Nervous tissue and the neuromuscular junction Flashcards
what does the afferent division of the CNS do?
provide input to the CNS from the periphery
what is the PNS?
the peripheral nervous system
what is the efferent division of the CNS do?
output from CNA to periphery
what is the CNS?
central nervous system
what are the divisions of the CNS?
the afferent division
the efferent division
what are the two components of the efferent division?
the somatic nervous system
The autonomic nervous system
what are the two inputs into the afferent division?
sensory stimuli
Visceral stimuli
what are the features of an neuon?
dendrites
Cell body
Axon hillock
Axon
Collateral
Axon terminals
how long is an axon?
may be 1mm to more than 1m long
what are multipolar neurons?
multiple dendrites project from the cell body
what are bipolar neurons?
single dendrite opposite from axon
what are pseudo-unipolar neurones”
Axon and dendrite rise from a common stem of the cell body
what is the nucleus of a neuron?
Large nucleus, often large, reflecting metabolic demand
does the neuron have lots of mitochondria?
yes
where is ER found in the neuron?
Lots of ER, particularly in large neurons. They can be found in dendrites but not in axons
what make up the cytoskeleton of a neuron?
Numerous neurofilaments. Together with microtubules make up the cytoskeleton.
what structures do neurons contain?
Rough endoplasmic reticulum
Nucleus
Mitochondria
Golgi apparatus
Synapse
Terminal bouton of adjacent neuron
Plasma membrane
what are the divisions of the central nervous system?
Macroscopically divided into grey matter and white matter
what is white matter?
The white matter in the cerebrum can be delineated with a dye with an affinity for myelin.
what is grey matter?
The outer cortex (C- gray matter) is composed of nerve cells and does not contain myelin
what makes up the grey matter?
neuron cell bodies, dendrites and axons
what makes up the white matter?
axons; many myelinated
what are the different glial support cells?
oligodendrocytes
astrocytes
microglia
ependymal cells
what is the function of oligodendrocytes?
CNS equivalent of Schwann cell
They Myelinate axons
what is the function of astrocytes?
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 the spinal cord
what are microglia?
specialised immunological cells of the CNS
what are the structures in the peripheral nerves?
fascicles
endoneurium
perineurium
epineurium
what is the fascicles?
a bundles of nerve fibres that form the nerve
what is the endoneurium?
Axons inside the fascicles are surrounded by collagenous support tissue
what is the perineurium?
The fascicles are enclosed in dense collagenous tissue
what is the epineurium?
The fascicles are bound together by loose collagenous tissue
how do large and small fibres differ?
in the degree to which they are enveloped
what is the function of schwann cells?
Peripheral nervous system axons are enveloped by Schwann cells, providing structural and metabolic support
what are small diameter axons?
axons of the autonomic system and small pain fibres are simply enveloped by the cytoplasm of Schwann cells
what are myelinated nerves?
the axon is invaginated into the schwann cell cytoplasm
the outer membrane of the schwann cell fuses to fom a mesaxon
what is a mesaxon?
when the outer membrane of the schwann cell fuses to the nerve
The mesaxon rotates around the axon, wrapping the axon in concentric layers of the membrane
what is the myelin sheath?
concentric layers of the axon membrane
what are the nodes of ranvier?
gaps where axons are not myelinated
why are nodes of ranvier important?
important in signal conduction along the axon
where is another place that the nodes of ranvier located?
also found in CNS with gaos in oligodendrocyte myelination
what is the axon resting membrane potential?
An electrical potential exists across the plasma membrane of all cells. The fluid inside the cell has an excess of negative charges and the fluid outside the cell has an excess of positive charges
what is the difference between myelinated cells and non-myelinated cells?
the non-myelinated nerves are much slower at conducting an action potential than myelinated nerves
how does an action potential travel in myelinated nerves?
action potential of myelinated nerves quickly jumps between nodes of ranvier
how does myelin help conduction of AP?
speeds up the conduction velocity
what is multiple sclerosis?
Autoimmune nervous system disease where immune system attacks the myelin of the CNS
what is the problem within the CNA for multiple sclerosis?
Damage to the myelin sheath
Slows down or blocks messages between the brain and the body
hwhat are the symptoms of multiple sclerosis?
Visual disturbances
Muscle weakness
Trouble with coordination and balance, numbness, prickling (“pins and needles”)
Thinking and memory problems
what is the cause of MS?
the cause is unknown
what is guillain-barre syndrome?
Autoimmune nervous system disease where immune system attacks the myelin of the PNS
what is the PNS?
the peripheral nervous system
what are the symptoms of guillain-barre syndrome?
Tingling in hands and feet
Progressing weakness of limbs and respiratory muscles
what causes guillain-barre syndrome?
unknown cause but usually associated with earlier infection
what do effects on the autonomic nervous system lead to?
altered heart rate and blood pressure
what are synapses?
synapses are specialised intercellular junctions which link neurons to each other and to muscles
where does a propagating axon terminate?
at the terminal bouton
how does an action potential propagate from a chemical synapse?
action potential from propagating axon elicits release of neurotransmitter from synaptic vesicles into synaptic cleft
what does the neurotransmitter do once released into the synaptic cleft?
neurotransmitter diffuses across the synaptic cleft and stimulates receptor on the postsynaptic membrane
what are some examples of neurotransmitters?
noradrenaline
glutamate
dopamine
acetyl-choline
serotonin
how are neurotransmitters synthesised?
via biochemical pathways
what deficiency causes neurotransmitter deficiency?
loss of GTP cyclohydrolase 1
what are the symptoms of GTPCH deficiency?
Early onset (4-5 months)
Intellectual disability
Convulsions
Irritability
Hypersalivation
Difficulty breathing
what is the neuromuscular junction?
the synapse between motor neurons and muscle fibre
what is the neuromuscular junction also known as?
the motor end plate
how do motor neurons branch?
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 neuron and connected skeletal muscle fibers
what do lots of fibres provide?
power
what do fewer fibres provide?
endurance
what allows a constant state of partial contraction?
alternation between motor neurons
what happens at the neuromuscular junction?
Acetylcholine released from synaptic vesicles
Binds to nicotinic ion channels that cause membrane depolarization
Secondary synaptic cleft caused by folding
where is the neuro muscular junction?
the NMJ occupies a recess on the muscle surface, sole plate
what is Myasthenia gravis?
Autoimmune disease, the body produces antibodies to nicotinic receptor
how does Myasthenia gravis occur?
Binding of acetylcholine is therefore blocked and muscle activation is inhibited
what is commonly effected in myasthenia gravis?
most commonly effected muscles
eyes
face
those associated with swallowing
how is myasthenia gravis treated?
with acetylcholinesterase inhibitors with alleviate symptoms
Immune supressors can also help
how does Botulinum toxin A work?
botulinum toxin A regulates ACh release from nerve terminals and thus selectively inhibits the underlying muscles ability to contract
