13. Nervous System 1 Flashcards
What is the nervous system?
A network of fibres which span the body, coordinating a diverse range of voluntary and involuntary actions.
What are the two main divisions of the nervous system and what do they consist of?
1) Central nervous system (CNS) consisting of the brain and spinal cord.
2) Peripheral nervous system (PNS) consisting of all nerves outside the CNS.
What are the 3 main functions of the nervous system and what are they carried by?
1) Sensory - detecting internal and external environmental changes.
Carried by sensory neurons.
2) Integration - processes sensory information by analysing, storing, and making decisions.
Carried by interneurons
3) Motor - produces a response to sensory information
Carried by motor neurons.§
What are the two subcategories of the PNS and their further subcategories?
Somatic nervous system which controls voluntary muscles and transmits sensory information
Autonomic nervous system works automatically and controls involuntary body functions to maintain homeostasis.
Within the ANS there is the sympathetic nervous system and parasympathetic nervous system.
What controls the ANS?
Hypothalamus
What are the two branches of the ANS and where are they located?
1) Sympathetic Nervous System -
Thoraco-lumbar innervation
2) Parasympathetic Nervous System -
Cranio-sacral innervation
List 3 ways in which the Sympathetic and Parasympathetic NS differ in their effects on parts of the body.
They typically have opposite effects on the body:
Eyes
SNS - Dilation
PSN - Constrictions
Lungs
SNS - Bronchodilation
PNS - Brochocontriction
Heart
SNS - Increases heart rate and blood pressure
PNS - decreases heart rate and blood pressure
GIT
SNS - Decreases motility and secretions
PNS - Increases motility and secretions
What is the Enteric Nervous System and what is its function?
The ‘brain’ of the GIT - containing around 100 million neurons.
1) Sensory neurons monitoring chemical changes and stretching of the walls
2) Motor neurons govern motility and secretions s
3) Interneurons connect the two plexus (submucosa and myenteric plexus)
What are the two types of cells in the nervous system and how do they differ?
1) Neurons
- Process and transmit information
- Electrically excitable
- Most diverse type of cell in the body
2) Neuroglia (aka glial cells)
- Supporting cells that nourish, support & protect (against pathogens) neurons
- Much smaller than neurons
- More numerous than neurons (90% brain volume)
- Can multiply / divide
What is a bundle of neurons called?
A nerve
Name the main structural elements of a neuron
Cell body
Dendrites
Axon
Myelin sheath and nodes of Ranvier
Terminal endings
What is found in grey and white matter?
Grey matter = mostly cell bodies along with dendrites and unmyelinated axons.
White matter = mostly myelinated axons
What is a collection of cell bodies clustered together referred to as?
Nuclei in CNS
Ganglia in PNS
Briefly describe what an axon is and it’s key structural units.
Long, cylindrical projections that carry nerve impulses towards another neuron away from the cell body.
Axon’s cell membrane is called the axolemma.
The ends are called axon terminals.
Axon bundles are called tracts (CNS) and nerves (PNS)
What is the myelin sheath? What is it formed from and what is its function?
Formed by glial cells, it is a multi-layered lipid and protein covering around the axons.
It electrically insulates the axon and increases the speed of nerve conduction.
What is the main co-factor needed for the production of myelin?
Vitamin B12
What are the 4 neuroglia cells found in the CNS? And what are their key functions?
1) Astrocytes
Contribute to the blood brain barrier
2) Oligodendrocytes
Myelinate axons in the CNS
3) Microglia
Phagocytic immune cells
4) Ependymal cells
Produce cerebrospinal fluid
What are the 2 neuroglia cells found in the PNS? And what are their key functions?
1) Schwann cells
Myelinate axons in the PNS increase speed of nerve impulse conduction
2) Satellite cells
Provide structural support and exchange substances
What are the 2 types of electrical signals in a neuron?
1) Graded potential
For short-distance communication with no threshold for stimulus
2) Action potential
For long-distance communication with an all-or-nothing threshold
Describe a neuron at resting potential
Created by a build up of negative ions on the inside of the cell membrane, relative to the extracellular fluid which contains more positive ions.
Approximately -70mV
Intracellular fluid rich in potassium (K+) and large negatively-charged proteins.
Extracellular fluid rich in Sodium (Na+) and Chlorine (Cl-)
What’s the role of the sodium-potassium pump?
It regains homeostasis after action potential.
Pumps 3 Sodium (Na+) out for every 2 Potassium (K+) back in using ATP.
Describe the two phases of action potential
1) Depolarisation
Triggered by stimulation of nerve endings.
Must reach threshold of -55mV
Na+ channels open allowing Na+ to flood into the cell
Intracellular fluid peaks at about +30mV more positive than extracellular fluid
2) Reposalisation
Potassium (K+) channels much slower to react.
As Na+ channels close, K+ channels open.
K+ flood out of the cell, restoring the membrane to -70mV
What is the refractory period?
Period after repolarisation in which the nerve cannot generate another action potential because Na+ and K+ are on the wrong sides of the membrane.
Sodium-potassium pump pumps 3 Na+ out for every 2 K+ back into the cell to restore resting potential.
What are the two refractory periods?
1) Absolute refractory period - even a strong impose cannot generate an action potential
2) Relative refractory period - larger than normal stimulus needed to generate an action potential
What types of conduction occur in myelinated axons?
Saltatory conduction - where the current jumps from node to node leading to a faster conduction.
It is more energy efficient as less ATP needed for sodium-potassium pumps.
What are the key components found at the end of an axon terminal? (4)
Synaptic end bulb - end of axon terminal
Synaptic cleft - gap between synaptic end bulb and post-synaptic neuron.
Synaptic vesicles - store neurotransmitters
Neurotransmitters - carry nerve impulses across the synaptic cleft
Describe what occurs when a synapse transmits a signal.
1) Action potential arrives.
Depolarisation causes calcium (Ca2+) channels to open sending Ca2+ into the synaptic bulb.
2) Increase in Ca2+ concentration causes exocytosis of synaptic vesicles releasing neurotransmitters into the synaptic cleft.
3) Neurotransmitters diffuse across the synapse and bind to receptors on the post-synaptic neuron.
4) The open ion channels generating action potential
What is a neurotransmitter and list the 4 categories.
Neurotransmitters are chemical messengers that get released from a pre-synaptic terminal, causing an effect on the post-synaptic cell.
They can be excitatory or inhibitory.
1) Amino acids (eg glutamate, GABA)
2) Monoamines (eg dopamine, serotonin)
3) Neuropeptides (eg endorphins)
4) Unique molecules (eg acetylcholine)
Briefly describe 2 amino acid neurotransmitters
Glutamate
- major excitatory neurotransmitter in CNS
- major role in memory and learning
GABA
- major inhibitory neurotransmitter in brain
- produced from glutamate using vitamin B6
- essential in preventing neural over-activity
Briefly describe 4 monoamine neurotransmitters
Serotonin (5-HTP)
- 95% produced in enteric nervous system
- vital role in GIT with motility & secretions
- also in attention, sleep, & pain regulation
Dopamine
- located in several areas in the brain
- synthesised from tyrosine (same as T3 & T4)
- key role in movement, reward mechanics, cognition and emotion
- dopamine depletion associated with Parkinsons disease.
Adrenaline
Noradrenaline
Briefly describe neuropeptides and name some examples.
Small proteins acting as neurotransmitters and hormones.
Act as neuromodulators.
Endorphins & dynorphins are opioids (natural pain relief)
Substance P enhances the feeling of pain
Briefly describe two ‘unique module’ neurotransmitters
Acetylcholine (ACH)
- Excitatory
- Muscle contractions and cognition
Nitric Oxide (NO)
- Excitatory
- Vasodilation
What are two enzymes used to break down some neurotransmitters?
Monoamine oxidase (MAO)
- breaks down monoaminies
Catechol-O-methyl transferase (COMT)
- Catalysis for breakdown of adrenaline, noradrenaline and dopamine.
Briefly describe the process of a touch sensation.
Graded potential in sensory nerves.
Triggers the formation of action potential which travels to CNS.
Neurotransmitters are released at synapse where there are interneurons.
Perception occurs in the brain where the touch is interpretted.
Describe whether neuroregeneration can occur in the CNS and PNS
Peripheral nervous system:
Fibres can regenerate if cell body and Schwann cells are intact
Central nervous system:
Nerve fibres cannot regenerate.
What is carpel tunnel syndrome?
The median nerve becomes compressed within the carpal tunnel passageway in the anterior wrist.
List 3 potential causes of carpal tunnel syndrome.
Fluid retention (pregnancy)
Overuse (vibrating tools)
RA
Hypothyroidism
Trauma (swelling)
Tumour or fracture in the wrist
List 2 signs/symptoms of carpal tunnel syndrome
Tingling, numbness, pain in the median nerve distribution.
Symptoms often worse at night.
Weakness of grip
How can you diagnose carpal tunnel syndrome?
Tinel’s test and Phalen’s test show positive
What allopathic treatment is there for carpal tunnel syndrome?
Anti-inflammatory drugs
Corticosteroid injection
Splinting wrist
Physiotherapy
Surgery
What is the pathology where the nerve that controls the facial muscles becomes inflamed and compressed?
Bell’s Palsy
List two possible causes for Bell’s Palsy
Viral (herpes simplex)
Surgery/injury
What are the signs and symptoms of Bell’s Palsy?
Sudden unilateral weakness or paralysis of the facial muscles.
Also cannot close affected eye.
Loss of taste and intolerance of loud noises.
What is Guillain-Barre Syndrome?
Autoimmune disease associated with acute, ascending, progressive inflammation and demyelination of the peripheral nerves.
What is the typical cause of Guillain-Barre Syndrome?
75% autoimmune response triggered by a recent infection (1-3 weeks after respiratory or GIT infection, or post-vaccination).
What are the signs and symptoms of Guillain-Barre Syndrome?
Sudden, progressive, bilateral, ascending paralysis.
Sensory changes
Neuropathic pain in the legs
What allopathic treatment is there for Guillain-Barre Syndrome?
Emergency care - intensive care.
Plasma exchange
What is Multiple Sclerosis and how does it occur?
Autoimmune inflammatory disease causing demyelination of axons in the CNS neurons.
T-lymphocytes attack myelin antigens.
Sclerosis (scarring) occurs in multiple areas along axons disrupting conduction.
What’s the prevalence of MS?
Usually occurs 20-50 years
Affecting women 2:1 to men.
Higher prevalence away from the equator
Typically follows a relapsing-remitting pattern
List 3 causes of MS
Vitamin D deficiency (production of myelin)
Vitamin B12 deficiency (myelin formation)
Genetic susceptibility
Viruses (EBV, Measles)
List 4 signs and symptoms of MS
Visual symptoms - blindness, double vision
Deafness
Loss of balance
Burning sensation
Tingling & loss of sensation
Bladder urgency
Cognitive changes
Weakness
List 2 allopathic and 3 natural treatments for MS
Allopathic:
Corticosteroids
Physiotherapy
Natural:
Anti-inflammatory diet
Ketogenic diet
Vitamin D & B12
What is Motor Neurone Disease (MND)?
The progressive degeneration of motor neurons in the spinal cord, motor cortex and brain stem.
What hypothesis is there for the cause of MND?
Abnormal mitochondrial function causing oxidative stress in motor neurons.
What’s the prevalence of MND?
Onset >40yrs highest 50-70 yrs
More commonly affects men
What are the signs and symptoms of MND?
Weakness in upper limbs (dropping objects)
Wasting hand muscles and tremor of limbs
Later stages can affect legs.
Death by respiratory failure (3-5yrs)
NB No cure / treatment
What is Dementia?
A syndrome caused by a number of brain disorders which cause:
- Memory loss
- Decline in other aspects of cognition
- Difficulty performing daily activities
What are the 2 most common causes of dementia?
Alzheimer’s disease (50%)
Degeneration of the cerebal cortex and reduced ATC production
Vascular dementia (25%)
Due to cerebrovascular disease (eg stroke) and poor oxygen delivery
What’s the pathophysiology of Alzheimers disease?
Abnormal beta-amyloid protein deposition.
Atrophy of neurons.
Less ATC.
Hippocampus among the first areas affected.
Amygdala often later affected.
List 5 possible causes of Alzheimer’s disease.
Heavy metal toxicity (high copper & mercury, aluminum)
Genetic links - ApoE4 gene
Chronic inflammation (sugars, dairy, gluten)
Pathogens (gingivitis, herpes simplex virus)
Oxidative stress
Chronic stress (high cortisol levels)
Cardiovascular disease
Nutritional deficiencies
Hormonal factors (oestrogen deficiency)
List 2 early and 2 later stage signs/symptoms of Alzheimer’s disease.
Early:
Slight memory loss - especially short-term
Confusion
Decreased initiative.
Later:
Significant memory loss (incl. long-term)
Mood disturbances
Loss of sense of self
Depression
What investigations can take place to diagnose Alzheimer’s Disease?
Mini mental state exam.
MRI
CT scan
What allopathic treatment is there for Alzheimer’s disease?
Acetylcholinesterase inhibitors (ineffective)
List 3 natural approaches can be taken to prevent Alzheimer’s disease
Ketogenic diet
Beta-carotene
Omega-3 fatty acids
B vitamins
Ginko
Tumeric
What is Parkinson’s Disease?
A progressive neurological movement disorder caused by a loss of dopaminergic neurons in the substantia nigra in the midbrain.
List 3 possible causes of Parkinson’s disease
Mitochondrial dysfunction (oxidative stress)
Diet low in polyunsaturated fats.
Toxins such as pesticides.
Genetics
What are the 2 main pathophysiological causes of Parkinson’s?
1) Degeneration of dopaminergic neurons in the substantial nigra. This dopamine deficiency results in less control of movement.
2) Build up abnormal proteins (Lewy bodies) within neurons.
List at least 3 signs/symptoms of Parkinson’s
Bradykinesia (short, shuffling steps)
Resting tremor
Muscle rigidity
Stooped posture
What is the main allopathic treatment for Parkinson’s
Dopamine replacement - levodopa
What natural support is there for Parkinson’s?
Anti-inflammatory
Anti-oxidant
B vitamins
Exercise
