Nervous System Flashcards
What is the nervous system
A network of fibres which span the body, coordinating a diverse range of voluntary & involuntary actions
Transmits signals
Rapidly responds to changes within the internal & external environment
Works alongside endocrine to maintain homeostasis
What are the two main divisions of the nervous system
- CNS - central consists of brain & spinal cord
- PNS - peripheral nerves (not in the CNS)
functions of the cns in sensory input
Detects internal & external environment changes e.g Proprioception, sensation etc
Impulse is carried by sensory neurons
What is proprioception
The awareness of body position in space
(Standing with eyes closed)
functions of the cns with integration impulses
Processes sensory info by analysing, storing & making decisions
Abundant in the brain ‘perception’
Carried by interneurons
functions of the ans with motor impulses
Produces a response to sensory info to effect change
Impulse is carried by motor neurons
Sympathetic vs parasympathetic nervous system
Sympathetic arouses the body to expend energy ‘fight or flight’
Vs
Parasympathetic controls body to maintain & conserve energy ‘rest & digest’
Where are the branches of the sympathetic nervous system
Found in the thoraco-lumbar region
In front of the ribs
What is the enteric ns known as
The ‘brain’ of the gut, containing around 100 million neurons
Functions independently but regulated via the autonomic ns
Links with the cns via sympathetic nerve fibres (vagus nerve) - involuntary
Contains all 3 neurons
What are the two parts of the enteric ns
Submucosal plexus - deals with sercetions
Myenteric plexus - gut motility
Where is serotonin found
Predominantly in digestive tract
95% serotonin found in enteric nervous system
What are the main two types of cells found in the nervous system
- Neurons - process & transmit information, structural & functional units, electrically excitable (make up 10% of brain)
- Neuroglia aka ‘glial cells’ - glue! Supporting cells that nourish, support & protect, 6 types: 4 in the cns & 2 in pns (90% brain volume)
What is a nerve
Made up of one - thousands of neurons
What parts do neurons contain
Cell body, nucleus, dendrites
Axon
Myelin sheath & nodes of Ranvier
Terminal endings
Possess electrical excitability: the ability to create a nerve impulse ‘action potential’
Amount set at birth !
What is a stimulus
Anything able to generate an action potential
The stimulus can be internal or external
What are bundles of cell bodies in the cns known as
Grey matter
Describes the appearance of tissue in the cns
In the cns known as nuclei
In the pns known as ganglia
What are dendrites
The receiving portion of the cell. They communicate with other neurons/dendrites
What is white matter
Describing axons surrounded by myelin (white coloured)
functions of the axons of a neuron
Projections that carry nerve impulses towards anothr neuron, away from the cell body
They are covered by a membrane known as the axolemma
Ends are called axon terminals
Bundles are called tracts in the cns & nerves in the pns
Slow regeneration
What is the biggest nerve in the body
The sciatic nerve
Runs down from pelvis through leg to foot and approx 1m in length
What are the 3 main tracts in the cns
2 tracts go up towards the brain are sensory tracts
1 tract that leads away from the brain is the motor tract
functions of the myelin sheath
A multi-layered lipid & protein covering around the axons
Can cover up to 100 layers
Electrically insulates the axon & increases the speed of nerve conduction
Vit B12 co-factor needed for production of myelin
What are the two glial cells that form myelin sheath
- Schwann cells - produce in the pns
- Oligodendrocytes - produce in the cns
Mostly takes place throughout childhood (by 3yrs age)
What are the gaps between myelin along the axon of a neuron known as
Nodes of Ranvier
Functions of neuroglia cells
Non-excitory, surround & bind neurons
Supply nutrients & oxygen to neurons
Destroy pathogens & remove dead neurons
Formation of new cells as can undergo division if neurons damaged
50x more prevelant than neurons
Functions of astrocytes in the cns
Most numerous & largest, bind neurons to their blood supply
Provide physical support
Make up the ‘blood brain barrier’
Functions of oligodendrocytes in the cns
Myelinate axons in the cns
Which insulates & increases speed of nerve impulses
Functions of microglia cells in the cns
Phagocytic - mobile & can multiply
Derived from monocytes that migrate to the cns before birth
Functions of ependymal cells in the cns
Produce cerebrospinal fluid (csf) which cilia circulate
Epithelial cells that line the 4 ventricles of the cerebrum & central canal of spinal cord
Functions of schwann cells in the pns
Produce myelin around axons
Which insulates & increases speed of nerve impulses
Also participates in axon regeneration
Functions of satellite cells in the pns
Provide structural support & area of substance exhchange
Surround cell bodies in the pns ganglia
What is the graded potential in a neuron
Electrical signal that travels around the cell body of a neuron
For short distance communication
Occur in dendrites & cell body
Longer duration
Has no threshold for a signal
What is the action potential in a neuron
The elctrical signal that passes through the axon to another neuron
Has a threshold to be sent
Used for long distance communication
Shorter duration
What ions help facilitate graded & action potentials
Sodium & potassium
What is the resting potential of a neuron
The neuron has a negative charge/ions which creates a difference in electrical charge to the extracellular fluid which contains more positive ions
The separation of charges creates potential energy (approx -70millivolts)
helping to facilitate graded & action potential
At rest neurons possess an electrochemical gradient across the cell membranr
What are ion channels
Transport channels for ions created by transmembrane proteins that span across neuron membranes
They open in response to a stimulus
What is the sodium-potassium pump
As sodium and potassium try to move through the ion channels to equalise, the separation of charged is maintained by the pump, pumping 3 Na+ out for every 2 K+ it pumps back in
(Active trabsport ATP)
What is the process of action potential
Action potential has a threshold of -55mV which stimulus must reach to create an action potential
- Depolarisation = Stimulus causes reversing of the membrane potential, negative 70mV potential reaches positive around 30mV. Na+ channels open with Na+ flooding into cell building positive charge
- Repolarisation = membrane restored to -70mV
K+ channels open more slowly for K+ to move out of cell
What is the refractory period of action potential
Period of time after repolarisation in which a nerve cannot generate another action potential because Na+ & K+ are on wrong sides of the membrane
What is the absolute refractory period
Even a strong impulse cannot generate another action potential
What is the relative refractory period
Larger than normal stimulus needed to generate an action potential
What does conduction describe
The movement of a nerve impulse along the axon of a neurom
How does an impulse travel along an unmyelinated axon
Membrane becomes depolarised in a continuous conduction away from the cell body down the axon
Depolarisation & repolarisation Occurs of each adjacent segment of cell membrane, occuring in one direction only
Eg olfactory nerve is unmyelinated hence slower reaction
How do the nodes of ranvier cause saltatory conduction
At each nodes there are high concentrations of Na+ gates which causes the appearance of the conduction leaping from node to node
Saltatory conduction is much more energy efficient as less ATP is needed for the sodium-potassium pumps
Hence these nerves are vital for rapid response reactions
Why can ice help relieve pain
Lower temperatures slows speed of impulses
How do local anaesthetics work in pain relief
Block Na+ gates, preventing them from opening & thus stopping an action potential from being formed, inhibiting the nerve from transmitting pain messages
What are the ends of axon terminals called
Synaptic end bulbs
Space between these & post-synaptic neuron is the synaptic cleft which is filled with interstitial fluid. The nerve impulse is carried across this fluid by chemical messengers aka ‘neurotransmitters’ which are stored in synaptic vesicles
What impact does increased calcium concentration (after depolarisation) have on synapses
Causes exocytosis of synaptic vesicles, releasing neurotransmitters into the synsptic cleft
What is a neurotransmitter (NT)
A chemical messenger that gets released from a pre-synaptic terminal, causing an effect on the post-synaptic cell
More than 100 have been identified
What are the main categories of neurotransmitters
- Amino acids e.g glutamate, GABA (formed from glutamine)
- Monoamines e.g dopamine, serotonin, adrenaline
- Neuropeptides e.g endorphins, substance P
- Unique molecules e.g acetylcholine
What 2 charectoristics can be used to distinguish neurotransmitters
- Excitory = depolarisation of the post-synaptic neuron. Opens Na+ ion channels, more positive inner membrane
- Inhibitory = hyperpolarisation of post-synaptic neuron. Opens K+ ion channels move out, inner membrane becoming more negative
How can neurotransmitters be inactivated & removed for process to be sble to start again
Can occur by diffusion, enzymes breakdown (eg MAO for serotonin) or re-absorption
What is glutamate (glutamic acid)
Major excitatory NT in the CNS
Plays a major role in memory & learning
Synthesised from glutamine
What is GABA
Major inhibitory NT in the brain, produced from glutamate
1/3 brain synapses use GABA
It is essential in preventing neural over-activity
What vitamin is needed for conversion of glutamate to GABA
Vitamin B6
What is serotonin
Produced from amino acid ‘tryptophan’
95% produced in enteric ns
Vital role in the GIT, involved in intestinal motility (peristalsis) & epithelial cell secretion
Also plays a role in attention, sleep & pain regulation
Removed from a synapse by the enzyme MAO
Where is dopamine located
In several areas of the brain includinh the substantia nigra
‘Black substance’ as appearance
What is dopamine
Found in substantia nigra
Synthesised from the amino acid ‘tyrosine’
Plays a key role in movement, reward mechanisms, regulating muscle tone (deficiency = parkinsons) , cognition & emotion
Also inhibitor for prolactin
Re-uptake or removed by enzymes MAO & COMT
What is the amino acid tyrosine used for
The production of thyroid hormones, adrenaline, melanin, T3 & T4, dopamine
What are two types of monoamine nuerotransmitters
Adrenaline & noradrenaline
Excitatory hormones, opens Na+ channels
Found in the sympathetic nervous system, motor neurons & adrenal medulla
Re-uptake or removal by enzymes MAO & COMT
What two enzymes break down neurotransmitters
MAO = found in neutons & astrocytes
Breakdowns monoamines
& COMT
Catalyses Break down of adrenaline, noradrenaline & dopamine
Function of neuropeptides
Work to influence pain
Eg endorphins reduce pain (opiod analgesics)
Substance p amplifies pain
role of acetylcholine as a neurotransmitter
Excitatory
Released in neuromuscular junction to cause electrical impulse to diffuse across muscle to cause contractions, also used in cognition
Deficiency = alzheimers
Botox blocks ACH
Role of neurotransmitter nitric oxide
Excitatory
Vasodilation - lasts less than 10s
Formed form arginine
Used for angina, viagra enhances
What is a dermatome
A distribution of skin where nerves run along
What parts of a nerve carry the two sensory & motor neurons
Outer part = sensory information
Inner = motor information
Which nerves can regenerate
Glial cells huge regenerative capacity
Peripheral nerves can regenerate if schwann cells & cell body are intact
Where is the carpal tunnel
A narrow passageway in the anterior wrist containing tendons & the median nerve. These carry sensory info to the hand & controls movement in the hand & fingers
In carpal tunnel syndrome the median nerve becomes compressed
What nerve is impacted in bell’s palsy
Facial nerve that controls facial muscles becomes inflamed or compressed
Usually due to viral infection or post surgery/injury
Symptoms guillain-barre syndrome associated with
Post-infectious, autoimmune triggered, de-myelinating disease with neuritis
Antibodies cross react with lipids in myelin
Acute, ascending paralysis, progressive inflammation & demyelination of peripheral nerves, neuropathic pain jnto legs
Emergency care needed as quick progression
Pathophysiology of ms
Autoimmune inflammatory disease causing demyelination of axons in CNS neurons
T-lymphocytes attack myelin antigens causing multiple areas of sclerosis along axons which disrupts conduction
Most commonly optic nerve symptoms first as higher myelinated nerve
Where are motor neurons affected in MND
Progressive degeneration of motor neurons in spinal cord, motor cortex & brain stem - weakness in upper limbs
Sensory functions remain intact
What id dementia
A SYNDROME
caused by a number of brain disorders which cause
Memory loss, decline in other brain cognition, difficulty performing daily activities
50% cases caused by alzheimers
Key characteristic for dementia & alzheimers
Deposition of protein plaques, beta-amyloid in brain & atrophy of neurons
Plus Degeneration of cerebral cortex & reduced acetylcholine
What areas of the brain does alzheimers affect
Neurodegeneration of cerebral cortex
Hippocampus is among first area affected (short term memories)
The amygdala is often affected later & is key centre for longer term memories & emotions
Additional areas become affected as disease progresses
Risk factors for alzheimers
Heavy metal toxicity as degenerate blood brain barrier eg excess mercury, aluminium, copper
& oxidative damage
Vaccines containing polysorbate 80
Genetic links ApoE4 gene
Chronic inflammation including insulin resistance, leaky gut etc
Cardiovasc disease, pathogenic organisims
B vitamin deficiencies, omega3s
Hormone deficiencies
What area of brain is affected in parkinsons
Loss of dopaminergic neurons in the substantia nigra - regulates movement & reward process
Accumulation of abnormal proteins “Lewy Bodies” also found within neurons
What is bradykinesia
Short shuffling steps with difficulty stopping/starting
A common sign of parkinsons
What area of brain is affected in huntingtons disease
Neurodegenerative disorder affecting the basal ganglia - resulting in loss of muscle co-ordination (jerky movements) with cognitive impairment & mood changes
A genetic association with defect on chromosome 4
