Nerves Flashcards
How are the nerves organised
The Central Nervous system and The peripheral nervous system
What is the CNS
Central nervous system which includes the brain and spinal cord
It receives, processes, interprets and stores information and sends messages destined for muscles, glands and organs
What is the PNS
The peripheral nervous system
Which transmits information to and from the CNS by way of sensory and motor nerves
What are the two divisions of the PNS
Somatic nervous system
Autonomic nervous system
How can the autonomic nervous system be further divided
Sympathetic: fight to flight
Parasympathetic: rest and digest
Enteric and cardiac plexus
What is the role of the autonomic nervous system
Regulates involuntary processes, including heart rate, respiration, digestion and pupil contraction
Operates automatically without conscious direction
What is the role of the somatic nervous system
Carries sensory information form the sensory organs to the CNS and relays motor commands to the muscle
Controls voluntary movements
What are the characteristics of neurones
Cells specialised for fast communication
High metabolic rates
Main component of brain’s grey matter
Can be classified by size, shape, connections, function, transmitters
What are the dendrites, axon, and synaptic terminals
Dendrites: signal inputs
Axon: signal conduction
Synaptic terminals: signal output
What are the three sizes of neurones
Multipolar neurone
Unipolar neurone
Bipolar neurone
What is contained within white matter
Axons carrying information to and from the brain
What are ganglia
Nodular masses of neurone cell bodies (ganglion cells) and supporting neuroglia (satellite cells)
What are the two types of ganglia in the PNS
Sensory: cell bodies of sensory neurones
Autonomic: cell bodies of efferent neurones from the autonomic nervous system
What are neuroglia
Supporting cells for neurones Regulate neurone metabolism and function Repair and recovery from injury Regulate blood brain barrier Destroy pathogens and remove dead neurones
What are the main types of neuroglia in the CNS
Astrocytes
Oligodendrocytes
Microglia
Ependyma
What are the main types of glial cells in the PNS
Satellite cells
Schwann cells
What is myelination
The process by which the fact membrane is generated around the axon
What is the spinal cord reflex pathway
Sensory receptor (site of stimulus) -> Sensory neurone (transmits afferent information to the CNS) -> Integration centre (one or more synapses within the CNS) -> Motor neurone (conducts efferent impulses to the effector organ) -> Effector (muscle fibre or gland response to impulses)
What is the average resting membrane potential
-65mV
What factors contribute to the resting membrane potential
Charged intracellular proteins
Na+/K+ pump
Potassium ions
Sodium ions
What is an action potential
The means by which a neurone sends information down its axon away from the cell body
It is an explosion of electrical activity that is created by a depolarising current
What is sensory transduction
Conversion of environmental or internal signals into electrochemical energy
What are the two types of synapses
Electrical: direct passage of current via ions flowing through gap junctions
Chemical: release of vesicles containing chemical transmitter which has an effect on receptors on a target cell
What is a neurotransmitter
A substance that is release at a synapse by one neurone that affects another cell, either neurone or effector organ in a specific manner
What is a neuromodulator
A substance that is release and modifies the action of a neurotransmitter but does not have a direct action itself
What is a neuroactive substance
A neutral tem is a substance is known to have an effect in the CNS but its precise action is not known
What is an inotropic receptor
A cluster of similar subunits forming ion channels that depolarise or hyper polarise the postsynaptic cell
What is a metabotropic receptor
A 7-transmembrane molecule coupled to intracellular proteins that transduce a signal to cell interior
What are the components of the motor unit
Motor unit consists of the motor nerve and all the muscle fibres innervated by that nerve with a size that depends on the function of the muscles
Where are the neurotransmitter vesicles
Neurotransmitter vesicles are lined up directly above structures on the postsynaptic cell known as postjunctional folds, which is where the neurotransmitter receptors are concentrated
What are the steps of neuromuscular transmission
Arrival of action potential depolarisation of terminal bouton -> Opening of voltage gated calcium channels -> Influx of calcium into the synaptic bouton -> Fusion of vesicles -> Exocytosis (release of ACh)-> Binding of ACh to nicotinic receptors on muscle cell membrane receptor activation -> Na+ enters -> membrane depolarisation
What drugs are used at the NMJ
Non depolarising competitive nAChR antagonist
Depolarising nAChR agonist
Cholinesterase inhibitors
What are some NMJ disorders
Lambert-eaton syndrome
Explain the functional anatomy of the neuromuscular junction
Highly specialised point of contact between the motor nerve cell carrying information from the CNS to the muscle fibre cells
What are non-depolarising competitive nAChR agonists
Mechanism: competes with ACh for nicotinic receptor binding sites causing gradual muscle paralysis
Reversed by AChR inhibitors
Hydrolysed by circulating esterase
Therapeutic use: surgery
Adverse effect: decrease BP, bronchospasm
Example: Tubocurarine
What are depolarising nAChR agonists
Mechanism: persistent depolarisation of the neuromuscular junction
Phase I: membrane depolarised causing brief period of muscle fasciculation (twitching)
Phase II: End plate eventually depolarises, but due to slow metabolism compared to ACh it continues to occupy the receptor (Flaccid paralysis)
Hydrolyse by circulating esterase
Therapeutic use: surgery given continuous IV short acting
Adverse effects: when administrated with halothane genetically susceptible people experience hyperthermia
Example: Succinylcholine
What are cholinesterase inhibitors
Mechanism: Inhibits AChR
Therapeutic use: antidote for non depolarising blockers. Treatment and diagnosis for myasthenia gravis. Nerve gas
Adverse effects: generalised cholinergic activation, abdominal cramping, diarrhoea, salivation, incontinence
Example: neostigmine
What are the three types of muscles
Skeletal
Smooth
Cardiac
What are the characteristics of cardiac muscle structure
Specialised form of skeletal muscle
Striated
Branched
Interconnected
Cardiac cells smaller the skeletal muscle cells
Rich in glycogen, myoglobin, and mitochondria
Contains actin and myosin myofilaments
What is the ultrastructure of cardiac muscle
Each cell usually contains 1-2 centrally located nuclei
Mitochondria comprises 30% of volume of cell vs only 2% in skeletal cell
What cell junctions make up an intercalated disc
Fascia adherens: anchoring sites for actin, connect to the closest sarcomere
Desmosomes (macula adherens): stop separation during contraction by binding intermediate filaments, joining the cells together.
Gap junctions: allow action potentials to spread between cardiac cells by permitting the passage of ions between cells, producing depolarisation of the heart muscle
What are the 4 main classes of antiarrhythmics
Class I: sodium channel blockers; treat ventricular ectopics
Class II: beta blockers; slow conduction in the SA and AV nodes
Class III: potassium channel blockers; treat ventricular tachycardia and atrial fibrillation
Class IV: calcium channel blockers; slow conduction in the SA and AV nodes
What are the upstrokes dependent on
SA and AV node action potential upstroke is Ca2+ dependent
Ventricular upstroke is Na+ dependent
What are the structural characteristics of smooth muscle
Usually 2 sheets of closely opposed fibres
Walls of all blood vessels except the smallest blood vessels and in the walls of hollow organs
Alternating contraction relaxation of 2 layers mixes substances in lumen of hollow organs causing peristalsis
What is the ultrastructure of smooth muscle
Fibres smaller than those in skeletal muscle
Spindle-shaped
Single central nucleus
More actin than myosin
No sarcomeres
Not well organised
No T-tubules and the sarcoplasmic reticulum is poorly developed
What are single-unit vs multi-unit smooth muscles
Single-unit: unitary smooth muscle, most common, gap junctions so act as a single-unit
Multi-unit: Lack gap junctions, cells innervated individually
What are the characteristics of pennate muscles
Feather-like in the arrangement of fascicles (fibre bundles)
Unipennate, bipennate, multipennate
What is the characteristic of fusiform muscles
Spindle-shaped
What is the characteristic of parallel muscles
The fascicles lie parallel to the long axis of the muscle
Flat muscles with parallel fibres often have aponeuroses
What is the characteristic of convergent muscles
Have a broad attachment from which the fascicles converge to a single tendon
What is the characteristic of circular muscles
Surround a body opening or orifice, constricting it when contracted
