8A Flashcards
what are the features found in all types of neurons
- a long fiber known as axon
- a cell body that contains nucleus and other cellular structures
- the end of axon is known as terminal axon that connects to all neurons to form network
- some neurons are myelinated ( their axon is insulated by a fatty layer known as myelin sheath, its made up of cells known as schwann cells which wrap themselves around the axon, there are insulated gaps known as nodes of ranvier, electrical impulses jump from node to other
- non-myelinated the axon is not insulated schwann cells, the impulses travel slowly
what are the three main types of neurons and what is their function
- sensory neurons carry impulses from receptors to the brain and spinal chord
- relay neurons are found within the CNS and connect sensory neurons to and motor neurons
- motor neurons carry impulses from CNS to effector muscles or glands
how are these types different from each other
motor, relay and sensory
Motor neurons
- a large cell body at one end
- many highly-branched dendrites
Relay neurons
- short axon and non-meyliated highly-branched dendrites
Sensory neurons
- a cell body that branches from the middle of axon and has no dendrites, the axon terminal is attached to a receptor cell,The section of neurone that links the axon terminal with the cell body is known as a dendron
how does the nervous system causes effectors to respond to stimuli
- receptor cells detect changes in the environment
- nerve impulses travel form the receptor cell along the sensory neuron to the central nervous system, the CNS acts as a coordinating centre for the impulses that arrive from the receptors, sending out a new set of impulses along motor neurons
- motor neurons send impulses to the effectors to bring about a response
what are the purpose of reflexes
- blinking prevents outer surface of the eye form drying out and forgein objects form entering ]
- coughing: prevents food from entering airways, and remove mucus from airways
- the pupil reflex prevents damage form bright light
- the knee reflex aids balance when standing upright
what does reflex arc mean
- a pathway along which impulses are transmitted from a receptor to an effector without involving conscious regions of the brain
what is the structure of spinal reflex
it is made up of two types of tissues know as white matter and grey matter, grey matter contains motor neurons along with relay neurons, white matter contains long myelinated axons
how is nerve impulse is conducted along an axon
- an impulse is a electric potential difference across the the neurone cell surface membrane include;
- resting potential
- action potential
how is the potential in resting axon
- the inside of the axon always has a negative electrical potential compared to outside the axon
how is a nerve impulse conducted in resting potential
- sodium-potassium pump is a carrier protein that pumps 3 potassium ions inside the cell and 2 sodium ions oustide to create gradient which causes ions to diffuse by facilitated diffusion through ions protein channels, potassium ions diffuse outside the cell in higher rate than sodium ions to create positive potential of -70mV the membrane is said to be polarised
how is a nerve impulse conducted in action potential
- to initiate a nerve impulse the membrane needs to be depolarised sodium ion channels start to open and sodium ions begin to move into the axon, this reduces differnce potential because less negative ions are inside the axon, the potential difference will reach -55mV known as the threshold potential, this will trigger voltage gated ion channel and more sodium ions will diffuse inside the cell which will cause the membrane potential to reach 30
what does happen after depolarisation
- repolarization occurs, all the voltage gated sodium channels close and potassium channels open ,allowing potassium ions to diffuse out of the axon
- there is a refractory period where the membrane potential is more negative than resting potential known as hyperpolarisation, potassium channels close, potassium-sodium pump works to restore resting potential
how is action potential transmitted through the axon
- it moves along the axon in a wave of depolarisation
- section of axon becomes depolarised as action potential moves along the axon the previous section becomes repolarised then when it moves to the next section the first section becomes resting, etc.
what does saltatory conduction mean
when the action potential appears to jump from one node to the next, which allows the impulse to travel much faster than in a unmyelinated axon
what is the role of myelination in saltatory conduction
- by insulating the axon membrane mylein increases the speed at which action potential can travel
- when sections of the axon are surrounded by myelin sheath depolarisation cannot occur as the myelin sheath stops the diffusion of sodium and potassium ions
- actional potential only occurs at nodes of ranvier
- sodium ions diffuse along the axon within the Schwann cells, when sodium ions arrive at nodes it depolarises, this is known as local currents
what is the structure of synapse
- a gap between the neurons known as the synaptic cleft
- the neurone before the synapse is known presynaptic neurone and has a rounded end known as the synaptic knob
- the neurone after the synapse is known as postsynaptic neurone
- impulses are passed by the diffusion of neurotransmitters
what is the function of synapse in nerve impulses
- when an action potential arrive at the end of the axon of the presynaptic neurone the membrane becomes depolarised which causes calcium channel to open, calcium ions will diffuse into the synaptic knob, which will cause vesicles to move towards the membrane of presynaptic to release neurotransmitters (acetylcholine)
- they will bind to the receptors of the prosynaptic neurone for sodium ions to diffuse and generate action potential, some neurotransmitters diffuse back but some are broken down by an enzyme called acetylcholinesterase
how does the pupil dilate and contract
- by pupil reflex which causes a change in diameter to control the amount of light hitting the retina
- the diameter is determined by two types of muscles
*The circular muscles contract to constrict the pupil
*The radial muscles contract to dilate the pupil - the two sets of muscles work opposite to each other
how does the pupil dilate and contract in dark
- contraction of the radial muscles in the iris of the eye causes the pupil to dilate
how does the pupil dilate and contract in bright light
-Contraction of the circular muscles in the iris of the eye causes the pupil to constrict
how does nicotine affects on nervous transmission
- nicotine binds to nicotinic receptor, preventing response to the stimuli
- stimulates dopamine
- nicotine increases heart rate and blood pressure
how does lidocaine affects on nervous transmission
- blocks voltage gated sodium channels, to numb small areas or regulate heart beat
how does cobra venom affects on nervous transmission
- a-cobratoxin binds the acetylcholine receptors to prevents generation of action potential, between motor neurone and muscle fiber this is called muscle paralysis
how does L-DOPA affects on nervous transmission
- its used to treat Parkinson’s disease, the levels of dopamine of people with parkinson’s disease is lower than usual
- L-DOPA is converted into dopamine by enzyme, so it can pass through barrier between brain and blood
how does MDMA affects on nervous transmission
MDMA (ecstasy) inhibits the reuptake of Serotonin by binding to the protein that allow that uptake of serotonin and and increases the release of serotonin
what does the retina contain
rod cells: located around the outer retina, sensitive to light, generates images in black and white only
- cone cells: found in the fovea, can be red-,green-, or blue-sensitive, images generated in colours red ,green, or blue
how do photoreceptors generate nerve impulse in rod cell
- rod cells initiate action potential in bipolar neuron when they are hyperpolarised
- in the dark, sodium ions are actively pumped out of the rod cell for it to diffuse into rod cell by cation channels, the rod cell becomes depolarised, the depolarised rod cells release inhibitory neurotransmitter to inhibit the generation of action potential
actional of rod cells in the light
- light bleaches rhodopsin, causing it to break, which causes sodium channels to close preventing sodium ions to diffuse back into the cell, which causes the cell to be more negative inside and become hyperpolarised, it will stops the release of of inhibitory neurotransmitter so action potential can be generated in bipolar neuron therefore nerve impulse is sent to the optic nerve
what is meant by the term habituation
- when a stimulus is repeated many times without negative outcome therefore the organism will no longer respond so no energy is wasted
what are the central and peripheral system
- central system consists of brain and spinal chord
- peripheral system consists of the neurons which extend to the rest of the body
what is phytochrome
- its a plant pigment that reacts to different types of light which exists in two forms:
- PR is the inactive form, it absorbs light from the red part
- PFR is the active red from where it absorbs far red light
- when PR absorbs red light its converted into PFR, when PFR absorbs far red light is converts into PR
how phytochcrome brings response respones in plants
- in germination, seeds exposed to red light would germinate while seeds exposed to far red light dont
- in flowering, during the day the levels of PFR increase while during the night levels of PR rise
- in trasncription it can act as a transcription factor which affects gene expression
how do plants respond to alter their growth
- by growth factors (plant hormones) where plants grow towards the light or against gravity some of these hormones are:
- Gibberellins: stimulates cell elongation, flowering and seed germination
- auxin (IAA): stimulates cell elongation in plant shoots and inhibits growth in cells in plant roots
how does auxin (IAA) brings about response
- it alters the transcription of genes that code for proteins involved in cell growth, IAA is produced by growing parts of the plant then its redistributed by enviromental stimuli which leads to uneven distribution of IAA
- light affects the growth of plant shoots in a response known as phototropsim, when light shines in one side IAA is transported to the other side, which causes a faster rate of cell elongation, the shoot will bend towards the light
- in roots, the higher conc. of IAA the lower rate of cell elongation
how does Gibberellins brings about response
- it controls seed germination, stem elongation, flowering and fruit development
- seed is in state of dormancy to survive harsh conditions until the conditions are suitable it will start to absorb water and begin germination, the embryo will release gibberellins, it will stimulate the cells to synthesis amylase where it causes increase in the transcription of genes coding for amylase, to produce glucose for respiration
where do each part of brain located
what is the function of cerebrum
the cerebrum carries out involved conscious activities, and its divided into two halves known as cerebral hemispheres, right hemisphere controls the left side of the body and the left controls the right side
what is the function of hypothalamus
the hypothalamus, monitors blood, release hormones or stimulates the neighbouring pituitary gland, it regulates body temperature, osmoregulation, regulating digestive activity, controlling the endocrine function
what is function of pituitary gland and cerebellum
- pituitary gland produces range of hormones, and divides into two sections the anterior pituitary and posterior pituitary
- the cerebellum coordinates movement
what is the function of medulla oblongata
- it controls the unconscious functions such as cardiac center and respiratory center
how is Computerised tomography (CT) used for medical diagnosis and the investigation of brain structure
- it produces cross-sectional image of the brain using x-ray radiation, which shows the physical structure of the brain
how is Magnetic Resonance Imaging (MRI) used for medical diagnosis and the investigation of brain structure
- use of magnetic field and radio waves to generate images through the body
- images produced are at higher resolution than CT
- it helps to identify areas of f abnormal or damaged tissue
