessels. Separated into parasympathetic and sympathetic.

ANS

Part of antagonistic muscle pair. relaxes as partner contracts. Action swapped to reverse the movement.

Antagonistic muscle

Part of the neuron. End of the axon. Information pass on via neurotransmitters

Axon terminals or synapses

Part of the neuron. Nerve fibre, one per neuron. From a few mm to 1m. Carries nerve signals to brain, spinal cord, muscle or glands.

Axons

1. Stored in Sarcoplasmic reticulum and are released when signals from NS arrive for contraction 2. Neurotransmitters from the neuron bind to the receptors and depolarises the membrane of the muscle fibre 3. Electrical impulse travels down the T-tubules 4. Which opens calcium stores 5. Ca2+ flow to the myofibrils 6. Triggers muscle contraction

Calcium (6 steps)

Heart muscle, involuntary contraction. Long cylindrical cells; ends of fibres split longitudinally into a small number of branches. Striated. One nucleus. Cells are connected to each other by intercalated disks. -separated cardiac muscle cells -cells can communicate through disks -when one fibre is excited, its excitation spreads across the heart

Cardiac muscle

Part of the neuron. Supports the cell and provides nutrition.

Cell body

Is a specialized sensory receptor cell which transduces (converts) a chemical substance (endogenous or induced) and generates a biological signal.

Chemoreceptors

Central nervous system. Brain and spinal cord.

CNS

Muscle shortens

Concentric muscle movement

1. When a muscle is relaxed, the Tropomyosin blocks the cross-bridge binding sites on Actin 2. If Ca2+ high and ATP available the Ca2+ binds to Troponin displacing Tropomyosin and making cross-bridge binding site available. 3. This allows ATP binding and contraction to take place.

Contraction Control (3 steps)

Part of the neuron. Multiple branching growths. Main receptors of the neuron, 1000’s of contact points

Dendrites

Muscle lengthens.

Eccentric muscle movement

Conduct impulses away from CNS (picking up food)

Efferent division

Outer protective layer of muscle

Epimysium

Sequence of events converting action potentials to muscle contraction. - AP travels along sarcolemma, conducting into cell via T-tubules -Excitation reaches SR, leading to the release of Ca2+ into the sarcoplasm

Excitation-Contraction Coupling (E-C Coupling)

A bundle containing muscle fibres

Fascicle

Part of sarcomere. Lighter area, middle of A band, where thin filaments do not reach.

H band

-During muscle contraction, myosin cross bridges pull of actin filaments causing them to slide inwards. - Space between Z-disks reduced as actin moves over myosin -Muscle contraction occurs as fibres shorten

Huxley’s Sliding Filament Theory

Part of sarcomere. Light. Remaining portion of thin filaments that do not project on to A band

I Band

To supply nerves to. E.g. the motor unit innervates a series of muscles.

Innervate

Ratio of motor neuron: muscle fibre. One nerve innervates at least one of the bodies 250 million muscle fibres -ratio of muscle fibres per motor neuron is related to muscle function -Small muscle (e.g. eye) have 5-15 muscle fibres per motor unit -Large muscles (e.g. gastrocnemius, lower leg) 1800 muscle fibres per motor unit.

Innervation ratio

Contract under tension but no movement created (e.g. holding but not moving a weight).

Isometric muscle movement

Contains enzymes involved in oxidative phosphorylation

Mitochondria

420,000 in the body

Motor Neuron

All the muscle fibres and motor neuron stimulated. -Axon leaves the spine as spinal nerve, extending to muscle. It is responsible for innervating - Each muscle fibre receives a single axon terminal from a somatic neuron. -However, each axon can have collateral branches to innervate and equal number of fibres

Motor Unit

Muscles pull by contracting, not pushing. Tendon at moving end is insertion. Tendon at non-moving end is origin. Muscles arranged in antagonistic pairs.

Muscle Action

Contractibility, extensibility, elasticity and irritability. Speed of contraction is modified to meet demands. Moves due to brain sending nervous impulses via a motor nerve. A single motor nerve may stimulate one fibre or 150 depending on the effect of action required.

Muscle Characteristics

Can shorten and thicken

Muscle Contractibility

1. ATP at Myosin hydrolysed to ADP and inorganic Phosphate (ADP + P) 2.Myosin head extends and attaches to binding site on actin. CROSS BRIDGE FORMS. 3. In a POWER STROKE the myosin pulls the actin towards the M-line 4. SARCOMERE shortens 5. ADP+P release. Myosin remains until a new ATP attaches 6. Either process REPEATS or myosin remains unattached and muscle is relaxed

Muscle Contraction (6 points)

Return to original shape after contraction

Muscle elasticity

Can stretch when fibres relax

Muscle extensibility

A muscle cell containing myofibrils

Muscle Fibre

Responds to stimuli from nerve impulse

Muscle Irritability

Concentric, Eccentric and Isometric

Muscle Movement Types

Millivolts

Fatty nonconductive insulator, covers some of the axon.

Myelin Sheath

A chain of contractile protein filaments- actin and myosin

Myofibril

Found in the myosin heads.

Myosin ATPase

Protein, thick filament. ≈ 1500 per myofibril. Each filament composed of two twisted strands called the heavy and light chains. Filament flexible at point of myosin head. Spacing maximises the chances for interaction with actin binding site.

Myosin

Central, automatic and peripheral nervous system 1. Controls internal environment 2. Voluntary control of movement 3. Memory 4. Learning

Nervous system (4 functions)

Chemical substance released by nerve fibres (axons). Transfers nervous impulse (electrical activity) to another nerve or tissue. Axon terminal>synapse>neurotransmitter>effect site.

Neurotransmitter

E.g. Tryptophan present in some foods such as eggs, meat, skimmed milk and bananas.

Neurotransmitter precursors

Exposed axon (myelin sheath is not continuous)

Node of Ranvier

Balances action of sympathic working to conserve energy. Sows down body processes. Effect= resting HR & RMR constriction of blood vessels.

Parasympathetic nervous system

Protective layer surrounding fasciculus

Perimysium

Is the chemical addition of a phosphoryl group (PO3-) to an organic molecule

Phosphorylation

Peripheral nervous system. Includes nose, eyes and peripheral nerves

PNS

Multiple action potentials (‘dominoes’)

Propagation

A sensory receptor which receives stimuli from within the body, especially one that responds to position and movement.

Proprioceptors

Allows the action potential to continue down the axon (if another can take place immediately, it can’t travel). ‘All or none’ principle.

Refractory period

-70 mV. Positive charge outside, negative charge inside.

Resting Potential

Resting metabolic rate. The total number of calories used when the body is a total rest.

RMR

The fine transparent tubular sheath which envelops the fibres of skeletal muscles

Sarcolemma

The functional unit of muscle fibre. Striated appearance due to arrangement of ‘bands’. Contains I Band (light, A Band (dark), H band (middle of A) and Z disk

Sarcomere

Cytoplasm, containing energy substrate and enzymes involved in many metabolic reactions.

Sarcoplasm

(SR) Storage site for Ca2+

Sarcoplasmic Reticulum

PNS specialised cells.

Schwann Cell

Slow twitch. Deep red, contracts slowly, can work for long periods. Found in large numbers in world class endurance runners.

Skeletal Muscle types Type 1

Type 1, Type 2, Type 2A and Type 2B

Skeletal Muscle types

Fast twitch. Paler. Contract quickly and powerfully but tire easily

Skeletal Muscle types Type 2

Fast oxidative, are found in large numbers in middle distance runners

Skeletal Muscle types Type 2A

Fast glycolytic, found in large numbers in the leg muscles of world-class sprinters.

Skeletal Muscle types Type 2B

Various structures and functions. Voluntary muscle. Supports respiration & movement of body fluids (peristalsis, pumping blood). Regulated body fluids (bladder). Produces heat, 70-80% energy expended during exercise. Many nuclei. Structure: Epimysium, perimysium, fascicle, muscle fibre, myofibril, sarcomere.

Skeletal Muscle

Located in walls of internal organs and tubes. Involuntary. Contraction generates pressure on and regulates movement of contents of these structures. No striations. Occur in sheets. No troponin-tropomyosin complex.

Smooth muscle

Voluntary control of muscle tissue

Somatic Control

Refers to outer body regions of the body. Part of PNS. Carries messages from spinal cord to skeletal muscle via motor neuron. -Such CA2+ is a prerequisite for muscular contraction

Somatic

Prepares body for expending energy and dealing with emergency situations. Effect= increase HR and RMR, dilation of blood vessels.

Sympathetic nervous system

End point of neuron

Synapse

Space between neuron and myofibre

Synaptic Cleft

Holds muscle to bone

Tendon

Point of excitation where motor neuron and muscle fibre meet. 1. AP reaches axon terminal 2. Ca2+ enters the axon terminal 3. Ach vesicles fuse with presynaptic membrane 4. Ach binds to postsynaptic receptors 5. Sodium channels open 6. Flow of sodium generates an AP

The neuromuscular junction (6 steps)

Functional unit of the nervous system. Designed to receive stimuli and conduct impulses. 2 main properties: -Excitability- ability to react -Contractibility ability to return to rest after excitement Motor Neurons or Sensory Neurons

The neuron. Definition and 2 main properties.

A regulatory protein that controls the interactions of actin and myosin as a part of the regulation of muscle contraction. Blocks actin-myosin binding site at rest.

Tropomyosin

Refers to a group of 3 regulatory proteins that help regulate the contractions of the heart and skeletal muscles. 3 binding sites: Ca2+, tropomyosin and actin.

Troponin

Permit transition of action potential into muscle cell

T-tubules

Cardiac, skeletal and smooth

Types of muscle

Part of sarcomere. Flat, cytoskeletal disk that connects the thin filaments of 2 adjoining sarcomeres.

Z disk

Somatic Nervous System

Skeletal Muscle is controlled by the....

ADP and phosphate ion

ATP decomposes to...

Motor unit

Motor neuron plus all muscles cells it innervates is called the...

Muscle fibre's plasma membrane

Sarcolemma

Found in the sarcoplasm. Contain the muscle fibres contractile 'machinery': actin and myosin

Myofibrils

At the myosin heads

Crossbridges

Actin binding site, ATP binding site or ADP + Phosphate ion binding site

Binding sites on myosin head are...(3)

Sarcoplasmic reticulum

Ca2+ stored in the....

Muscle fibre

Muscle cell also known as a

Sarcomere

The fundamental, repeating, unit of the the myofibrils

Na+ coming into the cell

Depolarisation

K+ moving out of the cell

Repolarisation

Neuromuscular System

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