39641904
Description
Flashcards by Darcey Griffiths, updated 4 days ago
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Created by Darcey Griffiths
11 days ago
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| Question | Answer |
| Stimulus meaning | a detectable change in the internal or external environment of an organism that produces a response in that organism. |
| How a stimulus works | Sensory receptors give an organism its senses. There are specialised sensory cells eg pressure sensors in the skin and in complex sense organs eg ear and eye. |
| More on sensory receptors | Sensory receptors are transducers as they detect energy in one form and convert it into electrical energy. The electrical impulses travels along neurones and are called nervous impulses. They initiate a response in an effector, which may be a muscle or a gland. |
| Stimulus= visible light | Sensory receptor location: retina Sense: sight |
| Stimulus: sound | Sensory receptor location: inner ear Sense: hearing |
| stimulus: pressure | Sensory receptor location: dermis of the skin Sense: touch |
| Stimulus: heavy pressure | Sensory receptor location: deeper in dermis of the skin Sense: pain |
| Stimulus: chemical pt1 | Sensory receptor location: nose Sense: smell |
| Stimulus: chemical pt2 | Sensory receptor location: tongue Sense: taste |
| Stimulus: temperature | Sensory receptor location: dermis of skin Sense: temperature |
| Stimulus: gravity | Sensory receptor location: middle ear Sense: balance |
| The nervous system has 2 parts- part 1- CNS | The central nervous system= brain and spinal cord CNS processes information provided by a stimulus. Both the brain and spinal cord are surrounded by tough membranes-collectively called meninges |
| CNS- spinal cord description | white matter contains nerve fibres surrounded by myelin which is fatty and looks Grey matter has much less myelin- is largely nerve fibres of relay neurones and cell bodies of relay and motor neurones |
| The nervous system has 2 parts- part 1- PNS | comprises: -somatic nervous system eg pairs of nerves that originate in the brain or the spinal cord and their branches |
| PNS pt 2 | These nerves contain the fibres of sensory neurones which carry impulses of receptors to the CNS and motor neurones which carries impulses away from CNS to effectors Also has autonomic nervous system provides unconscious control of the functions of internal organs eg heartbeat, digestion |
| The reflex arc | Simplest type of nervous response to stimulus= reflex arc Neural pathway taken by nervous impulse of reflex action eg withdrawal effect-instantly withdraw hand |
| Reflex action | Rapid, automatic response from nervous impulses initiated by a stimulus. Decision making areas of brain not involved/ involuntary. Reflex action= generally protective. |
| Elements of reflex arc | stimulus--- receptor---sensory neurone--- relay neurone in CNS---- motor neurone---effector---- response can be identified as any reflex action. |
| put diagram of reflex arc | h |
| reflex arc example | stimulus- heat sensory receptor- temp and pain receptors in the skin sensory neurone-sends impulse up the arm to the spinal cord CNS-relay neurone in spinal cord transmits an impulse from sensory neurone to a motor neurone Motor neurone- sends impulse to an effector- in this case a muscle Response- arm muscles contract and hand is removed from heat source |
| Reflex arc- example pupil reflex | stimulus- light sensory receptor- photosensitive cells in retina sensory neurone- optic nerve CNS-brain Motor neurone- carries impulse to muscles of iris response- iris muscles relax/ contract- altering pupil diameter |
| do diagram of spinal column-neurones | h |
| nerve nets-evolution | animals in the phyla that appear early on fossil record dont have nervous systems Those that appeared later have radical symmetry/ nervous system=nerve net eg phylum cnidaria-includes jellyfish those that appeared even later have bilateral symmetry and have CNS eg chordates |
| nerve net-description | Nerve net is the simplest type of nervous system- it's a diffused (distributed) network of cells that groups into a ganglia but doesn't form a brain |
| nerve net- cell types | Ganglion cells- provide connections in several directions Sensory cells- detect stimuli eg light, sound, touch, temperature |
| Hydra nerve net | Hydra is in phylum cnidaria nerve net- has a simple pattern,is easy to manipulate in exps, regenerates rapidly eg when replacing lost tentacle so- model organism for studying nerve nets |
| hydra- nerve net- ectoderm | Hydras nerve net is in its ectoderm-(outer 2 layers of body wall)- Nerve net allows hydra to sense light- physical contact and chemicals- so it can contract, perform locomotion, hunt and feed. Without a brain has complex movement/ behaviour- larger stimulus stimulates more cells-causes larger response |
| compare hydra to human | nervous system type- nerve net/ CNS NO. cell types in nervous system- 2/many Regeneration of neurones- Rapid/ slow if at all Myelin Sheath-Absent/present onduction speed- Slow approx 5m/s to Fast up to 120m/s |
| Neurones-description | Specialized cells adapted to rapidly carry nervous impulses from one body part to another- 3 types of neurones. |
| 3 types of neurones | sensory- carries impulses from sense receptors or organs into CNS Motor-Carry impulses from CNS to effector organs eg muscles/ glands Relay, connector or association- receive impulses from sensory neurones or other relay neurones and transmit them to motor or other relay neurones |
| Cell body/ centron function | contains a nucleus and granular cytoplasm |
| Cytoplasm function | Granular-- contains many ribosomes |
| Nucleus function | Holds DNA |
| Nissl granules | Cytoplasmic granules comprising ribosomes grouped on ER |
| Dendrite function | Thin fibre carrying impulses towards the cell body |
| Axon function | Thin fibre carrying impulses away from cell body, a cell body only has one axon. |
| Schwann cells function | Glial cells that surround and support nerve fibres. In vertebrate embryos, they wrap around the developing axons many times and withdraw their cytoplasm, leaving a multi latyered phospholipid myelin sheath |
| Myelin sheath function | electrical insulator- speeds up transmission of impulses |
| Nodes of Ranvier function | 1 um gaps in myelin sheath, where adjacent Schwann cells meet and where the axon membrane is exposed- allows impulses to be transferred rapidly |
| synaptic knob function | swelling at end of axon in which neurotransmitter is synthesised |
| Axon ending/ terminal function | Secretes neurotransmitter which transmits impulse to adjacent neurone |
| nervous impulse- resting potential | Neurone= an excitable cell- means it can change its resting potential resting potential- the potential difference across the membrane of a cell when no nervous impulse is being conducted, most cells aren't excitable. |
| nervous impulse- potential difference | Potential difference across a cell membrane = 70 mv- membrane is more negative inside so resting potential is -70 mv- potential difference across cell membrane means it's polarised |
| reason for resting potential 1 | Inside of the cell has a higher concentration of K+ ions and a lower concentration of Na+ ions compared to outside- Na+ moves out K+ moves in- 3 Na+ out for every 2K+ in |
| reason for resting potential 2 | Sodium Potassium exchange pumps pump K+ ions back into cell and and Na+ ions back out - they're trans membrane proteins with ATPase activity that transport K+ and Na+ ions across the membrane against conc gradient by active transport- maintain conc/uneven distribution of ions in the membrane |
| Reason for resting potential-3 | Voltage gated sodium channels- in axon membrane- doesn't open when Na+ wants to come back in but lets K+ out |
| Other reasons for resting potential | some of the channels allow K+ out in the membrane but not Na+ in- membrane is 100x more permeable to K+ |
| Action Potential Definition | The rapid rise and fall of electrical potential across a nerve cell membrane as a nervous impulse passes |
| The action potential | In an excitable cell, the potential across the membrane can alter. A nervous impulse is the transmission of a change in potential along a nerve fibre associated with the movement of sodium ions- voltage change is very small but can be picked up with by a pair of microelectrodes fed to an oscilloscope |
| Oscilloscope function | Oscilloscope trace is a graph showing voltage across membrane changes with time. Measures magnitude and speed of impulse transmission and helps us analyse patterns of impulses generated in different parts of the nervous system in different situations |
| conclusions drawn using oscilloscope | Neurones transmit electrical impulsesalong cell surface membrane surrounding axon- put microelectrode inside axon and one in bathing solution to find: Energy of stimulus causes some voltage gated sodium channels to open- allows Na+ to rapidly diffuse in. So, negative charge of -70mv inside axon rapidly becomes positive charge of +40mv - this is the action potential-cell membrane is depolarised |
| conclusions drawn using oscilloscope pt 2 | The potassium channels open and K+ ions diffuse out - cell becomes less positive- membrane becomes repolarised More K+ ions diffuse out than Na+ ions diffuse in so potential difference across the membrane becomes even more negative than resting potential- hyperpolarised sodium potassium pumps pumps K+ ions out and allows Na+ in- restores ion back to resting potential |
| Depolarisation definition | A temporary reversal of potential across the membrane of a neurone so the inside becomes less negative than the outside as an action potential is transmitted |
| How action potential travels along axon | Na+ ions move along axon due to their locally high concentration-move to lower concentration. In doing this they depolarise the adjacent section of the memrane-opens more voltage gated sodium channels in those regions- mopre sodium ions floods in- depolarises axon at this point - sodium ions then diffuse further down the axon |
| Absolute refractory period | Site of initial action potential- sodium channels- are inactivated- can't open again until resting potential has been re-established so new action potential can be initiated this is the absolute refractory period-lasts around 1ms-ensures nervous impulse travels in 1 direction |
| Relative refractory period | for next 3-4ms during hyperpolarisation if an impulse is strong enough a new action potential may pass - occurs while sodium and potassium pumps are restoring resting potential. |
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