irritability

Question 1

define irritability

Answer 1

the ability of living organisms to respond to changes in their internal and/or external environment `

Question 2

define stimulus

Answer 2

a detectable change in the environment

Question 3

define response

Answer 3

a change in state or activity of a cell or organism as result of a stimulus

Question 4

define receptor

Answer 4

a group of cells that receive information from a stimulus

Question 5

define effector

Answer 5

muscles and glands which produce a specific response to a detected stimulus

Question 6

why is irritability important?

Answer 6

1. allows organisms to sense and move away from danger
2. allows organism to detect and move towards nutrients/food and desirable environments
3. allows organisms to detect changes in their internal environment so that the desired state can be restored
   (homeostasis)

Question 7

what is the nervous system is divided into?

Answer 7

central nervous system – brain and spinal cord

peripheral nervous system – cranial and spinal nerves that connect to cns to other parts of the body

Question 8

what makes up both the cns and pns

Answer 8

neurones or nerve cells
transmit messages via electrical impulses
a bundle of neurons make up a nerve

Question 9

state the the three types of nerve cells

Answer 9

sensory neurones
intermediate/relay neurones
motor neurones

Question 10

list 6 parts of neurons

Answer 10

dendrites
cell body
axon
terminal endings
myelin sheath
node of ranvier

Question 11

define dendrites

Answer 11

tree like extensions at the beginning of nerve cell that help to receive signals from neighbouring nerve cells and transmit signals to cell body

Question 12

define cell body

Answer 12

maintains cell shape and supplies cell with energy

Question 13

define axon

Answer 13

elongated fibre that transmits signals from the cell body to terminal endings

Question 14

define terminal endings

Answer 14

transmit signals to other neurons

Question 15

define myelin sheath

Answer 15

made up of schwann cells wrapped around the axon, help to speed up transmission of signals along axon

Question 16

define node of ranvier

Answer 16

gap in the myeline sheath
facilitates the rapid conduction of nerve impulses

Question 17

define sensory neurones

Answer 17

transmit impulses from receptors in sense organs to relay neurons in cns
cell body somewhere along length of cell
very long dendrite
short axon

Question 18

define intermediate neurones

Answer 18

found in cns
transmit impulses from sensory neurones to motor neurones
highly branched dendrites
very short axon

Question 19

define motor neurones

Answer 19

transmit impulses from relay neurons in cns to effectors like glands and muscles
cell body at one end of cell
short dendrites
very long axon

Question 20

describe transmission across a synapse

Answer 20

the nerve cell before synapse is called presynaptic neurone whereas that of the nerve cell which is receiving the message is called the post synaptic neurone
electricsl impulses cannot move across the synapse so chemicals called neurotransmitters are used instead
when the electrical impulse reaches the pre-synaptic knob it stimulates the release of neurotransmitters from vesicles into synapse
these neurotransmitters move across cleft and bind to receptors on post-synaptic dendrite which stimulate the generation of an electrical impulse along post-synaptic neurone

Question 21

define synapse or synaptic cleft

Answer 21

small gap at the end of neurone

Question 22

define nervous pathways

Answer 22

a series of connected nerve cells along which electrical impulses travel
some are voluntary and some involuntary

Question 23

what is the nervous pathway

Answer 23

receptor
sensory neurone
relay neurone
motor neurone
effector

Question 24

define reflex action

Answer 24

rapid automatic involuntary response to a stimulus

Question 25

define cranial reflex

Answer 25

if the nervous pathway passes through the brain pupil reflex

Question 26

define spinal reflex

Answer 26

if the nervous pathway passes through the spine knee jerk relfex

Question 27

explain the pupil reflex

Answer 27

stimulus: bright light receptor: light-sensitive cells of retina impulses in sensory neurone impulses in relay neurone in cns impulses in motor neurone effector: circular muscles of iris response: muscles contract reducing the diameter of pupil

Question 28

define conditioned reflexes

Answer 28

not inherited reflex arcs but rather reflex arcs which are modified by experience and exposure to certain stimuli