Nervous tissue Flashcards
What are the two part of the nervous system?
- Central nervous system
- Peripheral nervous system
What makes up the CNS?
- Brain
- Spinal cord
What makes up the PNS?
- Cranial nerves
- Spinal nerves
What is the PNS divided up into?
- The somatic nervous system (SNS)
- The autonomic nervous system (ANS)
What are the two types of matter present in the brain?
- Gray matter
- White matter
What is gray matter composed of?
- Neuron perikarya (cell bodies)
- Glial cells
- Axons
- Dendrites
- Synapses
What is white matter composed of?
Axons, myelin sheath and glial cells
What is not present in white matter that is present in gray matter?
No neuron, perikarya or synapses
What are the two functional divisions of PNS?
- Sensory (afferent) divisions
- Motor (efferent) division
What does the sensory (afferent) divisions do?
Carries signals to the CNS
What does the motor (efferent) division do?
From CNS to effectors
What is are the divisions of sensory?
– Somatic division, eg touch, pressure
– Visceral sensory division, eg taste, hunger
What is are the divisions of sensory division? and give effectors for each
- Somatic motor division
Effectors: skeletal muscles - Visceral motor division (also called ANS)
Effectors: glands and cardiac/smooth muscles
What is the function of the somatic nervous system?
Motor innervation of all skeletal muscles
What is the function of the autonomic nervous system?
Motor innervation of smooth muscle, cardiac muscle, and glands.
What are the general functions of the visceral sensory?
Stretch, pain, temperature, chemical changes and irritation in viscera; nausea and hunger
What are the special functions of the visceral sensory?
Taste, smell
What are the general functions of the somatic sensory?
Touch, pain, pressure, vibration, temperature and propriception in skin, body wall and limbs
What are the special functions of the somatic sensory?
Hearing, equilibrium, vision
What are the major brain cell types?
- neurons
- astrocytes
- microglia
- oligodendrocytes (CNS)
- schwann Cells (PNS)
What is the function of oligodendrocytes?
Provide myelin sheaths that insulate axons
What is the function of capillaries (in brain)?
Form the blood-brain-barrier
What is the function of microglia?
The macrophages of the brain, provide an immune system against infections but release molecules that kill neurons
What is the function of astrocytes?
To release growth factors, create scar tissue, control
brain-blood-barrier
What is the soma?
The cell body
What is the function of dendrites?
They receive information
What is the synapse?
Where two neurons ‘meet’
What is the myelin sheath?
Protective neuronal ‘covering’
What are the three structural classifications of neurons?
- unipolar (1 branch)
- biopolar (2 branches)
- multipolar (many branches)
H & E function
Stains nucleus, no detail on cytoplasm can be seen
Nissl function
stains RNA – note absence from the axon (A)
Heavy metal impregnation technique function
Shows detail of the cytoplasm, negative image of the nucleus. Note the terminal boutons (B) making synapses with the cell body.
Gold method function
Provides excellent detail of neuronal shape shows the presence of cytoskeleton in the dendrites and axons; the blue counterstain shows the nuclei of surrounding cells.
Describe silver impregnation method
Purkinje cell in the cerebral cortex. These cells have a single small axon A at one pole and a finely branching dendritic tree at the other pole.
What is the function of sensory neurons?
- Nerves that make you feel
- Deliver info from sensory
receptors in PNS to CNS
What is the function of motor neurons?
- Nerves that make you move
- Deliver motor commands from CNS to PNS, muscle, glands
What is involved in neurotransmittion? (basic)
- Action potentials reach presynaptic terminal
- Stimulate Ca2+ entry
- Neurotransmitters released from synaptic vesicles
- Neurotransmitter crosses synaptic junction (synapse)
- On postsynaptic terminal transmitter binds receptor
- Receptor activated to transmit a signal in postsynaptic neuron
What is involved in neurotransmittion? (chemical)
- Presynaptic membrane depolarization induces
- Brief opening of calcium channels
- Calcium influx promotes exocytosis of synaptic vesticles with..
- Release of neurotransmitter
- Neurotransmitter reacts with receptors
- Promotes postsynaptic membrane depolarization
Diameter of synapytic vessels
40-60 nm
Where are synaptic vesicles concentrated?
In clusters at nerve terminals
What does neurotransmitter release involve?
- Targeting of SVs to release sites
- Docking of SVs to plasma
membrane - Priming to fuse SVs during impulse
- Fusion/exocytosis & transmitter release
- Retrieval of SV by endocytosis
‘KISS & RUN’ PROCESS
How do SVs recycle in presynaptic transmitter release?
Recycle without collapsing into membrane
What are two types of drugs?
- Agonist drugs
- Antagonists drugs
What is the function of agonist drugs?
Activate receptors like neurotransmitters
What is the function of antagonists drugs?
Inhibit receptors and block neurotransmitters binding to receptors
What are the steps in postsynaptic receptor activation?
- Neurotransmitters bind receptors
- Receptors are then activated
- Activation of receptors transmits signal into the cell
- Signals cause the cell to grow, die, move, etc
What does myelination aid with?
Signal conduction velocity down the axon
What is myelin?
An electrical insulator sheath wrapped around axons
What do oligodendrocytes produce?
Produce myelin on CNS axons
What do schwann cells produce?
Produce myelin on PNS axons
What are the short gaps in myelin along axons called?
Nodes of Ranvier
How many myelin sheaths does a schwann cell form?
One
What do myelin sheaths prevent?
Prevents flux of ions across the membrane
What is the distance between nodes of ranvier?
1mm
Where do the AP’s occur?
At ion channels
What do cable properties mean?
That the AP’s jump from node to node
What is the name for when the AP’s jump from node to node
Saltatory conduction
What does myelination aid with?
Proprogation down the axon
Name a consequence of demyelination
Multiple sclerosis
What is multiple sclerosis?
An auto Immune Disease which is when the body starts to destroy itself
What occurs in MS?
The body attacks and destroys the fatty tissue called myelin that insulates an axon/nerve, and is called demyelination.
What does MS affect?
The central nervous system and inflames the white matter in the brain which creates plaques.
What can occur if damage with MS is sever?
It can also destroy the nerve/axon itself
How does the PNS communicate with the CNS?
- Sensory (afferent) neurons conduct signals from receptors to the CNS
How does the PNS communicate with the CNS?
- Sensory (afferent) neurons conduct signals from receptors to the CNS
- Interneurons (association) are confined to the CNS
- Motor (efferent) neurons conduct signals from teh CNS to effectors such as muscles and glands
What is the sensory system composed of?
3 neurons
1oy Primary Neuron
2oy Secondary Neuron
3oy Tertiary Neuron
Where does interpretation of the three neurons occur?
In cortex
Afferents (direction)
Body to brain
Where does the 2oy secondary neuron run?
Up to thalamus
Where does the 3oy tertiary neuron run?
Up to cortex
Where is the 1oy primary neuron from?
Synapse
Efferents direction
Brain to body
General synapse basic connection
nerve-nerve
Neuromuscular junction basic connection
Nerve-muscle
Give the key features of generalised synapse
- Nerve-nerve synapse smaller than a NMJ with a narrower synaptic cleft
- Smooth postsynaptic membrane gives small surface area
- May be excitatory or inhibitory
- Numerous transmitter substances
What are the key features of the neuromuscular junction?
- NMJ is larger than a nerve-nerve synapse with a wider synaptic cleft
- Folds of postsynaptic membrane gives large surface area
- the NMJ is always excitatory
How many transmitter does the neuromuscular junction have?
One – Acetylcholine
How many muscle fibres in eye?
10
How many muscle fibres in biceps?
1000’s
What is the effect of curare on neurotransmission?
Blocks nicotinic acetylcholine receptor
What is the effect of curare on neurotransmission?
Blocks nicotinic acetylcholine receptor
What is the effect of organophosphates on neurotransmission?
Blocks acetylcholine-esterase
What is the effect of atropine on neurotransmission?
Blocks muscarinic acetylcholine receptor
What is the effect of botulinum toxin on neurotransmission?
Blocks acetylcholine release
What is the effect of black widow venom on neurotransmission?
Promotes acetylcholine release
What effect does curare have on muscle?
Muscle weakness
What effect does botulinum toxin have on muscle?
Muscle weakness
What effect does atropine have on muscle?
Dilates pupils, increases heart rate
What effect does black widow venom have on muscle?
Continuous contraction
What effect does organophosphates have on muscle?
Continuous contraction
What is myasthenia gravis?
An autoimmune disorder
What occurs in the body during myasthenia gravis?
Body makes antibodies that attack nicotinic ACh receptors at NMJ
What develops in myasthenia gravis?
Muscular weakness
Action potentials in myasthenia gravis?
Fewer action potentials in muscle so muscle contractile force is reduced
End plate potential of myasthenia gravis?
Smaller end plate potential which may be sub-threshold
Symtoms of myasthnia gravis
- Eye muscle weakness
- Weakness of other limbs
- Respiratory muscles – may need intubation to maintain airway
Treatments for myasthenia gravis
- Cholinesterase inhibitors eg neostigmine
- Immunosuppressants
Excitatory or inhibitory nerve-nerve synapse vs neuromuscular junction
NN - Excitatory or inhibitory
NMJ - always excitatory
Surface area of NN synapse vs NMJ
NN - smooth postsynaptic membrane gives small
surface area
NMJ - folds of postsynaptic membrane gives larger surface area
Size of NN synapse vs NMJ
NN- smaller with a narrower synaptic cleft
NMJ - larger with a wider synaptic cleft
Transmitter substances of NN vs NMJ
NN - numerous transmitter substances
NMJ - One transmitter – Acetylcholine
Potential of NN vs NMJ
NN - lower - always subthreshold
NMJ - higher - always suprathreshold
Summation in NN vs NMJ
NN - summation needed
NMJ - no summation needed
Give the functions of neuroglia
Protect the neurons and help them function - no axons or dendrites.
Give an example of neuroglia
In the fetus, guide young migrating neurons to their destinations
Number of neuroglia vs neuons
Neurons are outnumbered by neuroglia in the nervous system
What are the four types of neuroglial cells in the CNS?
- Astrocytes
- Oligodendrocytes
- Ependymal cells
- Microglia
What are the most abundant glial cells?
Astrocytes
What is the function of astrocytes?
- Form framework of CNS
- Link neurons to blood vessels
- Contribute to blood-brain barrier.
What do oligodendrocytes form?
Myelin sheaths in CNS
Function of ependymal cells
Line ventricles of the brain and central canal of the spinal cord; produce cerebral spinal fluid.
What are microglia formed from?
Monocytes
What is the function of microglia?
Engulf invading microbes
Where are microglia present?
In areas of infection, trauma or stroke
What are the two types of neuroglail cells in the PNS
- Schwann cells
- Satellite cells
What are schwann cells?
Myelinate fibers of PNS
What do schwann cells assist in?
In the regeneration of damaged fibres
Where are satellite cells present?
Surround cell bodies in ganglia
What is the function of satellite cells?
They regulate the chemical environment of the neurons
What do microglia act as?
Scavengers
Name a modified immune cell
Microglia
Give two functions of ependymal cells
- Create barriers between compartments
- Source of neural stem cells
Give a function of astrocytes
Take up K+, water, neurotransmitters
Give a function of schwann cells
Secrete neurotrophic factors
Give a functino of satellite cells
Support cell bodies
