coordination and response in humans- topic 19

• central nervous system is made up of the brain and spinal cord
• peripheral nervous system are nerve cells which carry information to or from the central nervous system such as motor neurons and sensory neurons
• nerve cell neurones , adapted to carry electrical impulses, have a long fibre (axon) which is insulated by a fatty myelin sheath. have tiny branches (dendrons) which branch further as dendrites at each end
• stimuli- receptors- sensory neuron- central nervous system- motor neuron-effectors
• receptors groups of specialised cells which detect a stimulus and stimulate electrical impulses in response. sene organs such as eye, skin and tongue contain groups of receptors.
• stimulus is a change in the environment such as temperature, chemicals or sound that stimulates a response by the organism
• effectors are muscles and glands which cause a response to electrical impulses
• eye is a sense organ contacting receptors sensitive to light intensity and colour
• cornea refracts light- bends it as it enters the eye
• iris controls how much light enters the pupil
• lens further refracts light too focus in onto the retina
• retina contains the light receptors
• optic nerve carries impulses between the eye and the brain
• ciliary muscles alters the shape of the lens so that the eye can focus
• suspensory ligament attaches the ciliary muscles to the lens
• fovea receives light, responsible for clear vision
• rods, no in retina- 120 million, concentrated- outer edges of the retina, works best in- dim light
• cones, no in retina- 7 million, concentrated- the fovea, works best in- bright light
• radial muscles widen the pupil when contracted to allow more light to enter the eye
• circular muscles close the pupil when contracted to prevent excess light from entering the eye, antagonistic muscle pairs
• accommodation is the change in the shape of the lens to focus near the distance objects, the lens reflects light onto the rods and cones in the retina
• close stands for, contracted ciliary muscles, loose suspensory ligaments, o shaped lens convex and wider, super refraction more light bends, eye exam technique
• explain what other measurements the teacher would need to make in order to calculate the speed of a nerve impulse, measure time taken for student A to feel hand being squeezed, speed equals distance divided by time
• describe wether the teachers method is likely to give an accurate estimate of the speed of the nerve impulse, not a reflex so need to allow for reaction time, may be an underestimate too slow
• sensory neurons carry signals from receptors to the spinal cord and brain
• relay neurons carry messages from one part of the CNS to the other
• motor neurons carry signals from the CNS to effectors
• synapses the gap between two dendrites of neurons
• neurotransmitters are chemicals used to transport signals across synapses
• a neuron releases the neurotransmitter into the synapse, the neurotransmitters diffuses across the synapse and makes the next neuron transmit an electrical signal
• reflex arcs are a way for the body to automatically and rapidly respond to a stimulus to minimise any further damage to the body. impulsive does not involve the brain, reflex actions are much quicker than other Motor movements
• sstorme, stimulus, sensory neurone, to, relay neurons, motor neuron, effector
• describe the structure and functioning of the withdrawal reflex of a finger from a hot object: receptors in skin surface detect stimulus, impulse movements, sensory neurone to relay neurone CNS, through the diffusion of neurotransmitters.
• homeostasis is keeping temperature (or water content) constant within a narrow range, maintaining a constant internal environment
• homeotherms are mammals and birds which are warm blooded, endothermic despite external changes they maintain their body temperature at 37 degrees since this is the optimum temperature for most bodily enzymes to function
• skin, is an Organ, collection of different tissues, working together to perform a specific function, largest organ of the body by surface area
• functions of skin, sensing pressure and temperature changes, acting as a barrier against pathogens, controls the balance of water, controls the balance of heat, blood capillary, sweat gland, hair follicle.
• adding water by drinking water based drinks, eating foods such as cucumber, produced during respiration
• losing water by excretion of urine, evaporation of sweat, egestion of faeces
• temperature control in warm conditions, enzymes denature , hyperthermia can occur, more blood flows to the skin surface to loose more heat since more radiation will occur,sweating: sweat will evaporate off the surface of the skin. regualated by the hypothalamus, vasodilation:blood vessels dilate so that heat can be radiated away