Leaving Certificate Agricultural Science

1. Leaving Certificate Agricultural Science The Nervous System

2. Introduction • The function of the nervous system is to allow the animal to quickly detect, communicate and co-ordinate information about its external and internal environment. • The two major parts of our nervous system are the central nervous system(CNS) and peripheral nervous system(PNS). • The CNS is made of the brain and spinal cord. • The cranial nerves, spinal nerves and ganglia make up the PNS. • The cranial nerves connect to the brain. • The cranial and spinal nerves contain the axons (fibres) of sensory and motor nerve cells. • Nerve cells are also known as neurons.

3. Types of Neurons Sensory Neurons • Sensory neurons carry electrical signals (impulses) from receptors or sense organs to the CNS. • Sensory neurons are also called afferent neurons. • The cell body of sensory neurons is outside the CNS in ganglia. Motor Neurons • Motor neurons carry impulses from the CNS to effector organs. • Motor neurons are also called efferent neurons. • The cell bodies of motor neurons are inside the CNS.

5. Bridging the Gap – The Synapse • A synapse is a specialised junction between a neuron and its target cell.

6. The Brain

7. Parts and Functions of the Brain • Cerebrum:centre for sensory and motor control, language, memory, intelligence, and consciousness. • Cerebellum:muscle co-ordination, movement and balance. • Medulla Oblongata:controls breathing and heart rate. • Hypothalamus:osmoregulation and temperature control. • Pituitary Gland:secretes a wide variety of hormones – a major endocrine gland.

8. The Reflex Action • A reflex action is a very fast unconscious response to an unexpected and potentially dangerous stimulus. • Examples of reflex action: knee jerk, eye blink, pupil size alteration, closure of the glottis on swallowing. • A reflex arcis a specific nerve pathway involved in a fast, unconscious response to an unexpected stimulus. • E.g.Spinal Reflex Action - the withdrawal of hand when finger jabbed unexpectedly with a pin.

10. The Reflex Action - 2 • Pain and pressure receptors in the skin are stimulated. • Sensory neurons carry the impulses to the spinal cord by way of the dorsal root. • An interneuronpicks up the impulse from the sensory and transmits it to the motorneuron. • At the same time the impulse is also transmitted to the brain. • The motor neuron stimulates the specific effector organ to make the appropriate response,  muscles in the arm are stimulated to contract pulling the hand away from the pin. • The response is very fact – occur before the brain is aware of the situation. • The brain, having received the information, may transmit impulses to other muscles to modify the response.