BIOM 1060 (Module 2)

Describe the divisions of the nervous system.

The nervous system is divided into two:

• Central nervous system → Composed of the brain and spinal cord

• Peripheral nervous system → Composed of spinal, cranial nerves and ganglia

From here the PNS divide’s into Afferent (sends out sensory impulses to the CNS) and Efferent (motor commands from the CNS to the effectors)

The Efferent is further split into somatic (voluntary movement, motor signals from the CNS to skeletal muscles e.g walking or stretching) and Autonomic (controls the involuntary movement, regulates heart rate and digestion)

And finally from her the Autonomic splits into Sympathetic (Fight or flight, increased heart rate, breathing) and parasympathetic (Rest and digest, decreased heart rate, and conservation of energy)

Name and describe the parts of the neuron

Cell body (soma)

• Nucleus, organelles

Dendrites

• Receive information

Axons

• send information as electrical signals (action potentials)

Axon hillock

• Where an action potential starts

Axon terminals

• Releases neurotransmitters to communicate with other cells

Myelination

Myelin protects and electrically insulates the axon, making it increase the speed of electrical signals

Created by:

• Schwann cells (PNS)

• Oligodendrocytes (CNS)

Neurons classified by functions

Sensory/Afferent

• Neurons sending sensory info to the CNS

Motor/Efferent

• Neurons sending motor info from the CNS

Interneurons

• Link sensory & motor neurons (mostly CNS) → enabling rapid reflexes that protect the body without waiting for brain processing.

What is RMP

The resting membrane potential (RMP) is the electrical potential difference across a neuron’s membrane when it is not transmitting an impulse, typically around −70 mV.

Describe how the movement of Na⁺ and K⁺ across the plasma membrane as well as the Na⁺-K⁺ pump results the RMP.

Leakage channels

Always open and allows the cell when necessary to become more negative, seen in muscle cells during RMP

Gated channels

Chemically gated:

• Only open when met with a appropriate neurotransmitter

Voltage gated:

• Open in response to changes in membrane potentials

Graded Potentials

Short lived, localised changes in membrane potentials

• Can be depolarisation or hyperpolarisation

Triggered by a stimulus that opens a chemically gated ion channels

• Postsynaptic graded potentials will occur when a neurotransmitter binds to a chemically gated ion on a postsynaptic neuron

Depolarisation

Decrease in membrane potential. inside of the cell becomes less negative than RMP

• Opening of gated Na+ channels (enters) → opposite of what happens in RMP

Hyperpolarisation

Increase in membrane potential. Inside of the cell becomes more negative than RMP

• Opening of K+ channels (leaves) or Cl- channels enters → opposite of what happens in RMP

Action potentials

Brief reversal of membrane potential (-70mV to +30mV in neurons)

Do not decay over distance

Involves special voltage-gated channels

Stages of action potentials

Important:

• The threshold must be reached in order for an action potential to even occur

Compare and contrast graded potentials and action potentials.

Similarities

• Both are changes in membrane potential

• Both involve movement of Na⁺ and K⁺ ions

• Both are used for neuronal communication

Differences

1. Location

• Graded: dendrites & cell body

• Action: axon

2. Type of channels

• Graded: chemically-gated (stimulus-controlled)

• Action: voltage-gated

3. Direction

• Graded: spreads in multiple directions

• Action: one direction along axon

4. Type of signal

• Graded: can be depolarising OR hyperpolarising

• Action: always follows the same pattern (depolarisation → repolarisation)

5. Distance

• Graded: short, decreases with distance

• Action: long, does not decrease

Refectory period and types

Time in which a region of a neuron cannot trigger another action potential time in which a region of a neuron cannot trigger another action potential.

Types:

Absolute refractory period: (Tends to be during depolarisation and repolarisation)

• Sodium channels are open or inactivated making it physically impossible for another action potential (enforces on way transmission)

• This is due to it already being in use

Relative refractory period: (Tends to be during hyperpolarisation)

• Sodium channels now closed (reset and ready)

• Action potential can occur however requiring a strong stimulus as the membrane is still very negative due to K+ still leaving (e.g a lot more neurotransmitters released)