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
