Neurophysiology I

Question 1

Describe the anatomical and functional divisions of the nervous system

Answer 1

The nervous system is divided into the
1. central nervous system (CNS): Brain & spinal cord
2. peripheral nervous system: everything else

Question 2

Compare and contrast the two divisions of the peripheral nervous system.
Somatic nervous system & autonomic nervous system

Answer 2

Autonomic: These are nervous system processes; your brain runs automatically without you thinking about them.

Somatic: These are functions you manage by thinking about them.

Question 2

Describe the structure of a typical neuron, including the key functions of each component

Answer 2

All neurons have dendrites, a cell body and axon.
1. Input zone:
- dendrites receive the messages and transfer them through the neuron
- Cell body/soma contains the genetic info and provides the cell structure
- nucleus controls/regulates cell activity

2. Axon Hillock/Trigger zone:
   Axon Hillock is the point where excitatory and inhibitory inputs come in and initiate electrical impulses.
3. Conducting zone:
   - Axon conducts the nerve signals & transmits them to the next neuron
   - Schwann cell produces myelin sheath
   - Myelin is the insulating layer so electrical impulses run fast and efficiently
4. Output zone:
   Axon terminals convert the electron signal along the axon into a chemical signal.

Question 3

Explain the roles of the different types of neuroglia

Answer 3

The four main types of neuroglial cells are astrocytes, microglia, oligodendrocytes, and Schwann Cells. Their functions include maintaining neuronal survivability, protecting the nervous system, and producing myelin

Question 4

Differentiate between resting, graded (local), and action potentials

Answer 4

Resting potential describes the membrane potential of a normal cell under homeostatic conditions, while graded and action potentials are changes in the membrane’s charge:

Resting potential: The baseline charge of a neuron’s membrane

Graded potential: A small change in the membrane’s charge that’s proportional to the size of a stimulus. Graded potentials are variable-strength signals that can only be conveyed over short distances. They occur on the dendrites and soma of a neuron.

Action potential: A massive depolarization that can be transferred over long distances. Action potentials are all-or-none events that originate at the axon hillock of a neuron. They occur when depolarization increases the membrane voltage so that it crosses a threshold value.

Question 5

Describe the electrochemical events of an action potential

Answer 5

The electrochemical events of an action potential are a rapid change in membrane voltage that occurs in three stages:

Depolarization
Sodium ion channels open, allowing positively charged sodium ions to flow into the cell. As the concentration gradients of ions begin to equalize, this makes the cell less polar.

Repolarization
Potassium ion channels open, allowing potassium ions to flow out of the cell, restoring the cell to its resting potential.

Hyperpolarization
The membrane potential dips below the resting voltage. This occurs because potassium channels stay open slightly longer than they should, allowing more positive ions to exit the neuron.

The action potential is generated by a triggering event, such as a signal from other cells connecting to the neuron. The action potential travels along the axon, releasing neurotransmitters at the axon terminals. These neurotransmitters then bind to receptors on the target cell, causing a response.

Action potentials can occur in many excitable cells, including neurons, cardiac muscle, and some endocrine cells.

Question 6

Explain the processes of synaptic transmission, including the role of key neurotransmitters

Answer 6

Neurotransmitters are chemical messengers that transmit signals from a neuron to a target cell across a synapse. including:

Acetylcholine
– Primary acts directly, binding to chemically (ligand)-gated ion channels
– Widespread activity in CNS and PNS

Biogenic amines
– E.g., Noradrenaline, dopamine, serotonin, histamine
– Primarily acts indirectly, G-proteins and second messengers

Amino acids
– E.g., GABA (inhibitory), glutamate (excitatory)
– Can act directly/indirectly, depends on receptor type
– Important activities in CNS – memory, learning, excitation (glutamate); inhibitory effects via opening Clchannels, opening K+ channels, blocking entry of Ca2+ (GABA)

Neuropeptides
– E.g., Substance P, opioids
– Acts indirectly, G-proteins and second messengers
– Important in pain pathways

Question 7

Differentiate between excitatory and inhibitory stimuli at the postsynaptic membrane

Answer 7

The main difference between excitatory and inhibitory stimuli at the postsynaptic membrane is the effect they have on the likelihood of a postsynaptic action potential occurring:

Excitatory postsynaptic potentials (EPSPs)
Increase the likelihood of an action potential. This happens when sodium channels open, causing the cell’s membrane potential to become more positive or depolarize.

Inhibitory postsynaptic potentials (IPSPs)
Decrease the likelihood of an action potential. This happens when chloride channels open, causing the cell’s membrane potential to become more negative or hyperpolarize.

EPSPs and IPSPs compete with each other at many synapses of a neuron. The outcome determines whether an action potential at the presynaptic terminal produces an action potential at the postsynaptic membrane.
Excitatory neurotransmitter receptors are clustered distally in the dendrites, while inhibitory receptors are closer to the cell body.