Topic 6 Flashcards
What is a stimulus
A detectable change in the internal or external environment of an organism that leads to a response in the organism.
How does the ability to respond to stimuli increase the chances of survival for an organism
To be able to detect and move away from harmful stimuli, such as predators and extremes of temperature or to detect and move towards a source of food clearly aid survival.
How are stimuli detected
Receptors
Outline receptors
-They are specific to one type of stimulus
-A coordinator formulates a suitable response to stimulus.
Outline a coordinator
Formulates a suitable response to a stimulus. It may be at molecular level or involve a large organ such as the brain
Outline effectors
A response is produced by an effector which may be at a molecular or involve the behaviour of a whole organism.
What are the types of communication and their advantages
-Hormonal communication which occurs via chemicals and is a relatively slow process
-The nervous system has many different receptors and effectors linked to a central coordinator
What is the simplest nervous response to a stimulus
A reflex arc
What are the two major divisions of the nervous system
The central nervous system, made up of the brain and spinal cord
The peripheral nervous system, made up of pairs of nerves that originate from the brain or spinal cord
Outline the subdivisions of the peripheral nervous system
-Sensory neurones: carry nerve impulses from receptors towards the central nervous system
-Motor neurones: carry nerve impulses away from the central nervous system to effectors
Outline the motor nervous system divisions
-The voluntary nervous system: carries nerve impulses to body muscles and is under voluntary control
-The autonomic nervous system, which carries nerve impulses to glands, smooth muscle and cardiac muscle and is not under voluntary control
Outline the spinal cord
A column of nervous tissue that runs along the back and lies inside the vertebral column for protection. It emerges at intervals along the spinal cord in pairs of nerves
What is a reflex
An involuntary response to a sensory stimulus
What is a reflex arc
The pathway of neurones involved in a reflex
What is a spinal reflex
A reflex with one of the neurones in the spinal cord
What is a spinal reflex
A reflex with one of the neurones in the spinal cord
The main stages of a spinal reflex arc:
- The stimulus
- A receptor
- A sensory neurone
- A coordinator
- A motor neurone
- An effector
- The response
Give an example of a spinal reflex arc (heat)
- heat from the hot object
- temperature receptors generate nerve impulses in the sensory neurone
- The sensory neurone passes nerve impulses to the spinal cord
- A coordinator links the sensory neurone to the motor neurone in the spinal cord
- Motor neurone carries nerve impulses from the spinal cord to a muscle in the upper arm
- an effector the muscle is stimulated to contract
- The hand is pulled away from the hot object
Why are reflex arcs important
-Unconscious so the brain can carry out more complex responses. Some impulses are sent to the brain so it is informed of what is happening and sometimes override the reflex
-Protects the body from harm. They are effective from birth and do not have to be learnt.
-They are fast. because the neurone pathway is short with very few synapses
-The absence of any decision making process also means the action is rapid
Outline features of all receptors
-Specific to a single type of stimulus
-Produces a generator potential by acting as a transducer: all stimuli involve a change in some form of energy. It is the role to convert the change in form of energy by the stimulus into a form (action potentials) that can be understood by the body
-They convert the energy of the stimulus into a nervous impulse known as a generator potential.
Outline features of the pacinian corpuscle
-It responds only to mechanical pressure and no other stimuli
-Transduces the mechanical energy of the stimulus into a generator potential
Where are pacinian corpuscles
-Occur deep in the skin and are most abundant on the fingers, soles of feet and external genitalia as well as joint, ligament and tendons
-In the centre of layers of tissue, each separated by a gel
Outline the structure of the pacinian corpuscle
-The sensory neurone ending at the centre of the Pacinian corpuscle has a special type of sodium channel in its plasma membrane. This is called a stretch-mediated sodium channel
Outline stretch-mediated sodium channels
Their permeability to sodium changes when they are deformed (e.g. by stretching)
How do pacinian corpuscles function in resting state
The stretch-mediated sodium channels of the membrane around the neurone of a Pacinian Corpuscle are too narrow to allow sodium ions to pass along them and the neurone has a resting potential.
What happens when pressure is applied to the Pacinian Corpuscle (4)
-It is deformed and the membrane around its neurone becomes stretched
-This stretching widens the sodium channels in the membrane and Na+ diffuses into the neurone
-The influx of Na+ changes the membrane potential producing a generator potential (depolarised)
-The generator potential in turn creates an action potential that passes along the neurone and then via other neurones, to the central nervous system
How do rod and cone cells work in the eyes
They are light receptors and are transducers by conserving light energy into the electrical energy of a nerve impulse
Outline rod cells
-Cannot distinguish different wavelengths of light and less to images only being seen in black and white
-There are more rod cells than cone cells
How do rod cells function
-Many rod cells are connected to a single sensory neurone in the optic nerve. They are used to detect light of low intensity. A certain threshold has to be exceeded before a generator potential is created in the bipolar cells to which they are connected.
Why is multiple rod cells being connected to a single bipolar cell an advantage
-There is a greater chance the threshold value will be exceeded than it only a single rod cell were connected to each bipolar cell.
-This is due to summation (rapid build-up of neurotransmitter in the synapse)
-As a result, rod cells allow us to see in low intensity, although only in black and white
How do rod cells respond to low-intensity light
-In order to create a generator potential, the pigment in the rod cells (rhodopsin) must be broken down. There is enough energy from low-intensity light to cause this breakdown.
Why do rod cells give low visual activity
-Many rod cells link to a single bipolar cell so light received by rod cells sharing the same neurone will only generate a single action potential travelling to the brain regardless of how many of the neurones are stimulated.
-In perception the brain cannot distinguish between the separate sources of light that stimulated them, so two dots close together cannot be resolved and will prepare as a single blob.