Lecture 8 Regulatory Mechanisms PDF

Lecture 8. Regulatory Mechanisms I. Intercellular Communication and the Endocrine System II. Nervous Coordination  Nervous System detection of external and internal stimuli control and coordination of responses to stimuli includes the brain, spinal cord, sense organs Neur...

Lecture 8. Regulatory Mechanisms I. Intercellular Communication and the Endocrine System II. Nervous Coordination  Nervous System detection of external and internal stimuli control and coordination of responses to stimuli includes the brain, spinal cord, sense organs Neurons: Functional Units of Nervous System sensory or afferent neuron motor or efferent neuron interneuron Neurons: Functional Units of Nervous System Neuroglia also known as glial cells non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for the brain's neurons i.e. astocyte, oligodendrocyte and microglia Astrocyte biochemical support of endothelial cells that form the blood-brain barrier provision of nutrients to the nervous tissue maintenance of extracellular ion balance with principal role in the repair and scarring process of the brain and spinal cord following traumatic injuries. Oligodendrocyte insulation of axons in the central nervous system (the brain and spinal cord) of higher vertebrates provision of nutrients to the nervous tissue Microglia the resident macrophages of the brain and spinal cord, and thus act as the first and main form of active immune defense in the central nervous system Patterns of Organization of Nervous System Nerve nets Patterns of Organization of Nervous System with cephalization come more complex nervous systems  Nature of Nerve Signals every cell has a voltage or membrane potential across its plasma membranes a membrane potential is a localized electrical gradient across membrane – anions are more concentrated within a cell – cations are more concentrated in the extracellular fluid  Measuring Membrane Potentials an unstimulated cell usually has a resting potential of -70mV  How a Cell Maintains a Membrane Potential – Cations K+ the principal intracellular cation Na+ is the principal extracellular cation – Anions proteins, amino acids, sulfate, and phosphate are the principal intracellular anions Cl– is principal extracellular anion  Ungated ion channels allow ions to diffuse across the plasma membrane – these channels are always open this diffusion does not achieve an equilibrium since Na-K pump transports these ions against their concentration gradients  changes in membrane potential of a neuron give rise to nerve impulses excitable cells have the ability to generate large changes in their membrane potentials – gated ion channels open or close in response to stimuli the subsequent diffusion of ions leads to a change in the membrane potential  Types of gated ions: – chemically-gated ion channels open or close in response to a chemical stimulus – voltage-gated ion channels open or close in response to a change in membrane potential  Graded Potentials: Hyperpolarization and Depolarization – graded potentials are changes in membrane potential  Hyperpolarization – Gated K+ channels open K+ diffuses out of the cell the membrane potential becomes more negative Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings  Depolarization. – Gated Na+ channels open Na+ diffuses into the cell the membrane potential becomes less negative. Fig. 48.8b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings  The Action Potential: All or Nothing Depolarization – if graded potentials sum to -55mV a threshold potential is achieved triggers an action potential – Axons only  In the resting state closed voltage-gated K+ channels open slowly in response to depolarization Voltage-gated Na+ channels have two gates – closed activation gates open rapidly in response to depolarization – open inactivation gates close slowly in response to depolarization  nerve impulses propagate themselves along an axon the action potential is repeatedly regenerated along the length of the axon  Saltatory conduction – in myelinated neurons only unmyelinated regions of the axon depolarize thus, the impulse moves faster than in unmyelinated neurons  Electrical Synapses – action potential travels directly from the presynaptic to the postsynaptic cells via gap junctions Chemical Synapses – more common than electrical synapses – postsynaptic chemically-gated channels exist for ions such as Na+, K+, and Cl- depending on which gates open the postsynaptic neuron can depolarize or hyperpolarize  Neurotransmitters Acetylcholine – excitatory to skeletal muscle – inhibitory to cardiac muscle – secreted by the CNS, PNS, and at vertebrate neuromuscular junctions  Biogenic Amines – Epinephrine and norepinephrine can have excitatory or inhibitory effects secreted by the CNS and PNS secreted by the adrenal glands epinephrine norepinephrine  Dopamine – generally excitatory; may be inhibitory at some sites widespread in the brain affects sleep, mood, attention, and learning – secreted by the CNS and PNS – a lack of dopamine in the brain is associated with Parkinson’s disease – excessive dopamine is linked to schizophrenia Parkinson’s disease degenerative disorder of the central nervous system that often impairs the sufferer's motor skills, speech, and other functions characterized by muscle rigidity, tremor, postural abnormalities, gait abnormalities, a slowing of physical movement (bradykinesia) and a loss of physical movement (akinesia) in extreme cases Schizoprenia mental disorder characterized by a disintegration of the process of thinking and of emotional responsiveness auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social or occupational dysfunction  Serotonin – generally inhibitory widespread in the brain affects sleep, mood, attention, and learning – secreted by the CNS  Amino Acids – Gamma aminobutyric acid (GABA) inhibitory secreted by the CNS and at invertebrate neuromuscular junctions – Glycine inhibitory secreted by the CNS  Amino Acids – Glutamate excitatory secreted by the CNS and at invertebrate neuromuscular junctions – Aspartate excitatory secreted by the CNS  Neuropeptides – Substance P excitatory secreted by the CNS and PNS – Met-enkephalin (an endorphin) generally inhibitory secreted by the CNS  Gases that act as local regulators – Nitric oxide – Carbon monoxide Vertebrate Nervous System  A ganglion is a cluster of nerve cell bodies within the peripheral nervous system. A nucleus is a cluster of nerve cell bodies within the central nervous system.  Cranial and Spinal Nerves 44  Brain and spinal cord – central canal is continuous with ventricles; contain cerebrospinal fluid (CSF) – white matter is composed of bundles of myelinated axons – gray matter consists of unmyelinated axons, nuclei, and dendrites  A Simple Nerve Circuit – the Reflex Arc in Vertebrates – A reflex is an autonomic response (Foramen of Monro) (Opticoel) (Aqueduct of Sylvius or Iter) – functions in homeostasis, coordination of movement, conduction of impulses to higher brain centers – relays information to and from higher brain centers  Midbrain – contains nuclei involved in the integration of sensory information superior colliculi are involved in the regulation of visual reflexes inferior colliculi are involved in the regulation of auditory reflexes  Medulla oblongata – contains nuclei that control visceral (autonomic homeostatic) functions – breathing – heartbeat and blood pressure – swallowing – vomiting – digestion Pons – contains nuclei involved in the regulation of visceral activities such as breathing  Cerebellum functions for coordination of motor activities, and perceptual and cognitive factors relays sensory information about joints, muscles, sight, and sound to the cerebrum. coordinates motor commands issued by the cerebrum  pineal gland – Epithalamus includes a choroid plexus and the pineal gland  thalamus relays all sensory information to the cerebrum relays motor information from the cerebrum receives input from the cerebrum receives input from brain centers involved in the regulation of emotion and arousal  hypothalamus regulates autonomic activity – contains nuclei involved in thermoregulation, hunger, thirst, and sexual and mating behavior – regulates the pituitary gland in mammals, the hypothalamic suprachiasmatic nuclei (SCN) function as a biological clock Cerebrum (outer covering of gray matter)  association areas (where sensory information is integrated and assessed and motor responses are planned) (memory, (sensory emotion, reception and planning, integration; judgement and taste) aggression) (learning, memory, hearing, smell, visual recognition, emotional behavior)  Lateralization of Brain Function – The left hemisphere specializes in language, math, logic operations, and the processing of serial sequences of information, and visual and auditory details specializes in detailed activities required for motor control – The right hemisphere specializes in pattern recognition, spatial relationships, nonverbal ideation, emotional processing, and the parallel processing of information  Language and Speech – Broca’s area usually located in the left hemisphere’s frontal lobe responsible for speech production – Wernicke’s area usually located in the right hemisphere’s temporal lobe responsible for the comprehension of speech – Other speech areas are involved in generating verbs to match nouns, grouping together related words, etc The Limbic System - hippocampus - olfactory cortex - inner portions of the cortex’s lobes - parts of the thalamus and hypothalamus The Limbic System mediates basic emotions (fear, anger), involved in emotional bonding, establishes emotional memory – e.g., the amygdala is involved in recognizing the emotional content of facial expression  Memory and Learning – short-term memory stored in the frontal lobes – establishment of long-term memory involves the hippocampus  The transfer of information from short-term to long-term memory – enhanced by repetition – influenced by emotional states mediated by the amygdala – Influenced by association with previously stored information.  Cranial Nerves nerves that emerge directly from the brain In humans, there are 12 pairs of cranial nerves 1st and 2nd pair – cerebrum 3rd – 12th pair – brainstem Cranial Nerves  Cranial Nerves Cranial Nerve Type I. Olfactory Sensory II. Optic Sensory III. Occulomotor Motor IV. Trochlear Motor V. Trigeminal Both VI. Abducent Motor VII. Facial Both VIII. Auditory Sensory IX. Glossopharyngeal Both X. Vagus Both XI. Accessory Motor XII. Hypoglossal Motor  Sensory Systems sensations begin as different forms of energy that are detected by sensory receptors – energy is converted to action potentials that travel to appropriate regions of the brain  Sensations are action potentials that reach the brain via sensory neurons. Perception is the awareness and interpretation of the sensation.  Sensory reception begins with the detection of stimulus energy by sensory receptors. – Exteroreceptors detect stimuli originating outside the body. – Interoreceptors detect stimuli originating inside the body. – Sensory receptors convey the energy of stimuli into membrane potentials and transmit signals to the nervous system. involves sensory transduction, amplification, transmission, and integration.  Sensory Transduction – conversion of stimulus energy into a change in membrane potential – Receptor potential: a sensory receptor’s version of a graded potential  Amplification – the strengthening of stimulus energy that can be detected by the nervous system  Transmission – the conduction of sensory impulses to the CNS – some sensory receptors must transmit chemical signals to sensory neurons the strength of the stimulus and receptor potential affects the amount of neurotransmitter released by the sensory receptor – some sensory receptors are sensory neurons the intensity of the receptor potential affects the frequency of action potentials  Integration – the processing of sensory information. begins at the sensory receptor –sensory adaptation is a decrease in responsiveness to continued stimulation –the sensitivity of a receptor to a stimulus will vary with environmental conditions Categories of Sensory Receptors  Mechanoreceptors respond to mechanical energy. – muscle spindle is an interoreceptor that responds to the stretching of skeletal muscle. – hair cells detect motion Pacinian corpuscle – mechanoreceptor in the skin that detects pressure and vibration  Pain receptors = nocioceptors – different types of pain receptors respond to different types of pain – Prostaglandins increase pain by decreasing a pain receptor’s threshold  Thermoreceptors respond to heat or cold – respond to both surface and body core temperature  Chemoreceptors respond to chemical stimuli. – general chemoreceptors transmit information about total solute concentration – specific chemoreceptors respond to specific types of molecules – internal chemoreceptors respond to glucose, O2, CO2, amino acids, etc. – external chemoreceptors are gustatory receptors and olfactory receptors  Electromagnetic receptors respond to electromagnetic energy – Photoreceptors respond to the radiation we know as visible light – Electroreceptors: some fish use electric currents to locate objects  Photoreceptors and Vision Eye cups are among the simplest photoreceptors – detect light intensity and direction — no image formation – the movement of a planarian is integrated with photoreception  Image-forming eyes – compound eyes of insects and crustaceans. Each eye consists of ommatidia, each with its own light-focusing lens.  Single-lens eyes of invertebrates such as jellies, polychaetes, spiders, and mollusks – the eye of an octopus works much like a camera and is similar to the vertebrate eye Vertebrate Eye  Accommodation is the focusing of light in the retina. – In squid, octopuses, and many fish this is accomplished by moving the lens forward and backward. – In mammals, accommodation is accomplished by changing the shape of the lens  Photoreceptors of the human retina – About 125 million rod cells – About 6 million cone cells  Rhodopsin (retinal + opsin) is the visual pigment of rods. The absorption of light by rhodopsin initiates a signal- transduction pathway.  Visual processing begins with rods and cones synapsing with bipolar cells – Bipolar cells synapse with ganglion cells Visual processing in the retina also involves horizontal cells and amacrine cells  Vertical pathway: photoreceptors bipolar cells ganglion cells’ axons.  Lateral pathways: – Photoreceptors horizontal cells other photoreceptors. Results in lateral inhibition. –More distance photoreceptors and bipolar cells are inhibited sharpens edges and enhances contrast in the image. – Photoreceptors bipolar cells amacrine cells ganglion cells. Also results in lateral inhibition, this time of the ganglion cells.  The optic nerves of the two eyes meet at the optic chiasm. – Where the nasal half of each tract crosses to the opposite side. Ganglion cell axons make up the optic tract. – Most synapse in the lateral geniculate nuclei of the thalamus. Neurons then convey information to the primary visual cortex of the optic lobe. Hearing and Equilibrium  Vibrations in the cochlear fluid basilar membrane vibrates hair cells brush against the tectorial membrane generation of an action potential in a sensory neuron.  Pitch is based on the location of the hair cells that depolarize. Volume is determined by the amplitude of the sound wave.  the inner ear also contains the organs of equilibrium  Statocysts are mechanoreceptors that function in an invertebrate’s sense of equilibrium.  sound sensitivity in insects depends on body hairs that vibrate in response to sound waves – different hairs respond to different frequencies many insects have a tympanic membrane stretched over a hollow chamber  Chemoreception: Taste and Smell taste receptors in insects are located on their feet  In mammals, taste receptors are located in taste buds, most of which are on the surface of the tongue. Each taste receptor responds to a wide array of chemicals.  Sensory receptors transduce stimulus energy and transmit signals to the nervous system  In mammals, olfactory receptors line the upper portion of the nasal cavity – the binding of odor molecules to olfactory receptors initiate signal transduction pathways