The Nervous System (Edexcel International A Level (IAL) Biology): Flashcards

True.

In a myelinated neurone the impulse jumps between the nodes of Ranvier, so it travels faster than in a non-myelinated neurone, where the impulse moves along the whole length of the axon.

A nerve is a bundle of neurones (axons) grouped together.

An effector is a part of the body, a muscle or a gland, that brings about a response to a stimulus.

A stimulus is a change in the internal or external environment that is detected by a receptor.

A motor neurone carries impulses from the CNS to an effector.

Muscles and glands.

It acts as a coordinating centre, deciding which part of the body responds and sending out impulses along motor neurones.

The sensory neurone.

It contracts to bring about a response, while a gland responds by secreting a substance.

stimulus → receptor → sensory neurone → CNS → motor neurone → effector.

True.

Both muscles and glands act as effectors that respond to a stimulus.

Nerve impulses travel from the receptor cells to the CNS along sensory neurones.

In the response pathway, the CNS sends impulses to the effector along a motor neurone.

A receptor cell is a specialised cell that detects a stimulus (a change in the environment).

A reflex arc is the pathway along which impulses travel from a receptor to an effector without involving the conscious parts of the brain.

A reflex response is an action that occurs automatically and rapidly without conscious thought.

Grey matter in the spinal cord contains the cell bodies of motor neurones together with the relay neurones.

White matter in the spinal cord contains the long myelinated axons that carry information through the spinal cord.

Sensory, relay and motor neurones.

In the grey matter of the spinal cord.

stimulus → receptor → sensory neurone → relay neurone in the spinal cord → motor neurone → effector → response.

They are automatic and rapid, which minimises damage to the body.

For example blinking, coughing, the pupil reflex and the knee reflex.

False.

Awareness occurs after the response, because the information takes longer to reach the conscious parts of the brain.

In a spinal reflex the relay neurone synapses with a motor neurone, which carries the impulse to the effector.

The white matter of the spinal cord contains long myelinated axons.

The resting potential is the potential difference across the axon membrane when a neurone is not transmitting an impulse, usually about -70 mV.

An action potential is a rapid reversal of the potential difference across the axon membrane, from about -70 mV to about +30 mV.

Depolarisation is the reversal of the membrane potential as sodium ions move into the axon, making the inside less negative.

The refractory period is the time when the membrane is hyperpolarised and cannot generate a new action potential.

It uses ATP to pump 3 Na⁺ out of the axon for every 2 K⁺ in, creating the ion concentration gradients.

The membrane is more permeable to potassium ions, so K⁺ diffuses out faster than Na⁺ diffuses in, leaving more positive ions outside.

Voltage-gated sodium ion channels open, causing a rapid influx of Na⁺ and the generation of an action potential.

Voltage-gated sodium channels close and potassium channels open, so K⁺ diffuses out of the axon, restoring a negative charge inside.

It makes action potentials discrete events; the membrane behind cannot be re-stimulated, so the impulse can only travel forwards.

False.

The membrane is hyperpolarised and unresponsive during the refractory period, so no new action potential can form.

The reversal of the membrane potential caused by sodium ions entering the axon is called depolarisation.

During repolarisation, potassium ions diffuse out of the axon through voltage-gated potassium channels.

Saltatory conduction is the process in which an action potential appears to 'jump' from one node of Ranvier to the next along a myelinated axon.

The nodes of Ranvier are the gaps between the Schwann cells where the axon membrane is exposed and action potentials can occur.

The myelin sheath is an insulating layer, made of Schwann cells, that surrounds the axon.

The myelin sheath insulates the membrane and stops the diffusion of sodium and potassium ions.

Only at the nodes of Ranvier.

Depolarisation must occur along the whole length of the axon membrane.

The diffusion of sodium ions along the axon within the Schwann cells to the next node of Ranvier.

It insulates the axon so the impulse undergoes saltatory conduction, greatly increasing the speed of conduction.

True.

In a myelinated axon the impulse jumps between the nodes of Ranvier by saltatory conduction, so it travels much faster.

The uninsulated gaps between the Schwann cells along a myelinated axon are called the nodes of Ranvier.

The 'jumping' of an action potential between the nodes of Ranvier is called saltatory conduction.

Schwann cells wrap around the axon to form the myelin sheath.

A synapse is the junction between two neurones across which an impulse is passed by a neurotransmitter.

A neurotransmitter is a chemical, such as acetylcholine, that diffuses across the synaptic cleft to transmit an impulse.

The synaptic cleft is the gap between the presynaptic and postsynaptic neurones.

An action potential opens voltage-gated calcium ion channels; Ca²⁺ diffuses in, causing vesicles to fuse with the membrane and release neurotransmitter by exocytosis.

Sodium ion channels open and Na⁺ diffuses in; if enough binds, an action potential is generated in the postsynaptic neurone.

Acetylcholinesterase; it prevents continued stimulation of the postsynaptic neurone.

False.

Neurotransmitter is released on one side and its receptors are on the other, so transmission is unidirectional.

Neurotransmitter is released from the presynaptic knob by exocytosis when vesicles fuse with the membrane.

Summation is the adding together of several impulses so that the threshold needed to generate an action potential in the postsynaptic neurone is reached.

The circular muscles of the iris contract in bright light to constrict the pupil, protecting the retina.

The radial muscles of the iris contract in dim (low) light to dilate the pupil, letting in more light.

True.

When one set of muscles contracts the other relaxes, and vice versa.

By altering events at synapses, either increasing or decreasing the transmission of impulses.

It mimics acetylcholine, binding to nicotinic receptors on the postsynaptic neurone to initiate an action potential.

It stimulates the release of dopamine from the brain's pleasure centres, which reinforces the rewarding behaviour.

Lidocaine is a local anaesthetic that blocks voltage-gated sodium channels, preventing an action potential.

It blocks voltage-gated sodium ion channels, preventing the influx of sodium ions needed for depolarisation.

It binds to acetylcholine receptors on the postsynaptic membrane, preventing Na⁺ influx and blocking action potentials, which can cause muscle paralysis.

Paralysis of the muscles that control breathing eventually leads to death.

It is converted into dopamine in the brain, increasing dopamine levels so more impulses are transmitted in the regions that control movement.

Dopamine cannot cross the barrier between the blood and the brain, whereas L-dopa can.

It inhibits the reuptake of serotonin into the presynaptic neurone and triggers further release of serotonin, increasing serotonin levels in the brain.

False.

Lidocaine blocks sodium channels, decreasing transmission, which is why it acts as a local anaesthetic.

L-dopa is a drug used to treat the symptoms of Parkinson's disease.

Rhodopsin is the light-sensitive pigment found in the rod cells of the retina.

Bleaching is the breaking apart of rhodopsin into retinal and opsin when light falls on a rod cell.

Retinal is one of the two products, along with opsin, formed when rhodopsin is bleached by light.

It is bleached, breaking apart into retinal and opsin.

Na⁺ is actively pumped out and then diffuses back in through cation (sodium) channels, keeping the cell depolarised.

It releases an inhibitory neurotransmitter that prevents an action potential being generated in the bipolar neurone.

Bleaching of rhodopsin closes the cation (sodium) channels, so Na⁺ cannot diffuse back in, and the inside becomes more negative.

It stops releasing the inhibitory neurotransmitter, so an action potential is generated in the bipolar neurone and passed to the optic neurone.

Sodium ion channels that allow the positively charged sodium ions to diffuse into the rod cell.

True.

Unlike most neurones, rod cells initiate impulses in the bipolar neurone when they are hyperpolarised, not depolarised.

The light-sensitive pigment found in rod cells is called rhodopsin.

In the light, the sodium ion channels close and the rod cell becomes hyperpolarised.

Habituation is when an animal learns not to respond to a repeated stimulus that has no harmful outcome.

It conserves energy by stopping animals responding to harmless (non-threatening) stimuli, leaving energy for essential survival processes.

The nervous system will respond to it again, for example a constant low sound that suddenly becomes louder.

No longer noticing a new smell or sound after a period of exposure to it.

Wild animals losing their fear of humans after regular non-harmful contact.

Fewer calcium ions enter the presynaptic neurone when an impulse arrives, so less neurotransmitter is released.

Less neurotransmitter binds, so fewer sodium ion channels open and the threshold potential is not reached, so no impulse reaches the effector.

False.

Less neurotransmitter is released, so an action potential is less likely and the animal does not respond.

Detecting and responding to stimuli requires energy, which must be conserved for essential survival processes.

If a stimulus is repeated many times with no negative outcome, an animal learns not to respond; this is called habituation.

During habituation, fewer calcium ions enter the presynaptic neurone, so less neurotransmitter is released.

An animal is habituated when it no longer responds to a stimulus it has learned is harmless.

The central nervous system (CNS) consists of the brain and the spinal cord.

The peripheral nervous system (PNS) consists of the nerves that extend from the CNS to the rest of the body.

A neurone is a nerve cell that transmits electrical impulses through the nervous system.

A nerve is a bundle of neurones.

An effector is a muscle or gland that carries out a response to a stimulus.

The central nervous system (CNS) and the peripheral nervous system (PNS).

It connects the receptors in the sense organs to the CNS, and connects the CNS to the effectors.

It acts as the coordinating centre for the impulses that come in from, and are sent out to, any part of the body.

Sensory, relay and motor neurones.

False.

The brain and spinal cord form the central nervous system (CNS).

The two parts of the mammalian nervous system are the central nervous system and the peripheral nervous system.

stimulus → receptor → sensory neurone → CNS → motor neurone → effector.