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Bio topic 8

QuestionAnswer
Sensory, relay, motor neurons Dendrites/dendron carries impulse to cell body Cell body contains nucleus, end for motor, along axon for sensory Axon carries impulse away from cell body, myelinated by Schwann cells
Schwann cells and Nodes of Ranvier Schwann cells wrap around the axon Made of lipids which insulate the axon Gaps between Schwann cells are called nodes of Ranvier involved in saltatory conduction
Response to a stimulus + reflex arc Receptor -> sensory -> brain -> motor -> effector Reflex arc skips the brain by using a relay neuron in the spinal cord making the arc faster
Pupil dilation and contraction Photoreceptors -> sensory -> relay -> parasympathetic -> motor -> radial/circular muscle In dark, radial contracts, circular relaxes, pupil dilates letting in more light Opposite in light
Resting potential Maintained at -70mV by the Na+/K+ pump which pumps out 3Na+ ions for every 2K+ ions pumped in K+ may try to diffuse out through K+ channels but is pulled back by the electrical gradient created at -70mV
Action potential Threshold of -55mV reached due to stimuli - voltage gated Na+ channels open - Na+ diffuses in depolarising the axon to +40mV - voltage gated K+ channels then open - K+ diffuses out repolarising the axon - axon hyperpolarised - resting potential restored
Saltatory conduction Schwann cells insulate the axon, ions cannot diffuse through the myelin sheath - action potential only occurs at nodes of Ranvier - local current are over longer distances so impulse jumps between nodes making it faster
Impulse at synapses 1. Depolarisation opens Ca2+ channels, Ca2+ diffuses into presynaptic membrane 2. Vesicles move and release neurotransmitters into cleft by exocytosis 3. They diffuse to postsynaptic membrane, bind to receptors, open Na+ channels, Na+ depolarises axon
Acetylcholine Type of neurotransmitter After binding to receptors they are broken down by acetylcholinesterase so it can no longer bind Breakdown products diffuse away or a reabsorbed by presynaptic membrane This maintains concentration gradient
Rod cells in dark Na+ can diffuse in through channels and is being pumped out so cell is slightly depolarised at -40mV - neurotransmitter is released into the inhibitory synapse so bipolar cell and optic nerve cannot be depolarised
Rod cells in light Rhodopsin absorbs light and broken down into opsin + retinal - opsin causes cation channels to close - no Na+ can enter while Na+ is pumped out hyperpolarising the cell - no neurotransmitter released so bipolar cell and optic nerve can be depolarised
Phytochromes Pr absorbs red light and converts to Pfr which converts back in dark or in far-red light Controls developmental processes like germination, flowering (long and short day), and greening They do this by interacting with transcription factors
IAA IAA loosens cell wall by making it more acidic (increasing H+ ions) Causes water to move in by osmosis by increasing potential difference inside the cell leading to cell elongation
Cerebral hemispheres - location and function Left and right side composed of lobes Frontal - decision making, reasoning, emotions, movement (primary motor cortex) Parietal - orientation, sensation, memory Temporal - auditory information, memory Occipital - visual information
Hypothalamus, cerebellum, medulla oblongata - location and function Hypothalamus: middle of corpus callosum - regulatory centre for temperature, sleep, hunger, thirst, and secretes hormones Cerebellum: lower back of brain - balance and movement Medulla oblongata: bottom of brainstem - regulates unconscious processes
CT scans (Computerised Axial Tomography) Thousands of x-rays rotate around the patient from different angles producing cross sectional images Used to look at structure but not function - used to detect and monitor brain disease
MRI (Magnetic Resonance Imaging) Uses magnetic fields and radio waves to produce cross sectional images which can be put together to give 3D images Can provide images of brain structure in greater resolution than CT - can diagnose brain tumours, strokes, brain injuries, infections
Created by: silver54331
 

 



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