Nervous System Flashcards
o Enclosed by the skull
o Contains about 100 billion neurons
Brain
o Twelve pairs (right and left) of cranial nerves, numbered I through XII,
emerge from the base of the brain.
Cranial nerves
a bundle of hundreds to thousands of axons plus associated
connective tissue and blood vessels that lies outside the brain and spinal
cord.
nerve
o Connects to the brain through the foramen magnum of the skull and is encircled by the bones of the vertebral column. o It contains about 100 million neurons.
Spinal cord
o Thirty-one pairs of spinal nerves emerge from the spinal cord, each serving a specific region on the right or left side of the
body.
Spinal nerves and their
branches
o Small masses of nervous tissue, consisting primarily of neuron cell bodies,
that are located outside the brain and spinal cord.
o closely associated with cranial and spinal nerves.
Ganglia
o In the walls of organs of the gastrointestinal tract, extensive networks of neurons
o help regulate the digestive system.
Enteric plexuses
o Dendrites of sensory neurons as well as separate, specialized cells that
monitor changes in the internal or external environment, such as
photoreceptors in the retina of the eye.
Sensory receptors
detect internal stimuli, such as an increase in blood acidity, and external stimuli
Sensory receptors
o possess electrical excitability, the ability to respond to a stimulus and convert it into an action potential.
Neurons
neurons three parts:
cell body
dendrites
axon
Contains a nucleus surrounded by cytoplasm that includes typical cellular organelles such as lysosomes, mitochondria, and a Golgi complex.
Cell body
▪ The receiving or input portions of a neuron.
▪ They usually are short, tapering, and highly branched.
Dendrites
▪ Propagates nerve impulses toward
another neuron, a muscle fiber, or a
gland cell.
▪ Long, thin, cylindrical projection
Axon
o Make up about half the volume of the CNS.
o Smaller than neurons, and they are 5 to 50 times more numerous.
o do not generate or propagate action potentials, and they can multiply and divide in the mature nervous system.
Neuroglia/ glia
Brain tumors derived from glia
gliomas
CNS types of neuroglia
astrocytes, oligodendrocytes,
microglia, and ependymal cells
PNS types of neuroglia
Schwann cells and satellite cells
Axons surrounded by a multilayered lipid and protein covering
myelin sheath, “myelinated”
Axons surrounded by a multilayered lipid and without protein covering
unmyelinated
Two types of neuroglia produce myelin sheaths
Schwann cells (in the PNS) Oligodendrocytes (in the CNS)
The outer nucleated cytoplasmic layer of the Schwann cell, which encloses the myelin sheath
neurolemma (sheath of
Schwann)
Gaps in the myelin sheath, appear at
intervals along the axon
nodes of Ranvier
a bundle of axons that is located in the CNS.
tract
composed primarily of myelinated axons. The whitish color
of myelin gives white matter its name.
White matter
appears grayish and contains
neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and
neuroglia.
gray matter
o Consists of the brain and spinal cord. o/processes many different kinds of incoming sensory information.
o It is also the source of thoughts,
emotions, and memories.
o contains most nerve impulses that stimulate muscles to contract and glands to secrete
Central Nervous System
o Includes all nervous tissue outside the CNS.
o Components include cranial nerves and their branches, spinal
nerves and their branches, ganglia, and sensory receptors.
Peripheral Nervous System
Consists of (1) sensory neurons that convey information from
somatic receptors in the head, body wall, and limbs and from
receptors for the special senses of vision, hearing, taste, and smell
to the CNS and (2) motor neurons that conduct impulses from the
CNS to skeletal muscles only. Because these motor responses can be consciously controlled, the action of this part of the PNS is
voluntary.
Somatic nervous system (SNS)
▪ Consists of (1) sensory neurons that convey information from
autonomic sensory receptors, located primarily in visceral organs
such as the stomach and lungs, to the CNS, and (2) motor neurons
that conduct nerve impulses from the CNS to smooth muscle,
cardiac muscle, and glands. Because its motor responses are not
normally under conscious control, the action of the ANS is
involuntary.
▪ The motor part consists of two branches, the sympathetic division and the parasympathetic division.
Autonomic nervous system (ANS)
the “brain of the gut,” is involuntary.
▪ Consists of approximately 100 million neurons in enteric plexuses
that extend most of the length of the gastrointestinal (GI) tract.
▪ chemical changes within the GI tract as well as the stretching of its walls. Enteric motor neurons
govern contraction of GI tract smooth muscle to propel food
Enteric nervous system (ENS)
Two types of connective tissue coverings of spinal cord
coverings—bony vertebrae and tough,
connective tissue meninges—plus a cushion of cerebrospinal fluid
located within the vertebral canal of the vertebral column.
spinal cord
three connective tissue coverings that encircle the spinal cord and brain.
surround the spinal cord and
are continuous with the cranial meninges, which encircle the brain.
Meninges
a. Dura mater
b) Arachnoid mater
c) Pia Mater
▪ Most superficial of the three spinal meninges
▪ Composed of dense, irregular
connective tissue.
Dura mater