The Muscular System

Define some of the functions of the muscular system

-              Balance

-              Posture

-              Respiration (autonomic nervous system)

-              Movement

-              Thermoregulation

-              Heartbeat

Name the different types of muscle 

• skeletal

• cardiac

• smooth

Describe the properties of skeletal muscle

• striated

• elongated cells

• multinucleated cells

• voluntary

Describe the properties of Cardiac muscle

• striated

• branched cells

• 1-3 central nuclei

• involuntary

List the properties of smooth muscle:

• nonstriated

• single central nucleus

• involuntary

• walls of hollow organs or blood vessles

• function: lines smooth organs, redirection of blood to skin

Describe the components of cardiac muscle

• Pericardium: dense fibrous tissue avoid heart becoming overstretched

• Myocardium: doing most of work in heart. contains actin and myosin. Responsible for forceful contractions. Left ventricle has largest myocardium (thickness of myocardium depends on activity)

• Endocardium (inner layer forms inner lining of heart). Single layer of epithelial cells. Provides smoothness to reduce friction = easy bloodflow. Located in blood vessels and hollow organs

List the different types of connective tissue that holds the muscle bundle together

• Epimysin

• Perimysin (contains bundles called fasciculi)

• Endomysium

Myofibril

Contains basic contractile elements of the muscle fiber

Sarcolemma

Plasma membrane surrounding the MF. Inside contains sarcoplasma (like gelatine, transports nutrients like protiens/ minerals/ fats)

T Tubules (aka transverse tubules)

Provide ‘pathways’ through the fibre - as transport network which allows comms through the muscle and between fibers. Vital for electrical impulses to pass through muscle fiber.

Sarcoplasmic reticulum

• Longitudinal network of tubules.

• Stores Ca²⁺ 

• parallel to myofibril. Provides structural stability.

• Plays role in depolarisation of electrical signals across muscle.

Nucleus

Control centre of the cell. Cellular regeneration, regrowth, repair.

Mitochondria

Energy centre of the cell.

Sarcomere

• Basic contractile structures

• make the muscle have light and dark areas (striations)

Myofilaments

• Actin

• Myosin

Z-line / Z-disk

Start and end of sarcomere. Individual sarcomeres either arranged in parallel or series. Denoted by Z-line.

M-line

Line of protein in centre of sarcomere. No actin filaments present.

A band

Area containing thick myosin filaments. Dark region. Located at center. Both actin and myosin overlapping.

I-band

Area containing only thin actin filaments

H zone

Gap between the ends of adjacent actin filaments. Within the A band. The dark line. a protein which provides attachment area for actin filaments.

Which structures on neurons help propagate the signal along?

• nodes of Ranvier

• Myelin sheath (de-myelination = disease damages myelin sheath = electrical signal disrupted)

Why are neurons described as excitable? 

They are transducers! They receive a range of stimuli which need to be converted into specific types of signals

Fascicle

a bundle of structures, such as nerve or muscle fibres

Describe the process of stimulating a muscle contraction

1. at rest, the motorneuron is polarised (negatively charged to -70mV) to create potential difference