What are the two main divisions of the nervous system?
- The central nervous system (brain and spinal chord).
- The peripheral nervous system (everything else).
What do cranial and spinal nerves have?
Sensory (afferent) motor (efferent) components, ganglia, and sensory receptors.
What does the sensory system consist of?
A variety of different receptors as well as sensory neurons.
What does the motor system do?
Conducts nerve impulses from the CNS to muscles and glands.
What other divisions is the PNS subdivided into?
- Somatic (voluntary),
- Autonomic (involuntary),
- Enteric nervous system
What does the somatic nervous system consist of?
- Sensory neurons that conduct impulses from cutaneous and special sense receptors to the CNS
- Motor neurons that conduct impulses from the CNS to skeletal muscle tissue
What does the autonomic nervous system contain?
Sensory neurons from visceral organs and motor neurons that convey impulses from the CNS to smooth muscle tissue, cardiac muscle tissue, and glands.
How can be signals be passed through the PNS?
- Nerves - Action potentials signal transduction along nerves and synapses.
- Muscle – Action potentials and the initiation and propagation of muscle contractions.
- Endocrine cells - Secretion of hormones.
Define the basic reflex arc.
Sensory Receptor -> [pass through a sensory ganglion] -> [enter dorsal horn of spinal cord] -> synapse on motor neurone in ventral grey matter -> [motor neurone leaves via ventral horn] -> innervation of motor organ e.g. muscle.
Define the basic properties of a neuron.
- The cell body (contains nucleus).
- Dendrites which spread out from the soma.
- An axon
What is the difference between axon and dendrite?
Axons deliver output whereas input is received by dendrites and the cell body.
What is a nerve?
Bundle of axons from many neurons (think trunking!)
Explain the electrical events that lead to an action potential.
- opening of voltage-gated Na+ channels
- Na+ ions will rush into the cell = depolarisation
- AP generated if threshold potential met
Explain the refractory period.
- The interval during which a second action potential absolutely cannot be initiated.
- This is because the all the Na+ channels that originally opened to depolarise the membrane are now inactivated.
What are the factors affecting rate of nerve conduction?
- Temperature
- Thickness/diameter of neurone
- Myelin sheath
Explain the myelin sheath.
- Produced by Schwann cells
- Electrically insulates the axon
- Has gaps called nodes of Ranvier which enable saltatory conduction
What is the relationship between nerve diameter and speed of impulse transmission?
Larger-diameter fibres conduct impulses faster than those with smaller diameters.
What codes the intensity of a stimulus and why?
-APs are an all or nothing event so intensity coded in the rate of impulse production i.e. the frequency of APs.
What is a synapse?
The junction between two neurons.
Explain the difference between an action potential and a graded potential.
- Graded potentials: Small deviation from the resting membrane potential that makes the membrane either more negative (hyperpolarisation) or more positive (depolarisation).
- Graded potentials can vary in amplitude.
What is an excitatory neurotransmitter?
One that can depolarise or make less negative the postsynaptic neuron’s membrane, bringing the membrane potential closer to threshold
What is an inhibitory neurotransmitter?
Hyperpolarises the membrane of the postsynaptic neuron, making the inside more negative and generation of a nerve impulse more difficult.
What are some important neurotransmitters in the PNS?
- Acetylcholine
- Adrenaline
