Vessels, nerves and muscles

Question 1

Describe the three layers of blood vessels

Answer 1

Tunica intima
• Innermost layer
• Composed of a thin layer of endothelial cells

Tunica media
• Consists of smooth muscles cells

Tunica externa/ adventitia • Loose connective tissue

Question 2

Identify and describe the histology of vessels and relate to function

Answer 2

Large elastic arteries:
• The tunica media is composed primarily of elastin
• This is so it can recoil after high blood flow
• Can be seen in the aorta
• When the heart contracts, and ejects blood into these arteries, the walls need to stretch to accommodate the blood surge, storing energy

Muscular arteries:
• Tunica media is composed primarily of smooth muscle
• Thus, they can constrict and relax

Veins:
• More collagen and very little elastin
• Wider and thin walled

Question 3

Identify and describe the histology of nerves.

Answer 3

Layers of a nerve:
• Endoneurium: Each nerve axon, or fiber is surrounded by the endoneurium. It is a thin layer of delicate connective tissue comprised of collagen fibers and GAGS

Perineurium:
* It is made up of layers of squamous cells and encloses a bundle/ fascicle of axon

Epineurium:
* Delicate connective tissue which encloses the peripheral nerve

Question 4

Identify and describe the histology of neurons and associated cells relate to function.

Mention:
Structure
Synpase
Myelin

Answer 4

Typical structure of a motor neuron:
• Most neurons are interneurons; they connect and are in between motor and sensory neurons
• Neurons have specialized projections calleddendritesandaxons.
• Dendrites bring information to the cell body and axons take information away from the cell body.

Synapse:
• Information from one neuron flows to another neuron across asynapse. The synapse contains a small gap separating neurons. The synapse consists of:
○ a presynaptic ending that containsneurotransmitters, mitochondria and other cell organelles
○ a postsynaptic ending that contains receptor sites for neurotransmitters
○ a synaptic cleft or space between the presynaptic and postsynaptic endings

Myelin:
• Composed of lipid. They wrap around the axon
• Glial cells form myelin. Oligodendrocytes for CNS and Schwann cells for PNS
• One oligodendrocyte can wrap around many axons, where as it is a one to one ratio with Schwann cells
• In Schwann cells, there are inner and outer collars, and gaps between each layer of myelin. These gaps are called S-L clefts, and the cytoplasm of the Schwann cell projects through these gaps so that it can nourish the inner collar and axon
• There are gaps called the nodes of Ranvier where there is no myelin. The propagation of an action potential is done through saltatory conduction

Question 5

Describe the histological features of smooth muscles cells

Answer 5

• Single cells
• Central nuclei
• Involuntary
* Found in vessels and viscera

Question 6

Describe the histological features of skeletal muscle

Answer 6

• Three layers; epimysium, perimysium and endomysium
  • Sarcolemma is the membrane which wraps each muscle fiber
  • The muscle fiber is made of tiny individual units called myofibrils
  • Myofibrils are composed of individual units called sarcomeres

Question 7

Describe the histological features of cardiac muscle

Answer 7

• Endocardium, myocardium and pericardium
• Intercalated discs lock the muscles together
• Gap junctions permit the transmission of electrical messages
• Macula adherens are the desmosome equivalent, and vimentin attachments instead of the keratin filaments
* Fascia adherens are anchoring sites for actin

Question 8

Describe the histological features of the sarcomere

Answer 8

• Actin: thin filament which is anchored to the z-disc
• Myosin: thick filament which is anchored to the m line
• H zone: light zone. Myosin filaments only
  
  • I band: light zone. Actin filaments only

• A band: dark zone.
Actin and myosin filaments overlap

• Z disc: is the disc which marks the beginning and ending of a sarcomere unit. This is where two actin filaments attach
* M line: This is where myofilaments attach

Question 9

Describe the process of contractility in terms of the smallest functional contractile unit in striated muscle

Answer 9

• The sarcoplasmic reticulum is a storage unit for Ca+
• When an action potential occurs, it travel down the t-tubule and into the SR
• This stimulates the release of Ca+ from the SR
• When Ca+ binds to the actin filaments, it exposes the binding sites where the myosin filaments will attach
• The myosin filaments pull the actin along its length
• Because the actin filaments are anchored to the z-line the sarcomere shortens from both sides when they slide across myosin filaments

Question 10

Describe skeletal muscle fiber diversity

Answer 10

Slow twitch (red fibres):
• Low strength, long endurance
• High myoglobin 
• Heaps of mitochondria for slow, sustained release of ATP
• Postural muscles for example

Fast twitch (white fibres):
• High strength, low endurance
• Lower myoglobin
• Fewer mitochondria
• Fine motor control muscles

Question 11

Distinguish the layers within:

• Vessels
• Nerves
• Cardiac muscles
• Skeletal muscles

Answer 11

Vessels:
Tunica intima, tunica media, tunica externa/ adventitia

Nerves:
Endoneurium, perineurium and epineurium

Cardiac muscles:
Endocardium, myocardium and pericardium

Skeletal muscles:
epimysium, perimysium and endomysium