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Neuroscience > Week 2: Mechanics of the nervous system > Flashcards

Week 2: Mechanics of the nervous system Flashcards

1
Q

CNS

A

Brain and Spinal Cord

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2
Q

PNS

A
  • Nerves (Cranial and Spinal)
    - Ganglia (a mass of nerve cell bodies)
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3
Q

What connect the 2 hemispheres of the brain?

A

corpus collosum

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4
Q

CNS: Spinal cord 3 major structures

A
  • Coordinating certain reflexes
    • Conduit for sensory and motor information
    • Afferent & efferent pathways (see later)
     Continuous with brain stem
     Long conical (round) structure
     Thickness of adult’s little finger
     Mediates information transmission between brain & body below the neck
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5
Q

What is the spinal cord protected by?

A

Protected by vertebrae (24 vertebra)
 Core of grey matter surrounded by white matter

  • white matter is myelination
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6
Q

Ventral meaning?

A

front

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7
Q

Dorsal meaning?

A

Back

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8
Q

Spinal nerves split into dorsal & ventral roots before entering spinal cord: afferent and efferent?

A

Afferent neuron axons ENTER the spinal cord in dorsal root & terminate in dorsal horn.

Efferent neurons have a cell body in ventral horn & axons LEAVE cord in ventral root

(see image)

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9
Q

PNS function

A

 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)
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10
Q

PNS: Nerves (& How many?!)

A

 Neuron axons grouped into bundles
 Only present in the PNS
 43 pairs

	* 12 cranial nerve pairs 
	* 31 spinal nerve pairs
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11
Q

PNS: Cranial nerves

A

12 pairs:

10 to brain stem (10 nerves)

I & II to forebrain (2 nerves)

  • information between the brain and body above the neck (exception: Vagus nerve goes to hear, liver… to internal organs, not directly to the body)
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12
Q

PNS: Spinal nerves

A
  • 31 pairs Each pair is associated with a particular segment of spinal cord
     Named dependent on vertebral level they attach
     Spinal nerves can contain sensory (afferent) & motor (efferent) fibres
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13
Q

Divisions of the PNS

A
  • somatic nervous system
  • autonomic nervous system
    —> Sympathetic NS
    —> Parasympathetic NS
    —> Enteric NS
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14
Q

PNS: Somatic NS

A
  • Voluntary control of body movement
    • Receives sensory information and controls spinal nerves that innervate skin, joints & muscles
      • Afferent neurons carry sensory info from skin (sensory neuron)
      • Efferent neurons control skeletal muscles via (motor neuron)
        Neurons are excitatory (for movement)
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15
Q

PNS: Autonomic NS

A
  • Controls involuntary functions and internal environment (part of homeostasis)
    • Afferent neurons carry sensory info from internal organs to CNS
    • Efferent neurons control smooth muscle (in veins, intestinal tracts..), cardiac muscle (heart) & glands (releasing hormones)
    • Neurons are excitatory or inhibitory
    • Has three further sub-divisions:
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16
Q

PNS: ANS: Sympathetic Nervous System (SNS)

A
  • Any responses for activities which expend energy
    • Coordinates Fight or Flight response
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17
Q

PNS: ANS: Parasympathetic nervous system (PSNS)

A
  • Activities involved with increase in the body’s supply of stored energy
    • Coordinates Rest and Relax response
    • Conservation of energy
    • (see examples in image below)
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18
Q

PNS: ANS: Enteric nervous system (ENS)

A
  • The “second brain” - If this is working well, so will our 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
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19
Q

Neurons

A
  • Transmit information to other neurons, muscle or gland cells
    • 80% of neurons are in the brain
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20
Q

1: Sensory neurons

A
  • 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)

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21
Q

2: Motor neurons

A
  • Part of PNS
    • Synapses from CNS 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
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22
Q

3: Interneurons (relay)

A
  • In CNS
    • Receives info from sensory neurons
    • Sends info to motor neurons
    • Integrate / change signal
      • Integrate: inputs from multiple afferent neurons – average signal
      • Change: Interneurons can provide excitatory or inhibitory signals
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23
Q

Neuronal membrane

A
  • Made of two layers of lipid molecules
    • Lipid molecules
      • Hydrophilic (water loving) heads
      • Hydrophobic (water hating) tails
    • Barrier: water soluble molecules cannot pass through
    • Particularly impermeable to ions (transporters & protein channels for ion movement)
    • (Phospholipid bilayer)
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24
Q

Fluid environment: Contains ions intra- and extracellularly (Salty banana?)

A

Cations (+ve)
- Sodium (Na+) predominantly extracellular
- Potassium (K+) predominantly intracellular

Anions (-ve)
- Chloride (Cl-) predominantly extracellular
- Organic ions (A-) Only inracellular

25
Q

Movements of ions (2 methods)

A

Ions move through gates because of:

Concentration gradients (via diffusion)

Electrical force (via electrostatic pressure)

26
Q

Diffusion

A

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

27
Q

Electrostatic pressure

A
  • Electrical charge produces an action:
    - Charges of opposite sign attract
    - Charges of same sign repel
    - Electrostatic pressure
    Leads to change from resting to action, or action to rest potential
28
Q

Neuron polarity at rest

A

Neuron is polarised

neurons are -ve charged compared to extracellular fluid (-70mv)

- -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

29
Q

Ion channels (leak channels)

A
  • Passive ion-specific conduits (constant movement of specific ions)
    • Selected ions rush down gradients of concentration (diffusion) & electric potential
    • Controlled by a gate
    • Concentrated around Nodes of Ranvier - efficient (where the AP moves along the axon)

Mechanically gated - controlled by movement

Voltage gated - controlled by changes in coltage

30
Q

Ion pumps (e.g. Sodium-Potassium pump)

A
  • Energy consuming (Uses ATP)
    • Active transport – against conc gradient
    • Maintains and builds gradients
    • Slower
31
Q

Potassium ions (K + )

A

(move out overall)

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 (so part of repolarisation, when K+ channels open)
Electrostatic pressure 
	- Not a lot of K+ moves out 
Ions will stop moving when opposing forces are equal (at equilibrium)   NB: this happens in a resting cell
32
Q

Chloride ions (Cl - )

A

(stay out overall)

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
33
Q

Sodium ions (Na + )

A

(move in overall)

Diffusion 
	- Na+ is highly concentrated outside cell 
	- Na+ wants to move into cell down concentration gradient
	- Causes a more positive charge in cell (so part of depolarisation, when Na+ channels open)
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 
	Note: There are few sodium channels so ion movement is slight
34
Q

Sodium/Potassium Pump
How does extracellular Na+ remain greatest?

A

3 Na+ in for every K+ out

35
Q

Resting membrane potential - Two forces act on ions

A

 Membrane is a barrier to ion movement

 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

 Difference in charge across membrane at rest = −70 mV (resting potential)

36
Q

Action potentials

A

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

sets off a change reaction of gates opening (e.g. sodium channels open = depolarisation)

This change later causes repolarisation as potassium channels open

37
Q

Phases of an action potential

A
  1. Depolarisation
  2. Repolarisation
  3. Hyperpolarisation
38
Q

Depolarisation

A

inside becomes more +ve

39
Q

Repolarisation

A

inside becomes more –ve

40
Q

hyperpolarisation

A

more –ve than at rest

41
Q

Triggering an action potential

A

Stimulus = causes small depolarisation (moves from -70mv towards 0mv)

(size of depolarisation is proportional to the size of the stimulus)

Threshold = ~ -55mv = an AP occurs automatically

42
Q

Features of an AP

A

once threshold reached (~ -55mv) an AP can be formed = +30mv

Large change in membrane potential (from -70mv to +30mv)

Very rapid (1-4ms)

Frequent (100’s per second) (frequency depends on stimulus intensity)

43
Q

What regulates the strength of a response?

A

 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

(see image to visually display this)

(Note: AP’s are subject to an ‘all or nothing law’)

44
Q

Depolarisation: ion movement

A
  • 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 (From -70 to -55) it activates voltage-gated channels in membrane
45
Q

Voltage-gated action potential:

A
  1. DEPOLARISATION Na+ channels open = inside more =ve
  2. Na+ channels become refractory at peak
  3. REPOLARISATION K+ channels open = K+ leave (efflux) = less +ve
  4. REFRACTORY PERIOD Overshoot caused by slow closing K+ channels
46
Q

Resetting

A

The Na+/K+ pump moves 3 SODIUM OUT for 2 POTASSIUM IN

The pump keeps Na+ conc low in neuron, whilst K+ diffuses back into neuron

= re-establishes resting membrane potential

47
Q

Movement of AP along neuron

A

Signal travels away from cell body towards axon terminals!!!

  • no decay
  • Termed AP PROPOGATION
  • Jumps along nodes of ranvier (Saltatory conduction)
48
Q

AP propagation

A
  • 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 - domino effect
     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
49
Q

Why is the refractory period important?

A
  • Prevents AP travelling backwards
  • Determines upper limit on AP frequency
50
Q

Synapses

A

▪ Neurotransmitter release from vesicles in terminal ends of axon

▪ Excite, inhibit or modulate postsynaptic cell

▪ 2 (or more) neurotransmitters released from each neuron

  • from electrical to chemical, to back

From electrical to chemical, then back

51
Q

Neurotransmitters (7 to remember)

A

▪ Acetylcholine
▪ Serotonin
▪ Dopamine
▪ Nor/epinephrine
▪ Endorphins
▪ GABA
▪ Glutamate

(more deets in another lecture)

52
Q

Reading: Glia/ Glial cells

A

surround neurons and hold them in place, controlling their supply of nutrients and some of the chemicals they need to exchange messages with other neurons.

special role in the CNS. Three important types are astrocytes, oligodendrocytes, and microglia.

53
Q

Reading: Astrocytes

A

A glial cell that provides support for neurons of the central nervous system, provides nutrients and other substances, and regulates the chemical composition of the extracellular fluid.

54
Q

Reading: Oligodendrocyte

A

A type of glial cell in the central nervous system that forms myelin sheaths.

55
Q

Reading: Microglia

A

The smallest of glial cells; they act as phagocytes and protect the brain from invading microorganisms.

Microglia are primarily responsible for the inflammatory reaction in response to brain damage, such as in a traumatic brain injury (Loane and Kumar, 2016).

56
Q

reading: Blood-brain barrier

A

a barrier exists between the blood and the fluid that surrounds the cells of the brain

selectively permeable

Unlike the rest of the body, capillaries don’t have gaps between them in the CNS (around brain and spinal cord).

many substances cannot leave the blood to enter the brain. The tightly packed cells of the capillaries in the brain make up the blood–brain barrier

57
Q

Reading: area postrema

A

A region of the medulla where the blood–brain barrier is weak; poisons can be detected there and can initiate vomiting

58
Q

Reading: Meninges

A

The entire nervous system — brain, spinal cord, cranial and spinal nerves, and peripheral ganglia — is covered by tough connective tissue. The protective sheaths around the brain and spinal cord are referred to as the meninges.

dura mater

arachnoid membrane

pia mater

subarachnoid space

Neuroscience (22 decks)

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