Download Nervous System

CHAPTER 9
The Nervous System
The Nervous System-Intro
• The nervous system is responsible for coordination and
integration.
• Feeling, thinking, remembering, moving, having awareness
• Nervous tissue consists of neurons which transmit
electrochemical nerve impulses to other neurons.
• Nervous tissue is composed of neurons and neuroglial cells.
• Neuroglial cells provide support, insulation, and nutrients to
neurons
• Neurons consist of a cell body and extensions called dendrites
and axons
• Axons send information in the form of nerve impulses; each neuron
has only one axon (usually)
• Dendrites are numerous and receive the nerve impulses
(electrochemical message)
CNS & PNS
• The organs of the nervous system can be divided
into two groups:
• Central Nervous System (CNS)
• The brain and the spinal cord
• Peripheral Nervous System (PNS)
• Nerves
• These two systems provide three general functionsintegrative, sensory, and motor
General Functions-Sensory
• Each peripheral neuron has a sensory receptor that
gathers info and detects changes inside and outside
the body.
• Monitor light and sound intensities
• Monitor temperature and oxygen level
• This information is converted into a nerve impulse that
travels up the peripheral nerve to the CNS (into the
spinal cord and on to the brain)
• Nerve impulses are converted into a sensation or a memory
or a thought
General Functions-Integrative
• The conscious or subconscious decisions we make
based on the nerve impulses gather by sensory
receptors are the integrative aspect of the nervous
system
• The desire to yawn is a subconscious reaction to low
oxygen levels detected by peripheral nerves
General Functions-Motor
• Motor functions (movement) are employed once
sensory information is integrated.
• Actually yawning (opening the mouth and inhaling) are
motor functions triggered by integrative and sensory
information
• SENSORYINTEGRATIVEMOTOR
PNS-Two Divisions
• Somatic Nervous System-Controls skeletal
muscles
• Autonomic Nervous System-Controls effectors
that are involuntary such as the heart, smooth
muscle in blood vessels, and various glands
Neuroglial Cells
• Neurons cannot exist without neuroglial cells.
• Neuroglial cells produce a fatty lipoprotein called
myelin.
• Special neuroglial cells called Schwann cells form a
myelin sheath around axons.
• Gaps between Schwann cells are called nodes of Ranvier.
• There are a great many more neuroglial cells than
neurons.
White vs Gray
• Axons with myelin sheaths are said to be myelinated.
• Areas within the CNS that are myelinated are called
white matter.
• Axons and neural cell bodies that are not myelinated
are said to be unmyelinated.
• These areas are called gray matter.
The Synapse
• Nerve impulses travel along nerve pathways.
• The junction between any two communicating neurons is
called a synapse.
• Neurotransmitters are biochemicals that cross the synaptic
cleft.
• Can you think of any?
• Acetylcholine, epinephrine, norepinephrine, serotonin, dopamine
• What happens if any of these neurotransmitters are out of
homeostatic balance?
Meninges
• Meninges lie between the bony coverings of the spinal cord
and brain. They are protective coverings.
• There are three layers to the meninges:
• Dura mater-outermost layer of the meninges
• White, tough connective tissue that contains many blood vessels and
nerves
• Arachnoid mater-middle layer of the meninges
• Thin, weblike membrane without blood vessels
• Pia mater-innermost layer of the meninges
• Very thin, contains many nerves and blood vessels that nourish the
underlying cells of the brain and spinal cord.
• Actually touches the brain and spinal cord, dipping into each crevice
Spinal Cord
• It is continuous with the brain.
• The spinal cord actually begins at the foramen magnum at the
base of the brain.
• It tapers to a point and terminates near the intervertebral disc
that separates the first and second lumbar vertebrae (last
discs).