Download The Nervous System

The Nervous System
Ch. 37
Who makes it, has no need of it.
Who buys it, has no use for it.
Who uses it can neither see nor feel it.
What is it?
Coffin
• What gets wetter and wetter the more it dries?
A Towel
• What are the next two numbers in this series: 2, 9, 16, 23, ..
30 and 37
• What does this say?
TOIMWN
I’m in town
Vertebrate Nervous System
• The Central Nervous System- consists of brain and spinal
cord
• The Peripheral Nervous System- consists of nerves and
ganglia outside the Central nervous system
Nervous Tissue
• 2 Cells of the Nervous System
• Neurons
• Neuroglia
Neuroglia
• Also called glial cells
• Microglia- phagocytic cells that remove bacteria and
debris
• Astrocytes- provide metabolic and structural support to
neurons
• Oligodendrocytes- form myelin sheath around axon
Neurons
• Consist of 3 major parts
• Cell Body- contains a nucleus and other organelles
• Dendrites- short, highly branched processes that receive signals and
transmit them to cell body.
• Axon- convey information to other neurons or cells
•
•
Sometimes covered by myelin sheath
Often called nerve fibers
Types of Neurons
• Motor Neurons
•
•
Take nerve impulses from the CNS to muscles or glands.
Said to have multipolar shape because they have many dendrites and a single axon
Types of Neurons
• Sensory (afferent) Neurons
•
•
Take nerve impulses from sensory receptors to CNS
Structure is unipolar because process from cell body branches to the periphery and
CNS
Types of Neurons
• Interneurons
•
•
Occur only within CNS
Have multipolar shape and convey impulses between various parts of the CNS
Transmitting Nerve Impulses
•
First hypothesized in early 1900s, but not able to be tested until
1960s.
• Electrodes were inserted into a giant axon of a squid. Voltage
was then measured between the inside and the outside of the
axon.
•
Voltage is the electrical potential difference between two points
• The electrical difference across a membrane is called the
membrane potential.
Transmitting Nerve Impulses
• Resting Potential
• When the axon is not conducting an impulse.
• There is a difference in ion distribution on either side of the axonal
membrane caused in part by the sodium-potassium pump.
• Voltage is about – 70 mV.
• Action Potential
• A rapid change in polarity across a portion of an axonal membrane
• A threshold is the minimum change in polarity that is required to
generate an action potential.
• Voltage swings from -70 mV to 40 mV.
Transmitting Nerve Impulses
• In nonmyelinated axons the action potential moves down an
axon one section at a time at a speed of about 1 m/s.
• In myelinated axons, the action potential “jumps” from node to
note.
• When the action potential moves on, the section goes through a
refractory period, in which Na+ gates are unable to open. This
causes the action potential to only move in one direction.
Transmission across a Synapse
• The ends of the axon are branched into axon terminals.
• The terminals are close to the dendrites of another neuron. The
space between the 2 neurons is called a synapse.
Transmission across a Synapse
• Impulses cannot travel across a synapse, so molecules called
neurotransmitters carry it.
• When an impulse reaches the axon terminals an gated channel
for Ca2+ opens and stimulates a vesicle to release
neurotransmitters.
• The neurotransmitters then attach to the dendrites of the next
neuron to carry on the impulse.
• After the impulse is passed on the neurotransmitters are
removed from the synapse.
Antidepressants
• Antidepressant drugs (ie: Prozac and Wellbutrin) work by
preventing the reuptake of neurotransmitters serotonin and
norepinephrine.
• This helps prolong the effect of these neurotransmitters and level
out the emotional state.
The Central Nervous System
• 3 Specific Functions
• Receives sensory input
• Performs integration
• Generates motor outputs
The Central Nervous System
• The brain and spinal cord are wrapped in 3 protective membranes called
meninges and the spaces between the meninges are filled with
cerebrospinal fluid.
The Spinal Cord
• The spinal cord is a bundle of nervous tissue enclosed in the vertebral
column.
• 2 functions of the spinal cord
•
•
Reflex actions
Provides communication between the brain and spinal nerves
The Spinal Cord
• Gray matter
• Consists of cell bodies and unmyelinated fibers
• Contains portions of sensory and motor neurons
• White matter
• Made up of bundles of myelinated long fibers of interneurons called
tracts
• Tracts are like super highways, constantly sending information between
the brain and the rest of the body
The Spinal Cord
• Damage to sections of the spinal cord can result in paralysis.
• Amyotrophic Lateral Sclerosis (ALS), also known as Lou Gehrig’s
disease, is caused by motor neurons in the brain and spinal cord
dying. This eventually leads to paralysis and patients cannot
breath properly.
• The Cerebrum
The Brain
• The largest, outermost portion of the brain
• Communicates with other parts of the brain and coordinates their
activities
• Split into 2 hemispheres, left and right, by the longitudinal fissure. Each
hemisphere receives information and controls the opposite side of the
brain.
• Sulci, shallow grooves, divide the hemispheres into lobes.
•
•
•
•
Frontal lobes control motor functions, memory, reasoning, and judgment
Parietal lobes control sensory reception and integration, as well as taste.
Temporal lobes receives auditory information
Occipital lobes receive information from the eyes
The Brain
• The Cerebral Cortex
• A thin layer of thin, convoluted grey matter covering the
cerebral hemispheres.
• Accounts for sensation, voluntary movement and all the
thought processes required for learning, memory, language
and speech.
• A stroke that affects the cerebral cortex could lead to
paralysis of one side of the body.
The Brain
• Basal Nuclei
• Masses of gray matter within white matter that integrate
motor commands, ensuring the correct muscle groups are
activated.
• Parkinson Disease results from loss of cells in the basal nuclei
that normally control release of dopamine.
The Brain
• Hypothalamus
• Helps maintain home0stasis by regulating hunger, sleep, thirst, body
temp., and water balance.
• Thalamas
• Receives all sensory input except smell
• Integrates the information then sends the appropriate portion to the
cerebrum
• Pineal Gland
• Secretes melatonin, the hormone that regulates sleep-wake cycle
The Brain
• Cerebellum
•
•
Largest part of the hind brain
Receives sensory input from the eyes, ears, joints, and muscles about current body position
• Brain Stem
•
•
Contains midbrain, the pons, and the medulla oblongata
This is where the tracts cross so right brain controls left side of body
• Medulla Oblongata
•
Regulates heart beat, breathing, swallowing and blood pressure
• Pons
•
Contains bundles of axons that form “bridges” between the cerebellum and the rest of the
CNS.
The Brain
• The Reticular Activating System
• Contains reticular formation, a complex network of nuclei and nerve
fibers that run the length of the brain stem
• Receives sensory signals and sends them up to higher centers
• Receives motor signals and sends them to the spinal cord
The Brain
• The Limbic System
• Blends higher mental function and primitive emotions into
one
• 2 significant structures
• Hippocampus- makes prefrontal area aware of past experiences
• Amygdala- causes experiences to have emotional overtones
Alzheimer Disease
• Patients have abnormal neurons throughout the brain, but
especially in the hippocampus and amygdala.
• The abnormalities are plaques containing beta amyloid
accumulated around axons and bundles of fibrous proteins
around the nucleus.
• Symptoms can be treated with cholinesterase inhibitors, which
increase levels of acetylcholine in the brain. (Neurotransmitter
that either excites or inhibits smooth muscles or glands
depending on their location)
The Peripheral Nervous System
• Contains Nerves
• 2 types of nerves
• Cranial Nerves
•
•
•
Humans have 12 pairs
A mixture of motor and sensory nerves
Concerned mostly with the head, neck, and facial regions of the body
• Spinal Nerves
•
•
Humans have 31 pairs
Extend from spinal cord by 2 short roots
• The dorsal roots contain axons of sensory neurons
• The ventral roots contain axons of motor neurons
The Peripheral Nervous System
• Contains 2 divisions
• The somatic system
• The autonomic system
The Peripheral Nervous System
• The Somatic System
• Take sensory information from external sensory receptors in the skin
and joints to the CNS
• Carries motor commands from CNS to the skeletal muscles
The Peripheral Nervous System
• Reflexes
•
•
•
Voluntary control of skeletal muscles originates in the brain
Reflexes are involuntary response to stimuli
Ex: Hand touches a sharp pin
The Peripheral Nervous System
• The Autonomic System
• Regulates activity of the cardiac and smooth muscles and
glands
• Divided in to two divisions: sympathetic and parasympathetic
• Both divisions:
• Function automatically and usually involuntarily
• Innervate all internal organs
• Use two neurons and one ganglion for each impulse
The Peripheral Nervous System
• Sympathetic Division
• Arises from the middle portion of the spinal cord and
terminate in ganglia near the cord
• Used in emergency situations- “fight or flight”
• Increases heartbeat and dilates the bronchi while inhibiting the
digestive system
The Peripheral Nervous System
• Parasympathetic Division
• Includes a few cranial nerves and fibers that arise from the bottom of the
spinal cord
• Called the “rest and digest division”
• Promotes internal responses associated with a relaxed state, ie: pupils to
contract, digestion of food, and slowed heatbeat