Download PG1006 Lecture 2 Nervous Tissue 1

PG1006
Lecture 2
Nervous Tissue 1-The Neuron
Dr. Neil Docherty
My Teaching Objec/ves 1.  Clarify the basic structural and func4onal organisa4on of the nervous system and dis4nguish what we mean by nerves, nerve cells and neurones 2.  Outline the key structural features of nerve cells or neurons 3.  Introduce the methods by which neurones physically interact and func4onally couple. From Lecture 1 Neurons communicate through electrical (graded poten4als and ac4ons poten4als) and chemical (neurotransmiDers) signalling Class Ques4on What is our understanding of what we are referring to when we talk about; -­‐Nerves? -­‐The nervous system? Structural Dis/nc/ons The Central and Peripheral Nervous Systems •  Central Nervous System (CNS) –  Brain –  Spinal cord •  Peripheral Nervous System (PNS) –  Nerve fibres that carry informa4on between the CNS and others parts of the body i.e. the periphery –  (Enteric nervous system) Func/onal Dis/nc/ons Soma/c and Autonomic Nervous Systems C.N.S.
Electrical conduction/Chemical transmission
(neurotransmission)
Autonomic Nervous System
(A.N.S.)
Somatic Nervous System
(S.N.S.)
Effector
function
USUALLY SUBCONSCIOUS
AND INVOLUNTARY
• Motility Related (Cardiac muscle and smooth muscle)
• Secretory (glands)
• Metabolic (liver and adipose tissue)
OFTEN CONSCIOUS AND
VOLUNTARY
• Skeletal muscle
Afferent
Interneurone
Organisationof
Multi-neuron Signalling
And Effector Activation
Efferent
Effector Organ
Neuronal Ultrastructure •  Specialised cell type – communica4on •  Func4ons •  Detec4on – receives informa4on •  Integra4on – processes informa4on •  Propaga4on – responds to informa4on •  Electrical and chemical signalling Wheater’s Func4onal Histology – chapter 7 •  4 basic parts of a neurones •  Cell body •  Dendrites •  Axons •  Synapses Neuronal Ultrastructure •  Cell Body –  Nucleus and organelles •  Dendrites –  Project from cell body –  Increase surface area available for receiving signals –  Signal towards the cell body •  Axons –  Elongated, tubular extensions –  Signal away from the cell body –  Varible length e.g 1m or 1mm. Cell Body Ultrastructure Classifying Neurones -­‐ Shape •  Mul4polar – most common •  e.g. motor neurones and interneurones •  Bipolar -­‐ •  e.g specialised sensory neurones •  Pseudo-­‐unipolar •  e.g. sensory neurones Afferent Neurones – Receive signals Efferent Neurones – Carry signals to effector organ e.g muscle Interneurones – Connect afferent and efferent Wheater’s Func4onal Histology – chapter 7 A C B D Methods of Study – light microscopy •  H & E staining (A+B) • Nissl method © •  Heavy metal impregna/on (D+E) •  Gold and Silver •  Details neuronal shape Important in history of field (See Golgi and Ramon y Cajal) •  Immunohistochemistry (F) •  Iden4fy neurone-­‐specific proteins E F How do neurones communicate with each other? •  Electrical signalling •  Chemical Signalling Excitable Membranes •  Res4ng Membrane Poten4al •  K+ efflux •  ECF becomes more +’ve •  ICF becomes more –’ve •  Depolarisa4on •  Na+ influx •  ICF becomes more +’ve •  ECF becomes more –’ve •  Repolarisa4on •  Na+ influx •  K+ efflux Changes in Membrane Poten/al •  Rapid changes in membrane poten4al occur in response to s4muli –  Generates an electrical signal Human Physiology by Lauralee Sherwood Chapter 4 2 Types of Electrical Signals •  Graded Poten4al –  Local changes in membrane potenAal –  Short distance signalling –  Occurs at dendrites and cell body •  Ac4on Poten4al –  Large changes in membrane potenAal (complete reversal of ions) –  Voltage-­‐gated Na+ and K+ channels –  Conducted along the enAre membrane –  Long distance signalling –  Occur at axonal hillock •  Dendrites – Input Zone •  Receive s4muli •  Produce a graded poten4al •  Spread of poten4al •  Axon Hillock – Triggering Zone •  Ac4on poten4als triggered •  Axon – Conduc1ng Zone •  Spread of ac4on poten4al •  Local current flow •  Synapse – Output Zone •  Sends signal to another neurone •  Sends signal to an effector organ Synapses •  Junc4on between two neurones –  Links presynap4c and postsynap4c neurone to transmit signal •  Stores synap4c vesicles containing neurotransmiDers –  NeurotransmiDer is a chemical messenger •  Ac4on poten4al at axonal terminal triggers opening of voltage-­‐gated Ca2+ channels •  Ca2+ induces release of neurotransmiDer into synap4c cleb •  Diffusion across synap4c cleb where it binds to receptors on post-­‐synap4c neurone, causing a change in its membrane poten4al Human Physiology by Lauralee Sherwood Chapter 4 Pre-synaptic
Post-synaptic
Human Physiology by Lauralee Sherwood Chapter 4 Types of Synapses •  Axodendri/c Synapse –  Axon of one neurone synapses with dendrite of another neurone •  Axosoma/c Synapse –  Axon of one neurone synapses with the cell body of another neurone •  Axoaxonic Synapse –  Axon of one neurone synapses with axon of another neurones Types of Responses •  Excitatory •  Inhibitory NeurotransmiYers •  Chemical Messengers e.g dopamine, acetylcholine, glutamate, GABA •  Func4on – transmit signal by diffusing across synap4c cleb and binding to receptors on post-­‐synap4c neurone •  Degraded quickly and recycled •  Excitatory and inhibitory –  E.g. Glutamate is excitatory – increases possibility of an ac4on poten4al –  E.g GABA is inhibitory – decreases possibility of an ac4on poten4al Your Learning from Today 1.  Define what a neuron is versus a nerve and how it fits in
to a system (the nervous system).
2.  Describe the basic ultrastructure of neurons.
3.  Explain how neurons couple both physically and
electrochemically.
Summary •  Neurones communicate through electrical and chemical signalling •  Synap4c input to dendrites results in graded poten4als •  Large graded poten4al can trigger ac4on poten4als in the axon hillock •  Ac4on poten4als are propagated down the axon towards the synapse •  At the synapse neurotransmiDers are released •  NeurotransmiDer ac4vates adjacent neurone