BAHS106 Physiology_TATagoe_2024.pdf

BAHS 106 Homeostasis and Cell Physiology DR. T A TAGOE By the end you should be able to…. Describe the organization of the human body Describe the cell and list functions of its components Define homeostasis and give some examples Explain the role of...

BAHS 106 Homeostasis and Cell Physiology DR. T A TAGOE By the end you should be able to…. Describe the organization of the human body Describe the cell and list functions of its components Define homeostasis and give some examples Explain the role of homeostasis in health and disease  Organisation of the human body Cells are the smallest function unit of the human body A group of cells having similar function is a tissue ◦ Primary types of tissue: Muscle, Nervous, Epithelial & Connective Two or more types of tissue come together to form an organ ◦ Tubular/hollow and Compact/parenchymal Organs A group of organs working together to carry out specific functions form a system. Organisation of the human body  Organisation of the human body Digestive System: digestion of food Excretory System: elimination of unwanted substances Cardiovascular System: transport of substances between organs Respiratory System: supply of oxygen and removal of carbon dioxide Reproductive System: reproduction Muscoskeletal System: stability and movement Nervous System: controls locomotion and bodily function including intellectual function Endocrine System: growth and regulation of body functions The Cell The Cell Membrane  The Cell Membrane Plasma membrane encloses cell and cell organelles Made of hydrophobic and hydrophillic components ◦ Semi-permeable and fluid-like ◦ “lipid bilayer” Integral proteins interact with “lipid bilayer” ◦ Passive transport pores and channels ◦ Active transport pumps and carriers ◦ Membrane-linked enzymes, receptors and transducers Sterols stabilize the lipid bilayer ◦ Cholesterol Cell membrane allows control of intra- &extracellular space  THE ORGANELLES Nucleus ◦ 1 Nuclear envelope ◦ Chromatin and DNA ◦ Nucleolus Mitochondria ◦ Double membrane ◦ Mitochondrial (maternal) DNA ◦ “Power House” of the cell ◦ Food converted into energy ◦ Adenosine triphosphate (ATP) ◦ Consumes Oxygen, produces CO2  THE ORGANELLES Endoplasmic Reticulum ◦ Site where cell membrane and exported material is made ◦ Ribosomes (rough) ◦ Make protiens ◦ Smooth ER- lipids Golgi Apparatus ◦ Recieves and modifies ◦ Directs new materials Lysosomes ◦ Intracellular digestion ◦ Releases nutrients ◦ Breakdown of waste  THE ORGANELLES Peroxisomes ◦ Hydrogen Peroxide generated and degraded Cytosol ◦ Water based gel ◦ Chemical reactions Cytoskeleton ◦ Filaments (actin, intermediate and microtubules) ◦ Movement of organelles and cell ◦ Structure/strengthen cell Vessicles ◦ Material transport ◦ Membrane, ER, Golgi derived vessicles HYDROSTATIC PRESSURE  IONIC STEADY STATES Potassium cations most abundant inside the cell Chloride anions ions most abundant outside the cell Sodium cations most abundant outside the cell MOLECULES RELATED TO CELL PERMEABILITY Depends on ◦ Molecules size (electrolytes more permeable) ◦ Polarity (hydrophillic) ◦ Charge (anion vs. cation) ◦ Water vs. lipid solubility  CROSSING THE MEMBRANE Simple or passive diffusion Passive transport ◦ Channels or pores ◦ Facilitated diffusion ◦ Solute molecule combines with a “carrier” or transporter ◦ Electrochemical gradients determines the direction ◦ Integral membrane proteins form channels Facilitated transport ◦ Assisted by membrane-floating proteins Active transport pumps & carriers ◦ ATP is required ◦ Enzymes and reactions may be required Modes of Transport Carrier-Mediated Transport Integral protein binds to the solute and undergo a conformational change to transport the solute across the membrane (Figure 4-21, pg 93)  Channel Mediated Transport Proteins form aqueous pores allowing specific solutes to pass across the membrane Allow much faster transport than carrier proteins Coupled Transport Some solutes “go along for the ride” with a carrier protien or an ionophore  MEMBRANE PERMEABILITY AND OSMOLARITY Plasma osmolarity influences the volume and shape of red blood cells (RBCs). The volume change is inversely related to the hemoglobin concentration A hypotonic solution causes the cells to take up water while a hypertonic solution causes the cells to loose water HOMEOSTASIS HOMEOSTASIS  BAHS 106 PHYSIOLOGY OF THE NERVOUS and SENSORY SYSTEMS DR. T A TAGOE By the end you should be able to…. Define the nervous system and its organization Describe the functions of the somatic and autonomic nervous system List specific brain regions and their associated function  THE NEURON Neurones are the basic unit of the nervous system and are responsible for the transmission of electrical impulses Dendrites: carry information to the cell body Cell body: integrates information Axon: sends information on to the next unit THE NERVOUS SYSTEM STRUCTURAL CLASSIFICATION OF NEURONES FUNCTIONAL CLASSIFICATION OF NEURONES THE CENTRAL NERVOUS SYSTEM  THE CEREBRUM There are over 100 billion neurones in the brain  THE CEREBELLUM The cerebellum, which stands for “little brain”, is a structure of the central nervous system. It has an important role in motor control, with cerebellar dysfunction often presenting with motor signs. Its function includes Motor Learning Timing of voluntary movement Coordinating involuntary movement Equilibrium and postural movements Brainstem Major Brain Stem Function and Activities Serves as a conduit connecting spinal cord to higher centers of the brain ◦ Sensory ascending pathways (dorsal): Relay nuclei, tracts ◦ Motor descending pathways (ventral): Tracts, motor nuclei brainstem Integrative functions and reflex centers ◦ Cerebellar pathways ◦ Complex motor patterns ◦ Respiratory and cardiovascular activity ◦ Regulation of arousal and level of consciousness Contains important nuclei of cranial nerves ◦ Midbrain: Cranial Nerves 3 and 4 ◦ Pons: Cranial Nerves 5,6,7 and 8 ◦ Medulla Oblongata: Cranial nerves 9, 10, 11 and 12 THE ENDOCRINE SYSTEM  THE LIMBIC SYSTEM Regulates behaviour and emotional responses THE PERIPHERAL NERVOUS SYSTEM ORGANISATION OF THE NERVOUS SYSTEM  THE AUTONOMIC NERVOUS SYSTEM The autonomic nervous system regulates process that take place unconsciously ◦ heartbeat, blood flow, breathing, and digestion ORGANISATION OF THE NERVOUS SYSTEM  Summary The nervous system is organised structurally and functionally The cerebrum can be divided into four lobes The nervous system can be divided into the central and peripheral nervous system The neuron is the basic unit of the nervous system Dendrites bring information to the cell body for synthesis and onward propagation along the axon Various systems and structures in the nervous system mediate specific functions  BAHS 106 PHYSIOLOGY OF THE SENSORY SYSTEMS DR. T A TAGOE By the end you should be able to…. Describe organisation of the nervous system List specific brain regions and their associated function Describe how sensory systems operate Explain the role of action potentials and the synapse in the nervous system THE SENSORY SYSTEM THE SENSORY SYSTEM  SENSORY SYSTEMS Each sensory system is specialised to detect one type of sensory stimulus Each system has a region of cortex primarily dedicated to it There are regions of overlap known as association areas  SENSORY CODING Modality: What type of signal is this? ◦ Sensory receptors are specialised for one type of stimulus although they have a higher threshold for other types of stimuli Location: Where is this signal coming from? ◦ The receptive field refers to the spatial distribution within which a neuron/unit responds to a stimulus Intensity: How strong or frequent is this signal? ◦ Determined by the amplitude of the stimulus applied. Increasing intensity will trigger an action potential, increase firing frequency. Duration: When does this signal start and end? ◦ Continuous stimulation typically leads to adaptation/desensitisation. Sensory Physiology There are four basic classes of receptors which allow us to sense changes in the environment ◦ Mechanical, Thermal, Electromagnetic and Chemical stimuli Visual System: Retina and photoceptors Auditory System: Coclea and hair cells Vestibular system: Vestibule and hair cells Somatosensory system: Skin and mechanical receptors Olfactory system: bipolar neurones Gustatory system: taste cells and receptors Visual System Visual System Optical Illusions Optical Illusions Auditory System Auditory System  SUMMARY Action potentials are a quick flip in the membrane polarity used to transmit signal in the nervous system The ionic components of the nervous system is critical for the conduction of action potentials The synapse is the junction between two neurons Sensory systems are each specialized to detect a specific stimuli  BAHS 106 PHYSIOLOGY OF THE SYNAPSES AND MUSCLES DR. T A TAGOE By the end you should be able to…. Describe the role of the spinal chord in sensory and motor systems State the mechanisms of a simple reflex arc with examples. Introduce functional properties of muscles  THE NEURON Neurones are the basic unit of the nervous system and are responsible for the transmission of electrical impulses Dendrites: carry information to the cell body Cell body: integrates information Axon: sends information on to the next unit There are over 100 billion neurones in the brain  IONS HAVE DIFFERENT INTRA- & EXTRACELLULAR CONCENTRATIONS Intracellular Extracellular Ionic Species Concentration Concentration Sodium (Na+) 15 mM 145 mM Potassium (K+) 150 mM 4 mM Calcium (Ca Calcium (Ca2+ 2+) 70 nM 2 mM Hydrogen ion (proton, 63 nM (pH 7.2) 40 nM (pH 7.4) H+) Magnesium (Mg2+) 0.5 mM 1 mM Chloride (Cl−) 10 mM 110 mM Bicarbonate (HCO3−) 15 mM 24 mM ACTION POTENTIALS ARE SIGNALS TRANSMITTED ALONG AXONS Action potential propagation along unmyelinated axons is slow Action potential propagation along myelinated axons is fast and described as saltatory conduction THE SYNAPSE The synapse is the junction between two neurones  Motor and somatosensory Cortex The motor and sensory region in the cortex are the highest order processing site for motor and somatosensory information respectively SOMATIC NERVOUS SYSTEM The somatic nervous system is a component of the peripheral nervous system associated with the voluntary control of the body movements via the use of skeletal muscles Organisation of the motor system  SPINAL NERVES  The spinal cord extends from the occipital bone of the skull to the second lumbar vertebra.  The spinal cord runs along the inside of the vertebral column.  The spinal cord is protected by three layers of meninges which provides physical stability and shock absorption:  the dura mater, the arachnoid mater, and the pia mater  Thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the head Figure 13.6  SPINAL CHORD PHYSIOLOGY Each segment of the spinal cord is associated with a pair of ganglia called dorsal root ganglia, which are situated just outside of the spinal cord and contain cell bodies of sensory neurons. Dorsal Root: Sensory Neurones Ventral Root: Motor Neurones  REFLEXES Reflexes are stereotyped and a particular stimulus evokes a specific corresponding reflex A subdivision of reflexes are rhythmic in nature, although largely involuntary remain subject to voluntary manipulations ◦ Walking, chewing, swallowing, scratching Motor Neurones Motor neurons are neurons which innervate muscles allowing contractions in response to an action potential 1. Signal from the axon terminal of the previous neuron travels down the motor neuron to the presynaptic axon terminal. 2. Opening of calcium channels in the membrane, allows calcium ions to enter the neuron. These ions interact with the SNARE complext, prompting the vesicles to fuse with the cell membrane. 3. Vesicles release the neurotransmiteer acetylcholine outside the cell, through the process of exocytosis. Acetylcholine reaches the 4. As a result, acetylcholine floods the synaptic cleft, where it can reach the postsynaptic membrane by diffusion. 5. Acetylcholine binds to acetylcholine receptors, also called nicotinic acetylcholine receptors. 6. Sodium channels open to allow sodium into the cell. This causes depolarization, permitting calcium ions to enter the cell and carry out muscle contractions. The Motor Unit Comprises the motor neurone and the skeletal muscle fibers it innervates ◦ Can be large or small Function is directly related to force of contractions ◦ Increase the frequency of action potentials to cause summation ◦ Increase the number of functional motor units by recruiting additional motor units to increase strength  Summary The sensory system sends afferent information to the brain via afferent pathways The motor system sends efferent information to the body via descending pathways A motor unit is made up of nerves and its connected muscle Different types of receptors mediate different sensory information Calcium ions are integral to muscle contraction