Neurones Flashcards
what is nervous tissue composed of
- Neruones – transits the information
- Glia – sepicalised support cells
what is the same as a PNS ganglion in the CNS
- a brain nucleus
what is brain nucleus or PNS ganglion
it is a collection of neurones with common circuitry and function that are found in the grey matter
in the PNS what is a collection of axons called
it is always called a nerve
in the CNS what is a collection of axons called
might be called various names including fasciculus, column, leminscus, tract or bundle
How do you stain cell bodies and the first part of dendrons
Staiend blue with nissl stain due to the large amouts of RER
describe the staining comparison between neurones and glial cells
Neruones are larger compared to the smaller glial cells
– but glial cells have more predominant nuclear staining are supporting glial stage – darker blue for the nucleus
What passes through the brain stem
- Axonal tracts carrying sensory input to the rest of the brain as well as morot outputs from the brain to the spinal cord pass through it
- Motor and sensory innervation ot the head and neck is carried in cranial nerves arising from the brain stem
What is a neurophil
It is a dense tangle of neuronal axons and dendrites and glial processes
- it is the site of communication between various components for example where synapses are formed between terminal boutons of axons and dendritic processes
dendrites ..
have spikes this is how you distinguish them from axons
- axons also have myelin sheaths making them easy to identify
how does myelin stain
Myelin stains in somium fixed preparations so axons have myelin sheaths that are easy to idetify
Describe the characteristics of the neurone
- Irritable and conductive – recepotrs and ion channelsl and membrane properties
Parts of the neuroen - Dendrities – sensory (afferent) – receive information and relay it to the cell body (electrical signals)
- Cell body – large nucleus, abudnatn in rer, performs synthetic and metabolic functions, integrates information at the axon hillock to produce axon potentails
Describe the parts of the neurone
- Cell body (or soma)
- axon - effector portion and propagates the action potential (efferent role goes away)
- terminal boutons - terminal expansions of the axon specialised for chemical neurotransmission, are at the end where cell to cell communication occurs at the synapses, within terminal boutons there are synaptic vesicles which contain the neurotransmitter used in chemical neurotransmission
- dendrites - these arise from the cell body (afferent role goes to)
- only one axon will leave the cell body
- action potential is initiated at the axon hillock
what increases the speed of the action potential
- myelination
- larger diameter
what does afferent mean
goes to
where does efferent mean
away from
what is the synapse
this is a intracellular junction between neurones
describe the structural of the synapse
- A synapse possess a mechnaisical cytoskeletal links and specilaisations for chemical neurotransmission
- The presynaptic side; the terminal bouton which contains neurotransmitter in synaptic vesicles
- Action potentials invading the bouton usually elicit the release of a neurotransmitter
- The synpatic cleft is a small space between the cells
- Post synaptic side – receptors for the neurotransmitter permit the seocnd cell to respond to the input
What do the glia do
- Provide structual, metabolic and defensive support for nervous tissue
What are the glia in the CNS
- Astrocytes
- Oligodendrocytes
- Ependymal cells - line the ventricles
- Microglia
what are the gila in the PNS
- Satellite cells – support like astoryctes
- Schwann cells – form myelin in PNS
What is the function of astrocytes
- Strucutral fraemwork for migration of cells
- Transport substances between blood vessels and extracelluar space
- Fibdrocollagenous scars – astrocytes support the scar as they proliferate at the site of injury
- Contribute to energy metabolism by releasing glucose
- Insulate neuronal cell bodies and dendrites at non-synaptic sites
- Form continuous layer over blood vessels: form and maintain the Blood- Brain- Barrier
- Form glial scars at sites of damage: gliosis
- regulate the composition of the extracellular environment of the CNS
What is the function of oligodendrocyte
- insulate axons preventing their spontansoues or accidental depolarisation
- produce myelin by wrapping around axons many times
- myelination of an axon increases action potentail conduction veloctiy as they insulate and act as a barrier against ion flux, allows action potential to jump from node of ranviers, this is saltatory conduction
- a singel oligodendroycte can insulate many axons
- common in white matter
- found in grey matter around neurones where they contribute to supportive roles in astrocytes
- have a clear round body
What is the function of ependymal cells
- epithelia like cells line cavities of the brain and spinal cord
- specialised type of ciliated, cubodial epithelium linign the ventricles of the brain
- they are modified in areas to form part of the choroid plexus that produces erebrospinal fluid which bathes the ventricles
What is the function of the microglia
- act as defensive cells of the CNS perform the function of macrophasges
- activated by damage or disease when they proliferate and enlarge and rapidly remove damaged cells and debris
- hard to identify without speciali stains
what is the function of satellite cells
- found in collections of cell bodies in the pNS
- peform similar functions to astrocytes as they physically and metabolically support neurones within the peripheral ganglia
what is the function of PNS Schwann cells
- funciton in the same as oligodendrocytes in the CNS – inulsation and myelin fomration
- each cell only myelinates one segment of myelin around an axon
- small diameter axons are enveloped by a cytoplasmic process of the Schwann cells these are called unmyelianted axons
- larger diameter firbes are wrapped by a variable number of layers of the schwann cell plasma memrbane which forms a yelin sheath these are myelinated aoxns
- envelop all axons in the PNS providing strucutre and metabolic support
Describe the overall function glial cells
- non neuronal supporting cells of the nervous tissue
- provide mechanical and metabolic support for neruones
- have protective roles in nervous tissue
- important in repair of nerveous system lesions
Describe peripheral nerves
- very little connective tissue is found in the CNS as most of its supporting functions are provided by neuroglia
- but peripheral nerves are invested with connective tissue sheaths which have morphologically similar to those found in surrounding muscles and termed the endoneurium, perinurium (surroudns the nerve fascicles) and epineurium
Describe the neuromuscular junction
- nuerotransmitter is acetylcholine which is released into the synaptic cleft
- the postsynaptic muscule plasma memrbane called the sacrolemma, is highly folded and forms secondary clefts
- the released acetylcholien binds to acetylcholine receptors on the skeletal muscle and initates a repsonse in the msucle firbe
- acetylcholiestrase is also found in the seocndary clefts
- the enzyme catalyses the break down of acetylcholien and thereby limits the duration of stimulation elicited by each nevre imupulse
Describe the motor unit
- the neuromuscualr junction or motor end plate is the speicla synpatic contact between a motor neuronea dn a skeletal muscle fibre
- motor neuroens may synapase with more than one muscle fibre
- the motor unit is a motor nueone and all the skeletal msucle fibres that it contacts
- all the fibres of a motor unit ocntract simultaneoulsy upon sitmulaution by the motor neurone
what has few motor units
- skeetal msucles which are involved in precise m- the terminal part of an axon divides into branches and eahc branch supplies a motor end plate with a terminal bouton ovements have motor units including only a few muscle fibres
what has a large number of motor units
- large abdominal muscles have motor units tht include over 100 muscle fibres
what does the terminal part of the axon do
- the terminal part of an axon divides into branches and eahc branch supplies a motor end plate with a terminal bouton
