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Biology 30Biology 30NERVOUS SYSTEMNERVOUS SYSTEM
1. Nervous System OverviewNervous System Overview2. The Neuron2. The Neuron3. Reflex Arc3. Reflex Arc4. The Action Potential4. The Action Potential5. The Synapse / Neurotransmitters5. The Synapse / Neurotransmitters6. Nervous System Diseases6. Nervous System Diseases7. Drugs7. Drugs8. PNS8. PNS9. CNS9. CNS10. The Brain10. The Brain
General FunctionsGeneral Functions
1. Reception
2. Conduction
3. Interpretation and Organization
4. Transmission
Nervous System OrganizationNervous System Organization
The Neuron- The Neuron- conducts nerve conducts nerve impulsesimpulses
The NeuronThe NeuronBasic parts: cell body- nucleus and cytoplasmDendrites-projection of cytoplasmAxon-extension of cytoplasmGlial Cells-non conducting support and metabolic
cells
Some neurons contain the following additional parts:
Schwann cells- a special kind of glial cell that produces a myelin sheath
myelin sheath-white fatty covering that insulates the axon
nodes of Ranvier-gaps in the myelin sheath
Myelination allows for faster transmission of the nerve impulse
The impulse “jumps” the node
Myelinated nerves in the brain are called white matter
Non- Myelinated = grey matter
Nerves of the PNS are myelinated
Neuron structure
Types of NeuronsTypes of NeuronsSensory Neurons (afferent) – carry
information from the receptors to the brain/spinal cord
Motor Neurons (efferent) – carry information from the brain to the muscles and glands
Interneurons (association) – organize and relay information within the brain and spinal cord.
Nerves
Individual neurons are organized into tissues called nerves.
Repairing Damaged NervesNerves in the PNS are surrounded by a thin
membrane called the neurilemma which helps to regenerate damaged axons
Nerves in CNS lack neurilemmas and cannot be repaired
Area of research: stem cells, brain band-aid
Reflex ArcReflex Arcautomatic, quick, involuntary responses to
internal or external stimuli.
does not immediately involve the brain.
allows quicker reaction times to a potentially harmful stimulus
Stretch ReflexStretch Reflex
5 Components of a Reflex Arc:5 Components of a Reflex Arc:
1. Sensory receptor2. Sensory neuron3. Interneuron4. Motor neuron5. Effector
Action PotentialAction Potential
an electrochemical event with a rapid change in polarity (relative electrical potential) down a nerve cell that results in the conduction of a nerve impulse.
1. Resting PotentialPolarization: voltage difference of -70mV across
a nerve cell membrane
caused by the sodium potassium pump: more sodium is pumped out than potassium is pumped in
also potassium moves out by diffusion more easily than sodium moves in
Result: excess positive charge outside the membrane and negative charge inside the membrane
2. Stimulation / Depolarization change in pH, pressure, or an electrical stimulus
cause the Na+ gates to open and Na+ rush into the cell.
membrane becomes depolarized (+ 40 mV)
3. Re-polarization Sodium gates close to stop inflow
change in electrical potential causes K+ channels to open and K+ ions rush out of the cell
Restores the polarized state but now is hyperpolarized – more positively charged on the outside than the resting state
(also the ion concentrations are reversed from the resting state )
4. Refractory period resting potential (-70mv) must be restored
before the neuron can fire again
Na+ are pumped out and K+ are pumped back into the cell using ATP energy.
The Action PotentialThe Action Potential
The Action Potential in ActionThe Action Potential in Action
Neuron Action Potential
Propagation
Saltatory Action
• the speed of the nerve impulse is increased by jumping from node of Ranvier to node of Ranvier (gated channels are found only at the nodes)
Propagation of the Action Potential
Threshold level – minimum depolarization that must be reached before sufficient Na+ gates open to continue the action potential
All or None Response – if the threshold level is not reached, the action potential will not occur at all. If the threshold is reached or exceeded a full action potential will result.
How do we differentiate intensity? Ex hot vs warm?
Intensity is determined by: 1. the number of neurons that fire simultaneously 2. the frequency at which the neurons fire 3. the threshold level of different neurons (lower threshold neurons are more likely to fire, and are found in more “sensitive” areas)
The Synapse and The Synapse and NeurotransmittersNeurotransmitters
the electrical impulse cannot cross the gap (synaptic cleft) to the next dendrite
neurotransmitters are stored in synaptic vesicles of the axon and are released to carry the information across the gap
The SynapseThe Synapse
Terminal Axon
Structures in the SynapseStructures in the SynapsePre-synaptic membrane – membrane found
at the synaptic ending of the neuron sending information
Post-synaptic membrane- membrane found at the dendrite of the neuron receiving information
Synaptic cleft – space between the pre and post synaptic membranes.
Neurotransmitters
1. excitatory neurotransmitters – cause the opening of Na+ channels to cause depolarization
2. inhibitory neurotransmitters –block Na+ channels and open K+ channels ions which causes hyper-polarization
-inhibits action potentials
Summation – the net effect of excitatory and inhibitory neurotransmitters
– If there is adequate excitation to reach the threshold, the neuron will fire.
--may require more than one neuron may require more than one neuron to release neurotransmittersto release neurotransmitters
A response may involve both excitatory and inhibitory neurotransmitters
Ex) Throwing a ball: Triceps contracts and bicep relaxes
Integration – the degree of sensation felt or the degree of response created by the brain depends on the number of neurons that fire
There are 9 universally recognized neurotransmitters: aspartate, glycine, GABA, glutamate, dopamine, nor-epinephrine, epinephrine, seratonin, and acetylcholine.
Some of the more common neurotransmitters Some of the more common neurotransmitters (and their enzymes) include:(and their enzymes) include:
Neurotransmitter Enzyme Function of Neurotransmitter
Acetylcholine Cholinesterase
Involved with muscle contraction of the skeletal muscles
Dopamine Monoamine oxidase enzyme
Responsible for voluntary movement and emotions of pleasure
Serotonin Monoamine oxidase enzyme
Regulates temperature, sensory perception, sleep and involved in mood stabilization and control
Nor-epinephrine Regulates the stress “fight or flight” response
GABA Inhibitory action of motor behavior
Removing Neurotransmitters
1. Degradation by enzymes in the synaptic cleft
2. Re-uptake by the pre-synaptic membrane
3. Diffusion out of the synaptic cleft4. Inability to bind due to competitive
inhibitors
The Effects of DrugsDrug – anything that is not food that alters
the normal bio-chemistry of the body in some way.
Stimulant – mimics neurotransmitter, decreases rate of breakdown of neurotransmitter or increases release of neurotransmitter
Depressant – blocks receptor site, decreases production of neurotransmitter, or increases the breakdown of neurotransmitter
Alcohol: - depressant -seems to enhance GABA -leads to lack of coordinated response, and
loss of normal social inhibitions. -may also weaken the effect of glutamine, an
excitatory neurotransmitter, leading to sluggishness and lack of co-ordination.
Close to Home Animation: Alcohol
Marijuana:
- a depressant and hallucinogen
-acts on the canniboid receptors of the brain that affect concentration, perception and movement.
-may have an impact on the activity of seratonin, GABA and norepinephrine in the brain
not physically addicting, however this is a gateway drug and may be psychologically addicting
Cocaine: -a stimulant
-blocks the re-uptake of dopamine, causing an adrenaline like effect from the dopamine
-as dopamine levels increase in the synapse, the body produces less, thus making cocaine very physically addicting
Close to Home Animation: Cocaine
Crystal meth:
-a stimulant
-passes directly through neuron membranes and causes excessive release of dopamine
-leads to feelings of euphoria, psychosis, delusions and extreme aggressiveness.
Ecstasy: - a stimulant and hallucinogen
-affects neurons in the brain by causing an over-production of serotonin.
-creates shorter feelings of pleasure, however use can result in brain damage, and cardiac arrest.
The venom of the black widow spider is called “latrotoxin”. This toxin results in a massive release of the neurotransmitter acetylcholine from the neuromuscular junctions of victims and may cause muscle spasms, pain, increased blood pressure, nausea and vomiting.
Diseases of the Nervous Diseases of the Nervous SystemSystem
Parkinson’s Disease: wide-eyed, unblinking expression, involuntary tremor, muscle rigidity, shuffling gait
-dopamine deficiency caused by the degeneration of dopamine producing cells in the brain
-
-caffeine may offer protection against Parkinson’s disease as it prevents loss of dopamine
Alzheimer’s Disease: characterized by loss of memory, senility, deterioration of cells in the basal nuclei, presence of tangles and plaques
-possibly due to a malfunction of acetylcholine
- seems to be linked to a gene located on chromosome #21
Schizophrenia: delusions, random thoughts, disjointed thoughts, sensory hallucinations
- may be the result of excessive activity of brain neurotransmitters such as dopamine
Huntington’s Disease: progressive deterioration of the nervous system that leads to writhing movements, insanity and eventually death
- seems to be caused by the malfunction of the inhibitory neurotransmitter GABA
Depression: low affect, feeling blue, lack of or excessive sleep and eating patterns
- seems to be linked to malfunctions in dopamine and seratonin, perhaps caused by an excess of monoamine oxidase enzymes
Stroke: caused by interruption of blood flow to the brain which causes brain cells to perish.
Epilepsy: is a seizure disorder where there is a sudden, un-explained surge of electrical activity through the brain with no specific known cause.
Epilepsy.com
Central Nervous System (CNS)
Is primarily responsible for the processing and organization of information.
The CNS consists of two major structures:
1. The Brain
2. The Spinal Cord
Spinal Cord
•Made of 31 segments
•Protected by the vertebrae
Spinal CordCentral Cavity – contains cerebrospinal fluid
White Matter – contains myelinated nerve cells
Grey Matter – contains un-myelinated nerve cells
Spinal CordDorsal Root Ganglion – entry of
sensory neurons to spinal cord and CNS, ganglion is the collection of cell bodies
Ventral Root – exit of motor neurons from the spinal cord
Meninges – 3 protective membranes surrounding the spinal cord and brain (dura mater, arachnoid, pia mater)
Meningitis is an infection of the meninges
Cerebrospinal Fluid – circulates between the inner and middle membranes of the brain and spinal cord. – Provides protection, nutrient / waste
exchange, etc.
Spinal Cord
Spinal Cord Functions 1. center for reflex action
2. provides a pathway for communication between the brain and peripheral nerves
The Brain
Hindbrain - The Unconscious Brain
– important for autonomic functions required for survival
Cerebellum – responsible for muscle co-ordination, posture, coordinated muscle movement and balance
Medulla oblongata – controls heartbeat, respiration, blood pressure, reflex center for vomiting, sneezing, hiccupping, coughing and swallowing
Pons – connects the cerebrum to other parts of the brain, regulates breathing rate
Midbrain – reflex center for head movements in response to visual stimuli, connects cerebrum to other parts of the brain
Forebrain – responsible for conscious and unconscious actions
Thalamus – central relay station
- directs incoming sensory information to the cerebrum
Hypothalamus – contains cells that produce some hormones, controls thirst, hunger, and controls many of the pituitary hormones
Cerebrum – largest part of the brain, left and right hemispheres. – responsible for intellect, memory,
consciousness and language.
Lobes of the Cerebral Cortex
Frontal Lobe –voluntary muscle movement, higher intellectual processes, personality
Temporal Lobe – hearing
Parietal Lobe –perceptions of touch, temperature, pressure, pain, etc from the skin
Occipital Lobe –vision
Olfactory Lobe –smell
Other parts of the brainLimbic System –emotions
Pituitary Gland- Master Gland– attaches to hypothalamus
Corpus Callosum – Bundle of nerves that connects the
two halves of the brain– allows for integrated thoughts and
coordinated responses
– Left brain – verbal, linguistic dominant
– Right brain – spatial, artistic, visual dominant
PET – Positron Emission Tomography– Radioactive chemicals are injected into the
bloodstream
– data is used to produce 2D or 3D images of the distribution of the chemicals throughout the brain and body.
SPECT-Single Photon Emission Computed Tomography
– radioactive tracers and a scanner record data
– computer constructs 2D or 3D images of the active brain regions.
MRI-Magnetic Resonance Imaging- magnetic fields and radio waves produce high-quality 2D or 3D images of brain structures without injecting radioactive tracers.
EEG-Electroencephalography
- electrodes placed on the scalp detect and measure patterns of electrical activity from the brain.
CT-Computed Tomography Scan
- a series of X-ray beams passed through the head.
-images are then developed on sensitive film.
-creates cross-sectional images of the brain
Peripheral Nervous System (PNS)
Cranial nerves – 12 pairs of sensory, motor and mixed nerves that control the face, neck and shoulders
Spinal Nerves – 31 pairs of nerves that emerge from the spinal cord by two roots (one pair for each segment)
Dorsal root nerves – contain sensory neurons and ganglia
Ventral root nerves – contain motor neurons
All other nerves not part of the CNS
Spinal Cord Injuries
The PNS is subdivided into two major parts:
1. The Somatic Nervous System
-contains all the nerves that serve the muscular-skeletal system and the sensory organs.
-conscious and deliberate.
2. The Autonomic Nervous System
-contains all the nerves that serve the internal organs.
-unconscious and automatic.
-made of two parts:
A. Sympathetic nervous system
-responsible for the fight or flight response
-ex) dilation of the pupils, increased heart rate, increased breathing rate, slowed digestion, enhanced performance, increase in blood sugar
B. Parasympathetic nervous system – responsible for the relaxation response (after fight or flight)
– http://itc.gsw.edu/faculty/gfisk/anim/autonomicns.swf
Fig 2 p 434Fig 2 p 434