The mechanics of the nervous system

Question 1

what is the brain (CNS)

Answer 1

• Localisation of functioning and specialisation of functioning of brain regions.
  
  • Where underlying mechanism for psychedelics is occurring
    ○ Greater communication of the brain areas.
    § Facilitates the functioning of the brain
  • Corpus colosseum is in the middle of each hemisphere and allows for communication between hemispheres
    ○ Determines the efficiency of the brain functions.
  • Different regions intercommunicate but have separate functions.
    ○ Join to make higher order functioning.
    Different lobes to the cerebellum

Question 2

what are the different parts of the brain?

Answer 2

frontal lobe
temporal lobe
occipital lobe
parietal lobe
cerebellum
spinal cord

Question 3

what is the spinal cord?

Answer 3

• Continuous with brain stem
  ○ Part of the brain
• Long conical structure
  ○ Vertebra in the brain have holes in the which is where this sits.
• Thickness of adult’s little finger
• Mediates information transmission between brain & body below the neck
• Protected by vertebrae (24 vertebra)
• Core of grey matter surrounded by white matter
  ○ White matter= fatty myelination of neurons.
  More white matter= better communication of neurons.

Question 4

what are the 3 major functions of the spinal cord?

Answer 4

○ Coordinating certain reflexes
○ Conduit for sensory and motor information
§ from brain to body= efferent pathway
§ Afferent pathways= body to brain

Question 5

what is the difference between afferent and efferent neurons?

Answer 5

• Afferent neuron axons enter cord in dorsal root & terminate in dorsal horn ENTER
• Afferent neurons go to the CNS
  ○ Carry info from the environment to the CNS.
• Efferent neurons have a cell body in ventral horn & axons leave cord in ventral root LEAVE
• Efferent neurons go to the effectors. (heart, muscles etc)
  What we want to change to adapt to our environment.

Question 6

what is the PNS function?

Answer 6

• Connects CNS to limbs & organs via cranial and spinal nerves
• Conveys info from environment to CNS (afferent neurons)
• Conveys messages from CNS to muscles and glands (efferent neurons)
• Each neurone is connected to receptors which receive info from the environment.
  ○ E.g.: light sensitive/ touch sensitive/ sound sensitive.

Question 7

what are the nerves in the PNS?

Answer 7

• Neuron axons grouped into bundles
  ○ Only exits in the PNS
• Only present in the PNS
• 43 pairs
  ○ 12 cranial nerve pairs (come off the brain)
  ○ 31 spinal nerve pairs (come off the spinal cord)

Question 8

what are the cranial nerves in the PNS?

Answer 8

• 12 pairs
  ○ 10 → brainstem
  ○ I & II → forebrain ( has two nerves coming put of it: olfactory and the oculomotor)
• Information between the brain and body above the neck
• Exception: Vagus nerve (goes to internal organs rather than body)

Question 9

what is the role of the spinal cord in the PNS?

Answer 9

• 31 pairs
• Each pair is associated with a particular segment of spinal cord
• Named dependent on vertebral level they attach
  ○ Depending on the vertebra they branch off.
• Spinal nerves can contain sensory & motor fibres
  ○ Sensory (afferent)
  ○ Motor (efferent)

Question 10

what are the divisions of the PNS?

Answer 10

peripheral nervous system splits into the somation nervous system (voluntary) and the autonomic nervous system (involuntary)
the autonomic nervous system then splits off into the sympathetic nervous system, parasympathetic system and entric nervous system.

Question 11

what is the somatic nervous system?

Answer 11

• Voluntary control of body movement
  ○ About movement
  ○ Make a decision to move
• Receives sensory information and controls spinal nerves that innervate skin, joints & muscles
  ○ That we act on
• Afferent neurons carry sensory info from skin (sensory neuron)
  ○ From skin to brain
  ○ Proprioceptor afferent nerves in the muscles (stop us over extending)
• Efferent neurons control skeletal muscles via (motor neuron)
  ○ Back to the body that control our movement.
• Neurons are excitatory
  If one end is stimulated of a neurone, it will continue to excite other neurones which stimulates movement at the end of it.

Question 12

what is the autonomic nervous system?

Answer 12

• Controls involuntary functions and internal environment
  ○ At a level we don’t think about.
  ○ Stabilising internal environment and conserving energy.
  
  • Branching off of parasympathetic (slow down) and sympathetic (energy, move away from danger) systems.
  • Enteric system (digestion and gut)
  • Afferent neurons carry sensory info from internal organs to CNS
    ○ From internal organs into CNS.
    ○ Mid and high brain- survival functions
  • Efferent neurons control smooth muscle (part of intestinal tract), cardiac muscle & glands
    ○ Stimulates enzymes to break food down
    ○ Speeds up heart rate or slows it down
  • Neurons are excitatory or inhibitory
    ○ Due to it being regulatory
  • Has three further sub-divisions:
    a. Sympathetic Nervous System,
    b. Parasympathetic Nervous System and
    Enteric Nervous System

Question 13

what is the sympathetic nervous system?

Answer 13

• Any responses for activities which expend energy
• Coordinates Fight or Flight response
• Expending of energy

Question 14

what is the parametric nervous system?

Answer 14

• Activities involved with increase in the body’s supply of stored energy
• Coordinates Rest and Relax response
  ○ reenergise
• Rest and digest
  Replenishing of energy

Question 15

what is the entric nervous system?

Answer 15

• The “second brain”
  ○ 100 million neurons (compared to 86 billion in the brain)
• Lines your gastrointestinal tract from oesophagus to rectum
• Main role is controlling digestion
  ○ swallowing
  ○ release of enzymes
  ○ control of blood to facilitate nutrient absorption

Question 16

what are the components of a nerons structure?

Answer 16

dendrites
nucleus
cell body/soma
myelin sheath
node of ravier
axon terminal
shwann cell

Question 17

what are sensory neurons?

Answer 17

• Part of PNS
• Contain sensory receptors for detecting sensory changes
• Sends information about these changes to CNS
• Cell body in PNS, axon enters CNS (axon terminals located in CNS)
• Receptors of sensory neurons

Question 18

what are motor neurons?

Answer 18

• Part of PNS
• Synapses to skeletal muscle to command movement or onto glands to release hormones
• Relays signal from CNS to PNS
• Dendrites & cell body in CNS, axon enters PNS
• Movement of muscle spinals
• Create contractions of the muscles.

Question 19

what are interneurons?

Answer 19

• In CNS
• Receives info from sensory neurons
• Sends info to motor neurons
• Link afferent and efferent nerves
• Integrate / change signal
  ○ Integrate: inputs from multiple afferent neurons – average signal (modulate)
  Change: Interneurons can provide excitatory or inhibitory signals (decision making processing)

Question 20

what are thge axons of the motor neurons located?

Answer 20

peripheral nervous system

Question 21

what is the neuronal membrane?

Answer 21

• Made of two layers of lipid molecules
• Lipid molecules
  ○ Hydrophilic (water loving) heads (attract water, want to go to intracellular and extracellular fluids)
  ○ Hydrophobic (water hating) tails
• Barrier: water soluble molecules cannot pass through
• Particularly impermeable to ions
  ○ Key part of the cell (particularly the axon)
  Cell is impermeable to ions.

Question 22

what is the fluid environment?

Answer 22

• Fluid environment containing ions
  ○ Intracellular fluid (internal)
  ○ Extracellular fluid (external)
• Anions (-ve)= Chloride (Cl-) Predominantly extracellular/ Organic ions (A-) Only intracellular
• Cations (+ve)= Sodium (Na+) Predominantly extracellular/ Potassium (K+) Predominantly intracellular
• Move around to create action potential.

Question 23

what are the movements of ions?

Answer 23

• Ions move because of:
  ○ Concentration gradients (via diffusion)
  Electrical force (via electrostatic pressure)

Question 24

what is diffusion?

Answer 24

• Ions are subject to the force of diffusion:
  ○ Even distribution within a given medium
  ○ Ions move from an area of high concentration to an area of low concentration, moving down the concentration gradient
  § Diffusion
  Electrical forces.

Question 25

what is electrostatic pressure?

Answer 25

• Starts the electrostatic pressure and then return back to resting.
• Electrical charge produces an action:
  ○ Charges of opposite sign attract (come together)
  ○ Charges of same sign repel (move away)
  ○ Electrostatic pressure

Question 26

what is electrical polarity of neurons?

Answer 26

• Neuron is polarised
• At rest, neurons are -ve charged compared to extracellular fluid
  ○ -ve charge occurs if there are less +ve ions and/or more –ve ions inside cell
• Whilst there is a difference in charge, an electrical force tends to move ions across the membrane
  ○ to keep it at resting potential
  ○ Uses energy (ATP)
  ○ Go against force to remain resting potential at -70mv

Question 27

what are border guards?

Answer 27

• Ligand gate= need protein to open gate
• Mechanically-gated= through movement can open the gate
• Always open= diffusion
• Voltage gated= change in charge they will either open or close

Question 28

what are ion channels (leak channels)?

Answer 28

• Passive ion specific conduits
  ○ Constant movement through open gates
• Selected ions rush down gradients of concentration & electric potential
• Controlled by a gate
• Sodium-potassium pump= pump out NA+ and in K+
• Only let specific ions to come through
  ○ Around the nodes of Ranvier
  ○ Efficient to have them in one place because otherwise there would be more energy used as they are spread out

Question 29

what are ion pumps?

Answer 29

• Energy consuming
  ○ Constant energy being used
• Active transport – against gradient
  ○ Uses ATP
  ○ Brain is most consuming organ of energy
• Maintains and builds gradients
• Slower pump of potassium in and sodium out
  ○ Wouldn’t work for action potential
  ○ Good for repolarisation

Question 30

what is a potassium ion (K+)?

Answer 30

• Diffusion
  ○ K+ highly concentrated in cell
  § K+ wants to move out of cell down concentration gradient
  ○ At rest, K+ leak channels allows K+ to leave neuron down concentration gradient
  ○ Inside cell becomes more -ve.
• Electrostatic pressure
  ○ Not a lot of K+ moves out
  ○ Mainly through diffusion
• Ions will stop moving when opposing forces are equal (at equilibrium)
• this happens in a resting cell

Question 31

what is a chloride ion (Cl-)?

Answer 31

• Diffusion
  ○ Cl- highly concentrated outside cell
  ○ Cl- wants to move into cell down concentration gradient
  
  • Electrostatic pressure
    ○ Inside of cell is -ve charged
    ○ Cl- also wants to move out of cell due to repel of electric charge
  • Net force for Cl- = stay where it is
    Natural equilibrium between intracellular and extracellular fluid.

Question 32

what is a sodium ions (Na+)?

Answer 32

• Diffusion
  ○ Na+ is highly concentrated outside cell trying to move inside
  ○ Na+ wants to move into cell down concentration gradient
• Electrostatic pressure
  ○ Inside of cell is -ve charged
  ○ Na+ also wants to move into cell due to electric charge attraction
• Net force for Na+ = move into cell
• Cant move in until action potential is released at the cell body (start of the axon) begins and opens the gate
  Cannot come in at rest
  there are few sodium channels so movement is light.

Question 33

which ion moves into a resting cell?

Answer 33

sodium

Question 34

what is the sodium-potassium pump?

Answer 34

sodium-potassium transporters move the ions in and out of the cell.
potassium to sodium ratio= 2:3

Question 35

what is the resting membrane potential?

Answer 35

• Two forces act on ions
• All forces are at equilibrium
• Membrane is a barrier to ion movement
  ○ All forces act to create the resting membrane potential
• At rest membrane is permeable to K+ so mainly K+ ions move
• K+ ion movement stops once opposing forces reach equilibrium
• Result: unequal distribution of positive & negative ions on the inside & outside of membrane
  ○ Ready to quickly release all the potassium to extracellular fluid and sodium to intracellular fluid
• Create depolarisation.
• difference in charge across membrane at res= -70mV

Question 36

what is an action potential?

Answer 36

Brief electrical impulse that provides the basis for conduction of information along an axon

Question 37

what are the phases of an action potential?

Answer 37

1. Depolarisation: inside becomes more +ve
2. Repolarisation: inside becomes more –ve
3. Hyperpolarisation: more –ve than at rest
   * Depolarisation stage= negative at rest, hits threshold and depolarises (+30mV)
   * Refractory period= stops charge going back until the resting level; has been reached.
   * Hyperpolarisation= potassium leaking out, slight delay before it closes its gate to readdress the balance to return to resting membrane potential

Question 38

what is neuron excitability?

Answer 38

• A stimulus causes small depolarisation (moves membrane potential towards 0 from -70 mV)
• Size of this depolarisation is proportional to size of stimulus
• If depolarisation reaches threshold (~ -55 mV) an AP occurs automatically
• size of depolarisation is proportional to the size of the stimulus.

Question 39

what are the features of an action potential?

Answer 39

• ‘all-or-nothing’ phenomena – AP only occurs if threshold is reached (at ~ -55 mV)
  ○ Continue down across next axon to repolarisation.
• FREQUENCY IS KEY
• Large change in membrane potential (-70 to +30 mV)
• Standard size & shape
• Very rapid (1-4 ms)
• Frequent (100’s per s)- depending on stimulus intensity
• Size of action potential is always the same
  Speed if contraction is determined by the frequency of the signals sent

Question 40

what phase of the action potential is characterised by the cell becoming more negative than at rest?

Answer 40

hyperpolarisation

Question 41

what regulates the strength of a response?

Answer 41

• APs are subject to an “all-or-nothing” law
• Strength of a response is not dictated by size of a single AP
• Strength is a function of the “rate” law
  Rate of neural firing
• Weak stimulus= not many action potentials
• Strong stimulus= lots of action potentials
• Stimulates the “all-or-nothing” law

Question 42

what is depolarisation?

Answer 42

• Stimulus causes a small amount of Na+ to move into the cell
• Na+ is +ve charged → neuron becomes less –ve (slightly depolarised)
• If depolarisation changes charge by +15 mV it activates voltage-gated channels in membrane
  ○ If threshold is reached, the other gates are stimulated and open up which allow more sodium into the cell.
  Voltage gated channels

Question 43

what are voltage-gated channels?

Answer 43

• Activated by changes in charge of membrane
• Two types important for the AP:
  ○ Voltage-gated Na+ channels
  ○ Voltage-gated K+ channels
  Specific to individual ions, don’t let both through.

Question 44

what is the process of voltage-gated action potentials?

Answer 44

1. Voltage-gated Na+ channels open. Na+ influx → more +ve
2. Na+ channels become refractory at peak
3. Voltage-gated K+ channels open. K+ efflux → less +ve
4. Open K+ channels allow outflow
5. Overshoot caused by slow closing K+ channels
   Prevent backward direction of action potential

Question 45

what is resetting an action potential?

Answer 45

• The Na+/ K+ ATPase Pump moves 3 Na+ OUT & 2 K+ IN
• The pump keeps Na+ conc. low in neuron
• K+ also diffuse back in to neuron
• This re-establishes resting membrane potential
• Ratio of potassium to sodium= 2:3

Question 46

which type of ion move during repolarisation?

Answer 46

potassium ions

Question 47

what is the movement along the neuron?

Answer 47

• Signal travels away from cell body towards axon terminals
• No decay
• Termed AP propagation
• Hits one node of Ranvier causing dissipation- takes time change in NA to set of voltage gate to set off next part of axon.

Question 48

what is AP Propagation?

Answer 48

• Na+ ions spread away from site of AP, change charge in nearby area of cell to be more +ve (depolarised)
• Triggers another AP in this nearby area
• Next AP occurs as previous AP starts to die out
• APs are triggered one after another all the way to axon terminals
• If axon branches, each branch continues the AP
• AP stays the same size
  Slight degradation between each node of Ranvier but the action potential continues at the same rate.

Question 49

what is the refactory period for an avction potential?

Answer 49

• Why is the refractory period important?
  ○ Prevents AP travelling backwards
  ○ Determines upper limit on AP frequency
  Refraction: the bending of light or sound as it passes through something like a wall (sound) or a window (light).

Question 50

what are synapses?

Answer 50

• Neurotransmitter release from vesicles in terminal ends of axon
• Excite, inhibit or modulate postsynaptic cell
  2 (or more) neurotransmitters released from each neuron

Question 51

give example of neurotransmitters?

Answer 51

Acetylcholine
Serotonin
Dopamine
Nor/epinephrine
Endorphins
GABA
Glutamate

Question 52

identify different types of monoamines:

Answer 52

seretonin
dopamine
epinephrine and noradrenaline

Question 53

what is seretonin?

Answer 53

○ Inhibitory
○ regulates mood, sleep patterns, libido, anxiety, appetite and pain.
* imbalances include seasonal affective disorder, anxiety, fibromyalgia and chronic pain. Medications that regulate serotonin and treat these disorders include selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs).

Question 54

what is dopamine?

Answer 54

○ Reward system including feeling pleasure, heightened arousal, and learning.
○ Dopamine also facilitates focus, concentration, memory, sleep, mood and motivation.
* Dysfunctions of the dopamine system include Parkinson’s disease, schizophrenia, bipolar disease, restless legs syndrome and attention deficit hyperactivity disorder (ADHD).

Question 55

what are epinephrine and noradrenaline?

Answer 55

○ Responsible for “fight-or-flight response” to fear and stress.
○ Stimulates body’s response by increasing heart rate, breathing, blood pressure, blood sugar, blood flow to muscles, heightened attention and focus.
* Excess epinephrine can lead to high blood pressure, diabetes, heart disease and other health problems.
* As a drug, epinephrine is used to treat anaphylaxis, asthma attacks, cardiac arrest and severe infections

Question 56

what are peptides?

Answer 56

• Endorphins. pain relievers
• play a role in perception of pain.
• “feel good” feelings.
• Low levels of endorphins may play a role in fibromyalgia and some types of headaches.

Question 57

identify differnt types of amino acids?

Answer 57

glutamate
gamma-aminobutyric acid (GABA)

Question 58

what is glutamate?

Answer 58

○ Most common excitatory neurotransmitter.
○ Most abundant neurotransmitter in brain.
○ Key role in cognitive functions like thinking, learning and memory.
* Imbalances in glutamate levels associated with Alzheimer’s disease, dementia, Parkinson’s disease and seizures.

Question 59

what is gamma-aminobutyric acid (GABA)

Answer 59

○ The most common inhibitory neurotransmitter of the nervous system, particularly in the brain.
* Regulates brain activity to prevent problems in the areas of anxiety, irritability, concentration, sleep, seizures and depression.