Animal Responses

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Animals need to respond to their environment to stay alive. This is done using nerves and hormones, to control responses ranging from muscle actions to escape a predator, to fine control of balance, posture and temperature regulation.

The nervous system is organised into the central and peripheral nervous systems. 
The CNS is the brain and the spinal cord, made up of intermediate neurones. It has a coordinating role and many synapses.
The PNS is made of up nerves from sense organs, to muscles and glands. It is made up of sensory and motor neurones and has a role in sensing stimuli and controll effectors. It conducts impulses to and from the CNS and includes both the somatic and autonomic systems.
The somatic nervous system is the control of consiscous activity. The autonomic nervous system controls unconsious activity, and is further divided in the sympathetic and parasympathetic nervous systems.
Sympathetic nervous system:

  • Most active in times of stress
  • The neurones of a pathway are linked at a ganglion just outside of the spinal cord
  • Pre-ganglion neurones are very short
  • Post-ganglio neurones secrete noradrenaline at the synapse between neurone and effector

Effects of action include:

  • Increased heart rate
  • Pupil dilation
  • Increased ventilation rate

Parasympathetic nervous system:

  • Most active in times of sleep and relaxation
  • The neurones of a pathway are linked at a ganglion within the target tissue, so pre-ganglion neurones vary in length
  • Post ganglion neurones secrete acetylcholine as the neurotransmitter at the synapse between neurone and effector

Effects of action include:

  • Decreased heart rate
  • Pupil constriction
  • Decreased venilation rate

The Cerebrum: Control of all higher order processes such as memory, language, emotions, thinking and planning.
The Cerebellum: Control and coordination of movement and posture.
The Medulla Oblongata: control of breathing, heart rate (rate of contraction of cardiac muscle) and smooth muscle of the gut
The Hypothalamus: Control of the autonomic nervous system and some endocrine glands.

The conscious decision to move voluntarily is initiated in the cerebellum. Neurones from the cerebellum carry imulses to the motor areas so that motor output to the effectors can be adjusted appropriately in these requirements.

Coordinated and appropriate movement requires the controlled action of skeletal muscles about joints. This can be seen in the movement of the elbow joint. 
1. Impulses arriving at the neuromuscular junction cause vesicles to fuse with the presynaptic membrane and to release acetylcholine into the gap.


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