2 Neurons - types A neuron is There are ___ types of neuron: Explain the major differences in appearance and functions betweenreceptor (sensory) neuronseffector (motor) neuronsconnector neurons (inter-neurons, association neurons, relay neurons)White matter consists ofGrey matter consists ofNeurons can be myelinated or unmyelinated. Explain the major differences betweenmyelinated neuronsunmyelinated neuronsA nerve fibre isA nerve isGanglia are
4 Neurons - types A neuron is a nerve cell There are 3 types of neuron: receptor (sensory) neurons– send information from receptors towards the brain/spinal cord. Have long dendrites (usually myelinated), shorter axons (often unmyelinated) , and cell body positioned off to one side.effector (motor) neurons – send information from the brain/spinal cord to muscles/glands (effectors). Have long axons (usually myelinated), shorter dendrites (usually unmyelinated), and cell body positioned towards the dendrite end of the neuron.connector neurons (inter-neurons, association neurons, relay neurons) – found in the brain/spinal cord, connecting motor and sensory neurons. Cell body is central, axons and dendrites are usually the same size, and often unmyelinated.White matter consists of myelinated fibresGrey matter consists of unmyelinated fibres and cell bodiesNeurons can be myelinated or unmyelinated. Explain the major differences betweenmyelinated neurons – have a myelin sheath, and a faster transmission of impulsesunmyelinated neurons – lack myelin sheaths and are slower in transmission of impulsesA nerve fibre is an extension of neuron (ie axon or dendrite)A nerve is a collection of nerve fibresGanglia are groups of nerve cell bodies outside the central nervous system
6 Neurons - structures Describe the functions of the following cell body DendriteAxonmyelin sheathSchwann cellnodes of Ranvieraxon terminalNeurilemmaNeuromuscular junction
7 Neurons - structures Describe the functions of the following cell body- general functioning of cell + metabolism – respiration, synthesis, etc, contains the nucleus, which controls cell activities.Dendrite - receive impulses + pass them on to the cell bodyAxon - carry impulses away from the cell bodymyelin sheath - protects neuron, and speeds up transmission of impulseSchwann cell – makes the myelin sheathnodes of Ranvier – speed up transmission of impulsesaxon terminal – passes impulse to a muscle/gland by means of chemicals (neurotransmitters), thus causing movement or change in activity (eg secretion)Neurilemma – helps repair and protect the neuronNeuromuscular junction – passes impulse to a muscle by means of chemicals (neurotransmitters), thus causing movement
8 How nerve impulses are generated in a neuron The transmission of a nerve impulse along a neuron from one end to the other occurs as a result of chemical changes across the membrane of the neuron.The membrane of an unstimulated neuron is polarized - there is a difference in electrical charge between the outside and inside of the membrane. The inside is negative with respect to the outside.Normally there is more sodium ions (Na+) on the outside and more potassium ions (K+) on the inside. Na+/K+ pumps in the membrane actively keep these ions on the correct side.The cell contains other ions, eg large, negatively charged proteins and nucleic acids, that contribute to the negative charge on the inside of the cell membraneGated channels open in response to neurotransmitters, changes in membrane potential, or other stimuli to let in ions. This changes the difference in electrical charge (depolarisation) and triggers an impulse.The change must be large enough to overcome the threshold, or no impulse will be generated. This is known as the ‘all or none rule’
9 Nerve impulses Nerve impulses are transmitted down a neuron The waves of depolarisation travel down the axon until the reach the axon terminal, where they trigger the release of neurotransmitters.These chemicals act as the stimulus to the nerve at the other end of the synapse (sensory or connector neurons) or trigger a change in an effector (motor neurons)In unmyelinated fibres, the impulse travels slowly along the entire fibre.In myelinated fibres, the impulse ‘jumps’ from one node of Ranvier to the next, and therefore moves more quickly.
10 Nerve transmissionDefine and explain the importance of the following in the generation and transmission of nerve impulses:Potential differenceMembrane potentialResting membrane potentialSodium potassium pumpPolarisationDepolarisationAction potentialRefractory periodSaltatory conductionAll-or-nothing response
11 Nerve transmissionDefine and explain the importance of the following in the generation and transmission of nerve impulses:Potential difference – differences in electrical charges between two placesMembrane potential - differences in electrical charges between inside and outside of membraneResting membrane potential - describes the unstimulated, polarized state of a neuron (at about −70 millivolts).Sodium potassium pump – special protein gates in cell membrane that use energy to transport sodium ions out and potassium ions inPolarisation – the situation where the membrane separates a more negative inside from a positive outside (ie has a potential difference)Depolarisation – when a stimulus is applied, the membrane is more permeable to Na+ and it floods in, reversing the polarisation, and generating an impulseAction potential – the rapid polarisation – depolarisation which causes a change in membrane voltage. The waves of action potentials along the nerve fibre form the impulseRefractory period - the axon can not respond to a new stimulus while it is re-establishing the original concentrations of the Na+ and K+ using the Na+/K+ pumps in the cell membrane.Saltatory conduction – describes the conduction of nerve impulses along a myelinated fibre – as it ‘jumps’ from one node of Ranvier to another. This is faster than in unmyelinated fibres.All-or-nothing response – a new impulse is only generated if the stimulus is greater than the threshold. Once the impulse is generated the size is the same regardless of size of initial stimulus.
12 SynapsesA synapse isMessages are transmitted across the synapse by n_____________________ which attach to r____________ in the membrane of the d_________ of the next neuron.Examples of neurotransmitters includeEnzymesMessages are transmitted to muscles across theby means ofMany nerve poisons work by disrupting synapse function – eg
13 Synapses A synapse is the gap between two neurons Messages are transmitted across the synapse by neurotransmitters which attach to receptors in the membrane of the dendrite of the next neuron.Examples of neurotransmitters include acetylcholine, adrenaline, dopamine, histamine.Enzymes remove the neurotransmitters and so clear the receptor sites for another messageMessages are transmitted to muscles across the neuromuscular junctionby means of neurotransmitters (usually acetylcholine)Many nerve poisons work by disrupting synapse function – eg curare, sedatives, insecticides
15 A – dendriteB – nucleusC – myelin sheathD – axonE – Schwann cellF – side or colateral branch of axonG – node of RanvierH - motor end plate/axon terminalI - neurilemmaA – motor neuronB – connector neuronC – sensory neuron1 – cell body of the sensory neuron2 – synapse3 – cell body of connector neuron4 – synapse5 – axon of motor neuron6 dendrite of motor neuron7 – muscle fibre8 – motor end plate9 – dendrite of sensory neuron10 – receptor cell
16 The spinal reflex arcDescribe the functions of the five components of a spinal reflex arcR__________________:S__________________:M_________________:E_________________:Spinal reflex arcs are important
18 The spinal reflex arcDescribe the functions of the five components of a spinal reflex arcReceptor: responds to change by initiating nerve impulse in sensory neuronSensory neuron: takes impulses into the central nervous systemSynapse: at least 2 neurons will be involved – sensory and motor. Sometimes there is more than 1 synapse as connector neurons may also be involvedMotor neuron: takes impulses to the effectorEffector: receives impulse and carries out a response (eg movement, change in activity)Spinal reflex arcs are important in protecting the body as they allow very fast responses to potentially harmful changes (eg removal of hand from hot object)