Lecture 14 Flashcards
Example of physiological muscle hypertrophy
Skeletal muscle changes with exercise
Example of pathological muscle hypertrophy
Cardiac muscle hypertrophy
Example of hyperplasia and hypertrophy
Increased size of the myometrium during pregnancy
Organisation of the nervous system
Anatomy of a neuron
Neurons all have the same basic strucuture but they vary in size and shape
3 main neuron shapes
Multi = One axon multiple dendrites
Bipolar = one axon one dendrite
Unipolar = common stem connecting axon and dentrite to cell body
Cellular features of a neauron
- large nucleus - reflecting metabolic demand
- many mitochondria
- lots of ER, particularly in larger neurons - can be found in dendrites but NOT AXONS
- numerous neurofilamnts together with microtubules make up the cytoskeleton
Synapses are found at dendrites and also cell body
Two types of matter the CNS is macroscopically divided into
- grey matter (neuron cell bodies, dendrites and axons)
- white matter (axons; many myelinated
What makes up the grey matter
- neuron cell bodies
- dendrites
- some axons
What makes up white matter
- axons; many myelinated
- lots of lipid in it which is why it is white - myelination is lipid
Does grey matter contain myelin?
No
What supports the CNS
Glial cells
4 glial support cells of the CNS
- oligodendrocytes
- astrocytes
- microglia
- ependymal cells
What are oligodendrocyte
CNS equivalent of Schwann cell myelinated axons
What do astrocytes do?
- provide mechanical support (also form part of the blood brain barrier)
What are ependymal cells?
Ciliated cuboidal epithelial cells which line the cavities of the brain and spinal cord
- epithelial cells
What are microglia
Specialised immunological cells of the CNS
Structure of peripheral nerves
- a nerve consists of one or more bundles of nerves fibres called fascicles
- axons inside the fascicles are surrounded by collagenous support tissue called endoneurium
- the fascicles are enclosed in dense callagenous tissue called perineurium
- the fascicles are bound together by loose collagenous tissue called epineurium
Schwann cells provide support to the PNS
What are PNS axons enveloped by and what does it provide?
PNS axons are an eloped by Schwann cells, providing structural and metabolic support
What is the factor that results in different degrees of evolopedness
Small diameter fibres are non-myelinated
Large diameter fibres are myelinated
Non-myelinated nerve features
Small diameter axons of the autonomic system and small pain fibres are simple enveloped by the cytoplasm of Schwann Cells
- no myelination
Features of myelinated nerves
- the axon is invaginated into the Schwann cell cytoplasm
- the outer membrane of the Schwann cell fuses to form a mesaxon
- the mesaxon rotates around the axon - wrapping the axon in concentric layers of membrane = myelin sheath
Histology of myelin
Do Shawna cells cover the entire axon?
Each Swann cell only covers a part of an axon
What are the gaps where axons are not myelinated called
Nodes of ranvier
What are nodes of ranvier ?
Gaps where axons are not myelinated
What are nodes of ranvier important for?
Important in signal conduction along axon
Are nodes of ranvier also found in the CNS?
Yes - gaos in oligodendrocyte myelination
What creates the resting membrane potential?
The fluid inside the cell has an excess of negative chargers and the fluid outside the cell has an excess of positive chargers.
- this action potential allows information to travel along the axon
Non-myelinated vs myelinated
- non-myelinated nerves are slower to conduct an action potential
- action potential of myelinated nerves jumps quickly between nodes of ranvier
MYELINATION SPEEDS UP CONDUCTION VELOCITY
- can localise channels at the nodes - allows the dollarisation / information to jump
What is multiple sclerosis?
Autoimmune nervous system disease where immune system attacks the myelin of the CNS
What does multiple sclerosis do?
Slows down or blocks messages between the brain and the body
Causes:
- visual disturbances
- muscle weakness
- trouble with coordination and balance numbness, prickling- pins and needles
- thinking and memory problems
Cause of multiples sclerosis and cure
Don’t know the cause
- no cure
What is Guillain-Barré syndrome ?
Autoimmune nervous system disease where immune system attacks the myelin of the PNS
What does Guillain-Barré syndrome cause?
Tingling in hands and feet
Progressing weakness of limbs and respiratory muscles
Effects on autonomic nervous system lead to altered heart rate and blood pressure
Cause unknown but usually associated with earlier infection
What are synapses
Specialised intercellular junctions which link neurons to eachother and to muscles
- pre-synaptic terminus
- post-synaptic terminus
- synaptic cleft with neurotransmitter released
Process of synaptic transmisssion at chemical synapses
- propergating axon terminates at the terminal bouton
- AP from propagating axon elicits release of neurotransmitter from synaptic vesicles into synaptic cleft
- neurotransmitter diffuses across synaptic cleft and stimulates receptor on the post-synaptic membrane
- this stimulates a response, usually an action potential, in the effector cell
- neurotransmitters include: Noradreanaine, glutamate, dopamine, ACh, seratonin
Neurotransmitter disorders
Neurotransmitters synthesised via biochemical pathways
- loss of enzyme GTP cyclohydrolase 1 leads to deficiency in several neurotransmitters
GTPCH deficiency:
- early onset (4-5 months)
- intellectual disability
- convulsions
- irritability
- hypersalvation
- difficulty breathing
Treatment with neurotransmitter precursors
Other deficiencies recapitulate effects
What is the neuromuscular junction
The synapse between motor neurons and muscle fibre
How many muscle fibres can one neuron innervate
Thousands of
One motor neuron can divide into many branches each ending in a neuromuscular junction - one neuron may innervate thousands of muscle fibres
What is a motor unit
Motor neural and all connected skeletal muscle fibres
Lots of fibres in a motor unit =
Fewer fibres in a motor unit =
Power
Endurance
Release of ACh at the neruomuscualr junction (motor end plate)
AP comes down the axon
ACh is released form synaptic vesicles
Binds to nicotinic ion channels that cause membrane depolarisation
Secondary synaptic cleft caused by folding (more surface area for more channels)
NMJ occupies a recess on the muscle surface: sole plate
Muscle fibre action potential
What is myasthenia gravis
Autoimmune disease - body produces antibodies to nicotinic receptor.
Binding of ACh is therefore blocked and muscle activation is inhibited
Most commonly affected muscles: eyes, face, those associated with swollaing
Acetylcholinesterase inhitiors alleviate symptoms
Immune suppressors can also help
Botox shit
Process of injecting Botox to elimitate skin wrinkles
Botulinum toxin A regulates ACh release from nerve terminals and thus selectively inhibits the underlying muscles ability to contract
Existing lines and furrows are thus smoothed
Toxin cleaves the protein involved in release of ACh from vesicle
