Organisation Of The Nervous System

Question 1

Outline the organisation of the nervous system

Answer 1

• central nervous system (CNS)
- made up of the brain and spinal chord
• peripheral nervous system (PNS)
- made up of nerves, efforts and receptors
- split into two different systems
–> somatic nervous system
- controls conscious activities e.g. running
–> autonomic nervous system
- controls unconscious activities e.g. digestion

Question 2

Outline the organisation of the autonomic nervous system

Answer 2

• sympathetic nervous system
- most active during times of stress
- the neurones of a pathway are linked at a ganglion just outside the spinal chord so pre-ganglionic neurones are very short
- post ganglionic neurones secrete noradrenaline as neurotransmitter
- causes increased heart rate, pupil dilation, increased ventilation rate, orgasm
• parasympathetic nervous system
- most active in sleep and relaxation
- the neurones of a pathway are linked at a ganglion within the target tissue so pre-ganglion neurones vary in length
- post ganglion neurones secrete acetylcholine as the neurotransmitter
- decreased heart rate, pupil constriction, decreased ventilation rate, sexual arousal

Question 3

Why do animals need to be able to respond to their environment?

Answer 3

• animals increase their chances of survival by responding to changes in their external environment
• they also respond to changes in their internal environment to make sure that the conditions are always optimal for their metabolism
• need a method of communication between sensors and effectors
• escape from predators
• balance and posture
• temperature regulation
• nerves and hormones coordinate responses

Question 4

Describe the fight of flight response

Answer 4

• sensory receptors detect environmental changes and carry action potentials to the CNS
• impulses are conducted to the cerebrum which uses the association centres to make decisions about how to respond
• impulses are sent down the somatic motor neurones to the skeletal muscles to bring about coordinated voluntary movement
• the hypothalamus is stimulated and sends impulses down the sympathetic part of the autonomic nervous system
• the adrenal glands are stimulated to release adrenaline
• the sympathetic nervous system and adrenaline have the following effects
- the cardiac accelerator nerve carries impulses to the heart which increases the heart rate and stroke volume
- blood pressure is increased
- increased breathing rate and breathing is deeper as the muscles around the bronchioles relax
- glycogen is converted into glucose so more glucose is available for muscles to respire
- muscles in the arterioles supplying blood to the skin and gut constrict and muscles in the arterioles supplying blood to the heart, lung and skeletal muscles dilate so blood is diverted from the skin and gut to the heart, lungs and skeletal muscles