Mammalian Nervous System: Neurones, Reflex Arc & Synapses

30 Question-and-Answer flashcards covering the structure and function of the mammalian nervous system, neurone types, reflex arcs, and synapse physiology.

What structures compose the central nervous system (CNS)?

The brain and spinal cord.

What structures compose the peripheral nervous system (PNS)?

All of the nerves outside the CNS; essentially the nerves serving the rest of the body.

In what form is information transmitted through the nervous system?

As nerve impulses—electrical signals that travel along neurones.

What is a bundle of neurones called?

A nerve.

Name the three main types of neurone in mammals.

Sensory neurones, relay (intermediate) neurones, and motor neurones.

What direction does a sensory neurone carry impulses?

From a sense organ (receptor) to the CNS.

Where are relay neurones located and what is their role?

They are inside the CNS and connect sensory neurones to motor neurones, acting as coordinators.

To what do motor neurones carry impulses?

To effectors such as muscles or glands.

Why is having a long axon advantageous to a neurone?

It reduces the number of synapses needed, so impulses travel faster.

What is the function of the myelin sheath and nodes of Ranvier?

The myelin sheath insulates the axon and the nodes allow the impulse to jump (saltatory conduction), speeding transmission.

What is the purpose of dendrites on a neurone’s cell body?

Dendrites allow a neurone to connect with many others and receive multiple impulses, forming networks.

How can you recognise a sensory neurone in a diagram?

It is long with a cell body branching off the middle of the axon.

How can you recognise a relay neurone in a diagram?

It is short with a small cell body at one end and many branched dendrites.

How can you recognise a motor neurone in a diagram?

It is long with a large cell body at one end and long dendrites extending from it.

Define a voluntary response.

A response you consciously decide to make that originates in the brain.

Define a reflex (involuntary) response.

An automatic, rapid response that does not involve the brain as the coordinator and occurs without conscious thought.

Why are reflex actions generally faster than voluntary actions?

Because the pathway bypasses the brain, involving only spinal cord relay neurones, reducing synaptic delay.

State three key characteristics of reflex actions.

Automatic, fast, and protective.

Outline the complete pathway of a reflex arc from stimulus to response.

Stimulus → receptor → sensory neurone → spinal cord (relay neurone) → motor neurone → effector → response.

In the pin–foot reflex, what acts as the stimulus and what is the effector?

The sharp pin is the stimulus; the muscle in the leg that contracts to pull the foot away is the effector.

What is a synapse?

A junction between two neurones where they meet but do not touch.

List the three main structural parts of a synapse.

Synaptic cleft (gap), presynaptic knob with neurotransmitter vesicles, and postsynaptic membrane with receptors.

Describe the first step in transmitting an impulse across a synapse.

The arriving electrical impulse triggers vesicles in the presynaptic knob to fuse with its membrane and release neurotransmitters.

What happens to neurotransmitter molecules after they cross the synaptic cleft?

They bind to receptors on the postsynaptic membrane, trigger a new impulse, then are broken down to stop further stimulation.

Why do impulses travel in only one direction across a synapse?

Neurotransmitters are only released from the presynaptic side and receptors are only on the postsynaptic side.

How can drugs such as heroin affect the nervous system?

They act at synapses, altering the action of neurotransmitters and therefore nervous system activity.

Give an analogy used to explain the role of synapses in directing impulses.

Synapses are like railway points that switch a train (impulse) onto the correct track toward its destination.

What exam tip is given regarding drawing arrows on a reflex arc diagram?

Remember to add arrows showing impulse direction on each neurone; it is an easy mark that students often miss.

Why is it important that vesicles remain in the presynaptic knob?

So that neurotransmitter can be released again and because vesicles don’t cross the synaptic cleft.

At what point in the nervous system are messages chemical rather than electrical?

At synapses, where electrical impulses are temporarily converted to chemical signals.