HSE208 T2 2023 ULO - Nervous System - PDF

HSE208 T2 2023 ULO TOPIC 1: Nervous System Describe the structure and function of the different types of neurons neurons can be split into 3 divisions: sensory, motor and interneurons. sensory/afferent neurons have the role of carrying information from the periphery of the body towards the CNS. moto...

HSE208 T2 2023 ULO TOPIC 1: Nervous System Describe the structure and function of the different types of neurons neurons can be split into 3 divisions: sensory, motor and interneurons. sensory/afferent neurons have the role of carrying information from the periphery of the body towards the CNS. motor/efferent neurons carry information from the CNS to the appropriate tissues, muscles, cells, etc. Its cell body has multiple dendrites, with a small amount sitting in the CNS, but the majority are in the PNS. interneurons make up 99% of neurons in the human body. They sit entirely in the CNS and have a role as signal changers and integrators. Describe the structure and function of the different types of glial cells in the body we have 5 different types of glial cells, 4 residing in the CNS and 2 in the PNS In the CNS we have: oligodendrocytes, astrocytes, ependymal cells and microglial cells. In the PNS we have: Schwann cells and satellite cells. Function Astrocytes (CNS) Microglial cells (CNS) Oligodendrocytes (CNS) Ependymal cells (CNS) Schwann cells (PNS) Satellite cells (PNS) Support and protect neurons from harm. Maintain chemical environment for nerve impulses. Help with growth and migration of neurons during brain development and forming of the blood brain barrier. Have a role in learning and memory Protect CNS cells from disease by engulfing them. Clear away debris from injured nervous tissue Produce and maintain myelin sheath Lines ventricles of the brain and spinal cord. Helps form cerebrospinal fluid and circulate it. Produce and maintain myelin sheath around a single axon and help regenerate axons Support neurons in the PNS ganglia. Regulate exchange of materials between the neurons and interstitial fluid Explain the structure and function of the myelin sheath and name the glial cells that are responsible for creating the myelin sheath in the CNS and in the PNS The myelin sheath is produced by the oligodendrocytes in the CNS and the Schwann cells in the PNS. The myelin sheath covers the axon portion of a neuron and acts as an insulator. It's role is to help speed up the propagation of action potentials. It is broken up by the nodes of Ranvier. With regards to neuronal communication, describe the factors involved in maintaining the neuronal cell membrane in the resting state When a cell is at rest, it is at a negative resting potentioal of -70 mv. This is due to a high amount of sodium and chloride ions sitting outside of the cell and potassium ions sitting inside the cell. The large proteins within the cell help maintain the negative resting state. We also have leaky channels. Potassium leaks out a bit and sodium leaks in. It cancels each other out to keep it more negative within the cell and more positive outside of the cell Describe the series of events that occur in one section of the cell membrane from the start of the action potential to when the action potential is complete Our sodium potassium pumps are set up to assist in action potentials. Explain the factors responsible for the one-way propagation of actions potentials throughout the entire excitable membrane We have voltage gated channels and they need a certain amount of stimulus to open or close in order to generate an action potential. The sodium gate is initial closed and then opens, allowing sodium ions to flood in and then it closes again. At the end of the depolarization state, that is when the potassium channel opens, allow for potassium ions out during the repolarisation phase. Explain the factors responsible for one-way propagation of action potentials throughout the entire excitable membrane Movement of an axon potential needs to move in direction along an axon The previous part of the membrane is in a refractory period. This means that it cannot respond to another part of stimulus cause it’s just had an action potential go through it. Thus, it can only move forward to sections that have yet to have the action potential pass through it. Describe the series of events that occur during salutatory conduction of a nerve impulse Saltatory = jumping, leaping This occurs in myelinated axons. The axon potentials jump to the unmyelinated part of the membrane The sodium ions move through the myelin membrane to set up the action potential in the exposed section. This allows for more rapid conduction. Draw the components of a chemical synapse and explain how the presynaptic cell communicates a message to the postsynaptic cell The body has 2 types of synapses: chemical and electrical Chemical synapses have synaptic clefts that sits between the pre and post synaptic cell When an acWon potenWal arrives at the synapWc terminal, synapWc vesicles release their contents (neurotransmiYer) into the synapWc cle[. The neurotransmiYer diffuses across the synapWc cle[ and binds to receptors in the membrane of the postsynapWc cell, sWmulaWng a response in the postsynapWc cell. List the components of the CNS and PNS and briefly explain the function of each The CNS in comprised of the brain and the spinal cord The PNS is comprised of the somatic and the autonomic nervous systems. The autonomic nervous systems can then be split into the sympathetic and parasympathetic systems. Our somatic system is voluntary and works to control skeletal muscle contraction as needed. It relies on acetylcholine as its neurotransmitter. It has a single neuron between the CNS and muscle cells, it innervates skeletal muscle cells and works to excite these cells. Our autonomic system is involuntary. It innervates smooth and cardiac muscle, glands and GI neurons, but has no innervation to skeletal muscle. It is excitable or inhibitory, hence the sympathetic and parasympathetic divisions. Our sympathetic system is responsible for increased HR, BP, RR, goosebumps, etc. Our parasympathetic system slows everything down and acts when we're at rest. List the components of the forebrain, hindbrain and brainstem and briefly explain the function of each Forebrain The cerebrum. This can be split into the frontal, parietal, occipital and temporal lobes, each with a different functions such as: perception, skilled movement, reasoning, learning and memory. Can be referred to as the cerebral cortex. Subcortical nuclei. This work subconsciously in the brain to help co-ordinate skeletal muscle activity and the basal nuclei that work to help control movement and posture and also have a role in memory. Limbic system. Can be divided into grey and white matter. Functions: learning, emotions, behaviour, visceral and endocrine roles, memory feeding, sex, anxiety, aggression and olfaction. Diencephalon: has a thalamus which acts as a relay centre for information and has a hypothalamus: important in the limbic system and has roles in thermoregulation, sex and feeding.. Hindbrain Cerebellum: movement, balance and co-ordination Brainstem Comprised of the midbrain, pons and medulla oblongata. Houses all the axons passing through the forebrain, spinal cord and cerebellum Houses nuclei for cranial nerves Contains info the cardio respiratory centres. Has reticular formations. These are throughout the brain and has a role in arousal and attention. Lobes of the cerebrum and their function Frontal Lobe: The frontal lobes are the largest of the four lobes responsible for many different functions. These include motor skills such as voluntary movement, speech, intellectual and behavioral functions. The areas that produce movement in parts of the body are found in the primary motor cortex or precentral gyrus. The prefrontal cortex plays an important part in memory, intelligence, concentration, temper and personality.The premotor cortex is a region found beside the primary motor cortex. It guides eye and head movements and a person’s sense of orientation. Broca's area, important in language production, is found in the frontal lobe, usually on the left side. Parietal Lobe: These lobes interpret simultaneously, signals received from other areas of the brain such as vision, hearing, motor, sensory and memory. A person’s memory, and the new sensory information received, give meaning to objects. Occipital Lobe: These lobes are located at the back of the brain and enable humans to receive and process visual informaWon. They influence how humans process colors and shapes. The occipital lobe on the right interprets visual signals from the le[ visual space, while the le[ occipital lobe performs the same funcWon for the right visual space. Temporal Lobe: These lobes are located on each side of the brain at about ear level, and can be divided into two parts. One part is on the boYom (ventral) of each hemisphere, and the other part is on the side (lateral) of each hemisphere. An area on the right side is involved in visual memory and helps humans recognize objects and peoples' faces. An area on the le[ side is involved in verbal memory and helps humans remember and understand language. The rear of the temporal lobe enables humans to interpret other people’s emoWons and reacWons. Explain the structure and function of the spinal cord and describe the events involved in a reflex arc Our spinal cord sits within our vertebrae column and is butterfly shaped. It is comprised of grey and white matter, with the nucleus sitting in the dorsal root ganglion. Grey matter is filled with interneuons, cell bodies and dendrites of efferent neurons, entering axons of afferent neurons and glial cells. It also has dorsal and ventral horns that project to their respective sides of the body. The white matter that surrounds the grey is made up of groups of myelinated axons. Signals that need to pass through the spinal cord go through the dorsal roots, into the grey matter and exit via the ventral roots to stimulate a response. Describe the general functions of the sympathetic and parasympathetic divisions of the autonomic nervous system Sympathetic: arousal, stress and emergency response, increase in heart rate and breathing, decrease in digestion and runs on noradrenaline (mostly) Parasympathetic: vegetative, non-urgent responses, decreases heart rate and breathing, has an increase in digestive activity and runs on acetylcholine. Distinguish between sensation and perception. Perception: it is our awareness of something, eg: aware that part of the body hurts. Organisation, association, context, memory, meaning and understanding. Sensation: the feeling of something, eg: something feels hot to touch. Sensation is when sensory info reaches our consciousness. Sensory transduction, sensory receptors, raw information. Describe the structure of the eye Our eyes have 3 layers. 1. sclera. This is the outer layer. This forms a connective tissue layer around the eye, except at the cornea. This layer serves as an attachment site for the muscles that move our eye in the socket. 2. Choroid. This is the next layer. This layer works to absorb light rays and becomes part of the iris. In this is ciliary muscle and zonular fibres that to determine the diameter of the pupil and control that amount of light that enters. Our lens sits behind the iris. 3. Retina. This is an extension of the brain, formed in the embryo. It forms the inner surface that contains the neurons, specifically sensory neurons known as photoreceptors: rods and cones. The eyes have 2 fluid filled sacs to provide support: 1. aqueous humor: this sits between the iris and the cornea 2. vitreous humor: this sits between the lens and the retina. Explain the structure of the photoreceptors (rods and cones) in the retina and describe how they transduce light signals into action potentials Rods: peripheral and function beset in low light conditions Cones: mostly central but some sit peripheral. Work best in bright light conditions. 3 types of cones are colour sensitive. They activate with different wave lengths and are sensitive to red, green and blue colours. Light signals between action potentials when photoreceptors interact with bipolar and ganglion cells. Describe the pathway of visual information from the eye to the visual cortex Photoreceptors > ganglion cells > thalamus Explain the role of the association areas in the perception of visual information The association areas of our brains are what makes things make sense. All the things that we see: colour, lines, patterns, etc all need to be interpreted by our brains Describe the structure of the ear External auditory canal: the outer ear where soundwaves enter. Tympanic membrane (eardrum): stretched across the end of the external canal. This vibrates and moves as soundwaves come in. Explain how sound is transmitted through the structures of the ear and describe how hair cells transduce sound waves into action potentials Sound has a frequency that allows us to hear sound waves. Frequency vibrates sound waves. Sound waves have several components: frequency (pitch), amplitude (loudness), location and complexity (timbre) There is the outer part of the ear, this is the part visible to us. You’ve got the inner ear and the cochlea. The cochlea contain the receptors for hearing. The tympanic membrane that sits at the end of the inner ear vibrates as sound wavs come in and moves the bones around it. The stapes moves as the tympanic membrane moves, this is connected to the vestibular part of the ear. This then causes the basilar membrane to move. There is transduction via little hair cells that will then pass the information onto the auditory centre of the brain. The auditory centre then has the job of interpreting the noise and defining what it is. Outline the organisation of neural systems controlling the body Our sensorimotor cortex includes both the sensory and motor cortexes. Motor control is under conscious control. Our muscle fibres contract in order to produce muscle movement. Our primary motor cortex needs incoming information in order to stimulate an action. There is lots of cross over between the brain and the other structures. The brainstem and the cerebellum give their input via the thalamus. Give a brief overview of role of proprioception in the control of movement and describe the structure and function of muscle spindles and Golgi tendon organs Proprioception: Gives us information on the movement and location of our limbs and muscles Muscle spindles: they have intrafusal vs extrafusal fibres (these have a neuron wrapped around them), length (afferent, intrafusal, sit within the muscle bed), alpha vs gamma (efferent, extrafusal, they sit outside the muscle bed). Muscle spindles filled with muscles cells (they are striated). The afferent neurons take info to the CNS about the stretch and contract of the muscles. Golgi tendon organ: attaches muscle to bone. Relays information about tension, inhibits contracting muscles or excites antagonistic muscles Explains the different reactions to the muscle spindle and GTO as the muscle changes. List the motor control centres of the human brain and give a brief description of the role of each centre in the control of movement Primary motor cortex, supplementary motor cortex and somatosensory cortex Motor cortex: adaptive, high level and fine control Motor homunculus: somatotopic map of the primary motor cortex Parietal lobe: space and visual control of prehension Basal nuclei: role in planning and monitoring movement Cerebellum: co-ordination, planning and fine tuning of movement. Highly involved in movement execution and gets lots of info via proprioceptors. Explain what an electroencephalogram (EEG) measures Records the electrical activity of the brain. Describe the pattern of electrical activity in the brain during alert wakefulness, drowsiness and Stage 1, Stage 2, Stage 3 and Rapid Eye Movement (REM) sleep In different parts of the sleep and wake cycle our brains have different levels of activity and have different types of waves. Stages of sleep: Stage 1: sleep (theta waves) Stage 2: sleep (spindles and K complexes) this is our deep sleep stage Stage 3: sleep (delta waves), slow wave sleep with synced electrical activity REM sleep: (rapid eye movement)(possibly mix of theta and beta waves). This is light sleep or awake but drowsy, technically still asleep. Important for body restoration. We remember dreams if we wake during this stage. Outline the physiological activities that occur during NREM and REM sleep REM (rapid eye movement): increases in heart rate, respiration, brain activity and paradoxical sleep. NREM (non rapid eye movement sleep): this is divided into the different stages of sleep List the brain regions involved in regulating states of consciousness Suprachiasmatic nucleus (SCN): sits in the hypothalamus. Main circadian pacemaker Monoaminergic RAS nuclei: reticular activating system (RAS) in the brain stem regions. Neurotransmitters: noradrenaline, histamine and serotonin. Increase excitability of synapses and brain activity. Orexin-secreting neurons: also involved. Acetylcholine secreting neurons Sleep centre (GABAergic neurons): secretes Gaba neurotransmitters, they're inhibitory and supress excitability to let us sleep. Define attention and list the neural mechanisms responsible for attention Attention: our awareness of things, both internal and external. Neural mechanisms: superior colliculus, RAS, pons, frontal and parietal lobes. "temporary set" of neurons. Damage to this can impair awareness. Neurons involved: cerebral cortex, thalamus and basal nuclei. Understand that a “temporary set” of active neurones working together are responsible for determining our conscious experience at any given point in time Our conscious experience refers to our awareness of something, be it internal or external, at any given time. Attention: selective attention, orienting response, pre attentive processing and habituation. Neural mechanism of attention: superior colliculus, reticular activating system (RAS), pons, frontal and parietal lobes Neural mechanisms of conscious experience: “temporary set” of neurons. They are activity in that particular moment for that particular thing we are focusing and on then will swap to a different set for something different. Cerebral cortex neurons are involved with potential input of neurons from other sections. List the regions of the brain involved in motivation Hypothalamus, midbrain, brainstem, spinal cord and cingulate cortex Motivation is about feeling a sense of reward for doing a behaviour. The opposite to this is punishment or lack of reward/pleasure. Give a brief outline of the structure and function of the limbic system Responsible for different emotions Structure: medial prefrontal cortex, cingulate gyrus, orbitofrontal cortex, basal nuclei, hypothalamus, amygdala, fornix, thalamic nuclei, mammillary body and hippocampus Describe the changes that occur in membrane permeability to Na+ and K+ ions when a neuron generates an action potential. At rest, the voltage of the membrane is -70 mV. Typical concentrations for sodium, potassium and chloride are as follows (mmol/L) ION Na+ ClK+ EXTRACELLULAR 145 100 5 INTRACELLULAR 15 7* 150 A permeable membrane means that it has open channels to only one type of ion When there are channels to both Na+ and K+, this will result in the change in voltage of the membrane. When Na+ ions flood in, it brings the membrane potential to +60mV, whereas when K+ ions flood in, it brings the membrane potential to -90mV When a membrane is maintained at the resting value, there’s a constant inwards and outwards leak of ions to keep the balance. The Na+/K+-ATPase pump is what keeps it all in check, for every 3 Na+ pumped out, 2 K+ ions are pumped in. Describe the main differences in structure and function between the sympathetic and parasympathetic divisions of the autonomic nervous system. These 2 systems oppose each other. Sympathetic = fight or flight Parasympathetic = rest and digest The sympathetic system is responsible for stimulating reactions throughout the body, eg: increased HR, goosebumps, increase breathing, etc The parasympathetic system works to slow down the body or works when the body slows down. Eg: lowering heart rate, digestion. Outline, in as much detail as possible, the sequence of events that occur from the time a sound wave enters the outer ear to sensory transduction of this sound wave within the inner ear. Sound is transmitted via the vibration of molecules, it can either be a gaseous, liquid or solid medium, most common is air. When there are no molecules, there’s no sound. The compression and refraction zones that accompany sound can change, the stronger they are, the more amplified the sound is. The faster the vibration, the higher the pitch of the sound. The receptor cells in the ear are located in the organ of Corti and are hair cells. The neurotransmitter released from each cell all band together and switch on protein-binding sites on the terminals of up to 30 afferent neurons. This causes a bunch of action potentials and all the axons band together to make the cochlear portion of the vestibulocochlear nerve. 1. Sound first enters into the external auditory canal (aka outer ear), this section will help to amplify and direct the sound. The sound then bounces off the walls of the ear, resulting in continuous vibrations. 2. Next is the tympanic membrane (aka eardrum), this is stretched across the end of the canal and begins to vibrate as the air molecules are pushed against it. The membrane can move either inwards or outwards depending on the compression or refraction. This membrane will vibrate slowly in response to lower frequency sounds and then vibrate quickly in response to high frequency sounds. 3. The middle ear follows the tympanic membrane. It is an air filled cavity in the temporal bone of the skull. This part of the ear is also connected to the pharynx via the eustachian tube. Sound passes through the tympanic membrane to the middle ear, which then leads sound to be transmitted to the inner ear. 4. The inner ear is a fluid filled space, sound must be amplified to be heard here. The three bones: the malleus, incus and stapes, sit in this space and vibrate to allow sound to be heard here. It is crucial for people to wear ear protection during periods of extremely loud noise as the ears can only handle so much. 5. Sound then goes through the cochlea. It is a spiral shaped structure in the inner ear. It is filled with sensory receptors for the auditory system. The cochlea duct that the receptors sit in is filled with fluid rich in K+ plus concentration and low in Na+. 6. Sound that passes through the cochlea and through the cochlea duct transmit pressure waves, these then cause vibrations that activate the receptors. These vibrations cause the basilar membrane to vibrate. This structure vibrates quite easily due to its stiff nature. 7. Nerve fibres from the cochlea enter the brainstem and connect with interneurons. the timing of low and high frequency sounds are used to determine where it came from. 8. After the brainstem, the information is passed to the thalamus and into the auditory cortex in the temporal lobe. Depending on the frequency, the information will be sent to a different part of the cortex that corresponds with the right frequency. From there, sound is interpreted and understood by the brain. Describe in detail the role of the muscle spindle organ in monitoring muscle length, and briefly contrast its function with that of the Golgi tendon organ. Muscle spindles are stretch receptors and respond to absolute magnitude of muscle stretch and the rate the stretch occurs. These are embedded within a muscle. They consist of peripheral endings of afferent nerve fibres that are all wrapped together in a connective tissue capsule. Muscle fibres inside the spindle are called intrafusal fibres and the skeletal fibres that form the bulk of the muscle and generate its force are called extrafusal fibres. Within a muscle spindle is 2 different types of stretch receptors: 1. Nuclear chin fibre: responds best to how a much is stretched 2. Nuclear bag fibre: responds to both the magnitude of a stretch and the speed that it happens. Extrafusal fibres of a muscle are activated by large-diameter motor neurons called alpha motor neurons. If action potentials along alpha motor neurons cause contraction of the extrafusal fibres, the resultant shortening of the muscle removes tension on the spindle and slows the rate of firing in the stretch receptor. Golgi tendon organs monitor muscle tension. Tension is dependent on muscle length, load on the muscles and the degree of muscle fatigue. GTO’s are endings of afferent nerve fibres that wrap around collagen bundles within the tendons. When muscles contract, tension is placed on the tendon. When this occurs, the GTO’s start up and generate action potentials that go to the CNS. Parts of the afferent neurons from the GTOs go into the brain so that we have an awareness of the forces on our muscles. TOPIC 2: THE ENDOCRINE SYSTEM Describe the role of the endocrine system and its components and define what a hormone is The second system that regulates the human body This system works to maintain long term processes like metabolism, growth and development, repair, reproduction and stress responses. It is comprised of endocrine glands. These secrete hormones to various organs throughout the body. Places within the body that hormones are secreted from are: hypothalamus, pituitary gland, pineal gland, thyroid gland, parathyroid gland, heart, stomach and intestines, skin, kidneys, adrenal glands, pancreatic islets, adipose tissues, testes (men only) and the following 3 are female only: ovarian follicle, corpus luteum and placenta (only during pregnancy) A hormone is a chemical messenger. Hormones enter into the bloodstream to be carried to their target cell. Hormone action can be inhibited, potentiated or counterbalanced by that of another hormone. Majority of physiological functions are controlled by multiple systems and hormones. Explain the chemical structure of amine, peptide and steroid hormones and give examples of each type of hormone Within the body there are 3 types of hormones: amine, peptide and steroid. Amine hormones: derivatives of the amino acid tyrosine. Within this group is thyroid hormones, catecholamines epinephrine and norepinephrine and dopamine. They are water soluble. Eg: tyrosine and tryptophan Chemical structure of an amine: made up of the thyroid hormones and catecholamines. The difference between T3 and T4 is one iodine atom. Peptide and protein hormones: majority of hormones are polypeptides. The shorter ones are refer to as peptide hormones and longer ones are referred to as proteins. Larger proteins that have a carbohydrate attached to them are called glycoproteins. Peptides are less than 200 amino acids in length, proteins are longer. Small peptide eg: vasopressin and glucagon, large peptide eg: insulin and growth hormone, protein eg: LH and FSH. Peptides begin being synthesized on the ribosomes of endocrine cells, they are then moved into the rough ER, it is then put into little packages to be secreted by the golgi apparatus. That whole process is called post translational modification. Eventually the hormone will be secreted by exocytosis to do its hormonal thing. They are water soluble. Steroid hormones: they have a ring like structure. These are primarily produced in the adrenal cortex and the gonads, also from the placenta during pregnancy. Vitamin D is converted in the body as an active steroid hormone. Steroids are derivatives of cholesterol, this makes them lipids and therefore, fat soluble. They are not stored in the cytosol but hang out around the membrane due to be fatty hormones. They will gradually synthesize into the blood and become reversibly bound to plasma carrier proteins. Eg: cortisol, glucocorticoids (adrenal cortex), aldosterone (adrenal cortex), testosterone (testes), estrogens and progesterone (ovaries), etc. Explain how hormones are produced and secreted Hormone action goes through 4 stages: production and secretion, transport, receptor binding and signal transduction pathways. Hormones are communication molecules Stage 1: Production and Secretion: has multiple factors that can trigger this. Plasma concentration of ions and nutrients. When this has changed, it sends a signal to the correct part of the body to secrete the appropriate hormone. Neural mechanisms, eg: stress will then lead to the secretion of cortisol. Environmental, eg: temperature, light or dark area, eg: darkness leads to secretion of melatonin for sleep. Other hormones. Lots of the hormones are regulated by the negative feedback loop, some work on positive feedback but not as many. The negative feedback loop is to help avoid an overreaction of hormones. Stage 2: Hormone Transport: once a hormone has been secreted it needs to go to its target tissue. Peptides can be dissolved in plasma but steroid hormones cannot. Steroid hormones will freely roam around until it does what it is meant to do, others can be bound to a carrier protein but that makes it inactive and need to detach in order to do what it needs to Stage 3: Receptor Binding: they need to find the cell that they are match for to complete their action. These cells will hold the specific receptor that the hormone is a match for. When it responds it will either respond intracellular or on the cell membrane. The intracellular receptor response occurs for lipid soluble hormones. The receptor is contained within the nucleus and the steroid binds to its receptor to trigger a complex that then triggers the transcription of a gene that will eventually lead to mRNA, leading to protein synthesis. For water soluble receptors, they need a membrane receptor as they cannot enter the cell. They need signal transduction processes Stage 4: Signal Transduction Pathways: if the incoming hormone is low in concentration, it needs to help get its information into the cell. Describe how hormones are transported in blood if they are water soluble or water insoluble Peptide and amine hormones are water soluble, meaning that when they enter the bloodstream they will dissolve into it Steroid hormones are fat soluble. Therefore they will not dissolve in the blood and will float around attached to plasma proteins. Outline how hormones bind to receptors of the target cell when those receptors are intracellular or when they are in the cell membrane and, in each case, describe how receptor binding brings about a change within the target cell When hormones are fat soluble, they will pass over the cell membrane and bind with an intracellular receptor. When hormones are water soluble, they need to attach to a receptor on the side of the membrane. This refers to the signal transduction processes. It will bind to a receptor that will then trigger responses within the cell. These cell responses can lead to opening or closing of ion channels, active transport, lipid or glycogen breakdown, protein synthesis, etc. Caffeine can inhibit some cellular responses. Disorders can occur at any of the steps of hormone action. Eg: diabetes. Treatments and inventions can help with this. Describe the structure and function of the hypothalamo-pituitary unit Comprised of the hypothalamus and the pituitary gland. This is the link between the nervous and the endocrine systems. The hypothalamus helps to regulate metabolic processes and autonimic ac\vi\es in the body The pituitary gland has 2 lobes: the anterior (nervous \ssue) and the posterior (endocrine \ssue), both responsible for the secre\on of different hormones. Responsible for: regulate growth and reproduc\on, u\lise nutrients, regulate metabolic rate and coordinate stress response. List the hormones that are produced in the hypothalamus and released by the posterior pituitary gland and outline the function of each The hypothalamus has a different rela\onship with each pituitary gland Hormones are synthesized in the hypothalamus and are then moved to the posterior gland for storage and secre\on The 2 hormones are: oxytocin (reproduc\ve hormone that regulates muscle contrac\on) and ADH aka vasopressin (this causes water reten\on to prevent dehydra\on) List the hormones that are produced by the hypothalamus and transported in the hypophyseal portal blood vessels to the anterior pituitary gland and outline the function of each Hypothalamus hormones act on specific anterior cells to release or inhibit the secre\on of anterior pituitary hormones Hormones here are: cor\cotrophin releasing hormone (CRH), growth hormone releasing hormone (GHRH), somatosta\n (SS), thyrotrophin releasing hormone (TRH), gonadotrophin releasing hormone (GnRH) and dopamine (DA) List the hormones that are produced in and secreted by the anterior pituitary gland and outline the function of each The anterior pituitary is the endocrine gland The hormones released here are regulated by the hormones that come from the hypothalamus Hormones released here: FSH, LH, growth hormone, TSH, prolac\n and ACTH Describe the structure and function of growth hormone including how it interacts with its target cell Growth hormone is a pep\de hormone, aka somatrophin or somatotrophin Water soluble Can circulate in blood bound to a specific protein It binds to a receptor on the lipid bilayer. When it binds to the external, it ac\vates the internal and triggers the transac\on pathway and then the transicp\on of genes There is a peak in GH around puberty and there is remodelling of \ssues around this \me. GH is secreted from the anterior pituitary in response to: ion and nutrient concentra\ons, sleep, stress and exercise and other hormones Regulated by short and long term feedback loops GH: bone growth, anabolic effects on muscle, increases lipolysis, decreases liver glucose uptake, s\mulates IGF-1 secre\on Describe the consequences of too little or too much growth hormone This can be a gene\c thing Too liale hormone: can result in dwarfism. Too much hormone: caused by a liale (non cancerous) tumour that constantly secretes hormone causing an excess. Can happen either before or aber puberty. There’s an increased development of growth in the long bones. Describe the location of the adrenal glands and the endocrine pancreas and explain their role in the regulation of carbohydrate metabolism The adrenal glands sit on the top of each kidney. The endocrine pancreas are a small part of the pancreas. Carb metabolism happens at 2 points in time: absorptive state (glucose ingested from food just after we’ve eaten) and post absorptive state (muscle glycogen breakdown. This is several hours after we’ve eaten) liver glucose production is also occurring. The endocrine pancreas is made up of pancreatic islets, this makes up 1%. They contain different types of cells: beta cells for the production of insulin and alpha cells which produce glucagon. Both of these are peptide hormones. Explain the structure of cortisol and adrenaline, describe where they are secreted from and explain their role in glucose metabolism The adrenal cortex secretes cortisol and the adrenal medulla secretes adrenaline Cortisol is a steroid hormone, meaning it’s fat soluble. It will bind to corticosteroid binding globulin (CBG) and albumin. It will find it’s intracellular receptor. Cortisol is highest first thing in the morning and lowest right before we go to bed. Cortisol during the absorptive state has little to no impact, however during the post absorptive state the following occurs: liver (glycogenolysis and gluconeogenesis), muscle (protein catabolism), adipose tissue (triglyceride breakdown) and inhibition of glucose uptake in the cells (not the brain cause it’s only fuel source is glucose) Adrenaline is a catecholamine and an amine hormone. It’s water soluble and will bind to a receptor on the plasma membrane and will regulate a cellular response via a second messenger. Adrenaline is involved in the fight or flight response. It has no role in the absorptive state, in the post absorptive state it has a role in the muscles, adipose tissue and liver. Explain the structure of insulin and glucagon, describe where they are secreted from and explain their role in glucose metabolism Insulin is released by beta cells and glucagon is released by alpha cells Both peptide hormones and are regulating by glucose concentrations It is also regulated by the ANS (-sym, +para), amino acids (increases) and glucose insulinotropic peptide (feed forward) Both are water soluble and activate with intracellular transduction pathways Insulin in the absorptive state: increases glucose uptake by all tissues, glycogen synthesis in liver and skeletal muscle, increased protein synthesis in the muscles and increased triglyceride synthesis in adipose tissues. Has little to no function in the post state. Glucagon has little to no affect in the absorptive state. In the post state is opposed the action of insulin on the liver. It breaks down glycogen in the liver and muscle to release it back into the bloodstream. Describe how plasma glucose concentrations are maintained in the absorptive and the post-absorptive states During the absorptive state, when the person eats, there’s an increase in glucose and the pancreas responds. This leads to an increase of glucose in the blood. During the post absorptive state, there is a response to decrease in glucose and glucagon is secreted TOPIC REVISION QUESTIONS What 1. 2. 3. are the three different hormone categories? Amine hormones Peptides/proteins Steroids Describe the intracellular signal transduction pathway/s used by lipid-soluble messengers. Give examples of intracellular signal transduction pathway/s that are activated by plasma-membrane receptors. What are the inputs to endocrine glands that control hormone secretion? Describe the anatomical and functional differences between the hypothalamus, and the posterior and anterior pituitary. The hypothalamus secretes and regulates hormones with the pituitary glands. What are the major hormones produced by the adrenal gland and their functions? Describe how the hypothalamo–pituitary adrenal axis functions. Identify the cells that make up the endocrine portion of the pancreas. Pancreatic islets The beta cells control insulin and the alpha cells control glucagon List the factors that control insulin secretion. What effects do the pancreatic hormones have on carbohydrate, lipid and protein metabolism? Topic 3: the cardiovascular system Outline the purpose of the cardiovascular system To pump blood around the body The transport of oxygen, hormones, nutrients and other substances to organs and tissues Transport of heat around the body 5% of blood is within the capillaries. Within the capillaries is where the exchange of waste products occurs Removal of metabolic waste products Describe the organisation of the cardiovascular system Pulmonary circulation: right ventricle to left atrium. Role is to reoxygenate blood and removed CO2 Systemic circulation: left ventricle to tissues in to right atrium. Arteries: carry blood away from the heart. Not all arteries have oxygenated blood Veins: carry blood toward the heart. Not all veins have deoxygenated blood Arterioles have smooth muscle that can contract. Veins in the systemic circuit can hold up to 60% of blood volume. Demonstrate an understanding of the relationship between pressure, flow and resistance Arteriolar radius is important for determining flow. This is the degree of constriction of the smooth muscle cells that surround the arterioles and changes to this can have massive effects on blood flow. Flow of any fluid is from a high to low pressure region. (Hydrostatic pressure: pressure exerted by a liquid in response to a force). BP is the HP pushing through the system Blood Flow = change in pressure / resistance Things that determine resistance: blood viscosity, length of the blood vessels (not as important cause this doesn’t change) and vessel radius Explain the relationship between cardiac anatomy and function Cardiac muscle cells are short, branched, mononucleated and connected to other cells by gap junctions, allowing for rapid electrical activity. The left is thicker ventricle as it needs to eject blood into the systemic circuit The valves open and close due to pressure differences between chambers. This helps to prevent backflow of blood Cardiac muscle cells are made up of: straited cells due to the thick and thin filaments in the sarcomeres, they’re shorter than skeletal muscles, rich in mitochondria but lack sarcoplasmic reticulum. The little gap junctions are important for the effectiveness of action potentials. Our heart needs coordinated contraction to be effective. The SA node is responsible for the depolarisation and contraction of the atria and then spreads to the AV node in order for contraction to begin again. Contrast cardiac action potentials to skeletal muscle action potentials AP in the heart is different to neurons or skeletal muscle cells Initially there’s a depolarisation but an influx of sodium ions. It then plateaus, this is to help avoid summation of contraction as we need a contract and relax pattern in the heart. During the plateau, there is entry of calcium and exit of potassium from the cell. This then changes, repolarisation occurs and potassium exits. Pacemaker potential. This is the cells of the SA node. The heart doesn’t rely on signals from the brain but the SA cells. These are important for regular heartbeat The previous AP triggers the next AP that creates the contract relax cycle Describe the relationship between the ECG and the events of the cardiac cycle Non-invasive way to measure heart electrical activity. Electrical events are caused by the polarisation and the repolarisation of the heart P wave: atrial depolarisation QRS complex: ventricular depolarisation T wave: ventricular repolarisation An ECG can be used as a diagnostic tool Discuss the role of calcium in cardiac action potential generation Calcium has an essential role in the excitation contraction coupling in cardiac cells. The amount of calcium entering the cell determines the strength of the contraction. (all notes for this on goodnotes pages) The cardiac muscle does have a plateau to prevent summation of contraction. Due to the long plateau, there is a longer refractory period. Describe the regulation of heart rate and stroke volume and how these contribute to cardiac output changes CO is the about of blood pumped from the heart per minute. CO = SV x HR HR is dictated by the SA node with input from both parts of the ANS SV is determined by the volume of blood in the ventricles at the end of ventricular relaxation, input to the ventricles from the sympatheWc division of the autonomic nervous system and the pressure already in the arterial system during ventricular contracWon (a[erload). Without SA node input we’d have a heart beat of 100 bpm (diagram pics on goodnotes pages) Explain how blood pressure changes throughout the vascular system There are differences in pressure between the pulmonary and systemic circuit There is a drop in pressure as it progresses through the arteries, arterioles, capillaries, venules and then veins Only 1/3 of the blood volume is taken up by the arterioles PP = SBP – DBP Factors influencing PP: stroke volume, speed of ejection and arterial compliance MAP = CO x TPR or DBP + 0.33PP Describe the role of arterioles in regulating blood pressure and blood flow Arterioles are also known as resistance vessels due to the presence of smooth muscle, which allows narrowing of the vessel. Arterioles can dilate or contract to regulate the flow of blood into the capillary bed. Arteriolar radius can be regulated by both intrinsic (local) and extrinsic (nervous and endocrine) mechanisms. Responsible for the greatest amount of TPR Determine blood flow via either vasoconstricWon or dilaWon Has spontaneous acWvity Local control: mechanisms independent of nerves and homones External control: nervous and endocrine systems. VasoconstricWon or vasodilaWon occurs depending on what receptor is present. More on goodnotes slides Illustrate how substances move in and out of capillaries >>>>>>>>>>>> The capillaries are the site of exchange between the blood and the surrounding tissues. The capillary walls are very thin to enhance the movement of fluids and other substances in and out of the capillary. Due to the pressures present, fluid tends to move out of capillaries at the arteriolar end of the capillary and back into the capillary at the venule end. More on goodnotes slides Describe how veins and venous return influence cardiovascular function Veins are the last part of the system Their role is to return the blood to the heart. They have valves to aid in venous return Venous pressure is important in regulation of venous return and stroke volume Determinants of venous pressure Pressure is determined by: venous fluid volume and the complaisance of the walls (change in volume/change in pressure) Skeletal muscle contraction decreases compliance. This puts pressure on the blood vessels Explain how blood flow can be regulated at the local and systemic level The functions of the heart and the vascular system need to be integrated and coordinated to optimise the delivery of blood to the organs in a way that matches the body’s needs. The needs of the body change throughout the day with the different activities that we undertake. This coordinated control is achieved through the actions of the nervous and endocrine systems with some of the control occurring at a local level. To facilitate blood flow to organs, it is important to maintain a consistent and stable mean arterial pressure (MAP). Steady state blood flow means that there’s an equal amount of flow going to different organs Arteriolar dilation and constriction occurs when there is one organ needing more or less blood flow At a systemic level is the regulation of blood pressure Flow = change in pressure/resistance CO = MAP/TPR MAP = CO x TPR BP is tightly regulated to ensure adequate perfusion of organs Big diagram for this on goodnotes Discuss short term (neural) control of blood pressure In the short term, blood pressure is regulated by neural mechanisms. Baroreceptors play a key role in detecWng sudden changes in blood pressure and the autonomic nervous systems plays a key role in the response. Baroreceptors are receptors that detect changes in pressure. There are some in the aorta and the Cortaid artery. This artery is connected to the brain Discuss mechanisms involved in long term regulation of blood pressure In the long term, changes in blood pressure are regulated by changes in blood volume. TOPIC REVISION QUESTIONS List the structures through which blood passes from systemic veins to systemic arteries. Name a vein that carries oxygenated blood. Name the major factor regulating resistance to blood flow and the blood vessels that contribute most to the regulation of resistance. What causes AV valves to shut? What causes the second heart sound? Describe (in sequence) the structures through which the wave of depolarisation travels in the heart. Draw a cardiac muscle cell action potential and explain its ionic bases. Explain what the term pacemaker potential means. What causes this phenomenon and how can it be regulated? Compare and contrast the sequence of events occurring during Excitation– Contraction coupling in cardiac and skeletal muscle. Explain why summation of contractions cannot occur in cardiac muscle. Draw a diagram of the pressure changes in the left atrium, left ventricle, and aorta throughout the cardiac cycle. Show when the valves open and close, when the heart sounds occur, and the pattern of ventricular filling and ejection. Are both sets of valves ever opened or closed at the same time during a cardiac cycle? Calculate the stroke volume when each cardiac cycle takes 0.5 sec and the cardiac output is 7.2 l/min. What are the two major factors influencing force of ventricular contraction? Calculate mean arterial pressure and pulse pressure if systolic and diastolic blood pressure are 140 and 80 mmHg, respectively. Describe the intrinsic and extrinsic mechanisms regulating arteriolar radius. Discuss the factors involved in regulating net fluid movement across the capillaries. List three factors that increase venous return. Describe the mechanisms involved with the short and long-term regulation of blood pressure. Topic 4: Respiratory System Outline the functions of the respiratory system Ventilation: “ the bulk flow of air along a pressure gradient between the atmosphere and alveoli. This includes both inspiration and expiration” VE = VT X Rf Ve = minute ventilation. The total volume of air that enters the lungs within one minute Vt = tidal volume. The volume of air typically inspired or expired in a single breath Rf = respiratory frequency. The number of breaths in one minute. How much air we breathe is a result of how deep and how much we breathe. Gas exchange occurs at the alveoli List the muscles responsible for ventilation Inspiration: sternocleidomastoid and scalenes, pec minor and external intercostals When the diaphragm contracts and flaYens, the base of the chest lowers. The external intercostals contract to pull the ribs up and away from the centre of the body. In high venWlaWon, addiWonal muscles also assist. The effect is the same for all muscles: To increase the volume of the thoracic cavity. Expiration: internal intercostals and abdominals By comparison, expiraWon is generally a passive process. Inspiratory muscles relax and elasWcity of the lung causes it to recoil inwards. Describe how tidal volume and respiratory frequency may vary to alter minute ventilation (VE) Changes to the rate of breathing can affect ventilation. Airway dilation (bronchioles): changes to the radius of the airways. This is determined by the smooth muscle of the airways and mucous accumulation. The larger the dilation, the easier the airflow. Asthma is an example of airway obstruction. Pressure gradient: between the lungs and the pleural cavity. Air into the lungs first needs the body to manipulate its internal pressure within the lungs so that it’s lower than the atmosphere. Transmural pressures: our thoracic cavity protects organs however also in this space, pressures occur to help drive ventilation with the respiratory muscles. The thoracic cavity can be split into the following: mediastinum, a membranous barrier including major vessels, airways and the heart. In our bodies, there are 4 pressure types to be considered and are influenced by the inspiratory muscles: - Atmospheric pressure (Patm): pressure of atmospheric air, 760mmHg at sea level - Intra-alveolar pressure (Palv): the pressure within the alveoli. 760 mmHg at rest after expiration. For alveoli to inflate with air, this pressure must be lower then Patm. - Intrapleural pressure (Pip): the pressure within the thoracic cavity. At rest, pressure lower than the atmosphere, roughly 756mmHg at sea level - Transpulmonary pressure (Ptp): Ptp = Palv – Pip. Often 4 mmHg at rest. Air will flow from higher to lower pressures. During the beginning of inspiration, we are neither breathing in or out. At this point, the lung is undergoing elastic recoil which prevents them expanding. For the alveoli to inflate, Palv needs to be less than Patm but currently 0 Mid inspiration results in muscle contraction of the inspiratory muscles. This forces is beyond that of the elastic recoil and increases the volume of the thoracic cavity and intrapleural space. This results in Palv being lower then Patm and so air flows in and inflates the lunges. As inspiration ends and expiration begins, the muscles contract but elastic recoil increases dur to the lungs being full of air. Mid expiration. This is when inspiration has ceased and elastic recoil causes the lungs and thoracic cavity to draw in. Air in the alveoli compresses, increasing Palv. This causes Palv to be greater than Patm and expiration occurs. Explain the factors that contribute to the ‘work’ of breathing Compliance is aka the work of breathing Compliance can be defined as: “the magnitude of the change in lung volume produced by a given change in transpulmonary pressure”. It is also view as how easy the lung can inflate. The 2 determinants of lung compliance is elasticity and surface tension. The greater the elasticity, the less work of breathing required. Elasticity of a lung can reduce in the presence of disease and scar tissue. Shallow breathing can be a sign of decreased lung elasticity, as well as elevated FEV1/FVC ratio Compliance of the lung determines how much the lung expands at any given Ptp FVC (Forced Vital Capacity): The maximal volume of air a person can forcibly exhale after full inhalation FEV1 (Forced Expiratory Volume – 1 s): The volume of air forcibly expired in the first second of breathing out. FEV1/FVC ratio: FEV1 divided by FVC. This can be expressed as the percentage of air forcibly expired that can be breathed out within the first second. In a healthy population, this value is about 0.8 (80%). Surface tension is the tendency for alveoli to collapse. Resistance is the 3rd type of work. Minor factor to work through in normal circumstances. It is influenced by the resistance of airways with little cartilage, thus influenced by the smooth muscle. Smooth muscles in the airways are responsible to: adrenaline, alveolar CO2 gas tension and irritants. Ventilation requirements at rest are quite low. However, required minute ventilation and the associated work of breathing during exercise (particularly intense prolonged exercise) can increase greatly: Rest = ~8-12 L.min-1 of air (~5% total body oxygen consumption) Exercise = ~100-250 L.min-1 (~20-25% total body oxygen consumption) Consider the physiological changes that are required to compensate for this extra requirement. In normal populations, how will the activity of respiratory muscles change? What will happen to the diameter of airways? What about rate or depth of breathing? Apply Fick’s law to describe factors that influence diffusion of gases Partial pressures influence the gas exchange across the membranes within the body. Aka diffusion down the pressure gradient. The partial pressure for any atmospheric gas (X) is dependent on various factors: Barometric pressure (PB): The air pressure of the local environment. This is 760 mmHg at sea level. The fractional concentration of the individual gas within the total mixed gas (FX). For example, at sea level, the concentration of air gases is: o O2 ≈ 21% o CO2 ≈ 0.03% o N2 ≈ 79% When we inspire, gases are diffused across the alveolar surface (O2 in; CO2 out). O2diffuses into capillaries within the lung and dissolves in the solution (i.e. plasma). Please note that a gas concentration ([X]) is proportional to PX. Gases are transported in pulmonary and systemic circulation to cells where O2 is used in cellular respiration by mitochondria, and this metabolism produces PCO2, which diffuses into the plasma. Gases then follow circulation back to lungs where CO2 diffuses out into the alveoli and then environment and O2 is replenished. Flick’s Law addresses the factors influencing gas diffusion: Lung surface area (50-100 m2). The larger the surface area of a membrane, the faster the rate of gaseous diffusion. This surface area generally increases with height! Although, this working surface area can also reduce with scarring. Thickness or diffusion distance (0.2-0.5 mm). The thinner the surface, the faster the rate of diffusion. This is why membranes for cells requiring high volumes of diffusion are very thin. ΔP – Partial pressure gradient. The greater the difference is pressures between surfaces, the faster the rate of diffusion. The change in partial pressures can be seen in the previous image. Dgas – Gas diffusion constant Gas diffusion constant is influenced by the gas solubility and the molecular weight of the gas. CO2 has one more carbon atom the O2. Explain the mechanisms responsible for transport of O2 and carbon dioxide (CO2) in blood Oxygen and carbon dioxide travel through the blood differently. O2 will diffuse from the alveolus, across the capillary wall and then will then travel dissolved within the plasma. 1.5% of O2 remains with in the plasma as dissolved O2, measured as PO2 Most the O2 will bind to haemoglobin as it goes towards the targeted tissues. The process for gas transport of CO2 is more complex. CO2 is produced by the cells, then dissolved CO2 diffuses through the capillary wall for transport to the lungs. A minor amount remains dissolved within the plasma (roughly 10%), whereas the rest enters red blood cells and follows one of three fates: Remains as dissolved CO2 within red blood cells. Binds to haemoglobin, similar to O2 (roughly 30% of total transported CO2). Combines with H2O (facilitated by carbonic anhydrase) to form carbonic acid. This dissociates to bicarbonate (HCO3-) and hydrogen (H+) ions. Bicarbonate ions (which include CO2) then leave the red blood cell in exchange for a chloride ion and circulate within the plasma (roughly 60% of total transported CO2). When this blood reaches the alveoli, the opposite processes occur to produce free dissolved CO2 within the plasma to diffuse through the capillary and alveolus walls. Due to the more complex process, gas transport of CO2 is slower than O2. Haemoglobin exists on red blood cells as a tetrameric globular protein; a four-sided structure containing four Haem groups (each containing one Fe2+) that each bind individual oxygen molecules. Haemoglobin undergoes cooperative reversible binding of up to four O2 molecules. In this case, cooperative means that after a single O2 molecule has bound to a Haem group, the structure changes shape slightly which increases the haemoglobin affinity to bind the remaining three O2 molecules. This makes the process more rapid as it continues. The same cooperative function occurs during O2 molecule unbinding too. Appropriate availability of haemoglobin results in it carrying 98.5% of O2 in whole blood. This is: 150 g/L in men and 130 g/L in women This supply of haemoglobin increases overall O2 carrying capacity, thereby increasing energy efficiency and reducing required ventilation. The figure below presents the haemoglobin-O2 dissociation curve. A sigmoid (S-shaped) curve presents for the percentage of total circulating haemoglobin saturated with O2 at different partial pressures of O2 (PO2) in the blood. Only dissolved gas contributes to the circulating PO2 and this value changes at different sites within the body (refer back to Figure 4.2.1 near the top of this page). Due to cooperative binding, haemoglobin saturation rises at an increasing rate then slows towards maximum saturation. This is because there is less available free haemoglobin for binding of dissolved O2. Therefore, haemoglobin saturation increases by little when at greater PO2. 100 mmHg is the PO2 in arteries leaving pulmonary circulation and 40 mmHg is PO2 after delivery to tissues. Remember that CO2 binds to haemoglobin from the tissues and roughly 30% of CO2 transport to the lungs is bound to haemoglobin. Describe the Bohr Effect and explain how it facilitates O2 transport to different areas of the body The Bohr Effect describes the changing properties of haemoglobin throughout the circulation. That is, there is an altered affinity of haemoglobin for O2 due to the effect of other factors/conditions. Factors such as increased PCO2, hydrogen ion (H+) concentration (increased acidity/reduced pH), and temperature are continuously exerted on the blood at the tissue level. Such factors are by-products of metabolism. Haemoglobin is exposed to the environment as it passes through tissue capillaries, reducing its affinity for O2 and resulting in haemoglobin offloading a greater volume of O2. This is reflected in a right-shift to the standard curve for haemoglobin saturation. List the parts of the central nervous system involved in control of respiration The control of the muscles that control respiratory is controlled via neuron excitation. Nerve innervation for these muscles is dependent of where breathing is at rest or is active. Respiration is mainly controlled within the brainstem and is governed by negative feedback loops. But it is not solely controlled here, as thoracic muscle stimulation is driven by the respiratory centres located in the pons and the medulla oblongata. All inspiratory neuron groups and linked and, somewhere within these groups, they contain self-exciting connections (may work without conscious control – e.g. during sleep). These connections produce rhythmic synchronised inspiratory activity. All expiratory neuron groups are linked and contain self-exciting connections (e.g. driving expiration during intense exercise). Although, if self-excitation is too weak and doesn’t reach the threshold for action potential and muscle stimulation, expiration remains a passive uncontrolled process. Limits to the duration and strength of inspiration and expiration are controlled by: o Inhibitory connections between inspiratory and expiratory neuron groups (in both directions). You can’t breathe in and out at the same time! o Feedback occurs via: § § Stretch and irritant receptors. Pulmonary stretch receptors in the tracheal and bronchial smooth muscle inhibit inhalation to prevent over-inflation. Circulatory and medullary chemoreceptors. This provides the common control theory that will be discussed below. Describe the roles of central and peripheral chemoreceptors in control of respiration 2 types of chemoreceptors work here: peripheral and central. Peripheral receptors are located on the carotid artery and the aortic bodies. Chemoreceptors in the carotid bodies are located near carotid sinus baroreceptors. They are sensitive to, and respond to, increases in the partial pressure of arterial CO2 (PaCO2) and H+ concentrations. Although, this contributes only about 20% of respiratory drive in normal conditions. They also respond to reductions in arterial O2 (PaO2)