Overview of the Nervous System Flashcards
How many genes in the nervous system?
- 14 000 of 20 000 genes are in the nervous system
How many genes are uniquely expressed in the nervous system?
- 6000
cells in the nervous system
- neurons and glial cells
Neurons
- specialized cells involved in (often) long-distance intercellular (between cells) communication and electrical signaling
Nucleus
- organelle that houses DNA
- where gene expression occurs
Soma
- also called cell body
- contains nucleus and other organelles
Dendrites
- tree-like projections that receive signals from other neurons and transmit them to the soma
Axon hillock
- located at the end of the soma; site where action potentials are generated
Axon
- extends from the axon hillock and carries action potential away from cell body down to the axon terminal, where it will communicate with other neurons or muscle cells
Myelin sheath
- discontinous sleeves of lipid-based insulation produced by oligodendrocytes (CNS) or Schwann cells (PNS) membrane
- helps increase speed of action potential
Nodes of Ranvier
- uninsulated gaps in the myelin sheath along the axon
- together with myelin, it helps increase the speed of action potential down the axon
Axon terminal
- also called presynaptic terminal or terminal button
- site at the end of the axon where neurotransmitters are stored
Synapse
- site of information exchange between two neurons
- often form between axon and dendrites of two neighbouring neurons but can occur between axon-axon or dendrite-dendrite
Glial cells
- non-neuronal cells that do no engage in electrical signalling
- function to provide metabolic and functional support for neurons in CNS and PNS
What are the glial cells in CNS?
ependymal cells, oligodendrocytes, astrocytes, and microglia
What are the glial cells in PNS?
satellite cells and Schwann cells
Ependymal cells
- lines the ventricles of the brain and spinal cord
- creates CSF
Oligodendrocytes
- lines axons in CNS, insulating them with a fatty substance called myelin
Astrocytes
- star-shaped cells that mediate levels of neurotransmitters around the synapse and regulate the ion concentrations
Microglia
- CNS macrophages involved in controlling local immune responses
- act primarily as scavengers that remove cellular debris from sites of injury
Satellite cells
- surround somata of neurons in the PNS
- similar to astrocytes, they assist in regulating the external chemical environment
Schwann cells
line axons in PNS, insulating them with myelin
Neural circuits
- arrangement of neurons interconnected by synapses that work together to perform a particular function
- ex. patellar (knee-jerk) reflex
Reflex
motor response to sensory input that doesn’t require consciousness
Monosynaptic
direct communication between sensory neuron and motor neuron
Central Nervous system
central processing centre that receives, integrates, and interprets information from periphery, and sends information back out to the periphery
Two main functions of CNS
- receiving and interpreting and relaying sensory information
- higher-order learning known as associational systems (e.g., learning, memory, emotions)
Peripheral nervous system
connects CNS to external environment and various organs
Somatic
- voluntary
- receives and responds to sensory input and innervates skeletal muscles
- responsible for voluntary motor functions
- e.g., walking
Autonomic
- involuntary
- also known as visceral
- controls internal organs and is responsible for involuntary bodily functions
- e.g., breathing, digestion
- split into two types; sympathetic and parasympathetic
Sympathetic
flight or fight
Parasympathetic
at rest
Genes
comprises of coding DNA sequences (exons) that are templates for mRNA that will ultimately be translated into a protein, and regulatory DNA sequences (promoters and introns) that control whether and in what quantities a gene is expressed given a cell type
Gap junctions
allow for cytoplasmic continuity and the direct transfer of electrical and chemical signals between cells in the nervous system
Synaptic cleft
site of extracellular proteins that influence the diffusion, binding and degradation of molecules including neurotransmitters
