Lecture 2: Neurophysiology pt 1

Question 1

What’s the difference between Afferent and Efferent?

Answer 1

Afferent: Info coming in form the nerve fibres to be processed (body to central nervous system)

Efferent: After info is processed a response is sent out away from the central nervous system to the body.

Question 2

What makes up the Central and Peripheral nervous system?

Answer 2

Central Nervous system: Brain and spinal cord

Peripheral nervous system:
- Sensory system (Sensory nerve fibres from sensory cells),
- Somatic motor system (Motor fibres to skeletal muscles for movement control)
- Autonomic system (Motor nerve fibers to glands, heart, smooth musculature)

Question 3

What 2 systems is the Autonomic system made of?

Answer 3

Sympathetic nervous system: Activated during critical situations (alarm bell related to stress)

Parasympathetic nervous system: Activated at rest (Background adjusting small changes)

Question 4

What are the 2 types of cells in the nervous system?

Answer 4

Neurons: Able to transmit info composed of a cell body and processes (axons and dendrites)

Glial Cells: Non-neural cells, 10X more abundant then neurons, do multiple tasks, provide support is biggest, participate in myelin formation, secrete glutamate, contact both blood vessels and neurons to transport nutrients since neurons don’t store glucose or oxygen.

Question 5

TRUE OR FALSE: there is only one category of neuron.

Answer 5

FALSE:

Neurons can be categorized based on the number of processes therefore there are 3
1.Multipolar-mainly in CNS
2.Pseudounipolar-mianly in PNS
3. Bipolar-mainly sensory organs

Question 6

TRUE OR FALSE: Neurons can be classified by function.

Answer 6

TRUE:

Sensory (afferent): From PNS to SNS
Motor (efferent): from CNS to muscles and glands
Interneurons (association): relay info between neurons w/in the CNS (different parts of the brain to integrate responses)
Specialized “receptors”: transducers=convert stimuli to signal

Question 7

What is the difference between grey and white matter?

Answer 7

Grey matter: corresponds to cell bodies (integration centres)
White matter: Corresponds to bundles of neurone processes with the white appliance due to myelin sheaths (layers of phospholipids give white appearance)

Question 8

TRUE OR FALSE: Every cell of the body possesses a membrane potential = Resting Membrane Potential (RMP).

Answer 8

TRUE: RMP results from a difference in charge across the cell membrane (between cytosol and extracellular fluid).
Inside membrane is NEGATIVE relative to outside. Absolute values differs between cell type and depends on amount of charges, ion channels and thickness of the membrane. Average in nerve cells around -70 to -90mV

Question 9

What combination of 3 things maintains the Resting Membrane Potential (RMP)?

Answer 9

Combination of:
1. Selective permeability (passive based on level of diffusion) Poors/channels
2. Na+/K+ pump on cell membrane (3 Na+ out 2 K+ in) to keep Na+ and K+ in different compartments
3. Large anions trapped in the inner surface of membrane. (since positive charge on outside attracts negative charge on inner surface of membrane)

Question 10

TRUE OR FLASE: In the maintenance of the RMP through selective permeability (diffusion) al the ions pass through at the same time and all have the same level of permeability?

Answer 10

FALSE: Selective permeability by diffusions involves passive leakage of ions. through channels (concentration gradients). Resting membrane permeable to K+, nearly permeable to Na+, Ca2+, Cl-. Therefore positive charges accumulate outside bc K+ keeps coming out with its positive charge.

Question 11

TRUE OR FALSE: The Ion pumps requires up to 40% of the ATP availability

Answer 11

TRUE.
-Goes against concentration gradient and for Na+ (bc the natural way for the ions to move is K+ out and Na+ in) against the membrane polarity (outside already positive relative to inside).
-Na+/K+ pump: Pumps 3 Na+ out and brings 2K+ in

Question 12

TRUE OR FALSE: Neurons store their own glucose or O2 therefore they don’t need a constant supply.

Answer 12

FALSE: Neurons DONT store glucose or O2 therefore they DO REQUIRE constant supply. Most at risk is neural tissue. Think about medical T.V shows, when a patient passes out/stops breathing and someone gets their heart started again after they went unconscious for a while without O2 they are brain dead.

Question 13

What are excitable cells and how does it relate to depolarization and repolarization?

Answer 13

Excitable cells: Cells that can generate electrical impulses (action potentials) but they need to be stimulated by chemical, electrical, or physical stimulations to induce a change in membrane potential to reach a THRESHOLD provoking the opening of voltage gated ion channels.

DEPOLARIZATION: Na+ channels open (or Ca+ for some nerve endings and smooth and cardiac muscle cells), Na+ rushes inside the cell, making the potential less negative and now inverted (positive).

REPOLARIZATION: Opening of K+ channels results in an outflow of K+ returning the potential to RMP

*Note: Now + charges came out, then channel closes but slower then Na+ so lose a little more K+ which will result to a more + charge outside.

Question 14

What is the process of the generation of action potentials in neurons?

Answer 14

-First an initial depolarization (stimulation) needs to reach threshold to provoke the opening of Na+ voltage gated channels known as DEPOLARIZATION
-After 0.5ms, opened Na+ channels close rapidly
-K+ voltage gated channels open (delayed compared to Na+) outflow of K+ AKA REPOLARIZATION
-K+ voltage gated channels then progressively close, outflow of K+ continues after reaching the RMP= HYPERPOLARIZATION
-Once all gated channels are closed, ions rejoin their respective compartments by diffusions and Na+/K+pumps

Question 15

What is a refractory period?

Answer 15

A refractory period allows the neurons not to be re-stimulated until RMP is restored. It’s the amount of time it takes to respond to a second stimuli or the time during which a cell is incapable of repeating an action potential.

Question 16

What is the all or none rule?

Answer 16

All or none rule: Nerve cells follow this rule, when threshold is met an AP is generated. The amplitude of the AP is fixed for the cell
-Intensity encoded by the frequency of Aps, not the amplitude. (my words: each cell has one threshold and same AP each time)

Question 17

What is the conduction of action potential in unmyelinated axons and myelinated axons?

Answer 17

Conduction of Action potential: De and Repolarization process (AP) propagate along the cell membrane, need for the change in potential to reach threshold on the nearby micro domain to trigger opening of gated channels

In unmyelinated axons: Only move in one direction can’t move backwards membrane is in refractory period. Think of it like wave of students in an arena have to go from one person to the next not skipping people.

In myelinated axons: AP occurs the same way but only at the nodes of Ranvier. Myelin prevents ion leakage, current jumps from one node to the other= SALTATORY CONDUCTION way faster. Velocity increased as less membrane affected = less energy required to transport ions.

Question 18

What does the nerve velocity depend on in myelinated axons?

Answer 18

It depends on dissipation of current: thickness of myelin, diameter of fibers (thicker = faster)

Question 19

What is synaptic transmission?

Answer 19

Continuity of signal b/w a neuron and other neurons or between a neuron and a target cell such as a skeletal muscles (neuromuscular synapse). Cell membrane made of phospholipids = electric insulator. A gap exsits between pre- and post-synaptic gap or cleft. In vertebrates, neural synapse = predominantly CHEMICAL synapse.

Question 20

What are neurotransmitters and how do they function?

Answer 20

Molecules able to transmit info from a neuron by converting the electrical signal (AP) into a chemical signal. Released by pre-synaptic neuron into the gap, bind to specific receptors on post-synaptic membrane, elicit a response. Postsynaptic folding is common in neuromuscular synapse (not in interneurons) = increases surface. Acetylcholine (ACh)= neuromuscular synapse transmitter

1. Action potential (AP)
2. AP opens voltage gated Ca2+ channels =in-flux of Ca2+
   3.Ca2+ triggers exocytosis (release of acetocholine)
3. Diffusion in the cleft
4. Binding to specific receptors
5. Ion channels open on post-synaptic membrane depolarization
6. Neurotransmitter inactivated termination of signal

Question 21

How are the transmission signs terminated?

Answer 21

Small molecules:
-Picked back up by presynaptic heron via endocytosis and recycled for next time
-Deactivated in the cleft by enzymes released by post-synaptic cell (ie Acetylcholine Esterase) AChE

Neuropeptides:
-After bind to receptor, can be internalized by post-synaptic cell via endocytosis and be degraded by cellular enzymes (extracellular peptidase) in the gap

A report can be desensitized (cant respond bc it has been saturated)

Question 22

TRUE OR FALSE: Excitatory synapse = depolarization = entry of Na+and Inhibitory synapse = hyperpolarization polarization = entry of Cl- and/or outflow of K+

Answer 22

TRUE (read following if need more info)

For neuromuscular synapse, 1 neuron = AP = muscle cell depolarization
BUT different for:
Neuron-Neuron synapse, 1 neron can receive impulse from multiple other neurons. Synapses can either be excitatory or inhibitory therefor 1 does not always lead to a response.