Post on 16-May-2015
Lecture 20:The Nervous System/Senses
Covers Chapter 38 & 39
Intro to Nervous System
• Primary Purpose: receive, process and transmit information
• Messages from the environment and from the body itself go to brain and tell it what’s happening. Brain gets info and tells body how to respond. – The cells that carry these “messages” are called
NEURONS.– Neurons bundled together are called NERVES.
NERVOUS SYSTEM
• 2 parts– Central Nervous System**
• Brain• Spinal Cord
– Peripheral Nervous System**• ALL Neurons/Nerves outside the CNS
CNS & PNS
3 major types of neurons/nerves
• **Sensory Nerves – carry nerve impulses TO the CNS
• **Motor Nerves – carry nerve impulses AWAY from the CNS
• **Interneurons - located WITHIN the CNS ONLY- connect sensory and motor neurons
stimulus
sensoryneuron spinal
cord
motorneuron
dorsal root
interneuron
ventralroot
The motorneuron stimulatesthe effector muscle
The effectormuscle causes awithdrawal response
A painfulstimulus activatesa pain sensoryneuron
The signal istransmitted by thepain sensory neuronto the spinal cord
The signal istransmitted to aninterneuron and thento a motor neuron
4
3
2
1
5
Fig. 38-10
Neuron*
• 3 parts of the neuron• 1.) Cell Body- contains nucleus• 2.) Dendrites – receives information from
nearby neurons.• 3.) Axon - electrical signals are transmitted to
end of neuron (synapse)• Synapse: place where neuron communicates
with a muscle fiber, gland or another neuron• Nerve signal sent between neurons takes the
form of neurotransmitters.
Dendrites:Receive signalsfrom other neurons
2
Cell body:Integrates signals;coordinates theneuron’s metabolicactivities
3
An actionpotential starts here4
Axon: Conductsthe action potential5
Dendrites(of other neurons):Receive signals
synapse
dendritereceptors
synapticterminal
7
Synaptic terminals:Transmit signals toother neurons
6
Synaptic terminals:Transmit signals fromother neurons
1
neurotransmitters
A Neuron
Fig. 38-1
What is the impulse/signal/message?
• Information is carried in the neuron as an electrical signal (called an action potential)– When a neuron is stimulated, ions within the
neuron (Na+, K+) move in/out and change the electrical charge of the neuron momentarily as the “message” is carried through the neuron
– After the action potential passes, neuron’s charge returns to normal
How is the message carried between neurons?*
• Neurons do not actually touch• The gap between neurons is the synaptic cleft• At the end of the axon, there is a synaptic terminal. • In the synaptic terminal, vesicles containing chemicals
(neurotransmitters) release neurotransmitters from the end of the axon when an action potential reaches the end of the axon.
• Neurotransmitters cross synaptic cleft and receptor proteins on the postsynaptic neuron “catch” the neurotransmitters
• This triggers an action potential in the postsynaptic neuron• This is how the action potential travels from one neuron to the
next
Neurotransmittersbind to receptors on thepostsynaptic neuron
dendrite ofpostsynapticneuron
receptor
neurotransmitter
ions
4
synapticvesicle
synaptic cleft
The positive charge ofthe action potential causesthe synaptic vesicles torelease neurotransmitters
An action potentialis initiated
The action potentialreaches the synapticterminal of thepresynaptic neuron
1
2
3
Neurotransmittersare taken back intothe synaptic terminal,are degraded, ordiffuse out of thesynaptic cleft
6
synaptic terminalof presynapticneuron
neurotransmitters
Neurotransmitterbinding causes ionchannels to open, andions flow in or out
5
The Structure and Function of the Synapse
Fig. 38-4
Types of Neurotransmitters
• Aspartate Serotonin
• Glutamate Endorphins
• GABA Cholyecystokinin
• Glycine Vasopressin
• Acetylcholine Somatostatin
• Dopamine
• Noepinephrine
RE-UPTAKE
• After crossing synapse, neurotransmitters are removed from synapse by one of two methods:– NT are reabsorbed by the pre-synaptic
neuron to be used again– Or NT are digested by enzymes in the
synaptic cleft
Synapse-REUPTAKE
Motor Neurons
• Motor nerves START in CNS• Motor nerves end in SKELETAL
MUSCLE. • MN control the actions and movements
we initiate ourselves as well as reactions to the sensory messages we get from the brain.
Myelin and the Myelin Sheath
• Many (not all) motor neurons have a covering over their axon called a myelin sheath.
• MS helps action potential (the message) travel faster along the axon to the next neuron.
• MS made of schwann cells.• Schwann cells contain lipids, which make the the
neuron look white, hence the term “white matter” • Unmyelinated neurons look gray, hence the term
“gray matter”.
The Sensory Nervous System
• Things that we “sense” in the world is picked up from sensory receptors, and sent by sensory nerves to the CNS.– 1.) General Senses*– 2.) Special Senses*
Receptors for the sensory nervous system*
• Receptors are specialized cells that can register stimuli from outside or inside the body and send the message (via action potential) to the CNS– Receptors can be
• Thermoreceptors: detect heat/cold• Mechanoreceptors: detect vibration, pressure, motion
and gravity• Photoreceptors: detect light• Chemoreceptors: detect odors & tastes• Nociceptors: detect pain
General Senses*
1.) Temperature (thermoreceptors)
2.) Pain (nociceptors)
3.) Touch (mechanoreceptors)
4.) Pressure (mechanoreceptors)ALL OF THE ABOVE RECEPTORS ARE
LOCATED IN THE SKIN.
5.) Proprioception- position of your limbs in space. (mechanoreceptors)
RECEPTORS LOCATED IN MUSCLES AND JOINTS.*
Paciniancorpuscle(vibration,rapid pressurechanges)
Meissner’scorpuscle(light touch,rapidmovement)
Ruffini corpuscle(pressure)
epidermis
dermis
subdermalconnective and adiposetissue
free nerve ending(hair movement)
free nerve ending(touch, heat, cold, pain)
Receptors in the Human Skin
Fig. 39-3
Special Senses*
Receptor location and type:
• 1.) Smell NOSE chemoreceptor• 2.) Taste TASTE BUDS chemoreceptor• 3.) Hearing INNER EAR
mechanoreceptor• 4.) Vision RETINA photoreceptor• 5.) Equilibrium INNER EAR mechanoreceptor
(gravity, motion, acceleration)
Sensory neurons of the special senses
Sense of taste. This map was later proven wrong. Receptors for each taste are spread
evenly over the tongue.
sclera
choroid
vitreous humor
retina
fovea
bloodvessels
opticnerve
blind spotlens muscle
aqueoushumor
cornea
lens pupil
eyelash
iris
ligaments
rod cone
signal-processingneurons
ganglioncells
light
(photoreceptors)
membrane discsbearing photopigmentmolecules
ganglion cellaxons formthe optic nerve
(a) Eye anatomy
(b) Cells of the retina
The Human Eye
Fig. 39-9
calcium carbonatestones
semicircularcanals
ampullae
ampullagelatinous material
hairshair cells
axons from theauditory nerve
cochlea
auditorynerve
saccule
utricle
gelatinous matrixhairshair cellsaxons from theauditory nerve
The Vestibular Apparatus
Fig. 39-6
The Brain
• Housed inside the skull for protection• Bathed in Cerebrospinal Fluid
(H20, proteins, glucose, WBC’s)• 100-200 BILLION NEURONS • 100 TRILLION GLIAL CELLS• *Glial Cells: Supportive cells that hold neurons in
place*– Supply nutrients and O2 to neurons*– Insulate one neuron from another*– Destroy bacteria and remove dead neurons*
Parts of the Brain***
• Forebrain: – Cerebrum: decision-making, emotion, language, interpreting
sensory information– Thalamus: pain, pressure, temperature– Hypothalamus: sex, hunger, thirst, body temp
• Midbrain: relay center. Coordinates information sent from hindbrain to forebrain
• Hindbrain:– Cerebellum: balance, coordination, movement– Medulla & Pons: swallowing, breathing, heart rate,
wakefulness
The Human Brain
Fig. 38-12
(a) A lateral section of the human brain (b) A cross-section of the brain
hypothalamus
meninges skull
corpuscallosum
thalamus
cerebellum
pons
medulla
spinal cord
cerebral cortex(gray matter)
myelinated axons(white matter)
basalganglia
hypothalamus
hippocampus
thalamus
corpuscallosum
substantia nigra
MIDBRAIN
HINDBRAIN
FOREBRAIN(within dashedblue line)
cerebralcortex
pituitarygland