Presentation on theme: "Biology 30 NERVOUS SYSTEM Nervous System Overview 1. Nervous System Overview 2. The Neuron 3. Reflex Arc 4. The Action Potential 5. The Synapse / Neurotransmitters."— Presentation transcript:
Biology 30 NERVOUS SYSTEM Nervous System Overview 1. Nervous System Overview 2. The Neuron 3. Reflex Arc 4. The Action Potential 5. The Synapse / Neurotransmitters 6. Nervous System Diseases 7. Drugs8. PNS9. CNS 10. The Brain
General Functions General Functions 1. Reception 2. Conduction 3. Interpretation and Organization 4. Transmission The nervous systems main function is to maintain homeostasis: a maintenance of the internal environment i.e. pH, body temp, glucose levels, BP, water levels, etc
Nervous System Organization
The Neuron- The functional unit of the nervous system, it conducts nerve impulses There are 3 kinds of neurons: – 1) sensory neurons (afferent)- take impulses from the body receptors to the CNS – 2) motor neurons (efferent)-take impulse away from the CNS and to the muscles and glands – 3) interneurons- are actually in the CNS (in the brain and spinal cord) – ***Neuroglia (glial cells)- supportive cells that aid the interneurons of the brain. Nourish neurons, removes waste from neurons, and protect neurons.
The Neuron has 3 basic Basic parts: 1) cell body- nucleus and cytoplasm 2) Dendrites-finger-like projections of cytoplasm of cell body. They receive information 3) Axon-extension of cytoplasm. Transmit impulse away from the body
Some neurons contain the following additional parts: Myelin Sheath-a white fatty covering that insulates the axon. Schwann cells produce the myelin sheath – Schwann cells- a special kind of glial cell that produces a myelin sheath that wraps around the axons as insulation – On top of protection, the myelin sheath allows for faster conduction of impulses and greater power of regeneration – The myelin sheath is NOT continuous but rather forms intermitted gaps called the Nodes of Ranvier. Impulses will now ‘jump’ from Node to Node rather then slowly moving through the entire length of the axon. (faster impulses)
All nerves of the PNS, as well as all motor and sensory neurons are myelinated, only some of the nerves in the CNS are myelinated – Non- Myelinated neurons in the brain= grey matter – Myelinated nerves in the brain are called white matter
Nerves Individual neurons are organized into tissues called nerves.
Repairing Damaged Nerves Nerves 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 Arc automatic, quick, involuntary responses to internal or external stimuli. does not immediately involve the brain. allows quicker reaction times to a potentially harmful stimulus
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5 Components of a Reflex Arc: 1. Sensory receptor -senses something 2. Sensory neuron -sends signal to the CNS 3. Interneuron- registers signal 4. Motor neuron -sends response back 5. Effector- caries out the action
Action Potential A nerve impulse is an action potential An action potential is 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.
Steps of a Nerve Impulse (Action Potential 1. Resting Potential Polarization: voltage difference of -70mV across a nerve cell membrane caused by the sodium potassium pump (gate): more sodium is pumped out than potassium is pumped in, resulting in a negative charge inside the axon of the neuron
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 A threshold stimulus must be applied (a change in pH, pressure, or an electrical stimulus) This causes the sodium potassium pump to cause Na+ gates to open and tons of Na+ rush into the cell, and small amounts of K+ to move out membrane becomes depolarized (+ 40 mV)
3. Re-polarization After the wave of impulse has move through Na+ 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 (over-shoot) (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
The Action Potential
The 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 (usually around +30mV) 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. The wave of depolarization is self propagating, meaning that it will continue without any aid until its passed on to the next neuron
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 Neurotransmitters Neurons are NOT physically attached to each other, but are separated by a gap (synaptic cleft), the electrical impulse cannot just simply cross the gap to the next dendrite, something is needed Neurotransmitters are stored in synaptic vesicles of the axon and are released to carry the information across this synaptic gap
The Synapse Terminal Axon
Structures in the Synapse Pre-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 continue the impulse across the synaptic cleft Crossing the impulse across the gap is a chemical reaction – 1) The end of pre-synaptic axon contains vesicles that have specialized neurotransmitters (NTs), as the impulse gets to the end of the axon the NTs are released in to the gap – 2) The NTs diffuse across the gap and attached to specialized receptors found on the post synaptic dendrite. – 3) The wave of depolarization continues on the through the next neuron
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 – at any given time there are many neurons acting and releasing NTs into the synaptic cleft, the net effect of excitatory and inhibitory neurotransmitters is called summation – ONLY if there is adequate excitation to reach the threshold, the neuron will fire.
- may require more than one neuron to 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 (and their enzymes) include: NeurotransmitterEnzymeFunction 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-epinephrineRegulates the stress “fight or flight” response GABAInhibitory action of motor behavior
Removing Neurotransmitters To be effective, the NTs must NOT linger around in the gap, other wise successive impulses will occur. NTs are removed from the gap by: 1. Degradation by enzymes in the synaptic cleft 2. Re-uptake by the pre-synaptic membrane 3. Diffusion out of the synaptic cleft 4. Inability to bind due to competitive inhibitors
The Effects of Drugs Drug – 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 System Parkinson’s Disease: wide-eyed, unblinking expression, involuntary tremor, muscle rigidity, shuffling gait. Ex. Muhammad Ali -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
Chemical Warfare 1) Nerve Gas: inhibit acetylcholinesterase (enzyme that removed acetylcholine from the synaptic gap). Causes spastic paralysis which is continues muscle spasms 2) Strychnine: similar to nerve gas, causes convulsions and spastic paralysis
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 Cord Dorsal 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 (A spinal tap is a needle that is inserted between 2 vertebrates into the meninges to check for meningitis)
Cerebrospinal Fluid – circulates between the inner and middle membranes of the brain and spinal cord. – Provides protection, nutrient / waste exchange, etc.
Spinal Cord Functions 1. center for reflex action 2. provides a pathway for communication between the brain and peripheral nerves
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 Also aids in sleep regulation, sexual arousal, emotions (anger, fear, pain, pleasure)
Cerebrum – largest part of the brain (80% of brain mass), left and right hemispheres. – responsible for intellect, memory, consciousness and language.
Lobes of the Cerebral Cortex Frontal Lobe –voluntary motor muscle movement, higher intellectual processes, personality/behavior, language
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 brain Limbic System –emotions, associated with hypothalamus
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 - non-voluntary actions -contains all the nerves that serve the internal organs. -unconscious and automatic. -made of two parts:
A. Sympathetic nervous system -responsible for the 4 Fs: fight, flight, fright, or having sex 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, flight, fright, having sex) - brings the body back to normal levels – onomicns.swf onomicns.swf