Biopsychology: The Nervous system and the Endocrine system

Definition: Consists of the central nervous system and the peripheral nervous system.

It is a specialised network of cells in the human body and is our primary internal communication system.

It has two main functions:

• to collect, process and respond to information in the environment
• to co-ordinate the working of different organs and cells in the body

It is divided up into two sub-systems:

• Central nervous system (CNS)
• Peripheral nervous system (PNS)

Definition: Consists of the brain and spinal cord and is the origin of all complex commands and decisions.

The brain is the centre of all conscious awareness.

The brains outer layer, the cerebral cortex is highly developed in human and is what distinguishes our higher mental functions from those of animals.
Only a few living creatures do not have a brain.

The brain is divided into two hemispheres.

The spinal cord is an extension of the brain.

It is responsible for the reflex actions such as pulling your hand away from a hot plate.

The CNS passes messages to and from the brain and connects nerves to the PNS.

Definition: Sends information to the CNS from the outside world, and transmits messages from the CNS to muscles and glands in the body.

The PNS transmits messages via millions of neurons (nerve cells), to and from the CNS.

The peripheral nervous system is further sub-divided into the:

• Autonomic nervous system
• Somatic nervous system

Definition: Transmits information to and from internal bodily organs. It is 'autonomic' as the system operates involuntarily (it is automatic). It has two main division: the symathetic and parasympathetic nervous systems.

The ANS govens vital functions in the body such as breathing, heart rate, digestion, sexual arousal and stress responses.

Definition: Transmits information from receptor cells in the sense organs to the CNS. It also receives information from the CNS that directs muscles to act.

The SNS controls muscle movement and receives information from sensory receptors.

Definition: one of the body's major imformation systems that instructs glands to release hormones directly into the bloodstream. These hormones are carried towards target organs in the body.

The endocrine system works alongside the nervous system to control vitak functions of the body.

The endocrine system acts much more slowly than the nervous system but it has very wide spread and powerful effects.

Definition: an organ in the body that synthesises substances such as hormones.

Various glands include the hypothalamus in the brain, the thyroid, the adrenals and the pancreas.

The major endocrine gland is the pituitary gland located in the brain. It is often called the 'master gland' because it controls the release of hormones from all other glands in the body.

Definition: chemical substances that circulate in the bloodstream and only affect target organs. They are produced in ;arge quantites but disappear quickly. Their effects are very powerful.

Most hormones affect cells in several organs or throughout the entire body, leading to many diverse and powerful responses.

For example, the thyroid gland produces the hormone thyroxine. This hormone affects cells in the heart to increase heart rate. It also affects cells throughout the body, increasing the metabolic rates which in turn affects the growth rates of the cells.

Definition: the way an animal responds when stressed. The body becomes physiologically aroused in readiness to fight an aggressor or, insome cases, flee.

The fight or flight response is an example of the endocrine system and the ANS working together.

For this to happen, a stressor such as a friend jumping out to scare you triggers a response from the hypothalamus which triggers activity in the sympathetic branch of the ANS.

The ANS then changes from its normal parasympathetic state (the resting state) into the sympathetic state (physiologically aroused state).

This causes the release of the stress hormone adrenaline to be released from the adrenal gland into the bloodstream.

Adrenaline triggers physiological changes in the body such as increased heart rate which creates the physiological arousal necessary for the fight ot flight response.

All of this happens the instant even a slight threat is detected and this is an autnomic response in the body.

Definition: a hormone produced by the adrenal glands which is part of the human body's immediate stress response system. Adrenaline has a strong effect on the cells of the cardiovascular system- stimulating the heart rate, contracting blood vessels and dilating air passages.

Once the threat has passed, the parasympathetic nervous system returns the body to its resting state.

The parasympathetic nervous system works to oppose the sympathetic nervous system and works to reduce the activities in the body that were increased by the actions of the sympathetic branch.

Definiton: the basic building blocks of the nervous system, neurons are nerve cells that process and transmit messages through electrical and chemical signals.

There are three different types of neurons:

• Sensory neurons
• Motor neurons
• Relay neurons

Sensory neurons: these carry messages from the PNS to the CNS, they have long dentrites and short axons

Motor neurons: these connect the CNS to effectors such as muscles and galnds. They have short dendrites and long axons.

Relay neurons: these connect the sosnsory neurons to the motor or other relay neurons. They have short dendrites and short axons.

They include a:

Cell body (or soma) that includes a nucleus that contains the genetic material of the cells.

Branch-like structures called dendrites that protrude from the cell body, these carry nerve impulses from neighbouring neurons towards the cell body.

The axon carries the impulse away from the cell body down the length of the neuron. The axon is ocvered in a fatty layer of myelin sheath.

The myelin sheath protects the axon and speeds up the electrical transmission of the impulse. The myelin sheath is segmented by gaps called nodes of Ranvier which speed up the transmission of the impulse by forcing the impulse to 'jump' across the gaps along the axon.

Finally at the end of the axon are terminal buttons that communicate with the next neuron in the chain across the gap known as the synapse.

Definition: the process by which neighbouring neurons communicate with each other by sending chemical signals/messages across the gap (the synapse) that separates them.

Neurons communicate with each other within groups known as neural networks. Each neuron is separated from the next by a tiny gap called the synapse. The signals within the neuron are electrical but to jump from neuron to neuron the signals are transmitted chemically across the synapse.

When the electrial impulse reaches the end of the neuron (the presynaptic terminal), it triggers the release of a neurontransmitter from tiny sacs called synaptic vesicles.

Definition: brain chemicals released from the synaptic vesicles that relay signals across the synapse from one neuron to another. Neurotransmitters can be broadly divided into those that perform an excitatory function and those that perform an inhibitory function.

Once the neurotransmitter crosses the gap, it is taken up by the postsynaptic receptor site (the dendrites on the next neuron. 

At this point the chemical signal is converted back into an electrical impulse.

Excitation: when a neurotransmitter, such as adrenaline, increases the positive charge of the postsynaptic neuron. This increases the likelihood that the neuron will fire and pass on the electrical impulse.

Inhibition: when a neurotransmitter, such as serotonin, increases the negative charge of the postsynaptic neuron. This decreases the likelihood that the neuron will fire and pass on the impulse.