response to stimuli summary

response to stimuli summary

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Control, genomes and environment
F215 Unit 8: Responding to the environment
Muscle action is controlled by the neuromuscular junction, which is similar to a synapse. An action potential arrives at the synaptic knob of the
motor neurone which contains vesicles of acetylcholine, and the impulse causes the vesicles to move and fuse with the cell surface membrane,
releasing ACh into the gap by exocytosis, where it diffuses across and binds to receptors on muscle fibres, causing a depolarisation of the muscular
membrane, which travels down T-tubules in the muscle, triggering the sarcoplasmic reticulum to release calcium ions from its stores
Similarities to the synapse Differences from the synapse
The nervous system can be divided into the central nervous system (CNS) which comprises the brain and spinal T-tubules carry the electrical signal quickly into the inside of the muscle
cord, and is made of white and grey matter. The peripheral nervous system (PNS) is made up of all the neurones both use acetylcholine as the neurotransmitter (provided the synapse
cell, whereas at a synaptic junction the message is passed on by the
in question is the cholinergic synapse)
which transmit messages into and out of the central nervous system movement of sodium ions
the enzyme acetylcholinesterase is involved in both for breaking down
The PNS has the sensory system which central nervous system peripheral nervous system the neuromuscular junction is only ever excitatory, whereas synapses
acetylcholine to maintain a concentration gradient and prevent
takes messages from the receptors to the (CNS) (PNS) can be either excitatory or inhibitory
constant impulses being transmitted
CNS, and the motor system which takes both are triggered by the arrival of an action potential on the pre- the synapse sends a message from neurone-to-neurone, whereas the
messages from the CNS to the effector brain spinal cord motor system sensory system
synaptic/motor neurone membrane neuromuscular junction transmits a signal from neurone-to-muscle
(messages from CNS (messages from
This motor system consists of the somatic nervous system to effector) receptor to CNS) Fibres of skeletal muscle are contained by a muscular membrane (sarcolemma) and contain cytoplasm (sarcoplasm), which are rich in mitochondria
which is responsible for sending messages to voluntary to supply the energy for contraction. The fibres are
(skeletal) muscles, and the autonomic nervous system autonomic system somatic system made up of muscular subunits called sarcomeres A-band
controls smooth and controls striated Z-line I-band I-band Z-line
which sends messages to involuntary muscles (cardiac and which give skeletal muscle its striated bands. They H-zone
cardiac muscle (voluntary) muscles
smooth muscle) comprise thick filaments made of myosin, and thin
filaments made up of actin, troponin and tropomyosin
The autonomic system can further be sympathetic system parasympathetic system
broken down into the sympathetic generally has an excitatory generally has a depressive When our muscles need to contract, a nerve impulse is
effect, most active during effect, most active during sent across the motor neurone which causes calcium ions
nervous system which is excitatory, and
times of stress sleep and relaxation to be released from the sarcoplasmic reticulum. These
the parasympathetic nervous system
which is inhibitory (depressive) ions enter the sarcomere and bind to troponin molecules
on the thin filaments, which causes the tropomyosin (a
In the autonomic system, two neurones run to each effector, meeting at a ganglion. The sympathetic branch has
protein which is long and at rest covers up actin binding
ganglions at the target organs (long pre-ganglionic neurones) and the parasympathetic branch has ganglions much M-line
sites) to move, revealing the actin binding sites
closer to the spinal cord (long post-ganglionic neurones). The other major difference is that the sympathetic system
uses the transmitter noradrenaline, and the parasympathetic system uses acetylcholine With the actin binding sites now free, the myosin heads of the thick filament
are able to move and bind to actin filaments, forming a cross-bridge. Myosin
heads at rest are attached to a molecule of ADP and a phosphate. When they
HUMAN BRAIN form a cross-bridge with the actin sites, they release the ADP and phosphate,
The largest part of the brain is the cerebrum, divided into four lobes (temporal, occipital, frontal and parietal) in two which releases energy, which is used to bend the heads towards the thin troponin tropomyosin actin
hemispheres. Each lobe contains many areas, which can be sensory areas (those which receive indirect impulses filaments, which pulls the thin filaments inwards (the power stroke)
from receptors), association areas (which use what has been learnt from past experiences to decide on an Once this has occurred, a molecule of ATP binds to the each myosin head, which causes them to dissociate from the actin, so there is no more cross-
appropriate response to a stimulus), and motor areas (those which send impulses to effectors ­ muscles and glands) bridge. This allows a very brief resting period, called the recovery stroke. The ATP is then immediately hydrolysed to form ADP and phosphate, and
The cerebrum is involved in muscular movement and coordination, but fine motor control is coordinated in motor the myosin is reset for another power stroke. As long as calcium ions remain present in the sarcomere, power strokes will continue. Calcium ions
areas in the cerebellum, which lies beneath the cerebrum will have to be removed by active transport when they are no longer needed, as it will be against the concentration gradient, a further use of ATP
Involved in a wide range of `higher functions', this four-lobed part of the brain is enlarged TYPES OF MUSCLE
cerebrum (cortex) in humans. It has been associated with personality, emotions, language, reasoning, visual
processing and also possibly consciousness There are three types of muscle: skeletal muscle (voluntary muscle or striated muscle), smooth muscle (involuntary muscle) and cardiac muscle
skeletal muscle smooth muscle cardiac muscle
Responsible for fine motor control (for example, gripping objects and playing the piano), as
well as posture, balance and walking (movement). It has also been connected with memory
Responsible for the control of basic vital functions, such as breathing and heart rate; the
medulla oblongata medulla is something we have in common with all vertebrates, and is also involved in
producing the `fight-or-flight' response
many mitochondria, multinucleated, striated, cells form connecting platforms
Involved in various homeostatic mechanisms, and contains different receptors (for non-striated, spindle-shaped cells, single
structure extensive sarcoplasmic reticulum, with each other called intercalated discs,
hypothalamus example, for water potential ­ osmoreceptors ­ and temperature ­ thermoreceptors), and nucleus in cells
striated (striped/banded) single nucleus in cells
is connected with the pituitary gland (for example, in osmoregulation)
Connects the two hemispheres of the brain, this is bigger in human females who use each leads to the movement of the skeleton involved in peristalsis (moving food the myogenic muscle is part of the
corpus callosum side equally, and smaller in males who have lateralised brains, using the right hemisphere function at joints, leading to the movement of along intestine) and temperature cardiovascular system, keeps the blood
more effectively limbs, contracts as described above regulation (vasoconstriction) stream flowing, supplies organs with blood

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