Module 5.1.3 – Nervous transmission

1. Module 5.1.3 – Nervous transmission Equipment: Spec: (c) the generation and transmission of nerve impulses in mammals To include how the resting potential is established and maintained and how an action potential is generated (including reference to positive feedback) and transmitted in a myelinated neurone AND the significance of the frequency of impulse transmission. • Pg.347-354 (c, d) Handouts:

6. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Starter What are the 3 types of neurones? Compare them. • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation Ext: How is each adapted to its function? • Sensory – carry messages from sensory receptor cells to relay or motor. 1 Dendron (to cell body) & 1 axon (away from cell body) • Relay – between neurones (sensory  relay  motor. Many short axons & dendrons. • Motor – from relay or sensory to an effector (muscle or gland). 1 long axon & many short dendrites.

7. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Myelination What is the purpose of myelin sheaths surrounding the axon? • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation Ext: Describe the structure of neurones in patients with Multiple Sclerosis (MS. The myelin sheath allows for increased speed of transmission, as the impulse travels only along the nodes of Ranvier.

8. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 • All sensory receptors: • Are specific to a single type of stimulus. • Act as a transducer – they convert a stimulus into a nerve impulse. Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Sensory receptors The body detects stimuli using specialised cells called sensory receptors. They are often located in sense organs, ie. the ear, eye. • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation Ext: Describe how a coordinated response is initiated by the brain. Sensory receptors examples Receptor  ____ neurone  _____ neurone  _____ neurone  effector cell

9. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Receptors on fingers Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Pacinian corpuscle They are specific receptors that detect mechanical pressure stimuli. • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation Located deep within your skin & most abundant in the fingers & soles of the feet. Ext: Suggest reasons why they are found deep in tissues? In your fingers & feet? Can also be found within joints, enabling you to know which joints are changing direction.

10. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Pacinian corpuscle How a Pacinian corpuscle converts mechanical pressure into a nerve impulse: • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation In its resting state, the Na ion channels in the sensory neurone’s membrane are too narrow to allow Na through. This is known as a “resting potential.” When pressure is applied to the P.C, the corpuscle changes shape, causing the membrane to stretch. When it stretches, the Na ion channels widen allows these ions to diffuse into the neurone.

11. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Pacinian corpuscle How a Pacinian corpuscle converts mechanical pressure into a nerve impulse: • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation • The influx of Na+ ions changes the potential of the membrane – it becomes depolarised. This causes a generator potential. • In turn, the generator potential creates an action potential (a nerve impulse) that passes along the sensory neurone. Then the action potential can be transmitted along neurones to the CNS.

12. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Sodium-Potassium pump Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Resting potential When a neurone is not transmitting an impulse, its potential difference across its membrane (inside vs. outside) is known as its resting potential. • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation Extracellular fluid It is a result of: Na+ are actively transported (ATP) out of the axon whilst K+ are pumped inside. [3 Na+ out for every 2 K+ in]. *Tip “K-IN vs. Na-OUT” B/c there is an imbalance of ions, this creates an electrochemical gradient. Most Na+ channels are closed whilst the K+ channels are open, allowing diffusion of K+ to continue. This creates a RP across the membrane of -70mV. Cytoplasm

13. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Action potential Animation of AP & channels The transmission of an electrical impulse from one neuron to another. • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation The neuron begins in its resting potential where some K channels are open but the Na channels are closed. The E of the stimulus triggers some Na voltage-gated ion channels to open, allowing Na+ to enter. This causes the inside of the neuron to be less (-). This change of charge causes more Na+ to open & more Na+ diffuse into the axon (positive feedback).

14. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Action potential The transmission of an electrical impulse from one neuron to another. • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation • 4. When the p.d. reaches ~+40 mV, the voltage-gated Na+ channels close & K+ channels open. Permeability of K increases. • K+ diffuse out of the axon down their electrochemical gradient, which reduces the charge, resulting in the inside becoming overall more (-). • Loads of K+ diffuse out of axon resulting in hyperpolarisation. Now the K+ channels will close & the Na-K pump becomes active again restoring the resting potential (now repolarised). Animation of AP & channels

15. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Stimulus intensity on impulse frequency • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation Nerve impulses are “all-or-none” responses as they must meet a threshold value to trigger a response. The larger the stimulus, the morefrequently the action potentials are generated.

16. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Measuring Action Potential • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation Ext: How does the body respond differently to a small vs. a large stimulus? [2] State what occurs in the neurone between 1 ms & 2 ms. State & explain how the membrane potential changes between 5.5 ms & 7 ms. Using the data in the graph, calculate the frequency of action potentials.

17. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Exam practise • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation Complete the exam practise provided.

18. Nervous transmission L.O. to describe the generation & transmission of nerve impulses in mammals. Module 5 Monday, 26 June 2017 Tasks STARTER Sensory receptors Resting potential Action potential Measuring A.P. Exam practise PLENARY Plenary • Key terms • Effector • Transducer • Paciniancorpuscle • Resting potential • Sodium ion channel • Depolarisation • Repolarisation Summary questions at the end of the section.