14. Nervous System Flashcards
1
Q
What is a nerve impulse?
A
An electrical signal that passes through the nerve cells
2
Q
Human Nervous System comprises of
A
CNS - Central nervous system - the brain and the spinal cord PNS - Peripheral nervous system - all of the nerves in the body
3
Q
What is a nerve
A
A bundle of neurones is known as a nerve
4
Q
The human nervous system
A
5
Q
Types of Neurone
A
- There are three main types of neurone: sensory, relay and motor
- Sensory neurones carry impulses from sense organs to the CNS (brain or spinal cord)
- Relay neurones are found inside the CNS and connect sensory and motor neurones
- Motor neurones carry impulses from the CNS to effectors (muscles or glands)
6
Q
A neurone
A
- Neurones have a long fibre (axon)
- This means that less time is wasted transferring the impulse from one cell to another
- The axon is insulated by a fatty sheath with small uninsulated sections along it (called nodes)
- This means that the electrical impulse does not travel down the whole axon, but jumps from one node to the next
- Their cell body contains many extensions called dendrites
- This means they can connect to many other neurones and receive impulses from them, forming a network for easy communication
7
Q
Identifying the types of neurone
A
- Sensory neurones are long and have a cell body branching off the middle of the axon
- Relay neurones are short and have a small cell body at one end with many dendrites branching off it
- Motor neurones are long and have a large cell body at one end with long dendrites branching off it
8
Q
Voluntary & Involuntary Responses
A
- A voluntary response is one where you make a conscious decision to carry out a particular action therefore it starts with your brain
- An involuntary (or reflex) response does not involve the brain as the coordinator of the reaction and you are not aware you have completed it until after you have carried it out
- Involuntary actions are usually ones which are essential to basic survival and are rapid, whereas voluntary responses often take longer as we consider what the response might be before doing it
9
Q
The Reflex Arc
A
- An involuntary (or reflex) response does not involve the brain as the coordinator of the reaction and you are not aware you have completed it until after you have carried it out
- This is an automatic and rapid response to a stimulus such as touching something sharp or hot
- As it does not involve the brain, a reflex response is quicker than any other type of nervous response
- This helps to minimise the damage to the body
10
Q
A reflex
A
- The pin (the stimulus) is detected by a pain/pressure/touch receptor in the skin
- Sensory neurone sends electrical impulses to the spinal cord (the coordinator)
- Electrical impulse is passed on to relay neurone in the spinal cord
- Relay neurone connects to motor neurone and passes the impulse on
- Motor neurone carries impulse to a muscle in the leg (the effector)
- The muscle will contract and pull the foot up and away from the sharp object (the response)
11
Q
The Synapse: Definition
A
The junction between two neurones is known as a synapse
12
Q
How an Impulse is Passed Across a Synapse
A
- Neurones never touch each other
- The junctions (gaps) in between them are called synapses
- The electrical impulse travels along the first axon
- This triggers the nerve-ending of the presynaptic neurone to release chemicalmessengers called neurotransmitters from vesicles which fuse with the presynaptic membrane
- The neurotransmitters diffuse across the synaptic gap and bind with receptor molecules on the membrane of the second neurone (known as the post synaptic membrane)
- This stimulates the second neurone to generate an electrical impulse that travels down the second axon
- The neurotransmitters are then destroyed to prevent continued stimulation of the second neurone which would cause repeated impulses to be sent
- Synapses ensure that impulses only travel in one direction, avoiding confusion within the nervous system if impulses were travelling in both directions
- As this is the only part of the nervous system where messages are chemical as opposed to electrical, it is the only place where drugs can act to affect the nervous system – eg this is where heroin works
13
Q
Receptors
A
- Receptors are groups of specialised cells
- They detect a change in the environment and stimulate electrical impulses in response
- Sense organs contain groups of receptors that respond to specific stimuli
- Once the receptor cell in the sense organ has been stimulated, it generates an electrical impulse
- This is passed on to a sensory neurone which carries the impulse to the central nervous system
- Here a response will be decided on and the impulse will be passed to a motor neurone (via a relay neurone)
- The motor neurone carries the impulse to the effector (muscle or gland)
- The effector carries out the response
14
Q
Sense Organs (Picture)
A
15
Q
Structure of the Eye & Functions
A
16
Q
Function of the parts of the eye
A
17
Q
The Pupil Reflex
A
- This is a reflex action carried out to protect the retina from damage in bright light and protect us from not seeing objects in dim light
- In dim light the pupil dilates (widens) in order to allow as much light into the eye as possible
- In bright light the pupil constricts (narrows) in order to prevent too much light entering the eye and damaging the retina
18
Q
How does the Pupil Reflex Work in DIM Light? (PICTURE)
A
19
Q
How does pupil reflex work in bright light?
A
20
Q
Comparison of Pupil reflex (table)
A
21
Q
Accomodation Viewing Near Objects
A
- The way the lens brings about fine focusing is called accommodation
- The lens is elastic and its shape can be changed when the suspensory ligaments attached to it become tight or loose
- The changes are brought about by the contraction or relaxation of the ciliary muscles
22
Q
Accomodation Viewing Distant Objects
A
- Ciliary muscles contract
- Suspensory ligaments slacken
- This allows lens to become fatter
- Light is refracted more
23
Q
Accomodation Viewing Near & Distant Objects (TABLE)
A
