Nervous System

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Nervous System
Functions of the Nervous System
• Detection of changes in and
outside the body.
• Integration of information
from each of the senses.
• Coordination of muscles,
organs, and glands.
Divisions of the Nervous System
• The Central
Nervous System
(CNS) includes the
brain and spinal cord.
• The Peripheral
Nervous System (PNS)
is all the nervous tissue
outside of the brain and
spinal cord.
▫ The afferent division
transmits information
from the senses towards
the brain.
▫ The efferent division
transmits commands to
the muscles and glands
from the brain.
• The efferent division of the PNS is divided into
two systems:
▫ The somatic nervous system (SNS) controls
skeletal muscle.
▫ The autonomic nervous system (ANS)
regulates involuntary smooth and cardiac muscle,
as well as glands.
 The sympathetic division includes “fight or
flight” responses.
 The parasympathetic division includes “rest and
digest” responses.
CENTRAL
NERVOUS
SYSTEM
Brain and
spinal
cord
Afferent
Division
PERIPHERAL
NERVOUS
SYSTEM
Efferent
Division
Somatic
nervous
system
Autonomic
nervous system
Parasympathetic
division
Somatic
sensory
receptors
Visceral
sensory
receptors
Skeletal
muscle
Sympathetic
division
Smooth
muscle
Cardiac
muscle
Glands
Neural Tissue
• Neurons are the
basic units of the
nervous system,
able to
communicate
with other cells.
• Neuroglia
support neurons
by regulating
their surrounding
environment.
Cell Body Nucleus
Myelin
Sheath
Node
Neuroglia
(produces myelin)
Axon
Dendrites
Axon
Terminals
Neurons
• Neurons are cells
specialized in
transmitting and
receiving messages.
▫ Dendrites receive
incoming signals.
▫ Axons conduct
impulses away from the
cell body.
▫ The cell body contains
the neuron’s organelles.
• Neuron axons have
myelin, thin pads of
lipids that serve as
electrical insulation.
▫ Myelinated neurons
can transmit
electrical signals
much faster, and
appear white.
• Demyelination is a progressive destruction of
myelin sheaths, causing a loss of sensation and
motor control.
▫ Examples include multiple sclerosis (MS) and
mercury poisoning.
How Do Neurons Send Signals?
• Nerve signals begin
with a stimulus is
required before a
nerve impulse begins
– either from another
neuron or from one of
the senses.
How Do Neurons Send Signals?
• Nerve signals are electrical impulses sent across
the membrane of neurons called action
potentials.
• The electrical impulses are generated by
changing amounts of ions inside and outside the
neuron.
▫
▫
▫
▫
Potassium, K+
Sodium, Na+
Chlorine, ClNegative-charged proteins, Pr-
Neuron Polarization
• A resting neuron has a negative potential of
about -70mV.
▫ This is the result of the proteins (Pr-) permanently
kept inside the cell.
• Depolarization occurs when a stimulus (such
as a neurotransmitter) causes a protein channel
to open.
▫
Na+ ions flood diffuse inside the cell membrane,
creating a positive charge across the membrane..
• The next step is repolarization; the return
to the original negative charge as K+ ions
diffuse out of the cell.
▫ So much K+ leaves the cell that it becomes
hyperpolarized, or more negative than its
original resting state.
• The sodium-potassium
ATP pump restores the
original concentrations of
K+ and Na+ through active
transport.
▫ The neuron is now able to
conduct another action
potential.
Action Potential Summary
Peak Action Potential
Repolarization
Depolarization
Hyperpolarization
Resting Potential
Na/K ATP
Pump
Transmission at a Synapse
• Eventually, the signal will reach the
synapse; a gap between the axon of the
neuron and another cell.
▫ A neurotransmitter
is released from the
axon of the previous
neuron.
▫ The neurotransmitter
passes through a gap
called a synaptic
cleft before reaching
the next cell.
• Cholinergic synapses
are found between
motor neurons and
muscle cells.
▫ The neurotransmitter
acetylcholine is
released and binds to
receptors on the muscle
cell.
▫ Acetylcholine is
eventually broken down
by an enzyme, ending
the process.
• Botulism is a disease caused by
the ingestion of bacterial toxins
from rotting food.
▫ The toxin prevents the release of
acetylcholine at cholinergic
receptors, causing paralysis.
• Tetanus is caused by a bacterial
toxin that inhibits the enzyme
that breaks down acetylcholine.
▫ This causes prolonged, painful
muscle contractions.
▫ Exposure to the bacteria is
through any would that
punctures the skin.
Neuron Classification
• Sensory neurons
receive information from
the peripheral nervous
system or special senses.
▫ Somatic receptors
detect information from
the outside world.
▫ Visceral receptors
monitor conditions
within organs such as
the lungs, stomach, etc.
• Motor neurons carry
signals from the central
nervous system to muscles
or organs.
▫ Somatic motor neurons
innervate voluntary skeletal
muscles.
▫ Autonomic motor
neurons innervate all
involuntary muscles,
including the heart
(cardiac), glands, and
hollow organs (smooth).
• Interneurons join other
neurons together.
Reflexes
• A reflex is a rapid,
involuntary response to
a stimulus.
▫ These actions occur
more quickly because
they occur over a
reflex arc, a pathway
that bypasses the brain.
The Reflex Arc
• A reflex arc begins with a stimulus at a sensory
neuron, such as pain or heat.
• The sensory neuron is depolarized, and the
signal is sent through its axon.
• The signal is processed by an interneuron in the
spinal cord, which then activates a motor
neuron.
• A neurotransmitter is released at a cholinergic
synapse.
• The muscle contracts in response to the
neurotransmitter, and the reflex is complete.
External Brain Anatomy
Central Sulcus Postcentral Gyrus
Precentral Gyrus
Parietal Lobe
Frontal Lobe
Parieto-Occipital
Sulcus
Occipital
Lobe
Lateral Sulcus
Temporal Lobe
Cerebellum
Medulla
Oblongata
Pons
Cerebrum
• The adult brain has six major regions.
• The cerebrum is the largest region, controlling
conscious thought, complex movements, and
memory.
• The frontal lobe controls movement, language, and
other higher-thinking functions.
• The temporal lobe contains the auditory, taste,
and olfactory areas.
• The parietal lobe integrates sensory information.
• The occipital lobe contains the vision center.
Parietal Lobe
Central Sulcus
Parieto-Occipital Sulcus
Frontal
Lobe
Occipital
Lobe
Corpus
Callosum
Pineal
Gland
Lateral
Ventricle
Hypothalamus
Pituitary Gland
Cerebellum
Thalamus
Pons
Medulla
Oblongata
Layers of the Cerebrum
• The cerebrum has two layers:
▫ Outer grey matter that contains neuron cell
bodies.
▫ Inner white matter that contains axons encased
in myelin sheaths.
Diencephalon
• The diencephalon integrates sensory
information and motor commands.
▫ The thalamus transfers impulses received from
sensory neurons to the correct region of the
cerebrum.
• The hypothalamus controls many aspects of
internal homeostasis, including body
temperature, water balance, and overall
metabolism.
• The pineal gland releases melatonin, a
hormone that regulates day-night cycles.
The Brain Stem
• The brain stem directly attaches the brain to
the spinal cord.
▫ The pons contains the neurons responsible for
controlling breathing (along with the medulla).
• The medulla oblongata is the lowest part of
the brain stem, merging into the spinal cord.
▫ Controls heart rate, blood pressure, swallowing,
vomiting, and breathing (with the pons).
Cerebellum
• The cerebellum coordinates posture, balance,
and body movements.
Protection of the CNS
• Due to their size and complex shape, neurons
cannot undergo mitosis and are irreplaceable.
• As a result, the CNS has more protection than
any other part of the body.
Protection of the CNS
• The first layer of protection are the flat bones of
the skull.
• Below the bone are the meninges, membranes
of connective tissue.
▫ Dura mater is the outermost thickest layer.
▫ Arachnoid mater is a network of blood vessels.
▫ Pia mater is the innermost layer.
Protection of the CNS
• Cerebrospinal fluid, similar to plasma,
circulates through a series of cavities called
ventricles throughout the brain.
▫ Provides a watery cushion that protects nervous
tissue from trauma.
• A blood-brain barrier, made of capillaries,
only allows water, glucose, and amino acids into
the brain area.
▫ Wastes, proteins, and cells are kept out.
Spinal Cord
• The spinal cord is essentially
a continuation of the brain
stem down the back towards
the pelvis.
▫ Bone, meninges, and
cerebrospinal fluid provide
protection.
▫ Spinal nerves are mixed
nerves that carry motor,
somatic, and autonomic
signals to the body from the
spinal cord.
CNS Disorders
• Encephalitis is an inflammation of the brain
itself, caused by a foreign substance or a virus.
▫ Headache, drowsiness, nausea, fever.
• Meningitis is an inflammation of the meninges
(membranes) of the brain and spinal cord.
▫ Fever, stiff neck
CNS Disorders
• Alzheimer’s
disease is a
degenerative disease
that causes a gradual
loss of neuron cell
bodies and synapses
in the cerebral cortex.
▫ Tends to affect new
memories first.
▫ Cause unknown.
CNS Disorders
• Brain tumors are masses of cells that
overgrow in specific areas of the brain.
▫ Symptoms vary depending on the exact region
affected by the tumor.
CNS Disorders
• A stroke occurs when a blood clot or ruptured
blood vessel interrupts blood flow to a specific
part of the brain.
▫ Brain cells die from lack of oxygen, causing
permanent damage in that region.
▫ Brain equivalent of a heart attack.
• A concussion is a traumatic brain injury
caused by an impact that is not absorbed by
cerebrospinal fluid and damages the brain itself.
Cranial Nerves
• The cranial nerves are 12
pairs of nerves, mostly from
the head and neck, that attach
directly to the brain.
▫ Bypass the spinal cord.
▫ Part of the autonomic nervous
system.
Cranial Nerves
I. Olfactory
▫
Smell (sensory)
II. Optic
▫
Vision (sensory)
III.Oculomotor
▫
Eye muscles (motor)
IV.Trochlear
▫
Eye muscles (motor)
V. Trigeminal
▫
Facial (sensory) , chewing muscles
(motor)
VI.Abducens
▫
Eye muscles (motor)
Cranial Nerves
VII.Facial
▫
Taste (sensory), facial muscles (motor)
VIII.Vestibulocochlear
▫
Balance and hearing (sensory)
IX.Glossopharyngeal
▫
Taste (sensory), swallowing (motor)
X. Vagus
▫
▫
Sensory and motor neurons that affect
sweating, peristalsis, heart rate, opening
the larynx for speech and breathing.
Has branches in the ear canal – cotton
swab cough.
Cranial Nerves
XI.Accessory Nerve
▫
Neck and upper back muscles (motor)
XII.Hypoglossal
▫
Tongue (motor)
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