Muscles and Motor Control

Question 1

Describe the characteristics of smooth muscle

Answer 1

• Description - small, spindle-shaped cells with tapered ends. Single, centrally located nucleus, non-striated
• Location - Walls of blood vessels, around hollow organs and respiratory, digestive, cardiovascular and reproductive tracts
• Innervation - can be self-contractile (dig. tract) or require direct Innervation by ANS
• FUNCTION - movement of food, urine and secretions. Regulation of the diameter of airways/blood vessels

Question 2

Describe the characteristics of skeletal muscle

Answer 2

• Description - very long striated cells. Multi-nucleus’ (100s) close to plasma membrane.
• Location - throughout the body, associated with bone and connective tissue.
• Innervation - voluntary/somatic motor nerves
• Function - movement, guards entrances to digestive, respiratory and urinary tracts. Generates heat, protects internal organs and stores nutrient reserve.

Question 3

Summarise the events that take place at the neuromuscular junction

Answer 3

1) electrical signals in MN axon
2) opening of Ca2+ channels in pre-synaptic MN plasma membrane.
3) Ca2+ enters axon - fusion of synaptic vesicles containing ACh with membrane
4) ACh released in the synaptic cleft and binds to ACh receptors at the top of the junction all folds
5) Degradation of ACh in the synaptic cleft by ACh-estersases
6) Opening of ACh-gated channels in membrane of muscle cell - Na+ and K+ enter the cell = electrical signal and muscle contraction

Question 4

Explain the ‘sliding-filament theory’ used to explain skeletal muscle contraction

Answer 4

1) ATP binds to myosin making it detach from actin
2) ATP turns into ADP, releasing energy to convert myosin heads into a ‘cocked state’
3) Ca2+ binds to troponin which exposed sites on actin than myosin can grab (cross-bridges)
4) Myosin then completes a ‘power-stroke’ pushing on the actin!

Question 5

Define the term motor unit and explain how the size of a motor unit relates to its function

Answer 5

• A motor unit is the basic unit of control of muscle contraction. A single muscle can be inner aged by up to 100 motor units. Each muscle fibre is innervated by a single motor unit.
• SMALL - fine control of movement (eye movement - 36 fibres)
• LARGE - increased strength (gastric muscles - 1000 fibres)

Question 6

Describe muscle fibres

Answer 6

• Contraction of the whole skeletal muscle occurs because of coordinated contraction of its individual fibres. They are arranged in bundles containing ‘slow’ and ‘fast’ myosins.
• Type 1 - slow contraction, low force, high endurance, aerobic metabolism
• Type 2a - fast contraction, medium force, medium endurance and mixed metabolism
• Type 2b - fast contraction, high force, low endurance, anaerobic respiration

Question 7

Describe the anatomical arrangement of a muscle

Answer 7

• Epimysium - dense collagen lager surrounding the muscle separating it from nearby tissues
• Perimysium - divides muscles into fascicles. Contains collagen, elastic fibres, nerves and blood vessels
• Endomysium - flexible later inside fascicles. Contain fine capillaries and nerve supply alimenting each muscle fibre.

Question 8

Distinguish between tendons and ligaments

Answer 8

• Tendons - fibrous connective tissue which attaches a muscle to a bone. Serves to move the bone or structure
• Ligaments - fibrous connective tissue which attached bone to bone. Serves to hold structures together and keep them stable

Question 9

Discuss the role of muscles in the tendon-jerk reflex

Answer 9

1) cell body of LMN is stimulated directly by the sensory neurone by muscle stretch with reflex hammers
2) sensory message transported in spinal cord via myelinated efferent axons (in PNS)
3) Afferent neurones synapse into LMN’s in the spinal cord = activation
4) Motor message transported to muscle fibres via myelinated axons (PNS)
5) Contraction of muscle fibres - reflex limb movement

Question 10

Describe the characteristics of cardiac muscle

Answer 10

• Description - small branched cells interconnected to other cardiomyocytes via selectively porous junctions. Striated with centrally located nucleus
• Location - heart
• Innervation - rely on cardiac self-contractile pacemaker cells for contraction altered by ANS
• Function - blood circulation and maintain hydrostatic BP

Question 11

The three basic types of connective tissue are:

Answer 11

Collagen, reticular and elastic

Question 12

Striped (striated) muscle is found in the?

Answer 12

Diaphragm

Question 13

Clinical testing of reflex arcs can:

Answer 13

Help identify the site or level of lesions correctly

Question 14

Skeletal muscle:

Answer 14

Is under voluntary control