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Nervous System Neurons

Cell body

Dendrite

Axon

Cells of the nervous system that processinformation.There about 10 billion of these; each cell hasabout 100,000 connections with other neurons.

The nucleus and biosynthetic centers are locatedhere.Make proteins and neurotransmitters.

Cell extensions that carry signals towards thesoma.

Also called the soma.

There are usually many dendrites.

A Cell extension that carries signals away fromthe soma.

There is only one axon per neuron.

Neuron types

Sensory

Motor

Interneuron

There are three general classes of neurons;

These cells carry signals towards the brain and spinal cord.They carry sensory information from receptors located around thebody which detect external stimuli (sight, sound) or internalconditions (blood pressure and temp.)

These cells carry signals away from the brain and spinal cord.They carry motor information from neurons located within the brainand cord to muscles, glands, the heart and other organs.These signals control the activity of these organs.

These are neurons located within the brain and cord.They receive sensory information, process it and then signal themotor neurons either to fire or not fire.

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Axon

Myelin sheathA Cell extension that carries signals away from the soma.

Many axon are coveredby an insulating sheathcalled myelin.

Myelin acts like theplastic insulationaround a wire; itkeeps the the nervesignals from leakingout of the axon andso prevents thesignals from beingdegraded.

It also helps to increase thespeed of a nerve impulse.

Action potentialThis is a term used to describe a nerve impulse.The distribution of ions across a neuron PM is uneven; there are moreNa+ outside and more K+inside.There are also many other ions that are unevenly distributed acrossthe membrane.This creates a charge difference across the membrane called thepotential difference (PD); inside is negative compared to the outside.An action potential is defined as a moving potential difference.A nerve impulse is therefore a moving PD; the PD moves down theaxon.

Synapse

synaptic end bulb

Neurotransmitters

Acetlycholine

noradrenaline

… is a junction between neurons or between a neuron and a musclecell..

…is found at the end of an axon. It has a bulbous structure and isfound within a synapse.

… or NTs are found within the end bulb. These are chemical substancesthat carry a signal over to the next neuron ( or muscle cell.).

…are found within the end bulb. These are chemical substances thatcarry a signal over to the next neuron ( or muscle cell.).

This is another type of neurotransmitter which is also a hormone.Alsocalled adrenaline.

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postsynaptic membrane

one-way transmission

… is the cell membrane of the cell on the other side of the synapse.It contains receptors which bind to the NTs.

When the NTs bind they generate new nerve signals (actionpotentials) in the postsynaptic cell membrane.

Because of the synapse’s structure signals can only travel from thepresynaptic cell to the postsynaptic cell.

Peripheral nervous system

Nerves

3 type1) sensory

2) motor

3) mixed

Are bundles of axons in the periphery of the body. They carry singalsto and form the brain and cord to the various organs of the body.

These are nerves which carry sensory information to the brain andcord; optic nerve.

These are nerves which carry motor information from the brain andcord to peripheral organs; these nerve control the activities of theseorgans.

Most nerves carry both sensory and motor information.

somatic nervous systemA division of the peripheral NS that carries motor information toskeletal muscles..

autonomic nervous system- ANS

Sympathetic

parasympathetic

A division of the peripheral NS that carries motor information tovisceral organs and glands, such as the stomach, heart, sweat glands.Etc.

A division of the ANS that triggers the “flight or fight response.”It activates those organs that will get you ready to deal with astressful situation:Increased heart rate and respiration, inc BP, inc sweating.

Slows down digestive and urinary activities; less blood flow throughthese organs.

Called the “rest and repose” division.Allows you to recover from stress; dec. HR and BO, dec. respirationrate, inc. blood flow to digestive and urinary organs.

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ReflexA reflex is a rapid, automatic response to a stimulus (a sensorysignal.)Reflexes allow you to engage in complex activities without you beingaware of every step needed to perform that activity.Most reflexes exist below the level of consciousness.

A receptor detects some change in internal or external conditions.

The receptor converts the change into a nerve signal which is sent tothe spinal cord.

The spinal cord processes the impulse and then sends an nerveimpulse back out to some organ in the periphery.This organ then acts to oppose the change that triggered the reflex;this is a type of negative feedback.Knee jerk reflex; ; limits the amount of stretching in a muscle.

Central nervous system

1) Spinal Cord

spinal nerves

Consists of the brain and the spinalcord.

Found with the vertebral canal ofthe spinal column.Is a bridge between theperiphery and the brain; sensoryand motor information form thebody flows through the cord.

There are 31 pairsof spinal nerveswhich carry bothmotor and sensoryinformation

It is also the place wheremany reflex centers arelocated.

2) Brain Stem

3) Cerebellum

4) Cerebrum

Above the top of the spinal cord. This is the place where manyautonomic processes are regulated; heart rate, BP, breathing, etc.

Just behind the brain stem. This structure regulates fine motorcontrol and coordinates muscle activities.Brings together information about body and limb position, speed androtation through space and based on this info determines how tomove a limb to accomplish a particular task.

The largest part of the brain; this is where cognitive function,memory, intellect and emotions reside.

The brain is made of 4 major lobes: frontal, temporal, parietal andoccipital.

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cerebral hemispheres

Cortex

corpus callosum

The brains consist of two major parts called the hemispheres.

…covers each hemispheres. It is about 3-6mm thick and is made ofneuron cell bodies (somas). Most of the 10 billion or so neurons arefound here.

The cortex is thrown into folds called convolutions which increase thesurface area for the cortex.

The two hemispheres are connected by a thick bundle of nerve fiberscalled the corpus callosum.This allows the two sides of the brain to communicate with eachother.

Information processing for memory and intellectual functions occurshere.

There are some differences in the functions between the twohemispheres: right side- spatial, intuitive. Left side- logical, verbal.

Limbic system

memory

This is part of the brain that is involved in learning andmemory.

It is very closely associated with the thalamus, which is involved inemotional responses.That is why events with strong emotional content are rememberedso vividly.

Memory is not localizedto any one region of thebrain; it appears to bedistribution in manyplaces and stored in theintrconnectionsbetween neurons.

The hippocampus is used for mapping memory; this structure enablesyou to figure where your are and where you’re going.

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Enkephalins and endorphinsWe’ve discussed neurotransmitters before; such as acetlycholine.

There are have over 50 different NTs identified as the present time.

Enkephalins: means “within the head substance”

This substance is released during stressful episodes, such as during amarathon run. It is responsible for “runner’s high.”

Endorphins: are “endogenous morphine” or morphine-like substancesmade by the body.

They are released when the body is experiencing pain: a natural pain-killer.

Diseases of the CNSEpilepsy

Parkinson disease

Stroke

Sometimes groups of neurons start to fire uncontrollably, thisgenerates a “storm” of electrical activity over the surface of thebrain resulting in a epileptic seizure.

The NT dopamine is lacking in the motor pathways of individualssuffering from Parkinson Disease. The symptoms include ataxia(difficulty walking) tremors and postural problems. It is treated with asynthetic dopamine called L-Dopa.

Similar to a heart attack, but in the brain. The blood vessels thatsupply parts of the brain are blocked, which results in the death ofneural tissue. The effects of a stroke are dependent on what part ofthe brain has been damaged.

Alzheimer's diseaseAffects some elderlyindividuals, although a fewpatients are affected in their40s.

The basic model of how ADworks is not clear, but this iswhat thought to happen.

There appears to be a build up of a material called amygdeloid plaguesand the formation of neurofibrillary tangles around or within the axon,respectively.

These deposits disrupt the transmission of normal nerve signals. Theprocess is chronic, progressive and there does not appear to be a cure atpresentThis results in a gradual loss of memory and cognitive functions; alsoemotional disturbances may be present. The identity of the person islost.