Compendium 8 Notes PDF

Compendium 8 Notes Lecture 1 Nervous system terminology - Neuron (nerve cell): basic structural and functional unit of the nervous system - Neuroglia: major supporting cells of neurons - Axon: nerve fibre - Nerve: bundle of axons (or nerve) fibres and their sheaths (outer cover...

Compendium 8 Notes Lecture 1 Nervous system terminology - Neuron (nerve cell): basic structural and functional unit of the nervous system - Neuroglia: major supporting cells of neurons - Axon: nerve fibre - Nerve: bundle of axons (or nerve) fibres and their sheaths (outer coverings) - Sensory receptors: separate specialised cells which detect temperature , pain, touch, light, sound, odour or other stimuli - Action potential: electronic signal, the way information travels in the nervous system - Effector organ or effector cell: the organ, tissue or in which an effect or action takes place - Synapse: junction of a neuron with another cell, this might be a muscle cell or another neuron Functions of the nervous system 1. Receive sensory input - Internal (monitoring homeostasis) - External (the environment outside the body) - The bodies way of making sense of its environment by using specialised cells 2. Integrate information - This occurs in the central nervous system - The body making sense of the sensory input so it can produce an appropriate response - The response may be immediate or it might be delayed, stored in the body 'for future reference' or completely ignored - This is depending on the type of stimulus the body reveives 3. Motor output - The body's response is relayed by the motor output - For example, the contraction of muscles or glands 4. Maintaining homeostasis - All of the above come together to achieve homeostasis, keep the body in equilibrium - The nervous system stimulates or inhibits activities to maintain homeostasis 5. Establish and maintain homeostasis - Thinking, memory and creating different types of emotion, having consciousness and making appropriate decisions Divisions of the nervous system 1. Central nervous system - Brain - Spinal cord - The decision makers of the body - These structures are very well protected by our skeleton 2. Peripheral nervous system - Sensory receptors - Cranial nerves -- 12 pairs - Nerves from brain - Spinal nerves -- 31 pairs - Nerves from spinal cord - Ganglia -- collection of neuron cell bodies outside of the central nervous system - Plexuses -- extensive network of usually axons outside of the central nervous system Functional divisions of the nervous system - The nervous system divides into the central and peripheral nervous system - These two systems interact - PNS senses something, sends message to CNS, CNS responds and sends a motor output through the PNS - PNS - Somatic nervous system - Sensory (afferent) - Motor (efferent) - Autonomic nervous system - Sensory (afferent) - Motor (efferent) - Sympathetic (Fight or flight) - Parasympathetic (Rest and digest) - Enteric nervous system - Sensory (afferent) - Motor (efferent) Somatic vs autonomic nervous system - Somatic - Voluntary and under conscious control - Action potentials in the motor neurons travel from the CNS to skeletal muscles - Single neuron system, one synapse - Cell bodies are located in the CNS - Skeletal muscle contractions are the response - Myelinated axons - Autonomic - Involuntary and under unconscious control - Action potentials in the motor neurons travel from the CNS to smooth or cardiac muscle, or glands - Two neuron system with two synapses - Cell bodies of the first neuron are located in the CNS and the second are in an autonomic ganglion - The target tissues can be stimulated or inhibited - The preganglionic are myelinated and the postganglionic are unmyelinated Enteric nervous system - Nerve plexus within the walls of the digestive tract - Sensory neurons connect the digestive tract to the central nervous system - Autonomic nervous system motor neurons connect the central nervous system to the digestive tract - Enteric neurons are confined to the enteric plexus - The digestive tract must be under very specific control to ensure muscle contractions and secretions are happening at the right times - Functions - Stimulate/inhibit smooth muscle contraction - Stimulate/inhibit gland secretion - Detect changes in the contents of the lumen - If its acidic it may stimulate the production of different types of enzymes Sensory vs motor division - Sensory - Also called the afferent division - Detects internal and external environmental stimuli - Collects input from specialised sensory receptors (neural cells or specialised cells) - Transmits input as electrical signals to the CNS (nerves) - The cell body of a sensory neuron is outside the CNS (dorsal root ganglion) - Motor - Also called the efferent division - Transmits electronic signals from the CNS to the effector (e.g., muscles and glands) - The cell body of the motor neuron is located in the CNS Autonomic nervous system (motor division) - Sympathetic - Fight or flight response - Thoraco-lumbar region of the spinal cord - Prepares the body for physical activity - Primes the body to act in threatening situations - Shorter neuron pathway leading to a faster response - Complementary to the action of the parasympathetic response - E.g. increased heart rate, increased respiratory rate, sweating and pupil dialation - Parasympathetic - Rest and digest/feed and breed response - Cranio-sacral region of the spinal cord - Relaxes the body inhibiting high energy functions - Longer neuron pathways meaning there is a slower response - The body feels relaxed - Complementary to the action of the sympathetic response - E.g., stimulates digestion, defaecation, diuresis(increased urine production), pupil contraction Lecture 2 Cells of the nervous system - Neuron - About 100 billion in the body - The structural and functional units of the nervous system - They collect and receive information from the external and internal environment, integrate it and send an appropriate response to the target - Classified based on structure and function - Neuroglia - 10-50 times more neuroglial cells, they make up half of the brains weight - Supporting cells (support the neurons) - Six different types, 4 in the CNS and 2 in the PNS Neuron - Highly modified to perform its function, electrically excitable as information travels through the body via electric impulses - Three main parts - Neuron cell body (soma) - Nucleus, nucleolus - Nissl bodies (rough endoplasmic reticulum) - Protein production - Golgi apparatus - Mitochondria - Other cell organelles - Dendrites - Highly branched extensions of the cell body - Cytoplasmic extensions - Generate an electric current when stimulated - Flow of current moves from the dendrites tip to the cell body - Have dendritic spines which are further extensions of the dendrites - The dendrites main function is to collect the stimuli - Axon - Often one arising from axon hillock (the cone shaped area where the cell body meets the azon) - The trigger zone is the axon hillock and the initial segment - The initial segment is where the axon hillock narrows and this is where action potentials are generated - Can vary in length from a few millimetres long to a few meters long - They can be branched (collateral axon) - Presynaptic terminal/axon terminals are the endings of axons - They are highly branched extensions of the axon - Terminal boutons, synaptic knobs - The ends of the axon terminals which are swollen, this is where the neurotransmitters are stored - Myelin sheath - Not all axons are myelinated but some are - The myelin sheath is made up of Schwann cells - A neuroglia cell - These cells surround themselves around the axon - The nucleus of these cells is located peripherally - Node of Ranvier - Gaps between the schwann cells where the axon is left unmyelinated - Unidirectional flow of impulse - Collects stimuli through dendrites, passes through axons to axon terminals Neurons -- structural classification (add some illustrations) - Multipolar (many) - The cell body has many extensions, lots of dendrites and an axon, it gives rise to many processes and is therefore a multipolar neuron - One cell body - Many dendritic processes and an axon - Motor neurons and interneurons - Bipolar (two) - The cell body has 2 extensions, one gives rise to dendrites and one gives rise to the axon and therefore is a bipolar neuron - One cell body and two processes, a dendrite and an axon - Specialised sensory neurons - Only found in Retina of the eye and nasal cavity - Unipolar/pseudo unipolar (one) - Only gives rise to one cell body extension, the axon and is therefore a unipolar neuron - One cell body and only one process, axon - Dendrites connected to sensory receptors, axon terminals to CNS - Sensory neurons Neurons -- functional classification - Sensory neuron - Conduct an action potential from sensory receptors to the central nervous system - Afferent neuron - Moto neuron - Conduct an action potential away from the central nervous system towards muscles or glands - Efferent neuron - Inter neuron - Conducts an action potential within the central nervous system from one neuron to another Neuroglia -- CNS - Astrocytes - Star shaped - Most numerous type of neuroglial cells in the brain - Highly branched cytoplasmic processes with end feet which surround blood vessels - Synaptic support, scaffold CNS cells and capillaries, control the blood brain barrier's permeability, homeostasis of the central nervous systems ions, form glial scar during injury - Regulates what can leave the blood and come into the brain tissue - Due to the presence of microfilaments in the cytoskeleton the astrocytes are able to support nerve neurons and blood vessels - By forming scar tissue around injury they stimulate healing but limits the regeneration of neurons - Synthesises, absorbs and recycles neurotransmitters (synaptic support) - Ependymal cells - Line the ventricles of the brain and the central canal of the spinal cord - Ciliated simple cuboidal or columnar, cilia to circulate the cerebral spinal fluid - Production, secretion and regulation of cerebral spinal fluid - Microglial cells - 10-15% of cells in the brain are microglial - Smallest of the neuroglial cells - Oval in shape with finger like projections - Resting microglia: patrol the central nervous system - Active microglia: becomes active when it detects injury or pathogens - Become active, mobile and phagocytic in response to inflammation - Phagocytose foreign substances, necrotic tissue and pathogens - Oligodendrocytes - Have cytoplasmic extensions that wrap around the axon forming the myolin sheath - Each cell can enclose multiple axons - Insulation of axons in the central nervous system - One oligodendrocyte can cover many axons Neuroglia -- PNS - Schwann cells - Have cytoplasmic extensions that wrap around the axon forming the myelin sheath - Each cell forms a part of the sheath around one axon - Insulates axons in the PNS - Leaves nodes of Ranvier in between - Satellite cells - Surrounds cell bodies in sensory and autonomic ganglia - Provides support and nutrition to cell bodies - Protects the cell from heavy metal poisons e.g. pb, hg Myelinated vs non-myelinated axons - Myelinated - Schwann cells (PNS) and oligodendrocytes (CNS) wrap repeatedly around the axon - Nodes of Ranvier - Saltatory conduction of electrical impulses - Faster nerve impulses - Unmyelinated axons - Axons rest in invaginations of Schwann cells (PNS) and oligodendrocytes (CNS) electrical impulses travel as a continuous wave - Thinner \>1micron, lower speed of nerve impulse conduction Grey matter vs white matter - Grey matter - Consists of neuronal cell bodies, dendrites, axon terminals, ganglia, unmyelinated axons, glial cells and synapses - Located on the periphery (outer cortex), in cerebrum, cerebellum, brainstem, diencephalon, deeper tissues in the brain (nuclei) - In the middle of the spinal cord, 'H' shaped grey column - White matter - Very few cell bodies, mainly long-range myelinated axons, deeper tissues (subcortical), nerves - White due to the myelin sheath - Lies on the inner side of the brain but the outer part of the spinal cord Lecture 3 Electrical signals - Electrical impulses: environment (external and internal), emotions, conscious thought, memory, actions of glands and muscles - Terminology - Resting membrane potential - Action potential - Graded potential - After potential - Depolarisation, repolarisation, hyperpolarisation - Membrane potential: measure of electric properties of a cell membrane - The membrane potential is determined by ionic concentration difference across the plasma membrane and permeability of the plasma membrane Cell membrane -- ionic concentration - Selectively permeable - Continuous communication between the intracellular and extracellular environment - Excitability in cells - Ion movement across the cell membrane - Difference in ionic concentration ( particularly for Na+ and K+) across the cell membrane - Na+/K+ pump - Higher concentration of Na+ and Cl- outside of the cell - Higher concentration of K+, proteins and PO4-3 inside the cell - If we compare extracellular with the intracellular environment they are electrically neutral - There is an equivalent total of cations and anions Cell membrane -- ion channels - Selectively permeable - This is based on size, solubility, polarity, gradient, cell requirement, ect. - As ions are charged they cent diffuse through the bilayer and must pass through specialised channels - Non-gated ion channels - Also known as 'leak' ion channels as they are always open - Ion specific - Movement based on the concentration gradient - The cell membrane has more K+ and Cl- leak ion channels compared to Na+ leak ion channels - There is more movement of potassium then sodium - Gated ion channels - Gates are closed and require signals to open them - Ion specific - Depending on the stimulant the gates can be classed as: - Ligand gated ion channels - Opened when a chemical attaches to the channel - Voltage gated ion channels - Opened by stimulation from a difference in charge - Other gated ion channels - Other stimuli such as temperature or pressure Resting membrane potential - Resting membrane potential is the difference in charge across the cell membrane in a resting cell - Measured in millivolts (mV) - The resting membrane potential of neurons is -70mV (considered a small magnitude) - The intracellular side is more negative compared to the extracellular side and this difference makes the plasma membrane polarised - Resting membrane potential is caused by the leak of ion channels and the Na+/K+ pump - Other cells have a resting membrane potential, it's not always -70mV Establishing a resting membrane potential (maybe add pictures to make it make sense) 1. In a resting cell there is a higher concentration of K+ inside the cell membrane and a higher concentration of Na+ outside of the cell membrane. Because the membrane is not permeable to negatively charged proteins they are isolated to the inside of the cell membrane 2. There are more K+ leak channels than Na+ leak channels. In the resting cell only the leak channels are opened; the gated channels are closed. Because of the ion concentration differences across the membrane K+ diffuses out of the cell, down its concentration gradient and sodium diffuses into the cell down its concentration gradient. The tendency for K+ to diffuse out of the cell is opposed by the tendency of the positively charged K+ ions to be attracted back into the cell by negatively charged proteins 3. The sodium potassium pump helps maintain the differential levels of Na+ and K+ by pumping three Na+ out of the cell in exchange for two K+ into the cell. The pump is driven by ATP hydrolysis. The resting membrane potential is established when the movement of K+ out of the cell is equal to the movement of K+ into the cell Action potential -- 1 - An action potential is how a neuron sends information down an axon, away from the cell body, to the effector - Multiple step process - Resting membrane potential - All gated Na+ and K+ channels are closed - K+ leak channels are open and allow movement of K+ out of the cell which creates negative intracellular change causing membrane potential - The Na+/K+ pump also contributes to membrane potential - Outside the cell is positive and nside the cell in negative Action potential -- 2 - Depolarisation - When the cell gets stimulated depolarisation occurs - Na+ voltage gated channels open and Na+ moves into the cell and inside the cell becomes more positive, due to the concentration gradient the Na+ wants to rush into the cell - K+ voltage gated channels are closed - Membrane potential becomes more positive (no longer -70mV, it increases past 0) - Depolarisation starts from a stimulus which must be strong enough to meet threshold and only then can an action potential occur (around -55mV) - Outside the neuron becomes negative and inside the cell becomes positive - Towards the end of depolarisation K+ channels start to open but they are slow to open Action potential -- 3 - Repolarisation - Na+ voltage gated channels close - K+ voltage gated channels open and K+ moves out of the cell and the intercellular side becomes more negative - Membrane potential becomes more negative - Extracellular environment becomes more positive - After repolarisation is established the potassium voltage gated channels close (they are slow to close) Action potential -- 4 - End of repolarisation, and the afterpotential - Na+ voltage gated channels close - K+ voltage gated channels close as well but they close slowly so K+ continues to leave the cell resulting in afterpotential - Afterpotential is where the membrane potential becomes very negative (-75/80mV) Action potential -- 5 - Na+ gated channels are closed - K+ gated channels are closed - Resting membrane potential is re-established (-70mV) by Na+/K+ pump (an active process against the concentration gradient) which redistributes ions as all Na+ and K+ gated channels are closed Relevant concepts - Depolarisation: where the membrane potential becomes more positive, i.e. the inside of the cell becomes more positive e.g. -70mV -\> -30mV - Repolarisation: membrane potential returns to normal, the outside of the cell becomes more positive - Hyperpolarisation: when the membrane potential becomes more negative i.e. the inside of the cell becomes more negative e.g. -70mV -\> -75mV - Afterpotential: a short period of hyperpolarisation of an action potential - Graded potential: short lived, localised changes in membrane potential - Can lead to action potentials - Often occur in dendrites or the cell body of a neuron - Ability to summate (multiple small graded potentials will add up) - Decremental -\> not able to transfer information over a long distance - All or none principle - If the stimulus is weak there will be no action potential but once threshold has been reached all action potentials will have the same magnitude. They won't be bigger given a stronger stimulus - A stronger stimulus will only result in increased frequency - Refractory period: from the point of threshold until the membrane potential has returned to -70mV after the afterpotential - Absolute refractory period: depolarisation and repolarisation, there is no chance an action potential can be triggered during this time - Relative refractory period: afterpotential, with extremely strong stimuli, action potentials could be generated in this time - Another action potential cannot be generated during the refractory period - The cell membrane needs to re-establish its resting membrane potential before it can start another action potential Propagation of axon potentials (visuals could be helpful) - This takes place in unmyelinated axons only - Following depolarisation, each segment of the axon membrane becomes repolarised - The propagation of the action potential occurs in one direction - 'Mexican wave' effect Saltatory conduction (visuals could be helpful) - Latin 'saltare' -- hop, leap - Propagation of action potentials in myelinated axons - Jumps from one node of Ranvier to the next - Increases the speed of transmission of the impulse Synapse - Junction of a neuron with another cell e.g. dendrites of another neuron, a muscle cell or a gland - A pre-synaptic (the cell transferring) and a post-synaptic cell (the cell receiving) - We can tell neurons are highly specific for their role as they have lots of dendrites to pick up any stimulation and they have lots presynaptic terminals to synapse with many other cells - A neuron can have thousands of synapses - Electrical synapse: a less common electrical signal, only in cardiac muscles and some smooth muscles. In these synapses the cells are connected by gap junctions - Chemical synapse: the most common type which uses chemical messengers called neurotransmitters to transmit an action potential across the synapse Chemical synapse (visuals could be helpful) - Components of a synapse - Pre-synaptic terminal - Pre-synaptic membrane - Post-synaptic membrane - Synaptic cleft - Neurotransmitters - Synaptic vesicles - Neurotransmitter release - An action potential arriving at the presynaptic terminal causes voltge gated Ca2+ channels to open - Ca2+ diffuses into the cell and stimulates exocytosis of the synaptic vesicles which release neurotransmitter molecules - Neurotransmitter molecules diffuse from the presynaptic terminal across the synaptic cleft - Neurotransmitter molecules combine with their receptor sites and cause ligand gated Na+ channels to open. Na+ diffuses into the cell and causes depolarisation - Neurotransmitter removal 1. Acetylcholine molecules bind to their receptors 2. Acetylcholine molecules unbind from their receptors 3. Acetylcholinesterase splits acetylcholine into choline and acetic acid which prevents acetylcholine from again binding to its receptors. Choline is taken up by the presynaptic terminal. 4. Choline is used to make new acetylcholine molecules that are packaged into synaptic vesicles 5. Other acetylcholine simply diffuse into the extracellular fluid away from the synaptic cleft Lecture 4 Introduction to spinal cord - The spinal cord is a part of the CNS - It extends from the brain at the level of the foramen magnum to the second lumbar vertebra along the posterior aspect of the body - The spinal cord is protected by the vertebral column which is a bony structure and the meninges which are which are made up of various layers of connective tissue. These surround the brain and spinal cord - The grey matter of the spinal cord is located on the interior part while the white matter is exterior - Each side of the grey matter of the spinal cord is organised into horns - Posterior (dorsal) horn - Lateral horn - Anterior (ventral) horn - The white matter is arranged into columns - Dorsal (posterior) column - Ventral (anterior) column - Lateral column - The anterior median fissure is the depression on the anterior side in the white matter - The posterior median sulcus is also a depression however it is much narrower and is located on the posterior side - The connection between the two sides of grey matter is called the grey commissure - In the centre of the grey commissure there is a hole known as the central canal - On the sides of the spinal cord there are root-like branches called rootlets and these rootlets arise from both the doral and the ventral side. The rootlets form roots, the dorsal and ventral roots. - The swelling on the dorsal side is called the dorsal root ganglion Organisation of neurons in the spinal cord and the spinal nerves - Information enters the CNS via the dorsal side and exits via the ventral side - Spinal nerves are mixed nerves because they have both sensory and motor information traveling through them Reflexes - Automatic response to a stimulus without a higher brain centre involvement - Are homeostatic doesn't require mental processing - Help to maintain homeostasis in the body - Are somatic or autonomic - Autonomic: blood pressure, carbon levels in the blood - Somatic: touching something hot, stepping on something sharp and posture - Produces the same stereotyped response from the spinal cord - Rapid, predictable and unlearned - No matter how mnay times you touch a hot stove your body will respond the same - The simplest reflex arcs don't involve interneurons - Monosynaptic vs polysynaptic Reflex arc 1 1. A sensory receptor detects a stimulus 2. A sensory neuron conducts action potentials through the nerve and dorsal root to the spinal cord 3. In the spina cord the neuron synapses with an interneuron (unless it is monosynaptic) 4. The interneuron synapses with a motor neuron 5. A motor neuron axon conducts action potentials through the central root and spinal nerve to the effector organ - Anatomical pathway of a reflex is called a reflex arc - Sensory receptor - Sensory neuron - Interneuron - Motor neuron - Effector organ Reflex arc 2 - After the response is produced by the reflex arc a signal is sent to the brain to inform it of what has just happened - The brain centres can supress and exaggerate the Types of reflexes - Somatic: involves skeletal muscles e.g. the patellar reflex - Autonomic: involves smooth muscles, cardiac muscles or viscera e.g. the pupillary reflex - Monosynaptic: Simple neuronal pathway sensory synapses with motor neuron (there is one synapse) e.g. stretch reflex - Polysynaptic: a complex pathway with multiple synapses with interneurons between sensory ad motor neurons e.g. knee jerk reflex, Golgi tendon reflex, Babinski reflex, pupillary reflex Reaction - Voluntary response to a stimulus - Initiated by a sensory stimulus - Relatively slower than a reflex - Involves the brain and spinal cord - Reaction time improves through repetition - E.g. catching a ball or dodging an incoming object Tutorial 1. D, C, A, E, F, B B, B, A, B, A 8\. they travel like a mexican wave or dominos down the axon to transmit information from one potin to another 9\. a reflex is an involuntary response where the nerves don't go via the brain, they only go through the spinal cord 1. PNS 2. Brain 3. Spinal cord 4. Somatic 5. Sympathetic 6. Parasympathetic 1. Skeletal muscle 2. Digestive system 3. The fight or flight response, increases the heart rate, raspatory rate and redirects blood flow to the limbs and dilates pupils 4. The rest and digest response, the heart rests, blood goes to the digestive system, pupils constrict cell body Nucleus Axon hillock Dendrite Axon Schwann cell Axon terminals Synaptic knobs they have lots of dendrites to receive and transmit information and lots of axon terminals to pass on information sensory neurons send messages towards the CNS motor neurons send messages away from the CNS towards muscles, organs or glands unipolar multipolar 6. The sensory neuron terminates in the spinal cord The motor neuron terminates in the muscle/effector 7. PNS in the dorsal root ganglion 8. Spinal cord Somatic is often skeletal muscles while autonomic is smooth muscles and glands When my knee was tapped my leg swung out Quadriceps femoris When the light was shone into the left eye both pupils constricted This change can not be voluntarily controlled so this is an autonomic reflex There are more potassium leak channels than sodium leak channels Potassium wants to travel outside the cell The sodium would like to travel into the cell