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

Nervous System Organization

The Neuron- conducts nerve impulses

The Neuron Basic parts: cell body- nucleus and cytoplasm Dendrites-projection of cytoplasm Axon-extension of cytoplasm Glial 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 Neurons Sensory 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 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

Stretch ReflexReflex Stretch ReflexReflex

5 Components of a Reflex Arc: 1. Sensory receptor 2. Sensory neuron 3. Interneuron 4. Motor neuron 5. Effector

Action 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 Potential Polarization: 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 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 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 Neurotransmitters 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 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 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 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 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 -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 Cord Central Cavity – contains cerebrospinal fluid White Matter – contains myelinated nerve cells Grey Matter – contains un-myelinated nerve cells

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

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 brain Limbic 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) – onomicns.swf onomicns.swf

Fig 2 p 434