5.1 Neuronal Communication Flashcards
How do animals respond to changes in the environment ?
They response through electrical responses through neurones and chemical responses through hormones.
How do plants respond to changes in the environment ?
Plants do not have a nervous system so only respond to changes through chemical responses via hormones.
Why do cells within a multicellular organism need to coordinate ?
They need to coordinate the function of different cells to operate effectively.
What is homeostasis ?
Coordination of organs in order to maintain a relatively constant internal environment. Eg. the digestive organs all work together to maintain a constant blood glucose concentration.
What is cell signalling ?
Communication at a cellular level. Occurs through one cell releasing a chemical which has an effect on another cell. They can transfer signals locally or across large distances.
What is the nervous system responsible for ?
The nervous system is responsible for detecting changes in the external and internal environment in order for a response to occur.
What is a stimulus ?
Change in the environment resulting in a response.
What are neurones ?
Specialised nerve cells that transmit electrical implulses rapidly around the body so the organism can respond to changes in the environment.
What is the structure of cell body of a neurone ?
Contains the nucleus surrounded by cytoplasm. In cytoplasm there is endoplasmic reticulum and mitochondria, involved in the production of neurotransmitters.
What is the structure of dendrons in a neurone ?
Short extensions from the cell body. They divide into smaller branches known as dendrites. They are responsible for transmitting impulses toward the cell body.
What is the structure of axons in a neurone ?
Singular, elongated nerve fibres that transmit impulses away from the cell body. The fibres can be very long and are cylindrical with a narrow region of cytoplasm with a plasma membrane.
What are sensory neurones ?
They transmit impulses from a sensory receptor cell to a relay or motor neurone or the brain. They have one dendron, which carries the impulse to the cell body and one axon, which carries impulse away from the cell body.
What are relay neurones ?
They transmit impulses between neurones. They have many short axons and dendrons.
What are motor neurones ?
Transmit impulses from a relay neurones or sensory neurone to an effector, such as a muscle or gland. They have one long axon and short dendrites.
What is the electrical impulse pathway ?
Receptor - sensory neurone - relay neurone - motor neurone - effector cell.
What is the myelin sheath ?
Many layers of plasma membrane that cover some neurones. It acts as an insulating layer and allows myelinated neurones to conduct the electrical impulse at a much faster speed than unmyelinated neurones.
What are Schwann cells ?
They produce layers of plasma membrane around an axon, this is called the myelin sheath. They are a type of glia cell.
What is saltatory conduction ?
When signal jumps from node to node, increasing speed of transmission by reducing distance travelled of electrical impulse.
What is multiple sclerosis ?
Autoimmune disease, where myelin is recognised as foreign so is broken down, reducing speed of transmission affecting mobility.
What is the Node of Ranvier ?
Gap between myelin sheath, where impulse jumps between to reduce distance and therefore increasing speed of transmission.
What is the stimulus for photoreceptors and what is a specific type ?
They respond to light and some are cone cells in the eye.
What is the stimulus for chemoreceptors and what is a specific type ?
They respond to chemicals and some are olfactory receptors found in ther nose.
What is the stimulus for thermoreceptors and what is a specific type ?
They respond to heat and some are End-bulb Krause cells found in the tongue.
What is the stimulus for mechanoreceptors and what is a specific type ?
They respond to pressure and movement and some are Pacinian corpuscle.
What are sensory receptors ?
Allow the body to detect changes in the environment and are often located in sense organs.
Are receptors specific ?
Yes receptors are specific to only one type of stimulus and act as transducers.
What are transducers ?
They convert stimulus into a nerve impulse, called a generator potential into an action potential.
What are pacinian corpuscle receptors ?
They are a type of receptor that responds to mechanical pressure. They are located deep within the skin and are most abundant in fingertips and sides of feet. Acts as a transducer.
What is the resting membrane potential of pacinian corpuscle receptors ?
-70 mV
What occurs to pacinian corpuscle when pressure is applied ?
Stretch-mediated sodium channels open causing Na+ ions to enter the receptor, causing depolarisation. This increases the voltage charge from -70mV and this initiates the generator potential.
What does the generator potential trigger ?
Triggers the action potential.
What is the resting membrane potential ?
Resting membrane potential is when the outside of the membrane is more positively charged than the inside, so it is polarised. It is normally around -70mV.
What does the sodium-potassium pump do in membrane of axon?
It actively pumps sodium ions out of the axon and potassium ions into the axon. For every 3Na + pumped out, 2K+ are pumped in.
What does sodium-potassium pump in membrane set up ?
Sets up the electrochemical gradient for sodium ions to diffuse back into the axon, and potassium ions back out.
What happens to channels when electrochemical gradient is set up ?
Potassium channels are now open to allow K+ ions to diffuse out of the axon. Most gated sodium channels are closed preventing the sodium ions from diffusing back into the axon.
How does the opening and closing of channels in axon membrane cause a resting potential of -70mV ?
Causes there to be more positively charged ions outside of the axon creating a resting potential of -70mV ?
What happens when a stimulus is detected by a sensory receptor ?
The energy of the stimulus temporarily reverses the charges on the axon membrane.
What happens when neurone has become depolarised ?
The potential difference across the membrane is approximately +40 mV so has become depolarised.
What happens when repolarisation of axon occurs ?
When the impulse passes, repolarisation occurs, when potential changes from + to -, and the neurone returns to its resting potential.
When does action potential occur ?
An action potential occurs when protein channels in the axon membrane change shape as a result of the change of voltage across its membrane.
What is propagation of action potential ?
Action potentials start at one end of the neurone and are propagated along the axon to the other end.
How does axon become propagated along the neurone ?
The polarisation of one region of the neurone acts as a stimulus for the depolarisation of the next region.
What is the refractory period ?
After an action potential there is a short period of time when the axon cannot be excited again as the voltage gate sodium channels remain closed.
Why is the refractory period needed ?
To ensure the action potential remains unidirectional as it cannot go back along the axon or to prevent it from overlapping.
What are 3 factors that speed up the action potential ?
Myelination, diameter of axon and temperature.
Why are nerve impulses described as all or nothing ?
This is because there is a threshold value that must be reached for a response to be triggered. No matter the stimulus, the same size action potential will be triggered.
What is a synapse ?
Junction between 2 neurones (or a neurone and an effector).
Ensures impulses are unidirectional and allows impulse from a neurone (or multiple neurones) to many neurones/ or one neurone.
What occurs when action potential reaches the pre-synaptic neurone ?
Causes voltage gated calcium channels to open, leading to an influx of Ca2+ diffusing down the electrochemical gradient causing vesicles to fuse to the plasma membrane of the pre synaptic neurone.
What occurs when synaptic vesicles fuse to the plasma membrane of pre-synaptic neurone ?
This causes neurotransmitters to diffuse across the synaptic cleft and fuse to the receptors causing voltage gated sodium channels causing them to open. This causes an influx of charge so the post-synaptic neurone is depolarised and causes a new action potential.
What occurs when the neurotransmitter has opened the voltage gates sodium channels ?
Enzymes, such as Acetylcholinesterase breaks down the neurotransmitters into acetyl and choline. These then diffuse down the concentration gradient, where ATP is used to reform bonds between back into the pre-synaptic neurones to be recycled.
What are excitatory neurotransmitters ?
They are neurotransmitters resulting in depolarisation of post synaptic neurone. If threshold is reached, an action potential is triggered.
What are inhibitory neurotransmitters ?
They are neurotransmitters that result in the hyper polarisation of post synaptic neurone. Prevents the action potential from being triggered.
What is spatial summation ?
When more than 1 pre-synaptic neurone is required for the threshold to be reached.
What is temporal summation ?
Constant firing of neurotransmitters in the pre-synaptic neurone until the threshold has been reached.
What does the central nervous system contain ?
Contains the brain and the spinal cord.
What does the peripheral nervous system contain ?
Has most of the sensory and motor neurones, as well as the pacinian corpuscle.
What is somatic nervous system responsible for ?
Responsible for conscious control. Eg., movement and speech.
What is the autonomic nervous stem responsible for ?
Responsible for the subconscious control as it frees up higher thinking. Eg., breathing, heart rate, blinking, digestion.
What does the sympathetic nervous system responsible for ?
‘Flight for fight’ and is controlled by the neurotransmitter, noradrenaline.
What is the parasympathetic nervous system responsible for ?
Responsible for relaxing responses and is controlled by the neurotransmitter, acetylcholine.
What is the cerebrum responsible for ?
Controls voluntary actions. Is highly convoluted, which increases SA.
What lobes are in the cerebrum and what are they responsible for ?
-Frontal lobe = problem solving, decision making, language
-Parietal lobe = sensory information
-Temporal lobe = listening, speech, communication.
-Occipital lobe = Vision
What is the cerebellum responsible for ?
Controls muscular movement, posture and balance. It does not initiate movement but coordinates it. Receives information from ears about balance and tone of muscles and tendons.
What is the medulla oblongata responsible for ?
Part of the brain stems that control reflex activities such as heart and breathing rate. Important in autonomic nervous system, controlling swallowing and coughing.
What is the hypothalamus responsible for ?
Controls and regulates release of hormones in the pituitary gland. Regulates homeostasis, hunger, etc.
What is the anterior pituitary gland responsible for ?
Produces and release of hormones that regulate many bodily functions.
What is the posterior pituitary gland responsible for ?
Stores and releases hormone that regulates many bodily functions.
What is a reflex ?
Involuntary response to a sensory stimulus.
What is the blinking reflex ?
Involuntary reflex of the eyelids when cornea is stimulated. It is a cranial reflex so occurs in the brains stem not the spinal cord.
What is the trigeminal nerve in the blinking reflex ?
Sensory neurone that synapses with the cornea receptor and motor neurone.
What is the knee jerk reflex ?
Spinal reflex so only goes to the spinal cord and is commonly tested by doctors to check reflex of the knee.
How does a knee reflex occur ?
When knee is tapped below the kneecap it stretches the patellar tendon and acts as a stimulus, which initiates the reflex arc. This causes the extensor muscle to contract.
What occurs at same time as contraction of extensor muscle in a knee reflex ?
Relay neurone inhibits a motor neurone of the flexor muscle, causing it to relax. This contraction, coordinated with the antagonistic flexor hamstring muscle, causes the leg to kick.
What are skeletal muscles ?
Make up bulk of body muscle tissue and are responsible for movement. They are striated in appearance and are a regular arrangement of muscle cells so contracts in one direction.
What are cardiac muscles ?
Found only in the heart. Myogenic, so contract without need for nervous stimulus, causing heart to beat regularly. They are also specialised striated arrangement. Fibres are branched and uninucleated.
What are smooth muscles ?
Found in many parts of the body and are non-striated. They are involuntary muscles and can remain contracted for a relatively long time. Fibres are spindle shaped and uninucleated.
What is the sarcolemma ?
Specialised plasma membrane for muscle fibres in skeletal muscles.
What is the sarcoplasmic reticulum ?
Specialised version of the ER that generated Ca2+ ions.
What are T tubules ?
Extend inward when there is Ca2+, so all myofibrils depolarise at the same time.
What are myofibrils ?
Cylindrical organelles made of protein and are specialised for contraction. They are thicker than actin filaments.
What is the sarcomere ?
Functional region of myofibril. When muscle contracts, sarcomere contracts. Has dark band (actin and myosin), light band (actin only) and the H zone (myosin only).
What is tropomyosin ?
Covers the binding sites on actin filaments in resting states.
What is troponin ?
Holds tropomyosin in place.
