Week 2 Flashcards
What are afferent neurones
Carry info from sensory receptors of the skin and other organs to CNS
What are efferent neurones
Carry motor info away from CNS to the muscles and glands of the body (PNS)
Where is the cell body located in Afferent neurones
Outside the spinal cord in the dorsal root ganglion
Cell body has a single axon that divides into 2 branches , one connected to sensory organ and another that carries sensory info to spinal cord via dorsal root
Where is the cell body located in efferent neurones
In the ventral horn of the spinal cord
Efferent axons leave spinal cord through the ventral root travel through spinal nerves and synapse with skeletal muscle cells found in neuromuscular junction
What is autonomic division
Regulates involuntary body responses
What is somatic division
Voluntary movement by skeletal muscles
What is the CNS
Brain and spinal cord
What is PNS
The nervous system outside the CNS
Connects sensory to CNS
Contains ganglia- collection of neuronal bodies found in the voluntary and autonomic branches of the peripheral nervous system
What are the three main types of neurones
Multipolar
Bipolar
Pseudo-unipolar
What are multipolar neurones
Motor/efferent
Single axon, many dendrites
What are bipolar neurones
Relay or special sense
One axon and one dendrite
What are pseudo-unipolar neurons
Sensory
Impulses don’t have to go through the cell body, one extension from its cell body
can go from dendrites to synapse
This neuron has an axon that’s split into two branches one to PNS and other to CNS
What are glial cells
Predominant cell type within the CNS
Responsible for creating optimum microenvironment for neuronal activity
Four main types:
Astrocytes
Microglia
Ependymal
Oligodendrocytes
What are astrocytes
Star shaped
Contribute to the blood-brain barrier
Most abundant cell type
Provide structural and metabolic support, provide nutrients to neurones such as cholesterol
Two types- fibrous (white matter), protoplasmic (grey matter)
What are microglia
Immune function- phagocytosis
Exist in 2 forms:
Resting (ramified)
Activated- phagocytic
Maintain brain homeostasis
Dysregulation can lead to neurological disease
Prevent pathogens entering CNS, clear dead neurones
What are ependymal cells
Simple ciliated epithelial cells lining the ventricles
Cerebrospinal fluid synthesis
Provides nutrients creates environment needed
Movement of cilia helps regulate CFS
What are oligodendrocytes
Only in CNS
Cells with few processes
Create myelin sheaths around neurones in the CNS
Provide metabolic support and electrical insulation
Have the ability to myelinate several neurons at a time
What are Schwann cells
Only in PNS
Myelinate one axon
Create myelin sheaths around neurones in PNS
Provide metabolic support and electrical insulation
What is myelination
Myelin is a lipid sheath 0.5-2.5 micrometers thick
Created by glial cells which surrounds axon of a neurone
Increases speed of conduction, provides protection and structural support
Saltatory conduction
Created by oligodendrocytes in CNS Schwann cells in PNS
Unmyelinated neurons
Axons are still surrounded by Schwann cells
The Schwann cells have a more supportive role
Myelin sheath doesn’t totally encapsulate neuron
What is the somatic nervous system
It’s a unique collection of tissues of the nervous system
Under direct command of the human organism- voluntary division of NS
It allows us to accurately localise sensations throughout the extent of the body
Also gives us awareness of our body position in 3D - proprioception
What are three muscle types
Skeletal (somatic)
Smooth- autonomic
Cardiac-autonomic
What are neuromuscular junctions/ motor end plates
Conduct stimuli to skeletal muscle
What is a fascicle
axon bundles
What is a nerve
Multiple fascicles of axons
What does the neuron consist of
Body (soma or perikaryon)- contains two structures Nissl substance and cytoskeletal components
Dendrites- multiple covered by dendritic spines, travels to the cell body
Axon- terminal portion has branches, each has a synaptic ending, away from the cell body
What are anaxonic neurons
Contain no axon
In CNS has coordinating function between neurons
Do not produce action potentials but regulate local electrical changes of adjacent neurons within brain or spinal cord
What do macrophages in the body tissues develop from
Monocytes in the blood flow that originate from the red bone marrow which would have had an embryonic precursor
This embryonic precursor cell also serves as an organ for microglia
So also are phagocytic cells and immunoprotect the brain and spinal cord
What is the function of microglia cells
To keep environment clear of debris, if infection occurs they become activated
They can phagocytose
Where are satellite and Schwann cells present
Only in PNS
What are the functions of satellite cells
Electrically insulates PNS cell bodies
Regulates nutrient and waste exchange for cell bodies in ganglia
What are the functions of neurolemmocyte
Surround and insulate PNS axons and myelinate those having large diameters
Allows for faster action potential propagation along an axon in the PNS
Neurolemmocytes also known as Schwann cells are glial cells found in the PNS
What is the epineurium
Outermost layer, covers the entire nerve
What is the perineurium
Separates nerves into fascicles and consists of neuroepithelial perineurial cells which are joined to each other by tight junctions to form the protective diffusion barrier
The blood-nerve barrier, responsible for maintaining the physiologic microenvironment of the endoneurium
What is the endoneurium
Surrounds individual axons and their associated Schwann cells
What is the electrical synapse
Fastest and most primitive
Between adjacent cells or neurites
Direct transfer of ionic current
Bi-directional
Allows synchronous activity
Relatively rare between neurons in the CNS
Glia-neuron, glia-glia communication
What is the chemical synapse
Close association between the presynaptic and the post synaptic membrane
Presynaptic terminal releases neurotransmitter
Diffuses across the synaptic cleft
Interacts with receptor on the postsynaptic membrane
Unidirectional transfer of information
How does a synapse work
Action potential invades nerve terminal sodium ions move in
Depolarisation triggers Ca2+ channel opening, calcium influx
Neurotransmitter release by exocytosis (Ca2+ dependent)
Diffusion across the synapse and receptor binding on postsynaptic membrane
Post synaptic effect
Rapid termination of signal by reuptake of neurotransmitter or enzymatic breakdown
Neurotransmitter receptors
Membrane spanning protein molecules
Transmitter binding causes structural/conformational change=signal
Receptors are specific for a neurotransmitter
One neurotransmitter- several receptor subtypes
Types of receptor signalling mechanisms
Ionotropic (receptor operated/ ligand gated channels)
Metabotropic G-protein coupled)
What is ionotropic
Transmitter binding
Conformational change
Channel opening
Ion movement
What is metabotropic
Transmitter binding
Conformational change
Activates G-protein
Activates ‘effector systems’
Indirect effects e.g. open or close ion channels, stimulate or inhibit enzymes/ secondary messenger systems
what is spatial summation
Summing of post synaptic potentials generated at separate synapses
What happens when the threshold is reached
Voltage dependant Na+ channels open
Action potential generated
What is temporal summation
Summing of post synaptic potentials generated at same synapse, if they occur in rapid succession
What is the specific functional modality of the majority of axons of a ventral root
Motor (somatic) neurone
EPSP
Excitatory post synaptic potential
IPSP
Inhibitory post synaptic potential
