Download Nervous System

General Functions of the
Nervous System
 Monitors changes
 Processes and Interprets
 Effects a Response
What is the Central Nervous
System
 The brain and the spinal cord make up the central
nervous system or CNS.
 It acts as the integrating and command centers of the
nervous system.
What is the Peripheral
Nervous System
 The part of the nervous system outside of the CNS.
 The nerves outside of the brain and spinal cord.
 They serve as communication lines between the body
and the brain and spinal cord.
Sensory (Afferent) Division
 Bring information to the spinal cord and brain.
 Fibers bringing information to the brain from skin,
muscles, and joints are called somatic sensory fibers.
 Fibers bringing information to the brain from visceral
organs are called visceral sensory fibers.
Motor (Efferent) Division
 Carries impulses from the CNS to effector organs
(muscles and glands).
 There are two subdivisions:
 Somatic Nervous System
 Allows conscious or voluntarily control of our skeletal
muscles (voluntary nervous system).
 Autonomic Nervous System
 Takes care of activities that are automatic or involuntary
such as smooth and cardiac muscles, and glands
(involuntary nervous system).
Two Principal Cell Types
 Supporting cells, also known as neuroglia.
 Astrocytes, microglia, Ependymal cells, Oligodendrocytes,
Schwann cells, and Satellite cells.
 Neurons.
Astrocytes
 Star-shaped cells.
 Nearly half of the neural tissue
 Form barrier between capillaries and neurons to protect
them from harmful substances in the blood.
 Braces neurons and anchors them to their nutrient
supply lines.
Microglia
 Spiderlike phagocytes that dispose of debris, including
dead brain cells and bacteria.
Ependymal Cells
 Line the cavities of the brain and the spinal cord.
 Cilia help to circulate the cerebrospinal fluid (CSF).
Oligodendrocytes
 Wrap their extensions around nerve fibers producing a
fatty insulating covering called myelin sheaths.
Schwann Cells
 Form the myelin sheaths around nerve fibers found in the
peripheral nervous system (PNS).
Satellite Cells
 They are the protective cushioning cells for the neurons.
The Neuron
Function of Neurons
 Highly specialized cells that transmit messages from one
part of the body to another.
 Neurons cannot divide or reproduce.
 They have three parts; dendrites, cell body, and an axon
Cell Body
 Metabolic center of the neuron
 Contains the usual cellular organelles except for
centrioles (which is why they do not divide).
Nissl Substance and
Neurofibrils
 This is the rough endoplasmic reticulum (ER) and their
filaments.
 They are important for maintaining the cell shape.
Dendrites
 These are processes that bring information toward the
cell body.
 They vary in number and length.
Axons
 These are processes that move the nerve impulse away
from the cell body.
 There is typically only one axon per neuron, but
occasionally there can be a collateral branch.
Neurotransmitters
 Chemicals released by the axonal terminals.
 There are over a hundred different neurotransmitters
that we know of.
 Dopamine, serotonin, acetylcholine, norepinephrine are
a few.
Synaptic cleft
 This is the gap found between an axonal terminal and the
next neuron.
Synapse
 This is the functional junction of the axonal terminal, the
synaptic cleft, and the next neuron.
Myelin
 It is a whitish, fatty material that has a waxy appearance.
 It protects and insulates the fibers and increases the
transmission rate of a nerve impulse.
Myelin Sheath and Neurilemma
 Myelin Sheath
 Encloses the axon.
 Neurilemma
 Is found external to the myelin
sheath.
 Together they enclose the axon
and insulate it.
Nodes of Ranvier
 This the gap, or indentation, found between Schwann
cells.
What are nuclei?
 They are clusters of neuron cell bodies found in the CNS
What are ganglia?
 These are small collections of cell bodies found in a few
sites OUTSIDE the CNS in the PNS.
Difference between gray matter
and white matter.
 White matter is made of dense collections of
MYELINATED fibers (tracts)
 Gray matter contains mostly UNMYELINATED fibers and
cell bodies.
Five types of sensory receptors
 Naked nerve endings – Pain and temperature receptors.
 Meissner’s corpuscle – light touch receptor.
 Pacinian corpuscle – deep pressure receptor.
 Golgi tendon organ (proprioceptor) – registers tension or
force.
 Muscle spindle (proprioceptor) – registers stretching.
What are association neurons?
 A third category of neurons.
 Also called interneurons.
 They connect the motor and sensory neurons.
 They allow communication between neurons.
Three types of neurons
 Multipolar neuron
 Containing several processes.
 All motor and association neurons are multipolar
 The most common structural type.
 Bipolar neuron
 Rare in adults.
 Found only in some special sense organs (eye, ear).
 Unipolar neuron
 Have a single process leaving the cell body.
 Moves nerve impulses both toward and away from the cell body.
Nerve Impulse Physiology
Polarized
 When the plasma membrane is resting or inactive.
 There are fewer positive ions sitting on the inner face of
the neuron’s plasma membrane than there are on its
outer face.
 The major positive ions inside the cell are potassium (K+)
 The major positive ions outside the cell are sodium (Na+)
Depolarization
 The inward rush of sodium ions changes the polarity of
the neuron’s membrane.
 The inside becomes more positive than the outside.
Action Potential
 Commonly referred to as the nerve impulse.
 It is an all-or-none response.
 Results when the stimulus is strong enough and the
sodium in-rush is great enough and depolarization
occurs.
Repolarization
 The outflow of positive ions from the cell which restores
the electrical conditions at the membrane.
 A neuron cannot conduct another impulse until the
neuron is repolarized.
Saltatory conduction
 Fibers that have myelin sheaths conduct impulses much
faster when they are insulted (myelinated).
 When myelinated the impulse jumps or leaps from node
to node along the length of the fiber (saltatory
conduction).
Reflex Arcs
 A reflex is a rapid, predictable, and involuntary response
to stimuli.
 They occur over a neural pathways and move in one
direction.
 There are a minimum of 5 elements
 Sensory receptor, a sensory neuron, the integration center,
the motor neuron, and finally the effector.
This ends Part 1 of Chapter 7