The Nervous System
http://www.innerbody.com/image/nervov.html
The Neuron
• the structural & functional unit of the nervous system (NS)
• specialized cell that send and receive electro­chemical signals Identify the following and state their function:
• dendrite
• cell body
• axon
• axon terminal
• myelin sheath
dendrite
myelin sheath
axon
axon terminal
cell body
node of Ranvier
Structure
1. Cell body:
• largest part of the neuron
• contains nucleus & organelles
• regulates the functions of the neuron
2. DendRites:
• Receive impulses
• carry impulse towaRds the cell body
• # can vary (1 to thousands)
3. Axons:
• long, narrow part of the neuron
• carry impulses Away from the cell body
• can vary in length (1mm­1m)
• may be very short or absent in some cases (S.C)
• may or may not be myelinated
4. Axon Terminal:
• part of the axon that synapses with another neuron
• release chemicals that excite or inhibit other cells
Neuron Parts
Additional Information ­ Neuron Structure
Myelin Sheath
• Produced by Schwann cells
• A white, fatty substance surrounding the axon
Saltatory Conduction
Cross section of myelin sheaths that surround axons (TEM x191,175). http://images.google.ca/imgres?imgurl=http://www.emc.maricopa.edu/faculty/farabee/BIOBK/neurons_
1.gif&imgrefurl=http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookNERV.html&h=433&w=452&sz=30&hl=en&start=16&um=1&tbnid=NcgPVJlT6fdLOM:&tbnh=122&tbnw=
127&prev=/images%3Fq%3Dmotor%2Bneuron%2Banimation%26svnum%3D10%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%3DN
• Not all axons are surrounded by this substance ­ those that are are said to be myelinated
• There are gaps in the myelin called the nodes of Ranvier
­ here the membrane of the axon is exposed
• Function ­ speeds up the rate of impulse transmission
Neuron Types & Functions
1. Sensory neurons
• relay information about the environment from a sensory receptor to the spinal cord & brain for processing
2. Motor neurons
• relay information from the brain and spinal cord to effectors
3. Interneurons
• carry information from one neuron to another within the brain and spinal cord
http://www.waybuilder.net/sweethaven/MedTech/Neurology/fig0104.jpg
The NS ­­ the big picture
• the human NS can be divided into 2 subsystems
Nervous System
Central Nervous System
(CNS)
Peripheral Nervous System
(PNS)
• brain + spinal cord
• controls most activities of the body
• network of nerves
• connect the CNS with the receptors & effectors
The CNS ­ the basics
Look at the following pictures. What is happening in each?
The CNS
Protection
1. Bone
­ brain: cranium
­ spinal cord: vertebrae of the spinal column
2. Three tough membranes ­ the meninges
­ dura mater
­ arachnoid
­ pia mater
3. Cerebrospinal fluid (CSF)
­ fills space b/n inner and middle membranes
­ fills ventricles
­ demo (http://faculty.washington.edu/chudler/chmodel.html#egg)
White Matter vs. Grey Matter
Grey Matter
• neural tissue comprised of nerve cells that lack a myelin sheath and neurolemma
• can not be regenerated after injury
• damage to grey matter is permanent
White Matter
• neural tissue comprised of nerve cells that have a myelin sheath and neurolemma (outer layer of the Schwann cell that promotes regeneration)
Biology Quiz
1. This organ has a fore, mid, and hind section.
2. This organ is 2% of the body weight.
3. This organ weighs about 1.4kg (3lbs).
4. This organ consumes 20% of all the oxygen used by the body.
5. This organ is highly textured.
6. This organ produces a variety of highly measurable waves.
7. This organ is made of more than 25 million neurons.
8. This organ has billions of synapses built into its structure.
9. This organ can store millions more bits of info than the most powerful computer.
The Brain
• divided into 3 sections
­ forebrain: cerebrum, thalamus, hypothalamus
­ midbrain
­ hindbrain: cerebellum, pons, medulla oblongata
Sheep brain
brain animation
Brain Components
Label the parts of the brain and learn their functions.
corpus callosum
lateral ventricle
hypothalamus
spinal cord
cerebrum
cerebellum
pons
pituitary gland
thalamus
medulla oblongata
midbrain
Label the parts of the brain and learn their functions.
cerebrum
corpus callosum
thalamus
lateral ventricle
midbrain
hypothalamus
pituitary gland
cerebellum
pons
medulla oblongata
spinal cord
The Cerebrum
• is divided into 2 halves ­ the left and right hemispheres
http://www.angelfire.com/wi/2brains/test.html
Hemispheric Dominance
• analytical, logical, language
• math & science
• holistic, intuitive, creative
• art & music
Cerebral Cortex
• the surface is highly convoluted which results in an increase in ______ _____
• the cerebral cortex is the thin layer that covers each hemisphere
­ made up of grey matter
• the 2 hemispheres are joined by the corpus callosum
­ made up of white matter
­ transfers impulses from one hemisphere to the other
Label the lobes of the cerebral cortex. Record their functions.
occipital lobe
temporal lobe
parietal lobe
frontal lobe
frontal lobe
parietal lobe
temporal lobe
occipital lobe
The Spinal Cord
Structure
• ~ 45 cms long
• extends from the base of the brain through the vertebrae of the spinal column
• foramen magnum ­ opening in skull where spinal cord emerges
• cross section
­ butterfly (or H shaped region) of grey matter surrounded by white matter
­ spinal canal is filled with CSF which surrounds and protect spinal cord
CSF
Note: the spinal canal refers to the space inside of the spinal column ­ not spinal cord ­ huge difference. Cerebrospinal fluid (CSF) is found between the middle and innermost meninges (arachnoid and pia mater). It surrounds and protects the spinal cord and brain!
Vertebra
Spinal nerve
Spinal cord
Intervertebral disk
Spinal Cord Functions
• connects nerves of PNS with brain
• controls certain reflexes
• ascending tracts of grey matter carry info to brain • descending tracts carry info from the brain
Spinal cord
Spinal nerve
Vertebra
Intervertebral disk
The Reflex Arc
• An automatic response to a stimulus
• No thought action
The Arc involves:
1. Sensory Receptor ­ sensory cell dendrites pick up info
2. Sensory Neuron ­ carries info from receptor to spinal cord
3. Interneuron ­ connecting link b/w sensory and motor neurons
4. Motor Neuron ­ carries info from spinal cord to muscles
5. Effector ­ muscle cell(s) that react to cause a response
Do we pull away before or after we feel the pain? Why is this so? stimulus (ex. finger touches tack)
sensory receptor detects stimulus
sensory neuron carries info to spinal cord
interneuron (in spinal cord) carries info to motor neuron
motor neuron activates effector (muscle)
response (ex. muscle contracts + pulls hand away)
Medical Animation Library ­ Reflex Response
Descriptions of each are included with the disorders page.
Electroencephalograph CAT Scan (x­rays ­> 3D image)
EEG (electrical activity)
PET Scan (regions that are active)
MRI (series of images ­> 3D image)
Disorders
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Multiple Sclerosis
Alzheimer's Disease
Parkinson's Disease
Meningitis
Huntington's Disease
Epilepsy
Vasculitis
Ischemic Stroke
Hemorrhagic Stroke
Depression
Schizophrenia
Bipolar Disorder
Panic Attacks
ALS
Drugs
• Depressants
• Stimulants
• Anaesthetics
Note: you should recognize these! Afternoon class, we didn't finish going over them, but you should know a few common examples of depressants and stimulants and what each does. Local vs general anaesthetic as well.
These can be found with the disorder descriptions. Also look at the answers to the drug crossword on the Worksheet Answers pages.
Technologies
• MRI
• EEG
• CAT Scan
• PET Scan
Animations (select from list ­ disorders + MRI + CATscan)
Subacute sclerosing panencephalitis (SSPE) ­ House
Descriptions of the disorders are found on the disorders page.
PNS
• includes all neurons that extend from the CNS
• these neurons connect the CNS to receptors & effectors
• the neurons are bundled together to form nerves
Nerve Definitions
Nerve
• bundles of nerve fibers (bundles of neurons) • bound together by connective tissue
Myelin Sheath
CNS, PNS, Nerves
Sensory nerves
• carry impulses from receptors to spinal cord and brain
Motor nerves
• carry impulses from brain and spinal cord to effectors
Mixed nerves
• made up of both sensory and motor fibers
Cranial Nerves
Cranial Nerves and Their Functions
• 12 pairs
• extend from the brain
• serve the sense organs and other structures of the head
• those serving the eyes, nose, and ears are mostly ___________
• the remained are a mix of both sensory and motor fibers
Spinal Nerves
• nerves connected to the spinal cord
• 31 pairs
• each pair serves a specific part of the body
• all are mixed nerves
PNS
Somatic Nervous System
Autonomic Nervous System
• involves both sensory and motor neurons
• involves motor neurons only
­ somatic sensory neurons provide info ~ both types motor neurons
• connects the CNS to
­ skin, skeletal muscle
­ other sense organs
• connects the CNS to ­ internal organs
• responsible for voluntary mvmts
(can think about and control most) • responsible for involuntary mvmts (no thought required, little/no control)
­ ex. heart rate, blood flow, breathing, swallowing, peristalsis
Autonomic Nervous System
sympathetic nervous system
parasympathetic nervous system
• organs of the autonomic nervous system contain nerve endings of both the sympathetic and parasympathetic nervous systems
• these two systems work opposite to one another on the same organ (ie. they are antagonistic)
controls organs when body is at rest
controls organs when when body is stressed ­ ex. fight or flight response
Sympathetic Nervous System
Parasympathetic Nervous System
• release norepinephrine at the synapse
• release acetylcholine at the synapse
• generally prepare the body for emergencies • generally promotes normal functon
­ "fight or flight"
­ "rest and digest"
• ex: increase heart rate and breathing rate
• ex: slows heart rate and breathing rate
Funny Animation
Animation
Human Nervous System
CNS
brain
­interprets sensory information
­controls most activities of body
PNS
spinal cord
­connects PNS with brain
­controls reflexes
somatic nervous system
­ sensory + motor neurons
­ voluntary control
­ skin, sense organs, skeletal muscle
autonomic nervous system
­ motor neurons
­ involuntary movements
­ internal organs (smooth + cardiac muscle)
sympathetic ­norepinephrine
­when stressed
­fight or flight
­inc heartrate, etc
parasympathetic
­acetylcholine
­when resting
­ rest + digest
­ slows heartrate..
Human Nervous System
CNS
brain
­interprets sensory information
­controls most activities of body
PNS
spinal cord
­connects PNS with brain
­controls reflexes
somatic nervous system
­ sensory + motor neurons
­ voluntary control
­ skin, sense organs, skeletal muscle
autonomic nervous system
­ motor neurons
­ involuntary movements
­ internal organs (smooth + cardiac muscle)
sympathetic ­when stressed
­fight or flight
­inc heartrate, etc
parasympathetic
­when resting
­ rest + digest
­ slows heartrate..
So how do the impulses travel through the NS?
Message transmission demo!
http://faculty.washington.edu/chudler/chmodel.html
Messages that travel throughout the nervous system are referred to as Electrochemical Messages
"Chemical"
­ neurotransmitters that are released by the presynaptic neuron travel across the synapse (space between neurons) and bind to dendrites of the post­synaptic neuron
"Electro"
­ region of depolarization (charge reversal) AKA action potential moves from the dendrites along the axon to the axon terminals
How a Neuron Fires ­ Action Potential (Electric part)
It is essentially the movement of Na+ and K+ ions that cause the neurons to be charged and to carry an impulse from one end to another.
Phase 1 ­ Resting Potential (­70mV)
• neuron is at rest ­­ is not firing
• established by ions, channels, and protein pumps
­ K+ channels are leaky so K+ can get to outside
­ Na+ channels are closed so Na+ stays outside
­ Sodium potassium pump moves 3Na+ out and 2K+ in
• Outside of the neuron (extracellular fluid)
­ pOsitive relative to the inside of the cell
­ high [Na+­ sOdium]
­ low [K+]
• iNside of the neuron (intracellular fluid)
­ Negative relative to the outside of the cell (­70mV)
­ high [K+]
­ low [Na+]
Action Potential
Phase 2 ­ Depolarization (reversal of charge)
Action Potential
• begins when a neuron is sufficiently stimulated
• Na+ channels begin to open • Na+ moves in and charge inside becomes more +ve
• at ­50mV Na+ channels open completely and Na+ rushes in until charge becomes +50mV
• now inside is more positive compared to the outside of the cell
Phase 3 ­ Repolarization (getting ­ve charge back on inside)
Action Potential
• Na+ gates close
• K+ gates open and K+ rushes to the outside
• this causes the outside to be more +ve again, but the ions are on the wrong side
Phase 4 ­ Refractory Period
• Na+/K+ pumps use ATP to move Na+ out and K+ (get ions on proper sides)
3 Na+ out and 2 K+ in
• While the pumps are at work, the neuron cannot transmit an impulse
• the length of time it takes to get the ions back to their original side is called the refractory period (~ 0.001 seconds)
• After the refractory period, that section of the axon returns to the resting state
Action Potential
McGraw­Hill Animations
How does the action potential move along the axon?
• the +ve ions on the inside of the cell are attracted to the ­ve charged ions in the resting area ahead of the depolarized area
• this causes depolarization to start in neighbouring area and continue along axon
• likewise, +ve ions on the outside of the cell are attracted to the ­ve ions where the action potential was originally created ­ this stimulates repolarization
McGraw­Hill Animations
Action Potential
1. Use your text ­ label the following on your diagram:
calcium channel
presynaptic neuron
repolarized
post­synaptic neuron
depolarized
receptor
vesicle
resting
synaptic gap
neurotransmitter
mitochondrion
2. Explain what happens when the wave of depolarization reaches the end of a presynaptic neuron (6 steps).
3. What does it mean if the post­synaptic neuron is excited? Inhibited?
4. How are NTs (neurotransmitters) broken down?
5. List and describe the 6 types of NTs listed.
6. Does the nerve impulse cross the synaptic gap? Explain.
The Synapse
• Neurons do not touch each other
• the gaps between neurons are called synapses
• one axon can synapse with 1 or many cells
repolarized
synaptic gap
depolarized
2+
++ +
Ca
2+
­ ­ ­ +­ ­ ­
Ca
resting
­
­+
+ ++ + + + +
Ca2+
­ ­ ­
+
­ ­ + + ++ +
Ca2+
­ ­ ­
+
­ ­ ­ + ++
­ ­­
calcium channel
receptor
pres
ynap
tic n
euro
n
vesicle
mitochondrion
neurotransmitter
post­synaptic neuron
What happens when the action potential reaches the axon terminals?
Use page 405 in your text to:
1. Define and diagram a presynaptic neuron, the synaptic gap (or cleft), a post­synaptic neuron, and synaptic vesicles.
2. Explain what happens when the wave of depolarization reaches the end of a presynaptic neuron (6 steps).
3. What does it mean if the post­synaptic neuron is excited? Inhibited?
4. How are NTs (neurotransmitters) broken down?
5. List and describe the 6 types of NTs listed.
6. Does the nerve impulse cross the synaptic gap? Explain.
What happens when the action potential reaches the axon terminals?
Use page 405 in your text to:
1. Define and diagram a presynaptic neuron, the synaptic gap (or cleft), a post­synaptic neuron, and synaptic vesicles.
Synapse Animation
Synapse Animation 2
Synapse Animation 3
McGraw­Hill Animations
2. Explain what happens when the wave of depolarization reaches the end of a presynaptic neuron (6 steps).
1. wave of depolarization reaches the axon terminal
2. triggers calicum ion gates to open
3. calcium influx causes vesicles to fuse with membrane and release NTs into the synaptic gap
4. NT attaches to specific receptors on post­synaptic neuron
5. post synaptic neuron is excited or inhibited
6. NT is broken down by an enzyme
3. What does it mean if the post­synaptic neuron is excited? Inhibited?
Excited ­ Na+ gates open and triggers a wave of depolarization
­ an action potential is generated in the post­synaptic neuron
Inhibited ­ makes the inside of the post­synaptic neuron more ­ve on the inside which raises the threshold
­ no action potential generated in post­synaptic neuron
4. How are NTs (neurotransmitters) broken down?
By enzymes released from the presynaptic neuron
5. List and describe the 6 types of NTs listed.
1. acetylcholine 2. noradrenaline 3. glutamate
4. GABA 5. dopamine
6. serotonin 6. Does the nerve impulse cross the synaptic gap? Explain.
No. Information is carried across the synaptic gap chemically via NTs.
Threshold Level
• in order for depolarization to occur, there must be a sufficient stimulus
• the threshold is the min amt of stimulation that must occur for a neuron to fire
Intensity
• the intensity of a nerve impulse (ie. the level of pain or degree of hotness felt) depends on the # of times the neuron fires • the greater the frequency of firing the greater the intensity
• Homework ­ using your textbook (pg. 403):
1. Describe why the threshold of a stimulus is like the trigger of a gun
2. Explain the all or none principle
Development of the myelin sheath. (A) Initially the unmyelinated axon lies in a pocket of the glial cell. (B) The glial­cell membrane then begins to coil around the axon. (C) The membrane winds tightly around the axon, forming a myelin sheath.
http://images.google.ca/imgres?
imgurl=http://instruct1.cit.cornell.edu/courses/biog105/pages/demos/105/unit9/media/
myelin­
sheath.1.jpg&imgrefurl=http://instruct1.cit.cornell.edu/courses/biog105/pages/demos
/105/unit9/myelinsheath.html&h=464&w=500&sz=75&hl=en&start=1&um=1&tbnid=
0n9mRHzH8CQ52M:&tbnh=121&tbnw=130&prev=/images%3Fq%3Dmyelin%
2Bsheath%26svnum%3D10%26um%3D1%26hl%3Den%26safe%3Dactive%26sa%
3DN
What if the neuron is myelinated?
Saltatory conduction ­ occurs when the axons are myelinated and causes the impulse to jump from one node to another.
http://kvhs.nbed.nb.ca/gallant/biology/saltatory_conduction.jpg
http://www.brainviews.com/abFiles/AniSalt.htm
Label the parts of the brain and learn their functions.
corpus callosum
lateral ventricle
hypothalamus
midbrain
cerebrum
cerebellum
pons
pituitary gland
thalamus
medulla oblongata
cerebrum
corpus callosum
lateral ventricle
midbrain
thalamus
pituitary gland
hypothalamus
pons
cerebellum
medulla oblongata
Label the lobes of the cerebral cortex. Record their functions.
occipital lobe
frontal lobe
parietal lobe
temporal lobe
Label the lobes of the cerebral cortex.
parietal lobe
frontal lobe
occipital lobe
temporal lobe