The Nervous System Flashcards
(13 cards)
Brain
Continuously receives and analyses sensory information, responding by controlling all bodily actions and functions.
Spinal Cord
Two major functions of the spinal cord are to:
- receive sensory information from the body (via the peripheral nervous system) and send these messages to the brain for processing
- receive motor information from the brain and send it to relevant parts of the body (via the peripheral nervous system) to control muscles, glands and internal organs so that appropriate actions can be taken
Peripheral Nervous System(PNS)
carries information to the CNS from the body’s muscles, organs and glands (about the internal environment) and from the sensory organs (about the external environment)
carries information from the CNS to the body’s muscles, organs and glands.
Somatic Nervous System(SNS)
The SNS is a subdivision of the PNS comprising a network of nerves that carries sensory information to (afferent) the CNS and motor information from (efferent) the CNS.
Sensory information is received at sensory receptor sites in the body (skin, muscles, joints and tendons) and carried along sensory neural pathways by sensory neurons.
Motor information is carried along motor neural pathways by motor neurons to skeletal muscles to control their activity by causing them to contract or relax.
Autonomic Nervous System
The ANS is a subdivision of the PNS that connects the CNS to the body’s internal organs (such as the heart, stomach and liver) and glands (such as sweat, salivary and adrenal glands), providing feedback to the brain about their activities.
The ANS is called ‘autonomous’ because many of the organs, glands and processes under its control are self-regulating and therefore occur without conscious effort and are not usually under our voluntary control.
Subdivisions of the Autonomic Nervous System
Sympathetic, Parasympathetic and Enteric nervous system
Sympathetic Nervous System
The sympathetic nervous system activates internal muscles, organs and glands to prepare the body for vigorous activity or to deal with a stressful or threatening situation. This is initiated by a stressor or fear stimulus and enhances survival by providing an immediate response, in a split second, to any kind of emergency.
Glands that are activated include the adrenal glands which release hormones (such as adrenaline and cortisol) into the bloodstream. These circulate throughout your body, enhancing the effects of the sympathetic system by activating and energising various muscles, organs and other glands in preparation for dealing with the stressor or potential threat.
Parasympathetic Nervous System
In times of minimal stress and in the absence of threat, the PNS helps to maintain the internal body environment in a steady, balanced state of normal functioning. The PNS generally has the effect of counterbalancing the activities of the sympathetic system.
The parasympathetic system dominates the sympathetic system most of the time.
The parasympathetic system:
reduces heart and breathing rates,
- and minimises the release of sugar and fats into the bloodstream.
The Enteric Nervous System(ENS)
The ENS is sometimes referred to as a ‘second brain’ because of its degree of autonomy (including its own memory of prior gut action), and its reliance on the same types of neurons and neurotransmitters that are found in the CNS.
Can function independently of the brain
Can carry out some of its functions in the digestive process without communicating with the brain (as has been demonstrated when the vagus nerve that directly connects the brain and gut is cut).
ENS activity is also influenced by external factors that ordinarily affect hunger, eating and digestion, including diet, cognitions, mood, or when there are disturbances to the gastrointestinal tract, such as the presence of foreign bacteria or viruses that may cause illness. The ENS also regulates the response to the food and drink that are taken in. In the case of food poisoning, the ENS can respond by initiating vomiting and diarrhoea.
Conscious Response
A reaction that involves awareness. You will have paid attention to the stimulus and therefore know about it. The response will usually be a voluntary reaction. The reaction is likely to be purposeful and you will be able to have some control over it.
Unconscious Response
An unconscious response to a sensory stimulus is a reaction that does not involve awareness. It is involuntary, unintentional, automatic and we cannot ordinarily control its occurrence.
Bodily responses regulated by the ANS occur automatically without conscious effort. For example, your ANS is unconsciously pumping blood from your heart, digesting your food and so on. You do not consciously have to think about making your heart beat, your eyes blink or your lungs fill with oxygen.
Spinal Reflex
A spinal reflex is an unconscious, automatic response controlled solely by neural circuits in the spinal cord. It is often referred to as a reflex arc because the response to an incoming stimulus is automatically ‘reflected back’ from the spinal cord without any initial input from the brain and before the brain processes a conscious perception of the stimulus.
The immediate response at the spinal cord enables a faster reaction time, a fraction of a second before the sensory information reaches the brain. Consequently, this type of spinal reflex involving a withdrawal reaction is believed to be an adaptive response.
