Transcript Sensory function

Nervous System
Components of the Nervous
System
• The nervous system includes the brain,
cranial nerves, spinal cord, spinal
nerves, ganglia, enteric plexuses, and
sensory receptors.
CNS
• Brain
• Spinal Cord
PNS
• includes all nervous tissue outside the
CNS.
•
•
•
•
Cranial Nerves = 12 X 2 =
Spinal Nerves = 31 X 2
Enteric plexuses
Sensory receptors
Function
• Sensory function. Sensory receptors
detect internal stimuli, such as an increase
in blood acidity, and external stimuli, such
as a raindrop landing on your arm.
• This sensory information is then carried
into the brain and spinal cord through
cranial and spinal nerves.
Intergration
• Integrative function. The nervous system
integrates (processes) sensory information by
analyzing and storing some of it and by making
decisions for appropriate responses.
• An important integrative function is perception,
the conscious awareness of sensory stimuli.
Perception occurs in the brain.
Motor Neuron
• Motor function. Once sensory information
is integrated, the nervous system may
elicit an appropriate motor response by
activating effectors (muscles and glands)
through cranial and spinal nerves.
Stimulation of the effectors causes
muscles to contract and glands to secrete.
Which types of neurons carry input to the
CNS and output from the CNS?
Neuron
• Structure of a typical neuron
• The arrows indicate the direction of
information flow: dendrites → cell body →
axon → axon terminals → synaptic end
bulbs.
• The basic parts of a neuron are: dendrites,
a a cell body, and a single axon
Neuroglia in the CNS and PNS
•
•
•
•
Astrocytes
Microglia
Oligodendrocytes
Schwann Cells
Gray and White Matter
• White matter is composed primarily of
myelinated axons.
• The whitish color of myelin gives white matter its
name.
• The gray matter of the nervous system contains
neuronal cell bodies, dendrites, unmyelinated
axons, axon terminals, and neuroglia.
• It appears grayish, rather than white, because
the cellular organelles impart a gray color and
there is little or no myelin in these areas.
Membrane Potential
is due to a small buildup of negatively
charged ions, mainly organic
phosphates (PO43-) and proteins, in the
cytosol just inside the membrane and
an equal buildup of positively charged
ions, mainly sodium ions (Na+), in the
interstitial fluid just outside the
membrane.
Membrane Potential
Action Potential (AP)
• When a stimulus depolarizes the
membrane to threshold, an action potential
is generated.
• An action potential consists of
depolarizing and repolarizing phases.
Which channels are open during depolarization?
During repolarization?
•
•
•
•
•
•
•
What are the meanings of the terms:
resting membrane potential
depolarization
repolarization
nerve impulse
refractory period?
How is saltatory conduction different from
continuous conduction?
Events at a Synapse
• A nerve impulse arrives at a synaptic end
bulb of a presynaptic axon.
• The depolarizing phase of the nerve
impulse opens voltage-gated Ca2+
channels, which are present in the
membrane of synaptic end bulbs.
• Because calcium ions are more concentrated in
the interstitial fluid, Ca2+ flows into the synaptic
end bulb through the opened channels.
• An increase in the concentration of Ca2+ inside
the synaptic end bulb triggers exocytosis of
some of the synaptic vesicles, which releases
thousands of neurotransmitter molecules into
the synaptic cleft.
• The neurotransmitter molecules diffuse
across the synaptic cleft and bind to
neurotransmitter receptors in the
postsynaptic neuron's plasma membrane.
• Binding of neurotransmitter molecules
opens ion channels, which allows certain
ions to flow across the membrane.
• As ions flow through the opened channels,
the voltage across the membrane
changes.
• Depending on which ions the channels
admit, the voltage change may be a
depolarization or a hyperpolarization.
• If a depolarization occurs in the
postsynaptic neuron and reaches
threshold, then it triggers one or more
nerve impulses.
Human Brain
Sensory Receptors
• Exteroceptors
• Interoceptors
Types of Sensory Receptors
•
•
•
•
•
Chemoreceptors
Pain receptors –nociceptors
Photoreceptors
Mechanoreceptors
Thermoreceptors
Other types of Sensory Receptors
• Proprioceptors are mechanoreceptorsinvolved in reflex actins to maintain muscle
tone, equilibrium and posture
• Cutaneous Receptors, which make the
skin sensitive to touch, pressure, pain, and
temperature (warmth and cold)
Senses
•
•
•
•
•
Nose-smell
Eyes-vision
Ears-hearing
Mouth-taste
Skin -touch
Sense of Taste and Smell
• Sense of taste : taste buds are located on
the tongue
• Others are located in the hard palate,
pharynx, epiglottis
• There are four primary types of taste:
sweet, sour, salty, and bitter.
Taste Buds
•
•
•
•
open at a taste pore
Have supporting cells and taste cells
The taste cells have extensions: microvilli
Sensory nerve fiber
Microvilli
• When you eat, the chemical molecules in
your food bind to the chemoreceptors of
the microvilli.
• Nerve signals are generated in sensory
nerve fibers that go to the brain.
• The signal is sent to the parietal lobe-the
area that interprets taste.
Chemoreceptors
Sense of Smell
• Approximately 80-90% of what we receive
as “taste” actually is due to the sense of
smell.
• Our sense of smell depends on between
10 and 20 million olfactory cells located
within olfactory epithelium high in the roof
of the nasal cavity.
Chemoreceptors
• Olfactory cells are modified neurons.
• Each cell ends in a tuft of about five olfactory
cilia, which bear receptor proteins for odor
molecules.
• When you smell a rose, the odor
molecules(chemicals) bind to the olfactory cilia.
The sensory neuron generates a nerve impulse
that moves along the sensory nerve which
reaches the olfactory bulb
Photoreceptors
•
•
•
•
Are located in the retina
Cone cells-black and white vision
Rod cells-color vision
See table 14.2
• The neurons communicate this information
via the olfactory tract to the olfactory area
of the cerebral cortex.
• The olfactory area is located in the
temporal lobe.
• When the action potential reaches the
temporal lobe (olfactory area) you know
you have smelled a rose.
Eye
Sense of Hearing
• The ear has three division: outer ear,
middle ear and inner ear.
• See figure 14.12
Inner Ear
•
•
•
•
Has three areas:
semicircular canals-equilibrium
Vestibule-equilibrium
Cochlea-hearing
• White matter
• Gray matter
• Hypothalamus
Thalamus
• Cerebellum
• Brain stem: midbrain, medulla
oblongata, pons
• The reticular formation
• Limbic System
• Sympathetic and parasympathetic
•
•
•
•
•
•
•
•
•
•
CNS
PNS
Crania nerves
Spinal nerves
Sensory receptors
Sensory neurons
Interneurons
Motor neurons
Motor receptors
Effectors
•
•
•
•
•
•
•
•
Dendrites
Axon
Myelin sheath
Node of Ranvier
Axon terminal
Cell body
See figure 13.2
How do the three different types of
neurons differ in structure?
• Neuroglia cells out number neurons
9:1(know all four)
•
•
•
•
•
•
•
•
•
•
Resting membrane
Action potential
Depolarization
Repolarization
Sodium-potossium pump
Sodium ion
Potassium ion
Saltatory conduction
Refractory period
The Synapse see figure 13.4
Neurotrnsmitter Molecules
•
•
•
•
•
•
Acetycholine
Norepinephrine
Dopamine
Serotonin
Glutamate
GABA
• Acetylcholinesterase