(a) discuss why animals need to respond to
- All organisms meed a method of communication between their sensors and their responsive systems (effectors)
- Animals need to be able to coordinate a set of responses if they are to stay alive.
(b) outline the organisation of the nervous system in terms of central and peripheral systems in humans; P1
- The brain and the spinal cord make up the central nervous system
- The rest of the nervous system is made up of the peripheral nervous system
- There are two major types of cell:
- (1) Neurones - that are specialised to carry electrical impulses, in the form of action potentials throughout the body (can be classified as sensory, motor and intermediate neurones)
- (2) Glial cells - help nutrients from the blood pass to neurones (especially in the brain and spinal cord) and maintains the correct balance of ions in the tissue fluid)
- Schwann cells (glial cells) form myelinations around the axons to insulate the electrical charge and to make it travel faster to effectors.
(b) outline the organisation of the nervous system in terms of the central nervous system; P2
- Most neurones are intermediate neurones and have short dendrites forming synapses with many other cells.
- The function of these neurones is to receive and integrate the information arriving via their synapses, and then to pass on the action potential to other neurones.
- Synapses can be excitatory - when an impulse arrives, this depolarises the post-synaptic membrane.
- Or they can be inhibitory - the arrival of an action potential prevents the post-synaptic membrane from depolarising.
(b) outline the organisation of the nervous system in terms of the peripheral nervous system ;P3
- Is made up of sensory neurones that carry action potentials from receptors towards the CNS , and motor neurones that carry action potentials from CNS to effectors.
- Cell bodies of sensory neurones lie outside the spinal cord, in dorsal root ganglia
- They pick up information from receptors and transmit action potentials to their cell bodies - the action potentials pass along axons into the CNS
- The cell bodies of many motor neurones are in the spinal cord and their long axons pass out towards effectors (muscle)
(c) outline the organisation and roles of the autonomic nervous system; P1
The ANS carries action potentials to all of the internal organs (sometimes called the viscera)
It controls the activity of smooth muscle (walls of arterioles) , heart rate of cardiac muscle and the activities of exocrine glands (salivary glands)
Autonomic means 'self governing' because its activities are not under voluntary control
It has a different function to the somatic NS and a different structural organisation
Somatic NS has cell bodies has their cell bodies in the CNS and long axons leading from cell bodies to the effector.
However, the cell bodies of motor neurones in the ANS have their cell bodies outside the the CNS in autonomic ganglia - preganglionic neurones carry action potentials from CNS to this ganglion
The autonomic NS is divided into two components - sympathetic and parasympathetic NS's
(c) outline the organisation and roles of the autonomic nervous system; P2
- Recap - its cell bodies lie in ganglia outside the spinal cord - axons of the preganglionic neurones pass out the ventral root of the spinal cord and synapse with the motor neurone cell bodies in these ganglia.
- From these ganglia, axons pass to all other organs within the body and form synapses with the muscles.
- The transmitter substance that carries the impulse across most of the synapses is noradrenaline (a stimulating impulse) - like pupils dilating, bronchi dilating
- Not all effects of the sympathetic nervous system are stimulatory - some neurones also use acetylcholine as the neurotransmitter that carries impulses to effector organs (sweat glands, erector muscles in the skin, blood vessels)
- This is very similar to the 'fight of flight' response when under stress - with direct activation of sympathetic nerves supplying the adrenal glands cause them to secrete adrenaline and noradrenaline into the blood .
- Effects include, increasing heart rate and force of contraction, pupils dilating, increases sweating in sweat glands and vasoconstriction of arterioles.