Nervous and endocrine system Flashcards
The nervous system
The nervous system is a specialised network of cells in the human body and is our primary internal communication system. It is based on electrical and chemical signals whereas the endocrine system facing page) is based on hormones.
The nervous system 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.
The nervous system is divided into two subsystems:
• Central nervous system (CNS).
• Peripheral nervous system (PNS).
The central nervous system
The CNS is made up of the brain and the spinal cord
• The brain is the centre of all conscious awareness. The brain’s outer layer, the cerebral cortex, is only 3 mm thick and covers the brain like an orange peel covers an orange.
It is only found in mammals.
The brain is highly developed in humans and is what distinguishes our higher mental functions from those of other animals. Only a few living creatures - sponges, sea squirts, jellyfish - do not have a brain.
The brain is divided into two hemispheres.
• The spinal cord is an extension of the brain. It passes messages to and from the brain and connects nerves to the PNS. It is also responsible for reflex actions such as pulling your hand away from a hot plate.
The peripheral nervous system
The PNS transmits messages, via millions of neurons (nerve cells), to and from the central nervous system. The peripheral nervous system is further subdivided into the:
• Autonomic nervous system (ANS) governs vital functions in the body such as breathing, heart rate, digestion, sexual arousal and stress responses.
• Somatic nervous system (SNS) governs muscle movement and receives information from sensory receptors.
the endocrine system
The endocrine system works alongside the nervous system to control vital functions in the body. The endocrine system acts more slowly than the nervous system but has very widespread and powerful effects. Various glands in the body, such as the thyroid gland, produce hormones. Hormones are secreted into the bloodstream and affect any cell in the body that has a receptor for that particular hormone.
Most hormones affect cells in more than one body organ, leading to many diverse and powerful responses. For example, the thyroid gland produces the hormone thyroxine. This hormone affects cells in the heart (increases heart rate). It also affects cells throughout the body increasing metabolic rates (the chemical processes taking place in the cells). This in turn affects growth rates.
The main glands of the endocrine system are shown in the diagram on the right. The key 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 the other endocrine glands in the body.
adrenal gland-adrenaline-getting our body ready for flight or fight
thyroid-thyroxine-increases heart rate/metabolic rate-affects growth rate
testicles-testosterone
ovaries-oestrogen
pineal gland-melatonin-start getting sleepy and then sleep when produced
Hormones affect any cells throughout the body that have receptors for that particular hormone.
This could in only in one particular organ, all throughout the entire body.
Key endocrine gland is the pituitary gland located in the brain-often called master gland because it controls release of hormones from all other endocrine glands in body.
systems working together
Often the endocrine system and the autonomic nervous system (ANS) work in parallel with one another, for instance during a stressful event. When a stressor is perceived (your friend jumps out to frighten you or you think about your upcoming exams) the first thing that happens is a part of the brain called the hypothalamus activates the pituitary gland and this triggers activity in the sympathetic branch of the autonomic nervous system. The ANS changes from its normal resting state (the parasympathetic state) to the physiologically aroused sympathetic state (try it - think of a scary film and your sympathetic nervous system will kick in).
Adrenaline The stress hormone adrenaline is released from the adrenal medulla (a part of the adrenal gland lying near your kidneys) into the bloodstream. Adrenaline triggers physiological changes in the body (eg increased heart rate) which creates the physiological arousal necessary for the fight or flight response.
Immediate and automatic All of this happens in an instant as soon as the threat is, detected (for example your heart starts beating faster almost as soon as you experience a fright). This is an acute response and an automatic reaction in the body. The physiological changes associated with this sympathetic response are listed in the table below right. These changes explain why stress, panic, or even excitement, are often experienced as a sick feeling (‘butterflies’ in your stomach - does that describe what you were feeling?).
Parasympathetic action Finally, once the threat has passed, the parasympathetic nervous system returns the body to its resting state. The parasympathetic branch of the ANS works in opposition to the sympathetic nervous system - its actions are antagonistic to the sympathetic system. The parasympathetic system acts as a ‘brake’ and reduces the activities of the body that were increased by the actions of the sympathetic branch. This is sometimes referred to as the rest and digest response.
sympathetic state
Increases heart rate
Increases breathing rate
Dilates pupils.
Inhibits digestion
Inhibits saliva production
Contracts rectum
