Nervous System Functions and Structure Quiz

Nervous Tissue 1

• Nervous tissue is responsible for functions like heartbeat, breathing, digestion, body temperature, planning, thinking, emotions and behaviours, sensation, and movement
• Nervous tissue comprises nerve conduction, structure of nervous tissue, and glial cells, and neuron structure.

Neuronal Structure

• A neuron is the functional unit of the nervous system.
• Neurons are specialized cells designed to transmit electrical impulses.
• Neurons share common structural features for sending and receiving information.
• Parts of a neuron: Nucleus, Cell body (Soma), Dendrite, Axon, Axon Terminals.

Neurone Types

• Multipolar: e.g., motor neurons
• Pseudo-unipolar: e.g., sensory neurons
• Bipolar: e.g., in retina or olfactory system
• Anaxonic: with no distinct axon

Neurones Form & Function

• Various examples of neuron types, including motor neurons (spinal cord), Purkinje cells (cerebellum), mitral cells (olfactory bulb) and pyramidal cells (cortex), are shown.
• Their shapes and roles are described

Glial Cells

• Glial cells are not directly involved with information processing but are essential for survival and function of the nervous system.
• Greek for "glue"
• Types of Glial Cells: CNS - Astrocyte, Oligodendrocyte, Microglia, Ependymal cell. PNS - Satellite cell, Schwann cell

Glial Cells Structure & Function

• Diagram displays structure, location and function of these cells
• Extracellular space, blood capillaries and cells (oligodendrocyte, astrocyte, ependymal cell, neuron, microglia)

Cells of the Nervous System Summary

• Neurones: Electrical signaling
• Astrocyte: Regulates extracellular microclimate, removing waste products, helps to control passage between blood & nervous tissue, scar formation
• Oligodendrocyte: Myelination - insulation for the axon & preventing degradation, enhances conduction speed
• Microglia: Immune response, phagocytosis
• Ependymal cell: Producing Cerebral Spinal Fluid (CSF)
• Satellite Cell: PNS support cells, similar to astrocytes in CNS
• Schwann Cell: Myelination - insulation for axon & preventing degradation, enhances conduction speed

Neurones At Rest

• At rest, the inside of the cell membrane has a negative charge (-70mV).
• This is due to an unequal distribution of sodium (Na+), potassium (K+) and chloride (Cl-) ions.
• Extracellular fluid has a net positive charge and intracellular cytoplasm has a net negative charge.
• A membrane potential of minus 70mV

Generation of an Action Potential

• A stimulus creates an influx of positively charged ions, changing the membrane voltage to positive (approximately +30/40mV) - depolarization.
• Rapid influx of Na+ ions followed by efflux of K+ ions forms the action potential.
• All or nothing principle: action potential either occurs or does not, and voltage is always the same magnitude.

Propagation

• Action potential is initiated at the axon hillock and propagates along the axon.
• Voltage-gated Na+ channels cause a regenerative current, maintaining action potential amplitude.

Propagation Velocity

• Action potential speed varies between neurons (0.1 m/s to 100 m/s)
• Myelin increases resistance of the membrane, preventing ion leakage.
• Saltatory conduction is faster in myelinated axons, with action potentials jumping between Nodes of Ranvier.
• Axon diameter and temperature also influence conduction velocity.

Synaptic Transmission

• Action potential reaches axon terminal, calcium channels open, neurotransmitters released into the synaptic cleft
• Neurotransmitter diffuses across cleft and binds to receptors on postsynaptic neuron.
• Activation of receptors opens Na+ channels, causing a postsynaptic potential.
• If threshold reached, AP generated in postsynaptic neuron.
• Neurotransmitters reabsorbed

Summation

• Individual stimuli might be insufficient to trigger an action potential, but their sum can exceed the threshold.
• Spatial summation: simultaneous stimuli from multiple synapses sum together to reach the threshold.
• Temporal Summation: multiple stimuli in rapid succession sum together to reach the threshold.

Blood Brain Barrier

• The BBB is a protective barrier between the blood and the brain.
• Epithelial cells, proteins and astrocytes form the BBB, selectively controlling what passes.