Neural Processing and the Endocrine System

Biological Level of Analysis

Neurons

Neurons (nerve cell) are the building blocks of neural information system (nervous system).

Types of neurons:Sensory neurons: carry messages from the body’s

tissues and sensory organs inwards to the brain and the spinal cord

Motor neurons: receive messages from the brain and spinal cord

Interneurons: neurons located inside the brain and spinal cord that process the messages and information as it comes from the sensory neurons and goes to the motor neurons

Neural Communication

The interneurons are the most complex and the most numerous. There are billions of interneurons in the nervous system. The sensory and motor neurons are by far outnumbered, there are few million of each of them.

Each neuron has the same basic form.Dendrite fibers receive messages/information

and conduct it to the cell body. The information is then passed by the axon to other neurons, muscles, or glands.

Axons speak. Dendrites listen.

Neurons

neuron

Motor neuron

3 Types of neurons

Axons are often long and can be several feet long. These axons are covered with a fatty covering known as the myelin sheath.

The myelin sheath is very important. It protects the axon and speeds the passage of information. It is produced by glia cells.

The myelin sheath is added as you age, until about 25. This impacts neural processing, judgment and self control.

If the myelin sheath degenerates , multiple sclerosis occurs. This occurs because the immune system has attacked the myelin sheath.

Neural impulses travel down an axon at speeds ranging from 2 miles an hour to 200 miles an hour.

Neurons transmit signals by an electrical impulse that travels on an axon. This is called an action potential.

Neurons

Neurons/ Action potential

Action Potential/Synapse

Neurons generate electrical impulses. This process involves the exchange of ions.

The fluid interior of a resting axon has an excess of negatively charged ions. The fluid outside the axon membrane has more positively charged ions. The is called the resting potential. The axon is very selective about what is allowed in, which is known as being selectively permeable. However when an neuron fires, the gates are literally opened. The positive ions go through the membrane, which depolarizes that section of the axon. This causes a domino effect , as each section of the axon’s channel opens.

After this firing, the neuron goes through a resting pause known as the refractory period. During this pause, the positive ions are pumped back out, which allows the neuron to fire again.

Action Potential

This process may repeat hundreds or thousand of times a second.

Each neuron must interpret the signal it receives from all the other neurons and make rapid fire decisions.

Most signals received by the neurons are excitatory, which is like pushing the gas pedal. Some signals are inhibitory, which is like pushing the brake. If excitatory – inhibitory exceeds a minimum intensity (threshold) an action potential is triggered.

Neuroglia cells are neural cells that provide the support network of cells surrounding the neurons and blood vessels of the brain and nervous system.

They are believed to outnumber neurons 10 to 1.There are three types:Oligodendroglia: found in the CNS, produce myelinSchwann cells perform the same function as above

but are found in the PNS. Only Schwann cells can help axons regenerate.

Astrocytes: star shaped, form most of the matrix in which neural cells are embedded and envelop blood vessels in the brain. The also absorb dead neural cells

Neuroglia cells

The synapse is the junction between the axon of one neuron and the dendrites/cell body of another neuron. This is the place where two neurons meet.

The gap between neurons is known as the synaptic gap or synaptic cleft. It is less than a millionth of an inch wide.

Neuron Communication

So how do neurons send information across the synaptic cleft?

When the action potential reaches the end of an axon (the terminal buttons), it triggers the release of neurotransmitters (chemical messengers).

Within the briefest period of time, these neurotransmitters cross the gap and bind to receptor sites on the next neuron. They fit like a key in a lock.

The NT unlocks channels on the receiving neuron and the electrically charged ions flow in. This either excites or inhibits the neuron’s readiness to fire.

Afterwards, in a process called reuptake, the sending neuron reabsorbs the extra NT.

Neuron Communication

Action Potential/Synaptic gap

There are many neurotransmitters that have a variety of effects on our behavior and emotions.

One example is ACh (acetylcholine). ACh impacts learning and memory but also movement. ACh is located at every connection between a motor neuron and a skeletal muscle. If the transmission of ACh is blocked we are unable to move and are paralyzed.

Each NT has its own pathway in the brain. The functions of the NT depends on where in the brain the pathway is located.

Neurotransmitters

Brainstem: affects basic functions like breathing and heartbeat.

Midbrain: affects functions like memory and emotion

Cortex: affects higher functions like memory integration, problem solving, and perception

NT pathways

Some Neurotransmitters

Drugs and other chemicals can replace the body’s own NTs. This can cause the body to stop production of the impacted NTs. Example: Opiates stop the body’s production of endorphins

Drugs and other chemicals affect the brain chemistry at synapses. This could happen as a NTs activity is blocked or increased.

Agonist molecules may be similar enough to a NT to bind to a receptor and block the real NT. They would amplify the normal sensations. Example: opiate drugs creating a high

Antagonists bind to receptors, but their effect is to block the NT’s functioning. Example: Botox blocks ACh release which paralyzes the muscles. Some antagonists are similar enough to block the receptor but not similar enough to trigger a response

How drugs impact Neurotransmission

NT Venn

The central nervous system (CNS) is composed of the brain and the spinal cord. It communicates with the body’s muscles, glands and sensory receptors through the peripheral nervous system (PNS).

The PNS transmits messages through the nerves which are bundles of axons. Therefore the neurons are the essential building blocks of your nervous system.

The Nervous System

The peripheral nervous system has two parts: the somatic nervous system and the autonomic nervous system.

The somatic nervous system allows the voluntary control of skeletal muscles. It is sometimes called the skeletal nervous system.

The autonomic nervous system controls our glands and the muscles of our internal organs. It operates on its own (autonomously) but can be overridden naturally.

The PNS

The ANS has two separate parts that create an opponent process system. Each performs a role that is the opposite of the other. This opposition creates homeostasis or balance.

The sympathetic nervous system arouses and expends energy. It responds to stressful situations. It will accelerate your heartbeat, raise your blood pressure, slow digestion and make you perspire. These biological changes all prepare you for the necessary action.

The parasympathetic nervous system does the opposite and takes over after the stress has subsided.

The ANS

The 40 billion neurons which each connect to countless other neurons makes your nervous system have roughly 400 trillion synapses. Across each synapse messages are being relayed every second.

The brain’s neurons cluster into neural networks. The neurons cluster together with other neurons to create fast, efficient pathways. Each neuron connects with countless other neurons to create a network. Dendrites are very important in this process. The more dendrites a neuron has the more connections it can make with other neurons, this helps to more readily pass messages along the chain.

The CNS

The spinal cord is the information highway. It connects the PNS to the brain. Neural fibers send messages up and down the highway.

Ascending: up; sensory informationDescending: down; motor control informationNeural pathways governing reflexes are very simple and

are a good example of the spinal cord’s function. A spinal reflex pathway is composed of one sensory

neuron (connected by interneuron) to one motor neuron. This pathway runs through the spinal cord and right back out. (pain reflex) this is why you may remove your hand from a heat source before you even process that you have felt heat. It seems as though your hand moved on its own.

The spinal cord

Sensory neurons connect to the spinal cord dorsally (to the back) and motor neurons connect in the anterior of the spinal cord. Therefore it is possible to lose all feeling in the lower body but still be able to move.

To feel pain or pleasure, the messages must reach the brain and this is done via the spinal cord.

The spinal cord

Reflex Arc

Sensory information enters the

body through receptor

cells

The brain processes

the sensory info and

decides what to do

Motor nerves receive

commands from the brain and

react

The second communication system of the body is the endocrine system. It is a slower system than the nervous system. It works through glands that secrete hormones into the bloodstream.

Hormones are chemical messengers that relay information to your body. They are secreted through the glands into the bloodstream and travel through your body. Some hormones are virtually identical to neurotransmitters. The main difference is location. Location of creation and reception.

The Endocrine System

HormonesSlow movingLonger effectsProduced by glandsPart of the endocrine

systemMay be chemically

the sameFlow through the

bloodstream

Fast movingShorter effectsProduced by neuronsPart of the nervous

systemMay be chemically

the sameFlow through the

neural process

Hormones vs Neurotransmitters

Neurotransmitters

Anterior pituitary gland: secretes growth hormone: too little— dwarfism; too much gigantism

Posterior pituitary gland: secretes vasopressin: constricts blood vessels, raises blood pressure: secretes oxytocin: starts labor for pregnant women, triggered by touch—appears to change brain signals related to social recognition via facial expression

Pituitary (as a whole) is a master gland, controlling the release of hormones by other glands

Thyroid: secretes thyroxine and triiodothyronine, increasing metabolic rate, growth and maturity

Parathyroids: release parathyroid hormone which increases blood calcium and decreases potassium

Glands and their hormones

Pancreas: secretes insulin which regulates the level of sugar in the bloodstream

Adrenal glands: release epinephrine (adrenaline) and norepinephrine (noradrenaline) active in the fight or flight response :also releases cortisol (stress hormone) which is linked to stress, arousal and memory

Testes release androgens, which promote sperm production and male sexual characteristics

Ovaries: secrete estrogen which promotes ovulation and female sexual characteristics

Pineal: secretes melatonin, which regulates the circadian rhythm, stimulated by darkness and inhibited by light, some evidence connects increased melatonin to SAD

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