Lecture 8, Introduction to the Nervous System Flashcards
There are two types of cells in the nervous system:
- neurons - excitable cells that have the ability to transmit electrical impulses (electrical stimulation)
A. the functional unit of the nervous system
B. these electrical impulses allow for
communication between neurons and with other
tissues
C. main function is in enabling cell-to-cell
communication (many different parts of our
bodies) - neuroglia (glial cells) - non-neuronal supporting ce;s
A. main function is to support neurons
B. are a type of connective tissue cells
C. do not have the ability to transmit electrical
impulses (only the role of the neuron)
the connection between a neuron and another cell is called a synpase
Neurons - Anatomy (anatomical structures)
definitions:
- soma: a cell body of a neuron
- dendrites: long projection extending from the soma
◦ function in receiving information and relaying it
back to the soma
◦ has dendritic spines that increase surface area
- axon: a long process extending from the soma that rely outgoing signal to target cells
◦ begins at axon hillock and ends at axon terminal
- myelin: an insulating sheath that forms over some neurons, that speeds up the transmission of an electrical signal down the axon
input (dendrites) -> soma -> (axon) output
Neurons - Classification and Types (5)
unipolar neurons: neurons that only have one main projection (axon) coming from the soma [eg. sensory neurons]
bipolar neurons: neurons that have two main projections coming from the soma (more traditional looking one) [eg. special sense neurons; smell/hearing
multipolar neurons: neurons that have more than two projections coming from the soma (several branch points of dendrites) [eg. somatic motor neurons]
anaxonic neurons: neurons that have large projections/axons coming from the soma (still have dendrites just not large projections meaning it only has incoming information (input) no output) [eg. brain]
Pseudo-unipolar neron
means it can look like a unipolar but it is only one branch extended (polarity - branch point from soma)
Nervous System - Organization
the nervous system makes up only ~3% of our body weight, but is one of the most essential and complex systems of the body
central nervous system (CNS)
- the brain and spinal cord)
peripheral nervous system (PNS)
- all the nervous tissue outside of the CNS
- nerves that connect the brain and spinal cord to muscles, glands, organs, etc.
- includes spinal nerves and cranial nerves
(everything else other than CNS)
- sensory (afferent) division sends signal TO the brain
- motor (efferent) division sends signal FROM the brain (does not always go to motor neurons or locomotion can also go to glands, smooths muscles etc.)
-> afferent first than efferent (effector)
Neurons - Myelin Sheath and Nodes of Ranvier
the axons of many neurons are wrapped in myelin sheath
- formed by oligodendrocytes (CNS) and schwann cells (PNS)
- one oligodendrocytes can form the myelin for up to 40 axons
- one schwann cell can only contribute to the myelin of one axon
the myelin sheath is not continous
- there are “gaps” in the sheath called Nodes of Ranvier (at these nodes, the axon is exposed to extracellular fluid)
- these nodes speed up the transmission of an action potential down the axon, and also conserves energy (not the myelin itself)
- in neurons that are sheathed in myelin, the AP skips the internodes, and travels rapidly from node to node
Neurons - functional classes
neurons are categorized into classes based on their function:
- afferent neurons (also called sensory neurons): convey signals from tissues and organs TO the
CNS
interneurons: convey signals between neurons WITHIN the CNS (within the brain or spinal cord)
efferent neurons (sometimes called motor neurons): convey signals FROM the CNS to gladns, tissues and organs
-> the cell bodies of both efferent neurons and interneurons are WITHIN the CNS
-> the cell bodies of afferent neurons are located in ganglia OUTSIDE of the CNS (in PNS)
Ganglion & Nucleus
ganglion: groups of neurons cell bodies that reside outside of CNS (plural = ganglia)
nucleus: groups of neuron bodies that reside inside the CNS ( plural = nuclei)
Functions of Neuroglia/Glial Cells
neuroglia or glial cells comprise more than half of the cells of the nervous system (neurones cannot function properly without them)
glial cells serve several functions:
- regulating the composition of extracellular fluid
- metabolic support for neurons
- formation of the myelin sheath
- formation of the blood-brain barrier (surround capillaries around the brain - things that are not supposed to reach the brain do not reach it)
- guide the development of neurons
- immune functions
- regulation of cerebrospinal fluid (CSF) production
Neuroglia Type - oligodendrocytes and schwann cells
oligodendrocytes - form the myelin sheath for neurons within the CNS and provide a structural framework
schwann cells - form the myelin sheath for neurons within the PNS
Neuroglia Type - microglia
phagocytes that consume debris, bacterial and dead cells
- is a type of CNS glial cell (not found in PNS)
- phagocyte: a type of cell that engulfs and “swallows” bacteria and debris
- microglia play a role in protecting the nervous system (immune function - protect from pathogens)
Neuroglia Type - astrocytes
another type of CNS glial cell with several key functions:
◦ regulates the composition of the extracellular
fluid within the CNS
‣ removes potassium ions and
neurotransmitters from the synaptic cleft and
surrounding extracellular areas
- formation of blood-brain-barrier
◦ anchors neurons to capillaries via the formation
of tight junctions
◦ serves to tightly control and regulate the
movement of substances from the capillary into
the CNS
- metabolic regulation
◦ regulate ion, nutrient, and dissolved-gas
concentrations (has to do with blood-brain-barrier)
- help guide neuronal development and synaptogenesis (secretion of growth factors, grow in certain directions)
◦ during embryonic development
Neuroglia Type - ependymal cells
epithelial cells that lines ventricles (in the brain) and central canal (surrounding the spinal cord) - protecting
- assist in producing, circulating and monitoring cerebrospinal fluid (CSF)
Neuroglia Type - satellite cells
surronding the soma of neurons, and help maintain the proper extracellular fluid environment (PNS)
- regulate the exchange of materials (ions, nutrients, metabolites) between the neuron and the extracellular fluid
- found in the PNS, not the CNS
- serve to protect and cushion the neurons in the PNS
- latching onto soma
- there is not anything protect the neurons in the PNS so satellite cells play a role in that
