BIOL 1050 Lecture 2 on Animal Form and Function PDF

BIOL*1050 Basic Principles of Animal Form and Function Lecture 2 Department of Animal Biosciences 1 Sensory input Integration in CNS Motor output Nervous system and endocrine system Stimulus‐response 2 Chapter 48, C...

BIOL*1050 Basic Principles of Animal Form and Function Lecture 2 Department of Animal Biosciences 1 Sensory input Integration in CNS Motor output Nervous system and endocrine system Stimulus‐response 2 Chapter 48, Campbell Biology, Pearson Canada Stimulus‐response 3 Stimulus‐response Chapter 48, Campbell Biology, Pearson Canada 4  THE NERVOUS SYSTEM Introduction Understanding animal behaviour: A look into the importance and the main functions of the nervous system 5 Importance It is the master controlling and communicating system of the body Every thought, action and emotion reflects its activity All body systems whether voluntary or involuntary are controlled by it 6 Functions Input: through millions of sensory receptors that monitor the changes (or stimuli) inside and outside the body Integration: processes and interprets the sensory input and decides what to do at each moment Output: effects or causes a response by activating muscles or glands (effectors) via motor output 7 Broad classification Structural classification: Central NS (CNS) and Peripheral NS (PNS) Functional classification (PNS): Sensory/afferent: Somatic fibres Visceral fibres Motor/efferent: Somatic nervous system (voluntary) Autonomic nervous system (involuntary) Sympathetic nervous system Parasympathetic nervous system 8 Nervous tissue A look into the make up of nerve tissue; its components and their functions 9 Types of cells There are two principal types of cells 1. Supporting cells/neuroglia/glial cells: Central nervous system (CNS) glia: Astrocytes Microglia Ependymal cells Oligodendrocytes Peripheral nervous system (PNS) glia: Schwann cells Satellite cells 2. Nerve cells/neurons 10 Neurons=nerve cells They transmit messages (nerve impulses) Contain a cell body: metabolic center with a nucleus surrounded by cytoplasm Fibers=Processes: Electrical signals toward the cell body = dendrites; there are up to hundreds of dendrites (dendr=tree) depending on the neuron type Electrical signals travel away from the cell body = axons; each neuron has only one axon 11 Cell body: collections of cell bodies are called ganglia Axon terminal: each one is separated from the next neuron by a gap = synaptic cleft; functional junction is the synapse Most nerve fibres are covered with a whitish, fatty material called a myelin sheath 12 Terminology Nuclei: clusters of neuron cell bodies in the CNS Ganglia: clusters of neuron cell bodies in the PNS Tracts: bundles of nerve fibres running through the CNS Nerves: bundles of nerve fibres running through the PNS White matter: dense collections of myelinated fibres Gray matter: mostly unmyelinated fibres and cell bodies 13 Functional classification Sensory neurons/afferent neurons: impulses from sensory receptors to the CNS, cell bodies are outside of the CNS Skin = cutaneous sense organs Muscles & tendons = proprioceptors Motor neurons/efferent neurons, cell bodies in the CNS Association neurons (interneurons): they connect the motor and sensory neurons (cell bodies in the CNS) 14  Example: Somatosensory system A look into nerve receptors and the various sensory input systems 15 Somatosensory information Other than vision, hearing, balance, taste, smell Neuron with free nerve endings, Specialized receptor: e.g. pain, temperature e.g. photoreceptor Neuron with encapsulated endings, e.g. pressure, touch Somatosensory information 16 Detecting and processing sensory information… Vision and hearing are often seen as the pinnacles of animal sensory abilities, but other sensory modalities are at least as vital. Animals can not live long without the mechano‐sensory feedback that makes successful motor behaviours possible or the perception of dangerous mechanical forces (as well as thermal). 17 Sensory input – example intact tissue 18 https://www.cell.com/iscience/pdf/S2589‐0042(21)00689‐1.pdf  Hair follicle mechanoreceptors, in which a nerve ending is wrapped around the base of a hair The movement of the hair stimulates the nerve ending Whiskers ‐ mechanoreceptors  Sensory input ‐ example tissue damage Goat with a broken horn Dog with a bite wound  Often convey the sensation of pain Activated by a variety of stimuli Extreme heat dog with Extreme cold a bee‐sting nose Chemical irritants Calor (heat), dolor (pain), rubor (redness) and tumor (swelling) Free nerve endings ‐ nociceptors Physiology of nerve impulses A look at how nerves transmit information to and from the brain 22  Neurons: Two major functional properties The ability to respond to a stimulus and convert it into a nerve impulse The ability to transmit the impulse to other neurons, muscles, or glands 23 Electrical conditions of an inactive neuron The plasma membrane of an inactive (resting) neuron is polarized = fewer positive ions sitting on the inner face than on its outer face The major positive ions outside the cell are sodium (Na+) The major positive ions inside the cell are potassium (K+) As long as the inside remains more negative than the outside, the neuron will stay inactive. 24 Stimulus initiates local depolarization E.g. Pressure stimuli excites a cutaneous receptor of the skin The permeability of the cell plasma membrane changes Sodium (Na+) is in much higher concentration outside the cell, it diffuses quickly into the neuron This event is called Depolarization. 25 Depolarization and generation of an action potential Stimulus is strong enough, sodium (Na+) & influx is great enough The local depolarization initiates and transmits a long‐ distance signal called action potential=nerve impulse All‐or None response=conducted over the entire length of the neuron, or it doesn’t happen at all. 26 Repolarization Immediately after the sodium ions rush into the neuron, the membrane becomes impermeable to sodium (Na+) permeable to potassium (K+) Potassium ions diffuse out of the neuron This outflow of positive ions restores the electrical conditions to the resting (polarized) condition. 27 Initial ionic conditions are restored After repolarization the initial concentrations of the sodium (Na+) and potassium (K+) ions inside and outside the neuron are restored by activation of the sodium‐potassium pump Pump uses (ATP) –cellular energy‐ to pump excess sodium ions out and bring potassium ions in This process spreads along the entire neuron 28 Apply your knowledge: Interesting…Neurotoxin (Tetrodotoxin) changes the action potential Example: Tetrodotoxin: is the poison that is produced by the puffer fish Pufferfish self ‐ defense? Tetrodotoxin binds to sodium channels and blocks their opening. An arriving neuronal stimulus cannot be passed along since the influx of Na+ ions is Pufferfish is a delicacy in prevented. No action potential can develop Japan, where it is known as fugu Pufferfish: human pain relief? Fish’s neurotoxin to improve lives Putzier, Frings, 2002, 32, 148–158. DOI: 10.1002/1521‐415X(200205)32:33.0.CO;2‐1 https://m.youtube.com/watch?v=he5lweH7JxM 30 Transmission of the signal at synapses How does the electrical impulse traveling along one neuron get across the synapse to the next neuron? The impulse doesn’t!!!! Instead a neurotransmitter (chemical) crosses the synapse (gap) to transmit the signal from one neuron to the next. 31 Synapses A neurotransmitter chemical crosses the gap to transmit the signal from one neuron to the next The neurotransmitter binds to a receptor on the next neuron and sodium entry, etc. occurs Most neurons communicate via chemical types of synapses, there are some examples of electrical types/neurons that are physically joined by gap junctions 32 Communication at chemical synapses Action potential reaches an axon terminal The electrical changes open calcium channels Vesicles containing the neurotransmitter fuse with the axon membrane and release the transmitter The neurotransmitter diffuses across the synapse to bind to receptors on the next neuron 33  The whole series of events described before will occur=ion channels opens, sodium entry, depolarization Neurotransmitter is removed from the synapse – either by diffusion away, by reuptake into the axon terminal, or by enzymatic breakdown = Ion channel closes This process limits the effect of each nerve impulse = ‘shorter than the blink of an eye’ 34 Neurotransmitter Chemicals that are used to relay, amplify and modulate signals between neurons 35 Some classes of Examples neurotransmitters Amino Acids Glutamate: primary excitatory neurotransmitter in the CNS GABA (gammaaminobutyric acid): primary inhibitory neurotransmitter in CNS Monoamines Catecholamines: Dopamine; Adrenaline; Noradrenaline Derived from the single amino acid tyrosine; Dopamine: involved in reward processing (pleasurable activities), motor behaviour, cognitive functions, etc. Serotonin (5‐HT): Derived from the amino acid tryptophan; 5‐HT system=very complex system (mood, aggression, sleep, feeding, gut motility; etc.) Acetylcholine Peripheral acetylcholine: main neurotransmitter at neuromuscular junctions Central acetylcholine: e.g. arousal and sleep (REM sleep), attention, learning, memory 36  Peripheral acetylcholine in action Neuron Acetylcholine (ACh) is a neurotransmitter that crosses a neuromuscular junction ACh excites the muscle‐cell membrane, causing depolarization and contraction of the muscle fibre. Muscle fiber ACh is not been released muscle can not contract Cholinesterase = breaks down Ach – fibre can repolarize 37 Action potential (video) 38 https://www.youtube.com/watch?v=XdCrZm_JAp0