Stimulus Response Model Flashcards
Internal factors that affect cells
- homeostasis
External factors that affect cells
- temperature
- light intensity
- gases
- nutrients
- water
- challenges from other organisms
Types of signals
- physical stimuli
- light
- heat
- touch/mechanical
- chemical stimuli
- nutrient molecules
- hormones
- neurotransmitters
- pheromones
- electrical signals
Stimulus response model
- stimulus
- receptors
- communication systems
- effector
- response
Nervous system
- fast
- neurons form nerve pathways
- electrical
- impulse is unidirectional
Structure of the nervous system
- CNS (central nervous system) brain and spinal cord
- PNS (peripheral nervous system) all other nerve cells
Neurons
- large cell body/soma: contains nucleus
- axon: carries information from cell body to terminal, is myelinated by Schwann cells, have endings called synaptic terminals which release neurotransmitters to repay signals to other cells
- dendrites: receive signals from other neurons, extensively branched, increase surface area of neuron
Types of neurons
- sensory neurons: communicate information about external and internal environments
- interneurons: integrate sensory input with motor input (only connect with other neurons)
- motor neurons: convey impulses from the CNS to effector cells
- afferent neurons: carry things from PNS to CNS (sensory neurons)
- efferent neurons: carry things from CNS to PNS (motor neurons) (made up of somatic and autonomic nervous systems)
Efferent neurons
- somatic nervous system: things you think about doing (voluntary)
- autonomic nervous system: things you can’t control (involuntary) (made up of the sympathetic and parasympathetic divisions)
Autonomic nervous system
- sympathetic: increases body functions; stress, fight or flight, prepares body for action
- parasympathetic: relaxes us
Reflex arc
- receptor detects stimulus which is transported via sensory neurons to interneurons
- interneurons send message to motor neurons which passes it on to the effector cells
- effector cells (muscles or glands) carry out the response
Action potentials
Signal is transmitted along the length of a neuron
- resting state: activation gates on Na+ and K+ channels are closed, and the membranes resting potential is maintained
- depolarisation: a stimulus opens to activation gates on some Na+ channels. The Na+ influx through those channels depolarises the membrane. If depolarisation reaches the threshold, it triggers an action potential
- rising phase of the action potential: Na+ influx makes the inside of the membrane positive, which makes the outside of the membrane negative
- falling phase of the action potential: inactivation gates on most Na+ channels close! blocking Na+ influx. The activation gates on most K+ channels open , permitting K+ efflux witch makes the inside of the cell negative
- undershoot: both gates of Na+ channels are closed, but activation gates on some K+ channels are open. As these gates close and the inactivation gates open on the Na+ channels! the membrane returns to it’s resting state
Communicate between nerve cells
- neurotransmitters
- neurohormones
Synapse
When an action potential depolarises the membrane of the synaptic terminal it opens voltage-gated Ca2+ channels in the membrane triggering an influx of Ca2+. The elevated Ca2+ concentration in the terminal causes synaptic vesicles to fuse with the presynaptic membrane. The vesicles release neurotransmitter into the synaptic cleft. The neurotransmitter binds to the receptor portion of ligand-gated ion channels in the post synaptic membrane, opening the channels. The neurotransmitter releases from the receptors and the channels close. Synaptic transmission ends when the neurotransmitter diffuses out of the synaptic cleft, is taken up by the synaptic terminal or another cell, or is degraded by an enzyme
Endocrine system
- slow
- produces hormones
- hormones are found in endocrine glands
- hormones only act on target cells
