Fundamentals of the nervous system and nervous tissue (1) Flashcards
Week 3
Two benefits of cells communicating via electrical and chemical signals?
1.Rapid and specific
2.Usually cause almost immediate responses.
What are the three overlapping functions of the nervous system?
1.Sensory input
2.Integration
3.Motor output
What is the sensory function of the nervous system?
-Information gathered by sensory receptors about internal and external changes
What is the integration function of the nervous system?
-Processing and interpretation of sensory input
What is the motor output function of the nervous system?
-Activation of effector organs (muscles and glands) produces a response
What are the 2 principle parts of the nervous system?
1.Central nervous system (CNS)
2.Peripheral nervous system (PNS)
What is the central nervous system? (2 parts)
1.Brain and spinal cord of dorsal body cavity
2.Integration and control center (interprets sensory input and dictates motor output)
What is the peripheral nervous system? (2 parts)
1.The portion of nervous system outside CNS
2.Consists mainly of nerves that extend from brain and spinal cord (Spinal nerves to and from spinal cord, Cranial nerves to and from brain)
Nervous tissue consists of which two principle cell types?
- Neuroglia (gial cells)= small cells that surround and wrap delicate neurons
- Neurons (nerve cells)= excitable cells that transmit electrical signals
What are the 4 main neuroglia support CNS neurons?
- Astrocytes
- Microglial cells
- Ependymal cells
- Oligodendrocytes
Points about astrocytes
1.Cling to neurons, synaptic endings and capillaries
2.Most abundant, versatile and highly branched glial cells
Some functions of astrocytes
-Support and brace neurons
-Guide migration of young neurons
-Participate in information processing in the brain
-Control the chemical environment around neurons
-Play role in exchanges between capillaries and neurons
Respond to nerve impulses and neurotransmitters
-Influence neuronal functioning
Points about microglial cells (include functions)
- Small ovoid cells with thorny processes that touch and monitor neurons
2.Migrate toward injured neurons
3.Can transform to phagocytize microorganisms and neuronal debris
Points about ependymal cells (and functions)
1.Are ciliated (Cilia beat to circulate cerebrospinal fluid -CSF)
2.Produce Cerebrospinal fluid to line the central cavitiees of the brain and spinal column.
Oligodendrocyte points and functions
- Branched cells
2.Processed wrap CNS nerve fibers, forming insulating myelin sheaths in thicker nerve fibers.
What are the two major neuroglia seen in the PNS?
1.Satellite cells
2.Schwann cells
Function and location of satellite cells
1.Function similar to astrocytes (in CNS)
2.Surround neuron cell bodies in PNS
Function and location of Schwann cells.
1.(Function similar to oligondendrocytes)- vital to regeneration of damaged peripheral nerve fibers
2.Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers.
What are neurons and their structure (function)
- Neurons (nerve cells) are structural units of nervous systems
- Large, highly specialised cells that conduct impulses
Special characteristics of neurons (3)
- Extreme longevity (they last a person’s lifetime)
- High metabolic rate: requires continuous supply of oxygen and glucose
- All have cell body and one or more processes.
What is the neuron cell body? (also known as soma) and function of its plasma membrane?
-Biosynthetic center of neuron
-(in most) The plasma membrane is part of the receptive region that receives input information from other neurons.
Name for clusters of neuron cell bodies in the CNS?
-Nuclei
Name for clusters of neuron cell bodies in the PNS
-Ganglia
Arm like processed that extend from cell body (CNS and PNS)
-CNS contains both neuron cell bodies and their processed
-PNS contains mostly neuron processes.
What are tracts
*Bundles of neuron processes in CNS
What are nerves
*Bundles of neuron processes in PNS
What are the two types of processes?
1.Dendrites
2.Axon
Describe the basic structure of a motor neuron (9)
- Dendrites (receptive regions)
- Cell body (biosynthetic centre and receptive region)
3.Nucleus & Nucleolus - Chromatophilic substance (rough endoplasmic reticulum)
5.Axon (impulse-generating and conducting region) - Schwann cell
- Myelin sheath gap (node of Ranvier)
8.Axon terminals (secretory region)
9.Terminal branches
How are organelles and molecules moved along axons?
Moved by motor proteins and cytoskeletal elements
Definition of anterograde
*Away from the cell body
-e.g. membrane components, enzymes, neurotransmitters, cytoskeletal elements.
Definition of retrograde
*Towards the cell body
-e.g. signal molecules, viruses, bacterial toxins, organelles to be degraded
Composition of myelin sheath
- Myelin, a whitish, protein-lipid substance
Function of myelin (2)
- Protect and electrically insulate axon
2.Increase speed of nerve impulse transmission
What are myelinated fibers?
*Segmented sheath suurrounds most long/large-diameter axons
What non-myelinated fibers?
*Do not contain sheath (conduct impulses more slowly)
What are the steps for the myelination of a nerve fiber (axon)
- Schwann cell envelopes axon
- The schwann cell rotates along the axon, wrapping its plasma membrane loosely around it in successive layers
3.The schwann cell cytoplasm is forced from between the membrane, the tight membrane wrappings surrounding the axon form the myelin sheath.
How are myelin sheaths presented in the CNS and how many axons can one cell wrap?
-Formed by processes of oligodendrocytes (not whole cells)
-Each cell can wrap 60 axons at once
What is white matter?
*Regions of the brain and spinal cord with dense collections of myelinated fibers (usually fiber tracts)
What is grey matter?
*Mostly neuron cell bodies, dendrites, axon terminals and non–myelinated fibers (areas where synapses occur between neurons- where integration and command initiation takes place)
What are the three types of neurons related to the CNS?
1.Sensory
2.Motor
3.Interneurons
Function of sensory neurons and where they are found.
- Transmit impulses from sensory receptors toward CNS
2.Cell bodies are located in ganglia in PNS
Function of Motor neurons and where they are found.
- Carry impulses from CNS to effectors
- Most cell bodies are located in CNS (except some autonomic neurons)
Function of interneurons, where they are found, percentage of them in the body
- Shuttle signals through CNS pathways
2.Lie between motor and sensory neurons, most are entirely in CNS - 99%
What does generating a resting membrane potential depend on? (2)
- Differences in K+ (higher inside) and Na+ (higher outside) conc inside and outside cells
- Differences in permeability of the plasma membrane to these ions
What is the transmembrane potential of a neuron usually around?
-70mV
Notes about the charge in the cytosol and extracellular fluid
- Cytosol contains an abundance of negatively charged proteins
2.Extrecellular fluid contains relatively few
-Therefore these proteins cannot cross the plasma membrane.
How can potassium ions diffuse out of the cell?
Via potassium leak channels
How does the sodium-potassium pump maintain a stable resting potential?
- It ejects 3Na+ for every 2K+ taken in from the extracellular fluid
How can sodium ions diffuse into the cell?
Sodium leak channels
