OCR Unit 2 Module 4: Responding to the Environment - Animal Responses

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Unit 2 Module 4: Responding to the Environment – Animal Responses

All living organisms need to respond to their environment. They need a communication system between receptors and effectors, so that they can respond adaptively to changes in both internal and external environments. They need to be able to coordinate a vast set of responses in order to stay alive, from coordinated voluntary muscle actions in order to run away from a predator, to the fine control of balance posture and temperature regulation

The nervous system can be divided into the central nervous system and the peripheral nervous system.

· The central nervous system (CNS) is made up of the brain and the spinal chord

· The peripheral nervous system consists of the nerves which run between the CNS and the rest of the body – from receptors and to effectors

o Somatic nervous system – includes all sensory neurones and also the motor neurones which run to the skeletal muscles

o Autonomic nervous system – consists of two sets of motor neurones, carrying impulses to effectors other than the skeletal muscles (glands, muscles of the heart and gut). Neurones of the sympathetic nervous system and parasympathetic nervous system use different neurotransmitters and so have different, often antagonistic, effects.

Conscious decision to move voluntary muscles is initiated in the cerebral hemisphere however this alone cannot operate the human body in a coordinated way. The fine control of muscular movements (walking, riding a bike, playing an instrument) requires a significant level of no conscious operation. For example, remaining balanced, judging the position of objects and limbs, operation of antagonistic muscles to coordinate contraction and relaxation.

Neurones from the cerebellum carry impulses to the motor areas so that motor output to the effectors can be adjusted appropriately in relation to these requirements. These activities are said to be programmed into our cerebellum which is why we often run on ‘auto-pilot’. The cerebellum contains over half of all of the nerve cells in the brain. Plays a key role in coordinating balance and movement by processing sensory information in the following areas:

· The retina

· The balance organs in the inner ear

· Specialised fibres in the muscles called “spindle” fibres which give information about muscle tension

· The joints

Muscles are only capable of producing a force when they contract, so the movement of any bone at a joint requires a coordinated action of at least two muscles. As one muscle is stimulated to contract the other must relax to allow for smooth movement.

Antagonistic muscles – A pair of muscles working opposite each other

The elbow is a synovial joint, these joints occur where a large degree of movement is required. Synovial fluid is a lubricant; it eases the movement of the bones at that joint. The biceps and triceps act antagonistically in order to move the forearm at the elbow. To contraction of the bicep causes the elbow to bend (flex). It is a flexor muscle. Contraction of


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