Neurophysiology

Question 1

Define equilibrium potential.

Answer 1

As an ion moves, the balance of electrical charge across the membrane changes. This changes the ‘driving force’ for the ion and reaches a point of equilibrium at equilibrium potential.

Question 2

Under physiological conditions, what is the equilibrium potential of potassium ions?

Answer 2

K+ = -95mV

Question 3

Under physiological conditions, what is the equilibrium potential of sodium ions?

Answer 3

Na+ = +61mV

Question 4

Under physiological conditions, what is the equilibrium potential of calcium ions?

Answer 4

Ca2+ = +137mV

Question 5

Under physiological conditions, what is the equilibrium potential of chloride ions?

Answer 5

Cl- = -65mV

Question 6

What is the equation to calculate equilibrium potentials?

Answer 6

Emv = 61.5 x log10 ([ion out]/[ion in])

Question 7

How must the equilibrium potential equation be changed when at room temperature, for divalent ions and for anions?

Answer 7

At room temperature, multiply by 58

For divalent ions, divide by 2

For anions, invert

Question 8

What is the Goldman GHK equation used to calculate? State the equation.

Answer 8

Membrane potential.

Vm = 61.5 x log10 (sum of permeabilities of EC ions/sum of permeabilities of IC ions)

Question 9

What does the speed of an action potential depend on?

Answer 9

Speed of action potentials depends on the size of the action potential and how leaky the potassium channels are.

Wider axons are less resistant and less leaky channels allow wave of depolarisation to travel further.

Question 10

What is a reflex?

Answer 10

Fast, involuntary, stereotypical motor response to a stimulus. Mediated by synapses in CNS, with degrees of higher control including voluntary control. Both stimulatory and inhibitory.

Question 11

What is meant by involuntary?

Answer 11

Suggests only involvement in autonomic homeostatic mechanisms but are key to coordinated movements and responses, which may be also under voluntary control.

Question 12

What 2 branches is the nervous system divided into? What do these control?

Answer 12

Somatic nervous system - voluntary, controls skeletal muscles

Autonomic nervous system - involuntary, controls smooth muscle, cardiac muscle and glands

Question 13

What 2 branches is the somatic nervous system divided into? What are these composed of?

Answer 13

Central nervous system - brain and spinal chord

Peripheral nervous system - sensory receptors, sensory neurones and motor neurones

Question 14

What are visceral responses?

Answer 14

Controlled by the autonomic system and effector structures are cardiac muscle, smooth muscle and glands.

Control of blood pressure, blushing and salivation.

Question 15

What 2 branches is the autonomic nervous system divided into?

Answer 15

Sympathetic - thoraco-lumbar

Parasympathetic - cranio-sacral

Question 16

What are some similarities between the sympathetic and parasympathetic pathways of ANS?

Answer 16

• Both show tonic (background) activity.
• Both can increase or decrease tonic activity from its resting level, which enables a wide range of modulation of activity.
• Structures within the CNS coordinate activity in both divisions of the ANS to regulate functions: control of blood pressure, breathing, body temperature, salivation, digestive function.
• Can both turn things ‘on’ and ‘off’.
• Both have acetylcholine neurotransmitter.

Question 17

What is a difference between the sympathetic and parasympathetic pathways of the ANS?

Answer 17

Sympathetic activation of a target structure is usually consistent with a diffuse and widespread ‘fight or flight’ response: increased heart rate, increased respiratory rate, increased blood glucose levels.

Parasympathetic activation is consistent with a ‘vegetative’ or resting state, typically rest and digest: digestion, lowered blood pressure and quiet breathing.

Question 18

What do afferent and efferent refer to in regard to CNS?

Answer 18

Afferent to CNS

Efferent away from CNS

Question 19

Describe the process of synaptic transmission in an excitatory synapse.

Answer 19

1. Nerve action potential.
2. Increased presynaptic calcium permeability, causing depolarisation from calcium influx.
3. Release of transmitter molecules by exocytosis of vesicles.
4. Interaction of transmitter with postsynaptic receptors.
5. Increase in postsynaptic permeability and postsynaptic current causes depolarisation in the postsynaptic neurone.
6. If the postsynaptic neurone is depolarised enough to threshold potential, an action potential is started in the post synaptic neurone.
7. Action potential at axon hillock, so excitatory post synaptic potentials (EPSP) must travel, so some scope for signal modulation.

Question 20

Name examples of excitatory and inhibitory neurotransmitters.

Answer 20

Excitatory neurotransmitters = glutamate and acetylcholine.

Inhibitory neurotransmitters = GABA and glycine.