Nervous coordination and muscles - Yr 2 Flashcards
(101 cards)
1
Q
CNS
A
The brain and spinal cord
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Q
Peripheral nervous system
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Pairs of nerves that originate from either the brain or spinal cord to the rest of the body. Divided into the sensory and motor nervous system.
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Neurone
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Specialised cells adapted to rapidly carrying electrochemical changes called nerve impulses from one part of the body to another eg sensory, motor and intermediate
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Sensory neurons
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Neurones which carry nerve impulses from receptors towards the CNS (an intermediate or motor neurone)
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Motor neurons
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Neurones which carry nerve impulses away from CNS (an intermediate or relay neurone) to an effector
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Intermediate or relay neurons
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A neurone which is a co-ordinator which transmit impulses between neurons, for example, from the sensory neurone to the motor neurone in the spinal cord.
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Stimulus
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A detectable change in the internal or external environment of an organism
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Response
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The result of a stimulus on an organism
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Receptor
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A cell or organ which detects a stimulus
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Effector
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A cell, tissue, organ or system which responds to a stimulus
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Coordinator
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The link between a sensory neurone and motor neurone in the spinal cord
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Reflex arc
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Pathway of neurones involved in a reflex: Stimulus receptor sensory neurone intermediate (relay) neurone motor neurone effector response.
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Somatic/Voluntary Nervous System
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A division of the motor nervous system which carries nerve impulses to body muscles and is under voluntary (conscious) control
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Autonomic
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A division of the motor nervous system which carries nerve impulses to glands, smooth and cardiac muscle and is not under voluntary control (subconscious)
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Sympathetic
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An autonomic pathway which stimulates effectors and so speeds up an activity
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Parasympathetic
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An autonomic pathway which inhibits effectors and so slows down an activity (parachute…)
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Pacinian corpuscle
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A sensory receptor which responds to change in mechanical pressure
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Stretch-mediated Na+ channels
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A special type of sodium channel which is found at the sensory neurone ending at the centre of the Pacinian corpuscle. Their permeability to sodium changes when they are deformed by stretching.
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Photoreceptors
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Light receptor cells of the mammalian eye found on the innermost layer, the retina. Two types: rod and cone cells. They act as transducers by conserving light energy into the electrical energy of a nerve impulse.
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Retina
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The innermost layer of the mammalian eye containing photoreceptors.
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Rod cells
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Cells in the retina which transduce light energy into a generator potential, based on intensity of light received. They respond to low-intensity light and give low visual acuity. Absent in the fovea.
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Cone cells
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Cells in the retina which transduce light energy into a generator potential, based on wavelength of light received. There are three different types, each responding to a different range of wavelength of light. Mainly concentrated in the fovea. Not sensitive to low-intensity light but give good visual acuity.
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Retinal convergence
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Many rods connected to one bipolar cell
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Visual acuity
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Ability to resolve fine detail
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Visual sensitivity
Ability to detect low light intensity
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Fovea
The point receives the highest intensity of light because light is focused by the lens on the part of the retina opposite the pupil. Cone cells are found here.
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Blind spot
The point of entry of the optic nerve on the retina which is insensitive to light.
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Optic nerve
Nerve which transmits impulses to the brain from the retina at the back of the eye
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Nerve impulse
A self-propagating wave of electrical disturbance theta travels along the surface of an axon membrane
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Na+ K+ Pump
A carrier protein which actively transports 2 potassium ions into the axon and 3 sodium ions out of the axon.
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Resting potential
A potential difference of -65mV found inside a resting neurone relative to its outside, which results in the axon being polarised.
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Generator potential
A nervous impulse produced by a sensory receptor following transduction (or conversion) of one form of energy into electrical energy
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Threshold value
The minimum level of stimulus needed to trigger an action potential
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Action potential
A temporary reversal of the charges across the axon membrane which increase from -65mV to +40mV, depolarising the membrane
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Polarised
Condition used to describe the axon when the inside of an axon is negatively charged relative to the outside (at the resting potential usually around 65mV). This is established because sodium ions are actively transported out of the axon and potassium ions actively transported into the axon by the sodium-potassium pump. The outward movement of sodium ions is greater than inward movement of potassium ions which means there are more sodium ions in the tissue fluid surrounding the axon than in the cytoplasm and more potassium ions in the cytoplasm than in the tissue fluid which creates an electrochemical gradient. Most of the gates in the channels that allow the potassium ions to diffuse back out of the axon are open, while most of the gates in the channels that allow sodium ions to diffuse back into the axon are closed.
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Voltage gated channels
Channels in the axon membrane which change shape, and hence open or close, depending on the voltage across the membrane.
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Depolarised
Condition used to describe the part of the axon membrane when the inside of the membrane has a positive charge of around +40mV (when an action potential is happening). This occurs because of a stimulus which causes some sodium voltage-gated channels in the axon membrane opening and sodium ions diffusing into the axon along their electrochemical gradient. More sodium channels open, causing an even greater influx of sodium ions by diffusion.
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Hyperpolarisation
When the inside of the axon is more negative (relative to the outside) than the usual. Caused because voltage-gated potassium channels open and the electrical gradient that prevented further outward movement of potassium ions is now reversed causing more potassium ion channels to open. The outward diffusion of these potassium ions causes a temporary overshoot of the electrical gradient.
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Repolarisation
When the resting potential of -65mV is re-established the axon is described as this. This happens because the closable gates on the potassium ion channels now close and the activities of the sodium-potassium pumps once again cause sodium ions to be pumped out and potassium ions in.
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Refractory period
Time period after an action potential when it is impossible for a further action potential to be generated because inward movement of sodium ions is prevented because the sodium voltage-gated channels are closed. Means that impulses are propagated in one direction only, allows discrete impulses and limits the number of action potentials.
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All-or-nothing principle
An action potential is exactly the same size, regardless of the size of the stimulus, providing it reaches the threshold value.
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Dendrons
Extensions of the cell body which subdivide into smaller branched fibres, called dendrites, that carry nerve impulses towards the cell body
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Axon
A single long fibre that carries nerve impulses away from the cell body
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Cell body
Contains all of the usual cell organelles, including a nucleus and large amounts of RER (associated with production of proteins and neurotransmitters).
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Schwann cells
wrap themselves around the axon many times, so that layers of their membranes build up around it. They protect the axon and provide electrical insulation. They also carry out phagocytosis (the removal of cell debris) and play a part in nerve regeneration.
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Node of Ranvier
Constrictions (gaps) between adjacent Schwann Cells where there is no myelin sheath (2-3µm long and every 1-3mm in humans).
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Myelin sheath
Covering to the axon and is made up of the membranes of the Schwann cells wrapped around a neurone which helps speed up impulse transmission
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Synapse
The point where the axon of one neurone connects with the dendrite of another or an effector: they help coordinate activities and are unidirectional.
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Cholinergic synapse
A synapse which links neurones to neurones or neurones to other effector organs, in which the neurotransmitter is acetylcholine, often found in peripheral NS. May be excitatory or inhibitory. Motor, sensory or intermediate neurones may be involved.
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Adrenergic synapse
A synapse in which the neurotransmitter is noradrenaline (epinephrine in the US), found in some synapses in the sympathetic system
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Neurotransmitter
A chemical which is secreted by a neurone within the nervous system to stimulate a target cell
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Hormonal or endocrine system
A communication system which transports hormones via the plasma to produce a slow, long-lasting response in the target cells
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Chemical mediators
Chemicals eg histamine, prostaglandins, released by some mammalian cells which have an effect on other nearby cells
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Acetylcholine
A neurotransmitter used at a cholinergic synapse. Released from synaptic vesicles in presynaptic neurones when an action potential reaches the synaptic knob. This neurotransmitter diffuses across the synaptic cleft and binds to specific receptor proteins on the postsynaptic neurone which leads to a new action potential in the postsynaptic neurone.
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Presynaptic neurone
Neurone that releases the neurotransmitter from synaptic vesicles when an action potential arrives at the end of it and causes calcium ion protein channels to open and calcium ions to influx in.
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Postsynaptic neurone
Neurone which has receptor sites that the neurotransmitter binds to after diffusing across the synaptic cleft.
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Presynaptic knob
The swollen portion of the presynaptic neurone.
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Synaptic cleft
The 20-30nm wide gap which is found between the presynaptic and postsynaptic neurone.
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Synaptic vesicle
Contain the neurotransmitter in the presynaptic neurone. The influx of calcium ions causes them to fuse with the presynaptic membrane, releasing neurotransmitter into the synaptic cleft.
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ACh Receptors
Found on the postsynaptic neurone of a cholinergic synapse where acetyl choline is the neurotransmitter. As acetylcholine binds to receptor sites on sodium ion protein channels in the membrane it causes the sodium ion protein channels to open, allowing sodium ions to diffuse in rapidly down a concentration gradient, setting up a new action potential in the postsynaptic neurone.
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Acetylcholine esterase enzyme
The enzyme which breaks down acetylcholine into choline and ethanoic acid (acetyl), removing it from the synaptic cleft (to prevent it continually stimulating the post-synaptic membrane).
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Excitatory synapses
Synapses that produce new action potentials when the neurotransmitter binds with the receptor proteins. The neurotransmitter binds to and causes sodium ion channels on the postsynaptic neurone to open (Na+ ions move in) causing a new action potential.
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Inhibitory synapses
Synapses which make it less likely that a new action potential will be created on the postsynaptic neurone. The neurotransmitter binds to and causes chloride ion channels on the postsynaptic neurone to open (Cl- ions move in) and causes potassium channels to open (K+ ions move out) making the inside of the postsynaptic membrane more negative and therefore less likely that a new impulse will be created.
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Summation
Can either be spatial or temporal. Allows a build up of neurotransmitter which enables low-frequency action potentials to trigger a new action potential in the postsynaptic neurone.
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Spatial summation
a number of presynaptic neurones together release enough neurotransmitter to exceed the threshold value of the postsynaptic neurone and therefore trigger a new action potential
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Temporal summation
one presynaptic neurone releases neurotransmitter many times over a short period- if the concentration of neurotransmitter exceeds the threshold of the postsynaptic neurone a new action potential will be triggered.
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Neuromuscular junction
The point at which a motor neurone meets a skeletal muscle fibre. Only excitatory synapses.
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Myogenic
Contraction is initiated from within the muscle itself, rather than by nervous impulse from outside (neurogenic).
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SAN
A distinct group of cells (pacemaker) within the right atrium of the heart where the initial stimulus for contraction originates. It has a basic rhythm of stimulation that determines the beat of the heart.
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AV Node
A second group of cells which lies between the atria. After a short delay, it conveys a wave of electrical excitation between the ventricles along the Purkinje tissue.
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Bundle of His
The structure that is made of the Purkinje tissue that conducts the wave through the atrioventricular septum to the base of the ventricles.
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Purkinje fibres
Specialised muscle fibres which convey the wave of electrical excitation between the ventricles and then releases the wave of excitation causing the ventricles to contract quickly at the same time from the bottom of the heart upwards.
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Medulla oblongata
Region of the brain which controls the heart rate. It has two centres – one which increases heart rate that is linked to the SAN by the sympathetic NS and one which decreases heart rate that is linked to the SAN by the parasympathetic NS.
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Pressure receptors
Occur within the walls of the carotid arteries and the aorta. If blood pressure is higher than normal these receptors transmit more nervous impulses to the centre in the medulla which decreases heart rate. If blood pressure is lower than normal these receptors transmit more nervous impulses to the centre in the medulla which increases heart rate.
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Chemo receptors
Occur within the walls of the carotid artery and are sensitive to changes in pH of the blood (due to changes in CO2 concentration). If pH decreases (higher concentration of CO2) these receptors increase the frequency of nervous impulses to the centre in the medulla that increases heart rate, leading to more carbon dioxide being removed.
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Skeletal muscle
Attached to bone and acts under voluntary, conscious control.
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Smooth muscle
Found in the walls of blood vessels and the gut – not under conscious control.
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Cardiac muscle
Found exclusively in the heart – not under conscious control.
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Sarcolemma
The fine transparent tubular sheath which envelops the fibres of skeletal muscles.
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Sarcoplasm
The cytoplasm and nuclei which muscle fibres share. It is mostly found around the circumference of the fibre. Within this there is a large concentration of mitochondria and endoplasmic reticulum.
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Sarcoplasmic reticulum
A large vesicle in a contracting muscle cell which contains the Ca2+ ions to allow the troponin to bind and filaments to slide
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Multi-nucleated
Contain more than one nucleus
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Myofibrils (muscle fibres)
A microscopic muscle fibre containing sarcoplasm and showing striped isotropic and anisotropic bands of actin and myosin
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Actin
A globular protein whose 2 molecules are arranged into long chains that are twisted around one another to form a helical strand.
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Myosin
Made of a fibrous protein arranged into a filament made up of several hundred molecules (the tail) and a globular protein formed into two bulbous structures at one end (the head).
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Tropomyosin
Forms long thin threads that are wound around actin filaments.
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A Band
Ansiotropic bands (dark) where thick and thin filaments overlap.
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I Band
Isotropic bands (light) where thick and thin filaments do not overlap.
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H zone
The centre of each A-band where there is a lighter-coloured region
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Z line
The centre of each I-band.
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Sarcomere
The distance between two adjacent Z-lines (the centres of adjacent I bands). Sarcomeres shorten and the pattern of light and dark band changes when a muscle contracts.
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Contraction
When a muscle undergoes this process the following happen: the I band becomes narrower, the Z-lines move closer together and the H-zone becomes narrower.
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Globular heads
Part of myosin that attaches to binding site on actin filaments (when tropomyosin no longer blocks it). The head of myosin can change angle which is necessary for the sliding filament mechanism of muscle contraction.
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Myosin binding site
Found on the actin molecule – can be blocked by tropomyosin.
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Ca2+
Causes the tropomyosin molecule to change shape and pull away from the binding sites on the actin molecule.
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ATP
Required to provide the energy for the myosin head to resume to its normal position.
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Phosphocreatine
A store is found in muscle that provides a reserve supply of phosphate, which can immediately recombine with ADP to re-form ATP.
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Slow twitch
Adapted for aerobic respiration and contract more slowly and provide less powerful contractions but can contract for long periods. Adapted to endurance work.
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Fast twitch
Adapted for anaerobic respiration and can contract more rapidly and produce powerful contraction but only for a short period. Adapted for intense exercise.
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Myoglobin
a red protein containing haem, which carries and stores oxygen in muscle cells. It is structurally similar to a subunit of haemoglobin.
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Sliding filament theor
A process which explains how muscles contract, involving actin and myosin molecules sliding past each other
