Neuronal communcation Flashcards
What is homeostasis and why is it needed?
different organs have different functions in the body and they must be coordinated to maintain a relatively constant internal environment e.g pancreas and liver work together to maintain blood glucose
What is cell signalling and what are the different ways it occurs?
coordination at a cellular level occurs through cell signalling. One cell releases a chemical which will affect the target cell: transfer of signals locally (between neurones) or over bigger distances (hormones)
How does coordination in plants happen?
The use of plant hormones (e.g phototropsim)
give two differences between hormonal and neuronal communication
Hormonal: uses chemicals in the endocrine system, much slower
Neuronal: uses electrical impulses, much faster communication
Role of neurones
transmit electrical impulses rapidly around the body so it can respond to internal and external stimuli, the different types of neurones carry information from sensory receptor to the effector
Cell body in neurones
Cell body: nucleus surrounded by cytoplasm, large amounts of endoplasmic reticulum and mitochondria which are involved in the production of neurotransmitters
Dendrons in neurones
short extensions that come from the cell body, they divide into smaller branches called dendrites and are responsible for transmitting electrical impulses towards the cell body
Axons in neurones
singular elongated nerve fibres that transmit impulses away from the cell body
Role of a Sensory neurones
transmit impulses from sensory receptors to a relay neurone, motor neurone or the brain.
Have one dendron to carry impulses to cell body (in the centre)
One axon to carry impulses away from cell body
Role of a relay neurone
Transmit impulses between neurones, many short axons and dendrons
Role of a Motor neurone
Transmit impulses from relay neurones to effectors, such as a muscle or a gland, one long axon and many short dendrites (cell body one end)
Myelinated neurones
Schwann cells produce the myelin sheath which covers the entire axon on myelinated neurones as an insulating layer
Effects of myelination
Insulating layer and makes conduction of impulses faster - myelinated impulses can travel as fast as 100m per second/ non-myelinated 1m every second
Nodes of Ranvier
small gaps between Schwann cells occurring every 1-3mm in humans.
This way the impulse has to jump from neurone to neurone which means it is transmitted faster.
Non-myelinated neurones have impulses travelling continuously along
Role of Sensory receptors
convert the stimulus they detect into a nerve impulse
Information is passed through the CNS to the brain
Features of sensory receptors
- specific to one type of stimulus
- act as a transducer, convert stimulus into an impulse called a generator potential
4 main types of sensory receptors
mechanoreceptor: pressure and movement (pacinian corpuscle)
chemoreceptor: chemicals (olfactory receptors)
thermoreceptor: heat (end-bulbs of krause)
photoreceptor: light (cone cell, different wavelengths of light)
Pacinian corpuscle
detect mechanical pressure
located deep within the skin and are most abundant in the hands and soles of feet
Structure of a pacinian corpuscle
end of a sensory neurone is found in the centre of the corpuscle surrounded by connective tissue
within the neurone’s membrane there are sodium ion channels which transport them through the membrane
Conversion in pacinian corpuscle
at normal state/resting potential, the stretch-mediated sodium ion channels are too narrow to allow sodium to pass through
When pressure is applied the corpuscle changes shape and the membrane around the neurone stretches
Sodium ion channels now widen and sodium can diffuse into the neurone
Influx of the ions changes the potential of the membrane so it is now depolarised which creates a generator potential
generator potential then creates an action potential
What is resting potential
the potential difference across the membrane when a neurone is not transmitting an impulse. The outside of the membrane is more positively charged than the inside of the axon. The membrane is polarised and is at a potential of about -70 mV
Outline the creation of a resting potential
- Sodium ions are actively transported out of the axon and potassium ions are transported in (ratio of 3:2).
- There are more sodiums outside of the axon and more potassiums inside the axon so the sodiums move back into the axon cytoplasm down the electrochemical gradient.
Most gated Na+ channels are closed but many K+ ones are open and so potassium can diffuse out
What is a neurotransmitter?
chemical messengers - endogenous chemicals that allow neurotransmission
What is an excitatory neurotransmitter?
neurotransmitter that results in the depolarisation of the postsynaptic neurone - if threshold is reached in the postsynaptic membrane an action potential is triggered
Give examples of excitatory neurotransmitters
Acetylcholine, dopamine, serotonin,
What is an inhibitory neurotransmitter?
neurotransmitter that results in the hyperpolarisation of the postsynaptic membrane. This prevents the action potential being triggered.
Give examples of inhibitory neurotransmitters
GABA, glycine
Describe the process of the transmission of impulses across synapses
- action potential reaches the end of the presynaptic neurone
- depolarisation of the presynaptic neurone causes calcium ion channels to open
- calcium ions diffuse into the presynaptic knob
- this causes synaptic vesicles to move the the membrane and fuse with it
- the neurotransmitter is released by exocytosis
- neurotransmitters diffuse across the synapse and bind with receptors of the postsynaptic membrane
- sodium ion channels open
- sodium ions channels diffuse into the postsynaptic neurone
- this triggers an action potential that is then propagated across the postsynaptic neurone
How and where is acetylcholine broken down?
Acetylcholinesterase breaks down Ach in the
What is saltatory conduction?
when the action potential ‘jumps’ from one node of ranvier to another - much faster than a wave of depolarisation along the whole length of the axon membrane
State two factors, other than myelination, that affect the speed at which an action potential travels
axon diameter - the bigger the diameter the faster the impulse
temperature - the higher the temp, the faster the nerve impulse (ions diffuse faster at high temps, but after 40 degrees the proteins in the channels can denature)
What is the all-or-nothing principle?
a certain threshold must be reached for an action potential to be created (usually -50mV)
what is spatial summation?
a number of presynaptic neurones connect to one postsynaptic neurone - each release neurotransmitter which builds up enough to trigger an action potential
What is temporal summation?
a single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period - this builds up in the synapse until the quantity is sufficient to trigger an action potential
What is the role of the cerebrum in the brain?
controls voluntary actions; learning, memory, personality and conscious thought
What is the role of the cerebellum?
controls unconscious functions; posture, balance, non-voluntary movement
Whats is the role of the medulla oblongata?
used in autonomic control; heart rate and breathing rate
What is the role of the hypothalamus?
regulatory centre for temperature and water balance - also controls complex patterns of feeding, sleeping and aggression
What is the role of the pituitary gland?
stores and releases hormones that regulate many body functions - the master gland
What areas does the cerebrum contain?
left and right hemispheres, somatosensory area, motor area, visual cortex
What covers the cerebrum?
the cerebral cortex - sophisticated processes such as reasoning and decision making occur here
What is the pituitary gland split into?
Anterior - produces hormones for reproduction and growth
Posterior - stores and releases hormones produced by the hypothalamus (such as ADH)
what is a reflex action?
the body’s response to danger without the use of conscious thought. A very fast action performed to prevent or minimise damage to the body
what is a knee jerk reflex?
a spinal reflex, the neural circuit only goes up to the spinal chord and not the brain
What is the blinking reflex?
involuntary blinking of the eyelids - occurs when the cornea is stimulated (eg by being touched)
When else does the blinking reflex occur, other than when the cornea is stimulated?
When there are sounds greater than 40-60 dB or as a result of very bright light
Why is the blinking reflex known as a cranial reflex?
it occurs only in the brain, not in the spinal chord
What is skeletal muscle?
make up the bulk of body muscle tissue - is responsible for movement
What is cardiac muscle?
only found in the heart, cardiac muscle cells are myogenic which means they can contract without the need for nervous stimulation (which is what causes the heart to beat in a regular rhythm)
What is involuntary/smooth muscle?
found in many parts of the body such as the walls of hollow organs such as the stomach or bladder and also in blood vessels and the digestive tract
