Biology F214: Section 1

Mind Map by emma_royal, updated more than 1 year ago
Created by emma_royal almost 6 years ago


Mind map detailing key points on Section 1 of the OCR Complete Revision Course

Resource summary

Biology F214: Section 1
1 Communication and Homeostasis
1.1 Nervous System
1.1.1 Types of Neuron Motor Neurone Short dendrites (CNS to Cell Body) One long axon (Cell Body to Effector cells) Sensory Neurons Short dendrites One long dendron to carry impulses from receptor cells to the cell body Short axon that carries impulses from the cell body to the CNS
1.1.2 Sensory Receptors Act as transducers (they convert one form of energy into another) Resting Potential Resting state, the inside of the cell is -ve so there is a p.d. across the membrane. This is maintained by ion pumps and ion channels Generator Potential Change due to a stimulus Due to the cell membrane becoming excited and more permeable, makes the inside of the cell more +ve The bigger the stimulus the bigger the generator potential Action Potential If the g.p. is big enough it'll trigger an a.p. (threshold level)
1.1.3 The Nervous Impulse r.p. => -70mV Sodium (3 x Na+) and Potassium (2 x K+) Use active transport to move Na+ out for K+ into cell Electrochemical Gradient Potassium channels also exist that allow K+ to move out by facilitated diffusion Action Potential STIMULUS - Sodium channels open, neurone becomes less negative DEPOLARISATION - p.d. reaches threshold (-55mV), voltage gated channels open so more sodium ions move in. REPOLARISATION - At +30mV, the sodium ion channels close and the potassium channels open. Neurone becomes more negative. HYPERPOLARISTION - Overshoot, P.d. becomes more -ve than resting potentialn (less than -70mV) R.P. - ion channels are reset Refractory period - too negative to become excited agian, makes a time delay, also it means the impulse can't travel backwards Waves of Depolaristion Mexican wave of sodium channels opening. The impulse propagates along the neuron, movement of action potential All-or-nothing The stimulus must reach the threshold to become an active action potential The bigger the stimulus the more frequent the impulses Speed of conduction Saltatory conduction, caused by the impulse jumping between nodes of Ranvier (between myelin sheaths made of Schwann cells) Faster if - big axon diameter or a higher temperature (until 40 degrees as enzymes will denature in the cells)
1.1.4 Synapses Neurotransmitters are removed from the synaptic cleft so the response doesn't keep happening, they're taken back to the pre-synaptic cleft, or they are broken down Example: Cholinergenic Synapse Neurotransmitter: Acetylcholine 1. ARRIVAL OF ACTION POTENTIAL Arrives as impulse at the presynaptic knob, this stimulates voltage-gated calcium ion channels. They diffuse in and are actively transported out. 2. FUSION OF VESICLES Ca+ causes vesicles containing acetylcholine to fuse with the presynaptic membrane 3. DIFFUSION OF ACh ACh diffuses across the cleft and binds to the specific cholinergic receptors on the postsynaptic membrane. This causes sodium ion channels in the postsynaptic neurone to open, which causes depolarisation. An action potential is generated if the threshold is reached. ACh is removed by acetylcholinerase (AchE) and the products are reabsorbed by the presynaptic neurone to make more ACh Disruption of synaptic transmission Same shape as neurotransmitters Nicotine AGONISTS Block receptors Muscle can't be stimulated, paralysis. Inhibit breakdown enzyme More neurotransmitters in the synaptic cleft to bind to receptors and they're there for longer Loss of nerve control Inhibit the release of neurotransmitters Fewer receptors are activated Block the calcium channels in the presynaptic knob, meaning fewer vesicles fuse with the membrane Roles of synapses Divergence One neuron is connected to many neurones, therefore information can be dispersed to different areas of the body Convergence Amplification Spatial summation Multiple synapses that together surpass the threshold potention Temporal Summantion Two or more nerve impulses arrive in quick succession from the same presynaptic neuron Unidirectional The presense of a pre and postsynaptic neuron means the impulse can only travel in one direction
1.1.5 Structure of the Nervous System CNS Peripheral NS Somatic NS (conscious activities) Autonomic NS (unconscious activities) Sympathetic NS (fight or flight) Parasympathetic NS (rest and digest)
1.1.6 Example: Heart Rate High Blood Pressure Impulses sent to m. oblongata which sends impulses along PARASYMPATHETIC neurones. ACETYLCHOLINE binds to SAN Heart rate decreases Baroreceptors detect Low Blood Pressure Baroreceptors detect. Impulses sent to m. oblongata which sends impulses along SYMPATHETIC neurones.NORADRENALINE binds to SAN Heart rate increases High Blood O2, Low CO2 or high blood pH Chemoreceptors detect Low Blood O2, High CO2 or high blood pH Chemoreceptors detect Adrenaline When an organism is threatened, adrenaline is released, it binds to specific receptors on the heart to increase contraction frequency and strength
1.2 Endocrine System
1.2.1 Hormonal Communication Information via chemical signals (hormones) that are secreted by glands. Many proteins are peptides e.g. insulin, however some are steriods, e.g. progesterone Glands can be stimulated by a change in concentration of a specific substance or by electical impulse Diffuse directly in the blood, binds to specific receptors on target cells. Tissues that contain a lot of target cells are kknown as target tissues
1.2.2 Glands endocrine - secrete hormones directly into the blood exocrine - secrete chemicals through ducts
1.2.3 Action of Hormones Hormones are first messengers, from the endocrine gland to the receptor Catalyses the action of a second messenger inside the cell Second messengers activate a cascade inside the cell Adrenaline Adrenal Gland Cortisol /Adrenalin Release when there is low concentration of glucose in the blood, when stressed and when exercising Activates glycogenolysis (As a first messenger) Adrenaline binds to receptors on many cells like liver cells It then activates an enzyme in the membrane that activates the second messenger called cAMP cAMP activates a cascade (that makes glucose more available to the cell)
1.2.4 The Pancreas Endocrine Function Islets of Langerhan Alpha cells Glucagon Binds receptors onto the cell membranes of liver cells (to release glycogen) and actives glycogenolysis (breaks down glycogen) and gluconeogenesis) Beta cells Insulin Increases the permeability of cell membranes to glucose and activates glycogenesis Exocrine Function Makes up most of the pancreas Acinar cells Secrete digestive enzymes into the pancreatic duct Blood Concentration Low High
1.2.5 Homeostasis The maintenance of a constant internal environment Keeping your internal environment roughly constant (within limits) Temperature As the rate of metabolic reactions increases (so does the kinetic energy) the temperature's increases in turn Too hot and enzymes will denature, to low and the enzyme activity will be reduced/ Negative feedback Involves receptors, a communication system and effectors The receptors detect change and the effectors counteract the change Only works within certain limits, always in flux Postive feedback Amplifies the change E.g. cervical dilation or platelets to form a clot
1.2.6 Temperature Ectotherms Relies on external temperature, also more active at higher temperature Endotherms Control body temperature using internal homeostasis Constantly have a high metabolic rate Can constantly be active at any temperature Mechanisms To reduce temperature Sweating, hairs lie flat, vasodilation To increase temperature Shivering, hormones, much less sweat, hairs stand up, vasoconstriction Uses the hypothalamus and thermoreceptors
1.2.7 Diabetes Mellitus Insulin from GM bacteria (rather than from a pigs pancreas) Cheaper, more produced, human so less likely to trigger an allergic response or be rejected, ethical reasons such as religion or vegetarianism. Could possibly cure with differentiated stem cells
1.3 Communication
1.3.1 Receptors and Effectors Responding to the Environment To aid survival make sure conditions are optimal for metabolism Any change to the internal or external environment (e.g. temperature, light intensity or pressure is called a stimulus Receptors are specific - e.g. pressure, light, glucose conc. therefore there are many different types of receptor, some are on the CSM and some are whole cells Effectors are cells that bring about a response to produce an effect. These include muscle or cells from in glands
1.3.2 Cell signalling Both nervous and hormonal Ways in which cells communicate with each other
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