CHAPTER 12 TEST REVIEW Flashcards
functions of the nervous system
Functions:
* Collect information
* Processes and evaluate information
* Initiate response to information
structural organization of nervous system
Structural organization: central vs peripheral
* Central nervous system (CNS) = brain and spinal cord
* Peripheral nervous system (PNS) = nerves and ganglia
connective tissue wrappings of the nerve
Epineurium: encloses entire nerve
* Thick layer of dense irregular connective tissue
Perineurium: wraps fascicle (bundle of axons in nerve)
* Layer of dense irregular connective tissue
Endoneurium: wraps an individual axon
* Delicate layer of areolar connective tissue
cranial/spinal nerves
Cranial nerves: extend from brain
Spinal nerves: extend from spinal cord
sensory/motor/mixed nerves
Sensory nerves contain sensory neurons sending signals to
CNS
Motor nerves contain motor neurons sending signals from CNS
Mixed nerves contain both sensory and motor neurons
* Most named nerves are in this category
* Individual axons in these nerves transmit only one type of information
ganglion
a cluster of neuron cell bodies in the PNS
neuron (define, parts, characteristics)
The neuron is the structural unit of nervous system
Neuron characteristics:
* Excitability: responsiveness to a stimulus
- Conductivity: ability to propagate electrical signal
- Secretion: release of neurotransmitter in response to
conductive activity - Extreme longevity: cell can live throughout person’s lifetime
- Amitotic: After fetal development, mitotic activity is lost in most
neurons
parts:
cell body
dendirtes
axon
cytoskeletion
structural classifications of neurons
Structural classification by number of processes coming
off soma
Multipolar neurons: many dendrites, one axon
* Most common type
Bipolar neurons: one dendrite and one axon
* Limited number; For example, in retina of the eye
Unipolar neurons (pseudounipolar): one process
extends from cell body
* Splits into two processes
* Peripheral process splits into several receptive dendrites
* Central process leads to synaptic knobs in CNS
Anaxonic neurons: have dendrites but no axons
functional classifications of neurons
Sensory neurons (afferent neurons)
* Conduct input from somatic and visceral receptors to CNS
* Most are unipolar (a few bipolar)
Motor neurons (efferent neurons)
* Conduct output from CNS to somatic and visceral effectors
* All are multipolar
Interneurons (association neurons)
* Receive, process, and integrate information from many other neurons
* Communicate between sensory and motor neurons
* Located within CNS; make up 99% of our neurons
* Generally are multipolar
synapse
Synapse: place where a neuron connects to another neuron
or an effector
* Two types: chemical and electrical
* Chemical synapses are far more common than electrical synapses
glial cells (definition, characteristics)
- Nonexcitable, support cells found in CNS and PNS
- Approximately same number of glial cells as there are
neurons - Glial cells account for about half the volume of nervous system
- General characteristics:
- Capable of mitosis
- Protect and nourish neurons
- Provide physical scaffolding for nervous tissue
- Guide migrating neurons during development
- Critical for normal function at neural synapses
Types of Glial Cells
Astrocytes (star-shaped cells)
* Have processes that end in perivascular feet
* Most abundant glial cell in CNS
Ependymal cells
* Line cavities in brain and spinal cord
Microglia
* Small cells that wander CNS and replicate in infection
Oligodendrocytes
* Large cells with slender extensions
* Extensions wrap around axons of neurons forming myelin
sheath
Glial cells of the PNS
Satellite cells
* Arranged around neuronal cell bodies in a ganglion
* Electrically insulate and regulate the exchange of nutrients and
wastes
Neurolemmocytes (Schwann cells)
* Elongated, flat cells that ensheath PNS axons with myelin
* Allows for faster action potential propagation
Clinical View: Tumors of the Central Nervous System
Neoplasms (tumors) from unregulated cell growth
Sometimes occur in CNS
Tumors originating from the brain, primary brain tumors
Typically originate in supporting tissues
* Tissues with capacity to undergo mitosis
* From meninges (protective membranes of CNS) or glial
cells
Gliomas, glial cell tumors
* May be benign
* May be malignant, capable of metastasizing
Clinical View: Nervous System Disorders Affecting
Myelin
Multiple sclerosis
* Progressive demyelination of neurons in CNS
* Autoimmune disorder: oligodendrocytes attacked by
immune cells
* Repeated inflammatory events causing scarring and
permanent loss of function
Guillain-Barré syndrome
* Loss of myelin from peripheral nerves due to inflammation
* Muscle weakness begins in distal limbs, advances to
proximal muscles
* Most function recovered with little medical intervention
