warm-up outline pages 222-230. the nervous system chapter 7
Post on 25-Dec-2015
213 Views
Preview:
TRANSCRIPT
Functions•Master controlling and communicating
system of the body
•Monitor changes (stimuli) both inside and outside of the body▫Gathered information is called sensory input
•Processes and interprets the sensory input and makes decisions about what should be done at every moment ▫This is called integration
•Does not work alone to regulate and maintain body homeostasis▫Endocrine system is a second important
regulating system Produces hormones Typically brings about its effects in a more
leisurely way
Organization of the Nervous System
•Structural Classification▫Central nervous system (CNS)
Brain and spinal cord Occupy the dorsal body cavity and act as the
integrating and command centers of the nervous system
Interpret incoming sensory information Issue instructions
▫Peripheral nervous system (PNS) Parts of the nervous system that are outside
of the CNS Consists mainly of the nerves that extend
from the brains and spinal cord Spinal nerves carry impulses to and from the
spinal cord Cranial nerves carry impulses to and from
the brain Serve as communication lines
Functional Classification•Concerned only with PNS structures•2 subdivisions
▫Sensory (afferent) division Consists of nerve fibers that convey impulses
to the CNS from sensory receptors located through the body Somatic (afferent fibers) – impulses from the
skin, skeletal muscles and joints Visceral fiber (visceral afferents) – impulses
from the visceral organs
▫Motor (efferent) division Carries impulses from the CNS to effector
organs, the muscles and glands Effect a motor response Two subdivisions
Somatic nervous system – voluntary nervous system
Autonomic nervous system (ANS) – involuntary nervous system▫Sympathetic ▫Parasympathetic
Supporting Cells•Neuroglia – supporting cells in the CNS
that are “lumped together”▫Many types of cells that support, insulate
and protect the neurons
•Glia – different types of neuroglia that have a special function
Types of Glial•Astrocytes
▫Star shaped▫Account for nearly half of the neural tissue▫Form a living barrier between capillaries
and neurons and play a role in making exchanges between them
▫Help control the chemical environment in the brain
•Microglia▫Spiderlike phagocytes▫Dispose of debris
•Ependymal▫Line the cavities of the brain and the spinal
cord▫Helps circulate the cerebrospinal fluid
•Oligodendrocytes▫Wrap their flat extensions tightly around
the nerve fibers▫Produce fatty insulating covering called the
myelin sheaths
•Glia do not transmit nerve impulses•Never lose their ability to divide•Most brain tumors are gliomas
•Supporting Cells in the PNS come in two major varieties▫Schwann cells
Form the myelin sheaths around the nerve cells that are found in the PNS
▫Satellite cells Act as protection, cushioning cells
Neurons•Also called nerve cells
•Highly specialized to transmit messages
•Have a cell body containing the nucleus and is the metabolic center of the cell▫No centrioles▫Very abundant are the
Nissl substances – specialized RER Neurofibrils – intermediate filaments that are
important in maintaining cell shape
•Extending from the cell body there are one or more slender processes (fibers)▫Vary in length▫Dendrites – convey incoming messages
(electrical signals) towards the cell body May have hundreds of branching dendrites
▫Axons – generate nerve impulses and typically conduct them away from the cell body Only has one Arise from the axon hillock Occasionally branch to give off a collateral
branch Branch profusely at their terminal end to
form the axon terminals
▫Terminals contain the neurotransmitters in tiny vesicles which are released when stimulated
▫Synaptic cleft separates the one neuron for the next The functional gap is the synapse
▫Myelin – whitish, fatty material with a waxy appearance surrounds most nerve fibers Protects and insulates the fibers along with
increasing the transmission rate
Outside the CNS, the myelination is done by Schwann cells A myelin sheath results from the myelination Most of the Schwann cell cytoplasm ends up
just beneath the outermost part of its plasma membrane and is called the neurilemma▫Remains intact (for the most part) when a
peripheral nerve fiber is damages, it plays an important role in fiber regeneration
Nodes of Ranvier form where there are gaps between the adjacent Schwann cells
•In the CNS, the oligodendrocytes form the myelin sheaths. ▫Coil around as many as 60 different nerve
fibers at a time▫Lack neurilemma
• Clusters of neuron cell body and collections of nerve fibers▫ In the CNS, the cell body clusters are called nuclei
Protected in the skull and vertebral column Do not routinely undergo cell division Carries out most of the metabolic functions
▫ In the PNS, small collections of cell bodies are called ganglia Found in few sites
▫ In the CNS, bundles of nerve fibers are called tracts White matter – dense collections of myelinated tracts Gray matter – mostly unmyelinated fibers and cell
bodies▫ In the PNS, bundles of nerve fibers are called
nerves
Neuron Classification•Functional
▫Groups neurons according to the direction the nerve impulse is traveling relative to the CNS
▫Sensory (afferent) neurons – carry impulses from sensory receptors to the CNS Cell bodies are always found in a ganglion
outside the CNS Keep use informed about what is happening
both inside and outside the body Dendrite endings are usually associated with
specialized receptors that are activated by specific changes occurring nearby.
Complex receptors may be discussed later; we will focus on the simpler type of sensory receptors found in the skin (cutaneous sense organs), muscles and tendons (proprioceptors).
The pain receptors (which are bare dendrite endings) are the least specialized cutaneous receptors as well as the most numerous.
Proprioceptors detect the amount of stretch (tension) skeletal muscles, their tendons and joints These allow the body to make the proper
adjustments to maintain balance and normal posture.
top related