Nerves And Muscles Flashcards
Why are nerve cells highly metabolically active
They maintain a large surface area of a cell membrane and constantly require energy to develop electrochemical gradients
How does the structure of a nervous out reflect its activity
Large nucleus with a large central nucleus: reflects a high degree of transcriptional activity
There is an abundant rough ER found in the cytoplasm: reflects the synthesis of proteins in the cytoplasm of the nerve cell body
What is Nissl substance
The abundant rER in nerve cell cytoplasm
Are peripheral motor ganglia synaptic stations?
Yes
Describe sensory ganglia
Eg
Contain cell bodies of sensory afferent pseudo unipolar neurons which transmit impulses from the peripheral receptors to the central nervous system
They are not synaptic stations
Eg dorsal root ganglia of spinal nerves and sensory ganglia of cranial nerves
What is the largest sympathetic ganglion
The stallate / cervicothoracic ganglion
What is the stellate ganglion formed from
The fusion of the inferior cervical ganglion and the first thoracic ganglion
The structure of sympathetic ganglia is similar to which other ganglion type
How are they different
Sensory ganglia
The sympathetic neuron cells are multipolar
What are the prevertebral ganglia
Ganglia in the sympathetic chain that lie below the end of the spinal cord which innervate the pelvic viscera
What is a nerve trunk
A nerve
Long collections of long cylindrical processes that contain nerve fibres
What is myelin
A leopard protein complex characterised by a large proportion of lipid ( 70–85%) relative to the proportion of protein (15 –30%)
How is the myelin sheath formed in the PNS
By Schwann cells, the PM of which wrap tightly around the axon in numerous concentric layers, preventing most leakage across the axon membrane
How much of the sheath does each Schwann cell form
How long are the nodes of Ranvier
1mm
0.5μm
Are Schwann cells associated with small diameter axons
Yes but these are simply enveloped by the cytoplasm of the Schwann cell and are non myelinated
These are not visible with LM unless silver or gold based techniques are used
How do oligodendrocytes form a myelin sheath
Individual oligodendrocyte from similar segment of myelin sheath around the axons like Schwann cells but for many separate axons simultaneously
Name a demyelinating disease of
a) PNS
b) CNS
What happens in each
a) Guillan-Barré syndrome - autoimmune attack on Schwann cells
b) MS - autoimmune attack against oligodendrocytes
Name a disease affecting the motor end plate
Describe it
Myasthenia gravis
The binding of ACh to this post signup take membrane is reduced due to decrease number of functional ACh receptors affecting the neuromuscular transmission
It is an autoimmune disease manifested by symptoms of fatigue and muscle weakness
Are all the cranial nerves mixed
No some are purely sensory or motor
Which is the most important cranial nerve of the parasympathetic outflow
10 (vagus)
How do the sympathetic preganglionic nerves leave the spinal cord
With the ventral roots of the T1 - L3/4 passing via the white rami communicantes to the paravertebral chain
How do parasympathetic ganglia appear
As slight swellings in nerve trunks
What are the 3 cranial parasympathetic nerves
Oculomotor
Facial
Glossopharnygeal
How big are first order autonomic neurons
Are they myelinated
About 2-5μm in diameter
Yes
Second order axons are non myelinated however
How fast do autonomic nerves conduct
Myelinated: 10m/s
Non myelinated: 1m/s
How much of our body weight is skeletal muscle
40%
What is a muscle fibre
The highly specialised muscle cell
It is a big elongated structure formed by the fusion of many cells
It contains many peripheral nuclei and its surface is bound by A single cell membrane: the sarcolemma
What is a myofibril
A closely packed, cylindrical array of filaments lying within the cytoplasm of the muscle cell
What is a myofilament
Are you strand of filamentous actin or myosin
Where are myosin filaments linked
At the M line
What is the sarcomere
The unit of contraction and the part of the myofibril between the 2 Z line a
Light I bands contain what
Actin filaments
What are the A bands
Dark bands of thick myosin filaments
What is the H band
The myosin regions not overlapping with actin
Why are I bands called I bands
They are monofringent and this isotopic
What does monofringent mean
Does not alter the plane are polarised light
How does the A band affect polarised light
They are bifringent so alter the polarised light in 2 planes and are anisotropic
How is calcium re-accumulated after muscle contraction
By the fenestrated collar
What are red muscle fibres
What is rich in myoglobin giving it the red colour
These are type one fibres and contain the most myoglobin and the greatest number of mitochondria you had that metabolism it depends on oxidative phosphorylation primarily
Capable of sustaining contraction and generate a slow twitch response to stimulation
What are Type II muscle fibres
White fibres
Contain much less myoglobin and a few mitochondria
They respond quickly to stimulation but cannot sustain contraction for long periods of time
They are specialised for anaerobic metabolism
Where are the following muscle fibres found:
a) type I
b) type II
a) in the postural muscles and limbs
b) in muscles responsible for intense but sporadic contraction eg biceps
Is a muscle either red or white fibre?
No Most muscles contain a mixture of type one and two fibres as well as scattered intermediate fibres
What are tendons made from
Why are they white
Connective tissue
They have a sparse blood supply
How does the tendon’s college fibres merge with the muscle
Blends with the epimysium and penetrates the muscle along with the perimysium
What is the epimysium and perimysium
Epimysium: A dense collagenous she is investing the muscle
Perimysium: A loose collagenous tissue surrounding each muscle bundle
What is endomysium
Loose connective tissue up occupying the spaces between individual muscle fibres
How does this size of cardiac muscle cells compare to skeletal muscle cells
Cardiac are much smaller
Cardiac=15μm in diameter and 100μm long
Skeletal= 100μm in diameter and several cm long
Describe the position of nuclei in cardiac muscle cells
Skeletal?
Each cell has 1 nucleus which lies deep in the cells
Skeletal muscle cells are multinucleate (can contain 100s of nuclei) which are found just inside the surface membrane, at the periphery of the fibre
How are cardiac muscle cells linked togther
By specialised intercellular junctional regions called intercalated discs
What are intercalated discs
Complex interdigitating junctions present at the sidelines
The action filament of the terminal sarcomere of each cell insert into a meshwork of specific protein adhesion molecules, forming a mechanically strong attachment between the cells through intermediate like junctions, Such that the pull of one contractile unit can be transmitted across the access to the next
How are cardiac muscle cells electrically linked
Along the side of the cells, next to the into collated discs, the cell membranes of adjacent cells come into close proximity to form gap junctions
Describe T tubules
They run in at the Z lines in the cardiac muscle and enter at the Boundry between the A and I bands in skeletal muscle
They are closing associated with membranes of the SR in both
In cardiac muscle the T tubule from diads with a terminal cisterna of the SR rather than triads as occurs in skeletal
True or false
The SR is less extensive in cardiac muscle
True
True or false:
The innervation of cardiac muscle is different from skeletal muscle
True
End plates are not present in cardiac
Where is the nucleus in smooth-muscle cells
In the centre
What are the equivalent of Z lines in the smooth-muscle
Dense bodies
What are dense bodies dense in
Electron dense
How are dense bodies bound to actin
By α- actin
How are the membranes of adjacent smooth-muscle cells separated
By a space containing into cellular matrix and collagen fibres
How is force transmitted between smooth-muscle cells
By junctions similar to desmosomes and there are regions where the adjacent membranes are parallel and very close together forming gap junctions which ensure electrical continuity between the cells to synchronise contractions
What is similar to the T tubular system in smooth-muscle
Caveolae
These are in pocketings of the plasma membrane
What are the two types of smooth muscle
Unitary/ visceral
Multi unit
Describe visceral smooth-muscle
Individual muscle fibres are linked by gap junctions and act as a unit
It is found predominantly in the wall of hollow viscera such as blood vessels and the gastrointestinal tract
Describe multi unit smooth-muscle
Consists of individual units without gap junctions. Muscle fibres are not linked, each one contracts independently.
It is found in locations such as the iris of the eye in which fine graded contractions take place
How big are smooth-muscle cells
Diameter: 2-10μm
Length: 50-400μm
What are the three layers of arteries, arterioles and veins
Tunica intima
Tunica media
Tunica adventitia
Describe tunica intima generally
What is it like in veins
The innermost coat of the walls of blood vessels
It is the endothelial am with adjacent basement membrane and some support in connective-tissue
in veins the internal elastic laminar is not that obvious
Describe the tunica intima in arteries
In arteries extends to and includes the internal elastic lamina – a substantial fenestrated tube elastin which can be easily identified in muscular arteries and arterioles
Large elastic arteries such as the aorta contain so many layers of elastin that is difficult to decide which one is the most substantial inner layer
Describe the tunica media
The middle layer
This is the part of the wall that contains smooth muscle
The outside is sometimes marked by the external elastic lamina
Describe the tunica media in arteries
Arteries always contain a substantial tunica media
In elastic arteries there is more elastin than smooth-muscle or collagen
In muscular arteries smooth-muscle predominates. Large muscular arteries contain many layers of smooth-muscle separated by incomplete sheets of elastin and collagen
Arterioles also have predominant tunica media but that muscle is decrease as they become smaller. Small arterioles my only contain a single layer of smooth muscle
Describe the tunica media of veins and venules
Veins have less smooth muscle than arteries
In areas where veins aren’t supported by surrounding tissue (eg in the legs) the amount of muscle is larger
Small venules lack muscle in their wall and may only consist of endothelium and a layer of connective tissue around it
Describe tunica adventitia
The outercoat
It is the sheath of connective tissue surrounding the puzzle and ties it into a tissue to which it runs
Consist mainly of collagen and is usually the most prominently in the wall of a vein
this is where you find the innervation of the vessel
What is the blood supply to blood vessels with thick walls
Which layer is it in
The vasa vasorum
Tunica adventitia
What are ‘resistance vessels’
What makes them responsible for peripheral resistance
Arterioles
Their small diameter (20-130μm)
How does the tunica media change as arterioles become smaller
The number of muscle layers decreases and the internal elastic lamina is lost
True or false
The lumen of arteries is similar to the size of the wall
True
Name a vein that has thicker muscular walls
Why is this
The saphenous vein
To withstand the hydrostatic pressure of a column of blood
How big are capillaries
5-10μm
What are capillaries lined by
Endothelium (simple squamous epithelium) on a basement membrane
What are pericytes
Associated with capillaries
Cells with contractile properties that wrap around the endothelial cells
Pericytes are undifferentiated cells, capable of giving rise to fibroblasts, smooth muscle cells and endothelial cell precursors for growth, branching and repair
What are the 3 types of capillaries
Continuous
Fenestrated
Sinusoidal/ discontinuous
Describe continuous capillaries
Where are they found
The most common capillary
Have continuous endothelial wall and are less permeable
They are found in connective tissue, muscle, lungs, brain and skin
Describe fenestrated capillaries
Have circular pores in the endothelium or very thin regions which is crossed only by a diaphragm that is thinner than a cell membrane
Their basement membrane is continuous
Where are fenestrated capillaries found
Kidneys
Small intestine
Endocrine glands
Describe sinusoidal capillaries
Fenestrated with the largest open pores without diaphragms in the endothelium
The basement membrane is discontinuous and highly permeable
Where are sinusoidal capillaries found
Where a close relationship between the circulation and parenchymal cells is required
Eg liver, spleen, lymphatic tissue, bone marrow and some endocrine glands
What are the 3 routes for exchange across the capillary wall
Diffusion across the endothelial wall
Diffusion between cells
Pinocytosis
Which substances easily cross capillary walls with or without fenestrations
What substances require fenestrations
Lipid soluble substances eg CO2, O2, alcohol
Water and hydrophilic substances
Where is the junctional seal in between capillary endothelial cells impermeable
In most of the CNS
What is pinocytosis
Large molecules can cross the endothelium in vesicles that are formed at one surface and discharge at the other
This is a feature of all capillaries especially in continuous capillaries
It is possible that vesicles May join together under some conditions to form a transitory channel across the endothelial layer
How can capillaries be made visible in LM
Injection of a special dye eg gelatin Carmine
Perfusion fixation which preserves then in their natural, open state
Where are lymphatic capillaries not found
CNS bone Cartilage Bone marrow Epithelia Placenta
How do the walls of lymphatic vessels relate to those of blood vessels
Larger lymphatic vessels resemble veins (and venules) and veins and lymph vessels have valves
Lymphatic capillaries are like those of blood vessels
How to tell the difference between lymphatics and blood vessels in LM
Presence of RBCs
If perfused, blood vessels are empty but the lymphatics contain a gel of plasma protein
What is the tunica intima like in lymphatics
Consists of endothelium and a v thin sub-endothelial layer of supporting tissue
Projects into valves which are composers of little supporting tissue (reticulin fibres and minimal ground substance) lines in both sides by endothelium
What is the tunica media like in lymphatics
Contains less smooth muscle, separated by collagen
What is the tunica adventitia like in lymphatics
Consists of connective tissue with fibroelastic fibres
Describe the wall of lymphatic capillaries
Consists of a single layer of thin endothelial cells, the basement membrane being rudimentary or absent
