Nervous System Physiology Quiz

Nervous System Physiology (Sensory Physiology)

• Sensory physiology examines how the nervous system detects and processes sensory information.
• The sensory system receives information from the environment, processes it, and transmits signals to the brain.
• This includes both external and internal environments.
• Sensory physiology covers basic principles, general sensation, tactile senses/proprioception, thermal sensation, pain, taste, smell, hearing, balance, and vision.

Agenda for Sensory Physiology

• The agenda for sensory physiology includes:
  • Basic principles of sensory physiology
  • General considerations of sensation
  • Tactile senses and proprioception
  • Thermal sensation
  • Pain
  • Taste
  • Smell
  • Hearing
  • Balance
  • Vision
  • Class exam

Nervous System (Functional Point of View)

• The nervous system is divided into the CNS and PNS.
• The CNS includes the brain and spinal cord.
• The PNS includes cranial nerves and spinal nerves.
• The Autonomic Nervous System (ANS) comprises of: sympathetic and parasympathetic nerves and ganglia and the enteric nervous system .

Main Parts of the Human Nervous System

• Central Nervous System (CNS): Brain and spinal cord.
• Peripheral Nervous System (PNS): Cranial nerves, ganglia, spinal nerves, sympathetic/parasympathetic nerves and ganglia, and the enteric nervous system.

Cells of the Nervous System

• Two main types of cells: Neurons (nerve cells) and Glia (glial cells).
• Neurons are the basic functional units of the nervous system, responsible for generating and conducting electrical signals.
  • Neurons are highly specialized cells.
  • Neurons have a high number: 10¹¹ - 10¹².
  • Neurons are excitable.
• Glial cells support and sustain neurons, both metabolically and physically.
  • Glia have a much higher number: 10¹³.
  • Glial cells are non-excitable.

Major Components of a Typical Neuron

• Soma/perikaryon: The cell body; containing the nucleus, mitochondria, and Nissl bodies (rough endoplasmic reticulum and Golgi apparatus) which are used in neuronal biosynthesis.
• Dendrites: Tapering and branching extensions of the soma that receive synaptic input (90%). They have a dendritic tree.
• Axon: An extension of the cell body carrying signals to muscle cells or neurons. It only has one axon.

Definitions

• Nucleus: A group of cell bodies of neurons in the CNS (plural: nuclei)
  • Examples include Dorsal column nuclei in the brain stem (gracilis and cuneate nuclei) and Inferior olive nucleus (ION) in the medulla.
• Ganglion: A group of cell bodies of neurons in the PNS (plural: ganglia)
  • Examples include Dorsal root ganglion (DRG) of spinal/cranial nerves

Classification of Neurons

• Neurons are categorized based on axon length, cell geometry, morphology (number of processes from soma), function, and type of neurotransmitter released.

Morphology of Neurons

• Unipolar (Invertebrates)
• Pseudounipolar(DRG; Dorsal root ganglion)
• Bipolar (Bipolar cell of retina)
• Multipolar (Purkinje cell of cerebellum)

DRG: Dorsal root ganglion (spinal nerves and sensory cranial nerves)

• This is a type of ganglion containing cell bodies of sensory neurons.
• Sensory neurons carry impulses from the periphery (skin, muscles, etc.) to the spinal cord and brain.

Information Coding in the Nervous System

• Information coding involves transmitting information in the nervous system.
• Sensory system information is mostly discarded.

Information Coding in the Nervous System

• Information is conveyed via graded potentials and action potentials.
• Graded potentials use Amplitude Modulation (AM); the magnitude of their signal is proportional to the magnitude of the stimulus.
• Action potentials use Frequency Modulation; which varies in the frequency output depending on the intensity of the stimulus. Frequency coding is more robust than amplitude coding in transmitting information.

Synaptic Transmission

• Synapse is the contact region between two neurons for communication, where neurons transfer information using neurotransmitters as chemical signals.

Types of Synapses

• Electrical synapse: Rapid transmission by direct flow of ions; found in some locations (2%).
  • Electrical synapses have connexins that form channels for transmitting electric signals between neurons.
• Chemical synapse: Neurotransmitter release mediates transmission & is unidirectional (98%).
  • The transfer of information from one neuron to another neuron can be excitatory (depolarization - EPSP) or inhibitory (hyperpolarization - IPSP)

Synaptic Potentials

• Synaptic potentials (EPSPs and IPSPs) are graded potentials produced in response to neurotransmitter release at synapses.
• EPSP (excitatory postsynaptic potential) is a depolarization that increases the likelihood of an action potential being generated.
• IPSP (inhibitory postsynaptic potential) is a hyperpolarization that reduces the likelihood of an action potential being generated.

Types of Neurotransmitters

• Small-molecule, rapidly-acting neurotransmitters: Acetylcholine; Noradrenaline/norepinephrine; Epinephrine/adrenaline; Dopamine; Serotonin; Melatonin; Histamine; Amino acids (gamma-aminobutyric acid, glycine, glutamate, aspartate); ATP; Arachidonic acid; Nitric oxide; Carbon monoxide.
• Large-molecule, slowly-acting neurotransmitters: Neuropeptides

Blood Brain Barrier (BBB)

• This vital barrier protects the brain from harmful substances whilst allowing essential nutrients to pass through.
• Astrocytes are part of the BBB; helping to control what enters the nervous system.

Glial Cells in the CNS

• Astrocytes: Vital for blood-brain barrier (BBB); maintenance of homeostasis in the brain
• Microglia: Macrophages; play an important role in the immune defense
• Ependymal cells: Line brain ventricles
• Oligodendrocytes: Produce myelin sheath in the CNS
• Schwann cells: Wrap axons in myelin in the PNS

Action Potential (AP)

• AP is a rapid, all-or-none change in membrane potential.
• Key characteristics of an AP is that it has a constant amplitude, cannot be summed, is not conducted without decrement; the magnitude of depolarization is amplified to a constant value at each point along the membrane; duration is constant; only a depolarization, and is initiated by a graded potential.
• The mechanism depends on voltage-gated ion channels.

Overview on First Session

• The nervous system has two main parts: CNS and PNS.
• Two types of cells in the NS are neurons and glia.
• Action potentials occur in two ways: Changes in membrane potential, and conduction of information.
• Two types of synapses in the NS are electrical and chemical.
• Neurotransmitters include small-molecule and large-molecule types.

This quiz covers the key concepts of sensory physiology, focusing on how the nervous system detects and processes sensory information. Topics include basic principles, general sensation, as well as specific senses like taste, smell, and vision. Test your understanding of how sensory information is transmitted to the brain and its significance in human physiology.