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KEY OUTCOMES extend knowledge of coordination and regulation of the living organism. understand the significant contribution of the nervous system to homeostasis. extend the understanding of signal transduction in cells with particular reference to neurons. gain an overview of interactions of the nervous and the endocrine systems. Case Study – Optic Nerve reading page 167 • glaucoma is one of the most frequent causes of blindness in dogs • the optic nerve comprises a million or more nerve fibres from neurons in the retina of the eye • damage to the optic nerve can have serious consequences with respect to vision ability. Tasks Quick Check 1 & 2 The Nervous System- Structural Classification reading pages 170-172 When classified according to structure, the nervous system has two subdivisions. 1. The central nervous system (CNS) consists of the brain and the spinal cord acts as the integrating and command center of the nervous system interprets incoming information and issues instructions based on past experience and current conditions 2. The peripheral nervous system (PNS) the part of the nervous system outside the CNS consists mainly of nerves that extend from the brain and spinal cord The Nervous System reading pages 170-172 Spinal Cord Brain Nerves Central Nervous System Peripheral Nervous System Peripheral Nervous System reading pages 170-171 Has two parts – the SENSORY DIVISION and MOTOR DIVISION. 1. 2. Sensory (Afferent) division: transmits sensory information about the external and internal environments to the CNS. Motor (Efferent) division: transmits information away from the CNS. Each part is either externally stimulated (somatic) or internally Sensory: Somatic Sensory (external stimuli)/ Visceral Sensory (internal stimuli) Motor: Somatic Motor (skeletal muscles)/ Autonomic Nervous System (internal muscles and glands) Structure Of The Nervous System Nervous System Central Nervous System CNS Peripheral Nervous System SENSORY DIVISION Spinal Chord Somatic Sensory Neurons Visceral Sensory Neurons Brain MOTOR DIVISION Somatic Motor Neurons Automatic Motor Neurons Brain Sensory (Afferent) Nervous System The Sensory Nervous System has two parts: 1. 2. Sensory Neuron Somatic Sensory Neurons carry information to the CNS from the external environment via the senses. Visceral Sensory Neurons carry information to the CNS from the internal environment (ie organs such as the heart) Skin receptors Motor Neuro n Interneuro Muscle • The sensory (afferent) nervous system sends information from receptors to the CNS. Motor (Efferent) Nervous System The Motor (Efferent) Nervous System has two parts: 1. the Somatic Nervous System transmits messages to skeletal muscles. It is also known as the voluntary nervous system. 2. the Autonomic Nervous System transmits messages to smooth muscle, cardiac muscle and glands. It is also known as the involuntary nervous system. • the motor division of the PNS sends information from the CNS to the muscles and glands. Lets Look more closely at the Motor (Efferent) Nervous System AUTONOMIC NERVOUS SYSTEM INVOLUNTARY – CNS to EFFECTORS Autonomic System The Autonomic system has two parts: • Sympathetic • Parasympatheitic Function: Control involuntary functions • • • • • • heartbeat blood pressure respiration perspiration digestion Can be influenced by thought and emotion PARASYMPATHETIC CENTRAL NERVOUS SYSTEM Brain Dilates pupil • “ Fight or flight” response Stimulates salivation Relaxes bronchi • Release adrenaline and noradrenaline Spinal cord Lungs Accelerates heartbeat • Increases heart rate and blood pressure Salivary glands Inhibits activity Heart Stomach Pancreas • • Increases blood flow to skeletal muscles Inhibits digestive functions Stimulates glucose Secretion of adrenaline, nonadrenaline Relaxes bladder Sympathetic Stimulates ejaculation ganglia in male Liver Adrenal gland Kidney PARASYMPATHETIC CENTRAL NERVOUS SYSTEM Brain • • Contracts pupil “ Rest and digest ” system Calms body to conserve and maintain energy Stimulates salivation Spinal cord Constricts bronchi Slows heartbeat • Lowers heartbeat, breathing rate, blood pressure Stimulates activity Stimulates gallbladder Gallbladder Contracts bladder Stimulates erection of sex organs Summary Of Autonomic Differences Autonomic nervous system controls physiological arousal Sympathetic division (arousing) Pupils dilate Parasympathetic division (calming) EYES Pupils contract SALiVATION Increases Perspires SKIN Dries Increases RESPiRATION Decreases Accelerates HEART Slows Inhibits DIGESTION Activates Decreases Secrete stress hormones ADRENAL GLANDS Decrease secretion of stress hormones Neurons Neurons (Nerve Cells) reading pages 172-175 • nerve cells or neurons are the basic structure of the nervous system • a typical neuron has: • • • • three types of neurons exist including: • • • • a nucleus within the cell body dendrites: highly branched extensions of the cell body that receive and then carry information towards the cell body an axon: an extension that carries information away from the cell body sensory (affector) neurons connecting (inter) neurons motor (effector) neurons the presence of the myelin sheath (on affector and effector neurons) increases the rate at which a nerve impulse is conducted along the axon. Tasks See figure 6.8 a, b and c Biozone 97-98 Neurons These extensions from the cell body vary in length, from microscopic, to just over a meter in some neurons. In humans, the longest ones reach from the lumbar region to the big toe. – Neuron processes that convey incoming message towards the cell body are dendrites – Those processes that conduct impulses away from the cell body are axons – All axons branch profusely at their terminal end, forming thousands of axonal terminals – These terminals contain hundreds of tiny vesicles that contain chemicals called neurotransmitters – Each axonal terminal is separated from the next neuron by a tiny gap called the synaptic cleft – Such a functional junction is called a synapse Cells of the nervous system. (a) A typical sensory neuron (b) A typical motor neuron (c) Structure of a nerve (d) A typical connector or inter neuron Relationship between different kinds of neurons. Task: See figure 6.8: copy and label Nerve Impulses -Summary reading page 174 • as an impulse moves along an axon, the permeability of the membrane changes so that positive Sodium ions (Na+) move into the neuron through ion channels • the change in permeability moves along the neuron • Sodium ions (NA+) move into the neuron causing achnage in polarity (from negative to positive). Potassium ions (K+) move out of the neuron (momentarily). When Na+ and K+ are momentarily together inside the neuron, the charge is positive • after a nerve impulse has passed along the membrane, the original distribution of ions across the membrane is restored • the larger the axon’s diameter, the faster the impulse moves along it • the presence of myelin increases the speed of an impulse • an unstimulated nerve is said to have ‘resting potential’ an activated nerve has ‘action potential’ (the wave being the action potential) See figure 6.10 (not error on stimulated axon) Task Biozone page 100 Transmission of Impulses Along a Neurone Nerve Impulse Transmission Cells are set up as electrically polarized. – They are in “resting state” – Ready to do work. – A more + charge outside the cell than inside – Created by Na+/K+ pumps Nerve Impulse Transmission ACTION POTENTIAL – These resting neurons are easy to knock off balance – Electrical, chemical, or mechanical stimulus can move them to an action state. – Once the “threshold” level is met, signal is sent. Myelination Schwann Cells – Act as insulators to the nerve – Lipo-protein based – Separated by Nodes of Ranvier Node of Ranvier Myelination cont Schwann Cell – Speed up conduction of impulse – Depolarization skips from one node to another. Synapse • Receptor site receives neurotransmitters • Neurotransmitters change permeability of membrane. • Ions flood into membrane setting off a action potential in post-synaptic cell. The Structure of a Synapse. Transmission between neurons Synapse The location between a neuron and its effector (nerve, muscle, gland.) Not in physical contact with effector. When signal reaches the synaptic cleft it releases Neurotransmitters (NT). NT Diffuse across cleft to receptor sites on postsynaptic site. Signal Transduction Across A Synapse Neurotransmitters Substance reading page 175-178 • are produced at the ends of axons and are packaged in vesicles (on the end of axons only!) • diffuse across the synapse and attach to receptors on the postsynaptic membrane • stimulate another neuron or effector • last for a very short time only (enzymes produced by muscles tissue inactive the substances for example) Example: acetycholine Communication by Neurohormones reading pages 176-177 • are chemicals released directly into the blood • travel to a target organ where the signal is transduced and the receptor cells respond • neurons in the hypothalamus of the brain has several different neurohormones. These are released into the blood and travel to the pituitary cells, both anterior and posterior, where they exert their effect Examples: thyrotropin-releasing hormone (TRH) signals anterior pituitary cells to produce thyroid stimulating hormone (TSH); This is an example of the nervous and endocrine systems interacting together See figure 6.14 & 6.15 Signals and Receptors • signal transduction is the process by which a cell converts one kind of signal into another by a series of relay molecules • signals initiating transduction include: • • • • • hormones neurotransmitters neurohormones environmental stimuli (i.e light) cellular responses to transduction include: • • activation of a gene- protein production alteration of cellular activity, such as • • • increased cellular secretions Changes in cell permeability Increased rates of chemical reactions Networks of nerve cells reading page 178 • neuron pathways are of two kinds: diverging or converging • diverging pathway: a single axon of one neuron branches and links up wit a larger number of postsynaptic neurons. • converging pathway: many persynaptic nerves cone together to influence a smaller number of synaptic neurons, ultimately one. • one advantage of the convergence system is that one cell can have multiple signals that influence an outcome. Figure 6.16 (next page) Reflex Simplest of neural responses. Involves as little as 3 neurons Shortens link between stimulus and response. Reflex Arc Sensory Neuron Interneuron Motor Neuron Create reflex arc Reflex Arc Reflex Acts in an “emergency response” Cuts time of response. Communication by neurohormones From the previous slide, it is evident that neurotransmitters signal other cells directly. However there are neurons that send signals via neurohormones Some neurons release chemicals called neurohormones into the blood. The blood carries the appropriate signal to the target organs that then respond. Communication by neurohormones These neurohormones are released into the blood, which then travel to the target organ which receives the signal thus resulting in a response from the receptor cell. For example, the hypothalamus of the brain has several different kinds of neurons each producing a different kind of neurohormone. These are released into the blood and travel to the cells of the anterior or posterior pituitary where they exert their Example of Communication by neurohormones Neurons in the hypothalamus in the brain secrete neurohormones [e.g. thyrotropin-releasing hormone (TRH)] into blood capillaries that become associated with the pituitary. Signals received by cells of the pituitary are transduced and the pituitary responds by producing a hormone as instructed [in this case thyroidstimulating hormone (TSH)]. This hormone enters the bloodstream and is transported to its target cells [in this case the thyroid gland]. Impeded Nerve Function reading page 178-182 • when adverse events impinge on facets of the hormonal and nervous systems, their normal functioning can be brought to a halt. • example: thyroid gland. Over activity shows excessive amounts of thyroxin are produced. • toxins can overwhelm the neuron transmission. • poisonous animals produce toxins to paralyse their prey or rebuff predators. Task Quick Check 6-11 page 182 The Central Nervous System readings page183-187 • • • • the brain and spinal cord together form the central nervous system. the brain plays a major role in homeostasis. a living brain has continuous electrical activity the distinct areas are visible in sections of a spinal cord. Tasks Quick Check 12-15 Comparing Nervous And Endocrine Systems. Nerve Action Endocrine system is faster Is slower shorter lived more sustained (longer acting) Why? Why? • Nerve action is due to electrical impulses, which travel very quickly (up to 200metres per second) • endocrine hormones travel from their production site via the bloodstream to their target cells • Transmitter substance is active at a synapse for a fraction of a second only and then is inactivated • Hormones must be metabolised before their actions stop and inactivation time can take hours or days. Case Studies of Homeostasis readings pages189-195 • • • Blood Glucose control Maintaining core temperature Maintaining water balance Control of Blood Pressure reading page 190 (draft) • • • • figure 6.31 page 190 blood pressure is under nervous and hormonal control. if a change in blood pressure occurs, events take place that counteract the initial change. a fall in blood pressure is followed by events that lead to a restoration of normal blood pressure. Maintaining Core Temperature reading page 191-192 (draft) • fig. 6.32, page 191. • when a person is exposed to the cold, the body responds in several ways to maintain a stable core temperature. Maintaining Water Balance reading page 192-193 (draft) • • • fig. 6.33 page 193 vasopressin and renin both play a role in conservation of water. kidneys are the major organs that control water balance. Tasks • Complete Biochallenge page 196. • Complete Chapter Review questions 197 – 198.